Abstract:
A universal joint ( 100 ) comprising a spider ( 102 ) having a trunnion ( 104 ) projecting outward from the spider is provided. A bearing ( 108 ) is disposed over a distal end of the trunnion with a lubricant passageway ( 110 ) disposed within the trunnion and in fluid communication with the bearing. A lubricant pressurizing system ( 112 ) is incorporated within the spider to bias or urge the lubricant through the lubricant passageway and toward the bearing. The trunnion may be tapered along its length and an outer edge ( 366 ) of the end of the trunnion may be radiused. The trunnion and/or bearing may further include a load carrying surface ( 114  and  158 ) comprised of a wear resistant material. The load carrying surface may be smooth or textured to retain a lubricant thereupon. The spider may include a plurality of cross grooves ( 126 ) and/or clearance radii ( 128 ) to aid in installation into the yoke.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/333,542, filed Nov. 27, 2001, which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to universal joints, and more specifically to universal joints formed to withstand high loads. 
     BACKGROUND OF THE INVENTION 
     A universal joint provides a means to couple two rotating shafts to one another in an end to end relationship despite the shafts not necessarily being in line with one another. In reference to automobiles, a pair of universal joints are often used to couple a rotating drive shaft at a first end to the output of a transmission or transfer case and at a second end to the input of a differential, which in turn drives the rear and or front wheels of the automobile. In front or four-wheel drive cars, universal joints are often employed to allow articulation between a pair of front axles extending in opposite directions from a front differential or transmission and a pair of stub axles carrying the wheels, thus permitting the front wheels to pivot to permit steerage. 
     Referring to  FIG. 1 , a previously developed universal joint  10  is depicted. The universal joint  10  is comprised of a main body, referred to as a cross or a spider  12 , having four co-planar trunnions  14  extending radially outward from the spider  12  at 90 degree intervals. Journals  16  are formed on the distal ends of the trunnions  14  to accept bearing cups  18  thereupon. Disposed between the bearing cups  18  and the  journals  16  are a plurality of needle roller bearings  20  used to reduce friction as the trunnions  14  rotate within the bearing cups  18 . 
     During installation, a first pair of collinear trunnions  14 A and  14 B are inserted within a pair of opposing bosses  22  of a first yoke  24  of a first drive shaft  26 . A pair of bearing cups  18  and needle roller bearings  20  are then inserted into the bosses  22  so as to be received upon the journals  16  of the trunnions  14 A and  14 B. The bearing cups  18  are secured with retaining rings  34 , as is well known in the art. A second pair of collinear trunnions  14 C and  14 D (not shown) are then inserted within a pair of opposing bosses  28  of a second yoke  30  of a second drive shaft  32 . A second pair of bearing cups  18  and needle roller bearings  20  are then inserted into the bosses  28  so as to be received upon the journals  16  of the trunnions  14 C and  14 D (not shown). The bearing cups  18  are secured with retaining rings  34 , as is well known in the art. Once the universal joint  10  is installed, the first drive shaft  26  may rotate with two degrees of freedom relative to the second drive shaft  32 , each degree of freedom defined by one of the collinear pairs of trunnions  14 A and  14 B or  14 C and  14 D. Thus, the first drive shaft  26  may rotate at an angle relative to the second drive shaft  32  during rotation of the shafts  26  and  32  without binding. 
     Still referring to  FIG. 1 , although previously developed universal joints are effective at transferring loads between two non-aligned shafts, they are not without their limitations and problems. Although previously developed universal joints  10  are adequate for use in low load conditions, they tend to break down when subjected to high loads imposed during severe usage situations. One reason lies in the use of needle roller bearings  20 . The needle roller bearings  20  of previously developed universal joints tend to concentrate the forces exerted between the journals  16  of the universal joint  10  and the bearing cups  18  along finite pressure lines. More specifically, the forces exerted between the journals  16  and the bearing cups  18  are concentrated along a first contact line formed between the inner surface of the bearing cups  18  as they engage the outer surfaces of the roller needle bearings  20 , and a second contact line formed by the outer surfaces of the journals  16  as they engage the roller needle bearings  20 . Thus, during high loads, the concentration of large forces upon the minimal contact area represented by the contact lines often causes premature failure of the universal joint  10 .  
