Vacuum brake booster with mechanical emergency braking assistance

Abstract

A vacuum brake booster ( ) has a vacuum chamber ( ) and a working chamber ( ) separated from one another in a pressure-proof manner by a movable wall ( ). A control valve ( ), which comprises a housing ( ) workingly coupled to the movable wall ( ), has a first valve seat ( ), which is disposed in the housing ( ) and to achieve a pressure difference at the movable wall ( ) is capable of controlling the supply of at least atmospheric pressure to the working chamber ( ) in dependence upon the displacement of an input element ( ) coupled to the first valve seat ( ). For improved boosting of the brake force during emergency braking operations, an armature ( ), which cooperates with a permanent magnet ( ), is provided in the control valve housing ( ) and is rigidly coupled on the one hand to the actuating element ( ) in actuating direction and on the other hand to the first valve seat ( ). The armature ( ) is resiliently preloaded counter to actuating direction and in the starting position of the control valve ( ) is held at a first distance from the permanent magnet ( ). The armature ( ), as it approaches the permanent magnet ( ) and is less than a previously defined second distance away, which is smaller than the first distance, is pulled by the permanent magnet ( ) counter to the resilient preloading force acting upon the armature ( ) and with simultaneous cancellation of its, in actuating direction, rigid coupling to the actuating element ( ) into contact with the permanent magnet ( ).