JP7179315B2 - multi-stage roots pump - Google Patents

Description

The present invention relates to a multi-stage roots pump, and more particularly to a multi-stage roots pump used for pumping, sucking or circulating gas in various chemical plants.

Traditionally, Roots-type pumps have been used in various chemical plants for pumping, sucking or circulating gases. A Roots-type pump has two rotors in a casing, which rotate in opposite directions with the same phase of rotation. While the two rotors rotate with a slight gap between them and the inner surface of the casing and between the rotors, a certain amount of gas trapped between them is transferred from the suction side (low pressure side) to the discharge side (high pressure side). ), and the gas is discharged by pushing it toward the high pressure side. When the rotor discharges gas, the high-pressure gas on the discharge side flows back into the casing, thereby compressing the discharged gas. When the gas pressure difference between the suction side and the discharge side is large and the amount of air discharged by the pump is large, a large shaft power is required, so a large driving motor is required and its power consumption increases. In addition, when the pressure ratio between the gas on the suction side and the gas on the discharge side is large, the temperature of the discharge gas becomes high due to the heat of compression, so the temperature of the rotating rotor rises. As a result, the rotating rotor and the casing, or between the rotors may come into contact with each other, making it impossible to operate. Therefore, the pressure ratio between the gas on the suction side and the gas on the discharge side at which the pump can be operated is limited.

Therefore, in order to reduce the shaft power of the pump and to suppress the temperature rise of the discharge gas to a temperature at which the pump can be operated, the pressure difference and the pressure ratio of the gas on the suction side and the discharge side are adjusted to a plurality of different moving volumes. Multi-stage roots pumps are widely used. As such a multistage Roots pump, for example, as shown in FIG. 23, a plurality of single stage Roots pumps (a Roots pump having only one pump operating region for compressing gas by one suction and one discharge). are arranged in series, and the discharge port of the pump in the preceding stage and the suction port of the pump in the subsequent stage are connected by piping (hereinafter referred to as "piping connection type"). Further, as shown in, for example, FIG. ) has also been proposed.

Utility Model Registration No. 3139905 Utility Model Registration No. 3176808

However, the pipe-connected multi-stage roots-type pump has a structure in which a plurality of single-stage roots-type pumps are connected in series via an external pipe. Due to its structure, the pipe-connected multi-stage roots pump has the problem that it requires a large installation area. Another problem is that the pulsation of gas generated in each single-stage roots-type pump causes noise and vibration from the pipe surface.

On the other hand, the multi-stage Roots type pump of serial internal type has a structure in which a plurality of stages of rotors are arranged in series in the axial direction of two rotating shafts that support the rotors. Structurally, in series internal multistage Roots pumps, the rotor shaft is long. There is also the problem that the rotating rotor and the inner surface of the casing are likely to come into contact with each other because the deflection of the rotor becomes large. Contact between the rotor and the inner surface of the casing will cause the pump to stop operating. Therefore, there is a demand for a multi-stage roots pump that can operate safely without contact between the rotor and the inner surface of the casing even under severe operating conditions such as operating conditions with a large pressure difference or sudden pressure fluctuations.

Therefore, the present invention has been made in view of the above circumstances, and is capable of reducing the installation area, reducing noise and vibration caused by pulsation, and preventing contact between the rotor and the inner surface of the casing even under severe operating conditions. It is an object of the present invention to provide a multi-stage Roots-type pump which is possible.

As a result of extensive research to solve the above problems, the present inventors have found that the following (1) and (2) make it possible to reduce the installation area of the multistage roots pump and reduce noise and vibration caused by pulsation. In addition, the inventors have found that contact between the rotor and the inner surface of the casing can be prevented even under severe operating conditions, and have completed the present invention based on this knowledge.
(1) Compression elements such as multiple stages of rotors are arranged in parallel with respect to the axial direction of the rotating shaft (2) Between at least one adjacent compression element among multiple stages of compression elements arranged in parallel Make the transfer volume ratio greater than 1

That is, the multi-stage roots pump according to the first aspect of the present invention comprises a pair of rotors rotatable in mutually opposite directions, and two rotary shafts rotatably supporting each of the pair of rotors. A plurality of stages of compression elements each independently provided, and a gas suction port and a gas discharge port are provided. A casing that houses the compression elements so that the compression elements are arranged in parallel, and a gas that is provided in the casing and exists between the low-pressure side compression element and the high-pressure side compression element that are arranged adjacent to each other. at least one intermediate discharge port that discharges to the outside, a cooling unit that is provided outside the casing and cools the gas discharged from the intermediate discharge port, and is provided in the casing and cooled by the cooling unit a first cooling gas introduction port that introduces gas into the compression element on the lower pressure side than the intermediate discharge port, and the following formula (1):
_RQ = _QthL / _QthH (1)
(However, in formula (1), Qth _L is the movement volume of the compression element on the low pressure side of the two adjacent compression elements, and Qth _H is the displacement of the compression element on the high pressure side of the two adjacent compression elements. is the displacement volume of the compression element.)
The moving volume ratio R _Q is 1 or more, and the moving volume ratio R _Q is greater than 1 between at least one adjacent compression element among the plurality of stages of compression elements arranged in parallel. .

The multi-stage roots pump of the first aspect further comprises a drive mechanism for rotationally driving the rotor, wherein the drive mechanism rotates between at least one adjacent compression element of the rotor on the low-pressure side of the compression element. The number of revolutions may be higher than the number of revolutions of the rotor in the compression element on the high pressure side.

In this case, the length and diameter of the pair of rotors in at least one of the compression elements may be the same as the length and diameter of the pair of rotors in the other compression element arranged in parallel. .

In the multi-stage roots pump of the first aspect comprising the drive mechanism, the number of compression elements is two, and the drive mechanism is arranged so that the shaft ends of the two rotary shafts of the first stage are meshed with each other. A pair of first timing gears provided in the second stage, a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage, and a pair of the first timing gears a first drive gear that meshes with one of the first timing gears; a second drive gear that meshes with one of the second timing gears of the pair of second timing gears; and a single drive shaft rotatably supporting the drive gear, wherein the first drive gear rotates so that the rotation speed of the rotor in the first stage is higher than the rotation speed of the rotor in the second stage. and the number of teeth of the second drive gear may be set.

Further, between at least one adjacent compression element of the multi-stage roots pump of the first aspect, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side meet the following conditions ( At least one of A) and condition (B) may be satisfied.
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side;

In this case, the multi-stage roots pump of the first aspect further comprises a drive mechanism for rotationally driving the rotor, wherein the drive mechanism changes the rotational speed of the rotor in the compression element on the low pressure side to It may be the same as the rotation speed of the rotor in the compression element.

In the multi-stage roots pump of the first aspect comprising the drive mechanism, the number of compression elements is two, and the drive mechanism is arranged so that the shaft ends of the two rotary shafts of the first stage are meshed with each other. A pair of first timing gears provided in the second stage, a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage, and a pair of the first timing gears a common drive gear that meshes with one of the first timing gear and one of the second timing gears of the pair of second timing gears; a drive shaft that rotatably supports the common drive gear; and the rotor in the compression element of the first stage and the rotor in the compression element of the second stage may satisfy at least one of the following conditions (A) and (B) .
(A) The length of the rotor in the compression element of the first stage is longer than the length of the rotor in the compression element of the second stage.
(B) The diameter of the rotor in the compression element of the first stage is larger than the diameter of the rotor in the compression element of the second stage.

Further, the multistage roots pump of the first aspect further includes a drive mechanism for rotationally driving the rotor, wherein the drive mechanism is arranged between at least one adjacent compression element such that, between the compression elements on the high pressure side, the The rotation speed of the rotor is higher than the rotation speed of the rotor in the compression element on the low pressure side, and between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor on the high pressure side The rotor in the compression element may satisfy at least one of the following conditions (A) and (B).
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side;

In this case, between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy both the condition (A) and the condition (B) may be satisfied.

In the multi-stage roots pump of the first aspect comprising the drive mechanism, the number of compression elements is two, and the drive mechanism is arranged so that the shaft ends of the two rotary shafts of the first stage are meshed with each other. A pair of first timing gears provided in the second stage, a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage, and a pair of the first timing gears a first drive gear that meshes with one of the first timing gears; a second drive gear that meshes with one of the second timing gears of the pair of second timing gears; and a single drive shaft rotatably supporting the drive gear, wherein the first drive gear rotates so that the rotation speed of the rotor in the second stage is higher than the rotation speed of the rotor in the first stage. and the number of teeth of the second drive gear may be set.

A multi-stage roots-type pump according to a second aspect of the present invention comprises a pair of rotors rotatable in mutually opposite directions, and two rotary shafts rotatably supporting each of the pair of rotors. A plurality of stages of compression elements each independently provided, and a gas suction port and a gas discharge port are provided. A casing that houses the compression elements so that the compression elements are arranged in parallel, and a drive mechanism that rotationally drives the rotor, wherein the following formula (1):
_RQ = _QthL / _QthH (1)
(However, in formula (1), Qth _L is the movement volume of the compression element on the low pressure side of the two adjacent compression elements, and Qth _H is the displacement of the compression element on the high pressure side of the two adjacent compression elements. is the displacement volume of the compression element.)
The moving volume ratio R _Q is 1 or more, and the moving volume ratio R _Q is greater than 1 between at least one adjacent compression element among the plurality of stages of compression elements arranged in parallel. , between at least one of the adjacent compression elements, the drive mechanism makes the rotation speed of the rotor in the compression element on the high pressure side higher than the rotation speed of the rotor in the compression element on the low pressure side; Between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy at least one of the following conditions (A) and (B): Be satisfied.
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side;

In the multi-stage roots pump of the second aspect, between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side meet the condition (A) and the above condition (B).

In the multi-stage roots pump of the second aspect, the number of compression elements is two, and the drive mechanism is a pair provided at the shaft ends of the two rotation shafts of the first stage so as to mesh with each other. a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage; and one of the pair of first timing gears, the first timing gear A first driving gear meshing with one timing gear, a second driving gear meshing with one of the second timing gears of the pair of second timing gears, and the first driving gear and the second driving gear are rotated. and a single drive shaft capable of supporting said first drive gear and said second drive such that the rotational speed of said rotor in a second stage is higher than the rotational speed of said rotor in a first stage. The number of gear teeth may be set.

In the multi-stage roots-type pump of the second aspect, the casing has at least one intermediate discharge for discharging gas existing between the adjacent low-pressure side compression element and the high-pressure side compression element to the outside. It may further have an outlet.

In the multi-stage roots pump according to the first and second aspects, the casing introduces cooling gas into the compression elements between a suction position where gas is sucked into the last stage compression element and the discharge port. You may further have the 2nd cooling gas introduction port which carries out. Alternatively, the interior of the casing may be divided into the same number of pump operating regions as the number of compression elements solely by the arrangement of the compression elements, and a plurality of the compression elements may be arranged in a single stage group within the integral casing. may be provided as

In the present invention, the "length" of the rotor means the length of the rotor in the rotation axis direction. Further, in the present invention, the "diameter" of the rotor refers to the diameter of a circle centered on the rotation center of the rotor in a cross section perpendicular to the rotation axis of the rotor (rotor profile) and in contact with the tip of the protruding portion of the rotor. .

According to the present invention, it is possible to reduce the installation area of the multi-stage roots pump, reduce noise and vibration due to pulsation, and prevent contact between the rotor and the inner surface of the casing even under severe operating conditions.

1 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a first embodiment; FIG. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1; FIG. 2 is a cross-sectional view taken along line III-III in FIG. 1; FIG. 2 is a cross-sectional view taken along line IV-IV of FIG. 1; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is an explanatory diagram showing an operation example of the multistage roots pump according to the first embodiment; FIG. 4 is a cross-sectional view showing the configuration of a multi-stage roots pump according to a first modified example of the first embodiment; FIG. 10 is an explanatory diagram showing the flow of cooling gas in a multistage roots pump according to a first modified example; FIG. 10 is an explanatory diagram showing the flow of cooling gas in a multistage roots pump according to a first modified example; FIG. 7 is a cross-sectional view showing the configuration of a multi-stage roots pump according to a second modification of the first embodiment; FIG. 5 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a second embodiment of the present invention; FIG. 12 is a cross-sectional view taken along line XI-XI of FIG. 11; FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. 11; FIG. 11 is a partial cross-sectional view showing the overall configuration of a multi-stage roots pump according to a third embodiment of the present invention; FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. 13; FIG. 14 is a cross-sectional view taken along line XV-XV of FIG. 13; FIG. 11 is a partial cross-sectional view showing the overall configuration of a multi-stage roots pump according to a fourth embodiment of the present invention; FIG. 17 is a cross-sectional view taken along line XVII-XVII of FIG. 16; FIG. 17 is a cross-sectional view taken along line XVIII-XVIII in FIG. 16; FIG. 17 is a cross-sectional view taken along line XIX-XIX in FIG. 16; FIG. 11 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a fifth embodiment of the present invention; 21 is a cross-sectional view taken along line XXI-XXI of FIG. 20; FIG. 21 is a cross-sectional view taken along line XXII-XXII of FIG. 20; FIG. 21 is a cross-sectional view taken along line XXIII-XXIII of FIG. 20; FIG. FIG. 12 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a sixth embodiment of the present invention; FIG. 25 is a cross-sectional view taken along line XXV-XXV of FIG. 24; FIG. 25 is a cross-sectional view taken along line XXVI-XXVI of FIG. 24; FIG. 4 is a cross-sectional view for explaining a leak area in the multistage roots pump according to the first embodiment; FIG. 4 is a cross-sectional view for explaining a leak area in the multistage roots pump according to the first embodiment; FIG. 11 is a cross-sectional view for explaining a leak area in a multistage roots pump according to a sixth embodiment; FIG. 11 is a cross-sectional view for explaining a leak area in a multistage roots pump according to a sixth embodiment; FIG. 11 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a seventh embodiment of the present invention; FIG. 32 is a cross-sectional view taken along line XXXII-XXXII of FIG. 31; FIG. 11 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to an eighth embodiment of the present invention; FIG. 34 is a cross-sectional view taken along line XXXIV-XXXIV of FIG. 33; FIG. 21 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a ninth embodiment of the present invention; FIG. 36 is a cross-sectional view taken along line XXXVI-XXXVI of FIG. 35; FIG. 36 is a cross-sectional view taken along line XXXVII-XXXVII of FIG. 35; FIG. 36 is a cross-sectional view taken along line XXXVIII-XXXVIII of FIG. 35; FIG. 20 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to a tenth embodiment of the present invention; FIG. 40 is a cross-sectional view taken along line XL-XL in FIG. 39; FIG. 21 is a partial cross-sectional view showing the overall configuration of a multistage roots pump according to an eleventh embodiment of the present invention; FIG. 42 is a cross-sectional view taken along line XLII-XLII in FIG. 41; FIG. 11 is an explanatory diagram showing an example of application of the multistage roots pump according to the first to eleventh embodiments; 1 is a side view showing an example of the configuration of a pipe-connected multistage roots pump; FIG. FIG. 2 is a partial cross-sectional view showing an example of the configuration of an in-line multistage roots pump. FIG. 11 is a graph showing calculation results of all-axis power in a pump of an example corresponding to the sixth embodiment of the present invention and a pump of a comparative example; FIG. FIG. 11 is a graph showing calculation results of all-axis power in a pump of an example corresponding to the seventh embodiment of the present invention and a pump of a comparative example; FIG. FIG. 11 is a graph showing calculation results of all-axis power in a pump of an example corresponding to the eighth embodiment of the present invention and a pump of a comparative example; FIG.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In addition, in this specification and the drawings, constituent elements with the same reference numerals have substantially the same structure or function. In addition, the multi-stage roots pump according to the present invention is a combination of at least two aspects of the first embodiment and modifications thereof, and the second to eleventh embodiments, as long as there is no technical contradiction. can be anything. Furthermore, the matters described in the preceding embodiments are also applied mutatis mutandis to the following modified examples and embodiments by appropriately replacing the symbols as long as they are not technically inconsistent.

[Relationship between the present invention and prior art]
First, referring to FIGS. 44 and 45, the configuration and problems of the pipe connection type and series internal type multi-stage Roots type pumps according to the prior art will be described, and then the present invention will be made to solve the problems. The outline of the multi-stage roots type pump according to

(Piping connection type multistage roots type pump)
As shown in FIG. 44 , an exterior two-stage roots-type pump 50 as an example of a pipe-connected multi-stage roots-type pump has two single-stage roots-type pumps 51 and 52 connected in series by an external pipe 53 . have a structure.

<Configuration>
A single-stage roots-type pump 51 (hereinafter simply referred to as "single-stage pump 51") is a pump on the low-pressure side, and a single-stage roots-type pump 52 (hereinafter simply referred to as "single-stage pump 52"). is the high pressure side pump. For example, when the exterior two-stage roots pump 50 is used as a vacuum pump, the single-stage pump 51 is a vacuum-side pump, and the single-stage pump 52 is an atmospheric pressure-side pump. The single-stage pump 51 has an inlet 51a for compressed gas, and the single-stage pump 52 has an outlet 52a for compressed gas. One end of the drive shaft 51b of the rotor (not shown) provided inside the casing of the single-stage pump 51 is connected to the motor 54, and the rotor (not shown) provided inside the casing of the single-stage pump 52 is driven. One end of the drive shaft 52 b is connected to the motor 54 .

The exterior two-stage roots type pump 50 compresses the gas sucked from the suction port 51a by the first-stage single-stage pump 51, and then transfers the compressed gas to the second-stage single-stage pump 52 through the pipe 53. The compressed gas is further compressed to the atmospheric pressure or a desired pressure by the stage pump 52, and the compressed gas is discharged from the discharge port 52a.

<Problems>
A pipe-connected multi-stage roots-type pump such as the exterior two-stage roots-type pump 50 has a structure in which a plurality of single-stage roots-type pumps (51, 52) are connected in series with an external pipe (53). Therefore, it has the following problems. First, it requires a large footprint for multiple single-stage roots pumps (51, 52). Secondly, the pressure loss when gas flows through the piping (53) connecting the single-stage roots pumps (51, 52) reduces the exhaust performance and reduces the pumps (51, 52). The power consumption of the driving motor (54) increases. Thirdly, the gas pulsation generated in each single-stage roots pump (51, 52) causes noise from the surface of the pipe (53) connecting the two single-stage roots pumps (51, 52). Along with this, the pipe (53) vibrates. Fourthly, since it is necessary to drive two single-stage roots pumps (51, 52), the drive shafts (51b, 52b) of the single-stage roots pumps (51, 52) are provided with shaft seal mechanisms (51b, 52b). (not shown) must be provided.

(In-line multi-stage roots type pump)
As shown in FIG. 45 , an internal two-stage roots-type pump 60 as an example of a serial internal-type multi-stage roots-type pump has a casing 61 in which two sets of rotors 62 and 63 are arranged in the axial direction of two rotating shafts 64 . has a structure that is arranged in series with That is, in the series internal multistage roots pump, the two sets of rotors 62 and 63 are coaxially arranged.

<Configuration>
The casing 61 has, for example, a suction port 61 a for compressed gas above the rotor 62 and a discharge port 61 b for compressed gas below the rotor 63 . The rotors 62 and 63 are each rotatably supported by a rotating shaft 64 and rotate in directions opposite to each other. A timing gear 65 is attached to each shaft end of the two rotating shafts 64 . The number of teeth of the timing gear 65 is set so that the two sets of rotors 62 and 63 rotate at the same rotational speed. Both ends of the rotary shaft 64 are supported by bearings 66A and 66B, respectively. A shaft end of the rotary shaft 64 opposite to the timing gear 65 is connected to a motor (not shown).

In addition, since the rotor 62 and the rotor 63 of the internal two-stage roots pump 60 are coaxially arranged in series, the gas compressed by the rotor 62 of the first stage (low pressure side) is transferred to the second stage (high pressure side). side) of the rotor 63. The gas flow path 67 has a portion extending in the longitudinal direction of the rotor 62 below the rotor 62 and a portion extending vertically between the rotors 62 and 63 . The vertically extending portion of the gas channel 67 is surrounded by a partition plate 68A that separates the end face of the rotor 62 from the gas channel 67 and a partition plate 68B that separates the end face of the rotor 63 from the gas channel 67. there is

The internal two-stage roots-type pump 60 compresses the gas sucked from the suction port 61a by the rotor 62 of the first stage, and then transfers the compressed gas to the rotor 63 of the second stage through the gas flow path 67. The compressed gas is further compressed to atmospheric pressure or a desired pressure, and the compressed gas is discharged from the discharge port 61b.

<Problems>
A series-internal multi-stage roots-type pump such as the internal two-stage roots-type pump 60 has a structure in which multiple stages of rotors (62, 63) are arranged in series along the axial direction of a rotating shaft (64). , has the following problems: First, a gas flow path (67) is required for transferring gas from the front (low pressure side) rotor (62) arranged axially in series to the rear (high pressure side) rotor (63). . In order to provide the gas flow path (67), partition plates (68A, 68B) are provided between the pump operation areas including the rotors (62, 63) of each stage, and the casing (61) is moved between the pump operation areas. It should be divided into numbers. Secondly, since the length of the rotating shaft (64) must be equal to or greater than the total length of the rotors (62, 63) arranged in series, the rotating shaft (64) becomes long. For example, in the internal two-stage roots type pump 60, when the movement volume ratio between the first stage and the second stage is set to about 1.6 to 1.8, the length of the rotary shaft 64 is the same as that of the rotor of the second stage. Assuming that the length of 63 is 1, a length of about 3, which is longer than 2.6 to 2.8, is required. Therefore, especially when a large-sized (long rotor length) rotor is provided, the rigidity is lowered. Thirdly, since the bearings (66A, 66B) that support the rotating shaft (64) at both ends are provided so as to sandwich a plurality of pump operating regions arranged in series in the axial direction, the bearings (66A, 66B) distance becomes longer. When the differential pressure between the suction pressure and the discharge pressure in each pump operating region increases due to the operating conditions of the pump, this differential pressure causes a large load in the direction perpendicular to the axis to be applied to the rotors (62, 63) in each pump operating region. be. In this case, if the distance between the bearings (66A, 66B) is long, the deflection of the rotating shaft (64) due to the load will increase, and there will be a slight difference between the outer peripheral surface of the rotors (62, 63) and the inner surface of the casing (61). The gap cannot be maintained. As a result, the outer peripheral surfaces of the rotating rotors (62, 63) come into contact with the inner surface of the casing (61), and the pump stops operating. Fourth, when the temperature of the rotating shaft (64) and rotors (62, 63) rises due to the compression heat of the gas, the rotating shaft (64) and rotors (62, 63) thermally expand. At this time, if the distance between the bearings (66A, 66B) is long, due to thermal expansion, the end face positions of the rotors (62, 63) on the bearing (66A) and bearing (66B) side will fluctuate greatly. Therefore, in order to prevent contact between the end surfaces of the rotors (62, 63) and the inner surface of the casing (61) during operation of the pump, the rotors (62, 63) and the casing (61) must be separated from each other in anticipation of large thermal expansion. A wide gap must be set between the inner surface of As a result, sufficient pumping performance of the pump cannot be obtained. Fifth, since the rotary shaft (64) is long, it becomes difficult to process and assemble the rotors (62, 63), casing (61), etc., and the precision of processing and assembly may be lowered. As described above, the rotors (62, 63), casing (61), etc. have low machining accuracy and assembly accuracy. Poor alignment affects the clearance between rotors (62, 63) and between rotors (62, 63) and casing (61). Therefore, the rotors (62, 63), the casing (61), etc. are required to have high machining accuracy and assembly accuracy. Therefore, the clearance between the rotors (62, 63) and the inner surface of the casing (61) needs to be widened with a certain amount of margin depending on the machining accuracy and assembly accuracy. As a result, it is not possible to obtain sufficient pumping performance of the pump in the same manner as described above.

(Multistage roots pump according to preferred embodiment of the present invention)
In order to solve the problems of the pipe connection type and series internal type multistage roots type pumps described above, the multistage roots type pump according to a preferred embodiment of the present invention mainly includes the following (A) and (B). ).
(A) Arranging multiple stages (multiple sets) of compression elements (rotors, rotating shafts, etc.) in parallel with respect to the axial direction of the rotating shaft (B) Multiple stages (multiple sets) of compression elements arranged in parallel Among them, at least one moving volume ratio R _Q (see formula (1) below) between adjacent compression elements should be greater than 1 R _Q = Qth _L /Qth _H (1)

However, in equation (1), Qth _L is the movement volume of the compression element on the low pressure side of the two adjacent compression elements, and Qth _H is the movement volume of the compression element on the high pressure side of the two adjacent compression elements. Volume.

The multistage Roots pump of the present invention has the above-described features, and thus has the following advantages compared to the above-described pipe connection type and series internal type multistage Roots pumps.

First, by arranging multiple compression elements in parallel in one casing, multiple single-stage pumps can be arranged in series like a pipe-connected multi-stage roots pump, and pipes can be connected between each single-stage pump. no need to connect with Therefore, the space required for installing a plurality of single-stage pumps and pipes can be reduced to a space equivalent to approximately one single-stage pump, thereby realizing space saving by reducing the installation area.

Secondly, in the pipe-connected multi-stage roots pump, the number of component parts such as a casing and a cover containing each mechanical element is required for two pumps. On the other hand, in the multi-stage roots pump of the present invention, since a plurality of compression elements are arranged in one casing, the number of components such as a casing and a cover containing each mechanical element is reduced for one pump. good. As a result, costs can be significantly reduced.

Thirdly, in the pipe-connected multi-stage roots pump, it is necessary to provide as many shaft sealing mechanisms as there are single-stage pumps. Even if it is a pump, it is enough to provide a shaft sealing mechanism for one pump.

Fourth, the multi-stage roots pump of the present invention does not require piping to connect a plurality of single-stage pumps, so noise and vibration generated from the piping and pressure loss when gas flows through the piping can be reduced. .

Fifth, in the multistage Roots pump of the present invention, by arranging a plurality of compression elements in parallel in one casing, partition plates ( For example, there is no need to provide the partition plates 68A and 68B described above. Therefore, according to the present invention, it is possible to divide the interior of the casing into a plurality (the number of compression elements) of the pump operation regions only by arranging the compression elements such as the rotors.

Sixthly, in the multi-stage Roots pump of the present invention, since a plurality of compression elements are arranged in parallel with respect to the axial direction of the rotary shaft, the rotary shaft and the casing are different from those of the series internal multi-stage Roots pump. The axis of rotation is shortened without being too long. Therefore, there is an advantage that the rigidity of the rotating shaft and casing is not lowered. In particular, this advantage is advantageous when the pump is intended to have a large air volume. That is, since the air volume of the pump is proportional to the length of the rotor, it is necessary to lengthen the rotor in order to increase the air volume. In this case, since multiple compression elements are arranged in series on the same rotating shaft, the rotating shaft becomes very long in the series internal multistage roots type pump, which reduces the rigidity and makes it difficult to manufacture the device. become. Therefore, it was difficult to increase the air volume with the series internal multi-stage Roots pump. On the other hand, in the multi-stage roots pump of the present invention, since a plurality of compression elements are arranged in parallel with respect to the axial direction of the rotary shaft, even if the length of the rotor is increased, the rigidity is lowered. Therefore, it is easy to increase the air volume.

Seventhly, since a plurality of compression elements are coaxially arranged in the series internal multistage roots pump, the casing and rotor require high machining and assembly accuracy, which increases the difficulty of manufacturing the pump. For example, the rotor and casing must be sized and precisely aligned between the pumping regions of each stage. If the machining accuracy and the assembly accuracy are lowered, the gap between the rotors and the gap between the rotor and the casing must be widened with a margin. In contrast, in the multi-stage Roots pump of the present invention, a plurality of compression elements are arranged in parallel on different axes, so that the dimensional accuracy and alignment accuracy between the pump operating regions of each stage are relatively high. Even if it is not necessary, it will be within a range that does not hinder the assembly and the performance of the pump. Therefore, the multi-stage roots pump of the present invention has the advantage that it does not require very high machining accuracy and assembly accuracy as compared with the series internal multi-stage roots pump.

<Problems specific to parallel internal multi-stage roots pumps and overview of solutions>
Here, the present inventors have developed a multi-stage roots type pump in which compression elements such as multiple stages of rotors are arranged in parallel with respect to the axial direction of the rotating shaft (hereinafter referred to as a "parallel internal multi-stage roots type pump"). ), it was found that the temperature of the discharged gas rises significantly compared to the pipe-connected multistage roots pump and the in-line multistage roots pump. This is because the gas that has been compressed by the compression element in the front stage (low pressure side) and the temperature has risen is directly sucked into the compression element in the rear stage (high pressure side) without being dissipated, and is further compressed by the compression element in the rear stage and the temperature rises. to rise. Such a temperature rise becomes more pronounced as the number of stages of the multi-stage roots pump increases. Thus, if the temperature of the gas increases significantly, the increase in temperature will also increase the thermal expansion of the rotor and casing. Therefore, in order to prevent contact between the rotor and the casing or between the rotors due to this thermal expansion, the gap between the rotor and the casing in the latter compression element and the gap between the rotors should be increased in advance. It is necessary to hold it and set it wide. As a result, it was found that the amount of gas leaked from the compression element in the latter stage, that is, the amount of gas that flows back from the high pressure side to the low pressure side increases, so that there is a problem that the volumetric efficiency decreases. Here, the "volumetric efficiency" of the multistage roots pump means the ratio of the actual air volume to the theoretical air volume derived from the structure of the multistage roots pump (actual air volume/theoretical air volume).

In addition, the more the amount of gas leaked from the compression element in the latter stage, that is, the amount of leakage from the discharge side (high pressure side) of the compression element in the latter stage to the suction side (lower pressure side) of the compression element in the latter stage, the greater the amount of leakage of the compression element in the latter stage. Suction pressure increases. When the suction pressure of the post-stage compression element increases, the differential pressure between the suction pressure of the post-stage compression element (equal to the discharge pressure of the pre-stage compression element) and the suction pressure of the pre-stage compression element increases. As a result, it was found that there is also a problem that the shaft power of the compression element in the front stage also increases.

On the other hand, in a pipe-connected multi-stage roots-type pump in which multiple single-stage roots-type pumps are connected by pipes, the gas compressed by the compression element in the previous stage (low-pressure side) passes through the pipes provided outside the casing. It is transferred to the compression element in the latter stage (high pressure side). Also, in a multi-stage Roots-type pump in which multiple stages of compression elements are arranged in series along the rotary shaft, the gas compressed by the compression elements of the previous stage passes through the gas flow path provided in the casing to the subsequent stage. of compression elements. In this way, in the pipe-connected multi-stage Roots pump and the in-line multi-stage Roots pump, the gas compressed by the front-stage compression element is not directly sucked into the rear-stage compression element, but once passes through the piping and gas flow path. do. As a result, the gas compressed by the preceding compression element radiates heat while passing through pipes and gas flow paths. temperature rise problem does not occur.

As described above, the inventors of the present invention have found that the parallel internal multistage roots pump has a new problem of suppressing an increase in the amount of gas leakage caused by a significant temperature rise of the gas in the compression element of the latter stage. I found something. This problem is peculiar to parallel internal multistage roots pumps, which does not occur in pipe connection type multistage roots pumps or series internal multistage roots pumps. If this problem is solved, it will be possible to suppress the decrease in gas compression efficiency and reduce the shaft power of the compression element in the preceding stage.

Therefore, in the multi-stage roots pumps according to the first to fifth embodiments described later, the gas present in the intermediate position between the front-stage (low-pressure side) compression element and the rear-stage (high-pressure side) compression element is discharged to the outside. The above problem is solved by providing a cooling mechanism that returns the heat to the compression element in the preceding stage after cooling. That is, by providing this cooling mechanism, the gas compressed by the compression element of the preceding stage can be cooled once and then sucked into the compression element of the subsequent stage, so that a significant temperature rise of the gas in the compression element of the subsequent stage can be prevented. . Therefore, according to the multi-stage Roots pumps according to the first to fifth embodiments, it is possible to suppress an increase in the amount of gas leakage caused by a significant temperature rise of the gas in the compression element of the latter stage.

Further, in the multi-stage roots pumps according to sixth to ninth embodiments described later, the size of the rotor included in the compression element in the latter stage (high pressure side) is set larger than the size of the rotor included in the compression element in the previous stage (low pressure side). The problem mentioned above is solved by making it small. That is, by reducing the size of the rear-stage rotor, the thermal expansion of the rear-stage rotor itself can be suppressed, so that the clearance between the rotors and between the rotor and the casing can be narrowed in advance. As a result, the amount of gas leaked from the compression element in the latter stage is reduced. Therefore, according to the multi-stage roots pumps according to the sixth to ninth embodiments, it is possible to suppress an increase in the amount of gas leaked due to a significant temperature rise of the gas in the compression element of the latter stage.

Furthermore, in the multi-stage roots-type pumps according to tenth and eleventh embodiments, which will be described later, there are two solutions: the cooling mechanism in the first to fifth embodiments, and the reduction in the size of the subsequent rotor in the sixth to ninth embodiments. By combining the above, the above-mentioned problems can be solved more reliably.

Hereinafter, as preferred embodiments of the present invention for solving the above-described problems, the configuration, operation and effects of multi-stage roots pumps according to the first to eleventh embodiments will be described. Here, the term "pump" as used herein is a concept including a blower and a vacuum pump. A blower is a device that draws in gas at atmospheric pressure, compresses it to a pressure above the atmospheric pressure, and then discharges it. A vacuum pump is a device that draws in gas at a pressure below the atmospheric pressure, compresses it to atmospheric pressure, and discharges it. is.

[First embodiment]
A multi-stage roots pump according to a first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 6C. FIG. 1 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 100 (hereinafter abbreviated as "pump 100") as an example of a multi-stage roots-type pump according to the present embodiment. 2, 3 and 4 are cross-sectional views taken along lines II-II, III-III and IV-IV of FIG. 1, respectively. 5A to 5E are explanatory diagrams showing a method of compressing gas by the multi-stage roots pump according to this embodiment. 6A to 6E are explanatory diagrams showing a gas cooling method using the multistage roots pump according to the present embodiment.

(Configuration of multistage roots pump)
As shown in FIGS. 1 to 4, the pump 100 is a two-stage roots pump, which is a type of rotary compressor, and includes a casing 110, two stages (two sets) of compression elements, a drive mechanism, and a cooling mechanism. and

<Casing>
The casing 110 is provided with a suction port 111 and a discharge port 113 for gas compressed by the pump 100 . In this embodiment, the suction port 111 is provided at the upper portion of the casing 110 in the vertical direction, and the discharge port 113 is provided at the lower portion of the casing 110 in the vertical direction. That is, pump 100 is of the bottom vertical discharge type. Not only in such a case, the gas introduced from the suction port 111 and the discharge port 113 is discharged from the discharge port 113 after being compressed by the first-stage compression element and the second-stage compression element. It is sufficient if it is provided in a position where it is For example, the suction port 111 may be provided on the upper portion of the casing 110 in the vertical direction, and the discharge port 113 may be provided on the side surface of the casing 110 (a lower horizontal discharge method may also be used). Moreover, although the pump 100 is a vertical pump, a horizontal pump may be used, and the suction port and the discharge port may be provided on the side surface of the casing.

In addition, as will be described later in detail, the casing 110 is arranged in the normal direction of the virtual plane containing the two rotating shafts 122, 122 of the compression elements of the same stage or the virtual plane containing the two rotating shafts 132, 132. , the compression elements are accommodated so that two stages of compression elements are arranged in parallel. Thus, in this embodiment, multiple stages of compression elements arranged in parallel with respect to the axial direction of the rotating shafts 122 and 132 are housed in the single casing 110, and external No particular piping or internal gas flow path is provided. Therefore, the gas compressed and discharged by the compression element of the front stage (first stage in this embodiment) is directly sucked (as it is) into the compression element of the rear stage (second stage in this embodiment).

The material of the casing 110 is not particularly limited as long as the casing 110 has sufficient strength and rigidity. etc. can be used.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 111 side and a second stage (high pressure side) compression element located on the discharge port 113 side are provided in the single casing 110. A two-stage compression element is provided. Between the two stages of compression elements, no partition plate or the like is provided, unlike the above-described series-internal multistage roots pump (see FIG. 45), and a plurality of compression elements are provided in an integral casing 110. provided as a single stage group. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 121 and 121 and two rotating shafts 122 and 122 . The second stage compression element has a pair of rotors 131 and 131 and two rotating shafts 132 and 132 .

As shown in FIG. 2, the rotor 121 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 121a, 121b, 121c projecting radially from the center of rotation. In addition, recesses 121d are provided between the protrusions 121a, 121b, and 121c. Similarly, the rotor 131 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 131a, 131b, 131c projecting radially from the center of rotation. In addition, recesses 131d are provided between the protrusions 131a, 131b, and 131c.

The pair of rotors 121, 121 are provided rotatably in directions opposite to each other. The two rotating shafts 122, 122 rotatably support a pair of rotors 121, 121 and are arranged parallel to each other. Also, the two rotating shafts 122, 122 are supported by two bearings 123A, 123B. Similarly, a pair of rotors 131, 131 are provided rotatably in directions opposite to each other. The two rotating shafts 132, 132 rotatably support a pair of rotors 131, 131 and are arranged parallel to each other. Also, the two rotating shafts 132, 132 are supported by two bearings 133A, 133B. Furthermore, in this embodiment, the rotating shaft 122 and the rotating shaft 132 are arranged so as to be parallel to each other. In the following description, the description of the rotor 131 that overlaps with that of the rotor 121 will be omitted as necessary, and the contents of the rotor 121 will be appropriately read.

Between the rotors 121 and 121 and the tips (leaf ends) of the protrusions 121a, 121b, and 121c and the casing 110 are arranged so that the pair of rotors 121 and 121 and the rotor 121 and the inner surface 110a of the casing 110 do not come into contact with each other. A rotor 121 is arranged with a small gap between the inner surface 110a of the . This gap may be set according to the required compression ratio so that the space surrounded by the two protruding parts of the casing 110 and the rotor 121 is sufficiently sealed, but should be as small as possible. is preferred. Specifically, the above gap is preferably, for example, 3 mm or less, more preferably 1 mm or less. Hereinafter, the state of having a slight gap in which the sufficient airtightness is maintained will be referred to as a "sealed" state. Rotation phases of the rotors 121, 121 are maintained by timing gears 161A, 161B, which will be described later, and the cross-sectional shape of the rotor 121 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Therefore, the rotation speed of the rotor can be increased, and since there is no wear, internal lubrication is unnecessary. Similarly, the rotor 131 is arranged so that a slight gap is formed between the paired rotor 131 and the inner surface 110 d of the casing 110 . Also, the pair of rotors 131, 131 can rotate in opposite directions while maintaining a small gap without coming into contact with each other.

