Abstract:
The present invention discloses a differential housing and a method operable to form the differential housing. The method includes the step of disposing a member having an outer surface on a mandrel. The member in the exemplary embodiment of the invention is a ring that enhances the strength of the finished differential housing. The method also includes the step of cold-working a housing preform by flow-forming the inner surface of the housing preform into conformance with the mandrel and with the outer surface of the member after said disposing step. The member is disposed in situ as the housing preform is cold-worked to produce the finished differential housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of a provisional application Ser. No. 60/656,363 filed on Feb. 25, 2005. 

   FIELD OF THE INVENTION 
   The invention relates to automotive driveline application and in particular to a flow-formed differential housing for retaining a differential mechanism, which transmits 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 
   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 opposing axle shafts of the differential mechanism allowing right and left wheels to rotate at different speeds, particularly important when negotiating a turn. While performing generally the same function, the differential mechanism has 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. 
   The art is replete with various methods of forming the aforementioned differential housings. The differential housings can be formed from a single casting that is machined subsequent to casting. The casting process enhances the control of wall thickness but produces a relatively heavy finished part. An continuing goal of vehicle manufacturers is to reduce the weight of each component of the vehicle. Flow forming is a process that can produce relatively lighter finished parts, but is limited with respect to the control of wall thickness. U.S. Pat. No. 6,061,907 to Victoria et al. discloses a method for forming a two-piece differential housing using a cold flow-forming process. 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 mandrel and flow-formed into a housing preform. Surface finishing is performed during the flow-forming process. Flow-formed differential housings can sometimes be compromised by sections of thin walls. These thin wall sections diminish the durability of the differential housing. 
   There is a constant need in the area of differential housings for an improved design of the differential housing formed by the cold flow-forming process that improves durability characteristics of the differential housing. 
   SUMMARY OF INVENTION 
   A differential housing for a differential mechanism of the present invention includes an annular wall circumscribing an axis for retaining the differential mechanism. A tubular member extends between the annular wall and the differential mechanism. The tubular member partially encapsulates the differential mechanism to distribute a pressure received from the differential mechanism evenly about the annular wall. The annular wall is partially deformed into the tubular member thereby forming a mechanical connection between the tubular member and the annular wall with the tubular member being immovably associated with the annular wall through the mechanical connection. 
   A method of the present invention is operable to form the aforementioned differential housing. The method includes the step of disposing the tubular member having the outer surface on a mandrel. The tubular member in the exemplary embodiment of the inventive method is a ring that enhances the strength of the finished differential housing. The method also includes the step of cold-working the annular wall, i.e. a housing preform, by flow-forming the annular wall into conformance with the mandrel and with the outer surface of the tubular member after said disposing step. The tubular member is disposed in situ as the housing preform is cold-worked to produce the finished differential housing. 
   One of the advantages of the present invention provides for an improved design of the differential housing that overcomes the problems associated with previously known differential housings by improving durability characteristics of the differential housing. 
   Another advantage of the present invention provides for an improved design of the differential housing that enhances the strength of the differential housing by increasing the wall thickness at a high-stress location. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a cross-sectional view of a finished differential housing according to an exemplary embodiment of the present invention; and 
       FIG. 2  is an exploded view relating to the method of manufacturing the finished differential housing according to the exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 1 and 2 , a differential assembly, generally shown at  10  of the present invention is designed for supporting a differential mechanism retained by a differential housing, generally shown at  12 . The differential mechanism is retained by the differential housing  12  and includes a pin  14  disposed in the differential housing  12 , a pair of beveled gears  16 ,  18  supported by the pin  14 , a pair of pinion or side gears  20 ,  22  presenting meshing or driving engagement with the beveled gears  16 ,  18  for transmitting torque from a transmission of a vehicle (not shown) to axle shafts (not shown) of the vehicle. The differential housing  12  is defined by an annular wall  24  exposed to inner surface  26  circumscribing an axis A for retaining the differential mechanism. 
   A tubular member, generally shown at  30  in  FIG. 2  extends between the annular wall  24  and the differential mechanism to partially encapsulate the differential mechanism. The tubular member  30  present spherical configuration and is truncated to two opposite sides, such as, for example, a first axial side  32  and a second axial side  34 . The tubular member  30  receives pressure from the differential mechanism, in particular from the pin  14  and the beveled gears  16 ,  18 , and distributes the evenly about the annular wall  24 . The annular wall  24  and the tubular member are mechanically interconnected one with another. Preferably, the annular wall  24  is partially deformed into the tubular member  30  with the tubular member  30  being immovably associated with the annular wall  24  to prevent axial movement of the tubular member  30  relative the annular wall  24 . 
   Alluding to the above, the mechanical connection is further defined by at least one radial discontinuity defined by a first notch, which is shown in phantom at  36  on the first axial side  32  of the tubular member  30 . The mechanical connection is further defined by at least one radial discontinuity defined by a second notch  38  formed on the second axial side  34 . Alternatively, the mechanical connection may include dimples  40 ,  42  or depressions defined in the outer surface  39  of the tubular member  30 . The dimples  40 ,  42  and/or the notches  36 ,  38  may include different configurations and are not intended to limit the scope of the present invention. Material from the housing preform  23  can be urged into the dimples  40 ,  42  during the flow forming process. 
