GB2603142A

GB2603142A - Thrust bearing

Info

Publication number: GB2603142A
Application number: GB2101097.0A
Authority: GB
Inventors: Hülsen Tobias
Original assignee: MinebeaMitsumi Inc
Current assignee: MinebeaMitsumi Inc
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2022-08-03
Also published as: GB202101097D0

Abstract

A thrust bearing 200 for use as a tram or a light rail coupling bearing is disclosed. The thrust bearing comprises a housing 201 having a base 205, a central post 207 upstanding from the base 205, and an inner ball 204 provided on the central post 207. An outer ball 203 is seated on and at least partially within the housing 201. At least one locking element 220 is arranged between the inner ball 204 and outer ball 203 so as to slidably retain the outer ball 203 in the housing 201. The at least one locking element 220 may have an outer bearing surface 221 and an inner bearing surface 222 that is in sliding arrangement with the outer ball 203 and the inner ball 202, respectively. A retainer 230 can be secured to the outer ball 203 to retain the at least one locking element 220. Optionally, a bearing insert 202 is arranged in the housing 201 to be in a sliding arrangement with the outer ball 203.

Description

Title: Thrust bearing

Description of Invention

This invention relates to a thrust bearing and more particularly to a thrust bearing for use as a tram and light rail coupling bearing.

A conventional design for a thrust bearing (coupling bearing) for use in the coupling between a carriage and a bogie or another carriage of a tram or similar light rail vehicle is shown in Figure 1 of the accompanying drawings. One part of the bearing is fixed to the carriage and the other part of the bearing is fixed to the bogie under the carriage allowing the bogie to rotate and pivot with respect to the carriage. This style of coupling bearing 1 comprises a generally cylindrical outer housing 2 having a circular base 3 provided with fixtures such as mounting holes 4 equispaced around the circular base 3 for attaching the outer housing 2 to the bogie. In the example shown in Figure 1, there are eight mounting holes 4 equispaced around the periphery of the circular base 3. The outer housing 2 is preferably manufactured from alloy steel.

A spherical insert 5 is fixed to the inside wall of the outer housing 2 and also rests upon the circular base 3. The spherical insert 5 has a load bearing surface 9 in the form of a spherical bearing surface. Lubrication grooves 70, 71 are provided through the outer housing 2 and the spherical insert 5 to lubricate the load bearing surface 9. The spherical insert 5 is manufactured from an engineering plastic based on Nylon, PETP, PE or PP. An outer ball 7 is seated on the spherical insert 5, an outer spherical bearing surface of the outer ball 7 having the same radius as the load bearing surface of the spherical insert 5. The outer ball 7 is rotatably mounted on the spherical insert 5 and can also accommodate rolling and pitching movement with respect to the outer housing 2. The outer ball 7 has an inner bearing surface and an outer spherical bearing surface 6. The outer ball is preferably manufactured from a corrosion resisting steel. An annular elastomeric seal 18 is attached to the top of the cylindrical side wall of the outer housing and makes sealing contract with the outer bearing surface of the outer ball.

An inner ball 10 having a spherical outer bearing surface is seated within the outer ball 7 on the inner bearing surface of the outer ball, thereby sandwiching (but not contacting) the outer ball 7 between the inner ball 10 and the spherical insert 5. The radius of the outer bearing surface of the inner ball 10 corresponds to the radius of the inner bearing surface of the outer ball 7.

The outer ball 7 is provided with eight fixing holes 11 which are equispaced around a rim of the outer ball 7. The fixing holes 11 are provided to allow the outer ball 7 to be fixedly attached to the carriage of a tram or similar vehicle.

The circular base 3 is provided with a central hole 12 which receives a through-bolt 13. The outer ball is also provided with a central aperture 14 so that the bolt 13 passes readily therethrough. Indeed, the central hole 14 of the outer ball 7 is spaced apart from the bolt 13 and an inner sleeve 15 which surrounds the bolt 13 in a slide-fit engagement by a clearance distance, which clearance distance allows the outer ball 7 to roll and pitch with respect to the outer housing 2.

Preferably, the central hole 14 through the outer ball 7 has a contact surface 16 which can engage an outer surface of the inner sleeve 15, thereby acting as an end stop.

