Power assist mechanism

Claim 1

A brake booster mechanism comprising a casing, at least one pressure reponsive power wall in said casing, valve mechanism means associated with said power wall and being movable relative thereto to control the differential pressure across the said power wall, actuating means connecting to a pedal for manually moving said valve mechanism means, output means for connecting the said power wall to a brake master piston, brake feel reaction means having a compressive member interposed between the said actuating means and the output means with a play clearance with respect to the actuating means in the retracted position thereof, and adjusting thread means for regulating said play clearance whereby during initial stage movement said actuating means is opposed by no brake reaction force through said compressive member until the actuating means becomes in abutment against the compressive member past the play clearance, and wherein said brake feel reaction means comprises a cage member, a head member connecting to said output means and slidably received in the cage member to define a chamber therein, said compressive member being held captive in the chamber, said actuating means being movable relative to and having an acting face exposed against a portion of the compressive member with said clearance maintained therebetween, said cage member being axially threaded on the external face thereof, said adjusting thread means being an internally threaded ring in engagement with the threaded cage while being normally spring-biased toward abutment engagement with said power wall.