TW202346713A - Vacuum pump - Google Patents

Abstract

Provided herein is a vacuum pump being able satisfactorily discharge powder contained in gas from a rotor chamber. The vacuum pump (1) is provided with: a pump housing (6) having a rotor chamber (5) inside; a pair of Roots rotor (8) arranged in the rotor chamber (5); and a pair of rotating shafts (9) supporting the above a pair of Roots rotor (8). The pump housing (6) has a gas inlet port (12) and a gas outlet port (13) connected to the rotor chamber (5). A connecting part (25) of the inner wall (22) forming the rotor chamber (5) and an inner wall (23) forming the gas outlet port (13) is located at the center of rotation (RC) and a lower stop (LP) of each Roots rotor (8). A lower stop (LP) on the rotor centerline (CL), or outside of the rotor centerline (CL).

Description

Vacuum pump

The present invention relates to a vacuum pump, and particularly to a vacuum pump suitable for exhausting processing gas used in the manufacture of semiconductor devices, liquid crystal panels, LEDs, solar cells, etc.

In the manufacturing process of semiconductor devices, liquid crystal panels, LEDs, solar cells, etc., processing gases are introduced into the processing chamber to perform various processes such as etching processing and CVD processing. The processing gas introduced into the processing chamber is exhausted by the vacuum pump. Generally speaking, vacuum pumps used in these manufacturing processes that require high cleanliness are so-called dry vacuum pumps that do not use oil in the gas flow path. A typical example of such a dry vacuum pump is a positive displacement vacuum pump that rotates a pair of Roots rotors arranged in a rotor chamber in opposite directions to transfer gas.

[Prior technical literature]

[Patent Document]

Patent Document 1: Japanese Patent Application Publication No. 2010-101321

The processing gas may contain powder composed of by-products. Such powder flows into the vacuum pump together with the processing gas. Most of the powder is discharged from the vacuum pump together with the processing gas, but part of the powder stays in the rotor chamber and gradually accumulates in the rotor chamber. Powder accumulates on the inner wall of the rotor chamber and the outer surface of the Roots rotor, and as a result, may hinder the rotation of the Roots rotor.

Therefore, the present invention provides a vacuum pump capable of efficiently discharging powder contained in gas from a rotor chamber.

In one aspect, a vacuum pump is provided, including: a pump housing having at least one rotor chamber inside; at least a pair of Roots rotors disposed in the rotor chamber; and at least a pair of rotation shafts supporting the at least one rotor chamber. A pair of Roots rotors; the pump housing system has a gas inlet and a gas outlet connected to the rotor chamber; the connection portion between the inner wall forming the rotor chamber and the inner wall forming the gas outlet is located through the rotation of each Roots rotor The rotor center line extending between the center and the bottom dead center, or located outside the aforementioned rotor center line.

In one aspect, the width of the gas outlet is greater than the width of the gas inlet.

In one aspect, the at least one pair of Roots rotors is at least one pair of two-blade Roots rotors, and the angle between the straight line from the rotation center to the connecting portion with respect to the center line of the rotors is in the range of 0 to 35 degrees. .

In one aspect, the at least one pair of Roots rotors is at least one pair of three-blade Roots rotors, and the angle between the straight line from the rotation center to the connecting portion with respect to the center line of the rotors is in the range of 0 to 45 degrees. within.

In one aspect, the aforementioned at least one pair of Roots rotors includes a pair of first Roots rotors and a pair of second Roots rotors, and the pair of second Roots rotors are arranged on the aforementioned pair in the gas transport direction. On the downstream side of the first Roots rotor; the aforementioned at least one rotor chamber system includes the aforementioned pair of third A first rotor chamber of a Roots rotor and a second rotor chamber equipped with the aforementioned pair of second Roots rotors; the aforementioned pump housing system has a first gas inlet and a first gas outlet connected to the aforementioned first rotor chamber, and The second gas inlet and the second gas outlet of the aforementioned second rotor chamber are connected; the first connection portion between the inner wall forming the aforementioned first rotor chamber and the inner wall forming the aforementioned first gas outlet is located through each first Roots rotor. The rotation center and the outer side of the first rotor center line extending at the bottom dead center; the second connection portion between the inner wall forming the second rotor chamber and the inner wall forming the second gas outlet is located through each second Roots The rotation center of the rotor is on the second rotor center line extending from the bottom dead center, or is located outside the second rotor center line; the width of the first gas outlet is greater than the width of the second gas outlet.

