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A fuel control method to reduce the harmful exhaust gas from SI engines is proposed. As is well known, both the amplitude and the frequency of the limit cycle in a conventional air-fuel ratio control system are determined uniquely by parameters in the system. And this limits our making full use of the oxygen storage effect of TWC. A simple model of TWC reaction revealed the relationship between maximum conversion efficiency and both the amplitude and the frequency in a air fuel control system. It also revealed that TWC conversion efficiency attained to maximum levels when both the amplitude and the frequency of the limit cycle are selected so as to make full use of the oxygen storage effect of TWC. In order to achieve this, it is necessary to vary both the amplitude and the frequency arbitrarily.

In this paper, an application of variable structure systems (VSS)(1) to electromagnetic-clutch (EMC) control for starting vehicles is studied. Using a conventional open-loop controller, there is the case that changes in EMC dynamics lead to undesirable vehicle vibration though it may be rare. First, to overcome the above problem, we developed a control strategy based on VSS. The VSS control is robust with respect to changes in EMC dynamics. Second, we discussed the chattering problem of this controller in application to actual vehicle control. Finally, we confirmed the validity of the proposed control strategy and the appropriateness of the conditions for reduced chattering derived by simulation. The validity of this control strategy was also confirmed experimentally.