JP2010159740A - Rotating vacuum pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotating vacuum pump for reducing frictional resistance due to foreign matter accumulated in a pump chamber. <P>SOLUTION: During driving, a space 66 is generated between a front side wall surface of a rear housing 4 and a rear side wall surface of a rotor 40 because a rotation shaft 30 including the rotor 40 has thermal expansion greater than that of a rotor housing 3 exposed to ambient air. The foreign matter 67 is easily accumulated in the space 66. When a multistage roots pump stops, the rotation shaft 30 including the rotor 40 thermally shrinks toward an initial-setting position, so that great pressing force is applied to the foreign matter 67. However, a coil spring 56 extends against the pressing force, so that the rotation shaft 30 is slightly displaced to the front side and the pressing force applied to the foreign matter 67 is reduced. Thus, the frictional force between the rotor 40 and the foreign matter 67 is reduced at the time of the re-operation of the multistage roots pump, and the multistage roots pump can be smoothly restarted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a rotary vacuum pump that rotates by a rotating shaft to transfer gas in a pump chamber and performs a suction action.

Patent Document 1 discloses a multistage roots pump which is one of rotary vacuum pumps. In the multi-stage Roots pump, two rotation shafts are arranged in parallel in the housing, and both ends are rotatably supported by bearings. Each of the plurality of rotors provided in each rotating shaft has a configuration of being accommodated in a plurality of pump chambers arranged in parallel in a direction perpendicular to the rotating shaft in the housing.

Specifically, a plurality of rotors provided on one rotating shaft make a pair with a plurality of rotors provided on the other rotating shaft, respectively, and are accommodated in the pump chambers in a meshed state. Each pump chamber has a suction region and a discharge region, and the discharge region of one pump chamber is connected to the suction region of the adjacent pump chamber via a communication path. The suction region of the pump chamber located on one end side is connected to the suction hole communicating with the outside, and the discharge region of the pump chamber located on the other end side is connected to the discharge port communicating with the outside.

One end of the one rotating shaft is connected to a drive source, a gear provided on the rotating shaft meshes with a gear provided on the other rotating shaft, and the rotating shafts rotate in opposite directions synchronously. . Patent Document 1
In the multi-stage Roots pump that is implemented, the one and the other rotary shafts define the position of the rotor in the pump chamber.
Alternatively, the movement in the direction of the rotation axis is prohibited by means such as press-fitting between the radial bearing on one end of the rotation shaft and the rotation shaft.

In the multi-stage type Roots pump configured as described above, the other rotating shaft is rotated by driving the one rotating shaft, and the pair of rotors housed in the pump chambers are rotated. The gas sucked into the pump chamber on the one end side through the suction port is transferred by being sequentially sucked into the adjacent pump chamber while being compressed by the rotation of the pair of rotors.
From the pump chamber on the other end side, the compressed gas is discharged to the outside through the discharge port.

JP 2008-51116 A

Since the multistage roots pump configured as described above generates high heat during operation, particularly on the discharge port side, the housing, the rotor, and the rotary shaft are thermally expanded. In addition, when the multistage roots pump is stopped, the housing, the rotor and the rotating shaft are cooled by the atmosphere.
Heat shrinks. However, during operation, the housing is in direct contact with the atmosphere and is susceptible to the cooling effect, but the rotor and the rotating shaft are present in the housing and do not receive the atmospheric cooling effect. For this reason, a difference in thermal expansion occurs between the housing, the rotor, and the rotating shaft, and the rotor and the rotating shaft are displaced more than the housing. Therefore, a large gap in the thrust direction is generated between the wall surface of the pump chamber, which is a part of the housing, and the wall surface of the rotor.

On the other hand, since powder or the like is mixed in the gas sucked into the pump chamber, foreign matter due to accumulation of powder or the like is easily generated in the large gap in the thrust direction. When the multi-stage Roots pump stops and heat shrinks with foreign matter accumulated, the rotor and rotating shaft cannot return to the initial set position due to the presence of foreign matter, and are strongly pressed against the foreign matter. . For this reason, when the multi-stage Roots pump is restarted, a large frictional resistance is generated between the rotor and the foreign matter, which may make the restart impossible.

The present invention provides a rotary vacuum pump that can relieve the frictional resistance during restart due to foreign matter accumulated in the pump chamber.

