MODULATED FUEL FEEDBACK-CONTROL OF A FUEL-INJECTION ENGINE USING A SWITCH TYPE OXYGEN SENSOR

The jump-ramp control algorithm has been widely adopted for the air-fu el ratio control in a fuel injection spark ignition (SI) engine by usi ng a conventional on-off type oxygen sensor. But the jump-ramp control method has limitations in improving the frequency and amplitude of th e air-fuel ratio oscillation. This study suggests a new feedback contr ol logic called modulated fuel feedback control, which has a concept o f pretuned air-fuel ratio oscillation. In the modulation method, the o xygen sensor output is not treated as on-off but as an analogue for fe edback. 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 tha t 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.