GB2560927A

GB2560927A - Pump bearing lubrication

Info

Publication number: GB2560927A
Application number: GB1704904.0A
Authority: GB
Inventors: Waye Andrew; Dudley Brewster Barrie
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2017-03-28
Filing date: 2017-03-28
Publication date: 2018-10-03
Anticipated expiration: 2037-03-28
Also published as: GB2560927B; GB201704904D0

Abstract

A pump, eg a turbomolecular vacuum pump, includes a rotor shaft 24, a rolling bearing 32 supporting the rotor shaft 24, a lubricant supply system having a lubricant reservoir 72 and a lubricant transfer device 38 provided on the rotor shaft, eg in the manner of a nut, to transfer lubricant received from the lubricant reservoir 72 to the rolling bearing 32. The lubricant transfer device 38 has an upstream end 60, eg with a convex end face, eg domed, that engages the lubricant reservoir 72 to draw lubricant from the lubricant reservoir when the rotor shaft 24 is rotating, and an outer surface 62, eg at an angle of at least 15o to the axis, extending from the upstream end 60 along which the lubricant is transported. The outer surface 62 has a downstream end 64 from which the lubricant is discharged to the rolling bearing. The reservoir 72 may contain pieces or layers of fibrous material into which the upstream end 60 of the lubricant transfer device 38 is pressed. The reservoir 72 may be biased, eg by compression springs (98, fig.5) against the upstream end 60 of the lubricant transfer device 38.

Description

(71) Applicant(s):

Edwards Limited (Incorporated in the United Kingdom)

Innovation Drive, BURGESS HILL, West Sussex, RH15 9TW, United Kingdom (72) Inventor(s):

Andrew Waye Barrie Dudley Brewster (56) Documents Cited:

GB 2533937 A EP 2390510 A2

CN 201851389 U JP 620177399 A (58) Field of Search:

INT CL F04D, F16C, F16N

Other: EPODOC, WPI, Patents Fulltext (74) Agent and/or Address for Service:

Edwards Limited

Innovation Drive, BURGESS HILL, West Sussex, RH15 9TW, United Kingdom (54) Title of the Invention: Pump bearing lubrication Abstract Title: Pump bearing lubrication (57) A pump, eg a turbomolecular vacuum pump, includes a rotor shaft 24, a rolling bearing 32 supporting the rotor shaft 24, a lubricant supply system having a lubricant reservoir 72 and a lubricant transfer device 38 provided on the rotor shaft, eg in the manner of a nut, to transfer lubricant received from the lubricant reservoir 72 to the rolling bearing 32. The lubricant transfer device 38 has an upstream end 60, eg with a convex end face, eg domed, that engages the lubricant reservoir 72 to draw lubricant from the lubricant reservoir when the rotor shaft 24 is rotating, and an outer surface 62, eg at an angle of at least 15° to the axis, extending from the upstream end 60 along which the lubricant is transported. The outer surface 62 has a downstream end 64 from which the lubricant is discharged to the rolling bearing. The reservoir 72 may contain pieces or layers of fibrous material into which the upstream end 60 of the lubricant transfer device 38 is pressed. The reservoir 72 may be biased, eg by compression springs (98, fig.5) against the upstream end 60 of the lubricant transfer device 38.

FIG 2

1/3

FIG 1

2/3

FIG 2 FIG 3

3/3

CM

CO

FIG 4 FIG 5

- 1 PUMP BEARING LUBRICATION

FIELD OF THE INVENTION

The invention relates to pump bearing lubrication and particularly, but not exclusively, to lubricating rolling bearings in turbomolecular pumps.

BACKGROUND OF THE INVENTION

Vacuum pumps typically include an impeller in the form of a rotor mounted on a rotor shaft for rotation relative to a surrounding stator. The rotor shaft is supported by a bearing arrangement that may comprise two bearings located at or intermediate respective ends of the shaft. One or both of these bearings may be a rolling bearing. Usually, the upper bearing is in the form of a magnetic bearing and the lower bearing is in the form of a rolling bearing.

