Vacuum type booster

Abstract

A vacuum type booster which includes a booster piston reciprocatively movable in a shell, a valve sleeve for a control valve fitted to the booster piston and having a disengagement preventive flange superposed on the piston, and a clamp plate engaged with pawls formed by cutting and bending portions of the booster piston for clamping the flange to the booster piston. The booster piston includes pairs of reinforcement ribs which cross the turning direction of the clamp plate and sandwich cutout holes resulting from formation of the pawls. A pair of the ribs on the rear side of the turning direction of the clamp plate permit the clamp plate to turn in a direction for engagement with the pawls and inhibits the clamp plate from turning in the disengaging direction. A space is provided between the outer peripheral part of the disengagement preventive flange and an engagement piece jointing part of the clamp plate body. The booster piston and the disengagement preventive flange include concave-convex engagement parts for inhibiting rotation of the valve sleeve. The booster piston is provided with further reinforcement ribs of an arcuate cross-sectional shape which project forwardly and are adapted to be in contact with the outer peripheral part of the rear surface of the flange. The disengagement preventive flange is also formed with a relief which extends around the outer peripheral part of the flange. A contact surface on the relief located away from the piston surface and reinforcement ribs on the piston serves to restrict forward deflection of the piston.