Abstract:
A spherical bearing arrangement comprising: a bearing housing; a plurality of split-ball portions which are together arranged in the housing to produce a composite ball having a spherical bearing surface, the composite ball having a bore passing therethrough, the bore having a central axis; and a bushing secured in the bore of the composite ball. A method of assembling a spherical bearing arrangement is also disclosed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of Great Britain Patent Application No. GB 0421122.3, filed on Sep. 22, 2004, which is incorporated herein by reference. 
   FIELD 
   The present invention relates to a spherical bearing arrangement and a method of assembly thereof. 
   BACKGROUND 
   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 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. 
   Mounting the ball into the housing of a spherical bearing arrangement has proved difficult, since any method must result in the torque of the bearing being substantially zero. A conventional method is to provide a single ball and swage the housing around the ball to fixedly retain it therein. However, ensuring the torque of such a bearing remains within a predetermined range has proved difficult. 
   Spherical bearings comprising a split-ball arrangement go some way to alleviating the problems associated with single ball spherical bearings. Such an arrangement commonly comprises two split-ball portions which, when mounted together in the bearing housing, collectively define a split-ball arrangement which serves, in principle, as the ball of a single-ball spherical bearing arrangement. 
   The main advantage of split-ball bearings is that they do not require swaging of the bearing housing and thus reduce manufacturing costs. The split-ball portions are mounted in turn, with one portion being installed into the housing and engaging with the bearing surface, and the second portion being inserted and twisted by 90° to coincide with the other split ball portion. Consequently, it is easier to produce a split ball spherical bearing having a torque of substantially zero, since each part can be manufactured separately from one another. 
   Since spherical bearings are commonly used in the aerospace industry, weight is of paramount importance. It is desirable, therefore, to manufacture spherical bearings from a lightweight material, such as titanium or a titanium alloy. However, such a material does not offer the most desirable wear characteristics. In use, a shaft is commonly located in a bore passing through the ball of a spherical bearing. Over time, because the lightweight material of the bore does not offer a good wear surface, the bore bearing surface degrades, and the life of the bearing is shortened. The spherical bearing arrangement may therefore need to be scrapped at great financial cost. 
   In the case of a single-ball spherical bearing arrangement, a bushing can be interference fit in the bore to reduce wear on the ball. However, in the case of a split ball bearing arrangement, an interference fit bushing cannot be used without affecting the torque of the split ball bearing arrangement. Therefore, bushings are not used in split ball arrangements. 
   There is therefore a need for a split ball bearing arrangement manufactured from a lightweight material, but offering suitable wear characteristics for a shaft passing therethrough. 
   SUMMARY 
   The present invention provides a spherical bearing arrangement which seeks to overcome the aforementioned problems. 
   Accordingly, one aspect of the present invention provides a spherical bearing arrangement comprising: a bearing housing; a plurality of split-ball portions which are together arranged in the housing to produce a composite ball having a spherical bearing surface, the composite ball having a bore passing therethrough, the bore having a central axis; and a bushing secured in the bore of the composite ball. 
   Preferably, there is no separation between the split-ball portions. 
   Alternatively, there may be separation between the split-ball portions. 
   Advantageously, the bushing is secured with a non-interference fit in the bore of the composite ball. 
   Conveniently, the bushing is secured in the bore of the composite ball so as to prevent axial displacement of the bushing in the bore. 
   Preferably, the split ball portions are substantially identical to each other. 
   Advantageously, there are two split ball portions. 
   Conveniently, the material of the bushing is pre-selected to be different to the material of the composite ball. 
   Preferably, a shaft is to be inserted into the bushing and the material of the bushing is pre-selected so as to offer desirable wear characteristics between the bushing and shaft. 
   Advantageously, the material of the bushing is a copper alloy. 
   Conveniently, the material of the composite ball is titanium or a titanium alloy. 
