Abstract:
A transmission for a vehicle including a hydrostatic regenerative braking system includes a first rotatable shaft having a first end adapted to be driven by a first prime mover and a second end adapted to be coupled to a vehicle driveline. A second shaft selectively drives the first shaft and is adapted to drive a hydraulic pump of a second prime mover. A planetary gearset includes a first member restricted from rotation, a second member and a third member. A transfer mechanism includes a first sprocket fixed for rotation with the second member, a second sprocket fixed for rotation with the input shaft and a flexible member interconnecting the first and second sprockets. A clutch transfers torque between the third member and the first shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/633,077 filed Dec. 8, 2009 which claims the benefit of U.S. Provisional Application No. 61/121,267, filed on Dec. 10, 2008. The entire disclosure of each of the above applications is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to hydrostatic regenerative braking for efficient use of energy of a vehicle. More particularly, a transmission for coordinating the flow of power between a prime mover, a hydraulic energy storage system and the vehicle wheels is discussed. 
     Regenerative drive systems including hybrid hydraulic arrangements have been applied to motor vehicles in the past. While conventional vehicle braking systems typically convert a vehicle&#39;s kinetic energy into heat energy, hydrostatic regenerative braking systems convert a moving vehicle&#39;s kinetic energy into stored hydraulic energy. The hydraulic energy is typically stored in an accumulator for later use to propel the vehicle. At least one hybrid hydraulic drive system includes a hydraulic pump/motor selectively operable to transfer energy from the vehicle driveline to a hydraulic storage device, such as during a braking event, or transfer energy from the hydraulic storage device to the driveline, such as during vehicle acceleration. When the hybrid hydraulic system stores power from the driveline, the hydraulic pump/motor acts as a pump to provide pressurized fluid to the accumulator. When the hybrid hydraulic system transfers power to the driveline, the hydraulic pump/motor acts as a motor driven by the energy stored in the accumulator. 
     Some vehicles include transmissions for transferring power between the driveline and the hydraulic storage device. At least one transmission cooperates with a hydrostatic regenerative braking system and includes a two gear design with a clutch positioned at an output shaft of the transmission. While this design may provide some benefit, it requires a relatively large diameter driven gear to provide a useful gear reduction ratio. Large packaging volume requirements and high weight are associated with this transmission. Due to the clutch being positioned downstream of the gear reduction mechanism, the clutch is required to transmit a torque approximately three times greater than the pump torque. A relatively large clutch is required to transfer the torque. The size and weight of the transmission are accordingly increased. Furthermore, with the two gear design, only one output drive ratio is available. To provide different versions with different ratios, new sets of gears for each ratio must be provided. Accordingly, a need exists in the art for an improved hydrostatic regenerative braking transmission. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A transmission for a vehicle including a driveline powered by first and second prime movers and a hydrostatic regenerative braking system for transferring energy from the driveline to the second prime mover is provided. The transmission includes a first rotatable shaft having a first end adapted to be driven by the first prime mover and a second end adapted to be coupled to the driveline. A second shaft selectively drives the first shaft and is adapted to drive a hydraulic pump/motor of the second prime mover. A planetary gearset includes a first member restricted from rotation, a second member and a third member. A transfer mechanism includes a first sprocket fixed for rotation with the second member, a second sprocket fixed for rotation with the second shaft and a flexible member interconnecting the first and second sprockets. A clutch transfers torque between the third member and the first shaft. 
     In another form, a transmission for a hydraulic hybrid vehicle includes a driveline powered by first and second prime movers. The vehicle also includes a hydrostatic regenerative braking system for transferring energy to the second prime mover. The transmission includes a through shaft having a first end adapted to be driven by the first prime mover and a second end adapted to be coupled to the driveline. An input shaft is selectively drivingly coupled to the through shaft and is adapted to drive a hydraulic pump/motor of the second prime mover. A planetary gearset includes a first member restricted from rotation, a second member fixed for rotation with the through shaft and a third member. A transfer mechanism includes a first sprocket, a second sprocket fixed for rotation with the input shaft and a flexible member drivingly interconnecting the first and second sprockets. A clutch is operable to transfer torque between the third member of the planetary gearset and the first sprocket. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic depicting a transmission of the present disclosure for use in an exemplary hydraulic hybrid vehicle; 
         FIG. 2  is a schematic depicting the transmission of the present invention in cooperation with a hydraulic energy storage system; 
         FIG. 3  is a sectional view of the transmission; and 
         FIG. 4  is a schematic depicting an alternate transmission. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     With reference to  FIG. 1  of the drawings, a parallel hydraulic hybrid powertrain  10  for a hybrid motor vehicle is shown to include an internal combustion engine  12  and a transmission  14  arranged to transfer motive power (i.e., drive torque) from engine  12  to a driveline  18 . In the particular arrangement shown, driveline  18  is the rear driveline and includes a pair of rear wheels  22  connected to a rear differential unit  24  associated with a rear axle assembly  26 . A rear prop shaft  28  interconnects rear differential  24  to a through shaft  30  of transmission  14 . A hydrostatic drive input shaft  32  of transmission  14  is drivingly coupled to an energy storage system  34 . A pair of front wheels  36  are rotatably supported on a front axle  38 . Powertrain  10  is also associated with a powertrain control system  42  generally shown to include an array of vehicle sensors  44 , a battery  46  and a controller  48 . As will be detailed, controller  48  is operable, among other things, to control actuation of power transfer between engine  12 , energy storage system  34  and driven wheels  22 . 