According to a first aspect of the present invention, a pump chamber is provided in a housing, a rotor disposed in the pump chamber is provided on a plurality of rotating shafts, and gas in the pump chamber is transferred by rotation of the plurality of rotating shafts. In the rotary vacuum pump that performs a suction action, the rotation shaft is restricted in a thrust direction movement that allows displacement in only one direction due to thermal expansion in the thrust direction of the rotor and the rotation shaft that occurs during operation of the rotary vacuum pump. And a first elastic member for applying a biasing force in a direction opposite to a direction allowing the thermal expansion with respect to the rotating shaft. According to the present invention of claim 1, during the operation of the rotary vacuum pump, the thrust gap generated in the pump chamber due to the difference in thermal expansion amount between the housing, the rotor, and the rotating shaft. Even if foreign matter accumulates, the frictional force between the housing and the rotor due to thermal contraction when the rotary vacuum pump is stopped can be absorbed by deformation of the first elastic member, and the rotary vacuum pump Can be restarted without any trouble.

The present invention according to claim 2 is characterized in that a second elastic member for applying a biasing force in a direction allowing the thermal expansion to the rotating shaft is provided. Positioning can be performed by two elastic members having a biasing force in the direction, and frictional resistance due to foreign matter accumulated in the pump chamber due to thermal expansion can be reduced.

  According to a third aspect of the present invention, the thrust direction movement restricting means includes a stepped portion formed on the rotating shaft and a bearing supporting the rotating shaft, and the stepped portion and the bearing are directly or indirectly connected. Therefore, the object of the present invention can be achieved by simple means.

  The present invention according to claim 4 is characterized in that the first elastic member is disposed between the stepped portion and the bearing, so that it is possible to suitably apply a biasing force to the rotating shaft. it can.

The present invention according to claim 5 is characterized in that the rotary vacuum pump is a multi-stage Roots pump, so that the present invention can be suitably implemented.

  In the present invention of claim 6, the direction in which the first elastic member applies a biasing force to the rotating shaft is the same as the gas transfer direction in the multistage roots pump, and the thrust direction movement Since the restricting means is arranged on the final stage side of the multistage roots pump in the previous period, the movement in the thrust direction can be regulated on the final stage side of the multistage roots pump. Leakage from the water can be effectively prevented.

The present invention can smoothly restart the rotary vacuum pump regardless of the accumulation of foreign matter in the pump chamber.

It is front sectional drawing of a multistage root pump. It is a plane sectional view of a multistage type Roots pump. It is a partial plane sectional view showing the time of thermal expansion. It is a partial plane sectional view showing the time of heat contraction. It is the sectional view on the AA line of FIG. FIG. 3 is a sectional view taken along line B-B in FIG. 2. It is a fragmentary sectional view showing a 2nd embodiment. It is a fragmentary sectional view showing a 3rd embodiment.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to a multistage roots pump will be described with reference to FIGS. In the specification of the present application, the direction of the multi-stage Roots pump is that the left side of FIGS. 1 to 4 is the front, the right side is the rear, the upper side is the upper side, the lower side is the lower side, and The left side will be described as the back side.

The housing 1 forming the outer shape of the multistage roots pump has a front housing 2, a rotor housing 3, a rear housing 4 and a gear housing 5 joined together in order from the front side.
For example, a bolt (not shown) or the like is integrated in a sealed state. Each of the housings 2 to 5 has a configuration in which a cylindrical body having a substantially elliptical inner space is vertically divided into two as shown in FIGS. 5 and 6. This two-part configuration is effective for assembling the multi-stage Roots pump. For example, after the members of each mechanism described later are mounted on the lower split cylindrical body, the upper split cylindrical body is covered and sealed. Assembly is performed so as to be integrated. In addition, since the 2 division structure of each housing 2-5 is not a thing closely related to this invention, detailed description is abbreviate | omitted. Moreover, each structure of a multistage roots pump is demonstrated based on the assembled state like each figure.

Inside the rotor housing 3, partition walls 6 to 9 that are divided into upper and lower parts so as to have an elliptical shape.
Are installed in order from the front side with a narrower interval, between the partition wall 6 and the front housing 2,
Pump chambers 10-1 between the partition walls 6-9 and between the partition wall 9 and the rear housing 4, respectively.
4 is formed. Therefore, each partition wall 6-9 is comprised as a part of rotor housing 3 for forming the pump chambers 10-14. Moreover, each pump chamber 10-14 has the volume reduced sequentially from the front side.

Each partition wall 6-9 has communication spaces 15-18 inside. As shown in FIG. 1, the communication spaces 15 to 18 have discharge passages 19 to 22 that open to the front side below, and suction passages 23 to 26 that open to the rear side.

