Brake pressure control valve of a double piping system

Claim 1

A brake pressure control valve for a double piping hydraulic braking system, comprising: a housing having a bore formed therein; a pair of substantially identical valve units coaxially and symmetrically arranged in said bore, each valve unit including a valve body, a pressure control piston and a spring, and being constructed to produce a controlled outlet hydraulic pressure in accordance with the magnitude of a hydraulic pressure applied thereto; a pair of free pistons respectively associated with the paired value units and contacting each other to be movable therewith, said free pistons supporting the associated valve bodies and one end of the associated springs to cause one of said valve units to produce, when the other valve unit fails to operate, an outlet hydraulic pressure which is equal to the applied pressure in magnitude; and a self-centering promoting means which causes each of the springs to apply no force to the corresponding free piston when said corresponding free piston moves away from its home position toward the other of said free pistons, said self-centering promoting means comprising: associated with said each valve unit: a valve casing; a hollow member retained in said casing to retain substantially all essential parts of the associated valve unit in the casing, said hollow member having a shoulder portion which protrudes into the interior of said casing; a radially outwardly projected portion of the associated free piston being axially slidably received in said hollow member, said associated free piston having an outside end contacting the other free piston of said pair of free pistons; and an annular spring seat on which said one end of said spring is seated, said spring seat being in abutment with both said shoulder portion and said radially outwardly projected portion at the same time when said associated piston assumes its home position.