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

PCT No. PCT/EP93/00855 Sec. 371 Date Aug. 19, 1994 Sec. 102(e) Date Aug. 19, 1994 PCT Filed Apr. 6, 1993 PCT Pub. No. WO93/21048 PCT Pub. Date Oct. 28, 1993.Two chambers (12, 14) in a booster casing (10) are separated by a movable wall (16) which is connected to a valve housing (22). The housing contains a movable sealing member (60) with which a first valve seat (24), formed in the valve housing (22), and a second valve seat (32), formed on a movable valve closing member (30), are associated. The valve closing member (30) is guided for axial displacement on a piston (42) and designed as the armature of an electromagnet (40) which is arranged inside the valve housing (22) in such a way that, when energized, it moves the valve closing member (30) away from the sealing member (60) against the resistance of a valve spring (38). The piston (42) is guided for axial displacement in the valve housing (22) and serves to transmit actuating forces from an actuator member (44) to an output member (50). An abutment member (52) fastened to the piston (42) extends outwardly with axial clearance through radial recesses (34, 36) formed in the valve closing member (30) and the valve housing (22), respectively. The abutment member defines a common position of rest of the valve closing member (30) and the piston (42) by abutting against a stop (54) formed at a booster casing (10), when the actuator member (44) is inoperative. At this position of rest, the valve spring (38) holds both the valve closing member (30) against the abutment member (52) and the second valve seat (32) against the sealing member (60).