GB2421058A

GB2421058A - A spherical bearing arrangement

Info

Publication number: GB2421058A
Application number: GB0427268A
Authority: GB
Inventors: Paul Smith; Allen Clarke; David Shore
Original assignee: Minebea Co Ltd
Current assignee: Minebea Co Ltd
Priority date: 2004-12-13
Filing date: 2004-12-13
Publication date: 2006-06-14
Also published as: GB0427268D0

Abstract

A spherical bearing arrangement comprises a ball 3 and a bearing housing 2. The ball 3 is mounted in the bearing housing 2 with respective bearing surfaces 6, 7 of the ball 3 and the housing 2 being in sliding contact with one another. A recess 16 is provided for accommodating a seal 13 in one of the bearing surfaces 6, 7 and the other bearing surface 6, 7 is in sliding contact with an inner edge 11 of the recess 16 but not an outer edge 12. The outer edge 12 of the recess 16 is preferably proximate an axial end of the housing 2 and two recesses 16 may be present with lubricant held in the space provided between the recess 16. At least one of the edges 11, 12 of the recess 16 has a smooth transition which may have a non-constant radius or a constant radius of at least 0.1mm. The ball 3 or the housing 2 are preferably manufacture from titanium or a titanium alloy and may include a coating applied using physical vapour deposition. The arrangement reduces wear on the bearing surfaces.

Description

PATENTS ACT 1977 P 19305GB - LDH/APH/szl/cgJvj

DESCRWTION OF INVENTION

"SPHERICAL BEARING ARRANGEMENT" THE PRESENT INVENTION relates to a spherical bearing arrangement.

The art of spherical bearings and, indeed, bearings in general, requires the provision of precision engineered bearing surfaces, wherein tolerances must be strictly adhered to, to ensure the smooth and effective operation of the bearings. As a consequence of keeping within these tolerances, bearings and especially spherical bearings are often expensive to manufacture.

There is a need, therefore, to maintain the high quality of the bearing surfaces and to protect them from damage as much as possible.

Spherical bearings comprise a ball mounted in a bearing housing, wherein, typically, a bore passes through the ball. The ball comprises a spherical ball bearing surface and the bearing housing comprises a spherical housing bearing surface. In use, the two bearing surfaces slidably engage with one another to form a bearing interface. To reduce wear of the bearing surfaces, it is known to provide lubricant at the bearing interface.

In order to retain lubricant in the vicinity of the bearing interface, and to prevent it from leaking from the spherical bearing arrangement as a result of the motion of the ball with respect to the bearing housing, it is known to provide a recess at each axial end of the housing bearing surface, the recess for accommodating a seal therein. These recesses are commonly circumferential.

Consequently, lubricant present at the bearing interface between the two seals is prevented from leaking out of the spherical bearing arrangement.

Whilst the lubricant present between the seals at each axial end of the bearing housing bearing surface acts to reduce degradation of the bearing surfaces, there is at least one portion of the bearing interface adjacent to the seals where lubricant is not provided. Thus, due to the lack of lubricant provided along this portion, significant wear occurs on the bearing surfaces.

Further, the recesses of known arrangements are provided in the bearing housing by turning by turning. As a consequence, sharp edges are presented at the edges of the recesses. Consequently, when the ball is mounted in the bearing housing so that the respective bearing surfaces slidably engage with one another, the sharp edges presented at the edges of the recesses can degrade the ball bearing surface, leading to a reduced life or, indeed, terminal damage to the spherical bearing arrangement - which spherical bearing arrangement must then be scrapped at significant financial cost.

Spherical bearings have found much use in the aerospace industry and thus weight is of paramount importance. Whereas the use of copper alloy or steel in bearings for other applications is acceptable, it is desirable to use light weight metals in the aerospace industry. Thus, a common material used in the manufacture of spherical bearings is titanium or titanium alloy. However, titanium does not have the most desirable wear characteristics, thus any sharp edges presented to a titanium bearing surface cause rapid degradation thereof.

Accordingly, it is known to provide a coating on bearing surfaces to in an attempt to reduce wear and degradation of the bearing surfaces.

