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 to an engine cylinder during operation of a fuel pump that delivers fuel to the accumulator, comprising:

determining an average pressure of the fuel accumulator during a first time period before a fuel injection event wherein the fuel injector injects fuel from the fuel accumulator to the engine cylinder;

predicting a mass of fuel delivered to the fuel accumulator by the fuel pump during a pumping event (Q pump );

determining an average pressure of the fuel accumulator during a second time period after the fuel injection event;

estimating a leakage of fuel;

computing the quantity of fuel injected by the fuel injector by adding the average pressure during the first time period to Q pump , and subtracting the average pressure during the second time period and the 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 after the first time period and before the fuel injection event.

3. The method of claim 1 , wherein Q pump is zero.

4. The method of claim 1 , wherein predicting Q pump 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 Q pump ,

determining a converged value of the estimated SOP position, and

determining a converged value of the estimated Q pump ; and

using the adaptive model to predict Q pump 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 f cam 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 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 to an engine cylinder during operation of a fuel pump that delivers fuel to the accumulator, comprising:

a pressure sensor position to measure pressure of fuel in the fuel accumulator;

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

a processor in communication with the pressure sensor to receive pressure values representing the measured pressure of the fuel in the fuel accumulator and in communication with the temperature sensor to receive temperature values representing the measured temperature of the fuel in the fuel accumulator;

wherein the processor is configured to

determine an average pressure of the fuel accumulator during a first time period before a fuel injection event wherein the fuel injector injects fuel from the fuel accumulator to the engine cylinder,

predict a mass of fuel delivered to the fuel accumulator by the fuel pump during a pumping event (Q pump ),

determine an average pressure of the fuel accumulator during a second time period after the fuel injection event,

estimate a leakage of fuel,

compute the quantity of fuel injected by the fuel injector by adding the average pressure during the first time period to Q pump , and subtracting the average pressure during the second time period and 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 system of claim 11 , wherein the pumping event occurs after the first time period and before the fuel injection event.

13. The system of claim 11 , wherein Q pump is zero.

14. The system of claim 11 , wherein the processor is further configured to predict Q pump by generating an adaptive model of operation of the fuel pump by

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

using the estimated SOP position to estimate Q pump ,

determining a converged value of the estimated SOP position, and

determining a converged value of the estimated Q pump ; and

using the adaptive model to predict Q pump 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 system of claim 14 , wherein the processor is configured to estimate a 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 system of claim 15 , wherein the processor is 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 system of claim 15 , wherein the processor is 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 system of claim 14 , wherein the adaptive model uses the relationship Qpump=fcam(EOP−SOP)*A*δ(P,T)−t*L(P,T), wherein f cam 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 system 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 system of claim 11 , wherein the processor is 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.