Patent ID: 7232022

Claim:
A clutch-purpose hydraulic servo, comprising: a cylinder member having a cylinder portion; a piston member for pressing a friction plate; a return spring that presses the piston member toward the cylinder portion; a cancel plate that is restricted at least from moving to a side opposite from the return spring in an axial direction and that receives a reaction force of the return spring, wherein the cylinder member is disposed as a separate member on a shaft member on which the cancel plate is disposed and which undergoes the same rotation as the cylinder member; an operating oil chamber formed between the piston member and the cylinder portion so as to press the piston member based on a supplied oil pressure; a cancel oil chamber formed between the piston member and the cancel plate; and a stopper device that prevents the cylinder member from movement to a side opposite from the cancel plate in an axial direction, relative to the shaft member, wherein restriction of a movement of the cylinder member to a side of the cancel plate in an axial direction is achieved by such an arrangement that a force, that presses the cylinder member to a side of the stopper device, is always greater than a force, that presses the cylinder member to the side of the cancel plate, based on a spring force of the return spring, an oil pressure in the cancel oil chamber and an oil pressure in the operating oil chamber.