Electronically controlled inlet metered single piston fuel pump

1. A fuel pump comprising:

an infeed passage for low pressure feed fuel;

a pumping chamber in fluid communication with the infeed passage;

a pumping plunger reciprocable in the pumping chamber between an intake phase that draws low pressure fuel from the infeed passage into the pumping chamber and pumping phase that increases the pressure in the pumping chamber to a higher pressure for delivery to a common rail through a discharge valve;

an inlet metering valve in the infeed passage for delivering metered quantities of low pressure feed fuel through a variable opening to the pumping chamber, said inlet metering valve having an inlet metering valve member movable between an open position corresponding to maximum flow through the variable opening and a closed position of the metering valve corresponding to zero flow through the variable opening to the pumping chamber;

an inlet check valve between the metering valve and the pumping chamber, biased against a seat to permit feed flow to the pumping chamber during the intake phase and to prevent fuel pumped at high pressure from flowing into the infeed passage during the pumping phase;

an actuator operatively connected to move and maintain said inlet metering valve member in positions between said open and closed positions during said intake phase to vary the opening of the inlet metering valve commensurate with an infeed fuel quantity demand for the intake phase in the pumping chamber; and

means for opening the inlet check valve while the inlet metering valve is in said closed position.

2. The fuel pump of claim 1 , wherein said inlet metering valve comprises a piston valve element, and said means for opening the check valve is an axial end face of said piston valve element that mechanically displaces the check valve.

3. The fuel pump of claim 1 , wherein the inlet metering valve is proportionally controllable to travel between an open and said closed position and said travel to the closed position provides said means for opening the check valve.

4. The fuel pump of claim 3 , wherein said inlet metering valve member comprises a piston valve element, and said means for opening the check valve is an axial end face of said piston valve element that mechanically displaces the check valve.

5. The fuel pump of claim 1 , wherein the actuator is a proportional solenoid and the inlet metering valve member includes a piston valve element that holds open the inlet check valve only when the piston travels to said closed position.

6. The fuel pump of claim 5 , wherein the infeed passage includes an inlet plenum and the opening is an axially aligned slot that is selectively increased and decreased in flow area to present a variable flow cross-section as the inlet metering valve piston travels farther and closer to the check valve, respectively.

7. The fuel pump of claim 6 , wherein the inlet check valve is disposed adjacent one end of the slot.

8. The fuel pump of claim 7 , wherein at a maximum travel of the piston valve element toward the check valve, the piston valve element closes the slot and a leading end of the piston extends beyond the slot to mechanically open the check valve.

9. The fuel pump of claim 1 , wherein the inlet check valve is mounted in a common sub-assembly with the inlet metering valve.

10. The fuel pump of claim 1 , wherein

the pump includes a high pressure discharge passage from the pumping chamber, an outlet check valve in the high pressure passage, and a pressure relief valve in fluid communication with the high pressure passage; and

the inlet metering valve, the inlet check valve, the outlet check valve and the pressure relief valve are all mounted to the pump on a common axis.

11. The fuel pump of claim 1 , wherein

the inlet metering valve is a normally closed proportional solenoid operated valve with a piston valve element that travels between an open position and said closed position; and

the piston valve element has sufficient travel to mechanically hold open the inlet check valve when the piston valve element closes the opening while a zero or a low level of current is supplied to the proportional solenoid.

12. The fuel pump of claim 1 , wherein

the inlet check valve when seated is disposed at a distance “X” downstream of the opening;

the inlet metering valve is a proportional valve and said inlet metering valve member includes a valve element that travels across said opening between said open position and said closed position to thereby selectively increase and decrease a variable flow cross section of the opening as the inlet metering valve element travels farther from and closer to the check valve, respectively; and

at a maximum travel of the valve element toward the check valve, the valve element closes the opening and extends at least the distance “X” beyond the opening to mechanically lift the check valve from its seat.

13. A method of operating a fuel pump with an infeed passage for low pressure fuel; a pumping chamber in fluid communication with the infeed passage; a pumping plunger continuously reciprocable in the pumping chamber commensurate with engine speed between an intake phase that draws low pressure fuel from the infeed passage into the pumping chamber and pumping phase that increases the fuel pressure in the pumping chamber for delivery to a common rail through an outlet check valve; a metering valve in the infeed passage for delivering metered quantities of low pressure fuel to the pumping chamber, said metering valve including a metering valve element movable between an open position corresponding to maximum flow through said infeed passage and a closed position corresponding to no flow through said infeed passage; an inlet check valve between the inlet metering valve and the pumping chamber, biased to permit feed flow to the pumping chamber during the intake phase and prevent fuel pumped at high pressure from flowing into the infeed passage during the pumping phase; and a control system that displaces the metering valve element among positions maintained between said open and closed positions during said intake phase according to demand for pumped fuel, said control system closes the metering valve when no fuel is to be pumped to the common rail; wherein the improvement comprises a step wherein the control system opens the inlet check valve while the inlet metering valve is closed and no fuel is to be pumped to the common rail.

14. The method of claim 13 , wherein the improvement comprises mechanically opening the inlet check valve by said metering valve element of the inlet metering valve.

15. The method of claim 13 , wherein the improvement comprises that the inlet metering valve receives inlet flow through an inlet flow orifice;

the control system controls a proportional solenoid that displaces the inlet metering valve element across the inlet flow orifice between said open and closed positions according to demand for pumped fuel; and

the metering valve element is displaceable to a maximum closed position that closes the inlet flow orifice and opens the inlet check valve.

16. The method of claim 15 , wherein the improvement comprises

positioning the displaceable valve element to completely cover the inlet flow orifice in a first closed valve position when the control system determines that no fuel is required to be pumped into the common rail;

determining whether the pressure in the common rail exceeds a threshold pressure while the control system determines that no fuel is required to be pumped into the common rail; and

if the pressure in the common rail exceeds said threshold pressure while the control system determines that no fuel is required to be pumped into the common rail, further displacing the valve element into said maximum closed position that mechanically opens the inlet check valve while the valve element continues to completely cover the inlet orifice.