Abstract:
A differential comprises a die formed housing having a spherical inner volume. A subassembly is disposed in the spherical inner volume of the housing. A die formed cover is fixedly attached to the die formed housing for enclosing the subassembly with the housing. A ring gear is connected to the housing for transmitting torque from a prime mover through the differential. The differential is both light and strong and reasonably inexpensive to manufacture.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to differentials for vehicles. More specifically, the present invention relates to a differential with at least part of its housing being die formed.  
       BACKGROUND OF THE INVENTION  
       [0002]     Differentials are employed in vehicles to permit the two wheels on an axle to rotate at different velocities when rounding the slightest corner. In rear wheel drive vehicles, the differential is employed at the rear axle and the converse is true in front wheel drive vehicles. Four-wheel drive vehicles employ a differential at each axle; that is, both front and rear.  
         [0003]     Differentials are robustly manufactured, as their housings must accommodate high torques and loadings without breaking and without distorting, as the alignment of various components within the differential are critical and require the housing to resist deformations to maintain their alignment. Conventionally, differentials have been made with one-piece cast iron housings and, due to the relative low strength of cast iron; these housings have required relatively thick walls to carry the expected loads. Further exacerbating this problem is the fact that conventional differential housings typically include a pair of large openings on opposing sides of the housing to permit assembly of the differential. These large openings represent a significant potential weakness in the housing, which must be countered by further strengthening the housing by increasing the wall thickness. An increase in the amount of cast iron employed in the housing undesirably increases its weight, volume, and cost.  
         [0004]     Previous attempts have been made to provide an improved differential. For example, U.S. Pat. Nos. 6,061,907 and 6,176,152 to Victoria teach the manufacture of a differential housing from steel using a cold flow-forming and/or cold spin-forming process. By employing steel for the housing, rather than cast iron, the required strength of the housing can be obtained with a thinner gauge, lower weight housing.  
         [0005]     While the differential housing taught by Victoria is an improvement over conventional differential housings, it still suffers from disadvantages in that cold flow forming and/or cold spin-forming are expensive and time consuming manufacturing processes.  
         [0006]     Thus, it is desirable to provide a differential housing of steel or the like and a method of manufacturing the housing, which avoids the problems and/or disadvantages of the prior art.  
       SUMMARY OF THE INVENTION  
       [0007]     According to one aspect of the present invention, there is provided a differential having a die formed differential housing having a spherical inner volume and a subassembly disposed in the spherical inner volume. The subassembly including at least one pinion shaft, at least one pair of bevel pinions disposed on the at least one pinion shaft and at least one pair of bevel gears linked with the at least one pair of bevel pinions. A die formed housing cover is attached to the die formed differential housing for enclosing the subassembly within the differential housing. A ring gear is connected to the differential housing for transmitting torque from a prime mover.  
         [0008]     According to another aspect of the present invention, there is provided a method of manufacturing a differential comprising the steps of: (i) die forming a differential housing from a blank, the differential housing including a spherical inner volume and a hub portion having a bore; (ii) die forming a housing cover from a blank, the housing cover including a hub portion having a bore; (iii) assembling a sub-assembly of a pinion shaft, at least two bevel pinions and at least two complementary bevel gears; (iv) inserting the sub-assembly into the spherical inner volume of the differential housing such that the bore of the housing aligns with an inner splined aperture on one bevel gear to receive a splined portion of an axle; (v) fitting the housing cover to the differential housing to enclose the sub-assembly such that the bore of the housing cover aligns with an inner splined aperture on another bevel gear to receive a splined portion of another axle; (vi) attaching the housing cover to the differential housing; and (vii) connecting a ring gear to the differential housing.  
