TW201410981A - Vacuum pump - Google Patents

Abstract

A vacuum pump, particularly a turbomolecular pump, comprises a rotor shaft (10) which is arranged in a pump housing (12) and is supported by two bearing assemblies (14). One of the bearing assemblies (14) comprises a rolling bearing (16). According to the invention, it is provided that the rolling bearing (16) is surrounded by a shell (22) which is arranged in the pump housing (12) via rolling bodies (28) allowing for a radial displacement of the rolling bearing (16).

Description

Vacuum pump

The present invention relates to a vacuum pump, and more particularly to a turbomolecular pump.

A vacuum pump such as a turbomolecular pump includes a rotor shaft inside the pump housing, such as a pump element of the rotor. Particularly in the case of a turbomolecular pump, the rotor shaft is driven at a high rotational speed of, for example, 60,000 rpm. The rotor shaft is supported via two bearing assemblies. The bearing assembly includes a magnetic bearing or a rolling bearing, respectively. In such a rapidly rotating rotor shaft, the bearing assembly must have high rigidity in the axial direction. A further requirement is that one of the two bearing assemblies is perpendicular to the longitudinal axis of the rotor, i.e., has a radial mobility. Typically, this radial rate of movement is achieved in the bearing on the pressure side. In the case of a vertically arranged rotor shaft, the bearing assembly is typically a lower bearing assembly.

An elastic ring is known, for example, from the European patent EP 2 126 365. In particular, due to the required axial rigidity, the shear stress occurring between the outer bearing ring and the adjacent components causes a large radial force. This radial force has an adverse effect.

A vacuum is known from the European patent EP 1 618 308. A pump comprising a rotor shaft supported via two bearing arrangements. The bearing device described in the European patent EP 1 618 308 comprises a rolling bearing supporting a shaft. The outer ring of this ball bearing is surrounded by an elastic ring. The elastic ring is disposed in an annular groove of the housing. In addition to the elastic ring that allows radial movement of the rolling bearing, an axial bearing is provided. The balls of the axial bearing are arranged axially with respect to the outer bearing ring. The ball position of such a bearing is between the surface of the bearing ring extending perpendicular to the longitudinal axis and the surface of the housing extending perpendicularly to the longitudinal axis of the rotor shaft. Thus, the bearing is provided for axial support of the outer bearing ring, but at the same time radial movement of the outer bearing ring and thus the radial movement of the entire rolling bearing may occur. The axial support of the rolling bearing on the outer bearing ring is provided in accordance with the European patent EP 1 618 308, which has the disadvantage that the ball diameter for achieving the axial bearing is limited by the width of the outer ring end face of the rolling bearing. Also, the axial ball bearing housing can no longer be controlled during the installation process. Furthermore, the required step holes and the required clearances in the housing are difficult to handle and measure.

It is an object of the present invention to provide a vacuum pump, in particular a turbomolecular pump, wherein the rotor shaft, while ensuring high axial rigidity, allows for easy and frictionless radial movement in at least one bearing assembly of the loaded rotor shaft. rate.

According to the present invention, the above objects are achieved by the features defined in the first item of the patent application scope.

The vacuum pump of the present invention, in particular the turbomolecular pump, comprises a pump housing which is usually composed of a plurality of parts. Within the pump housing, the rotor shaft is supported by two bearing assemblies. The rotor shaft is loaded like a pump such as a rotor element. At least one of the two bearing assemblies includes a rolling bearing. This bearing assembly is preferably attached to the bearing assembly on the pressure side. If the rotor shaft is vertically arranged, the bearing assembly on the pressure side is usually the lower bearing assembly. The bearing assembly on the suction side is in the case of a vertical rotor shaft, typically an upper bearing assembly, which may also include a rolling bearing. Preferably, the suction side bearing comprises a magnetic bearing.

A bearing assembly including a rolling bearing is provided with an outer casing that at least partially surrounds the rolling bearing, preferably completely surrounding the rolling bearing. The outer casing is designed and separately configured to allow radial displacement of the rolling bearing. This can be achieved by rolling elements, preferably balls. Due to the arrangement of rolling elements such as, for example, balls, which are provided to achieve a radial movement rate in relation to the outer casing surrounding the rolling bearing, the rolling bodies of such bearings are arranged on a relatively large radius. This has the advantage that the restoring moment will be greater in the case of axial forces that are eccentric or inclined to the axis of the shaft. Thereby, the rotor shaft is restored to the reference position, and the optimum position is individually improved.

According to a further preferred embodiment of the invention, the outer casing surrounds the outer ring of the rolling bearing. In particular, by selecting the material and by attaching the outer casing to the outer ring of the rolling bearing, the outer casing itself can have a certain damping property, in particular to prevent vibration of the critical frequency from being transmitted to the rotor shaft.

