Vacuum pump

Abstract

A vacuum pump with improved back pressure characteristics during large flow exhaust. The vacuum pump (1) includes a frame (2), a rotor cylinder portion (23), and a stator cylinder portion (6). The frame (2) has a gas suction port (14) for suctioning gas and a gas exhaust port (16) for exhausting the suctioned gas. The rotor cylinder portion (23) is housed in the frame (2). The stator cylinder portion (6) is housed in the frame (2) and is disposed opposite the rotor cylinder portion (23). A thread groove (60) is formed on the facing surface of one of the stator cylinder portion (6) and the rotor cylinder portion (23). The end (6b) on the exhaust side is smaller than the end (6a) on the suction side with respect to the groove depth (D) of the thread groove (60). The suction side is larger than the exhaust side with respect to the reduction ratio of the groove depth (D).

Description

Technical Field

[0001] This invention relates to a vacuum pump. Background Technology

[0002] Vacuum pumps are used in fields such as semiconductor manufacturing equipment to create a high vacuum environment (see, for example, Patent Document 1).

[0003] The vacuum pump shown in Patent Document 1 includes a turbine pump section disposed on the intake port side and a drag pump section disposed on the exhaust port side.

[0004] When using a turbomolecular pump for exhaust, the performance indicators include the intake pressure relative to the flow rate of the gas. As the gas flow rate increases, the intake pressure increases.

[0005] In addition, back pressure characteristics are another performance indicator used when using a turbomolecular pump for exhaust. Back pressure characteristics represent the change in intake pressure as the exhaust port pressure of the turbomolecular pump increases, given a constant amount of gas introduced. As the exhaust port pressure increases, the number of gas molecules flowing backward from the exhaust side to the intake side increases, thus increasing the intake port pressure. A higher exhaust port pressure at which the intake pressure begins to rise reduces the number of backward-flowing gas molecules, resulting in better back pressure characteristics.

[0006] [Existing Technical Documents]

[0007] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2021-102926 Summary of the Invention

[0009] [The problem the invention aims to solve]

[0010] On the other hand, in recent years, the gas flow rate to turbomolecular pumps has tended to increase, requiring a reduction in the intake pressure during high-flow exhaust.

[0011] To reduce the intake pressure during high-flow exhaust, it is effective to design the drag pump section to increase its flow conductance. However, with this design, not only does the number of gas molecules moving from the intake side to the exhaust side increase, but the number of gas molecules flowing backward from the exhaust side to the intake side also increases, thus worsening the back pressure characteristics.

[0012] The purpose of this invention is to provide a vacuum pump that can handle large-flow exhaust and improve back pressure characteristics.

[0013] [Technical means to solve the problem]

[0014] One embodiment of the vacuum pump of the present invention includes a housing, a rotor cylindrical portion, and a stator cylindrical portion. The housing has an intake port for drawing in gas and an exhaust port for discharging the drawn-in gas. The rotor cylindrical portion is housed in the housing. The stator cylindrical portion is housed in the housing and is disposed facing the rotor cylindrical portion. A threaded groove is formed on one of the facing surfaces of the stator cylindrical portion and the rotor cylindrical portion. Regarding the groove depth, the exhaust-side end is smaller than the intake-side end. Regarding the reduction ratio of the groove depth, the intake side is larger than the exhaust side.

[0015] [The effects of the invention]

[0016] Based on the above-described form of the present invention, a vacuum pump capable of handling large-flow exhaust and improving back pressure characteristics can be provided. Attached Figure Description

[0017] Figure 1 This is an external view of the vacuum pump according to Embodiment 1.

[0018] Figure 2 This is a perspective view of the stator cylinder of the vacuum pump in Embodiment 1 as seen from the suction side.

[0019] Figure 3 From and Figure 2 A perspective view of the stator cylinder of the vacuum pump in Embodiment 1, viewed from the opposite side.

[0020] Figure 4 (a) is a diagram showing the thread teeth near the suction side end of the stator cylinder of the vacuum pump in Embodiment 1, viewed from the inside. Figure 4 (b) is a diagram showing the thread teeth near the exhaust side end of the stator cylinder of the vacuum pump in Embodiment 1 as viewed from the inside.

[0021] Figure 5 This is a cross-sectional view of the stator cylinder of the vacuum pump in Embodiment 1, which is perpendicular to the thread angle.

[0022] Figure 6 This is a diagram showing the variation in the depth of the threaded grooves in the stator cylinder of the vacuum pump in Embodiment 1.

[0023] Figure 7 This is a graph showing the change in thread groove depth in the comparative example.

[0024] Figure 8 It is a graph showing the change in the intake side pressure relative to the exhaust side pressure of the tow pump section in Example 1 and Comparative Example 1.

[0025] Figure 9 It is a graph showing the change in the intake side pressure relative to the exhaust side pressure of the tow pump section in Example 1 and Comparative Example 1.

[0026] Figure 10 It is a graph showing the change in the intake side pressure relative to the exhaust side pressure of the tow pump section in Example 2 and Comparative Example 2.

[0027] Figure 11 It is a graph showing the change in the intake side pressure relative to the exhaust side pressure of the tow pump section in Example 2 and Comparative Example 2.

[0028] Figure 12 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the tow pump section in Examples 3, 4 and Comparative Example 2.

[0029] Figure 13 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the tow pump section in Examples 3, 4 and Comparative Example 2.

[0030] Figure 14 This is a diagram showing the change in the depth of the threaded grooves in the stator cylinder of the vacuum pump in Embodiment 2.

[0031] Figure 15 This is a diagram showing the change in the depth of the threaded groove in the stator cylinder of the vacuum pump in Embodiment 2.

[0032] Figure 16 This is a diagram showing the change in the depth of the threaded grooves in the stator cylinder of the vacuum pump in Embodiment 2.

[0033] Figure 17 This is a diagram showing the change in the depth of the threaded grooves in the stator cylinder of the vacuum pump in Embodiment 2.

[0034] Figure 18 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 5 to 7 and Comparative Example 4.

[0035] Figure 19 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 5 to 7 and Comparative Example 4.

[0036] Figure 20 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 8 to 10 and Comparative Example 5.

[0037] Figure 21 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 8 to 10 and Comparative Example 5.

[0038] Figure 22It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the tow pump section in Examples 11, 12 and Comparative Example 5.

[0039] Figure 23 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the tow pump section in Examples 11, 12 and Comparative Example 5.

[0040] Figure 24 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 13 to 15 and Comparative Example 5.