         [0009]     The present invention provides a novel differential and method of a making the differential wherein the differential housing and housing closure are manufactured by die forming to obtain a differential which is both light and strong and reasonably inexpensive to manufacture. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
         [0011]      FIG. 1  is a cross-sectional view of a differential in accordance with one embodiment of the present invention;  
         [0012]      FIG. 2  is a partially cut-away perspective view of the differential of  FIG. 1 ;  
         [0013]      FIGS. 3   a ,  3   b ,  3   c  and  3   d  shows the stages of a method of die forming a differential housing in accordance with one embodiment of the present invention;  
         [0014]      FIG. 4  is an isometric view of the differential housing of  FIG. 3   d;    
         [0015]      FIGS. 5   a  and  5   b  show the stages of a method of die forming a differential housing cover in accordance with one embodiment of the present invention;  
         [0016]      FIG. 6  is an isometric view of the differential housing cover of  FIG. 5   b;    
         [0017]      FIGS. 7   a ,  7   b ,  7   c ,  7   d  and  7   e  show steps to assemble the die formed differential of  FIG. 1 ;  
         [0018]      FIG. 8  is a cross-sectional view of the differential of  FIG. 1  with different bearings; and  
         [0019]      FIG. 9  is a cross-sectional view of the differential of  FIG. 1  with a welded ring gear. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     A differential in accordance with one embodiment of the present invention is indicated generally at  40  in  FIGS. 1 and 2 . In these Figures, and the others of this description, like elements are indicated with like reference numerals.  
         [0021]     Differential  40  includes a die formed housing  44 , further discussed below, with a flange  46  to which a differential ring gear  48  is attached, in the illustrated embodiment, by rivets  52  although, as will be apparent to those of skill in the art any suitable method of attachment, including bolts, welding, etc. can be employed.  
         [0022]     Torque from a transmission or prime mover, not shown, is transferred from ring gear  48  through housing  44  to pinion shaft  56  which, in turn, drives a pair of bevel pinions  60 . As will be apparent to those of skill in the art, pinion shaft  56  can ride in suitable bores in housing  44 , as will be described in more detail below or pinion shaft  56  can ride in suitable bushings (not shown) which can be provided in bores in housing  44 . Bevel pinions  60  engage with complementary bevel gears  64  which are connected to a right and left axle shaft (not shown) respectively which engage, via splines, with a central bore in each respective bevel gear  64 . A washer  66  having a complementary shape to the inner surface of housing  44  and to the spherical surfaces of bevel pinions  60  and bevel gears  64  and having a central bore through which pinion shaft  56  passes, is installed between the inner surface of housing  44  and pinions  60  and gears  64 .  
         [0023]     A housing cover  68 , which is also preferably die formed as described below, is attached to housing  44  to close the differential  40  and to provide support for a bearing to carry differential  40  in its casing (not shown). Housing cover  68  can be attached to housing  44  in any suitable manner, as will occur to those of skill in the art, including welding and/or using a fastener.  
         [0024]      FIGS. 3   a ,  3   b ,  3   c  and  3   d  show a presently preferred method of die forming a housing  44 . A die forming operation as described herein includes contacting a work piece with a pair of punches and dies to shape the work piece in a desired orientation. In a first step, as shown in  FIG. 3   a , a die blank  100  is provided. The blank  100  is preferably a disc shaped body made from ductile material such as low carbon steel.  
         [0025]     In a next step, shown in  FIG. 3   b , one or more pairs of punches and dies contact the blank  100  to form a generally cup shaped body  104 . The cup shaped body  104  may be formed in a single die forming operation, or alternatively using a plurality of die forming operations to form various portions of the cup shaped body  104 . The cup shaped body  104  includes a flange  108 , a generally conical support portion  116 , and a generally spherical inner portion  112  that defines a generally spherical inner volume  110 . A small central bore  120  is also formed in the center of spherical portion  112 .  
         [0026]     In a following step, as shown in  FIG. 3   c , bore  120  is formed into hub portion  124  through one or more die forming operations and cup shaped body  104  can be machined as indicated by dashed line  128 , if necessary, to achieve desired tolerances and clearances. For example, hub portion  124  can be machined to form a journal and shoulder to receive a bearing, as indicated by dashed line  130 .  
         [0027]     In a final step, as shown in  FIGS. 3   d  and  4 , cup shaped body  104  is machined to include: attachment points  132  (if necessary) for ring gear  48 , journals and bores  136  for pinion shafts  56 , oil lubrication holes  140  and a ledge or surface  144  to which housing cover  68  can be attached.  
