Method for estimating an hydraulic dwell time between two injection pulses of a fuel injector

1. A method for estimating an hydraulic dwell time between a first injection pulse and a second injection pulse performed by a fuel injector of an internal combustion engine, the method comprising the steps of:

determining a value of an electric dwell time between the first injection pulse (P) and the second injection pulse;

estimating an injector closing delay value of an injector closing delay between an instant in which an electric closing command of the first injection pulse is generated and an instant in which the fuel injector closes;

estimating an injector opening delay value of an injector opening delay between an instant in which an electric opening command of the second injection pulse is generated and an instant in which the fuel injector opens;

calculating a value of the hydraulic dwell time as a function of the electric dwell time of the injector closing delay value and of the injector opening delay value.

2. The method according to claim 1 , wherein the estimating of the injector closing delay value comprises the steps of:

determining a fuel rail pressure value of a pressure inside a fuel rail hydraulically connected with the fuel injector;

determining an electric energizing time value of an electric energizing time of the first injection pulse; and

estimating the injector closing delay value of the injector closing delay on a basis of the fuel rail pressure value and of the electric energizing time value.

3. The method according to claim 2 , wherein the injector closing delay value of the injector closing delay is estimated with an empirically determined map correlating the injector closing delay value to the fuel rail pressure value and to the electric energizing time value.

4. The method according to claim 2 , wherein said injector closing delay value of the injector closing delay is estimated with a mathematical model, which returns the injector closing delay value of the injector closing delay as a function of the fuel rail pressure value and of the electric energizing time value.

5. The method according to claim 2 , wherein the injector closing delay value of the injector closing delay can be corrected by applying to it an empirically determined correction factor.

6. The method according to claim 1 , wherein the estimating of said injector opening delay comprises the steps of:

determining a fuel rail pressure value of a pressure inside a fuel rail hydraulically connected with the fuel injector; and

estimating the injector opening delay value of said injector opening delay on a basis of said fuel rail pressure value.

7. The method according to claim 6 , wherein said injector opening delay value of the injector opening delay is estimated with an empirically determined map correlating the injector opening delay value to the fuel rail pressure value.

8. The method according to claim 6 , wherein said injector opening delay value of the injector opening delay is estimated with a mathematical model, which returns the injector opening delay value of the injector opening delay as a function of the fuel rail pressure value.

9. The method according to claim 6 , wherein the injector opening delay value of the injector opening delay can be corrected by applying to it an empirically determined correction factor.

10. A method for operating a fuel injector of an internal combustion engine, comprising the steps of:

determining a fuel quantity to be injected by said fuel injector in a course of an injection pulse;

estimating a hydraulic dwell time value of a hydraulic dwell time between said injection pulse and a previous injection pulse performed by the fuel injector;

estimating a pressure value in said fuel injector on a basis of said hydraulic dwell time value of the hydraulic dwell time;

using said fuel quantity and said pressure value, in order to determine an electric energizing time value of an electric energizing time of the injection pulse; and

operating the fuel injector according to the electric energizing time value of the electric energizing time.

11. An internal combustion engine comprising:

a fuel injector; and

an engine control unit connected to the fuel injector, the engine control unit configured to:

determine a value of an electric dwell time between a first injection pulse and a second injection pulse;

estimate an injector closing delay value of an injector closing delay between an instant in which an electric closing command of the first injection pulse is generated and an instant in which the fuel injector closes;

estimate an injector opening delay value of an injector opening delay between an instant in which an electric opening command of the second injection pulse is generated and an instant in which the fuel injector opens; and

calculate a value of a hydraulic dwell time as a function of the electric dwell time of the injector closing delay value and of the injector opening delay value.

12. The internal combustion engine according to claim 11 , wherein the estimate of the injector closing delay value comprises:

determining a fuel rail pressure value of a pressure inside a fuel rail hydraulically connected with the fuel injector;

determining an electric energizing time value of an electric energizing time of the first injection pulse; and

estimating the injector closing delay value of the injector closing delay on a basis of the fuel rail pressure value and of the electric energizing time value.

13. The internal combustion engine according to claim 12 , wherein the injector closing delay value of the injector closing delay is estimated with an empirically determined map correlating the injector closing delay value to the fuel rail pressure value and to the electric energizing time value.

14. The internal combustion engine according to claim 12 , wherein said injector closing delay value of the injector closing delay is estimated with a mathematical model, which returns the injector closing delay value of the injector closing delay as a function of the fuel rail pressure value and of the electric energizing time value.

15. The internal combustion engine according to claim 12 , wherein the injector closing delay value of the injector closing delay can be corrected by applying to it an empirically determined correction factor.

16. The internal combustion engine according to claim 11 , wherein the estimate of said injector opening delay comprises:

determining a fuel rail pressure value of a pressure inside a fuel rail hydraulically connected with the fuel injector; and

estimating the injector opening delay value of said injector opening delay on a basis of said fuel rail pressure value.

17. The internal combustion engine according to claim 16 , wherein said injector opening delay value of the injector opening delay is estimated with an empirically determined map correlating the injector opening delay value to the fuel rail pressure value.

18. The internal combustion engine according to claim 16 , wherein said injector opening delay value of the injector opening delay is estimated with a mathematical model, which returns the injector opening delay value of the injector opening delay as a function of the fuel rail pressure value.

19. The internal combustion engine according to claim 16 , wherein the injector opening delay value of the injector opening delay can be corrected by applying to it an empirically determined correction factor.