Braking pressure control device

A braking pressure control device for an automotive vehicle wheel brake system having an automatic control operating with hydraulic fluid, said wheel brake system including a master cylinder, at least one wheel brake cylinder, at least one normally open inlet valve controlling communication of said master cylinder and pump with said wheel cylinder and at least one normally closed outlet valve for said wheel cylinder allowing outflow of hydraulic fluid from said wheel cylinder to a low pressure region in the system, at least one motor-driven pump for generating pressurized hydraulic fluid, an electronic control unit, said pressure control device including means responsive to opening of said outlet valve and a resulting pressure drop in the outlet line of said wheel cylinder to close said inlet valve, said braking pressure control device comprising a valve housing, an inner piston, an outer stepped diameter piston having a larger diameter portion and a smaller diameter portion, said inner piston slidable within said outer piston, said outer piston slidable in said valve housing, said outer piston stepped diameter forming a piston step;

• a master cylinder pressure chamber defined in said outer piston with channels in said housing and said outer piston enabling pressurization of said master cylinder pressure chamber with hydraulic fluid from said pump or master cylinder, said inlet valve including an inlet valve seat formed in said outer piston adjacent said master cylinder pressure chamber and an inlet valve closure element carried within said outer piston in said master cylinder pressure chamber to be movable onto and off said valve seat, a spring urging said closure element onto said valve sat, a wheel cylinder pressure chamber defined in said outer piston and channel in said housing and outer piston allowing a fluid connection to said wheel cylinder, pressure in said wheel cylinder chamber exerted on said outer piston step, said master cylinder pressure chamber communicating with said wheel cylinder pressure chamber through said valve seat with said inlet valve closure element moved off said valve seat, an outlet chamber in said inner piston and channels in said valve housing, outer piston and inner piston allowing connection to a low pressure region of said system via said outlet valve, said channels in said housing and outer piston forming a control edge upon movement of said outer piston from an abutting position against said housing;
• a portion of said inner piston engagable with said inlet valve closure element upon movement towards said closure element to move said valve closure element off said valve seat, said inner piston portion configured to allow flow out of said wheel cylinder pressure chamber through said valve seat and into said wheel cylinder pressure chamber, an inner channel in said inner piston communicating said wheel cylinder pressure chamber with said outlet chamber with said inner piston portion moved out of engagement with said closure element, a spring in said outer piston urging said inner piston portion into engagement with said closure element, a control spring in said housing acting on said outer piston urging said outer piston towards said abutting position against said wheel cylinder chamber, pressure on said step in said outer piston directed so as to urge said outer piston away from said position abutting said housing.