   Another aspect of the present invention provides a method of assembling a spherical bearing arrangement, the arrangement comprising a bearing housing; a plurality of split-ball portions; and a bushing, the method comprising the steps of: inserting the plurality of split-ball portions into the bearing housing so as to define a composite ball having a bore passing therethrough; and securing the bushing into the bore of the composite ball. 
   Preferably, the plurality of split-ball portions are inserted into the bearing housing sequentially, prior to securing the bushing in the bore. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying figures, in which: 
       FIG. 1  shows a perspective view of a spherical bearing arrangement; 
       FIG. 2  shows a cross section of the spherical bearing arrangement of  FIG. 1  along line  2 - 2 ; 
       FIGS. 3-5  show stages of assembly for the spherical bearing arrangement of  FIGS. 1 and 2 ; 
       FIG. 6  shows a perspective view of a spherical bearing arrangement embodying the present invention; 
       FIG. 7  shows a cross section of the spherical bearing arrangement of  FIG. 6  along line  7 - 7 ; and 
       FIG. 8  shows an enlarged cross section of area C of  FIG. 7 . 
   

   DETAILED DESCRIPTION 
     FIGS. 1 and 2  show a spherical bearing arrangement  1 , comprising a bearing housing  2  with a composite ball  3  mounted therein. The bearing housing  2  is substantially annular and comprises: a cylindrical outer surface  4 ; two axial end faces  5 ; and an inner surface comprising a spherical housing bearing surface  6 . The bearing housing  2  further has a central axis  7 . The bearing housing  2  has a circumferential, radially extending flange  8  proximate an axial end face  5  of the bearing housing  2 . The flange  8  carries three equi-spaced lobes  9  which each protrude from the flange  8 . The equi-spaced lobes  9  are each provided with an aperture  10  through which a bolt or the like can pass, for fixing the bearing housing  2  by the lobes  9  to another object. 
   The composite ball  3  is substantially spherical in shape, providing: a spherical composite ball bearing surface  11 ; two axial end faces  12 ; and a bore  13  with a central axis  14 . The composite ball bearing surface  11  conforms to the housing bearing surface  6  such that the bearing surfaces  6 ,  11  are in sliding contact with one another. Preferably, there is zero torque between the composite ball  3  and the bearing housing  2 . 
   The composite ball  3  is formed from two substantially identical split-ball portions  15   a ,  15   b . Each split ball portion  15   a ,  15   b  comprises: a hemi-spherical split ball bearing surface  16 ; two axial end faces  17 ; a semi-cylindrical inner surface  18  defining one half of the composite ball bore  13 ; and two separation faces  19 . The separation faces  19  of each split ball portion  15  are substantially co-planar. 
   Preferably, the split ball portions  15   a ,  15   b  and the bearing housing  2  are made of titanium, a titanium alloy, or some other suitable light weight material. More preferably, the split ball portions  15   a ,  15   b  and bearing housing  2  are made of titanium alloy TA6V as per ASNA3307. Advantageously, the titanium alloy is coated with titanium nitride using a plasma assisted physical vapour deposition method. 
     FIGS. 3 to 5  show stages of assembly for the spherical bearing arrangement  1  of  FIGS. 1 and 2 .  FIG. 3  shows the bearing housing  2  of  FIGS. 1 and 2  with split ball portion  15   a  seated therein, so that the split ball bearing surface  16  contacts the housing bearing surface  6 . The split ball portion  15  is then rotated by 90 degrees about an axis  20  perpendicular to the bearing housing central axis  7 , so that more of the split ball bearing surface  16  is contacting the housing bearing surface  6 . Such an arrangement is shown in  FIG. 4 . It will be appreciated that when in the position shown in  FIG. 4 , the axial end faces  17  of the split ball portion  15   a  will be parallel to the respective axial end faces  5  of the bearing housing  2 . 
   Split ball portion  15   b  is then inserted into the bearing housing  2  in a similar manner to split ball portion  15   a , so that the split ball bearing surface  16  contacts the housing bearing surface  6 . Such an arrangement is shown in  FIG. 5 . 