Here, each of the protruding portions 121a, 121b, 121c of the pair of rotors 121, 121 rotates around the center of the rotation shaft 122 that supports the rotor 121, and rotates at a rotation angle of 115 degrees or more. preferably remain sealed to the inner surface of the For this purpose, a line segment connecting the end 110b of the inner surface 110a of the first stage (low pressure side) of the casing 110 on the side of the suction port 111 and the center of rotation of the rotor 121, and the compression of the second stage (high pressure side) of the inner surface 110a. The shape of the casing 110 may be set so that the angle θ between the end 110c on the element side and the line segment connecting the rotation center of the rotor 121 is in the range of 115 degrees or more. The same applies to the pair of rotors 131, 131. A line segment connecting the end 110e of the second stage inner surface 110d of the casing 110 on the side of the first stage compression element and the rotation center of the rotor 131, It is preferable to set the shape of the casing 110 so that the angle θ between the end 110 f of the inner surface 110 a on the discharge port 113 side and the line segment connecting the center of rotation of the rotor 131 is in the range of 115 degrees or more. As a result, the gas compressed by the rotors 121 and 131 can be prevented from flowing back to the suction port 111 side, and as a result, a sufficiently sealed state is maintained. The point that the angle θ is preferably set to be in the range of 115 degrees or more is the same for each embodiment described later.

In the pump 100, the rotor 121, the rotary shaft 122, etc., which are the first-stage compression elements, and the rotor 131, the rotary shaft 132, etc., which are the second-stage compression elements are arranged in the same stage in the single casing 110. They are arranged in parallel along the normal direction of an imaginary plane containing the two rotating shafts 122, 122 (or the two rotating shafts 132, 132). That is, the rotor 121 in the first stage and the rotor 131 in the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are in parallel. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 111, the first-stage rotor 121, the second-stage rotor 131, and the gas discharge port 113 are arranged side by side in the vertical direction. Therefore, when gas is introduced into the casing 110 from the suction port 111 (arrow Gs in FIG. 2), it travels vertically downward, is compressed by the rotor 121, and then flows into the first stage compression element and the second stage compression element. (arrow Gm in FIG. 2). The gas compressed by the rotor 121 further travels vertically downward, is compressed by the second-stage rotor 131, and is then directly discharged from the discharge port 113 to the outside of the casing 110 (arrow Gd in FIG. 2).

Thus, according to the pump 100 according to the present embodiment, the first stage rotor 121 and the second stage rotor 131 are arranged in parallel on different shafts within the single casing 110 . Therefore, unlike the in-line multi-stage roots pump, the arrangement of the rotors 121 and 131 can be achieved without providing a partition between the first-stage compression element (rotor 121) and the second-stage compression element (rotor 131). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of an in-line multi-stage roots pump, if it has two stages of rotors, the length of the rotating shaft is required to be equal to or longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, it is possible to suppress a decrease in rigidity of the rotating shafts 122 and 132 and the casing 110 . In particular, even if the length of the rotors 121 and 131 is lengthened in order to increase the air volume of the pump 100, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and the alignment accuracy between the first stage and the second stage pump operation areas are not so high, they are within a range that does not hinder the performance of the pump 100 in terms of assembly and performance. Accuracy and assembly accuracy are not required.

Further, as will be described later, the length L1 of the rotor 121 of the first stage and the length L2 of the rotor 131 of the second stage can be the same length (L1=L2). Therefore, according to the pump 100 of the present embodiment, the same rotors (rotors having the same shape and size) can be used for the first-stage rotor 121 and the second-stage rotor 131, so the number of types of parts can be reduced. Since the same rotor can be used, there is an advantage that assembly is easy. As a result, it leads to improvement of production efficiency and reduction of cost.

As the material for the rotors 121 and 131, a material that can be easily processed with high precision is suitable. For example, cast iron (FC), ductile cast iron (FCD), etc. can be used.

<Transfer volume ratio>
In the pump 100 of this embodiment, between the first-stage compression element (rotor 121) and the second-stage compression element (rotor 131) arranged in parallel on separate rotating shafts, the following formula (1) is _greater than 1;
_RQ = _QthL / _QthH (1)

However, in formula (1), Qth _L is the displacement volume of the low-pressure side compression element (first-stage compression element in this embodiment) of the first-stage compression element and the second-stage compression element, Qth _H is the displacement volume of the high pressure side compression element (the second stage compression element in this embodiment).

Here, the details of the displacement volume ratio _RQ will be described with reference to FIGS. 1 and 2 again. First, the displacement Qth in the present embodiment is a so-called displacement amount, which is proportional to the rotational speed N and is the theoretical volume per time of the space surrounded by the casing 110 and the rotor 121 or rotor 131. is. According to JIS B0132:2005, the amount of displacement is the volume per unit time displaced by the compression elements (rotors 121 and 131 in this embodiment). Further, the volume per rotation displaced by the compression elements (rotors 121 and 131 in this embodiment) is also referred to as displacement volume Vth. That is, the movement volume Qth (m ³ /min) is represented by the following formula (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

However, in equation (2), A is the area of movement per revolution, and L is the length of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in the cross-section perpendicular to the axis of rotation 122, 132. FIG.

The displacement volume ratio _RQ in the pump 100 of this embodiment is calculated as follows. First, taking the first stage rotor 121 as an example, each time the pair of left and right rotors 121, 121 makes one rotation, gas is sucked and discharged six times (the left rotor 121 and the right rotor 121 respectively. and 3 times each) is repeated. The same applies to the second stage rotor 131 . Here, as shown in FIG. 2, a section of a cross section perpendicular to the rotating shaft 122 of the space surrounded by the two protrusions (for example, the protrusion 121a and the protrusion 121b) of the rotor 121 and the inner surface 110a of the casing 110 is taken. Assuming that the area is S1, the moving area A1 of the first stage (low pressure side) compression element is A1=6×S1. Similarly, if S2 is the cross-sectional area of the cross section of the space surrounded by the two protruding portions of the rotor 131 (for example, the protruding portion 131b and the protruding portion 131c) and the inner surface 110d of the casing 110 perpendicular to the rotating shaft 132, then 2 The moving area A2 of the compression element on the stage (high pressure side) is A2=6×S2. From the above, the movement volume ratio R _Q1-2 between the first stage and the second stage is expressed by the following formula (3).

However, in equation (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, N1 is the rotation speed of the first stage rotor 121, N2 is the second stage It represents the rotation speed of the rotor 131 . Here, rotors 121 and 131 have the same diameter and shape. Therefore, the moving area A1 of the first stage is equal to the moving area A2 of the second stage. Also, as shown in FIG. 1, the length L1 of the rotor 121 and the length L2 of the rotor 131 are equal. Therefore, the above formula (3) can be rewritten as the following formula (3-1).

Therefore, in this embodiment, in order to make the moving volume ratio R _Q1-2 between the first stage and the second stage greater than 1, the rotational speed N1 of the first stage rotor 121 is set to should be higher than the rotational speed N2 of (N1>N2). Thus, in the present embodiment, the rotational speed ratio (N1/N2) between the rotational speed N1 of the first stage compression element and the rotational speed N2 of the second stage compression element allows the is _determined . As a result, the length L1 of the rotor 121 in the first stage and the length L2 of the rotor 131 in the second stage can be made the same, so that the rotor 121 in the first stage and the rotor 131 in the second stage can be used as parts of the pump 100. can be standardized as As a result, the number of types of parts can be reduced, leading to improved production efficiency and reduced costs. Also, normally, it is necessary to use pumps having different performances for a 50 Hz motor and a 60 Hz motor. By changing the ratio, it can be used in common for both a 50 Hz motor and a 60 Hz motor. Furthermore, by changing the speed reduction ratio of drive gear 165 and drive gear 166 and adjusting the rotational speed ratio between the first-stage compression element and the second-stage compression element, the movement volume ratio R _Q1-2 is changed. The air volume of 100 can be easily adjusted.

On the other hand, in a pipe-connected two-stage roots-type pump, if the moving volume ratio is to be 1 or more, two single-stage pumps with different rotor lengths are arranged in series. As a result, the device becomes very large. In addition, if it is desired to increase the moving volume ratio to 1 or more in a two-stage roots type pump of in-line internal type, it is necessary to arrange two sets of rotors of different lengths coaxially in series, since the rotational speed ratio cannot be changed. become. Therefore, the rotating shaft of the rotor becomes very long. According to the pump 100 of this embodiment, these problems can also be solved.

In general, in a single-stage roots pump, its shaft power is determined by the pressure difference between the suction port and the discharge port and its displacement volume. Specifically, the theoretical shaft power Lth(s) of a single-stage Roots pump is calculated by the moving volume Qths of the single-stage Roots pump, the discharge pressure Ps, and the suction pressure Pd, as shown in the following equation (4-1). ΔP (ΔP=Pd−Ps). Therefore, if the difference (ΔP) between the discharge pressure and the suction pressure is constant, the single-stage roots pump requires shaft power proportional to the displacement (Qths).
Lth(s)=Qths×ΔP (4-1)

On the other hand, as shown in the following equation (4-2), the shaft power Lth (m) of the multi-stage roots pump is calculated as follows: Assuming that the number of stages i of the multi-stage roots pump is n, the difference between the discharge pressure and the suction pressure at each stage is: It is the sum of the products of the difference ΔPi and the movement volume Qthi.

For example, the theoretical driving force Lth(2) of a two-stage roots pump is expressed by the following equation (4-3). However, Lth1 and Lth2 are represented by equations (4-4) and (4-5), respectively.
Lth(2)=Lth1+Lth2 (4-3)
Lth1=Qth1×ΔP1 (4-4)
Lth2=Qth2×ΔP2 (4-5)

However, in equations (4-3), (4-4) and (4-5), Lth1 is the theoretical power of the first stage pump, Lth2 is the theoretical power of the second stage pump, and Qth1 is the first stage The movement volume of the pump, Qth2 is the movement volume of the second stage pump, ΔP1 is the second stage suction pressure Ps2 (the second stage suction pressure Ps2 is equal to the first stage discharge pressure) and the first stage The difference from the suction pressure Ps1 (ΔP1=Ps2−Ps1), and ΔP2 is the difference between the discharge pressure Pd and the second stage suction pressure Ps2 (ΔP2=Pd−Ps2).

Here, when the exhaust performance of the two-stage roots pump is the same as that of the single stage roots pump, the suction pressure Ps of the single stage roots pump and the first stage suction pressure Ps1 of the two stage roots pump is equal to , Pd-Ps=(Pd-Ps2)+(Ps2-Ps1), and the following equation (4-6) holds. That is, the difference ΔP between the discharge pressure Pd and the suction pressure Ps is the sum of ΔP1 and ΔP2. Therefore, in the two-stage roots type pump, the pressure increase (ΔP) of the single stage roots type pump is divided between the pressure increase (ΔP1) of the first stage pump and the pressure increase (ΔP2) of the second stage pump. It can be boosted.
ΔP=ΔP1+ΔP2 (4-6)

Further, when the pumping performance of the two-stage roots pump is the same as that of the single-stage roots pump, the relationship of the following equation (4-7) is satisfied.
Qths=Qth1 (4-7)

At this time, if the movement volume ratio R _Q1-2 (=Qth1/Qth2) between the first stage and the second stage is greater than 1, that is, the movement volume Qth2 of the second stage is smaller than the movement volume Qth1 of the first stage. Then, as described above, since the shaft power is proportional to the movement volume, the shaft power can be reduced in proportion to the reduced movement volume. Specifically, in a two-stage roots-type pump in which the moving volume ratio R _Q1-2 is greater than 1, the difference ΔQth _1-2 (=Qth1-Qth2) between the moving volume Qth1 of the first stage and the moving volume Qth2 of the second stage is and ΔP2 (ΔQth ₁₋₂ ×ΔP2), the shaft power can be reduced compared to a single-stage roots pump with the same exhaust performance.

Similarly, for example, the theoretical driving force Lth(3) of a three-stage roots pump is represented by the following equation (4-8). However, Lth1, Lth2 and Lth3 are represented by equations (4-9), (4-10) and (4-11), respectively.
Lth(3)=Lth1+Lth2+Lth3 (4-8)
Lth1=Qth1×ΔP1 (4-9)
Lth2=Qth2×ΔP2 (4-10)
Lth3=Qth3×ΔP3 (4-11)

However, in formulas (4-8), (4-9), (4-10) and (4-11), Lth1 is the theoretical power of the first-stage pump, Lth2 is the theoretical power of the second-stage pump, Lth3 is the theoretical power of the third-stage pump, Qth1 is the displacement of the first-stage pump, Qth2 is the displacement of the second-stage pump, Qth3 is the displacement of the third-stage pump, and ΔP1 is the second-stage pump. The difference between the suction pressure Ps2 (the suction pressure Ps2 of the second stage is equal to the discharge pressure of the first stage) and the suction pressure Ps1 of the first stage (ΔP1=Ps2−Ps1), and ΔP2 is the suction pressure of the third stage. The difference between Ps3 (the suction pressure Ps3 of the third stage is equal to the discharge pressure of the second stage) and the suction pressure Ps2 of the second stage (ΔP2=Ps3−Ps2), ΔP3 is the discharge pressure Pd and the third stage It is the difference (ΔP3=Pd−Ps3) from the suction pressure Ps3.

Here, when the pumping performance of the three-stage roots type pump is the same as that of the single-stage roots type pump, the suction pressure Ps of the single-stage roots type pump and the suction pressure Ps1 of the first stage of the two-stage roots type pump are is equal to , the relationship of the following equation (4-12) holds as in the case of the two-stage roots pump. That is, the difference ΔP between the discharge pressure Pd and the suction pressure Ps is the sum of ΔP1, ΔP2, and ΔP3. Therefore, in the three-stage roots pump, the pressure increase (ΔP) of the single-stage roots pump is divided into the pressure increase of the first stage pump (ΔP1), the pressure increase of the second stage pump (ΔP2), and the pressure increase of the third stage pump (ΔP2). The pressure can be increased by sharing with the pressure increase of the pump (.DELTA.P3).
ΔP=ΔP1+ΔP2+ΔP3 (4-12)

Further, when the pumping performance of the three-stage roots pump is the same as the pumping performance of the single stage roots pump, the relationship of the following equation (4-7) is satisfied as in the case of the two-stage roots pump.
Qths=Qth1 (4-7)

At this time, the moving volume ratio R _Q1-2 (=Qth1/Qth2) between the first stage and the second stage is greater than 1, and the moving volume ratio R _Q2-3 (=Qth2/ Qth3) is greater than 1, that is, if the second-stage movement volume Qth2 is smaller than the first-stage movement volume Qth1 and the third-stage movement volume Qth3 is smaller than the second-stage movement volume Qth2 , As described above, since the shaft power is proportional to the movement volume, the shaft power can be reduced in proportion to the reduced movement volume. Specifically, a three-stage roots-type pump in which the moving volume ratio R _Q1-2 is greater than 1 and the moving volume ratio R _Q2-3 is greater than 1 has a moving volume Qth1 in the first stage and a moving volume Qth1 in the second stage. In addition to the product of the difference ΔQth _1-2 (=Qth1-Qth2) of the volume Qth2 and ΔP2 (ΔQth _1-2 ×ΔP2), the difference ΔQth ₂₋ between the second stage movement volume Qth2 and the third stage movement volume Qth3 ₃ (= _Qth2 -Qth3) and .DELTA.P3 (.DELTA.Qth.sub.2-3.times..DELTA.P3) can reduce shaft power compared to a single-stage roots pump with the same exhaust performance.

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 167 of the pump 100 can be reduced.

<Drive Mechanism>
As shown in FIGS. 1, 3 and 4, the drive mechanism of this embodiment includes a pair of first timing gears 161 (161A, 161B), a pair of second timing gears 162 (162A, 162B), and , a first drive gear 165, a second drive gear 166 and a single drive shaft 167 which is the motor input shaft.

A pair of first timing gears 161A and 161B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 122 of the first stage, and are arranged so that the rotation phases of the pair of rotors 121 and 121 match each other. , have the same number of teeth. A pair of second timing gears 162A and 162B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 132 of the second stage, and are arranged so that the rotation phases of the pair of rotors 131 and 131 match each other. , have the same number of teeth.

Here, if the rotational phases of the pair of rotors 121, 121 (or the pair of rotors 131, 131) deviate, the pair of rotors 121, 121 (or the pair of rotors 131, 131) come into contact with each other. There is a risk. Therefore, as the material of the first timing gear 161 and the second timing gear 162, it is preferable to use a material having excellent strength and hardness, such as chromium molybdenum steel. Further, it is more preferable to improve the durability of the first timing gear 161 and the second timing gear 162 by carburizing, quenching and polishing after processing the chromium molybdenum steel into the desired shape of the timing gear. .

The first drive gear 165 is provided so as to mesh with one of the pair of first timing gears 161, the first timing gear 161A, and the second drive gear 166 is engaged with the pair of second timing gears. 162 is provided so as to mesh with one of the second timing gears 162A. Furthermore, the drive shaft 167 rotatably supports the first drive gear 165 and the second drive gear 166 . That is, the first drive gear 165 and the second drive gear 166 are rotatably supported by the same drive shaft. The drive shaft 167 is supported by a bearing 168A provided in a side cover 180 and a bearing 168B provided in a bearing/gear chamber 173, which will be described later. A shaft end of the drive shaft 167 on the side of the bearing 168B is connected to a motor (not shown).

As described above, in this embodiment, the length L1 of the rotor 121 and the length L2 of the rotor 131 are the same. Therefore, in order to make the movement volume ratio larger than 1 (R _Q >1), the rotation speed of the rotor 121 in the first stage must be higher than the rotation speed of the rotor 131 in the second stage. In other words, the rotation speed of the rotor 121 in the first stage needs to be faster than the rotation speed of the rotor 131 in the second stage. Therefore, in pump 100, the number of teeth of first drive gear 165 and second drive gear 166 is set such that the number of rotations of rotor 121 in the first stage is higher than the number of rotations of rotor 131 in the second stage. For example, when the rotation speed of the rotation shafts 122 and 132 is reduced from the rotation speed of the drive shaft 167, the first drive gear 165 is set so that the reduction ratio is smaller than the reduction ratio of the second drive gear 166. The number of teeth of the drive gear 165 and the second drive gear 166 should be set. The term "reduction ratio" as used herein refers to the ratio of the number of teeth of the drive gear and the timing gear that mesh with each other (=the number of teeth of the timing gear/the number of teeth of the drive gear). In this case, if the number of teeth of the first timing gear 161 and the number of teeth of the second timing gear 162 are the same, the number of teeth of the first drive gear 165 should be larger than that of the second drive gear 166 . The speed reduction ratio of each drive gear 165, 166 may be appropriately determined so as to obtain the desired movement volume ratio _RQ . On the other hand, even if the rotation speed of the rotation shafts 122 and 132 is increased from the rotation speed of the drive shaft 167 or in the same case, the rotation speed of the rotor 121 in the first stage is equal to the rotation speed of the rotor 131 in the second stage. There is no problem if the number of teeth of the first drive gear 165 and the second drive gear 166 is set so as to be higher than the number.

<Cooling mechanism>
As shown in FIG. 2, the pump 100 includes, as a cooling mechanism, a cooler 1, an intermediate discharge port 115, and an intermediate backflow cooling gas inlet 116 (hereinafter simply referred to as "cooling gas inlet 116"). and are provided. The cooler 1 is an example of the cooling section of this embodiment, and is provided outside the casing 110 . At least one intermediate outlet 115 is provided on the side surface of the casing 110 . The cooling gas introduction port 116 is an example of the first cooling gas introduction port of the present embodiment, and at least one cooling gas introduction port is provided on the side surface of the casing 110 .

Cooler 1 is connected to intermediate outlet 115 and cooling gas inlet 116 and cools the gas discharged from intermediate outlet 115 . Although the cooler 1 is not particularly limited, for example, various heat exchangers such as a plate type, a shell and tube type (multi-tube type), a fin tube type, a spiral type, and an air-cooled type can be used. Further, as the cooling unit of the present invention, a pipe (not shown) connecting the intermediate discharge port 115 and the cooling gas inlet 116 may be provided outside the casing 110 without providing the cooler 1 . In this case, the gas discharged from the intermediate outlet 115 is cooled by radiating heat when passing through the pipe. When emphasizing the cooling efficiency, the heat exchanger as described above is provided, and when emphasizing the energy efficiency of the pump 100 as a whole, only the above piping is preferably provided.

The intermediate discharge port 115 discharges the gas existing between the low-pressure side (first stage in this embodiment) compression element and the high-pressure side (second stage in this embodiment) compression element that are adjacent to each other. As indicated by an arrow Ge in FIG. The intermediate discharge port 115 is provided at an intermediate position between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. The example shown in FIG. 2 shows an example in which only one intermediate outlet 115 is provided on the left side surface of the casing 110, but the number of intermediate outlets 115 is not particularly limited, and two or more outlets may be provided. good. For example, in the cross section shown in FIG. 2 , one more point may be provided not only on the left side of casing 110 but also on the right side. Also, when viewed from the front side of the cross section shown in FIG. An intermediate outlet 115 may be provided at an intermediate position between the eye (high pressure side) and the compression element.

The cooling gas inlet 116 (116A, 116B) feeds the gas cooled by the cooler 1 to a compression element on the lower pressure side than the intermediate outlet 115 (in this embodiment, the pressure of the gas discharged from the intermediate outlet 115 is It is a suction port for introducing into the first stage compression element) where gas with a pressure lower than is present. The cooling gas inlet 116 is provided at a position where the gas cooled by the cooler 1 can be mixed with the moving volume Qth1 portion sucked (scraped) by the rotor 121 of the first stage.

Here, the pressure (intermediate pressure Pm) at an intermediate position between the discharge side of the first stage compression element provided with the intermediate discharge port 115 and the suction side of the second stage compression element is the pressure of the first stage compression element (rotor 121) and this pressure is also equal to the suction pressure to the second stage compression element (rotor 131). Since the intermediate pressure Pm is equal to or higher than the pressure Pr of the space surrounded by the rotor 121 and the casing 110 (Pm≧Pr), the gas discharged from the intermediate discharge port 115 passes through the cooler 1 and is circulated. be. As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element. As a result, it is possible to suppress a significant temperature rise of the gas compressed by the second-stage compression element.

Note that FIG. 2 shows an example in which the cooling gas introduction ports 116 are provided on each of the left and right sides of the casing 110 (two locations in total), but the number of the cooling gas introduction ports 116 is not particularly limited. However, as long as at least one cooling gas inlet 116 is provided, the effect of suppressing a significant temperature rise of the gas can be obtained. In order to enhance the cooling effect of the gas sucked into the second-stage compression element, it is preferable that the number of cooling gas introduction ports 116 is large. In particular, in order to uniformly cool the inside of casing 110, as shown in FIG.

The pump 100 is also provided with a check valve 3 connected to the cooler 1 . The check valve 3 is closed by the differential pressure from the atmospheric pressure when the intermediate pressure Pm is below the atmospheric pressure, and is opened when the intermediate pressure Pm is above the atmospheric pressure. When the check valve 3 is open, the gas discharged from the intermediate discharge port 115 is discharged to the atmosphere having a pressure lower than that of the first-stage compression element, and when the check valve 3 is closed, It is introduced into the first-stage compression element from the cooling gas inlet 116 .

By providing the cooling mechanism of this embodiment having the above-described configuration, the temperature of the gas discharged from the first-stage compression element is lowered, so the thermal expansion of the second-stage rotor and casing is also reduced. Therefore, the gap between the rotor and the casing and the gap between the rotors in the second stage compression element can be narrowed. As a result, the amount of gas leaked from the second-stage compression element, that is, the amount of gas flowing back from the high pressure side to the low pressure side is reduced, thereby improving the volumetric efficiency.

Also, the amount of gas leaked from the second stage compression element, that is, the leakage amount from the discharge side (high pressure side) of the second stage compression element to the suction side (low pressure side) of the second stage compression element decreases. , the suction pressure of the second stage compression element decreases. When the suction pressure of the second-stage compression element decreases, the pressure difference between the suction pressure of the second-stage compression element (equal to the discharge pressure of the first-stage compression element) and the suction pressure of the first-stage compression element increases. become smaller. As a result, the shaft power of the first stage compression element can be reduced.

<Second cooling gas inlet>
In the pump 100 of the present embodiment, the casing 110 is positioned between the suction position (above intermediate position) where gas is sucked into the final stage (second stage in this embodiment) compression element and the discharge port 113. It further has a backflow cooling gas inlet 117 (hereinafter simply referred to as "cooling gas inlet 117") for introducing the cooling gas C into the interior of the . This cooling gas inlet 117 is an example of a second cooling gas inlet according to the present embodiment. More specifically, the cooling gas introduction port 117 allows the cooling gas C introduced into the casing 110 to mix with the movement volume Qth2 portion sucked (scraped) by the second stage rotor 131. position.

Further, as the cooling gas C, a gas whose temperature is lower than the temperature of the gas in the moving volume portion drawn by the second stage rotor 131 and whose pressure is equivalent to the discharge pressure Pd of the pump 100 is used. In this embodiment, the air in the atmosphere or the discharge gas discharged from the casing 110 of the pump 100 is cooled by radiating heat as it passes through a pipe or the like, or the discharge gas discharged from the casing 110 is cooled. It is used as a cooling gas C to be introduced into the casing 110 after being cooled by a vessel or the like. This cooling method is called a "backflow cooling method" because the gas discharged from the casing 110 is returned (backflowed) into the casing 110 after cooling.

In general, the higher the pressure ratio (discharge pressure/suction pressure), the more the sucked gas is compressed, and the higher the temperature of the discharged gas. In such a case, the temperature of the discharged gas can be lowered by providing the cooling gas introduction port 117 and introducing the cooling gas C into the casing 110 by the backflow cooling method. Therefore, when the temperature of the suction gas is high, it is generally necessary to cool the suction gas with a precooler or the like. Can be sucked without cooling. For example, even if the temperature of the intake gas is about 120° C., the intake gas can be sucked into the casing 110 without being cooled, although it varies somewhat depending on the operating conditions of the pump and the like.

Also, the usable pressure range of vacuum pumps and blowers may be determined by the temperature of the discharge gas. By using the backflow cooling method of the present embodiment, the temperature of the discharged gas can be kept low, so the usable pressure range can be greatly expanded.

Furthermore, when the backflow cooling method is used, cooling water for cooling the lubricating oil is not required when the temperature of the intake gas is normal temperature. Sealing water is sometimes used to cool the vacuum pump, but it cannot be used depending on the application and suction gas. In that case, the use of a backflow cooling system allows operation of the pump 100 without the use of sealing water.

In addition, when the backflow cooling method is adopted for the vacuum pump, since air in the atmosphere can be used as the cooling gas C, the discharge gas can be reduced simply by providing the cooling gas introduction port 117 capable of taking in the air in the atmosphere. The temperature can be sufficiently lowered. Therefore, the structure of the pump 100 is not complicated. Even in other cases, the gas discharged from the vacuum pump or blower can be used as the cooling gas C by cooling it with a cooler (not shown) or the like installed outside the pump 100 .

FIG. 2 shows an example in which the cooling gas inlets 117 are provided on both left and right sides of the casing 110 , but the cooling gas inlets 117 are provided only on either the left or right side of the casing 110 . may be provided. However, in order to sufficiently obtain the effect of uniformly lowering the temperature of the discharge gas, it is preferable that the cooling gas introduction ports 117 are provided on both left and right sides of the casing 110 .

<Other configurations>
In addition, the pump 100 of this embodiment has side covers 180 as intermediate chambers between the casing 110 and the bearing/gear chamber 173 and between the casing 110 and the bearing chamber 174 . As shown in FIG. 1, since the side cover 180 is provided with the sealing mechanisms Sb and Sc, the first timing gear 161, the second timing gear 162, the first driving gear 165, the second driving gear 166, and the bearings Lubricating oil of 123A, 123B, 133A, and 133B does not leak into casing 110, and deterioration of lubricating oil due to drain contained in gas sucked into casing 110 can be prevented. As a method for lubricating the first timing gear 161, the second timing gear 162, the first drive gear 165, the second drive gear 166, the bearings 123A, 123B, 133A, and 133B, for example, splash lubrication can be used. It is not limited.

In addition to the seal mechanism provided in the side cover 180 described above, as shown in FIG. In the pump 100 of the present embodiment, two stages of compression elements are provided as a single stage group within the single casing 110. Therefore, unlike the pipe-connected multistage roots type pump, the shaft sealing mechanism of the drive shaft 167 is can be installed in one place. The sealing method for the sealing mechanisms Sb and Sc and the shaft sealing mechanism Sa is not particularly limited, and may be appropriately selected according to the type of gas to be compressed by the pump 100 . Specifically, as the seal mechanisms Sb and Sc and the shaft seal mechanism Sa, oil seals, labyrinth seals, mechanical seals (single mechanical seal, double mechanical seal), etc. can be used alone or in combination.

(Operation of multistage roots pump)
Next, referring to FIGS. 1 to 6E, a method of driving the pump 100 having the above-described configuration, and a method of compressing gas and cooling the gas by the pump 100 will be described.

<Pump driving method>
As shown in FIGS. 1 to 4, when drive shaft 167 is rotated by a motor (not shown), first drive gear 165 and second drive gear 166 supported by drive shaft 167 are driven to rotate in the same direction. Next, of the pair of first timing gears 161A and 161B, one of the first timing gears 161A meshing with the first driving gear 165 rotates in the opposite direction to the first driving gear 165. As shown in FIG. The rotation speed of the first timing gear 161A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the first timing gear 161A/the number of teeth of the first drive gear 165). Also, the other first timing gear 161B meshing with the first timing gear 161A has the same number of teeth as the first timing gear 161A, so it rotates in the opposite direction to the first timing gear 161A at the same number of revolutions. As a result, the pair of rotors 121, 121 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 121, 121, the gas near the suction port 111 is sucked into the casing 110 through the suction port 111 (arrow Gs in FIG. 2), then compressed by the rotor 121 and discharged to the intermediate position. (arrow Gm in FIG. 2).

Similarly, of the pair of second timing gears 162A and 162B, one of the second timing gears 162A meshing with the second drive gear 166 rotates in the opposite direction to the second drive gear 166. As shown in FIG. The rotation speed of the second timing gear 162A at this time is a reduction ratio ( The rotation speed is reduced by the number of teeth of the second timing gear 162A/the number of teeth of the second drive gear 166). Also, the other second timing gear 162B meshing with the second timing gear 162A has the same number of teeth as the second timing gear 162A, so it rotates in the opposite direction at the same number of rotations as the second timing gear 162A. . As a result, the pair of rotors 131, 131 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 131, 131, the gas compressed by the rotor 121 of the first stage and discharged to the intermediate position is swept into the rotor 131 of the second stage from the intermediate position (see arrow in FIG. 2). Gm), it is then compressed by the rotor 131 and discharged to the outside from the discharge port 113 (arrow Gd in FIG. 2).

Further, as described above, in the present embodiment, the gas present in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 115 to the outside of the casing 110 and cooled by the cooler 1. Later, it is introduced into the first-stage compression element (inside the space surrounded by rotor 121 and casing 110) through two cooling gas introduction ports 116A and 116B provided on both left and right sides of casing 110. FIG. At this time, the pressure at the intermediate position (intermediate pressure) Pm is higher than the pressure in the space surrounded by the rotor 121 and the casing 110, so the gas discharged from the intermediate discharge port 115 passes through the cooler 1 , circulating. More specifically, as indicated by arrow Ge in FIG. is introduced into the region surrounded by the first stage rotor 121 and the casing 110 (moving volume Qth1 portion), and then discharged to the intermediate position again. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 115, and the gas cooled by the cooler 1 flows into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed.

Furthermore, when the intermediate pressure Pm is equal to or higher than the atmospheric pressure, the check valve 3 is opened, and the pressure difference between the intermediate pressure Pm and the atmospheric pressure causes the gas existing at the intermediate position to be pushed out from the intermediate discharge port 115 to a higher pressure. (arrow Ge and arrow Gd in FIG. 2), and the intermediate pressure Pm drops below atmospheric pressure. Therefore, since the suction pressure to the second-stage compression element (rotor 131) becomes smaller, the suction pressure to the first-stage compression element (rotor 121) and the suction pressure to the second-stage compression element (rotor 131) can be reduced. As a result, the power of the motor that operates the pump 100 can be reduced. In particular, when the pump 100 starts to draw gas toward the suction port 111, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the reduction ratio of the first drive gear 165 with respect to the first timing gear 161A is smaller than the reduction ratio of the second drive gear 166 with respect to the second timing gear 162A. Therefore, the rotation speed N1 of the rotor 121 becomes higher than the rotation speed N2 of the rotor 131. Further, the length L1 of the rotor 121 and the length L2 of the rotor 131 are equal, and the rotors 121 and 131 have the same shape. is _greater than one.

<Gas compression method>
Next, a method of compressing gas by the pump 100 will be described with reference to FIGS. 5A to 5E. In FIGS. 5A to 5E, coarse dot hatching indicates low pressure portions (low pressure portions), and fine dot hatching indicates high pressure portions (high pressure portions). Further, the method of compressing gas will be described by taking the first-stage (low-pressure side) compression element of the two-stage compression elements of the pump 100 as an example.

As described above, inside the casing 110, the pair of rotors 121 and the pair of rotors 131 are separated from each other with a slight gap between the inner surface 110a of the casing 110, between the rotors 121 and between the rotors 131. Rotate in the opposite direction. At this time, when one rotor 121 (for example, the rotor 121 on the left side in the illustrated example) has a tip of a protruding portion 121a (hereinafter referred to as a “leaf tip 121a”) passes through the suction port 111, the casing 110 A certain amount of low-pressure gas captured between is transferred from the suction port 111 side to the discharge port 113 side, and is discharged in the form of being pushed to the high-pressure side.

Specifically, first, the leaf end 121a of one rotor 121 passes through the suction port 111, as shown in FIG. 5A. At this time, the tip of the projecting portion 121b (hereinafter referred to as "leaf end 121b") is in a sealed state with the inner surface 110a. After that, as shown in FIG. 5B, when the leaf end 121a and the end portion 110b of the inner surface 110a on the suction port 111 side are sealed, the leaf end 121a and the leaf end 121b are surrounded by the inner surface 110a. A volume V of low pressure gas is trapped. Furthermore, as shown in FIG. 5C, the low-pressure gas of volume V is transferred toward the discharge port 113 side while maintaining the sealed state between the leaf ends 121a and 121b and the inner surface 110a. Next, as shown in FIG. 5D, the leaf end 121b reaches the end 110c of the inner surface 110a on the side of the second-stage compression element while the volume V of the low-pressure gas is still trapped, and is shown in FIG. 5E. As shown, the moment the leaf end 121b rotates further from there and reaches the intermediate position on the second stage compression element side, the intermediate pressure gas on the discharge side (higher pressure than the low pressure gas) is released into the first stage pump. Flowing back into the working area, the low pressure gas is compressed under back pressure.

After that, although not shown, in the second stage compression element, as in the first stage, the gas discharged from the rotor 121 is pushed by the two leaf ends of the rotor 131 and the inner surface 110d of the casing 110. After being captured by the rotor 131 in the enclosed volume V and transported to the discharge port 113 side, it is compressed (backflow compression) by the reverse flow of the high pressure gas on the discharge side and discharged from the discharge port 113 to the outside of the casing 110 .

As described above, when the high-pressure gas on the discharge side backflows and the low-pressure gas on the suction side is back-compressed, a rapid pressure change occurs. This pressure change causes the pump 100 to make noise. On the other hand, in the present embodiment, since the three-leaf rotors are used as the rotors 121 and 131, compared with the two-leaf rotor described later, the cycle of the pressure change is 2/3, Also, the maximum value of the pressure peak is reduced. As a result, the pump 100 smoothly back-compresses the gas, thereby reducing noise.

<Gas cooling method>
Next, referring to FIGS. 6A to 6E, a gas cooling method (a cooling method using a backflow cooling method) when the pump 100 is used as a vacuum pump will be described. In FIGS. 6A to 6E, coarse dot hatching indicates a vacuum region (suction pressure region), and fine dot hatching indicates an atmospheric pressure region (ejection pressure region). As used herein, "vacuum" means pressure below atmospheric pressure and does not mean absolute vacuum. Further, the gas cooling method will be described by taking the second-stage (high-pressure side) compression element of the two-stage compression elements of the pump 100 as an example.

The gas cooling method of the present embodiment employs the above-described backflow cooling method, and is specifically as follows. First, as shown in FIG. 6A, one rotor 131 (in the illustrated example, the rotor 131 on the left side) has a tip of a protruding portion 131a (hereinafter referred to as a “leaf end 131a”) that is compressed in the first stage. Pass through intermediate positions between elements. At this time, the tip of the projecting portion 131b (hereinafter referred to as "leaf end 131b") is in a sealed state with the inner surface 110d. Thereafter, as shown in FIG. 6B, when the leaf end 131a and the end portion 110e of the inner surface 110d on the side of the first compression element are sealed, the tip and the inner surface of the leaf end 131a and the leaf end 131b are sealed. As the evacuated gas of volume V bounded by 110d is captured from the vacuum region, cooling gas C at the same pressure as the discharge pressure (atmospheric pressure) begins to flow back into the evacuated gas side of volume V. FIG. FIG. 6B shows the state in which the discharge pressure and the atmospheric pressure cooling gas C have begun to be mixed with the gas in the vacuum state by the gradation of the density of the dots. Further, as shown in FIG. 6C, as the rotor 131 rotates, the cooling gas C flows into the gas side of the volume V while maintaining the sealed state between the leaf ends 131a and 131b and the inner surfaces 110d and 110h. Fully flowing, the pressure of the volume V of gas approaches the discharge pressure (atmospheric pressure). Next, as shown in FIG. 6D, when the rotor 131 rotates further and the leaf tip 131b reaches the end 110f of the inner surface 110d on the side of the outlet 113 while the volume V of gas remains trapped, The pressure of the gas of volume V becomes almost the same as the discharge pressure, and the body is in a state immediately before the discharge port 113 and the space in which the gas of volume V is captured communicate with each other. After that, when the rotor 131 rotates further, as shown in FIG. 6E, the leaf end 131b reaches the discharge port 113, and the volume V of gas is pushed out to the discharge port 113 side.

As described above, the temperature of the discharged gas can be lowered by introducing the cooling gas C into the casing 110 using the backflow cooling method of the present embodiment. As a result, the various effects described above can be obtained.

(First modified example)
Next, referring to FIG. 7, a first modified example in which the shapes of the rotors 121 and 131 of this embodiment are changed will be described. A multi-stage roots pump 101 (hereinafter referred to as "pump 101") according to this modification is a modification that differs from the pump 100 according to the above-described first embodiment only in the shape of the rotor. This modified example can also be applied as modified examples of the second to eleventh embodiments described later.

