vacuum pump

Abstract

To provide a vacuum pump with improved back pressure characteristics during a large-flow-rate exhaust.SOLUTION: A vacuum pump 1 comprises a housing 2, a rotor cylindrical part 23 and a stator cylindrical part 6. The housing 2 has a suction port 14 that suctions gas, and an exhaust port 16 that discharges the suctioned gas. The rotor cylindrical part 23 is housed in the housing 2. The stator cylindrical part 6 is housed in the housing 2, and arranged so as to face the rotor cylindrical part 23. A thread groove 60 is formed in one facing surface of the stator cylindrical part 6 and the rotor cylindrical part 23. A groove depth D of the thread groove 60 is smaller at an exhaust side end 6b than at a suction side end 6a. A rate of decrease of the groove depth D is larger on the suction side than on the exhaust side.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a vacuum pump. [Background technology]

[0002] BACKGROUND ART In the field of semiconductor manufacturing equipment and the like, vacuum pumps are used to create a high vacuum atmosphere (see, for example, Patent Document 1).

[0003] The vacuum pump shown in Patent Document 1 is provided with a turbine pump section arranged on the intake port side and a drag pump section arranged on the exhaust port side.

[0004] A performance index for exhausting with a turbomolecular pump is the intake port pressure relative to the gas flow rate, and the intake port pressure increases as the gas flow rate increases.

[0005] Another performance index used when using a turbomolecular pump for exhaust is the backpressure characteristic. Backpressure characteristics are measured by increasing the pressure at the exhaust port of the turbomolecular pump while a constant amount of gas is introduced. As the exhaust port pressure increases, the number of gas molecules that flow back from the exhaust side to the intake side increases, causing the pressure on the intake side to increase. The higher the exhaust port pressure at which the inlet port pressure begins to increase, the more effectively the gas molecules that flow back can be reduced, and the better the backpressure characteristic is considered to be. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-102926 Summary of the Invention [Problem to be solved by the invention]

[0007] On the other hand, in recent years, the flow rate of gas flowing into turbomolecular pumps has tended to increase, and there is a demand for reducing the intake port pressure when exhausting a large flow rate.

[0008] In order to reduce the intake port pressure during high-flow exhaust, it is effective to design the drag pump so that its conductance is increased. However, this design not only increases the number of gas molecules moving from the intake side to the exhaust side, but also increases the number of gas molecules flowing back from the exhaust side to the intake side, resulting in poor backpressure characteristics.

[0009] An object of the present invention is to provide a vacuum pump that can accommodate large flow rate exhaust and has improved back pressure characteristics. [Means for solving the problem]

[0010] A vacuum pump according to one aspect of the present invention comprises 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 gas. The rotor cylindrical portion is housed in the housing. The stator cylindrical portion is housed in the housing and disposed opposite the rotor cylindrical portion. A thread groove is formed on one of the opposing surfaces of the stator cylindrical portion and the rotor cylindrical portion. The groove depth is smaller at the exhaust side end than at the intake side end. The rate of decrease in groove depth is greater on the intake side than on the exhaust side. [Effects of the Invention]

[0011] According to the above-described aspects of the present invention, it is possible to provide a vacuum pump that can handle large flow rate exhaust and has improved back pressure characteristics. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an external view of a vacuum pump according to a first embodiment. [Figure 2] 1 is a perspective view of a stator cylindrical portion of a vacuum pump according to a first embodiment, viewed from the intake side. [Figure 3] 3 is a perspective view of the stator cylindrical portion of the vacuum pump according to the first embodiment, viewed from the opposite side to that of FIG. 2. FIG. [Figure 4]FIG. 1(a) is a view from the inside of the threads near the intake end of the stator cylindrical portion of the vacuum pump according to embodiment 1, and FIG. 1(b) is a view from the inside of the threads near the exhaust end of the stator cylindrical portion of the vacuum pump according to embodiment 1. [Figure 5] 1 is a cross-sectional view perpendicular to the screw angle of a cylindrical stator portion of a vacuum pump according to a first embodiment. [Figure 6] FIG. 4 is a diagram showing changes in the thread groove depth of the cylindrical stator portion of the vacuum pump according to the first embodiment. [Figure 7] FIG. 10 is a diagram showing the change in thread groove depth in a comparative example. [Figure 8] FIG. 1 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of a drag pump section in Example 1 and Comparative Example 1. [Figure 9] FIG. 1 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of a drag pump section in Example 1 and Comparative Example 1. [Figure 10] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Example 2 and Comparative Example 2. [Figure 11] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Example 2 and Comparative Example 2. [Figure 12] FIG. 10 is a graph showing the change in intake-side pressure relative to the exhaust-side pressure of the drag pump section in Examples 3 and 4 and Comparative Example 2. [Figure 13] FIG. 10 is a graph showing the change in intake-side pressure relative to the exhaust-side pressure of the drag pump section in Examples 3 and 4 and Comparative Example 2. [Figure 14] FIG. 10 is a diagram showing changes in the thread groove depth of the cylindrical stator portion of the vacuum pump according to the second embodiment. [Figure 15] FIG. 10 is a diagram showing changes in the thread groove depth of the cylindrical stator portion of the vacuum pump according to the second embodiment. [Figure 16] FIG. 10 is a diagram showing changes in the thread groove depth of the cylindrical stator portion of the vacuum pump according to the second embodiment. [Figure 17]FIG. 10 is a diagram showing changes in the thread groove depth of the cylindrical stator portion of the vacuum pump according to the second embodiment. [Figure 18] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 5 to 7 and Comparative Example 4. [Figure 19] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 5 to 7 and Comparative Example 4. [Figure 20] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 8 to 10 and Comparative Example 5. [Figure 21] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 8 to 10 and Comparative Example 5. [Figure 22] FIG. 10 is a graph showing the change in intake-side pressure relative to the exhaust-side pressure of the drag pump section in Examples 11 and 12 and Comparative Example 5. [Figure 23] FIG. 10 is a graph showing the change in intake-side pressure relative to the exhaust-side pressure of the drag pump section in Examples 11 and 12 and Comparative Example 5. [Figure 24] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 13 to 15 and Comparative Example 5. [Figure 25] FIG. 10 is a graph showing changes in intake-side pressure relative to exhaust-side pressure of the drag pump section in Examples 13 to 15 and Comparative Example 5. [Figure 26] FIG. 10 is a diagram showing a change in thread groove depth in a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vacuum pump according to an embodiment of the present disclosure will now be described with reference to the drawings.

