Electrohydraulic control apparatus

Claim 1

An electrohydraulic control assembly for controlling the operating direction of a bidirectional hydraulic work motor, comprising, a control valve unit including a motor controlling slide valve with pressure chambers on opposite sides thereof, neutral position springs and means in said chambers for maintaining said slide valve in a neutral position in the absence of unequal pressures in said chambers, said slide valve being selectively movable in opposite directions from a neutral position in response to pressure in either of said chambers for motor controlling purposes, a source of pressurized fluid and an exhaust tank, a hydraulic bridge circuit between said source and said tank having two supply branches connected to said source and two exhaust branches connected to said tank, pressure holding means between said exhaust branches and said tank for holding the bridge outlet pressure above atmospheric pressure, said bridge circuit having diagonally opposite ports between said supply and exhaust branches connected to said slide valve pressure chambers, valves having pressure operated chambers including a pressure operated supply valve in each supply branch and a pressure operated exhaust valve in each exhaust branch, said supply and exhaust valves being pressure operable to closed positions, pressure dissipation means between said pressure operated chambers of said exhaust valves and said tank to effect unloading of said exhaust valves in the absence of loading pressures, said exhaust valves having ball type closure elements, solenoid pilot valve means connected to respective pairs of said pressure operated chambers of said supply and exhaust valves to effect selective closing of said valves to selectively pressurize and exhaust said control valve unit chambers to cause said slide valve to move in a selected direction, said slide valve having rapid movement to a neutral position upon the deenergization of a respective pair of solenoid pilot valve means and the subsequent release of operating pressures in said bridge valves by the action of one of said neutral position springs causing said slide valve to move and force fluid from one of said chambers to the other through said bridge valves in said exhaust branches, and valve opening spring biasing means for each of said exhaust valves for rapidly overcoming said pressure holding and dissipation means to rapidly open said ball type closure elements thereof in the absence of a closing control pressure to avoid a cavitational action by preventing the closing of an exhaust valve due to a strong suction developed in one of said chambers as a result of said rapid movement of said slide valve.