Piezo stack temperature estimator

Abstract

The invention relates to a method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump. The piezoelectric actuator body is housed within a volume of fuel. The method comprises determining a temperature (T—INJ IN, T—PUMP IN) of fuel upstream of the fuel volume, determining a temperature (T—CYL) of the engine housing, and estimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the upstream temperature (T—INJ IN, T—PUMP IN) and the temperature (T—CYL) of the engine housing. By considering the heat transfer between the piezoelectric actuator body, the injector and fuel within the volume, and the heat transfer due to fuel flow through the volume for an injection, the temperature of the piezoelectric actuator body can be estimated by modelling or mapping.

Description

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a fuel injection system including a fuel injector having a piezoelectric stack for controlling injection,

FIG. 2 is block diagram of several elements of the fuel injection system in FIG. 1 to illustrate the heat transfer paths between the elements,

FIG. 3 is a block diagram to illustrate the method steps of a first embodiment of the invention employing a mapping function,

FIG. 4 is a control flow diagram to illustrate the method steps of a second embodiment of the invention employing a modelling function, and

FIG. 5 is a block diagram to illustrate the method steps of a third embodiment of the invention employing an alternative mapping function to that shown in FIG. 3.

Claims

1. A method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump, the piezoelectric actuator body being located within a fuel volume which receives fuel from the high pressure fuel pump, in use, the method comprising: determining a first temperature (T—PUMP IN, T—INJ IN) of fuel upstream of the fuel volume,determining a temperature (T—CYL) of the engine housing, andestimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the first temperature (T—PUMP IN, T—INJ IN) and the temperature (T—CYL) of the engine housing.

2. The method as claimed in claim 1, wherein the step of determining the first temperature includes determining a temperature (T—INJ IN) of fuel at an inlet of the fuel injector.

3. The method as claimed in claim 2, further comprising; determining a pump outlet temperature (T—PUMP OUT) of fuel at an outlet of the high pressure fuel pump; anddetermining the injector inlet temperature (T—INJ IN) based on the pump outlet temperature (T—PUMP OUT).

4. The method as claimed in claim 3, wherein determining the pump outlet temperature (T—PUMP OUT) includes: measuring a pump inlet temperature (T—PUMP IN) at an inlet to the high pressure fuel pump (10),measuring the pressure of fuel (P—RAIL) at the high pressure fuel pump outlet, andcalculating the pump outlet temperature (T—PUMP OUT) based on the pump inlet temperature (T—PUMP IN), the measured fuel pressure (P—RAIL) and a pump gain factor (G).

5. The method as claimed in claim 3, wherein the injector inlet temperature (T—INJ IN) is determined as being equal to the pump outlet temperature (T—PUMP OUT).

6. The method as claimed in claim 3, including determining the injector inlet temperature (T—INJ IN) based on the pump outlet temperature (T—PUMP OUT) and a predetermined time constant (τ1) representative of at least one system characteristic between the pump outlet (14) and the injector inlet.

7. The method as claimed in claim 6, wherein the system characteristic includes a time lag between the pump outlet temperature (T—PUMP OUT) and the injector inlet temperature (T—INJ IN).

8. The method as claimed in claim 2, including estimating a steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body by means of a mapping function (40) which receives inputs of the injector inlet temperature (T—INJ IN), the temperature (T—CYL) of the engine housing, an engine speed condition and a fuel delivery condition.

9. The method as claimed in claim 8, including controlling the fuel injector in dependence upon the estimated steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body.

10. The method as claimed in claim 8, wherein the mapping function compares a value based on the engine housing temperature (T—CYL) and the injector inlet temperature (T—INJ IN) with a predetermined calibration value (R), the method further comprising estimating the steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body on the basis of the comparison.

11. The method as claimed in claim 10, wherein the value is the ratio of (i) the difference between the estimated steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body and the injector inlet temperature (T—INJ IN) and (ii) the difference between the engine housing temperature (T—CYL) and the injector inlet temperature (T—INJ IN).

12. The method as claimed in claim 10, including determining the predetermined calibration value.

13. The method as claimed in claim 12, wherein determining the predetermined calibration value includes: measuring the injector inlet temperature (T—INJ IN) using an injector inlet temperature sensor;determining the temperature of the engine housing (T—CYL);measuring the steady state temperature of the piezoelectric actuator body (T—STACK STEADY STATE) using a piezoelectric temperature sensor; andcalculating the predetermined calibration value as a ratio of (i) the difference between the measured steady state temperature of the piezoelectric actuator body (T—STACK STEADY STATE) and the injector inlet temperature (T—INJ IN) and (ii) the difference between the measured engine housing temperature (T—CYL) and the injector inlet temperature (T—INJ IN).

