Abstract:
The present invention includes a differential housing and a method for forming the differential housing. The method includes the step of cold-working a first housing preform by one of a group consisting of spin-forming or flow-forming the inner surface of the preform into conformance with a contour of a first mandrel to form the differential housing. The method also includes the step of installing a differential mechanism subassembly including a plurality of gears and a pin in the differential housing. The method also includes the step of releasibly connecting a housing portion of the differential housing with one of a lid and a second gear assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of a provisional application Ser. No. 60/656,817 filed on Feb. 25, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to an automotive driveline application and in particular to a flow-formed differential housing for supporting a differential mechanism for transmitting torque from a transmission of a vehicle to axle shafts of the vehicle and a method of forming the flow-formed differential housing.  
       BACKGROUND OF THE INVENTION  
       [0003]     A differential housing supports a differential mechanism having gears that transmit torque from a transmission of a vehicle to axle shafts of the vehicle. Generally, bevels gears of the differential mechanism are housed in the differential housing. Alternatively, planetary gears can also be housed in the differential housing. The typical differential mechanism of the vehicle transmission is designed to transmit torque from a transmission output to the opposing axle shafts allowing right and left wheels to rotate at different speeds, particularly important when negotiating a turn. While performing generally the same function, differential mechanism have different dimensional requirements for rear wheel and front wheel drive vehicles. Specifically, differentials intended for use on the front wheel drive vehicles require a beveled and even annular shape in order to compensate for both the smaller packaging area available and to account for the steering characteristics of the front wheels of the vehicle.  
         [0004]     Rear wheel drive vehicles are typically larger and require more torque production than the front wheel drive vehicles and include sport utility, pick-ups, and even heavy duty vehicles. Therefore, the rear wheel drive differential is typically dimensioned larger with heavier gauge steel than is a front wheel drive differential. Iron castings presently used to form a housing of a differential requires a large number of machining operations to produce finished parts having the dimensions necessary to provide adequate tolerances to support the gears disposed within the housing.  
         [0005]     Given the high torque requirements that is typical of the rear wheel drive vehicle, it is believed that the differential housing should include a more dimensionally stable and durable configuration than what is required of a front wheel drive differential housing. Furthermore, many of the manufacturing drawbacks of cast differential housings have resulted in excessive cost of a typical vehicle transmission.  
         [0006]     The art is replete with various designs of the differential housings and methods of forming the differential mechanisms, which are disclosed in the U.S. Pat. No. 6,045,479 to Victoria et al; U.S. Pat. No. 6,061,907 to Victoria et al; U.S. Pat. No. 6,176,152 to Victoria et al.; and U.S. Pat. No. 6,379,277 to Victoria et al. Each of the aforementioned United States Patents discloses a method of forming a differential housing using a cold flow-forming process. While the differential housing formed by the process disclosed in these prior art references are believed to be effective for use in a front wheel drive transmission, it is believed that the differential housings will not be as effective for use in a rear wheel drive vehicle. However, the dimensional improvements produced by the cold flow-forming process that enable sheet steel to be used to form the differential housing can also be used to form a differential housing for a rear wheel drive differential. Therefore, the cold flow-forming process disclosed in these prior art patents are included by reference herein.  
         [0007]     The differential housings, as disclosed in the aforementioned prior art references, are formed from a single casting that is machined subsequent to casting. In particular, a housing portion is formed in a series of steps starting with a cup-shaped workpiece. The cup-shaped workpiece is fitted over a chuck and flow-formed into a housing preform. Operations such drilling and surface finishing are performed on the housing preform subsequent to the flow-forming process. Gears are placed in the differential housing and the housing is permanently sealed. After being sealed, the entire assembly cannot be serviced and must be replaced if one of the internal components fails.  
         [0008]     There is a constant need in the area of differential housings, formed by the cold flow-forming process and by forging and the like, for an improved design of the differential housing that is easily disassembled and is easily serviceable in a short period of time, particularly when one or more of the gears need to be replaced without having to replace the entire differential housing.  
