US20130121858A1

US20130121858A1 - Vacuum pump

Info

Publication number: US20130121858A1
Application number: US13/625,882
Authority: US
Inventors: Yukiteru Sekita
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 2011-11-15
Filing date: 2012-09-25
Publication date: 2013-05-16
Also published as: CN103104539B; JP5919745B2; CN103104539A; JP2013104370A

Abstract

The present invention provides a vacuum pump capable of suppressing the structure from becoming complicated and improving the damping effect. The vacuum pump includes: a holding mechanism for clamping an outer race of the ball bearing in an axial direction and holding the outer race so that the outer race moves along a radial direction; and an elastic member disposed at an outer circumferential side of the outer race. The elastic member is disposed in contact with or close to the outer circumferential side of the outer race. Oil or grease is injected into a gap between the elastic member and the outer race. Through holding the outer race against the elastic member, the elastic member is deformed to suppress vibration. Furthermore, through injecting oil or grease into the gap, the damping effect can be further improved.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serial no.
2011-249507, filed on Nov. 15, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a vacuum pump, wherein a permanent magnet and a ball bearing are used for a bearing.
2. Description of Related Art
A bearing mechanism of a turbomolecular pump includes a structure using a ball bearing only, a structure using a ball bearing and a permanent magnet, and a magnetic bearing structure using an electromagnet only. A constitution as recorded in Japan Domestic Re-publication of PCT International Application Patent No. 2006-001243 is already known for a turbomolecular pump having the structure using a ball bearing and a permanent magnet.
Generally, the rotation frequency of a turbomolecular pump is higher than the resonant frequency (secondary critical speed) of a rotator, so that it is necessary to pass through the resonant frequency (secondary critical speed) when a pump starts and stops. The rotator vibrates when passing through the resonant frequency, but in the case of a bearing using an electromagnet, the vibration of a rotary shaft can be actively controlled. However, in the case of the structure using a permanent magnet and a ball bearing, the vibration cannot be actively controlled. Therefore, in the technology recorded in Japan Domestic Re-publication of PCT International Application Patent No. 2006-001243, a damper to reduce vibration is disposed on a portion where the ball bearing is disposed.
However, in the case of a turbomolecular pump with the constitution of using a permanent magnet and a ball bearing to support the rotator, and when passing through the critical speed, the rotation of the rotator in the portion of the permanent magnet is relatively large. Therefore, according to Japan Domestic Re-publication of PCT International Application Patent No. 2006-001243, an O ring is used to support an axially central portion at the outer circumference of the bearing, the rotary shaft is easy to incline and the damping effect is easily worsened. In addition, according to the damper mechanism recorded in Japan Domestic Re-publication of PCT International Application Patent No. 2006-001243, a double-sleeve structure is disposed outside a ball bearing, and a gel is disposed between two sleeves which are separated by the O ring. However, the structure is complicated and a large number of components are used.

SUMMARY OF THE INVENTION

The present invention provides a vacuum pump, in which a ball bearing is used for supporting a rotor formed with an exhaust function portion, and a motor is used to make the rotor rotate for vacuum exhaustion. The vacuum pump includes: a holding mechanism, clamping an outer race of the ball bearing in an axial direction and holding the outer race in a manner that the outer race can move along a radial direction; a housing, formed on a pump seat and accommodating the holding mechanism; and an elastic member, disposed in contact with or close to an outer circumferential side of the outer race.
According to an exemplary embodiment of the present invention, the elastic member is a ring-shaped elastic member disposed in the manner of surrounding an outer circumference of the outer race through a gap between the elastic member and the outer circumference of the outer race, and at least oil or grease is injected into the gap.
According to an exemplary embodiment of the present invention, the vacuum pump further includes: an outer circumferential side gap formed between an outer circumference of the elastic member and the housing; and oil or grease is injected into the circumferential side gap.
According to an exemplary embodiment of the present invention, the elastic member is a ring-shaped elastic member disposed in the manner of contacting with an axial centre of an outer circumferential surface of the outer race and arranged in the manner of forming a gap between the outer circumferential surface of the outer race and the housing, and at least oil or grease is injected into the gap.
According to an exemplary embodiment of the present invention, the elastic member is made of metal.
According to an exemplary embodiment of the present invention, the holding mechanism includes: a pair of pressure plates respectively arranged at two axial ends of the outer race; and an elastic support member disposed between each of the pair of pressure plates and the housing.
According to the present invention, in the vacuum pump of the embodiment, a ball bearing is used to support a rotor, the structure is simple and the damping effect is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a turbomolecular pump according to an exemplary embodiment of the present invention.