According to the present invention, the width of the gas outlet communicating with the rotor chamber becomes larger, making it difficult for powder contained in the gas to stay in the rotor chamber. As a result, the powder is discharged from the rotor chamber together with the gas, and the amount of powder accumulated in the rotor chamber can be reduced.

1: Vacuum pump

2: Electric motor

2A:Motor rotor

2B: Motor stator

5,5A,5B,5C,5D,5E: Rotor chamber

6: Pump housing

6A, 6B: Side wall

8,8A,8B,8C,8D,8E:Roots rotor

9:Rotation axis

12,12A,12B,12C,12D,12E: Gas inlet

13,13A,13B,13C,13D,13E: Gas outlet

14: Motor housing

16:Gear housing

17:Bearing

18:Bearing

20:Gear

22: Inner wall of pump housing

22A, 22E: Inner wall of rotor chamber

23,23A,23E: Inner wall of gas outlet

25:Connection part

25A:Connection part

CL, CL1, CL2: rotor center line

CP: Center point of the rotor chamber

LP, LP1, LP2: Bottom dead center of Roots rotor

NL, NL1, NL2: straight line

RC, RC1, RC2: Rotation center of Roots rotor

W1,W2,W3,W4,W5,W6: Width

α, α1, α2: angle

FIG. 1 is a cross-sectional view showing an embodiment of the vacuum pump device.

Fig. 2 is a cross-sectional view along line A-A in Fig. 1 .

3 is a cross-sectional view showing another embodiment of the connection portion between the inner wall forming the rotor chamber and the inner wall forming the gas outlet.

4 is a cross-sectional view showing another embodiment of the connection portion between the inner wall forming the rotor chamber and the inner wall forming the gas outlet.

5 is a cross-sectional view showing another embodiment of the gas outlet.

FIG. 6 is a cross-sectional view showing an embodiment of the three-blade Roots rotor.

7 is a cross-sectional view showing another embodiment of the vacuum pump device.

Fig. 8 is a cross-sectional view taken along line B-B in Fig. 7 .

Fig. 9 is a cross-sectional view taken along line C-C in Fig. 7 .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing an embodiment of the vacuum pump device. The vacuum pump device of the embodiment described below is a positive displacement vacuum pump device. In particular, the vacuum pump device shown in FIG. 1 is a so-called dry vacuum pump device that does not use oil in the gas flow path. Since the vaporized oil in the dry vacuum pump device does not flow to the upstream side, it can be suitably used in a semiconductor device manufacturing device that requires high cleanliness.

As shown in FIG. 1 , the vacuum pump device includes a vacuum pump 1 and an electric motor 2 that drives the vacuum pump 1 . The vacuum pump 1 includes a pump housing 6 having a rotor chamber 5 inside, a pair of Roots rotors 8 arranged in the rotor chamber 5 , and a pair of rotation shafts 9 supporting the pair of Roots rotors 8 . Each Roots rotor 8 and each rotation shaft 9 may be an integral structure. In FIG. 1 , only one Roots rotor 8 and one rotation shaft 9 are depicted, but a pair of Roots rotors 8 are arranged in the rotor chamber 5 and supported by a pair of rotation shafts 9 respectively. The electric motor 2 is connected to one of the pair of rotating shafts 9 . In one embodiment, a pair of electric motors 2 and a pair of rotation shafts 9 may be respectively connected.

The Roots rotor 8 in this embodiment is a single-stage pump rotor, but in one embodiment, the Roots rotor 8 may also be a multi-stage pump rotor.