   Preferably, to aid insertion of split ball portion  15   b , the axial length of the split ball portions  15   a ,  15   b  is smaller than the diameter of the composite ball bore  13 , but this is not essential. 
   As with split ball portion  15   a , split ball portion  15   b  is then rotated by 90 degrees about an axis  20  perpendicular to the bearing housing central axis  7 , so that more of the split ball bearing surface  16  is contacting the housing bearing surface  6 . Such an arrangement is shown in  FIGS. 1 and 2 . Consequently, the respective separation faces  19  of the two split ball portions  15   a ,  15   b  slide over one another and are preferably frictionally engaged with one another. 
   It will be appreciated that, in the orientation described, with reference to  FIGS. 1 and 2 , the central axis  14  of the composite ball  3  will be coaxial with the central axis  7  of the bearing housing  2 . 
   As aforementioned, the torque of the spherical bearing arrangement  1  (between the composite ball bearing surface  11  and the housing bearing surface  6 ) is preferably zero. The composite ball  3  can therefore rotate freely within the bearing housing  2 . It is possible, therefore, for the split ball portions  15   a ,  15   b  to misalign with respect to one another, thus not offering a purely cylindrical bore  13  for the insertion of a shaft. Such misalignment can occur either by the separation faces  19  sliding in relation to one another, or by the separation faces  19  moving toward or away from one another. However, in accordance with embodiments of the present invention, a bushing  22  is provided in the bore  13  of the composite ball  3 . 
   The spherical bearing arrangement  21  of  FIGS. 6 and 7  comprises the bearing housing  2 , with the composite ball  3  mounted therein and a bushing  22  which is secured in the bore  13  of the composite ball  3 . The bushing  22  is cylindrical, and comprises: two axial ends  23 ; an outer surface  24  and an inner surface  25 ; and a central axis  26 . Preferably, the bushing  22  is made of copper alloy. More preferably, the bushing  22  is made of beryllium copper, CuBe 1.9 as per ASNA3417. The material of the bushing  22  offers a better wear surface than the material of the bore  13  of the composite ball  3 . 
   An annular flange  27  is located at one axial end  23  of the bushing  22  and projects radially outwardly to provide a stop  28 . The outer surface of the other axial end  23  of the bushing  22  is threaded so as to receive a correspondingly threaded nut  29  to provide a further stop  28 . The nut  29  is preferably made of copper. Preferably, as shown in  FIG. 8 , at least one hole  30  is drilled at the interface  31  between the threaded portion of the bushing  22  and the nut  29  and a peg  32  secured therein. Such an arrangement is known in the art as “pegging”. By securing a peg  32  into the hole  30 , the nut  29  is locked with respect to the threaded portion, so that movement between these parts is prevented—thus, the nut  29  does not become loose during use. The peg  32  is preferably made of steel. 
   Alternatively, the stop  28  at each end of the bushing  22  could comprise a nut  29  and threaded portion arrangement. 
   The provision of a stop at both ends of the bushing allows the bushing to be retained in the composite ball when subjected to axial forces, such as those encountered in landing gear Pintle bearings. When assembled, axial displacement of the bushing relative to the composite ball is prevented by abutment of one of the stops against a respective axial end face of the composite ball. Whilst, in use, these axial forces may act in both directions along the central axis of the bushing. It is also envisaged that any axial force could normally be present in only one direction so there would only need to be one stop located at an axial end of the bushing. Such a singular stop could comprise either a flange, or a nut and threaded portion arrangement. 
   It is critical that when the bushing is subjected to axial forces, in normal use, the bearing still operates effectively. That is to say: the torque experienced between the composite ball and the housing must remain within a predetermined range, regardless of the level or direction of axial force imposed on the bushing. Securing the bushing with a non-interference fit in the composite ball is critical and conveniently prevents any unwanted variation in torque between the composite ball and housing. This is different to the arrangement provided in the prior art, for example in U.S. Pat. No. 4,251,122. 