[0041] Figure 25 It is a graph showing the change of the suction side pressure relative to the exhaust side pressure of the towing pump section in Examples 13 to 15 and Comparative Example 5.

[0042] Figure 26 This is a diagram showing the variation in the thread groove depth in a modified embodiment.

[0043] [Explanation of Symbols]

[0044] 1: Vacuum pump

[0045] 2: Frame

[0046] 3: Rotor

[0047] 4: Motor

[0048] 5: Stator blade unit

[0049] 6: Stator cylindrical section

[0050] 6a: End

[0051] 6b: End

[0052] 6s: Inner circumferential surface

[0053] 8: Chassis

[0054] 9: Base

[0055] 10: Fixed flange

[0056] 11: First end

[0057] 12: Second end

[0058] 13: Side profile

[0059] 14: Intake port

[0060] 15: Base end

[0061] 16: Exhaust port

[0062] 20: Bolt

[0063] 21: Axis

[0064] 22: Rotor blade unit

[0065] 23: Rotor cylindrical section

[0066] 23s: outer periphery

[0067] 24A-24C: Bearings

[0068] 25: Rotor blades

[0069] 26: Motor rotor

[0070] 27: Motor stator

[0071] 28: Stator blades

[0072] 29a: Protective bearing

[0073] 29b: Protective bearing

[0074] 60: Threaded groove

[0075] 61: Main body of the cylindrical section

[0076] 61s: Inner circumferential surface

[0077] 62: Thread teeth

[0078] 62a: Frontend

[0079] 62': Threaded teeth

[0080] 63: Groove section

[0081] 71: Inhalation side

[0082] 72: Exhaust side section

[0083] 73: Changes

[0084] 74: End portion

[0085] 75: End portion

[0086] 1062: Thread teeth

[0087] P1: Turbine section

[0088] P2: Trailer Pump Unit

[0089] S1: First Internal Space

[0090] S2: Second Internal Space Detailed Implementation

[0091] Hereinafter, a vacuum pump according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0092] (Implementation Method 1)

[0093] The vacuum pump of Embodiment 1 will be described below.

[0094] (Overview of Vacuum Pump 1)

[0095] Figure 1 This is a cross-sectional view of the vacuum pump 1 according to the embodiment.

[0096] Vacuum pump 1 includes a turbine section P1 and a drag pump section P2. Turbine section P1 constitutes a turbomolecular pump. Dragging pump section P2 constitutes a grooved pump. Vacuum pump 1 is connected to an exhaust device that includes an exhaust target space. Gas from the exhaust target space is exhausted by turbine section P1, then by drag pump section P2, and finally exhausted outside vacuum pump 1.

[0097] like Figure 1 As shown, the vacuum pump 1 includes: a frame 2 (an example of a housing), a rotor 3, a motor 4, multiple stator blade units 5, and a stator cylindrical section 6. The frame 2 houses the rotor 3, the motor 4, the multiple stator blade units 5, and the stator cylindrical section 6.

[0098] (Frame 2)

[0099] The frame 2 has a housing 8, a base 9, and a fixing flange 10. The frame 2 is made of metal such as aluminum alloy or iron. The housing 8 is a cylindrical component with a fixing flange 10 at one end.

[0100] The housing 8 houses multiple stator blade units 5 and multi-stage rotor blade units 22 disposed on the rotor 3. The housing 8 has a first end portion 11, a second end portion 12, and a side portion 13.

[0101] The first end 11 is mounted on the exhaust device. An intake port 14 is provided at the first end 11. The second end 12 is located on the side opposite to the fixed flange 10 in the axial direction A1 of the rotor 3. The second end 12 is connected to the base 9. The side portion 13 connects the first end 11 and the second end 12. A first internal space S1 is formed inside the housing 8.

[0102] The base 9 is configured to block the opening at the second end 12 of the housing 8. The base 9 houses the stator cylindrical portion 6 and the rotor cylindrical portion 23 disposed on the rotor 3. The base 9 has a base end 15 and an exhaust port 16. The base end 15 is connected to the second end 12 of the housing 8. A second internal space S2 is formed inside the base 9. The second internal space S2 communicates with the first internal space S1. The exhaust port 16 communicates with the second internal space S2.

[0103] A fixed flange 10 is connected to the housing 8. The fixed flange 10 protrudes from the housing 8. The fixed flange 10 is fixed to the exhaust device by bolts 20. Furthermore, the term "connection" is defined as including the joining of mutually independent components. Additionally, the term "connection" is defined as including the connection of various parts within a single component.

[0104] (Rotor 3)

[0105] The rotor 3 has a shaft 21, a multi-stage rotor blade unit 22, and a rotor cylindrical part 23.

[0106] Shaft 21 extends along the axial direction A1 of rotor 3. In the following description, in the axial direction A1, the direction from housing 8 toward base 9 is defined as downward, and the opposite direction is defined as upward.

[0107] The vacuum pump 1 includes a protective bearing 29a, a protective bearing 29b, and multiple bearings 24A-24C. Protective bearings 29a and 29b function as touchdown bearings to limit the radial runout of the shaft 21. Protective bearings 29a and 29b are mounted on a base 9. When the shaft 21 is rotating stably, the shaft 21 does not contact the protective bearings 29a or 29b. However, under conditions of significant disturbance, or when the runout of the shaft 21 is large during acceleration or deceleration, the shaft 21 comes into contact with the inner surface of the inner ring of the protective bearings 29a or 29b. Protective bearings 29a and 29b can be, for example, ball bearings.

[0108] Multiple bearings 24A-24C support the rotor 3 so that it can rotate. The multiple bearings 24A-24C are mounted on the base 9. The multiple bearings 24A-24C may include, for example, magnetic bearings. However, the multiple bearings 24A-24C may also include other types of bearings such as ball bearings.

[0109] Multistage rotor blade units 22 are respectively connected to shaft 21. The multistage rotor blade units 22 are arranged at intervals along the axial direction A1. Each rotor blade unit 22 includes multiple rotor blades 25, which, although not shown in the figure, extend radially about shaft 21. Furthermore, in the figures, only one of the multistage rotor blade units 22 and one of the multiple rotor blades 25 are labeled; the symbols for the other rotor blade units 22 and other rotor blades 25 are omitted.

[0110] The rotor cylindrical portion 23 is connected to the shaft 21. The rotor cylindrical portion 23 is disposed below the rotor blade unit 22. The rotor cylindrical portion 23 is cylindrical and extends along the axial direction A1. The rotor cylindrical portion 23 is disposed on the outer periphery of the shaft 21 in a manner that surrounds the shaft 21. The outer periphery surface 23s of the rotor cylindrical portion 23 is a cylindrical curved surface.

