AUTOMATIC BRAKE POWER ASSIST

摘要

PROBLEM TO BE SOLVED: To make an output variation of a brake power assist as small as possible, or substantially zero even if a magnitude of negative pressure introduced to a constant pressure camber varies. SOLUTION: An automatic brake power assist has a solenoid 38 which causes a plunger 17 constituting a valve mechanism 15 to advance separately from an input shaft 32 to achieve switching a passage of the valve mechanism 15. The plunger 17 has a piston 39 where an atmospheric pressure introduced to an atmospheric pressure camber 40 is applied to a front side of the piston 39 and an pressure of constant pressure chambers A, C introduced to a negative pressure chamber 41 is applied to a rear side thereof to energize the piston 39 toward the rear side. It is preferable that a pressure receiving area of the piston 39 is set to be substantially equal to that of a velief valve seat 18 of the plunger 17.