       SUMMARY OF INVENTION  
       [0009]     A differential housing of the present invention is designed for supporting a differential mechanism having a pin, a pair of axle shafts, i.e. the shafts, and a set of gears, such as pinion gears and beveled gears, disposed on the axle shafts and the pin and presenting driving engagement therebetween for transmitting torque from a transmission of a vehicle to the shafts. The shafts and the gears are disposed in the differential housing. A housing portion of the differential housing is defined by an annular wall circumscribing an axis. The annular wall is exposed to an open end for receiving one of the shafts. The annular wall is further exposed to an open front being opposite from the open end. A lid or a secondary gear assembly of the differential housing is attached to the open front thereby forming an enclosure within the housing portion for engaging the shafts and the gears therein. A locking device defined by a snap-ring extends peripherally about the housing portion at the open front. The snap-ring is elastically deformed between a stressed position and an unstressed position for releasibly connecting the lid to the housing portion for forming the enclosure within the housing portion to support the differential mechanism and for selectively removing the shafts and the gears of the differential mechanism from the enclosure when the snap-ring is in the stressed position as the lid is removed from the engagement with the housing portion.  
         [0010]     An inventive method of forming the aforementioned differential housing includes the step of cold-working a first housing preform by one of a group consisting of spin-forming or flow-forming the inner surface of the preform into conformance with a contour of a first mandrel to form a differential housing. The method also includes the step of installing a differential mechanism subassembly including the aforementioned plurality of gears and a pin in the differential housing. The method also includes the step of releasibly connecting the housing portion of the differential housing with one of a lid and a secondary gear assembly.  
         [0011]     One of the advantages of the present invention is that the releasable connection between the lid or the secondary gear assembly and the housing portion of the differential housing allows the differential housing to be easily serviced. For example, one or more of the gears can be replaced without having to replace the entire differential housing, which is required of prior art differential housings formed by cold working. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other 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:  
         [0013]      FIG. 1A  is a cross-sectional view of a first exemplary embodiment of a differential housing of the present invention;  
         [0014]      FIG. 1B  is a partially exploded view of the first exemplary embodiment of the differential housing;  
         [0015]      FIG. 1C  is a fragmental view of a housing portion and a lid of the differential housing with the lid connected to the housing portion by a snap-ring having a beveled peripheral edge;  
         [0016]      FIG. 1D  is a fragmental view of the housing portion and the lid connected by a snap-ring having a V-shaped or tapered peripheral edge;  
         [0017]      FIG. 2  is a perspective view of a second exemplary embodiment of the differential housing;  
         [0018]      FIG. 3  is a cross-sectional view taken along section lines  3 - 3  in  FIG. 2 ;  
         [0019]      FIG. 4  is right-hand view of the second exemplary embodiment of the differential housing;  
         [0020]      FIG. 5  is a cross-sectional view taken along section lines  5 - 5  in  FIG. 4 ;  
         [0021]      FIG. 6  is a perspective view of the a gear assembly received in differential housing according to a third exemplary embodiment of the present invention;  
         [0022]      FIG. 7  is a perspective view of the differential housing according to the third exemplary embodiment of the present invention; and  
         [0023]      FIG. 8  is a cut-away view showing the gear assembly and differential housing of the third exemplary embodiment of the present invention engaged with respect to one another.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     A differential housing assembly  10  of the present invention is designed for supporting a differential mechanism or differential mechanism subassembly (to be discussed in details further below) for transmitting torque from a transmission of a vehicle (not shown) to axle shafts (not shown) of the differential mechanism of the vehicle. Plurality of different embodiments of the invention are shown in the Figures of the application. Similar features are shown in the various embodiments of the invention. Similar features have been numbered with a common two-digit reference numeral and have been differentiated by a third digit placed before the two common digits. Similar features are structured similarly, operate similarly, and/or have the same function unless otherwise indicated by the drawings or this specification. Furthermore, particular features of one embodiment can replace corresponding features in another embodiment unless otherwise indicated by the drawings or this specification.  
         [0025]     Referring now to  FIG. 1 , in a first exemplary embodiment of the invention, the differential housing assembly  10  includes a differential housing or housing portion  12  and a lid  14 . The differential housing  12  is formed according the cold forming process set forth in the U.S. Pat. No. 6,061,907 to Victoria et al., which is hereby incorporated by reference in its entirety. The housing portion  12  is defined by an annular wall circumscribing an axis A with the annular wall exposed to an open end, generally indicated at  13 , for receiving one of the shafts and an open front, generally indicated at  15 , opposite from the open end  13 . The lid  14  is releasibly engaged with the differential housing  12 .  
