Recently, automotive emission regulations are being further tightened, such as the Tier III/LEV III in the U.S. As a result, reducing cost of after-treatment systems to meet these strict regulations has become an urgent issue, and then the demand for high-precision air-fuel ratio (A/F) control which can achieve this cost reduction is high [1]. On the other hand, in order to meet rapidly changing market needs, it is becoming difficult to keep enough development periods that enable sufficient calibration by trial-and-error, such as feedback-gain calibration. This leads to an increase in three-way catalytic converter costs in some cases.
For these reasons, it is necessary to construct control system that can make full use of hardware capabilities, can shorten development periods regardless of the skill level of engineers. A new robust control method is accomplished in this study, which can provide optimal performance in accordance with the Universal Exhaust Gas Oxygen (UEGO) sensor response, which changes according to the vehicle operating condition, and also eliminates trial-and-error elements, enables direct calibration.
The results of these investigations showed that it is possible to obtain a feedback controller with a target disturbance sensitivity function. It is confirmed that all parameters can be determined by measuring the UEGO sensor response characteristics, and the A/F control accuracy was enhanced by 35% compared to conventional feedback control, when the deviation between the target equivalence ratio and the actual equivalence ratio is used as the evaluation index.