Pressure control valve for a vehicle hydraulic brake system

Claim 1

A pressure control valve for a vehicle hydraulic brake system including a first brake circuit connected between front wheel brake cylinders of a vehicle and one pressure chamber of a tandem master cylinder and a second brake circuit associated with rear wheel brake cylinders of said vehicle comprising: a housing having a longitudinal axis and a first bore coaxial of said axis; a pressure chamber disposed in said first bore adjacent one end thereof coupled to said one chamber; a regulator inlet chamber disposed in said first bore adjacent the other end thereof coupled to the other chamber of said master cylinder; a regulator outlet chamber disposed in said first bore spaced from and communicating with said regulator inlet chamber through a fluid passageway within said first bore coaxial of said axis, said regulator outlet chamber being coupled to said rear wheel brake cylinders; a valve having a closure member disposed in a controlling relationship with said fluid passageway; an annular piston disposed in said first bore slidable therein between limits, said annular piston having one annular surface thereof providing a boundary for said regulator oulet chamber and subject to regulated pressure of said second brake circuit, the other annular surface thereof providing a boundary for said pressure chamber and subjected to pressure of said first brake circuit, and a second bore in said annular piston coaxial of said axis; and a control piston preloaded by a spring extending through and slidable in said second bore having one end thereof in a controlling relationship with said closure member and bearing on said annular piston in the direction of said spring, and the other end thereof bearing against said spring and having an annular surface providing the other boundary for said pressure chamber and being subjected to pressure of said first brake circuit.