[0111] (Motor 4)

[0112] Motor 4 drives rotor 3 to rotate. Motor 4 can be, for example, a direct current (DC) brushless motor. Motor 4 has a motor rotor 26 and a motor stator 27. Motor rotor 26 is mounted on shaft 21. Motor stator 27 is mounted on base 9. Motor stator 27 and motor rotor 26 are arranged opposite each other.

[0113] (Multi-stage stator blade unit 5)

[0114] Multistage stator blade units 5 are connected to the housing 8. The multistage stator blade units 5 are arranged spaced apart from each other along the axial direction A1. Each multistage stator blade unit 5 is positioned between multistage rotor blade units 22. Each stator blade unit 5 includes multiple stator blades 28. Although not shown in the figure, the multiple stator blades 28 extend radially about the shaft 21.

[0115] The multi-stage rotor blade unit 22 and the multi-stage stator blade unit 5 constitute the turbine section P1 (turbomolecular pump). Furthermore, in the accompanying drawings, only one of the multiple stator blade units 5 and one of the multiple stator blades 28 are labeled, while the symbols for the other stator blade units 5 and other stator blades 28 are omitted.

[0116] (Stator cylindrical section 6)

[0117] The stator cylindrical section 6 is disposed radially outside the rotor cylindrical section 23. The stator cylindrical section 6 is connected to the base 9. The stator cylindrical section 6 is disposed radially opposite to the rotor cylindrical section 23.

[0118] A helical threaded groove 60 (described later) is provided on the inner circumferential surface 6s (an example of an opposing surface) of the stator cylindrical section 6. The rotor cylindrical section 23 and the stator cylindrical section 6 constitute a drag pump section P2 (threaded groove pump). Furthermore, in Figure 1 In the diagram, the outer direction of radial B is represented by B1, and the inner direction of radial B is represented by B2. Additionally, the end 6a on the intake port 14 side of the stator cylindrical portion 6 is shown, and the end 6b on the exhaust port 16 side is shown.

[0119] Figure 2 This is a perspective view of the stator cylindrical section 6 as seen from the intake side. Figure 3 This is a perspective view of the stator cylindrical section 6 as seen from the exhaust side. The so-called intake side is the upper side where the intake port 14 is located, and the so-called exhaust side is the lower side where the exhaust port 16 is located.

[0120] The stator cylindrical portion 6 has a threaded groove 60 on its inner circumferential surface 6s. The stator cylindrical portion 6 has a cylindrical body 61 and multiple threaded teeth 62. The multiple threaded teeth 62 extend from the inner circumferential surface 61s in an inward direction B2 (see reference). Figure 1 The threaded teeth 62 are spirally formed from end 6a to end 6b. The inwardly protruding front end of the threaded teeth 62 in the direction of B2 is designated as 62a. The front end 62a is formed parallel to the axial direction A1.

[0121] The threaded groove 60 on the inner circumferential surface 6s is formed by the inner circumferential surface 61s between the threaded teeth 62 and the threaded teeth 62. The elements for designing the threaded groove 60 of the stator cylindrical part 6, namely the thread angle, groove depth, thread inner diameter, number of threaded teeth, and groove width ratio, are explained.

[0122] Figure 4 (a) is a diagram showing the end 6a of the thread 62 viewed from the inside. Figure 4 (b) is a diagram showing the end 6b of the thread tooth 62 viewed from the inside.

[0123] The thread angle is the angle relative to a plane perpendicular to the axis of rotation (axial direction A1). This plane is in... Figure 4 (a) and Figure 4 In (b), F is represented by a double-dotted line.

[0124] exist Figure 4 In (a), end 6a aligns with plane F, and the angle α formed between the forming direction C of thread tooth 62 and end 6a is the thread angle on the suction side. Additionally, in Figure 4 In (b), end 6b is aligned with plane F, and the angle β formed between the forming direction C of thread tooth 62 and end 6b is the thread angle on the venting side.

[0125] Figure 5 It is a diagram showing a cross-section perpendicular to the forming direction (angle of the thread tooth) of the helical thread tooth 62.

[0126] The space between adjacent thread teeth 62 forms a groove portion 63, and the inner circumferential surface 61s corresponds to the bottom of the groove portion 63. The groove depth D is the length from the inner front end 62a of the thread tooth 62 to the inner circumferential surface 61s of the cylindrical body 61. Regarding the groove depth D of the thread groove 60, the following will be used... Figure 6 To elaborate, the depth decreases from end 6a toward end 6b. Alternatively, it can be said that the height from the inner circumferential surface 61s to the tip of the thread tooth 62 decreases as it moves from end 6a toward end 6b.

[0127] The inner diameter of the thread is the diameter of the thread tooth 62 located further inward than the front end 62a. The inner diameter is determined by the outer diameter of the rotor cylindrical portion 23 and the clearance between the rotor cylindrical portion 23 and the front end 62a of the thread tooth 62. Figure 5 In this context, the radius of the thread inner diameter is represented by r / 2.

[0128] The number of thread teeth refers to the number of thread teeth 62 arranged in a circumferential 360-degree range. In this embodiment, as... Figure 2 and Figure 3 As shown, as an example, six threads 62 are formed. The six threads 62 are arranged at 60-degree intervals in a cross-section perpendicular to the axial direction A1.

[0129] The groove width ratio is the ratio of the width W1 of the groove portion 63 to the sum of the width W1 of the groove portion 63 and the width W2 of the thread tooth 62, taken from a section perpendicular to the forming direction of the thread tooth 62. That is, the groove width ratio is represented by W1 / (W1+W2), and is a value greater than 0 and less than 1.

[0130] Figure 6 This is a graph showing the variation of the groove depth D along the axial direction A1. Figure 6 In the diagram, the upper part represents the intake side, and the lower part represents the exhaust side. The groove depth D at end 6a represents the intake side groove depth Da. The groove depth D at end 6b represents the exhaust side groove depth Db.

[0131] The exhaust side groove depth Db is smaller than the intake side groove depth Da. The groove depth D decreases from end 6a toward end 6b.

