1990-02-01

An Indirect Sensing Technique for Closed-Loop Diesel Fuel Quantity Control 900494

Despite significant advances in electronic control technology applied to diesel engines, commercially available injection systems for automotive diesel engines remain limited by the open-loop mapping of the injection pump. An initial calibration is relied upon to translate a fuel delivery command to an actual fuel quantity. In practice, however, these two variables may be substantially different due to the effects of mechanical wear, repair, and the wide range of operating conditions. Possible ramifications of this discrepancy are excessive exhaust smoke due to overfueling, increased fuel consumption, degraded driveability, and poor idle characteristics. The major obstacle to closing the fuel control loop is the lack of a suitable sensor for instantaneous fuel delivery from the injector.
An indirect fuel delivery sensing mechanism based upon the use of the injector needle lift in conjunction with the fuel temperature is evaluated. An estimation of the injection rate characteristic is determined from real-time analysis of the needle lift signal using a high-speed sensor processor. Integration of the rate characteristic and temperature correction yields a total mass delivery estimate for use as a feedback quantity for closed-loop fuel control. Signal processing algorithms are derived from computer modeling of the injector and verified experimentally. Possible long-term decalibration due to nozzle coking is studied. Advantages and limitations of the technique are identified.

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