The pump housing 6 has a gas inlet 12 and a gas outlet 13 in communication with the rotor chamber 5 . The gas inlet 12 is connected to a chamber (not shown) that is to be filled with gas. In one example, the gas inlet 12 is connected to a processing chamber of a semiconductor device manufacturing apparatus, and the vacuum pump 1 is used to exhaust the processing gas introduced into the processing chamber.

The vacuum pump 1 further includes a gear housing 16 located outside the side wall 6A of the pump housing 6 . A pair of gears 20 meshing with each other is arranged inside the gear housing 16 . Additionally, only one gear 20 is depicted in FIG. 1 . These gears 20 are respectively fixed to the rotating shaft 9 . The motor 2 is rotated by a motor driver (not shown), and one rotation shaft 9 connected to the motor 2 rotates the other rotation shaft 9 not connected to the motor 2 in the opposite direction via the gear 20 .

The rotating shaft 9 is rotatably supported by a bearing 17 held by one side wall 6A of the pump housing 6 and a bearing 18 held by the other side wall 6B of the pump housing 6 . The electric motor 2 has a motor housing 14 located outside the side wall 6B of the pump housing 6 , and a motor rotor 2A and a motor stator 2B arranged in the motor housing 14 .

In one embodiment, a pair of electric motors 2 are provided, respectively connected to a pair of rotation shafts 9 . The pair of electric motors 2 are synchronously rotated in opposite directions by a motor driver (not shown), so that the pair of rotating shafts 9 and the pair of Roots rotors 8 are synchronously rotated in opposite directions. The function of the gear 20 in this case is to prevent the synchronous rotation of the Roots rotor 8 from being out of balance due to sudden external factors.

When the Roots rotor 8 rotates due to the electric motor 2 , gas is sucked into the pump housing 6 from the gas inlet 12 . The gas is transported from the gas inlet 12 to the gas outlet 13 by the rotating Roots rotor 8 .

Fig. 2 is a cross-sectional view along line A-A in Fig. 1 . As shown in FIG. 2 , each Roots rotor 8 of this embodiment is a two-blade Roots rotor. The gas inlet 12 is located on one side of the pump housing 6 , and the gas outlet 13 is located on the opposite side of the pump housing 6 . A pair of Roots rotors 8 is located between the gas inlet 12 and the gas outlet 13 . The Roots rotor 8 is not in contact with the inner wall 22 of the pump housing 6 forming the rotor chamber 5, and Moreover, the two Roots rotors 8 are not in contact with each other. These Roots rotors 8 rotate in opposite directions as indicated by arrows in the rotor chamber 5 .

As the Roots rotor 8 rotates, a closed space is formed between the outer surface of the Roots rotor 8 and the inner wall 22 forming the rotor chamber 5 . The gas flowing in from the gas inlet 12 fills the enclosed space, and the gas is transported from the gas inlet 12 to the gas outlet 13 by rotating the pair of Roots rotors 8 in opposite directions. By continuously transporting the gas in such a closed space, the gas is exhausted by the vacuum pump 1 .

The gas inlet 12 and the gas outlet 13 are in communication with the rotor chamber 5 . The inner wall 23 forming the gas outlet 13 is connected to the inner wall 22 forming the rotor chamber 5 . As shown in FIG. 2 , the connection portion 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 is located outside the rotor center line CL. The rotor center line CL is a straight line extending through the rotation center RC and the bottom dead center LP of each Roots rotor 8 . The bottom dead center LP of the Roots rotor 8 is equivalent to the lowermost end of the rotating Roots rotor 8 . Here, “located outside the rotor center line CL” means a position across the rotor center line CL from the center point CP of the rotor chamber 5 .

The width W2 of the gas outlet 13 is larger than the width W1 of the gas inlet 12 . For example, the width W2 of the gas outlet 13 is 1.1 to 2.0 times the width W1 of the gas inlet 12, preferably 1.7 times.

