Abstract:
A spider for use in a compact universal joint, includes a spider body having a hollow cylindrical portion and two opposed tenons projecting radially outward from the hollow cylindrical portion along a common axis. The hollow cylindrical portion is adapted for installation of bearings therein for pivotal support of the cross body on a pin mounted in a first yoke of the universal joint, and the tenons are adapted for mounting within bearings in a second yoke thereof.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to universal joints and more particularly to cross and bearing assemblies for use in single and double cardan constant velocity universal joints as are used in automotive steering columns and other mechanical applications. 
     A common single cardan universal joint has two yokes, each of which has two ears with transverse bearing bores at a first end and a shaft attachment means at a second end for connection to some drive source such as a steering wheel or an automotive transmission and a driven object such as a steering gear or an automotive differential. The yokes are connected together by a cross and bearing assembly which consists of a body, commonly referred to as a spider or cross, with first and second orthogonal axes defined by four tenons projecting from a center portion outwardly on the axes. 
     The single cardan universal joint is assembled by fishing the tenons of the first axis of the spider into the bearing bores in the ears of one yoke, as seen in FIG. 5 a , and pressing bearings into the bearing bores to fit over the tenons of the spider and to thereby position the spider both radially and axially in the yoke while permitting the spider to rotate within the yoke. The ears of the yoke must have bearing bores large enough and must be separated by a sufficient distance to permit the spider to be tilted enough to permit the tenons of the spider to be fished into the bearing bores. The universal joint is completed by repeating the assembly process on the second yoke and the tenons of the second axis of the spider. The resulting universal joint assembly is capable of flexing about the two orthogonal axes of the spider, or cross, which joins the two yokes together. 
     To provide constant velocity smooth rotary motion between shafts which lie in a common plane but have centerlines that are angularly displaced from each other, double cardan constant velocity joints are used. These consist of two single cardan universal joints, as described above, with a center housing substituted for the second yoke in each joint and a centering ball and socket added to the proximal ends of the first and second yokes, respectively. (Proximal with respect to the center housing.) The centering ball and socket assures that the angular misalignment between the two shafts will be equally divided about the center housing. The center housing has two pairs of bearing bores in ears at opposite ends, each pair of bores being aligned on an axis which is parallel to the axis of the other pair. The double cardan joint is assembled by attaching one pair of tenons of each of the two spiders to the ears at opposite ends of the center housing. This is usually done by pressing bearings on the tenons in the bearing bores of the ears of the center housing. The remaining tenons of each spider are attached to a yoke which is connected to a driving or driven member. 
     When used in automotive steering columns, both double cardan constant velocity joints and single cardan joints are difficult to install and connect because of the very limited space and visibility available under the dashboard and between the dash panel and the steering gear box. Because the ears of the yoke and center housing must support the bearings in which the tenons are pivoted, they must necessarily be thick enough that the bearings cannot rock when installed. They must also be wide enough to provide sufficient radial support for the bearing under the heaviest anticipated loads. This requires larger heavier yokes. 
     The added thickness and width requirements also extend to the ears of center housings of double cardan joints. Moreover, the diameter of the center housing must be larger to accommodate the greater thickness of the yokes and their ears. These requirements add to the weight and cost of the cardan joints and to the difficulty of fitting the cardan joints into the cramped quarters afforded by automotive design. Thus, the structural limitations imposed by the spider result in a size, weight, and cost penalty to the design of the automobile. 
     The foregoing illustrates limitations known to exist in present single and double cardan constant velocity joints for Use in automotive steering columns. Thus, it would clearly be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, this is accomplished by providing a spider for use in a compact universal joint, said spider comprising a spider body having a hollow cylindrical portion and two opposed tenons projecting on a common axis radially outward from said hollow cylindrical portion, said hollow cylindrical portion being adapted for installation of bearings therein for pivotal support of said cross body on a pin mounted in a first yoke of said universal joint, and said tenons being adapted for mounting within bearings in a second yoke thereof. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic exploded perspective view of a common universal joint showing a cross and bearing assembly of the prior art; 
     FIG. 2 is a schematic exploded perspective view of a universal joint Including a compact cross and bearing assembly according to the invention; 
     FIG. 3 is a schematic sectional view of a double cardan constant velocity joint of the prior art; 
     FIG. 4 is a schematic sectional view of a double cardan constant velocity joint using a spider made according to the invention; and 
     FIGS. 5 a  and  5   b  illustrate the difference in space required for threading standard trunnions into bearing bores in the ears of a yoke and the straight sliding insertion of the hollow cylindrical portion of the spider of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a schematic exploded view of a simple single cardan (universal) joint  5  of the prior art which is assembled as described above. It includes a first yoke  10  and a second yoke  11 , each of which has two ears  13  with bearing bores  14  for supporting bearings, and a cross and bearing assembly. The cross and bearing assembly includes a cross body or spider  12 , which may be formed by any of several well known methods and which has four cylindrical tenons  15  projecting outwardly from the cross body on two orthogonal axes. Bearings  16  and seals  17  are provided for the tenons  15  for attachment in the bearing bores  14  of the yoke ears  13  to provide a reduced-friction coupling. In this design, the bearings  16  are supported in the bearing bores of the ears  13 , which must be sufficiently thick and sufficiently wide to support the bearings under load without permitting them to rock within the bore. Although this results in an excellent universal joint, it is a relatively large, heavy, and costly joint which is difficult to assemble into automotive steering shafts in the cramped installation space available. 
