Method for checking the plausibility of measurements of an actuator current and use of the method

A method for checking a plausibility of a measurement of an actuator current through a two-terminal actuator, the two-terminal actuator having an inductive load L and a resistive load R, wherein a first terminal of the two-terminal actuator is connected to a supply voltage via a pulse width modulated switch, and to ground via a freewheeling diode, which is disposed in reverse bias, wherein a second terminal of the two-terminal actuator is connected to said ground, which comprises the steps of:

• obtaining measured values including summation current measured values for an average summation current through the pulse width modulated switch, and actuator current measured values for an average actuator current through the second terminal for at least three different duty cycles of a pulse width modulation of the pulse width modulated switch, in a steady state;
• approximating a dependency of the average summation current on a duty cycle by a summation current polynomial ÎS(TV;
• TV,1, TV,2, . . . TV,N) having polynomial coefficients αS,0, αS,1, . . . αS,N-1 that is fitted to at least three of the summation current measured values;
• approximating a dependency of the average actuator current on the duty cycle by an actuator current polynomial ÎA(TV;
• TV,1, TV,2, . . . TV,N) having polynomial coefficients αA,0, αA,1, . . . αA,N-1 that is fitted to at least three of the actuator current measured values;
• calculating an absolute difference between the actuator current polynomial ÎA(TV;
• TV,1, TV,2, . . . TV,N) and the summation current polynomial ÎS(TV;
• TV,1, TV,2, . . . TV,N) for the duty cycle of one (TV=1) and for the duty cycle of zero (TV=0);
• comparing the absolute difference with predetermined corresponding tolerances;
• and
• determining the measurement of the actuator current to be implausible when at least one of the predetermined corresponding tolerances is exceeded.