Abstract:
The present invention provides a seal apparatus for a transmission pump. The seal apparatus includes a ring seal configured to seal a gap defined between a transmission pump body and a hub in order to reduce hydraulic fluid leakage. An O-ring is placed around the ring seal such that the O-ring engages the transmission pump body in an axial direction. A retainer ring is disposed around the hub, and a torque converter seal is disposed radially between the transmission pump body and the hub. The torque converter seal applies an axial force which is transferred through the retainer ring in order to compresses the O-ring against the transmission pump body to seal in parallel with the ring seal such that the rate of hydraulic fluid leaking from the transmission pump is reduced. A corresponding method for sealing a transmission pump is also provided.

Description:
TECHNICAL FIELD 
       [0001]    The present invention pertains generally to a method and apparatus providing a transmission pump seal. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional transmission pumps are driven by output from the engine in order to transfer hydraulic fluid and thereby meet cooling, lubrication, and pressure requirements of the transmission. The transmission pump includes a pump body which is stationary relative to the transmission housing, and a pump drive gear which is rotatable within the pump body to drive the pump. Rotational forces from the engine may be transferred to the pump drive gear via a torque converter hub. It is known that transmission pumps can leak, and that such leakage diminishes pump efficiency and vehicle fuel economy. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides a seal apparatus for a transmission pump. The seal apparatus includes a ring seal configured to seal a gap defined between a transmission pump body and a hub in order to reduce hydraulic fluid leakage. An O-ring is placed around the ring seal such that the O-ring engages the transmission pump body in an axial direction. A retainer ring configured to axially retain the ring seal and the O-ring is disposed around the hub. A torque converter seal is disposed radially between the transmission pump body and the hub. The torque converter seal applies an axial force which is transferred through the retainer ring in order to compresses the O-ring against the transmission pump body to seal in parallel with the ring seal such that the rate of hydraulic fluid leaking from the transmission pump is reduced. 
         [0004]    The seal apparatus may also include a snap ring configured to engage and thereby axially retain the torque converter seal. 
         [0005]    The ring seal may be generally cylindrical, or alternatively may define a v-shaped cross-section. 
         [0006]    The ring seal may be composed of polytetrafluoroethylene (PTFE), steel, cast iron or any other suitably matched material. 
         [0007]    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 
         [0008]      FIG. 1  is a partial cross-sectional view of a transmission assembly operatively connected to a torque converter; and 
           [0009]      FIG. 2  is a more detailed cross-sectional view of a transmission pump. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0010]    Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a partial cross-sectional view of a transmission  8  in accordance with the present invention. According to the preferred embodiment shown, the transmission  8  is operatively connected to a torque converter  10 ; however alternate embodiments may replace the torque converter  10  with a damper assembly (not shown), or other rotating cylindrical shaft member. For illustrative purposes, only the top half of the transmission  8  and the torque converter  10  are shown. It should be appreciated, however, that the transmission  8  and torque converter  10  are generally symmetrical about the center line  12  of the transmission input shaft  14 . 
         [0011]    The torque converter  10  includes a torque converter housing  15  which is formed to define a generally cylindrical torque converter hub  16 . The torque converter hub  16  includes an end portion  18  with multiple flat sections  19  that are adapted to engage and thereby drive a pump drive gear  26  as will be described in detail hereinafter. The torque converter  10  is operatively connected to an engine (not shown) such that the torque converter hub  16  rotates about the center line  12  at engine speed. 
         [0012]    The transmission  8  includes a transmission pump  20  configured to transfer hydraulic fluid to meet any cooling, lubrication, and pressure requirements of the transmission  8 . The transmission pump  20  includes a pump body  22  and a pump cover  24  defining a pump cavity  23  therebetween; and a pump drive gear  26 . Rotation of the pump drive gear  26  powers the pump  20  to pressurize hydraulic fluid within the pump cavity  23 . The pump drive gear  26  defines opposing side portions  28   a ,  28   b , and generally flat engagement portions  32 . The engagement portions  32  of the drive gear  26  are engaged by the flat sections  19  of the torque converter hub  16  such that the rotation of the torque converter hub  16  is imparted to the drive gear  26  thereby powering the pump  20 . While the drive gear  26  is preferably mechanically coupled to the torque converter hub  16  via the geometry of the flat engagement portions  32  and the flat sections  19 , other conventional coupling geometries such as, for example, a splined interface may be envisioned. 
         [0013]    A bushing  40  is configured to radially support the pump body  22  on the torque converter hub  16  such that the torque converter hub  16  is rotatable. The bushing  40  of the present invention is primarily configured to bear the weight of the torque converter  10 , torque converter imbalance loads, and the radial loads generated at the pump drive gear  26 , and therefore the bushing  40  differs from more conventional designs wherein similarly disposed bushings serve both load bearing and sealing functions. The bushing  40  is preferably press fit into engagement with the pump body  22  so that there is no relative rotation therebetween. The bushing  40  is generally cylindrical and defines opposing end portions  42 ,  44  (shown in  FIG. 2 ). 
         [0014]    The transmission  8  includes a stator shaft  30  at least partially circumscribed by the torque converter hub  16  and which is operatively connected to both the pump cover  24  and the torque converter  10 . The stator shaft  30  is shown as being integral with the pump cover  24 , however, these components may alternatively be separate and connected together in any known manner. A chamber  34  is at least partially defined by the pump cover  24  and the stator shaft  30 . The chamber  34  fills with pressurized hydraulic fluid when the torque converter  10  is operating in a “lock-up mode”. As is known in the art, torque converter “lock-up mode” is a mode wherein the torque converter turbine  36  and the torque converter pump  38  are coupled and rotate together in order to improve efficiency. 
