Abstract:
A vehicle differential case is disclosed, the case having an interior and an exterior configuration which provides an increased internal volume for, among other things, lubricant for components of the differential mechanism, while at the same time providing excellent structural strength. Importantly, the weight versus stiffness ratio of the differential case so described is significantly improved compared to known differential cases.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a case half for a differential which is reduced in weight from known devices while having improved structural integrity, and increased internal capacity for lubricant in order to better lubricate the differential components located inside the case.  
         [0002]      FIGS. 5 and 6  herein illustrate a prior art differential case which is commonly owned by the assignee of the present application. As will be readily apparent to those skilled in the art, the prior art differential case has a limited internal lubricant capacity by virtue of smaller lubricant reservoirs, and the greater wall thickness of the prior art case contributes to its greater weight.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention relates to a differential case comprising an output shaft hub for mounting a differential bearing, and a flange having a plurality of fastener apertures for mounting a ring gear. In between the output shaft hub and the flange is a portion having an inner and outer surface. At least the inner surface of the portion between the output shaft hub and the flange has a plurality of depressions which alternate with an equal number of substantially hollow ribs. Each depression connects an internal spider support and a pinion thrust surface to a segmented side gear internal thrust surface, and the like number of substantially hollow ribs form one or more lubricant reservoirs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     The structure and operation of the invention, together with further advantages thereof, may best be understood by reference to the accompanying drawings and the following descriptions.  
         [0005]      FIG. 1  is a perspective view of the configuration of the outer surface of the differential case;  
         [0006]      FIG. 2  is a perspective view of the configuration of the inner surface and interior volume of the differential case;  
         [0007]      FIG. 3  is a cross sectional view of the differential case taken along lines  3 - 3  of  FIG. 2 .  
         [0008]      FIG. 4  is a cross section view of the differential case taken along lines  4 - 4  of  FIG. 2 .  
         [0009]      FIG. 5  is a perspective view of the configuration of the outer surface of a prior art differential case.  
         [0010]      FIG. 6  is a perspective view of the configuration of the inner surface of the prior art differential case of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     While the invention may be susceptible to different embodiments, there is shown in the drawings and the following detailed discussion, a preferred embodiment with the understanding that this present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that as illustrated and described herein.  
         [0012]     The present invention is primarily concerned with a lightweight differential case  10 . The case houses a differential mechanism which forms a portion of a vehicle drivetrain, such as a truck drivetrain.  
         [0013]     The subject differential case  10  affords a number of advantages, besides lighter weight, over conventional differential cases. For example, the novel configuration of the differential case provides an increased interior volume, a portion of which volume is available to contain additional lubricant, thus improving the lubrication of the differential gears and other components housed in the subject differential case  10 . Preferably, the internal volume of the differential case which is available for gearing and lubricant is approximately 40% of the total exterior volume of the differential case  10  where the total exterior volume is defined as the volume enclosed by a revolved surface that is the projected side view external envelope of the differential case.  
         [0014]     Such advantages are accomplished by a differential case  10  generally having a configuration defined by: an output shaft hub  12  at one extremity, a flange  14 , having a plurality of fastener apertures  16  therein at the other extremity, and therebetween, a differential case body portion  18 . As best seen in  FIG. 2 , the inner surface of the differential case body portion  18  is defined by a plurality of depressions  20  which alternate with an equal number of substantially hollow ribs  22 . Each such internal depression  20  forms an internal spider arm support  24  and a pinion thrust surface  26 , which pinion thrust surface  26  is connected to a segmented side gear internal thrust surface  28 . Additionally, each rib  22  may form a lubricant reservoir.  