         [0028]     As will be apparent to those of skill in the art, further processing of differential housing  44  and/or housing cover  68  can be performed if required. For example, heat-treating of housing  44  and/or cover  68  can be performed if desired to further strengthen these components. Also, welds, gussets and other strengthening structures can be added if desired.  
         [0029]      FIGS. 5   a  and  5   b  illustrate the steps in a preferred method of manufacturing housing cover  68 . Similar to the method discussed above for forming housing  44 , a disc shaped blank (not shown), preferably made from ductile material such as low carbon steel, is die formed, by die forming operations with one or more punch and die pairs to obtain the cup shaped body  160  shown in  FIG. 5   a . The cup shaped body  160  includes a spherical inner portion  164  and a hub portion  168 . A central bore  161  is also formed in the center of the spherical inner portion  164 .  
         [0030]     In an optional next machining step, inner portion  164  can be machined, as indicated by dashed line  172  to a required final shape. Additionally, hub portion  168  can be machined to provide a journal and shoulder for a bearing, as indicated by dashed line  176 . Also, to provide for connection of the housing cover  68  to housing  44 , an edge  180  can be machined to a required tolerance as indicated by dashed line  184 .  
         [0031]     In a final step of manufacturing the housing cover  68 , as shown in  FIGS. 5   b  and  6 , two or more oil lubrication holes  188  can be machined into the cup shaped body  160 . Additionally, the cup shaped body  160  can be machined forming journals and bores  192  for pinion shaft  56 .  
         [0032]      FIGS. 7   a  through  7   e  show preferred steps for assembling differential  40 . As illustrated in  FIG. 7   a , a subassembly  200  is first assembled from bevel gears  64 , meshed bevel pinions  60 , washer  66  and pinion shaft  56 , which is inserted, into bevel pinions  60 . Subassembly  200  is next installed inside the inner volume  110  of housing  44 , with the ends of pinion shaft  56  being received in journals and bores  136  formed in housing  44 . The subassembly  200  is installed such that the bore  136  aligns with an inner splined aperture (not shown) formed on one of the bevel gears  64  for receiving a splined portion of an axle (not shown).  
         [0033]     Next, as shown in  FIG. 7   b , housing cover  68  is fitted to housing  44  bringing edge  180  of housing cover  68  into contact with surface  144  while ensuring that journals and bores  192  correctly engage pinion shaft  56 . Housing cover  68  is then permanently welded, or otherwise connected, to housing  44  at  196 , as best shown in  FIG. 7   c.    
         [0034]     Next, differential ring gear  48  is connected to housing  44  by rivets  52 , or another suitable connection means, as shown in  FIG. 7   d.    
         [0035]     Finally, assembly is completed by adding bushings  202  and bearings  204 , which can be tapered roller bearings or radial ball bearings or any other suitable bearings, to the hubs  124 ,  168  of housing  44  and housing cover  68  as illustrated in  FIG. 7   e . The assembled differential  40  can then be installed in a casing, as required.  
         [0036]     As will be apparent to those of skill in the art, depending upon the torque which differential  40  is intended to carry, differential  40  can include three or four pinion shafts  56  and associated pinions  60  to increase the contact area between pinions  60  and bevel gears  64  to better carry the torque.  
         [0037]      FIG. 8  shows an alternative embodiment of differential  40 , wherein bearings  204  include a long inner race  208 , thus eliminating the need for bushings  202 .  
         [0038]      FIG. 9  shows another alternative embodiment of differential  40 , wherein ring gear  48  is connected to housing  44  by welding, rather than by rivets or screws. As illustrated, housing  44  is slightly modified in shape relative to the above-described embodiment wherein the laterally extending flange  46  is removed and, a cylindrical flange  212  is provided to which ring gear  48  is welded via a bead  216  of weld.  
         [0039]     The die forming of differential housing  44  and housing cover  68  provides several advantages over the prior art. The above-mentioned disadvantages with respect to the size and weight of cast iron housings are avoided. Further, die forming is a relatively fast process, compared to cold flow-forming and/or cold spin-forming and is less expensive to employ. Further, the die forming process better supports flexible manufacturing techniques. A manufacturing line established to manufacture the housing and housing cover for one differential could easily and quickly have its pairs of dies and punches changed to manufacture other differentials.  
         [0040]     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.