Abstract:
A lube pump is provided for supplying lubricant to various components of a power transmission unit of the type used in motor vehicles. The lube pump includes a pump assembly and a coupling mechanism for releaseably coupling the pump assembly to a driven shaft. The coupling is operable to release the pump assembly when the rotary speed of the shaft exceeds a threshold value.

Description:
CROSS REFERENCE 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/388,067 filed Mar. 23, 2006, which claims the benefit of U.S. Provisional Application Ser. No. 60/668,455 filed Apr. 5, 2005. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to fluid pumps and, more particularly, to a torque limited fluid pump for use in power transmission units of the type installed in motor vehicles. 
       BACKGROUND OF THE INVENTION 
       [0003]    As is well known, fluid pumps are used in power transmission units of the type installed in motor vehicles for supplying lubricant to the rotary drive components. Such power transmission units typically include manual and automatic transmissions and transaxles, four-wheel drive transfer cases and all-wheel drive power transfer assemblies. In many applications, the lube pump is a gerotor pump having an eccentric outer rotor and an inner rotor that is fixed for rotation with a drive member such as, for example, a drive shaft. The inner rotor has external lobes which are meshed with and eccentrically offset from internal lobes formed on the outer rotor. The rotors are rotatably disposed in a pressure chamber formed in a pump housing that is non-rotationally fixed within the power transmission unit. Rotation of the drive shaft results in the rotors generating a pumping action such that fluid is drawn from a sump in the power transmission unit into a low pressure inlet side of the pressure chamber and is subsequently discharged from a high pressure outlet side of the pressure chamber at an increased fluid pressure. The higher pressure fluid is delivered from the pump outlet through one or more fluid flow passages to specific locations along the driven shaft to lubricate rotary components and/or cool frictional components. One example of a bi-directional gerotor-type lube pump is disclosed in commonly-owned U.S. Pat. No. 6,017,202. 
         [0004]    While gerotor pumps have widespread application in lubrication systems, several drawbacks result in undesirable compromises in their function and structure. For example, most conventional gerotor pumps are extremely inefficient, and are typically incapable of providing adequate lubricant flow at low rotary speeds while providing too much lubricant flow at high rotary speeds. To remedy such functional drawbacks, it is known to replace the conventional gerotor pump with a more expensive variable displacement lube pump or an electrically-controlled lube pump. Thus, a continuing need exists to develop alternatives to conventional gerotor lube pumps for use in power transmission units. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the present invention to provide a rotary-driven fluid pump having a torque-limiting mechanism. 
         [0006]    As a further object of the present invention, the fluid pump includes a pump member driven by a shaft for generating a pumping action within a pressure chamber and a torque-limiting coupling that is operably disposed between the pump member and the shaft. 
         [0007]    As a related object of the present invention, the rotary-driven fluid pump is a gerotor pump having inner and outer rotors while the torque-limiting coupling is operably disposed between the drive shaft and the inner rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Further objects, features and advantages associated with the present invention will be readily apparent from the following detailed specification and the appended claims which, in conjunction with the drawings, set forth the best mode now contemplated for carrying out the invention. Referring to the drawings: 
           [0009]      FIG. 1  is a partial sectional view of a fluid pump constructed according to the present invention and installed in an exemplary power transmission unit; 
           [0010]      FIG. 2  is an end view of the fluid pump; 
           [0011]      FIG. 3  is an enlarged partial view taken from  FIG. 1  illustrating a torque-limiting coupling in greater detail; 
           [0012]      FIG. 4  is a partial sectional view of the fluid pump constructed according to an alternative embodiment of the present invention. 