[0014] (Embodiment 1) The vacuum pump of the first embodiment will be described below.

[0015] (Vacuum Pump 1 Overview) FIG. 1 is a cross-sectional view of a vacuum pump 1 according to an embodiment.

[0016] The vacuum pump 1 includes a turbine section P1 and a drag pump section P2. The turbine section P1 constitutes a turbomolecular pump. The drag pump section P2 constitutes a threaded pump. The vacuum pump 1 is connected to an evacuation target device including an evacuation target space. Gas from the evacuation target space is exhausted by the turbine section P1, then exhausted by the drag pump section P2, and then exhausted to the outside of the vacuum pump 1.

[0017] 1, the vacuum pump 1 has a housing 2 (an example of a housing), a rotor 3, a motor 4, a plurality of stator blade units 5, and a stator cylindrical portion 6. The housing 2 accommodates the rotor 3, the motor 4, the plurality of stator blade units 5, and the stator cylindrical portion 6.

[0018] (Case 2) The housing 2 has a casing 8, a base 9, and a fixing flange 10. The housing 2 is made of a metal such as an aluminum alloy or iron. The casing 8 is a cylindrical member having the fixing flange 10 at one end.

[0019] The casing 8 houses a plurality of stator blade units 5 and a plurality of stages of rotor blade units 22 provided on the rotor 3. The casing 8 has a first end 11, a second end 12, and a side surface 13.

[0020] The first end 11 is attached to the exhaust target device. An intake port 14 is provided at the first end 11. The second end 12 is located on the opposite side of the fixing 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 casing 8.

[0021] The base 9 is disposed so as to close the opening on the second end 12 side of the casing 8. The base 9 houses the stator cylindrical portion 6 and the rotor cylindrical portion 23 provided on the rotor 3. The base 9 has a base end portion 15 and an exhaust port 16. The base end portion 15 is connected to the second end portion 12 of the casing 8. A second internal space S2 is formed inside the base 9. The second internal space S2 is in communication with the first internal space S1. The exhaust port 16 is in communication with the second internal space S2.

[0022] The fixing flange 10 is connected to the casing 8. The fixing flange 10 protrudes from the casing 8. The fixing flange 10 is fixed to the exhaust target device with bolts 20. Note that "connection" includes joining of separate members to each other. Also, "connection" includes the joining of separate parts of an integrated member.

[0023] (Rotor 3) The rotor 3 has a shaft 21, multiple stages of rotor blade units 22, and a rotor cylindrical portion .

[0024] The shaft 21 extends in the axial direction A1 of the rotor 3. In the following description, in the axial direction A1, the direction from the casing 8 toward the base 9 is defined as downward, and the opposite direction is defined as upward.

[0025] The vacuum pump 1 includes a protective bearing 29 and a plurality of bearings 24A-24C. The protective bearing 29 functions as a touchdown bearing that limits radial runout of the upper side of the shaft 21. The protective bearing 29 is attached to the base 9. When the shaft 21 is rotating steadily, the shaft 21 and the protective bearing 29 are not in contact with each other, but when a large disturbance is applied or when the whirling of the shaft 21 increases during acceleration or deceleration of rotation, the shaft 21 comes into contact with the inner surface of the inner ring of the protective bearing 29. The protective bearing 29 can be, for example, a ball bearing.

[0026] The plurality of bearings 24A-24C rotatably support the rotor 3. The plurality of bearings 24A-24C are attached to the base 9. The plurality of bearings 24A-24C include, for example, magnetic bearings. However, the plurality of bearings 24A-24C may also include other types of bearings, such as ball bearings.

[0027] The multiple stages of rotor blade units 22 are each connected to the shaft 21. The multiple stages of rotor blade units 22 are arranged at intervals from one another in the axial direction A1. Each rotor blade unit 22 includes a plurality of rotor blades 25, and although not shown, each of the multiple rotor blades 25 extends radially from the shaft 21. Note that in the drawings, only one of the multiple stages of rotor blade units 22 and one of the multiple rotor blades 25 is labeled with a reference numeral, and the reference numerals for the other rotor blade units 22 and other rotor blades 25 are omitted.

[0028] 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 in the axial direction A1. The rotor cylindrical portion 23 is disposed on the outer periphery of the shaft 21 so as to surround the shaft 21. An outer periphery surface 23s of the rotor cylindrical portion 23 is a cylindrical curved surface.

[0029] (Motor 4) The motor 4 drives the rotor 3 to rotate. For example, a DC brushless motor is used as the motor 4. The motor 4 has a motor rotor 26 and a motor stator 27. The motor rotor 26 is attached to the shaft 21. The motor stator 27 is attached to the base 9. The motor stator 27 is disposed opposite the motor rotor 26.

[0030] (Multi-stage stator blade unit 5) The multiple stages of stator blade units 5 are connected to the inner surface of the casing 8. The multiple stages of stator blade units 5 are arranged at intervals from one another in the axial direction A1. Each of the multiple stages of stator blade units 5 is arranged between the multiple stages of rotor blade units 22. Each of the stator blade units 5 includes a plurality of stator blades 28. Although not shown in the figure, the multiple stator blades 28 each extend radially from the shaft 21 as a center.

[0031] The multiple stages of rotor blade units 22 and the multiple stages of stator blade units 5 constitute a turbine section P1 (turbomolecular pump). Note that in the drawings, only one of the multiple stator blade units 5 and one of the multiple stator blades 28 are labeled with a reference numeral, and the reference numerals of the other stator blade units 5 and other stator blades 28 are omitted.

[0032] (Stator cylindrical part 6) The stator cylindrical portion 6 is disposed radially outside the rotor cylindrical portion 23. The stator cylindrical portion 6 is connected to a base 9. The stator cylindrical portion 6 is disposed facing the rotor cylindrical portion 23 in the radial direction of the rotor cylindrical portion 23.

