Abstract:
A pump assembly includes a pump housing, a stator ring supported within the pump housing, and a pump ring also rotatably supported within the pump housing. The pump ring interfaces with the stator ring to define a plurality of variable volume pressure chambers. A cover plate covers the stator ring and pumping ring within the pump housing. The cover plate is axially displaceable relative to the pump housing and defines a wall of each of the pressure chambers. Pressure within the pressure chambers induces linear movement of the cover plate away from the stator ring and the pump ring.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to fluid pumps, and more particularly to a high efficiency expanding gerotor pump.  
       BACKGROUND OF THE INVENTION  
       [0002]     Gerotor pumps are commonly used in power transfer assembly of the type installed in motor vehicles for supplying lubrication to the rotary components as well as for cooling torque transfer assemblies such as, for example, multi-plate friction clutches. Such power transfer assemblies include manual and automatic transmissions, transaxles, power take-off units, all-wheel drive couplings and four-wheel drive transfer cases. Typically, the gerotor pump has an outer ring defining a pumping chamber and an inner ring that is positioned in the pumping chamber and which is fixed for rotation with a driven member (i.e., a shaft, etc.). The inner ring has external lobes which are meshed with, and eccentrically offset, from internal lobes formed on the outer ring. Because the number of internal lobes is greater than the number of external lobes, driven rotation of the inner ring results in a pumping action such that a supply of hydraulic fluid is drawn from a sump in the power transfer assembly into the suction side of the pumping chamber and is discharged from the pressure side of the pumping chamber at an increased pressure.  
         [0003]     Traditionally, the gerotor pump is continuously driven regardless of the lubrication and/or cooling needs. In addition, as the rotational speed of the driven member increases, the pressure generated by the gerotor pump correspondingly increases. As a result, additional energy is used to drive the pump, thereby reducing the overall efficiency of the power transfer assembly.  
       SUMMARY OF THE INVENTION  
       [0004]     Accordingly, the present invention is directed to a high efficiency expandable pump assembly. The pump assembly includes a pump housing, a stator ring that is supported within the pump housing, and a pump ring that is rotatably supported within the pump housing. The pump ring interfaces with the stator ring to define a plurality of variable volume pressure chambers. A cover plate covers the stator ring and pump ring within the pump housing. The cover plate is axially displaceable relative to the pump housing and defines a wall of each of the pressure chambers. The fluid pressure within each of the pressure chambers induces linear movement of the cover plate away from the stator ring and the pump ring.  
         [0005]     In one feature, the stator ring and the pump ring move linearly based on the pressure within the pressure chambers such that each remain centered between the cover plate and the pump housing.  
         [0006]     In other features, the pump assembly further includes a biasing member that biases the cover plate toward the stator ring and the pump ring. In accordance with a preferred construction, the biasing member is a resilient seal component having a circular doughnut-shaped cross-section. As an alternative, the biasing member may include a square shaped cross-section. In yet another alternative, the biasing member may include a D-shaped cross-section.  
         [0007]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0009]      FIG. 1  is a schematic illustration of an exemplary vehicle drivetrain having one or more power transfer assemblies equipped with a high efficiency gerotor pump according to the present invention;  
         [0010]      FIG. 2  is a schematic illustration of a power take-off unit equipped with the gerotor pump of the present invention;  
         [0011]      FIG. 3  is a partial cross-sectional view of a power transfer assembly equipped with a high efficiency gerotor pump according to the present invention;  
         [0012]      FIG. 4  is a plan view of components of the gerotor pump;  
         [0013]      FIG. 5  is a cross-sectional view of an alternative biasing member of the gerotor pump; and  
         [0014]      FIG. 6  is a cross-sectional view of another alternative biasing member of the gerotor pump.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0016]     Referring primarily to  FIG. 1 , a schematic layout for a vehicular drivetrain  10  is shown to include a powertrain  12  driving a first or primary driveline  14  and a second or secondary driveline  16 . Powertrain  12  includes an engine  18  and a transaxle  20  arranged to provide motive power (i.e., drive torque) through a front differential  21  to a pair of wheels  22  associated with primary driveline  14 . In particular, primary driveline  14  includes a pair of halfshafts  24  connecting wheels  22  to front differential  21  associated with transaxle  20 . Secondary driveline  16  includes a power take-off unit (PTU)  26  driven by transaxle  20 , a prop shaft  28  driven by PTU  26 , a pair of axleshafts  30  connected to a pair of wheels  32  and a drive axle assembly  34  operable to transfer drive torque from propshaft  28  to one or both axleshafts  30 . As will be detailed, the present invention is directed to use on an improved fluid pump in any one of the power transfer assemblies associated with drivetrain  10  for the purpose of providing lubrication to the rotary components and/or hydraulic actuation of one or more torque transfer devices.  
