Patent ID: 7258217

Claim:
A frictional engagement structure using multiple disks, the frictional engagement structure being adapted to an automatic transmission including a casing, the frictional engagement structure comprising: a first drum arranged at an inner periphery of the casing; a second drum arranged at an inner periphery of the first drum; a plurality of first friction plates splined to one of the casing and the first drum; a plurality of second friction plates splined to the second drum, the first and second friction plates being arranged alternately in a direction of an axis of rotation of the first and second drums; a piston that presses the first friction plates through a disk spring, the piston ensuring coupling between the first friction plates and the second friction plates to frictionally engage the one of the casing and the first drum with the second drum; and a spring bearing member arranged between the first friction plates and the disk spring, the spring bearing member comprising a plate portion substantially parallel to the first friction plates and an outer peripheral portion arranged substantially perpendicular to the first friction plates and interposed between the disk spring and one of the first drum and the casing, wherein the outer peripheral portion has an inner peripheral surface receiving the disk spring, and wherein the spring bearing member is formed with a recess at a corner where the inner peripheral surface of the outer peripheral portion meets a flat surface of the plate portion opposite to the piston.