Abstract:
A planetary differential including a differential case rotatable about an axis and a method of manufacturing thereof. The differential case includes a cover, a housing, an annulus gear, and a ring gear. The differential case defines a differential cavity having a clutch cavity and a planet cavity separated by a retainer plate coupled to the housing. The modular nature of this system allows both open and torque biasing constructions in the same packaging space. The method of manufacturing the differential includes the steps of coupling a retainer plate to the housing between the clutch cavity and the axial opening, placing a planetary gear set in the planetary cavity, and fixing the housing to the annulus gear and ring gear.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is generally directed to a planetary differential and, more particularly, to a planetary differential that is readily configured as either a torque biasing or an open differential. An additional feature of the planetary differential is a defined torque transfer path that excludes the differential case housing and/or cover so as to permit the use of a lighter weight planetary differential and a greater variety of manufacturing techniques. 
     Numerous types and configurations of differentials are used in the drivelines of vehicles for transferring torque between rotatable elements such as shafts. These types include an axle differential wherein a drive shaft rotates a hypoid or spiral bevel pinion gear, which rotates a like ring gear fixed to a case that houses differential gears coupled to drive either an output axle or half-shafts. Axle differentials may be of the torque biasing or open type. In torque biasing axle differentials, the amount of torque transferred to each axle or half-shaft is controllable by a torque biasing mechanism such as a clutch. In open differentials, the axle or half-shafts are free to rotate relative to one another. Torque biasing differentials are commonly used to counter slip of a driven wheel as well as in torque steering and other applications. 
     Commonly available differentials have various differential case configurations and non-interchangeable operative components depending on whether the differential is a torque biasing or an open type. As a result, if the vehicle manufacturer desires to provide torque biasing and open differential options for a single vehicle platform, the vehicle frame and other components are commonly modified to accommodate the specific differential configuration. 
     Further, in conventional designs, the differential case is in the torque transfer path between the external ring gear and the differential gearing, e.g., planetary or pinion differential. As a result, the differential case is subjected to torque loading during operation. This differential case loading requires a robust differential case that negatively impacts the overall weight of the differential and limits the processes and material that may be used during manufacture. 
     SUMMARY OF THE INVENTION 
     The planetary differential of the present invention addresses the above and other deficiencies in the art. The planetary differential includes a differential case rotatable about an axis. The differential case includes a cover, a housing, an annulus gear, and a ring gear. The differential case defines a differential cavity having a clutch cavity and a planetary cavity. The planetary differential further includes a retainer plate coupled to the housing to separate the clutch and planetary cavities. 
     The present invention is further directed to a method of manufacturing a planetary differential having a differential case with a cover and a housing, an annulus gear, and a ring gear. The differential case again has a clutch cavity and axial opening defined by the housing and a planetary cavity. The method includes the steps of coupling a retainer plate to the housing between the clutch cavity and the axial opening, placing a planetary gear set in the planetary cavity, and fastening the housing to either the annulus gear or the ring gear. 
     Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which: 
         FIG. 1  is a sectional view of the differential according to the present invention configured to function as a torque biasing planetary differential; 
         FIG. 2  is a sectional view of the differential according to the present invention configured to function as an open planetary differential; 
         FIG. 3  is a sectional view of the differential case shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a sectional view of a second embodiment of the differential case; 
         FIG. 5  is a sectional view of a third embodiment of the differential case; 
         FIG. 6  is a sectional view of a fourth embodiment of the differential case; and 
         FIG. 7  is a sectional view of a fifth embodiment of the differential case. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is generally directed to a planetary differential  10  for communicating torque from a rotary drive, such as the illustrated hypoid or spiral bevel pinion gear  12 , to first and second output half-shafts  14  and  16 . The differential  10  includes a stationary enclosure  18  supported by the vehicle frame in a conventional manner. The first and second output shafts  14  and  16  are supported for rotation about an axis  22  within the stationary enclosure  18 . The differential  10  further includes a differential case  13  generally disposed within the enclosure  18  for rotation about the axis  22 . 