[0033] A helical thread groove 60 (described later) is provided on an inner peripheral surface 6s (an example of an opposing surface) of the stator cylindrical portion 6. The rotor cylindrical portion 23 and the stator cylindrical portion 6 constitute a drag pump portion P2 (thread groove pump). In FIG. 1, the outer side of the radial direction B is indicated by B1, and the inner side of the radial direction B is indicated by B2. Also shown is an end 6a of the stator cylindrical portion 6 on the intake port 14 side, and an end 6b on the exhaust port 16 side.

[0034] Fig. 2 is a perspective view of the stator cylindrical portion 6 as viewed from the intake side. Fig. 3 is a perspective view of the stator cylindrical portion 6 as viewed from the exhaust side. The intake side refers to the upper side where the intake port 14 is located, and the exhaust side refers to the lower side where the exhaust port 16 is located.

[0035] The stator cylindrical portion 6 has a screw groove 60 on its inner circumferential surface 6s. The stator cylindrical portion 6 has a cylindrical portion main body 61 and a plurality of screw threads 62. The plurality of screw threads 62 protrude from the inner circumferential surface 61s in an inward direction B2 (see FIG. 1). The plurality of screw threads 62 are formed in a spiral shape from end 6a to end 6b. The tip of the screw thread 62 protruding in the inward direction B2 is indicated as 62a. The tip 62a is formed parallel to the axial direction A1.

[0036] The thread groove 60 on the inner peripheral surface 6s is formed by the threads 62 and the inner peripheral surface 61s between the threads 62. The elements to be considered when designing the thread groove 60 of the stator cylindrical portion 6, namely, the thread angle, groove depth, inner diameter of the screw, number of threads, and groove width ratio, will be described below.

[0037] Fig. 4(a) is a view of an end 6a of the thread 62 as viewed from the inside, and Fig. 4(b) is a view of an end 6b of the thread 62 as viewed from the inside.

[0038] The screw angle is the angle with respect to a plane perpendicular to the rotation axis (axial direction A1), which is shown by a two-dot chain line as F in Figures 4(a) and 4(b).

[0039] In Figure 4(a), end 6a and plane F coincide with each other, and the angle α formed between end 6a and direction C of thread 62 is the thread angle on the intake side. In Figure 4(b), end 6b and plane F coincide with each other, and the angle β formed between end 6b and direction C of thread 62 is the thread angle on the exhaust side.

[0040] FIG. 5 is a diagram showing a cross section perpendicular to the direction in which the helical thread 62 is formed (the angle of the thread).

[0041] The space between adjacent threads 62 forms a groove portion 63, and the inner circumferential surface 61s corresponds to the groove bottom of the groove portion 63. The groove depth D is the length from the inner tip 62a of the thread 62 to the inner circumferential surface 61s of the cylindrical main body 61. The groove depth D of the thread groove 60 will be explained in detail using FIG. 6 described later, but it becomes shallower from the end 6a to the end 6b. It can also be said that the height from the inner circumferential surface 61s to the tip of the thread 62 becomes lower from the end 6a to the end 6b.

[0042] The inner diameter of the screw is the diameter inside the tip 62a of the screw thread 62. The inner diameter of the screw is set by the outer diameter of the rotor cylindrical portion 23 and the gap between the rotor cylindrical portion 23 and the tip 62a of the screw thread 62. In Figure 4, the radius of the inner diameter of the screw is shown as r / 2.

[0043] The number of threads refers to the number of threads 62 arranged in 360 degrees in the circumferential direction. In this embodiment, as an example, six threads 62 are formed, as shown in Figures 2 and 3. The six threads 62 are arranged at 60-degree intervals in a cross section perpendicular to the axial direction A1.

[0044] 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 62 when cut along a cross section perpendicular to the formation direction of the thread 62. In other words, the groove width ratio is expressed as W1 / (W1+W2) and is a value greater than 0 and less than 1.

[0045] Fig. 6 is a diagram showing the change in groove depth D in the axial direction A1. In Fig. 6, the upper side indicates the intake side and the lower side indicates the exhaust side. The groove depth D at end 6a is shown as intake side groove depth Da. The groove depth D at end 6b is shown as exhaust side groove depth Db.

[0046] The exhaust side groove depth Db is smaller than the intake side groove depth Da. The groove depth D decreases from the end 6a toward the end 6b.

[0047] The inner circumferential surface 61s of the cylindrical main body 61 has an intake side portion 71 (an example of a first portion) and an exhaust side portion 72 (an example of a second portion). The intake side portion 71 is a portion where the groove depth D decreases at a constant rate of decrease Ea. The exhaust side portion 72 is located closer to the end 6b (exhaust side) than the intake side portion 71. The exhaust side portion 72 is a portion where the groove depth D decreases at a constant rate of decrease Eb. The rate of decrease Eb of the exhaust side portion 72 is smaller than the rate of decrease Ea of the intake side portion 71, and is set to Ea > Eb. The rate of decrease is calculated by dividing the amount of decrease in the groove depth D when moving a predetermined distance from the end 6a toward the end 6b along the axial direction A1 by a predetermined amount.

[0048] The end of the intake-side portion 71 on the end 6b side is connected to the end of the exhaust-side portion 72 on the end 6a side. Because the reduction rate is constant, the intake-side portion 71 and the exhaust-side portion 72 are shown as a straight line in FIG. 6. The portion where the intake-side portion 71 and the exhaust-side portion 72 connect is shown as a transition portion 73 where the reduction rate changes. The groove depth D in this transition portion 73 is shown as a transition portion groove depth Dc. As shown in FIGS. 2 and 3, the transition portion 73 is formed along a circumference on a plane perpendicular to the axial direction A1. Although a step is formed at the tip 62a of the thread 62b on this circumference in FIGS. 2 and 3, this step need not be formed. Note that FIG. 6, as well as FIGS. 7, 14 to 17, and 26 described below, show a state in which no step is formed at the tip 62a.

[0049] It is preferable that the intake side groove depth Da, the exhaust side groove depth Db, and the transition portion groove depth Dc satisfy the following (Equation 1).

[0050] Db≦Dc<(Da+Db)×0.5 (Formula 1) Furthermore, it is preferable that the intake side groove depth Da, the exhaust side groove depth Db, and the transition portion groove depth Dc further satisfy the following (Equation 2).