     Further, the grease delivery systems of previously developed universal joints are inadequate to supply grease at sufficiently high pressures to maintain the bearing cups in an adequate state of lubrication when subjected to high loads. Moreover, existing universal joints  10  depend on centrifugal forces to supply grease to the bearing cups. The pressure created through centrifugal forces may be insufficient to adequately pressurize the grease for high load conditions. This is especially true for universal joints  10  exhibited to high loads and low revolution (i.e. low RPM) conditions. Further still, the manner of installation of existing universal joints limits the size of the spider that may be used, thus limiting the strength of the universal joint, thereby increasing the potential of failure of the universal joint. Further yet, under high torque conditions, previously developed trunnions tend to dig into the needle roller bearings as the bearing cups cant and/or deform under the load. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a universal joint including a spider having at least one trunnion projecting outward from the spider is provided. The universal joint further includes a bearing disposable on a distal end of the trunnion, a lubricant passageway disposed within the trunnion and in fluid communication with the bearing, and a lubricant delivery system disposed within the spider and adaptable to urge a lubricant when present within the lubricant passageway toward the bearing. 
     The trunnion may be tapered toward the distal end of the trunnion. The outer edge of an end surface of the trunnion may be radiused. The lubricant delivery system may include a resilient member adaptable to act upon the lubricant to pressurize the lubricant. The bearing may be further comprised of a load carrying surface for engagement with the trunnion, wherein the load carrying surface is comprised of a wear resistant material. 
     The bearing may further include a load carrying surface for engagement with the trunnion, wherein the load carrying surface is textured to retain a lubricant thereupon. The trunnion may include a surface for receiving the bearing comprising a wear resistant material. The spider may include a plurality of cuts positioned on the outer surface of the spider to provide additional clearance during installation of the universal joint upon a yoke. The distal end of the trunnion may include a clearance radius to provide additional  clearance during installation of the universal joint upon a yoke. The wear resistant materials of the universal joint may include a material selected from the group consisting of chromium nitride, titanium nitride, titanium carbonitride, zirconium nitride, aluminum titanium nitride, titanium aluminum, zirconium nitride, and aluminum oxide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of a previously developed universal joint; 
         FIG. 2  is an exploded perspective view of one embodiment of a universal joint formed in accordance with the present invention, shown in relation to a first and a second drive shaft; 
         FIG. 3  is a perspective view of one embodiment of a spider formed in accordance with the present invention and suitable for use in the universal joint depicted in  FIG. 2 ; 
         FIG. 4  is a planar view of the spider depicted in  FIG. 3 ; 
         FIG. 5  is an elevation view of the spider depicted in  FIG. 3 ; 
         FIG. 6  is a perspective view of one embodiment of a bearing cup formed in accordance with the present invention and suitable for use in the universal joint depicted in  FIG. 2 , the bearing cap depicted with a textured inner surface; 
         FIG. 7  is a cross-sectional view of the bearing cup depicted in  FIG. 6 , the cross-sectional cut taken substantially through Section  7 — 7  of  FIG. 6 ; 
         FIG. 8  is an elevation view of the spider depicted in  FIG. 3 , the spider shown as the spider is inserted within a yoke, illustrating how a radiused surface and a clearance cut disposed on the spider aid in providing clearance during the insertion of the spider within the yoke; 
         FIG. 9  is a perspective view of an alternate embodiment of a bearing cup formed in accordance with the present invention and suitable for use in the universal joint depicted in  FIG. 2 , the bearing cup depicted with a smooth inner surface; 
         FIG. 10  is a cross-sectional view of the bearing cup depicted in  FIG. 9 , the cross-sectional cut taken substantially through Section  10 — 10  of  FIG. 9 ;  
         FIG. 11  is a planar view of an alternate embodiment of a spider formed in accordance with the present invention, the spider having trunnions with journal surfaces which taper linearly inward toward the distal ends of the trunnions; and 
         FIG. 12  is a planar view of a further alternate embodiment of a spider formed in accordance with the present invention, the spider having trunnions with journal surfaces which taper arcuately inward toward the distal ends of the trunnions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  shows an exploded perspective view of one embodiment of a universal joint  100  formed in accordance with the present invention. The universal joint  100  is suitable for use in high load, low revolution conditions, and may be assembled within the yokes of an existing drive axle or drive line despite the enlarged size of a spider  102 . Notably, the illustrated embodiment of the universal joint  100  is absent of roller needle bearings commonly found in previously developed universal joints. 
