JPH11107951A - Postive displacement type pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive displacement type pump which can be continuously driven even though the temperature of the exhaust port side is high. SOLUTION: A bearing device 41 on the exhaust port side of a positive displacement type pump is composed of rolling elements 61c, 62c which can be rotated around the rotary center axis of a rotor, outer races 61a, 62a interposed between the rolling elements 61c, 62c and a housing 11. Further, these outer races 61a, 62a are resiliently supported to the housing 11 through the intermediary of resilient members 71, 72.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive displacement pump suitable for a positive displacement pump, for example, a vacuum pump for evacuating a compressive fluid in which air or another gas is mixed.

[0002]

2. Description of the Related Art Conventionally, positive displacement pumps such as a roots type, a claw type, and a screw type have been widely used as vacuum pumps used for evacuation for obtaining a low-pressure working space. During the evacuation operation of this type of positive displacement pump, the gas transfer chamber whose volume has been reduced at a predetermined compression rate during the transfer to the outlet is continuously connected to the outlet one after another, and the air is exhausted to the atmosphere. You. The heat generated by the adiabatic compression for the exhaust and the loss cycle in which the gas flowing backward from the atmosphere side (discharge port side) into the pump (the subsequent gas transfer chamber side) due to the leakage is returned to the atmosphere side again, etc. The outlet side becomes hot. At this time, the rotor shaft near the discharge port and its bearing inner ring become considerably hot and undergo a large thermal expansion, whereas the pump housing holding the bearing's outer ring is exposed to the atmosphere to release heat and force. Since the temperature rise is suppressed by cooling by water cooling and thermal expansion is not so large, that is, due to such a thermal expansion difference, an excessive load (contact pressure) acts on the contact surface between the rolling element of the bearing and the inner and outer rings.

[0003]

Therefore, in the conventional positive displacement pump as described above, when the temperature on the discharge port side increases, the difference in thermal expansion increases and seizure of the bearing occurs. It has to be used under operating conditions (for example, conditions such as pump speed) where the temperature does not exceed a predetermined value. As a result, for example, when a conventional pump is used for evacuation of a semiconductor manufacturing apparatus, a specific pump exhausted from the low-pressure working space is particularly provided on the outer periphery of the rotor on the suction port side where the temperature is relatively low (for example, 100 degrees or less). There is a problem that a solid product resulting from a gas (for example, a reaction gas in a thin film forming process by a CVD method) adheres, and frequent maintenance is required to remove the solid product.

The present invention has been made in view of the above problems to be solved, and an object of the present invention is to provide a positive displacement pump which can be operated continuously even when the temperature on the discharge side is increased.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a housing having a suction port and a discharge port and having a rotor chamber formed therein; A rotor is rotatably provided in the rotor chamber so as to suck the compressible fluid into the chamber and discharge the fluid from the outlet, and is interposed between the housing and the rotation center axis of the rotor, and the rotor is rotatable in the housing. And a bearing device on the discharge port side supporting the positive displacement pump,
The bearing device has a rolling element that can roll around a rotation center axis of the rotor, and an outer ring interposed between the rolling element and a housing, and the outer ring of the bearing device is configured to be heated due to a temperature rise. Even when there is a large temperature difference between the rotor and the housing, a gap is provided between the rotor and the housing inner periphery, and the rotor is supported by the housing via an elastic member.

In such a configuration, the outer ring of the bearing device is elastically supported by the housing via the elastic member,
Since the thermal expansion of the rotation center shaft of the rotor and the bearing is absorbed by the elastic member elastically deformed with the thermal expansion,
It is possible to prevent an excessive load from acting on the bearing. As a result, the vacuum pump can be operated in a state where the outlet side of the pump is at a considerably high temperature.

