Abstract:
A tripod includes a tripod bearing assembly. The tripod bearing assembly has a spider with a trunion radially projecting therefrom. The trunion has a bearing surface formed thereupon. A needle bearing assembly is provided for installation on the bearing surface of said trunion. The bearing assembly includes an outer race, a plurality of rollers and a cage for retaining the rollers to the outer race without bearing against an inner race prior to installation on the trunion.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a tripod bearing assembly, particularly for a motor vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    Tripod bearing assemblies of the prior art include a spider with three trunions drivably engaged with an outer member to transmit torque from a first shaft to a second shaft. The tripod bearing assembly permits angular and axial displacement between the two shafts during dynamic rotation of the assembly. Typically, a needle bearing is provided between each trunion and the outer member.  
           [0003]    The needle bearing of the prior art is generally assembled to the trunion in one of two manners and particularly designed therefor. A first bearing type and assembly method is illustrated in FIG. 1. The trunion supports a plurality of needles which support a roller which engages a branch of an outer member of a constant velocity joint. In the prior art assembly shown in FIG. 1, the needles bear directly on a bearing surface machined onto the trunion. An outer bearing is provided between the needles and the outer member (the outer member is not shown). The needles are therefore assembled between the trunion and the outer bearing. Such an assembly requires a large amount of labor or specialized machinery to enable the assembly of the individual needles in this manner. It would therefore be desirable to provide an assembly in which the needles were assembled in a subassembly prior to installation onto the trunion.  
           [0004]    A second type of bearing is illustrated in FIGS. 2 and 3. This assembly includes a preassembled needle bearing interposed between a trunion and outer member. The needles are assembled into a bearing assembly prior to installation of the bearing assembly onto a trunion.  
           [0005]    The prior art assembly shown in FIGS. 2 and 3 includes a means for displacing the bearing assembly relative to the trunion. As illustrated in FIG. 2, the displacement comprises an angular movement of the trunion relative to the inner race of the bearing assembly.  
           [0006]    [0006]FIG. 3 illustrates an alternate means for displacing the bearing assembly relative to the trunion comprising an axial movement of the trunion relative to the inner race of the bearing assembly. These prior art configurations require a bearing provided between the trunion and the needle bearing and also require additional machining of the trunion to permit the axial sliding movement. It would be desirable to provide a trunion assembly which includes needle bearings which are preassembled into a bearing assembly which is subsequently assembled onto the trunion, but which does not require relative axial or rotational movement to the trunion, so machining of the trunion is minimized.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the objects of this invention, an improved tripod assembly is provided. The tripod includes a tripod bearing assembly. The tripod bearing assembly has a spider with a trunion radially projecting therefrom. The trunion has a bearing surface formed thereupon. A needle bearing assembly is provided for installation on the bearing surface of said trunion. The bearing assembly includes an outer race, a plurality of rollers and a cage for retaining the rollers to the outer race without bearing against an inner race prior to installation on the trunion.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is an exploded view of a prior art trunion of a tripod bearing assembly.  
         [0009]    [0009]FIG. 2 is a partial side sectional view of an alternative prior art tripod bearing assembly.  
         [0010]    [0010]FIG. 3 is a partial end sectional view of the prior art tripod shown in FIG. 2.  
         [0011]    [0011]FIG. 4 is a partial sectional view of a needle roller assembly being installed on a trunion according to the present invention.  
         [0012]    [0012]FIG. 5 is a partial sectional view of a needle roller assembly being installed on a trunion according to an alternative embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0013]    [0013]FIG. 4 illustrates a tripod bearing assembly  10 . The assembly  10  includes a spider  12  having three trunions  20  equally spaced. A bearing  40  is pressed fit onto the trunion  20 . The bearing  40  includes an inner race  42  supporting a plurality of needles  46 , and an outer race  48  supported by the needles  46 . In a preferred embodiment, the inner race comprises a formed cup, preferably formed by drawing the inner race to the necessary shape. The outer race  48  is rotatable relative to the inner race  42  on the needles  46 . The outer race  48  drivably engages an outer member (not shown) in a manner known to one skilled in the art.  
