Electrohydraulic flow control apparatus

Claim 1

FLOW CONTROL APPARATUS FOR MAINTAINING A PREDETERMINED RATE OF FLOW OF FLUID UNDER PRESSURE TO A WORK LOAD UNDER VARIABLE PRESSURE CONDITIONS, COMPRISING, (A) VARIABLE ORIFICE MEANS, SAID VARIABLE ORIFICE MEANS COMPRISING A BODY HAVING A BORE THEREIN, AN INLET PORT AND AN OUTLET PORT COMMUNICATING WITH SAID BORE AT SPACED POSITIONS, A MOVABLE VALVE MEMBER SLIDABLE IN SAID BORE, SAID MEMBER HAVING A FLUID PASSAGEWAY CENTRALLY FORMED THEREIN WHICH COOPERATES WITH ONE OF SAID PORTS TO FORM A VARIABLE ORIFICE REGULATING THE FLOW OF FLUID FROM SAID INLET PORT TO SAID OUTLET PORT THROUGH SAID PASSAGEWAY, THE AREA OF SAID ORIFICE CHANGING AS SAID VALVE MEMBER IS MOVED AXIALLY, SAID MEMBER HAVING OPPOSED SURFACES OF EQUAL AREAS PRESENTED TO TWO OPPOSED PRESSURE CONTROL CHAMBERS DEFINED IN SAID BORE, BOTH SAID CHAMBERS BEING ISOLATED FROM SAID PASSAGEWAY, INLET PORT AND OUTLET PORT, THERE BEING NO OTHER SURFACES OF SAID MEMBER EXPOSED TO FLUID PRESSURE TENDING TO MOVE SAID MEMBER AXIALLY, AND ELASTIC MEANS BIASING SAID MEMBER IN A DIRECTION TENDING TO CLOSE SAID VARIABLE ORIFICE, (B) PRESSURE COMPENSATOR MEANS MAINTAINING A PRESSURE DIFFERENTIAL BETWEEN FLUID PRESSURES AT SAID INLET PORT AND OUTLET PORT WHICH IS SUBSTANTIALLY CONSTANT FOR ANY GIVEN POSITION OF SAID MEMBER WITH RESPECT TO SAID BODY, AND (C) ELECTRICALLY CONTROLLABLE MEANS FOR ESTABLISHING A PRESSURE DIFFERENTIAL BETWEEN THE PRESSURES OF FLUID IN SAID TWO CONTROL CHAMBERS, SAID ELECTRICALLY CONTROLLABLE MEANS HAVING AN INLET CONNECTED TO ONE OF SAID CONTROL CHAMBERS AND AN OUTLET CONNECTED TO THE OTHER OF SAID TWO CONTROL CHAMBERS AND TO A FLUID DRAIN, MEANS INCLUDING A FLOW RESTRICTOR CONNECTING SAID INLET TO A SOURCE OF PRESSURE FLUID, THE FLUID FORCE ARISING FROM THE PRESSURE DIFFERENTIAL ESTABLISHED BY SAID ELECTRICALLY CONTROLLABLE MEANS BEING THE SOLE PRESSURE DIFFERENTIAL FLUID FORCE WHICH IS EXERTED ON SAID MOVABLE MEMBER TENDING TO MOVE SAID MOVABLE MEMBER TO VARY THE AREA OF SAID ORIFICE.