Diaphragm brake booster

Claim 1

A diaphragm brake booster comprising: a housing; a diaphragm having a central opening disposed in the said housing and axially movable within said housing; a power piston having an integral annular flange defining a power piston annular groove for receiving therein the inner periphery of the central opening of said diaphragm, said power piston and diaphragm defining first and second chambers, said first chamber being always connected to a vacuum source and said second chamber being normally connected to said first chamber through fluid passage means provided in said power piston, said annular flange having a radial slot; air passage means provided in said power piston and connectable to said second chamber; valve means disposed in said power piston between said air passage means and fluid passage means for preventing fluid communication between said fluid passage means and said second chamber and thereafter for introducing atmospheric pressure into said second chamber; an operator-operated means for actuating said valve means in response to manual operation; said valve means including a plunger having a plunger annular groove defining a reduced diameter portion of said plunger, being operatively engaged with said operator-operated means and axially movable relative to said power piston; a key member including a radially extending portion and an axially extending portion, said radially extending portion disposed in said power piston and engaging said plunger at said reduced diameter portion, the thickness of said radially extending portion being less than the width of said plunger annular groove for preventing excess axial movement of said plunger, said axially extending portion extending through said radial slot for abutting and being supported by said power piston in said power piston annular groove between said power piston and the inner periphery of said diaghragm central opening.