A typical rolling bearing comprises an inner race fixed relative to the rotor shaft, an outer race fixed relative to the pump housing, a plurality of rolling elements located between the races and a cage configured to maintain a desired spacing between the rolling elements. Adequate lubrication is essential to ensure accurate and reliable operation of rolling bearings. The main purpose of the lubricant is to establish a loadcarrying film that separates the bearing components in rolling and sliding contact in order to minimise friction and wear. Other purposes may include the prevention of oxidation or corrosion of the bearing components, the formation of a barrier to contaminants and the transfer of heat away from the bearing components. The lubricant is generally in the form of either oil or grease (a mixture of oil and a thickening agent).

Vacuum pumps using oil-lubricated bearings have an oil feed system that feeds a continuous supply of oil to the bearing. The continuous supply of oil allows the oil to serye as a coolant. This allows the bearing to nm faster than a bearing lubricated with grease or the like. Rolling bearings in turbomolecular pumps have traditionally been supplied with oil using a wicking system. A wicking system may comprise a felt wick that is partially submerged in an oil reservoir that feeds oil to a conical oil feed nut mounted on the shaft. When the shaft rotates, oil travels along the conical surface of

-2the feed nut to the bearing. The oil then passes through the bearing and is returned to the reservoir.

The feed rate of oil to the bearing may be affected by a number of factors, including the taper angle of the feed nut, the rate of transfer of oil from the wick to the feed nut, the surface finish of the feed nut, temperature and the speed of rotation of the rotor shaft. Consequently, the degree of control over the oil feed rate may be relatively poor.

Typically, a felt wicking system comprises an annular body that functions as a reservoir and a finger that projects radially inwardly from the annular body to engage the outer surface of the oil feed nut at a position approximately midway along the length of the nut. The relative velocity between the finger and oil feed nut at the point of contact is high, which may result in frictional heating damage to the fibres of the felt wick. Fibres may be drawn out of the wick and carried up the conical surface of the oil feed nut and into the bearing. Additionally, contact between the oil feed nut and finger tends to be over a very small surface area, which limits the oil flow capacity between the two parts.

SUMMARY OF THE INVENTION

The invention provides a pump as specified in claim 1.

The invention also includes a pump lubricant transfer device as specified in claim 9.

The invention also includes a method of providing rolling bearing lubrication in a pump as specified in claim 12.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be well understood, some examples will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a turbomolecular pump;

-3 Figure 2 is a schematic representation of a lubricant transfer device and lubricant reservoir of the turbomolecular pump;

Figure 3 is a simplified view corresponding to Figure 2 showing modifications to the lubricant transfer device and the lubricant reservoir;

Figure 4 is a simplified view corresponding to Figure 2 showing alternative modifications to the lubricant transfer device and lubricant reservoir; and

Figure 5 is a simplified view corresponding to Figure 2 showing other modifications to the lubricant transfer device and lubricant reservoir.

DETAILED DESCRIPTION

Referring to Figure 1, a turbomolecular pump 10 comprises a housing (or casing) 12, a pumping mechanism 14 disposed in the housing, an inlet 16 and an outlet 18. The pumping mechanism 14 comprises a turbomolecular pumping mechanism comprising a plurality of rotor blades 20 disposed in interleaving relationship with a plurality of stator discs 22. The rotor blades 20 are mounted on, or integral with, a rotor shaft 24 that has a longitudinal axis (axis of rotation) 26. The rotor shaft 24 is driven to rotate about the axis of rotation 26 by a motor 28. The pumping mechanism 14 may additionally comprise a molecular drag pumping mechanism 30, which may be a Gaede mechanism, a Holweck mechanism or a Siegbahn mechanism. There may be additional, or alternative, mechanisms downstream of the molecular drag pumping mechanism such as an aerodynamic pumping mechanism comprising a regenerative mechanism.

