Abstract:
A pump system that pressurizes a fluid includes a shaft, a first rotor and a second rotor that is selectively driven by the shaft. Relative rotation between the first rotor and the second rotor generates variable sized pockets therebetween to pressurize the fluid. A clutch regulates a degree of coupling of the rotor to the shaft between a decoupled state and a coupled state to regulate the relative rotation between the first and second rotors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit to U.S. Provisional Application No. 60/716,381 filed Sep. 12, 2005, the entire disclosure of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to torque couplings for use in vehicular power transfer systems and, more particularly, to torque couplings equipped with a mechanism for selectively connecting a fluid pump.  
       BACKGROUND OF THE INVENTION  
       [0003]     Power transfer systems of the type used in motor vehicles including, but not limited to, transfer cases, power take-off units (PTU) and drive axles are commonly equipped with a torque biasing system. Typical torque biasing systems function to regulate the transfer of drive torque between an input and an output. Typically, a multi-plate friction clutch pack is operably disposed between the input and the output and engagement of the clutch pack is varied to regulate the amount of drive torque transferred from the input to the output. For example, there is no torque transfer from the input to the output when the clutch pack is disengaged. In contrast, all of the drive torque is transferred from the input to the output when the clutch pack is fully engaged. When the clutch pack is partially engaged, a corresponding portion of the drive torque is transferred.  
         [0004]     The degree of clutch pack engagement is adjusted by an engagement force that is imparted on the clutch pack via a clutch actuator system. Traditional clutch actuator systems include a power-operated drive mechanism that is operable to drive a clutch operator mechanism. The clutch operator mechanism converts the force or torque generated by the power-operated drive mechanism into the engagement force, which can be amplified prior to being applied to the clutch pack. The power-operated drive mechanism is typically controlled based on control signals generated by an electronic control system.  
         [0005]     The quality and accuracy of torque transfer across the clutch pack is based on the frictional interface between the clutch plates. When the clutch pack is partially engaged, the clutch plates slip relative to one another and generate heat. To remove such heat, lubricating fluid is typically directed through the clutch pack to cool the plates as well as other clutch pack components. Excessive heat generation, however, can degrade the lubricating fluid and damage the clutch plates and/or the clutch pack components. Additionally, traction control systems require the clutch control system to respond to torque commands in a quick and accurate manner. The accuracy of meeting the torque request is largely dependent on the coefficient of friction of the clutch pack. It has been demonstrated that this coefficient can change quite rapidly under various loading and/or slip conditions. In particular, the coefficient tends to fade due to significant temperature increases in the clutch pack which result from insufficient rate of heat removal. The heat removal rate is primarily dependent upon the flow rate and condition of the lubricating fluid.  
         [0006]     Traditional lubrication systems typically include a shaft-driven fluid pump that supplies the lubricating fluid to the clutch pack. The fluid pump is usually a unidirectional pump such that it provides no fluid flow when the vehicle is in the reverse mode of operation, even though torque requests may still occur. For instance, the vehicle may be subjected to backing up a dirt, gravel or snow-packed hill where operation in the AWD/4WD mode may be needed. Additionally, shaft-driven pumps are always driven when the vehicle is in forward motion. In many cases, however, the flow of lubricating fluid is not required until heat is actually generated on the highly loaded components, such as during clutch slip conditions. Furthermore, because shaft-driven fluid pumps are always pumping, inefficiencies are realized and fuel economy is negatively impacted.  
         [0007]     Another shortfall of traditional lubrication systems is the increased pump capacity required to deliver sufficient lubricating fluid to the clutch pack at lower shaft speeds. Low shaft speeds are typically encountered in parking lot maneuvers, where tests for torque accuracy are typically performed. Increasing the pump capacity further increases the negative impact the lubrication system has on fuel economy, as well as creating potential for pump cavitation at higher shaft speeds.  
