Abstract:
A method is disclosed for making a differential housing having a ring gear integrally formed therein. The method includes the steps of forging a conical frustum from a steel rod; deforming the frustum between upper and lower die halves of a tool to produce a differential housing having an annular rim; and forging a plurality of teeth in the annular rim defining the rim gear.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to transaxles for an automotive vehicle, and more particularly, to a differential housing with an integrated ring gear and a method of forming the housing with the ring gear integrated therewith.  
           [0003]    2. Description of the Related Art  
           [0004]    Differential mechanisms are widely used in drive axles in automobiles for transmitting torque from an engine driven transmission output to left and right axle shaft for transferring force to wheels secured to the ends of the axle shafts. The differential mechanism typically includes a plurality of gears for allowing the left and right axle shafts to rotate at different speeds while still transmitting torque to the wheels driven by the axle shafts.  
           [0005]    Conventional differential mechanisms include an outer housing and a separate ring gear fixedly secured to the outer housing. Producing separate housings and rings gears and later interconnecting the ring gears to the housings requires numerous machining and welding operations. Conventional welding operations generate heat in an amount sufficient to distort the housing and the ring gear.  
           [0006]    Accordingly, it remains desirable to have a method of forming a differential housing having a ring gear integrally formed therein without the need to weld together a housing and a ring gear.  
         SUMMARY OF THE INVENTION  
         [0007]    According to one aspect of the invention, a method is disclosed for making a differential housing having a ring gear integrally formed therein. The method includes the steps of forging a conical frustum from a steel rod; deforming the frustum between upper and lower die halves of a tool to produce a differential housing having an annular rim; and forging a plurality of teeth in the annular rim defining the ring gear.  
           [0008]    According to another aspect of the invention, a differential housing is also disclosed. The housing comprises a bell shaped body extending between a cylindrical first end and an opposing annular second end, and a ring gear integrally formed in the opposing annular second end. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0010]    [0010]FIG. 1 is a cross sectional view of a prior art differential assembly;  
         [0011]    [0011]FIG. 2 is a perspective view, partially cut away, of a second prior art differential assembly;  
         [0012]    [0012]FIGS. 3 a  and  3   b  are perspective and cross sectional views, respectively, of a differential assembly according to one embodiment of the invention;  
         [0013]    [0013]FIGS. 4 a - d  are cross sectional views of the differential assembly;  
         [0014]    [0014]FIG. 5 is a cross sectional view of a housing cover preform;  
         [0015]    [0015]FIG. 6 is a cross sectional view of a housing cover of the differential assembly formed from the preform shown in FIG. 5;  
         [0016]    [0016]FIG. 7 is a cross sectional view of a housing preform;  
         [0017]    [0017]FIG. 8 is a cross sectional view of a housing of the differential assembly formed from the preform shown in FIG. 7;  
         [0018]    [0018]FIGS. 9 a - 9   f  are of cross sectional views of the housing illustrating the sequence of the method of forming the housing;  
         [0019]    [0019]FIGS. 10 a - c  are cross sectional views of a second embodiment of the differential housing;  
         [0020]    [0020]FIG. 11 is a cross sectional view of a third embodiment of the differential housing;  
         [0021]    [0021]FIG. 12 is a cross sectional view of a housing cover preform according to the third embodiment;  
         [0022]    [0022]FIG. 13 is a cross sectional view of fourth embodiment of the differential assembly having a stamped housing cover;  
         [0023]    [0023]FIG. 14 is a cross sectional view of a stamped housing cover preform according to the fourth embodiment;  
         [0024]    [0024]FIG. 15 is a perspective view of the housing according to the first embodiment;  
         [0025]    [0025]FIG. 16 is a perspective view of the housing cover according to the first embodiment;  
         [0026]    [0026]FIG. 17 is a perspective view of a one-piece spherical washer according to one embodiment of the invention;  
         [0027]    [0027]FIG. 18 is a perspective view of flat washers within the differential housing; and  
         [0028]    [0028]FIG. 19 is a perspective view of spherical washers within the differential housing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring to FIG. 1 there is shown a conventional prior art differential assembly  200  for transmitting torque from a transmission to axle shafts of driven wheels allowing the two wheels to rotate at different speeds. The conventional differential assembly  200  includes a housing  90  formed from a one-piece iron casting having two wide-open windows  91  for installing a subassembly of internal bevel gears and pinions. A ring gear  92  is fixedly secured to the housing  90  by bolts  93 , rivets or other suitable attachment means. The ring gear  92  is driven by torque provided by a transmission output pinion gear (not shown). The torque is then transmitted through the housing  90  to the pinion shaft  86 , which carries bevel pinions  87  in rotation. Finally, axle shafts are driven through bevel gears  88 , which mesh with the bevel pinions  87 .  
