Double acting friction band for gear ratio control of planetary gear sets

摘要

An automatic transmission has a planetary gear set with a ratio controlling rotatable reaction element capable of either clockwise or counterclockwise rotation in accordance with different inputs to the gear set and resultant reactive torque loads applied thereto. A circular double acting brake band is used to selectively hold the reaction element stationary when desired and has opposite end portions that alternately serve as control application inputs or a grounding function. In one operative mode, a first end portion of the band receives an apply control force causing the second end portion to be grounded so that the band frictionally secures the reaction element from rotation in a first rotary direction and to thereby enable a first gear ratio. In another operative mode, the second end portion of the band receives an apply control force in direction opposite to the other apply force to cause the first end portion to be grounded so that the band frictionally secures the reaction element from rotation in a second rotary direction opposite the first rotary direction and to thereby enable a second gear ratio. With the brake band selectively activated from either end portion and anchored at the other end portion, the band is wrappingly energization about the reaction element in accordance with the direction of reaction torque thereon. The activation of the brake band is preferably by a hydraulic piston-operated band-locking lever with a pair of arm portions for selectively apply a force to either of the opposite end portions of the brake band.