Frictional engagement device for an automatic transmission

摘要

A frictional engagement device for an automatic transmission, by which an input shaft and an output shaft are engaged or disengaged by use of oil pressure. A casing connected to an input shaft and a first piston disposed in the casing define a first oil pressure chamber. The first piston is rotationally movable by predetermined angle and is axially movable by predetermined distance relative to the casing. A second piston disposed in the first piston defines a second oil pressure chamber with the first piston, and the second piston is axially movable relative to the first piston. Separator plates axially slidably connected to the first piston and clutch discs axially slidably connected to a hub which is fixedly connected to the output shaft are engaged by a displacement of the second piston by supplying pressurized oil to the second oil pressure chamber and/or to the first oil pressure chamber. The oil passages in the casing and the first piston connect to each other when one of them rotationally moves relative to the other after the first piston is displaced with supplying pressurized oil to the first oil pressure chamber. The pressurized oil supplied to the first oil pressure chamber is then discharged and the engagement is released.