         [0026]     The differential mechanism of the differential housing assembly  10  also includes gears  16 ,  18 ,  20 ,  22  and a pin  24  presenting driving or meshing engagement therebetween. After the differential housing  12  has been formed according to the cold forming process set forth in the United States Patent No.  6 , 061 , 907  to Victoria et al., a longitudinal aperture  26  is formed and finished. The longitudinal aperture  26  receives a shaft (not shown. The shaft defines splines (not shown) which matingly engage splines  28  defined by the gear  16 . Also, a transverse aperture  30  is formed and finished. The transverse aperture  30  passes through the differential housing  12 . The pin  24  is received in the transverse aperture  30 . The lid  14  is releasibly associated with the differential housing  12  after the gears  16 ,  18 ,  20 ,  22  have been assembled and inserted into the differential housing  12 . The lid  14  defines a second longitudinal aperture  32  which receives a second shaft (not shown). The second shaft defines splines (not shown) which matingly engage splines defined by the gear  18 .  
         [0027]     The lid  14  and the differential housing  12  are releasibly engaged with respect to one another with a locking device such as, for example a snap-ring  36  extending into a groove  38  defined in the differential housing  12 . The snap-ring  36  extends peripherally about the inner surface of the differential housing  12  at the open front  15 . The snap-ring  36  is elastically deformed between a stressed position and an unstressed position to remove the lid  14  from the differential housing  12  and to connect the lid  14  to the differential housing  12 , respectively. When the snap-ring  36  is disengaged from the groove  38 , the lid  14  is removed from the differential housing  12  to allow a technician (not shown) to remove the differential mechanism from the enclosure to replace one or all of the gears  16 ,  18 ,  20 ,  22 . When the differential mechanism is serviced, the technician re-connects the lid  14  with the differential housing  12  as the snap-ring  36  is moved the stressed position to the unstressed position as the snap-ring  36  is radially retracted, disposed over the lid  14  and then allowed to radially expand from the stressed position to the unstressed position with the snap-ring  36  engaging the groove  38  to form the enclosure within the differential housing  12 . The releasable connection between the lid  14  and the differential housing  12  allows the differential housing  12  of the differential assembly  10  to be easily serviced in a short period of time. For example, one or more of the gears  16 ,  18 ,  20 ,  22  can be replaced without having to replace the entire differential housing assembly  10 .  
         [0028]     As best illustrated in  FIGS. 1C and 1D  the snap-ring  36  and the respective peripheral groove  38 . In one embodiment, as illustrated in  FIG. 1C , the snap-ring  36  extends to a peripheral edge having a beveled configuration. The peripheral groove  38  presents a configuration to complement the beveled configuration of the snap-ring  36 .  FIG. 1D  illustrates an alternative embodiment of a snap-ring  336  having a tapered or a V-shaped peripheral edge to complement with a V-shaped groove  338  defined in the differential housing  12 . Those skilled in the mechanical art will appreciate that other configurations of the snap-ring  34  and the peripheral groove may be utilized in practicing the invention.  
         [0029]     Referring now to  FIGS. 2-5 , in a second exemplary embodiment of the invention, a differential housing assembly  110  includes a differential housing  112  and a secondary gear assembly  40 . The secondary gear assembly  40  includes a support housing  41  and a plurality of secondary gears  43  rotatably supported  45  by the support housing  41 . The support housing  41  extends to a peripheral edge  47  that abuts the differential housing  112 . The differential housing assembly  110  also includes gears  116 ,  118 ,  120 ,  122  and a pin  124 . After the differential housing  112  has been formed according to the cold forming process set forth in the U.S. Pat. No. 6,061,907 to Victoria et al., a longitudinal aperture  126  is formed and finished. The longitudinal aperture  126  receives a shaft. The shaft (not shown) defines splines which matingly engage splines  128  defined by the gear  118 . Also, a transverse aperture  130  is formed and finished. The transverse aperture  130  passes through the differential housing  112 . The pin  124  is received in the transverse aperture  130 .  
         [0030]     The differential housing  112  and the secondary gear assembly  40  defining mating castle-teeth. For example, the differential housing  112  forms first connectors such as castle teeth  42 ,  44 ,  46 ,  48 ,  50 ,  52  and the secondary gear assembly  40  forms second connectors such as castle teeth  54 ,  56 . The castle teeth  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56  engage one another to prevent relative rotation between the differential housing  112  and the secondary gear assembly  40 . As shown in  FIG. 5 , the castle teeth, such as castle-tooth  42 , of the differential housing  112  extend radially inward greater than the castle teeth, such as castle-tooth  56 , of the secondary gear assembly  40 .  
