Air-fuel ratio control system

Claim 1

In an air-fuel ratio control system for an internal combustion engine having an induction passage, means for supplying air-fuel mixture, an electromagnetic valve for correcting the air-fuel ratio of the air-fuel mixture supplied by the supply means, an O 2 sensor for detecting oxygen concentration in exhaust gases, and a feedback control circuit including comparator means for comparing the output of the O 2 sensor with a reference value and for producing an output signal responsive to the comparison, PI circuit means responsive to the output signal of the comparator means for producing a PI value, and pulse generating circuit means responsive to the PI value for generating pulses duty ratio of which is dependent on the PI value, the pulses being for driving the electromagnetic valve to correct the air-fuel ratio, the improvement comprising: engine speed detecting means for producing an engine speed signal when the engine speed is lower than a predetermined engine speed; engine deceleration detecting means for producing a deceleration signal at a predetermined deceleration; deciding means responsive to the engine speed signal and deceleration signal for producing a particular idling signal; correcting means responsive to the particular idling signal for correcting the PI value to a PI value operative to rapidly changing the duty ratio of the pulses so as to enrich the air-fuel mixture.