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A robust cruise control system using a disturbance observer is proposed. A control design method based on the two-degree-of-freedom (2-DOF) control including a disturbance observer is introduced. The proposed controller provides that: (1) input command responses are not affected by driving condition, such as vehicle speed, and road gradient (2) input command response and disturbance suppression performance can be designed independently (3) choice of an appropriate parameter value in the disturbance observer depending on the throttle opening gives a proper trade-off between the robust performance and the robust stability over a wide driving range. Simulation and experimental results show that the proposed system is robust against both parameter variations and disturbances.

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.