The rotor shaft 24 is supported by a plurality of bearings 32, 34. The plurality of hearings may comprise two hearings 32, 34 positioned at, or adjacent, respective ends of the rotor shaft 24 as shown, or alternatively, intermediate the ends. In the example illustrated by Figure 1, a rolling bearing 32 supports a first end portion of the rotor shaft 24 and a magnetic bearing 34 supports a second end portion of the rotor shaft 24. A second rolling bearing may be used as an alternative to the magnetic bearing 34. When

-4a magnetic bearing 34 is used, a back-up rolling bearing (not shown) may optionally be provided.

The turbomolecular pump 10 additionally comprises a lubricant supply system 36 and a lubricant transfer device 38 provided on the rotor shaft 24 to transfer lubricant from the lubricant supply system 36 to the rolling bearing 32.

The rolling bearing 32 may be fixed directly to the housing 12 or mounted via a bearing support 40. The bearing support 40 may be an essentially inflexible part that is fixed to the housing 12. Alternatively, the bearing support 40 may be configured to provide limited flexing in both radial and axial directions of the rolling bearing 32. A flexing bearing support 40 may be configured to damp vibrations of the rotor shaft 24 and rolling bearing 32 during use of the turbomolecular pump 10.

Referring to Figures 1 and 2, the rolling bearing 32 comprises an inner race 44 fixed relative to the rotor shaft 24, an outer race 46 fixed relative to the housing 12 via the bearing support 40, a plurality of rolling elements 48 disposed between the inner and outer races and a cage 50 that is configured to provide a desired spacing between the rolling elements. The rolling bearing 32 is configured to allow relative rotation of the inner and outer races 44, 46 so that the bearing can support the rotor shaft 24 during rotation of the rotor shaft relative to the housing 12.

The rolling bearing 32 is supplied with a lubricant from the lubricant supply system 36 to establish a load-carrying film that separates the rolling elements 48 and cage 50 from one another and from the inner and outer races 44, 46 to minimise friction and wear. The lubricant is liquid and may be an oil.

Referring to Figure 2, the lubricant transfer device 38 comprises an upstream end 60, and an outer surface 62 that extends from the upstream end and has a downstream end 64. The outer surface 62 tapers radially outwardly with respect to the rotor shaft 24 in the direction away from the upstream end 60 towards the downstream end 64. The lubricant transfer device 38 may be provided with a blind bore 66 that extends axially

- 5 inwardly from the downstream end 60. The bore 66 receives an end 68 of the rotor shaft 24 and may be provided with internal threading 69 to allow the lubricant transfer device 38 to be secured to the rotor shaft 24 by screwing to external threading 70 provided on the rotor shaft.

The upstream end 60 of the lubricant transfer device 38 may comprise a convex end face. In cross section the upstream end 60 may have an arcuate profile. The upstream end 60 may be configured as a dome. As described in more detail below, the upstream end 60 engages a lubricant reservoir 72 of the lubricant supply system 36 to receive lubricant from the lubricant reservoir 72 for transfer to the rolling bearing 32 via the downstream end 64 of the outer surface 62.

The lubricant reservoir 72 comprises a resilient porous structure through which a liquid lubricant, for example an oil, can move towards the upstream end 60 of the lubricant transfer device 38. The lubricant reservoir 72 may comprise one or more pieces, or layers, of a stable fibrous material via. which the lubricant can migrate by a wicking action. The fibrous material may be felt. In some examples the lubricant reservoir 72 may comprise a plurality of relatively thin planar pads stacked one upon another. In examples in which the lubricant reservoir comprises a plurality of members, for example stacked layers, more than one material may be used. This may allow the selection of a reservoir portion with optimised resilience characteristics to engage the lubricant transfer device and a portion, or portions with optimised lubricant holding and migration characteristics to hold a body of lubricant and facilitate movement of that lubricant towards the lubricant transfer device

The lubricant reservoir 72 comprises a surface 74 that faces the upstream end 60 of the lubricant transfer device 38 and the rolling bearing 32. As viewed in Figure 2, the surface 74 faces upwardly. The surface 74 extends transverse to the longitudinal axis 26 of the rotor shaft 24. The surface 74 may be generally planar, at least in the area of contact with the lubricant transfer device 38. The surface 74, or at least the area of contact with the lubricant transfer device 38, may be disposed at least substantially perpendicular to the longitudinal axis 26.