In FIG. 1, each of the pump chambers 10 to 14 forms a gas suction region in the upper space, and forms a gas discharge region in the lower side. The pump chamber 10 communicates the suction region with the suction port 27 connected to the outside provided above the rotor housing 3, and the discharge region communicates with the discharge passage 19 of the partition wall 6. The pump chambers 11 to 13 formed between the partition walls 6 to 9 communicate the suction region with the suction passages 23 to 25 of the partition walls 6 to 8, respectively, and discharge the discharge regions to the partition walls 6 to 9, respectively. It communicates with the passages 19-22. The pump chamber 14 communicates the suction area with the suction passage 26 of the partition wall 9,
The discharge passage communicates with a discharge port 28 connected to the outside provided below the rotor housing 3.

In the above configuration, the suction port 27 and the suction passages 23 to 26 are respectively connected to the pump chambers 10 to 10.
14, and the discharge passages 19 to 22 and the discharge port 28 are provided in each pump chamber 1.
A gas discharge unit for 0 to 14 is configured.

Two rotating shafts 29 and 30 are arranged in parallel so as to penetrate from the front side to the rear side at a substantially central portion in the housing 1. The rotary shafts 29 and 30 each include a plurality of cross-shaped (see FIG. 5) rotors 31 to 40 integrated on the peripheral surface. The rotors 31 and 36 are meshed so as to form a pair and are rotatably accommodated in the pump chamber 10.
39 is rotatably accommodated in the pump chamber 11, the rotors 33 and 38 are accommodated in the pump chamber 12, the rotors 34 and 39 are accommodated in the pump chamber 13, and the rotors 35 and 40 are accommodated in the pump chamber 14.

Front end portions of the rotary shafts 29 and 30 are respectively attached to the front housing 2 with bearings 41 and 42.
It is rotatably supported by. The bearings 41 and 42 are movable in the thrust direction with respect to the front housing 2. Ring members 43, 44 are fixed to the peripheral surfaces of the rotary shafts 29, 30, and disc springs 45, 46 as second elastic members are interposed between the ring members 43, 44 and the front housing 2. Accordingly, the rotary shafts 29 and 30 are configured to receive a biasing force toward the front side by the disc springs 45 and 46 via the bearings 41 and 42 and the ring members 43 and 44. Seal members 47 and 48 are mounted between the outer peripheral surfaces of the ring members 43 and 44 and the inner peripheral surface of the front housing 2 so that the gas in the pump chamber 10 does not leak to the outside. Reference numeral 65 denotes a cover that covers front end portions of the rotary shafts 29 and 30.

The rear sides of the rotary shafts 29 and 30 are rotatably supported by bearings 51 and 52,
52 is supported by holders 49 and 50 mounted on the inner peripheral surface of the rear housing 4. Spring bearing rings 53 and 54 fixed by screwing are disposed on the peripheral surfaces of the rotary shafts 29 and 30 at positions further to the rear side than the bearings 51 and 52. Spring bearing ring 53,
54 is fixed to the rotary shafts 29 and 30 by appropriate means after the mounting position is adjusted.
If a double nut or the like is used, the configuration is simple.

  Between the inner rings of the bearings 51 and 52 and the spring receiving rings 53 and 54, coil springs 55 and 56, which are first elastic members of the present invention configured as compression springs, are mounted. Energizing the rear side. The rotary shafts 29 and 30 are configured to be allowed to move in the thrust direction with respect to the bearings 51 and 52. Preferably, the spring force of the coil springs 55 and 56 is set strongly with respect to the disc springs 45 and 46, so that the rotating shafts 29 and 30 can be in a state of being positioned on the rearmost side.

  In the space in the rear housing 4 located on the front side of the bearings 51 and 52, labyrinth mechanisms 57 and 58 are disposed on the rotary shafts 29 and 30, and the space between the pump chamber 14 and the space on the bearings 51 and 52 side is provided. The gap is sealed. The rear end portions of the rotary shafts 29 and 30 protruding into the internal space of the gear housing 5 are provided with gears 59 and 60, respectively, and rotation transmission is performed by the engagement of both the gears 59 and 60. The rotating shaft 29 is connected to the motor shaft 61 of the motor M fixed to the rear side outer end surface of the gear housing 5 by a joint 62 and receives the driving force of the motor M.

The discharge port 28 communicated with the discharge region of the pump chamber 14 as the final stage is connected to the muffler 63 and the discharge mechanism 64, and the gas discharged from the pump chamber 14 is discharged to the exhaust gas processing apparatus (not shown) via the discharge mechanism 64. Is done.

