Abstract

A friction brake band actuating system for automatic transmissions operative for obtaining smooth self-synchronized freewheeler type shifts without the use of one-way roller or sprag clutches. The band functions normally like a conventional brake band providing engine braking while the vehicle is coasting. For both upshifting and downshifting, the actuating system is staged in a one-way mode at the beginning of the shift event. In the one-way mode the self-synchronizing brake band utilizes the band reaction force to regulate a common pressure, which is acting on the apply piston and also on a reaction piston provided for counteracting the force at the band anchor end. The resulting torque capacity of the band varies in direct relationship with the torque the band is transmitting. Consequently, when at the torque reversal point the transmitted torque drops to zero, the torque capacity of the band also drops to a near-zero value and the band becomes automatically released and the brake drum free to turn in opposite direction. The band is fully disengaged after the shift is completed to eliminate the remaining slight residual drag. A bi-directional version of the self-synchronizing band is also included.