Abstract:
A torque transfer coupling includes first and second rotary members. A transfer clutch operatively connects the first and second rotary members. A piston, disposed in a piston chamber, is actuable to engage the transfer clutch. A hydraulic pump in fluid communication with a sump containing hydraulic fluid has a first pump member fixed for rotation with the first rotary member and a second pump member fixed for rotation with the second rotary member such that relative rotation between the first and the second pump members generates a fluid pumping action. A first flow path supplies hydraulic fluid from the hydraulic pump to the piston chamber. A second flow path supplies hydraulic fluid from the piston chamber to a control valve for regulating the pressure of the hydraulic fluid supplied to the piston chamber. The second flow path includes an aperture extending through the second pump member.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to electronically-controlled hydraulic couplings for use in motor vehicle driveline applications for limiting slip and transferring torque between rotary members. 
         [0002]    In all wheel drive applications, hydraulic couplings have been used to automatically control the transfer of drive torque from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, such as used in association with a differential in an axle assembly, a full-time transfer case, or a transaxle, hydraulic couplings have been used to limit slip and bias the torque split between two rotary members. Examples of known hydraulic couplings which are adaptable for such driveline applications include viscous couplings, geared traction units, and electronically-controlled, hydraulically-actuated friction clutches generally similar to those shown and described in U.S. Pat. Nos. 5,148,900, 5,358,454, 4,649,459, 5,704,863, 5,779,013, 6,051,903, 6,578,685 and 6,953,411. 
         [0003]    In response to increased consumer demand for motor vehicles with traction control systems, hydraulic couplings are currently being used in a variety of driveline applications. Such hydraulic couplings rely on hydromechanics and pressure-sensitive valve elements to passively respond to a limited range of vehicle operating conditions. These hydraulic couplings are susceptible to improvements that enhance their performance, such as a more controlled response to a wider range of vehicle operating conditions. With this in mind, a need exists to develop improved hydraulic couplings that advance the art. 
       SUMMARY 
       [0004]    A torque transfer coupling for use in a motor vehicle driveline includes first and second rotary members. A transfer clutch operatively connects the first and second rotary members. A piston, disposed in a piston chamber, is actuable to engage the transfer clutch. A hydraulic pump in fluid communication with a sump containing hydraulic fluid has a first pump member fixed for rotation with the first rotary member and a second pump member fixed for rotation with the second rotary member such that relative rotation between the first and the second pump members generates a fluid pumping action. A first flow path supplies hydraulic fluid from the hydraulic pump to the piston chamber. A second flow path supplies hydraulic fluid from the piston chamber to a control valve for regulating the pressure of the hydraulic fluid supplied to the piston chamber. The second flow path includes an aperture extending through the second pump member. 
         [0005]    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 
         [0006]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0007]      FIG. 1  is a perspective view illustrating a hydraulic coupling according to the present disclosure; 
           [0008]      FIGS. 2   a  and  2   b  are exploded perspective views depicting the components of the hydraulic coupling shown in  FIG. 1 ; 
           [0009]      FIG. 3  is a sectional view illustrating the hydraulic coupling operatively coupled between first and second rotary members; 
           [0010]      FIG. 4  is a perspective view of a first toothed pump member of the hydraulic coupling of the present disclosure; 
           [0011]      FIG. 5  is a schematic illustration of a hydraulic circuit associated with the hydraulic coupling of  FIG. 1 ; and 
           [0012]      FIG. 6  is a schematic of a vehicle equipped with the hydraulic coupling of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0014]    In general, the present invention is directed to an actively-controlled hydromechanical limited slip and torque transfer apparatus, hereinafter referred to as a hydraulic coupling. The hydraulic coupling is well-suited for vehicular driveline applications requiring torque transfer or slip limiting control between a pair of rotary members. Driveline applications for the hydraulic coupling include, but are not limited to, limited slip axle differentials, power take-offs and in-line couplings for all-wheel drive vehicles, on-demand couplings and limited slip differentials in four-wheel drive transfer cases, and limited slip differentials in transaxles. 
