Abstract:
A method for assembling a ball and socket assembly ( 10 ) includes loading a housing ( 14 ) with a resilient preload washer ( 28 ), an inner bearing ( 30 ), a ball stud ( 12 ) and an outer bearing ( 36 ). A loading tool ( 50 ) forcefully compresses the assembled components, as a unit, to an overload compression condition ( 54 ), and then reduces the compression until an ideal compression condition ( 56 ) is achieved. The outer bearing ( 36 ) is staked in position while the loading tool ( 50 ) holds the assembled components in the ideal compression condition ( 56 ). Following the staking operation, the loading tool ( 50 ) can be removed, and a final crimping operation permanently sets the outer bearing ( 36 ) in position and holds the articulating components in the ideal, pre-load clearance established. The subject method is particularly well-suited for high production set-ups in which precise pre-load clearances must be achieved at high through put rates.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a ball and socket type joint of the type used in vehicular steering and chassis applications, and more particularly toward such a ball socket assembly in which a pre-established compressive load is captured between the articulating components during an assembly operation. 
     2. Related Art 
     Ball and socket type assemblies are typically used in vehicular applications where three-dimensional movement of a wheel, and in particular a steerable wheel, is required when a vehicle is turning and/or the suspension is accommodating movement over rough terrain. In the normal course of operation, ball sockets are subjected to very high stresses. These stresses are transmitted through the stud of the ball socket assembly into an associated suspension member, which may be a steering knuckle, control arm, steering link, rack and pinion unit or other feature. 
     In particularly demanding applications, such as, for example, experienced by off-road vehicles and commercial vehicles, it is sometimes desirable to fabricate the components in a ball and socket assembly from metallic compositions. Thus, an “all metal” design can provide enhanced durability as compared with the prior art, light-duty structures which incorporate plastic and/or elastomeric pre-loaded articulating components. 
     During the manufacturing assembly operation, the ball stud of a ball and socket type assembly is loaded into a housing and captured between outer and inner bearing pieces to establish the articulating joint. A resilient spring-like member is typically placed into service between the housing and the articulating components to facilitate the pre-load compression setting. This resilient member may comprise a Belleville washer or similar type spring component or may comprise a polymeric elastomer for this purpose. Such prior art light-duty ball and socket assemblies which utilize plastic and/or elastomeric components are relatively forgiving in their assembly methods needed to achieve and maintain a preload compression setting, as compared with the heavy-duty all metal designs. Rather, the more durable all metal type ball and socket assemblies have proven to be extremely sensitive to the pre-load compression stresses established during the assembly operations. This sensitivity frustrates high through-put manufacturing as well as complicates a consistent quality achievement in mass production settings. Accordingly, there is a need for an improved method of controlling the pre-load clearance in a ball and socket assembly, and in particular within such assemblies of the “all metal” type. 
     SUMMARY OF THE INVENTION 
     The subject invention comprises a method of assembling a ball-and-socket type mechanism with a permanent pre-load compression between the articulating components. The method comprises the steps of providing a housing, a resilient member, an inner bearing having a wear surface, an articulating ball stud, and an outer bearing having a wear surface. The method further includes placing into the housing the resilient member, the inner bearing against the resilient member, the ball stud in sliding contact with the wear surface of the inner bearing and the outer bearing with its wear surface in sliding contact with the ball stud. The outer bearing, ball stud and inner bearing are then compressed as a unit against the resilient member until an ideal compression condition is achieved. The ideal compression condition is maintained while the outer bearing is fixed in a set position in the housing to capture the ideal compression condition between the outer bearing, the ball stud and the inner bearing. 
     The subject invention provides a method for positioning and locking the outer bearing in position while the ideal compression is maintained. The subject invention is particularly advantageous in ball and socket type assemblies in which the pre-load compression and clearance is particularly sensitive. Such sensitivity arises in certain all metal component designs, but may also be an issue in some hybrid assemblies which may include non-metal bearing members as well. 
