EP4682381A1

EP4682381A1 - Vacuum pump

Info

Publication number: EP4682381A1
Application number: EP25189341.8A
Authority: EP
Inventors: Tetsuro Sugiura; Masami Nagayama; Masashi Obuchi; Anagha KAMATKAR
Original assignee: Ebara Corp
Current assignee: Ebara Corp
Priority date: 2024-07-17
Filing date: 2025-07-14
Publication date: 2026-01-21
Also published as: JP2026013457A; KR20260012141A; CN121363533A

Abstract

Each of the first Roots rotor (8) and the second Roots rotor (9) has an involute side surface (31) having a shape of an involute curve, an arcuate convex surface (34) located radially outwardly of the involute side surface (31), an outer smooth curved surface (35) smoothly coupling the involute side surface (31) to the arcuate convex surface (34), an arcuate concave surface (36) located radially inwardly of the involute side surface (31), and an inner smooth curved surface (37) smoothly coupling the involute side surface (31) to the arcuate concave surface (36). A radius of curvature (R1) of the arcuate convex surface (34) is smaller than a radius of curvature (R2) of the arcuate concave surface (36).

Description

BACKGROUND OF THE INVENTION

Field of the Invention:

The present invention relates to a vacuum pump, and more particularly to a vacuum pump suitable for use in evacuating a process gas used in manufacturing of semiconductor devices, liquid crystal panels, LEDs, solar cells, or the like.

Description of the Related Art:

In process of manufacturing semiconductor devices, liquid crystal panels, LEDs, solar cells, etc., a process gas is introduced into a process chamber to perform a certain type of process, such as etching process or CVD process. The process gas that has been introduced into the process chamber is exhausted by a vacuum pump. Generally, the vacuum pump used in these manufacturing processes that require high cleanliness is so-called dry vacuum pump that does not use oil in its gas flow passage. One typical example of such a dry vacuum pump is a positive-displacement vacuum pump having a pair of Roots rotors in a rotor chamber which are rotated in opposite directions to deliver the gas.

Citation List

Patent Literature

Patent document 1: International laid-open patent publication No. H1-077782 A process gas may contain particles of by-products. Such particles flow into the vacuum pump along with the process gas. Moreover, depending on conditions in the vacuum pump (e.g., temperature, pressure), particles may be generated in the vacuum pump after the process gas flows into the vacuum pump. Most of the particles are discharged from the vacuum pump along with the process gas, but some of the particles remain in the rotor chamber and gradually accumulate in the rotor chamber. In particular, when convex and concave surfaces of two opposing Roots rotors are in surface contact (technically, the Roots rotors are in non-contact in reality), there is no place for the particles to escape. As a result, the particles are strongly sandwiched between the convex and concave surfaces of the Roots rotors, thus possibly hindering the rotation of the Roots rotors.
On the other hand, in order to improve pump efficiency, it is desirable that a gap between the Roots rotors is as small as possible. Therefore, after the Roots rotors are manufactured and assembled, the gap between the Roots rotors is measured using a feeler gauge. The feeler gauge is composed of multiple thin metal leaves with different thicknesses. A thickness of a metal leaf that can be inserted into the gap between the Roots rotors corresponds to the gap between the Roots rotors.
However, an outer peripheral surface of each Roots rotor is composed of a combination of a circular arc and an involute curve, so that the circular arc is not smoothly connected to the involute curve. Therefore, the metal leaf of the feeler gauge cannot deform along the outer peripheral surface of the Roots rotor, and only a metal leaf having a thickness smaller than the actual gap can be inserted into the gap between the Roots rotors. As a result, the feeler gauge may not be able to measure the gap between the Roots rotors correctly.