Preferably, the inner sleeve is manufactured as a cold drawn seamless steel tube. The inner sleeve also acts as a spacer separating the inner ball 10 from the circular base 3 of the outer housing by a pre-determined distance, that distance being substantially equal to the separation distance between the inner ball 10 and the spherical insert 5.

The bolt 13 also passes through a central hole 17 in the inner ball 10 with a slide fit engagement, the end of the bolt protruding past the inner ball 10. A nut 20 is screwed onto the bolt 13. The nut 20 is provided with a threaded hole 21 which receives a grub screw 22. The grub screw 22 can be tightened down onto the bolt 13 thereby locking the nut 20 onto the bolt 13.

The bolt 13 has a head which is also securely fastened to the circular base 3.

Two threaded blind bores holes are provided on diametrically opposite sides of the central hole 12 on the circular base 3. Two through holes 24 are provided in the bolt head. A locking screw 25 is passed through each of the through holes into the threaded bores and tightened to lock the bolt head to the circular base 3.

The above-mentioned conventional coupling bearing is complex in design having ten components: an outer housing, a spherical insert, an outer ball, an inner ball, a seal, bolt, inner sleeve, nut, grub screw and bolt head locking 20 screws.

During any assembly or disassembly of the coupling bearing 1 to/from a carriage or a bogie, access is required to the underside of the tram. Clearly, the requirement to access the coupling from the underside is undesirable especially when there is low ground clearance.

The nut 20 and grub screw 22 together with the locking screws 25 in the design have the potential to work loose or break and, if they do so, then the nut can be detached from the bolt and the bolt can drop through the coupling bearing and down on to the track. Furthermore, the loss of the bolt from the assembly would mean that the carriage and bogie could become readily separated -an occurrence which is preferably avoided in a crash situation.

In order to address some the disadvantages of the arrangement illustrated in Figure 1, the applicant previously presented the coupling bearing shown in Figure 2, disclosed in W003/029065.

Unlike the outer housing 2 of Figure 1, the outer housing 101 of the coupling bearing of Figure 2 is not provided with a central hole 12 but instead provides an integrally formed central post 107 which stands upwardly from the circular base 105 projecting into the cylindrical volume defined by the cylindrical side wall of the outer housing 101. The central post 107 is substantially frustoconical and terminates in a cylindrical portion 108. The central post 107 is of substantially the same height as the cylindrical side wall of the outer housing 101.

The spherical insert 102 is fixedly mounted to an inner surface of the side wall of the outer housing 101 and also to an inner surface of the circular base 105.

The spherical insert 102 has a load bearing surface 109 which is spherical, the spherical insert 102 preferably being manufactured from an engineering plastic such as PETP with PTFE or other lubricating additives. The spherical insert 102 can also be referred to as a lubrication insert or a thermoplastic insert.

The outer ball 103 is an annulus having inner and outer spherical bearing surfaces. The outer ball 103 sits on the load bearing surface 109 provided by the spherical insert 102. The outer ball 103 has a spherical outer bearing surface 110 and a spherical inner bearing surface 111 and is formed generally as an annular truncated hemispheroid. The central aperture of the annulus, preferably has a chamfered surface 112.

The inner ball 104 has a spherical outer bearing surface 113 and is formed generally as a truncated hem ispheroid having two flat substantially circular and parallel surfaces. The inner ball 104 has a cylindrical recess in the smaller of the circular surfaces in which a top cylindrical section 108 of the post 107 is located, such that the outer ball 103 is sandwiched between the inner ball 104 and the spherical insert 102 of the outer housing 101.

In the example shown in Figure 2, five equispaced bores 114 are provided in the inner ball 104 which align which five threaded holes 115 provided in the post 107. Locking screws 116 pass through the bores 114 in the inner ball 104 and are screwed into the threaded holes 115 in the post 107. Preferably, the locking screws 116 are countersunk into the body of the inner ball 104 so that the upper surface of the inner ball 104 has a flush profile.

Although the arrangement illustrated in Figure 2 overcomes the problems of the arrangement of Figure 1, any upward load acting on the inner ball is limited by the strength of the locking screws and their interface with the inner ball (i.e. number of locking screws, location, tightening conditions).