As shown in FIG. 7, the pump 101 has a pair of rotors 141, 151 and two rotary shafts 142, 152 as first-stage and second-stage compression elements, respectively.

<Rotors 141, 151>
The rotor 141 is a two-leaf rotor, and its rotor profile has a so-called eyebrow-shaped cross-sectional shape with two protruding portions 141a and 141b radially protruding from the center of rotation. A recess 141d is provided between each projection 141a and 141b. Similarly, the rotor 151 is also a two-leaf rotor, and its rotor profile has a so-called cocoon-shaped cross-sectional shape with two pieces of projections 151a and 151b projecting radially from the center of rotation. A recess 151d is provided between each projection 151a and 151b. In the following description, the description of the rotor 151 that overlaps with that of the rotor 141 will be omitted as necessary, and the contents of the rotor 141 will be appropriately read.

Between the rotors 141 and 141 and between the tips (leaf ends) of the protrusions 141a and 141b and the inner surface of the casing 110, so that the pair of rotors 141 and 141 and the rotor 141 and the inner surface 110a of the casing 110 do not come into contact with each other. A rotor 141 is arranged so that a slight gap is formed between 110a (in a sealed state).

Here, each of the protruding portions 141a and 141b of the pair of rotors 141 and 141 rotates around the center of the rotating shaft 142 that supports the rotor 141, and the inner surface of the casing 110a rotates at a rotation angle of 175 degrees or more. preferably remain sealed between For this purpose, a line segment connecting the end 110b of the inner surface 110a of the first stage (low pressure side) of the casing 110 on the side of the suction port 111 and the center of rotation of the rotor 141, and the compression of the second stage (high pressure side) of the inner surface 110a. The shape of the casing 110 may be set so that the angle θ between the end 110c on the element side and the line segment connecting the center of rotation of the rotor 141 is in the range of 175 degrees or more. The same applies to the pair of rotors 151, 151. A line segment connecting the end portion 110e of the second stage inner surface 110d of the casing 110 on the side of the first stage compression element and the rotation center of the rotor 151, It is preferable to set the shape of the casing 110 so that the angle θ between the end 110f of the inner surface 110d on the discharge port 113 side and the line segment connecting the center of rotation of the rotor 151 is in the range of 175 degrees or more. As a result, the gas compressed by the rotors 141 and 151 can be prevented from flowing back to the suction port 111 side, and as a result, a sufficiently sealed state is maintained.

<Transfer volume ratio>
The displacement volume ratio _RQ in the pump 101 of this modification is calculated as follows. First, each time the pair of right and left rotors 141 and 151 makes one rotation, gas is sucked and discharged four times (one rotor 141 and 151, two times each). Here, if the cross-sectional area of the cross section perpendicular to the rotating shaft 142 of the space surrounded by the two protrusions (the protrusion 141a and the protrusion 141b) of the rotor 141 and the inner surface 110a of the casing 110 is S1', one step The moving area A1 of the second (low pressure side) compression element is A1=4×S1′. Similarly, if the cross-sectional area of the cross section perpendicular to the rotating shaft 152 of the space surrounded by the two protruding portions (protruding portion 151a and protruding portion 151b) of the rotor 151 and the inner surface 110d of the casing 110 is S2', the two-stage The moving area A2 of the second (high pressure side) compression element is A2=4×S2′. Thus, in this modified example, the method of calculating the moving areas A1 and A2 is different from that in the first embodiment. Since other points are the same as those of the first embodiment, description thereof is omitted.

<Precautions for backflow cooling>
Here, with reference to FIGS. 8A and 8B, points to consider when cooling the discharge gas by adopting the backflow cooling method in the pump 101 according to this modification will be described. 8A and 8B both show that the cooling gas C from the cooling gas inlet 117 passes through the gap g1 between the inner surface 110d of the casing 110 and the rotor 151 and is captured by the inner surface 110d of the casing 110 and the rotor 151. It shows the state where the gas has started to be introduced. Thus, at the stage when the cooling gas C starts to be introduced, as shown in FIG. If not, the gas captured from this gap will return to the first stage (low pressure side) compression element, and the compression ratio will decrease. Therefore, as shown in FIG. 8B, at the stage when the cooling gas C starts to be introduced, it is necessary that the inner surface 110d of the casing 110 and the rotor 151 are in a sealed state (broken line in FIG. 8B). (see circled s2 in ).

<Difference in usage>
The application of the pump 101 according to this modification is not particularly limited, but when adopting a two-leaf rotor like the rotors 141 and 151 of this modification, the pump 101 can be used as a wet vacuum pump. is preferred. On the other hand, like the rotors 121 and 131 of the first embodiment, when adopting a three-lobe rotor, it is preferable to use the pump 100 as a dry blower. Examples of systems using wet vacuum pumps include oxygen generators (PSA/VSA), and examples of systems using dry blowers include nitrogen ( _N2 ) start-up blowers.

(Second modified example)
Next, a second modified example in which the shape of the rotor 121 of this embodiment is changed will be described with reference to FIG. A multi-stage roots-type pump 102 (hereinafter referred to as "pump 102") according to this modification is a modification that differs from the pump 100 according to the above-described first embodiment only in the shape of the rotor in the first stage. be. This modified example can also be applied as modified examples of the second to eleventh embodiments described later.

As shown in FIG. 9, the pump 101 has a pair of rotors 141, 131 and two rotary shafts 142, 132 as first-stage and second-stage compression elements, respectively. That is, in the pump 101, the first stage rotor 141 is the same two-leaf rotor as in the first modified example, and the second stage rotor 131 is the same three-leaf rotor as in the first embodiment. Other configurations and operations are the same as those of the first embodiment or the first modified example described above. Contrary to the example shown in FIG. 9, the present invention also employs the same three-lobe rotor as in the first embodiment as the rotor in the first stage, and the same two-lobe rotor as in the first modified example as the rotor in the second stage. included in the range of

[Second embodiment]
Next, a multi-stage roots pump according to a second embodiment of the present invention will be described in detail with reference to FIGS. 10 to 12. FIG. FIG. 10 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 200 (hereinafter abbreviated as "pump 200") as an example of a multi-stage roots-type pump according to the present embodiment. FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. 12 is a cross-sectional view taken along line XII-XII in FIG. 10. FIG. In the pump 100 of the first embodiment, the first stage (low pressure side) rotor 121 and the second stage (high pressure side) rotor 131 have the same length and diameter, and the rotation speed of the first stage rotor 121 is is higher than the rotation speed of the rotor 131 in the second stage, in the pump 200 according to this embodiment, the rotation speed and diameter of the rotor 221 in the first stage and the rotor 231 in the second stage are equal, Moreover, this is an example in which the length of the rotor 221 in the first stage is longer than the length of the rotor 231 in the second stage. In addition, below, the description which overlaps with 1st Embodiment is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 10 to 12, the pump 200 is a two-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 210, two-stage compression elements, a drive mechanism, and a cooling mechanism. Prepare.

<Casing>
The configuration and function of the casing 210 are similar to those of the casing 110 according to the first embodiment.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 211 side and a second stage (high pressure side) compression element located on the discharge port 213 side are provided in the single casing 210. A two-stage compression element is provided. A partition plate or the like is not provided between the two stages of compression elements unlike the series internal multi-stage roots type pump, and a plurality of compression elements are provided as a single stage group within the integral casing 210. ing. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 221 and 221 and two rotating shafts 222 and 222 . The second stage compression element has a pair of rotors 231 and 231 and two rotating shafts 232 and 232 .

As shown in FIG. 11, the rotor 221 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 221a, 221b, 221c projecting radially from the center of rotation. In addition, recesses 221d are provided between the protrusions 221a, 221b, and 221c. Similarly, the rotor 231 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 231a, 231b, 231c projecting radially from the center of rotation. Further, recesses 231d are provided between the protrusions 231a, 231b, and 231c.

The pair of rotors 221, 221 are provided rotatably in directions opposite to each other. The two rotating shafts 222, 222 rotatably support a pair of rotors 221, 221 and are arranged parallel to each other. Also, the two rotating shafts 222 , 222 are supported by two bearings 223 , 223 . Similarly, a pair of rotors 231, 231 are provided rotatably in directions opposite to each other. The two rotating shafts 232, 232 rotatably support a pair of rotors 231, 231 and are arranged parallel to each other. Also, the two rotating shafts 232 , 232 are supported by two bearings 233 , 233 . Furthermore, in this embodiment, the rotating shaft 222 and the rotating shaft 232 are arranged so as to be parallel to each other. In the following description, the description of the rotor 231 that overlaps with that of the rotor 221 will be omitted as necessary, and the contents of the rotor 221 will be read appropriately.

Between the rotors 221 and 221 and the tips (leaf ends) of the protrusions 221a, 221b, and 221c and the casing 210 are arranged so that the pair of rotors 221 and 221 and the rotor 221 and the inner surface 210a of the casing 210 do not come into contact with each other. A rotor 221 is arranged so that a small gap is formed between the inner surface 210a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 221, 221 are maintained by timing gears 261A, 261B, which will be described later, and the cross-sectional shape of the rotor 221 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 231 is arranged so that a slight gap is formed between the paired rotor 231 and the inner surface 210 d of the casing 210 . Also, the pair of rotors 231, 231 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Other configurations and functions of the rotors 221 and 231 are similar to those of the rotors 121 and 131 according to the first embodiment.

In the pump 200, as in the pump 100 of the first embodiment, the rotor 221, the rotating shaft 222, etc., which are the first-stage compression elements, and the rotor 231, the rotating shaft 232, etc., which are the second-stage compression elements, Within the single casing 210, they are arranged in parallel along the normal direction of an imaginary plane containing the two rotating shafts 222, 222 (or the two rotating shafts 232, 232) of the same stage. That is, the rotor 221 in the first stage and the rotor 231 in the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are in parallel. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 211, the first-stage rotor 221, the second-stage rotor 231, and the gas discharge port 213 are arranged side by side in the vertical direction. Therefore, when the gas is introduced into the casing 210 from the suction port 211 (arrow Gs in FIG. 11), it travels vertically downward, is compressed by the rotor 221, and then passes through the first stage compression element and the second stage compression element. (arrow Gm in FIG. 11). The gas compressed by the rotor 221 further travels vertically downward, is compressed by the second-stage rotor 231, and is then directly discharged from the discharge port 213 to the outside of the casing 210 (arrow Gd in FIG. 11).

Thus, according to the pump 200 according to the present embodiment, the first stage rotor 221 and the second stage rotor 231 are arranged in parallel on separate shafts within the single casing 210 . Therefore, unlike the in-line multistage roots pump, the rotors 221 and 231 can be arranged without providing a partition between the first stage compression element (rotor 221) and the second stage compression element (rotor 231). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of an in-line multi-stage roots pump, if it has two stages of rotors, the length of the rotary shaft is required to be equal to or longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, it is possible to suppress a decrease in rigidity of the rotating shafts 222 and 232 and the casing 210 . In particular, even if the length of the rotors 221 and 231 is lengthened in order to increase the air volume of the pump 200, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and the alignment accuracy between the first stage and the second stage pump operation areas are not so high, they are within a range that does not affect the performance of the pump 200 in terms of assembly and performance. Accuracy and assembly accuracy are not required.

<Transfer volume ratio>
Also in the pump 200 of this embodiment, between the first-stage compression element (rotor 221) and the second-stage compression element (rotor 231) arranged in parallel on separate rotating shafts, the following formula (1 ) is _greater than 1.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in this embodiment is a so-called displacement amount, which is the theoretical volume per time of the space surrounded by the casing 210 and the rotor 221 or the rotor 231, which is proportional to the rotational speed N. . That is, as described above, the movement volume Qth (m ³ /min) is represented by the following equation (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, A is the area of movement per revolution, L is the length of the rotor, and N is the number of rotations of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the axis of rotation 222, 232. FIG.

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 200 of this embodiment is calculated by the following equation (3).

However, in formula (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 221, L2 is the length of the second stage rotor 231, N1 is the rotation speed of the first stage rotor 221, and N2 is the second stage rotor 231. represents the number of rotations of

Here, the pump 200 of this embodiment differs from the first embodiment described above in that the length L1 of the rotor 221 of the first stage differs from the length L2 of the rotor 231 of the second stage. Therefore, the pump 200 has the advantage that the same rotors (rotors having the same shape and size) can be used for the first stage rotor 221 and the second stage rotor 231, like the pump 100 according to the first embodiment. Can not. On the other hand, according to the pump 200, since the length L1 of the first stage rotor 221 is longer than the length L2 of the second stage rotor 231 (L1>L2), the first stage rotor 221 Even if the rotational speed N1 of the second stage rotor 231 and the rotational speed N2 of the second stage rotor 231 are the same (that is, N1=N2), the displacement volume ratio _RQ can be 1 or more.

In pump 200, rotors 221 and 231 have the same diameter and shape. Therefore, the moving area A1 of the first stage is equal to the moving area A2 of the second stage. Further, the rotation speed N1 of the rotor 221 and the rotation speed N2 of the rotor 231 are equal. Therefore, the above formula (3) can be rewritten as the following formula (3-2).

Therefore, in this embodiment, in order to make the moving volume ratio R _Q1-2 between the first stage and the second stage larger than 1, the length L1 of the rotor 221 of the first stage is set to the length of the rotor 231 of the second stage. is longer than the length L2 (L1>L2). As described above, in the present embodiment, the rotor length ratio (L1/L2) of the length L1 of the rotor 221 of the first stage and the length L2 of the rotor 231 of the second stage determines the length of the first stage and the second stage. A moving volume ratio R _Q1-2 between is determined. As a result, the rotation speed N1 of the rotor 221 in the first stage and the rotation speed N2 of the rotor 231 in the second stage can be made the same. be.

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 267 of the pump 200 can be reduced.

<Drive Mechanism>
As shown in FIGS. 10 and 12, the drive mechanism of this embodiment includes a pair of first timing gears 261 (261A, 261B), a pair of second timing gears 262 (262A, 262B), and a common drive mechanism. It has a gear 265 and a single drive shaft 267 which is the motor input shaft.

A pair of first timing gears 261A and 261B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 222 of the first stage, and are arranged so that the rotation phases of the pair of rotors 221 and 221 match each other. , have the same number of teeth. A pair of second timing gears 262A and 262B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 232 of the second stage, and are arranged so that the rotation phases of the pair of rotors 231 and 231 match each other. , have the same number of teeth. The material of the first timing gear 261 and the second timing gear 262 is the same as the material of the first timing gear 161 and the second timing gear 162 according to the first embodiment.

In addition, the common drive gear 265 meshes with both the first timing gear 261A, which is one of the pair of first timing gears 261, and the second timing gear 262A, which is one of the pair of second timing gears 262. is provided as follows. Further, drive shaft 267 rotatably supports common drive gear 265 . The drive shaft 267 is supported by a bearing 268 provided in the side cover 280 and a bearing 268 provided in the bearing/gear chamber 273 . The shaft end of the drive shaft 267 on the bearing 268 side provided in the bearing/gear chamber 273 is connected to a motor (not shown).

As described above, the length L1 of the rotor 221 is longer than the length L2 of the rotor 231 in this embodiment. Therefore, in order to make the movement volume ratio greater than 1 (R _Q >1), the rotation speed of the rotor 221 in the first stage may be the same as the rotation speed of the rotor 231 in the second stage. In other words, the rotational speed of the rotor 221 in the first stage can be made the same as the rotational speed of the rotor 231 in the second stage. Therefore, in the pump 200, the first timing gear 261 and the second timing gear 262 having the same number of teeth are used so that the rotation speed of the rotor 221 at the first stage is the same as the rotation speed of the rotor 231 at the second stage. are meshed with the common drive gear 265. The length of each rotor 221, 231 may be appropriately determined so as to obtain the desired air volume and movement volume ratio _RQ .

<Cooling mechanism>
As shown in FIG. 11, the casing 210 according to this embodiment also has an intermediate discharge port 215 and an intermediate backflow cooling gas introduction port 216 as an example of a first cooling gas introduction port according to this embodiment (hereinafter simply referred to as “cooling gas inlet”). A gas introduction port 216” is provided. The intermediate outlet 215 and the cooling gas inlet 216 respectively have the same configurations, functions and effects as the intermediate outlet 115 and the cooling gas inlet 116 according to the first embodiment. A cooler 1 as an example of the cooling unit according to the present embodiment is connected to the intermediate discharge port 215 and the cooling gas introduction port 216 . A check valve 3 is also connected to the cooler 1 .

<Second cooling gas inlet>
As shown in FIG. 11, a casing 210 according to the present embodiment is also provided with a backflow cooling gas introduction port 217 having the same configuration, function and effect as the cooling gas introduction port 117 according to the first embodiment.

<Other configurations>
In addition, the pump 200 of this embodiment has side covers 280 as intermediate chambers between the casing 210 and the bearing/gear chamber 273 and between the casing 210 and the bearing chamber 274 . This side cover 280 has substantially the same configuration and function as the side cover 180 according to the first embodiment. The pump 200 is also provided with the same sealing mechanism and shaft sealing mechanism as the pump 100 according to the first embodiment.

(Operation of multistage roots pump)
Next, a method of driving the pump 200 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 200 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIGS. 10 to 12, when the drive shaft 267 is rotated by a motor (not shown), the common drive gear 265 supported by the drive shaft 267 is rotationally driven. Next, of the pair of first timing gears 261A and 261B, one of the first timing gears 261A meshing with the common drive gear 265 rotates in the opposite direction to the common drive gear 265. As shown in FIG. The rotation speed of the first timing gear 261A at this time is a reduction ratio (first The rotation speed is reduced by the number of teeth of the timing gear 261A/the number of teeth of the common driving gear 265). Also, the other first timing gear 261B meshing with the first timing gear 261A has the same number of teeth as the first timing gear 261A, so it rotates in the opposite direction to the first timing gear 261A at the same number of revolutions. As a result, the pair of rotors 221, 221 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 221, 221, the gas near the suction port 211 is sucked into the casing 210 through the suction port 211 (arrow Gs in FIG. 11), then compressed by the rotor 221 and discharged to the intermediate position. (arrow Gm in FIG. 11).

Similarly, of the pair of second timing gears 262A and 262B, one of the second timing gears 262A meshing with the common driving gear 265 rotates in the opposite direction to the common driving gear 265. The rotation speed of the second timing gear 262A at this time is a reduction ratio (second The rotation speed is reduced by the number of teeth of the timing gear 262A/the number of teeth of the common drive gear 265). Here, since the first timing gear 261A and the second timing gear 262A have the same number of teeth and mesh with the same common drive gear 265, the rotation direction and rotation speed of the second timing gear 262A are It becomes the same as the first timing gear 261A. Also, the other second timing gear 262B meshing with the second timing gear 262A has the same number of teeth as the second timing gear 262A, so it rotates in the opposite direction at the same number of rotations as the second timing gear 262A. . As a result, the pair of rotors 231, 231 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 231, 231, the gas compressed by the rotor 221 of the first stage and discharged to the intermediate position is swept into the rotor 231 of the second stage from the intermediate position (arrow in FIG. 11). Gm), it is then compressed by the rotor 231 and discharged to the outside from the discharge port 213 (arrow Gd in FIG. 11).

Further, in the present embodiment, as in the first embodiment, the gas present in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 215 to the outside of the casing 210, and is discharged from the cooler 1. After being cooled, it is introduced into the first-stage compression element (inside the space surrounded by rotor 221 and casing 210) through two cooling gas introduction ports 216A and 216B provided on both left and right sides of casing 210. be. At this time, since the pressure at the intermediate position (intermediate pressure) Pm is equal to or higher than the pressure in the space surrounded by the rotor 221 and the casing 210, the gas discharged from the intermediate discharge port 215 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge in FIG. 11, the gas discharged from the intermediate discharge port 215 is cooled by the cooler 1, and is introduced into the compression element at the first stage from the cooling gas introduction port 216. is introduced into the region surrounded by the first stage rotor 221 and the casing 210 (moving volume Qth1 portion), and then discharged to the intermediate position again. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 215, and the gas cooled by the cooler 1 is discharged into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed.

Furthermore, when the intermediate pressure Pm is equal to or higher than the atmospheric pressure, the check valve 3 is opened, and the pressure difference between the intermediate pressure Pm and the atmospheric pressure causes the gas existing at the intermediate position to be pushed out from the intermediate discharge port 215 to a higher pressure. (arrow Ge and arrow Gd in FIG. 11), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second stage compression element (rotor 231) becomes smaller, the suction pressure to the first stage compression element (rotor 221) and the suction pressure to the second stage compression element (rotor 231) can be reduced. As a result, the power of the motor that operates the pump 200 can be reduced. In particular, when the pump 200 starts to draw gas toward the suction port 211, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the length L1 of the rotor 221 is longer than the length L2 of the rotor 231. As shown in FIG. Also, the reduction ratio of the common drive gear 265 with respect to the first timing gear 261A is the same as the reduction ratio of the common drive gear 265 with respect to the second timing gear 262A. Therefore, the rotation speed N1 of the rotor 221 is the same as the rotation speed N2 of the rotor 231. FIG. Further, since the rotors 221 and 231 have the same shape, the volumetric displacement ratio _RQ between the first-stage compression element and the second-stage compression element is greater than 1, as described above.

[Third embodiment]
Next, a multi-stage roots pump according to a third embodiment of the present invention will be described in detail with reference to FIGS. 13 to 15. FIG. FIG. 13 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 300 (hereinafter abbreviated as "pump 300") as an example of a multi-stage roots-type pump according to the present embodiment. 14 is a cross-sectional view taken along line XIV-XIV in FIG. 13. FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 13. FIG. In the pump 100 of the first embodiment, the first stage (low pressure side) rotor 121 and the second stage (high pressure side) rotor 131 have the same length and diameter, and the rotation speed of the first stage rotor 121 is is higher than the rotation speed of the rotor 131 in the second stage, in the pump 300 according to this embodiment, the rotation speed and length of the rotor 321 in the first stage and the rotor 331 in the second stage are equal. Also, the diameter of the rotor 321 in the first stage is larger than the diameter of the rotor 331 in the second stage. In addition, below, the description which overlaps with 1st Embodiment is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 13 to 15, the pump 300 is a two-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 310, two-stage compression elements, a drive mechanism, and a cooling mechanism. Prepare.

<Casing>
The configuration and function of the casing 310 are similar to those of the casing 110 according to the first embodiment.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 311 side and a second stage (high pressure side) compression element located on the discharge port 313 side are provided in the single casing 310. A two-stage compression element is provided. A partition plate or the like is not provided between the two stages of compression elements unlike the series internal multi-stage roots type pump, and a plurality of compression elements are provided as a single stage group within the integral casing 310. ing. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 321 and 321 and two rotating shafts 322 and 322 . The second stage compression element has a pair of rotors 331 and 331 and two rotating shafts 332 and 332 .

As shown in FIG. 14, the rotor 321 is a three-lobe rotor, and its rotor profile is shaped to have three protruding portions 321a, 321b, 321c radially protruding from the center of rotation. In addition, recesses 321d are provided between the protrusions 321a, 321b, and 321c. Similarly, the rotor 331 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 331a, 331b, 331c projecting radially from the center of rotation. In addition, recesses 331d are provided between the protrusions 331a, 331b, and 331c.

The pair of rotors 321, 321 are provided rotatably in directions opposite to each other. The two rotating shafts 322, 322 rotatably support a pair of rotors 321, 321 and are arranged parallel to each other. Also, the two rotating shafts 322 , 322 are supported by two bearings 323 , 323 . Similarly, a pair of rotors 331, 331 are provided rotatably in directions opposite to each other. The two rotating shafts 332, 332 rotatably support a pair of rotors 331, 331 and are arranged parallel to each other. Also, the two rotating shafts 332 , 332 are supported by two bearings 333 , 333 . Furthermore, in this embodiment, the rotating shaft 322 and the rotating shaft 332 are arranged so as to be parallel to each other. In the following description, the description of the rotor 331 that overlaps with that of the rotor 321 will be omitted as necessary, and the contents of the rotor 321 will be replaced as appropriate.

Between the rotors 321 and 321 and the tips (leaf ends) of the protrusions 321a, 321b, and 321c and the casing 310 are arranged so that the pair of rotors 321 and 321 and the rotor 321 and the inner surface 310a of the casing 310 do not come into contact with each other. A rotor 321 is arranged with a small gap between the inner surface 310a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 321, 321 are maintained by timing gears 361A, 361B, which will be described later, and the cross-sectional shape of the rotor 321 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 331 is arranged so that a slight gap is formed between the paired rotor 331 and the inner surface 310 d of the casing 310 . Also, the pair of rotors 331, 331 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Other configurations and functions of the rotors 321 and 331 are similar to those of the rotors 121 and 131 according to the first embodiment.

In the pump 300, as in the pump 100 of the first embodiment, the rotor 321, the rotating shaft 322, etc., which are the first-stage compression elements, and the rotor 331, the rotating shaft 332, etc., which are the second-stage compression elements, Within a single casing 310, they are arranged in parallel along the normal direction of an imaginary plane containing two rotating shafts 322, 322 (or two rotating shafts 332, 332) of the same stage. That is, the rotor 321 of the first stage and the rotor 331 of the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are parallel to each other. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 311, the first-stage rotor 321, the second-stage rotor 331, and the gas discharge port 313 are arranged side by side in the vertical direction. Therefore, when the gas is introduced into the casing 310 from the suction port 311 (arrow Gs in FIG. 14), it travels vertically downward, is compressed by the rotor 321, and then passes through the first stage compression element and the second stage compression element. (arrow Gm in FIG. 14). The gas compressed by the rotor 321 further travels vertically downward, is compressed by the second-stage rotor 331, and is then directly discharged from the discharge port 313 to the outside of the casing 310 (arrow Gd in FIG. 14).

Thus, according to the pump 300 according to the present embodiment, the rotor 321 of the first stage and the rotor 331 of the second stage are arranged in parallel on separate axes within the single casing 310 . Therefore, unlike the in-line multistage roots pump, the rotors 321 and 331 can be arranged without providing a partition between the first stage compression element (rotor 321) and the second stage compression element (rotor 331). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of a series-internal multistage roots pump, if it has two stages of rotors, the length of the rotary shaft is required to be longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for one rotor. Therefore, it is possible to suppress a decrease in rigidity of the rotating shafts 322 and 332 and the casing 310 . In particular, even if the length of the rotors 321 and 331 is lengthened in order to increase the air volume of the pump 300, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and the alignment accuracy between the first stage and the second stage pump operation areas are not so high, they are within a range that does not affect the performance of the pump 300 in terms of assembly and performance. Precision and assembly accuracy are not required.

<Transfer volume ratio>
Also in the pump 300 of the present embodiment, between the first-stage compression element (rotor 321) and the second-stage compression element (rotor 331) arranged in parallel on separate rotating shafts, the following formula (1 ) is _greater than 1.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in this embodiment is a so-called displacement amount, which is a theoretical volume per hour of the space surrounded by the casing 310 and the rotor 321 or the rotor 331, which is proportional to the rotational speed N. . That is, as described above, the movement volume Qth (m ³ /min) is represented by the following equation (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, A is the area of movement per revolution, L is the length of the rotor, and N is the number of rotations of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the rotation axes 322 and 332 .

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 300 of this embodiment is calculated by the following equation (3).

However, in formula (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 321, L2 is the length of the second stage rotor 331, N1 is the rotation speed of the first stage rotor 321, and N2 is the second stage rotor 331. represents the number of rotations of

Here, the pump 300 of this embodiment differs from the first embodiment described above in that the diameter D1 of the rotor 321 of the first stage is different from the diameter D2 of the rotor 331 of the second stage. Therefore, the pump 300 enjoys the advantage that the same rotors (rotors having the same shape and size) can be used for the first-stage rotor 321 and the second-stage rotor 331, like the pump 100 according to the first embodiment. Can not. On the other hand, according to the pump 300, since the diameter D1 of the rotor 321 of the first stage is larger than the diameter D2 of the rotor 331 of the second stage (D1>D2), the rotation of the rotor 321 of the first stage Even if the number N1 and the rotational speed N2 of the second stage rotor 331 are the same (that is, N1=N2), the displacement volume ratio _RQ can be made 1 or more.

In pump 300 , diameter D1 of rotor 321 is larger than diameter D2 of rotor 331 . Therefore, the moving area A1 of the first stage is larger than the moving area A2 of the second stage (A1>A2). Further, the length L1 of the rotor 321 and the length L2 of the rotor 331 are equal, and the rotation speed N1 of the rotor 321 and the rotation speed N2 of the rotor 331 are equal. Therefore, the above formula (3) can be rewritten as the following formula (3-3).

Therefore, in the present embodiment, in order to make the moving volume ratio _RQ1-2 between the first stage and the second stage greater than 1, the diameter D1 of the rotor 321 of the first stage is changed to that of the rotor 331 of the second stage. By making it larger than the diameter D2, the movement area A1 of the first stage should be made larger than the movement area A2 of the second stage (A1>A2). Thus, in the present embodiment, the rotor diameter ratio (D1/D2) of the diameter D1 of the rotor 321 in the first stage and the diameter D2 of the rotor 331 in the second stage (D1/D2), in other words, the moving areas A1 and 2 The moving volume ratio (A1/A2) of the moving area A2 of the stage determines the moving volume ratio R _Q1-2 between the first stage and the second stage.

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 367 of the pump 300 can be reduced.

<Drive Mechanism>
As shown in FIGS. 13 and 15, the drive mechanism of this embodiment includes a pair of first timing gears 361 (361A, 361B), a pair of second timing gears 362 (362A, 362B), and a first It comprises a drive gear 365, a second drive gear 366 and a single drive shaft 367 which is the motor input shaft.

A pair of first timing gears 361A and 361B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 322 of the first stage, and are arranged so that the rotation phases of the pair of rotors 321 and 321 match each other. , have the same number of teeth. A pair of second timing gears 362A and 362B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 332 of the second stage, and are arranged so that the rotation phases of the pair of rotors 331 and 331 match each other. , have the same number of teeth. The material of the first timing gear 361 and the second timing gear 362 is the same as the material of the first timing gear 161 and the second timing gear 162 according to the first embodiment.

Also, the first drive gear 365 is provided so as to mesh with one of the pair of first timing gears 361, the first timing gear 361A, and the second drive gear 366 is provided so as to mesh with the pair of second timing gears. 362 is provided so as to mesh with one of the second timing gears 362A. Furthermore, the drive shaft 367 rotatably supports the first drive gear 365 and the second drive gear 366 . The drive shaft 367 is supported by a bearing 368 provided in the side cover 380 and a bearing 368 provided in the bearing/gear chamber 373 . The shaft end of the drive shaft 367 on the bearing 368 side provided in the bearing/gear chamber 373 is connected to a motor (not shown).

As described above, the diameter D1 of the rotor 321 is larger than the diameter D2 of the rotor 331 in this embodiment. Therefore, in order to make the movement volume ratio greater than 1 (R _Q >1), the rotation speed of the rotor 321 in the first stage may be the same as the rotation speed of the rotor 331 in the second stage. In other words, the rotational speed of the rotor 321 in the first stage can be made the same as the rotational speed of the rotor 331 in the second stage. Therefore, in the pump 300, the first timing gear 361, the second timing gear 362, the first driving gear 365 and The number of teeth of the second drive gear 366 is set. For example, when reducing the rotation speed of the rotation shafts 322 and 332 from the rotation speed of the drive shaft 367, the first timing is set so that the reduction ratio of the first drive gear 365 is equal to the reduction ratio of the second drive gear 366. The number of teeth of gear 361, second timing gear 362, first drive gear 365 and second drive gear 366 may be set. The "reduction ratio" here is the same as in the first embodiment. In this case, the ratio between the number of teeth of the first driving gear 365 and the number of teeth of the first timing gear 361 (=the number of teeth of the first timing gear 361/the number of teeth of the first driving gear 365) and the number of teeth of the second timing gear 362 (=the number of teeth of the second timing gear 362/the number of teeth of the second drive gear 366). On the other hand, even when the rotation speed of the rotation shafts 322 and 332 is increased from the rotation speed of the drive shaft 367 or in the same case, the rotation speed of the rotor 321 in the first stage is equal to the rotation speed of the rotor 331 in the second stage. The number of teeth of the first drive gear 365 and the number of teeth of the second drive gear 366 may be set to be equal to the number of teeth. The diameters of the rotors 321 and 331 may be appropriately determined so as to obtain the desired air volume and movement volume ratio _RQ .

<Cooling mechanism>
As shown in FIG. 14, the casing 310 according to this embodiment also has an intermediate discharge port 315 and an intermediate backflow cooling gas introduction port 316 (hereinafter simply referred to as “cooling gas introduction port”) as an example of a first cooling gas introduction port according to this embodiment. A gas inlet port 316” is provided. The intermediate outlet 315 and the cooling gas inlet 316 have the same configuration, function and effect as the intermediate outlet 115 and the cooling gas inlet 116 according to the first embodiment, respectively. A cooler 1 as an example of the cooling unit according to the present embodiment is connected to the intermediate discharge port 315 and the cooling gas introduction port 316 . A check valve 3 is also connected to the cooler 1 .

<Second cooling gas inlet>
As shown in FIG. 14, a casing 310 according to the present embodiment is also provided with a backflow cooling gas introduction port 317 having the same configuration, function and effect as the cooling gas introduction port 317 according to the first embodiment.

<Other configurations>
In addition, the pump 300 of this embodiment has side covers 380 as intermediate chambers between the casing 310 and the bearing/gear chamber 373 and between the casing 310 and the bearing chamber 374 . This side cover 380 has substantially the same configuration and function as the side cover 180 according to the first embodiment. Further, the pump 300 is also provided with the same sealing mechanism and shaft sealing mechanism as the pump 100 according to the first embodiment.

(Operation of multistage roots pump)
Next, a method for driving the pump 300 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 300 are the same as those of the pump 100 of the first embodiment described above.

As shown in FIGS. 13 to 15, a first drive gear 365 and a second drive gear 366 supported by a drive shaft 367 are rotationally driven in the same direction. Next, of the pair of first timing gears 361A and 361B, one of the first timing gears 361A meshing with the first drive gear 365 rotates in the opposite direction to the first drive gear 365. As shown in FIG. The rotation speed of the first timing gear 361A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the first timing gear 361A/the number of teeth of the first drive gear 365). Also, the other first timing gear 361B meshing with the first timing gear 361A has the same number of teeth as the first timing gear 361A, so it rotates in the opposite direction to the first timing gear 361A at the same number of revolutions. As a result, the pair of rotors 321, 321 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 321, 321, the gas near the suction port 311 is sucked into the casing 310 through the suction port 311 (arrow Gs in FIG. 14), then compressed by the rotor 321 and discharged to the intermediate position. (arrow Gm in FIG. 14).

Similarly, of the pair of second timing gears 362A and 362B, one of the second timing gears 362A meshing with the second drive gear 366 rotates in the opposite direction to the second drive gear 366. The rotation speed of the second timing gear 362A at this time is a reduction ratio ( The rotation speed is reduced by the number of teeth of the second timing gear 362A/the number of teeth of the second drive gear 366). Also, the other second timing gear 362B meshing with the second timing gear 362A has the same number of teeth as the second timing gear 362A, so it rotates in the opposite direction at the same number of rotations as the second timing gear 362A. . As a result, the pair of rotors 331, 331 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 331, 331, the gas compressed by the rotor 321 of the first stage and discharged to the intermediate position is swept into the rotor 331 of the second stage from the intermediate position (arrow in FIG. 14). Gm), it is then compressed by the rotor 331 and discharged to the outside from the discharge port 313 (arrow Gd in FIG. 14).

Here, in this embodiment, the first drive gear 365 and the second drive gear 366 are supported by the same drive shaft 367, and the number of teeth of the first drive gear 365 and the number of teeth of the first timing gear 361A are equal to each other. is equal to the speed reduction ratio calculated from the ratio of the number of teeth of the second drive gear 366 and the number of teeth of the second timing gear 362A. Therefore, the rotation speed of the first timing gear 361 and the rotation speed of the second timing gear 362 are equal.

Further, in this embodiment, as in the first embodiment, the gas present in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 315 to the outside of the casing 310, and is discharged from the cooler 1. After being cooled, it is introduced into the first-stage compression element (inside the space surrounded by rotor 321 and casing 310) through two cooling gas introduction ports 316A and 316B provided on both left and right sides of casing 310. be. At this time, the pressure at the intermediate position (intermediate pressure) Pm is higher than the pressure in the space surrounded by the rotor 321 and the casing 310, so the gas discharged from the intermediate discharge port 315 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge in FIG. 14, the gas discharged from the intermediate discharge port 315 is cooled by the cooler 1, and is introduced into the compression element at the first stage from the cooling gas introduction port 316. is introduced into the area surrounded by the first stage rotor 321 and the casing 310 (moving volume Qth1 portion), and then discharged to the intermediate position again. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 315, and the gas cooled by the cooler 1 is discharged into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed.

Furthermore, when the intermediate pressure Pm is equal to or higher than the atmospheric pressure, the check valve 3 is opened, and the pressure difference between the intermediate pressure Pm and the atmospheric pressure causes the gas existing at the intermediate position to be pushed out from the intermediate discharge port 315 to a higher pressure. (arrow Ge and arrow Gd in FIG. 14), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second stage compression element (rotor 331) becomes smaller, the suction pressure to the first stage compression element (rotor 321) and the suction pressure to the second stage compression element (rotor 331) can be reduced. As a result, the power of the motor that operates the pump 300 can be reduced. In particular, when the pump 300 starts to draw gas toward the suction port 311, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the diameter D1 of the rotor 321 is larger than the diameter D2 of the rotor 331 . Also, the reduction ratio of the first driving gear 365 with respect to the first timing gear 361A is the same as the reduction ratio of the second driving gear 366 with respect to the second timing gear 362A. Therefore, the rotation speed N1 of the rotor 321 is the same as the rotation speed N2 of the rotor 331. FIG. Further, since the length L1 of the rotor 321 and the length L2 of the rotor 331 are the same, as described above, the movement volume ratio _RQ between the first stage compression element and the second stage compression element is greater than 1.

[Fourth embodiment]
Next, a multistage roots pump according to a fourth embodiment of the present invention will be described in detail with reference to FIGS. 16 to 19. FIG. FIG. 16 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 400 (hereinafter abbreviated as "pump 400") as an example of a multi-stage roots-type pump according to the present embodiment. 17, 18 and 19 are cross-sectional views taken along lines XVII-XVII, XVIII-XVIII and XIX-XIX of FIG. 16, respectively. Although the pumps 100, 200, and 300 of the first to third embodiments described above are examples of two-stage Roots pumps having two-stage compression elements, the pump 400 according to the present embodiment has three-stage compression. 3 is an example of a three-stage roots-type pump with elements. Here, the relationship between the first stage (lowest pressure side) compression element and the second stage (intermediate) compression element is the first stage compression element and the second stage compression element of the pump 100 according to the first embodiment. The relationship between the second stage (intermediate) compression element and the third stage (highest pressure side) compression element is the same as that of the first stage compression element of the pump 200 according to the second embodiment. The relationship is the same as that of the second-stage compression element. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 16 to 19, the pump 400 is a three-stage roots pump, which is a type of rotary compressor, and includes a casing 410, three stages (three sets) of compression elements, a drive mechanism, and a cooling mechanism. and

<Casing>
The configuration and function of the casing 410 are similar to those of the casing 110 according to the first embodiment.