[0051] 1.5≦Da / Db (Formula 2) Furthermore, it is preferable that the intake side groove depth Da satisfies the following (Equation 3).

[0052] 8 mm ≤ Da ··· (Equation 3) Also, when the length along the axial direction A1 from the end 6a to the changing portion 73 is defined as La, and the length along the axial direction A1 from the end 6a to the end 6b is defined as Lb, it is preferable to satisfy the following (Equation 4).

[0053] 0 < La < Lb × 2 / 3 ··· (Equation 4) With the above configuration, by making the reduction rate of the groove depth D larger on the intake port 14 side than on the exhaust port 16 side, it becomes easier to send gas molecules from the intake port 14 side of the screw groove 60 to the exhaust port 16 side. Also, by making the reduction rate of the groove depth D smaller on the exhaust port 16 side than on the intake port 14 side, it is possible to prevent the backflow of gas molecules from the exhaust port 16 side to the intake port 14 side of the screw groove 60.

[0054] Therefore, even when the conductance on the intake side of the drag pump section P2 composed of the rotor cylinder section 23 and the stator cylinder section 6 is increased, the backpressure characteristics can be improved. Note that the conductance of the drag pump section P2 can be increased by enlarging the gas flow path. That is, by enlarging the flow path of the groove portion 63 of the screw groove 60, the conductance of the drag pump section P2 can be improved. Enlarging the flow path of the groove portion 63 is realized by increasing the groove depth D, reducing the number of threads 62 forming the screw groove 60, or increasing the groove width ratio W1 / (W1 + W2), etc.

[0055] (Example) Hereinafter, the vacuum pump 1 of the present embodiment will be further described using examples.

[0056] In Examples 1 to 3, as shown in (Table 1) to (Table 3) in each example, performance calculations were performed by changing each element of the drag pump section P2.

[0057] For each example, performance calculations for a comparative example were also performed at the same time. Figure 7 is a diagram showing the change in groove depth D in the cylindrical body 1061 and thread 1062 of the comparative example. The groove depth D from the tip 1062a of the thread 1062 to the inner circumferential surface 1061s of the cylindrical body 1061 decreases at a constant rate from end 6a to end 6b, and changes linearly. In other words, unlike the examples, the comparative example does not have a portion where the groove depth changes.

[0058] Example 1 The elements of the drag pump section P2 were set to the values ​​shown in Table 1, and performance calculations were carried out. The results are shown in FIGS.

[0059] (Table 1) TIFF0007746864000001.tif8393 In the thread groove 60 of the present embodiment 1, a transition portion 73 where the groove depth Dc is 7 mm is provided at a position that is 50% of Lb (La=Lb / 2).

[0060] FIG. 8 is a diagram showing the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Example 1 and Comparative Example 1. FIG. 9 is a diagram showing the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Example 1 and Comparative Example 1. In FIGS. 8 and 9, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This is the ratio when the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 20 Pa is used as the reference. In FIGS. 8 and 9, Example 1 is shown by a solid line, and Comparative Example 1 is shown by a two-dot chain line.

[0061] 8 and 9, even when large amounts of exhaust such as 2000 sccm or 3000 sccm are performed, the increase in intake-side pressure due to the increase in exhaust-side pressure is suppressed in Example 1 compared to Comparative Example 1. Therefore, it can be seen that the back pressure characteristics are improved in Example 1 compared to Comparative Example 1.

[0062] Example 2 The elements of the drag pump section P2 were set to the values ​​shown in Table 2, and the performance calculation results are shown in FIGS.

[0063] (Table 2) TIFF0007746864000002.tif8293 In the screw groove 60 of the second embodiment, a transition portion 73 where the groove depth Dc is 4 mm is provided at a position that is 50% of Lb (La=Lb / 2).

[0064] FIG. 10 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Example 2 and Comparative Example 2. FIG. 11 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Example 2 and Comparative Example 2. In FIGS. 10 and 11, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This is the ratio when the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 20 Pa is used as the reference. In FIGS. 10 and 11, Example 2 is shown by a solid line, and Comparative Example 2 is shown by a two-dot chain line.

[0065] 10 and 11, even when large amounts of exhaust such as 2000 sccm or 3000 sccm are performed, the increase in intake-side pressure due to the increase in exhaust-side pressure is suppressed in Example 2 compared to Comparative Example 2. Therefore, it can be seen that the back pressure characteristics of Example 2 are improved compared to Comparative Example 2.

[0066] (Examples 3 and 4) The elements of the drag pump section P2 were set to the values ​​shown in Table 3, and the performance calculation results are shown in FIGS.

[0067] (Table 3) TIFF0007746864000003.tif8093 In the thread groove 60 of Example 3, a transition portion 73 where the groove depth Dc is 12 mm is provided at a position that is 33% of Lb (La=0.33×Lb).

[0068] The thread groove 60 of Example 4 is provided with a transition portion 73 at a position that is 66% of Lb (La=0.66×Lb) where the groove depth Dc is 12 mm.

[0069] FIG. 12 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Examples 3 and 4 and Comparative Example 3. FIG. 13 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Examples 3 and 4 and Comparative Example 3. In FIGS. 12 and 13, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This ratio is based on the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 20 Pa. In FIGS. 12 and 13, Example 3 is shown by a solid line, Example 4 is shown by a dashed line, and Comparative Example 3 is shown by a two-dot chain line.

[0070] 12 and 13, even when large amounts of exhaust such as 2000 sccm or 3000 sccm are performed, the increase in intake-side pressure due to the increase in exhaust-side pressure is suppressed in Examples 3 and 4 compared to Comparative Example 3. Therefore, it can be seen that the back pressure characteristics are improved in Examples 3 and 4 compared to Comparative Example 3.

[0071] (Embodiment 2) The following describes a vacuum pump of embodiment 2. The vacuum pump of embodiment 2 differs from the vacuum pump of embodiment 1 in the change in groove depth D of the thread groove 60 of the stator cylindrical portion 6. In embodiment 2, the differences from the embodiment will be mainly described.

