System and method for measuring fuel injection during pump operation

1. A method of controlling operation of a fuel injector in response to measuring a quantity of fuel injected by the fuel injector from a fuel accumulator during operation of a fuel pump that delivers fuel to the accumulator, comprising:

determining a change in pressure value of the fuel accumulator before and after a fuel injection event;

predicting an amount of fuel delivered to the fuel accumulator by the fuel pump during a pumping event (Qpump) and an amount of fuel leakage;

computing the quantity of fuel injected by the fuel injector by adding the change in pressure value to Qpump, and subtracting the amount of fuel leakage; and

using the computed quantity of fuel injected by the fuel injector to control operation of the fuel injector during a subsequent fuel injection event.

2. The method of claim 1 , wherein the pumping event occurs before the fuel injection event.

3. The method of claim 1 , wherein Qpump is zero.

4. The method of claim 1 , wherein predicting Qpump includes generating an adaptive model of operation of the fuel pump, including:

estimating a start of pumping (“SOP”) position of a plunger of the fuel pump,

using the estimated SOP position to estimate Qpump,

determining a converged value of the estimated SOP position, and

determining a converged value of the estimated Upump; and

using the adaptive model to predict Qpump by inputting to the model the converged value of the estimated SOP position, a measured pressure of fuel in the fuel accumulator and a measured temperature of fuel in the fuel accumulator.

5. The method of claim 4 , wherein estimating a SOP position includes:

receiving raw measurements of pressure of fuel in the fuel accumulator:

identifying quiet segments in the raw measurements;

fitting a model to the identified quiet segments; using the fitted model to determine an output representing a propagation of the pressure of fuel in the fuel accumulator without disturbance from pumping events; and

identifying a divergence between the fitted model output and the raw measurements of pressure of fuel in the fuel accumulator.

6. The method of claim 5 , wherein identifying quiet segments includes filtering the raw measurements with a median filter having a length corresponding to a frequency of oscillation of the pressure of fuel in the fuel accumulator.

7. The method of claim 5 , wherein identifying quiet segments further includes evaluating a derivative of the filtered raw measurements to identify segments of the derivative having approximately zero slope.

8. The method of claim 4 , wherein the adaptive model uses the relationship Qpump=fcam(EOP−SOP)*A*δ(P, T)−t*L(P, T), wherein fcam is a table correlating positions of the plunger to a crank angle of an engine, EOP is an end of pumping position of the plunger, A is an area of the plunger, δ(P, T) is a density of fuel in the fuel accumulator, t is a duration of the pumping event, and L(P,T) is a leakage of fuel from the pump.

9. The method of claim 8 , wherein at least one of δ(P, T) and L(P,T) is modeled by either a first order polynomial in a fuel temperature dimension or at least a second order polynomial in a fuel pressure dimension.

10. The method of claim 1 , wherein using the computed quantity of fuel injected by the fuel injector to control operation of the fuel injector includes adapting an ON time equation corresponding to the fuel injector.

11. A processor for controlling operation of a fuel injector in response to measuring a quantity of fuel injected by the fuel injector during operation of a fuel pump that delivers fuel to a fuel accumulator, the processor configured to:

receive, from a pressure sensor; pressure values representing a measured pressure of fuel in the fuel accumulator before and after a fuel injection event;

determine a change in pressure value of the fuel accumulator from the received pressure values;

predict an amount of fuel delivered, to the fuel accumulator by the fuel pump during a pumping event (Qpump) and an amount of fuel leakage;

compute the quantity of fuel injected by the fuel injector by adding the change in pressure value to Qpump, and subtracting the leakage; and

use the computed quantity of fuel injected by the fuel injector to control operation of the fuel injector during a subsequent fuel injection event.

12. The processor of claim 11 , wherein the pumping event occurs before the fuel injection event.

13. The processor of claim 11 , wherein Qpump is zero.

14. The processor of claim 11 , further configured to:

estimate a start of pumping (“SOP”) position of a plunger of the fuel pump;

estimate Qpump using the estimated SOP position;

determine a converged value of the estimated SOP position;

determine a converged value of the estimated Qpump; and

generate an adaptive model of operation of the fuel pump,

wherein the model is used to predict Qpump by inputting to the model the converged value of the estimated SOP position, a measured pressure of fuel in the fuel accumulator and a measured temperature of fuel in the fuel accumulator.

15. The processor of claim 14 , wherein the processor is configured to estimate the SOP position by:

receiving raw measurements of pressure of fuel in the fuel accumulator;

identifying quiet segments in the raw measurements;

fitting a model to the identified quiet segments;

using the fitted model to determine an output representing a propagation of the pressure of fuel in the fuel accumulator without disturbance from pumping events; and

identifying a divergence between the fitted model output and the raw measurements of pressure of fuel in the fuel accumulator.

16. The processor of claim 15 , further configured to identify quiet segments by filtering the raw measurements with a median filter having a length corresponding to a frequency of oscillation of the pressure of fuel in the fuel accumulator.

17. The processor of claim 15 , further configured to identify quiet segments by evaluating a derivative of the filtered raw measurements to identify segments of the derivative having approximately zero slope.

18. The processor of claim 14 , wherein the adaptive model uses the relationship Qpump=fcam(EOP−SOP)*A*δ(P, T)−t*L(P, T), wherein fcam is a table correlating positions of the plunger to a crank angle of an engine, EOP is an end of pumping position of the plunger, A is an area of the plunger, δ(P, T) is a density of fuel in the fuel accumulator, t is a duration of the pumping event, and L(P, T) is a leakage of fuel from the pump.

19. The processor of claim 18 , wherein at least one of δ(P, T) and L(P, T) is modeled by either a first order polynomial in a fuel temperature dimension or at least a second order polynomial in a fuel pressure dimension.

20. The processor of claim 11 , further configured to use the computed quantity of fuel injected by the fuel injector to control operation of the fuel injector by adapting an ON time equation corresponding to the fuel injector.

21. A system for controlling operation of a fuel injector in response to measuring a quantity of fuel injected by the fuel injector from a fuel accumulator during operation of a fuel pump that delivers fuel to the accumulator, comprising:

a pressure sensor positioned to measure pressure of fuel in the fuel accumulator; and

a processor in communication with the pressure sensor and configured to:

receive, from the pressure sensor, pressure values representing the measured pressure of the fuel in the fuel accumulator before and after a fuel injection event;

determine a change in pressure value of the fuel accumulator from the received pressure values;

predict an amount of fuel delivered to the fuel accumulator by the fuel pump during a pumping event (Qpump) and an amount of fuel leakage;

compute the quantity of fuel injected by the fuel injector by adding the change in pressure value to Qpump, and subtracting the amount of fuel leakage; and

use the computed quantity of fuel injected by the fuel injector to control operation of the fuel injector during a subsequent fuel injection event.