Examples of gases processed by the vacuum pump 1 of this embodiment include processing gases used in semiconductor device manufacturing equipment such as CVD equipment and etching equipment. The processing gas contains powder composed of by-products. As can be seen from FIG. 2 , since the width W2 of the gas outlet 13 is larger than the width W1 of the gas inlet 12 , it is difficult for the powder to stay in the rotor chamber 5 . As a result, it is difficult for the powder to accumulate in the rotor chamber 5 . Therefore, according to this embodiment, it is possible to prevent rotation failure (for example, rotation stop) of the Roots rotor 8 due to accumulation of powder in the rotor chamber 5 .

In this embodiment, each Roots rotor 8 is a two-blade Roots rotor. In order to transport gas from the gas inlet 12 to the gas outlet 13 , a closed space needs to be formed between the outer surface of the Roots rotor 8 and the inner wall 22 forming the rotor chamber 5 . From this point of view, the connection 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 is closer to the gas outlet 13 than to the gas inlet 12 . The angle α of the straight line NL from the rotation center RC to the connecting portion 25 with respect to the rotor center line CL is in the range of 0 to 35 degrees. In one embodiment, the connecting portion 25 may also be located on the rotor centerline CL.

Although the width W2 of the gas outlet 13 is larger than the width W1 of the gas inlet 12, as mentioned above, a closed space is formed between the outer surface of the Roots rotor 8 and the inner wall 22 forming the rotor chamber 5. Therefore, the discharge of the vacuum pump 1 Gas performance is not substantially reduced.

In the embodiment shown in FIG. 2 , the arrangement of the connecting portion 25 associated with one of the two Roots rotors 8 and the rotor center line CL has been described. However, the connection associated with the other Roots rotor 8 The arrangement of the parts and the center line of the rotor is also the same, so repeated explanations and illustrations of symbols are omitted.

As shown in FIG. 3 , the connection portion 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 may have an arc-shaped cross section. Alternatively, as shown in FIG. 4 , the connection portion 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 may have a chamfered cross section. According to the shape shown in FIGS. 3 and 4 , gas turbulence is less likely to occur, and the powder can be smoothly transported to the gas outlet 13 .

In the embodiment shown in FIGS. 2 to 4 , the inner wall 23 forming the gas outlet 13 is parallel to the rotor centerline CL, and the width of the gas outlet 13 is constant. As shown in FIG. 5 , in one embodiment, the inner wall 23 forming the gas outlet 13 may be inclined outward with the distance from the center point CP of the rotor chamber 5 . That is, the width of the gas outlet 13 may also be the same as the distance from the rotor The distance between the center points CP of the chamber 5 gradually becomes larger together. By adopting such a shape, the gas containing the powder can pass through the gas outlet 13 smoothly.

As shown in Figure 6, the Roots rotor 8 may also be a three-blade Roots rotor. In the embodiment shown in FIG. 6 , the connection portion 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 is also located through the rotation center RC and the bottom dead center LP of each Roots rotor 8 On the extended rotor center line CL, or located outside the rotor center line CL. The structure of the embodiment of FIG. 6 which is not particularly described is the same as that of the embodiment described with reference to FIG. 2 , and therefore repeated description is omitted.

As in the embodiment described with reference to FIG. 2 , a closed space needs to be formed between the outer surface of the Roots rotor 8 and the inner wall 22 forming the rotor chamber 5 . From this point of view, in the embodiment shown in FIG. 6 , the angle α of the straight line NL from the rotation center RC to the connecting portion 25 with respect to the rotor center line CL is in the range of 0 to 45 degrees.

Although not shown in the figure, the Roots rotor 8 may also be a Roots rotor with four or more blades. In this case, the connection portion 25 between the inner wall 22 forming the rotor chamber 5 and the inner wall 23 forming the gas outlet 13 is also located on the rotor center line CL extending through the rotation center RC and the bottom dead center LP of each Roots rotor 8 on, or outside the rotor centerline CL. Since the width of the gas outlet 13 is larger than the width of the gas inlet 12 , it is difficult for the powder to stay in the rotor chamber 5 , and as a result, it is difficult for the powder to accumulate in the rotor chamber 5 .