FIG. 2 is a partial enlarged view of the ball bearing 8.

FIG. 3 illustrates the first modified embodiment.

FIG. 4 illustrates the second modified embodiment.

FIG. 5 illustrates the third modified embodiment.

FIG. 6A illustrates the fourth modified embodiment.

FIG. 6B illustrates a protruding portion of the metal elastic member of FIG. 6A.

DESCRIPTION OF THE IMPLEMENTATION MANNERS

In the following, the exemplary embodiments of the present invention are illustrated with reference to the accompanying drawings. FIG. 1 illustrates a vacuum pump of an exemplary embodiment of the present invention, and is a schematic cross-sectional view of a turbomolecular pump. A rotary vane 30 and a cylindrical portion 31 used as an exhaust function portion are formed in a rotor 3. A fixed vane 20 is disposed corresponding to the rotary vane 30. In addition, a fixed cylinder (not shown in FIG. 1) used as a fixed side exhaust function portion is disposed corresponding to the cylindrical portion 31.
The rotor 3 is coupled to a shaft 1, and the shaft 1 is driven to rotate by a motor 4. The rotor 3 coupled to the shaft 1 is rotatably supported by using a magnetic bearing having permanent magnets 6 and 7 and a ball bearing 8. For the ball bearing 8, for example, an angular contact ball bearing is used. The cylindrical permanent magnet 6 is fixed on the rotor 3. On the other hand, the permanent magnet 7 at a fixed side is held on a magnet seat 11, and is arranged opposite to an inner circumferential side of the permanent magnet 6.
The magnet seat 11 is fixed on a flange plate portion of a pump casing 10. In an example shown in FIG. 1, a beam portion of the magnet seat 11 and a spacer ring 5 for positioning the fixed vane 20 are held in a manner of being held between the flange plate portion of the pump casing 10 and a seat 2. A bearing seat 13 for holding a ball bearing 9 is fixed at a centre of the magnet seat 11.
The ball bearing 9 is disposed for restraining the vibration of an upper portion of the shaft 1 in a radial direction, and a gap is formed between an inner race of the ball bearing 9 and the shaft 1. The size of the gap is set to be smaller than the size of the gap between the permanent magnet 6 and the permanent magnet 7. Accordingly, in the case that the rotor 3 rotates and when it passes through the critical speed, the contact between the permanent magnet 6 and the permanent magnet 7 is avoided.
FIG. 2 is a partial enlarged view of a ball bearing 8 disposed at a lower portion of the shaft 1. The ball bearing 8 is installed on a shaft portion formed at a lower portion of the shaft 1, and a nut 40 is used to fix an inner race 80. On the other hand, an outer race 81 of the ball bearing 8 is fixed inside a concave portion 22 (called a housing 22 in the following) formed in the seat 2.
In the housing 22, an outer race 81 is held by a pair of pressure plates 44 and 45 in an axial direction, and an elastic support member 42 is disposed between the housing 22 and the pressure plate 45 and between a housing cover 21 and the pressure plate 44, respectively. The housing cover 21 is fixed on the seat 2 by using a screw. For the elastic support member 42, a metal member or rubber as elastic as a spring is used. In addition, as for the shape, a ring-shaped elastic support member 42 can be used, whereas a gap can be left for arranging multiple elastic support members 42 into a ring shape.
In this way, the outer race 81 is elastically supported by the housing 22 through a holding mechanism 22 (the pressure plates 44 and 45, the elastic support member 42), thereby realizing a structure capable of achieving radial vibration of the ball bearing 8. For example, in the case that rubber is used as the elastic support member 42, through arranging the elastic support member 42 into a flat shape in the axial direction, the ball bearing 8 can be prevented from inclinations, and a sliding in the radial direction can be achieved.
In the housing 22, a ring-shaped elastic member 41 is disposed in the manner of contacting with an outer circumferential surface of the outer race 81. Because the outer race 81 held by the pressure plates 44 and 45 is elastically supported by the elastic member 41 and the elastic support member 42, a rotator vibrates along the radial direction when passing through the critical speed. In addition, through consuming a part of vibration energy during deformations of the elastic member 41 and the elastic support member 42, the vibration is suppressed.
In addition, it is set that the elastic member 41 and the elastic support member 42 used as damping members are directly accommodated inside the housing 22 formed in the seat 2, so that the number of components can be reduced. Further, because the elastic support member 42 and the pressure plates 44 and 45 are used for axial support for the outer race 81, compared with the aforementioned structures, the shaft does not incline easily.
In addition, in the example, the elastic member 41 and the elastic support member 42 are disposed as a ring shape and also multiple elastic members can be arranged at a circumference centred on the axis of the ball bearing 8. The elastic support member 42 is made of a material such as a rubber-based material, for example, an O-ring used as a sealing member can also be used. For example, in the case that an O-ring is used, the hardness of the O-ring is appropriately selected according to the weight of the rotator or a vibration condition.