Further, the outer ring comprises a first outer ring and a second outer ring having contact surfaces inclined in opposite directions with respect to the rotation center axis of the rotor. When two sets are provided so as to be in contact with the contact surfaces of the two outer rings, respectively, and when biasing means for biasing the first outer ring and the second outer ring in the axial direction are provided, the thermal expansion of the rotor rotation center shaft, the inner ring and the rolling elements Is absorbed by the axial displacement of the first outer ring and the second outer ring with respect to the inner ring, and the change in the contact pressure acting on the rolling elements is more effectively suppressed.
It is possible to cope with a larger thermal expansion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 3
FIG. 1 is a view showing one embodiment of a positive displacement pump according to the present invention, and shows an example in which the present invention is applied to a screw type vacuum pump. First, the structure will be described. In FIGS. 1 and 2, reference numeral 11 denotes a pump housing in which a rotor chamber 12 is formed. The pump housing 11 has a suction port 11a and a discharge port 11b (FIG. 1). 2). Reference numerals 21 and 22 denote male and female screw rotors rotatably housed in the rotor chamber 12 of the pump housing 11 with a small gap (for example, about 50 μm). Of the screw rotors 21 and 22, the male screw rotor 21 is formed in a male screw shape, and the female screw rotor 22 is formed in a female screw shape in a reverse screw direction to the rotor 21,
The screw rotors 21 and 22 are arranged in parallel inside the pump housing 11 with a small gap (for example, about 50 μm), and are driven in mutually opposite directions by driving means described later.

The pump housing 11 and the screw rotors 21 and 22 are made of SUS316L (stainless copper). However, such a material may be, for example, SCM435 (chromium molybdenum copper) or an aluminum alloy, or a combination of these materials. Pump housing 11 and rotors 21 and 22 in rotor chamber 12
2, a plurality of spiral working chambers 25, 26 (gas transfer chambers) partitioned by portions close to the rotors 21, 22 are formed. 22 has a predetermined volume according to the lead length in each transfer section. When the rotors 21 and 22 rotate, the working chambers 25 and 26 increase the volume to a predetermined value in the transfer section on the suction side communicating with the suction port 11a to perform a suction action, and the suction chamber 11 Outlet 11b
In the intermediate transfer section not communicating with the discharge port 11b, the transfer is performed with a predetermined volume, and in the transfer section on the discharge side communicating with the discharge port 11b, the volume is reduced to a minimum to generate a discharge pressure of about atmospheric pressure or more, thereby performing the discharge action. It has become. By changing the lead lengths of the screw rotors 21 and 22 and the cross-sectional areas of the screw grooves, the volumes of the working chambers 25 and 26 may be gradually reduced (in multiple stages) in the intermediate transfer section. .

Further, the screw rotors 21 and 22 are formed integrally with rotor shafts 31 and 32 (rotation center axes) which are rotation center axes thereof.
One end portions 31a and 32 protruding from both axial ends of the first and second axial directions.
a and the other end portions 31b and 32b. 41, 4
Reference numeral 2 denotes a first bearing interposed between one end portions 31a and 32a of the rotor shafts 31 and 32 and shaft hole portions 13a and 14a of the pump housing 11, respectively. These are second bearings interposed between the other end portions 31b and 32b and the shaft holes 13b and 14b of the pump housing 11, respectively. These first and second bearings 4
1 to 44 connect the rotors 21 and 22 to the pump housing 11.
It has the function of supporting it rotatably. The first bearing devices 41 and 42 have a detailed configuration described later,
The second bearings 43 and 44 have a function of regulating the axial displacement of the rotors 21 and 22 with respect to the pump housing 11, while the second bearings 43 and 44 support the rotor 2 with respect to the pump housing 11.
1 and 22 (specifically, the first bearing device 4
The rotor shafts 31, 32, the axial displacement of which is restricted by the end portions 31 a, 32 a, are extended by thermal expansion and the other end portions 31 b, 32 b are displaced. .