FIG. 7 is a cross-sectional view showing another embodiment of the vacuum pump 1 . The vacuum pump 1 of this embodiment is a multi-stage vacuum pump. The description of the embodiment with reference to FIGS. 1 to 6 can also be applied to the structure and operation of this embodiment, and therefore the repeated description is omitted.

As shown in FIG. 7 , the vacuum pump 1 is provided with: a pump housing 6 having a plurality of rotor chambers 5A to 5E inside; a plurality of pairs of Roots rotors 8A to 8E respectively arranged in the rotor chambers 5A to 5E; and a plurality of pairs of Roots rotors that are supported. There are a pair of rotating shafts 9 of the rotors 8A~8E. The Roots rotors 8A to 8E and the rotating shaft 9 may be an integral structure. In Figure 1, only a set of Roots rotors 8A~8E and a rotating shaft 9 are depicted. However, a plurality of pairs of Roots rotors 8A to 8E are respectively arranged in the rotor chambers 5A to 5E and supported by a pair of rotating shafts 9 . The electric motor 2 is connected to one of the pair of rotating shafts 9 . In one embodiment, a pair of electric motors 2 may be connected to a pair of rotation shafts 9 respectively.

Roots rotors 8A to 8E and rotor chambers 5A to 5E are arranged along the gas transport direction. That is, the Roots rotor 8A and the rotor chamber 5A are located on the most upstream side in the gas conveyance direction in the pump casing 6 . Roots rotor 8B and rotor chamber 5B are located on the downstream side of Roots rotor 8A and rotor chamber 5A. Roots rotor 8C and rotor chamber 5C are located on the downstream side of Roots rotor 8B and rotor chamber 5B. Roots rotor 8D and rotor chamber 5D The Roots rotor 8E and the rotor chamber 5E are located downstream of the Roots rotor 8C and the rotor chamber 5C, and the Roots rotor 8E and the rotor chamber 5E are located downstream of the Roots rotor 8D and the rotor chamber 5D. The Roots rotor 8E and the rotor chamber 5E are located on the most downstream side in the gas conveyance direction in the pump casing 6 .

The pump housing 6 has a gas inlet 12A and a gas outlet 13A connected to the rotor chamber 5A; a gas inlet 12B and a gas outlet 13B connected to the rotor chamber 5B; a gas inlet 12C and a gas outlet 13C connected to the rotor chamber 5C; and a gas inlet 12C and a gas outlet 13C connected to the rotor chamber 5C. The gas inlet 12D and the gas outlet 13D communicate with the chamber 5D; and the gas inlet 12E and the gas outlet 13E communicate with the rotor chamber 5E. The gas outlet 13A communicates with the gas inlet 12B through a flow path not shown. The gas outlet 13B communicates with the gas inlet 12C through a flow path not shown. The gas outlet 13C communicates with the gas inlet 12D through a flow path not shown. , the gas outlet 13D communicates with the gas inlet 12E via a flow path (not shown).

When the motor 2 rotates the Roots rotors 8A to 8E, gas is sucked into the rotor chamber 5A through the gas inlet 12A. The gas is sequentially compressed by the Roots rotors 8A to 8E in the rotor chambers 5A to 5E, and is discharged from the pump housing 6 through the gas outlet 13E.

Fig. 8 is a cross-sectional view taken along line B-B in Fig. 7 . As shown in FIG. 8 , Roots rotors 8A to 8E of this embodiment are three-blade Roots rotors. The connection portion 25A between the inner wall 22A forming the rotor chamber 5A and the inner wall 23A forming the gas outlet 13A is located through the rotation center RC1 of the Roots rotor 8A. and outside the rotor centerline CL1 of the bottom dead center LP1. The angle α1 of the straight line NL1 from the rotation center RC1 of the Roots rotor 8A to the connecting portion 25A with respect to the rotor center line CL1 is in the range of 0 to 45 degrees. The width W4 of the gas outlet 13A is larger than the width W3 of the gas inlet 12A.