         [0031]     The differential housing  112  and the secondary gear assembly  40  are releasibly engaged with one other with a snap-ring  136  terminated into fingers  137  adaptable to be engaged by the technician in a manner known to those skilled in the art to manipulate the snap-ring  136  between the stressed and unstressed positions. The secondary gear assembly  40  includes a peripheral notch  139  defined in the peripheral edge  47  of the support housing  41  to form a clearance for the snap-ring  136  as will be discussed further below. The thickness of the peripheral edge  47  and the size of the peripheral notch  139 , as shown in  FIG. 3 , may vary and are not intended to limit the present invention. The snap-ring  136  is releasibly associated with the differential housing  112  after the gears  116 ,  118 ,  120 ,  122  have been assembled and inserted into the housing  12 . The mandrel used in the cold forming process used to form the differential housing  112  can include an annular projection so that the differential housing  112  is formed with an annular groove  138 . When the snap-ring  136  is disengaged from the groove  138  and disposed in the peripheral notch  139 , the secondary gear assembly  40  is removed from the differential housing  112  to allow the technician to remove the differential mechanism from the enclosure to replace one or all of the gears  116 ,  118 ,  120 ,  122 . When the differential mechanism is serviced, the technician re-connects the secondary gear assembly  40  with the differential housing  112  as the snap-ring  136  is moved the stressed position, i.e. out from the peripheral notch  139  to the unstressed position as the snap-ring  136  is radially retracted to the groove  138  with the snap-ring  136  engaging the groove  138  to form the enclosure within the differential housing  112  after the secondary gear assembly  40  is placed over the gears  116 ,  118 ,  120 ,  122 . The releasable connection, i.e. the snap-ring  136 , between the secondary gear assembly  40  and the differential housing  112  allows the differential housing assembly  110  to be easily serviced. For example, one or more of the gears  116 ,  118 ,  120 ,  122  are replaceable without having to replace the entire differential housing assembly  110 .  
         [0032]     Referring now to  FIGS. 6-8 , in a third exemplary embodiment of the invention, a differential housing assembly  210  includes a differential housing  212  and a secondary gear assembly  240 . The secondary gear assembly  240  includes a support housing  241  and a plurality of secondary gears  243  rotatably supported  245  by the support housing  241 . The differential housing assembly  210  also includes gears  216 ,  218 ,  220 ,  222  and a pin  224 . After the differential housing  212  has been formed according to the cold forming process set forth in U.S. Pat. No. 6,061,907 to Victoria et al., a longitudinal aperture  226  is formed and finished. The longitudinal aperture  226  receives a shaft (not shown). The shaft defines splines (not shown) which matingly engage splines (not shown) defined by the gear  218 . Also, a transverse aperture (not shown) is formed and finished. The transverse aperture passes through the differential housing  212 . The pin  224  is received in the transverse aperture.  
         [0033]     The differential housing  212  defines a plurality of notches, such as notch  58 , and the secondary gear assembly  240  defines a plurality of teeth, such as tooth  60 . The teeth and notches engage one another and cooperate to prevent relative rotation between the differential housing  212  and the secondary gear assembly  240 .  
         [0034]     The differential housing  212  and the secondary gear assembly  240  are releasibly engaged with one other with a snap-ring  236 . The functional characteristics of the snap-ring  236  are identical to the functional characteristics of the snap-ring  36  and  136 . The secondary gear assembly  240  is releasibly associated with the differential housing  212  after the gears  216 ,  218 ,  220 ,  222  have been assembled. The mandrel used in the cold forming process used to form the differential housing  212  can include an annular projection so that the differential housing  212  is formed with an annular groove  238 . After the secondary gear assembly  240  is placed over the gears  216 ,  218 ,  220 ,  222 , the snap-ring  236  is radially retracted, disposed over the secondary gear assembly  240  and then allowed to radially expand into the groove  238 . The releasable connection between the secondary gear assembly  240  and the differential housing  212  allows the differential housing assembly  210  to be easily serviced. For example, one or more of the gears  216 ,  218 ,  220 ,  222  are replaceable without having to replace the entire differential housing assembly  210 . Those skilled in the art will appreciate that the locking device, i.e. the snap-ring  36  of the present invention is not intended to be limited to differential housing assembly formed by the cold forming process and may be utilized by other forger or iron casted differential housing assemblies.  
         [0035]     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.