Accordingly, the present invention provides a thrust bearing comprising: a housing having a base, a central post upstanding from the base, and an inner ball provided on the central post; an outer ball seated on and at least partially within the housing; and at least one locking element arranged between the inner ball and outer ball so as to slidably retain the outer ball in the housing.

In at least one embodiment, the outer ball comprises an outer bearing surface.

In at least one embodiment, the housing comprises a bearing surface and the outer bearing surface of the outer ball is arranged in a sliding arrangement with the bearing surface of the housing.

In at least one embodiment, the thrust bearing comprises a bearing insert arranged in the housing, the bearing insert providing a bearing surface of the housing.

In at least one embodiment, the inner ball comprises a bearing surface.

In at least one embodiment, the at least one locking element comprises an inner bearing surface and the inner bearing surface of the at least one locking element is arranged in a sliding arrangement with the bearing surface of the inner ball.

In at least one embodiment, the outer ball comprises an inner bearing surface and the at least one locking element comprises an outer bearing surface, wherein the inner bearing surface of the outer ball corresponds to the outer bearing surface of the locking element.

In at least one embodiment, the at least one locking element is securable to the outer ball.

In at least one embodiment, the thrust bearing further comprises a retainer to retain the at least one locking element in the thrust bearing.

In at least one embodiment, the retainer is securable to the outer ball.

In at least one embodiment, the outer ball comprises an inner bearing surface.

In at least one embodiment, the at least one locking element comprises an outer bearing surface and the outer bearing surface of the at least one locking element is arranged in a sliding arrangement with the inner bearing surface of the outer ball.

In at least one embodiment, the inner ball comprises a bearing surface and the at least one locking element comprises an inner bearing surface, wherein the bearing surface of the inner ball corresponds to the inner bearing surface of the at least one locking element.

In at least one embodiment, the at least one locking element is securable to the housing.

In at least one embodiment, the at least one locking element is securable to the inner ball and/or central post.

In at least one embodiment, the thrust bearing further comprises a plurality of locking screws to secure the at least one locking element to the inner ball.

In at least one embodiment, the inner ball comprises an axial end face, and the plurality of screws pass through the axial end face and are received in a corresponding threaded aperture in the inner bearing surface of the at least one locking element.

In at least one embodiment: the housing comprises a spherical bearing surface, the outer ball comprises an inner spherical bearing surface and an outer spherical bearing surface, the at least one locking element comprises an inner spherical bearing surface and an outer spherical bearing surface, and the inner ball comprises a spherical bearing surface, wherein the spherical bearing surfaces are substantially concentric with one another.

In at least one embodiment, there are at least two locking elements.

In at least one embodiment, each of the locking elements comprises a first and second axial face and a first and second radial split face.

Embodiments of the present invention will now be described, by way of non-limiting example only, with reference to the figures, in which: FIGURE 1 is a cross-section through a conventional thrust bearing; FIGURE 2 is a cross-section through another conventional thrust bearing; FIGURE 3 is a cross-section through a thrust bearing embodying the present invention; and FIGURE 4 shows the assembly process of the thrust bearing of Figure 3; and FIGURE 5 is a cross-section through another thrust bearing embodying the present invention.

The present invention stems from a realisation that the central post of the conventional thrust bearing arrangement (such as that in Figure 2) has a much bigger cross section than the combined cross section of the locking screws. The applicant has acknowledged that it may offer increased load transmission by avoiding the use of a discrete inner ball which has to be screwed to the central post.

In a thrust bearing embodying the present invention, the inner ball is not provided as a discrete item, separate to the central post and housing. Rather, in at least one embodiment, the inner ball is integrally formed with the base and central post of the housing. In at least one embodiment, the housing (comprising a base, central post and inner ball) is manufactured from the same material billet. In another embodiment, at least the inner ball could be manufactured discretely from the base and/or central post, but the components are then welded/fused together so as to form a substantially integral housing.

As the reader will appreciate, if the inner ball 104 of the known arrangement shown in Figure 2 was formed integrally with the post 107, this would prevent the insertion of the outer ball 103 into the housing 101. Embodiments of the present invention overcome this issue by providing an outer ball 203, 303, having different dimensions to the known outer ball 103. An outer ball 203, 303 of a thrust bearing 200, 300 embodying the present invention is able to be inserted into the housing 201 by virtue of the additional provision of at least one locking element 220, 320.

