Patent ID: 8061188

Claim:
A method for determining the functional state of a piezoelectric injector of an internal combustion engine, wherein the input variables of a control loop for fuel injection are voltage and charge, the method comprising the steps of: measuring a plurality of capacitance values for the piezoelectric injector over time, each capacitance value measured during ambient conditions of the internal combustion engine, calculating a capacitance profile or functional equation for the piezoelectric injector with the aid of a mathematical approximation method based on the plurality of capacitance value measurements over time, the capacitance profile or functional equation representing an approximation of the long-term change in capacitance of the piezoelectric injector due to aging of the piezoelectric injector, measuring a current capacitance value for the piezoelectric injector, determining a reference capacitance value based on the capacitance profile or functional equation representing the long-term change in capacitance due to aging of the piezoelectric injector, and detecting an impending failure of the piezoelectric injector if the measured capacitance value lies outside a first upper and lower tolerance range around the reference capacitance profile.