SUMMARY OF THE INVENTION

The present invention provides a vacuum pump capable of preventing particles from being caught between Roots rotors, capable of maintaining smooth rotation of the Roots rotors, and capable of allowing a feeler gauge to accurately measure a gap between the Root rotors.
In an embodiment, there is provided a vacuum pump comprising: a pump casing having at least one rotor chamber therein; and a first Roots rotor and a second Roots rotor arranged in parallel in the rotor chamber, wherein each of the first Roots rotor and the second Roots rotor has an involute side surface having a shape of an involute curve, an arcuate convex surface located radially outwardly of the involute side surface, an outer smooth curved surface smoothly coupling the involute side surface to the arcuate convex surface, an arcuate concave surface located radially inwardly of the involute side surface, and an inner smooth curved surface smoothly coupling the involute side surface to the arcuate concave surface, and a radius of curvature of the arcuate convex surface is smaller than a radius of curvature of the arcuate concave surface.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface is shorter than the involute side surface.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape of Bezier curve.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape of spline curve.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape of kernel curve.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape of natural spline curve.
In an embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape of B-spline curve.
In an embodiment, each of the arcuate convex surface and the arcuate concave surface is longer than the involute side surface.
In an embodiment, a width of a space formed between the arcuate convex surface and the arcuate concave surface when facing each other increases with a distance from a position of a minimum clearance between the arcuate convex surface and the arcuate concave surface.
In an embodiment, the radius of curvature of the arcuate convex surface is 0.2 to 0.9 times the radius of curvature of the arcuate concave surface.
Since the radius of curvature of the arcuate convex surface of the first Roots rotor is smaller than the radius of curvature of the arcuate concave surface of the second Roots rotor, a minimum clearance is formed between one point on the arcuate convex surface of the first Roots rotor and one point on the arcuate concave surface of the second Roots rotor. A clearance between the Roots rotors gradually increases on both sides of the minimum clearance. Therefore, the particles are less likely to be sandwiched between the arcuate convex surface of the first Roots rotor and the arcuate concave surface of the second Roots rotor. As a result, the Roots rotors can maintain their smooth rotation.
The involute side surface and the arcuate convex surface are smoothly coupled by the outer smooth curved surface, and the involute side surface and the arcuate concave surface are smoothly coupled by the inner smooth curved surface. Therefore, when the gap between the first Roots rotor and the second Roots rotor is measured, a metal leaf of a feeler gauge can be smoothly deformed along the outer circumferential surfaces of the first Roots rotor and the second Roots rotor. As a result, the feeler gauge can accurately measure the gap between the first Roots rotor and the second Roots rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of a vacuum pump apparatus;
FIG. 2 is a cross-sectional view taken along a line A-A of FIG. 1;
FIG. 3 is an enlarged view of a Roots rotor;
FIG. 4 is an enlarged view showing an embodiment of an involute side surface, an outer smooth curved surface, an inner smooth curved surface, an arcuate convex surface, and an arcuate concave surface;
FIG. 5 is an enlarged view illustrating a clearance between Roots rotors;
FIG. 6 is a diagram showing two Roots rotors when rotating in opposite directions; and
FIG. 7 is a diagram showing an embodiment of three-lobe Roots rotors.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an embodiment of a vacuum pump apparatus, and FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. The vacuum pump apparatus of the embodiment described below is a positive displacement vacuum pump apparatus. In particular, the vacuum pump apparatus shown in FIGS. 1 and 2 is a so-called dry vacuum pump apparatus that does not use oil in its gas flow passage. Since vaporized oil does not flow to an upstream side, the dry vacuum pump apparatus is suitable for use in semiconductor device manufacturing apparatus that requires high cleanliness.
As shown in FIG. 1, the vacuum pump apparatus includes a vacuum pump 1 and an electric motor 2 that drives the vacuum pump 1. The vacuum pump 1 of this embodiment is a single-stage vacuum pump. Specifically, the vacuum pump 1 includes a pump casing 6 having a rotor chamber 5 therein, single-stage Roots rotors 8 and 9 arranged in the rotor chamber 5, and a pair of rotational shafts 11 and 12 that support the Roots rotors 8 and 9, respectively. In one embodiment, the vacuum pump 1 may be a multi-stage vacuum pump having multi-stage Roots rotors arranged in a plurality of rotor chambers.
Although only the Roots rotor 8 and the rotational shaft 11 are depicted in FIG. 1, the Roots rotor 8 and the Roots rotor 9 are arranged in parallel in the pump casing 6, and the rotational shaft 11 and the rotational shaft 12 are arranged in parallel. FIG. 2 shows the Roots rotor 8 and the Roots rotor 9 arranged in parallel. The Roots rotor 8 is supported by the rotational shaft 11, and the Roots rotor 9 is supported by the rotational shaft 12.
