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.
In a hydraulic control system for a road grader of the type having a plurality of position adjusting mechanisms for a blade assembly controlled by closed center control valves, respectively, an automatic pressure regulator, comprising: an unloading valve including a housing having a bore and an inlet passage connected to said bore and adapted for connection to a source of pressurized fluid, a flow control element in said bore shiftable between closed and bypass positions, spring means urging said flow control element toward said closed position, a first hydraulic actuator in fluid communication with said inlet passage and acting on said flow control element to urge said flow control element to said bypass position upon the inlet passage pressure reaching a first pressure level, and a second hydraulic actuator adapted for connection to said control valves and acting on said flow control element to move it to said closed position when said pressure delivered by any one of said control valves reaches a second pressure level which substantially exceeds said first pressure level, and a pressure limiting valve including a housing, a bore in said housing, an inlet port to said bore in said housing adapted to communicate with a source of pressurized fluid, an outlet port connected to said bore and adapted for connection in fluid delivery relation to said control valves, a flow control spool shiftable between open and closed positions, spring means biasing said spool toward its open position, and hydraulic pressure responsive actuating means subject to pressure delivered to said control valves and acting on said flow control spool to shift it to its closed position upon the pressure of fluid delivered to said control valves exceeding a predetermined pressure substantially that of said second pressure level.
Claim 2
Dependent Claim
291 words
In a hydraulic control system for a road grader of the type having a plurality of position adjusting mechanisms for a blade assembly controlled by closed center control valves, respectively, an automatic pressure regulator, comprising: an unloading valve including a housing having a bore and an inlet passage connected to said bore and adapted for connection to a source of pressurized fluid, a flow control element in said bore shiftable between closed and bypass positions, spring means urging said flow control element toward said closed position, a first hydraulic actuator in fluid communication with said inlet passage and acting on said flow control element to urge said flow control element to said bypass position upon the inlet passage pressure reaching a first pressure level, and a second hydraulic actuator adapted for connection to said control valves and acting on said flow control element to move it to said closed position when said pressure delivered by any one of said control valves reaches a second pressure level which substantially exceeds said first pressure level, and a pressure limiting valve including a housing, a bore in said housing, an inlet port to said bore in said housing adapted to communicate with a source of pressurized fluid, an outlet port connected to said bore and adapted for connection in fluid delivery relation to said control valves, a flow control spool shiftable between open and closed positions, spring means biasing said spool toward its open position, and hydraulic pressure responsive actuating means subject to pressure delivered to said control valves and acting on said flow control spool to shift it to its closed position upon the pressure of fluid delivered to said control valves exceeding a predetermined pressure substantially that of said second pressure level.
Claim 3
Dependent Claim
16 words
The invention of claim 1 wherein said predetermined pressure is slightly below said second pressure level.