   When the spool member  22  of the arrangement in US &#39;122 is subjected to an axial force, the spool member  22  moves with respect to the housing. However, because of the mating threads provided on the inner surface of the spherical segments  26  and the outer surface of the spool member  22 , any axial movement between these two parts will cause the respective threads to “ride up” upon one another, having the effect that the spherical segments will move radially outwardly from the spool member  22 , thus increasing the torque between the ball and the housing. This interference fit between the spool and the ball is exactly the arrangement embodiments of the present invention avoid. The requirement for a non-interference fit between the ball and bushing in arrangements embodying the present invention is the technical feature which prevents any increase in torque between the composite ball and the housing. The interference fit, as disclosed in US &#39;122, causes the undesirable variation (increase) in torque. Even with the alternative arrangement disclosed in the passage from line 68 of column 4, to line 4 of column 5 of US &#39;122, where the threading is only provided on a portion of the inner surface of the spherical surface and the outer surface of the spool member  22 , the same problem is still experienced. 
   The provision of the bushing in the bore of the composite ball offers a bearing surface for the shaft to contact with. Preferably, the material of the bushing is different to the material of the split ball portions. Advantagously, the material of the bushing offers more suitable wear characteristics than the material of the bore of the composite ball. These wear characteristics are preselected to be suitable to the material of the shaft to be inserted in the bushing. Thus, in operation, the amount of wear experienced between the bushing and the shaft should be less than the wear that would be experienced if a bushing were not to be used. Advantageously, should wear occur, however, on the bushing, it can merely be replaced by a new bushing without the need to scrap the entire spherical bearing arrangement. 
   There is little or no torque present between the outer cylindrical surface of the bushing and the inner cylindrical bore surface of the composite ball. The abutment of the at least one stop against at least one axial end face of the composite ball will preferably offer a torque higher than any torque that might be present between a shaft inserted in the bore and the inner bushing bearing surface. Consequently, in use, the bushing will preferably not rotate relative to the composite ball and thus there will be little or no wear of the composite ball bore bearing surface. 
   A further advantage of embodiments of the present invention is that the mechanics of inserting a shaft into the composite ball is simplified since the split ball portions are effectively sleeved by the bushing so as to present an aperture for the shaft without discontinuities. Consequently, the split ball portions will not misalign in the bearing housing during transportation or installation of the bearing arrangement because of the bushing holding the split ball portions in their assembled configuration. 
   Whilst the examples hereinbefore described prescribe the provision of two, identical, split ball portions, it will be readily appreciated that the present invention is not limited to such an arrangement. Indeed, there can be provided more than two split ball portions without departing from the essence of the present invention. Moreover, the split ball portions need not be identical to each other. Thus, there could be provided three split ball portions: one portion comprising a “half-ball”; and the two other split ball portions comprising a “quarter-ball” respectively. The assembly of such an arrangement could comprise the separate insertion of the two quarter balls, followed by the insertion of the half-ball; or, alternatively, the initial insertion of the half-ball, with the subsequent insertion of the two quarter-balls simultaneously. However, a person skilled in the art will readily appreciate that the number and shape of the split balls is not essential to the realisation of the present invention. 
   Whilst the respective separation faces of the above example are frictionally engaged with one another—i.e. there is little or no gap therebetween—it is also envisaged that a gap could be present. It will be readily appreciated by someone skilled in the art that the presence/lack of a gap between the separation faces is insignificant to the realisation of the present invention. However, should there exist a substantial gap, then the aforementioned problems associated with misalignment will be further compounded, and the benefits of the present invention even more apparent. Pleasingly, with a bushing inserted in the composite ball, no splits or cracks are present in the surface presented to the external surface of the shaft—thus any lubricant between the shaft and the bushing surface will not be lost between splits or cracks in the composite ball. 
   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.