The Roots rotor 8 and the Roots rotor 9 are not in contact with each other, and the Roots rotors 8 and 9 are not in contact with an inner surface of the pump casing 6. Therefore, the Roots rotors 8 and 9 can rotate smoothly in the pump casing 6 without using lubricating oil.
The Roots rotor 8 and the rotational shaft 11 may be an integral structure. Similarly, the Roots rotor 9 and the rotational shaft 12 may be an integral structure. The electric motor 2 is coupled to one of the rotational shafts 11 and 12. In one embodiment, a pair of electric motors 2 may be coupled to the rotational shafts 11 and 12, respectively.
The pump casing 6 has a gas inlet 14 and a gas outlet 15 that communicate with the rotor chamber 5. The gas inlet 14 is coupled to a chamber (not shown) filled with a gas to be delivered. In one example, the gas inlet 14 is coupled to a process chamber of a semiconductor-device manufacturing apparatus, and the vacuum pump 1 is used to evacuate a process gas that has been introduced into the process chamber.
The vacuum pump 1 further includes a gear housing 16 located outwardly of a side wall 6A of the pump casing 6. A pair of gears 20 that mesh with each other are arranged in the gear housing 16. In FIG. 1, only one gear 20 is depicted. These gears 20 are fixed to the rotational shafts 11 and 12, respectively. The electric motor 2 is rotated by a motor driver (not shown). One of the rotational shafts 11 and 12 to which the electric motor 2 is coupled is rotated by the electric motor 2. This rotation is transmitted via the gears 20 to other one of the rotational shafts 11 and 12 to which the electric motor 2 is not coupled to thereby rotate the other rotational shaft in the opposite direction.
The rotational shafts 11 and 12 are rotatably supported by bearings 17 held on the side wall 6A of the pump casing 6 and bearings 18 held on other side wall 6B of the pump casing 6. The electric motor 2 includes a motor housing 22 located outwardly of the side wall 6B of the pump casing 6, and a motor rotor 2A and a motor stator 2B arranged in the motor housing 22.
In one embodiment, a pair of electric motors 2 coupled to the rotational shafts 11 and 12, respectively, may be provided. The pair of electric motors 2 are synchronously rotated in opposite directions by a motor driver (not shown), so that the rotational shafts 11 and 12 and the Roots rotors 8 and 9 are synchronously rotated in the opposite directions, as shown in FIG. 2. The role of the gears 20 in this case is to prevent out of the synchronized rotation of the Roots rotors due to a sudden external cause.
When the electric motor 2 rotates the Roots rotors 8 and 9, gas is sucked into the rotor chamber 5 through the gas inlet 14. The gas is delivered to the gas outlet 15 by the rotation of the Roots rotors 8 and 9 in the rotor chamber 5, and is discharged from the pump casing 6 through the gas outlet 15.
The Roots rotors 8 and 9 have the same outer shape. Therefore, the Roots rotor 8 will be described below. FIG. 3 is an enlarged view of the Roots rotor 8. As shown in FIG. 3, the Roots rotor 8 has an involute side surface 31 having a shape of an involute curve, an arcuate convex surface 34 located radially outwardly of the involute side surface 31, an outer smooth curved surface 35 smoothly coupling the involute side surface 31 to the arcuate convex surface 34, an arcuate concave surface 36 located radially inwardly of the involute side surface 31, and an inner smooth curved surface 37 smoothly coupling the involute side surface 31 to the arcuate concave surface 36.
FIG. 4 is an enlarged view showing an embodiment of the involute side surface 31, the outer smooth curved surface 35, the inner smooth curved surface 37, the arcuate convex surface 34, and the arcuate concave surface 36. As shown in FIG. 4, the outer smooth curved surface 35 is located between the arcuate convex surface 34 and the involute surface 31, and both ends of the outer smooth curved surface 35 are connected to the arcuate convex surface 34 and the involute surface 31, respectively. The inner smooth curved surface 37 is located between the involute surface 31 and the arcuate concave surface 36, and both ends of the inner smooth curved surface 37 are connected to the involute surface 31 and the arcuate concave surface 36, respectively. Each of the outer smooth curved surface 35 and the inner smooth curved surface 37 is shorter than the involute side surface 31.
As shown in FIG. 4, the outer smooth curved surface 35 smoothly couples the involute side surface 31 to the arcuate convex surface 34, and the inner smooth curved surface 37 smoothly couples the involute side surface 31 to the arcuate concave surface 36, so that there are no corners on the outer circumferential surface of the Roots rotor 8. The Roots rotor 9 also has the same shape. Therefore, when a gap between the Roots rotor 8 and the Roots rotor 9 is measured using a feeler gauge, a metal leaf of the feeler gauge can be smoothly deformed along the outer circumferential surfaces of the Roots rotor 8 and the Roots rotor 9. As a result, the feeler gauge can accurately measure the gap between the Roots rotor 8 and the Roots rotor 9.
In this embodiment, each of the outer smooth curved surface 35 and the inner smooth curved surface 37 has a shape of Bezier curve. The Bezier curve can make the outer smooth curved surface 35 and the inner smooth curved surface 37 smooth. In other embodiments, each of the outer smooth curved surface 35 and the inner smooth curved surface 37 may have a shape of spline curve, kernel curve, natural spline curve, or B-spline curve. The kernel curve is a curve used to estimate a distribution of points using kernel density estimation. Factors that determine the shape of the kernel curve include a kernel function and a bandwidth. The kernel function is a function that determines a weight that influences each point, and the bandwidth is a parameter that determines a width of the kernel, which affects a smoothness of the kernel curve.
