Variable displacement pumps
In accordance with at least one aspect of this disclosure, a variable displacement pump system can include, a variable displacement pump disposed in a main line and configured to supply pressure to receive a low pressure fluid and to output a high pressure fluid. The main line can connect a hydraulic fluid source to a plurality of system actuators, where the variable displacement pump is disposed in the main line between the hydraulic fluid source and the plurality of system actuators to pressurize the hydraulic fluid.
1. A system, comprising:
a variable displacement pump disposed in a main line and configured to receive a low pressure fluid and to output a high pressure fluid;
a pressure port disposed in the main line downstream of the variable displacement pump configured to port a portion of the high pressure fluid from the main line to a bias pressure line;
a controllable valve disposed in the bias pressure line configured to meter a pressure of the bias pressure line;
a pressure actuated main piston disposed in the bias pressure line upstream of the controllable valve relative to the output of the variable displacement pump, and wherein the pressure actuated main piston is connected directly to the variable displacement pump by a mechanical linkage and configured to control displacement of the variable displacement pump at a predetermined pressure set point;
a biasing member operatively connected to the pressure actuated main piston and configured to bias the main piston to a position to achieve a pressure output for the predetermined pressure set point; and
a pressure actuated biasing piston operatively connected to the biasing member and configured to bias the pressure actuated main piston, wherein the biasing piston is in the bias pressure line downstream of the controllable valve, wherein the output from the controllable valve is a bias pressure that moves the pressure actuating biasing piston to a desired position to change a preloaded spring force of the biasing member acting on the main piston.
2. The system as recited in claim 1 , wherein the controllable valve includes an electrohydraulic servo valve.
3. The system as recited in claim 1 , further comprising:
an electronic controller configured to control the controllable valve;
a first sensor in communication with the electronic controller and configured to sense a position of the pressure actuated main piston; and
a second sensor in communication with the electronic controller and configured to sense a position of the pressure actuated biasing piston.
4. The system as recited in claim 3 , further comprising:
a third sensor in communication with the electronic controller and configured to sense a position of the mechanical linkage; and
a fourth sensor in communication with the electronic controller and configured to sense a position of the controllable valve.