System error analysis of open loop fuelling control
Open-loop fuelling control is a typical function used in engine management system for small engines. And this function is also applied for some special states for automotive engines.
This report analysed the robustness of system and assessed the main elements could influence it. Finally the accuracy of TPS(throttle position sensor) is found as the weakest link in this system, more attention should be paid to the angular resolution. A sample application is given, and potentiometer with angle error of less than ��0.54�� is found to be needed (within small angle range).
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5. Conclusion
�� AFr error of carburettor application under the typical conditions, which is about ��15%, considering it being adaptive system, it is much more accurate than the current application. To achieve the equivalent accuracy level, a high angular resolution is necessary at idle and low part load, for this particular system special potentiometer with angle error of less than ��0.54�� is needed(within small angle range);
�� to improve the system accuracy, the most important thing is to improve the accuracy of throttle potentiometer,
�� injector could be improved accuracy if only two orifices are machined (assume the fuel flow rate is adequate for application),
�� Locations of air temp. sensor and atmospheric pressure sensor could be considered due to the affection on system error,
�� The error of throttle area decreases with smaller throttle body fully closed angle (used to set datum of throttle).