As shown in FIG. 3, the Roots rotor 8 is a so-called two-lobe Roots rotor having two protrusions. Therefore, the Roots rotor 8 has two arcuate convex surfaces 34, four involute side surfaces 31, four outer smooth curved surfaces 35, four inner smooth curved surfaces 37, and two arcuate concave surfaces 36. The two arcuate convex surfaces 34 are coupled to outer ends of the four outer smooth curved surfaces 35, and the two arcuate concave surfaces 36 are coupled to inner ends of the four inner smooth curved surfaces 37. Each of the arcuate convex surfaces 34 and the arcuate concave surfaces 36 is longer than the involute side surfaces 31.
A radius of curvature R1 of the arcuate convex surface 34 is smaller than a radius of curvature R2 of the arcuate concave surface 36. In one embodiment, the radius of curvature R1 of the arcuate convex surface 34 is 0.2 to 0.9 times the radius of curvature R2 of the arcuate concave surface 36. Therefore, as shown in FIG. 5 when the arcuate convex surface 34 of the Roots rotor 8 faces the arcuate concave surface 36 of the Roots rotor 9, only one point on the arcuate convex surface 34 of the Roots rotor 8 and one point on the arcuate concave surface 36 of the Roots rotor 9 are close to each other, and as a result, a minimum clearance G1min is formed between the arcuate convex surface 34 and the arcuate concave surface 36. A width W of a space 40 formed between the arcuate convex surface 34 of the Roots rotor 8 and the arcuate concave surface 36 of the Roots rotor 9 gradually increases according to a distance from a position at which the minimum clearance G1min is formed.
Since the radius of curvature R1 of the arcuate convex surface 34 of the Roots rotor 8 is smaller than the radius of curvature R2 of the arcuate concave surface 36 of the Roots rotor 9, the minimum clearance G1min is formed between one point on the arcuate convex surface 34 of the Roots rotor 8 and one point on the arcuate concave surface 36 of the Roots rotor 9, and a clearance between the Roots rotors 8 and 9 gradually increases on both sides of the minimum clearance G1min. Therefore, the particles are less likely to be sandwiched between the arcuate convex surface 34 of the Roots rotor 8 and the arcuate concave surface 36 of the Roots rotor 9. As a result, the Roots rotors 8 and 9 can maintain smooth rotation.
FIG. 6 is a diagram showing the two Roots rotors 8 and 9 when rotating in the opposite directions. As shown in FIG. 6, the involute side surfaces 31 of the Roots rotor 8 and the Roots rotor 9 face each other, and do not face the arcuate convex surface 34 and the arcuate concave surface 36. On the other hand, the arcuate convex surface 34 of the Roots rotor 8 faces the arcuate concave surface 36 of the Roots rotor 9 and does not face the involute side surface 31 of the Roots rotor 9. Similarly, the arcuate convex surface 34 of the Roots rotor 9 faces the arcuate concave surface 36 of the Roots rotor 8 and does not face the involute side surface 31 of the Roots rotor 8. When the Roots rotor 8 and the Roots rotor 9 are making one rotation, the Roots rotor 8 and the Roots rotor 9 are not in line contact but are in point contact (technically the Roots rotors 8 and 9 are in non-contact in reality). Therefore, particles are less likely to be caught between the Roots rotor 8 and the Roots rotor 9. A clearance G2 between the involute side surfaces 31 of the two Roots rotors 8 and 9 is constant at all times.
The involute side surface 31 is a surface that curves outward. Therefore, the clearance G2 is formed between one point on the involute side surface 31 of the Roots rotor 8 and one point on the involute side surface 31 of the Roots rotor 9, and a clearance between the Roots rotors 8 and 9 increases on both sides of the clearance G2. Due to such point contact (actually non-contact) of the involute side surfaces 31, particles are less likely to be caught between the involute side surface 31 of the Roots rotor 8 and the involute side surface 31 of the Roots rotor 9.
Although the Roots rotors 8 and 9 of the embodiments described above are two-lobe Roots rotors each having two protrusions, the present invention is not limited to the above embodiments. The present invention can be applied to three-lobe Roots rotor having three protrusions and multi-lobe Roots rotor having four or more protrusions.
For example, FIG. 7 is a diagram showing an embodiment of a three-lobe Roots rotor. In this embodiment also, each of Roots rotors 51 and 52 has an involute side surface 31 having a shape of an involute curve, an arcuate convex surface 34 located radially outwardly of the involute side surface 31, an outer smooth curved surface 35 smoothly coupling the involute side surface 31 to the arcuate convex surface 34, an arcuate concave surface 36 located radially inwardly of the involute side surface 31, and an inner smooth curved surface 37 smoothly coupling the involute side surface 31 to the arcuate concave surface 36. A radius of curvature R3 of the arcuate convex surface 34 is smaller than a radius of curvature R4 of the arcuate concave surface 36. Configurations of the three-lobe Roots rotors 51 and 52 in this embodiment that are not particularly described are the same as those of the above embodiments described with reference to FIGS. 1 to 6, so that overlapping descriptions will be omitted.
The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by limitation of the claims.