     According to another aspect of the invention, a method is provided for assembling an all-metal ball-and-socket type mechanism with a permanent pre-load compression between its articulating components. This method comprises the steps of: providing a metal housing, a metal resilient preload member, and metallic inner bearing having a wear surface, an articulating metal ball stud, and a metallic outer bearing having a wear surface; placing into the housing the resilient preload member, the inner bearing against the resilient preload member, the ball stud in sliding contact with the wear surface of the inner bearing, and the outer bearing with its wear surface in sliding contact with the ball stud; compressing the outer bearing, ball stud and inner bearing as a unit against the resilient preload member until an over-load compression condition or state is reached; reducing the compression load within the socket until an ideal compression condition is achieved between the outer bearing, ball stud and inner bearing; maintaining the ideal compression condition while simultaneously deforming the housing into the outer bearing so as to fix the outer bearing position in the housing and thereby capture the ideal compression condition within the all metal ball and socket mechanism. In a further aspect, the method may include a step of re-forming an up-standing edge of the housing to further effect a fixation of the bearing and the socket preload after the step of deforming the housing into the outer bearing. Alternatively, compressing the socket to an optimal preload without first overloading is an acceptable method of setting the socket preload. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
         FIG. 1  is a cross-sectional view of a ball and socket assembly according to the subject invention; 
         FIG. 1A  is an enlargement of section A of  FIG. 1 ; 
         FIG. 2  is a elevation view of the ball and socket assembly of  FIG. 1 ; 
         FIG. 3  is an exploded view of the ball and socket assembly as shown prior to an assembly operation; 
         FIG. 4  is a simplified view depicting the method step of compressing the outer bearing, ball stud and inner bearing as a unit against the resilient member until an over-compression condition is achieved; 
         FIG. 5  is a view as in  FIG. 4 , but depicting the method step of reducing the compression stress until an ideal compression condition is achieved, and maintaining that ideal compression condition while simultaneously deforming the housing into recesses in the outer bearing to secure the position of the outer bearing in the socket; 
         FIG. 6  is a view depicting the step of crimping an up-standing edge of the housing to complete the assembly operation; 
         FIG. 7  is an exploded perspective view of a complete ball and socket type mechanism according to the subject invention; and 
         FIG. 8  is a side elevation view in partial cross-section of the assembled ball and socket type mechanism of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a ball-and-socket type mechanism is generally shown at  10 . The ball and socket assembly  10  includes a ball portion  12  which is captured in a receiving socket of a ball joint housing, generally indicated at  14 . Thus, the ball end  12  forms the male portion of a full articulating joint which facilitates the three-dimensional movement necessary to accommodate wheel turning and suspension travel in a vehicular chassis system. A shank  16  extends from the ball end  12  and acts as the anchoring device for connecting the ball joint assembly  10  within its intended application. For example, the shank  16  is shown in  FIGS. 7 and 8  comprising an elongated shaft having a threaded end adapted to be connected, for example, to a vehicular suspension component. 
     The housing  14  is of the closed end type in which a generally cylindrical sidewall  18  is open at one end and closed at the other end. Housing  14  is preferably formed from a metal having sufficient ductility to permit deformation as localized described elsewhere herein, such as many grades of steel. The closed end, as shown in the Figures, includes a threaded post  20  to facilitate connection relative to a suspension component or anchoring feature. The threaded post  20  may include a lubrication passage  22  through which grease or other lubricant can be pumped into the sliding surfaces of the articulating joint. The cylindrical sidewall  18  has, at its open end, an up-standing edge  24 , defining the entrance to an inner chamber  26 . While generally circular in cross-section, the inner chamber  26  may have varying dimension areas, such as a minor internal diameter adjacent the closed bottom end, and a major diameter adjacent the up-standing edge. 
     The ball joint assembly  10  further includes a resilient preload member  28  which, in the preferred embodiment, comprises a Belleville washer type spring, particularly a metal Belleville washer type spring  28 . Notwithstanding, the resilient preload member  28  could be configured of other spring-like materials and spring configurations, including a coil spring, bent leaf spring, compressible elastomeric material, or any other known resilient material or composition which can be elastically deformed to provide a spring force to preload ball and socket assembly  10  and meet other requirements of the components of assembly  10 , such as resistance to oil, grease or other lubricants used in assembly  10 . The resilient preload member  28  is disposed inside the inner chamber  26 , adjacent the closed bottom end. 
