Glowplug temperature estimation method and device

1. A method for controlling a glowplug of a compression-ignition engine, the method comprising:

determining a supplied power to the glowplug and a combustion chamber temperature;

predicting a glowplug temperature of the glowplug; and

controlling a power supply to the glowplug using a predicted glowplug temperature,

wherein the predicted glowplug temperature is derived from a numerical solution of a differential equation for the glowplug temperature, and

wherein the differential equation for the glowplug temperature is nonlinear in the glowplug temperature.

2. The method according to claim 1 ,

wherein the differential equation for the glowplug temperature is derived from a power balance equation comprising at least Pg, Pi, Pe, Pc,

wherein Pg models the supplied power to the glowplug, Pi models an energy stored in the glowplug per unit of time, Pe models a radiation energy per unit of time, Pc models a heat energy per unit of time, the heat energy being transferred by convection or conduction.

3. The method according to claim 1 , wherein the differential equation takes a form:

Pg ( t )= A*d/dtTg ( t )+ B*Tg ( t )+ C*Tg ( t ) 4 +D ( t )

wherein Pg is a supplied energy to the glowplug, Tg is the glowplug temperature, A, B, C are derived from precalibrated values and D(t) is a function of the combustion chamber temperature.

4. The method according to claim 1 , wherein the power supply to the glowplug is controlled by controlling an opening time of a glowplug relay.

5. The method according to claim 1 , wherein the power supply to the glowplug is controlled by controlling an opening time of a transistor.

6. The method according to claim 1 , wherein the combustion chamber temperature is derived from an engine coolant temperature.

7. The method according to claim 6 , wherein the combustion chamber temperature is further derived from an engine load.

8. A device for controlling a glowplug temperature of a glowplug, comprising:

a derivation device adapted to derive a combustion chamber temperature;

a prediction device adapted to predict a predicted glowplug temperature from at least a supplied power to the glowplug and the combustion chamber temperature; and

a controller adapted to control a power supply to the glowplug using the predicted glowplug temperature;

wherein the predicted glowplug temperature is derived from a numerical solution of a differential equation for the glowplug temperature, and

wherein the differential equation for the glowplug temperature is nonlinear in the glowplug temperature.

9. The device according to claim 8 , further comprising a second derivation device adapted to derive an amount of transferred heat energy, a heat energy being transferred by radiation transfer between the glowplug and a combustion chamber.

10. The device according to claim 8 , further comprising a third derivation device adapted to derive a temperature control value for the glowplug temperature from the predicted glowplug temperature.

11. The device according to claim 8 , further comprising a computational device adapted to compute a pulse width of a pulse width modulation from a temperature control value.

12. A non-transitory computer readable medium embodying a computer program product, the computer program product comprising:

a control program, the control program configured to control a glowplug of a compression-ignition engine, the control program further configured to:

determine a supplied power to the glowplug and a combustion chamber temperature;

predict a glowplug temperature of the glowplug; and

control a power supply to the glowplug using a predicted glowplug temperature,

wherein the predicted glowplug temperature is derived from a numerical solution of a differential equation for the glowplug temperature, and

wherein the differential equation for the glowplug temperature is nonlinear in the glowplug temperature.

13. The computer readable medium embodying the computer program product to claim 12 ,

wherein the differential equation for the glowplug temperature is derived from a power balance equation comprising at least Pg, Pi, Pe, Pc,

wherein Pg models the supplied power to the glow plug, Pi models an energy stored in the glowplug per unit of time, Pe models a radiation energy per unit of time, Pc models a heat energy per unit of time, the heat energy being transferred by convection or conduction.

14. The computer readable medium embodying the computer program product to claim 12 , wherein the differential equation takes a form:

Pg ( t )= A*d/dtTg ( t )+ B*Tg ( t )+ C*Tg ( t )4 +D ( t )

wherein Pg is a supplied energy to the glowplug, Tg is the glowplug temperature, A, B, C are derived from precalibrated values and D(t) is a function of the combustion chamber temperature.

15. The computer readable medium embodying the computer program product to claim 12 , wherein the power supply to the glowplug is controlled by controlling an opening time of a glowplug relay.

16. The computer readable medium embodying the computer program product to claim 12 , wherein the power supply to the glowplug is controlled by controlling an opening time of a transistor.

17. The computer readable medium embodying the computer program product to claim 12 , wherein the combustion chamber temperature is derived from an engine coolant temperature.

18. The computer readable medium embodying the computer program product to claim 17 , wherein the combustion chamber temperature is further derived from an engine load.