         [0008]     Thus, a need exists to provide an improved lubrication system for use in torque couplings of the type used in vehicular power transfer systems. The improved lubrication system would overcome the drawbacks associated with conventional lubrication systems by providing superior heat removal characteristics while aiding in extending the service life of the clutch plates.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an objective of the present invention to provide an on-demand lubrication system for power transfer assemblies of the type used for transferring drive torque and/or limiting slip in vehicular driveline applications.  
         [0010]     It is another objective of the present invention to provide an on-demand lubrication system having a fluid pump and a pump clutch that is operable to shift the fluid pump between an operative state and a non-operative state.  
         [0011]     A related objective of the present invention is related to providing the pump clutch with a mechanism for selectively coupling and uncoupling a pump component of the fluid pump to a driven shaft for establishing its operative and non-operative states.  
         [0012]     Accordingly, the present invention provides a pump system for selectively pressurizing a fluid. The pump system includes a shaft, a fluid pump having a pump component that can selectively driven by the shaft, and a pump clutch. When driven by the shaft, the pump component generates a pumping action that is operable for drawing low pressure fluid from a sump and a discharging fluid at a higher pressure. The pump clutch is operable to selectively couple the pump component to the shaft and can be selectively shifted between a decoupled state and a coupled state for regulating functional operation of the fluid pump.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Further objects, features and advantages of the present invention will become apparent to those skilled in the art from analysis of the following written description, the appended claims, and accompanying drawings in which:  
         [0014]      FIG. 1  illustrates an exemplary drivetrain of a four-wheel drive vehicle equipped with a power transfer system having a torque transfer mechanism according to the present invention;  
         [0015]      FIG. 2  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a first embodiment of the present invention;  
         [0016]      FIG. 3  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a second embodiment of the present invention;  
         [0017]      FIG. 4  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a third embodiment of the present invention;  
         [0018]      FIG. 5  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a fourth embodiment of the present invention;  
         [0019]      FIG. 6  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a fifth embodiment of the present invention; and  
         [0020]      FIG. 7  is a sectional view of a torque transfer mechanism having a pump clutch operable for selectively engaging a fluid pump according to a sixth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     The present invention is directed to a torque transfer mechanism that can be adaptively controlled for modulating the torque transferred from a first rotary member to a second rotary member. The torque transfer mechanism finds particular application in power transfer systems for use in motor vehicle. Thus, while the present invention is hereinafter described in association with a particular arrangement for use in a specific driveline application, it will be understood that the arrangement shown and described is merely intended to illustrate possible embodiments of the present invention.  
         [0022]     With particular reference to  FIG. 1 , a schematic layout of an exemplary vehicle drivetrain  10  is shown to include a powertrain  12 , a first or primary driveline  14  driven by powertrain  12 , and a second or secondary driveline  16 . Powertrain  12  includes an engine  18  and a multi-speed transaxle  20  arranged to normally provide motive power (i.e., drive torque) to a pair of first wheels  22  associated with primary driveline  14 . Primary driveline  14  further includes a pair of axleshafts  24  connecting wheels  22  to a differential unit  25  associated with transaxle  20 .  
         [0023]     Secondary driveline  16  includes a power take-off unit (PTU)  26  driven by the output of differential unit  25  within transaxle  20 , a propshaft  28  driven by PTU  26 , a pair of axleshafts  30  connected to a pair of second wheels  32 , and a power transfer device  34  that is operable to selectively transfer drive torque from propshaft  28  to axleshafts  30 . Power transfer device  34  is provided as a drive axle assembly and includes a torque transfer mechanism  38  and a differential unit  40 . Torque transfer mechanism  38  functions to selectively transfer drive torque from propshaft  28  to differential unit  40  which, in turn, drives axleshaft  30 . More specifically, torque transfer mechanism  38  includes an input shaft  42  driven by propshaft  28  and a pinion shaft  44  that drives differential unit  40 .  
