Electro-hydraulic control valve

Claim 1

An electro-hydraulic control valve comprising a central body part, an axial bore in the body part and a valve member slidable therein, at least the end portions of said valve member being formed from magnetisable material, a pair of solenoid devices mounted at the opposite ends of said bore, each of said devices including a winding which can be energised to exert a magnetic force on the respective end portion of the valve member to pull the valve member towards the respective end of the bore, groove means comprising five axially spaced circumferential grooves formed in the wall of the bore, the central one of said grooves being an inlet groove and being connected in use to a fluid pressure source, the outer pair of grooves being drain grooves and being connected in use to a drain, the inner pair of grooves being outlet grooves and being connected in use to the opposite ends of a double acting fluid pressure operable mechanism, the valve member having three axially spaced sets of recesses in its peripheral surface, said grooves and recesses being arranged so that in the intermediate position of the valve member the grooves will be covered by the valve member and as the valve member is moved to one side or the other, the central groove will be placed in communication with one of said outlet grooves, the other outlet groove being placed in communication with the adjacent one of the drain grooves, a pair of blind drillings extending inwardly from the ends of the valve member, cylindrical members slidable in said drillings respectively and passages connecting the inner ends of said drillings with said outlet grooves respectively whereby the valve member is subject to a force which depends upon the fluid pressures in said outlet grooves, the force acting to oppose movement of the valve member by the solenoid devices.