         [0015]     As best seen in  FIG. 1 , the configuration of the external surface of the differential case body portion  18  is largely defined by the interior structure just described. Consequently, the external surface of the differential case body  18  comprises a plurality of raised portions  30  defined by the internal ribs  22  alternating with an equal number of non-raised portions  32  defined by the internal depressions  20 , as best seen in  FIGS. 3 and 4 . As will be noted in  FIG. 1 , the alternating raised portions  30  and non-raised portions  32  of the outer surface extend, substantially, the length of the body portion  18  of the differential case  10  between the output shaft hub  12  more specifically, the output shaft hub bearing shoulder  13 , and the flange  14 . Similarly, as shown in  FIG. 2 , the alternating hollow ribs  22  and depressions  20  internal to the differential case  10  extend, substantially, the length of the body portion  18  of the differential case  10 .  
         [0016]     With continuing reference to  FIG. 2 , four internal surface depressions  20  and a like number of alternating substantially hollow ribs  22  are shown. It is, however, within the scope of the invention for the number of internal surface depressions  20  and substantially hollow ribs  22  to also be two or three in number.  
         [0017]     Similarly, as illustrated in  FIG. 1 , there are four raised portions  30  and four non-raised portions  32  shown on the exterior of the differential case body portion  18 . When there are either two or three internal surface depressions  20  and an equal number of substantially hollow ribs  22 , there will likewise be two or three raised portions  30  and non-raised portions  32  comprising the exterior configuration of the differential case body portion  18 .  
         [0018]     As light weight is an objective of the present invention, the type of material utilized to form the differential case  10 , the method by which the case is formed, and the amount of material contained in the differential case  10  must all be considered.  
         [0019]     With regard to material, the differential case  10  may be produced from any suitable material, for example, steel, iron, aluminum, and composite material, such as carbon fiber and resin.  
         [0020]     Where the material of the differential case  10  is a metal, the case may be forged or cast. The configuration of the differential case  10  of the present invention allows forging or casting, without a need for substantial post-production machining. By way of example, only 20-50% of the side gear thrust surface area, out of the full 360° annular surface area of the interior surface area of the present differential case  10  requires postproduction machining. Minimal machining results in a substantial cost savings in the manufacturing process.  
         [0021]     The use of modern casting and forging techniques, in turn, allows precise control over the wall thickness of the subject differential case  10 . Variations of no more than ±50% from the average wall thickness of the case are necessary to produce the present differential case  10 . This may be contrasted to conventional differential cases, where such variation may be ±75% from average wall thickness, in addition to an average that is thicker than the present invention.  
         [0022]     The subject differential case  10  may be said to have surface draft, by which term is meant, the taper of the inner and other surfaces of a part to be cast or forged utilizing a two-piece mold, such that the part will readily release from the mold when the casting or forging process is complete.  
         [0023]     The subject differential case  10 , despite its lighter weight is still stronger than conventional differential cases such as is shown in  FIGS. 5 and 6 . In part, this improved strength is believed to be attributable to the configuration of the differential case body portion  18  whereby the raised portions  30  and non-raised portions  32  are connected by vertical radially outwardly extending walls  34 , shown in  FIGS. 1 and 2 , which are orthogonal to a central axis  36 . As previously noted, this configuration is also reflected in the interior structure of the differential case body portion  18 . As used herein “central axis” means an imaginary line extending through the center of the opening forming the output shaft hub  12  along the length of the body of the differential case  18  and through the center of the opening formed by the flange  14 .  
         [0024]     A further advantage of the present differential case  10  is that the external depressions  20  formed by the internal hollow ribs  22  provide a means for output shaft hub  12  bearing puller access  38 , which is often not provided on conventional differential cases.  
         [0025]     As best seen in  FIG. 2 , four differential spider arm supports  24  are shown as formed in the interior surface of the mounting flange  14 . In accordance with the present invention, the number of spider arm supports  24  is equal to the number of substantially hollow ribs  22  which alternate with a like number of depressions  20  to, substantially, form the interior volume of the differential case  10 . As previously described, it is within the scope of the present invention for the number of hollow ribs  22 , and thus, the number of spider arm supports  24  in the mounting flange  14  to number two, three, or four.  
         [0026]     While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from its spirit and scope.