         [0024]     Vehicle drivetrain  10  further includes a control system  50 , vehicle sensors  52  and a mode select mechanism  54 . Control system  50  regulates actuation of torque transfer mechanism  38 . Vehicle sensors  52  detect dynamic and operational characteristics of drivetrain  10 . Mode select mechanism  54  enables an operator to select one of a plurality of available drive modes. In this embodiment, drive modes include a two-wheel drive mode, a locked (“part-time”) four-wheel drive mode, and an adaptive (“on-demand”) four-wheel drive mode. In this regard, torque biasing mechanism  38  can be selectively engaged for transferring drive torque from input shaft  42  to pinion shaft  44  for establishing both of the part-time and on-demand four-wheel drive modes. An electronic control unit (ECU)  56  controls operation of the components associated with control system  50  which, in turn, controls torque transfer mechanism  38 .  
         [0025]     Referring now to  FIG. 2 , a partial cross-section of torque transfer mechanism  38  is illustrated. Torque transfer mechanism  38  includes a housing  60  that encloses a hydraulic pump  62 , a transfer clutch  64 , a clutch actuator  65  and a pump clutch  66 . In operation, input shaft  42  is selectively coupled to pinion shaft  44  via engagement of transfer clutch  64 . Transfer clutch  64  is varied between a disengaged state and an engaged state to regulate torque transfer between input shaft  42  and pinion shaft  44 . More specifically, clutch actuator  65  regulates the degree of engagement of a clutch pack associated with transfer clutch  64 , as described in further detail below. Hydraulic pump  62  is operable to provide pressurized fluid for cooling the clutch pack based on relative rotation between input shaft  42  and pinion shaft  44 . In addition, pump clutch  66  is operable to regulate the pumping action of pump  62 . More specifically, pump clutch  66  regulates operation of pump  62  between a disengaged state and an engaged state to vary the pressure of the fluid discharged therefrom, as explained in further detail below.  
         [0026]     Transfer clutch  64  includes a drum  68  that is fixed for rotation with pinion shaft  44  and a hub  70  that is fixed for rotation with input shaft  42 . A first plurality of clutch plates  74  are fixed to drum  68  and extend radially inward. A second plurality of clutch plates  76  are fixed to hub  70  and extend radially outward and are interleaved with clutch plates  74 . The degree of engagement of the multi-plate clutch pack, and therefore the amount of torque transferred therethrough, is based on the interaction of clutch plates  74  and  76 . More specifically, in a disengaged state, clutch plates  74  and  76  slip relative to one another and no torque is transferred through transfer clutch  64 . In a fully engaged state, there is no relative slip between clutch plates  74  and  76  and 100% of the drive torque is transferred from input shaft  42  to pinion shaft  44 . In a partially engaged state, the degree of relative slip between clutch plates  74  and  76  varies and a corresponding amount of drive torque is transferred through transfer clutch  64 .  
         [0027]     Clutch actuator  65  controls the degree of clutch pack engagement and includes an electric motor  80  having a motor shaft  81  driving first and second gearsets  82  and  84 , a reaction cam plate  86  and an engagement cam plate  88 . First gearset  82  includes a first pinion gear  90  that is meshed with a first drive gear  92 . First pinion gear  90  is integrally formed on a stub shaft  93  that is driven by motor shaft  81 . In addition, first drive gear  92  is integrally formed on a first tubular hub  94  that is rotatably supported on input shaft  42 . Second gearset  84  includes a second pinion gear  96  formed on stub shaft  93  and which is meshed with a second drive gear  98 . Second drive gear  98  is integrally formed on a second tubular hub  100  that is rotatably supported on first hub  94 . As seen, first hub  94  is in splined engagement with engagement cam plate  88  while second hub  100  is in splined engagement with reaction cam plate  86 . Reaction cam plate  86  includes one or more ramped grooves  102  while engagement plate  88  also includes a corresponding number of ramped grooves  104 . Rolling elements  106  are disposed between reaction cam plate  86  and engagement cam plate  88  and ride within aligned sets of ramped grooves  102  and  104 .  