Reference numeral 50 denotes a driving means for driving the screw rotors 21 and 22, and an electric motor 51 connected to the rotor shaft 31 of the male screw rotor 21 and the same number of teeth fixed to the rotor shafts 31 and 32 and meshing with each other. And transmission gears 52 and 53 which are timing gears. As shown in FIG. 1, first bearing devices 41, 42
Are a pair of angular contact ball bearings 61 and 62 interposed between the pump housing 11 and one end portions 31a and 32a of the rotor shafts 31 and 32, and a pair of disc springs 63 and
64. Angular contact ball bearings 61 and 62
Are arranged, for example, at a contact angle of 30 ° and opposite to each other with the disc springs 63 and 64 interposed therebetween. Further, each of the angular ball bearings 61 and 62 is provided in the shaft hole 1 of the pump housing 11.
Outer rings 61a, 62a housed in a predetermined gap 13d in 3a, 14a, and one end 31 of rotor shafts 31, 32
a, 32a, and steel rolling elements, such as balls 61c, 62c, which roll around the rotor shafts 31, 32 while being in contact with the outer rings 61a, 62a and the inner rings 61b, 62b. It is composed of

The disc springs 63 and 64 are provided with angular contact ball bearings 6.
The urging means urges the outer rings 61a, 62a in directions axially separated from each other (predetermined urging direction), and the balls 61 are formed via the outer rings 61a, 62a.
A predetermined preload is applied to the outer ring 61 and the outer race 61c.
a, 62a are allowed to be displaced in a direction opposite to the biasing direction due to thermal expansion. In the vicinity of the openings of the shaft holes 13a, 14a of the pump housing 11, a retaining ring 15, which restricts the interval between the outer rings 62a to a predetermined value or less against the urging force from the disc springs 63, 64, is attached by a bolt 16. Have been. Also, the rotor shaft 3
The inner rings 61b and 62b are provided with outer rings 61b and 62b, respectively.
The spacer rings 17a and 17b are spaced from the rotor shafts 31 and 32 at substantially equal intervals to the rotor shafts 31 and 32, and the inner rings 61b and 62b are integrally fixed to the rotor shafts 31 and 32 via the spacer rings 17a and 17b. A nut 18 is attached.

Further, the outer rings 61a, 62a of the angular ball bearings 61, 62 and the shaft hole 13 of the pump housing 11 are provided.
A pair of elastic rings 71 and 72 are interposed in a compressed state between a and a. These elastic rings 71, 7
Reference numeral 2 denotes a plurality of annular grooves 13c formed in a shaft hole 13a and a similar annular groove in a shaft hole 14a formed of a known leaf spring material, each of which is curved into, for example, a "<"-shaped cross section. The rotor shafts 31 and 32 are fitted with the shaft holes 13a and 14 via the angular ball bearings 61 and 62, respectively.
It can be stably supported on the central axis of a. In place of the elastic rings 71 and 72, a leaf spring material provided with a plurality of inner protrusions or cut-and-raised portions which are spaced apart at equal intervals in the circumferential direction and project inward at a predetermined height, and a wire or plate material for spring are used. The outer rings 61a and 62a may be elastically supported using a ring-shaped metal spring having a predetermined wavelength in the circumferential direction, an elastic member containing heat-resistant resin, an O-ring having excellent heat resistance, or the like. .

In the above configuration, when the male screw rotor 21 is driven by the electric motor 51 of the driving means 50, the female screw rotor 2 is driven via the transmission gears 52 and 53.
2 is driven in synchronization with the male screw rotor 21 in the opposite direction, and a plurality of helical working chambers 25 and 26 partitioned by adjacent portions of both rotors 21 and 22 are connected to the suction side communicating with the suction port 11a. In the transfer section, the volume is increased to a predetermined value to perform the suction action, and the suction port 11a is also connected to the discharge port 11b.
In the intermediate transfer section which does not communicate with the discharge port 11b, the transfer is performed at a predetermined volume or while gradually decreasing the volume. In the transfer section on the discharge side communicating with the discharge port 11b, the volume is reduced to a minimum to perform the discharge operation.

