Pneumatic booster with electromagnetic servo control, especially for motor vehicle brake systems

Claim 1

A pneumatic booster with electromagnetic servo control, for motor vehicle brake systems, comprising a booster casing (10) inside which a first chamber (12) and a second chamber (14) are separated from each other by a movable wall (16), a valve housing (22) which is connected to the movable wall (16) for joint axial relative movement with respect to the booster casing (10) and which includes a first valve seat (24), a sealing member (60) which is arranged to be axially movable inside the valve housing (22) and is biased in a direction towards the first valve seat (24), a piston (42) which is guided in the valve housing (22) so as to be axially displaceable and designed to transmit actuating forces from an actuator member (44) to an output member (50), a valve closing member (30) which is guided in the valve housing (22) so as to be axially displaceable with respect to the piston (42) and has a second valve seat (32) for cooperation with the sealing member (60), an abutment member (52) which projects to the outside substantially radially through a recess (36) formed in the valve housing (22) and defines an inoperative position of the piston (42) with respect to the booster casing (10) by abutting against a stop (54) formed at the booster casing (10), when the actuator member (44) is not actuated, a valve spring (38) which biases the valve closing member (30) in the direction of the sealing member (60), and an electromagnet (40) which, when energized, moves the valve closing member (30) away from the sealing member (60) against the resistance of the valve spring (38), characterized in that the abutment member (52) is connected firmly to the piston (42) and received in the recess (36) of the valve housing (22) and in a corresponding radial recess (34) of the valve closing member (30) with an axial clearance of such dimensions that the valve spring (38) holds the valve closing member (30) against the abutment member (52) when the electromagnet (40) is not energized, simultaneously holding the second valve seat (32) against the sealing member (60) when the piston (42) is in said inoperative position.