Vacuum servo unit for a vehicle braking system

摘要

A vacuum servo unit includes a partition member having an outer periphery that engages the movable wall member in an air tight manner. A receiving chamber is defined between the partition member and the movable wall member, and the receiving chamber is adapted to be communicated with the atmosphere. A passage that introduces atmospheric air into the receiving chamber is engaged in an air tight manner with the partition member and extends through the constant pressure chamber. A change member in the form of a solenoid valve selectively communicates the receiving chamber with the constant pressure chamber or with the atmosphere. Accordingly, the servo efficiency of the vacuum servo unit is increased. In addition, the unit can be operated automatically by supplying electric power to thereby increase brake force so that the brake feeling is advanced.