     Referring to  FIGS. 2–5 , the universal joint  100  is comprised of a main body, referred to as a cross or a spider  102 , having four co-planar trunnions  104 A,  104 B,  104 C, and  104 D extending radially outward from the spider  102  at 90 degree intervals. Journals  106  are formed on the distal ends of the trunnions  104  to accept bearing cups  108  thereupon. The bearing cups  108  are rotatingly received by the journals  106  to reduce friction as the trunnions  104  rotate within the stationary bearing cups  108 . Lubricant passageways  110  are concentrically bored through each trunnion  104 . A lubricant pressurization system  112  is disposed within each lubricant passageway  110  to provide a lubricant  160  at an elevated pressure to each bearing cup  108 . Of note, in reference to the description of the illustrated embodiment, the elements of the trunnions  104 A,  104 B,  104 C, and  104 D, along with the bearing cups  108 , lubricant passageways  110 , etc., are substantially identical to one another. Therefore, where context permits, reference in the following description to one of the elements shall be understood as also referring to the other elements which are substantially identical to the described element. 
     During installation, a fluid pressurization system  102  is inserted within each trunnion  104 . Then, a first pair of collinear trunnions  104 A and  104 B are inserted within the opposing bosses  22  of a first yoke  24  of a first drive shaft  26 . A pair of bearing cups  108  are then inserted into the bosses  22  so as to be received upon the journals  106  of  the trunnions  104 A and  104 B. The bearing cups  108  are secured with retaining rings  34  as is well known in the art. A second pair of collinear trunnions  104 C and  104 D are then inserted within opposing bosses  28  of a second yoke  30  of a second drive shaft  32 . A second pair of bearing cups  108  are then inserted into the bosses  28  so as to be received upon the journals  106  of the trunnions  104 C and  104 D. The bearing cups  108  are secured with retaining rings  34 , as is well known in the art. Once the universal joint  100  is installed, the first drive shaft  26  may rotate with two degrees of freedom relative to the second drive shaft  32 , each degree of freedom defined by one of the pairs of collinear trunnions  104 A and  104 B or  104 C and  104 D. Thus, the first drive shaft  26  may rotate at an angle relative to the second drive shaft  32  during rotation of the shafts  26  and  32  without binding. 
     In light of the above general description of the universal joint  100 , the individual components of the universal joint  100  will now be discussed in greater detail. The discussion of the components of the universal joint  100  will begin with a detailed description of the spider  102 . As discussed above, the spider  102  has four co-planar trunnions  104 A,  104 B,  104 C, and  104 D extending radially outward from the spider  102  at 90 degree intervals. The trunnions  104  are machined to form precision journals  106  thereupon. The journals  106  are sized and shaped to receive close fitting bearing cups  108  thereupon. The surface of the journals  106  are preferably finished so as to have a surface finish sufficiently smooth as to be amenable to the application of a wear resistant layer  114  by an ionically bonded thin film application technique, such as Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD), as will be discussed in further detail below. Typically, the journals  106  are finished to have a surface smoothness of 64 microinches or less, with a preferred value of 16 microinches or less. 
     The wear resistant layer  114  is a solid, hard, thin-film layer applied to improve the wear resistant characteristics of the journal  106  and optionally, reduce friction. The hardness of the wear resistant layer  114  should be about 1000 Vickers or greater, with preferred values falling above approximately 2000 Vickers. Further, the wear resistant layer  114  is thin, approximately 10 microns or less, with preferred values between 2 and 6 microns.  
     Preferably, the wear resistant layer is applied by well known thin-film application techniques, such as through PVD or CVD coating technologies. Some suitable materials for PVD or CVD application of the wear resistant layer  114  are Chromium Nitride (CrN), Titanium Nitride (TiN), Titanium Carbonitride (TiCN), Zirconium Nitride (ZrN), Aluminum Titanium Nitride (AlTiN), Titanium Aluminum (TiAl), Zirconium Nitride (ZrN), Aluminum Oxide (Al 2 O 3 ), Molybdenum Disulfide Titanium Nitride, (MoSTiN) and Carbon (C). 
