Vacuum brake booster with mechanical emergency braking assistance and improved noise damping

Abstract

A vacuum brake booster ( ) has a vacuum chamber ( ) and a working chamber ( ), which are separated in a pressure-proof manner from one another by a movable wall ( ). A control valve ( ) having a housing ( ), which is workingly coupled to the movable wall ( ) and in which a first valve seat ( ) is disposed, in order to achieve a pressure difference at the movable wall ( ) controls the supply of at least atmospheric pressure to the working chamber ( ) in dependence upon the displacement of an input element ( ), which is coupled to the first valve seat ( ), of the brake booster ( ). Disposed in the control valve housing ( ) is an armature ( ), which cooperates with a permanent magnet ( ) and which is coupled on the one hand to the input element ( ) in actuating direction and on the other hand to the first valve seat ( ). A spring ( ) biases the armature ( ) counter to actuating direction and in the starting position of the control valve ( ) holds the armature ( ) at a first distance from the permanent magnet ( ). The armature ( ) in the course of a movement towards the permanent magnet ( ), when it is less than a previously fixed second distance, which is less than the first distance, away from the permanent magnet ( ), is pulled counter to the force exerted by the spring ( ) upon the armature ( ) and with simultaneous cancellation of its, in actuating direction, rigid coupling to the input element ( ) into abutment with the permanent magnet ( ). To dampen undesirable impact noises, the spring ( ), which biases the armature ( ) counter to actuating direction, is mechanically coupled to the input element in such a way as to cushion the return stroke motion of the input element ( ), which follows a detaching of the armature ( ) from the permanent magnet ( ), before the input element ( ) has completed its maximum possible return stroke relative to the control valve housing ( ).