Abstract:
A method for making a differential housing having a ring gear integrally formed therein includes the steps of providing a differential housing having an annular rim integrally preformed therein; supporting the differential housing between upper and lower halves of a rotatable holding tool such that the annular rim extends radially outwardly from the holding tool for movement therewith; providing a thickening tool having a tool surface engagable with the annular rim during rotation of the holding tool to form a thickened lip; and providing a gear forming tool engagable with the thickened lip during rotation of the holding tool, whereby a plurality of teeth are formed along the lip to form the ring gear.

Description:
FIELD OF THE INVENTION 
   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. 
   DESCRIPTION OF THE RELATED ART 
   Differential mechanisms are widely used in drive axles in automobiles for transmitting torque from an engine driven transmission output to left and right axle shafts. Wheels are typically 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. 
   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. Further, the heat generated during the welding operations tends to distort the housing and the ring gear. 
   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 separate a housing and a ring gear. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention, a method of making a differential housing having a ring gear integrally formed therein is provided. The method includes the steps of providing a housing blank having an annular rim integrally preformed therein; supporting the housing blank in a rotatable holding tool so that the annular rim extends radially outwardly from the holding tool for rotation therewith; rotating the holding tool; providing a thickening tool for engaging the annular rim during rotation of the holding tool, whereby the annular rim is plastically deformed to form a lip; and providing a gear forming tool for engaging the lip during rotation of the holding tool, whereby a plurality of teeth are formed along the lip to form the ring gear. Also disclosed is a differential housing having an integrally formed ring gear. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a perspective view of a differential assembly according to one aspect of the invention; 
       FIG. 2  is a cross sectional view of a die tool and housing blank formed in the die tool according to one aspect of the invention; 
       FIG. 3  is a cross sectional view of a holding tool and a thickening tool for forming a thickened lip in the housing blank; 
       FIG. 4  is a cross sectional view of the holding tool and a second thickening tool; 
       FIG. 5  is a cross sectional view of the holding tool and a gear forming tool for forming the ring gear from the thickened lip; 
       FIG. 6  is a cross sectional view of the die tool according to a second embodiment of the invention; and 
       FIG. 7  is a cross sectional view of the die tool according to a third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the figures, a differential assembly for a transaxle in an automotive vehicle is generally indicated at  10  in  FIG. 1 . The differential assembly  10  includes a plurality of pinion gears  12  matingly engaged, as known by those of ordinary skill in the art, for transmitting torque from a transmission output (not shown) to left and right axle shafts and for allowing the left and right axle shafts to rotate at different speeds. The pinion gears are operatively supported by a differential housing  20 . The housing  20  includes a generally bell shaped body  22  extending between a generally cylindrical first end  24  and an opposite annular second end  26 . A ring gear  30  is integrally formed in the second end  26  of the housing  20 . A method of integrally forming the ring gear  30  into the second end  26  of the housing is described in detail below. 
   Referring to  FIG. 2 , a mandrel or lower die  40  is provided having a pre-shaped, positive lower tool surface  42 . An upper die  50  is provided having a pre-shaped upper tool surface  52 . The upper tool surface  52  is generally complementary to the lower tool surface  42 . The upper die  50  is forcibly movable relative to the lower die  40  between an open position, as shown in  FIG. 2 , and a closed position against the lower die  40 , by any suitable means, such as a hydraulic press assembly. In the closed position, a cavity  58  is defined between the tool surfaces  42 ,  52  of the lower  40  and upper  50  dies that generally define the desired shape of the housing  20 . In the open position, the lower die  40  is exposed to allow the placement or removal of a housing blank  60 . 
   While the upper die  50  is in the open position, a pre-formed housing blank  60  is placed onto the lower tool surface  42 . The upper die  50  is forcibly moved to the closed position, whereby the housing blank  60  is compressed between the lower  42  and upper  52  tool surfaces. The housing blank  60  is flow or cold formed to retain the general shape of the cavity  58 . An annular rim  62  is formed in the housing blank  60  defining a rim axis  61 . 