     A stepped or shoulder portion  156  is located at the base of each trunnion  104 . The stepped portion  156  is formed by stepping out the diameter of the trunnion  104 , thereby forming an annular band or shoulder extending outward circumferentially around the trunnion  104 . The stepped portion  156  aids in increasing the strength of the trunnion  104 . 
     Bored concentrically through the center of each trunnion  104  is a lubricant passageway  110 . Each lubricant passageway houses a lubricant pressurization system  112 . Referring to  FIG. 2 , each lubricant pressurization system  112  includes a compressible medium, such as a spring  116 , selected to bias a piston  118  outward toward the bearing cup  108 . In the illustrated embodiment, a well known music wire spring is utilized. The piston  118  is formed from a rigid material, with the piston  118  of the preferred embodiment manufactured from an acetal resin, such as DUPONT DELRIN® acetal resin, a material well known in the art. The piston may have an annular exterior groove for receiving an O-ring  120  therewithin. The O-ring  120  sealingly engages the inner surface of the lubricant passageway  110 , providing a pressure seal therebetween. 
     In operation, a lubricant  160 , such as an ultra high temperature, high-pressure anti-seize lubricating grease, one suitable example being a soft metal based grease, such as a moly-graphite and/or copper-graphite based grease, is applied against the crown  122  of the piston  118 . The application of the lubricant  160  in this matter causes the piston  118  to be forced inward, thereby compressing the spring  116 . The lubricant  160  is applied at a sufficiently high pressure, such as about 300 psi, by a grease gun or other similar device to initially pressurize the lubricant  160  within the lubricant passageway  110 . Once the pressurized grease delivery source has been removed, the spring  116 , in coordination with the piston  118 , biases the lubricant  160  outward toward the bearing cup  108  to supply an adequate quantity of lubricant at a sufficient pressure to  the bearing cup  108 . The lubricant  160  serves to reduce the wear and friction associated with the rotation of the journals  106  within the bearing cups  108 . 
     In operation, the lubricant  160  is slowly pressed outward and eventually released from the bearing cups  108  and into the environment. Thus, fresh lubricant  160  is constantly supplied to the bearing cups  108 . The pressurized supply of lubricant  160  helps to impede the entrance of contaminates into the bearing cups  108  while also aiding the removal of any contaminates that may inadvertently be present within the bearing cups  108 , such as contaminates produced from the wear of the components of the universal joint  100 . Further, while the pressurization system  112  aids in replenishing any lubricant  160  consumed or released from the bearing cups  108 , the high pressure of the lubricant aids in lubricating the bearing cups  108  and the trunnions  104  as they rotate relative to one another, even at low RPMs. 
     More specifically, in previously developed universal joints, centrifugal forces exerted upon the lubricant during rotation of the universal joint were often relied upon to deliver the lubricant to the bearing cups. However, in high load, low RPM situations, this has been found to be inadequate. In contrast, the lubricant pressurization system  112  of the present invention delivers a lubricant  160  at an elevated pressure, such as about 300 psi, independent of the RPM of the universal joint  100 . Further, even at high RPM, centrifugal forces can not be depended upon to provide lubricant at sufficiently high pressures to force the lubricant between the load bearing surfaces of the universal joint when subjected to high loads. In the illustrated embodiment, the lubricant is pressurized to a sufficient degree to allow the lubricant to infiltrate the annulus formed between the bearing cups  108  and the journals  106  under high load conditions. Preferably, the lubricant  160  is pressurized between 100 PSI and 600 PSI, with a preferred value of 300 PSI. 
     The spider  102  of the illustrated embodiment of the present invention is modified to allow an enlarged spider to be installed within the existing, i.e. stock sized, yokes of drive axles and drive lines. In this regard, clearance cuts or notches  126  may be cut or otherwise formed transversely across the main body of the spider  102  near the base of the trunnions  104 . The clearance notches  126  are oriented perpendicular to the axis of the trunnion  104  located adjacent to the clearance notch  126 . A pair of parallel oriented clearance notches  126  may be formed on a first side of the spider  102 , positioned at the  base of a first pair of collinear trunnions  104 C and  140 D to assist in inserting the spider  102  within a first yoke. A second pair of parallel oriented clearance notches  126  may be formed on a second side of the spider  102 , positioned at the bases of a second pair of collinear trunnions  104 C and  104 D to assist in inserting the spider  102  within a second yoke. In the illustrated embodiment, the clearance notches  126  define an elliptical shape due to the fact that the notches are formed across the cylindrical shape of the trunnion bases. However, as should be apparent to one skilled in the art, the cut path should be selected to best match the geometry of the yoke  24  during insertion of the spider  102  within the yoke  24 , as shown in  FIG. 8 , and therefore is not restricted to a specific elliptic cut path or even an elliptic cut path. 