         [0017]     Referring now to  FIG. 2 , PTU  26  is schematically shown in association with front differential  21  of transaxle  20 . In particular, front differential  21  includes a carrier  36 , a pair of side gears  38  that are fixed for driven rotation with axleshafts  24 , and a pair of pinion gears  40  rotatably driven by carrier  36  and meshed with side gears  38 . An output gear  42  on a transmission shaft  44  associated with transaxle  20  drives a drive gear  46  fixed to carrier  36  for transferring drive torque through front differential  21  to axleshafts  24 .  
         [0018]     PTU  26  is shown to include a transfer shaft  48  driven by carrier  36 , a clutch drum  50 , a hub  52  driven by transfer shaft  48 , a clutch pack  54  disposed between drum  50  and hub  52 , a clutch actuator  56  and a transfer gearset  58 . As seen, transfer gearset  58  includes a ring gear  60  driven by drum  50  that is meshed with a pinion gear  62  fixed for rotation with a pinion shaft  64  that, in turn, drives prop shaft  28 . Clutch actuator  56  is operable to generate and apply a clutch engagement force on clutch pack  54 , thereby transferring drive torque from transfer shaft  48  to gearset  58  which, in turn, transfers such drive torque to rear axle assembly  24  via prop shaft  28 . Actuator  56  includes a fluid pump  66  driven by transfer shaft  48 , a source of hydraulic fluid such as sump  68 , and a piston  70  disposed in a pressure chamber. Pump  66  is operable to draw fluid from sump  68  and deliver high pressure fluid to the pressure chamber for controlling sliding movement of piston  70  relative to clutch pack  54 , in turn, and the magnitude of the clutch engagement force exerted thereon. In addition to clutch actuation, pump  66  functions to draw fluid from sump  68  and supply fluid through lubrication and/or cooling flow paths to cool clutch pack  54  and lubricate various rotary components of PTU  26  and differential  21 .  
         [0019]     Fluid pump  66  is a bidirectional rotary-driven gerator pump. A similar gerotor pump is disclosed in commonly assigned U.S. Pat. No. 6,017,202, issued Jan. 25, 2000 and which is expressly incorporated herein by reference. Gerotor pump  66  is contemplated for use in any pump applications requiring a supply of fluid to be delivered to a single pump outlet regardless of the direction of rotation, as discussed further below. Referring to  FIG. 3 , gerotor pump  66  is shown to include a pump housing  72 , a gerotor assembly  74 , an inlet valve assembly  76 , and an outlet valve assembly  78 . Gerotor pump  66  is a self-contained unit and includes a cover plate  80 . Components of gerotor pump  66  are disposed within pump housing  72  and are covered by cover plate  80 .  
         [0020]     Gerotor pump  66  can be installed within exemplary PTU  26 , which includes a shaft  82  that is rotatably supported in a housing  84  via a bearing assembly  86 . Shaft  82  is rotatable about a first rotary axis “A”. Gerotor assembly  74  is seated within a cavity  88  in pump housing  72 . Cover plate  80  is slidably disposed within a recess  90  in pump housing  72  and is adapted to enclose gerotor assembly  74  within cavity  88  of pump housing  72 . Cover plate  80  includes an anti-rotation tab  92  that is retained in a slot  94  formed in housing  72 . In addition, a biasing member  96  is disposed between cover plate  60  and a retention ring  98 . Biasing member  96  is preferably constructed as an annular resilient component, such as a rubber ring seal. Although biasing member  96  is illustrated having a doughnut-shaped cross-section, it is anticipated that other cross-sections can be implemented. More particularly,  FIGS. 5 and 6  respectively illustrate a D-shaped cross-section and a square-shaped cross-section. Pump housing  72  can be non-rotatably fixed to case  84  in a number of manners including, but not limited to a series of radially-extending tabs  100 , which are adapted for receipt in complementary keyways (not shown) formed in the housing  84 .  
         [0021]     Gerotor assembly  74  includes a pump ring  102  and a stator ring  104 . Pump ring  102  has a central aperture with internal splines  106  adapted for meshed engagement with external splines  108  formed on shaft  82 . In this manner, pump ring  102  is fixed for rotation with shaft  82  to rotate about first rotary axis “A”. Rotation of shaft  82  induces rotation of pump ring  102 , which draws hydraulic fluid through an inlet hose  110  from the sump area. Stator ring  104  is supported in cavity or pump chamber  88  formed in pump housing  72 . Pump chamber  88  is circular and extends inwardly from a front face  112  of pump housing  72 . Pump chamber  88  is defined by a planar pump surface  114 , which is parallel to the front face  112  and a circumferential side wall  116  that extends transversely with respect to pump surface  114 . Further, the origin of pump chamber  88  is radially offset from the first rotary axis “A” of shaft  82  and is shown by construction line “B” in  FIG. 3 . Thus, stator ring  104  is retained within pump chamber  88  such that its rear surface  118  abuts pump surface  114  while its peripheral edge surface  120  abuts outer side wall  116 .  