         [0015]    Referring to  FIG. 2 , the pump  20  is shown in more detail. Hydraulic fluid from the pump cavity  23  can leak along the opposing side portions  28   a ,  28   b  of the pump drive gear  26 , and between the bushing  40  and the torque converter hub  16  as shown with arrows representing leaked hydraulic fluid. Additionally, when the torque converter  10  (shown in  FIG. 1 ) is in lock-up mode, pressurized hydraulic fluid in the chamber  34  can leak between the bushing  40  and the torque converter hub  16 . A torque converter seal  46  is provided to catch and thereby preserve the hydraulic fluid which leaks past the bushing  40 . The torque converter seal  46  generally includes an elastomeric seal member  48  integrally molded onto a metallic carrier  50 . A garter spring  52  applies radial pressure bringing the seal member  48  into engagement with the torque converter hub  16  to form a seal at the interface therebetween. A snap ring  54  engages the metallic carrier  50  to axially retain the torque converter seal  46 . 
         [0016]    The pressurized hydraulic fluid which leaks past the bushing  40  and is then caught by the torque converter seal  46  accumulates in a cavity  56 . The pressurized hydraulic fluid in the cavity  56  is ultimately transferred to a low-pressure sump or reservoir (not shown). It should be appreciated that the energy expended to increase the pressure of the hydraulic fluid which leaks past the bushing  40  is wasted and that such leakage is therefore inefficient. Accordingly, the present invention incorporates a ring seal  66 , an O-ring  68  and a vented retainer ring  70 , described in detail hereinafter, in order to reduce the amount of pressurized hydraulic fluid leakage and thereby improve the efficiency of the pump  20 . It should be appreciated that the O-ring  68  may alternatively be replaced with any elastomeric member which is compressible and circumferentially disposed and may, for example, be integrally bonded onto the vented retainer ring  70  to form a single component. 
         [0017]    The pump body  22  defines a seal recess  72  adapted to position and retain the ring seal  66 . The ring seal  66  circumscribes a portion of the torque converter hub  16 , engages the end portion  44  of the bushing  40 , and is disposed at least partially within the seal recess  72 . Radial clearance between the seal recess  72  and the ring seal  66 , and axial clearance between the end portion  44  and the ring seal  66  are required such that the ring seal  66  generally floats in both the radial and axial directions. The ring seal  66  is not radially constrained by the pump body  22  other than when the O-ring  68  is compressed in an axial direction. The composition of the ring seal  66  can be selected to produce a given leakage flow rate and may include, for example, steel, iron, or plastic. According to the preferred embodiment of the present invention, the ring seal  66  is composed of polytetrafluoroethylene (PTFE). The ring seal  66  can be configured to define the generally cylindrical shape shown in  FIG. 2 , or alternatively can define a V-shaped cross-section with a metered orifice (not shown). 
         [0018]    A portion of the pump body  22  which defines the seal recess  72  also forms a protrusion  74  extending in an axial direction toward the torque converter  10  (shown in  FIG. 1 ). The ring seal  66  is radially retained between the protrusion  74  and the torque converter hub  16 . The pressurized hydraulic fluid which leaks past the bushing  40  follows either a first flow path between the protrusion  74  and the ring seal  66 , or a second flow path between the ring seal  66  and the torque converter hub  16 , as shown with arrows representing leaked hydraulic fluid. It has been observed that the implementation of the ring seal  66  reduces the amount of pressurized hydraulic fluid leakage from the pump  20  as compared to conventional designs which rely on a bushing to seal. 
         [0019]    The rate of pressurized hydraulic fluid leakage can be further reduced with the addition of the O-ring  68  which is configured to restrict the flow path defined between the protrusion  74  and the ring seal  66 . The O-ring  68  is disposed radially around the ring seal  66 , and is axially positioned to engage the protrusion  74 . Therefore, the O-ring  68  is configured to form a first seal at the interface between the O-ring  68  and the ring seal  66 ; a second seal at the interface between the O-ring  68  and the protrusion  74 ; and a third seal at the interfaces between the O-ring  68  and the vented retainer ring  70 . 
         [0020]    The vented retainer ring  70  is disposed radially around the torque converter hub  16 , and is configured to axially retain the ring seal  66  and the O-ring  68 . Additionally, the vented retainer ring  70  applies an axial force tending to compress the O-ring  68  against the protrusion  74 . More precisely, during installation the metallic carrier  50  of the torque converter seal  46  is forcibly pushed into engagement with the vented retainer ring  70 , and such forcible engagement is maintained with the addition of the snap ring  54 . The installation of the metallic carrier  50  in this manner applies an axial force to the vented retainer ring  70 , and the vented retainer ring  70  transfers this force to the O-ring  68 . Advantageously, the compression of the O-ring  68  against the protrusion  74  forms a tighter seal therebetween. As the O-ring  68  is compressed against the protrusion  74 , the O-ring  68  is deformed to increase the area of contact and thereby accommodate for stack variations. Additionally, hydraulic pressure between bushing end  44  and pump seal recess  72  pushes the ring seal  66  into the vented retainer ring  70  to form an axial seal, and the PTFE ring seal  66  is radially compressed to seal against the torque converter hub  16 . 
         [0021]    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.