Relief Slot For A Load Bearing Assembly

Abstract

A load bearing assembly comprises: a lug body; an outer race disposed within and supported by the lug body; an inner race disposed within and supported by the outer race; and a relief slot defined between the adjacent surfaces of the outer race and the lug body, wherein the relief slot is formed in the surface of the outer race.

Claims

1. A load bearing assembly comprising: a lug body; an outer race disposed within and supported by the lug body; an inner race disposed within and supported by the outer race; and a relief slot defined between the adjacent surfaces of the outer race and the lug body, wherein the relief slot is formed in the surface of the outer race.

2. A load bearing assembly as claimed in claim 1, wherein the lug body comprises a bore for housing the outer race, wherein the bore is devoid of regions in which forces and stress concentrate.

3. A load bearing assembly as claims in claim 2, wherein the bore has a circular cross-section.

4. A load bearing assembly as claimed in claim 1, wherein the relief slot is defined in the surface of the outer race circumferentially perpendicular to the primary load bearing region of the surface.

5. A load bearing assembly as claimed in claim 1, wherein the relief slot is filled with a flexible adhesive and/or sealant.

6. A load bearing assembly as claimed claim 1, wherein the outer race comprises a tab or lip which has been swaged into a recess defined in the lug body.

7. A load bearing assembly as claimed in claim 6, wherein the tab is circumferentially proximate the primary load bearing region of the outer race.

8. A load bearing assembly as claimed in claim 1, wherein the relief slot is defined in the surface of the outer race over an arc in the range 45-90 degrees.

9. A load bearing assembly as claimed in claim 1, wherein the relief slot is defined in the surface of the outer race to a depth of 0.1-0.5 millimetres.

10. A load bearing assembly as claimed in claim 1, comprising a second relief slot on an opposite side of the outer race.

11. A method of manufacturing a load bearing assembly including a lug body, an outer race disposed within and supported by the lug body, and an inner race disposed within and supported by the outer race; the method comprising: providing a relief slot formed in the outer race between the adjacent surfaces of the outer race and the lug body.

12. A method as claimed in claim 11, comprising filling the relief slot with a flexible adhesive or sealant.

13. A method as claimed in claim 11, comprising swaging a tab of the outer race into a recess defined in the lug body.

14. A method as claimed in claim 11, comprising inserting the outer race into a bore of the lug body, wherein the bore is devoid of regions in which forces and stress concentrate.

15. A method as claimed in claim 14, wherein the bore has a circular cross section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An exemplary embodiment of the present disclosure will now be described by way of example only and with reference to the accompanying drawings in which:

[0021] FIG. 1 shows a load bearing assembly;

[0022] FIG. 2 shows an exploded view of a load bearing assembly;

[0023] FIG. 3 shows a section view of a relief slot in a magnification of a portion of a load bearing assembly;

[0024] FIG. 4 shows a section view of portion of a load bearing assembly;

[0025] FIG. 5 shows the load bearing assembly of FIG. 5 from another direction.

DETAILED DESCRIPTION

[0026] FIG. 1 shows an exemplary load bearing assembly 100 comprising a spherical bearing comprising an inner race 110 and an outer race 120, and a lug body 130. A liner 150 may be disposed between the inner race 110 and the outer race 120 to facilitate relative movement therebetween.

[0027] The inner race 110 is disposed rotatably within the outer race 120, and the outer race 120 is disposed securely within the lug body 130. The inner race 110 is therefore mounted within the lug body 130 by the outer race 120. The outer race 120 is fixed with respect to the lug body 130, and the inner race 110 is moveable with respect to both the outer race 120 and the lug body 130.

[0028] The lug body 130 may comprise a connection means 132 (for example a threaded portion) to connect the lug body 130 to a load. The lug body 130 defines an axis A along which the load may be directed, e.g. in the direction of the arrow 190. This is the primary load path through the lug body 130. The load bearing assembly may also bear load in the direction indicated by arrow 192. The load borne in the direction of arrow 192 may typically be less than the load borne in the direction of arrow 190. The load may also be directed along arrow 194.

[0029] The direction of the load may be along any of the arrows 190, 192, 194, or any combination of those directions. It may also change directions, particularly reversing direction, regularly and frequently. Such changing of the load leads to fretting and component fatigue as described earlier.

[0030] FIG. 2 shows an exploded view of the load bearing assembly 100, with a magnified view of the edge of the outer race 120. The spherical bearing comprising the inner race 110 and the outer race 120 is inserted into a bore within the lug body 130. The outer race 120 is then swaged to secure it within the lug body 130. The swaging process forms indent 122 in the outer race 120.