Also, the outer casing can be designed such that the outer casing itself forms the outer ring of the rolling bearing. This embodiment provides the advantage that the bearing assembly requires less radial mounting space. This installation space can be further reduced by also omitting the inner ring of the rolling bearing and forming directly on the surface of the rotor shaft. In this radially very small bearing assembly, the rolling elements of the rolling bearing are thus arranged in close proximity between the rotor shaft and the housing.

In order to form a bearing with a minimum size in the axial direction as well Preferably, the rolling elements that allow radial movement are axially disposed within the rolling bearing.

According to a preferred embodiment of the invention, the outer casing is formed with a radial collar that supports the rolling bodies. Thus, the rolling bodies are arranged between the radially arranged collar of the housing and the surface of the pump housing or connected to the components of the pump housing. Thereby, in a simple manner feasible in the invention, the radial movement of the bearing assembly is allowed, in most cases the radial movement of the lower bearing assembly and thus the pendulum movement of the rotor shaft.

Preferably, one surface of the collar is parallel to the housing surface of the pump housing. Due to the relatively small radial movement, the two surfaces can be planar. Since the rotor shaft performs a pendulum motion, it is preferred that at least one of the two opposite surfaces is spherical. In this design, the radius of the sphere preferably corresponds to the radius of the pendulum motion.

According to a preferred embodiment of the invention, the surface of the housing is formed by a preferably hardened disc inserted into the pump housing, the balls of the rolling bearing abutting the surface of the housing. This has the advantage that the balls do not cause damage such as dents in the housing. Since a preferably hardened disc is provided, the choice of housing material is not affected by surface properties. Therefore, to form the housing, a relatively soft housing material can also be selected.

The rolling bodies of the rotor shaft, which respectively permit the rolling and pendulum movement of the rotor shaft, are preferably arranged in the cage-like retaining element, thereby defining the position of the rolling bodies.

According to yet another preferred embodiment of the invention, the damping element is disposed between the outer casing and the pump housing. The damping element is designed to define the position of the bearing assembly in its unloaded state. Another purpose of the damping element is Allowing radial movement of individual bearing assemblies, however, also buffering this motion. The damping element preferably completely surrounds the housing. Preferably, the damping element is annular. The damping element can be partially received in the recess of the pump housing. Preferably, the axial position of the damping element is selected such that the latter is substantially disposed at the height of the rolling elements of the rolling bearing.

According to yet another preferred embodiment, the outer casing includes a radially inwardly retaining collar. In the assembled state, the outer ring of the rolling bearing abuts on the retaining collar. The retaining collar axially defines the position of the outer ring of the rolling bearing. In particular, the outer ring of the rolling bearing can be fastened to the outer casing by means of a press-fit connection.

Thus, in accordance with a preferred embodiment, the outer casing includes a radially inward, preferably annular, retaining collar and a radially outward, preferably equally annular, collar.

The preferred inventive design of the bearing assembly, particularly the lower bearing assembly, permits the application of axial forces to position the rotor shaft in the pump housing with high axial stiffness. The bearing assembly is in a direction perpendicular to the axis of the shaft and in a radial direction, respectively, so that the rotor shaft can be easily and frictionally moved. The force required to move the bearing assembly perpendicular to the rotor axis is independent of the axial force or only slightly related to the axial force.

Yet another advantage of providing a housing around the rolling bearing includes that a bore can be provided in the pump housing without forming a step. Therefore, the drilled hole is a simple through hole. Moreover, the surface of the housing that allows the radial movement of the rolling elements to abut can be made with small tolerances. In yet another advantage, the housing surface can have a large axial runout tolerance. In particular, the balls of the axial bearing are arranged in a larger straight line than the balls provided on the end side of the outer bearing ring as described in the European patent EP 1 618 308. On the path. In the case of the same angular deviation, the axial runout measured in millimeters can be greater.

10‧‧‧Rotor shaft

12‧‧‧ pump housing

14‧‧‧ bearing assembly

16‧‧‧ rolling bearings

18‧‧‧ Inner Ring

20‧‧‧Outer Ring

22‧‧‧ Shell

24‧‧‧ collar

26‧‧‧ Surface of collar 24

28‧‧‧ rolling elements

30‧‧‧ radial or pendulum movement

32‧‧‧Retaining components

34‧‧‧Ring disc

36‧‧‧Shell surface

38‧‧‧ Keep the collar

40‧‧‧damage element

42‧‧‧ trench

BRIEF DESCRIPTION OF THE DRAWINGS The following description of the drawings, which are incorporated in A schematic cross-sectional view of a first preferred embodiment of a bearing assembly in accordance with the present invention, and a second cross-sectional view of a second preferred embodiment of a bearing assembly in accordance with the present invention.

A rotor shaft 10 such as a vacuum pump such as a turbomolecular pump carries a rotor (not shown). The rotor shaft 10 is supported in the pump housing 12 via a bearing assembly, preferably a lower bearing assembly 14. Yet another bearing assembly, for example formed as a magnetic bearing, is disposed above the rotor and on the other side of the rotor, respectively. The bearing assembly 14 shown here is typically disposed on the pressure side relative to the rotor.

