Vacuum pump

Abstract

A pump insert (50) for supporting a rotor (14) of a pump comprises an annular resilient support (52) for engaging the body (26) of the pump, the support (52) extending about a rolling bearing (10) having an inner race (12) for engaging the rotor (14), an axially preloaded outer race (16) fixed to the support (52), and a plurality of rolling elements (18) located between the races. During assembly, the rolling bearing (10) can be accurately positioned within the support (52) so that there is a very low tolerance stack-up when the insert (50) is fitted to the rotor (14). Consequently, the position of the rotor (14) will hardly change, if at all, when the rolling bearing (10) is replaced during servicing of the pump.

Claims

1. An insert for insertion around a rotor of a pump, the insert comprising a metallic, annular resilient support comprising inner and outer annular portions connected by a plurality of flexible members, the resilient support extending about a rolling bearing having an inner race, an axially preloaded outer race comprising an outer surface fixedly attached to an inner surface of the inner annular portion of the resilient support by an adhesive, and a plurality of rolling elements located between the races wherein the outer race is positioned on the inner surface at a location determined by an axial load applied to the outer race as the inner race is moved in an opposite direction from the axial load.

2. The insert according to claim 1, wherein an axial end surface of the inner race is axially displaced relative to an axial end surface of the resilient support.

3. The insert according to claim 2, wherein the end surface of the inner race is axially displaced relative to the end surface of the resilient support by a distance in a range from 1 to 3 mm.

4. The insert according to claim 1, wherein each of the flexible members is an elongate, arcuate member substantially concentric with the inner and outer annular portions.

5. The insert according to claim 4, wherein the flexible members are circumferentially aligned.

6. The insert according to claim 1, wherein the flexible members provide a plurality of integral leaf springs of the resilient support.

7. The insert according to claim 1, wherein the metallic material comprises one of tempered steel, aluminium, titanium, phosphor bronze, beryllium copper, an alloy of aluminium and an alloy of titanium.

8. A method of assembling a vacuum pump comprising a body and a rotor supported for rotation relative to the body, the method comprising the steps of sliding an insert according to claim 1 over the rotor until an axial end surface of the support engages the body and an axial end surface of the inner race of the bearing engages the rotor, and securing the insert to the rotor.

9. A vacuum pump comprising a body and a rotor supported for rotation relative to the body by an insert inserted around the rotor, the insert comprising a metallic, annular resilient support comprising inner and outer annular portions connected by a plurality of flexible members, the resilient support extending about a rolling bearing having an inner race, an axially preloaded outer race having an outer surface fixed to an inner surface of the inner annular portion of the resilient support so as to prevent axial movement of the rolling bearing relative to the resilient support, and a plurality of rolling elements located between the races, wherein the outer race is positioned on the inner surface at a location determined by an axial load applied to the outer race as the inner race is moved in an opposite direction from the axial load.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates a cross-sectional view of a known rolling bearing supporting the rotor of a pump;

(3) FIG. 2 illustrates a cross-sectional view of a pump insert including a rolling bearing;

(4) FIG. 3 illustrates a perspective view of the resilient support of the insert of FIG. 2;

(5) FIG. 4 illustrates a method of assembling the insert of FIG. 2; and

(6) FIG. 5 illustrates a cross-sectional view of the insert of FIG. 2 supporting the rotor of a pump.

DETAILED DESCRIPTION

(7) FIG. 2 illustrates a cross-sectional view of the pump insert 50, which forms part of a bearing arrangement of a pump. The insert 50 comprises a known rolling bearing 10 as described above with reference to FIG. 1, and which comprises an inner race 12, an outer race 16, and a plurality of rolling elements 18, supported by a cage 20, for allowing relative rotation of the inner race 12 and the outer race 16. The rolling bearing 10 is lubricated to establish a load-carrying film separating the bearing components in rolling and sliding contact in order to minimize friction and wear, and shield elements 22 are provided to resist seepage of lubricant from the rolling bearing 10.