[0132] The inner circumferential surface 61s of the cylindrical body 61 has an intake side portion 71 (an example of the first portion) and an exhaust side portion 72 (an example of the second portion). The intake side portion 71 is the portion where the groove depth D decreases by a constant reduction ratio Ea. The exhaust side portion 72 is located further towards the end 6b (exhaust side) than the intake side portion 71. The exhaust side portion 72 is the portion where the groove depth D decreases by a constant reduction ratio Eb. The reduction ratio Eb of the exhaust side portion 72 is smaller than the reduction ratio Ea of the intake side portion 71, and is set to Ea > Eb. The reduction ratio is obtained by dividing the reduction amount of the groove depth D when moving a predetermined amount along the axial direction A1 from end 6a towards end 6b by a predetermined amount.

[0133] The end 6b of the intake side portion 71 is connected to the end 6a of the exhaust side portion 72. Because the reduction ratio is constant, therefore... Figure 6 The intake side portion 71 and the exhaust side portion 72 are shown in a straight line. The portion connecting the intake side portion 71 and the exhaust side portion 72 is illustrated as the variable portion 73, where the reduction ratio changes. The groove depth D at the variable portion 73 is represented as the variable portion groove depth Dc. Figure 2 and Figure 3 As shown, the variation portion 73 is formed along the circumference of a plane perpendicular to the axial direction A1. Additionally, in Figure 2 and Figure 3In the process, a step is formed at the front end 62a of the thread tooth 62 on the circumference, but a step may not be formed. Furthermore, in Figure 6 and the following Figure 7 , Figures 14-17 and Figure 26 In the middle, it indicates that no step difference has been formed in the front end 62a.

[0134] The intake side groove depth Da, the exhaust side groove depth Db, and the variable part groove depth Dc are preferably satisfied with the following (Equation 1).

[0135] Db≤Dc<(Da+Db)×0.5···(Formula 1)

[0136] Furthermore, the intake side groove depth Da, the exhaust side groove depth Db, and the variable part groove depth Dc are more preferably satisfied by the following (Equation 2).

[0137] 1.5≤Da / Db···(Equation 2)

[0138] Furthermore, the intake side groove depth Da is preferably satisfied with the following (Equation 3).

[0139] 8mm≤Da···(Equation 3)

[0140] Furthermore, if the length along the axial direction A1 from end 6a to the variation portion 73 is set as La, and the length along the axial direction A1 from end 6a to end 6b is set as Lb, then it is preferable to satisfy the following (Equation 4).

[0141] 0<La<Lb×2 / 3···(Formula 4)

[0142] According to the structure described above, by making the reduction ratio of the groove depth D greater on the intake port 14 side than on the exhaust port 16 side, gas molecules can be easily delivered from the intake port 14 side of the threaded groove 60 to the exhaust port 16 side. Furthermore, by making the reduction ratio of the groove depth D smaller on the exhaust port 16 side than on the intake port 14 side, it is possible to prevent gas molecules from flowing back from the exhaust port 16 side to the intake port 14 side of the threaded groove 60.

[0143] Therefore, even when increasing the flow conductance on the suction side of the traction pump section P2, which is composed of the rotor cylindrical section 23 and the stator cylindrical section 6, the back pressure characteristics can be improved. Furthermore, the flow conductance of the traction pump section P2 can be increased by increasing the gas flow path. That is, the flow conductance of the traction pump section P2 can be increased by increasing the flow path of the groove portion 63 of the threaded groove 60. Increasing the flow path of the groove portion 63 is achieved by increasing the groove depth D, reducing the number of thread teeth 62 forming the threaded groove 60, or increasing the groove width ratio W1 / (W1+W2), etc.

[0144] (Example)

[0145] The vacuum pump 1 of this embodiment will be further described below using examples.

[0146] In Examples 1 to 3, as shown in Tables 1 to 3 of each example, the performance of each element of the towing pump unit P2 was changed and calculated.

[0147] In each embodiment, the performance calculations in the comparative examples were also performed simultaneously. Figure 7 This diagram illustrates the variation of the groove depth D in the cylindrical body 1061 and the threaded tooth 1062 of the comparative example. The groove depth D from the front end 1062a of the threaded tooth 1062 to the inner circumferential surface 1061s of the cylindrical body 1061 decreases linearly from end 6a towards end 6b at a constant ratio. That is, unlike the embodiment, the comparative example does not include a portion where the groove depth varies.

[0148] (Example 1)

[0149] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 1, and the results of the performance calculations are presented below. Figure 8 and Figure 9 .

[0150] (Table 1)

[0151]

[0152] In the threaded groove 60 of this embodiment 1, a variable portion 73 with a groove depth Dc of 7 mm is provided at a position of 50% of Lb (La = Lb / 2).

[0153] Figure 8 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Example 1 and Comparative Example 1. Figure 9 This is a graph showing the relationship between the intake and exhaust pressures of the traction pump unit P2 when N2 is exhausted at 3000 sccm in Example 1 and Comparative Example 1. Figure 8 and Figure 9 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 20 Pa. Figure 8 and Figure 9 In the text, Example 1 is represented by a solid line, and Comparative Example 1 is represented by a double-dotted line.

[0154] like Figure 8 and Figure 9As shown, even with large exhaust volumes of 2000 sccm or 3000 sccm, in Example 1, the increase in intake pressure caused by the increase in exhaust-side pressure was suppressed compared to Comparative Example 1. Therefore, it can be seen that in this Example 1, the back pressure characteristics are improved compared to Comparative Example 1.

[0155] (Example 2)

[0156] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 2, and the results of the performance calculations are presented below. Figure 10 and Figure 11 .

[0157] (Table 2)

[0158]

[0159] In the threaded groove 60 of this embodiment 2, a variable portion 73 with a groove depth Dc of 4 mm is provided at a position of 50% of Lb (La = Lb / 2).

[0160] Figure 10 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Example 2 and Comparative Example 2. Figure 11 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 3000 sccm in Example 2 and Comparative Example 2. Figure 10 and Figure 11 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 20 Pa. Figure 10 and Figure 11 In the text, Example 2 is represented by a solid line, and Comparative Example 2 is represented by a double-dotted line.

[0161] like Figure 10 and Figure 11 As shown, even with large exhaust volumes of 2000 sccm or 3000 sccm, in Example 2, the increase in intake pressure caused by the increase in exhaust pressure was suppressed compared to Comparative Example 2. Therefore, it can be seen that the back pressure characteristics are improved in Example 2 compared to Comparative Example 2.

[0162] (Example 3, Example 4)

[0163] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 3, and the results of the performance calculations are presented below. Figure 12 and Figure 13 .

[0164] (Table 3)

[0165]

[0166] In the threaded groove 60 of embodiment 3, a variable portion 73 with a groove depth Dc of 12 mm is provided at a position of 33% of Lb (La = 0.33 × Lb).

