Discharge control strategy for a piezoelectric fuel injector of an i.c. engine

The invention relates a method for controlling a piezoelectric injector for metering fuel inside the cylinder of a combustion engine, wherein the injector comprises an injection needle operated by means of a piezoelectric actuator and wherein a discharge control strategy is applied to the piezoelectric actuator. The method comprises the following steps (i) calculate a discharge time setpoint (Ts) in function of at least an engine operating parameter, (ii) sample, during a fuel injection cycle, the discharge time (Tm) of the piezoelectric actuator, (iii) determine the difference between the discharge setpoint time (Ts) and the sampled discharge time (Tm) and (iv) use the difference between Ts and Tm to generate a correction index to be applied, during the next fuel injection cycle, to the discharge control strategy to discharge the piezoelectric actuator in order to minimize that difference.