The multi-stage Roots pump having the above configuration operates as follows. The rotating shaft 29 is rotated by the driving force of the motor M, and the rotating shaft 30 is rotated via the gears 59 and 60. Rotating shaft 29
The rotors 31 to 35 and the rotors 36 to 40 of the rotating shaft 30 are rotated in the pump chambers 10 to 14 in pairs. As the rotary shafts 29 and 30 rotate, gas is sucked from the suction port 27.

The gas sucked into the suction area of the pump chamber 10 which is the first stage from the suction port 27 is the rotor 31,
It is transferred to the discharge region by 36 and sucked into the suction region of the adjacent second stage pump chamber 11 through the discharge passage 19, the communication space 15 and the suction passage 23 of the partition wall 6. The gas sucked into the pump chamber 11 is transferred to the discharge region by the rotors 32 and 37, and the discharge passage 20 in the partition wall 7.
Then, the air is sucked into the third pump chamber 12 through the communication space 16 and the suction passage 24. Similarly, the gas in the pump chamber 12 is sequentially transferred to the pump chamber 13 as the fourth stage and the pump chamber 14 as the final stage.

The gas sucked from the suction port 27 is sequentially compressed while being transferred from the pump chamber 10 to the pump chamber 14, and is discharged to the discharge port 28 as a high-temperature and high-pressure gas. For this reason, the partition walls 6-9
The rotor housing 3 including the rotary shafts 29 and 30 including the rotors 31 to 40 are thermally expanded and displaced in the thrust direction and the radial direction. The rotation shafts 29 and 30 are attached to the rotor housing 3 and the rear housing 4 so as to allow displacement in the thrust direction due to the thermal expansion. The rear side surfaces of the flange portions 29a and 30a formed so as to form stepped portions on the rotary shafts 29 and 30 positioned in the rear housing 4 are in contact with the front side end surfaces of the labyrinth mechanisms 57 and 58. Accordingly, the rotation shafts 29 and 30 are restricted from moving to the rear side by the bearings 51 and 52 which are support portions on one end side, and the flange portions 29a and 30a of the rotation shafts 29 and 30, the labyrinth mechanisms 57 and 58, the bearing 51, 52 constitutes a thrust direction movement restricting means. The flange portions 29a and 30a of the rotary shafts 29 and 30 may be formed by a circlip.
The multi-stage Roots pump has a structure in which the housing 1 is fixed to a mounting base (not shown) with an anti-vibration rubber (not shown) interposed therebetween, and the motor M is attached to the rear end surface of the housing 1 in a suspended state. Therefore, the thermal expansion of the housing 1 is absorbed by the vibration isolating rubber.

The first embodiment configured as described above operates as follows.
Regarding the state of each part during the operation of the multi-stage roots pump, the rotor 36 to the rotary shaft 30
A description will be given based on FIG. 3 and FIG. The gas sucked into the first-stage pump chamber 10 by the operation of the multistage roots pump is transferred to the final-stage pump chamber 14 while being sequentially compressed. In the pump chamber 14, a gas having a high temperature due to high compression is discharged. For this reason, the rotor housing 3 including the partition walls 6 to 9 and the rotating shaft 30 including the rotors 36 to 40 are thermally expanded in the radial direction and the thrust direction by thermal expansion.

Among these, since the thermal expansion in the thrust direction is only allowed to be displaced in one direction, it is displaced toward the gas suction portion side on the front side (see the arrow direction in FIG. 3). The displacement due to thermal expansion is greatest around the pump chamber 14. However, since the outer periphery of the rotor housing 3 is exposed to the outside air, the rotor housing 3 is always in a state of receiving a cooling effect including the partition walls 6 to 9. On the other hand, the rotary shaft 30 including the rotors 36 to 40 separated from the rotor housing 3 and housed therein does not receive a cooling effect by the outside air. Therefore, as indicated by the lengths of the arrows in FIG. 3, the relationship between the thermal expansion amount and the housing side thermal expansion α <the rotation shaft side thermal expansion β occurs.

In particular, a large gap 66 is generated between the front side wall surface of the rear housing 4 constituting the pump chamber 14 and the rear side wall surface of the rotor 40. Powder or the like mixed in the gas transferred through the pump chambers 10 to 14 is particularly likely to accumulate in the large gap 66, and a lump of foreign matter 67 (see FIG. 4) is generated here. Since the gap 66 is large during the operation of the multistage roots pump, there is no particular problem. However, when the multi-stage Roots pump is stopped, the heating source by the high temperature gas disappears, so that the whole is rapidly cooled.

