A method for controlling the actuation of a piezo-electric element in a fuel injector

摘要

A piezo-electric element for actuating a fuel injector has a predetermined actuation stroke (Hsetpoint). The actuation stroke is converted to a charge quantity setpoint (QCsetpoint). The conversion may me achieved by reference to pre-stored values 60 and corrected to account for example temperature variations (T). The setpoint charge is compared 61 with the actual charge delivered (QCactual). A control signal (Son) is derived based on this comparison (for example via a PI controller 62). A further signal (idon) is derived to determine the average charge to be applied over the duration of the fuel injection event (ton) (for example QCsetpoint divided by the time ton). The further signal (idon) is then adjusted by the control signal (Son) to account for the variation between the setpoint charge and the actual charge. The corrected signal (idon) is then used to drive the actuator. A similar method is disclosed to control the setpoint charge of the piezo-electric element after the fuel injection event has been completed. The method accounts for 'influence quantities' on the piezo element, for example temperature variations, ageing effects and production tolerances.