Here, the casing 410 is a virtual plane containing the two rotating shafts 422, 422 of the compression elements of the same stage, a virtual plane containing the two rotating shafts 432, 432, or two rotating shafts 442, 442 Compression elements are accommodated so that three stages of compression elements are arranged in parallel along the normal direction of a virtual plane including . Thus, in this embodiment, multiple stages of compression elements arranged in parallel with respect to the axial direction of the rotating shafts 422, 432, and 442 are housed in a single casing 410, and the compression elements are connected. No external piping or internal gas passages are provided. Therefore, the gas compressed by the first-stage compression element and discharged is directly sucked (as it is) into the second-stage compression element, compressed and then discharged, and then directly ( as it is) sucked in. Therefore, the temperature rise of the gas compressed by each compression element of the three-stage roots type pump is more serious than that of the two-stage roots type pump. Therefore, in the present embodiment, as will be described later in detail, not only the cooling of the gas existing in the intermediate position between the first and second stages but also the cooling of the gas existing in the intermediate position between the second and third stages is performed. Cooling of the gas is also performed.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 411 side and a third stage (high pressure side) compression element located on the discharge port 413 side are provided in the single casing 410. and a second-stage (intermediate) compression element disposed between the first-stage and third-stage compression elements. No partition plate or the like is provided between the three stages of compression elements, and a plurality of compression elements are provided as a single stage group within the integral casing 410 . Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 421 and 421 and two rotating shafts 422 and 422 . The second stage compression element has a pair of rotors 431 and 431 and two rotating shafts 432 and 432 . The third stage compression element has a pair of rotors 441 and 441 and two rotating shafts 442 and 442 .

As shown in FIG. 17, the rotor 421 is a three-lobe rotor, and its rotor profile is shaped to have three protruding portions 421a, 421b, 421c radially protruding from the center of rotation. In addition, recesses 421d are provided between the protrusions 421a, 421b, and 421c. Similarly, the rotor 431 is also a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 431a, 431b, 431c projecting radially from the center of rotation. Further, recesses 431d are provided between the protrusions 431a, 431b, and 431c. Similarly, the rotor 441 is also a three-lobed rotor, and its rotor profile is shaped with three pieces of projections 441a, 441b, 441c projecting radially from the center of rotation. Further, recesses 441d are provided between the protrusions 441a, 441b, and 441c.

The pair of rotors 421, 421 are provided rotatably in directions opposite to each other. The two rotating shafts 422, 422 rotatably support a pair of rotors 421, 421 and are arranged parallel to each other. Also, the two rotating shafts 422 , 422 are supported by two bearings 423 , 423 . Similarly, a pair of rotors 431, 431 are provided rotatably in directions opposite to each other. The two rotating shafts 432, 432 rotatably support a pair of rotors 431, 431 and are arranged parallel to each other. Also, the two rotating shafts 432 , 432 are supported by two bearings 433 , 433 . Similarly, a pair of rotors 441, 441 are also provided rotatably in directions opposite to each other. The two rotating shafts 442, 442 rotatably support a pair of rotors 441, 441 and are arranged parallel to each other. Also, the two rotating shafts 442 , 442 are supported by two bearings 443 , 443 . Furthermore, in this embodiment, the rotating shaft 422, the rotating shaft 432, and the rotating shaft 442 are arranged so as to be parallel to each other. In the following description, the description of the rotors 431 and 441 overlapping with that of the rotor 421 will be omitted as necessary, and the contents of the rotor 421 will be read appropriately.

Between the rotors 421 and 421 and the tips (leaf ends) of the projections 421a, 421b, and 421c and the casing 410 are arranged so that the pair of rotors 421 and 421 and the rotor 421 and the inner surface 410a of the casing 410 do not come into contact with each other. A rotor 421 is arranged with a small gap between the inner surface 410a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 421 and 421 are maintained by timing gears 461A and 461B, which will be described later, and the cross-sectional shape of the rotor 421 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 431 is arranged so that a slight gap is formed between the paired rotor 431 and the inner surface 410 d of the casing 410 . Also, the pair of rotors 431, 431 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Similarly, the rotor 441 is arranged so that a slight gap is formed between the paired rotor 441 and the inner surface 410 g of the casing 410 . Also, the pair of rotors 441, 441 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Other configurations and functions of the rotors 421, 431, and 441 are the same as those of the rotors according to the above-described embodiments.

In the pump 400, a rotor 421, a rotating shaft 422, etc., which are first-stage compression elements, a rotor 431, a rotating shaft 432, etc., which are second-stage compression elements, and a rotor 441, which is a third-stage compression element, are rotated. Axes 442, etc. are virtual shafts that include two rotary shafts 422, 422 (or two rotary shafts 432, 432, or two rotary shafts 442, 442) of the same stage in a single casing 410. are arranged in parallel along the normal direction of the plane of That is, the rotor 421 of the first stage, the rotor 431 of the second stage, and the rotor 441 of the third stage are each supported by different shafts, and the two rotation shafts of the same stage are parallel to each other. and the two rotating shafts of different stages are also arranged parallel to each other. In other words, the gas suction port 411, the first rotor 421, the second rotor 431, the third rotor 441, and the gas discharge port 413 are arranged vertically. Therefore, when the gas is introduced into the casing 410 from the suction port 411 (arrow Gs in FIG. 17), it travels vertically downward, is compressed by the rotor 421, and then passes through the first stage compression element and the second stage compression element. (arrow Gm1 in FIG. 17). The gas compressed by the rotor 421 further advances vertically downward, and after being compressed by the second-stage rotor 431, advances between the second-stage compression element and the third-stage compression element (arrow Gm2 in FIG. 17). ). The gas compressed by the rotor 431 further travels vertically downward, and after being compressed by the third-stage rotor 441, is directly discharged outside the casing 410 through the discharge port 413 (arrow Gd in FIG. 17).

Thus, according to the pump 400 according to the present embodiment, the rotor 421 of the first stage, the rotor 431 of the second stage, and the rotor 441 of the third stage are arranged on different axes in the single casing 410. arranged in parallel. Therefore, between the first-stage compression element (rotor 421) and the second-stage compression element (rotor 431), and between the second-stage compression element (rotor 431) and the third-stage compression element (rotor 441) The arrangement of the rotors 421, 431, and 441 itself can divide the pump operation regions of the three-stage compression elements without providing a partition between them. In addition, in the case of a series-internal multistage roots pump, if it has three stages of rotors, the length of the rotating shaft is required to be equal to or longer than three rotors. 441 are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, a decrease in rigidity of the rotating shafts 422, 432, 442 and the casing 410 can be suppressed. In particular, even if the lengths of the rotors 421, 431, and 441 are lengthened in order to increase the air volume of the pump 400, the rigidity does not decrease, which facilitates increasing the air volume. Furthermore, even if the dimensional accuracy and positioning accuracy are not so high between the pump operating regions of the first stage, the second stage, and the third stage, they are within a range that does not hinder the assembly and the performance of the pump 400 . , so high machining accuracy and assembly accuracy are not required. Here, multi-stage roots type pumps having three or more stages of compression elements have problems such as reduced rigidity of the rotating shaft and casing, difficulty in increasing air volume, and the need for high machining and assembly accuracy. It becomes even more serious than in the case of pumps. In such a case, the pump 400 according to the present embodiment solves all of the above problems, and therefore has a great advantage in arranging a plurality of compression elements in parallel on separate shafts.

Further, as will be described later, the length L1 of the rotor 421 of the first stage and the length L2 of the rotor 431 of the second stage can be the same length. Therefore, according to the pump 400 of the present embodiment, the same rotors (rotors having the same shape and size) can be used for the first stage rotor 421 and the second stage rotor 431, so there is an advantage that the types of parts can be reduced. There is As a result, it leads to improvement of production efficiency and reduction of cost.

<Transfer volume ratio>
In the pump 400 of this embodiment, between the first-stage compression element (rotor 421) and the second-stage compression element (rotor 431) arranged in parallel on separate rotating shafts, the following formula (1) is _greater than 1;
_RQ = _QthL / _QthH (1)

However, when obtaining the displacement volume ratio R _Q1-2 between the first stage and the second stage, in equation (1), Qth _L is the low pressure side of the first stage compression element and the second stage compression element. is the displacement volume of the compression element (in this embodiment, the first stage compression element), and Qth _H is the displacement volume of the high pressure side compression element (in this embodiment, the second stage compression element).

Here, the movement volume Qth in the present embodiment is a so-called displacement amount, which is proportional to the number of rotations N, and is the theoretical amount per hour of the space surrounded by the casing 410 and the rotor 421, the rotor 431, or the rotor 441. Volume. That is, the movement volume Qth (m ³ /min) is represented by the following formula (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, N is the number of rotations of the rotor, A is the moving area per revolution, and L is the length of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the rotation axes 422, 432, 442.

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 400 of this embodiment is calculated as follows. First, taking the first stage rotor 421 as an example, each time the pair of left and right rotors 421, 421 rotates, gas is sucked and discharged six times (the left rotor 421 and the right rotor 421 each rotate 6 times). and 3 times each) is repeated. The same applies to the second stage rotor 431 . Here, as shown in FIG. 17, a section of a cross section perpendicular to the rotating shaft 422 of the space surrounded by the two protrusions (for example, the protrusion 421a and the protrusion 421b) of the rotor 421 and the inner surface 410a of the casing 410 is taken. Assuming that the area is S1, the moving area A1 of the first stage (low pressure side) compression element is A1=6×S1. Similarly, if S2 is the cross-sectional area of the cross section perpendicular to the rotation axis 432 of the space surrounded by the two protrusions (for example, the protrusion 431b and the protrusion 431c) of the rotor 431 and the inner surface 410d of the casing 410, then 2 The moving area A2 of the compression element on the stage (high pressure side) is A2=6×S2. From the above, the movement volume ratio R _Q1-2 between the first stage and the second stage is expressed by the following formula (3).

However, in equation (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, N1 is the rotation speed of the first stage rotor 421, N2 is the second stage It represents the rotation speed of the rotor 431 . Here, rotors 421 and 431 have the same diameter and shape. Therefore, the moving area A1 of the first stage is equal to the moving area A2 of the second stage. Also, as shown in FIG. 16, the length L1 of the rotor 421 and the length L2 of the rotor 431 are equal. Therefore, the above formula (3) can be rewritten as the following formula (3-1).

Therefore, in this embodiment, in order to make the moving volume ratio R _Q1-2 between the first stage and the second stage greater than 1, the rotational speed N1 of the first stage rotor 421 is set to should be higher than the rotational speed N2 of (N1>N2). Thus, between the first stage and the second stage in this embodiment, the number of revolutions N1 of the first stage compression element and the number of revolutions N2 of the second stage compression element (N1/N2) , the displacement volume ratio R _Q1-2 between the first stage and the second stage is determined. As a result, the length L1 of the rotor 421 in the first stage and the length L2 of the rotor 431 in the second stage can be made the same, so that the rotor 421 in the first stage and the rotor 431 in the second stage can be used as components of the pump 400. can be standardized as

Further, in pump 400, between the second-stage compression element (rotor 431) and the third-stage compression element (rotor 441) arranged in parallel on separate rotating shafts, the above equation (1) The represented transfer volume ratio _RQ is greater than one.

However, when obtaining the movement volume ratio R _Q2-3 between the second stage and the third stage, Qth _L in the equation (1) is the low pressure side of the second stage compression element and the third stage compression element. and Qth _H is the displacement of the high-pressure side compression element (the third-stage compression element in the present embodiment).

As described above, the movement volume Qth (m ³ /min) is represented by the above formula (2). Therefore, the displacement volume ratio R _Q2-3 between the second stage and the third stage in the pump 400 of this embodiment is calculated as follows. First, taking the second-stage rotor 431 as an example, each time the pair of left and right rotors 431, 431 rotates, gas is sucked and discharged six times (the left rotor 431 and the right rotor 431 each rotate 6 times). and 3 times each) is repeated. The same applies to the third stage rotor 441 . Here, as described above, the moving area A2 of the second stage (intermediate) compression element is A2=6×S2. Similarly, if S3 is the cross-sectional area of the cross section perpendicular to the rotating shaft 442 of the space surrounded by the two protruding portions of the rotor 441 (for example, the protruding portion 441b and the protruding portion 441c) and the inner surface 410g of the casing 410, then 3 The moving area A3 of the compression element on the stage (high pressure side) is A3=6×S3. From the above, the movement volume ratio R _Q2-3 between the second stage and the third stage is expressed by the following formula (5).

However, in equation (5), Qth2 is the movement volume of the second-stage compression element, Qth3 is the movement volume of the third-stage compression element, N2 is the rotation speed of the second-stage rotor 431, and N3 is the third-stage It represents the rotation speed of the rotor 441 . Here, in the pump 400 of this embodiment, the length L2 of the rotor 431 of the second stage differs from the length L3 of the rotor 441 of the third stage. Therefore, in the relationship between the second stage and the third stage of the pump 400, the same rotor (shape and The advantage of being able to use rotors of the same size cannot be enjoyed. On the other hand, since the length L2 of the second-stage rotor 431 is longer than the length L3 of the third-stage rotor 441 (L2>L3), the rotational speed N2 of the second-stage rotor 431 and Even if the rotation speed N3 of the third-stage rotor 441 is the same (that is, N2=N3), the displacement volume ratio R _Q2-3 can be 1 or more.

In pump 400, rotors 431 and 441 have the same diameter and shape. Therefore, the moving area A2 of the second stage is equal to the moving area A3 of the third stage. Further, the rotational speed N2 of the rotor 431 and the rotational speed N3 of the rotor 441 are equal. Therefore, the above formula (5) can be rewritten as the following formula (5-1).

Therefore, in this embodiment, in order to make the moving volume ratio R _Q2-3 between the second stage and the third stage greater than 1, the length L2 of the rotor 431 of the second stage is set to the length of the rotor 441 of the third stage. is larger than the length L3 (L2>L3). Thus, in the present embodiment, the rotor length ratio (L2/L3) between the length L2 of the rotor 431 of the second stage and the length L3 of the rotor 441 of the third stage determines the A moving volume ratio R _Q2-3 between is determined. As a result, the rotation speed N2 of the rotor 431 in the second stage and the rotation speed N3 of the rotor 441 in the third stage can be made the same, so that the gear structure can be simplified and the number of gears can be reduced, as will be described later in detail. be.

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 467 of the pump 400 can be reduced. In the present embodiment, both the moving volume ratio R _Q1-2 between the first stage and the second stage and the moving volume ratio R _Q2-3 between the second stage and the third stage are greater than 1. A case is illustrated. In this case, the effect of reducing the shaft power can be significantly improved. However, in the three-stage roots pump according to the present invention, at least one of R _Q1-2 and R _Q2-3 should have a movement volume ratio greater than one. For example, a three-stage roots pump in which either one of R _Q1-2 and R _Q2-3 is greater than one and the other is one can also be used as a multi-stage roots pump according to the present invention.

<Drive Mechanism>
As shown in FIGS. 16, 18 and 19, the drive mechanism of this embodiment includes a pair of first timing gears 461 (461A, 461B), a pair of second timing gears 462 (462A, 462B), and , a pair of third timing gears 463 (463A, 463B), a first drive gear 464, a second drive gear 465, a third drive gear 466, and a drive shaft 467 that is a motor input shaft.

A pair of first timing gears 461A and 461B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 422 of the first stage, and are arranged so that the rotation phases of the pair of rotors 421 and 421 match each other. , have the same number of teeth. A pair of second timing gears 462A and 462B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 432 of the second stage, and are arranged so that the rotation phases of the pair of rotors 431 and 431 match each other. , have the same number of teeth. A pair of third timing gears 463A and 463B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 442 of the second stage, and are arranged so that the rotation phases of the pair of rotors 431 and 431 match each other. , have the same number of teeth.

Also, the first drive gear 464 is provided so as to mesh with one of the pair of first timing gears 461, the first timing gear 461A, and the second drive gear 465 is engaged with the pair of second timing gears. 462 is provided so as to mesh with one of the second timing gears 462A. In addition, the third drive gear 466 is connected to both the second timing gear 462B, which is one of the pair of second timing gears 462, and the third timing gear 463B, which is one of the pair of third timing gears 463. arranged to mesh. Furthermore, the drive shaft 467 rotatably supports the first drive gear 464 and the second drive gear 465 . That is, the first drive gear 464 and the second drive gear 465 are rotatably supported by the same drive shaft. The drive shaft 467 is supported by a bearing 468 provided in a side cover 480 and a bearing 468 provided in a bearing/gear chamber 473, which will be described later. A shaft end of the drive shaft 467 on the bearing 468 side provided in the bearing/gear chamber 473 is connected to a motor (not shown). Also, the third drive gear 466 is provided at the end of the rotating shaft 469 . A shaft end of the rotary shaft 469 on which the third drive gear 466 is not provided is supported by a bearing 470 provided on a side cover 480 which will be described later.

As described above, in this embodiment, the length L1 of the rotor 421 and the length L2 of the rotor 431 are the same. Therefore, in order to make the movement volume ratio between the first stage and the second stage larger than 1 (R _Q1-2 >1), the rotational speed of the first stage rotor 421 is set to should be higher than the rpm of the In other words, the rotation speed of the rotor 421 in the first stage needs to be faster than the rotation speed of the rotor 431 in the second stage. Therefore, in pump 400, the number of teeth of first drive gear 464 and second drive gear 465 is set such that the rotation speed of rotor 421 in the first stage is higher than the rotation speed of rotor 431 in the second stage. For example, when reducing the rotation speed of the rotation shafts 422 and 432 from the rotation speed of the drive shaft 467 , the first drive gear 464 has a lower speed reduction ratio than the second drive gear 465 . The number of teeth of the driving gear 464 and the second driving gear 465 should be set. In this case, if the number of teeth of the first timing gear 461 and the number of teeth of the second timing gear 462 are the same, the number of teeth of the first drive gear 464 should be larger than that of the second drive gear 465 . The speed reduction ratio of each drive gear 464, 465 may be appropriately determined so as to obtain the desired movement volume ratio _RQ1-2 . On the other hand, even if the rotation speed of the rotation shafts 422 and 432 is increased from the rotation speed of the drive shaft 467 or in the same case, the rotation speed of the rotor 421 in the first stage is equal to the rotation speed of the rotor 431 in the second stage. There is no problem if the number of teeth of the first drive gear 464 and the second drive gear 465 is set so as to be higher than the number.

Also, in this embodiment, the length L2 of the rotor 431 is longer than the length L3 of the rotor 441 . Therefore, in order to make the movement volume ratio between the second stage and the third stage larger than 1 (R _Q2-3 >1), the rotational speed of the second stage rotor 431 must be set to can be the same as the number of revolutions of In other words, the rotational speed of the rotor 431 in the second stage can be made the same as the rotational speed of the rotor 441 in the third stage. Therefore, in the pump 400, the second timing gear 462 and the third timing gear 463 having the same number of teeth are used so that the rotation speed of the rotor 431 at the second stage is the same as the rotation speed of the rotor 441 at the third stage. is meshed with the third drive gear 466 of . The length of each rotor 431, 441 may be appropriately determined so as to obtain the desired air volume and movement volume ratio _RQ2-3 .

<Cooling mechanism>
As shown in FIG. 17, the pump 400 includes coolers 1 and 2, intermediate discharge ports 415 and 417, and intermediate backflow cooling gas inlets 416 and 418 (hereinafter simply referred to as "cooling gas inlet 416") as cooling mechanisms. , 418”) are provided. The coolers 1 and 2 are an example of the cooling section of this embodiment, and are provided outside the casing 410 . At least one intermediate discharge port 415 , 417 is provided on each side surface of the casing 410 . The cooling gas introduction ports 416 and 418 are examples of the first cooling gas introduction ports of the present embodiment, and at least one each is provided on the side surface of the casing 410 .

Cooler 1 is connected to intermediate outlet 415 and cooling gas inlet 416 and cools the gas discharged from intermediate outlet 415 . Cooler 2 is connected to intermediate outlet 417 and cooling gas inlet 418 and cools the gas discharged from intermediate outlet 417 . Although the coolers 1 and 2 are not particularly limited, for example, various heat exchangers such as plate type, shell and tube type (multi-tube type), fin tube type, spiral type, and air cooling type can be used. Further, as the cooling unit of the present invention, a pipe (not shown) connecting the intermediate discharge port 415 and the cooling gas introduction port 416 without providing the coolers 1 and 2, the intermediate discharge port 417 and the cooling gas introduction A pipe (not shown) connecting with the port 418 may be provided outside the casing 110 . In this case, the gas discharged from the intermediate outlets 415 and 417 is cooled by radiating heat when passing through the pipes. When emphasizing the cooling efficiency, the heat exchanger as described above is provided, and when emphasizing the energy efficiency of the pump 400 as a whole, only the above piping is preferably provided.

The intermediate discharge port 415 discharges the gas existing between the low-pressure side (first stage in this embodiment) compression element and the high-pressure side (second stage in this embodiment) compression element that are adjacent to each other. As indicated by an arrow Ge1 in FIG. The intermediate discharge port 415 is provided at an intermediate position between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. The example shown in FIG. 17 shows an example in which only one intermediate outlet 415 is provided on the left side surface of the casing 410, but the number of intermediate outlets 415 is not particularly limited, and two or more outlets may be provided. good. For example, in the cross section shown in FIG. 17 , one more point may be provided not only on the left side of casing 410 but also on the right side. Also, when viewed from the front side of the cross section shown in FIG. An intermediate outlet 415 may be provided at an intermediate position between the eye (high pressure side) and the compression element. In addition, the intermediate discharge port 417 is provided between the low-pressure side (second stage in this embodiment) compression element and the high-pressure side (third stage in this embodiment) compression element that are adjacent to each other. to the outside of the casing 410 as indicated by an arrow Ge2 in FIG. The intermediate discharge port 417 is provided at an intermediate position between adjacent compression elements, that is, between the second stage (low pressure side) compression element and the third stage (high pressure side) compression element. As with the intermediate outlets 415, the number of the intermediate outlets 417 is not particularly limited. As shown in FIG. may be provided at two or more locations on the side surface of the .

The cooling gas inlet 416 (416A, 416B) feeds the gas cooled by the cooler 1 to a compression element on the lower pressure side than the intermediate outlet 415 (in this embodiment, the pressure of the gas discharged from the intermediate outlet 415 is It is a suction port for introducing into the first stage compression element) where gas with a pressure lower than is present. The cooling gas introduction port 416 is provided at a position where the gas cooled by the cooler 1 can mix with the moving volume Qth1 portion sucked (scraped) by the first stage rotor 421 . In addition, the cooling gas inlet 418 (418A, 418B) feeds the gas cooled by the cooler 2 to the compression element on the lower pressure side than the intermediate outlet 417 (in this embodiment, the gas discharged from the intermediate outlet 417). is a suction port for introducing gas into the second stage compression element) where gas with a pressure lower than the pressure of is present. The cooling gas introduction port 418 is provided at a position where the gas cooled by the cooler 2 can mix with the movement volume Qth2 portion sucked (scraped) by the second stage rotor 431 .

Here, the pressure (intermediate pressure Pm1) at an intermediate position between the discharge side of the first-stage compression element provided with the intermediate discharge port 415 and the suction side of the second-stage compression element is the pressure of the first-stage compression element (rotor 421) and this pressure is also equal to the suction pressure to the second stage compression element (rotor 431). Since the intermediate pressure Pm1 is greater than or equal to the pressure Pr1 of the space surrounded by the rotor 421 and the casing 410 (Pm1≧Pr1), the gas discharged from the intermediate discharge port 415 passes through the cooler 1 and is circulated. be. As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element. As a result, it is possible to suppress a significant temperature rise of the gas compressed by the second-stage compression element. Similarly, the pressure (intermediate pressure Pm2) at an intermediate position between the discharge side of the second-stage compression element provided with the intermediate discharge port 417 and the suction side of the third-stage compression element is the pressure of the second-stage compression element (rotor 431) and this pressure is also equal to the suction pressure to the third stage compression element (rotor 441). Since the intermediate pressure Pm2 is equal to or higher than the pressure Pr2 of the space surrounded by the rotor 431 and the casing 410 (Pm2≧Pr2), the gas discharged from the intermediate discharge port 417 passes through the cooler 2 and is circulated. be. As a result, the temperature of the gas discharged from the second stage compression element decreases, so the gas whose temperature has risen due to being compressed by the second stage (low pressure side) compression element does not dissipate heat and the third stage (high pressure side) side) can be prevented from being directly sucked into the compression element. As a result, it is possible to suppress a significant temperature rise of the gas compressed by the third-stage compression element.

FIG. 17 shows an example in which one cooling gas introduction port 416 is provided on each of the left and right side surfaces of the casing 410 (two locations in total), but the number of cooling gas introduction ports 416 is not particularly limited. As long as at least one cooling gas introduction port 416 is provided, the effect of suppressing a significant temperature rise of the gas can be obtained. In order to enhance the cooling effect of the gas sucked into the second-stage compression element, it is preferable that the number of cooling gas introduction ports 416 is large. In particular, in order to uniformly cool the inside of casing 410, as shown in FIG. Similarly, the number of cooling gas inlets 418 is not particularly limited, and as long as at least one cooling gas inlet 418 is provided, the effect of suppressing a significant temperature rise of the gas can be obtained. In order to enhance the cooling effect of the gas sucked into the third-stage compression element, it is preferable that the number of cooling gas introduction ports 418 is large. In particular, in order to uniformly cool the inside of casing 410, as shown in FIG. 17, it is preferable that cooling gas inlet 418 introduces the gas cooled by cooler 2 from both left and right sides of casing 410. As shown in FIG.

The pump 400 is also provided with a check valve 3 connected to the cooler 1 and a check valve 4 connected to the cooler 2 . The check valve 3 is closed by the differential pressure from the atmospheric pressure when the intermediate pressure Pm1 at the intermediate position between the first-stage compression element and the second-stage compression element is equal to or lower than the atmospheric pressure. It is opened when Pm1 is equal to or higher than the atmospheric pressure. When the check valve 3 is open, the gas discharged from the intermediate discharge port 415 is discharged to the atmosphere having a pressure lower than that of the first-stage compression element, and when the check valve 3 is closed, It is introduced into the first-stage compression element from the cooling gas inlet 416 . Similarly, the check valve 4 is closed by the differential pressure from the atmospheric pressure when the intermediate pressure Pm2 at the intermediate position between the second-stage compression element and the third-stage compression element is lower than the atmospheric pressure. , is opened when the intermediate pressure Pm2 is greater than or equal to the atmospheric pressure. When the check valve 4 is open, the gas discharged from the intermediate discharge port 417 is discharged to the atmosphere with a pressure lower than that of the second stage compression element, and when the check valve 4 is closed, It is introduced into the first-stage compression element from the cooling gas inlet 418 .

By providing the cooling mechanism of this embodiment having the configuration described above, the temperature of the gas discharged from the first-stage compression element is lowered, and the temperature of the gas discharged from the second-stage compression element is also lowered. Therefore, the thermal expansion of the second and third stage rotors and casings is also reduced. Therefore, the gap between the rotor and the casing and the gap between the rotors in the second and third stage compression elements can be narrowed. In particular, in the third-stage compression element, there is a large difference in the temperature of the discharged gas between when the cooling mechanism described above is provided and when it is not provided. As a result, the amount of gas leaked from the second and third stage compression elements (especially the amount of gas leaked from the third stage compression element), that is, the amount of gas flowing back from the high pressure side to the low pressure side is reduced. , the volumetric efficiency is improved.

Also, the amount of gas leaked from the second stage compression element, that is, the leakage amount from the discharge side (high pressure side) of the second stage compression element to the suction side (low pressure side) of the second stage compression element decreases. , the suction pressure of the second stage compression element decreases. When the suction pressure of the second-stage compression element decreases, the pressure difference between the suction pressure of the second-stage compression element (equal to the discharge pressure of the first-stage compression element) and the suction pressure of the first-stage compression element increases. become smaller. As a result, the shaft power of the first stage compression element can be reduced. Furthermore, the leakage amount of gas in the third stage compression element, that is, the leakage amount from the discharge side (high pressure side) of the third stage compression element to the suction side (low pressure side) of the third stage compression element decreases. , the suction pressure of the third stage compression element decreases. When the suction pressure of the third-stage compression element decreases, the pressure difference between the suction pressure of the third-stage compression element (equal to the discharge pressure of the second-stage compression element) and the suction pressure of the second-stage compression element increases. become smaller. As a result, the shaft power of the second stage compression element can also be reduced. Thus, a multi-stage roots pump having three or more stages of compression elements has a greater effect of reducing shaft power than a multi-stage roots pump having two stages of compression elements.

In this embodiment, a cooling mechanism (that is, a cooling mechanism consisting of the intermediate discharge port 415, the cooler 1, and the cooling gas inlet 416) for cooling the gas at the intermediate position between the 1st and 2nd stages; Two cooling mechanisms are provided for cooling the gas at the intermediate position between the three stages (that is, the cooling mechanism consisting of the intermediate outlet 417, the cooler 2, and the cooling gas inlet 418). Even if only one of the cooling mechanisms is provided, the effect of suppressing the above-described remarkable temperature rise of the discharged gas can be obtained. However, in order to more reliably suppress the temperature rise of the discharge gas, it is preferable to provide both of the two cooling mechanisms described above.

<Second cooling gas inlet>
In the pump 400 of this embodiment, the casing 410 is positioned between the suction position (above intermediate position) where gas is sucked into the final stage (third stage in this embodiment) compression element and the discharge port 413. It further has a backflow cooling gas introduction port 419 (hereinafter simply referred to as "cooling gas introduction port 419") for introducing the cooling gas C into the interior of the . This cooling gas inlet 419 is an example of a second cooling gas inlet according to the present embodiment. The cooling gas inlet 419 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 400 of this embodiment has side covers 480 as intermediate chambers between the casing 410 and the bearing/gear chamber 473 and between the casing 410 and the bearing chamber 474 . This side cover 480 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

(Operation of multistage roots pump)
Next, a method of driving the pump 400 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 400 are the same as those of the pump 100 of the first embodiment described above.

<How to drive the pump>
As shown in FIGS. 16 to 19, when drive shaft 467 is rotated by a motor (not shown), first drive gear 464 and second drive gear 465 supported by drive shaft 467 are driven to rotate in the same direction. Next, of the pair of first timing gears 461A and 461B, one of the first timing gears 461A meshing with the first drive gear 464 rotates in the opposite direction to the first drive gear 464. As shown in FIG. The rotation speed of the first timing gear 461A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the first timing gear 461A/the number of teeth of the first drive gear 464). Also, the other first timing gear 461B meshing with the first timing gear 461A has the same number of teeth as the first timing gear 461A, so it rotates at the same number of rotations in the opposite direction as the first timing gear 461A. As a result, the pair of rotors 421, 421 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 421, 421, the gas in the vicinity of the suction port 411 is sucked into the casing 410 through the suction port 411 (arrow Gs in FIG. 17), and then compressed by the rotor 421 to reach the first stage. It is discharged to the intermediate position of the second stage (arrow Gm1 in FIG. 17).

Similarly, of the pair of second timing gears 462A and 462B, one of the second timing gears 462A meshing with the second drive gear 465 rotates in the opposite direction to the second drive gear 465. The rotation speed of the second timing gear 462A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the second timing gear 462A/the number of teeth of the second driving gear 465). Also, the other second timing gear 462B meshing with the second timing gear 462A has the same number of teeth as the second timing gear 462A, so it rotates at the same number of revolutions in the opposite direction as the second timing gear 462A. As a result, the pair of rotors 431, 431 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 431, 431, the gas compressed by the first-stage rotor 421 and discharged to the intermediate position is swept from the intermediate position into the second-stage rotor 431 (see FIG. 17). Arrow Gm1) is compressed by the rotor 431 and discharged to an intermediate position between the second stage and the third stage (arrow Gm2 in FIG. 17).

Further, the third drive gear 466 meshing with the second timing gear 462B rotates in the opposite direction to the second timing gear 462B. Also, of the pair of third timing gears 463A and 463B, the third timing gear 463B that meshes with the third drive gear 466 rotates in the opposite direction to the third drive gear 466. Here, since the second timing gear 462B and the third timing gear 463B have the same number of teeth and mesh with the common third drive gear 466, the rotation direction and rotation speed of the third timing gear 463B are is the same as the second timing gear 462B. Also, the other third timing gear 463A meshing with the third timing gear 463B has the same number of teeth as the third timing gear 463B, so it rotates at the same number of rotations in the opposite direction as the third timing gear 463B. As a result, the pair of rotors 441, 441 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 441, 441, the gas compressed by the second-stage rotor 431 and discharged to the intermediate position is swept from the intermediate position into the third-stage rotor 441 (Fig. 17). arrow Gm2), and is compressed by the rotor 441 and discharged to the outside from the discharge port 413 (arrow Gd in FIG. 17).

Further, in the present embodiment, the gas present in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 415 to the outside of the casing 410, cooled by the cooler 1, and then discharged from the casing 410. It is introduced into the first-stage compression element (inside the space surrounded by the rotor 421 and the casing 410) from two cooling gas introduction ports 416A and 416B provided on both left and right sides. At this time, the pressure at the intermediate position (intermediate pressure) Pm1 is higher than the pressure in the space surrounded by the rotor 421 and the casing 410, so the gas discharged from the intermediate discharge port 415 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge1 in FIG. 17, the gas discharged from the intermediate discharge port 415 is cooled by the cooler 1, and is discharged from the cooling gas introduction port 416 to the first stage compression element. is introduced into the area surrounded by the first stage rotor 421 and the casing 410 (moving volume Qth1 portion), and then discharged again to the intermediate position between the first stage and the second stage. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 415, and the gas cooled by the cooler 1 flows into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed. Similarly, in the present embodiment, the gas present in the intermediate position between the second stage and the third stage is discharged from the intermediate discharge port 417 to the outside of the casing 410, cooled by the cooler 2, and then discharged to the casing 410. The cooling gas is introduced into the second-stage compression element (inside the space surrounded by the rotor 431 and the casing 410) from two cooling gas introduction ports 418A and 418B provided on both left and right sides of the . At this time, the pressure at the intermediate position (intermediate pressure) Pm2 is higher than the pressure in the space surrounded by the rotor 431 and the casing 410, so the gas discharged from the intermediate discharge port 417 passes through the cooler 2 , circulating. More specifically, as indicated by an arrow Ge2 in FIG. 17, the gas discharged from the intermediate discharge port 417 is cooled by the cooler 2, and is discharged from the cooling gas introduction port 418 into the second stage compression element, specifically is introduced into the area surrounded by the second stage rotor 431 and the casing 410 (moving volume Qth2 portion), and then discharged again to the intermediate position between the second stage and the third stage. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 417, and the gas cooled by the cooler 2 is discharged into the second stage compression element. always introduced in As a result, the temperature of the gas discharged from the second stage compression element decreases, so the gas whose temperature has risen due to being compressed by the second stage (low pressure side) compression element does not dissipate heat and the third stage (high pressure side) side) can be prevented from being directly sucked into the compression element of the third stage, and a significant temperature rise of the gas compressed by the third-stage compression element can be suppressed.

Furthermore, when the pressure (intermediate pressure) Pm1 at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to be discharged from the intermediate discharge port 415 to the atmosphere with a lower pressure ( Arrows Ge1 and Gd in FIG. 17), the intermediate pressure Pm1 drops below the atmospheric pressure. Similarly, when the pressure (intermediate pressure) Pm2 at the intermediate position between the second stage and the third stage is equal to or higher than the atmospheric pressure, the gas is discharged from the intermediate discharge port 417 to the atmosphere with a lower pressure due to the pressure difference. (arrow Ge2 and arrow Gd in FIG. 17), the intermediate pressure Pm2 drops below atmospheric pressure. Therefore, since the suction pressure to the compression elements (rotors 431, 441) of the second and third stages becomes smaller, the suction pressure Ps2 of the second stage and the pressure of the gas sucked from the suction port 411 (the first stage suction pressure The difference ΔP1 from the pressure Ps1) and the difference ΔP2 between the third-stage suction pressure Ps3 and the second-stage suction pressure Ps2 can be reduced. As a result, the power of the motor that operates the pump 400 can be reduced. In particular, when the pump 400 starts to draw gas toward the suction port 411, the intermediate pressures Pm1 and Pm2 are likely to be higher than the atmospheric pressure. .

In this embodiment, the reduction ratio of the first drive gear 464 with respect to the first timing gear 461A is smaller than the reduction ratio of the third drive gear 466 with respect to the second timing gear 462A. Therefore, the rotation speed N1 of the rotor 421 becomes higher than the rotation speed N2 of the rotor 431. Further, the length L1 of the rotor 421 and the length L2 of the rotor 431 are equal, and the rotors 421 and 431 have the same shape. is _larger than 1.

On the other hand, length L2 of rotor 431 is longer than length L3 of rotor 441 . Also, the reduction ratio of the third driving gear 466 with respect to the second timing gear 462B is the same as the reduction ratio of the third driving gear 466 with respect to the third timing gear 463B. Therefore, the rotation speed N2 of the rotor 431 is the same as the rotation speed N3 of the rotor 441. FIG. Further, since the rotor 431 and the rotor 441 have the same shape, as described above, the movement volume ratio R _Q2-3 between the second stage compression element and the third stage compression element is larger than 1. Become.

That is, the relationship between the first stage and the second stage in this embodiment is the same as in the first embodiment (the length of the rotors of the first stage and the second stage is the same, but the rotation speed is different). The relationship between the second and third stages is the same as in the second embodiment (the lengths of the rotors of the second and third stages are different, and the number of revolutions is the same).

[Fifth embodiment]
Next, a multi-stage roots pump according to a fifth embodiment of the present invention will be described in detail with reference to FIGS. 20 to 23. FIG. FIG. 20 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 500 (hereinafter abbreviated as "pump 500") as an example of a multi-stage roots-type pump according to the present embodiment. 21, 22 and 23 are cross-sectional views taken along lines XXI-XXI, XXII-XXII and XXIII-XXIII of FIG. 20, respectively. The pump 500 of the fifth embodiment is an example of a three-stage roots pump having three stages of compression elements, like the pump 400 of the fourth embodiment. Here, the relationship between the first stage (the lowest pressure side) and the second stage (intermediate) is the same as the relationship between the first stage and the second stage of the pump 400 according to the fourth embodiment. In this example, the relationship between (middle) and the third stage (highest pressure side) is different from the relationship between the second stage and the third stage of the pump 400 according to the fourth embodiment. Specifically, in the pump 500, the second (intermediate) rotor 531 and the third (high pressure side) rotor 541 have the same length, and the rotation speed of the second stage rotor 531 is three stages. This is an example in which the rotational speed is higher than that of the eye rotor 541 . In the following description, points different from the fourth embodiment will be mainly described, and descriptions that overlap with the above-described embodiments will be omitted as appropriate.

