Abstract:
A torque vectoring differential includes a pair of planetary gear assemblies having a common planet gear carrier which is driven from the output of a transmission. Each of the planetary gear assemblies include a ring gear that may be individually and selectively grounded (braked) to a stationary housing by a friction brake and a sun gear that is coupled through an axle to a respective drive wheel. Selective activation of the brakes controls the distribution, i.e., vectoring, of torque to each of the drive wheels. Each planetary gear assembly includes elongated planet gears which mesh not only with their respective sun and ring gears but also with the planet gears of the other planetary gear assembly.

Description:
FIELD 
       [0001]    The present disclosure relates to differentials for motor vehicles and more particularly to differentials for motor vehicles having integrated torque vectoring. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0003]    In recent years, motor vehicles, especially passenger cars and light trucks, have been the subject of intense effort to improve handling performance in both routine and emergency driving conditions. While the emphasis has been on the latter, it has been accompanied by the realization that aggressive, active control systems can prevent a routine or substantially routine driving condition from escalating into an emergency situation. 
         [0004]    Accordingly, traction control and torque distribution powertrain systems have been developed concurrently with anti-lock brake systems (ABS) and other vehicular safety systems. Generally speaking, traction control and torque distribution powertrain systems encompass controlled mechanical, electro-mechanical or hydro-mechanical systems which control both the generation of torque by controlling operational aspects of the prime mover or the distribution of torque to the two or four driving wheels of the vehicle by controlling transmission, transfer case and differential components. 
       SUMMARY 
       [0005]    The present invention provides a differential for a motor vehicle powertrain having integrated torque vectoring. The differential of the present invention provides vehicle handling enhancement in vehicle systems often referred to as stability control systems. The differential of the present invention includes a pair of side-by-side planetary gear assemblies having a common planet gear carrier which is driven by the output of a transmission. Each of the planetary gear assemblies include a ring gear that may be individually and selectively grounded (braked) to a stationary differential housing by a respective friction brake and a sun gear that is coupled through an axle to a respective drive wheel. Each planetary gear assembly includes elongated planet gears which mesh not only with their respective sun and ring gears but also with the planet gears of the other planetary gear assembly. Selective activation of the brakes controls the distribution, i.e., vectoring, of torque to each of the drive wheels. The differential also includes an optional limited slip clutch disposed between a sun gear and a ring gear of one of the planetary gear assemblies. 
         [0006]    Thus it is an aspect of the present invention to provide a torque vectoring differential having a pair of planetary gear assemblies disposed side-by-side. 
         [0007]    It is a further aspect of the present invention to provide a torque vectoring differential having a pair of independently operable brakes operably disposed between a respective ring gear of the pair of planetary gear assemblies and ground. 
         [0008]    It is a still further aspect of the present invention to provide a torque vectoring differential having elongated planet gears which mesh not only with their associated sun and ring gears but also with the planet gears of the other planetary gear assembly. 
         [0009]    It is a still further aspect of the present invention to provide a torque vectoring differential having an optional clutch disposed between the ring and sun gears of a planetary gear assembly for limiting slip of the differential. 
         [0010]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0011]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0012]      FIG. 1  is a lever diagram of a torque vectoring differential according to the present invention; 
           [0013]      FIG. 2  is a diagrammatic view of a torque vectoring differential according to the present invention and associated components of a motor vehicle; and 
           [0014]      FIG. 3  is a side elevational view of the planetary gear assemblies of a torque vectoring differential according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0016]    With reference now to  FIG. 1 , a torque vectoring differential for a motor vehicle according to the present invention is illustrated in a lever diagram and designated by the reference number  10 . A lever diagram is a schematic representation of the components of a device such as a differential or an automatic transmission wherein a planetary gear assembly is represented by a vertical bar or lever and the components of the planetary gear assembly such as the sun gear, the planet gear carrier and the ring gear are represented by nodes. The relative lengths of the vertical bars between the nodes represent the ratios between the components. Mechanical couplings or interconnections between the nodes such as shafts or quills are represented by horizontal lines and torque transmitting devices such as friction clutches and brakes are represented by interleaved or nested fingers. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper No. 810102 entitled, “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising which is fully incorporated herein by reference. 
         [0017]    The torque vectoring differential  10  includes an input shaft  12 , a first or left output half shaft or axle  14 , a second or right output half shaft or axle  16  and a stationary housing  18  which is referred to in reference to  FIG. 1  as ground. The single five node lever  20  represents two planetary gear assemblies  30  and  50 . A first or left planetary gear assembly  30  includes a first node  32  which is connected to and drives the first or left output half shaft or axle  14 , a second node  34  which is connected to and driven by the input shaft  12  and a third node  36 . A second or right planetary gear assembly  50  includes a first node  52  which is connected to and drives the second or right output half shaft or axle  16 , a second node  54  which is common with the second node  34  of the first planetary gear assembly  30  and which is connected to and driven by the input shaft  12  and a third node  56 . 
         [0018]    The third node  36  of the first or left planetary gear assembly  30  is coupled to one side, for example an input side, of a first or left friction brake assembly  38  and the other side of the first or left friction brake assembly  38  is connected to ground  18 . The third node  56  of the second or right planetary gear assembly  50  is coupled to one side, for example an input side, of a second or right friction brake assembly  58  and the other side of the second or right friction brake assembly  58  is connected to ground  18 . 