As shown in Figure 3, a thrust bearing 200 embodying the present invention comprises a housing 201 having a base 205, a central post 207 upstanding from the base 205 and an inner ball 204 provided on the central post 207. The reader will note that the general shape of the base 205, central post 207 and inner ball 204 generally corresponds to that of the corresponding components of the known thrust bearing 101 shown in figure 2. That is to say that the base 205 may be substantially circular, with a substantially cylindrical wall extending upwardly from the base 205. The cylindrical wall generally provides a cylindrical volume within the housing 201. The central post 207 may be substantially frustoconical.

In at least one embodiment, the thrust bearing 200 is further provided with a bearing insert 202. The bearing insert 202 presents a load bearing surface 209. In the embodiment shown, the load bearing surface 209 is a spherical bearing surface. The load bearing surface 209 may be broadly similar to the load bearing surface 9, 109 of the arrangements shown in Figures 1 and 2.

The housing 201 comprises a plurality of holes 206, which may be threaded, to enable the housing 201 to be secured to a component of the vehicle in which the thrust bearing 200 may be installed. Additionally or alternatively, the plurality of holes 206 may be used to secure the bearing insert 202 into the bearing housing 201, by passing screws through the holes 206 and at least partially into the bearing insert 202. The material of the housing 201 and/or bearing insert 202 may comprise any of the materials discussed in relation to the known arrangements of Figures 1 and 2. The bearing insert 202 may further comprise lubrication grooves such as those shown in Figure 1. The holes 206 may take the same or similar form as those 4, 106 of the arrangements shown in Figures 1 and 2.

The thrust bearing 200 shown in Figure 3 further comprises an outer ball 203 seated on and at least partially within the housing 201. In the configuration shown in Figure 3, the outer ball 203 is generally arranged between the inner ball 204 and bearing insert 202.

The outer ball 203 comprises an outer spherical bearing surface 210. When the outer ball 203 is assembled into the housing 201, the outer spherical bearing surface 210 abuts the load bearing surface 209 of the bearing insert 202. In at least one embodiment, the outer spherical bearing surface 210 of the outer ball 203 substantially corresponds to the load bearing surface 209 of the bearing insert 202. In at least one embodiment, the radii of the respective spherical bearing surfaces 210, 209, substantially correspond to one another.

The outer spherical bearing surface 210 of the outer ball 203 is arranged in a substantially sliding arrangement with the load bearing surface 209 of the bearing insert 202. Consequently, as with the known arrangements shown in Figures 1 and 2, and with thrust bearings generally, the outer ball 203 is mounted into the housing 201 so as to accommodate a rolling and pitching movement with respect to the bearing insert 202. One or both of the spherical bearing surfaces 210, 209 may be provided with a lubricant and/or lubricating material. At least some or all of the bearing insert 202 may be comprised of a lubricating material, such as polytetrafluoroethylene (PTFE).

The outer ball 203 further comprises a plurality of fixing holes 218, which may be equispaced around the surface of the outer ball 203, to allow the outer ball 203 to be secured to a corresponding component of the vehicle into which the thrust bearing 200 is assembled in use. The fixing holes 218 may take the same or similar form as those 118, 11, of the arrangements shown in Figures 1 and 2.

The outer ball 203 further comprises an inner bearing surface 211. In at least one embodiment, both the outer bearing surface 210 and inner bearing surface 211 of the outer ball 203 are spherical bearing surfaces. In at least one embodiment, the outer bearing surface 210 and inner bearing surface 211 are concentric spherical bearing surfaces.

The outer ball 203 takes the form of an annular truncated hemi-spheroid. There is a central aperture 212 in the annulus, having a generally cylindrical inner surface. With reference to Figure 3, it will be noted that the diameter of the central aperture 212 is greater than the diameter of the largest part (axial end face) of the inner ball 204. This allows the insertion of the outer ball 203 into the housing 201, so that the inner ball 204 may be received within the central aperture 212 of the outer ball 203, allowing the outer spherical bearing surface 210 of the outer ball 203 to be seated on the spherical load bearing surface 209 of the bearing insert 202.