[0167] In the threaded groove 60 of embodiment 4, a variable portion 73 with a groove depth Dc of 12 mm is provided at a position of 66% of Lb (La = 0.66 × Lb).

[0168] Figure 12 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the towing pump unit P2 when N2 is exhausted at 2000 sccm in Examples 3, 4 and Comparative Example 3. Figure 13 This is a graph showing the relationship between the intake and exhaust pressures of the traction pump unit P2 when N2 is exhausted at 3000 sccm in Examples 3, 4, and Comparative Example 3. Figure 12 and Figure 13 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 20 Pa. Figure 12 and Figure 13 In the text, Example 3 is represented by a solid line, Example 4 by a dotted line, and Comparative Example 3 by a double dotted line.

[0169] like Figure 12 and Figure 13 As shown, even with large exhaust volumes of 2000 sccm or 3000 sccm, Examples 3 and 4, compared to Comparative Example 3, suppressed the increase in intake pressure caused by the increase in exhaust-side pressure. Therefore, it can be seen that in Examples 3 and 4, the back pressure characteristics are improved compared to Comparative Example 3.

[0170] (Implementation Method 2)

[0171] The vacuum pump of Embodiment 2 will now be described. In the vacuum pump of Embodiment 2, the groove depth D of the threaded groove 60 of the stator cylindrical portion 6 differs from that of the vacuum pump of Embodiment 1. In this Embodiment 2, the description will focus on the differences from Embodiment 1.

[0172] In the stator cylindrical portion 6 of Embodiment 1, a variation portion is provided between the end 6a on the intake side and the end 6b on the exhaust side, where the reduction ratio of the groove depth D changes. However, in the stator cylindrical portion of Embodiment 2, multiple variation portions are provided.

[0173] Figure 14This is a diagram showing the change in groove depth D along the axial direction A1 of the stator cylindrical portion 6 in Embodiment 2.

[0174] exist Figure 14 In the diagram, the upper part represents the intake side, and the lower part represents the exhaust side. The groove depth D at end 6a represents the intake side groove depth Da. The groove depth D at end 6b represents the exhaust side groove depth Db. The exhaust side groove depth Db is formed to be smaller than the intake side groove depth Da.

[0175] The inner circumferential surface 61s of the cylindrical body 61 in Embodiment 2 has a first reduction portion 171, a second reduction portion 172, and a third reduction portion 173 arranged sequentially from the intake side toward the exhaust side. The first reduction portion 171 is the portion where the groove depth D is reduced by a constant reduction ratio E1. The second reduction portion 172 is the portion where the groove depth D is reduced by a constant reduction ratio E2. The third reduction portion 173 is the portion where the groove depth D is reduced by a constant reduction ratio E3. The reduction ratio is obtained by dividing the reduction in groove depth D when moving a predetermined amount along the axial direction A1 from end 6a toward end 6b by a predetermined amount. Because the reduction ratio is constant, therefore... Figure 14 The first reduction portion 171, the second reduction portion 172, and the third reduction portion 173 are represented by a straight line.

[0176] The first reduction portion 171 is formed from end 6a toward the exhaust side. The exhaust-side end of the first reduction portion 171 is connected to the intake-side end of the second reduction portion 172. The portion where the first reduction portion 171 and the second reduction portion 172 are connected is illustrated as a first variation portion 175 where the reduction ratio changes. The groove depth D at the first variation portion 175 is denoted as the variation portion groove depth Dd. The first variation portion 175 is formed on a circumference along a plane perpendicular to the axial direction A1.

[0177] The third reduction portion 173 is formed from end 6b toward the intake side. The intake side end of the third reduction portion 173 is connected to the exhaust side end of the second reduction portion 172. The portion where the second reduction portion 172 and the third reduction portion 173 are connected is illustrated as a second variation portion 176 where the reduction ratio changes. The groove depth D at the second variation portion 176 is denoted as the variation portion groove depth De. The second variation portion 176 is formed on a circumference along a plane perpendicular to the axial direction A1.

[0178] exist Figure 14 In the stator cylindrical section shown, the reduction ratio E1 of the first reduction portion 171 is set to be greater than or equal to the reduction ratio E2 of the second reduction portion 172 and greater than or equal to the reduction ratio E3 of the third reduction portion 173.

[0179] In addition, not limited to Figure 14The structure can be configured such that the groove depth Db of the exhaust-side end 6b is smaller than the groove depth Da of the intake-side end 6a, and the reduction ratio of the groove depth is greater on the intake side than on the exhaust side. For example, it could also be... Figure 15 or Figure 16 The structure of the stator cylindrical section.

[0180] exist Figure 15 In the stator cylindrical section 6 shown, and Figure 14 Compared to the stator cylindrical portion shown, the reduction ratio E1 of the first reduction portion 171 is set to be greater than the reduction ratio E3 of the third reduction portion 173 and greater than the reduction ratio E2 of the second reduction portion 172.

[0181] exist Figure 16 In the stator cylindrical section 6 shown, and Figure 14 Compared to the stator cylindrical portion shown, the reduction ratio E2 of the second reduction portion 172 is set to be greater than the reduction ratio E1 of the first reduction portion 171 and greater than the reduction ratio E3 of the third reduction portion 173.

[0182] In addition, Figures 14-16 The stator cylindrical section shown has two sections where the reduction ratio changes, but three sections can also be provided. Figure 17 This is a diagram showing the change in groove depth D along the axial direction A1 of the stator cylinder section, where the reduction ratio of the three groove depths changes.

[0183] exist Figure 17 In the structure shown, Figure 14 A fourth reduction section 174 is also provided between the third reduction section 173 and end 6b, as described in the text. The portion where the third reduction section 173 and the fourth reduction section 174 connect is designated as the third variation section 177. The fourth reduction section 174 is the portion where the groove depth D is reduced at a constant reduction ratio E4. Figure 17 In the structure shown, the reduction ratio E1 of the first reduction portion 171 is set to be greater than or equal to the reduction ratio E2 of the second reduction portion 172, which in turn is greater than or equal to the reduction ratio E3 of the third reduction portion 173, which in turn is greater than or equal to the reduction ratio E4 of the fourth reduction portion 174. Furthermore, the groove depth at the third variation portion 177 is represented as the variation portion groove depth Df.

[0184] Thus, a stator cylinder section can be provided with four different constant reduction ratios, or with three variation sections where the reduction ratio changes.