(Configuration of multistage roots pump)
As shown in FIGS. 20 to 23, the pump 500 is a three-stage roots pump, which is a type of rotary compressor, and includes a casing 510, three stages (three sets) of compression elements, a drive mechanism, and a cooling mechanism. and

<Casing>
The configuration and function of casing 510 are similar to casing 410 according to the fourth embodiment.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 511 side and a third stage (high pressure side) compression element located on the discharge port 513 side are provided in the single casing 510. and a second-stage (intermediate) compression element disposed between the first-stage and third-stage compression elements. No partition plate or the like is provided between the three stages of compression elements, and a plurality of compression elements are provided as a single stage group within the integral casing 510 . Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 521 and 521 and two rotating shafts 522 and 522 . The second stage compression element has a pair of rotors 531 and 531 and two rotating shafts 532 and 532 . The third stage compression element has a pair of rotors 541 and 541 and two rotating shafts 542 and 542 .

As shown in FIG. 21, the rotor 521 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 521a, 521b, 521c projecting radially from the center of rotation. In addition, recesses 521d are provided between the protrusions 521a, 521b, and 521c. Similarly, the rotor 531 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 531a, 531b, 531c projecting radially from the center of rotation. In addition, recesses 531d are provided between the protrusions 531a, 531b, and 531c. Similarly, the rotor 541 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 541a, 541b, 541c projecting radially from the center of rotation. In addition, recesses 541d are provided between the protrusions 541a, 541b, and 541c.

The pair of rotors 521, 521 are provided rotatably in directions opposite to each other. The two rotating shafts 522, 522 rotatably support a pair of rotors 521, 521 and are arranged parallel to each other. Also, the two rotating shafts 522 , 522 are supported by two bearings 523 , 523 . Similarly, a pair of rotors 531, 531 are provided rotatably in directions opposite to each other. The two rotating shafts 532, 532 rotatably support a pair of rotors 531, 531 and are arranged parallel to each other. Also, the two rotating shafts 532 , 532 are supported by two bearings 533 , 533 . Similarly, a pair of rotors 541, 541 are also provided rotatably in directions opposite to each other. The two rotating shafts 542, 542 rotatably support a pair of rotors 541, 541 and are arranged parallel to each other. Also, the two rotating shafts 542 and 542 are supported by two bearings 543 and 543 . Furthermore, in this embodiment, the rotating shaft 522, the rotating shaft 532, and the rotating shaft 542 are arranged so as to be parallel to each other. In the following description, the description of the rotors 531 and 541 that overlaps with that of the rotor 521 will be omitted as necessary, and the contents of the rotor 521 will be read appropriately.

Between the rotors 521 and 521 and between the tips (leaf ends) of the projections 521a, 521b and 521c and the casing 510, so that the pair of rotors 521 and 521 and the rotor 521 and the inner surface 510a of the casing 510 do not come into contact with each other. A rotor 521 is arranged with a slight gap between the inner surface 510a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 521 and 521 are maintained by timing gears 561A and 561B, which will be described later, and the cross-sectional shape of the rotor 521 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 531 is arranged so that a slight gap is formed between the paired rotor 531 and the inner surface 510 d of the casing 510 . Also, the pair of rotors 531, 531 can rotate in opposite directions while maintaining a small gap without contacting each other. Similarly, the rotor 541 is arranged so that a slight gap is formed between the paired rotor 541 and the inner surface 510 g of the casing 510 . Also, the pair of rotors 541, 541 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Other configurations and functions of the rotors 521, 531, and 541 are the same as those of the rotors according to the above-described embodiments.

In the pump 500, a rotor 521, a rotating shaft 522, etc., which are first-stage compression elements, a rotor 531, a rotating shaft 532, etc., which are second-stage compression elements, a rotor 541, which is a third-stage compression element, and a rotation Axes 542, etc. are virtual shafts that include two rotary shafts 522, 522 (or two rotary shafts 532, 532, or two rotary shafts 542, 542) of the same stage in a single casing 510. are arranged in parallel along the normal direction of the plane of That is, the first-stage rotor 521, the second-stage rotor 531, and the third-stage rotor 541 are each supported by different shafts, and the two rotation shafts of the same stage are parallel to each other. and the two rotating shafts of different stages are also arranged parallel to each other. In other words, the gas suction port 511, the first stage rotor 521, the second stage rotor 531, the third stage rotor 541 and the gas discharge port 513 are arranged side by side along the vertical direction. Therefore, when the gas is introduced into the casing 510 from the suction port 511 (arrow Gs in FIG. 21), it travels vertically downward, is compressed by the rotor 521, and then passes through the first stage compression element and the second stage compression element. (arrow Gm1 in FIG. 21). The gas compressed by the rotor 521 further travels vertically downward, and after being compressed by the second-stage rotor 531, travels between the second-stage compression element and the third-stage compression element (arrow Gm2 in FIG. 21). ). The gas compressed by the rotor 531 further travels vertically downward, and after being compressed by the third-stage rotor 541, is directly discharged out of the casing 510 through the discharge port 513 (arrow Gd in FIG. 21).

Thus, according to the pump 500 according to the present embodiment, the rotor 521 of the first stage, the rotor 531 of the second stage, and the rotor 541 of the third stage are arranged on different axes in the single casing 510. arranged in parallel. Therefore, between the first-stage compression element (rotor 521) and the second-stage compression element (rotor 531), and between the second-stage compression element (rotor 531) and the third-stage compression element (rotor 541) The arrangement of the rotors 521, 531, and 541 itself can divide the three-stage compression element pump operation regions without providing a partition between them. In addition, in the case of a series-internal multistage roots-type pump, if it has three stages of rotors, the length of the rotating shaft of three rotors or more is required. 541 are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. The effect produced by such a configuration is the same as that of the fourth embodiment.

Further, as will be described later, the length L1 of the first stage rotor 521, the length L2 of the second stage rotor 531, and the length L3 of the third stage rotor 541 can all be the same length. Therefore, according to the pump 500 of the present embodiment, the same rotors (rotors having the same shape and size) can be used for the first-stage rotor 521, the second-stage rotor 531, and the third-stage rotor 541. The number of types of rotors can be reduced, and the same rotor can be used, which greatly simplifies assembly. As a result, it leads to further improvement of production efficiency and further reduction of cost.

<Transfer volume ratio>
In the pump 500 of the present embodiment, between the first-stage compression element (rotor 521) and the second-stage compression element (rotor 531) arranged in parallel on another rotating shaft, Similarly, the moving volume ratio _RQ represented by the following formula (1) is greater than one.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in the present embodiment is a so-called displacement amount, which is proportional to the rotational speed N, and is the theoretical amount per hour of the space surrounded by the casing 510 and the rotor 521, the rotor 531, or the rotor 541. Volume. That is, the movement volume Qth (m ³ /min) is represented by the following formula (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, N is the number of rotations of the rotor, A is the moving area per revolution, and L is the length of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the axis of rotation 522, 532, 542.

The moving volume ratio R Q1-2 between the first stage and the second stage in the pump 500 of the present embodiment is the moving volume ratio R _Q1- between the first stage and the second stage in the pump 400 of the fourth embodiment _{. 2} , detailed description is omitted.

Further, in the pump 500, between the second-stage compression element (rotor 531) and the third-stage compression element (rotor 541) arranged in parallel on separate rotating shafts, the above equation (1) The represented transfer volume ratio _RQ is greater than one.

However, when obtaining the movement volume ratio R _Q2-3 between the second stage and the third stage, Qth _L in the equation (1) is the low pressure side of the second stage compression element and the third stage compression element. and Qth _H is the displacement of the high-pressure side compression element (the third-stage compression element in the present embodiment).

As described above, the movement volume Qth (m ³ /min) is represented by the above formula (2). Therefore, the displacement volume ratio R _Q2-3 between the second stage and the third stage in the pump 500 of this embodiment is calculated as follows. First, taking the second stage rotor 531 as an example, each time the pair of left and right rotors 531, 531 makes one rotation, gas is sucked and discharged six times (the left rotor 531 and the right rotor 531 each perform gas intake and discharge six times). and 3 times each) is repeated. The same applies to the third stage rotor 541 . Here, as described above, the moving area A2 of the second stage (intermediate) compression element is A2=6×S2. Similarly, if S3 is the cross-sectional area of the cross section perpendicular to the rotating shaft 542 of the space surrounded by the two protruding portions of the rotor 541 (for example, the protruding portion 541b and the protruding portion 541c) and the inner surface 510g of the casing 510, then 3 The moving area A3 of the compression element on the stage (high pressure side) is A3=6×S3. From the above, the movement volume ratio R _Q2-3 between the second stage and the third stage is expressed by the following formula (5).

However, in equation (5), Qth2 is the movement volume of the second stage compression element, Qth3 is the movement volume of the third stage compression element, N2 is the rotation speed of the second stage rotor 531, N3 is the third stage It represents the rotation speed of the rotor 541 . Here, the rotors 531 and 541 have the same diameter and shape. Therefore, the moving area A2 of the second stage is equal to the moving area A3 of the third stage. Also, as shown in FIG. 20, the length L2 of the rotor 531 and the length L3 of the rotor 541 are equal. Therefore, the above formula (5) can be rewritten as the following formula (5-2).

Therefore, in this embodiment, in order to make the moving volume ratio R _Q2-3 between the second stage and the third stage greater than 1, the rotational speed N2 of the second stage rotor 531 is set to should be higher than the rotational speed N3 of (N2>N3). Here, in order to make the moving volume ratio _RQ1-2 between the first stage and the second stage greater than 1, the rotational speed N1 of the rotor 521 in the first stage must be higher than the rotor rotational speed N2 in the second stage. Since it should be higher (N1>N2), the relationship between the rotational speeds of the rotors 521, 531 and 541 is N1>N2>N3 in this embodiment. In this way, even between the second stage and the third stage in this embodiment, the rotation speed ratio (N2/N3) between the rotation speed N2 of the second stage compression element and the rotation speed N3 of the third stage compression element , the displacement volume ratio R _Q2-3 between the second stage and the third stage is determined. As a result, the length L1 of the rotor 521 of the first stage, the length L2 of the rotor 531 of the second stage, and the length L3 of the rotor 541 of the third stage can all be made the same. 521 , the second stage rotor 531 and the third stage rotor 541 can all be made common as parts of the pump 500 .

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 567 of the pump 500 can be reduced. In the present embodiment, both the moving volume ratio R _Q1-2 between the first stage and the second stage and the moving volume ratio R _Q2-3 between the second stage and the third stage are greater than 1. A case is illustrated. In this case, the effect of reducing the shaft power can be significantly improved. However, in the three-stage roots pump according to the present invention, at least one of R _Q1-2 and R _Q2-3 should have a movement volume ratio greater than one. For example, a three-stage roots pump in which either one of R _Q1-2 and R _Q2-3 is greater than one and the other is one can also be used as a multi-stage roots pump according to the present invention.

<Drive Mechanism>
As shown in FIGS. 20, 22 and 23, the drive mechanism of this embodiment includes a pair of first timing gears 561 (561A, 561B), a pair of second timing gears 562 (562A, 562B), and , a pair of third timing gears 563 (563A, 563B), a first drive gear 564, a second drive gear 565, a 2-3 stage intermediate gear 566, a third drive gear 567, and a motor input shaft and a drive shaft 568 .

A pair of first timing gears 561A and 561B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 522 of the first stage, and are arranged so that the rotation phases of the pair of rotors 521 and 521 match each other. , have the same number of teeth. A pair of second timing gears 562A and 562B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 532 of the second stage, and are arranged so that the rotation phases of the pair of rotors 531 and 531 match each other. , have the same number of teeth. A pair of third timing gears 563A and 563B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 542 of the second stage, and are arranged so that the rotation phases of the pair of rotors 531 and 531 match each other. , have the same number of teeth.

The first drive gear 564 is provided so as to mesh with one of the pair of first timing gears 561, the first timing gear 561A, and the second drive gear 565 is engaged with the pair of second timing gears. 562, and the third drive gear 567 is provided to mesh with one of the pair of third timing gears 563, the third timing gear 563A. It is The 2nd-3rd step intermediate gear 566 is provided so as to mesh with one second timing gear 562A of the pair of second timing gears 562 . That is, the second timing gear 562A is provided so as to mesh with both the second drive gear 565 and the intermediate gear 566 between 2nd and 3rd stages. Furthermore, the drive shaft 568 rotatably supports the first drive gear 564 and the second drive gear 565 . That is, the first drive gear 564 and the second drive gear 565 are rotatably supported by the same drive shaft. The drive shaft 568 is supported by a bearing 569 provided in a side cover 580 and a bearing 569 provided in a bearing/gear chamber 573, which will be described later. The shaft end of the drive shaft 568 on the bearing 569 side provided in the bearing/gear chamber 573 is connected to a motor (not shown). Also, the intermediate gear 566 between 2nd and 3rd stages and the third drive gear 567 are rotatably supported by the same rotating shaft 570 . One shaft end of the rotating shaft 570 (the shaft end on the side of the intermediate gear between the second and third stages) is supported by a bearing 571 provided in the side cover 480, and the other shaft end (the shaft end on the side of the third drive gear 571) is supported. ) is supported by a bearing 571 provided in a bearing/gear chamber 573 .

As described above, in this embodiment, the length L1 of the rotor 521, the length L2 of the rotor 531, and the length L3 of the rotor 541 are the same. Therefore, in order to make the movement volume ratio between the first stage and the second stage larger than 1 (R _Q1-2 >1), the rotational speed of the first stage rotor 521 is set to should be higher than the rpm of the In other words, the rotation speed of the rotor 521 in the first stage needs to be faster than the rotation speed of the rotor 531 in the second stage. Therefore, in pump 500, the number of teeth of first drive gear 564 and second drive gear 565 is set such that the rotation speed of rotor 521 in the first stage is higher than the rotation speed of rotor 531 in the second stage. For example, when reducing the rotation speed of the rotation shafts 522 and 532 from the rotation speed of the drive shaft 568 , the first drive gear 564 has a lower speed reduction ratio than the second drive gear 565 . The number of teeth of the driving gear 564 and the second driving gear 565 should be set. In this case, if the number of teeth of the first timing gear 561 and the number of teeth of the second timing gear 562 are the same, the number of teeth of the first driving gear 564 should be larger than that of the second driving gear 565 . The speed reduction ratio of each drive gear 564, 565 may be appropriately determined so as to obtain the desired movement volume ratio _RQ1-2 . On the other hand, even when the rotation speed of the rotation shafts 522 and 532 is increased from the rotation speed of the drive shaft 568 or in the same case, the rotation speed of the rotor 521 in the first stage is equal to the rotation speed of the rotor 531 in the second stage. There is no problem if the number of teeth of the first drive gear 564 and the second drive gear 565 is set so as to be higher than the number.

Similarly, in order to make the movement volume ratio between the second stage and the third stage greater than 1 (R _Q2-3 >1), the rotation speed of the second stage rotor 531 is set to It is necessary to make it higher than the 541 rotation speed (faster than the rotation speed). Therefore, in the pump 500, the number of teeth of the intermediate gear 566 between the second and third stages and the third drive gear 567 is set so that the rotation speed of the rotor 531 of the second stage is higher than the rotation speed of the rotor 541 of the third stage. be done. In the illustrated example, the 2nd-3rd step intermediate gear 566 and the third drive gear 567 supported by the same rotary shaft 570 have the same rotational speed. Therefore, the speed reduction ratio of the second timing gear 562 reduced by the intermediate gear 566 between the 2nd and 3rd stages is smaller than the reduction ratio of the third timing gear 563 reduced by the third driving gear 567. The number of teeth of the three-stage intermediate gear 566 and the third driving gear 567 may be set. In this case, assuming that the second timing gear 562 and the third timing gear 563 have the same number of teeth, the number of teeth of the second-to-third stage intermediate gear 566 should be larger than the number of teeth of the third drive gear 567. . The speed reduction ratio of the 2nd-3rd step intermediate gear 566 and the third drive gear 567 may be appropriately determined so as to obtain the desired movement volume ratio R _Q2-3 . Even with a gear configuration other than this, the 2nd-3rd stage intermediate gear 566 and the third driving gear are arranged so that the rotation speed of the rotor 531 in the second stage is higher than the rotation speed of the rotor 541 in the third stage. It does not matter if the number of teeth of the gear 567 is set. The rotational speeds of the rotors 521, 531, and 541 may be appropriately determined so as to obtain the desired air volume and movement volume ratios R _Q1-2 and R _Q2-3 .

<Cooling mechanism>
As shown in FIG. 21, the pump 500 includes coolers 1 and 2, intermediate outlets 515 and 517, and intermediate backflow cooling gas inlets 516 and 518 (hereinafter simply referred to as "cooling gas inlet 516") as cooling mechanisms. , 518”) are provided. The coolers 1 and 2 are an example of the cooling section of this embodiment, and are provided outside the casing 510 . At least one intermediate discharge port 515 , 517 is provided on each side surface of the casing 510 . The cooling gas introduction ports 516 and 518 are examples of the first cooling gas introduction ports of this embodiment, and at least one each is provided on the side surface of the casing 510 .

Cooler 1 is connected to intermediate outlet 515 and cooling gas inlet 516 and cools the gas discharged from intermediate outlet 515 . Cooler 2 is connected to intermediate outlet 517 and cooling gas inlet 518 and cools the gas discharged from intermediate outlet 517 . As the coolers 1 and 2, the same ones as in the fourth embodiment can be used.

The intermediate outlets 515, 517 have substantially the same configuration and function as the intermediate outlets 415, 417 according to the fourth embodiment, respectively.

The cooling gas inlets 516 (516A, 516B) have substantially the same function and configuration as the cooling gas inlets 416 (416A, 416B) according to the fourth embodiment, and the cooling gas inlets 518 (518A, 518B) have substantially the same function and configuration as the cooling gas introduction ports 418 (418A, 418B) according to the fourth embodiment.

Here, the pressure (intermediate pressure Pm1) at the intermediate position between the discharge side of the first-stage compression element provided with the intermediate discharge port 515 and the suction side of the second-stage compression element is the pressure of the first-stage compression element (rotor 521) and this pressure is also equal to the suction pressure to the second stage compression element (rotor 531). Since the intermediate pressure Pm1 is equal to or higher than the pressure Pr1 of the space surrounded by the rotor 521 and the casing 510 (Pm1≧Pr1), the gas discharged from the intermediate discharge port 515 passes through the cooler 1 and is circulated. be. As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element. As a result, it is possible to suppress a significant temperature rise of the gas compressed by the second-stage compression element. Similarly, the pressure (intermediate pressure Pm2) at an intermediate position between the discharge side of the second-stage compression element provided with the intermediate discharge port 517 and the suction side of the third-stage compression element is the pressure of the second-stage compression element (rotor 531) and this pressure is also equal to the suction pressure to the third stage compression element (rotor 541). Since the intermediate pressure Pm2 is equal to or higher than the pressure Pr2 of the space surrounded by the rotor 531 and the casing 510 (Pm2≧Pr2), the gas discharged from the intermediate discharge port 517 passes through the cooler 2 and is circulated. be. As a result, the temperature of the gas discharged from the second stage compression element decreases, so the gas whose temperature has risen due to being compressed by the second stage (low pressure side) compression element does not dissipate heat and the third stage (high pressure side) side) can be prevented from being directly sucked into the compression element. As a result, it is possible to suppress a significant temperature rise of the gas compressed by the third-stage compression element.

A cooling mechanism (that is, a cooling mechanism consisting of an intermediate discharge port 515, a cooler 1, and a cooling gas inlet 516) for cooling the gas at the intermediate position between the 1st and 2nd stages, and the gas at the intermediate position between the 2nd and 3rd stages (that is, the cooling mechanism consisting of the intermediate discharge port 517, the cooler 2, and the cooling gas inlet 518), the effect of suppressing the temperature rise of the discharge gas can be obtained even if only one of them is used. As in the fourth embodiment, it is better to provide both in order to reliably suppress the temperature rise of the discharge gas.

As for the number of the cooling gas inlets 516 and 518, as with the cooling gas inlets 416 and 418 according to the fourth embodiment, if at least one is provided, the effect of suppressing the above-described significant temperature rise of the gas is obtained. is obtained. However, in order to uniformly cool the inside of the casing 510, as shown in FIG. is preferred.

Further, the pump 500 is provided with the check valve 3 connected to the cooler 1 and the check valve 4 connected to the cooler 2, like the pump 400 of the fourth embodiment. The configurations and functions of the check valves 3 and 4 are the same as those of the fourth embodiment, so detailed description thereof will be omitted.

By providing the cooling mechanism of this embodiment having the configuration described above, the temperature of the gas discharged from the first-stage compression element is lowered, and the temperature of the gas discharged from the second-stage compression element is also lowered. Therefore, the thermal expansion of the second and third stage rotors and casings is also reduced. Therefore, the gap between the rotor and the casing and the gap between the rotors in the second and third stage compression elements can be narrowed. In particular, in the third-stage compression element, there is a large difference in the temperature of the discharged gas between when the cooling mechanism described above is provided and when it is not provided. As a result, the amount of gas leaked from the second and third stage compression elements (especially the amount of gas leaked from the third stage compression element), that is, the amount of gas flowing back from the high pressure side to the low pressure side is reduced. , the volumetric efficiency is improved.

Also, the amount of gas leaked from the second stage compression element, that is, the leakage amount from the discharge side (high pressure side) of the second stage compression element to the suction side (low pressure side) of the second stage compression element decreases. , the suction pressure of the second stage compression element decreases. When the suction pressure of the second-stage compression element decreases, the pressure difference between the suction pressure of the second-stage compression element (equal to the discharge pressure of the first-stage compression element) and the suction pressure of the first-stage compression element increases. become smaller. As a result, the shaft power of the first stage compression element can be reduced. Furthermore, the leakage amount of gas in the third stage compression element, that is, the leakage amount from the discharge side (high pressure side) of the third stage compression element to the suction side (low pressure side) of the third stage compression element decreases. , the suction pressure of the third stage compression element decreases. When the suction pressure of the third-stage compression element decreases, the pressure difference between the suction pressure of the third-stage compression element (equal to the discharge pressure of the second-stage compression element) and the suction pressure of the second-stage compression element increases. become smaller. As a result, the shaft power of the second stage compression element can also be reduced. Thus, a multi-stage roots pump having three or more stages of compression elements has a greater effect of reducing shaft power than a multi-stage roots pump having two stages of compression elements.

<Second cooling gas inlet>
In the pump 500 of this embodiment, the casing 510 is positioned between the suction position (above intermediate position) where gas is sucked into the last stage (third stage in this embodiment) compression element and the discharge port 513. It further has a backflow cooling gas introduction port 519 (hereinafter simply referred to as "cooling gas introduction port 519") for introducing cooling gas C into the interior. This cooling gas introduction port 519 is an example of a second cooling gas introduction port according to this embodiment. The cooling gas inlet 519 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 500 of this embodiment has side covers 580 as intermediate chambers between the casing 510 and the bearing/gear chamber 573 and between the casing 510 and the bearing chamber 574 . This side cover 580 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

(Operation of multistage roots pump)
Next, a method for driving the pump 500 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 500 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIGS. 20 to 23, when drive shaft 568 is rotated by a motor (not shown), first drive gear 564 and second drive gear 565 supported by drive shaft 568 are driven to rotate in the same direction. Next, of the pair of first timing gears 561A and 561B, one of the first timing gears 561A meshing with the first driving gear 564 rotates in the opposite direction to the first driving gear 564. The rotation speed of the first timing gear 561A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the first timing gear 561A/the number of teeth of the first drive gear 564). Also, the other first timing gear 561B meshing with the first timing gear 561A has the same number of teeth as the first timing gear 561A, so it rotates at the same number of rotations in the opposite direction as the first timing gear 561A. As a result, the pair of rotors 521, 521 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 521, 521, the gas in the vicinity of the suction port 511 is sucked into the casing 510 through the suction port 511 (arrow Gs in FIG. 21), and then compressed by the rotor 521 to reach the first stage. It is discharged to the intermediate position of the second stage (arrow Gm1 in FIG. 21).

Similarly, of the pair of second timing gears 562A and 562B, one of the second timing gears 562A meshing with the second drive gear 565 rotates in the opposite direction to the second drive gear 565. The rotation speed of the second timing gear 562A at this time is a reduction ratio ( The rotation speed is reduced by the number of teeth of the second timing gear 562A/the number of teeth of the second drive gear 565). Also, the other second timing gear 562B meshing with the second timing gear 562A has the same number of teeth as the second timing gear 562A, so it rotates at the same number of rotations in the opposite direction as the second timing gear 562A. As a result, the pair of rotors 531, 531 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 531, 531, the gas compressed by the first-stage rotor 521 and discharged to the intermediate position is swept from the intermediate position into the second-stage rotor 531 (see FIG. 21). Arrow Gm1) is compressed by the rotor 531 and discharged to an intermediate position between the second stage and the third stage (arrow Gm2 in FIG. 21).

Further, the 2-3 step intermediate gear 566 meshing with the second timing gear 562A rotates in the direction opposite to the second timing gear 562A. Here, since the 2nd-3rd stage intermediate gear 566 and the third driving gear 567 are supported by the common rotating shaft 570, the 2nd-3rd stage intermediate gear 566 and the third driving gear 567 are rotated in the same direction. and rotate at the same rotational speed. Also, of the pair of third timing gears 563A and 563B, the third timing gear 563A that meshes with the third driving gear 567 rotates in the opposite direction to the third driving gear 567. The rotation speed of the third timing gear 563A at this time is a reduction ratio ( The rotation speed is reduced by the number of teeth of the third timing gear 563A/the number of teeth of the third driving gear 567). The number of revolutions of the third drive gear 567 is increased by the gear ratio calculated from the ratio of the number of teeth between the second timing gear 562A and the intermediate gear 566 between the second and third stages. It is the same as the number of revolutions of 566. Since the other third timing gear 563B meshing with the third timing gear 563A has the same number of teeth as the third timing gear 563A, it rotates at the same number of rotations in the opposite direction as the third timing gear 563A. As a result, the pair of rotors 541, 541 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 541, 541, the gas compressed by the second-stage rotor 531 and discharged to the intermediate position is swept from the intermediate position into the third-stage rotor 541 (Fig. 21). arrow Gm2), and is compressed by the rotor 541 and discharged to the outside from the discharge port 513 (arrow Gd in FIG. 21).

Further, in the present embodiment, the gas existing in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 515 to the outside of the casing 510, cooled by the cooler 1, and then discharged from the casing 510. It is introduced into the first-stage compression element (inside the space surrounded by the rotor 521 and the casing 510) from two cooling gas introduction ports 516A and 516B provided on both left and right sides. At this time, the pressure at the intermediate position (intermediate pressure) Pm1 is higher than the pressure in the space surrounded by the rotor 521 and the casing 510, so the gas discharged from the intermediate discharge port 515 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge1 in FIG. 21, the gas discharged from the intermediate discharge port 515 is cooled by the cooler 1, and is introduced from the cooling gas introduction port 516 into the first-stage compression element. is introduced into the region surrounded by the first-stage rotor 521 and the casing 510 (moving volume Qth1 portion), and then discharged again to an intermediate position between the first and second stages. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 515, and the gas cooled by the cooler 1 flows into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed. Similarly, in the present embodiment, the gas present in the intermediate position between the second stage and the third stage is discharged from the intermediate discharge port 517 to the outside of the casing 510, cooled by the cooler 2, and then discharged to the casing 510. The cooling gas is introduced into the second-stage compression element (inside the space surrounded by the rotor 531 and the casing 510) from two cooling gas introduction ports 518A and 518B provided on both left and right sides of the . At this time, the pressure at the intermediate position (intermediate pressure) Pm2 is higher than the pressure in the space surrounded by the rotor 531 and the casing 510, so the gas discharged from the intermediate discharge port 517 passes through the cooler 2 , circulating. More specifically, as indicated by an arrow Ge2 in FIG. 21, the gas discharged from the intermediate discharge port 517 is cooled by the cooler 2, and is discharged from the cooling gas introduction port 518 into the second-stage compression element. is introduced into the region surrounded by the second stage rotor 531 and the casing 510 (moving volume Qth2 portion), and then discharged again to the intermediate position between the second stage and the third stage. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 517, and the gas cooled by the cooler 2 is discharged into the second stage compression element. always introduced in As a result, the temperature of the gas discharged from the second-stage compression element decreases, so the gas that has been compressed by the second-stage (low-pressure side) compression element and the temperature rises does not dissipate heat, and the third-stage (high-pressure side) side) can be prevented from being directly sucked into the compression element of the third stage, and a significant temperature rise of the gas compressed by the third-stage compression element can be suppressed.

Furthermore, when the pressure (intermediate pressure) Pm1 at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to be discharged from the intermediate discharge port 515 to the atmosphere with a lower pressure ( Arrows Ge1 and Gd in FIG. 21), the intermediate pressure Pm1 drops below the atmospheric pressure. Similarly, when the pressure (intermediate pressure) Pm2 at the intermediate position between the second stage and the third stage is equal to or higher than the atmospheric pressure, the gas is discharged from the intermediate discharge port 517 to the atmosphere with a lower pressure due to the pressure difference. (arrow Ge2 and arrow Gd in FIG. 21), the intermediate pressure Pm2 drops below the atmospheric pressure. Therefore, since the suction pressure to the compression elements (rotors 531, 541) of the second and third stages becomes smaller, the suction pressure Ps2 of the second stage and the pressure of the gas sucked from the suction port 511 (the first stage suction pressure The difference ΔP1 from the pressure Ps1) and the difference ΔP2 between the third-stage suction pressure Ps3 and the second-stage suction pressure Ps2 can be reduced. As a result, the power of the motor that operates the pump 500 can be reduced. In particular, when the pump 500 starts to draw gas toward the suction port 511, the intermediate pressures Pm1 and Pm2 are likely to be higher than the atmospheric pressure. .

In this embodiment, the reduction ratio of the first driving gear 564 with the first timing gear 561A is smaller than the reduction ratio of the intermediate gear 566 between the second and third stages with the second timing gear 562A. . Therefore, the rotation speed N1 of the rotor 521 becomes higher than the rotation speed N2 of the rotor 531. In addition, the length L1 of the rotor 521 and the length L2 of the rotor 531 are equal, and the rotors 521 and 531 have the same shape. is _larger than 1.

Similarly, the reduction ratio of the 2nd-3rd stage intermediate gear 566 between the second timing gear 562A is smaller than the reduction ratio of the third driving gear 567 between the third timing gear 563A. Therefore, the rotation speed N2 of the rotor 531 becomes higher than the rotation speed N3 of the rotor 541. In addition, the length L2 of the rotor 531 and the length L3 of the rotor 541 are equal, and the rotors 531 and 541 have the same shape. is _larger than 1.

That is, the relationship between the first and second stages and the relationship between the second and third stages in this embodiment are both the same as in the first embodiment (the first, second, and third The length of the eye rotor is the same, but the number of revolutions is different).

[Sixth embodiment]
Next, a multi-stage roots pump according to a sixth embodiment of the present invention will be described in detail with reference to FIGS. 24 to 30. FIG. FIG. 24 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 600 (hereinafter abbreviated as "pump 600") as an example of a multi-stage roots-type pump according to the present embodiment. 25 and 26 are cross-sectional views taken along lines XXV--XXV and XXVI--XXVI of FIG. 24, respectively. 27 and 28 are cross-sectional views for explaining the leakage area in the pump 100 according to the first embodiment, and FIGS. 29 and 30 are for explaining the leakage area in the pump 600 according to the present embodiment. It is a sectional view. In the pump 100 of the first embodiment, the first stage (low pressure side) rotor 121 and the second stage (high pressure side) rotor 131 have the same length and diameter, and the rotation speed of the first stage rotor 121 is is higher than the rotation speed of the rotor 131 of the second stage, in the pump 600 according to this embodiment, the length and diameter of the rotor 621 of the first stage are equal to the length of the rotor 631 of the second stage. This is an example in which the rotor 621 in the first stage has a higher rotational speed than the rotor 631 in the second stage. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 24 to 26, the pump 600 is a two-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 610, two stages (two sets) of compression elements, and a drive mechanism. Prepare.

<Casing>
The configuration and function of the casing 610 are similar to those of the casing 110 according to the first embodiment. It differs from the embodiment. In addition, neither the cooler 1 nor the check valve 3 are provided in this embodiment.

In addition, the casing 610 is arranged along the normal direction of the virtual plane containing the two rotating shafts 622, 622 or the two rotating shafts 632, 632 of the compression elements of the same stage. The compression elements are housed so that the elements are arranged side-by-side. Thus, in this embodiment, multiple stages of compression elements arranged in parallel with respect to the axial direction of the rotating shafts 622 and 632 are housed in a single casing 610, and external No particular piping or internal gas flow path is provided. Therefore, the gas compressed and discharged by the compression element of the front stage (in this embodiment, the first stage) is directly (as is) sucked into the compression element of the rear stage (in this embodiment, the second stage).

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 611 side and a second stage (high pressure side) compression element located on the discharge port 613 side are provided in the single casing 610. A two-stage compression element is provided. A partition plate or the like is not provided between the two stages of compression elements unlike the series internal multi-stage roots type pump, and a plurality of compression elements are provided as a single stage group within the integral casing 610. ing. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 621 and 621 and two rotating shafts 622 and 622 . The second stage compression element has a pair of rotors 631 and 631 and two rotating shafts 632 and 632 .

As shown in FIG. 25, the rotor 621 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 621a, 621b, 621c projecting radially from the center of rotation. A recess 621d is provided between each projection 621a, 621b, 621c. Similarly, the rotor 631 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 631a, 631b, 631c projecting radially from the center of rotation. A recess 631d is provided between each projection 631a, 631b, 631c.

A pair of rotors 621, 621 are provided rotatably in directions opposite to each other. The two rotating shafts 622, 622 rotatably support a pair of rotors 621, 621 and are arranged parallel to each other. Also, the two rotating shafts 622 , 622 are supported by two bearings 623 , 623 . Similarly, a pair of rotors 631, 631 are provided rotatably in directions opposite to each other. The two rotating shafts 632, 632 rotatably support a pair of rotors 631, 631 and are arranged parallel to each other. Also, the two rotating shafts 632 , 632 are supported by two bearings 633 , 633 . Furthermore, in this embodiment, the rotating shaft 622 and the rotating shaft 632 are arranged so as to be parallel to each other. In the following description, the description of the rotor 631 that overlaps with that of the rotor 621 will be omitted as necessary, and the contents of the rotor 621 will be appropriately read.

Between the rotors 621 and 621 and between the tips (leaf ends) of the projections 621a, 621b and 621c and the casing 610, so that the pair of rotors 621 and 621 and the rotor 621 and the inner surface 610a of the casing 610 do not come into contact with each other. A rotor 621 is arranged with a small gap between the inner surface 610a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 621, 621 are maintained by timing gears 661A, 661B, which will be described later, and the cross-sectional shape of the rotor 621 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 631 is arranged so that a slight gap is formed between the paired rotor 631 and the inner surface 610 d of the casing 610 . Also, the pair of rotors 631, 631 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Here, in the present embodiment, as will be described later, the clearances between the rotors 631 in the second stage and between the rotor 631 and the casing 610 are larger than those between the rotors 621 in the first stage and between the rotor 621 and the casing 610 . is set narrower than the gap between Other configurations and functions of the rotors 621 and 631 are the same as those of the rotors according to the above embodiments.

In the pump 600, the rotor 621, the rotating shaft 622, etc., which are the first-stage compression elements, and the rotor 631, the rotating shaft 632, etc., which are the second-stage compression elements are arranged in a single casing 610 at the same stage. They are arranged in parallel along the normal direction of an imaginary plane containing the two rotation axes 622, 622 (or the two rotation axes 632, 632). That is, the rotor 621 in the first stage and the rotor 631 in the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are in parallel. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 611, the first-stage rotor 621, the second-stage rotor 631, and the gas discharge port 613 are arranged side by side in the vertical direction. Therefore, when the gas is introduced into the casing 610 from the suction port 611 (arrow Gs in FIG. 25), it travels vertically downward, is compressed by the rotor 621, and then passes through the first-stage compression element and the second-stage compression element. (arrow Gm in FIG. 25). The gas compressed by the rotor 621 further travels vertically downward, is compressed by the second-stage rotor 631, and is then directly discharged from the discharge port 613 to the outside of the casing 610 (arrow Gd in FIG. 25).

Thus, according to the pump 600 according to the present embodiment, the first stage rotor 621 and the second stage rotor 631 are arranged in parallel on separate shafts within the single casing 610 . Therefore, unlike the in-line multi-stage roots pump, the rotors 621 and 631 can be arranged without providing a partition between the first-stage compression element (rotor 621) and the second-stage compression element (rotor 631). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of an in-line multi-stage roots pump, if it has two stages of rotors, the length of the rotating shaft is required to be equal to or longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, it is possible to suppress a decrease in rigidity of the rotating shafts 622 and 632 and the casing 610 . In particular, even if the length of the rotors 621 and 631 is lengthened in order to increase the air volume of the pump 600, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and positioning accuracy between the first and second stage pump operating regions are not so high, they can be accommodated within a range that does not hinder the performance of the pump 600 in terms of assembly and performance. Accuracy and assembly accuracy are not required.

<Transfer volume ratio>
Also in the pump 600 of this embodiment, between the first-stage compression element (rotor 621) and the second-stage compression element (rotor 631) arranged in parallel on separate rotating shafts, the following formula (1 ) is _greater than 1.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in this embodiment is a so-called displacement amount, which is the theoretical volume per time of the space surrounded by the casing 610 and the rotor 621 or rotor 631, which is proportional to the rotational speed N. . That is, as described above, the movement volume Qth (m ³ /min) is represented by the following equation (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, A is the area of movement per revolution, L is the length of the rotor, and N is the number of rotations of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the axis of rotation 622, 632.