(8) The rolling bearing 10 is located within an annular resilient support 52, which is illustrated in more detail in FIG. 3. The resilient support 52 comprises a metallic member having integral inner and outer annular portions 54, 56 connected together by a plurality of integral flexible members 58 formed by machining slots 60 in the support 52. Each flexible member 58 is connected by a first resilient hinge 62 to the inner portion 54, and by a second resilient hinge 64 to the outer portion 56. Each flexible member 58 is in the form of an elongate, arcuate member substantially concentric with the inner and outer annular portions 54, 56, and, as illustrated in FIG. 3, the flexible members 58 are preferably circumferentially aligned. The flexible members 58 of the resilient support 52 thus provide integral leaf springs of the resilient support 52.

(9) Returning to FIG. 2, the outer radial surface 38 of the outer race 16 of the bearing 10 is fixed to the inner, axially extending cylindrical surface 66 of inner portion 54 of the support 52, preferably using an adhesive. The bearing 10 is preferably positioned within the support 52 at a location at which the axial end surface 32 of the inner race 12 of the bearing 10 is axially displaced from the axial end surface 68 by a desired amount y, which is preferably in the range from 1 to 3 mm, and which in a preferred embodiment is 1.8 mm.

(10) FIG. 4 illustrates a method of assembling the insert 50. A spacer 80 is used to position the bearing 10 at the desired location within the support 52. The spacer 80 has a support engaging portion 82 for engaging the axial end surface 68 of the support 52, and a bearing engaging portion 84 for engaging the axial end surface 32 of the inner race 12 of the bearing 10. The support engaging portion 82 has an annular, planar surface 86 which is located on the axial end surface 68 of the support 52 so that the bearing engaging portion 84 of the spacer 80 protrudes into the bore 70 of the support 52 by the desired amount γ. The bearing 10 is inserted into the bore 70 of the support 52, and is pushed towards the spacer 80 until the axial end surface 32 of the inner race 12 engages the axial end surface 88 of the bearing engaging portion 84 of the spacer 80. The bearing 10 is then fixed to the support 52, preferably using an adhesive to adhere the outer radial surface 38 of the outer race 16 of the bearing 10 to the inner cylindrical surface 66 of inner portion 54 of the support 52.

(11) As also illustrated in FIG. 4, a resilient member 90, preferably a tension spring, is located between the spacer 80 and the bearing 10. The resilient member 90 preferably has one end connected to the annular surface 86 of the spacer 80 to retain the resilient member in position. As the bearing 10 is moved towards the spacer 80, the resilient member 90 is compressed between the spacer 80 and the outer race 16 of the bearing 10 to exert an axial load on the outer race 16. When the bearing 10 is positioned at the desired location, this resilient member 90 applies a known axial load to the outer race 16, so that in the assembled insert 50 the outer race 16 is axially preloaded.

(12) A set of inserts 50 can thus be assembled, sequentially, using the spacer 80 so that, within the set, each rolling bearing 10 is located at the same position relative to its support 52, and each rolling bearing 10 has the same axial preload.

(13) FIG. 5 illustrates the insert 50 in situ about the rotor 14 of a vacuum pump. During assembly of the pump, and with the rotor 14 restrained to inhibit its rotation, the insert 50 is located over the end 15 of the rotor 14, and is slid along the rotor 14 until the axial end surface 68 of the support 52 engages the pump body 26 and the axial end surface 32 of the inner race 12 of the bearing 10 engages the abutment surface 34 of the rotor 14. The oil nut 30 is then screwed on to the end of the rotor 14 to secure the inner race 12 of the bearing 10 to the rotor 14. If the pump also has a magnetic bearing forming part of its bearing arrangement for supporting the rotor, the mounting for the magnetic stator rings of the magnetic bearing is adjusted to exert a desired axial preload on the rotor 14.

(14) During servicing of the pump when it is in situ for evacuating a tool, the rotor 14 is again restrained to prevent its rotation, the oil nut is unscrewed from the rotor 14 and the insert 50 is removed from the pump. A fresh insert 50 is then inserted on to the rotor 14 and slid in position, and the oil nut 30 is screwed back on to the rotor to retain the insert 50 in position. As there is a very low tolerance stack-up between the axial end surface 68 of the support 52 and the axial end surface 32 of the inner race 12 of the bearing 10, the axial position of the rotor 14 will hardly change, if at all, as a result of changing the insert 50. Consequently, there is no need to disconnect the pump from the tool to adjust the axial preload on the rotor 14.