In the illustrated embodiment, the bearing assembly 14 includes a rolling bearing 16 formed as a ball bearing and includes an inner ring 18 and an outer ring 20 disposed on the shaft 10. The outer ring 20 is not disposed directly within the housing 12 but is supported by the outer casing 22.

The outer casing 22 has a Z-shaped cross section and includes a radially extending collar 24. The collar extends radially outward relative to the substantially cylindrical inner casing portion and has an annular shape. A plurality of rolling bodies 28 are provided between the surface 26 of the collar 24 and the housing 12, which are distributed along the circumference. Rolling body The provision of 28 allows for radial or pendulum motion of the rotor shaft 10 as indicated by arrow 30.

The rolling bodies 28 are preferably arranged in the cage-like retaining element 32 to clearly define the position of the individual rolling bodies.

An annular disc 34 can be disposed within the housing 12. Thereby, the rolling bodies 28 do not abut against the immediately adjacent casing surface 36, but abut against the casing surface 36 formed by the discs 34.

The outer casing 22 in turn includes a retaining collar 38. This collar also has an annular shape and extends radially inwardly to clearly define the position of the outer ring 20 relative to the outer casing 22.

To cushion the radial movement, a damping element 40 such as an O-ring is disposed between the outer casing 22 and the pump housing 12. The damping element 40 surrounds the outer casing 22 in an annular configuration and is preferably disposed in the groove 42 of the housing 12.

Regarding still another preferred embodiment shown in FIG. 2, the same or similar components are denoted by the same reference numerals.

The fundamental difference of this embodiment is that the bearing assembly 14 is shorter in the axial direction, i.e., in the longitudinal direction. For this purpose, the outer casing 22 forms a collar 24 that is axially disposed within the rolling bearing 16 and its sides, respectively.

Further, in the preferred embodiment shown in Fig. 2, the disc 34 preferably made of a sintered material is not provided. Of course, in the case of selecting a material, the disc 34 may be omitted in the embodiment according to Fig. 1.

The present invention has been described and illustrated with reference to the particular illustrative embodiments, which are not intended to limit the invention. Those who are familiar with the skill of the art show that they are not allowed to leave the patent application scope. Various changes and modifications can be made in the true scope of the invention as defined. Therefore, it is intended that the present invention include all such changes and modifications and their equivalents within the scope of the appended claims.

10‧‧‧Rotor shaft

12‧‧‧ pump housing

14‧‧‧ bearing assembly

16‧‧‧ rolling bearings

18‧‧‧ Inner Ring

20‧‧‧Outer Ring

22‧‧‧ Shell

24‧‧‧ collar

26‧‧‧ Surface of collar 24

28‧‧‧ rolling elements

30‧‧‧ radial or pendulum movement

32‧‧‧Retaining components

34‧‧‧Ring disc

36‧‧‧Shell surface

38‧‧‧ Keep the collar

40‧‧‧damage element

42‧‧‧ trench

Claims (11)

A vacuum pump, in particular a turbomolecular pump, comprising: a rotor shaft (10) disposed in a pump housing (12) and supported by two bearing assemblies (14); one of the bearing assemblies (14) A rolling bearing (16) is included; wherein the bearing (16) is surrounded by a casing (22) disposed in the pump casing (12) via rolling elements (28) that permit radial displacement of the rolling bearing (16) )in. A vacuum pump according to claim 1, wherein the outer casing (22) carries the outer ring (20) of the rolling bearing (16) or forms an outer ring of the rolling bearing. A vacuum pump according to claim 1 or 2, wherein the outer casing (22) comprises a radial collar (24) carrying the rolling body (28). A vacuum pump according to claim 3, wherein the upper side (26) of the collar (24) is parallel to the housing surface (36). A vacuum pump according to claim 4, wherein the casing surface (36) is formed by a preferably hardened disc (34) inserted into the pump casing (12). The vacuum pump of any one of claims 1 to 5, wherein the damping element (40) is disposed between the outer casing (22) and the pump casing (12). A vacuum pump according to claim 6, wherein the damping member (40) surrounds the outer casing (22) and preferably has an annular shape. A vacuum pump according to any one of claims 1 to 7, wherein a retaining member (32) is provided which defines the position of the rolling body (28). The vacuum pump of any one of claims 2 to 8, wherein the outer casing (22) includes the outer ring (20) abutting the rolling bearing (16) The collar is retained radially inwardly (38). The vacuum pump of claim 9, wherein the retaining collar (38) and the collar (24) carrying the rolling body (28) are axially displaced relative to each other. A vacuum pump according to any one of claims 1 to 10, wherein the rolling body (28) is axially disposed within the rolling bearing (16).