Patent ID: 7856964

Claim:
A method for controlling the displacement of a stack of a piezoelectric actuator for use in a fuel injector in a fuel system, the method comprising; determining an operating parameter of the fuel system, determining a desired amount of charge (ΔQ) to be added or removed from the stack, selecting a drive current level (PO, SO) and a drive time (t open , t close ) 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 (t open , t close ) in order to add or remove the desired amount of charge (ΔQ), further including removing charge from the stack during a primary opening phase/time (6, POT) at a rate determined by a primary opening current level (PO), and adding charge to the stack during a primary closing phase/time (8, PCT) at a rate determined by a primary closing current level (PC), further comprising one or more additional damping phases before and/or after the primary opening phase/time (POT) and/or further comprising one or more additional damping phases before and/or after the primary closing phase/time (PCT), further comprising determining a current level and duration for the or each additional damping phase, and assigning a priority value to the or each additional damping phase.