Patent ID: 8113595

Claim:
An electrically boosted vehicle brake system having a master cylinder, an operator brake pedal, and individual wheel brake actuators, comprising: a master cylinder housing; a generally cylindrical bore in said housing; a first piston reciprocably disposed in said bore defining in conjunction therewith a first variable volume chamber; and an electromechanical arrangement coupled to said first piston and operable in response to operator brake pedal force to urge said first piston in a direction to decrease said first chamber volume and apply fluid pressure to certain ones of the wheel brake actuators; the electromechanical arrangement including a reversible electric motor having an output shaft with a threaded portion extending into the bore and a nut threadedly received on the threaded portion, an arrangement for preventing nut rotation about the shaft, the nut engaging and moving the first piston in a direction to decrease said first chamber volume and apply power boosted fluid pressure to the certain ones of the wheel brake actuators in response to shaft rotation in a first sense and releasing said first piston allowing an increase in said first chamber volume in response to shaft rotation in a second sense.