FIG. 4 shows the stop of the multistage roots pump. The rotor housing 3 including the partition walls 6 to 9 and the rotary shaft 30 including the rotors 36 to 40 are displaced to the rear side so as to return to the initial setting position due to thermal contraction. The rotary shaft 30 including the rotors 36 to 40 having a large amount of thermal expansion also has a large amount of thermal contraction, and a relationship of housing side thermal contraction γ <rotational axis side thermal contraction δ occurs as indicated by the length of the arrow in FIG. However, foreign matter 67 accumulated during operation exists in the gap 66 of the pump chamber 14.

  When the rotor 40 attempts to return to the initial setting position, the foreign matter 67 is sandwiched between the rotor 40 and the front side wall surface of the rear housing 4 in the pump chamber 14 by the spring force of the coil spring 56. Although the foreign matter 67 becomes a large rotational resistance with respect to the rotor 40, in this embodiment, the rotating shaft 30 is maintained in a slightly displaced state toward the front side due to the extension of the coil spring 56. For this reason, the foreign matter 67 is prevented from being bitten by being strongly pressed between the rotor 40 and the front side wall surface of the rear housing 4 due to the thermal contraction of the rotor 40. Even if the foreign matter 67 accumulates in any gap between the pump chambers 10 to 14, it is between the rotors 36 to 40, the front side wall surface of the rear housing 4, the partition walls 6 to 9, and the rear side wall surface of the front housing 2. It is possible to prevent the foreign matter 67 from being caught in

When the multistage roots pump is instructed to restart after that, the pressing force of the rotor 40 against the foreign matter 67 is small and the frictional resistance is small. The foreign matter 67 is expected to be gradually removed by the gas pressure and the rotation of the rotor 40 during the re-operation of the multistage roots pump. Even if the foreign matter 67 remains deposited, the rotor 40 is not strongly pressed against the foreign matter 67 due to the extension of the coil spring 56, so that the multistage roots pump does not hinder the operation.

The first embodiment described above has the following operational effects.
(1) It is possible to suppress the generation of a large frictional resistance due to the accumulation of the foreign matter 67 with a simple configuration in which the coil springs 55 and 56 are urged to displace the rotation shafts 29 and 30 in the rotation axis direction. .
(2) The disc springs 45 and 46 and the coil spring 5 on the front side and the rear side of the housing 1, respectively.
By interposing 5 and 56, the initial setting positions of the rotors 36 to 40 in the pump chambers 10 to 14 can be easily positioned.
(3) The direction in which the coil springs 55 and 56 apply the urging force to the rotary shafts 29 and 30 is the same as the gas transfer direction in the multistage roots pump, and the flange portions 29a and 30a of the rotary shafts 29 and 30 are the same. The labyrinth mechanisms 57 and 58 and the bearings 51 and 52 can restrict the movement in the thrust direction on the final stage side of the multistage roots pump, and can effectively prevent leakage from the pump chamber 14 at the final stage.

The present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible within the scope of the spirit of the present invention, and can be implemented as follows.

(1) The first elastic member of the present invention is not limited to the coil springs 55 and 56, and may be a disc spring or an elastic member such as resin or rubber.
(2) The first elastic members such as the coil springs 55 and 56 are not limited to the rear side, and may be disposed at the front side or at an intermediate position between the rear side and the front side.

(3) The first elastic member indicated by the coil springs 55 and 56 is not limited to the configuration provided on the rotary shafts 29 and 30 as in the first embodiment, and the rotary shafts 29 and 30 are rotated. It is possible to dispose at another position as long as it can be biased in the axial direction. In the following description of each embodiment, numerals in parentheses indicate constituent members on the rotating shaft 30 side shown in FIG. For example, in the second embodiment shown in FIG. 7, the bearing 51 (52) is configured to be slidable integrally with the rotary shaft 29 (30) and the outer ring of the bearing 51 (52) is attached to the holder 49 (50). Installed restriction plate 68 (
69). Accordingly, the rotation shaft 29 (30) and the bearing 51 (52) are restricted from moving to the rear side (right side in FIG. 7), but are allowed to move to the front side (left side in FIG. 7) due to thermal expansion. . The coil spring 70 (71) which is the first elastic member of the present invention is a holder 49 (50).
Is disposed between the projection 72 (73) formed on the front side and the outer ring of the bearing 51 (52). The coil spring 70 (71) biases the rotating shaft 29 (30) and the bearing 51 (52) in a direction opposite to the direction moved by thermal expansion (the right side in FIG. 7). The second embodiment can be expected to have the same effect as the first embodiment.