The surface 214 of the outer ball 203 bounded by the central aperture 212 and outer spherical bearing surface 210 may be chamfered, as with the arrangements shown in Figures 1 and 2, or otherwise generally correspond to the outer surface of the post 207. This arrangement, as with the corresponding arrangements shown in Figures 1 and 2, may limit the extent of pitching and/or rolling of the thrust bearing 200 in use.

The thrust bearing 200 further comprises at least one locking element 220 5 which is arranged between the inner ball 204 and the outer ball 203 so as to slideably retain the outer ball 203 in the housing 201.

In the embodiment shown, there are two locking elements 220, each taking the general form of a crescent. There may be three or more locking elements 220.

Each locking element 220 comprises an inner spherical bearing surface 222 which, in use, is arranged in a sliding arrangement with the bearing surface 213 of the inner ball 204.

Each locking element 220 further comprises an outer bearing surface 221.

The outer bearing surface 221 of each locking element 220 generally corresponds to the inner bearing surface 211 of the outer ball 203. The radii of the outer bearing surface 221 and inner bearing surface 211 may be substantially the same.

In the embodiment shown in Figure 3, each locking element 220, when assembled, is securable to the outer ball 203. That is to say that, when secured, there is no, or substantially no, relative sliding motion between the outer bearing surface 221 of the locking element 220 and the inner bearing surface 211 of the outer ball 203.

In at least one embodiment, so as to substantially prevent relative movement between each locking element 220 and outer ball 203, there is provided a retainer 230, which retains each locking element 220 in the thrust bearing 200.

The retainer 230 is securable to the outer ball 203. In at least one embodiment, an inner surface 215 of the outer ball 203 may comprise a circumferential groove, which may capture the retainer 230 therein. At least part of the retainer 230 may be spring loaded so as to provide a radial force which retains the retainer 230 in the groove and/or against the inner surface 215. Alternatively or additionally, the retainer 230 may be secured, for example by screws, to the outer ball 203.

A lower part of the inner bearing surface 211 of the outer ball 203 may be provided with a shoulder 216, against which the locking element 220 may abut in use.

The locking element 220 comprises a first axial face 223, and a second axial face 224. The first axial face 223 may be substantially planar and, in use, sits substantially coplanar with the top axial surface of the inner ball 204, as illustrated in Figure 3. At least a part of the second axial face 224 may abut against the shoulder 216 of the inner bearing surface 211 of the outer ball 203.

In at least one embodiment, when the retainer 230 is in place, the distance between the lower surface of the retainer 230 and the shoulder 216 of the outer ball 203 is substantially equal to the distance between the first 223 and second 224 axial surfaces of the locking element 220. This arrangement then substantially prevents any relative movement between the locking element 220 and outer ball 203.

The two locking elements 220 are effectively C-shaped' when viewed from above (along the central axis of the arrangement). At a first end of the locking element 220, there is a first radial split face 225, which is bounded by the outer bearing surface 221, first axial face 223, inner bearing surface 222 and second axial face 224. At a second, opposing, end of the locking element 220, there is a second radial split face 226, which is bounded by the outer bearing surface 221, first axial face 223, inner bearing surface 222 and second axial face 224.

The first 225 and second 226 radial split faces are substantially co-planar with one another.

When the locking elements 220 are retained in place in the outer ball 203, they are effectively sandwiched between the outer ball 203 and the inner ball 204. The retainer 230 prevents the unintended disassembly of the locking elements 220 and outer ball 203. The thrust bearing 200 allows relative sliding movement between the inner spherical bearing surface 222 of the locking element 220 and the spherical bearing surface 213 of the inner ball 204.

When the locking elements 220 are assembled, the first radial split face 225 of a first locking element 220 is adjacent the second radial split face 226 of the second locking element 220, and the second radial split face 226 of the first locking element 220 is adjacent the first radial split face 225 of the second locking element 220.

A benefit of this arrangement is that, without the individual locking screws 116 as required by the known thrust bearing 100 shown in Figure 2, any load imparted on the thrust bearing 200 is spread across the arrangement, rather than focussed on any potential weak points such as individual fixing screws 116 as in the arrangement shown in figure 2.

