Torque transfer devices of the type typically used in automatic transmissions for vehicles are interposed between two relatively rotatable members. That is, a torque transfer device may be interposed between an input shaft and an output shaft, or between a rotatable shaft and a fixedly positioned member, commonly designated as "ground." Hence, one of the relatively rotatable members may be either rotatable or fixed, but the other relatively rotatable member is rotatable. A torque transfer device may, therefore, operate either as a clutch operatively to join two rotatable members or as a brake operatively to connect a rotatable member to ground.
A typical torque transfer device comprises a plurality of apply or first torque plates that are nonrotatably connected to one of the relatively rotatable members (as by a plurality of tangs on each of the first torque plates which engage a grooved spline arrangement on the relatively rotatable input member). The typical torque transfer device also employs a plurality of interleaved reaction or second torque plates that are nonrotatably connected to the other of the relatively rotatable members (as by a plurality of tangs on each of the second torque plates which engage a grooved spline arrangement on the relatively rotatable output member or ground). Annular friction disks are generally interposed between the successively interleaved first and second torque plates, and to assure that the several friction disks will not be displaced when they are not compressed between the successive first and second torque plates, each friction disk is preferably secured to one of the torque plates between which it is sandwiched.
Torque transfer devices are commonly actuated by a piston mechanism that axially compresses and releases the interleaved torque plates. Upon the application of pressure by the piston mechanism, the angular velocity of, for example, an output shaft will assume the angular velocity of an input shaft, and the power delivered by the input shaft is thereby transmitted through the torque transfer device to the output shaft. In this situation the torque transfer device is operating as a clutch.
As implicit from its name, a torque transfer device transmits torque when engaged but torque transfer devices also absorb the shift energy during power shifts, and dissipate that energy as heat. A typical torque transfer device requires approximately 0.5 seconds to be compressed sufficiently to eliminate relative rotation between the first and second torque plates. A considerable amount of heat can be generated during the approximately 0.5 seconds required to eliminate relative rotation between the first and second torque plates in a torque transfer device.
Conventional torque transfer devices are cooled by the circulation of transmission fluid, which is continuously supplied and is, in fact, propelled between the interleaved torque plates by centrifugal forces when the torque plates are not compressed.
Cooling the torque transfer device improves its durability and lengthens its useful life. However, the lubrication process is also the primary source of slip or spin-loss, as the interleaved torque plates rotatably slide relative to one another during the application and release of compressive engagement. Given the means by which prior known torque transfer devices have been cooled, it has not been heretofore possible simultaneously to reduce spin-loss and enhance cooling. Instead, trade-offs must be accepted. Either the durability of the torque transfer apparatus is compromised--as a result of insufficient cooling--or fuel economy is compromised--as a result of slip loss between the torque plates in the torque transfer device.
Another disadvantage of the prior known cooling systems for torque transfer devices is that it has not heretofore been practical to supply continuous cooling to the interleaved torque plates--not only because such cooling would exacerbate the condition which causes slip-loss but also because such an approach would likely require a circulating pump of considerably higher capacity than is required for circulation of the transmission lubricant which serves as the cooling medium. All considered therefore, continuous cooling would raise the cost of the torque transfer device and decrease the power transferred therethrough.