Patent ID: 6361125
Filing Date: 2002-03-26
Classification: B60T

Abstract:
A hydraulic brake booster comprising:a primary master cylinder which generates an output hydraulic pressure in response to a brake operation input; a hydraulic power source; a fluid tank which stores fluid for said hydraulic power source; and a proportional booster valve which proportionally boosts an output hydraulic pressure from said primary master cylinder and supplies the output hydraulic pressure so boosted to wheel brakes, said proportional booster valve including: a casing having a cylinder bore; a control piston unit defining in conjunction with said cylinder bore, a controlling hydraulic pressure chamber introducing an output hydraulic pressure from said primary master cylinder and a boosting hydraulic pressure chamber generating a boosting hydraulic pressure for actuating wheel brakes, said control piston fitted in said cylinder bore so as to reciprocate between a first position and a second position in response to hydraulic pressures of said controlling hydraulic pressure chamber and said boosting hydraulic pressure chamber; an inlet valve communicating between said hydraulic power source and said boosting hydraulic pressure chamber in response to the movement of said control piston unit; and an outlet valve communicating between said boosting hydraulic pressure chamber and said fluid tank in response to the movement of said control piston unit, whereby a hydraulic pressure boosted in proportion to the hydraulic pressure of said controlling hydraulic pressure chamber is generated in said boosting hydraulic pressure chamber; a secondary master cylinder disposed between said boosting hydraulic pressure chamber of said proportional booster valve and said wheel brakes, said secondary master cylinder comprising: a cylinder body formed with a cylinder bore; an operating piston fitted in said cylinder bore so as to reciprocate between a third position and a fourth position, said operating piston dividing the interior of said cylinder body into a front output hydraulic pressure chamber, an intermediate primary input hydraulic pressure chamber and a rear secondary input hydraulic pressure chamber, said third position defining a maximum second input hydraulic pressure chamber, said fourth position defining a minimum second input hydraulic pressure chamber; a return spring biasing said operating piston toward said fourth position of said operating piston; and a valve unit communicating between said primary input hydraulic pressure chamber and said output hydraulic pressure chamber when said operating piston is located at said fourth position and cutting off a communication between said primary input hydraulic pressure chamber and said output hydraulic pressure chamber when said operating piston is located at said third position, wherein said primary input hydraulic pressure chamber is connected to an output port of said primary master cylinder, said secondary input hydraulic pressure chamber is connected to said boosting hydraulic pressure chamber of said proportional booster valve, and said output hydraulic pressure chamber is connected to said wheel brakes.