Abstract:
An improved seal assembly is provided that minimizes loss of transmission pump pressure by controlling fluid flow past a torque converter hub bushing to meet bushing lubrication requirements without unnecessarily diminishing pump pressure and while also minimizing frictional losses. The seal assembly includes a rigid carrier adapted to fit between a pump body member and the torque converter hub. An elastomeric lip extends from the rigid carrier. A contact layer is connected to the elastomeric lip and configured to sealingly contact the torque converter hub. The contact layer is integral with and harder than the elastomeric lip, therefore minimizing frictional losses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/939,916 filed May 24, 2007, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates to a seal assembly for a transmission pump. 
     BACKGROUND OF THE INVENTION 
     Hydraulic transmission pumps are typically powered by a hub attached to a torque converter which in turn is driven by engine output. A bushing is positioned between the torque converter hub and a stationary body member of the pump to permit relative rotation of the torque converter hub. The transmission pump provides pressurized fluid to meet the cooling, lubrication, and clutch apply pressure requirements of the transmission. Loss of pump pressure through leakage reduces the efficiency of the transmission. Pump seals are typically provided to maintain pump pressure. The bushing must be lubricated, so some of the pressurized fluid is typically directed through a gap between the bushing and the torque converter hub. A seal assembly is typically provided at the side of the bushing opposite the pump to prevent escape of the transmission fluid outside of the transmission. 
     SUMMARY OF THE INVENTION 
     An improved seal assembly is provided that: minimizes loss of transmission pump pressure by controlling fluid flow past the torque converter hub bushing to satisfy bushing lubrication requirements without allowing excess fluid flow that unnecessarily diminishes pump pressure, while also minimizing frictional losses and reducing assembly time and error. The seal assembly includes a rigid carrier adapted to fit between the pump body member and the torque converter hub. An elastomeric lip extends from the rigid carrier. A contact layer is connected to the elastomeric lip and is configured to sealingly contact the torque converter hub. The contact layer is harder than the elastomeric lip, and therefore reduces friction losses at the rotating torque converter hub. Notably, the elastomeric lip and contact layer are integrally connected with the rigid carrier, whether by overmolding, adhesion, or other known methods, and there is thus no frictional loss between the lip and the rigid carrier. The rigid carrier has an orifice positioned in fluid connection with the gap and sized to control (i.e., minimize) the flow of fluid from the pump cavity through the gap, to minimize pump pressure loss. The rigid carrier also has vent openings that permit fluid that has flowed through the orifice to return to a sump. Preferably, a seal member such as another elastomeric lip or an O-ring is operatively connected to the rigid carrier to sealingly contact the pump body member, thus partially defining a pressurized cavity on a side of the rigid carrier adjacent the bushing, upstream of the orifice. 
     A torque converter assembly is provided that includes the torque converter hub, the pump, the bushing and the seal assembly described above. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration in fragmentary, partially cross-sectional view of a transmission having a torque converter assembly and a pump seal assembly; 
         FIG. 2  is a schematic illustration in fragmentary, partially cross-sectional view of the pump seal assembly of  FIG. 1  having an elastomeric lip with a contact layer, an elastomeric seal member, and an orifice through a carrier member; and 
         FIG. 3  is a schematic illustration in fragmentary, partially cross-sectional view of an alternative pump seal assembly for use in the transmission of FIG.  1  having an O-ring for the seal member in lieu of the elastomeric seal member of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a transmission  10  includes a torque converter assembly  12  with a rotor  14  driven by an engine or other power source (not shown) and a torque converter hub  16  connected for rotation with the rotor  14 , as is known. The torque converter hub  16  drivingly engages a pump gear  18  of a transmission pump  20  to pressurize fluid which is transferred from discharge pump cavity  22 , partially defined by a stationary pump body member  23 , to various components of the transmission  10  to meet hydraulic power requirements. A cavity  24  is primarily filled from oil transfer channels in the pump  20  that provide controlled supply pressure to a torque converter clutch  25  or, when the torque converter clutch  25  is off, lubrication flow and pressure. The cavity  24  can also fill with pressurized fluid leakage past the pump gear  18 . A bushing  26  is press fit between the pump body member  23  and the torque converter hub  16  to permit rotation of the torque converter hub  16  relative to the pump body member  23 . A pump cover  27  is secured to the pump body member  23  to close the pump  18 . As better viewed in  FIG. 2 , a clearance gap  28  is maintained between the torque converter hub  16  and the bushing  26  to permit lubrication and cooling of the bushing  26 . The gap  28  extends the axial length of the bushing  26  and permits flow of the pressurized fluid from cavity  24  to a cavity  30  at the other end of the bushing  26 . 