First Modified Embodiment

FIG. 3 illustrates the first modified embodiment. In addition, same reference numerals are given to the part of same constituting elements shown in FIG. 2, and in the following, the different parts are illustrated in the following. In the modified embodiment, as shown in FIG. 2, an elastic member 41 is formed in a manner of constantly contacting with an outer race 81 of a ball bearing 8. On the other hand, in the first modified embodiment shown in FIG. 3, a slight gap 47 is formed between an elastic member 46 and the outer race 81, and the gap 47 is injected with oil which exerts the function of an oil film damper. In this case, oil should at least be injected into the gap 47, but oil can also be injected into the gap at an upper portion of the elastic member 46.
If a shaft 1 vibrates along a radial direction when passing through a critical speed, the oil injected into the gap 47 exerts the function of a damper, so that a damping effect can be improved. The size of the gap 47 is about 0.1 mm to 0.2 mm. In the case of large vibration as that when passing through the critical speed, the outer race 81 contacts with the elastic member 46 and causes a deformation of the elastic member 46, so that the elastic member 46 also exerts the function of a damper.

Second Modified Embodiment

FIG. 4 illustrates the second modified embodiment. In the first modified embodiment shown in FIG. 3, a gap 47 is formed between an elastic member 46 and an outer race. However, in the modified embodiment shown in FIG. 4, an inner diameter of an elastic member 49 is set to be the size of the gap 47 formed between the elastic member 49 and the outer race 81, and an outer diameter of the elastic member 49 is set between the elastic member 49 and a housing 22 in the manner of forming a gap 48. Each gap is injected with oil.
The size of the gap of an inner periphery and an outer periphery of the elastic member 49 is set to be about 0.1 mm to 0.2 mm in the same way as in the first variation, and the size of a gap in an axial direction of the elastic member 49 is set to be about 10 μm to 20 μm. Therefore, when passing through a critical speed, associated to the case of a shaft 1 vibrating along a radial direction, the elastic member 49 also vibrates along the radial direction, so that the oil injected into gaps 47 and 48 of the inner periphery and the outer periphery of the elastic member 49 exerts the function of an oil film damper. Compared with the case illustrated in FIG. 3, the damping effect is improved to a degree of forming the gap 48. In addition, when vibration amplitude of the shaft 1 is relatively large, not only the elastic member 49 vibrates, but also the outer race 81 contacts against the elastic member 49 and causes a deformation.