   The first notch  36  and the second notch  38  are radially spaced 180 degrees from one another and extend axially away from one another. As will be discussed further below in details at least one portion, generally indicated at  46  of the annular wall  24  is deformed into at least one of the notches  36 ,  38  to mechanically interconnect the tubular member  30  with the annular wall  24 . A seat, generally indicated at  48 , is defined in the annular wall  24 . The seat  48  presents a configuration complementary to the shape of the tubular member  30  to engage the tubular member  30  and prevent axial movement of the tubular member  30  relative the annular wall  24 . A lid  50  is attached to the annular wall  24  thereby forming an enclosure, generally indicated at  52 , within the annular wall  24  for retaining the differential mechanism. 
   Alluding to the above, a method of the present invention includes the steps of disposing the tubular member  30  on a mandrel  60  and cold-working a housing preform  62  defining an inner surface  64  by flow-forming the inner surface  64  of the housing preform  62  into conformance with the mandrel  60  and the outer surface  39  of the tubular member  30  after the disposing step. In operation of the exemplary embodiment of the invention, the tubular member  30  is received by the mandrel  60 , the mandrel  60  is inserted in an aperture  66  defined by the tubular member  30 , and the housing preform  62  is placed over the mandrel  60  and the tubular member  30 . A flow-forming tool, similar to the tooling described and shown in the U.S. Pat. No. 6,061,907 to Victoria et al., works the housing preform  62  to produce an otherwise finished differential housing  12 . The U.S. Pat. No. 6,061,907 to Victoria et al., is hereby incorporated by reference to the present application. Supplementary operations such drilling or surface finishing can be performed on the housing  12  after the flow-forming process. 
   Alluding to the above, the cold-working step of the method of the invention can also be defined as forming the annular wall  24  or the housing from the housing preform  62  with the tubular member  30  disposed in situ with respect to the annular wall  24 . The flow-forming process is performed on the housing preform  62  while the housing preform  62  covers or encloses the tubular member  30 . After the flow-forming process, the housing preform  62  can be considered as substantially finished housing  12  with the tubular member  30  fixed relative to the substantially finished housing  12 . 
   The method of the invention can also include the step of forming at least one radial discontinuity defined by the first notch  36  on the outer surface  39  of the tubular member  30  before the cold-working step. At any point along the axis A of the tubular member  30 , the outer surface  39  defines a circle in a plane transverse to the axis A. Alluding to the above, the radial discontinuity or the first notch  36  is a portion of the outer surface  39  that breaks the circular shape of the outer surface  39  in a plane transverse to the axis A. The cold-working step of the method of the invention can also include the step of urging the portion of the housing preform  62  into the at least one of the first notch  36  and the second notch  38 . 
   During the flow-forming process, material of the housing preform  62  is moved or shift as desired. Movement of the material of the housing preform  62  can be desired to increase the thickness  68  of the annular wall  24  in particular portions of the finished housing  12 . In the exemplary embodiment of the invention, material of the housing preform  62  is moved or urged by tooling to occupy the space defined by the first radial discontinuity or the first notch  36 . As a result, the tubular member  30  is fixedly associated with housing  12  after the flow forming process. The forming of the radial discontinuity step of the method of the invention can also include the step of disposing the first radial discontinuity or the first notch  36  on the first axial side of the tubular member  30  and the second radial discontinuity or the second notch  38  on the second axial side of the tubular member  30 . The tubular member  30  can have as many radial discontinuities as desired. The otherwise smooth outer surface  39  of the tubular member  30  can define numerous radial discontinuities, appearing non-smooth. As the number of radial discontinuities increases, movement between the tubular member  30  and the housing preform  62  is less likely. 
   Corresponding portions of the housing preform  62  are urged into each radial discontinuity or the first and second notches  36 ,  38 , respectively, during the flow-forming process. In the exemplary embodiment of the invention, the tubular member  30  is substantially spherical and truncated on opposite sides  32 ,  34 . Also, the first and second notches  36 ,  38  extend axially away from one another. At least one portion  46  of the housing preform  62  is disposed in at least one of the first and second notches  36 ,  38 . In alternative embodiments of the invention, the radial discontinuities are formed as one or more dimples, such as dimples  40 ,  42 . 
   As result, the tubular member  30  would be immovably associated with the finished housing  12  after the flow forming process. In the exemplary embodiment of the invention, the finished housing  12  is assembled to other components to form the inventive differential assembly  10 . After the finished housing  12  has been formed from the housing preform  62  with the tubular member  30  disposed in situ, a longitudinal aperture  70  is formed and finished. The longitudinal aperture  70  receives one of the axle shafts (not shown), which defines splines thereby matingly engaging splines  72  defined by the gear  20 . Also, a transverse aperture  74  is formed and finished. The transverse aperture  74  passes through the finished housing  12  and the tubular member  30 . The pin  14  is received in the transverse aperture  74 . The lid  50  is fixedly associated with the finished housing  12  after the gears  16 ,  18 ,  20 ,  22  have been assembled. The lid  50  defines a second longitudinal aperture  76  which receives one of the axle shafts. The other axle shaft (not shown) extends through defines splines which matingly engage splines  78  defined by the gear  22 . 
   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.