     An inner bearing  30  rests upon the resilient preload member  28 , within the inner chamber  26  of the housing  14 . The inner bearing  30  is preferably, although not necessarily, of all metal construction in design for particularly demanding applications which require especially durable product designs. Inner bearing  30  may also be made from certain engineering plastic materials, ceramics, various composites and combinations of the above. The inner bearing  30  includes a generally flat bottom surface bearing in pressing contact against the resilient preload member  28 . A lubrication passage  32  aligns with the lubrication passage  22  through the threaded post  20  so as to communicate grease pushed therethrough onto a wear surface  34 . The ball portion  12  may be semi-spherical, ellipsoidal or any suitable curvilinear profile, and is placed in sliding contact with the wear surface  34  of the inner bearing  30  and provides an articulation surface when the ball and socket assembly  10  is placed in compression loading mode. In the embodiment shown in  FIGS. 1 ,  1 A and  2 , the wear surface  34  is semi-spherical; however, wear surface  34  may have any surface profile which is suited for operative bearing engagement with ball portion  12  such as, for example, semi-spherical, ellipsoidal and other curvilinear shapes and profiles. These curvilinear profiles may also include surfaces which have combinations of curvilinear and linear elements as is well-known in the art associated with bearing surfaces for ball portion  12  members. Preferably, the inner bearing  30  has a diameter sized for a close clearance fit within the inner chamber  26  of the housing  14 . 
     An outer bearing  36  also has a wear surface  38  which captures an upper portion of the ball end  12  as viewed from  FIG. 1  so as to hold the ball and socket assembly in articulating, sliding contact during tensile loading modes of operation. The outer bearing  36  slides over the shank  16  and seats within the inner chamber  26  adjacent its up-standing edge  24 . The outer surface  39  of the outer bearing  36  may include ring-like ribs  40 . The outer surface of bearing  36  has a slip fit or sliding contact relationship with the inner surface of the sidewall  18  when bearing  36  is installed within sidewall  18 . The slip fit allows bearing  36  to be positioned axially within sidewall  18  prior to its position being fixed, as further described herein. The outer bearing  36  also includes an axially extending rim  42  which, when loaded into the housing  14 , faces in a direction away from the inner chamber  26 . Outer bearing  36  may be made from the same materials as that of inner bearing  30 ; however, each of inner bearing  30  and outer bearing  36  may be made from any of the materials mentioned above, and these materials may be selected independently from one another. Further, outer bearing  36  may also utilize a profile that is semi-spherical as shown in  FIG. 1 , or may have any of the profiles described above with respect to inner bearing  30 , and the profiles of inner bearing  30  and outer bearing  36  may be selected independently from one another, so long as they are adapted for operative engagement with ball portion  12  in the manner described herein. 
     The outer surface of the sidewall  18  may be provided with a retaining groove  44  for the purpose of retaining a dust boot  46  such as depicted in  FIGS. 7 and 8 . A band or wire clamp  48  may be employed to help hold the dust boot  46  in position on the exterior of the housing  14 . However, other well-known apparatus and means for retaining dust boot  46  may also be employed, such as certain other clamping members, retention features such as protruding lips on one or both of the boot or housing, adhesives and the like. Also, the employment of groove  44  dust boot  46  and a clamping means  48  is optional, since in some embodiments of ball joint assembly  10 , a dust boot is not required, or need not be attached directly to the exterior of housing  14 . 