         [0028]     Electric motor  80  induces common rotation of first pinion gear  90  and second pinion gear  96  which, in turn, respectively drive first and second drive gears  92  and  98 . The number of gear teeth selected for the gear components of first gearset  82  and second gearset  84  are adapted to generate relative rotation between first hub  94  and second hub  100  in response to rotation of motor shaft  81 . Accordingly, such relative rotation results in similar relative rotation between reaction cam plate  86  and engagement cam plate  88 . As engagement cam plate  88  rotates relative to reaction cam plate  86 , rolling elements  106  ride within ramped grooves  102  and  104  and cause engagement cam plate  88  to move axially relative to reaction cam plate  86 . In this manner, engagement cam plate  88  is capable of exerting a linearly-directed clutch engagement force on the clutch pack so as to regulate engagement of transfer clutch  64 .  
         [0029]     Pump  62  is shown as a gerotor-type pump and includes an inner pump rotor  110  and an outer pump rotor  112 . As will be detailed, inner pump rotor  110  is selectively coupled to input shaft  42  through pump clutch  66 . Inner rotor  110  is fixed (i.e., splined) for common rotation with a pump hub  114 . Pump hub  114  is concentrically aligned with and free to rotate about input shaft  42 . Outer pump rotor  112  is supported in a pump housing  116  which is non-rotatably fixed via a splined connection  118  to housing  60 . Pumping chambers are defined between the inner and outer pump rotors. The volume of the pumping chambers varies based on relative rotation between inner and outer rotors  110  and  112 . More specifically, when inner pump rotor  110  is caused to rotate at a different speed than outer pump rotor  112 , the pumping chambers are induced to expand and contract. Expansion of the pumping chambers draws fluid into a pumping chamber from a sump while contraction of a pumping chamber pressurizes and discharges the fluid from pump  62 . As seen in  FIG. 2 , fluid from the sump is drawn through an inlet hose  120  to an inlet chamber  122  of pump  62 . The higher pressure fluid is discharged into an outlet chamber  124  and is supplied via flow paths to lubricate and cool the clutch pack as well as other rotary components and bearings.  
         [0030]     Pump clutch  66  includes an electromagnetic (EM) actuator  140 , a first clutch plate  142  and a second clutch plate  144 . EM actuator  140  is fixed to housing  60  and first clutch plate  142  is splined to input shaft  42  for common rotation therewith. Second clutch plate  144  is fixed (i.e., splined) for rotation with inner rotor  110  of pump  62  via hub  114  and is slidable along the axis A. Specifically, second clutch plate  144  is coupled via a splined connection  146  to hub  114 . Pump clutch  66  is operable in an “engaged” state to couple inner rotor  110  for rotation with input shaft  42  and in a second or “disengaged” state to de-couple inner rotor  110  from rotation with input shaft  42 . More specifically, when EM coil  140  is energized, second clutch plate  144  slides along the A axis and is coupled to first clutch plate  142 . In this manner, inner rotor  110  is driven by input shaft  42  through engagement of first and second clutch plate  142  and  144  so as to permit pump  62  to generate the fluid pumping action. When EM coil  140  is de-energized, second clutch plate  144  is free to rotate independent of first clutch plate  142 , whereby inner rotor  110  is not driven by input shaft  42 . EM coil  140  receives electric control signals from ECU  56 .  
         [0031]     Referring now to  FIG. 3 , torque transfer mechanism  38  is now shown to include an alternative pump clutch  148  that selectively enables pump  62  to pump cooling fluid to the clutch pack of transfer clutch  64 . Pump clutch  148  includes an electric motor  150 , a screw drive mechanism  152  and a sliding hub  154 . Screw drive mechanism  152  includes a threaded shaft  156  driven by electric motor  150  and a collar  158  that is in threaded engagement with threaded shaft  156  and which is axially movable along the axis of threaded shaft  156 . Collar  158  engages hub  154  to axially move hub  154  along the A axis of input shaft  42 . Hub  154  is fixed for rotation with input shaft  42  via a splined engagement  159 . Hub  154  includes external clutch teeth  160  that can selectively engage internal clutch teeth  162  on inner rotor  110  of pump  62 . In a disengaged mode, motor  150  drives screw  156  until collar  158  is retracted, whereby hub  154  is also moved to a retracted position. As such, clutch teeth  160  on hub  154  are moved out of engagement with clutch teeth  162  on inner rotor  110 , whereby no fluid is pumped through pump  62 . In an engaged mode, electric motor  150  drives screw  156  until collar  158  axially moves hub  154  to an extended position whereat its clutch teeth  160  engage clutch teeth  162  on inner rotor  110 , thereby fixing inner rotor  110  for rotation with hub  154 . In this manner, inner rotor  110  can rotate relative to outer rotor  112  and fluid is pumped through pump  62 .  