     The differential case  13  is shown to include a cover  30 , a housing  32 , an annulus gear  34 , and a ring gear  36  meshed with the like pinion gear  12  to rotatably drive the differential case  13 . By this configuration, the differential case  13  generally forms a differential cavity  40  ( FIG. 3 ). The housing  32  includes an axial opening  42 , a clutch cavity  44  within the differential cavity  40  and a threaded segment  46  between the axial opening  42  and clutch cavity  44 . The differential cavity  40  also includes a planetary cavity  50  that accommodates a planetary gear set as hereinafter described. A retainer plate  54  ( FIGS. 1 and 2 ) includes threads  56  configured to engage the threaded segment  46  and couple the retainer plate to the housing between the clutch cavity  44  and planetary cavity  50 . The threaded engagement between the retainer plate  54  and housing  32  permits adjustment of the axial position relative to the clutch cavity  44 . The retainer plate  54  resists axial forces from the planetary gear set, particularly the planetary carrier, such that the planetary differential  10  may be selectively configured to function as a torque biasing differential or an open differential as described in greater detail below. 
     The aforementioned planetary gear set, indicated by reference numeral  60  ( FIGS. 1 and 2 ), includes a planetary carrier  62  having a pedestaled flange  64  and an axial hub  66 , inner and outer planetary gears  68  and  70 , respectively, which are coupled to rotate with and relative to the planetary carrier  62  via planet shafts  72 . The planetary gear set  60  further includes a sun gear  74  having an internally splined bore  76  that receives a cooperatively splined end on the first output shaft  14  to rotationally couple the first output shaft to the sun gear. Similarly, the planetary carrier  62  includes an internally splined bore  78  to rotationally drive the second output shaft  16 . As with conventional planetary differentials, the outer planet gears  70  are meshed with the annulus gear  34  and the inner planet gear  68 . The inner planet gears  68  are in turn meshed with the sun gear  74 . For completeness, it is noted that the annulus gear  34  preferably has twice the number of teeth as the sun gear  74  to ensure that the rotational velocity of the sun gear and planetary carrier  62  at the axle shafts is equal but opposite when the associated vehicle traverses a curve. 
     The planetary differential  10  is further illustrated in  FIG. 1  to include a torque biasing assembly  84  including a clutch pack  86  and a clutch actuator  88 . As noted above, the planetary differential  10  may be configured to function as either a torque biasing differential or an open differential. In the latter case, the clutch pack  86  and clutch actuator  88  are omitted as shown in  FIG. 2 . Where torque biasing is desired, the clutch pack  86  and actuator  88  are included as shown in  FIG. 1 . 
     To facilitate these dual applications, the differential housing  32  may include suitable assembly holes to accommodate actuating pistons passing between the clutch pack  86  and actuator  88  in a manner generally known in the art. For completeness, it is noted that the torque biasing assembly will generally also include suitable bearings. Further, while a variety of clutch packs and actuators generally known in the art may be suitable for the planetary differential of the present invention, the illustrated embodiment of the clutch pack  86  includes interleaved first and second clutch plates  92  and  94 , respectively, and an actively controllable actuator capable of biasing torque between the first and second output shafts without a predetermined magnitude of differential movement between the planetary carrier  62  and housing  32 . In the illustrated embodiment, the first clutch plates  92  rotate with the housing  32  and the second clutch plates  94  rotate with the planetary carrier hub  66 . To facilitate the rotational coupling between these elements, the hub  66  and housing  32  may be provided with external and internal splines, such as the splines  96  shown in  FIG. 3 . The retainer plate  54 , in addition to being axially adjustable to accommodate tolerance variations in the clutch pack and planetary carrier, also functions as a reactor plate for the clutch pack when the planetary differential is configured to function as a torque biasing differential. 
     In addition to the configuration described above facilitating the modularity of the planetary differential, that is, its ready conversion from or to a torque biasing differential or an open differential, the configuration of the differential case  13  facilitates assembly of the differential and reduces the necessary robustness and associated costs of the cover  30  and housing  32 . Robustness and cost benefits are achieved in part by removing the cover  30  and housing  32  from the torque path thereby increasing manufacturing options. 