     Referring now to  FIGS. 3-6 , a method of assembling the subject ball and socket assembly  10  is depicted, wherein a fixed pre-load compression is established between the articulating components. The method comprises the steps of placing into the housing  14  the preload member  28 , followed by the inner bearing  30 , the ball portion  12  and finally the outer bearing  36 , with the wear surfaces  34 ,  38  of the inner  30  and outer  36  bearings placed into sliding contact with the ball portion  12 . Once these components have been assembled together, the compression loading tool  50  is placed into contact with the rim  42  on the outer bearing  36 . The loading tool  50  is illustratively depicted as a cage-like device, but in practice may take any suitable form. A compressive load  52  is then placed on the loading tool  50  until such time as an overload compression condition  54  is reached. The overload compression condition  54  represents an essentially solid component condition under which the inner bearing  30 , ball portion  12  and outer bearing  36  are subjected to compressive stresses in excess of the desired pre-load and sufficient to remove the axial lash from the ball and socket assembly  10 . The method further includes reducing the compression stresses within the resilient spring member  28  until an ideal compression condition  56  is achieved between the outer bearing  36 , the ball stud  12  and the inner bearing  30 . Alternately, rather than imposing an overload compression condition  54 , loading tool  50  may be used to compress the components to an ideal condition  56  directly, without first achieving an overload condition. Simple dial gauges superimposed over the compressive load  52  are used to artistically represent the change in compressive loading between overload  54  and ideal  56  conditions. During the step of reducing the compression stress, the resilient preload member  28  is committed to relax slightly, until a prescribed amount of clearance between the components and a fixed preload of the ball and socket assembly  10  is established between the bottom of the inner bearing  30  and the closed bottom end in the inner chamber  26 . While loading tool  50  continues to apply a compressive load which is maintained at the ideal compression condition  56 , a staking operation simultaneously deforms the sidewall  18  of the housing  14  into the rings  40  of the outer bearing  36 , as shown in  FIG. 5 . This staking operation fixes or locks the axial position of outer bearing  36  within the housing  14  by pressing sidewall  18  into pressed contact with outer surface  39  of outer bearing  36 , thereby fixing the ideal compression condition  56  and preload within the ball and socket assembly  10 . The staking operation results in at least one, and preferably a plurality of discrete indentations  58  disposed about the housing  14  as perhaps best shown in  FIG. 2 . In a preferred embodiment, these indentations  58  represent deformation of sidewall  18  and are transferred through the sidewall  18  and the deformed portion  41  of sidewall  18  is pressed into the rings  40  about the outer bearing  36 , thus fixing its axial position within housing  14  so that the loading tool  50  can be removed. Alternately, rather than just staking in discreet locations around the periphery of housing  14 , other means and methods of deforming sidewall  18  may be employed in order to deform a portion  41  of sidewall  18  into a mating capture feature, such as ring grooves  40 , located on the outer surface  39  of outer bearing  36 . For example, roll-forming or spin-forming a groove into sidewall  18  may be used to form a deformed portion  41  of sidewall  18  having the shape of a inwardly protruding rings  58 ′ which may operatively engage with ring grooves  40  of outer bearing  36 . As is also shown in  FIG. 6 , when staking is employed, optionally, the staking tool  62  may be left in place during subsequent forming operations as described below, in order to further ensure that the position of outer bearing  36  is maintained within housing  14  during these operations. Even after the loading tool  50  is removed, the ideal compression condition  56  and preload of ball and socket assembly  10  is maintained between the various articulating components. 
     In  FIG. 6 , an optional step is depicted wherein an up-standing edge  24  of the sidewall  18  is used to further ensure that the ideal compression condition  56  and preload of the ball and socket assembly  10  is maintained. In the embodiment illustrated in  FIGS. 1 ,  1 A and  2 , the up-standing edge  24  of sidewall  18  is re-formed so as to capture outer bearing  36  on axially extending rim  42 . Crimping rollers  60  graphically illustrate this operation; however, a pressing or other metal re-forming operation may be used to re-form the up-standing edge  24  and further fix the outer bearing  36  in position, such as spin-forming, roll-forming and other well-known re-forming methods for closing up-standing edge  24  against outer bearing  36  in pressing contact. 
     Accordingly, the method as described here for controlling the pre-load and clearance in an all metal ball and socket assembly  10  results in higher production through-puts and improved tolerance quality. Specifically, the step of positioning and fixing the outer bearing  36  prior to the final re-forming operation enables the subject ball and socket assembly  10  to be manufactured to a higher quality standard at lower costs. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.