The displacement volume ratio _RQ in the pump 600 of this embodiment is calculated as follows. First, taking the rotor 621 of the first stage as an example, each time the pair of left and right rotors 621, 621 rotates, the gas is sucked and discharged six times (the left rotor 621 and the right rotor 621 each rotate 6 times). and 3 times each) is repeated. The same applies to the second stage rotor 631 . Here, as shown in FIG. 25, a cross section perpendicular to the rotating shaft 622 of the space surrounded by the two protrusions (for example, the protrusion 621a and the protrusion 621b) of the rotor 621 and the inner surface 610a of the casing 610 is taken. Assuming that the area is S1, the moving area A1 of the first stage (low pressure side) compression element is A1=6×S1. Similarly, if S2 is the cross-sectional area of the cross section perpendicular to the rotating shaft 632 of the space surrounded by the two protrusions (for example, the protrusion 631a and the protrusion 631b) of the rotor 631 and the inner surface 610d of the casing 610, then 2 The moving area A2 of the compression element on the stage (high pressure side) is A2=6×S2. From the above, the movement volume ratio R _Q1-2 between the first stage and the second stage is expressed by the following formula (3).

However, in formula (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 621, L2 is the length of the second stage rotor 631, N1 is the rotation speed of the first stage rotor 621, and N2 is the second stage rotor 631. represents the number of rotations of

Here, in the pump 600 of this embodiment, the diameter D1 of the rotor 621 is larger than the diameter D2 of the rotor 631 (D1>D2). Therefore, the moving area A1 of the first stage is larger than the moving area A2 of the second stage (A1>A2). Also, the length L1 of the first stage rotor 621 is longer than the length L2 of the second stage rotor 631 (L1>L2). On the other hand, the rotation speed N1 of the first stage rotor 621 is lower than the rotation speed N2 of the second stage rotor 631 (N1<N2). Even in such a case, if the moving volume ratio _RQ can be set to 1 or more, unlike the first embodiment, the rotation speed of the rotor 631 of the second stage (high pressure side) can be reduced to that of the rotor 631 of the first stage ( It may be higher than the rotation speed of the rotor 621 on the low pressure side).

As can be seen from the configuration of the pump 600 according to the sixth embodiment, as long as the moving volume ratio _RQ between adjacent compression elements can be set to 1 or more, the first stage compression element and the second stage compression element The diameter and length of the rotors and the number of revolutions of each rotor can be freely designed together with the compression element. For example, as in this embodiment, when the diameter D1 of the first stage (low pressure side) rotor 621 is made larger than the diameter D2 of the second stage (high pressure side) rotor 631, the displacement volume ratio _RQ is Although it is necessary to satisfy the requirement of 1 or more, the length of the rotor 621 in the first stage is equal to or longer than the length of the rotor 631 in the second stage, and the rotation speed of the rotor 621 in the first stage is equal to or greater than that of the rotor 621 in the second stage. In some cases, the rotation speed is equal to or lower than the rotation speed of the rotor 631 .

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 667 of the pump 600 can be reduced.

<Drive Mechanism>
As shown in FIGS. 24 and 26, the drive mechanism of this embodiment includes a pair of first timing gears 661, a pair of second timing gears 662, a first drive gear 665, a second drive gear 666 and and a single drive shaft 667 which is the motor input shaft.

A pair of first timing gears 661A and 661B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 622 of the first stage. , have the same number of teeth. A pair of second timing gears 662A and 662B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 632 of the second stage, and are arranged so that the rotation phases of the pair of rotors 631 and 631 match each other. , have the same number of teeth.

Also, the first drive gear 665 is provided so as to mesh with one of the pair of first timing gears 661, the first timing gear 661A, and the second drive gear 666 is provided so as to mesh with the pair of second timing gears. 662 is provided so as to mesh with one of the second timing gears 662A. Furthermore, the drive shaft 667 rotatably supports the first drive gear 665 and the second drive gear 666 . That is, the first drive gear 665 and the second drive gear 666 are rotatably supported by the same drive shaft. The drive shaft 667 is supported by a bearing 668 provided in the side cover 680 and a bearing 668 provided in the bearing/gear chamber 673 . The shaft end of the drive shaft 667 on the bearing 668 side provided in the bearing/gear chamber 673 is connected to a motor (not shown).

As described above, in this embodiment, the rotation speed of the rotor 631 in the second stage is higher than the rotation speed of the rotor 621 in the first stage. In other words, the rotation speed of the rotor 631 in the second stage is faster than the rotation speed of the rotor 621 in the first stage. Therefore, in pump 600, the number of teeth of first drive gear 665 and second drive gear 666 is set so that the rotation speed of rotor 631 in the second stage is higher than the rotation speed of rotor 621 in the first stage. FIG. 26 shows an example in which the rotational speed of the rotating shaft 622 is reduced from the rotational speed of the drive shaft 667 and the rotational speed of the rotating shaft 632 is increased. In the example shown in FIG. 26, the number of teeth of the first timing gear 661 is greater than that of the first driving gear 665, and the number of teeth of the first driving gear 665 is greater than that of the second driving gear 666. The number of teeth of the second timing gear 662 is smaller than the number of teeth of the second drive gear 666 .

<Intermediate outlet>
When the pump 600 of this embodiment is used as a vacuum pump, the casing 610 is positioned between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. An intermediate discharge port 615 for discharging gas to the outside may be further provided at an intermediate position of . The example shown in FIG. 25 shows an example in which only one intermediate outlet 615 is provided on the left side surface of the casing 610, but the number of intermediate outlets 615 is not particularly limited, and two or more outlets may be provided. good. For example, in the cross section shown in FIG. 615 may be provided.

The intermediate discharge port 615 is provided to reduce the shaft power of the pump 600 used as a vacuum pump. First, the shaft power will be described. As described above, the first stage shaft power Lth1 is the difference ΔP1 (ΔP1=Ps2−Ps1 ) and the movement volume Qth1 of the first stage (Lth1=ΔP1×Qth1). Similarly, the second-stage shaft power Lth2 is the product of the difference ΔP2 (ΔP2=Pd−Ps2) between the discharge pressure Pd and the second-stage suction pressure Ps2 and the second-stage displacement volume Qth2 (Lth2=ΔP2 x Qth2). As the ΔP1 and ΔP2 are larger and the moving volumes Qth1 and Qth2 are larger, the shaft power Lth1 and Lth2 are larger, so a motor with large power is required.

Next, the intermediate discharge port 615 will be described. The intermediate discharge port 615 is provided at an intermediate position between the discharge side of the first stage compression element and the suction side of the second stage compression element. The pressure at this intermediate position (intermediate pressure Pm) is equal to the discharge pressure from the first stage compression element (rotor 621), and this pressure is also the suction pressure to the second stage compression element (rotor 631). equal.

In the case of a vacuum pump, gas sucked from the suction port 611 is compressed to atmospheric pressure at the discharge port 613 . In other words, compression to atmospheric pressure is sufficient, but when the suction pressure in the first stage increases, the suction pressure in the second stage (both discharge pressure and intermediate pressure in the first stage are equal) rises above atmospheric pressure. there is something As described above, the first stage shaft power Lth1 is the product of ΔP1 (ΔP1=Ps2−Ps1) and the first stage movement volume Qth1 (Lth1=ΔP1×Qth1). power increases. This is also noticeable when the pump is started when the first stage suction pressure and the second stage suction pressure are both at atmospheric pressure and the exhaust starts. Therefore, in order to reduce the power of the motor, it is preferable to make ΔP1 as small as possible.

Therefore, by providing an intermediate discharge port 615 communicating with the external atmosphere at an intermediate position between the first stage and the second stage, when the intermediate pressure Pm is equal to or higher than the atmospheric pressure, the gas is discharged intermediately due to the pressure difference. From the outlet 615, it is discharged to the atmosphere with a lower pressure (arrow Ge in FIG. 25), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second-stage compression element (rotor 631) is reduced, ΔP1 can be reduced. As a result, the power of the motor that operates the pump 600 can be reduced. In particular, when the pump 600 is started, the first-stage compression element and the second-stage compression element both start exhausting from the state of atmospheric pressure. Therefore, when the pump 600 starts to draw gas toward the suction port 611, when the suction pressure of the second stage is atmospheric pressure and the atmospheric pressure gas is transferred from the first stage compression element, the intermediate The pressure Pm rises to the product of the atmospheric pressure and the displacement volume ratio _RQ . As described above, when the pump 600 starts to draw gas, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In addition, when the intermediate discharge port 615 is provided, it is necessary to provide the intermediate discharge port 615 with a check valve (not shown). By providing the check valve, when the intermediate pressure Pm is lower than the atmospheric pressure, the check valve closes due to the pressure difference from the atmospheric pressure, and when the intermediate pressure Pm is higher than the atmospheric pressure, the check valve opens. , is exhausted to lower pressure atmosphere.

<Second cooling gas inlet>
In the pump 600 of this embodiment, the casing 610 is positioned between the suction position (above intermediate position) where gas is sucked into the final stage (second stage in this embodiment) compression element and the discharge port 613. It further has a backflow cooling gas introduction port 617 (hereinafter simply referred to as "cooling gas introduction port 617") for introducing cooling gas C into the interior. This cooling gas introduction port 617 is an example of a second cooling gas introduction port according to this embodiment. The cooling gas inlet 617 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 600 of this embodiment has side covers 680 as intermediate chambers between the casing 610 and the bearing/gear chamber 673 and between the casing 610 and the bearing chamber 674 . This side cover 680 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

<Amount of gas leakage>
The amount of gas leakage in each compression element included in the multistage roots pump will be described with reference to FIGS. 27 to 30. FIG. 27 is a cross-sectional view cut along line XXVII-XXVII of FIG. 28, and FIG. 29 is a cross-sectional view cut along line XXIX-XXIX of FIG.

The amount of gas leakage QL from the discharge side (high pressure side) to the suction side (low pressure side) in the compression element is the differential pressure ΔP (=Pd−Ps) between the suction pressure Ps and the discharge pressure Pd of the multistage roots pump, and the leakage area AL formed by the gap between the rotors, between the rotor and the casing, or the like. Assuming that the differential pressure ΔP is constant, the smaller the leakage area AL, the smaller the gas leakage amount QL from the discharge side to the suction side. When the gas leakage amount QL from the discharge side (high pressure side) to the suction side (low pressure side) of the compression element in the latter stage decreases, the suction pressure _PsH to the compression element in the latter stage decreases. When the suction pressure PsH decreases, the differential pressure with _respect to the suction pressure _PsL to the compression element of the previous stage decreases, so the shaft power of the compression element of the previous stage decreases. The gas leakage area AL in the pump 600 according to the present embodiment will be described below in comparison with the gas leakage area AL in the pump 100 according to the first embodiment.

First, as shown in FIGS. 27 and 28, in the pump 100 according to the first embodiment, the total leakage area AL1 in the first-stage compression element and the total leakage area AL2 in the second-stage compression element are as follows. (6) and (7).
AL1=Ar1+Ax1+As1 (6)
AL2=Ar2+Ax2+As2 (7)

However, in equation (6), Ar1 is the leakage area formed by the gap between the tip of the protruding portion of the rotor 121 of the first stage and the inner surface of the casing 110, and Ax1 is formed by the gap between the rotors 121. As1 is the leakage area formed by the gap between both ends (rotor sides) in the length direction of the rotor 121 and the casing 110. Further, in equation (7), Ar2 is the leakage area formed by the gap between the tip of the protruding portion of the second stage rotor 131 and the inner surface of the casing 110, and Ax2 is formed by the gap between the rotors 131. As2 is the leakage area formed by the gap between the rotor side of the rotor 131 and the casing 110 .

Also, the leak areas Ar1, Ax1, As1, Ar2, Ax2, and As2 are obtained by the following equations (6-1) to (6-3) and (7-1) to (7-3).
Ar1=2×Cr1×L1 (6-1)
Ax1=Cx1×L1 (6-2)
As1=CsA1×(D1+H1)+CsB1×(D1+H1) (6-3)
Ar2=2×Cr2×L2 (7-1)
Ax2=Cx2×L2 (7-2)
As2=CsA2×(D2+H2)+CsB2×(D2+H2) (7-3)

However, in equations (6-1) to (6-3) and (7-1) to (7-3), Cr1 and Cr2 are the tips of the protrusions of rotors 121 and 131 and the inner surface of casing 110, respectively. is the distance in the cross section shown in FIG. Cx1 and Cx2 are the distances between the rotors 121 and 131 in the section shown in FIG. 27, respectively. CsA1 and CsA2 are the distances in the cross section shown in FIG. CsB1 and CsB2 are the distances in the cross section shown in FIG. Also, L1 and L2 are the lengths of the rotors 121 and 131, respectively, and D1 and D2 are the diameters of the rotors 121 and 131, respectively.

Here, as described above, in the case of a parallel internal multistage roots pump such as the pump 100, if the cooling mechanism is not provided as in the first embodiment, the first stage (low pressure side) compression The gas compressed by the element is directly sucked into the second-stage (high-pressure side) compression element without releasing heat, and is further compressed by the second-stage compression element, thereby significantly increasing the temperature of the gas. Therefore, in the first embodiment, the temperature rise of the gas in the second-stage compression element is suppressed by constantly cooling the gas in the intermediate position by the cooling mechanism. Therefore, it is not necessary to widen the gaps Cr2, Cx2, CsA2, and CsB2 in anticipation of thermal expansion of the rotor 131 .

If the pump 100 were not provided with a cooling mechanism, the gaps Cr2, Cx2, CsA2, and CsB2 would need to be widened in anticipation of the thermal expansion of the rotor 131. FIG. As a result, the leak areas Ar2, Ax2, and As2 in the second-stage compression elements increase (that is, the total leak area AL2 increases), and the amount of gas leaked from the discharge side to the suction side increases.

Next, as shown in FIGS. 29 and 30, also in the pump 600 according to the present embodiment, the total leakage area AL1 in the first-stage compression element and the total leakage area AL2 in the second-stage compression element are, respectively, It is represented by the above equations (6) and (7).

However, in equation (6), Ar1 is the leakage area formed by the gap between the tip of the protrusion of the rotor 621 of the first stage and the inner surface of the casing 610, and Ax1 is formed by the gap between the rotors 621. As1 is the leakage area formed by the gap between both ends (rotor sides) in the length direction of the rotor 621 and the casing 610 . In equation (7), Ar2 is the leakage area formed by the gap between the tip of the protruding portion of the second stage rotor 631 and the inner surface of the casing 610, and Ax2 is formed by the gap between the rotors 631. As2 is the leakage area formed by the gap between the rotor side of the rotor 631 and the casing 610 .

Also, in the pump 600, the leakage areas Ar1, Ax1, As1, Ar2, Ax2, and As2 are calculated by the above formulas (6-1) to (6-3) and (7-1) to (7-3). be done.

However, in equations (6-1) to (6-3) and (7-1) to (7-3), Cr1 and Cr2 are the tips of the protrusions of rotors 621 and 631 and the inner surface of casing 610, respectively. is the distance in the cross section shown in FIG. Cx1 and Cx2 are the distances between the rotors 621 and 631 in the section shown in FIG. 29, respectively. CsA1 and CsA2 are the distances in the cross section shown in FIG. CsB1 and CsB2 are the distances in the cross section shown in FIG. Also, L1 and L2 are the lengths of the rotors 621 and 631, respectively, and D1 and D2 are the diameters of the rotors 621 and 631, respectively.

Here, the gaps between the rotors and between the rotor and the casing are set in consideration of the amount of thermal expansion of the rotor and casing. The smaller the diameter of the rotor, the smaller each gap can be set. In the pump 600 according to the present embodiment, the length L2 of the rotor 631 of the second stage is smaller than the length L1 of the rotor 621 of the first stage, and the diameter D2 of the rotor 631 of the second stage is equal to that of the rotor 631 of the first stage. smaller than the diameter D1 of the rotor 621 of the eye. Therefore, since the amount of thermal expansion of the rotor 631 is small, the gaps Cr2, Cx2, CsA2, and CsB2 in the second-stage compression element of the pump 600 are replaced by the gaps Cr1, Cx1, and CsA1 in the first-stage compression element. , CsB1. As a result, the leakage areas Ar2, Ax2, and As2 in the second-stage compression elements of the pump 600 become smaller (that is, the total leakage area AL2 becomes smaller), and the gas leakage amount QL from the discharge side to the suction side decreases. .

As described above, like the pump 600 according to this embodiment, by reducing the size of the rotor (in this embodiment, the second stage rotor 631) in the compression element on the high pressure side, Even without providing a cooling mechanism like the pump 100 or the like, it is possible to reduce the gas leakage amount QL from the discharge side (high pressure side) to the suction side (low pressure side) of the compression element on the high pressure side. On the other hand, as the size of the second-stage rotor 631 becomes smaller, the movement volume per rotation of the second-stage compression element becomes smaller. The eye movement volume Qth2 is adjusted to a predetermined size.

For example, after reducing the size of the rotor 631 in the second stage, if the rotation speed N2 of the rotor 631 is the same as the rotation speed N1 of the rotor 621 in the first stage or lower than the rotation speed N1 of the rotor 621, The movement volume Qth2 of the second stage compression element becomes too small. Here, since the specification of the pressure ratio r for the pump as a whole is fixed (for example, r ≤ 3 in the case of a two-stage roots pump), if the displacement volume Qth2 of the second-stage compression element becomes small, , it is necessary to increase the movement volume Qth1 of the first-stage compression element accordingly. Therefore, in such a case, the movement volume Qth1 becomes too large as the movement volume Qth2 becomes too small. That is, the moving volume ratio R _Q (=Qth2/Qth1) becomes too large. If the first-stage movement volume Qth1 becomes too large, the compression rate of the gas compressed by the first-stage compression element also increases. The amount of rise will also increase. In addition, if the movement volume ratio _RQ becomes too large, the proportion of work shared by the first-stage compression element with respect to the second-stage compression element becomes high, so the shaft power of the first stage becomes too large. .

Therefore, in the pump 600 according to the present embodiment, even when the size of the second stage rotor 631 is reduced, the second stage rotor 631 is By increasing the rotational speed N2 (higher than the rotational speed N1 of the rotor 621 of the first stage), the displacement volume _Qth2 of the second stage compression element is adjusted appropriately so that the displacement volume ratio RQ does not become too large. adjusted for size.

According to the pump 600 according to the present embodiment having the above configuration, as described above, by reducing the size of the rotor 631, the leakage amount QL2 in the second stage compression element is reduced. The suction pressure _PsH to the compression element drops. When the suction pressure _PsH decreases, the pressure difference from the suction pressure _PsL to the first stage compression element decreases, so the shaft power of the first stage compression element decreases. On the other hand, since the suction pressure _PsH to the second stage compression element decreases, the differential pressure with the discharge pressure _PdH from the second stage compression element increases, so the shaft power of the second stage increases. Become. However, since the size of the rotor 631 of the second stage is small, the increase in the shaft power of the second stage is smaller than the decrease of the shaft power of the first stage. do. This is also shown in Examples described later.

(Operation of multistage roots pump)
Next, a method of driving the pump 600 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 600 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIGS. 24 and 26, when the drive shaft 667 is rotated by a motor (not shown), the first drive gear 665 and the second drive gear 666 supported by the drive shaft 667 are rotated in the same direction. Next, of the pair of first timing gears 661A and 661B, one of the first timing gears 661A meshing with the first driving gear 665 rotates in the opposite direction to the first driving gear 665. The rotation speed of the first timing gear 661A at this time is a reduction ratio ( The rotational speed is reduced by the number of teeth of the first timing gear 661A/the number of teeth of the first drive gear 665). In addition, since the other first timing gear 661B meshing with the one first timing gear 661A has the same number of teeth as the first timing gear 661A, it rotates at the same number of rotations in the direction opposite to that of the first timing gear 661A. do. As a result, the pair of rotors 621, 621 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 621, 621, the gas near the suction port 611 is sucked into the casing 610 through the suction port 611 (arrow Gs in FIG. 25), then compressed by the rotor 621 and discharged to the intermediate position. (arrow Gm in FIG. 25).

Similarly, of the pair of second timing gears 662A and 662B, one of the second timing gears 662A meshing with the second driving gear 666 rotates in the opposite direction to the second driving gear 666. The number of rotations of the second timing gear 662A at this time is a gear ratio ( The rotation speed is increased by (the number of teeth of the second timing gear 662A/the number of teeth of the second driving gear 666). In addition, since the other second timing gear 662B meshing with the one second timing gear 662A has the same number of teeth as the one second timing gear 662A, it rotates in the same direction as the second timing gear 662A. Rotate by number. As a result, the pair of rotors 631, 631 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 631, 631, the gas compressed by the first-stage rotor 621 and discharged to the intermediate position is swept into the second-stage rotor 631 from the intermediate position (see the arrow in FIG. 25). Gm), it is then compressed by the rotor 631 and discharged to the outside from the discharge port 613 (arrow Gd in FIG. 25).

Further, in this embodiment, when the pressure (intermediate pressure) Pm at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to flow out of the intermediate discharge port 615 at a lower pressure. It is discharged to the atmosphere (arrow Ge in FIG. 25), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second-stage compression element (rotor 631) becomes smaller, the difference between the second-stage suction pressure Ps2 and the pressure of the gas sucked from the suction port 611 (first-stage suction pressure Ps1) ΔP1 can be reduced. As a result, the power of the motor that operates the pump 600 can be reduced. In particular, when the pump 600 starts to draw gas toward the suction port 611, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the number of teeth of each gear is determined so that the rotation speed of the first timing gear 661 is reduced while the rotation speed of the second timing gear 662 is increased. Also, the diameter D1 of the rotor 621 is larger than the diameter D2 of the rotor 631 . Furthermore, length L1 of rotor 621 is longer than length L2 of rotor 631 . Even under such special conditions, it is possible to make the volumetric displacement ratio _RQ larger than 1 as described above.

[Seventh Embodiment]
Next, a multi-stage roots pump according to a seventh embodiment of the present invention will be described in detail with reference to FIGS. 31 and 32. FIG. FIG. 31 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 700 (hereinafter abbreviated as "pump 700") as an example of a multi-stage roots-type pump according to the present embodiment. 32 is a cross-sectional view taken along line XXXII-XXXII of FIG. 31. FIG. The pump 600 of the sixth embodiment is an example in which the first stage (low pressure side) rotor 621 and the second stage (high pressure side) rotor 631 have different lengths and diameters. 700 states that the length of the rotor 721 of the first stage is greater than the length of the rotor 731 of the second stage, and the diameter of the rotor 721 of the first stage is equal to the diameter of the rotor 731 of the second stage. For example. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 31 and 32, the pump 700 is a two-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 710, two stages (two sets) of compression elements, and a drive mechanism. Prepare.

<Casing>
The configuration and function of casing 710 are similar to casing 610 according to the sixth embodiment.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 711 side and a second stage (high pressure side) compression element located on the discharge port 713 side are provided in the single casing 710. A two-stage compression element is provided. A partition plate or the like is not provided between the two stages of the compression elements unlike the series internal multi-stage roots type pump, and a plurality of compression elements are provided as a single stage group within the integral casing 710. ing. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 721 and 721 and two rotating shafts 722 and 722 . The second stage compression element has a pair of rotors 731 and 731 and two rotating shafts 732 and 732 .

As shown in FIG. 32, the rotor 721 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 721a, 721b, 721c projecting radially from the center of rotation. In addition, recesses 721d are provided between the protrusions 721a, 721b, and 721c. Similarly, the rotor 731 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 731a, 731b, 731c projecting radially from the center of rotation. Further, recesses 731d are provided between the protrusions 731a, 731b, and 731c.

The pair of rotors 721, 721 are provided rotatably in directions opposite to each other. The two rotating shafts 722, 722 rotatably support a pair of rotors 721, 721 and are arranged parallel to each other. Also, the two rotating shafts 722 , 722 are supported by two bearings 723 , 723 . Similarly, a pair of rotors 731, 731 are provided rotatably in directions opposite to each other. The two rotating shafts 732, 732 rotatably support a pair of rotors 731, 731 and are arranged parallel to each other. Also, the two rotating shafts 732 , 732 are supported by two bearings 733 , 733 . Furthermore, in this embodiment, the rotating shaft 722 and the rotating shaft 732 are arranged so as to be parallel to each other. In the following description, the description of the rotor 731 that overlaps with that of the rotor 721 will be omitted as necessary, and the contents of the rotor 721 will be replaced as appropriate.

Between the rotors 721 and 721 and the tips (leaf ends) of the protrusions 721a, 721b, and 721c and the casing 710 are arranged so that the pair of rotors 721 and 721 and the rotor 721 and the inner surface 710a of the casing 710 do not come into contact with each other. A rotor 721 is arranged with a slight gap between the inner surface 710a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 721, 721 are maintained by timing gears 761, 761, which will be described later, and the cross-sectional shape of the rotor 721 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 731 is arranged so that a slight gap is formed between the paired rotor 731 and the inner surface 710 d of the casing 710 . Also, the pair of rotors 731, 731 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Here, in the present embodiment, as will be described later, the clearances between the rotors 731 in the second stage and between the rotor 731 and the casing 710 are larger than the clearances between the rotors 721 in the first stage and between the rotor 721 and the casing 710 . is set narrower than the gap between Other configurations and functions of the rotors 721 and 731 are the same as those of the rotors according to the above embodiments.

In the pump 700, the rotor 721, the rotating shaft 722, etc., which are the first stage compression elements, and the rotor 731, the rotating shaft 732, etc. which are the second stage compression elements are arranged in a single casing 710 at the same stage. They are arranged in parallel along the normal direction of an imaginary plane containing the two rotation axes 722, 722 (or the two rotation axes 732, 732). That is, the rotor 721 of the first stage and the rotor 731 of the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are parallel to each other. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 711, the first-stage rotor 721, the second-stage rotor 731, and the gas discharge port 713 are arranged side by side in the vertical direction. Therefore, when the gas is introduced into the casing 710 from the suction port 711 (arrow Gs in FIG. 32), it travels vertically downward, is compressed by the rotor 721, and then passes through the first stage compression element and the second stage compression element. (arrow Gm in FIG. 32). The gas compressed by the rotor 721 further travels vertically downward, is compressed by the second-stage rotor 731, and is then directly discharged from the discharge port 713 to the outside of the casing 710 (arrow Gd in FIG. 32).

Thus, according to the pump 700 according to the present embodiment, the first stage rotor 721 and the second stage rotor 731 are arranged in parallel on different shafts within the single casing 710 . Therefore, unlike the in-line multistage roots pump, the rotors 721 and 731 can be arranged without providing a partition between the first stage compression element (rotor 721) and the second stage compression element (rotor 731). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of a series internal multi-stage roots pump, if it has two stages of rotors, the length of the rotating shaft is required to be equal to or longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, a decrease in rigidity of the rotating shafts 722 and 732 and the casing 710 can be suppressed. In particular, even if the length of the rotors 721 and 731 is lengthened in order to increase the air volume of the pump 700, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and alignment accuracy between the first stage and second stage pump operation areas are not so high, they are within a range that does not hinder the performance of the pump 700 in terms of assembly and performance. Accuracy and assembly accuracy are not required.

<Transfer volume ratio>
Also in the pump 700 of this embodiment, between the first-stage compression element (rotor 721) and the second-stage compression element (rotor 731) arranged in parallel on separate rotating shafts, the following formula (1 ) is _greater than 1.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in this embodiment is a so-called displacement amount, which is the theoretical volume per hour of the space surrounded by the casing 710 and the rotor 721 or 731, which is proportional to the rotational speed N. . That is, as described above, the movement volume Qth (m ³ /min) is represented by the following equation (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, A is the area of movement per revolution, L is the length of the rotor, and N is the number of rotations of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the rotation axes 722 and 732 .

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 700 of this embodiment is expressed by the following equation (3), as in the sixth embodiment described above.

However, in equation (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 721, L2 is the length of the second stage rotor 731, N1 is the rotation speed of the first stage rotor 721, and N2 is the second stage rotor 731. represents the number of rotations of

Here, in the pump 700 of this embodiment, the diameter D1 of the rotor 721 is equal to the diameter D2 of the rotor 731 (D1=D2), so the movement area A1 of the first stage is equal to the movement area A2 of the second stage. (A1=A2). Also, the length L1 of the first stage rotor 721 is longer than the length L2 of the second stage rotor 731 (L1>L2). On the other hand, the rotation speed N1 of the first stage rotor 721 is lower than the rotation speed N2 of the second stage rotor 731 (N1<N2). Even in such a case, if the moving volume ratio _RQ can be set to 1 or more, unlike the first embodiment, the rotation speed of the rotor 731 of the second stage (high pressure side) can be reduced to that of the rotor 731 of the first stage ( It may be higher than the rotation speed of the rotor 721 on the low pressure side).

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 767 of the pump 700 can be reduced.

<Drive Mechanism>
As shown in FIG. 31, the drive mechanism of this embodiment includes a pair of first timing gears 761, a pair of second timing gears 762, a first drive gear 765, a second drive gear 766, a motor and a single drive shaft 767 which is the input shaft.

A pair of first timing gears 761, 761 are provided so as to mesh with each other at the shaft ends of the two rotating shafts 722 of the first stage, and are arranged so that the rotation phases of the pair of rotors 721, 721 match each other. , have the same number of teeth. A pair of second timing gears 762, 762 are provided so as to mesh with each other at the shaft ends of the two rotating shafts 732 of the second stage, and are arranged so that the rotation phases of the pair of rotors 731, 731 match each other. , have the same number of teeth.

Also, the first drive gear 765 is provided so as to mesh with one of the pair of first timing gears 761, the first timing gear 761, and the second drive gear 766 is provided so as to mesh with the pair of second timing gears. It is provided so as to mesh with one of the second timing gears 762 of 762 . Furthermore, the drive shaft 767 rotatably supports the first drive gear 765 and the second drive gear 766 . That is, the first drive gear 765 and the second drive gear 766 are rotatably supported by the same drive shaft. The drive shaft 767 is supported by a bearing 768 provided in the side cover 780 and a bearing 768 provided in the bearing/gear chamber 773 . The shaft end of the drive shaft 767 on the bearing 768 side provided in the bearing/gear chamber 773 is connected to a motor (not shown).

As described above, in this embodiment, the rotation speed of the rotor 731 in the second stage is higher than the rotation speed of the rotor 721 in the first stage. In other words, the rotation speed of the rotor 731 in the second stage is faster than the rotation speed of the rotor 721 in the first stage. Therefore, in pump 700, the number of teeth of first drive gear 765 and second drive gear 766 is set so that the rotation speed of rotor 731 in the second stage is higher than the rotation speed of rotor 721 in the first stage. FIG. 31 shows an example in which the rotation speed of the drive shaft 767 is reduced from that of the rotation shaft 722 and the rotation speed of the rotation shaft 732 is increased. In the example shown in FIG. 31, the number of teeth of the first timing gear 761 is greater than that of the first driving gear 765, and the number of teeth of the first driving gear 765 is greater than that of the second driving gear 766. The number of teeth of the second timing gear 762 is less than the number of teeth of the second drive gear 766 .

<Intermediate outlet>
When the pump 700 of this embodiment is used as a vacuum pump, the casing 710 is positioned between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. An intermediate discharge port 715 for discharging gas to the outside may be further provided at an intermediate position of . The example shown in FIG. 32 shows an example in which only one intermediate outlet 715 is provided on the left side surface of the casing 710, but the number of intermediate outlets 715 is not particularly limited, and two or more outlets may be provided. good. For example, in the cross section shown in FIG. 715 may be provided. The intermediate outlet 715 has substantially the same configuration and function as the intermediate outlet 615 according to the sixth embodiment.

<Second cooling gas inlet>
In the pump 700 of the present embodiment, the casing 710 is positioned between the suction position (above intermediate position) where gas is sucked into the last stage (second stage in this embodiment) compression element and the discharge port 713. It further has a backflow cooling gas introduction port 717 (hereinafter simply referred to as "cooling gas introduction port 717") for introducing cooling gas C into the interior of the . This cooling gas introduction port 717 is an example of a second cooling gas introduction port according to this embodiment. The cooling gas inlet 717 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 700 of this embodiment has side covers 780 as intermediate chambers between the casing 710 and the bearing/gear chamber 773 and between the casing 710 and the bearing chamber 774 . This side cover 780 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

<Amount of gas leakage>
The gas leakage amount QL in the second-stage compression element is basically the same as in the above-described sixth embodiment, but differs in the following points. That is, in this embodiment, since the diameter D2 of the rotor 731 is equal to the diameter D1 of the rotor 721, the clearance Cr2 between the rotor 731 and the casing 710 in the second stage compression element and the clearance Cx2 between the rotors 731 is smaller than in the sixth embodiment. Therefore, the effect of reducing the leakage areas Ar2 and Ax2 in the second-stage compression element is smaller than in the sixth embodiment. However, since the effect of reducing the clearances CsA2 and CsB2 on the rotor side of the rotor 731 can be the same as in the sixth embodiment, the effect of reducing the total leakage area AL2 in the second-stage compression element can be sufficiently obtained in this embodiment as well. be done. As a result, the leakage amount QL of gas from the discharge side to the suction side in the second stage compression element is reduced. However, in order to further enhance the effect of reducing the total leak area AL2, it is preferable to make the diameter D2 of the rotor 731 smaller than the diameter D1 of the rotor 721 as in the sixth embodiment described above.

(Operation of multistage roots pump)
Next, a method of driving pump 700 having the above configuration will be described. The gas compression method and gas cooling method by the pump 700 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIG. 31, when the drive shaft 767 is rotated by a motor (not shown), the first drive gear 765 and the second drive gear 766 supported by the drive shaft 767 are rotationally driven in the same direction. Next, of the pair of first timing gears 761 , 761 , one of the first timing gears 761 meshing with the first driving gear 765 rotates in the opposite direction to the first driving gear 765 . The rotation speed of one of the first timing gears 761 at this time is calculated from the rotation speed of the first drive gear 765 and the ratio between the number of teeth of the first drive gear 765 and the number of teeth of the first timing gear 761. (Number of teeth of one first timing gear 761/number of teeth of first drive gear 765). In addition, since the other first timing gear 761 meshing with the one first timing gear 761 has the same number of teeth as the one first timing gear 761, it has the same number of teeth in the opposite direction as the one first timing gear 761. Rotate at rpm. As a result, the pair of rotors 721, 721 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 721, 721, the gas near the suction port 711 is sucked into the casing 710 through the suction port 711 (arrow Gs in FIG. 32), then compressed by the rotor 721 and discharged to the intermediate position. (arrow Gm in FIG. 32).

Similarly, of the pair of second timing gears 762 , 762 , one of the second timing gears 762 meshing with the second drive gear 766 rotates in the opposite direction to the second drive gear 766 . The rotation speed of one of the second timing gears 762 at this time is calculated from the rotation speed of the second drive gear 766 and the ratio of the number of teeth of the second drive gear 766 to the number of teeth of the one second timing gear 762. The number of revolutions is increased by the gear ratio (the number of teeth of one of the second timing gears 762/the number of teeth of the second driving gear 766). In addition, the other second timing gear 762 meshing with the one second timing gear 762 has the same number of teeth as the one second timing gear 762, so that the one second timing gear 762 and the other second timing gear 762 are engaged in opposite directions. rotate at the same speed. As a result, the pair of rotors 731, 731 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 731, 731, the gas compressed by the first stage rotor 721 and discharged to the intermediate position is swept into the second stage rotor 731 from the intermediate position (arrow in FIG. 32). Gm), it is then compressed by the rotor 731 and discharged to the outside from the discharge port 713 (arrow Gd in FIG. 32).

Further, in this embodiment, when the pressure (intermediate pressure) Pm at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to flow out of the intermediate discharge port 715 at a lower pressure. It is discharged to the atmosphere (arrow Ge in FIG. 32), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second-stage compression element (rotor 731) becomes smaller, the difference between the second-stage suction pressure Ps2 and the pressure of the gas sucked from the suction port 711 (first-stage suction pressure Ps1) ΔP1 can be reduced. As a result, the power of the motor that operates the pump 700 can be reduced. In particular, when the pump 700 starts to draw gas toward the suction port 711, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the number of teeth of each gear is determined so that the rotational speed of the first timing gear 761 is reduced while the rotational speed of the second timing gear 762 is increased. Also, the length L1 of the rotor 721 is longer than the length L2 of the rotor 731 . Even under such special conditions, it is possible to make the volumetric displacement ratio _RQ larger than 1 as described above.

[Eighth Embodiment]
Next, a multi-stage roots pump according to an eighth embodiment of the present invention will be described in detail with reference to FIGS. 33 and 34. FIG. FIG. 33 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 800 (hereinafter abbreviated as "pump 800") as an example of a multi-stage roots-type pump according to the present embodiment. 34 is a cross-sectional view taken along line XXXIV-XXXIV of FIG. 33. FIG. The pump 600 of the sixth embodiment is an example in which the first stage (low pressure side) rotor 621 and the second stage (high pressure side) rotor 631 have different lengths and diameters. 800 states that the diameter of the rotor 821 of the first stage is larger than the diameter of the rotor 831 of the second stage, and the length of the rotor 821 of the first stage is equal to the length of the rotor 831 of the second stage. For example. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 33 and 34, the pump 800 is a two-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 810, two stages (two sets) of compression elements, and a drive mechanism. Prepare.

<Casing>
The configuration and function of casing 810 are similar to casing 610 according to the sixth embodiment.

<Compression element>
As the compression element of this embodiment, a first stage (low pressure side) compression element located on the suction port 811 side and a second stage (high pressure side) compression element located on the discharge port 813 side are provided in the single casing 810. A two-stage compression element is provided. A partition plate or the like is not provided between the two stages of the compression elements unlike the series internal multi-stage roots type pump, and a plurality of compression elements are provided as a single stage group within the integral casing 810. ing. Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first stage compression element has a pair of rotors 821 and 821 and two rotating shafts 822 and 822 . The second stage compression element has a pair of rotors 831 and 831 and two rotating shafts 832 and 832 .

As shown in FIG. 34, the rotor 821 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of protrusions 821a, 821b, 821c radially protruding from the center of rotation. A recess 821d is provided between each projection 821a, 821b, 821c. Similarly, the rotor 831 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 831a, 831b, 831c projecting radially from the center of rotation. In addition, recesses 831d are provided between the protrusions 831a, 831b, and 831c.

The pair of rotors 821, 821 are provided rotatably in directions opposite to each other. The two rotating shafts 822, 822 rotatably support a pair of rotors 821, 821 and are arranged parallel to each other. Also, the two rotating shafts 822 , 822 are supported by two bearings 823 , 823 . Similarly, a pair of rotors 831, 831 are provided rotatably in directions opposite to each other. The two rotating shafts 832, 832 rotatably support a pair of rotors 831, 831 and are arranged parallel to each other. Also, the two rotating shafts 832 , 832 are supported by two bearings 833 , 833 . Furthermore, in this embodiment, the rotating shaft 822 and the rotating shaft 832 are arranged so as to be parallel to each other. In the following description, the description of the rotor 831 that overlaps with that of the rotor 821 will be omitted as necessary, and the contents of the rotor 821 will be read appropriately.

