Variable pump control for hydraulic fan drive

A pump control arrangement for controlling the displacement of a variable displacement pump that receives fluid from a reservoir, the variable displacement pump having a pressure outlet port and a displacement changing actuator operative to change the displacement of the variable displacement pump between a minimum and a maximum position, the pump control arrangement being adapted for use in a fan drive system having a fluid motor fluidity connected to the variable displacement pump, the pump control arrangement comprising:

• a load margin valve arrangement disposed between the pressure outlet port of the variable displacement pump and the displacement changing actuator, the load margin valve arrangement having first and second ends each defining pressure responsive chambers with the first end being spring biased to a position to pass fluid from the variable displacement pump therethrough and the second end thereof being connected to the pressure outlet port of the variable displacement pump;
• and
• a proportional solenoid valve arrangement connected to the pressure outlet port of the variable displacement pump and operative to control the flow of pressurized fluid to and from the displacement changing actuator, the proportional solenoid valve arrangement includes a spring biasing mechanism, a proportional valve, and a proportional solenoid, the proportional valve having first and second ends with the spring biasing mechanism disposed at the first end and a pressure chamber defined at the second end and being connected downstream of the proportional valve, the spring biasing mechanism being operative to bias the proportional valve to a position to pass fluid from the variable displacement pump therethrough, and the proportional solenoid is disposed at the second end of the proportional valve and operative to provide a variable force in opposition to the spring bias acting at the first end, the proportional valve is a three-way valve having a first port connected to the reservoir, a second port connected to the pressure outlet port of the variable displacement pump, and a third port connected to the pressure chamber at the first end of the load margin valve arrangement, the proportional valve being movable between first and second positions and at the first position thereof the pressure chamber at the first end of the load margin valve arrangement is in communication with the pressure outlet port of the variable displacement pump and blocked from the reservoir and at the second position thereof the pressure chamber at the first end is in communication with the reservoir and blocked from the pressure outlet port of the variable displacement pump.

A pump control arrangement for controlling the displacement of a variable displacement pump having a pressure outlet port and a displacement changing actuator operative to change the displacement of the variable displacement pump between a minimum and a maximum position, the pump control arrangement being adapted for use in a fan drive system having a fluid motor fluidity connected to the variable displacement pump, the pump control arrangement comprising:

• a load margin valve arrangement having first and second ends each defining pressure responsive chambers with the first end being spring biased to a flow passing position, the load margin valve arrangement being disposed between the pressure outlet port of the variable displacement pump and the displacement changing actuator and the second end thereof being connected to the pressure outlet port of the variable displacement pump;
• a pressure cutoff valve having first and second ends with the first end being spring biased to a flow passing position and the second end being connected to the pressure outlet port of the variable displacement pump, the pressure cutoff valve being disposed between the load margin valve arrangement and the displacement changing actuator of the variable displacement pump;
• and
• a proportional solenoid valve arrangement being disposed between the pressure outlet port of the variable displacement pump and the first end of the load margin valve arrangement, the proportional solenoid valve arrangement includes a spring biasing mechanism, a proportional valve, and a proportional solenoid, the proportional valve having first and second ends with the spring biasing mechanism disposed at the first end and a pressure chamber defined at the second end, the second end being connected between the proportional valve and the first end of the load margin valve arrangement, the spring biasing mechanism being operative to bias the proportional valve to a flow passing position, and the proportional solenoid is disposed at the second end of the proportional valve and operative to provide a variable force in opposition to the spring bias at the first end.