-6The upstream end 60 of the lubricant transfer device 38 is in face-to-face engagement with the surface 74 of the reservoir 72. The arrangement of the lubricant transfer device 38 and the reservoir 72 may be such that the upstream end 60 is pressed into the surface 74 causing the reservoir to deform at least in the region of contact. This may ensure engagement between the upstream end 60 and the reservoir 72 is maintained and may provide a compensation mechani sm in the event of wear of the reservoir during use of the turbomolecular pump 10. The resilience of the reservoir material, or at least of the portion engaging the upstream end 60, may also compensate for component and assembly tolerances. Furthermore, the resilience of the reservoi r material may provide axial damping for the rotor shaft 24.

In use, as the lubricant transfer device 38 rotates wdth the rotor shaft 24, lubricant is drawn from the lubricant reservoir 72 onto upstream end 60 of the lubricant transfer device from where it migrates along the outer surface 62 to the downstream end 64 of the outer surface 62. The lubricant is thrown, or otherwise delivered, from the downstream end 64 into the rolling bearing 32. Although not shown, those skilled in the art will understand that the lubricant supply system 36 may comprise suitable channelling and the like to return lubricant from the rolling bearing 32 to the lubricant reservoir 72 so that the lubricant can be recirculated.

An advantage of the illustrated arrangement, as compared wdth conventional bearing lubrication arrangements in turbomolecular pumps, is that the surface 74 of the reservoir is engaged by the slowest moving part of the lubricant transfer device 38. This may reduce the li kelihood of friction and heat damage to the reservoir 72 and when, for example, the reservoir is made of a fibrous material, reduce the incidence of damaged fibres being picked up by the lubricant transfer device 38 and fed into the rolling bearing 32.

Figure 3 shows a modification to the lubricant transfer device 38, in this example, a bore 80 extends axially inwardly from the upstream end 60 of the lubricant transfer device 38 towards the bore 66. The bores 66, 80 may join to form a continuous through-7hole. The bore 80 is profiled to receive a driving tool by means of which the lubricant transfer device 38 can be screwed tightly onto the rotor shaft 24. The bore 80 may be produced by broaching or spark erosion and may, for example, have a hexagonal profile to accept an Allen key. Additionally, the reservoir 72 is modified by the inclusion of an annular wall 75 projecting from the surface 74 and extending about the lubricant transfer device 38. The annular wall 75 increases the lubricant holding capacity of the reservoir 72 as compared with the reservoir shown in Figure 2.

Figure 4 shows alternative modifications that may be made to the arrangement shown in Figure 2. In this example, the lubricant transfer device 38 is provided with a transverse through-hole 86. The transverse through-hole 86 may extend perpendicular to the longitudinal axis of the lubricant transfer device 38, which is coincident with the longitudinal axis 26 of the rotor shaft 24. The through-hole 86 may have a circular cross-section configured to receive a circular rod, or Tommy bar, by which the lubricant transfer device 38 may be screwed tightly onto the rotor shaft 24. As an alternative to a Tommy bar, the through-hole may be sized for engagement by a suitable pin spanner. In examples designed for use with a pin spanner, a blind hole rather than a through-hole may be provided and there may be more than one blind hole to provide greater access possibilities for insertion of the spanner.