Between the rotors 821 and 821 and between the tips (leaf ends) of the projections 821a, 821b and 821c and the casing 810, so that the pair of rotors 821 and 821 and the rotor 821 and the inner surface 810a of the casing 810 do not come into contact with each other. A rotor 821 is arranged with a slight gap between the inner surface 810a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 821, 821 are maintained by timing gears 861, 861, which will be described later, and the cross-sectional shape of the rotor 821 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 831 is arranged so that a slight gap is formed between the paired rotor 831 and the inner surface 810 d of the casing 810 . Also, the pair of rotors 831, 831 can rotate in opposite directions while maintaining a small gap without coming into contact with each other. Here, in this embodiment, as will be described later, the clearances between the rotors 831 in the second stage and between the rotor 831 and the casing 810 are larger than those between the rotors 821 in the first stage and between the rotor 821 and the casing 810 . is set narrower than the gap between Other configurations and functions of the rotors 821 and 831 are the same as those of the rotors according to the above embodiments.

In the pump 800, the rotor 821, the rotating shaft 822, etc., which are the first-stage compression elements, and the rotor 831, the rotating shaft 832, etc., which are the second-stage compression elements are arranged in a single casing 810 at the same stage. They are arranged in parallel along the normal direction of an imaginary plane containing the two rotation axes 822, 822 (or the two rotation axes 832, 832). That is, the rotor 821 in the first stage and the rotor 831 in the second stage are respectively supported by different shafts, and the two rotating shafts of the same stage are parallel to each other, and the two rotors of the different stages are parallel to each other. The axes of rotation of the books are also arranged parallel to each other. In other words, the gas suction port 811, the first-stage rotor 821, the second-stage rotor 831, and the gas discharge port 813 are arranged side by side in the vertical direction. Therefore, when the gas is introduced into the casing 810 from the suction port 811 (arrow Gs in FIG. 34), it travels vertically downward, is compressed by the rotor 821, and then passes through the first stage compression element and the second stage compression element. (arrow Gm in FIG. 34). The gas compressed by the rotor 821 further travels vertically downward, is compressed by the second-stage rotor 831, and is then directly discharged from the discharge port 813 to the outside of the casing 810 (arrow Gd in FIG. 34).

Thus, according to the pump 800 according to the present embodiment, the first-stage rotor 821 and the second-stage rotor 831 are arranged in parallel on separate shafts within the single casing 810 . Therefore, unlike the in-line multi-stage roots pump, the rotors 821 and 831 can be arranged without providing a partition between the first-stage compression element (rotor 821) and the second-stage compression element (rotor 831). As such, it can be divided into two stages of compression element pumping regions. In addition, in the case of a series-internal multistage roots-type pump, if it has two stages of rotors, the length of the rotary shaft is required to be equal to or longer than two rotors. Since the rotors are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, it is possible to suppress a decrease in rigidity of the rotating shafts 822 and 832 and the casing 810 . In particular, even if the length of the rotors 821 and 831 is lengthened in order to increase the air volume of the pump 800, the rigidity does not decrease, so the increase in air volume is facilitated. Furthermore, even if the dimensional accuracy and alignment accuracy between the first and second stage pump operation areas are not so high, they can be accommodated within a range that does not hinder the performance of the pump 800 in terms of assembly and performance. Accuracy and assembly accuracy are not required.

<Transfer volume ratio>
Also in the pump 800 of this embodiment, between the first-stage compression element (rotor 821) and the second-stage compression element (rotor 831) arranged in parallel on separate rotating shafts, the following formula (1 ) is _greater than 1.
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in this embodiment is a so-called displacement amount, which is proportional to the rotational speed N and is the theoretical volume per time of the space surrounded by the casing 810 and the rotor 821 or 831. . That is, as described above, the movement volume Qth (m ³ /min) is represented by the following equation (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, A is the area of movement per revolution, L is the length of the rotor, and N is the number of rotations of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the axis of rotation 822, 832.

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 800 of this embodiment is expressed by the following equation (3), as in the sixth embodiment described above.

However, in formula (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 821, L2 is the length of the second stage rotor 831, N1 is the rotation speed of the first stage rotor 821, and N2 is the second stage rotor 831. represents the number of rotations of

Here, in the pump 800 of this embodiment, since the diameter D1 of the rotor 821 is larger than the diameter D2 of the rotor 831 (D1>D2), the moving area A1 of the first stage is larger than the moving area A2 of the second stage. Large (A1>A2). Also, the length L1 of the first stage rotor 821 is equal to the length L2 of the second stage rotor 831 (L1=L2). On the other hand, the rotation speed N1 of the first stage rotor 821 is lower than the rotation speed N2 of the second stage rotor 831 (N1<N2). Even in such a case, if the moving volume ratio _RQ can be set to 1 or more, unlike the first embodiment, the rotation speed of the rotor 831 of the second stage (high pressure side) can be reduced to that of the rotor 831 of the first stage ( It may be higher than the rotation speed of the rotor 821 on the low pressure side).

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 867 of the pump 800 can be reduced.

<Drive Mechanism>
As shown in FIG. 33, the drive mechanism of this embodiment includes a pair of first timing gears 861, a pair of second timing gears 862, a first drive gear 865, a second drive gear 866, a motor and a single drive shaft 867 which is the input shaft.

A pair of first timing gears 861, 861 are provided so as to mesh with each other at the shaft ends of the two rotating shafts 822 of the first stage, and are arranged so that the rotation phases of the pair of rotors 821, 821 match each other. , have the same number of teeth. A pair of second timing gears 862, 862 are provided so as to mesh with each other at the shaft ends of the two rotating shafts 832 of the second stage, and are arranged so that the rotation phases of the pair of rotors 831, 831 match each other. , have the same number of teeth.

Also, the first drive gear 865 is provided so as to mesh with one of the pair of first timing gears 861, the first timing gear 861, and the second drive gear 866 is provided so as to mesh with the pair of second timing gears. It is provided so as to mesh with one second timing gear 862 of 862 . Furthermore, the drive shaft 867 rotatably supports the first drive gear 865 and the second drive gear 866 . That is, the first drive gear 865 and the second drive gear 866 are rotatably supported by the same drive shaft. The drive shaft 867 is supported by a bearing 868 provided in the side cover 880 and a bearing 868 provided in the bearing/gear chamber 873 . The shaft end of the drive shaft 867 on the bearing 868 side provided in the bearing/gear chamber 873 is connected to a motor (not shown).

As described above, in this embodiment, the rotation speed of the rotor 831 in the second stage is higher than the rotation speed of the rotor 821 in the first stage. In other words, the rotation speed of the rotor 831 in the second stage is faster than the rotation speed of the rotor 821 in the first stage. Therefore, in pump 800, the number of teeth of first drive gear 865 and second drive gear 866 is set such that the rotation speed of rotor 831 in the second stage is higher than the rotation speed of rotor 821 in the first stage. FIG. 33 shows an example in which the rotational speed of the rotating shaft 822 is reduced from the rotational speed of the drive shaft 867 and the rotational speed of the rotating shaft 832 is increased. In the example shown in FIG. 33, the number of teeth of the first timing gear 861 is greater than that of the first driving gear 865, and the number of teeth of the first driving gear 865 is greater than that of the second driving gear 866. The number of teeth of the second timing gear 862 is less than the number of teeth of the second drive gear 866 .

<Intermediate outlet>
When the pump 800 of this embodiment is used as a vacuum pump, the casing 810 is positioned between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. An intermediate discharge port 815 for discharging gas to the outside may be further provided at an intermediate position of . The example shown in FIG. 34 shows an example in which only one intermediate outlet 815 is provided on the left side surface of the casing 810, but the number of intermediate outlets 815 is not particularly limited, and two or more outlets may be provided. good. For example, in the cross section shown in FIG. 34, on the right side of the casing 810, an intermediate discharge port is provided at an intermediate position between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. 815 may be provided. The intermediate outlet 815 has substantially the same configuration and function as the intermediate outlet 615 according to the sixth embodiment.

<Second cooling gas inlet>
In the pump 800 of the present embodiment, the casing 810 is positioned between the suction position (above intermediate position) where gas is sucked into the last stage (second stage in this embodiment) compression element and the discharge port 813. It further has a backflow cooling gas inlet 817 (hereinafter simply referred to as "cooling gas inlet 817") for introducing the cooling gas C into the interior of the . This cooling gas introduction port 817 is an example of a second cooling gas introduction port according to this embodiment. The cooling gas inlet 817 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 800 of this embodiment has side covers 880 as intermediate chambers between the casing 810 and the bearing/gear chamber 873 and between the casing 810 and the bearing chamber 874 . This side cover 880 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

<Amount of gas leakage>
The gas leakage amount QL in the second-stage compression element is basically the same as in the above-described sixth embodiment, but differs in the following points. That is, in this embodiment, since the length L2 of the rotor 831 is equal to the length L1 of the rotor 821, the effect of reducing the rotor-side gaps CsA2 and CsB2 of the rotor 831 in the second-stage compression element is the same as in the sixth embodiment. less than Therefore, the effect of reducing the leakage area As2 in the second-stage compression element is smaller than in the sixth embodiment. However, since the effect of reducing the clearance Cr2 between the rotor 831 and the casing 810 and the clearance Cx2 between the rotors 731 can be the same as in the sixth embodiment, the effect of reducing the total leakage area AL2 in the second stage compression element is sufficiently obtained in this embodiment as well. As a result, the leakage amount QL of gas from the discharge side to the suction side in the second stage compression element is reduced. However, in order to further enhance the effect of reducing the total leak area AL2, it is preferable to make the length L2 of the rotor 831 shorter than the length L1 of the rotor 821 as in the sixth embodiment described above.

(Operation of multistage roots pump)
Next, a method of driving the pump 800 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 800 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIG. 33, when the drive shaft 867 is rotated by a motor (not shown), the first drive gear 865 and the second drive gear 866 supported by the drive shaft 867 are rotated in the same direction. Next, of the pair of first timing gears 861 , 861 , one of the first timing gears 861 meshing with the first driving gear 865 rotates in the opposite direction to the first driving gear 865 . The rotation speed of one of the first timing gears 861 at this time is calculated from the rotation speed of the first drive gear 865 and the ratio between the number of teeth of the first drive gear 865 and the number of teeth of the first timing gear 861. (Number of teeth of one first timing gear 861/number of teeth of first drive gear 865). In addition, since the other first timing gear 861 that meshes with the one first timing gear 861 has the same number of teeth as the one first timing gear 861, it has the same number of teeth in the opposite direction as the one first timing gear 861. Rotate at rpm. As a result, the pair of rotors 821, 821 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 821, 821, the gas near the suction port 811 is sucked into the casing 810 through the suction port 811 (arrow Gs in FIG. 34), then compressed by the rotor 821 and discharged to the intermediate position. (arrow Gm in FIG. 34).

Similarly, of the pair of second timing gears 862 , 862 , one of the second timing gears 862 meshing with the second drive gear 866 rotates in the opposite direction to the second drive gear 866 . The rotation speed of one of the second timing gears 862 at this time is calculated from the rotation speed of the second drive gear 866 and the ratio of the number of teeth of the second drive gear 866 to the number of teeth of the one second timing gear 862. The number of revolutions is increased by the gear ratio (the number of teeth of one of the second timing gears 862/the number of teeth of the second drive gear 866). In addition, since the other second timing gear 862 meshing with the one second timing gear 862 has the same number of teeth as the one second timing gear 862, the second timing gear 862 and the one second timing gear 862 are engaged in opposite directions. rotate at the same speed. As a result, the pair of rotors 831, 831 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 831, 831, the gas compressed by the first-stage rotor 821 and discharged to the intermediate position is swept into the second-stage rotor 831 from the intermediate position (arrow in FIG. 34). Gm), it is then compressed by the rotor 831 and discharged to the outside from the discharge port 813 (arrow Gd in FIG. 34).

Further, in this embodiment, when the pressure (intermediate pressure) Pm at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to flow out of the intermediate discharge port 815 at a lower pressure. It is discharged to the atmosphere (arrow Ge in FIG. 34), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second-stage compression element (rotor 831) becomes smaller, the difference between the second-stage suction pressure Ps2 and the pressure of the gas sucked from the suction port 811 (first-stage suction pressure Ps1) ΔP1 can be reduced. As a result, the power of the motor that operates the pump 800 can be reduced. In particular, when the pump 800 starts to draw gas toward the suction port 811, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the number of teeth of each gear is determined so that the rotational speed of the first timing gear 861 is reduced while the rotational speed of the second timing gear 862 is increased. Also, the diameter D1 of the rotor 821 is larger than the diameter D2 of the rotor 831 . Even under such special conditions, it is possible to make the volumetric displacement ratio _RQ larger than 1 as described above.

[Ninth Embodiment]
Next, a multi-stage roots pump according to a ninth embodiment of the present invention will be described in detail with reference to FIGS. 35 to 38. FIG. FIG. 35 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 900 (hereinafter abbreviated as “pump 900”) as an example of a multi-stage roots-type pump according to the present embodiment. 36, 37 and 38 are cross-sectional views taken along lines XXXVI-XXXVI, XXXVII-XXXVII and XXXVIII-XXXVIII of FIG. 35, respectively. The pumps 600, 700, and 800 of the sixth to eighth embodiments described above are examples of two-stage roots-type pumps having two-stage compression elements. 3 is an example of a three-stage roots-type pump with elements. Here, the relationship between the first stage (lowest pressure side) compression element and the second stage (middle) compression element and the second stage (middle) compression element and the third stage (most high pressure side) compression element are the same as those between the first stage compression element and the second stage compression element of the pump 600 according to the sixth embodiment. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 35 to 38, the pump 900 is a three-stage roots pump, which is a type of rotary compressor, and mainly includes a casing 910, three stages (three sets) of compression elements, and a drive mechanism. Prepare.

<Casing>
The configuration and function of casing 910 are the same as those of casing 610 according to the sixth embodiment.

Here, the casing 910 is a virtual plane including two rotating shafts 922 and 922 of the compression element of the same stage, a virtual plane including two rotating shafts 932 and 932, or two rotating shafts 942 and 942. Compression elements are accommodated so that three stages of compression elements are arranged in parallel along the normal direction of a virtual plane including . Thus, in this embodiment, multiple stages of compression elements arranged in parallel with respect to the axial direction of the rotating shafts 922, 932, and 942 are housed in a single casing 910, and the compression elements are connected. No external piping or internal gas passages are provided. Therefore, the gas compressed and discharged by the first-stage compression element is directly sucked (as it is) into the second-stage compression element, compressed and then discharged, and further directly ( as it is) sucked in. Therefore, the temperature rise of the gas compressed by each compression element of the three-stage roots type pump is more serious than that of the two-stage roots type pump. Therefore, in this embodiment, as will be described later in detail, not only the cooling of the gas existing in the intermediate position between the first and second stages but also the cooling of the gas existing in the intermediate position between the second and third stages is performed. Cooling of the gas is also performed.

<Compression element>
As the compression elements of this embodiment, a first stage (low pressure side) compression element located on the suction port 911 side and a third stage (high pressure side) compression element located on the discharge port 913 side are provided in the single casing 910. and a second-stage (intermediate) compression element disposed between the first-stage and third-stage compression elements. No partition plate or the like is provided between the three stages of compression elements, and a plurality of compression elements are provided as a single stage group within the integral casing 910 . Each stage compression element independently has a pair of rotors and two rotary shafts that support the pair of rotors. Specifically, in this embodiment, the first-stage compression element has a pair of rotors 921 and 921 and two rotating shafts 922 and 922 . The second stage compression element has a pair of rotors 931 and 931 and two rotating shafts 932 and 932 . The third stage compression element has a pair of rotors 941 and 941 and two rotating shafts 942 and 942 .

As shown in FIG. 36, the rotor 921 is a three-lobe rotor, and its rotor profile is shaped to have three pieces of projections 921a, 921b, 921c projecting radially from the center of rotation. In addition, recesses 921d are provided between the protrusions 921a, 921b, and 921c. Similarly, the rotor 931 is also a three-lobed rotor, and its rotor profile is shaped with three pieces of projections 931a, 931b, 931c projecting radially from the center of rotation. In addition, recesses 931d are provided between the projections 931a, 931b, and 931c. Similarly, the rotor 941 is also a three-lobe rotor, and its rotor profile is shaped with three pieces of projections 941a, 941b, 941c projecting radially from the center of rotation. In addition, recesses 941d are provided between the protrusions 941a, 941b, and 941c.

A pair of rotors 921, 921 are provided rotatably in directions opposite to each other. The two rotating shafts 922, 922 rotatably support a pair of rotors 921, 921 and are arranged parallel to each other. Also, the two rotating shafts 922 , 922 are supported by two bearings 923 , 923 . Similarly, a pair of rotors 931, 931 are provided rotatably in directions opposite to each other. The two rotating shafts 932, 932 rotatably support a pair of rotors 931, 931 and are arranged parallel to each other. Also, the two rotating shafts 932 and 932 are supported by two bearings 933 and 933 . Similarly, a pair of rotors 941, 941 are also provided rotatably in directions opposite to each other. The two rotating shafts 942, 942 rotatably support a pair of rotors 941, 941 and are arranged parallel to each other. Also, the two rotating shafts 942 and 942 are supported by two bearings 943 and 943 . Furthermore, in this embodiment, the rotating shaft 922, the rotating shaft 932, and the rotating shaft 942 are arranged so as to be parallel to each other. It should be noted that, hereinafter, regarding the rotors 931 and 941, the description that overlaps with the rotor 921 will be omitted as necessary, and the contents of the rotor 921 will be read appropriately.

Between the rotors 921 and 921 and the tips (leaf ends) of the protrusions 921a, 921b, and 921c and the casing 910 are arranged so that the pair of rotors 921 and 921 and the rotor 921 and the inner surface 910a of the casing 910 do not come into contact with each other. A rotor 921 is arranged with a slight gap between the inner surface 910a of the . The size of this gap is the same as in the first embodiment. Rotation phases of the rotors 921 and 921 are maintained by timing gears 961A and 961B, which will be described later, and the cross-sectional shape of the rotor 921 is, for example, a so-called involute curve. They can rotate in opposite directions without touching each other while remaining sealed. Similarly, the rotor 931 is arranged so that a slight gap is formed between the paired rotor 931 and the inner surface 910 d of the casing 910 . Also, the pair of rotors 931, 931 can rotate in opposite directions while maintaining a small gap without contacting each other. Similarly, the rotor 941 is arranged so that a slight gap is formed between the paired rotor 941 and the inner surface 910 g of the casing 910 . Also, the pair of rotors 941, 941 can rotate in opposite directions while keeping a small gap without contacting each other. Other configurations and functions of the rotors 921, 931, and 941 are the same as those of the rotors according to the above-described embodiments.

In the pump 900, a rotor 921, a rotating shaft 922, etc., which are first-stage compression elements, a rotor 931, a rotating shaft 932, etc., which are second-stage compression elements, a rotor 941, which is a third-stage compression element, and a rotation Axes 942, etc. are virtual shafts that include two rotary shafts 922, 922 (or two rotary shafts 932, 932, or two rotary shafts 942, 942) of the same stage in a single casing 910. are arranged in parallel along the normal direction of the plane of That is, the rotor 921 of the first stage, the rotor 931 of the second stage, and the rotor 941 of the third stage are each supported by different shafts, and the two rotation shafts of the same stage are parallel to each other. and the two rotating shafts of different stages are also arranged parallel to each other. In other words, the gas suction port 911, the first stage rotor 921, the second stage rotor 931, the third stage rotor 941, and the gas discharge port 913 are arranged side by side along the vertical direction. Therefore, when gas is introduced into the casing 910 from the suction port 911 (arrow Gs in FIG. 36), it travels vertically downward, is compressed by the rotor 921, and then passes through the first stage compression element and the second stage compression element. (arrow Gm1 in FIG. 36). The gas compressed by the rotor 921 further travels vertically downward, and after being compressed by the second-stage rotor 931, travels between the second-stage compression element and the third-stage compression element (arrow Gm2 in FIG. 36). ). The gas compressed by the rotor 931 further travels vertically downward, is compressed by the third-stage rotor 941, and is then discharged from the discharge port 913 to the outside of the casing 910 (arrow Gd in FIG. 36).

Thus, according to the pump 900 according to the present embodiment, the rotor 921 of the first stage, the rotor 931 of the second stage, and the rotor 941 of the third stage are arranged on different axes in the single casing 910. arranged in parallel. Therefore, between the first-stage compression element (rotor 921) and the second-stage compression element (rotor 931), and between the second-stage compression element (rotor 931) and the third-stage compression element (rotor 941) The arrangement of the rotors 921, 931, and 941 itself can divide the pump operation regions of the three-stage compression elements without providing a partition between them. In addition, in the case of a series-internal multistage roots-type pump, if it has three stages of rotors, the length of the rotating shaft of three rotors or more is required. 941 are arranged in parallel on different shafts, the length of the rotation shaft of the rotor is sufficient for about one rotor. Therefore, a decrease in rigidity of the rotating shafts 922, 932, 942 and the casing 910 can be suppressed. In particular, even if the lengths of the rotors 921, 931, and 941 are lengthened in order to increase the air volume of the pump 900, there is no reduction in rigidity, which facilitates increasing the air volume. Furthermore, even if the dimensional accuracy and alignment accuracy are not so high between the first, second, and third pump operating regions, they are within a range that does not hinder assembly and the performance of the pump 900 . , so high machining accuracy and assembly accuracy are not required. Here, multi-stage roots type pumps having three or more stages of compression elements have problems such as reduced rigidity of the rotating shaft and casing, difficulty in increasing air volume, and the need for high machining and assembly accuracy. It becomes even more serious than in the case of pumps. In such a case, according to the pump 900 according to the present embodiment, all the above problems are solved, so there is a great merit in arranging a plurality of compression elements in parallel on separate shafts.

<Transfer volume ratio>
In the pump 900 of the present embodiment, between the first-stage compression element (rotor 921) and the second-stage compression element (rotor 931) arranged in parallel on separate rotating shafts, the following formula (1) is _greater than 1;
_RQ = _QthL / _QthH (1)

Here, the movement volume Qth in the present embodiment is a so-called displacement amount, which is proportional to the rotation speed N, and the theoretical amount per hour of the space surrounded by the casing 910 and the rotor 921, the rotor 931, or the rotor 941. Volume. That is, the movement volume Qth (m ³ /min) is represented by the following formula (2).
Qth=Vth(m ³ /rev)×N(min ⁻¹ )
=A (m ² /rev) x L (m) x N (min ^-1 ) (2)

where, in equation (2), Vth is the displacement, N is the number of rotations of the rotor, A is the moving area per revolution, and L is the length of the rotor. The area of movement A is the cross-sectional area of the displacement volume Vt in a cross-section perpendicular to the axis of rotation 922, 932, 942.

The displacement volume ratio R _Q1-2 between the first stage and the second stage in the pump 900 of the present embodiment is expressed by the following formula (3), as in the fourth embodiment.

However, in formula (3), Qth1 is the movement volume of the first stage compression element, Qth2 is the movement volume of the second stage compression element, A1 is the movement area of the first stage compression element, A2 is the second stage The moving area of the compression element, L1 is the length of the first stage rotor 921, L2 is the length of the second stage rotor 931, N1 is the rotation speed of the first stage rotor 921, and N2 is the second stage rotor 931. represents the number of rotations of

Here, in the pump 900 of this embodiment, the diameter D1 of the rotor 921 is larger than the diameter D2 of the rotor 931 (D1>D2). Therefore, the moving area A1 of the first stage is larger than the moving area A2 of the second stage (A1>A2). Also, the length L1 of the rotor 921 of the first stage is longer than the length L2 of the rotor 931 of the second stage (L1>L2). On the other hand, the rotation speed N1 of the first stage rotor 921 is lower than the rotation speed N2 of the second stage rotor 931 (N1<N2). Even in such a case, if the moving volume ratio _RQ can be set to 1 or more, unlike the fourth embodiment and the like, the rotation speed of the rotor 931 of the second stage (high pressure side) can be reduced to that of the first stage. It may be higher than the rotation speed of the rotor 921 (low pressure side).

Further, in the pump 900, between the second-stage compression element (rotor 931) and the third-stage compression element (rotor 941) arranged in parallel on separate rotating shafts, the above equation (1) The represented transfer volume ratio _RQ is greater than one.

However, when obtaining the movement volume ratio R _Q2-3 between the second stage and the third stage, Qth _L in the equation (1) is the low pressure side of the second stage compression element and the third stage compression element. and Qth _H is the displacement of the high-pressure side compression element (the third-stage compression element in the present embodiment).

As described above, the movement volume Qth (m ³ /min) is represented by the above formula (2). Therefore, the displacement volume ratio R _Q2-3 between the second stage and the third stage in the pump 900 of this embodiment is expressed by the following equation (5), as in the fourth embodiment.

However, in equation (5), Qth2 is the movement volume of the second-stage compression element, Qth3 is the movement volume of the third-stage compression element, N2 is the rotation speed of the second-stage rotor 931, and N3 is the third-stage It represents the rotation speed of the rotor 941 .

Here, in the pump 900 of this embodiment, the diameter D2 of the rotor 931 is larger than the diameter D3 of the rotor 941 (D2>D3). Therefore, the moving area A2 of the second stage is larger than the moving area A3 of the third stage (A2>A3). Also, the length L2 of the second stage rotor 931 is longer than the length L3 of the second stage rotor 941 (L2>L3). On the other hand, the rotation speed N2 of the second stage rotor 931 is lower than the rotation speed N3 of the third stage rotor 941 (N2<N3). Even in such a case, if the moving volume ratio _RQ can be set to 1 or more, unlike the fourth embodiment and the like, the rotation speed of the third stage (high pressure side) rotor 941 can be changed to that of the second stage. It may be higher than the rotation speed of the rotor 931 (low pressure side).

As described above, when the displacement volume ratio _RQ is greater than 1, the shaft power of the drive shaft 967 of the pump 900 can be reduced. In the present embodiment, both the moving volume ratio R _Q1-2 between the first stage and the second stage and the moving volume ratio R _Q2-3 between the second stage and the third stage are greater than 1. A case is illustrated. In this case, the effect of reducing the shaft power can be significantly improved. However, in the three-stage roots pump according to the present invention, at least one of R _Q1-2 and R _Q2-3 should have a movement volume ratio greater than one. For example, a three-stage roots pump in which either one of R _Q1-2 and R _Q2-3 is greater than one and the other is one can also be used as a multi-stage roots pump according to the present invention.

<Drive Mechanism>
As shown in FIGS. 35, 37 and 38, the drive mechanism of this embodiment includes a pair of first timing gears 961 (961A, 961B), a pair of second timing gears 962 (962A, 962B), and , a pair of third timing gears 963 (963A, 963B), a 1st-2nd step intermediate gear 964, a 2nd-3rd step intermediate gear 965, and a drive shaft 967 which is a motor input shaft.

A pair of first timing gears 961A and 961B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 922 of the first stage, and are arranged so that the rotation phases of the pair of rotors 921 and 921 match each other. , have the same number of teeth. A pair of second timing gears 962A and 962B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 932 of the second stage, and are arranged so that the rotation phases of the pair of rotors 931 and 931 match each other. , have the same number of teeth. A pair of third timing gears 963A and 963B are provided so as to mesh with each other at the shaft ends of the two rotating shafts 942 of the second stage, so that the rotation phases of the pair of rotors 931 and 931 match each other. , have the same number of teeth.

The 1st-2nd step intermediate gear 964 includes a first timing gear 961A, which is one of the pair of first timing gears 961, and a second timing gear 962A, which is one of the pair of second timing gears 962. , and the 2-3 step intermediate gear 965 is one of the pair of second timing gears 962 and one of the second timing gear 962A and the pair of third timing gears 963. It is provided so as to mesh with both of the third timing gears 963A. Further, the drive shaft 967 rotatably supports the 1st-2nd stage intermediate gear 964 . The drive shaft 967 is supported by a bearing 968 provided in a side cover 980 and a bearing 968 provided in a bearing/gear chamber 973, which will be described later. The shaft end of the drive shaft 967 on the bearing 968 side provided in the bearing/gear chamber 973 is connected to a motor (not shown). Also, the 2nd-3rd stage intermediate gear 965 is rotatably supported by a rotating shaft 969 . The rotating shaft 969 is supported by a bearing 970 provided in the side cover 980 and a bearing 970 provided in the bearing/gear chamber 973 .

As described above, in this embodiment, the rotation speed of the rotor 931 in the second stage is higher than the rotation speed of the rotor 921 in the first stage. In other words, the rotation speed of the rotor 931 in the second stage is faster than the rotation speed of the rotor 921 in the first stage. Therefore, in the pump 900, the first timing gear 961, the second timing gear 962, and the intermediate gear between the first and second stages are arranged so that the rotation speed of the rotor 931 of the second stage is higher than the rotation speed of the rotor 921 of the first stage. 964 teeth are set. FIGS. 35 and 38 show examples of reducing the rotational speed of the rotating shafts 922 and 932 from the rotating speed of the drive shaft 967, for example. In the example shown in FIGS. 35 and 38, a first timing gear 961 and a second timing gear 962 mesh with a common 1st-2nd step intermediate gear 964, and the number of teeth of the first timing gear 961 and the second timing gear 962 is are larger than the number of teeth of the intermediate gear 964 between 1st and 2nd stage. In addition, the speed reduction ratio (the number of teeth of the first timing gear 961 / the number of teeth of the intermediate gear 964 between 1st and 2nd stage) is calculated from the ratio of the number of teeth of the intermediate gear 964 between 1st and 2nd stage to the number of teeth of the first timing gear 961. number of teeth) is the reduction ratio (number of teeth of second timing gear 962/1-2 stage The number of teeth of the first timing gear 961 is greater than the number of teeth of the second timing gear 962 so as to be greater than the number of teeth of the intermediate gear 964 . As a result, the rotation speed of the rotor 931 in the second stage becomes higher than the rotation speed of the rotor 921 in the first stage.

Further, in the present embodiment, the rotation speed of the rotor 941 in the third stage is higher than the rotation speed of the rotor 931 in the second stage. In other words, the rotation speed of the rotor 941 in the third stage is faster than the rotation speed of the rotor 931 in the second stage. Therefore, in the pump 900, the second timing gear 962, the third timing gear 963, and the intermediate gear between the 2nd and 3rd stages are arranged so that the rotation speed of the rotor 941 of the third stage is higher than that of the rotor 931 of the second stage. 965 teeth are set. 35 and 38 show examples in which the rotation speed of the rotation shaft 969 is increased from the rotation speed of the second timing gear 962 and the rotation speed of the third timing gear 963 is decreased from the rotation speed of the rotation shaft 969. It is shown. In the example shown in FIGS. 35 and 38, the second timing gear 962 and the third timing gear 963 mesh with a common intermediate gear 965 between the second and third stages, and the number of teeth of the second timing gear 962 and the third timing gear 963 is are larger than the number of teeth of the intermediate gear 965 between the 2nd and 3rd stages. In addition, the speed reduction ratio (the number of teeth of the second timing gear 962/the number of teeth of the intermediate gear 965) number of teeth) is the reduction ratio (number of teeth of the third timing gear 963/2-3 stages The number of teeth of the second timing gear 962 is larger than the number of teeth of the third timing gear 963 so as to be larger than the number of teeth of the intermediate gear 965 . As a result, the rotation speed of the rotor 941 in the third stage becomes higher than the rotation speed of the rotor 931 in the second stage.

<Intermediate outlet>
When the pump 900 of this embodiment is used as a vacuum pump, the casing 910 is positioned between adjacent compression elements, that is, between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element. and intermediate positions between the second stage (low pressure side) compression element and the third stage (high pressure side) compression element. You may have more. The example shown in FIG. 36 shows an example in which only one intermediate discharge port 915, 917 is provided on the left side surface of casing 910, but the number of intermediate discharge ports 915, 917 is not particularly limited. , may be provided at two or more locations. For example, in the cross section shown in FIG. 36, an intermediate discharge port 915 is located at an intermediate position between the first stage (low pressure side) compression element and the second stage (high pressure side) compression element on the right side surface of the casing 910. may be provided, and an intermediate discharge port 917 may be provided at an intermediate position between the second stage (low pressure side) compression element and the third stage (high pressure side) compression element. Other than that, the intermediate outlets 915 and 917 have substantially the same configuration and function as the intermediate outlet 615 according to the sixth embodiment.

<Second cooling gas inlet>
In the pump 900 of this embodiment, the casing 910 is positioned between the suction position (above intermediate position) where gas is sucked into the final stage (third stage in this embodiment) compression element and the discharge port 913. It further has a backflow cooling gas introduction port 919 (hereinafter simply referred to as "cooling gas introduction port 919") for introducing the cooling gas C into the interior. This cooling gas introduction port 919 is an example of a second cooling gas introduction port according to this embodiment. The cooling gas inlet 919 has substantially the same configuration and function as the cooling gas inlet 117 according to the first embodiment.

<Other configurations>
In addition, the pump 900 of this embodiment has side covers 980 as intermediate chambers between the casing 910 and the bearing/gear chamber 973 and between the casing 910 and the bearing chamber 974 . This side cover 980 has substantially the same configuration and function as the side cover 180 according to the first embodiment.

(Operation of multistage roots pump)
Next, a method of driving the pump 900 having the configuration described above will be described. The gas compression method and gas cooling method by the pump 900 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIGS. 35 to 38, when the drive shaft 967 is rotated by a motor (not shown), the 1st-2nd intermediate gear 964 supported by the drive shaft 967 is rotationally driven. Next, of the pair of first timing gears 961A and 961B, one of the first timing gears 961A meshing with the intermediate gear 964 between 1-2 steps rotates in the direction opposite to the intermediate gear 964 between 1-2 steps. The number of rotations of the first timing gear 961A at this time is determined from the number of rotations of the intermediate gear 964 between 1st and 2nd stage, and from the ratio of the number of teeth of the intermediate gear 964 between 1st and 2nd stage to the number of teeth of the first timing gear 961A. The rotational speed is reduced by the calculated speed reduction ratio (the number of teeth of the first timing gear 961A/the number of teeth of the intermediate gear 964 between 1st and 2nd stages). Also, the other first timing gear 961B meshing with the first timing gear 961A has the same number of teeth as the first timing gear 961A, so it rotates at the same number of rotations in the opposite direction as the first timing gear 961A. As a result, the pair of rotors 921, 921 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 921, 921, the gas in the vicinity of the suction port 911 is sucked into the casing 910 through the suction port 911 (arrow Gs in FIG. 36), and then compressed by the rotor 921 to reach the first stage. It is discharged to the intermediate position of the second stage (arrow Gm1 in FIG. 36).

Similarly, of the pair of second timing gears 962A and 962B, one of the second timing gears 962A meshing with the intermediate gear 964 between 1-2 steps rotates in the direction opposite to the intermediate gear 964 between 1-2 steps. . The number of rotations of the second timing gear 962A at this time is determined from the number of rotations of the 1st-2nd stage intermediate gear 964, and from the ratio of the number of teeth of the 1st-2nd stage intermediate gear 964 to the number of teeth of the second timing gear 962A. The rotational speed is reduced by the calculated speed reduction ratio (the number of teeth of the second timing gear 962A/the number of teeth of the intermediate gear 964 between 1st and 2nd stages). Also, the other second timing gear 962B meshing with the second timing gear 962A has the same number of teeth as the second timing gear 962A, so it rotates at the same number of revolutions in the opposite direction as the second timing gear 962A. As a result, the pair of rotors 931, 931 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 931, 931, the gas compressed by the first-stage rotor 921 and discharged to the intermediate position is swept from the intermediate position into the second-stage rotor 931 (see FIG. 36). Arrow Gm1) is compressed by the rotor 931 and discharged to an intermediate position between the second stage and the third stage (arrow Gm2 in FIG. 36).

Further, the 2-3 step intermediate gear 965 meshing with the second timing gear 962A rotates in the direction opposite to the second timing gear 962A. Further, of the pair of third timing gears 963A and 963B, the third timing gear 963A that meshes with the intermediate gear 965 between 2nd and 3rd stage rotates in the direction opposite to that of the intermediate gear 965 between 2nd and 3rd stage. Also, the other third timing gear 963B meshing with the third timing gear 963A has the same number of teeth as the third timing gear 963A, so it rotates at the same number of rotations in the opposite direction as the third timing gear 963A. As a result, the pair of rotors 941, 941 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 941, 941, the gas compressed by the second-stage rotor 931 and discharged to the intermediate position is swept from the intermediate position into the third-stage rotor 941 (Fig. 36). arrow Gm2), and is compressed by the rotor 941 and discharged to the outside from the discharge port 913 (arrow Gd in FIG. 36).

Further, in the present embodiment, when the pressure (intermediate pressure) Pm1 at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, gas is discharged from the intermediate discharge port 915 due to the pressure difference. It is discharged to the atmosphere (arrows Ge1 and Gd in FIG. 36), and the intermediate pressure Pm1 drops below the atmospheric pressure. Similarly, when the pressure (intermediate pressure) Pm2 at the intermediate position between the second stage and the third stage is equal to or higher than the atmospheric pressure, the gas is discharged from the intermediate discharge port 917 to the atmosphere with a lower pressure due to the pressure difference. (arrow Ge2 and arrow Gd in FIG. 36), the intermediate pressure Pm2 drops below the atmospheric pressure. Therefore, since the suction pressure to the compression elements (rotors 931, 941) of the second and third stages becomes small, the suction pressure Ps2 of the second stage and the pressure of the gas sucked from the suction port 911 (suction pressure of the first stage) The difference ΔP1 from the pressure Ps1) and the difference ΔP2 between the third-stage suction pressure Ps3 and the second-stage suction pressure Ps2 can be reduced. As a result, the power of the motor that operates the pump 900 can be reduced. Especially at the stage when the pump 900 starts to draw gas toward the suction port 911, the intermediate pressures Pm1 and Pm2 are likely to be higher than the atmospheric pressure. .

In the present embodiment, the reduction ratio of the 1st-2nd stage intermediate gear 964 with the first timing gear 961A is larger than the reduction ratio of the 1st-2nd stage intermediate gear 964 with the second timing gear 962A. It's becoming Therefore, the rotation speed N1 of the rotor 921 becomes lower than the rotation speed N2 of the rotor 931. Also, the length L1 of the rotor 921 is longer than the length L2 of the rotor 931 and the diameter D1 of the rotor 921 is larger than the diameter D2 of the rotor 931 . Even under such special conditions, it is possible to make the volumetric displacement ratio R _Q1-2 greater than 1 as described above.

Further, the reduction ratio of the 2nd-3rd step intermediate gear 965 between the second timing gear 962A is larger than the reduction ratio of the 2nd-3rd step intermediate gear 965 between the third timing gear 963A. . Therefore, the rotation speed N2 of the rotor 931 becomes lower than the rotation speed N3 of the rotor 941. Also, the length L2 of the rotor 931 is longer than the length L3 of the rotor 941 and the diameter D2 of the rotor 931 is larger than the diameter D3 of the rotor 941 . Even under such special conditions, it is possible to make the volumetric displacement ratio R _Q2-3 greater than 1 as described above.