[0185] In addition, Figure 17In the structure shown, as long as there exists a structure where the groove depth Db of the exhaust-side end 6b is smaller than the groove depth Da of the intake-side end 6a, and the reduction ratio of the groove depth is greater on the intake side than on the exhaust side, the reduction ratios between the reduced portions can also be different. Although not as in the case of a structure with two varying portions ( Figures 14-16 The diagram is as shown, but for example, it can also be set such that the reduction ratio E1 of the first reduction portion 171 ≥ the reduction ratio E2 of the second reduction portion 172 ≥ the reduction ratio E4 of the fourth reduction portion 174 ≥ the reduction ratio E3 of the third reduction portion 173. As shown in Examples 8 to 15 below, the sizes of the reduction ratio E1 of the first reduction portion 171, the reduction ratio E2 of the second reduction portion 172, the reduction ratio E3 of the third reduction portion 173, and the reduction ratio E4 of the fourth reduction portion 174 can be changed.

[0186] (Example)

[0187] The following examples will be used to describe the implementation methods in detail.

[0188] (Examples 5 to 7)

[0189] In Examples 5 to 7 and Comparative Example 4 below, the elements of the towing pump unit P2 are set to the values ​​shown in Table 4.

[0190] (Table 4)

[0191]

[0192] In addition, the length Lc from the intake end 6a of the stator cylindrical portion 6 to the first variation portion 175 is set to 40mm, and the length Ld from the end 6a to the second variation portion 176 is set to 70mm.

[0193] The stator cylindrical section in Example 5 is Figure 14 The shape shown is set such that the reduction ratio E1 of the first reduction portion 171 is greater than the reduction ratio E2 of the second reduction portion 172, which is greater than the reduction ratio E3 of the third reduction portion 173.

[0194] The stator cylindrical section in Example 6 is Figure 15 The shape shown is set such that the reduction ratio E1 of the first reduction portion 171 is greater than the reduction ratio E3 of the third reduction portion 173, which is greater than the reduction ratio E2 of the second reduction portion 172.

[0195] The stator cylindrical section in Example 7 is Figure 16 The shape shown is set such that the reduction ratio E2 of the second reduction portion 172 is greater than the reduction ratio E1 of the first reduction portion 171 and the reduction ratio E3 of the third reduction portion 173.

[0196] The stator cylindrical portion of Comparative Example 4 is as described above. Figure 7 The shape is such that the groove depth D decreases linearly from end 6a toward end 6b at a constant ratio.

[0197] The dimensions of the stator cylinder in Comparative Example 4 and Examples 5 to 7 are shown in Table 5 below.

[0198] (Table 5)

[0199]

[0200] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 4 and Table 5, and the results of the performance calculations are presented below. Figure 18 and Figure 19 .

[0201] Figure 18 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Examples 5 to 7 and Comparative Example 4. Figure 19 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 3000 sccm in Examples 5 to 7 and Comparative Example 4. Figure 18 and Figure 19 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 10 Pa. Figure 18 and Figure 19 In the diagram, Example 5 is represented by a solid line, Example 6 by a dashed line, Example 7 by a dotted line, and Comparative Example 4 by a double dotted line.

[0202] like Figure 18 and Figure 19 As shown, even with large exhaust volumes of 2000 sccm or 3000 sccm, in Examples 5 to 7, compared to Comparative Example 4, the increase in intake pressure caused by the increase in exhaust-side pressure was suppressed. Therefore, it can be seen that in Examples 5 to 7, the back pressure characteristics were improved compared to Comparative Example 4. It is therefore preferable that the portion with the largest reduction in groove depth is positioned closer to the intake side than the portion with the smallest reduction in groove depth.

[0203] Furthermore, by comparing Example 5 with Example 7, it can be seen that when the portion with the largest reduction in groove depth is positioned closest to the intake side, the back pressure characteristics are further improved, which is therefore preferred. Furthermore, by comparing Example 5 with Example 6, it can be seen that when the portion with the smallest reduction in groove depth is positioned closest to the exhaust side, the back pressure characteristics are further improved, which is therefore preferred.

[0204] (Examples 8 to 15)

[0205] In the following Examples 8 to 15, the elements of the towing pump unit P2 are set to the values ​​shown in Table 6.

[0206] (Table 6)

[0207]

[0208] In addition, such as Figure 17 As shown, the length Lc from the intake end 6a of the stator cylindrical portion 6 to the first variation portion 175 is set to 25mm, the length Ld from the end 6a to the second variation portion 176 is set to 50mm, and the length Le from the end 6a to the third variation portion 177 is set to 75mm.

[0209] The stator cylindrical section in Example 8 is Figure 17 The shape shown represents an example where the reduction ratio E1 of the first reduction portion 171 is greater than or equal to the reduction ratio E2 of the second reduction portion 172, which is greater than or equal to the reduction ratio E3 of the third reduction portion 173, which is greater than or equal to the reduction ratio E4 of the fourth reduction portion 174.

[0210] The stator cylindrical portion in Embodiment 9 represents an example where the reduction ratio E1 of the first reduction portion 171 is greater than or equal to the reduction ratio E2 of the second reduction portion 172, which is greater than or equal to the reduction ratio E4 of the fourth reduction portion 174, which is greater than or equal to the reduction ratio E3 of the third reduction portion 173.

[0211] The stator cylindrical portion in Example 10 represents an example where the reduction ratio E1 of the first reduction portion 171 is greater than or equal to the reduction ratio E3 of the third reduction portion 173, which is greater than or equal to the reduction ratio E2 of the second reduction portion 172, which is greater than or equal to the reduction ratio E4 of the fourth reduction portion 174.

[0212] The stator cylindrical portion in Example 11 represents an example where the reduction ratio E2 of the second reduction portion 172 is ≥ the reduction ratio E1 of the first reduction portion 171 is ≥ the reduction ratio E3 of the third reduction portion 173 is ≥ the reduction ratio E4 of the fourth reduction portion 174.

[0213] The stator cylindrical portion in Example 12 represents an example where the reduction ratio E2 of the second reduction portion 172 is greater than or equal to the reduction ratio E1 of the first reduction portion 171, greater than or equal to the reduction ratio E4 of the fourth reduction portion 174, and greater than or equal to the reduction ratio E3 of the third reduction portion 173.

[0214] The stator cylindrical portion in Example 13 represents an example where the reduction ratio E3 of the third reduction portion 173 is ≥ the reduction ratio E1 of the first reduction portion 171 ≥ the reduction ratio E2 of the second reduction portion 172 ≥ the reduction ratio E4 of the fourth reduction portion 174.