         [0032]     Referring now to  FIG. 4 , torque transfer mechanism  38  is shown to include another alternative pump clutch  170  that selectively enables pump  62  to pump cooling fluid to the clutch pack. Pump clutch  170  includes an electromagnetic (EM) solenoid  172 , a lever  174  and a sliding hub  176 . EM solenoid  172  is selectively energized and de-energized by control system  50 . Lever  174  is generally L-shaped and is pivotally supported by housing  60 . Lever  174  engages hub  176  to axially move hub  176  along the A axis. Hub  176  is fixed for rotation with input shaft  42  via a splined engagement  179 . Hub  176  includes a conical face surface  178  that can selectively engage a conical face surface  180  formed on inner rotor  110  of pump  62 . In a disengaged mode, EM solenoid  172  is de-energized and hub  176  is retracted such that its conical face surface  178  is released from engagement with conical face surface  180  on inner rotor  110 , whereby no fluid is pumped through pump  62 . In an engaged mode, EM solenoid  172  is energized to move lever  174  so as to engage inner rotor  110  and hub  176  for common rotation. In this manner, inner rotor  110  rotates relative to outer rotor  112  and fluid is pumped through pump  62 .  
         [0033]     Referring now to  FIG. 5 , torque transfer mechanism  38  is shown to include another alternative pump actuator  170 ′ that selectively enables pump  62  to pump cooling fluid to the clutch pack of transfer clutch  64 . The pump actuator  170 ′ includes an electromagnetic (EM) solenoid  172 ′ having an axially displaceable plunger  173 , a pivot lever  174 ′ and a sliding hub  176 ′. EM solenoid  172 ′ is selectively energized and de-energized by control system  50 . Lever  174 ′ is pivotally supported by housing  60 . Lever  174 ′ engages hub  176 ′ to axially move hub  176 ′ along the A axis in response to pivotal movement of lever  174 ′. Hub  176 ′ is fixed for rotation with input shaft  42  via a splined engagement  179 ′. Hub  176 ′ includes a conical face surface  178 ′ that is adapted to selectively engage a conical face surface  180 ′ on inner rotor  110  of pump  62 . In a disengaged mode, EM solenoid  172 ′ is de-energized and plunger  173  is extended such that hub  176 ′ is retracted out of engagement with inner rotor  110 , whereby no fluid is pumped through pump  62 . In an engaged mode, EM solenoid  172 ′ is energized to retract plunger  173  and extend lever  174 ′ so as to engage inner rotor  110  and hub  176 ′ for common rotation. In this manner, inner rotor  110  rotates relative to outer rotor  112  and fluid is pumped through pump  62 .  
         [0034]     Referring now to  FIG. 6 , torque transfer mechanism  38  includes still another alternative pump actuator  190  that selectively enables pump  62  to pump cooling fluid to the clutch pack of transfer clutch  64 . Pump actuator  190  includes an electromagnetic (EM) coil  192 , a clutch pack  194  of interleaved clutch plates, a ball ramp unit  197  and a hub  198 . Ball ramp unit  197  includes a stop plate  196  that is rotatably supported about input shaft  42  and has a ramped groove  200 . Hub  198  is fixed for rotation with input shaft  42  via a splined engagement  201  and is axially movable along the A axis. Hub  198  also includes a ramped groove  202  that corresponds to ramped groove  200  of stop plate  196 . A ball  204  rides within ramped grooves  200  and  202  to regulate the axial position of hub  198  along the A axis. Hub  198  further includes a conical face surface  206  that corresponds to a conical face surface  208  on inner rotor  110  of pump  62 . The conical faces  206  and  208  can be placed in selective engagement so as to permit inner rotor  110  to rotate relative to outer rotor  112  and pump fluid through pump  62 .  
