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

Abstract

Despite significant advances in electronic control technology applied to diesel engines, commercially available injection sys tems for automotive diesel engines remain limited by the open loop mapplng 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 sub stantially 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 overfuel ing, 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 nee dle lift in conjunction with the fuel tempera ture is evaluated. An estimation of the injection rate characteristic is determined from real-time analysis of the needle lift signal using a high-spee d sensor processor. Integration of the rate characteris tic 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 verifi ed experimentally. Possible long-term decalibra tion due to nozzle coking is studied. Advantages and limitations of the technique are identified. BACKGROUND AND PROBLEM DESCRIPTION Although diesel engines and lnjection systems represent a mature technology, it is only ln recent years that electronic con trols have been successfull y applied. The majority of diesel appli cations are still mechanicall y controlled, with no electronics involved other than the fuel shutoff solenoid valve control. The potential benefits of microprocessor-based control applied to diesel engines have been well established [Reams82, Kihara83, Martlnsons82, Trenne82, Kawai84]. However, many of the improvements made possible by advanced electronic control