[0215] The stator cylindrical portion in Example 14 represents an example where the reduction ratio E2 of the second reduction portion 172 is greater than the reduction ratio E3 of the third reduction portion 173, which is greater than the reduction ratio E1 of the first reduction portion 171, which is greater than the reduction ratio E4 of the fourth reduction portion 174.

[0216] The stator cylindrical portion in Example 15 represents an example where the reduction ratio E3 of the third reduction portion 173 is greater than or equal to the reduction ratio E2 of the second reduction portion 172, greater than or equal to the reduction ratio E1 of the first reduction portion 171, and greater than or equal to the reduction ratio E4 of the fourth reduction portion 174.

[0217] The stator cylindrical portion of Comparative Example 5 is as described above. Figure 7 The shape is such that the groove depth D decreases linearly from end 6a toward end 6b at a constant ratio.

[0218] (Table 7)

[0219]

[0220] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 6 and Table 7, and the results of the performance calculations are presented below. Figure 20 and Figure 21 .

[0221] Figure 20 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Examples 8 to 10 and Comparative Example 5. Figure 21 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the traction pump section P2 when N2 is exhausted at 3000 sccm in Examples 8 to 10 and Comparative Example 5. Figure 20 and Figure 21 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 10 Pa. Figure 20 and Figure 21 In the diagram, Example 8 is represented by a solid line, Example 9 by a dashed line, Example 10 by a dotted line, and Comparative Example 5 by a double dotted line.

[0222] (Table 8)

[0223]

[0224] The parameters of the towing pump unit P2 were set to the values ​​shown in (Table 6) and (Table 8), and the results of the performance calculations are shown below. Figure 22 and Figure 23 .

[0225] Figure 22 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Examples 11, 12 and Comparative Example 5. Figure 23 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 3000 sccm in Examples 11, 12, and Comparative Example 5. Figure 22 and Figure 23 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 10 Pa. Figure 22 and Figure 23 In the diagram, Example 11 is represented by a solid line, Example 12 by a dashed line, and Comparative Example 5 by a double-dotted line.

[0226] (Table 9)

[0227]

[0228] The parameters of the towing pump unit P2 were set to the values ​​shown in Table 6 and Table 9, and the results of the performance calculations are presented below. Figure 24 and Figure 25 .

[0229] Figure 24 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 2000 sccm in Examples 13 to 15 and Comparative Example 5. Figure 25 This is a graph showing the relationship between the intake side pressure and the exhaust side pressure of the tractor pump unit P2 when N2 is exhausted at 3000 sccm in Examples 13 to 15 and Comparative Example 5. Figure 24 and Figure 25 In the figure, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the ratio of the intake-side pressure. This ratio is based on the intake-side pressure of the tow pump unit P2 when the exhaust-side pressure of P2 is 10 Pa. Figure 24 and Figure 25 In the diagram, Example 13 is represented by a solid line, Example 14 by a dashed line, Example 15 by a dotted line, and Comparative Example 5 by a double dotted line.

[0230] like Figures 20-25As shown, even with large exhaust volumes of 2000 sccm or 3000 sccm, in Examples 8 to 15, compared to Comparative Example 5, the increase in intake pressure caused by the increase in exhaust-side pressure was suppressed. Therefore, it can be seen that in Examples 8 to 15, the back pressure characteristics were improved compared to Comparative Example 5. It is therefore preferable that the portion with the largest reduction in groove depth is positioned closer to the intake side than the portion with the smallest reduction in groove depth.

[0231] Furthermore, by comparing Example 8 with Examples 13 and 14, it is found that the portion with the largest reduction in groove depth is preferably located at the intake side. Furthermore, by comparing Example 8 with Example 9, it is found that when the portion with the smallest reduction in groove depth is located at the exhaust side, the back pressure characteristics are further improved, which is therefore preferred.

[0232] (Other implementation methods)

[0233] The above describes one embodiment of the present invention, but the present invention is not limited to the described embodiment and various modifications can be made without departing from the spirit of the invention.

[0234] In the described embodiment, since the reduction ratio is constant in the intake side portion 71 and the exhaust side portion 72, the front end 62a is formed in a straight line, but it can also be formed in a curved manner by passing through the variation portion 73. Thus, the reduction ratio in the intake side portion 71 only needs to be greater than the reduction ratio in the exhaust side portion 72, and the reduction ratio does not need to be constant.

[0235] In the described embodiment, a threaded groove is formed on the inner circumferential surface 6s of the stator cylindrical portion 6, but a threaded groove may also be formed on the outer circumferential surface of the rotor cylindrical portion 23. Alternatively, the stator cylindrical portion 6 may be integrated with the base 9.

[0236] In the described embodiment, as an example, five to eight threaded teeth 62 are formed, but it may also be less than five or more than eight.

[0237] In the described embodiment, as an example of the first part, the intake side end of the intake side portion 71 coincides with end 6a, and the exhaust side end of the exhaust side portion 72 coincides with end 6b. However, a cylindrical body and a threaded portion may also be provided on the intake side of the intake side portion 71. Similarly, a cylindrical body and a threaded portion may also be provided on the exhaust side of the exhaust side portion 72. Figure 26This diagram shows the variation of the groove depth D from the tip 62a' of the threaded tooth 62' to the inner circumferential surface 61s' of the cylindrical body 61' in the modified example. In the inner circumferential surface 61s' of the cylindrical body 61', an end portion 74 is provided between the intake side portion 71 and the end 6a, and an end portion 75 is provided between the exhaust side portion 72 and the end 6b. Figure 26 In the modified example shown, the groove depth D of the end portion 74 is formed to be constant at the same height as the groove depth Da of the end portion 71 on the intake port 14 side. Furthermore, in Figure 26 In the modified example shown, the groove depth D of the end portion 75 is formed to be constant at the same height as the groove depth Db of the end on the exhaust port 16 side of the exhaust side portion 72. Alternatively, the end portions 74 and 75 may be formed such that the groove depth D decreases from end 6a toward end 6b.

[0238] (form)

[0239] Those skilled in the art will understand that the above-described exemplary embodiments are specific examples of the following forms.

[0240] (First configuration) The vacuum pump includes a housing, a rotor cylindrical section, and a stator cylindrical section. The housing has an intake port for drawing in gas and an exhaust port for discharging the drawn-in gas. The rotor cylindrical section is housed within the housing. The stator cylindrical section is housed within the housing and is arranged facing the rotor cylindrical section. A threaded groove is formed on one of the facing surfaces of the stator cylindrical section and the rotor cylindrical section. Regarding the groove depth, the exhaust-side end is smaller than the intake-side end. Regarding the reduction ratio of the groove depth, the intake side is larger than the exhaust side.