     To further assist in inserting the enlarged spider  102  within a yoke, the outer ends of the journals  106  may be radiused or chamfered. More specifically, a portion of a circular edge  130  formed at the interface of the cylindrically shaped journals  106  and the circular end face  132  is relieved with a clearance radius  128  to provide additional clearance during insertion of the spider  102  in a yoke  24 , as depicted in  FIG. 8 . In the illustrated embodiment, the clearance radius  128  is shown as curvilinear in shape. Although the clearance radius  128  is described and shown with particularity, it should be apparent to one skilled in the art that the clearance radius  128  may be formed in any number of ways. Moreover, the shape of the clearance radius  128  should be selected to best match the geometry of the yoke  24  during insertion of the spider  102  within the yoke  24 , as shown in  FIG. 8 , as should be apparent to one skilled in the art. 
     Referring to  FIGS. 2 ,  6 , and  7 , one embodiment of a bearing cup  108  formed in accordance with the present invention will now be described in greater detail. The bearing cup  108  may be formed in the shape of a cylinder  109  having a closed end  134  and an opposed open end  136 . Disposed circumferentially about the exterior of the cylinder  109  is an annular groove  138  sized to receive a well known retaining ring  34  therein. Bored or otherwise formed through the closed end  134  is a threaded zerk or lubricant fitting mounting aperture  154  sized to receive a zerk or lubricant fitting  142  therein. The interior surface  146  of the cylinder  109  may be textured. In the illustrated embodiment, the textured interior surface  146  includes a plurality of dimples  150 . The dimples  150  serve to store pockets of lubricant therein to assist in maintaining a sufficient supply of lubricant disposed between the bearing cups  108  and the journals  106 .  Although the textured interior surface  146  of the illustrated embodiment of the bearing cup  108  is textured through the application of a plurality of dimples  150 , it should be apparent to one skilled in the art that the surface may be textured in other suitable manners such as would retain lubricant thereupon. 
     The diameter of the inner surface  146  of the cylinder  109  is stepped outward adjacent to the open end  136 , thereby creating a channel  152  for receiving the shoulder portion  156  (see  FIG. 4 ) of the trunnion  104 . 
     The inner surface  146  of the cylinder  109  may be finished so as to have a surface finish sufficiently smooth as to be amendable to the application of a wear resistant layer  158  by a thin film application technique, such as PVD, as will be discussed in further detail below. The inner surface  146  of the bearing cups  108  are finished to have a surface smoothness of 64 microinches, with a preferred value of 16 microinches or less. The wear resistant layer  158  is a solid, hard, thin-film layer applied to improve the wear resistant characteristics of the inner surface  146  of the bearing cup  108  and optionally, reduce friction. The hardness of the layer should be about 1000 Vickers or greater, with preferred values falling above about 2000 Vickers. Further, the wear resistant layer  158  is thin, approximately 10 microns or less, with preferred values between 2 and 6 microns. 
     Preferably, the wear resistant layer is applied by well known ionically bonded thin-film application techniques, such as through PVD or CVD coating technologies as described above. 
       FIGS. 9 and 10 , show an alternate embodiment of a bearing cup  208  formed in accordance with the present invention and suitable for use with the spiders  102 ,  302 , and  402  depicted in  FIGS. 3–5 ,  11 , and  12 . The bearing cup  208  may be substantially similar to the bearing cup  108  depicted in  FIGS. 6 and 7 , with the exception that the inner surface  246  of the bearing cup  208  is smooth. Like the embodiment of the bearing cup  108  depicted in  FIGS. 6 and 7 , the inner surface  246  includes a wear-resistant layer  258 , substantially similar to the wear-resistant layer  158  described above. 