Fig. 9 is a cross-sectional view taken along line C-C in Fig. 7 . As shown in FIG. 9 , the connection portion 25E between the inner wall 22E forming the rotor chamber 5E and the inner wall 23E forming the gas outlet 13E is located outside the rotor center line CL2 passing through the rotation center RC2 and the bottom dead center LP2 of the Roots rotor 8E. In one implementation, the connection portion 25E may also be located on the rotor centerline CL2. The angle α2 between the rotation center RC2 of the Roots rotor 8E and the straight line NL2 connecting the connecting portion 25E with respect to the rotor center line CL2 is in the range of 0 to 45 degrees, and is smaller than the angle α1 shown in FIG. 8 . The width W6 of the gas outlet 13E is larger than the width W5 of the gas inlet 12E.

Although not shown in the figure, the connection portion forming the inner wall of the rotor chamber 5B and the inner wall forming the gas outlet 13B, the connection portion forming the inner wall of the rotor chamber 5C and the inner wall forming the gas outlet 13C, and the inner wall forming the rotor chamber 5D. The connection parts of the wall and the inner wall forming the gas outlet 13D are respectively located outside the corresponding rotor center line, or on the corresponding rotor center line.

According to the embodiment described with reference to FIGS. 7 to 9 , the widths of the gas outlets 13A to 13E are respectively larger than the widths of the gas inlets 12A to 12E. Therefore, it is difficult for the powder to stay in the rotor chambers 5A to 5E. As a result, it is difficult for the powder to stay in the rotor chambers 5A to 5E. Accumulated in rotor chambers 5A~5E.

According to a comparison between FIG. 8 and FIG. 9 , it can be seen that the width W4 of the gas outlet 13A shown in FIG. 8 is larger than the width W6 of the gas outlet 13E shown in FIG. 9 . This is based on the following powder flow simulation results: The powder flow simulation results show that increasing the width of the gas outlet on the low pressure side and making the width of the gas outlet relatively small on the atmospheric pressure side promotes the discharge of powder. According to this embodiment, the powder can be discharged from the pump casing 6 through the rotor chambers 5A to 5E in order.

The relationship between the widths of the gas outlets 13A to 13E is not particularly limited, as long as the width of the gas outlet 13A is larger than the width of the gas outlet 13E. For example, you can also Therefore, the widths of the gas outlets 13A, 13B, and 13C are the same as each other and are larger than the widths of the gas outlets 13D and 13E. In other examples, the widths of the gas outlets 13A, 13B, 13C, 13D, and 13E may gradually become smaller along with the gas transport direction in the pump casing 6 .

The vacuum pump 1 shown in FIG. 7 is a five-stage vacuum pump, but the number of stages of the Roots rotor 8 is not particularly limited. For example, the vacuum pump 1 may be a two-stage vacuum pump including two pairs of Roots rotors, or a multi-stage vacuum pump including six or more pairs of Roots rotors.

The above-mentioned embodiments are described so that a person having ordinary knowledge in the technical field to which the present invention belongs can implement the present invention. Anyone skilled in the art can, of course, implement the respective modifications of the above embodiments, and the technical idea of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but should be construed to have the broadest scope of the technical idea defined by the claims.

5:Rotor chamber

6: Pump housing

8:Roots rotor

12:Gas inlet

13:Gas outlet

22: Inner wall of pump housing

23: Inner wall of gas outlet

25:Connection part

CL: rotor center line

CP: Center point of the rotor chamber

LP: Bottom dead center of Roots rotor

NL: straight line

RC: Rotation center of Roots rotor

W1, W2: Width

Claims (7)