[0072] In the stator cylindrical portion 6 of the above-mentioned embodiment 1, there is one change portion between the end 6a on the intake side and the end 6b on the exhaust side, where the rate of decrease of the groove depth D changes, but in the stator cylindrical portion of this embodiment 2, there are multiple change portions.

[0073] FIG. 14 is a diagram showing the change in groove depth D in the axial direction A1 of the stator cylindrical portion 6 of the second embodiment.

[0074] In Figure 14, the upper side indicates the intake side and the lower side indicates the exhaust side. The groove depth D at end 6a is shown as intake side groove depth Da. The groove depth D at end 6b is shown as exhaust side groove depth Db. The exhaust side groove depth Db is formed smaller than the intake side groove depth Da.

[0075] The inner circumferential surface 61s of the cylindrical main body 61 in the second embodiment has a first reduced portion 171, a second reduced portion 172, and a third reduced portion 173, arranged in this order from the intake side to the exhaust side. The first reduced portion 171 is a portion where the groove depth D decreases at a constant reduced rate E1. The second reduced portion 172 is a portion where the groove depth D decreases at a constant reduced rate E2. The third reduced portion 173 is a portion where the groove depth D decreases at a constant reduced rate E3. The reduced rate is calculated by dividing the amount of reduction in the groove depth D when moving a predetermined distance from the end 6a toward the end 6b along the axial direction A1 by a predetermined amount. Because the reduced rate is constant, the first reduced portion 171, the second reduced portion 172, and the third reduced portion 173 are shown as straight lines in FIG. 14 .

[0076] The first reduced portion 171 is formed from the end 6a toward the exhaust side. The exhaust side end of the first reduced portion 171 is connected to the intake side end of the second reduced portion 172. The portion where the first reduced portion 171 and the second reduced portion 172 are connected is illustrated as a first changed portion 175 where the reduction rate changes. The groove depth D in this first changed portion 175 is shown as a changed portion groove depth Dd. The first changed portion 175 is formed along the circumference on a plane perpendicular to the axial direction A1.

[0077] The third reduced portion 173 is formed from the end 6b toward the intake side. The intake side end of the third reduced portion 173 is connected to the exhaust side end of the second reduced portion 172. The portion where the second reduced portion 172 and the third reduced portion 173 are connected is illustrated as a second changed portion 176 where the reduction rate changes. The groove depth D in this second changed portion 176 is shown as the changed portion groove depth De. The second changed portion 176 is formed along the circumference on a plane perpendicular to the axial direction A1.

[0078] In the stator cylindrical portion shown in FIG. 14, the decrease rate E1 of the first decrease portion 171≧the decrease rate E2 of the second decrease portion 172≧the decrease rate E3 of the third decrease portion 173.

[0079] The configuration is not limited to that shown in FIG. 14 , and any configuration may be used in which the groove depth Db at the exhaust-side end 6b is smaller than the groove depth Da at the intake-side end 6a, and the rate of decrease in the groove depth on the intake side is greater than that on the exhaust side, such as the configuration of the stator cylindrical portion shown in FIG. 15 or 16 .

[0080] In the stator cylindrical portion 6 shown in Figure 15, compared to the stator cylindrical portion shown in Figure 14, the reduction rate E1 of the first reduction portion 171 is set to be greater than or equal to the reduction rate E3 of the third reduction portion 173 and greater than or equal to the reduction rate E2 of the second reduction portion 172.

[0081] In the stator cylindrical portion 6 shown in Figure 16, compared to the stator cylindrical portion shown in Figure 14, the reduction rate E2 of the second reduction portion 172 is set to be greater than or equal to the reduction rate E1 of the first reduction portion 171 and greater than or equal to the reduction rate E3 of the third reduction portion 173.

[0082] 14 to 16, two change portions where the reduction rate changes are provided, but three may be provided. Fig. 17 is a diagram showing the change in groove depth D in the axial direction A1 of a stator cylindrical portion provided with three change portions where the reduction rate of the groove depth changes.

[0083] In the configuration shown in FIG. 17, a fourth decreased portion 174 is further provided between the third decreased portion 173 and the end 6b described in FIG. 14. The portion where the third decreased portion 173 and the fourth decreased portion 174 are connected is shown as a third varying portion 177. The fourth decreased portion 174 is a portion where the groove depth D decreases at a constant rate of decrease E4. In the configuration shown in FIG. 14, the following is set: rate of decrease E1 of the first decreased portion 171 ≥ rate of decrease E2 of the second decreased portion 172 ≥ rate of decrease E3 of the third decreased portion 173 ≥ rate of decrease E4 of the fourth decreased portion 174. The groove depth in the third decreased portion 177 is shown as a varying portion groove depth Df.

[0084] In this way, the stator cylindrical portion may be provided with four portions with different constant reduction rates and three varying portions with varying reduction rates.

[0085] 17, if the groove depth Db at the exhaust-side end 6b is smaller than the groove depth Da at the intake-side end 6a, and the groove depth reduction rate on the intake side is greater than that on the exhaust side, the reduction rates may be different between the reduction portions. Although not shown in the figures, as in the case of a configuration having two change portions (FIGS. 14 to 16), the reduction rate E1 of the first reduction portion 171 may be set to be greater than or equal to the reduction rate E2 of the second reduction portion 172, greater than or equal to the reduction rate E4 of the fourth reduction portion 174, or greater than or equal to the reduction rate E3 of the third reduction portion 173. As shown in Examples 8 to 15 below, the reduction rate E1 of the first reduction portion 171, the reduction rate E2 of the second reduction portion 172, the reduction rate E3 of the third reduction portion 173, and the reduction rate E4 of the fourth reduction portion 174 may be set to be greater than or equal to the reduction rate E3 of the third reduction portion 173.

[0086] (Example) The following describes the embodiment in detail using examples.

[0087] Examples 5 to 7 In the following Examples 5 to 7 and Comparative Example 4, the various elements of the drag pump section P2 were set to the values ​​shown in Table 4.

[0088] (Table 4) TIFF0007746864000004.tif8194 Furthermore, the length Lc from the intake side end 6a of the stator cylindrical portion 6 to the first transition portion 175 was set to 40 mm, and the length Ld from the end 6a to the second transition portion 176 was set to 70 mm.