In this operating state, the working chambers 25 and 26 are successively communicated with the discharge port 11b on the discharge port 11b side to be exhausted to the atmosphere. However, heat generated by adiabatic compression for the exhaust, The pump housing 1 from the atmosphere side (the working chambers 25 and 26 side communicating with the discharge port 11b) due to leakage.
The temperature of the outlet 11b becomes high due to a loss cycle or the like in which the gas entering the inside 1 (the subsequent working chamber) is returned to the atmosphere again. Also, during operation, most of the working chambers 25 and 26 are in a vacuum state to perform a heat insulating function, so that the pump housing 11 can radiate heat to the outside air and has a relatively low temperature, whereas the pump housing 11 has a relatively high temperature. Heat is less likely to be transmitted from the side 22 to the pump housing 11 side. Therefore, the screw rotors 21 and 22 and the rotor shafts 31 and 32 undergo large thermal expansion due to the temperature of the discharge port 11b of the pump housing 11 becoming extremely high, whereas the thermal expansion of the pump housing 11 does not result in such large thermal expansion. Becomes

In this operating state, the rotor shafts 31, 3
2 is extended in the axial direction by thermal expansion, the other end portions 31b and 32b of the rotor shafts 31 and 32 are connected to the second bearings 43 and 32, respectively.
44, the first bearing device 4 is kept in a state in which the axial clearance between the pump housing 11 on the discharge port 11b side and the screw rotors 21 and 22 is kept in a substantially constant range.
The rotor shafts 31 and 32 are formed by the shaft holes 13 a and 1 of the pump housing 11 by the first and second bearings 43 and 44.
4a is stably supported on the central axis.

When the temperature on the discharge port 11b side rises with the operation, the rotor shafts 31, 32 and the bearings 61, 32
The temperature difference between the housing 62 and the housing 11 increases, and the outer rings 61a, 62 of the angular contact ball bearings 61, 62, as shown by broken lines in FIG. 3 (shown exaggerated for convenience).
a is axially displaced toward each other by the pressing force from the balls 61c and 62c, and compresses the disc springs 63 and 64. Therefore, a load within a predetermined range according to the urging force from the disc springs 63 and 64 acts on the balls 61c and 62c of the angular ball bearings 61 and 62, and an excessive load does not act. At this time, the outer ring 61
a, 62a are shaft holes 13a, 1 of the pump housing 11;
4a (inner wall surface), the elastic rings 71 and 72 are elastically deformed so as to enlarge their inner diameters, and the outer rings 61a and 62
absorbs the thermal expansion of a. This allows the pump outlet 1
Even if the 1b side becomes extremely hot, the outer rings 61a, 6
A required gap or at least a tightening allowance at room temperature of a conventional bearing is secured between the shaft 2a and the shaft holes 13a and 14a, so that the outer races 61a and 62a can move in the axial direction.

In order to facilitate understanding of such an operation, the operation will be described with reference to a comparative example shown in FIG. As shown in FIG. 4, a pair of angular ball bearings 1 and 2 are arranged such that the inner peripheral surfaces (rolling surfaces) of their outer rings 1a and 2a are inclined in opposite directions, and between the outer rings 1a and 2a. It is also conceivable to contract the disc springs 3 and 4 so that the outer rings 1a and 2a approach each other due to the thermal expansion (expansion of the diameter) of both inner rings due to a temperature rise during operation. This way,
The outer rings 1a and 2a can be held directly in the shaft holes of the pump housing 6, and the elastic rings 71 and 7 of the present embodiment can be held.
It also seems that 2 is unnecessary. However, if the temperature difference between the rotor shaft 5 and the pump housing 6 becomes considerably large due to the high temperature of the discharge port 11b of the pump, the outer rings 1a, 2 of the angular ball bearings 1, 2 are assumed to be large.
a is greatly expanded and becomes tightly fitted in the shaft hole of the pump housing 6, and the effect of absorbing the thermal expansion on the rotor shaft 5 side by the axial displacement of the outer rings 1a and 2a cannot be obtained. Therefore, in such a bearing structure, when the exhaust side of the pump becomes extremely hot, the bearing 1
Inevitably, an excessive load acts on the rolling elements 1b and 2b, and the bearing life is sharply reduced.