     Referring primarily to  FIGS. 2 and 3 , the components of transmission  14  and energy storage system  34  are illustrated in sufficient detail to provide a clear understanding of their construction and operation. To this end, transmission  14  includes a housing  54  constructed from a first shell  56 , a second shell  58  and a third shell  60  interconnected to one another along their periphery. Through shaft  30  extends through housing  54  and includes a first end  62  having an input flange  64  fixed for rotation with through shaft  30 . Input flange  64  is driven by a rotary output of engine  12 . Through shaft  30  includes a second end  66  extending beyond housing  54  and fixed for rotation with an output flange  68 . Output flange  68  is fixed for rotation with prop shaft  28 . First and second bearings  70 ,  72  support through shaft  30  for rotation within housing  54 . A seal assembly  74  is positioned radially between input flange  64  and housing  54  to restrict ingress of contaminants toward bearing  70 . In similar fashion, a seal assembly  76  is radially positioned between output flange  68  and housing  54  to protect bearing  72  from contamination and retain lubricant. 
     Transmission  14  includes a planetary gearset  80 , a friction clutch  82  and a chain drive assembly  84  for transferring energy between driveline  18  and energy storage system  34 . As will be described in greater detail, friction clutch  82  is operable to selectively drivingly interconnect through shaft  30  and input shaft  32 . Accordingly, friction clutch  82  is controlled to selectively transfer energy to or transfer energy from energy storage system  34 . 
     Planetary gearset  80  includes a sun gear  90  supported for rotation on through shaft  30  by a bearing  92 . Sun gear  90  includes an axially extending sleeve portion  94  fixed for rotation with the drum  96  of friction clutch  82 . Planetary gearset  80  also includes a carrier  98  having a plurality of pinion shafts  100  rotatably supporting pinion gears  102 . A ring gear  104  is fixed for rotation with housing  54 . Pinion gears  102  are in constant meshed engagement with sun gear  90  and ring gear  104 . Carrier  98  is fixed for rotation with through shaft  30 . The number of teeth on the sun gear  90 , pinion gears  102  and ring gear  104  define the gear reduction ratio provided by planetary gearset  80 . In the embodiment depicted in  FIG. 3 , planetary gearset  80  provides a planetary gear reduction ratio of 2.72:1. It should be appreciated that other gear reduction ratios may be provided, if desired. A planetary gear reduction ratio of 3.21:1 is also contemplated. 
     Clutch  82  includes a hub  110  supported for rotation within housing  54  by bearings  112 ,  114 . Clutch  82  further includes a plurality of outer clutch plates  116  fixed for rotation with but axially movable relative to drum  96 . A plurality of inner clutch plates  118  are fixed for rotation and axially movable relative to hub  110 . An apply plate  120  is axially movable to apply a compressive force to inner clutch plates  118  and outer clutch plates  116  to transfer torque between drum  96  and hub  110 . An axially movable piston  121  is positioned within a cavity  122 . Pressurized fluid may be provided to cavity  122  to cause axial translation of piston  121 . A thrust bearing  124  is axially positioned between piston  121  and apply plate  120  to allow relative rotation therebetween. The magnitude of torque transferred by friction clutch  82  may be controlled by varying the magnitude of pressure provided to cavity  122 . A return spring  126  urges apply plate  120  away from the interleaved inner and outer clutch plates  118 ,  116 . 
     Clutch  82  is operable in an open mode when apply plate  120  is not forced into contact with inner clutch plates  118  and outer clutch plates  116 . At this time, torque is not transferred between through shaft  30  and hydrostatic drive input shaft  32 . Friction clutch  82  is also operable in a torque transferring or closed mode by providing pressurized fluid to cavity  122 , causing piston  121  to transfer force through apply plate  120  and frictionally engage the inner clutch plates  118  with outer clutch plates  116 . At this time, torque is transferred from shaft  30  through carrier  98 , planetary gearset  80 , drum  96 , hub  110  and chain drive assembly  84  to input shaft  32 . 
     Chain drive assembly  84  includes a first sprocket  130  fixed for rotation with hub  110 . A second sprocket  132  is fixed for rotation with hydrostatic drive input shaft  32 . A flexible power transfer member such as a chain  134  drivingly interconnects first sprocket  130  and second sprocket  132 . It should be appreciated that through shaft  30  rotates about an axis of rotation  136  while hydrostatic drive input shaft  32  and second sprocket  132  rotate about an axis of rotation identified at reference numeral  138 . Axes  136  and  138  extend substantially parallel to one another. 