In this example, the reservoir 72 is mounted on a support 88 that defines a recess 90. The recess 90 is disposed opposite the upstream end 60 of the lubricant transfer device 38. This allows deflection of the reservoir 72 (not shown in the drawing) in response to engagement with the upstream end 60 so that the surface 74 is biased into engagement with the lubricant transfer device 38 by virtue of the inherent resilience of the material. This may ensure that contact between the upstream end 60 and the reservoir 72 is maintained and provide a tolerance and wear compensation mechanism that is one or both of greater and more predictable than is possible with the arrangement shown in Figure 2. Again, the flexible engagement between the upstream end 60 of the lubricant transfer device 32 and the reservoir 72 may provide axial damping for the rotor shaft 24.

- 8 Figure 5 shows other alternative modifications that may be made to the arrangement shown in Figure 2 In this example, a biasing mechanism is provided to press the reservoir 72 into engagement with the upstream end 60 of the lubricant transfer device 38. The biasing mechanism may comprise one or more biasing elements 98 arranged to push the reservoir 72 towards the lubricant transfer device 38. For example, a plurality of compression springs may be arranged to press a backing member 100 against the reservoir 72 to push the reservoir towards the lubricant transfer device 38. A backing member 100 is not essential as arrangements in which the biasing elements 98 act directly on the reservoir 72 are possible. However, particularly in examples in which the reservoir 72 is relatively more flexible, it may be desirable to have a relatively stiffer backing member 100 so that a substantially uniform pressure is applied to the reservoir 72. The backing member 100 may be non-porous. Alternatively, the backing member 100 may be made of a porous material or provided with apertures 102 and the biasing elements 98 may be disposed in a lubricant tank 104 so that the reservoir 72 can be fed with lubricant via the apertures 102. In the illustrated example the backing member 100 extends across at least substantially the entire width of the lubricant reservoir 100. In other examples, one or more biasing members 98, and optionally a backing member 100, may be configured to act on just the region of the lubricant reservoir 72 that engages the upstream end 60 of the lubricant transfer device 38. Thus, as viewed in Figure 5, the central region of the lubricant reservoir 72 would be raised with respect to the surrounding region, which may sit in the bottom of a lubricant container so that the lubricant is wicked to the central region. Again, the flexible engagement between the upstream end 60 of the lubricant transfer device 38 and the reservoir 72 may provide a mechanism that provides compensation for component and assembly tolerances, a wear compensation mechanism or axial damping for the rotor shaft 24.

As shown in the illustrated examples, the lubricant transfer device may be screwed onto the end of a rotor shaft in the manner of a nut. The lubricant transfer device may be provided with a wide variety of formations, such as shaped bores or external flats to enable it to be tightly secured to the rotor shaft. However, the lubricant transfer device is not limited to implementation as a nut-like structure. In principle, the lubricant

-9transfer device may be a body made of one or more parts secured to the rotor shaft such that an end of the body is in direct engagement with the lubricant reservoir to allow lubricant to be drawn from the reservoir onto the engaging end and then moved along the outer surface of the lubricant transfer device towards the downstream end of the outer surface, from where it is discharged into a rolling bearing. Thus, for example, as shown in Figure 5, the lubricant transfer device may comprise a sleeve that is securable to the rotor shaft and has an end face that directly contacts the lubricant reservoir. The reservoir contacting end face of the lubricant transfer device may be completely closed to provide a relatively larger contact area or include an opening for insertion of a tool.

It will be understood that by providing direct contact between an end face of the lubricant transfer device and the lubricant reservoir, it is possible provide a contact area that is substantially larger than in conventional arrangements in which a finger contacts the outer surface of an oil feed nut. This provides the possibility of significantly larger lubricant transfer rates. This may facilitate the use of rolling bearings in which the cage is piloted on the inner race which, as compared with outer race piloted bearings, require relatively larger lubricant flows that may not be possible using conventional lubricant supply systems and feed nuts.

