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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.

We have applied a non–linear control system to a hydraulically–operated continuous valve timing control (C–VTC) now in the mainstream of variable valve actuation systems. The system applied this time is a sliding mode control (SMC), which is found of late in a number of applications. Hydraulic pressure serving as the driving source of the C–VTC and the mechanism of the C–VTC have non–linear characteristics. We have investigated certain problems which occur, influenced by this non–linearity, when using a PID controller for C–VTC control. Typical issues include a large program memory size because of the large number of control parameters, a resultant considerable number of man–hours required for adaptation, and the low compatibility of response performance both for large step operations and for small step operations. Furthermore, high machining accuracy is required for the mechanical components.