Patent ID: 7647864

Claim:
A piston for a hydraulic clutch comprising: a piston main body having a pressure receiving portion extending in a diametrical direction and a cylinder portion bent from the pressure receiving portion so as to extend, and arranged within a clutch cylinder so as to be movable in an axial direction; and a seal ring fitted and attached to the piston main body, said seal ring including: a metal ring constituted by a fitting tube portion fitted and attached to said cylinder portion and a flange portion extending in a diametrical direction from one end in the axial direction so as to oppose said pressure receiving portion in the axial direction; and a seal main body integrally formed on the metal ring and made of an elastic material, said seal main body including: a film base portion coating an entire surface of the metal ring; a first seal lip integrally formed on the film base portion and brought into close contact with a cylindrical inner surface of said clutch cylinder so as to be slidable in the axial direction; a second seal lip integrally formed on the film base portion and extending from an end portion of said flange portion so as to be brought into close contact with said pressure receiving portion; an axial direction compression seal portion integrally formed on the film base portion and provided on an opposing surface to said pressure receiving portion on said flange portion and interposed in a state of being compressed in the axial direction with respect to said pressure receiving portion; and a diametrical direction compression seal portion integrally formed on the film base portion and provided on an opposing surface to said cylindrical tube on the fitting tube portion and interposed in a state of being compressed in the diametrical direction with respect to said cylindrical portion.