Abstract:
A cast aluminum differential housing for a motor vehicle powertrain having cast iron inserts. The housing is cast of light weight aluminum which weighs approximately one-third that of iron which has formerly been used to fabricate such housings. At locations of significant loads and wear, such as the mountings for the stub shaft associated with the two idler bevel gears, iron inserts are cast into the housing. The housing thus weighs significantly less than a comparable iron differential housing but since the two significant wear and load bearing regions include cast iron inserts, the aluminum differential housing of the present invention has the ruggedness, durability and service life of the much heavier iron housing.

Description:
FIELD 
       [0001]    The present disclosure relates to differential housings for motor vehicle powertrains and more particularly to lightweight cast aluminum differential housings for motor vehicle powertrains having cast iron inserts. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    Virtually every motor vehicle having a conventional powertrain includes a at least one differential which both directs drive torque to left and right front or rear wheels and allows the wheels to rotate at different speeds without scrubbing or winding up the rear axles as the vehicle turns and negotiates corners. The differential includes a cage or housing which is driven through a hypoid and ring gear assembly and contains two bevel idler gears in constant mesh with two gears connected to the left and right axles which drive the associated wheels. The cage or housing is typically cast iron and includes journal bearings which support a stub shaft upon which the idler gears are disposed. Because of the power applied to the differential and the forces experienced by the gears, shafts and bearings associated with them, the choice of cast iron for the housing is generally accepted as good engineering. 
         [0004]    Unfortunately, because of its size, the weight of a cast iron differential housing can be significant. As is well known, automobile manufacturers are under constant and increasing pressure to improve the fuel economy of their vehicles and one of the most direct paths to improved fuel economy is to reduce the weight of the vehicle. Such weight reduction, however, cannot be done at the expense of the ruggedness and service life of the vehicle and its components. Thus, one true challenge of improved fuel economy is the reduction of vehicle weight without any impact on the quality of the vehicle, its ruggedness and service life. 
         [0005]    The present invention is directed to both weight reduction of the differential cage or housing and maintenance of its quality and ruggedness. 
       SUMMARY 
       [0006]    The present invention provides a cast aluminum differential cage of housing. The housing is cast of light weight aluminum which weighs approximately one-third that of iron which has formerly been used to fabricate such housings. At locations of significant loads and wear, such as the mountings for the stub shaft associated with the two idler bevel gears, iron inserts are cast into the housing. The housing thus weighs significantly less than a comparable iron differential cage housing but since the two significant wear and load bearing regions include cast iron inserts, the aluminum differential housing of the present invention has the ruggedness, durability and service life of the much heavier prior art iron housing. 
         [0007]    Thus it is an aspect of the present invention to provide an aluminum differential housing. 
         [0008]    It is a further aspect of the present invention to provide a cast aluminum differential housing. 
         [0009]    It is a still further aspect of the present invention to provide an aluminum differential housing for a motor vehicle powertrain. 
         [0010]    It is a still further aspect of the present invention to provide a light weight cast aluminum differential housing for a motor vehicle powertrain. 
         [0011]    It is a still further aspect of the present invention to provide an aluminum differential housing having at least two cast iron inserts. 
         [0012]    It is a further aspect of the present invention to provide a cast aluminum differential housing having at least two cast iron inserts. 
         [0013]    It is a still further aspect of the present invention to provide an aluminum differential housing for a motor vehicle powertrain having cast iron inserts. 
         [0014]    It is a still further aspect of the present invention to provide a light weight cast aluminum differential housing for a motor vehicle powertrain having cast iron inserts. 
         [0015]    It is a still further aspect of the present invention to provide an aluminum differential housing for a motor vehicle powertrain having cast iron inserts which support an idler gear stub shaft. 
         [0016]    It is a still further aspect of the present invention to provide a light weight cast aluminum differential housing for a motor vehicle powertrain having cast iron inserts which support the idler gear stub shaft. 