(4) In the third embodiment shown in FIG. 8, the bearing 51 (52) and the holder 49 (50) are configured to be slidable integrally with the rotary shaft 29 (30). Bearing 51 (52), holder 49
(50) and the rotary shaft 29 (30), the flange portions 29a, 30a of the rotary shaft 29 (30) shown in FIGS. 1 and 2 come into contact with the labyrinth mechanisms 57, 58, so that the rear side (FIG.
Movement to the right side) is restricted, and movement to the front side (left side in FIG. 8) due to thermal expansion is allowed. The coil spring 74 (75) which is the first elastic member of the present invention is the holder 49 (50
) Between the rear-side protruding portion 76 (77) and the rear-side cutout portion 78 (79) of the rear housing 4. The coil spring 74 (75) has a rotating shaft 29 (30) and a bearing 51 (52).
The holder 49 (50) is urged in the direction opposite to the direction moved by thermal expansion (the right side in FIG. 8). The third embodiment can be expected to have the same effect as that of the first embodiment.

(5) Instead of the disc springs 45 and 46 which are the second elastic members, a rigid regulating member capable of regulating the movement of the rotary shafts 29 and 30 to the rear side by the coil springs 55 and 56 is provided. Also, the operational effects of the present invention can be obtained.
(6) The displacement direction of the rotor housing 3 including the partition walls 6 to 9 and the rotating shafts 29 and 30 including the rotors 31 to 40 due to thermal expansion is not limited to the suction unit side as in the first embodiment, and is a discharge unit. You may comprise so that it may displace only to the side.
(7) The housing 1 does not necessarily need to be divided into two parts, and can be formed as an integral type or divided into three or more parts.
(8) The present invention is not limited to a multi-stage roots pump, and can be implemented in a roots pump having one pump chamber.
(9) The present invention is not limited to the roots pump, and can be implemented in a rotary vacuum pump using, for example, a screw pump or a gear pump.

DESCRIPTION OF SYMBOLS 1 Housing 2 Front housing 3 Rotor housing 4 Rear housing 5 Gear housing 6-9 Partition wall 10-14 Pump chamber 15-18 Communication space 19-22 Discharge passage 23-26 Suction passage 27 Suction port 28 Discharge port 29, 30 Rotating shaft 31 to 40 Rotor 41, 42, 51, 52 Bearing 45, 46 Disc spring 53, 54 Spring receiving ring 55, 56, 70, 71, 74, 75 Coil spring 64 Discharge mechanism 66 Clearance 67 Foreign matter 72, 73, 76, 77 Protrusion part 78, 79 Notch part M Motor

Claims (6)

In a rotary vacuum pump in which a pump chamber is provided in a housing, a rotor arranged in the pump chamber is provided on a plurality of rotating shafts, and a gas in the pump chamber is transferred by the rotation of the plurality of rotating shafts to perform a suction action ,
The rotating shaft includes thrust direction movement restricting means that allows displacement due to thermal expansion in the thrust direction of the rotor and the rotating shaft generated during operation of the rotary vacuum pump in only one direction, and the heat with respect to the rotating shaft. A rotary vacuum pump comprising a first elastic member that applies a biasing force in a direction opposite to a direction allowing expansion. 2. The rotary vacuum pump according to claim 1, further comprising a second elastic member that applies an urging force in a direction allowing the thermal expansion to the rotation shaft.   The thrust direction movement restricting means includes a step portion formed on the rotating shaft and a bearing supporting the rotating shaft, and the thrust direction movement is controlled by direct or indirect contact between the step portion and the bearing. The rotary vacuum pump according to claim 1 or 2, wherein the rotary vacuum pump is regulated.   The rotary vacuum pump according to claim 3, wherein the first elastic member is disposed between the stepped portion and the bearing. The rotary vacuum pump according to any one of claims 1 to 4, wherein the rotary vacuum pump is a multistage roots pump.   The direction in which the first elastic member applies an urging force to the rotating shaft is the same as the gas transfer direction in the multi-stage Roots pump, and the thrust direction movement restricting means is provided in the multi-stage Roots pump. The rotary vacuum pump according to claim 5, wherein the rotary vacuum pump is disposed on a final stage side.