Electrohydraulic control arrangement

Claim 1

Electrohydraulic control valve for a hydraulic power device (17, 17''), said valve having: a valve housing (10) formed with a slider bore (18) and a control pisTon chamber (37, 39); a spool slider (19) slidable in said bore; supply duct means interconnecting said bore with a pressure line (11, 13) and a return line (14); operating duct means (15, 16) for interconnecting said slider bore with said power device, said spool valve interrupting communication between said supply duct means and said operating duct means when said spool valve is in centered position; and means controlling the position of said spool slider (19) comprising: centering means (34) to center said spool slider and maintain said slider centered in said bore; a differential control piston (36) having a larger (41) and a smaller (38) acting surface connected to said spool slider, said piston being slidable in said control piston chamber (37, 39) and subdividing said chamber into a first, smaller chamber (37) and a second, larger chamber (39); a first electromagnetically operated valve means (47) and a connecting duct (46) interconnecting and controlling flow between said first and said second chamber; a first duct (42) directly connecting said first smaller chamber (37) and said pressure line; and a second valve means (45) and a second duct (44) connected to and controlling flow from said second larger chamber (39) to the return line, whereby, when both electromagnetic valve means (45, 47) are closed, the second, larger chamber is isolated from the supply line (11) by the closed first valve means (47) and from the return line (14) by the closed second valve means (45) and the differential control piston (36) will remain in the position commanded by said hydraulic fluid admitted to the respective chambers before closing of both said valve means.