Adaptive controller with delay compensation for Air-Fuel Ratio regulation in SI engines

Stringent requirements to maintain low emission levels over the vehicle lifetime constrain the combustion Air-Fuel Ratio (AFR) within a narrow band around the stoichiometric value and hence pose a challenging AFR control problem. In order to match the desired AFR level Universal Exhaust Gas Oxygen (UEGO) sensors have been recently employed within control loops involving nonlinear engine dynamics. Sensor measurement uncertainties and inevitable effects of aging of these sensors motivate the use of online tuning algorithms for the controller gains. In this paper we develop an adaptive control structure which consists of an adaptive PI controller and an adaptive Smith predictor for time-delay systems with unknown plant parameters. We implement our control design using a plant model representing simplified engine dynamics with a constant UEGO sensor delay based on the assumption that the overall time constant of the plant is unknown. The performance of the adaptive controller is demonstrated through simulation scenarios where additional benefits of our design approach can be observed.