           [0013]      FIGS. 5A and 5B  are end and side views of a torque-limiting coupling associated with the fluid pump shown in  FIG. 4 ; 
           [0014]      FIGS. 5C and 5D  are end and side views of an alternative construction for the torque-limiting coupling shown in  FIGS. 5A and 5B ; 
           [0015]      FIG. 6  is a partial sectional view of a fluid pump of the present invention constructed according to another alternative embodiment; 
           [0016]      FIG. 7  is a sectional view taken along line A-A shown in  FIG. 6 ; 
           [0017]      FIG. 8  is a partial sectional view of a fluid pump constructed according to a further alternative embodiment of the present invention; and 
           [0018]      FIG. 9  is a partial sectional view taken along line B-B of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring primarily to  FIGS. 1 and 2 , the components of a torque-limited mechanically-driven fluid pump, hereafter referred to as gerotor pump  10 , are shown. In general, gerotor pump  10  is contemplated for use in virtually any pump application requiring a supply of fluid to be delivered from a sump to a remote location for the purpose of lubricating and/or cooling rotary components. In general, gerotor pump  10  includes a pump housing assembly  12 , a gerotor assembly  14  and a torque-limiting mechanism  16 . In the embodiment shown, gerotor pump  10  is installed within a power transmission unit  18  having a casing  20  and a shaft  22  that is supported in casing  20  via a bearing assembly  24  for rotation about a first rotary axis “A”. Pump housing assembly  12  is shown to include a pump housing  26  and a cover plate  28  which together define a circular pump chamber  30  within which gerotor assembly  14  is operably disposed. The origin of circular pump chamber  30  is offset from rotary axis “A” of shaft  22 , as shown by construction line “B” in  FIG. 2 . Pump housing  26  is non-rotatably fixed to casing  20  such as, for example, via a plurality of bolts  32  only one of which is shown. 
         [0020]    Gerotor assembly  14  includes an inner rotor (hereinafter referred to as pump ring  34 ) and an outer rotor (hereinafter referred to as stator ring  36 ) that are rotatably disposed in pump chamber  30 . Pump ring  34  has a circular aperture defining an inner wall surface  38  that is coaxially disposed relative to shaft  22  for rotation about rotary axis “A” and a contoured outer peripheral wall surface  40  which defines a series of external lobes  42 . Likewise, stator ring  36  includes a circular outer wall surface  44  and an inner peripheral wall surface  46  which defines a series of internal lobes  48 . As seen, outer wall surface  44  of stator ring  36  is in sliding engagement with an inner wall surface  50  of pump chamber  30 . In the embodiment shown, pump ring  34  has six external lobes  42  while stator ring  36  has seven internal lobes  48 . Alternative numbers of external lobes  42  and internal lobes  48  can be employed to vary the pumping capacity of pump  10  as long as the number of internal lobes  48  is one greater than the number of external lobes  42 . 
         [0021]    Pump ring  34  is shown in  FIG. 2  with its lobes  42  of outer peripheral surface  40  engaged with various points along inner peripheral wall surface  46  of stator ring  36  to define a series of pressure chambers therebetween. Upon rotation of pump ring  34  about rotary axis “A”, stator ring  36  is caused to rotate in pump chamber  30  about axis “B” at a reduced speed relative to the rotary speed of pump ring  34 . Such relative and eccentric rotation causes a progressive reduction in the volume of the pressure chambers, thereby generating a pumping action such that fluid is drawn from the sump through an inlet tube  52 . As best seen from  FIG. 1 , Inlet tube  52  communicates with an inlet port  54  formed in pump housing  26  which, in turn, supplies fluid to an inlet chamber  56  that communicates with pump chamber  30 . The pumping action caused by rotation between pump ring  34  and stator ring  36  within pump chamber  30  causes the fluid to ultimately be discharged into an annular outlet chamber  58  formed in pump housing  26  at the higher outlet pressure. Fluid discharged from outlet chamber  58  is delivered to a central lubrication passage  60  formed in shaft  22  via a plurality of radial supply bores  62 . Central passage  60  communicates with various rotary elements located downstream of fluid pump  10  such as, for example, bearings, journal sleeves, speed gears and friction clutch packs via a series of radial lubrication and cooling delivery bores (not shown) also formed in shaft  22 . 