         [0035]     A first plurality of the clutch plates associated with clutch pack  194  are fixed to housing  60  and extend radially inward toward stop plate  196 . A second plurality of clutch plates associated with clutch pack  194  are fixed for rotation with stop plate  196 . In an engaged mode, EM coil  192  is energized to draw interleaved clutch plates  194  into engagement. In this manner, stop plate  196  is braked against rotation. As a result, hub  198  rotates relative to stop plate  196  inducing ball  204  to ride up ramped grooves  200  and  202 . Ball  204  axially pushes hub  198  away from stop plate  196  and into engagement with inner rotor  110  to fix inner rotor  110  for rotation with hub  198 . In a disengaged mode, EM coil  192  is de-energized and stop plate  196  is free to rotate about input shaft  42 . As a result, ball  204  relieves pressure on hub  198  such that hub  198  is permitted to disengage inner rotor  110 .  
         [0036]     Referring now to  FIG. 7 , torque transfer mechanism  38  is shown to include another alternative pump clutch  190 ′ that selectively enables pump  62  to pump cooling fluid to the clutch pack of transfer clutch  64 . Pump actuator  190 ′ includes an electromagnetic (EM) coil  192 ′, a set of interleaved plates  194 ′, a ball ramp unit  197 ′ and a hub  198 ′. Ball ramp unit  197 ′ includes a stop plate  196 ′ that is rotatably supported about input shaft  42  and includes a ramped groove  200 ′. Hub  198 ′ is fixed for rotation with input shaft  42  via a splined engagement  201 ′ and is axially movable along the axis A. Hub  198 ′ also includes a ramped groove  202 ′ that corresponds to ramped groove  200 ′ of stop plate  196 ′. A ball  204 ′ rides within ramped grooves  200 ′ and  202 ′ to regulate a position of hub  198 ′ along the axis A. Hub  198 ′ further includes and a conical face  206 ′ that corresponds to a conical face  208 ′ of inner rotor  110  of pump  62 . Conical faces  206  and  208  are in selective engagement to rotate inner rotor  110  relative to outer rotor  112  and pump through pump  62 . A spring  210 ′ biases hub  198 ′ toward inner rotor  110 .  
         [0037]     A first plurality of interleaved plates  194 ′ are fixed to housing  60  and extend radially inward toward stop plate  196 ′. A second plurality of interleaved plates  194 ′ are fixed for rotation with stop plate  196 ′. In a disengaged mode, EM coil  192 ′ is energized to draw interleaved plates  194 ′ into engagement. In this manner, stop plate  196 ′ is braked against rotation. As a result, hub  198 ′ rotates relative to stop plate  196 ′ inducing ball  204 ′ to ride up ramped grooves  200 ′ and  202 ′. Ball  204 ′ pushes hub  198 ′ away from stop plate  196 ′ and against bias force of the spring  210 ′. In an engaged mode, EM coil  192 ′ is de-energized and stop plate  196 ′ is free to rotate about input shaft  42 . As a result, ball  204 ′ relieves pressure on hub  198 ′ and hub  198  is pushed by the bias force of spring  210 ′ into engagement with inner rotor  110 .  
         [0038]     A number of preferred embodiments have been disclosed to provide those skilled in the art an understanding of the best mode currently contemplated for the operation and construction of the present invention. The invention being thus described, it will be obvious that various modifications can be made without departing from the true spirit and scope of the invention, and all such modifications as would be considered by those skilled in the art are intended to be included within the scope of the following claims.