Seal assembly for reducing fluid loss from transmission pump

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.

The invention relates to a seal assembly for a transmission pump.

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.

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.

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 .

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.