     Referring to  FIG. 2 , a transmission pump seal assembly  32  is positioned adjacent the cavity  30  and partially defines as well as seals the cavity  30 . The seal assembly  32  is configured to fit over the pump body member  23 , with a snap ring  31  maintaining its axial position, and preferably nests within recesses  33  formed in the pump body member  23 . The seal assembly  32  controls the fluid flow past the bushing  26  to meet bushing lubrication and cooling requirements while minimizing or eliminating excess fluid flow and associated hydrodynamic energy loss due to wasted pressurized fluid. Specifically, the seal assembly  32  includes an elastomeric lip  34  with contact layer  36 , a seal member  38  supported on a first carrier member  40  of a rigid annular carrier  42 , a lip seal assembly  44  including a lip seal  46  extending from a second carrier member  48  of the carrier  42  and a biasing member  49 . The transmission pump seal assembly  32  controls pressure at cavity  30  by controlling the fluid flow from the cavity  30  through a control orifice  50  through the first carrier member  40  to another cavity  52  defined by the seal assembly  32  from which the fluid vents through multiple circumferentially-spaced vent openings  54  (one shown), through a passage  56  defined in the pump body member  23  to a fluid sump (not shown). As is evident in  FIG. 1 , the passage  56  has a circumferential portion adjacent the seal assembly  32  as well as a radial portion that vents the circumferential portion to the sump. 
     The characteristics of each of the components of the seal assembly  32  and their functional cooperation to reduce pump pressure loss, minimize frictional loss, and improve assembly time and reliability are now described in greater detail. The first carrier member  40  and the second carrier member  48  are preferably a rigid material such as stamped steel or plastic. The elastomeric lip  34 , the lip seal  46  and the seal member  38  are preferably all of a rubber of similar material molded-over or otherwise applied or adhered to the respective carrier members  40 ,  48 , as is known in the art. 
     The contact layer  36  is applied at a radially outer surface of the elastomeric lip  34  such that it is positioned for sealing contact with the torque converter hub  16 . The contact layer  36  is of a harder material than the elastomeric lip  34  so that friction with the rotating torque converter hub  16  is less than if the more compliant elastomeric lip  34  directly contacted the torque converter hub  16 . Preferably, the contact layer  36  is polytetrafluoroethylene (PTFE). A preferred PTFE material for the contact layer is 15% glass filled having a durometer hardness of 98 (A scale) and a tensile strength of 13.8 MPa. Additionally, because the contact layer  36  is integrally secured to the lip  34 , which in turn is integrally secured to the first carrier member  40 , there is no relative rotation or frictional loss between the lip  34 , contact layer  36  and first carrier member  40 . 
     The annular seal member  38  may be a molded-over lip seal as shown in  FIG. 2 . Alternatively, the seal member may be an annular O-ring  38 A, as shown in the embodiment of the pump seal assembly  32 A of  FIG. 3 . The remaining components of the pump seal assembly  32 A are identical to those of the lip seal assembly  44  of  FIG. 2 . 
     The lip seal assembly  44  includes the lip seal  46 , which is preferably molded-over rubber on the second carrier member  48 . The biasing member  49  is preferably a garter spring that is tucked inward of the lip seal  46  and biases the lip seal  46  radially-outward, into sealing contact with the torque converter hub  16 . 
     To assemble the seal assembly  32  and then install it in the transmission  10 , the lip  34 , lip seal  46  and seal member  38  are first molded to the respective carrier members  40 ,  48 . The contact layer  36  is then applied to the lip  34  by any known technique. The first carrier member  40  is then press fit over the second carrier member  48 . The biasing member  49  is tucked under the lip seal  46 . The assembled seal assembly  32  is thus a unitary module, reducing assembly time for installation on the torque converter hub  16  in comparison with seal assemblies that are multiple independent components. 
     The assembled pump seal assembly  32  is then press fit over the pump body member  23  and positioned axially until the seal member  38  contacts the pump body member  23  adjacent the passage  56 . Finally, the torque converter hub  16  is piloted over the seal assembly  32  and bushing  26 . Because the contact layer  36  is relatively hard, there is less chance for damage to the lip  34  than if the elastomeric material of the lip  34  directly contacted the torque converter hub as the torque converter hub  16  is piloted over the seal assembly  32 . As the torque converter hub  16  slides past the lip seal  46 , the biasing member  49  compresses radially inward to allow clearance while maintaining radially outward force sufficient to sealingly contact the lip seal  46  with the torque converter hub  16 . 
     Once installed, the pump seal assembly  32  seals off and defines the cavity  30  as well as the seal cavity  52 . The only outlet for the cavity  30  is through the orifice  50  to the seal cavity  52 . The size of the orifice  50  and the size of the vent openings  54  determine the steady state fluid pressure in the cavity  30  and seal cavity  52 , and control the rate of fluid flow therethrough, thus controlling the pressure and flow rate of the fluid upstream through the gap  28 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.