Abstract: A power control system for a machine having an engine, a hydraulic system, a boom function, and a swing function is disclosed which comprises a sensor for determining the temperature of the engine, a sensor for determining the temperature of the hydraulic system, a cooling system associated with the engine, a cooling system associated with the hydraulic system, a controller connected to the sensors and the cooling systems, the controller for receiving the temperatures of the engine and the hydraulic system and for determining whether the temperatures are within acceptable ranges, the controller for detecting when a boom function and a swing function have been requested.

Abstract: A hydraulic track tensioning circuit is connected to an idler wheel of a track drive mechanism to maintain a tension in a track proportional to the drawbar pull of the track drive mechanism. The tensioning circuit includes a variable pressure relief valve having a variable pressure setting controller which controls the tensioning pressure in a supply line connected to a hydraulic tensioning cylinder in response to the highest pressure in a pair of motor ports of a reversible hydraulic drive motor operative to propel the track drive mechanism.

Abstract: Neutralizer valves are useful in hydraulic steering systems to hydraulically stop the steering motion. However the known neutralizer valve arrangements will not work in load sensing hydrostatic steering systems. The subject load sensing hydrostatic steering system has a limit valve disposed in a load pressure signal signal line to normally communicate a load pressure siganl from a steering valve to a displacement controller of a load sensing variable displacement pump so that the displacement of the pump is regulated to meet the demand for pressurized fluid by the steering valve. When a pair of vehicle members reach a preselected position during a steering maneuver, the limit valve is moved to a position interrupting communication of the load pressure signal to the displacement controller causing the pump to destroke to its minimum output thereby stopping the flow of pressurized fluid to the steering valve and to a pair of steering cylinders.

Abstract: A signal valve (38) is connected to a supply conduit (16) connecting a pump (11) with a control valve (14) for transmitting an artificial load signal to a load signal chamber (34) of a pressure compensated unloader valve (27) when the control valve is at an operating position and the pressure in the supply conduit (16) is below a preselected value. This moves a valve member (31) of the unloader valve (27) to a blocking position causing essentially full pump flow to be directed to the hydraulic jack for decreasing the response time in situations wherein the hydraulic jack has cavitated and no positive load pressure signal is present.

Abstract: A control mechanism (48) is provided to controllably maintain a constant force on an actuator (18) and provide fluid flow to a downstream control valve (24) by controlling a pilot differential pressure between first and second ends (38,40) of a pilot operated control valve (14). A two position valve (56,66) acting in response to a predetermined pressure level in the actuator (18) modulatably controls the flow of pressurized pilot fluid to the pilot operated control valve (14) to position the pilot operated control valve (14). This maintains the pressure in the actuator (18) at the predetermined pressure level and passes the excess flow of fluid from a source (12) to the downstream control valve (24).

Abstract: A valve controls fluid flow to a fluid jack by movement of a single valve spool to a first position. A check valve and bypass valve cooperate to pass fluid exhausted from the fluid jack to a tank bypassing the single valve spool. Movement of the bypass valve is controlled by developing a controlled pressure drop between the fluid in the fluid jack and the fluid between the check valve and the single valve spool in response to the valve spool being moved to a second position.

Abstract: A hydraulic motor and control system which comprises a pump delivering fluid to a control valve. The control valve has a Float position which connects a first end of the motor to sump, a First position for applying fluid from the pump to power the motor in a first direction by delivering fluid to the motor's first end via a flow path and a Second position in which the motor moves in a second and opposite direction. A conduit connects the control valve to the sump. A check valve is provided in the flow path which always allows flow therethrough towards the motor's first end and normally blocks reverse flow therethrough. A mechanism opens the check valve to permit reverse flow therethrough responsive to operation of the control valve in the Float position and in the Second position.

Abstract: A fluid control valve includes a valve body having a pump inlet port and a drain outlet port and is of a construction sufficient for connecting the pump inlet port to a relatively high pressure pump and the drain outlet port to a substantially atmospheric pressure reservoir. A valve spool has a metering slot leading from the peripheral surface of a first land to a peripheral surface of a second land, the metering slot including a substantially cylindrical pocket recessed into the second land, and a groove formed in the first land and a reduced diameter portion positioned between the lands. The groove connects the peripheral surface of the first land with the cylindrical pocket and has an arcuate surface portion leading from the peripheral surface of the first land and an elongated bottom surface positioned substantially parallel to the longitudinal axis of the spool and tangent to the arcuate surface portion.