With known spherical bearing arrangements made of copper alloy or steel, the wear occurring outside of the lubricated area has not been found to be a significant problem in the past, since wear occurs on the housing bearing surface in this area until the housing bearing surface and ball bearing surface are no longer in sliding contact with one another. However, titanium or titanium alloy spherical bearing arrangements allow significant wear to occur. Especially with the provision of a coating on the bearing surfaces, the sharp edges presented by the recesses, and the lack of lubrication have been found to cause lifting or galling of the coating, thus increasing degradation of the bearing arrangement.

As a further consequence of such pickup or galling, particles removed from the bearing surfaces and fragments of lifted coating are picked up by the lubricated ball bearing surface as the spherical bearing rotates in use. The lubricant containing this abrasive particulate matter spreads to the main lubricated area between the lubrication seals, thus causing further degradation of the bearing surfaces and lifting or galling of the coating, which can significantly reduce the life of the spherical bearing arrangement.

The present invention seeks to overcome the problems as aforementioned.

Accordingly, one aspect of the present invention provides a spherical bearing arrangement, comprising: a ball; and a bearing housing, the ball being mounted in the bearing housing with respective bearing surfaces of the ball and bearing housing in sliding contact with one another, wherein a recess for accommodating a seal is provided in the bearing surface of one of the ball and bearing housing, the bearing surface of the other of the bearing housing and ball being in sliding contact with an inner edge of the recess but not an outer edge.

Preferably, the bearing housing has a central axis and the outer edge of the recess is proximate an axial end of the bearing housing.

Advantageously, a seal is provided in the recess.

Conveniently, there are two recesses, the inner edges of the recesses bounding a portion of the bearing surface within which lubricant is retained.

Preferably, lubricant is provided between the two recesses.

Advantagesously, at least one of the edges of the recess has a smooth transition therealong.

Conveniently, the edge having a smooth transition is a radiussed edge.

Preferably, the radius is not constant.

Alternatively, the radius is constant.

Advantageously, the radius is at least 0.1mm.

Conveniently, the radius of the inner edge is between 0.1 - 0.3mm.

Preferably, the radius of the outer edge is between 0.4 - 0.6mm.

Advantageously, the recess is provided in the bearing housing bearing surface.

Alternatively, or in addition to, the recess is provided in the bearing surface of the ball.

Conveniently, the material of at least one of the bearing housing or ball is titanium or titanium alloy.

Preferably, a coating is provided on a bearing surface.

Advantageously, the coating is provided by PVD.

Another aspect of the present invention provides a spherical bearing housing for mounting a ball therein, comprising: a bearing surface having a recess for accommodating a seal, wherein, in use, the bearing surface is in sliding contact with a bearing surface of a ball, the bearing surface of the ball being in sliding contact with an inner edge of the recess but not an outer edge.

The present invention will now be described, by way of example, with reference to the accompanying figures, in which: Figure 1 shows an axial cross-section of a spherical bearing arrangement not embodying the present invention; Figure 2 shows an axial cross-section of a spherical bearing arrangement embodying the present invention; Figure 3 shows an enlarged view of area A of Figure 2; Figure 4 shows an axial cross- section of another embodiment of the present invention.

Figure 1 shows an axial cross-section of a spherical bearing arrangement 1 comprising a bearing housing 2 with a ball 3 mounted therein. The bearing housing 2 is substantially annular and comprises: a cylindrical outer surface 4; two axial end faces 5 (one of which is shown); and a spherical housing bearing surface 6.

The ball 3 is substantially spherical in shape, providing a spherical ball bearing surface 7 conforming to the housing bearing surface 6 such that the bearing surfaces 6, 7 are in sliding contact with one another to form a bearing interface. The ball 3 further comprises: two axial end faces 8 (one of which is shown); and a central bore 9.

Further, the housing bearing surface 6 is provided with a recess 10 sized for retaining a seal therein. The recess 10 is a cirumferential recess having an inner edge 11 and an outer edge 12. In use, a seal 13 is provided in the recess, which seal 13 is then interposed between the recess 10 and the ball bearing surface 7. The seal 13 acts to prevent any lubricant present at the bearing interface 6, 7 from leaking across the recess 10. An inner surface of the recess does not contact the ball bearing surface 7 in use.

