Vacuum brake booster with mechanical emergency braking assistance

Abstract

A vacuum brake booster ( ) has a vacuum chamber ( ) and a working chamber ( ), which are separated from one another in a pressure-proof manner by a movable wall ( ). A control valve ( ), which has a housing ( ) workingly coupled to the movable wall ( ), has a valve seat ( ), which is disposed in the housing ( ) and which in dependence upon the displacement of an input element ( ) may control the supply of at least atmospheric pressure to the working chamber ( ) in order to achieve a pressure difference at the movable wall ( ). For improved braking force assistance during emergency braking operations, an armature ( ) cooperating with a permanent magnet ( ) is provided in the control valve housing ( ) and coupled in actuating direction to the actuating element ( ). The armature ( ) is spring-biased counter to actuating direction and, in the normal position of the control valve ( ), is held at a first distance from the permanent magnet ( ). In the course of an approach towards the permanent magnet ( ) the armature ( ), when it 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 spring bias acting upon the armature ( ) and with simultaneous cancellation of its, in actuating direction, rigid coupling to the actuating element ( ) into abutment with the permanent magnet ( ). For adjusting the distance between the armature ( ) and the permanent magnet ( ) in the non-actuated state of the vacuum brake booster ( ), the axial position of the permanent magnet ( ) relative to the control valve housing ( ) and/or the distance between the armature ( ) and the valve seat ( ) is adjustable.