Method for controlling the temperature of a glow plug
The invention relates to a method for controlling the temperature of a glow plug ( 1 ), wherein a setpoint temperature (T set ) is used to determine a setpoint value (R set ) of a temperature-dependent electric variable and an effective voltage (U eff ) which is generated by pulse width modulation is applied to the glow plug ( 1 ) and is used as correcting variable. According to the invention, it is provided that a mathematical model ( 4 ) is used to calculate an expected value (R e ) of the electric variable, the electric variable is measured, a first error signal e 1 (t) is generated by evaluating the calculated value (R e ), a value calculated from the effective voltage (U eff ) and the error signal (e 1 (t)) is used as the input variable of the mathematical model ( 4 ), wherein the mathematical model ( 4 ) uses the input variable to calculate an output variable (X) which defines the expected value (R e ) of the electric variable, and wherein the output variable (X) of the mathematical model ( 4 ) is used to calculate a corrected value for the effective voltage (U eff ) and the effective voltage (U eff ) is changed to the corrected value.
1. A method for closed-loop controlling the temperature of a glow plug, wherein
a) a setpoint temperature is used to determine a setpoint value of a temperature-dependent electric variable, and
b) an effective voltage which is generated by pulse width modulation is applied to the glow plug, wherein
c) a mathematical model comprising a linear differential equation, which calculates an output variable from an input variable and provides the output variable at its output, is used to calculate an expected value of the temperature-dependent electric variable,
d) a measured value of the temperature-dependent electric variable is measured,
e) a first error signal is generated by comparing the calculated expected value of the temperature-dependent electric variable with the measured value of the temperature-dependent electric variable,
f) value calculated from the effective voltage and the first error signal is used as a new input variable of the mathematical model, wherein the mathematical model calculates a new output variable from the new input variable, said new output variable defining a new expected value of the temperature-dependent electric variable, and
g) the new output variable of the mathematical model and the setpoint value of the temperature dependent electric variable are used to calculate a corrected value for the effective voltage and the effective voltage is changed to the corrected value thereby controlling the temperature of the glow plug,
h) wherein the closed-loop controlling method repeats itself starting at step d.
2. The method according to claim 1 , wherein the temperature-dependent electric variable is an electric resistance.
3. The method according to claim 1 , wherein the output variable is proportional to the expected value of the electric variable.
4. The method according to claim 1 , wherein to calculate the corrected value for the effective voltage, a value calculated from the output variable is compared with the setpoint value or with a variable determined from the setpoint value and the extent of the change in the effective voltage is the greater, the greater the difference determined in the comparison.
5. The method according to claim 1 , wherein the corrected value for the effective voltage is calculated by adding a voltage value which is proportional to the difference between the setpoint value and the calculated value to the instantaneous value of the effective voltage.
6. The method according to claim 1 , wherein a second error signal which is used to correct the setpoint value is generated by evaluating the calculated value.
7. The method according to claim 6 , wherein the second error signal is generated by comparing the calculated value with the measured value.
8. The method according to claim 7 , wherein the second error signal is proportional to the difference between the calculated value and the measured value.
9. The method according to claim 6 , wherein use is made of a further mathematical model of the glow plug, wherein the value of the effective voltage applied to the glow plug is used as the input variable of the further mathematical model and the second error signal is generated by comparing the output variables of the two models.
10. The method according to claim 9 , wherein the second error signal is proportional to the difference between the two output variables.
11. The method according to claim 9 , wherein the two mathematical models are identical.
12. The method according to claim 6 , wherein the second error signal and the setpoint value are used to determine a correction of the setpoint value by means of a family of characteristics.
13. The method according to claim 1 , wherein to calculate the input variable, the first error signal is combined with the value of the effective voltage in an additive manner.
14. The method according to claim 1 , wherein the temperature-dependent electric variable is an electric conductance.
15. The method according to claim 1 , wherein the temperature-dependent electric variable is an inductance.