Known spherical bearing arrangements are provided with a recess 10 at each axial end of the housing bearing surface 6, each recess 10 for accommodating a seal 13 therein. Therefore, any lubricant present at the bearing interface 6,7 between the two seals 13 is prevented from leaking out of the spherical bearing arrangement 1. However, as can be seen from Figure 1, there is at least a portion 14 of the bearing interface 6, 7 adjacent the outer edge 12 of the recess 10 where there is no provision for lubricant retention. Any lubricant that is present at this portion 14 is likely to leak from the bearing arrangement 1, in use, due to the motion of the ball 3 with respect to the housing 2.

As the ball 3 rotates relative to the bearing housing 2, wear occurs on the unlubricated portion 14 of the ball bearing surface 7 and that of the housing bearing surface 6. If the bearing surfaces are provided with a coating, lifting or galling of the coating can occur. As a result of this rotation, lubricant residue on the ball bearing surface 7 is likely to pick up any particles removed from the housing bearing surface 6 or ball bearing surface 7 or indeed fragments of lifted coating, thus forming an abrasive slurry - which slurry then spreads across the bearing interface 6, 7 and causes further abrasion of the bearing surfaces 6,7 and lifting and galling of the coating, even in the portion of the bearing interface 6,7 that is provided with lubricant retention means.

Still further, the recesses 10 of known spherical bearing arrangements present a sharp edge at the inner 11 and outer edges 12. As a consequence, the sharp edges degrade the ball bearing surface 7 or cause lifting or galling of a coating provided thereon. The outer edge 12 especially causes rapid wear of the ball bearing surface 7 and lifting or galling of the coating, since there is no lubricant provided in the vicinity thereof. However, even the inner edge 11 - which inner edge 11 is typically lubricated - can cause significant damage to the ball bearing surface 7 or lifting or galling of the coating.

Figure 2 shows a spherical bearing arrangement 15 embodying the present invention. The outer edge 12 of the recess 16 provided in the housing bearing surface 6 is not in sliding contact with the ball bearing surface 7.

Consequently, a portion 17 of the bearing housing 2 adjacent the outer edge 12 of the recess 16 is also not in sliding contact with the ball bearing surface 7. In use, a seal 13 provided in the recess 16 acts to retain any lubricant provided, and prevent it from leaking out of the spherical bearing arrangement 15.

An advantage of spherical bearing arrangements embodying the present invention is that the ball bearing surface 7 is only in sliding contact with portions of the housing bearing surface 6 bounded by the recesses 16. In use, lubricant is provided between these recesses 16 - which recesses have seals located therein - thus reducing degradation of the bearing surfaces 6, 7 or lifting or galling of any coating provided thereon.

As can be more clearly seen in Figure 3, an enlarged view of area A of Figure 2, showing the recess 16 of a spherical bearing arrangement 15 embodying the claimed invention, the inner 11 and outer edges 12 are provided with a smooth transition 18 therealong. Most preferably, the smooth transition 18 is a radiussed edge. Conveniently, the radius is constant about the radiussed edge. Advantageously, the radius is at least 0.1 mm. Preferably, the radius r2 on the inner edge 11 is between 0.1 mm 0.3 mm, most preferably the radius r2 is 0.2 mm. Conveniently, the radius r1 of the outer edge 12 is between 0.4 - 0.6 mm. Most conveniently, the radius r1 is 0.5 mm.

However, it is envisaged that the radius need not be constant in order to provide the benefits of the claimed invention. Thus, the radius of a radiussed edge adjacent the housing bearing surface 6 or portion 17 could be less than the radius adjacent an inner surface of the recess 16. Conversely, the radius adjacent the housing bearing surface 6 or portion 17 could be greater than the radius adjacent an inner surface of the recess 16.

It is preferable that a smooth transition 18 is provided on the inner edge 11 of the recess 16, which inner edge 11, in use, is in sliding contact with the ball bearing surface 7. However, whilst the outer edge 12 is not in sliding contact with the ball bearing surface 7 in use, it is advantageous to provide a smooth transition 18 thereon. In use, it is likely that the seal 13 will rotate and move within the recess 16 as the ball 3 rotates relative to the bearing housing 2, and a sharp edge being presented by the outer edge 12 could conceivably also cause damage to the seal 13. However, recesses of spherical bearing arrangements embodying the claimed invention do not present a sharp edge and thus do not cause damage to a seal 13 located in the recess.