[0031] FIG. 3 shows a magnification of the large, dashed, leftmost circle of FIG. 1. It also shows a magnification of the indicated region near the top of the relief slot 140. The lug body 130 and the outer race 120 are visible in FIG. 3. Relief slot 140 is formed in the surface of the outer race 120. The relief slot 140 is formed only in the surface of the outer race 120, and has an inner surface 142 and an outer surface 144. The inner surface 142 of the relief slot 140 is on the outer race 120, and the outer surface 144 of the relief slot 140 is on the lug body. Since the relief slot 140 is formed (e.g. cut or machined) into the outer race 120, the cross-section of the bore in the lug body 130 is circular. Hence concentrations of stress in discontinuities of the surface of the lug body 130 are avoided, and fretting fatigue of the lug body 130 is reduced substantially.

[0032] The relief slot 140 has a width 6, and hence is defined a depth δ in to the outer race 120. The outermost surface 124 of the outer race 120 (i.e. the surface contacting the lug body 130) has the same centre of curvature O as that of the inner surface 142 of the relief slot 140. However, the relief slot 140 has a smaller radius of curvature than that of the outermost surface 124 of the outer race 120. Hence, the relief slot 140 has a constant depth δ across substantially its entire arc. Alternatively, the relief slot 140 may have a varying depth along its length.

[0033] The relief slot 140 is formed on an arc of Φ degrees and extends about the circumference of the outer race 120, symmetrically about the horizontal axis 192 (shown in FIG. 3). The angle Φ may be chosen depending on how the load bearing assembly is to be used. The angle Φ may be up to 90 degrees, for example about 80 degrees.

[0034] At the ends of the relief slot 140, the inner surface 142 gradually rises towards the outer surface 144 to become the outermost surface 124 of the outer race 120. The gradual gradient helps prevent stress concentrations within the outer race 120, thereby reducing fretting fatigue.

[0035] The relief slot 140 may have a width (in the direction of the arrow 194 in FIG. 1) of substantially all of the outer race 120, or of a portion of the outer race 120.

[0036] A flexible adhesive 146 is disposed within the relief slot 140, and serves to secure the outer race (and therefore also the inner race 110) within the lug body 130. An example of a suitable flexible adhesive is. Loctite, but other suitable compositions exist, such as sealant compounds.

[0037] As will be apparent from consideration of FIGS. 1 and 3 together, the relief slot 140 is defined in the outer race 130 at a position most distant from the axis A, perpendicular to the primary load path. Hence, the relief slot 140 is defined at a region which serves a lesser load bearing capacity than the regions through which the axis A passes. The primary load path passes though the surfaces at the top and bottom (relative to FIG. 1) of the outer race 120 and lug body 130.

[0038] FIG. 4 shows a perpendicular cross-section through the region of the assembly indicated by the smaller, dashed circle in FIG. 1. A tab 126 (not shown in FIG. 1) is formed on the outer race 120, and is deformed into a recess 134 defined in the lug body 130. FIG. 5 shows the same arrangement from the same perspective as FIG. 1. The tab 126 of the outer race 120 therefore locks the orientation of the outer race 120 relative to the lug body 130. The tab 126 is located in line with the axis A and the primary load path 190, opposite to the applied tensile load along the primary load path 190. Consequently, the primary loads through the assembly do not apply shear forces to the tab 126. A corresponding tab 126 is formed at the opposite side of the outer race 126, symmetrically to the tab 126 depicted in FIGS. 4 and 5. Any suitable number of tabs 126 may be used, though having only two per face of the assembly benefits from the lack of shear forces through the tabs 126 from the primary load path.

[0039] Although only one relief slot 140 has been depicted, the load bearing assembly comprises a second similar relief slot 140 on the opposite side of the outer race 120. The provision of the relief slots 140 as described herein provides fretting fatigue relief to the spherical bearing outer race 120. Moreover, it may substantially reduce the probability of catastrophic failure of the lug body 130, since the lug body 130 may have a circular bore which distributes loads more evenly than one with discontinuities defined in its surface. Further, even if the load bearing assembly fails as a consequence of fretting fatigue of the spherical bearing, it will not be a catastrophic failure as the failed spherical bearing can be retained within the lug body 130. Therefore, the assembly can continue to function (albeit at a reduced capacity) until maintenance can be carried out. Finally, rotation of the outer race 120 within the lug body 130 can be prevented, either by filling the relief slots with a flexible retaining substance or by physically deforming the tabs 126 on the outer lip of the outer race 120 into the recesses 134 on the lug body 130. This will allow the position of the relief slot 140 to remain as built.

[0040] The assembly and method described herein and shown in the drawings provide a load bearing assembly which reduces the possibility of a catastrophic failure caused by fretting. While the apparatus and methods herein have been shown and described with reference to an exemplary system, those skilled in the art will appreciate that changes and/or modifications may be made thereto without departing from the scope of the present disclosure as defined by the appended claims.