Patent ID: 8051839

Claim:
A method of operating a fuel injector including a piezoelectric actuator having a stack of piezoelectric elements, and wherein, in use, the injector communicates with a fuel rail, the method comprising: (a) applying a discharge current to the actuator for a discharge phase (T 0 to T 1 ) so as to discharge the stack from a first differential voltage level across the stack to a second differential voltage level across the stack so as to initiate an injection event; (b) maintaining the second differential voltage level for a period of time (T 1 to T 2 , defined as the “dwell period”); and (c) determining at least two engine parameters, the at least two engine parameters being selected from: fuel pressure in the fuel rail; the discharge period (T 0 to T 2 ) of the next fuel injection event (defined as the “electric pulse time”); and the piezoelectric stack temperature; and (d) applying a charge current to the actuator for a charge period so as to charge the stack from the second differential voltage level to a third differential voltage level so as to terminate the injection event; wherein the third differential voltage level is selected in dependence on the at least two engine parameters.