[0089] The stator cylindrical portion in the fifth embodiment has a shape shown in FIG. 14, and the reduction rate E1 of the first reduced portion 171≧the reduction rate E2 of the second reduced portion 172≧the reduction rate E3 of the third reduced portion 173.

[0090] The stator cylindrical portion in the sixth embodiment has a shape shown in FIG. 15, and the reduction rate E1 of the first reduced portion 171≧the reduction rate E3 of the third reduced portion 173≧the reduction rate E2 of the second reduced portion 172.

[0091] The stator cylindrical portion in the seventh embodiment has a shape shown in FIG. 16, and the decrease rate E2 of the second decreased portion 172≧the decrease rate E1 of the first decreased portion 171≧the decrease rate E3 of the third decreased portion 173.

[0092] The stator cylindrical portion of Comparative Example 4 has the shape shown in FIG. 7 described above, and the groove depth D decreases linearly from the end 6a toward the end 6b at a constant rate.

[0093] The dimensions of the stator cylindrical portion in Comparative Example 4 and Examples 5 to 7 are shown in Table 5 below. (Table 5) TIFF0007746864000005.tif63168 The elements of the drag pump section P2 were set to the values ​​shown in Table 4 and Table 5, and performance calculations were performed. The calculations are shown in FIGS.

[0094] FIG. 18 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Examples 5 to 7 and Comparative Example 4. FIG. 19 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Examples 5 to 7 and Comparative Example 4. In FIGS. 18 and 19, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This ratio is based on the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 10 Pa. In FIGS. 18 and 19, Example 5 is shown by a solid line, Example 6 is shown by a dotted line, Example 7 is shown by a dashed-dotted line, and Comparative Example 4 is shown by a two-dot chain line.

[0095] 18 and 19, even when large amounts of exhaust such as 2000 sccm or 3000 sccm are performed, the increase in intake-side pressure due to the increase in exhaust-side pressure is suppressed in Examples 5 to 7 compared to Comparative Example 4. Therefore, it is understood that the back pressure characteristics are improved in Examples 5 to 7 compared to Comparative Example 4. This shows that it is preferable for the portion with the largest reduction rate in groove depth to be located closer to the intake side than the portion with the smallest reduction rate in groove depth.

[0096] Furthermore, by comparing Example 5 with Example 7, it can be seen that the back pressure characteristics are more improved when the portion with the largest reduction rate in groove depth is located closest to the intake side, and by comparing Example 5 with Example 6, it can be seen that the back pressure characteristics are more improved when the portion with the smallest reduction rate in groove depth is located closest to the exhaust side.

[0097] (Examples 8 to 15) In the following Examples 8 to 15, the elements of the drag pump section P2 were set to the values ​​shown in Table 6.

[0098] (Table 6) TIFF0007746864000006.tif8198 Also, as shown in Figure 17, the length Lc from the intake side end 6a of the stator cylindrical portion 6 to the first change portion 175 was set to 25 mm, the length Ld from the end 6a to the second change portion 176 was set to 50 mm, and the length Le from the end 6a to the third change portion 177 was set to 75 mm.

[0099] The stator cylindrical portion in Example 8 has the shape shown in Figure 17, and shows an example where the reduction rate E1 of the first reduction portion 171 is set to be greater than or equal to the reduction rate E2 of the second reduction portion 172, greater than or equal to the reduction rate E3 of the third reduction portion 173, and greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0100] The stator cylindrical portion in Example 9 shows an example where the reduction rate E1 of the first reduction portion 171 is set to be greater than or equal to the reduction rate E2 of the second reduction portion 172, greater than or equal to the reduction rate E4 of the fourth reduction portion 174, and greater than or equal to the reduction rate E3 of the third reduction portion 173.

[0101] The stator cylindrical portion in Example 10 shows an example where the reduction rate E1 of the first reduction portion 171 is set to be greater than or equal to the reduction rate E3 of the third reduction portion 173, greater than or equal to the reduction rate E2 of the second reduction portion 172, and greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0102] The stator cylindrical portion in Example 11 shows an example where the reduction rate E2 of the second reduction portion 172 is set to be greater than or equal to the reduction rate E1 of the first reduction portion 171, greater than or equal to the reduction rate E3 of the third reduction portion 173, and greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0103] The stator cylindrical portion in Example 12 shows an example where the reduction rate E2 of the second reduction portion 172 ≧ the reduction rate E1 of the first reduction portion 171 ≧ the reduction rate E4 of the fourth reduction portion 174 ≧ the reduction rate E3 of the third reduction portion 173.

[0104] The stator cylindrical portion in Example 13 shows an example where the reduction rate E3 of the third reduction portion 173 is set to be greater than or equal to the reduction rate E1 of the first reduction portion 171, greater than or equal to the reduction rate E2 of the second reduction portion 172, and greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0105] The stator cylindrical portion in Example 14 shows an example where the reduction rate E2 of the second reduction portion 172 is set to be greater than or equal to the reduction rate E3 of the third reduction portion 173, and the reduction rate E1 of the first reduction portion 171 is set to be greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0106] The stator cylindrical portion in Example 15 shows an example where the reduction rate E3 of the third reduction portion 173 is set to be greater than or equal to the reduction rate E2 of the second reduction portion 172, greater than or equal to the reduction rate E1 of the first reduction portion 171, and greater than or equal to the reduction rate E4 of the fourth reduction portion 174.

[0107] The cylindrical stator portion of Comparative Example 5 has the shape shown in FIG. 7 described above, and the groove depth D decreases linearly from the end 6a toward the end 6b at a constant rate.

[0108] (Table 7) TIFF0007746864000007.tif81170 The elements of the drag pump section P2 were set to the values ​​shown in Table 6 and Table 7, and performance calculations were performed. The calculations are shown in FIGS. 20 and 21.

[0109] FIG. 20 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Examples 8 to 10 and Comparative Example 5. FIG. 21 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Examples 8 to 10 and Comparative Example 5. In FIGS. 20 and 21, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This ratio is based on the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 10 Pa. In FIGS. 20 and 21, Example 8 is shown by a solid line, Example 9 is shown by a dotted line, Example 10 is shown by a dashed-dotted line, and Comparative Example 5 is shown by a two-dot chain line.