14. The method as claimed in claim 8, further comprising estimating a dynamic temperature (T—STACK DYNAMIC) of the piezoelectric body based on the estimated steady state temperature (T—STACK STEADY STATE).

15. The method as claimed in claim 14, further comprising controlling the fuel injector in dependence upon the estimated dynamic temperature (T—STACK DYNAMIC) of the piezoelectric actuator body.

16. The method as claimed in claim 15, wherein controlling the fuel injector includes controlling voltage and/or charge transfer to and from the piezoelectric actuator body.

17. The method as claimed in claim 1, wherein the step of determining the first temperature includes determining a pump inlet temperature (T—PUMP IN) at an inlet to the high pressure fuel pump.

18. The method as claimed in claim 17, further comprising determining a pressure (P—RAIL) of fuel at an outlet of the high pressure fuel pump and estimating a steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body by means of a mapping function which receives inputs of the pump inlet temperature (T—PUMP IN), the temperature (T—CYL) of the engine housing, the pressure of fuel (P—RAIL) at the high pressure fuel pump outlet, an engine speed condition and a fuel delivery condition.

19. The method as claimed in claim 18, further comprising estimating a dynamic temperature (T—STACK DYNAMIC) of the piezoelectric body based on the estimated steady state temperature (T—STACK STEADY STATE).

20. The method as claimed in claim 18, including controlling the fuel injector in dependence upon the estimated steady state temperature (T—STACK STEADY STATE) of the piezoelectric actuator body.

21. The method as claimed in claim 19, including controlling the fuel injector in dependence upon the estimated dynamic temperature (T—STACK DYNAMIC) of the piezoelectric actuator body.

22. The method as claimed in claim 21, wherein controlling the fuel injector includes controlling voltage and/or charge transfer to and from the piezoelectric actuator body.

23. The method as claimed in claim 2, including estimating a dynamic temperature (T—STACK DYNAMIC) of the piezoelectric actuator body by means of a thermal model of heat transfer between the piezoelectric actuator body, the injector body and the fuel volume, wherein the thermal model receives inputs based on injector inlet temperature (T—INJ IN) and the temperature (T—CYL) of the engine housing.

24. The method as claimed in claim 23, wherein the thermal model further receives inputs based on an engine speed condition and a fuel delivery condition.

25. The method as claimed in claim 23, wherein the thermal model includes a sub-model of heat transfer to and from the piezoelectric body.

26. The method as claimed in claim 23, wherein the thermal model includes a sub-model of heat transfer to and from the fuel within the fuel volume.

27. The method as claimed in claim 23, wherein the thermal model includes a sub-model of heat transfer to and from the fuel injector.

28. The method as claimed in claim 23, further comprising controlling the fuel injector in dependence upon the estimated dynamic temperature (T—STACK DYNAMIC) of the piezoelectric actuator body.

29. The method as claimed in claim 1, wherein determining the temperature (T—CYL) of the engine housing includes measuring the temperature (T—CYL) of the engine housing using a temperature sensor.

30. The method as claimed in claim 1, including providing an engine coolant for cooling the engine housing, wherein determining the temperature (T—CYL) of the engine housing includes estimating the temperature of temperature (T—CYL) of the engine housing based on the temperature of the engine coolant.

31. A method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump, the piezoelectric actuator body being located within a fuel volume which receives fuel from the high pressure fuel pump, in use, the method comprising: determining a first temperature (T—INJ IN) of fuel at an inlet of the fuel injector,determining a temperature (T—CYL) of the engine housing,estimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the first temperature (T—INJ IN) and the temperature (T—CYL) of the engine housing, andcontrolling the piezoelectric actuator body on the basis of the estimated temperature.

32. A method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump, the piezoelectric actuator body being located within a fuel volume which receives fuel from the high pressure fuel pump, in use, the method comprising: determining a pump inlet temperature (T—PUMP IN) at an inlet to the high pressure fuel pump,determining a temperature (T—CYL) of the engine housing,estimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the pump inlet temperature (T—PUMP IN) and the temperature (T—CYL) of the engine housing, andcontrolling the piezoelectric actuator body on the basis of the estimated temperature.

33. A computer program product comprising at least one computer program software portion which, when executed in an execution environment, is operable to implement one or more of the steps of claim 1.

34. A data storage medium having the or each computer software portion of claim 33 stored thereon.

35. A microcomputer provided with a data storage medium as claimed in claim 34.