Fluid control system for earthworking apparatus including automatic pressure regulating means

Abstract

Abstract The control box jaw clutches of a motor grader are hydraulically operated through parallel connected closed center control valves. An automatic pressure regulator is interposed between the source of pressurized fluid and the parallel connected inputs to the control valves. When all the control valves are in neutral, an unloading valve in the pressure regulator bypasses fluid flow from the pressure source to the reservoir at a moderate pressure. When any one of the control valves is moved to an operating position, the unloading valve is automatically conditioned to establish a higher operating pressure. The higher operating pressure is established by hydraulically biasing the unloading valve fluid flow control element by pressurized fluid delivered to the jaw clutch actuators by the associated control valve. Upon the controlled apparatus moving to a limit position, a dumping valve is opened, thereby reducing the pressure to the jaw clutch actuator allowing the centering spring in the jaw clutch mechanism to return it to neutral position even though its control valve is still in an operating position. The reduction in control valve operating pressure, resulting from opening of the dumping valve, reduces the fluid pressure bias on the unloading valve flow control element thereby reducing the bypass pressure level until the 100 psi level is re-established. Fluid bypassed by the unloading valve element is delivered to an auxiliary control valve circuit having a high pressure relief valve. A pressure limiting valve downstream of the unloading valve prevents the jaw clutch control circuits from being subjected to more than an intermediate pressure.

Inventors

• 👤 F Mcray

Bibliographic Details