[Tenth embodiment]
Next, the multi-stage roots pump according to the tenth embodiment of the present invention will be described in detail with reference to FIGS. 39 and 40. FIG. FIG. 39 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 1000 (hereinafter abbreviated as "pump 1000") as an example of a multi-stage roots-type pump according to the present embodiment. 40 is a cross-sectional view taken along line XL-XL in FIG. 39. FIG. A pump 1000 according to the present embodiment is an example in which the pump 600 according to the sixth embodiment is provided with a cooling mechanism similar to that of the first embodiment. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 39 and 40, the pump 1000 is a two-stage roots pump, which is a type of rotary compressor, and includes a casing 610, two stages (two sets) of compression elements, a drive mechanism, and a cooling mechanism. and

<Casing>
The casing of this embodiment is similar to the casing 610 according to the sixth embodiment. In this embodiment, the casing 610 is provided with an intermediate backflow cooling gas inlet 1016, which will be described later.

<Compression element, drive mechanism>
Since the compression element and drive mechanism of this embodiment are the same as those of the sixth embodiment, detailed description thereof will be omitted.

<Transfer volume ratio>
The movement volume ratio of the pump 1000 of this embodiment is also the same as that of the sixth embodiment, so detailed description thereof will be omitted.

<Cooling mechanism>
As shown in FIG. 40, the casing 610 according to this embodiment also has an intermediate discharge port 615 and an intermediate backflow cooling gas introduction port 1016 as an example of a first cooling gas introduction port according to this embodiment (hereinafter simply referred to as “cooling gas introduction port 1016”) is provided. The intermediate outlet 615 and the cooling gas inlet 1016 have the same configurations, functions and effects as the intermediate outlet 115 and the cooling gas inlet 116 according to the first embodiment, respectively. A cooler 1 as an example of the cooling unit according to the present embodiment is connected to the intermediate outlet 615 and the cooling gas inlet 1016 . A check valve 3 is also connected to the cooler 1 .

<Second cooling gas inlet>
As shown in FIG. 40, a backflow cooling gas inlet 617 is provided as in the sixth embodiment.

<Other configurations>
In addition, the configuration of the pump 1000 of this embodiment is the same as that of the pump 600 of the sixth embodiment.

<Amount of gas leakage>
The gas leakage amount QL from the discharge side (high pressure side) to the suction side (low pressure side) in the second stage compression element is also the same as in the sixth embodiment.

As described above, the pump 1000 according to the present embodiment solves the problem of suppressing an increase in the amount of gas leakage caused by a significant temperature rise of the gas in the compression element of the latter stage (the second stage in the present embodiment). In contrast, two solutions are adopted: providing a cooling mechanism and reducing the rotor size of the latter stage (second stage). Therefore, the effect of reducing the leakage amount QL of gas from the discharge side to the suction side in the second stage compression element is extremely excellent. That is, by providing a cooling mechanism consisting of the intermediate discharge port 615, the cooler 1, and the cooling gas inlet 1016, the amount of thermal expansion of the rotor 631 is suppressed by suppressing the temperature rise of the gas compressed by the second stage compression element. and the effect of reducing the amount of thermal expansion of the rotor 631 by reducing the length L2 and diameter D2 of the rotor 631 itself.

(Operation of multistage roots pump)
Next, a method of driving pump 1000 having the above configuration will be described. The gas compression method and gas cooling method by the pump 1000 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIG. 39, in the pump 1000 according to the present embodiment, as in the sixth embodiment, the pair of rotors 621, 621 rotate at the same rotational speed in opposite directions while maintaining the rotational phase. to rotate. Due to the rotation of the pair of rotors 621, 621, the gas near the suction port 611 is sucked into the casing 610 through the suction port 611 (arrow Gs in FIG. 40), then compressed by the rotor 621 and discharged to the intermediate position. (arrow Gm in FIG. 40).

Also, as in the sixth embodiment, the pair of rotors 631, 631 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 631, 631, the gas compressed by the first stage rotor 621 and discharged to the intermediate position is swept into the second stage rotor 631 from the intermediate position (see arrow in FIG. 40). Gm), it is then compressed by the rotor 631 and discharged to the outside from the discharge port 613 (arrow Gd in FIG. 40).

Here, in the present embodiment, as in the first embodiment, the gas present in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 615 to the outside of the casing 610, and then introduced into the first-stage compression element (inside the space surrounded by the rotor 621 and the casing 610) from the two cooling gas introduction ports 1016A and 1016B provided on both left and right sides of the casing 610. be done. At this time, the pressure at the intermediate position (intermediate pressure) Pm is higher than the pressure in the space surrounded by the rotor 621 and the casing 610, so the gas discharged from the intermediate discharge port 615 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge in FIG. 40, the gas discharged from the intermediate discharge port 615 is cooled by the cooler 1, and is discharged from the cooling gas introduction port 1016 to the first stage compression element. is introduced into the region surrounded by the first stage rotor 621 and the casing 610 (moving volume Qth1 portion), and then discharged to the intermediate position again. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 615, and the gas cooled by the cooler 1 is discharged into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed.

Further, when the intermediate pressure Pm is equal to or higher than the atmospheric pressure, the check valve 3 is opened, and the pressure difference between the intermediate pressure Pm and the atmospheric pressure causes the gas existing at the intermediate position to be pushed out from the intermediate discharge port 615 to a higher pressure. (arrow Ge and arrow Gd in FIG. 40), and the intermediate pressure Pm drops below the atmospheric pressure. Therefore, since the suction pressure to the second stage compression element (rotor 631) becomes smaller, the suction pressure to the first stage compression element (rotor 621) and the suction pressure to the second stage compression element (rotor 631) can be reduced. As a result, the power of the motor that operates the pump 1000 can be reduced. In particular, when the pump 1000 starts to draw gas toward the suction port 611, the intermediate pressure Pm tends to be higher than the atmospheric pressure.

In this embodiment, the number of teeth of each gear is determined so that the rotation speed of the first timing gear 661 is reduced while the rotation speed of the second timing gear 662 is increased. Also, the diameter D1 of the rotor 621 is larger than the diameter D2 of the rotor 631 . Furthermore, length L1 of rotor 621 is longer than length L2 of rotor 631 . Even under such special conditions, it is possible to make the volumetric displacement ratio _RQ larger than 1 as described above.

[Eleventh embodiment]
Next, the multi-stage roots pump according to the eleventh embodiment of the present invention will be described in detail with reference to FIGS. 41 and 42. FIG. FIG. 41 is a partial cross-sectional view showing the overall configuration of an internal two-stage roots-type pump 1100 (hereinafter abbreviated as "pump 1100") as an example of a multi-stage roots-type pump according to the present embodiment. 42 is a cross-sectional view taken along line XLII-XLII in FIG. 41. FIG. A pump 1100 according to the present embodiment is an example in which the pump 900 according to the ninth embodiment is provided with a cooling mechanism similar to that of the first embodiment. In addition, below, the description which overlaps with embodiment mentioned above is abbreviate|omitted suitably.

(Configuration of multistage roots pump)
As shown in FIGS. 41 and 42, the pump 1100 is a three-stage roots pump, which is a type of rotary compressor, and includes a casing 910, three stages (three sets) of compression elements, a drive mechanism, and a cooling mechanism. and

<Casing>
The casing of this embodiment is similar to the casing 910 according to the ninth embodiment. In this embodiment, the casing 910 is provided with intermediate backflow cooling gas introduction ports 1116 and 1118, which will be described later.

<Compression element, drive mechanism>
Since the compression element and drive mechanism of this embodiment are the same as those of the ninth embodiment, detailed description thereof will be omitted.

<Transfer volume ratio>
Since the movement volume ratio in the pump 1100 of this embodiment is also the same as that of the ninth embodiment, detailed description thereof will be omitted.

<Cooling mechanism>
As shown in FIG. 42, the casing 910 according to the present embodiment also has intermediate discharge ports 915 and 917 and an intermediate backflow cooling gas introduction port 1116 as an example of a first cooling gas introduction port according to the present embodiment (hereinafter simply referred to as “cooling gas inlet 1116”) and an intermediate backflow cooling gas inlet 1118 (hereinafter simply referred to as “cooling gas inlet 1118”) are provided. Intermediate outlets 915, 917 and cooling gas inlets 1116, 1118 have the same configurations, functions, and effects as intermediate outlets 415, 417 and cooling gas inlets 416, 418, respectively, according to the fourth embodiment. Further, the cooler 1 as an example of the cooling unit according to the present embodiment is connected to the intermediate outlet 915 and the cooling gas inlet 1116, and the cooler 2 is connected to the intermediate outlet 917 and the cooling gas inlet 1118. be. A check valve 3 is also connected to the cooler 1 , and a check valve 4 is also connected to the cooler 2 .

<Second cooling gas inlet>
As shown in FIG. 42, a backflow cooling gas introduction port 919 is provided as in the ninth embodiment.

<Other configurations>
In addition, the configuration of the pump 1100 of this embodiment is the same as that of the pump 900 of the ninth embodiment.

<Amount of gas leakage>
The gas leakage amount QL from the discharge side (high pressure side) to the suction side (low pressure side) in the second and third stage compression elements is also the same as in the ninth embodiment.

As described above, in the pump 1100 according to the present embodiment, an increase in the amount of gas leakage caused by a significant temperature rise of the gas in the compression elements of the latter stages (the second and third stages in the present embodiment) is suppressed. , two solutions are adopted: providing a cooling mechanism and reducing the size of the rotors in the latter stages (second stage and third stage). Therefore, the effect of reducing the leakage amount QL of gas from the discharge side to the suction side in the second and third stage compression elements is extremely excellent. That is, by providing a cooling mechanism consisting of an intermediate discharge port 915, a cooler 1, and a cooling gas inlet 1116, and a cooling mechanism consisting of an intermediate discharge port 917, a cooler 2, and a cooling gas inlet 1118, the second stage and The effect of reducing the amount of thermal expansion of the rotors 931 and 941 by suppressing the temperature rise of the gas compressed by the third stage compression element, and the lengths L2 and L3 and the diameters D2 and D3 of the rotors 931 and 941 themselves are reduced. By doing so, a synergistic effect of reducing the amount of thermal expansion of the rotors 931 and 941 can be obtained.

(Operation of multistage roots pump)
Next, a method of driving pump 1100 having the above configuration will be described. The gas compression method and gas cooling method by the pump 1100 are the same as those of the pump 100 of the first embodiment described above.

<Pump driving method>
As shown in FIG. 41, in a pump 1100 according to this embodiment, as in the ninth embodiment, a pair of rotors 921, 921 rotate at the same rotational speed in opposite directions while maintaining the rotational phase. to rotate. Due to the rotation of the pair of rotors 921, 921, the gas in the vicinity of the suction port 911 is sucked into the casing 910 through the suction port 911 (arrow Gs in FIG. 42) and then compressed by the rotor 921 to the first stage. It is discharged to the intermediate position of the second stage (arrow Gm1 in FIG. 42).

Also, as in the ninth embodiment, the pair of rotors 931, 931 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 931, 931, the gas compressed by the first stage rotor 921 and discharged to the intermediate position is swept into the second stage rotor 931 from the intermediate position (Fig. 42). Arrow Gm1) is compressed by the rotor 931 and discharged to an intermediate position between the second stage and the third stage (arrow Gm2 in FIG. 42).

Furthermore, as in the ninth embodiment, the pair of rotors 941, 941 rotate in opposite directions at the same rotational speed while maintaining the rotational phase. Due to the rotation of the pair of rotors 941, 941, the gas compressed by the second-stage rotor 931 and discharged to the intermediate position is swept from the intermediate position into the third-stage rotor 941 (Fig. 42). arrow Gm2), and is compressed by the rotor 941 and discharged to the outside from the discharge port 913 (arrow Gd in FIG. 42).

Here, in the present embodiment, as in the fourth embodiment, the gas existing in the intermediate position between the first stage and the second stage is discharged from the intermediate discharge port 915 to the outside of the casing 910, and the cooler 1 and then introduced into the first-stage compression element (inside the space surrounded by the rotor 921 and the casing 910) from the two cooling gas introduction ports 1116A and 1116B provided on both left and right sides of the casing 910. be done. At this time, the pressure at the intermediate position (intermediate pressure) Pm1 is higher than the pressure in the space surrounded by the rotor 921 and the casing 910, so the gas discharged from the intermediate discharge port 915 passes through the cooler 1 , circulating. More specifically, as indicated by an arrow Ge1 in FIG. 42, the gas discharged from the intermediate discharge port 915 is cooled by the cooler 1, and is discharged from the cooling gas introduction port 1116 into the first-stage compression element. is introduced into the region surrounded by the rotor 921 and the casing 910 of the first stage (moving volume Qth1 portion), and then discharged again to the intermediate position between the first stage and the second stage. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 915, and the gas cooled by the cooler 1 flows into the first stage compression element. always introduced in As a result, the temperature of the gas discharged from the first-stage compression element decreases, so the gas that has been compressed by the first-stage (low-pressure side) compression element and rises in temperature does not dissipate heat, and the second-stage (high-pressure side) can be prevented from being directly sucked into the compression element of the second stage, and a significant temperature rise of the gas compressed by the second-stage compression element can be suppressed. Similarly, in the present embodiment, the gas present in the intermediate position between the second stage and the third stage is discharged from the intermediate discharge port 917 to the outside of the casing 910, cooled by the cooler 2, and then discharged to the casing 910. The cooling gas is introduced into the second-stage compression element (inside the space surrounded by the rotor 931 and the casing 910) from two cooling gas introduction ports 1118A and 1118B provided on both left and right sides of the . At this time, the pressure at the intermediate position (intermediate pressure) Pm2 is higher than the pressure in the space surrounded by the rotor 931 and the casing 910, so the gas discharged from the intermediate discharge port 917 passes through the cooler 2 , circulating. More specifically, as indicated by an arrow Ge2 in FIG. 42, the gas discharged from the intermediate discharge port 917 is cooled by the cooler 2, and is discharged from the cooling gas introduction port 1118 to the second-stage compression element. is introduced into the area surrounded by the second stage rotor 931 and the casing 910 (moving volume Qth2 portion), and then discharged again to the intermediate position between the second stage and the third stage. Therefore, even if a device such as a blower for discharging the gas at the intermediate position is not separately provided, the gas at the intermediate position is always discharged from the intermediate discharge port 917, and the gas cooled by the cooler 2 is discharged into the second stage compression element. always introduced in As a result, the temperature of the gas discharged from the second stage compression element decreases, so the gas whose temperature has risen due to being compressed by the second stage (low pressure side) compression element does not dissipate heat and the third stage (high pressure side) side) can be prevented from being directly sucked into the compression element of the third stage, and a significant temperature rise of the gas compressed by the third-stage compression element can be suppressed.

Furthermore, when the pressure (intermediate pressure) Pm1 at the intermediate position between the first stage and the second stage is equal to or higher than the atmospheric pressure, the pressure difference causes the gas to be discharged from the intermediate discharge port 915 to the atmosphere with a lower pressure ( Arrows Ge1 and Gd in FIG. 42), intermediate pressure Pm1 drops below atmospheric pressure. Similarly, when the pressure (intermediate pressure) Pm2 at the intermediate position between the second stage and the third stage is equal to or higher than the atmospheric pressure, the gas is discharged from the intermediate discharge port 917 to the atmosphere with a lower pressure due to the pressure difference. (arrow Ge2 and arrow Gd in FIG. 42), the intermediate pressure Pm2 drops below the atmospheric pressure. Therefore, since the suction pressure to the compression elements (rotors 931, 941) of the second and third stages becomes small, the suction pressure Ps2 of the second stage and the pressure of the gas sucked from the suction port 911 (suction pressure of the first stage) The difference ΔP1 from the pressure Ps1) and the difference ΔP2 between the third-stage suction pressure Ps3 and the second-stage suction pressure Ps2 can be reduced. As a result, the power of the motor that operates the pump 1100 can be reduced. Especially at the stage when the pump 1100 starts to draw gas toward the suction port 911, the intermediate pressures Pm1 and Pm2 are likely to be higher than the atmospheric pressure. .

In the present embodiment, the reduction ratio of the 1st-2nd stage intermediate gear 964 between the first timing gear 961 and the 1st-2nd stage intermediate gear 964 is larger than the reduction ratio of the 1st-2nd stage intermediate gear 964 between the second timing gear 962. It's becoming Therefore, the rotation speed N1 of the rotor 921 becomes lower than the rotation speed N2 of the rotor 931. Also, the length L1 of the rotor 921 is longer than the length L2 of the rotor 931 and the diameter D1 of the rotor 921 is larger than the diameter D2 of the rotor 931 . Even under such special conditions, it is possible to make the volumetric displacement ratio R _Q1-2 greater than 1 as described above.

In addition, the reduction ratio of the intermediate gear 965 between 2nd and 3rd stages with the second timing gear 962 is larger than the reduction ratio of the intermediate gear 965 between 2nd and 3rd stages with the third timing gear 963. . Therefore, the rotation speed N2 of the rotor 931 becomes lower than the rotation speed N3 of the rotor 941. Also, the length L2 of the rotor 931 is longer than the length L3 of the rotor 941 and the diameter D2 of the rotor 931 is larger than the diameter D3 of the rotor 941 . Even under such special conditions, it is possible to make the volumetric displacement ratio R _Q2-3 greater than 1 as described above.

[Uses of multi-stage roots pumps]
As described above, the pumps 100 (including the first and second modifications), 200, 300, 400, 500, 600, 700, 800, and 900 according to the first to eleventh embodiments are preferred embodiments of the present invention. , 1000, 1100 have been described in detail, an example of a preferred application of the pump will now be described.

Note that the discharge pressure when the multistage roots pump of each embodiment described above is used as a blower and the suction pressure when the multistage roots pump of each embodiment is used as a vacuum pump are, for example, When a multi-stage roots pump is used as a vacuum pump, the maximum suction pressure (gauge pressure) can be about -80 kPa (20 kPa in absolute pressure). Further, the amount of gas sucked by the multistage roots pump of each embodiment can be, for example, 1 to 400 m ³ /min. Examples of applications where the performance of the multistage roots pumps (pumps 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100) of each embodiment can be utilized include the following applications: Examples include:

(Application example: Oxygen generator)
Referring to FIG. 43, pumps 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 according to first to eleventh embodiments and pumps according to first and second modifications An example of applications to which 101 and 102 can be applied will be described. FIG. 43 shows the overall configuration of the oxygen generator 10. As shown in FIG.

The oxygen generator 10 is a device that uses an adsorbent and removes nitrogen gas and the like from the air to produce oxygen gas with a concentration of 90 to 93%. Compared to liquid oxygen, it is cheaper and can supply stable oxygen, so it is introduced in situations where a large amount of oxygen is used. As the oxygen generator 10, there are two types: PSA (Pressure Swing Adsorption) and VSA (Vacuum Swing Adsorption). Since the VSA oxygen generator is easy to switch between start and stop, cryogenic separation, which is complicated to start up, is possible. It is used as an oxygen generator in place of

As shown in FIG. 43, the oxygen generator 10 includes a feed air blower 11, two adsorption towers 12A and 12B, a pressure equalization tower 13, an oxygen booster blower 14, an aftercooler 15, and a decompression pump 16. , an exhaust silencer 17 and a valve skid 18 . Air, which is a raw material, is led by a raw air blower 11 to adsorption towers 12A and 12B filled with molecular sieves. The adsorption towers 12A and 12B are composed of two towers, and oxygen with a constant concentration is continuously generated in the adsorption towers 12A and 12B. While adsorption is being performed in one adsorption tower (e.g., adsorption tower 12A), another adsorption tower (e.g., adsorption tower 12B) is regenerated, and after a certain period of time, adsorption is performed. is switched. Regeneration (desorption) of the adsorbent that has adsorbed impurities such as nitrogen gas is performed by reducing the pressure in the adsorption towers 12A and 12B. The oxygen-based gas from which impurities such as nitrogen gas have been removed from the raw material air is led to the pressure equalizing tower 13 and adjusted to a constant pressure, and then pressurized by the oxygen pressurizing blower 14 . Since the temperature of the gas rises when the pressure is increased, the aftercooler 15 cools the gas sent from the oxygen pressure booster blower 14 to obtain oxygen gas with a concentration of 90 to 93%. The aftercooler 15 cools the gas by flowing cooling water, for example. On the other hand, impurities such as nitrogen gas are discharged from the exhaust silencer 17 as exhaust gas after being decompressed and desorbed by the decompression pump 16 from the adsorbent in the adsorption towers 12A and 12B.

In the oxygen generator 10 as described above, for example, in order to regenerate (desorb) the adsorbent that adsorbs impurities such as nitrogen gas according to the above-described embodiment, the pressure in the adsorption towers 12A and 12B is changed from the atmospheric pressure to −80 kPaG. Pumps 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, etc. are preferably used as the decompression pump 16 that repeatedly decompresses the pressure to a certain extent in a short time.

Although the preferred embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the above-described embodiments. That is, it is understood that other forms or various modifications that can be conceived by those skilled in the art within the scope of the invention described in the claims also belong to the technical scope of the present invention.

For example, in the above embodiment, a case of a vertical multi-stage roots pump has been described, but the multi-stage roots pump according to the present invention may be a horizontal multi-stage roots pump.

Further, in the above embodiment, the two-stage Roots-type pump and the three-stage Roots-type pump have been described, but the multi-stage Roots-type pump according to the present invention is a multi-stage Roots-type pump having four or more stages of compression elements. may

Further, in the above embodiment, the case where the compression element has a two-lobe rotor and a three-lobe rotor has been described, but in the multi-stage roots pump according to the present invention, the compression element is a multi-stage roots pump having rotors of four or more lobes. may The four-leaf rotor can be used, for example, in compressors and the like.

Further, in the above embodiment, the case where the moving volume ratio R _Q between all adjacent compression elements is greater than 1 has been described, but the multi-stage roots type pump according to the present invention is a multi-stage roots type pump with three or more stages. In some cases, the moving volume ratio R _Q may be greater than 1 between some of the compression elements, and between the remaining adjacent compression elements, the moving volume ratio R _Q may be 1 (the moving volume on the low pressure side and the moving volume on the high pressure side equal movement volumes).

Further, in the above embodiment, the length and diameter of the rotors included in the adjacent compression elements are set to be the same when the movement volume ratio _RQ is set to 1 or more by the rotation speed ratio of the rotors between the adjacent compression elements. Although the case has been described, if the requirement that the moving volume ratio _RQ is 1 or more is satisfied, the length and diameter of the rotors included in adjacent compression elements are not necessarily the same in the multi-stage roots pump according to the present invention. good too. In other words, the size (length, diameter, etc.) of the rotor is not particularly limited as long as it satisfies the requirement that the moving volume ratio _RQ is 1 or more.

Further, in the above embodiment, when changing the length of the rotors between the adjacent compression elements so that the moving volume ratio _RQ is 1 or more, the rotation speeds of the rotors of the adjacent compression elements are set to be the same. Although the case has been described, as long as the requirement that the moving volume ratio R _Q is 1 or more is satisfied, in the multi-stage roots pump according to the present invention, the rotation speeds of the rotors of adjacent compression elements may not necessarily be the same. .

Further, in the above-described second embodiment, the number of rotations of the rotor in the first stage and the number of rotations of the rotor in the second stage are equal, the diameter of the rotor in the first stage is equal to the diameter of the rotor in the second stage, and An example in which the length of the rotor in the first stage is longer than the length of the rotor in the second stage has been given. Furthermore, in the third embodiment, the number of rotations of the rotor in the first stage and the number of rotations of the rotor in the second stage are equal, the length of the rotor in the first stage and the length of the rotor in the second stage are equal, and An example is given in which the diameter of the rotor in the first stage is larger than the diameter of the rotor in the second stage. However, the present invention is not limited to these examples. and the diameter of the rotor in the first stage is larger than that of the rotor in the second stage.

Further, in the tenth and eleventh embodiments described above, the case where the cooling mechanism is provided in the sixth and ninth embodiments, respectively, has been exemplified and explained. The present invention also includes the case where it is provided.

[EXAMPLES] Next, although an Example and a comparative example demonstrate this invention still more concretely, this invention is not limited at all by these examples. In the following examples, the effect of improving the all-axis power of the sixth to eighth embodiments described above was verified.

All shaft powers of the two-stage roots pumps of Examples 6-1 to 6-3, 7-1 to 7-3, 8-1 to 8-3 and Comparative Example 1 shown in Table 1 were calculated. Examples 6-1 to 6-3 are examples of pumps having the configuration of the pump 600 described above. Examples 7-1 to 7-3 are examples of pumps having the configuration of the pump 700 described above. Examples 8-1 to 8-3 are examples of pumps having the configuration of the pump 800 described above. Comparative Example 1 is an example of a pump having a configuration in which cooler 1, check valve 3, intermediate discharge port 115, cooling gas inlet 116, and cooling gas inlet 117 are removed from pump 100 described above. The following (a) to (c) were used as calculation conditions.
(a) In any of the examples and comparative examples, the ratio of the volume transferred between the first stage and the second stage (=moved volume Qth1 of the first stage/moved volume Qth2 of the second stage) was set to 1.8.
(b) The diameter, length, and number of rotations of the first-stage rotor were the same in all the examples and comparative examples. Note that the rotation speed of the first stage was set to 1000 rpm.
(c) The conditions shown in Table 1 below were used for the diameter, length and number of revolutions of the second stage rotor.

In Table 1, the rotor rotation speed ratio is the ratio of the rotation speed of the second-stage rotor to the rotation speed of the first-stage rotor, and the rotor diameter ratio is the diameter of the second-stage rotor to the diameter of the first-stage rotor. The rotor length ratio is the ratio of the length of the second stage rotor to the length of the first stage rotor. For example, in Comparative Example 1, the rotation speed of the rotor in the second stage is lower than that of the rotor in the first stage, the diameter of the rotor in the first stage is equal to the diameter of the rotor in the second stage, and the rotor in the first stage In this example, the length of the first rotor is equal to the length of the rotor of the second stage. Further, in Examples 6-1 to 6-3, the rotation speed of the rotor in the second stage is higher than the rotation speed of the rotor in the first stage, and the diameter of the rotor in the second stage is higher than the diameter of the rotor in the first stage. is smaller, and the length of the rotor in the second stage is shorter than the length of the rotor in the first stage. Further, in Examples 7-1 to 7-3, the rotation speed of the rotor in the second stage is higher than that of the rotor in the first stage, and the diameter of the rotor in the first stage and the diameter of the rotor in the second stage are different. In this example, the length of the rotor in the second stage is equal and shorter than the length of the rotor in the first stage. Further, in Examples 8-1 to 8-3, the rotation speed of the rotor in the second stage is higher than the rotation speed of the rotor in the first stage, and the diameter of the rotor in the second stage is higher than the diameter of the rotor in the first stage. is smaller, and the length of the rotor in the first stage is equal to the length of the rotor in the second stage.

The shaft power Lth1 (kW) of the first-stage compression element in each example and comparative example was calculated by the following formula (A).
Lth1 (kW)=(1.667/100)×Qth1 (m ³ /min)×ΔP1 (kPa) (A)

Further, the axial power Lth2 (kW) of the second-stage compression element in each example and comparative example was calculated by the following formula (B).
Lth2 (kW)=(1.667/100)×Qth2 (m ³ /min)×ΔP2 (kPa) (B)

However, in the above formulas (A) and (B), Qth1 and Qth2 are the displacement volumes (m ³ /min) of the first and second stage compression elements, respectively, and ΔP1 is the leakage air volume. is the differential pressure (kPa abs.) obtained by subtracting the suction pressure to the first stage compression element from the suction pressure to the second stage compression element, and ΔP2 is the discharge pressure from the second stage compression element , is the differential pressure (kPa abs.) obtained by subtracting the suction pressure to the second-stage compression element in consideration of the leakage air volume.

Further, from the shaft powers Lth1 and Lth2 determined by the above formulas (A) and (B), the total shaft power Lth (kW) of the entire pump was calculated by the following formula (C).
Lth (kW) = Lth1 (kW) + Lth2 (kW) (C)

Further, the total shaft power (kW) in each example and comparative example was calculated for each case where the suction pressure (kPa abs.) to the first stage compression element was 10 kPa, 20 kPa, 30 kPa, 40 kPa and 50 kPa. . The theoretical value of the suction pressure (kPa abs.) to the second stage compression element at this time is, as described above, a moving volume ratio of 1.8 (therefore, the pressure ratio of the first stage compression element is 1.8), resulting in 18 kPa, 36 kPa, 54 kPa, 72 kPa and 90 kPa, respectively. Table 2 shows the all-shaft power (kW) calculated as described above. Table 3 shows the rate of decrease (%) of the all-shaft power of each example with respect to the all-shaft power of Comparative Example 1.

46 to 48 show graphs comparing all-axis power (kW) between each example and Comparative Example 1. FIG.

As shown in Tables 2 and 3 and FIGS. 46 to 48, it was found that the shaft power of all the example pumps can be reduced more than the pump of comparative example 1 with respect to the total shaft power. By making the diameter of the rotor of the second stage smaller than that of the rotor of the first stage or the length of the rotor of the second stage shorter than that of the rotor of the first stage, the leakage area becomes smaller. can reduce the amount of leakage in the compression element of When the second-stage leakage amount decreases, the suction pressure to the second-stage compression element decreases, and the differential pressure from the suction pressure to the first-stage compression element decreases. can be reduced. On the other hand, as described above, although the axial power of the second stage increases, the effect of reducing the axial power of the first stage, which has a large moving volume, is large. (total shaft power) is also reduced. This was demonstrated in this example.

Further, in all the examples, the power of all shafts decreased as the rotation speed of the second-stage rotor was increased (as the rotor rotation speed ratio was increased). Furthermore, as for the reduction effect of all-axis power, the reduction effect of Examples 6-1 to 6-3 corresponding to the sixth embodiment is greater than that of Examples 7-1 to 7-3 and 7-3 corresponding to the seventh embodiment. It was larger than Examples 8-1 to 8-3 corresponding to the eight embodiments. For example, if the first stage suction pressure is 20 kPa abs. In the case of (approximately −80 kPa G in gauge pressure), the shaft power was reduced by approximately 10% at maximum compared to Comparative Example 1 (Example 6-3).

100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 Multistage roots pump 110, 210, 310, 410, 510, 610, 710, 810, 910, 101, 1110 Casing 111, 211 , 311, 411, 511, 611, 711, 811, 911, 1011, 1111 Suction port 113, 213, 313, 413, 513, 613, 713, 813, 913, 1013, 1113 Discharge port 115, 215, 315, 415 , 417, 515, 517, 615, 715, 815, 915, 917, 1015, 1115, 1117 Intermediate outlet 116, 216, 316, 416, 418, 516, 518, 616, 716, 816, 916, 918, 1016 , 1116, 1118 Intermediate backflow cooling gas inlets 117, 217, 317, 419, 519, 617, 717, 817, 919, 1017, 1119 Backflow cooling gas inlets 121, 131, 141, 151, 221, 231, 321, 331, 421, 431, 441, 521, 531, 541, 621, 631, 721, 731, 821, 831, 921, 931, 941 Rotor 122, 132, 142, 152, 222, 232, 322, 332, 422, 432, 442, 522, 532, 542, 622, 632, 722, 732, 822, 832, 922, 932, 942 Rotating shaft 161, 261, 361, 461, 561, 661, 761, 861, 961 First timing gear 162, 262, 362, 462, 562, 662, 762, 862, 962 Second timing gear 265, 365 Common drive gear 463, 563, 963 Third timing gear 165, 265, 365, 464, 564, 665, 765, 865 1st drive gear 166, 366, 465, 565, 666, 766, 866 2nd drive gear 466, 567 3rd drive gear 964 Intermediate gear between 1st and 2nd stage 566, 965 Intermediate gear between 2nd and 3rd stage

Claims (17)

a plurality of stages of compression elements each independently having a pair of rotors rotatable in directions opposite to each other and two rotating shafts rotatably supporting each of the pair of rotors;
A gas suction port and a gas discharge port are provided, and the compression elements are arranged in parallel along the normal direction of a plane containing the two rotation axes of the compression elements of the same stage. a casing housing the element;
at least one intermediate discharge port provided in the casing for discharging gas existing between the low-pressure side compression element and the high-pressure side compression element that are adjacent to each other;
a cooling unit provided outside the casing for cooling the gas discharged from the intermediate discharge port;
a first cooling gas introduction port provided in the casing for introducing gas cooled by the cooling section into the compression element on the lower pressure side than the intermediate discharge port;
with
Formula (1) below:
_RQ = _QthL / _QthH (1)
(However, in formula (1), Qth _L is the movement volume of the compression element on the low pressure side of the two adjacent compression elements, and Qth _H is the displacement of the compression element on the high pressure side of the two adjacent compression elements. is the displacement volume of the compression element.)
The moving volume ratio R _Q is 1 or more, and the moving volume ratio R _Q is greater than 1 between at least one adjacent compression element among the plurality of stages of compression elements arranged in parallel. , multi-stage roots type pump. further comprising a drive mechanism that rotationally drives the rotor,
2. The drive mechanism, between at least one adjacent compression element, makes the rotation speed of the rotor in the compression element on the low pressure side higher than the rotation speed of the rotor in the compression element on the high pressure side. A multi-stage roots pump as described in . 3. The method of claim 2, wherein the length and diameter of the pair of rotors in at least one of the compression elements is the same as the length and diameter of the pair of rotors in another of the compression elements arranged side by side. Multi-stage roots type pump. The number of compression elements is two,
The drive mechanism
a pair of first timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the first stage;
a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage;
a first drive gear meshing with one of the pair of first timing gears;
a second driving gear that meshes with one of the pair of second timing gears;
a single drive shaft rotatably supporting the first drive gear and the second drive gear;
has
4. The number of teeth of said first drive gear and said second drive gear are set so that the number of rotations of said rotor in the first stage is higher than the number of rotations of said rotor in the second stage. A multi-stage roots pump as described. Between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy at least one of the following conditions (A) and (B): A multi-stage roots pump according to claim 1.
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side; further comprising a drive mechanism that rotationally drives the rotor,
6. A multi-stage roots pump according to claim 5, wherein said drive mechanism makes the number of rotations of said rotor in said compression element on the low pressure side the same as the number of rotations of said rotor in said compression element on the high pressure side. The number of compression elements is two,
The drive mechanism
a pair of first timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the first stage;
a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage;
a common drive gear that meshes with both the first timing gear of the pair of first timing gears and the second timing gear of the pair of second timing gears;
a drive shaft that rotatably supports the common drive gear;
7. The rotor according to claim 6, wherein the rotor in the first-stage compression element and the rotor in the second-stage compression element satisfy at least one of the following conditions (A) and (B): Multi-stage roots type pump.
(A) The length of the rotor in the compression element of the first stage is longer than the length of the rotor in the compression element of the second stage.
(B) The diameter of the rotor in the compression element of the first stage is larger than the diameter of the rotor in the compression element of the second stage. further comprising a drive mechanism that rotationally drives the rotor,
The drive mechanism makes the rotation speed of the rotor in the compression element on the high pressure side higher than the rotation speed of the rotor in the compression element on the low pressure side between at least one of the adjacent compression elements, and
between at least one adjacent compression element;
2. The multistage roots according to claim 1, wherein the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy at least one of the following conditions (A) and (B): formula pump.
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side; Between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy both the condition (A) and the condition (B). 9. A multi-stage roots pump according to claim 8. The number of compression elements is two,
The drive mechanism
a pair of first timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the first stage;
a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage;
a first drive gear meshing with one of the pair of first timing gears;
a second driving gear that meshes with one of the pair of second timing gears;
a single drive shaft rotatably supporting the first drive gear and the second drive gear;
has
10. The number of teeth of said first drive gear and said second drive gear are set so that the number of rotations of said rotor in the second stage is higher than the number of rotations of said rotor in the first stage. A multi-stage roots pump as described. a plurality of stages of compression elements each independently having a pair of rotors rotatable in directions opposite to each other and two rotating shafts rotatably supporting each of the pair of rotors;
A gas suction port and a gas discharge port are provided, and the compression elements are arranged in parallel along the normal direction of a plane containing the two rotation axes of the compression elements of the same stage. a casing housing the element;
a drive mechanism that drives the rotor to rotate;
with
Formula (1) below:
_RQ = _QthL / _QthH (1)
(However, in formula (1), Qth _L is the movement volume of the compression element on the low pressure side of the two adjacent compression elements, and Qth _H is the displacement of the compression element on the high pressure side of the two adjacent compression elements. is the displacement volume of the compression element.)
The moving volume ratio R _Q is 1 or more, and the moving volume ratio R _Q is greater than 1 between at least one adjacent compression element among the plurality of stages of compression elements arranged in parallel. ,
The drive mechanism makes the rotation speed of the rotor in the compression element on the high pressure side higher than the rotation speed of the rotor in the compression element on the low pressure side between at least one of the adjacent compression elements, and
Between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy at least one of the following conditions (A) and (B): Satisfying, multi-stage roots pump.
(A) The length of the rotor in the compression element on the low pressure side is longer than the length of the rotor in the compression element on the high pressure side.
(B) the diameter of the rotor in the compression element on the low pressure side is larger than the diameter of the rotor in the compression element on the high pressure side; Between at least one adjacent compression element, the rotor in the compression element on the low pressure side and the rotor in the compression element on the high pressure side satisfy both the condition (A) and the condition (B). 12. The multi-stage roots pump of claim 11. The number of compression elements is two,
The drive mechanism
a pair of first timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the first stage;
a pair of second timing gears provided so as to mesh with each other at the shaft ends of the two rotating shafts of the second stage;
a first drive gear meshing with one of the pair of first timing gears;
a second driving gear that meshes with one of the pair of second timing gears;
a single drive shaft rotatably supporting the first drive gear and the second drive gear;
has
13. The number of teeth of said first drive gear and said second drive gear is set so that the number of rotations of said rotor in the second stage is higher than the number of rotations of said rotor in the first stage. A multi-stage roots pump as described. The casing of claims 11 to 13, further comprising at least one intermediate discharge port for discharging gas existing between the low-pressure side compression element and the high-pressure side compression element that are adjacently arranged to the outside. A multi-stage roots pump according to any one of the preceding claims. The casing further has a second cooling gas introduction port for introducing cooling gas into the compression element between a suction position where gas is sucked into the last stage compression element and the discharge port. 15. A multi-stage roots pump according to any one of clauses 14 to 14. 16. A multi-stage roots pump according to any one of claims 1 to 15, characterized in that the interior of the casing is divided into the same number of pump working areas as there are compression elements solely by the arrangement of the compression elements. . A multi-stage roots pump according to any one of the preceding claims, characterized in that a plurality of said compression elements are provided as a single stage group within said unitary casing.

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