     FIG. 2 shows a universal joint  50  made with a compact cross and bearing assembly  35  according to the invention. In this case, yoke  20  has two ears  22  with cylindrical bores  24  on a common transverse axis. Yoke  30  also has ears  32  with cylindrical bores  34  on a common transverse axis, but it should be noted that the diameters of bores  24 , of yoke  20 , are smaller than are those of bores  34  of yoke  30 . Bores  24  are sized to fit pin  29 , while bores  34  are sized for bearings  28 . Pins  29  fit within bearings  28 , which, in turn, fit within the bore  26  of the hollow cylindrical portion of the cross body  25 . The axial length of the bore  26  of the hollow cylindrical portion is only long enough to accommodate the bearings  28  and seals  31 . Thus, ears  22  only need to be separated enough to span the length of the hollow cylindrical portion of the cross  25  which slides between the ears without the need for tilting. Since the pins  29  are installed through the bores  24  into the bearings  28  in the already aligned cross bore  26 , there is no need to provide the added separation required for fishing the trunnions  27  into the bores  34  of the ears  32 . Seals  31 , only two of which are shown, are provided to retain lubricant within the four bearings  28  and to exclude contamination. The seals may be eliminated if sealed bearings are used. By using the pin  29 , the width and thickness of the ears  22  may be reduced since there is no tendency of the stationary pins to rock within the ears. This permits fabrication of the yoke from thinner gauge, lighter weight, and less costly material, resulting in a smaller envelope for the ears of the yoke  20  and a more compact universal joint. It should be noted that only a single bearing  28 , of greater length than those of the Fig., may be used in the cross bore  26  if the design load permits. 
     In double cardan constant-velocity (DCCV) joints, as seen in FIGS. 3 and 4, the compactness permitted by the invention is more obvious. The prior art DCCV joint  60  of FIG. 3 has two yokes  40 ,  41  with sidewalls  44 ,  45 , a center housing  42 , and a centering ball  48  and a centering socket  49  extending from the yokes to interengage within the center housing. The spiders  12  have tenons  15 , pivotally supported by bearings  46  with bearing caps  46 A and seals  47  which are pressed into the yoke sidewalls  44 ,  45 . FIG. 3 thus illustrates the larger ear size, both thickness and width, of yokes  40 ,  41  which are dictated by the requirements for bearing support and fit within the yoke sidewalls  44 ,  45 . This results in a yoke width WP for the prior art DCCV joint  60  which requires a larger center housing  42  to accommodate the larger yokes  40 ,  41  during rotation and articulation of the joint. The ears of the center housing  42  are mostly hidden by the yokes  40 ,  41  but must be as thick and wide as the sidewalls  44 ,  45  of the yokes in order to provide the same stable bearing support as the yokes. The thick wall requirement of the center housing resulting from the need for this support is clearly seen in FIG.  3 . Note that the tenons on both axes of the cross body  12  of the prior art are of equal length, thus the outside width of the ears of the center housing must be at least as large as WP, and the thickness must be the same as that of the sidewalls  44 ,  45  of the yokes to provide equal support to the bearings. 
     FIG. 4 shows a DCCV joint  70  made using the compact spider of the invention, which, as was illustrated in FIG. 2, allowed reduction of the width of ears  22 ; because use of the spider  25  of the invention eliminates the need for bearings within the ears to support the pin  29 . Joint  70  consists of two yokes  71 ,  72  which are joined by a center housing  52 . The pins  59  are pressed into the sidewalls of the yokes  71 ,  72  and through the bearings  28  and seals  31 , if required, which are fitted in the hollow portion  66  of the spider body of the invention in carriers  58 . Note that the carriers  58  are only an option for handling the bearings and seals and may be dispensed with using other handling techniques, especially when using a single sealed bearing. The tenons of the other axis, which are unseen in this figure, are similar to those of the prior art in FIG.  3  and are similarly installed in the ears of the center housing  52 . During rotation in a non-aligned condition, the yokes  71 ,  72  pivot on the pins  59  about the ears of the center housing  52 , and on the (unseen) tenons between the ears of the center housing. The ears of the yokes  71 ,  72  of the invention are thin and narrow, as described above, and are easily accommodated by the compact center housing. The compact design of the DCCV joint permitted by the spider of this invention results in yokes  71 ,  72  and a center housing  52  which can be fitted into a small operating envelope. 
     The widths of the yokes  71 ,  72 , permitted by the stationary pins  59  of the invention, can be as small as “WI” in FIG. 4; but, even without thinning the sidewalls, the yokes can be made as small as “WI′”. Both options permit use of a smaller center housing  52 . 
     FIGS. 5 a  and  5   b  illustrate how fishing the tenons  27  into the bearing bores  14  of the yoke ears  13  requires greater separation “S+ΔS” between the ears than does the straight translation permitted by the hollow member with its installed bearings. The spider  25 , in FIG. 5 a , must be tilted sufficiently to permit insertion of one tenon  27  into the bearing bore  14  of one ear  13  and then must be swung in so that the other tenon aligns with the opposite bore. It is clear that the ears  13  must be far enough apart for the end of the second tenon  27  to pass the ear as it is swung into alignment and that the bearing bores  14  must be large enough to permit insertion of the tenon at an angle. The hollow member of the spider  25  has a length S and is inserted, as shown in FIG. 5 b , by sliding it directly between the ears  22  without the need for tilting the spider. The length S of the hollow member need only be enough to accommodate a bearing of sufficient length to carry the: design service load of the universal joint. This allows the ears  22  to be spaced by only S, which is ΔS less than ears  32  of FIG. 5 a  and permits smaller and narrower ears and yokes, thereby reducing the size and weight requirements in the steering system of the vehicle.