Variable displacement pump with active bypass feedback control

1. A system comprising:

a variable displacement pump;

a metering valve in an output line for controlling outlet flow from the variable displacement pump to at least one fuel nozzle;

a bypass line connected for fluid communication from the output line to an input line in fluid communication with an inlet of the variable displacement pump for bypassing a portion of pump flow from the outlet of the variable displacement pump, wherein the bypass line connects to the output line upstream of the metering valve via a pressure tap and connects to the output line downstream of the metering valve;

a pressure regulating valve in the bypass line configured to control pressure drop across the metering valve by bypassing a portion of the pump flow back through the variable displacement pump;

a position sensor operatively connected to sense position of a valve component of the pressure regulating valve; and

a control system operatively connected to receive input from the position sensor and operatively connected to control displacement of the variable displacement pump based on the position of the valve component.

2. The system as recited in claim 1 , wherein the valve component is a piston slideably engaged inside a valve housing.

3. The system as recited in claim 2 , wherein the position sensor includes a linear variable differential transformer (LVDT) operatively connected between the piston and the valve housing to measure position of the piston relative to the valve housing.

4. The system as recited in claim 1 , further comprising the least one fuel nozzle in fluid communication with the output line downstream of the metering valve, wherein the variable displacement pump is configured to supply fuel to the at least one fuel nozzle.

5. The system as recited in claim 1 , wherein the control system includes a controller configured to compare position feedback from the position sensor to a requested position and to output a control signal for control of displacement of the variable displacement pump.

6. The system as recited in claim 5 , wherein the control system includes an electrohydraulic servo valve (EHSV) operatively connected to the controller and to the variable displacement pump to actuate an adjustment of displacement of the variable displacement pump in response to the control signal from the controller.

7. The system as recited in claim 1 , further comprising an actuator line parallel to the variable displacement pump and connected to the output line to provide actuation pressure from pump output of the variable displacement pump.

8. A method of controlling a variable displacement pump comprising:

measuring position of a valve component in a pressuring regulating valve in a bypass line bypassing an outlet of the variable displacement pump; and

adjusting displacement of the variable displacement pump based on position of the valve component, wherein the bypass line connects to the output line upstream of a metering valve via a pressure tap and connects to the output line downstream of the metering valve.

9. The method as recited in claim 8 , further comprising controlling flow output from the variable displacement pump with the metering valve in an output line in fluid communication with the variable displacement pump, wherein an inlet of the bypass line is connected to the output line upstream of the metering valve.

10. The method as recited in claim 8 , further comprising hydraulically controlling pressure change across the metering valve by bypassing a portion of pump flow through the bypass line.

11. The method as recited in claim 10 , wherein measuring position of the valve component includes using a position sensor operatively connected between a piston and a valve housing to measure position of the piston relative to the valve housing, wherein the position sensor includes a linear variable differential transformer (LVDT).

12. The method as recited in claim 8 , further comprising supplying fuel to at least one fuel nozzle from the variable displacement pump.

13. The method as recited in claim 12 , wherein adjusting displacement of the variable displacement pump based on position of the valve component includes comparing position feedback from the position sensor to a requested position and to output a control signal for control of displacement of the variable displacement pump.

14. The method as recited in claim 13 , further comprising using an electrohydraulic servo valve (EHSV) to actuate an adjustment of displacement of the variable displacement pump.

15. The system as recited in claim 1 , wherein the metering valve is hydromechanically controlled by bypassing a portion of pump flow through the bypass line using the pressure regulating valve.