Third Modified Embodiment

FIG. 5 illustrates the third modified embodiment. In the third modified embodiment, a ring-shaped elastic member 50 is disposed in a manner of contacting with approximately an axial centre of an outer race 81 of a ball bearing 8. A gap 51 is formed at two axial ends of the elastic member 50, and the gap 51 is injected with oil which exerts the function of an oil film damper. In this case, the elastic member 50 and the oil of the gap 51 exert the function of a damper at the same time. In addition, although the elastic member 50 is arranged at the axial centre of the outer race 81 of the ball bearing 8 in the same manner as in the structure recorded in Japan Domestic Re-publication of PCT International Application Patent No. 2006-001243, the oil injected into the gap 51 exerts the function of the damper, so that the bearing can be prevented from inclinations.

Fourth Modified Embodiment

FIG. 6 illustrates the fourth modified embodiment. In FIG. 2 to FIG. 5, an elastic member 41 such as an O-ring is disposed on the outer circumferential side of the bearing 8, but a material of the elastic member is not limited to a rubber material or elastic resin, which, for example, can also be a metal. FIG. 6A refers to an example of a metal elastic member 52, which is formed into a ring shape from a metal corrugated board. A ring-shaped member denoted by chain double-dashed lines is a member denoted by overlapping the elastic member 41 in FIG. 2 and the metal elastic member 52.
In the case of a large pump, the weight of a rotator also increases, so that in the case that vibration becomes large, the amount of deformation becomes excessively large when using the elastic member made of a rubber material. Therefore, the metal elastic member 52 is preferably used. In addition, in FIG. 6A, an example in which the metal elastic member 52 is used in place of the elastic member 41 is taken for illustration. Elastic members 46, 49, and 50 shown in FIG. 3 to FIG. 5 can also be replaced, and the metal elastic member of the shape shown in FIG. 6A and FIG. 6B is used.
In the case that the metal elastic member is used in place of the elastic members 41 and 50, an inner circumferential surface of a housing 22 and an outer circumferential surface of an outer race 81 contact with the metal elastic member 52, but through injecting oil into a wavy gap, and the oil can exert the function of an oil film damper. The metal elastic members have various structures. For example, as shown in FIG. 6B, multiple protruding portions 53 a can be formed around an outer circumferential surface of a ring-shaped plate 53.
In addition, the oil is injected into the gap in the implementation manner; however, grease can also be injected in place of oil instead. A vibration damping effect can be produced by using grease, and the vibration of a shaft 1 when passing through a critical speed is thereby suppressed. In addition, the present invention is not limited to a turbomolecular pump, but can also be applied to a vacuum pump having a same bearing structure, for example, a vacuum pump such as a drag pump.
Each embodiment can be used alone respectively, or can also be used in combination. Because the effects of the implementation manners can be carried out separately or in combination. In addition, as long as the features of the present invention are not affected, the present invention is not limited by the implementation manners.

Claims

What is claimed is:

1. A vacuum pump using a ball bearing for supporting a rotor formed with an exhaust function portion and using a motor to make the rotor rotate for vacuum exhaustion, comprising:

a holding mechanism, clamping an outer race of the ball bearing in an axial direction and holding the outer race in a manner that the outer race is adapted to moves along a radial direction;

a housing, formed on a pump seat and accommodating the holding mechanism; and

an elastic member, located in the housing and disposed in contact with or close to an outer circumferential side of the outer race.

2. The vacuum pump according to claim 1, wherein

the elastic member is a ring-shaped elastic member disposed in a manner of surrounding an outer circumference of the outer race through a gap; and

at least oil or grease is injected into the gap.

3. The vacuum pump according to claim 2, wherein

an outer circumferential side gap is formed between the outer circumference of the elastic member and the housing; and

the oil or the grease is injected into the outer circumferential side gap.

4. The vacuum pump according to claim 1, wherein

the elastic member is a ring-shaped elastic member disposed in a manner of contacting with an axial centre of an outer circumferential surface of the outer race and arranged in a manner of forming a gap between the outer circumferential surface of the outer race and the housing; and

at least oil or grease is injected into the gap.

5. The vacuum pump according to claim 1, wherein:

the elastic member is made of metal.

6. The vacuum pump according to claim 1, wherein

the holding mechanism includes:

a pair of pressure plates, respectively disposed at two axial ends of the outer race; and

an elastic support member, disposed between each of the pair of pressure plates and the housing.