US Patent 7856964 Method of controlling a piezoelectric actuator

A method for controlling the displacement of a stack of a piezoelectric actuator for use in a fuel injector comprises determining a desired amount of charge (ΔQ) to be added or removed from the stack. The method further comprises determining an operating parameter of the fuel system and selecting a drive current level (PO, SO) and a drive time (topen, tclose) in accordance with the desired amount of charge (ΔQ) and the operating parameter, and driving the drive current through the stack for the drive time (topen, tclose) in order to add or remove the desired amount of charge (ΔQ).