Figure 4 illustrates a method of assembly of a thrust bearing 200 embodying the present invention. The sequence (steps of assembly) is indicated by the arrows illustrated with numbers "1", "2" and "3".

Firstly, the outer ball 203 is lowered onto the housing 201, such that the inner ball 204 is received through the central aperture 212 of the outer ball 203, until the outer spherical bearing surface 210 of the outer ball 203 is seated on the spherical load bearing surface 209 of the bearing insert 202.

Secondly, the two locking elements 220 are held above the thrust bearing 200 arrangement, such as shown in Figure 4. They are then rotated into place, as indicated by the arrows illustrated with number "2" in Figure 4. Because the outer bearing surface 221 of the locking element 220 generally corresponds to the inner bearing surface 211 of the outer ball 203; and the inner bearing surface 222 of the locking element 220 generally corresponds to the bearing surface 213 of the inner ball 204, the locking elements 220 are received with a sliding fit. By virtue of this arrangement, the locking elements 220 must be rotated about an axis at the intersection of the two perpendicular dash-dot lines shown in Figure 4. The point about which the locking elements 220 are rotated is the centre of the radii of the inner spherical bearing surface 211 of the outer ball 203, the outer spherical bearing surface 221 and inner spherical bearing surface 222 of the locking elements 220 and the spherical bearing surface 213 of the inner ball 204.

The two locking elements 220 may be installed simultaneously or concurrently.

Once the locking elements 220 are arranged in place, the retainer 230 may then be inserted into the outer ball 203 (step 3), to retain the locking elements 220 therein.

In the embodiment of the thrust bearing 200 illustrated in Figures 3 and 4, the locking elements 220 are secured relative to the outer ball 203. In this arrangement, as well as the sliding bearing interface between the outer bearing surface 210 of the outer ball 203 and the load bearing surface 209 of the bearing insert 202, there is also a sliding bearing interface between the bearing surface 213 of the inner ball 204 and the inner bearing surface 222 of the locking element 220. These are the sliding bearing interfaces which accommodate the rolling/pitching movement in use.

As noted above, there is no relative sliding motion, in use, between the outer bearing surface 221 of the locking element 220 and the inner bearing surface 211 of the outer ball 203. The relative sliding motion only occurs during assembly and disassembly.

Another thrust bearing 300 embodying the present invention is illustrated in Figure 5. In this embodiment, the locking element 320 is secured relative to the inner ball 304, rather than to the outer ball 303. Accordingly, the sliding bearing interface, in use, is between the inner bearing surface 311 of the outer ball 303 and the outer bearing surface 321 of the locking element 320, as well as between the outer bearing surface 310 of the outer ball 303 and the load bearing surface 309 of the bearing insert 302 Generally, the features and arrangement of the housing 301 of the embodiment shown in Figure 5 may be substantially the same as those of the housing 201 of the embodiment shown in Figure 3. That is to say that the housing 301 comprises a base 305, a central post 307 upstanding from the base 305 and an inner ball 304 provided on the central post 307. The fixing holes 318 may take the same or similar form as those 218, 118, 11, of the arrangements shown in Figures 1 to 4.

The outer ball 303 is generally similar to the outer ball 203 shown in Figure 3, apart from not having the shoulder 216 Instead, the inner surface 311 of the outer ball 303 presents a substantially continuous spherical bearing surface 311.

In the thrust bearing 300 shown in Figure 5, there may be provided at least two locking elements 320, which slide into place in a similar way as shown in Figure 4. As will be noted from Figure 5, the second axial face 324 of the locking elements 320 extends further than the equivalent in the locking element 220 of the arrangement shown in Figure 3. The second axial face 324 of the locking element 320 may substantially abut against the outer surface of the central post 307. This is because, in use, there is substantially no movement between the inner ball 304 and the locking elements 320 in this embodiment. Instead, there is an operational sliding relationship between the outer bearing surface 321 of the locking elements 320 and the inner bearing surface 311 of the outer ball 303.

The first axial face 323 of the locking elements 320 may be substantially flush with the top surface of the inner ball 304.

The locking elements 320 may be similar in form to the locking elements 220 10 shown in Figures 3 and 4. The locking elements 320 may comprise first 325 and second 326 radial split faces which substantially abut one another when the locking elements 320 are assembled.

