Most modern spark ignited (SI) internal combustion engines maintain their air-to-fuel ratio (AFR) at a desired level to maximize the three-way catalyst conversion efficiency and to extend its life. However, maintaining the engine AFR during its transient operation is quite challenging due to rapid changes of driver demands. Conventional transient AFR control is based upon the inverse dynamics of the engine port-fuel-injection well-wetting dynamics and the measured mass air flow rate. This paper develops a dynamic linear quadratic (LQ) tracking controller to regulate the AFR using a control oriented model of the wall wetting dynamics of a port fuel injector (PFI) and estimated transport delays of the airflow travel and throttle dynamics. The LQ tracking controller is designed to optimally track the measured airflow through the throttle during engine transients over a given time interval. The performance of the optimal LQ tracking controller was compared with the conventional inverse fueling dynamics through simulations and showed improvement over the baseline controller.

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