         [0030]    [0030]FIG. 2 illustrates another conventional prior art differential assembly  200 ′. The differential housing includes a flow-formed or spin-formed housing  94  and housing cover  96 , which are interconnected mutually by laser welding, or other suitable interconnecting means. A ring gear  97  is fixedly secured to a flange  95  of the housing  94  by welding. Bevel gears, bevel pinions, a pinion shaft and washers  19  are installed inside the housing.  
         [0031]    Referring to FIGS. 3 a  and  3   b , a differential assembly is generally indicated at  300  according to one embodiment of the invention. Torque from a transmission (not shown) is transmitted through a differential gear and housing  1  preferably formed in a forging operation, as will be described in detail below. The torque is transferred to a bevel pinion shaft  5 , which, in turn, drives a pair of bevel pinions  4 . Torque from bevel pinions  4  is transmitted to a pair of bevel gears  3 , which are interconnected to left, and right axle shafts (not shown) through a spline formed in an internal diameter of the bevel gears  3 . The bevel pinion shaft  5 , bevel pinions  4 , and bevel gears  3  are assembled between the differential housing  1  and differential housing cover  2 . In a preferred aspect of the present invention, the differential housing  1  and cover  2  are formed in a forging operation. The housing cover  2  provides a support  16  for a bearing (not shown) linked to the differential assembly  300 . A second support  46 , similar to the first support  16  is formed on an opposing side of the housing  1 . A pair of bevel pinion washers  7  and bevel gear washers  6  are assembled between the bevel pinions  4  and bevel gears  5  and inside surface  53  of the housing.  
         [0032]    [0032]FIGS. 4 a - d  illustrate preferred steps for assembling the differential assembly  300 . In a first step, a subassembly  8  including the bevel gears  3 , bevel pinions  4  meshed with the bevel gears  3 , washers  6  and  7  covering spherical surfaces of bevel gears  3  and pinions  4 , and the bevel pinion shaft  5  inserted into holes formed in two bevel pinions  4  as well as the washers  7  are installed inside of the differential housing  1 . Each end of the bevel pinion shaft  5  is seated within a semi-circular recess  51  formed in the housing  1  that is best shown in FIG. 15.  
         [0033]    In a second step, an external cylindrical surface  21  of the housing cover  2  is fitted within the internal cylindrical surface  50  of the housing  1 . The housing cover  2  includes semi-circular recesses  22 , as best shown in FIG. 16, to accommodate respective ends of each bevel pinion shaft  5 .  
         [0034]    In a third step, the housing  1  and the housing cover  2  are interconnected by welding, or other suitable methods known by those skilled in the art.  
         [0035]    In a fourth step, radial ball bearings  61  and  62  or tapered roller bearings are fitted on journals  16 ,  46  formed in the housing cover  2  adjacent shoulder  17 ,  45  respectively.  
         [0036]    Because the torque transmitted through the differential assembly  300  is very high, the differential assembly  300  may include three or four pinions  4  supported on the housing  1  using pinion shafts  5 , meshing with the bevel gears  3  and spaced mutually about a central axis.  
         [0037]    Referring to FIG. 5, there is shown a preferred forged housing cover preform  10 . The housing cover preform  10  includes a wall  12  and an inner spherical surface  11 . The dotted line shown indicates an intended final shape of the housing cover  2  after machining.  