         [0022]    Referring primarily to  FIG. 3 , torque-limiting coupling mechanism  16  is shown to include a drag ring assembly  70  that is operable for releaseably coupling pump ring  34  for rotation with shaft  22  using a friction interface therebetween. Drag ring assembly  70  includes a drag ring  72  and a drag seal  74 . Drag ring  72  includes a flanged tubular sleeve  76  and an annular friction coupling ring  78 . Preferably, sleeve  76  is made from a rigid material and has an outer surface  80  permanently secured within aperture  38  for common rotation with pump ring  34 . Likewise, coupling ring  78  is preferably made of a resilient material and has its outer circumferential edge surface  82  permanently secured to an inner cylindrical surface  84  of sleeve  76 . An inner circumferential edge surface  86  of coupling ring  78  is frictionally retained on outer wall surface  87  of shaft  22 . The frictional interface between coupling ring  78  and shaft  22  is operable to cause pump ring  34  to rotate with shaft  22  without slip therebetween until the rotational speed of shaft  22  exceeds a threshold value. Once this rotary speed threshold value is exceeded, the torque required to drive pump  10  will exceed the torque limit of coupling ring  78  and cause it to slip, thereby causing relative rotation between shaft  22  and pump ring  34 . Drag seal  74  surrounds coupling ring  78  and is sized to provide a desired compressive clamping force on shaft  22  that will be overcome upon shaft  22  exceeding the threshold rotary speed. Preferably, drag seal  74  is retained in a groove  88  formed in coupling ring  78 . 
         [0023]    Referring now to  FIGS. 4 ,  5 A and  5 B, pump  10  is shown with a different torque-limiting coupling mechanism  16 A that is arranged to releaseably couple pump ring  34  of gerotor assembly  14  to shaft  22 . In particular, torque-limiting coupling  16 A includes a coupling ring  90  having a circular aperture with an inner wall surface  92  fitted on shaft  22  and which is split by a through slot  94 . A lug  96  extends from coupling ring  90  and is nested with a keyway slot  98  formed in pump ring  34 . As seen, coupling ring  90  further includes an oil channel  100  that is in fluid communication with central passage  60  via one or more radial supply bores  102 . Preferably, the frictional engagement of coupling ring  90  with shaft  22  will be controlled by the interference fit between inner surface  92  of coupling ring  90  and outer surface  87  of shaft  22 . This frictional interface may be designed to provide different slip conditions based on: the type of material used for split coupling ring  90 ; the optional use of frictional materials on inner wall surface  92  of coupling ring  90 ; and the use of retaining members (i.e., clamps, springs, seals, etc.). For example, by adjusting the size, weight, and weight distribution of coupling ring  90 , the number of retaining members, and/or the size of oil channel  100 , any desired level of shaft torque (based on its rotary speed) can be selected to initiate slip between coupling ring  90  and shaft  22 . As seen, a retainer ring  104  surrounds and exerts a compressive load on coupling ring  90  for providing frictional engagement with shaft  22 . A stop ring  106  limits axial movement of coupling ring  90  relative to pump ring  34  while a pair of O-ring seals  108  are seated in grooves  109  formed in coupling ring  90  to provide a fluid-tight seal between coupling ring  90  and shaft  22  on opposite sides of oil channel  100 . 
         [0024]    In operation, fluid discharged from pump  10  due to rotation of shaft  22  is delivered to oil channel  100  via central passage  60  and supply ports  102 . Since most lubrication systems use fixed orifice delivery bores, an increase in the fluid pressure is generated in passage  60  as the flow rate through pump  10  increases. The flow rate is governed by the rotary speed of shaft  22  which, therefore, causes the fluid pressure to increase. This increased fluid pressure is delivered to oil channel  100  which then acts to cause radial expansion of coupling ring  90  due to slot  94 . As noted, seals  108  are provided to maintain fluid pressure within oil channel  100 . Once the threshold rotary speed value is reached by shaft  22 , the centrifugal forces and fluid pressure in channel  100  cause coupling ring  90  and pump ring  34  to slip relative to shaft  22 , thereby limiting the maximum fluid pressure that can be generated by pump  10 .  FIGS. 5C and 5D  are generally similar to  FIGS. 5A and 5B  except that a coupling ring  90 ′ is shown to have an eccentric outer configuration to provide and additional centrifugal effect to its clamping characteristics. 