         [0014]    The trunion  20  includes an outer diameter  30  which is sized to be press fit to the inner surface  44  of the inner bearing  40 . The press fit of the bearing  40  to the trunion  20  and the inner race  42  eliminate the need for machining (such as turning or grinding) of the outer diameter  30  of the trunion  20 , since it is not a bearing surface. Thus, the trunion may be assembled “as formed” without finish machining in this embodiment. The spider  12  could, for example, be forged, then have the bearing assemblies  40  press fit onto the trunions  20 , then finally assembled into a constant velocity joint assembly for use in an automobile.  
         [0015]    An undercut  52  is preferably formed on the trunion to further eliminate the need for any finish machining of the spider at this surface. The bearing  40  is axially restrained in a first direction by a shoulder  54  provided on the spider adjacent undercut  52 . A snap ring groove  50  is provided at the distal end of the trunion  20  to engage a snap ring (not shown) to axially retain the bearing  40  to the spider  12  in the opposite direction. Thus, during operation of the joint  10 , the bearing  40  is axially fixed to the trunion  20  between the snap ring groove  50  and the shoulder  54  without the need for finish machining. The press fit also aids in axially retaining the bearing  40  to the trunion  20 .  
         [0016]    The outer race  48  rotates circumferentially about the trunion  20 . The outer member (not shown) is able to rotate or move axially relative to the outer race  48  in a manner known to one skilled in the art, similar to the manner described in U.S. Pat. No. 4,693,698, which is incorporated herein by reference. The tripod thus accommodates any angular deflection of the joint or relative axial movement.  
         [0017]    The bearing surface  30  of the trunion  20  comprises a cylinder. The engagement of this cylindrical trunion with the inner surface  44  of the bearing  40  prevents angular displacement therebetween.  
         [0018]    In an alternative embodiment, as shown in FIG. 5, a bearing assembly  60  is fit onto a spider  14 . The spider includes three trunions  72  as described above with reference to FIG. 4. Each trunion  72  includes a finished bearing surface  74 . The needles  64  of the bearing  60  rotate at  62  on the bearing surface  74  as an inner race in a manner similar to that described in the &#39;698 patent. The bearing  60  includes a plurality of needles  64 , an outer race  66 , and a cage  68  to retain the needles  64  after assembly to the outer race  66 , prior to installation onto the trunion  72 . Thus the bearing assembly  60  is shipped as a modular unit and pressed fit onto the trunion  14  in a simple manner, without the need to handle loose needles at the tripod assembly source. The cage is preferably made from a glass-filled polymer as is known to one skilled in the art. The cage includes a plurality of pockets for retaining the needles to the outer race as is known to one skilled in the art. In an alternative embodiment, the cage is formed from steel.  
         [0019]    In a manner similar to that described above with reference to FIG. 4, the bearing  60  is retained after assembly in a first axial direction by a shoulder  80  provided on the spider  14  adjacent trunion  72 . An undercut  78  is provided on the trunion  72  to simplify finish machining. A groove  76  is provided at the opposite end of the trunion  72 . A snap ring  77  is installed in the groove  76  after the bearing  60  is assembled to retain the bearing  60  in the second axial direction. In this embodiment, the trunion preferably includes a ground surface  74 , since it is a bearing surface. The cage  68  serves as an assembly aid to prevent the need for assembling the needles at final assembly of the joint, as the bearing  60  is shipped as an assembly.  
         [0020]    The above spider assembly has been describe with reference to a constant velocity joint. However, one skilled in the art recognizes that these concepts maybe used in a universal joint.  
         [0021]    It is to be understood that the embodiments of the invention described above are merely illustrative of application of principals of the present invention. Numerous modifications maybe made to the methods and apparatus described above without departing from the true spirit and scope of the invention.