Method and device for controlling an injector

A control device for controlling a plurality of injectors of a combustion engine, wherein each injector comprises an injection valve housing with an injection valve cavity, a valve needle axially movable with the injection valve cavity, a valve seat on which the valve needle rests in a closed position and from which the valve needle is lifted for an open position, a spring element positioned between (a) a calibration tube fixed in an axial position during manufacturing and (b) the valve needle, wherein the fixed axial position of the calibration tube defines an injector-specific spring preload force exerted by the spring element on the valve needle acting to urge the valve needle in the closed position, an actuator assembly configured to displace the valve needle away from the closed position, wherein different ones of the plurality of injectors have different injector-specific spring preload forces based on different fixed axial positions of the calibration tubes of the respective injectors, the control device comprising:

• a processor;
• and
• computer instructions stored in non-transitory computer-readable media and executable by the processor to determine an injector-specific set-point opening time for injections by different ones of the plurality of injectors, wherein determining the injector-specific set-point opening time for a respective injection by a respective injector comprises:
• determining an injector-specific spring preload force calibration value for the respective injector representing the injector-specific spring preload force defined by the fixed axial position of the calibration tube of the respective injector,
• determining a base opening time as a function of a fluid volume to be dispensed by the respective injector for the respective injection,
• determining a pulse width offset for the respective injection as a function of the injector-specific spring preload force calibration value of the respective injector,
• determining a set-point opening time length for the respective injection based on (a) the base opening time and (b) the determined pulse width offset, and
• controlling the valve needle of the respective injector to be in the open position by energizing the actuator assembly with a current signal or a voltage signal based on the determined set-point opening time length,
• wherein different pulse width offsets are determined for injections of the same fluid volume by different ones of the plurality of injectors based on the determination of each pulse width offset as a function of the injector-specific spring preload force calibration value of the respective injector performing each respective injection.