   Referring to  FIGS. 3 and 4 , a first holding tool  70  having a generally cylindrical outer peripheral surface  71  is provided. The first holding tool  70  includes upper  72  and lower  74  holding members. The first holding tool  70  is rotatably supported by external support means (not shown) for rotation about a first rotary axis  75 . The upper  72  and lower  74  holding members have complementary upper  76  and lower  78  clamping surfaces, respectively, adapted for nestingly supporting the housing blank  60  therebetween. The upper  76  and lower  78  clamping surfaces each extend between the outer peripheral surface  71 . The housing blank  60  is placed into and clamped between the upper  76  and lower  78  clamping surfaces such that the rim axis  61  is aligned with the first rotary axis  75  and the rim  62  protrudes radially beyond the outer peripheral surface  71 . 
   A thickening tool  80  having a forming surface  82  for plastically deforming the rim  62  is provided and rotatably supported by external support means (not shown) for rotation about a second rotary axis  83 . 
   The first holding tool  70  and thickening tool  80  are rotated in opposite directions about their respective first  75  and second  83  rotary axes by any suitable means, such as an electric motor, at preselected fixed or variable speeds. The housing blank  60 , clamped between the upper  76  and lower  78  clamping surfaces, rotates with the holding tool  70 . The thickening tool  80  is displaced toward the first holding tool  70  by any suitable means, such as a hydraulic cylinder, so that the forming surface  82  frictionally engages the rim  62 . The forming surface  82  is forcibly held against the rim  62  until the outer periphery of the rim  62  is plastically deformed into a thickened or bulbuous annular lip  84 , as shown in  FIG. 3 . The forming surface  82  may be held against the rim  62  continuously in a single pass or in successive passes until a desired shape of the lip  84  is achieved. Second  88  or third (not shown) thickening tools may be utilized in succession until the desired shape of the lip  84  is achieved, as shown in  FIG. 4 . The housing blank  60  is removed from between the upper  76  and lower  78  clamping surfaces. 
   Referring to  FIG. 5 , a second holding tool  90  having a generally cylindrical outer peripheral surface  91  is provided. The second holding tool  90  includes upper  92  and lower  94  holding members. The second holding tool  90  is rotatably supported by external support means (not shown(for rotation about a third rotary axis  95 . The upper  92  and lower  94  holding members have complementary upper  96  and lower  98  clamping surfaces, respectively adapted for nestingly supporting the housing blank  60  therebetween. The upper  96  and lower  98  clamping surfaces each extend between the outer peripheral surface  91  of the second holding tool  90 . The housing blank  60  is placed into and clamped between the upper  96  and lower  98  clamping surfaces such that the rim axis  61  is aligned with the third rotary axis  95  and the bulbuous lip  84  protrudes radially beyond the outer peripheral surface  91 . 
   A gear forming tool  100  having a gear forming surface  102  for forming the teeth of the rim gear  30  is provided and rotatably supported by external support means (not shown) for rotation about a fourth rotary axis  104 . 
   The second holding tool  90  and the gear forming tool  100  are rotated in opposite directions about their respective third  95  and fourth  104  rotary axes by any suitable means, such as an electric motor, at preselected fixed or variable speeds. The housing blank  60 , clamped between the upper  96  and lower  98  clamping surfaces, rotates with the second holding tool  90 . The gear forming tool  100  is displaced toward the second holding tool  90  by any suitable means, such as a hydraulic cylinder, so that the gear forming surface  102  frictionally engages the lip  84 . The gear forming surface  102  is forcibly held against the lip  84 . The gear forming surface  102  cuts and plastically deforms the lip  84  to form the teeth of the rim gear  30 . The gear forming surface  102  may be applied to the lip  84  in successive steps until a final desired shape for the teeth of the rim gear  30  is achieved. Thus, a rim gear  30  is integrally formed in the housing  20  without welding and with minimal material loss. 
   An alternative method of integrally forming the rim gear  30  in the housing  20  is shown in  FIG. 6 . The upper die  150  is forcibly moved to the closed position, whereby the housing blank  160  is compressed between the lower  142  and upper  152  tool surfaces of the lower  140  and upper  150  dies. The housing blank  160  is flow or cold formed to retain the general shape of the cavity  158  formed between the lower  142  and upper  152  tool surfaces in the closed position. A thickened lip  184  is formed in the housing blank  160  without the intermediate steps of utilizing successive thickening tools. The rim gear  30  is cut and formed from the thickened lip  184 , as discussed. 
   As best shown in  FIG. 7  excess material  185  may be subsequently removed from the thickened lip  184  prior to forming the teeth of the rim gear  30  to achieve a desired shape of the lip  184  not possible with flow or cold forming alone. 
   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. 
   Many modification 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.