     Referring to  FIG. 11 , an alternate embodiment of a spider  302  formed in accordance with the present invention is illustrated. The spider  302  is substantially similar to the spider  102  depicted in  FIGS. 3–5 , with the exception of the journals  306 , which are tapered. More specifically, the journals  306  are formed in the shape of a truncated cone that tapers inward toward the distal end of the trunnions  304 A,   304 B,  304 C, and  304 D, such that the base of the journal  306  is of a greater diameter than the diameter of the journal  306  measured at its distal end. The amount of taper depicted in  FIG. 11  is exaggerated to illustrate the concept. In one actual embodiment of the spider  302 , the diameter of the base of the journal  306 , represented by the arrow indicated by reference numeral  364 , may be about 0.002″ greater than the diameter of the journal  306  measured at the distal end of the journal  306 , as represented by the arrow indicated by reference numeral  362 . Although a specific amount of taper is disclosed for the illustrated embodiment, it should be apparent to one skilled in the art the amount of taper may be varied from the amount disclosed while remaining within the scope of the present invention. 
     In addition to the tapering of the trunnions  304 , an outer edge  366  of the end surface of the trunnion is radiused. The size of the radius depicted in  FIG. 11  is exaggerated to illustrate the concept. For instance, in one embodiment of the spider  302 , the outer edge  366  may be comprised of about a 0.06″ radius. Although a specific radius is disclosed above, it should be apparent to one skilled in the art that the length of the radius may vary from the length disclosed while remaining within the scope of the present invention. 
     The tapering of the journal  306  and the radiusing of the outer edge  366  of the end surface aids in increasing the longevity of the universal joint. More specifically, under full load torque, a bearing cup rotatingly received upon the trunnion  304  tends to cant and/or deform under the full load torque. The tapering of the journal  306  and radiusing of the outer edge  366  decreases wear under these conditions by impeding the outer edge  366  from digging into the bearing cup as the bearing cup cants upon the trunnion  304 . Also, by tapering the trunnions  306 , and by radiusing the circular edge  330 , the load may be spread more evenly along the journal surface  306  since the journal surface  306  is tapered to match the cant of the bearing cup under full load torque. It is to be understood that the tapering of the journal  306  and the radiusing of the outer edge  366  may be employed individually or in combination upon any of the spiders disclosed herein. 
     Referring to  FIG. 12 , a second alternate embodiment of a spider  402  formed in accordance with the present invention is depicted. The second alternate embodiment depicted in  FIG. 12  is similar to the alternate embodiment depicted in  FIG. 11   with the exception of the manner of tapering of the journals  406 . The journals  406  of the second alternate embodiment are tapered in an arcuate manner such that the journals  406  are shaped so as to represent the upper half of a barrel. Like the embodiment depicted in  FIG. 11 , a circular edge  466  of an end surface of the trunnions  404 A,  404 B,  404 C, and  404 D may be radiused. Although a specific shape is described for providing the arcuate taper, it should be apparent to one skilled in the art that additional arcuate shapes are suitable for use with and within the scope of the present invention. 
     Of note, the amount of taper depicted in  FIG. 12  is exaggerated to illustrate the concept. In one embodiment of the spider  402 , the diameter of the base of the journal  406 , represented by the arrow indicated by reference numeral  464 , may be about 0.002″ greater than the diameter of the journal  406  measured at the distal end of the journal  406 , as represented by the arrow indicated by reference numeral  462 . Although a specific amount of taper is disclosed for the illustrated embodiment, it should be apparent to one skilled in the art the amount of taper may be varied from the amount disclosed while remaining within the scope of the present invention. 
     Likewise, the size of the radius depicted in  FIG. 12  is exaggerated to illustrate the concept. For instance, in one actual embodiment of the spider  402 , the outer edge  466  may be comprised of about a 0.060″radius. Although a specific radius is disclosed above, it should be apparent to one skilled in the art that the length of the radius may vary from the length disclosed while remaining within the scope of the present invention. 
     Although the illustrated embodiments are depicted with a wear resistant layer on both the trunnions and on the bearing cups, it should be apparent to those skilled in the art that the wear resistant layer may be disposed solely on the trunnions or solely on the bearing cups, without departing from the spirit and scope of the present invention. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.