Brake booster

A hydraulic braking system comprising:

• a brake pedal;
• a master cylinder coupled with the brake pedal;
• a hydraulic control unit coupled with a plurality of wheel brakes;
• and
• a brake booster coupled between the master cylinder and the hydraulic control unit, the brake booster including
• 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 in fluid communication with the master cylinder;
• and
• a second fluid chamber having an opening in fluid communication with the hydraulic control unit;
• wherein the screw drive arrangement is movable relative to a piston of the piston assembly between an engaged position, in which the first fluid chamber is isolated from the second fluid chamber, and a disengaged position in which the first fluid chamber is not isolated from the second fluid chamber.