       FIGS. 3–7  illustrate alternative configurations of the differential case  13 , each designed to provide modularity, assembly, and/or manufacturing benefits. More particularly, as noted above, the differential case  13  generally includes the cover  30 , housing  32 , annulus gear  34 , and hypoid or spiral bevel ring gear  36 . While the ring gear  36  is illustrated in the attached drawings and specifically referred to herein as a hypoid or spiral bevel gear, the invention may be used with other ring gear configurations including helical or spur gears. As shown in  FIGS. 3–7 , each of these components may be manufactured separately ( FIG. 4 ) or certain components may be integrally formed or consolidated with one another (FIGS.  3  and  5 – 7 ). The configuration of each of these embodiments and preferred assembly sequences for the planetary differential  10  will now be described with reference to the respective figures. Notwithstanding the illustrative examples provided below, those skilled in the art will appreciate that modifications to the assembly sequences and the specific embodiments may be made without departing from the spirit and scope of the invention. 
     As shown in  FIG. 4 , each of the cover  30 , housing  32 , annulus gear  34 , and hypoid or spiral bevel ring gear  36  may be formed separately such that, when assembled, the case  13  defines the differential cavity  40  with the clutch cavity  44  and planetary cavity  50 . The annulus gear  34  is rigidly connected to the torque transferring ring gear  36 . As a result, the cover  30  and housing  32  are removed from the torque transfer path to reduce the load requirements and cost of these components as well as permit use of alternative manufacturing techniques, such as orbital forging/forming and flow forming. Similar manufacturing and cost benefits are realized from the embodiments shown in FIGS.  3  and  5 – 7  as discussed below. With respect to the embodiment shown in  FIG. 3 , torque is transmitted from the hypoid or spiral bevel pinion gear  12  ( FIG. 1 ) to the mating like ring gear  36 , to the annulus gear  34 , and then to the planetary gear set  60  and first and second output shafts  14  and  16 . By this configuration, the cover  30  and housing  32  are not required to accommodate significant torque loads. Rather, the cover and housing support the internal components of the differential, enhance lubrication, support the torque biasing actuator, and resist the axial and separating loads imparted by the gearing as well as any biasing torque and axial load imparted by the biasing device. 
     The configuration of the differential case  13  also facilitates assembly of the planetary differential  10 . With respect to the four-piece differential case embodiment illustrated in  FIG. 4 , assembly of the planetary differential  10  includes the steps of laser welding the cover  30  to the annulus gear  34  to define an annulus/cover assembly and disposing the planetary gear set  60  within the planetary cavity  50 . The clutch pack (if a torque biasing differential is desired) may be disposed within the clutch cavity  44  defined by the housing  32  and the retainer plate  54  is secured to the housing. The assembled housing is then aligned with and laser welded to the annulus/cover assembly. The resulting housing/annulus/cover assembly is aligned, press fit and laser welded to the hypoid or spiral bevel ring gear. Those skilled in the art will appreciate that while a preferred assembly process has been described with regard to the embodiment shown in  FIG. 4 , other processes may be used. For example, the sequence of the welding of the hypoid or spiral bevel ring gear to the annulus gear may occur at any time during assembly. Further, while the components of the differential case are preferably laser welded to one another in order to facilitate assembly, other welding or fastening techniques (such as friction welding, splined couplings, or press fit engagements) may be used to rotationally couple the components. 
     The three-piece differential case embodiment shown in  FIGS. 1 and 2  is also illustrated in  FIG. 3 . In this embodiment, the annulus gear  34  is integral with the hypoid or spiral bevel ring gear  36  to form an annulus/ring gear assembly. The housing  32  is welded to the annulus/ring gear assembly to form a housing/annulus/ring gear assembly and, if desired, the clutch pack is disposed in the clutch cavity  44 . The planetary gear set  60  is then disposed in the planet cavity  50  and the cover  30  is aligned, press fit, and welded to the ring gear/housing assembly. This embodiment again isolates the cover  30  and housing  32  from the torque transfer path. 
