Development of Next-Generation Air-Fuel Ratio Control System, “COSMIC”

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. Furthermore, a linearized oxygen sensor capable of detecting air-fuel ratios has been also developed at a reasonable cost to exploit the high controllability and good robustness of the control system. In consequence, a sophisticated but low-cost air-fuel ratio control system was successfully developed.