         [0025]      FIG. 6  illustrates pump  10  equipped with yet another torque-limiting coupling mechanism  16 B arranged for releaseably coupling pump ring  34  to shaft  22 . In particular, torque-limiting coupling  16 B includes a coupling ring  110  having a sinsusoidal aperture  112  encircling shaft  22  and which is split via a through slot  114 . A lug  116  extends from coupling ring  110  and is nested in keyway slot  98  formed in pump ring  34 . As best seen from  FIG. 7 , the sinsusoidal configuration of coupling ring  110  defines a series of oil chambers  118  separated by radial lugs  120  that engage outer surface  87  of shaft  22 . A radial supply bore  122  provides fluid communication between central passage  60  in shaft  22  and chambers  118  in coupling ring  110 . A ball  124  is biased by a spring  126  into engagement with sinsusoidal aperture  112  within one of chambers  118 . Ball  124  and spring  126  are retained in an enlarged portion of supply bore  122 . 
         [0026]    In operation, fluid discharged from pump  10  due to rotation of shaft  22  is delivered from central passage  60  to chamber  118  within which ball  124  is disposed via supply bore  122 . As the fluid pressure in passage  60  increases with increased rotary speed of shaft  22 , the biasing force exerted by spring  126  on ball  124  is augmented by the fluid pressure in bore  122 , thereby causing radial expansion of coupling ring  110 . Once the threshold rotary speed value is reached by shaft  22 , the frictional interface between lugs  120  and shaft surface  87  is overcome so as to permit shaft  22  to rotate relative to coupling ring  110  and pump ring  34 , thereby limiting the maximum fluid pressure generated by pump  10 . Ball  124  rotates with shaft  22  and moves into and out of retention with sequential chambers  118  until the speed of shaft  22  is reduced to permit ball  124  to retracted so as to re-establish frictional engagement of coupling ring  110  with shaft  22 . 
         [0027]    Referring now to  FIGS. 8 and 9 , another embodiment of a torque-limiting coupling mechanism  16 C is shown installed within power transmission unit  18  in association with fluid pump  10  for releaseably coupling pump ring  34  to shaft  22 . Torque-limiting coupling  16 C includes a friction sleeve  140  encircling shaft  22  and having a through slot  142  to define a split sleeve configuration. Sleeve  140  further includes one or more lugs  144  that are nested in corresponding keyways  146  formed in pump ring  34 . Torque-limiting coupling  16 C further includes a drive casing  148  that is fixed for rotation with shaft  22  and has a pair of radially-inwardly extending spacer lugs  150 . Lugs  150  are arranged to define a pair of force chambers  152 A and  152 B in conjunction with sleeve  140 . As seen, a pair of arcuate friction shoes  154 A and  154 B are retained in corresponding force chambers  152 A and  152 B. Friction shoe  154 A has an inner wall surface  156 A adapted to be biased into frictional engagement with an outer wall surface  158  of sleeve  140  via a first plurality of biasing springs  160 A. Springs  160 A are retained in retention cavities  162 A formed in drive casing  148 . Likewise, friction shoe  154 B has an inner wall surface  156 B adapted to be biased into frictional engagement with outer wall surface  158  of sleeve  140  via a second plurality of biasing springs  160 B. Springs  160 B are likewise retained in retention cavities  162 B formed in casing  148 . 
         [0028]    In operation, springs  160 A and  160 B cause corresponding friction shoes  154 A and  154 B to apply a frictional engagement force on sleeve  140  for causing a clamping force to be applied by sleeve  140  on shaft  22 . As such, sleeve  140  is releaseably coupled for rotation with shaft  22 , thereby releaseably coupling pump ring  34  for rotation with shaft  22 . This clamped engagement of sleeve  140  with shaft  22  is maintained until the rotary speed of shaft  22  exceeds a threshold value at which point the centrifugal forces acting on shoes  154 A and  154 B oppose and overcome the biasing force of springs  160 A and  160 B. As such, sleeve  140  and pump ring  34  begin to slip relative to shaft  22 , thereby limiting the fluid pressure generated by pump  10 . 
         [0029]    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.