Hydraulic power brake booster and open center control valve therefor

Claim 1

A hydraulic brake booster comprising: a housing; a power piston reciprocably received in said housing and defining therewith an inlet chamber operatively fluid connected to a source of hydraulic fluid pressure and an outlet chamber on the other side of said piston from said inlet chamber; said piston having a stepped recess therein opening on the inlet chamber side thereof and a passage therethrough fluid connecting said recess and said outlet chamber; an input member extending into said inlet chamber and connected to be actuated by a brake pedal; an output member engageable with said power piston to transmit force between said power piston and a master cylinder and extending out of said outlet chamber; and open center control valve means including a radially floating first valve element received in said piston recess and an axially movable second valve element on said input member, said valve elements having mating frusto-conical valve faces for controlling fluid flow between said inlet and outlet chambers, an annular retainer circumferentially engaging said piston in axially locked relation and axially engaging said first valve element in axial force exerting relation and retaining said first valve element against axial movement relative to said piston while resistably permitting radial floating movement of said first valve element in said piston recess, yieldable means urging said second valve element axially away from said first valve element and in position against a stop provided on said housing, and reaction means subject to a force indicative of the booster output and transmitting said force to said input member; said valve elements being initially engageable in mating relation upon brake actuation to center said first valve element relative to said second valve element to establish and maintain a concentric annular orifice between said faces.