Patent ID: 8657088

Claim:
A lock-up clutch comprising: a front cover connected with an engine side rotation member, a lock-up piston torque-transmittably connected with a transmission input shaft side rotation member through a damper device, a plurality of torque transmitting plates intervening between the front cover and the lock-up piston, and a plurality of annular friction materials forming three or more friction surfaces between two of the front cover, the lock-up piston and the torque transmitting plates, the friction materials being constituted by a first friction material frictionally contactable with the front cover, a second friction material frictionally contactable with the lock-up piston, and at least one third friction material frictionally contactable with at least one of the torque transmitting plates, the three or more surfaces being constituted by outside friction surfaces respectively formed by the first friction material and the second friction material and each having a small area, and inside friction surface formed by the third friction material and each having a large area, the first friction material, the second friction material, and the third friction material respectively having friction surface side portions each formed with at least one circumferential groove circumferentially extending, the circumferential grooves being constituted by first circumferential grooves respectively formed on the first friction material and the second friction material and each having a large area, and second circumferential grooves formed on the third friction material and each having a small area.