     In the three-piece differential case embodiment illustrated in  FIG. 5 , the cover  30  is formed integral with the annulus gear  34  to form a cover/annulus assembly that further defines the planetary cavity  50 . The planetary gear set  60  is then disposed in the planetary cavity and, if desired, the clutch pack is disposed in the clutch cavity  44  of the housing  32 . The components are then aligned and press fit together whereupon the cover/annulus assembly and housing  32  are welded to the hypoid or spiral bevel ring gear  36 . In this embodiment, the cover  30 , being integral with the annulus gear  34 , may be subjected to torque transfer loading. However, the housing  32  is again isolated from the torque transfer path. 
     In the three-piece planetary differential embodiment illustrated in  FIG. 6 , the housing  32  is formed integral with the annulus gear  34  to form a housing/annulus assembly which is welded to the hypoid or spiral bevel ring gear  36 . The internal components, including the planetary gear set  60  and torque biasing assembly  84  (if desired), are assembled and the cover  30  and housing/annulus assembly are welded to the hypoid or spiral bevel ring gear  36 . In this embodiment, the housing  32 , being integral with the annulus gear  34 , may be subjected to torque transfer loading. However, the cover  30  is again isolated from the torque transfer path. 
     In the two-piece differential embodiment illustrated in  FIG. 7 , the cover  30  is formed integral with the annulus gear  34  and the hypoid or spiral bevel ring gear  36  to form a cover/annulus/gear assembly. The components of the planetary gear set  60  and, if desired, torque biasing assembly  84 , are then disposed in the appropriate cavities and the housing  32  is welded to the cover/annulus/gear assembly. In this embodiment, the cover  30 , being integral with the annulus gear  34  and ring gear  36 , may be subjected to torque transfer loading. However, the housing  32  is again isolated from the torque transfer path. 
     As generally indicated above, the configuration of the differential case  13  provides numerous operational, assembly, and manufacturing advantages over prior art differentials. Conventionally, differential cases are cast iron components with thick sections to compensate for porosity. Casting precision is limited by numerous factors, including material flow and mold shift, and differential cases commonly require extensive machining. The planetary differential  10  of the present invention provides a torque transfer path that minimizes the load requirements of selected components of the differential case  13 , e.g., cover  30  and housing  32 , and permits the use of more efficient and precise manufacturing processes such as flow and orbital forming. In these processes only a small region of the component is plastically deformed at any instant thereby allowing the forces applied by the forming tool to be localized, resulting in thinner and lighter sections, sharper radii and tighter tolerances compared to conventional casting or forging processes. Further, flow forming allows variable wall thicknesses to be produced and more effectively places material where it is needed for strength and stiffness. Other sheet shaping processes, such as stamping, generally do not provide the desired thickness variation. Orbital forming reduces forming loads compared to conventional forging, which may be limited by press load capacity, provides greater manufacturing precision, and reduces machining for certain defined components of the differential case such as internal and external teeth, splines and lugs. In addition, removal of the cover  30  and/or housing  32  from the torque transfer path as described above permits the use of cold formable materials (such as low carbon steel), again reducing manufacturing costs in workpiece, tooling and, with the elimination of high temperatures, processing as compared to conventional hot forging. 
     The covers  30  shown in  FIGS. 3 ,  4 , and  6  and the consolidated cover/annulus gear  30 / 34  in  FIG. 5  are excellent applications of the flow forming process. The planetary carrier  62  shown in  FIGS. 1 ,  2 , and  3  can be produced cost effectively by combining the orbital process to produce a preform with a subsequent flow forming processes to sharpen detail. This is also true for the housing  32  shown in  FIGS. 3 ,  4 ,  5  and  7 , and the consolidated housing/annulus gear  32 / 34  shown in  FIG. 6 . Orbital forming is well suited to the production of the consolidated cover/annulus gear/ring gear  30 / 34 / 36  shown in  FIG. 7 . 
     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.