Patent ID: 8496302

Claim:
A brake booster for use in a hydraulic braking system having a brake pedal, a master cylinder, and a hydraulic control unit, the brake booster comprising: a housing; a screw drive arrangement positioned at least partially in the housing; a motor coupled to the housing for actuating the screw drive arrangement; and a piston assembly positioned in the housing, the piston assembly and the housing together at least partially defining a first fluid chamber having an opening for providing fluid communication with the master cylinder; and a second fluid chamber having an opening for providing fluid communication with the hydraulic control unit; wherein the screw drive arrangement is operable to move a piston of the piston assembly for varying the volume of the second fluid chamber; and wherein movement of the piston does not vary the volume of the first fluid chamber; wherein the screw drive arrangement includes a rotor driven by the motor; wherein the screw drive arrangement further includes a screw coupled to the rotor for rotation therewith; and a nut positioned over the screw; wherein rotation of the screw in a first direction causes movement of the nut in a direction toward the piston assembly; wherein the nut includes a sealing surface selectively engageable with the piston to seal an opening in the piston, thereby isolating the first fluid chamber from the second fluid chamber.