Patent ID: 6345565
Filing Date: 2002-02-12
Classification: B60T

Abstract:
A vacuum servo unit for a vehicle brake system comprising:a housing defining at least a pressure space therein and defining an axial direction: a movable wall provided in the housing capable of advancement and retraction along the axial direction of the housing, the movable wall dividing de pressure space into a front chamber and a rear chamber; a power piston coupled to the movable wall; an input member fitted in the power piston so as to be movable back and forth along the axial direction of the housing; an input rod having a front portion and a rear portion, the front portion being coupled to the input member, the rear portion capable of being coupled to a brake operation member, the front portion being in engagement with the rear portion within the power piston in such a manner that the front portion is movable relative to the rear portion, the input rod being movable along the axial direction of the housing together with the brake operation member; a valve mechanism having an atmosphere valve and a negative pressure valve, the valve mechanism establishing fluid communication between the rear chamber and the atmospheric pressure by opening the atmosphere valve which provides advancing power to the power piston simultaneous with an interruption fluid communication between the rear chamber and the front chamber caused by closing the negative pressure valve when a stroke of the input member caused by the depression of the brake operation member exceeds a set value; an output member for outputting the advancing power of the power piston caused by the depression of the brake operation member; an actuator providing a different advancing power to the power piston independent of the brake operation member; retaining means for holding an initial condition of both the front portion and the rear portion, the retaining means comprising an engaging portion on the rear portion and a hooked member on the housing; and wherein the engaging portion on the rear portion is movable forth-and-back relative to the rear portion.