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For compliance with the exhaust emission regulations, such as SULEV and STAGE4, a new air-fuel ratio control system has been developed. The concept behind this system is that the best performance of air-fuel ratio control is achieved with the minimum of man-hours of adaptation. The system consists of a section in which an engine's air-fuel ratio is fed back and a section in which the amount of oxygen stored by the catalyst is predicted and controlled. In the feedback section, a high-precision air-fuel ratio control was achieved. In the oxygen storage mass predicting and controlling section, a catalyst model was incorporated to predict the amount of oxygen in the catalyst. The important point to note in this control system is that the air-fuel ratio feedback section requires no adaptation work when using an actual engine.

The purpose of this study is to develop control-oriented modeling methodology and apply to an actual control design in turbocharged spark ignition engines. A grey-box modeling approach was adapted to accelerate the system calibration time, while providing accurate system dynamics. An engine simulator based on first principles models was utilized to investigate the statistical model derivation process. A recursive least squares method with forgetting factor was employed to estimate model parameters related to turbocharger and vehicle/drivetrain behaviors, which seemed to be major factors causing delay of turbocharger system. The concept was demonstrated through its application to the actual control design, and the reliability of the proposed method was theoretically investigated. According to the model evaluation results, approximated behavior models are in good agreement with time series data yielded by the engine simulator under various transient operations.