         [0015]    Referring initially to  FIGS. 1-4  of the drawings, a hydraulic coupling according to a preferred embodiment of the present invention is generally identified with reference numeral  10 . Hydraulic coupling  10  is located in a driveline apparatus having a housing  12  and is operatively coupled between a first rotary member, hereinafter referred to as first shaft  14 , and second rotary member, hereinafter referred to as second shaft  16 . Shafts  14  and  16  are rotatable relative to one another. As will become apparent, hydraulic coupling  10  is controlled by an electronic control module  20  for automatically controlling torque transfer and speed differentiation between shafts  14  and  16 . Electronic control module  20  may monitor vehicle system information and hydraulic coupling information including, but not limited to, wheel speed, throttle position, steering angle, yaw rate, oil sump temperature, oil outlet temperature and clutch pressure, as provided by vehicle sensors  21 . Other information available on the CAN database may also be used. Control module  20  controls a flow control valve assembly  22  associated with hydraulic coupling  10 . Control valve assembly  22  may be a pulse-width modulated (PWM) valve. 
         [0016]    In general, hydraulic coupling  10  comprises two portions: an actuator assembly  24 , and a transfer clutch  26  for transferring drive torque from a faster rotating shaft to a slower rotating shaft in response to speed differentiation therebetween. Transfer clutch  26  is a hydraulically-actuated multi-plate clutch assembly operably coupled between first shaft  14  and second shaft  16 . Transfer clutch  26  includes a drum  28  fixed for rotation with first shaft  14  and a hub  32  fixed for rotation with second shaft  16 . 
         [0017]    Actuator assembly  24  includes a hydraulic pump  34  and a piston assembly  36 . Hydraulic pump  34  includes a pump housing  40  and a cover  42  secured thereto via fasteners  44  or other methods. Pump housing  40  and cover  42  are fixed for rotation with drum  28  and first shaft  14 . The axial position of cover  42  is maintained by a ring  45 . Preferably, hydraulic pump  34  is a bi-directional gerotor pump having a first toothed pump member  46  fixed (i.e., keyed) for rotation with hub  32  and a second toothed pump member  48  positioned within a recess  50  formed in pump housing  40 . A valve body  52  is fixed to housing  12  by a ring  53 . A bearing  54  rotatably supports cover  42  within valve body  52 . With such an arrangement, relative rotation between first shaft  14  and second shaft  16  results in a pumping action which draws fluid from an inlet reservoir  56  on the suction side of pump  34  to an outlet reservoir  58  on the discharge side of pump  34 . Inlet reservoir  56  is in fluid communication with a fluid-filled sump  60  via a sump passage  62  formed in valve body  52 . To facilitate pumping action in both directions of rotation, hydraulic pump  34  includes suitable one-way check valves similar to the arrangement shown in commonly-owned U.S. Pat. Nos. 6,041,903 and 6,578,685 which are incorporated by reference 
         [0018]    Transfer clutch  26  includes a clutch pack  64  having a plurality of inner clutch plates  66  fixed (i.e., splined) to hub  32  that are interleaved with a plurality of outer clutch plates  68  fixed (i.e., splined) to drum  28 . Drum  28  is rotatably supported within housing  12  by a bearing  70 . A seal  71  is pressed into an aperture formed in housing  12  and sealingly engages drum  28 . In addition, hub  32  is rotatably supported within drum  28  by a bearing  72 . 
         [0019]    Piston assembly  36  includes an actuation member or piston  74  disposed in a piston chamber  76 . Piston chamber  76  is defined by a cylindrical segment  78  of pump housing  40  and an inner surface  80  of drum  28 . Piston  74  is supported for axial sliding movement within piston chamber  76  relative to interleaved multi-plate clutch pack  64  for selectively applying a compressive clutch engagement force thereon, thereby transferring drive torque from first shaft  14  (via drum  28 ) to second shaft  16  (via hub  32 ) or vise versa. 