On the other hand, in the pump according to the present embodiment, the elastic rings 71, 72 are elastically deformed so as to enlarge their inner diameters and reliably absorb the thermal expansion of the outer rings 61a, 62a. Rotor shaft 31,
32 is in a high-speed continuous operation state in which the temperatures at the one end portions 31a and 32a become considerably high, so
a, 32a even in a high temperature operating state in which the temperature difference between the housing 11 and the housing 11 becomes very large.
The axial displacement of the a and 62a is not hindered, and the balls 61c and 62c are always given a predetermined level of preload in accordance with the urging force from the disc springs 63 and 64.
Stable bearing performance of the angular contact ball bearings 61 and 62 can be maintained.

As described above, in the vacuum pump of the present embodiment, the outer rings 61a, 6 of the angular ball bearings 61, 62 are provided.
Elastic ring 7 provided between 2a and pump housing 11
1, 72, the outer rings 61a, 62a of the angular contact ball bearings 61, 62 even when the thermal expansion is large due to the continuous operation.
Is reliably displaced in the axial direction, and the contact pressure acting on the balls 61c, 62c can be kept within a favorable load range according to the spring pressure of the disc springs 63, 64. Therefore, the operation can be performed in a state where the temperature on the side of the discharge port 11b is high, and as a result, the operation at high speed can be performed. Also,
For example, a specific gas (CVD
Even when a solid product is likely to be generated due to a reaction gas in a thin film forming process by a vacuum method, the temperature inside the pump is in a temperature range where the solid product is generated (for example, 150 to 2).
Conventional operating temperature range lower than the predetermined temperature of about 00 ゜ C)
, It is possible to perform an operation that deviates from the temperature to the high temperature side, and it is possible to reduce the number of maintenance operations for removing solid products. In addition, continuous operation can be performed for a long time, and as a result, it is possible to eliminate the need to use a conventional mechanical booster pump, which can be said to partially bear the calorific value of the evacuation system. Become.

In the above-described embodiment, the ball bearings 61 and 62 each having a pair of outer rings and inner rings have been described as an example. However, the inner rings 61b and 62b fixed at a fixed interval with the spacer ring 17a interposed therebetween are provided. It may be integrated, or some annular bearing groove may be provided on the rotor shaft 31, 32 side. In addition, a pair of angular contact ball bearings in which the inclination directions of the contact surfaces of the inner and outer rings are opposite to those in the above example are provided, the outer ring is fixed in the axial direction via a spacer ring, and the inner ring is attached in a direction to separate in the axial direction. It is also conceivable to provide a biasing disc spring.

FIG. 5 is a sectional view of a main part showing another embodiment of the positive displacement pump according to the present invention. In this embodiment, the same components as those of the above-described embodiment are denoted by the same reference numerals as those described above, and detailed description thereof will be omitted. Differences from the above-described embodiment will be described below. In this pump, a pair of angular contact ball bearings 81 and 82 are arranged adjacent to each other, and a pair of O-rings 8 which are elastic rings are provided between outer rings 81 a and 82 a and the pump housing 11.
3 and the outer ring 82a of the outer bearing 82.
Disc springs 84 and 85 (biasing means) are contracted between the lock ring 15 and the retaining ring 15. 86 is an angular contact ball bearing 81,
The stopper 82 is fixed to the rotor shaft 31 together with the inner rings 81b, 82b by a nut 18 to prevent the inner rings 81b, 82b from coming off.

