Pressure limiter for hydraulic brake booster

A hydraulic brake booster having a housing with a pair of bores therein, said bores communicating with a pressure chamber, a pressure responsive piston slidably received in one of said bores, said piston cooperating with means for effecting a brake application responsive to movement of said piston;

• an inlet, an outlet and a vent port all communicating with the other of said bores for communicating pressurized fluid through said housing, said other bore being stepped to provide a small diameter portion and a large diameter portion, a pressure responsive valve member slidably received in said small diameter portion, said valve member being movable relative to said housing between a first position in which said valve member communicates said inlet with said outlet and closes communication from said inlet to said pressure chamber while communicating said vent port with said pressure chamber and a second position in which said valve member restricts communication between said inlet and outlet and opens communication from said inlet to said pressure chamber while closing communication between said pressure chamber and said vent port, a ring member slidably received in said large diameter portion and cooperating with said valve member to define an annular chamber radially disposed between said valve member and said large diameter portion and communicating with said vent port, said ring member defining a first area which is exposed to said annular chamber and a second oppositely disposed area which is exposed to said pressure chamber, said vent port providing communication with said annular chamber, yieldable resilient input means for moving said valve member from said first position toward said second position, said ring member producing a force opposing movement of said valve member toward said second position responsive to the pressure differential between pressurized fluid in said pressure chamber acting on said second area and vent port pressure in said annular chamber acting on said first area, said input means yielding responsive to said force at a predetermined pressure differential to prevent further communication of pressurized fluid to said pressure chamber and said vent port intersecting said other bore substantially at an axial intersection between said small and large diameter portions to remain continuously open to said annular chamber in all positions of said pressure responsive valve member during the brake application.