[0241] In the first type of vacuum pump, the groove depth of the threaded groove is set such that the exhaust side end is smaller than the intake side end, and the reduction ratio of the groove depth is set such that the intake side is larger than the exhaust side. Thus, by increasing the reduction ratio of the groove depth on the intake side, gas molecules are easily directed from the intake side of the threaded groove to the exhaust side. Furthermore, by decreasing the reduction ratio of the groove depth on the exhaust side, backflow of gas molecules from the exhaust side of the threaded groove to the intake side can be prevented.

[0242] Therefore, even when the flow conductance of the drag pump section, which consists of the rotor cylindrical section and the stator cylindrical section, is increased, the back pressure characteristics can be improved.

[0243] Furthermore, by improving back pressure characteristics, even with higher exhaust-side pressure, the pressure rise on the intake side can be reduced. This allows for the selection of a smaller auxiliary pump, which is the primary cause of increased pressure on the exhaust side. Consequently, design flexibility is achieved, costs are reduced, and maintainability is improved.

[0244] (Second Embodiment) According to the vacuum pump of the first embodiment, the threaded groove has a first portion and a second portion. The reduction ratio of the groove depth in the first portion is constant. Compared with the first portion, the second portion is disposed closer to the exhaust side, and the reduction ratio of its groove depth is constant. The reduction ratio of the first portion is greater than the reduction ratio of the second portion.

[0245] In the second type of vacuum pump, gas molecules are easily fed to the exhaust side in the first part, and gas molecules are less likely to flow backward in the second part. Therefore, even when the flow conductance of the drag pump section composed of the rotor cylindrical section and the stator cylindrical section is increased, the back pressure characteristics can be improved.

[0246] (Third form) According to the vacuum pump of the second form, the first part and the second part are connected at the changing part. If the groove depth at the suction side end of the first part is set as Da, the groove depth at the exhaust side end of the second part is set as Db, and the groove depth at the changing part is set as Dc, then Db≤Dc≤(Da+Db)×0.5 is satisfied.

[0247] In the third type of vacuum pump, by satisfying Db≤Dc≤(Da+Db)×0.5, the back pressure characteristics can be improved even when the flow conductance of the drag pump section is increased.

[0248] (Fourth form) According to the vacuum pump of the third form, if the length along the axial direction of the rotor cylinder from the end of the first part on the suction side to the variable part is set as La, and the length along the axial direction from the end of the first part on the suction side to the end of the second part on the exhaust side is set as Lb, then 0 < La < Lb × 2 / 3 is satisfied.

[0249] In the fourth type of vacuum pump, by satisfying 0 < La < Lb×2 / 3, the back pressure characteristics can be improved even when the flow conductance of the drag pump section is increased.

[0250] (Fifth Form) According to the third or fourth form of vacuum pump, where 1.5≤Da / Db is also satisfied.

[0251] In the fifth type of vacuum pump, by satisfying 1.5≤Da / Db, the back pressure characteristics can be improved even when the flow conductance of the drag pump section is increased.

[0252] (Sixth form) According to the vacuum pump of the first form, the threaded groove has multiple portions with different reduction ratios in groove depth. The portion with the largest reduction ratio in groove depth is positioned closer to the suction side compared to the portion with the smallest reduction ratio in groove depth.

[0253] In the sixth type of vacuum pump, by placing the part with the largest reduction in groove depth closer to the suction side compared to the part with the smallest reduction in groove depth, gas molecules can be easily sent to the exhaust side on the suction side of the thread groove, preventing gas molecules from flowing back from the exhaust side of the thread groove to the suction side.

[0254] Therefore, even with increased flow conductance of the drag pump section, back pressure characteristics can be improved.

[0255] (Seventh Form) According to the vacuum pump of the sixth form, the part with the largest reduction in groove depth is located at the part closest to the suction side among the multiple parts.

[0256] In the seventh type of vacuum pump, gas molecules are more easily delivered to the exhaust side from the intake side of the threaded groove.

[0257] (Eighth Form) According to the sixth or seventh form of the vacuum pump, the part with the smallest reduction in groove depth is located at the exhaust side of the multiple parts.

[0258] In the eighth type of vacuum pump, it is possible to further prevent gas molecules from flowing back from the exhaust side of the threaded groove to the intake side.

Claims

1. A vacuum pump, characterized in that, include: The housing has an intake port for drawing in gas and an exhaust port for discharging the drawn-in gas. The rotor cylindrical portion is housed within the casing; as well as The stator cylindrical section is housed within the housing and is arranged facing the rotor cylindrical section. A threaded groove is formed on one of the facing surfaces of the stator cylindrical section and the rotor cylindrical section. Regarding the groove depth, the exhaust side end is smaller than the intake side end. Regarding the reduction ratio of the groove depth, the reduction is greater on the intake side than on the exhaust side. The threaded groove has: In the first part, the reduction rate of the groove depth is constant; as well as The second part, compared to the first part, is positioned closer to the exhaust side, and the reduction ratio of the groove depth remains constant. The reduction rate of the first part is greater than the reduction rate of the second part. Furthermore, the first part and the second part are connected in the portion where the reduction ratio changes. If the groove depth at the intake side end of the first part is set to Da, The groove depth at the exhaust side end of the second part is set to Db. Set the groove depth at the changed portion to Dc. Then it satisfies Db≤Dc≤(Da+Db)×0.

5.

2. The vacuum pump according to claim 1, wherein If the length from the end of the first part on the intake side to the variable part along the axial direction of the rotor cylinder is defined as La, Let Lb be the length along the axial direction from the end of the first part on the intake side to the end of the second part on the exhaust side. Then it satisfies 0 < La < Lb × 2 / 3.

3. The vacuum pump according to claim 1 or 2, wherein It also satisfies 1.5≤Da / Db.

4. The vacuum pump according to claim 1, wherein The threaded groove has multiple portions with different reduction ratios in groove depth. The portion of the groove depth with the largest reduction ratio is positioned closer to the intake side compared to the portion with the smallest reduction ratio.

5. The vacuum pump according to claim 4, wherein The portion with the largest reduction in groove depth is located at the part closest to the intake side among the plurality of portions.

6. The vacuum pump according to claim 4 or 5, wherein The portion with the smallest reduction in groove depth is located at the part closest to the exhaust side among the plurality of portions.

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