There may be provided a plurality of locking screws 330 to secure the locking elements 320 to the inner ball 304. The inner ball 304 may comprise a corresponding plurality of through holes 331, through which the locking screws 330 are received in use. A threaded end of the locking screws 330 may be received in a corresponding threaded aperture in the inner bearing surface 322 of the locking elements 320.

As with the embodiment of the thrust bearing 200 shown in Figure 3, the thrust bearing 300 shown in Figure 5 results in substantially the same arrangement. That is to say that the outer ball 203 is retained in and sandwiched between the inner ball 204, 304 and housing 201, 301 so as to allow a rolling and/or pitching motion of the outer ball 203, 303 relative to the housing 201, 301.

Effectively, both are alternative solutions to the known problems of the arrangements shown in Figures 1 and 2.

In at least one embodiment, all of the bearing surfaces of the components are spherical and substantially concentric with one another. When assembled, the respective centres of all of the bearing surfaces may sit at substantially the same point.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

Claims 1. A thrust bearing comprising: a housing having a base, a central post upstanding from the base, and an inner ball provided on the central post; an outer ball seated on and at least partially within the housing; and at least one locking element arranged between the inner ball and outer ball so as to slidably retain the outer ball in the housing.
2. A thrust bearing according to claim 1, wherein the outer ball comprises an outer bearing surface.
3. A thrust bearing according to claim 2 wherein the housing comprises a bearing surface and the outer bearing surface of the outer ball is arranged in a sliding arrangement with the bearing surface of the housing.
4. A thrust bearing according to any preceding claim, comprising a bearing insert arranged in the housing, the bearing insert providing a bearing surface of the housing.
5. A thrust bearing according to any preceding claim, wherein the inner ball comprises a bearing surface.
6. A thrust bearing according to claim 5, wherein the at least one locking element comprises an inner bearing surface and the inner bearing surface of the at least one locking element is arranged in a sliding arrangement with the bearing surface of the inner ball.
7 A thrust bearing according to any preceding claim, wherein the outer ball comprises an inner bearing surface and the at least one locking element comprises an outer bearing surface, wherein the inner bearing surface of the outer ball corresponds to the outer bearing surface of the locking element.
8. A thrust bearing according to any preceding claim, wherein the at least one locking element is securable to the outer ball.
9. A thrust bearing according to any preceding claim, further comprising a retainer to retain the at least one locking element in the thrust bearing.
10. A thrust bearing according to claim 9, wherein the retainer is securable to the outer ball.
11. A thrust bearing according to any of claims 1 to 4, wherein the outer ball comprises an inner bearing surface.
12. A thrust bearing according to claim 11, wherein the at least one locking element comprises an outer bearing surface and the outer bearing surface of the at least one locking element is arranged in a sliding arrangement with the inner bearing surface of the outer ball.
13. A thrust bearing according to any preceding claim, wherein the inner ball comprises a bearing surface and the at least one locking element comprises an inner bearing surface, wherein the bearing surface of the inner ball corresponds to the inner bearing surface of the at least one locking element.
14. A thrust bearing according to any of claims 11 to 13, wherein the at least one locking element is securable to the housing.
15. A thrust bearing according to claim 14, wherein the at least one locking element is securable to the inner ball and/or central post.
16. A thrust bearing according to claim 15, further comprising a plurality of locking screws to secure the at least one locking element to the inner ball.
17. A thrust bearing according to claim 16, wherein the inner ball comprises an axial end face, and the plurality of screws pass through the axial end face and are received in a corresponding threaded aperture in the inner bearing surface of the at least one locking element.
18. A thrust bearing according to any preceding claim, wherein the housing comprises a spherical bearing surface, the outer ball comprises an inner spherical bearing surface and an outer spherical bearing surface, the at least one locking element comprises an inner spherical bearing surface and an outer spherical bearing surface, and the inner ball comprises a spherical bearing surface, wherein the spherical bearing surfaces are substantially concentric with one another.
19. A thrust bearing according to any preceding claim, wherein there are at least two locking elements.
20. A thrust bearing according to claim 19, wherein each of the locking elements comprises a first and second axial face and a first and second radial split face.