Having contact between the lubricant reservoir and lubricant transfer device made with an end face of the lubricant transfer device rather than its sides may allow the lubricant transfer device to be made shorter than a conventional oil feed nut. A conventional oil feed nut has a relatively shallow taper angle. This is to ensure that the contact pressure with the felt finger is relatively insensitive to the axial positioning of the finger, which in turn is a function of the combined thickness tolerance of the stacked felts. For example, a conventional oil feed nut for an 8mm rolling bearing may have a taper angle β = 6.2° and a length of 30mm. This angle β equates to a change in radius of approximately 0.1 mm for an axial movement of 1mm (tan β = approximately 0.109). In this case (assuming tolerances of metal parts are negligible) an axial dimensional tolerance of ±1 mm in the felt assembly causes a tolerance of ±0.1 mm in the radial precompression of the finger, which must be added to the ±0.15 mm radial tolerance on the “finger” felt. Thus, a desired total tolerance of ±0.25 mm on radial pre-compression

- 10 can be achieved. Obtaining this desired tolerance and significantly increasing the taper angle so as to allow a significant decrease in the length of the nut is not possible. For example, doubling the taper angle to 12°, would double the contribution from axial tolerance, making a total of ±0.35 mm tolerance on radial pre-compression. Some allowance is also desirable to take account of some subsequent wear, relaxation or deterioration of the felt so a shallow taper angle is needed.

Making contact with an end face of the lubricant transfer device means that the tolerance may be determined by just one layer of reservoir material, or at least a reduced number of layers, as compared with a conventional lubrication system, thereby reducing the tolerance stack up. As described above, compensation mechanisms may be provided to cope with this. Accordingly, the taper angle B of the outer surface can be increased so that the length of the lubricant transfer device can be significantly decreased as compared with a conventional oil feed nut designed to supply the same size of rolling bearing. The practical limitation on the length of the lubricant transfer device is having sufficient material to secure it to the rotor shaft. Thus, for examples such as that shown in Figure 2, there needs to be sufficient length for an internal thread capable of securing the lubricant transfer device (and the rolling bearing) to the rotor shaft.

A lubricant transfer device as illustrated by way of example in by Figures 1 to 5 configured to deliver lubricant to an 8mm rolling bearing may have a taper angle B of approximately 15 to 25° with a length of approximately 9 to 16mm. This may produce an overall length saving in a pump of up to around 8mm, which may represent a significant saving in length where a pump needs to be made compact or, in the case of turbomolecular pump, allow the inclusion of another rotor/stator stage, so giving increased compression for the same overall pump length/height. Such a lubricant transfer device may have an upstream radius of approximately 3 to 6mm and be arranged to produce a depression of approximately 0.5mm in a lubricant reservoir having a thickness of approximately 3mm at the region of engagement with the lubricant transfer device. This may produce a contact area approximately in the range 9.5 to 17mm². It will be understood that these figures are given purely by way of

- 11 example and should not be taken as limiting. For other sizes of nut there may be proportionate changes in the dimensions mentioned and in some cases a lubricant transfer device may be configured to provide an increased contact between the lubricant transfer device and lubricant reservoir where length/height reduction is not required or to take advantage of other space usage advantages that may arise from having a lubricant reservoir arranged to contact an end of the lubricant transfer device, rather than having to make a side contact with the device.

The possibility of having a relatively shorter lubricant transfer device provides other 10 potential advantages. It can be shown that for a rotor with a lubricant transfer device carried on an end of the rotor shaft, the length and mass of the lubricant transfer device may significantly affect the dynamic behaviour of the rotor. A reduction in the length and mass of the lubricant transfer device (and possibly a consequential reduction in the length of the rotor shaft) may reduce dynamic flexing and vibration of the rotor shaft.

Thus, being able to design lubricant transfer devices that may be shorter and have a lower mass than conventional oil feed nuts may provide greater flexibility and opportunity in tuning rotor designs to move vibrational modes away from the pump running speed, or speeds. It will be understood that in this case, the potential benefit arises from a reduction in the length/height of the rotor, rather than in the overall length/height of the pump, which in some examples may be unchanged or even increased.

