Abstract
Abstract
The jump—ramp control algorithm has been widely adopted for the air—fuel ratio control in a fuel injection spark ignition (SI) engine by using a conventional on—off type oxygen sensor. But the jump—ramp control method has limitations in improving the frequency and amplitude of the air—fuel ratio oscillation. This study suggests a new feedback control logic called modulated fuel feedback control, which has a concept of pretuned air—fuel ratio oscillation. In the modulation method, the oxygen sensor output is not treated as on—off but as an analogue for feedback. By using the modulation method, the frequency and amplitude of the air—fuel ratio oscillation can be controllable to some extent to improve the conversion efficiency of a three-way catalyst. The results show that the performance of the modulation method is better than that of the jump—ramp control method in reducing the amplitude of the air—fuel ratio oscillation as well as in increasing the frequency of the air—fuel ratio oscillation.
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