         [0022]     Stator ring  104  includes a generally sinusoidal aperture defined by an inner peripheral surface  124  formed between a front surface  126  and rear surface  118 . Inner peripheral surface  124  defines a series of lobes  128  interconnected by a series of recessed root segments  130 . Pump ring  102  has an outer peripheral surface  132  defined between a front surface  134  and a rear surface  136 . Outer peripheral surface  132  defines a series of external lobes  138  interconnected by a series of web segments  140 . In the embodiment shown, stator ring  104  has seven lobes  128  while pump ring  102  has six lobes  138 . Alternative numbers of lobes can be used to vary the pumping capacity, whereby the number of lobes  128  on stator ring  104  is one greater than the number of lobes  138  on pump ring  102 .  
         [0023]     With particular reference to  FIG. 4 , pump ring  102  is shown with its outer peripheral surface  132  engaged with various points along inner peripheral surface  124  of stator ring  104  to define a series of pressure chambers  142  therebetween. More specifically, pressure chambers  142  are defined by peripheral surfaces  124  and  132 , pump surface  114  and cover plate  80 . Upon rotation of pump ring  102  about the “A” axis, stator ring  104  is induced to rotate in pump chamber  88  about the “B” axis at a reduced speed relative to the rotary speed of pump ring  102 . This induces a progressive reduction in the size of pressure chambers  142  to generate a pumping action. More specifically, low pressure fluid is drawn from sump  68  into pressure chambers  142  through inlet valve assembly  76  and high pressure fluid is exhausted from pressure chambers  142  through outlet valve assembly  78 . As is known, inlet valve assembly  76  functions to permit fluid to be supplied to inlet chambers (not shown) formed in pump housing  72  while outlet valve assembly  78  controls fluid delivery from outlet chambers  150  in pump housing  72  to a discharge flowpath  152 . Flowpath  152  is shown to include an annular chamber  154  in pump housing  72  that communicates with a series of radial ports  156  in shaft  82 . Ports  156  communicate with a central passage  158  which is used to provide pressurized fluid to locations along shaft  82 .  
         [0024]     As pumping ring  102  and stator ring  104  are induced to rotate, they rub against pump housing surface  114  and cover plate  80 . This would typically result in pumping inefficiencies and energy losses. However, as the speed differential between pump ring  102  and stator ring  104  increases, the pressure within the pressure chambers  142  correspondingly increases. Eventually, there is sufficient pressure build-up within pressure chambers  142  to impart a linear force on cover plate  80 , inducing cover plate  80  to move away from gerotor assembly  74  and resiliently push against biasing member  96 . In this manner, when the fluid pressure achieves a predetermined threshold, cover plate  80  is induced to move which, in turn, functions to increase the volume of pressure chambers  142 .  
         [0025]     Opening of pressure chambers  142  results in an increase in the gap between cover plate  80  and pump surface  114 . Pump ring  102  and stator ring  104  automatically center themselves between cover plate  80  and pump surface  114 . In this manner, pump ring  102  and stator ring  104  are offset from both cover plate  80  and pump housing surface  114 . Fluid is able to seep in between the pump components and cover plate  80  and in between the pump components and pump surface  114  to lubricate the interface therebetween. Viscous forces within gerotor pump  66  drop and pumping efficiency is increased.  
         [0026]     As the gap between cover plate  80  and pump surface  114  increases a threshold point is achieved, whereby the pressure within pressure chambers  142  decreases. As the pressure within pressure chambers  142  decreases, the biasing force of biasing member  96  induces cover plate  80  to move back toward gerotor assembly  74 , thereby closing pressure chambers  142 . Closing of pressure chambers  142  results in a pressure increase within pressure chambers  142 , as described above. Eventually, the gap between cover plate  80  and pump surface  114  stabilizes as a balance is achieved between the linear force generated by the fluid pressure within pressure chambers  142  and the biasing force of biasing member  96  balance. In this manner, losses incurred as a result of the continuous pumping action of gerotor pump  66  are significantly reduced by the reduced viscous forces between the pump components.  
         [0027]     The description of the invention is merely exemplary in nature and, thus, 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.