Model comparison for feedforward air/fuel ratio control

This paper outlines the development and use of a feedforward control scheme applied to a simulated engine air/fuel (A/F) ratio system. This system is nonlinear with operating point dependent dynamics and a time delay which varies as a function of engine speed and inlet manifold air mass flow rate. In the feedforward scheme described, a model is used to predict the air flow into the engine. Two models are considered: a dynamic fuzzy model, and a static look-up table of air flow rate mapped against engine crankshaft speed and throttle plate angle. It is found that the feedforward control scheme, using a suitable model, is able to reduce transient deviations in A/F ratio, due to load/speed disturbances, compared to those observed using a predictive PID control scheme. Further comparison is made between the look-up table and fuzzy model based feedforward schemes and some interesting observations are noted.