         [0038]    [0038]FIG. 6 shows a cross section of the preferred housing cover  2 , which is machined from the housing cover preform  10  shown in FIG. 5. The machining step includes forming a journal surface  16  and shoulder used to install bearing  61 . The machining step also includes forming an internal cylindrical surface  19  for allowing insertion of an axle shaft. The machining step also includes forming an internal spherical surface  20  to receive the bevel gears  3 , bevel pinions  4 , and washers  7 , as previously described above. Additionally, the machining step includes forming an external cylindrical surface  21 , a circular surface  23  and semi-circular recesses  22  in the preform  10  to produce the housing cover  2 .  
         [0039]    Referring to FIG. 7, there is shown a cross section of a forged housing preform  28  including an integrated gear region. The gear region includes a gear rim area  30 , support area  31 , wall  32 , internal spherical area  33 , speed-sensor teeth  34  and bearing area  35 . The dotted line indicates an intended final shape of the housing  1  after machining.  
         [0040]    Referring to FIG. 8, the housing  1  is shown, which was machined from the housing preform  28  shown in FIG. 7. A journal surface  46  and shoulder  45  are formed in the machining step for installing bearing  62 : Also an outside diameter  44  of speed-sensor teeth  34 , a shoulder  43  and an area  48  are formed in the machining step. An internal spherical surface  49  for installing bevel gears  3 , pinions  4  and washers  7  is also formed in the: machining step. An internal cylindrical surface  50 , circular surface  53  and semi-circular recesses  51  are also formed in the machining step. Gear teeth  40  are cut and lubrication oil holes  52  are drilled and reamed as part of the machining step used to form the housing  1 .  
         [0041]    Referring to FIGS. 9 a - f  there is shown preferred steps for forging the housing preform  28  and machining the preform  28  to form the housing  1 . In a first step a steel rod  59  is forged into a conical frustum  60 , shown in  9   b . In a second step, frustum  60  is then formed by punch and die operations into a primary preform  61  having the gear rim area  30 , support area  31 , wall  32 , and internal spherical area  33 , as shown in FIG. 9 c . In a third step, the primary preform  61  is forged into workpiece  62 , shown in FIG. 9 d , having speed-sensor teeth  34 , area  35  and a blind hole  63  formed by the punch and die operations. In a fourth step, the blind hole  63  is pierced forming hole  64  of the housing preform  28 . In a fifth step, the preform  28  is machined forming gear teeth  40 . In a sixth step, the preform  28  is heat-treated and finish machined or ground to final dimensions forming the housing  1 , shown in FIG. 9 f.    
         [0042]    Referring to FIGS. 10 a - c , a second embodiment of the differential housing  400  is shown. The housing preform  70  is forged without speed-sensor teeth  34  as described above with respect to the first embodiment. A forged external surface  65  is machined forming an external surface  66  of a housing  71 . A speed-sensor gear  67  is pressed into the external surface  66  before the bearings  61  and  62  are fitted.  
         [0043]    Referring to FIGS. 11 and 12, a third embodiment of the differential housing  500  is shown. The third embodiment of the differential housing  500  differs from the first embodiment of the differential housing  1  in that the forged housing cover  2 , shown in FIG. 4, is replaced by a spin-formed or flow-formed housing cover  77 . The spin-formed or flow-formed housing cover preform  75  is shown having an inner spherical surface  76  that does not need to be machined after the initial spin-forming or flow-forming process. The dotted line indicates the intended shape of the spin-formed or flow-formed housing cover  77  after machining its exterior to form the final shaped housing cover  77 .  
         [0044]    Referring to FIGS. 13 and 14, a fourth embodiment of the differential assembly  600  is shown having a stamped housing cover  82 . The stamped housing cover preform  80  is shown having an inner spherical surface  81  that does not need to be machined. The dotted line indicates the intended shape of the stamped housing cover  82  after machining.  
         [0045]    Referring to FIGS.  17 - 19 , there are shown various embodiments of washers  6  and  7 . In a first aspect, a one-piece spherical washer  100  is shown in FIG. 17. Preferably, the washer  100  is made of plastic. In FIG. 18, two flat washers  102  are shown. In FIG. 19, two spherical washers  101  are shown having lubrication oil slots  105  and  106  formed, respectively, therein. The materials of washers  101  and  102  may be steel, plastic or any other appropriate material.  
         [0046]    The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.  
         [0047]    Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.