[0110] (Table 8) TIFF0007746864000008.tif88170 The elements of the drag pump section P2 were set to the values ​​shown in Table 6 and Table 8, and performance calculations were performed. The calculations are shown in FIGS.

[0111] FIG. 22 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Examples 11 and 12 and Comparative Example 5. FIG. 23 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Examples 11 and 12 and Comparative Example 5. In FIGS. 22 and 23, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This ratio is based on the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 10 Pa. In FIGS. 22 and 23, Example 11 is shown by a solid line, Example 12 is shown by a dotted line, and Comparative Example 5 is shown by a two-dot chain line. (Table 9) TIFF0007746864000009.tif74170 The elements of the drag pump section P2 were set to the values ​​shown in Table 6 and Table 9, and performance calculations were performed. The calculations are shown in FIGS.

[0112] FIG. 24 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 2000 sccm in Examples 13 to 15 and Comparative Example 5. FIG. 25 shows the relationship between the intake-side pressure and the exhaust-side pressure of the drag pump section P2 when N2 was pumped at 3000 sccm in Examples 13 to 15 and Comparative Example 5. In FIGS. 24 and 25, the horizontal axis represents the exhaust-side pressure, and the vertical axis represents the intake-side pressure ratio. This ratio is based on the intake-side pressure of the drag pump section P2 when the exhaust-side pressure of the drag pump section P2 is 10 Pa. In FIGS. 24 and 25, Example 13 is shown by a solid line, Example 14 is shown by a dotted line, Example 15 is shown by a dashed-dot line, and Comparative Example 5 is shown by a two-dot chain line.

[0113] 20 to 25, even when large amounts of exhaust such as 2000 sccm or 3000 sccm are performed, the increase in intake-side pressure due to the increase in exhaust-side pressure is suppressed in Examples 8 to 15 compared to Comparative Example 5. Therefore, it can be seen that the back pressure characteristics are improved in Examples 8 to 15 compared to Comparative Example 5. This shows that it is preferable for the portion with the largest reduction rate in groove depth to be located closer to the intake side than the portion with the smallest reduction rate in groove depth.

[0114] Furthermore, for example, by comparing Example 8 with Examples 13 and 14, it is found that it is preferable for the portion with the largest reduction rate in groove depth to be located closest to the intake side. Also, for example, by comparing Example 8 with Example 9, it is found that it is preferable for the portion with the smallest reduction rate in groove depth to be located closest to the exhaust side, as this will further improve the back pressure characteristics.

[0115] (Other embodiments) Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0116] In the above embodiment, the tip 62a is formed in a straight line because the rate of decrease is constant in the intake-side portion 71 and the exhaust-side portion 72, but it may be formed in a curved shape so as to pass through the transition portion 73. In other words, it is only necessary that the rate of decrease in the intake-side portion 71 is greater than the rate of decrease in the exhaust-side portion 72, and the rate of decrease does not have to be constant.

[0117] In the above embodiment, the thread grooves are formed on the inner peripheral surface 6s of the stator cylindrical portion 6, but the thread grooves may be formed on the outer peripheral surface of the rotor cylindrical portion 23. In addition, the stator cylindrical portion 6 may be integrated with the base 9.

[0118] In the above embodiment, five to eight threads 62 are formed as an example, but the number may be five or less, or eight or more.

[0119] In the above embodiment, the intake-side end of the intake-side portion 71, which is an example of a first portion, coincides with the end 6a, and the exhaust-side end of the exhaust-side portion 72 coincides with the end 6b. However, a cylindrical body and a threaded portion may be further provided on the intake side of the intake-side portion 71. Furthermore, a cylindrical body and a threaded portion may be further provided on the exhaust side of the exhaust-side portion 72. FIG. 26 shows the change in groove depth D from the tip 62a' of the thread 62' to the inner circumferential surface 61s' of the cylindrical body 61' in a modified example. On 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. In the modified example shown in FIG. 26, the groove depth D of the end portion 74 is formed at a constant height equal to the groove depth Da of the end of the intake-side portion 71 on the intake port 14 side. 26, the groove depth D of the end portion 75 is formed to be constant and the same height as the groove depth Db of the end of the exhaust port 16 side of the exhaust-side portion 72. Note that the end portions 74, 75 may be formed so that the groove depth D decreases from the end 6a toward the end 6b.

[0120] (Aspect) It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0121] (First aspect) A vacuum pump includes a housing, a rotor cylindrical portion, and a stator cylindrical portion. The housing has an intake port for sucking in gas and an exhaust port for discharging the sucked gas. The rotor cylindrical portion is housed in the housing. The stator cylindrical portion is housed in the housing and is disposed opposite the rotor cylindrical portion. A thread groove is formed on one of the opposing surfaces of the stator cylindrical portion and the rotor cylindrical portion. The groove depth is smaller at the exhaust side end than at the intake side end. The rate of decrease in groove depth is greater on the intake side than on the exhaust side.

[0122] In the vacuum pump according to the first aspect, the groove depth of the thread groove is smaller at the exhaust end than at the intake end, and the rate of decrease in the groove depth is set to be larger at the intake side than at the exhaust side. By increasing the rate of decrease in the groove depth at the intake side, gas molecules can be more easily sent from the intake side of the thread groove to the exhaust side. Furthermore, by decreasing the rate of decrease in the groove depth at the exhaust side, gas molecules can be prevented from flowing back from the exhaust side to the intake side of the thread groove.

[0123] Therefore, even if the conductance of the drag pump section formed by the rotor cylindrical section and the stator cylindrical section is increased, the back pressure characteristics can be improved.

[0124] Furthermore, by improving the back pressure characteristics, the increase in pressure on the intake side can be reduced even with a higher exhaust pressure, making it possible to select a smaller auxiliary pump, which is a factor that leads to an increase in pressure on the exhaust port side.This allows for greater design freedom, reduces costs, and improves maintainability.

[0125] (Second Aspect) In the vacuum pump according to the first aspect, the thread groove has a first portion and a second portion. The first portion has a constant rate of decrease in groove depth. The second portion is located closer to the exhaust side than the first portion and also has a constant rate of decrease in groove depth. The rate of decrease in the first portion is greater than the rate of decrease in the second portion.