Also in the present embodiment, when the outer rings 81a, 82a of the angular ball bearings 81, 82 expand significantly, the diameter of the outer rings 81a, 82a is increased by the O-ring 8.
3 ensures absorption. Therefore,
Even during continuous operation, the inner ring 8 of the outer rings 81a and 82a
Axial displacement and disc spring 8 relative to 1b, 82b
4 and 85 to maintain an appropriate biasing force to prevent an excessive load from acting on the balls 81c and 82c (rolling elements) of the angular ball bearings 81 and 82, and obtain the same effect as the above-described embodiment. be able to.

In the above description, the embodiment of the present invention has been described by taking a vacuum pump as an example. However, the present invention having a characteristic of a bearing device can be applied not only to a vacuum pump but also to a compression pump. .

[0025]

According to the present invention, since the outer ring of the bearing device is elastically supported by the housing via the elastic member, the thermal expansion of the rotation center shaft of the rotor and the bearing can be reliably absorbed by the elastic member, and the pump can be used. It is possible to prevent an excessive load from acting on the bearing even when the discharge port side is in an operation state in which the temperature is considerably high. As a result, operation at high speed rotation becomes possible. Further, the pump can be used under operating conditions in which the temperature of the inside of the pump rises to a temperature range in which the solid product due to the reaction gas or the like does not easily adhere to the outer periphery of the rotor. The number of times of maintenance for removing can be reduced.

Further, by providing an urging means for urging the first and second outer races in the axial direction and allowing relative axial displacement of both outer races with respect to the inner race, the rotor rotation center shaft and the rolling element The contact pressure acting on the rolling elements can be kept within a good range according to the urging force of the urging means by absorbing the thermal expansion of the first and second outer races by the axial displacement of the first and second outer rings, and the durability is further improved. Can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of a positive displacement pump according to the present invention.

FIG. 2 is a plan sectional view of the positive displacement pump of one embodiment.

FIG. 3 is an operation explanatory view of a bearing device in the positive displacement pump of one embodiment.

FIG. 4 is a sectional view showing a bearing device of a comparative example.

FIG. 5 is a sectional view of a main part of another embodiment of the positive displacement pump according to the present invention.

[Explanation of symbols]

 Reference Signs List 11 pump housing 11a suction port 11b discharge port 12 rotor chamber 13a, 13b, 14a, 14b shaft hole 21, 22 screw rotor (rotor) 25, 26 working chamber (gas transfer chamber) 31, 32 rotor shaft (rotation center shaft) 41, 42 First bearing device (bearing device) 43, 44 Second bearing (bearing on suction side) 61, 62; 81, 82 Angular contact ball bearing 61a; 81a Outer ring (first outer ring) 62a; 82a Outer ring ( 2nd outer ring) 61b, 62b; 81b, 82b Inner ring 61c, 62c; 81c Ball (rolling element) 63, 64; 83, 84 Disc spring (biasing means)

Claims (2)

[Claims] 1. A housing having a suction port and a discharge port and having a rotor chamber formed therein, a rotation center shaft, and a suction port for sucking a compressible fluid from the suction port into the rotor chamber and discharging the fluid. A rotor rotatably provided in the rotor chamber so that the rotor is discharged from the housing, and a bearing device at a discharge port side interposed between the housing and the rotation center axis of the rotor and rotatably supporting the rotor in the housing. In the positive displacement pump, the bearing device includes: a rolling element that can roll around the rotor shaft; and an outer ring interposed between the rolling element and the housing. A gap between the rotor and the housing even when there is a large temperature difference between the rotor and the housing, and the housing is supported by the housing via an elastic member. Flop. 2. The outer ring comprises a first outer ring and a second outer ring having contact surfaces inclined in directions opposite to each other with respect to the rotation center axis of the rotor, and the rolling elements contact the contact surfaces of the two outer rings, respectively. Yo 2
2. The positive displacement pump according to claim 1, further comprising: a biasing unit that is provided as a set and biases the first outer ring and the second outer ring in an axial direction. 3.