         [0017]    Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0018]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0019]      FIG. 1  is a diagrammatic view of a front wheel drive motor vehicle transmission and differential according to the present invention; 
           [0020]      FIG. 2  is a full sectional view of a motor vehicle differential having a differential cage or housing according to the present invention; 
           [0021]      FIGS. 3A and 3B  are perspective views of the two iron inserts which support the idler gear stub shaft; 
           [0022]      FIG. 4  is a plan view with portions broken away of a motor vehicle differential cage or housing according to the present invention; and 
           [0023]      FIG. 5  is a plan view of a motor vehicle differential hub or housing according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0025]    With reference to  FIGS. 1 and 2 , a front wheel drive motor vehicle automatic transmission and differential assembly is illustrated and designated by the reference number  10 . The automatic transmission and differential assembly  10  includes a cast metal, multiple piece housing H which supports, locates and protect the various components of the assembly  10 . The components of the manual transmission and differential assembly  10  include a clutch  12  which drives an input shaft  14 , a plurality of mating gear assemblies  16  and an output shaft  18  which drives a differential  20  incorporating to the present invention. 
         [0026]    The output shaft  18  of the transmission assembly  10  includes a spur or hypoid gear  22  which engages and drives a ring gear  24 . The ring gear  24  includes gear teeth  26  complementary to the teeth on the hypoid gear  22  and is secured by a plurality of threaded fasteners  28  which extend through openings  29  in the ring gear  24 , through a first differential hub or housing  30  and into a second differential cage or housing  50 . 
         [0027]    The first differential hub or housing  30  includes a relatively thin outer flange  32  having a plurality of through openings or apertures  34  aligned with the openings  29  and the threaded fasteners  28 . Adjacent the outer flange  32  is a projection or lug  36 , the purpose of which will be explained subsequently. The differential hub or housing  30  also includes a center opening  38  adapted to receive an axle, an interior shoulder and wall  42  and an exterior shoulder and circumferential wall  44  which receives an anti-friction ball bearing assembly  46  which is supported in the housing H. 
         [0028]    Referring now to  FIG. 2 , the second differential cage or housing  50  is generally hemi-spherical in shape and includes a flange  52  which is complementary to and engages the outer flange  32  of the first differential hub or housing  30  and the ring gear  24  and includes a plurality of threaded through openings  54  which receive the threaded fasteners  28  which secure the ring gear  24  and the first differential hub or housing  30  to the second differential cage or housing  50 . 
         [0029]    The second differential cage or housing  50  includes a center through opening  56  adapted to receive an axle, an interior shoulder and wall  58  and an exterior shoulder and circumferential wall  60  which receives a second anti-friction ball bearing assembly  62  which is supported in the housing H. The interior shoulder and wall  42  of the first differential hub or housing  30  and the interior shoulder and wall  56  of the second differential cage or housing  50  symmetrically receive the left and right bevel gears  66 L and  66 R. Thrust bearings  68  are preferably interposed between the bevel gears  66 L and  66 R and the inner surface of the first differential hub  30  and the second differential cage  50 . Each of the bevel gears  66 L and  66 R includes female splines  72  which engage and drive complementary male splines  74  on both of the left and right drive axles  76 L and  76 R. 
         [0030]    Referring now to  FIGS. 2, 3A, 3B and 4 , disposed perpendicularly to the axis of the drive axles  76 L and  76 R is a stub shaft  80  which receives and locates a pair of bevel idler gears  82 A and  82 B. Both of the idler gears  82 A and  82 B are in constant mesh with the left and right bevel gears  66 L and  66 R. The stub shaft  80  is supported on a pair of cast iron inserts which are cast in place in the second differential cage or housing  50 . 