Figure 4 shows another embodiment of the claimed invention. In this example, a recess 16 is provided in the ball bearing surface 7 instead of the housing bearing surface 6. Accordingly, the bearing housing 2 provides a spherical housing bearing surface 6 without any recesses being provided therein.

Preferably, if a recess for accommodating a seal is provided in the bearing surface of the bearing housing of a spherical bearing arrangement embodying the present invention, then the ball is preferably a split-ball assembly. Conversely, should a recess for accommodating a seal be provided in the bearing surface of the ball of a spherical bearing arrangement embodying the present invention, then the bearing housing is preferably a split housing.

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 Preferably, any internal corners of the inner surface of the recess have a radiussed edge. Most preferably, the radius is no more than 0.8 mm.

Preferably, the material of a least one of the bearing housing 2 or ball 3 embodying the claimed invention is titanium or titanium alloy.

Advantageously, a coating is provided on a bearing surface. Conveniently, the coating is applied using physical vapour deposition (PVD). Preferably, the coating is titanium nitride (TiN) or another suitable PVD coating such as chromium nitride (CrN) or titanium aluminium nitride (TiA1N). The provision of radiussed edges (radius in the order of at least 0.1 mm) has been found to be especially beneficial in extending the life of bearing arrangements incorporating such a coating.

Whilst the provision of two recesses in the housing bearing surface or ball bearing surface has been discussed, it will of course be appreciated that the claimed invention is not limited to such an arrangement. Indeed, spherical bearing arrangements embodying the present invention could be provided with a single recess for accommodating a seal therein, wherein any lubricant provided on one side of the seal is retained thereagainst by the forces of gravity or any other force.

Claims

1. A spherical bearing arrangement, comprising: aball; and a bearing housing, the ball being mounted in the bearing housing with respective bearing surfaces of the ball and bearing housing in sliding contact with one another, wherein a recess for accommodating a seal is provided in the bearing surface of one of the ball and bearing housing, the bearing surface of the other of the bearing housing and ball being in sliding contact with an inner edge of the recess but not an outer edge.

2. A spherical bearing arrangement according to claim 1, wherein the bearing housing has a central axis and the outer edge of the recess is proximate an axial end of the bearing housing.

3. A spherical bearing arrangement according to any preceding claim, wherein a seal is provided in the recess.

4. A spherical bearing arrangement according to any preceding claim, wherein there are two recesses, the inner edges of the recesses bounding a portion of the bearing surface within which lubricant is retained.

5. A spherical bearing arrangement according to Claim 4, wherein lubricant is provided between the two recesses.

6. A spherical bearing arrangement according to any preceding claim, wherein at least one of the edges of the recess has a smooth transition therealong.

7. A spherical bearing arrangement according to Claim 6, wherein the edge having a smooth transition is a radiussed edge.

8. A spherical bearing arrangement according to Claim 7, wherein the radius is not constant.

9. A spherical bearing arrangement according to Claim 7, wherein the radius is constant.

10. A spherical bearing arrangement according to any of Claims 7 to 9, wherein the radius is at least 0.1 mm.

11. A spherical bearing arrangement according to any of Claims 7 to 10, wherein the radius of the inner edge is between 0.1 - 0.3mm.

12. A spherical bearing arrangement according to any of Claims 7 to 11, wherein the radius of the outer edge is between 0.4 - 0.6mm.

13. A spherical bearing arrangement according to any preceding claim, wherein the recess is provided in the bearing housing bearing surface.

14. A spherical bearing arrangement according to any preceding claim, wherein the recess is provided in the bearing surface of the ball.

15. A spherical bearing arrangement according to any preceding claim, wherein the material of at least one of the bearing housing or ball is titanium or titanium alloy.

16. A spherical bearing arrangement according to any preceding claim, wherein a coating is provided on a bearing surface.

17. A spherical bearing arrangement according to Claim 16, wherein the coating is provided by PYD.

18. A spherical bearing housing for mounting a ball therein, comprising: a bearing surface having a recess for accommodating a seal, wherein, in use, the bearing surface is in sliding contact with a bearing surface of a ball, the bearing surface of the ball being in sliding contact with an inner edge of the recess but not an outer edge.

19. A spherical bearing arrangement as herein before described, with reference to and as shown in Figures 2 to 4.

20. A spherical bearing housing as herein before described, with reference to and as shown in Figure 2 to 4.

21. Any novel feature or combination of features described herein.