A vacuum pump having: a pump housing having at least one rotor chamber internally; At least one pair of Roots rotors is arranged in the aforementioned rotor chamber; and At least one pair of rotating shafts supports the aforementioned at least one pair of Roots rotors; The aforementioned pump housing system has a gas inlet and a gas outlet connected to the aforementioned rotor chamber; The connection portion between the inner wall forming the rotor chamber and the inner wall forming the gas outlet is located on a rotor center line extending through the rotation center and bottom dead center of each Roots rotor, or is located outside the rotor center line. The vacuum pump according to claim 1, wherein, The width of the aforementioned gas outlet is greater than the width of the aforementioned gas inlet. A vacuum pump as claimed in claim 1 or 2, wherein, The at least one pair of Roots rotors is at least one pair of two-blade Roots rotors, and the angle between the straight line from the rotation center to the connecting portion with respect to the center line of the rotors is in the range of 0 to 35 degrees. A vacuum pump as claimed in claim 1 or 2, wherein, The at least one pair of Roots rotors is at least one pair of three-blade Roots rotors, and the angle between the straight line from the rotation center to the connecting portion with respect to the center line of the rotors is in the range of 0 to 45 degrees. A vacuum pump as claimed in claim 1 or 2, wherein, The at least one pair of Roots rotors includes a pair of first Roots rotors and a pair of second Roots rotors, and the pair of second Roots rotors is disposed in the gas transport direction between the pair of first Roots rotors. the downstream side; The at least one rotor chamber includes a first rotor chamber configured with the pair of first Roots rotors, and a second rotor chamber configured with the pair of second Roots rotors; The aforementioned pump housing system has a first gas inlet and a first gas outlet communicated with the aforementioned first rotor chamber, and a second gas inlet and a second gas outlet communicated with the aforementioned second rotor chamber; The first connection portion between the inner wall forming the first rotor chamber and the inner wall forming the first gas outlet is located outside the first rotor center line extending through the rotation center and the bottom dead center of each first Roots rotor. ; The second connection portion between the inner wall forming the second rotor chamber and the inner wall forming the second gas outlet is located on a second rotor center line extending through the rotation center and bottom dead center of each second Roots rotor, or Located outside the center line of the aforementioned second rotor; The width of the first gas outlet is greater than the width of the second gas outlet. The vacuum pump according to claim 3, wherein, The at least one pair of Roots rotors includes a pair of first Roots rotors and a pair of second Roots rotors, and the pair of second Roots rotors is disposed in the gas transport direction between the pair of first Roots rotors. the downstream side; The at least one rotor chamber includes a first rotor chamber configured with the pair of first Roots rotors, and a second rotor chamber configured with the pair of second Roots rotors; The aforementioned pump housing system has a first gas inlet and a first gas outlet communicated with the aforementioned first rotor chamber, and a second gas inlet and a second gas outlet communicated with the aforementioned second rotor chamber; The first connection portion between the inner wall forming the first rotor chamber and the inner wall forming the first gas outlet is located outside the first rotor center line extending through the rotation center and the bottom dead center of each first Roots rotor. ; The second connection portion between the inner wall forming the second rotor chamber and the inner wall forming the second gas outlet is located on a second rotor center line extending through the rotation center and bottom dead center of each second Roots rotor, or Located outside the center line of the aforementioned second rotor; The width of the first gas outlet is greater than the width of the second gas outlet. The vacuum pump according to claim 4, wherein, The at least one pair of Roots rotors includes a pair of first Roots rotors and a pair of second Roots rotors, and the pair of second Roots rotors is disposed in the gas transport direction between the pair of first Roots rotors. the downstream side; The at least one rotor chamber includes a first rotor chamber configured with the pair of first Roots rotors, and a second rotor chamber configured with the pair of second Roots rotors; The aforementioned pump housing system has a first gas inlet and a first gas outlet communicated with the aforementioned first rotor chamber, and a second gas inlet and a second gas outlet communicated with the aforementioned second rotor chamber; The first connection portion between the inner wall forming the first rotor chamber and the inner wall forming the first gas outlet is located outside the first rotor center line extending through the rotation center and the bottom dead center of each first Roots rotor. ; The second connection portion between the inner wall forming the second rotor chamber and the inner wall forming the second gas outlet is located on a second rotor center line extending through the rotation center and bottom dead center of each second Roots rotor, or Located outside the center line of the aforementioned second rotor; The width of the first gas outlet is greater than the width of the second gas outlet.

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