         [0031]    A first cast iron insert  90  includes an end flange  92 , a pair of diametrically opposed, axially extending webs or ribs  94 , a through circular opening  96  which receives the stub shaft  80  and an aligned pair of transverse openings  98  which receive a retaining pin  102 . The end flange  92  assists and ensures the proper location of the first insert  90  in a mold (not illustrated) during die casting of the second differential cage or housing  50  and the webs or ribs  94  assist secure attachment of the first insert  90  in the second differential cage or housing  50  and prevent its rotation. The retaining pin  102  extends through the aligned openings  98  in the first insert  90  and a complementary aligned opening  104  in the stub shaft  80  to retain the stub shaft in the second differential cage or housing  50 . The projection or lug  36  of the first differential hub or housing  30  engages the retaining pin  102  and maintains it in the position illustrated in  FIG. 2 . 
         [0032]    A second cast iron insert  110  includes an end flange  112 , a pair of diametrically opposed, axially extending webs or ribs  114  and a through circular opening  116  which receives the stub shaft  80 . The end flange  112  assists and ensures the proper location of the second insert  110  in the mold (not illustrated) during die casting of the second differential cage or housing  50  and the webs or ribs  114  assist secure attachment of the second insert  110  in the second differential cage or housing  50  and prevent its rotation. 
         [0033]    Referring now to  FIGS. 2 and 4 , the second differential cage or housing  50 , as noted above, includes a plurality of threaded through openings  54  arranged in a bolt circle. The cage or housing  50  also includes a plurality of obliquely oriented strengthening ribs  122 . Preferably, one of the ribs  122  is associated with each of the openings  54 . Disposed between each of the strengthening ribs  122  is an opening or aperture  124  which facilitates movement of lubrication oil through the second differential cage or housing  50  and into and out of the interior of the differential cage or housing  50  where the gears  66 L,  66 R,  82 A and  82 B and the stub shaft  80  reside. 
         [0034]    Referring now to  FIGS. 2 and 5 , the first differential hub or housing  30 , as noted above, includes the outer flange  32  having the plurality of through openings or apertures  34 , the center opening  38  adapted to receive the axle  76 L, and the exterior shoulder and circumferential wall  44  which receives the anti-friction ball bearing assembly  46 . The differential hub or housing  30 , like the differential cage or housing  50 , also includes a plurality of obliquely oriented strengthening ribs  126  which alternate with a like plurality of openings or apertures  128  which facilitate movement of lubrication oil into and out of the differential hub or housing  30 . 
         [0035]    The first differential hub or housing  30  and the second differential cage or housing  50  are preferably die cast of an aluminum alloy such as ANSI 383 or a similar material having good strength and casting characteristics. The iron inserts  90  and  110  are preferably fabricated of nodular cast iron having approximately 3.3% carbon, approximately 2.30% silicon, approximately 0.60% manganese and other trace elements or a similar material. As noted above, the iron inserts  90  and  110  are cast in place in the second differential cage or housing  50 . By “cast in place,” it is meant that the iron inserts  90  and  110  are first cast and finished by any suitable machining or surface finishing process and then are appropriately positioned in the mold (not illustrated) for the second differential cage or housing  50  which is subsequently filled with aluminum. 
         [0036]    A differential  20  incorporating the first differential hub or housing  30  and the second differential cage or housing  50  provides many improvements and enhancements over a prior art iron differential cage. First of all, the weight of an iron differential cage may be approximately 1800 grams whereas the differential hub  30  and the differential cage  50  weigh approximately 800 grams. This represents a weight reduction of 1 kilogram or about 55%. Second of all, because the differential hub  30  and the differential cage  50  are separate, smaller castings than the prior art cage, the accuracy and integrity of the castings are improved, resulting in fewer castings rejected for defects. Furthermore, the strengthening ribs  122  concentrate metal in regions of higher stress whereas the lubrication openings  124  are in regions of lower stress. This combination of features improves the overall strength and rigidity of the differential cage or housing  50  while reducing its weight. Finally, of course, the reduced weight of the differential hub  30  and the differential cage  50  stated above reduces vehicle weight and improves fuel economy. 
         [0037]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.