The invention has been described and illustrated in connection with turbomolecular pumps. It will be understood that in principle the invention is equally applicable to the lubrication of rolling bearings in other forms of pump.

Claims

1. A pump comprising: a rotor shaft;

a rolling bearing supporting said rotor shaft; a lubricant reservoir; and a lubricant transfer device provided on said rotor shaft to transfer lubricant received from said lubricant reservoir to said rolling bearing, wherein said lubricant transfer device comprises a body comprising an upstream end that engages said lubricant reservoir to draw lubricant from the lubricant reservoir when, in use, said rotor shaft is rotated and an outer surface that extends from said upstream end and has a downstream end from which said lubricant is discharged to said rolling bearing.

2. A pump as claimed in claim 1, wherein said upstream end comprises a convex end face.

3. A pump as claimed in claim 2, wherein in cross section said convex end face has an arcuate profile.

4. A pump as claimed in claim 1, 2 or 3, wherein in a direction from said upstream end towards said downstream end said outer surface tapers radially outwardly with respect to said rotor shaft.

5. A pump as claimed in claim 4, wherein said rotor shaft has a longitudinal axis and said outer surface is inclined at an angle B with respect to said longitudinal axis and B is at least 15°.

6. A pump as claimed in any one of the preceding claims, wherein said lubricant reservoir comprises a surface portion engaged by said upstream end and said surface portion faces said rolling bearing.

- 13

7. A pump as claimed in claim 6, wherein said surface portion extends perpendicular to said longitudinal axis.

8. A pump as claimed in any one of the preceding claims, further comprising a turbomolecular pumping mechanism.

9. A pump lubricant transfer device to be secured to a pump rotor shaft to transfer lubricant from a lubricant reservoir to a rolling bearing that supports said rotor shaft, said lubricant transfer device comprises a convex upstream end to engage said lubricant reservoir and an outer surface extending from said upstream end that has a downstream end from which, in use, lubricant drawn onto said upstream end is discharged, wherein in a direction away from said upstream end towards said downstream end said outer surface tapers radially outwardly with respect to a longitudinal axis of the lubricant transfer device.

10. A pump lubricant transfer device as claimed in claim 9, wherein in cross section, said convex end face has an arcuate profile.

11. A pump lubricant transfer device as claimed in claim 9 or 10, wherein said outer surface is inclined at an angle B with respect to said longitudinal axis and B is at least 15°.

12. A method of providing rolling bearing lubrication in a pump the method comprising:

providing a rotor shaft having a longitudinal axis and a rolling bearing supporting said rotor shaft;

providing a lubricant reservoir;

providing a lubricant transfer device on said rotor shaft to transfer lubricant from the lubricant reservoir to said rolling bearing, the lubricant transfer device comprising an upstream end and an outer surface extending from said upstream end that has a downstream end and in a direction from said upstream end towards said downstream end tapers outwardly with respect to said longitudinal axis; and

- 14 engaging said upstream end with a surface of said lubricant reservoir so that in use, when said lubricant transfer device rotates with said rotor shaft, lubricant from said reservoir is picked up on said upstream end and transfers from said upstream end along said outer surface to said downstream end for discharge to said rolling bearing.

13. A method as claimed in claim 12, further comprising providing said lubricant reservoir such that said surface engaged by said upstream end extends transverse to said longitudinal axis of said rotor shaft.

14. A method as claimed in claim 12 or 13, further comprising providing said lubricant reservoir such that said surface faces said rolling bearing.

15. A method as claimed in claim 12, 13 or 14, wherein said upstream end is convex.

16. A method as claimed in claim 15, wherein in cross section said upstream end has an arcuate profile.

17. A method as claimed in claim 16, wherein said upstream end is dome-shaped.

18. A method as claimed in any one of claims 12 to 17, wherein said outer surface is inclined at an angle B with respect to said longitudinal axis and B is at least 15°.

Intellectual

Property

Office

Application No: GB1704904.0 Examiner: John Twin