[0126] In the vacuum pump according to the second aspect, the first section facilitates sending gas molecules to the exhaust side, and the second section makes it difficult for gas molecules to flow back, thereby improving the back pressure characteristics even when the conductance of the drag pump section formed by the rotor cylindrical section and the stator cylindrical section is increased.

[0127] (Aspect 3) In the vacuum pump according to the second aspect, the first part and the second part are connected by a changing part. Let the groove depth at the intake side end of the first part be Da, the groove depth at the exhaust side end of the second part be Db, and the groove depth at the changing part be Dc. Then, Db ≦ Dc ≦ (Da + Db) × 0.5 is satisfied.

[0128] In the vacuum pump according to the third aspect, by satisfying Db ≦ Dc ≦ (Da + Db) × 0.5, even when the conductance of the drag pump part is increased, the backpressure characteristics can be improved.

[0129] (Aspect 4) In the vacuum pump according to the second aspect, let the length along the axial direction of the rotor cylinder part from the intake side end of the first part to the changing part be La, and the length along the axial direction from the intake side end of the first part to the exhaust side end of the second part be Lb. Then, 0 < La < Lb × 2 / 3 is satisfied.

[0130] In the vacuum pump according to the fourth aspect, by satisfying 0 < La < Lb × 2 / 3, even when the conductance of the drag pump part is increased, the backpressure characteristics can be improved.

[0131] (Aspect 5) In the vacuum pump according to the third or fourth aspect, 1.5 ≦ Da / further satisfies Db.

[0132] In the vacuum pump according to the fifth aspect, by satisfying 1.5 ≦ Da / Db, even when the conductance of the drag pump part is increased, the backpressure characteristics can be improved.

[0133] (Aspect 6) In the vacuum pump according to the first aspect, the screw groove has a plurality of parts with different rates of decrease in groove depth. The part with the largest rate of decrease in groove depth is arranged on the intake side rather than the part with the smallest rate of decrease in groove depth.

[0134] In the vacuum pump according to the sixth aspect, by arranging the portion where the groove depth reduction rate is greatest on the intake side of the portion where the groove depth reduction rate is smallest, it becomes easier to send gas molecules to the exhaust side on the intake side of the groove, and it is possible to prevent gas molecules from flowing back from the exhaust side of the groove to the intake side.

[0135] Therefore, even if the conductance of the drag pump section is increased, the back pressure characteristics can be improved.

[0136] (Seventh Aspect) In the vacuum pump according to the sixth aspect, the portion where the reduction rate of the groove depth is greatest is disposed on the most intake side of the plurality of portions.

[0137] In the vacuum pump according to the seventh aspect, gas molecules can be more easily sent from the intake side of the thread groove to the exhaust side.

[0138] (Eighth Aspect) In the vacuum pump according to the sixth or seventh aspect, the portion where the rate of reduction in the groove depth is smallest is disposed on the most exhaust side of the plurality of portions.

[0139] In the vacuum pump according to the eighth aspect, it is possible to further prevent gas molecules from flowing back from the exhaust side to the intake side of the thread groove. [Explanation of symbols]

[0140] 1: vacuum pump, 2: housing, 3: rotor, 4: motor, 5: stator blade unit, 6: stator cylindrical portion, 6a: end, 6b: end, 6s: inner peripheral surface, 8: casing, 9: base, 10: fixing flange, 11: first end, 12: second end, 13: side portion, 14: intake port, 15: base end, 16: exhaust port, 20: bolt, 21: shaft, 22: rotor blade unit, 23: rotor cylindrical portion, 23s: outer peripheral surface, 24A-24C: bearings , 25: rotor blade, 26: motor rotor, 27: motor stator, 28: stator blade, 29: protective bearing, 60: screw groove, 61: cylindrical body, 61s: inner surface, 62: screw thread, 62a: tip, 62´: screw thread, 63: groove portion, 71: intake side portion, 72: exhaust side portion, 73: transition portion, 74: end portion, 75: end portion, 1062: screw thread, P1: turbine portion, P2: drag pump portion, S1: first internal space, S2: second internal space

Claims

1. a housing having an intake port for drawing in gas and an exhaust port for discharging the drawn gas; a rotor cylindrical portion accommodated in the housing; a stator cylindrical portion accommodated in the housing and disposed opposite the rotor cylindrical portion, a thread groove is formed on one of the opposing surfaces of the stator cylindrical portion and the rotor cylindrical portion, The groove depth of the screw groove is smaller at the exhaust side end than at the intake side end, the rate of decrease in the groove depth is greater on the intake side than on the exhaust side, The screw groove is a first portion in which the groove depth decreases at a constant decreasing rate; a second portion disposed closer to the exhaust side than the first portion, in which the groove depth decreases at a constant decreasing rate; The reduction rate of the first portion is greater than the reduction rate of the second portion; the first portion and the second portion are connected by a portion where the rate of decrease changes, the groove depth at the intake side end of the first portion is Da, the groove depth at the exhaust side end of the second portion is Db; When the groove depth in the transition portion is Dc, Db≦Dc≦(Da+Db)×0.5 is satisfied. Vacuum pump.

2. a length along the axial direction of the rotor cylindrical portion from the intake side end of the first portion to the transition portion is defined as La; When the length along the axial direction from the intake side end of the first portion to the exhaust side end of the second portion is Lb, 0<La<Lb×2 / 3 is satisfied.

2. The vacuum pump according to claim 1.

3. Further satisfying 1.5≦Da / Db, 3. A vacuum pump according to claim 1 or 2.

4. The thread groove has a plurality of portions where the groove depth reduction rate is different, The portion where the groove depth reduction rate is greatest is located closer to the intake side than the portion where the groove depth reduction rate is smallest.

2. The vacuum pump according to claim 1.

5. The portion with the largest rate of reduction in groove depth is disposed closest to the intake side among the plurality of portions.

5. A vacuum pump according to claim 4.

6. the portion with the smallest rate of decrease in groove depth is disposed closest to the exhaust side among the plurality of portions; 6. A vacuum pump according to claim 4 or 5.

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