Claims

A vacuum pump comprising:
a pump casing having at least one rotor chamber therein; and

a first Roots rotor and a second Roots rotor arranged in parallel in the rotor chamber,

wherein each of the first Roots rotor and the second Roots rotor has an involute side surface having a shape of an involute curve, an arcuate convex surface located radially outwardly of the involute side surface, an outer smooth curved surface smoothly coupling the involute side surface to the arcuate convex surface, an arcuate concave surface located radially inwardly of the involute side surface, and an inner smooth curved surface smoothly coupling the involute side surface to the arcuate concave surface, and

a radius of curvature of the arcuate convex surface is smaller than a radius of curvature of the arcuate concave surface.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface is shorter than the involute side surface.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape of Bezier curve.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape of spline curve.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape of kernel curve.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape of natural spline curve.
The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape of B-spline curve.
The vacuum pump according to claim 1, wherein each of the arcuate convex surface and the arcuate concave surface is longer than the involute side surface.
The vacuum pump according to claim 1, wherein a width of a space formed between the arcuate convex surface and the arcuate concave surface when facing each other increases with a distance from a position of a minimum clearance between the arcuate convex surface and the arcuate concave surface.
The vacuum pump according to claim 1, wherein the radius of curvature of the arcuate convex surface is 0.2 to 0.9 times the radius of curvature of the arcuate concave surface.