         [0020]    As most clearly shown in  FIGS. 3 and 5 , sump  60  is in communication with inlet reservoir  56  via sump passage  62  formed in valve body  52 . A first pair of cover passages  90  communicate with inlet reservoir  56  and a pair of pump inlet ports  92 . A pair of inlet check valves  94  allows fluid to flow in one direction from inlet reservoir  56  to pump inlet ports  92  but restricts fluid flow in the reverse direction. One-way inlet check valves  94  move between “open” and “closed” positions in response to the direction of pumping action generated by pump  34 . Rotation of the pump components in a first direction acts to open one of inlet check valves  94  and close the other for permitting fluid to be drawn from inlet reservoir  56 . The opposite occurs in the case of pumping in the reverse rotary direction, thereby assuring bi-directional operation of pump  34 . Inlet check valves  94  are preferably reed-type valves fastened by rivets  92  to cover  42 . Inlet check valves  94  are of the normally-closed type. 
         [0021]    A pair of pump housing passages  100  communicate with a pair of pump outlet ports  102  and with piston chamber  76 . Pump outlet check valves  104  allow fluid to flow from pump outlet ports  102  through pump housing  40  and into piston chamber  76 . As before, the direction of pumping action establishes which of outlet check valves  104  is in its “open” position and which is in its “closed” position to deliver pump pressure to piston chamber  76 . Upon cessation of pumping action, both outlet check valves  104  return to their closed position to maintain fluid pressure in piston chamber  76 . Thus, outlet check valves  104  are also of the normally-closed variety. 
         [0022]    Multiple pump housing passages  106  extend through pump housing  40 . Passages  106  may be integrally formed within pump housing  40  without machining. Passages  106  are in communication with a first groove  107  formed in first toothed pump member  46 . Pump member passageways  108  are aligned with first groove  107  and extend through the thickness of first toothed pump member  46 . A second groove  109  is formed on the opposite side of first toothed pump member  46  as first groove  107 . Passageways  108  communicate with second groove  109 . First toothed pump member  46  may be formed from powdered metal such that the teeth, first groove  107 , second groove  109  and pump member passageways  108  may be formed during powdered metal processing such that subsequent machining is not required. Second cover passages  110  communicate with second groove  109 . A cover groove  111  is formed on cover  42  to allow fluid communication between second cover passage  110  and a first valve body passage  112  extending through valve body  52 . It should be appreciated that grooves  107  and  109  may be formed on either pump housing  40  or cover  42 . 
         [0023]    A valve inlet passage  114  extends through housing  12  and is in communication with first body valve passage  112  and a valve inlet  116 . A valve outlet  118  is in communication with a valve outlet passage  120  extending through housing  12 . A second valve body passage  122  communicates with valve outlet passage  120  and sump  60 . Fluid may be selectively allowed to pass from valve inlet  116  to valve outlet  118  by actuation of control valve assembly  22 . 
         [0024]    The amount of drive torque transferred between first shaft  14  and second shaft  16  is proportional to the magnitude of the clutch engagement force exerted by piston  74  on clutch pack  64 . A clutch engagement force is a function of the fluid pressure within piston chamber  76 . The magnitude of the fluid pressure delivered to piston chamber  76  is determined by control valve assembly  22  which has a movable valve element, the position of which is controlled by an electric control signal generated by control module  20 . The remaining fluid passes through valve outlet passage  120  and second valve body passage  122  to sump  60 . The control pressure may be closely controlled due to the use of control valve assembly  22 . 
         [0025]    Referring to  FIG. 6 , an all-wheel drive vehicle is shown to include an engine  200 , a front wheel drive transaxle  202  for delivering drive torque from engine  200  to front wheels  204  via front axle-shafts  206 , and a power take-off driveline  208  for automatically delivering drive torque to rear wheels  210  via a rear axle assembly  212  when slip occurs across the hydraulic coupling when control module  20  determines to transfer torque. Driveline  208  includes a power take-off unit or PTU  214  which is driven by an output of transaxle  202  and a propshaft  216  delivering power from PTU  214  to a final drive unit  218  of rear axle assembly  212 . Hydraulic coupling  10  is shown in both of two optional positions. In the first position, the coupling is located for progressively transferring power from PTU  214  to propshaft  216 . In the second position, the coupling is located for progressively transferring power from propshaft  216  to final drive unit  218 . Obviously, only one coupling is required but is shown in both locations to clearly indicate the various options made available with coupling  10 . 
         [0026]    Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments 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 may be made therein without departing from the spirit and scope of the invention as defined in the following claims.