     The drive ratio provided by chain drive assembly  84  may be chosen from two or more chain drive modules depending on the customer&#39;s needs. It is contemplated that three different chain drive ratios may be provided through various combinations of two different sprockets. In particular, it is contemplated that a first chain drive module having a chain drive ratio of 1.20:1 may be provided by forming 40 teeth on second sprocket  132  and forming 48 teeth on first sprocket  130 . Coupled in combination with a planetary gear reduction ratio of 2.72:1 previously described, power may be provided from energy storage system  34  through transmission  14  at an overall drive ratio of 3.26:1. Alternatively, a second chain drive module having a drive ratio of 1:1 may be provided if both sprockets  130 ,  132  were equipped with 40 or 48 teeth. If the chain drive ratio is 1:1, the overall drive ratio of transmission  14  will be the same as the planetary gear reduction ratio of 2.72:1. Lastly, it is contemplated that a third chain drive module having a chain drive ratio of 0.83:1 may be provided by fixing the  48  tooth sprocket for rotation with input shaft  32  and fixing the  40  tooth sprocket for rotation with hub  110 . An overall drive ratio of 2:27:1 results. 
     As best shown in  FIG. 2 , energy storage system  34  includes a hydraulic pump/motor  150  drivingly coupled to hydrostatic drive input shaft  32 . Hydraulic pump/motor  150  includes an inlet  152  in communication with a low pressure reservoir or sump  154 . Pump/motor  150  includes an outlet  156  in communication with highly pressurized fluid. A valve  158  is plumbed in communication with outlet  156 . A high pressure accumulator  160  is positioned downstream of valve  158 . A pressure relief valve  164  is in communication with accumulator  160  and operable to transfer fluid to sump  154  if an over pressure condition exists. Valve  158  is a solenoid-controlled, two-position valve operable to selectively open and close a passageway between outlet  156  and accumulator  160 . 
     Pump/motor  150  may be an adjustable displacement axial piston pump or some other type of variable output pump. During vehicle braking, variable pump/motor  150  is provided energy from the vehicle driveline by applying friction clutch  82 . The braking torque may be controlled by adjusting the displacement of pump/motor  150 . During the pumping operation, controller  48  signals valve  158  to allow pressurized fluid to be pumped from pump/motor  150  to accumulator  160 . Once the accumulator charging process has been completed, controller  48  signals valve  158  to move to the closed position thereby trapping pressurized fluid within accumulator  160 . Substantially at the same time, controller  48  signals friction clutch  82  to operate in the open mode. At this time, motive power for the vehicle is provided only by engine  12  and torque is not transferred between driveline  18  and energy storage system  34 . 
     To transfer torque to driven wheels  22 , clutch  82  may remain in the open mode if power is to be transferred only from engine  12  to driveline  18  and rear wheels  22 . If a supplemental hydrostatic power flow to rear wheels  22  is desired, controller  48  moves valve  158  to allow fluid communication between accumulator  160  and pump/motor  150 . Pressurized fluid acting on pump/motor  150  drives hydrostatic drive input shaft  32  and chain drive assembly  84 . Pressurized fluid, possibly from another source, is provided to cavity  122  to act on piston  121  and place friction clutch in a torque transferring or closed mode. As such, torque continues to be transferred through clutch  82 , planetary gearset  80  and through shaft  30  to drive rear wheels  22 . To exit the hydrostatic assist mode, controller  48  causes valve  158  to shift and block fluid transfer between accumulator  160  and pump/motor  150 . Furthermore, clutch  82  is placed in the open mode. It is contemplated that the charging and discharging of accumulator  160  may occur throughout vehicle operation to greatly improve the energy efficiency of the vehicle. 
       FIG. 4  depicts an alternate transmission  200  for use in a parallel hydraulic hybrid vehicle as previously described in relation to transmission  14 . Transmission  200  is substantially similar to transmission  14 . Accordingly, similar elements will be identified with like reference numerals including an “a” suffix. Primarily, transmission  200  differs from transmission  14  in that the position of friction clutch  82   a  relative to planetary gearset  80   a  is reversed with regard to the relative position of friction clutch  82  and planetary gearset  80 . In particular, when power flows from energy storage system  34 , clutch  82   a  is located downstream of planetary gearset  80   a . Accordingly, the clutch torque capacity of clutch  82   a  must be higher than that of clutch  82  previously described. However, it should also be appreciated that the carrier  98 , pinion gears  102  and sun gear  90  of transmission  14  rotate when through shaft  30  rotates. Corresponding parasitic losses are associated with the configuration of transmission  14 . On the contrary, the components of planetary gearset  80   a  of transmission  200  only rotate when clutch  82   a  is in the closed position. During vehicle operation when clutch  82   a  is open, the components of planetary gearset  80   a  are not rotated. It should be appreciated that chain drive assemblies  84  and  84   a  rotate only when clutches  82  and  82   a  are closed. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.