         [0019]    Referring now to  FIGS. 2 and 3 , the torque vectoring differential  10  includes the input shaft  12  which is connected to and drives a common planet gear carrier  34 ,  54 . The first or left output half shaft or axle  14  is coupled to and driven by a first or left sun gear  32  of the first of left planetary gear assembly  30  and the second or right output half shaft or axle  16  is coupled to and driven by a second or right sun gear  52  of the second or right planetary gear assembly  50 . The first or left planetary gear assembly  30  also includes a first or left ring gear  36  which is connected to the input side of the first or left friction brake assembly  38  having a plurality of input friction plates or discs  40 . Interleaved with the plurality of input plates or discs  40  and connected to ground or the housing  18  are a plurality of stationary or ground plates or discs  42 . A first or left operator or actuator  44  is disposed in proximate, operable relationship to the interleaved plates or discs  40  and  42 . The first of left operator or actuator  44  is preferably hydraulic but may be electric or pneumatic. 
         [0020]    The second or right planetary gear assembly  50  also includes a second or right ring gear  56  which is connected to the input side of the second friction brake assembly  58  having a plurality of input friction plates or discs  60 . Interleaved with the plurality of input plates or discs  60  and connected to ground or the housing  18  are a plurality of stationary or ground plates or discs  62 . A second or right operator or actuator  64  is disposed in proximate, operable relationship to the interleaved plates or discs  60  and  62 . The second or right operator or actuator  64  is also preferably hydraulic but may be electric or pneumatic. 
         [0021]    Alternatively, certain connections to the first planetary gear assembly  30  and the second planetary gear assembly  50  may be reversed, with first or left output half shaft or axle  14  connected to the first or left ring gear  36 , the first or left friction brake assembly  38  connected to the first or left sun gear  32 , the second or right output half shaft or axle  16  connected to the second or right ring gear  56  and the second friction brake assembly  58  connected to the second or right sun gear  52 . 
         [0022]    Disposed within the common planet gear carrier  34 ,  54  are a first plurality, typically three, of left planet gears  46  which are rotatably disposed on a like plurality of stub shafts  48 . If desired, needle or roller bearing assemblies (not illustrated) may be located between the planet gears  46  and the stub shafts  48  to reduce friction and spin losses. The first plurality of left planet gears  46  are in constant mesh with the first or left sun gear  32  and the first or left ring gear  36 . The first plurality of left planet gears  46  are elongated as best illustrated in  FIG. 3  and are also on constant mesh with a respective one of a second plurality of right planet gears  66  which are also elongated and rotatably disposed on stub shafts  68  in the common carrier  34 ,  54 . Again. If desired, needle or roller bearings (not illustrated) may be located between the planet gears  66  and the stub shafts  68 . In addition to meshing with the first plurality of left planet gears  46 , the second plurality of right planet gears  66  are in constant mesh with the second or right sun gear  52  and the second or right ring gear  56 . 
         [0023]    It should be appreciated and understood that the various corresponding components of the first or left planetary gear assembly  30  and the second or right planetary gear assembly  50 , that is the sun gears  32  and  52 , the planet gears  46  and  66  and the ring gears  36  and  56  are the identical size and include the same size, pitch and number of teeth such that an even and equal torque split and delivery to the left and right axles or half shafts  14  and  16  occurs when the left and right friction brake assemblies  38  and  58  are fully released. 
         [0024]    Several associated components cooperate with the torque vectoring differential  10  and are illustrated in  FIG. 2 . Disposed in sensing relationship with the first or left output half shaft or axle  14  is a first or left speed sensor assembly  72  and similarly disposed with the second or right output half shaft or axle  16  is a second or right speed sensor assembly  74 . The speed of the input shaft  12  will generally be provided by an output speed sensor in the vehicle transmission (not illustrated) but, if desired, a dedicated input speed sensor assembly  76  may be disposed in sensing relationship with the input shaft  12 . Preferably, the speed sensor assemblies  72 ,  74  and  76  are Hall effect sensors although other sensor types such as optical or variable reluctance sensors may be utilized. The outputs of the speed sensor assemblies  72 ,  74  and  76  are provided to a control module  80  such as a chassis control module (CCM) or similar device. The control module  80  typically includes, for example, input devices, one or more microprocessors, storage, look up tables and output devices that control the first or left brake operator or actuator  44 , the second or right brake operator or actuator  64  and a limited slip clutch operator  96  as described directly below. 
         [0025]    The torque vectoring differential  10  also optionally includes a controlled or modulating limited slip clutch  90 . The limited slip clutch  90  includes a first plurality of friction plates or discs  92  that are connected to the first or left ring gear  36  of the first or left planetary gear assembly  30  and a second plurality of friction plates or discs  94  are interleaved with the first plurality of plates or discs  92  and connected to the first or left sun gear  32  of the first or left planetary gear assembly  30  (and/or the first or left output shaft  14 ). The limited slip clutch  90  also includes a third hydraulic, electric or pneumatic operator or actuator  96  which is preferably under the control of the control module  80 . 
         [0026]    Briefly, in operation, the brake assemblies  38  and  58  of the torque vectoring differential  10  may be partially or fully engaged to partially or fully inhibit differentiation by the pair of planetary gear assemblies  30  and  50  and direct more or less torque to one or the other of the axles or half shafts  14  and  16 . The limited slip clutch  90  may be partially of fully engaged to partially or fully inhibit differentiation by the pair of planetary gear assemblies  30  and  50 . 
         [0027]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.