Fuel system with variable output fuel pump

1. A liquid pumping system, comprising:

a pump including an electric motor, and a pump outlet through which liquid is discharged under pressure;

a controller coupled to the pump to vary the power provided to the motor to vary the flow rate of liquid discharged from the pump outlet;

a pressure regulator having an inlet communicated with the pump outlet, a regulator outlet from which liquid is discharged from the regulator, a bypass outlet through which liquid is discharged from the regulator, and a pressure responsive valve that opens when the pressure of liquid acting on the valve is greater than a threshold pressure to permit liquid flow through the bypass outlet; and

a flow sensor communicated with the bypass outlet to sense or determine a flow rate of liquid at or downstream of the bypass outlet, the flow sensor also communicated with the controller to provide an indication of the bypassed liquid flow rate to the controller.

2. The system of claim 1 which also includes a second controller that is communicated with the controller coupled to the pump, the second controller providing an indication of the liquid demand in the system to the controller coupled to the pump.

3. The system of claim 1 wherein the electric motor includes brushes and has a minimum current level below which increased wear of the brushes will occur, and wherein the controller varies power to the pump as a function of the bypassed liquid flow rate and as a function of the minimum current level.

4. The system of claim 1 wherein the controller varies the power to the pump as a function of the bypassed liquid flow rate.

5. The system of claim 1 wherein the flow sensor is a switch that has one state when there is no flow at the switch and another state when there is flow at the switch.

6. The system of claim 5 wherein the one state of the switch is open and the another state of the switch is closed.

7. The system of claim 1 wherein the flow sensor is a pressure switch that detects the presence or absence of a liquid pressure at the switch, or changes in pressure in a flow of liquid communicated with the switch.

8. A method of operating an electric motor liquid pump that provides an output flow of liquid to a pressure regulator having a bypass outlet through which liquid is diverted in at least some operating conditions, comprising:

determining if the rate or amount of flow through the bypass outlet is above or below a threshold flow; and

varying electric power provided to the motor of the pump in response to the flow through the bypass outlet.

9. The method of claim 8 wherein said at least one threshold flow rate is zero.

10. The method of claim 8 which also comprises the step of storing in memory the amount by which the power provided to the pump is varied, and using the stored amount as a calibration or correction value to alter the pump power duty cycle for future operation of the pump.

11. The method of claim 8 which also includes the steps of:

determining a demanded liquid flow rate;

providing power to the pump at a level to cause the pump to supply liquid at a flow rate that exceeds the demanded liquid flow rate and thereby cause liquid flow through the bypass outlet.

12. The method of claim 11 wherein the demanded liquid flow rate is determined by at least one sensor that is responsive to one or more of throttle position, engine speed, engine load, and/or one or more properties of an exhaust gas emitted from the engine.

13. A method of operating a liquid pump with an electric, comprising:

determining or accessing from memory a minimum current level for the electric motor of the pump;

determining a demanded liquid flow rate;

determining if the demanded liquid flow rate corresponds to a current level that is less than the minimum current level; and

providing current to the electric motor of the pump at a level greater than is necessary to cause the pump to meet the demanded liquid flow rate if the demanded liquid flow rate corresponds to a current level that is less than the minimum current level.

14. The method of claim 13 wherein the minimum current level is chosen to reduce wear of brushes in the pump.

15. The method of claim 13 wherein when the electric motor of the pump is provided with a current greater than necessary to cause the pump to meet the demanded liquid flow rate, the method further comprises bypassing a portion of the liquid discharged from the pump.