ENGINE AIR-FUEL RATIO CONTROL UNIT

PURPOSE:To make it possible to exactly control the air-fuel ratio even when the target air-fuel ratio which is determined from an operating condition discriminating signal by a control circuit varies, by carrying out the feedback control of air fuel ratio by means of an exhaust gas sensor so that the air fuel ratio meets the target value. CONSTITUTION:An operating condition discriminating sensor 10 delivers signals indicating engine speed, negative pressure, throttle position etc., to an operating condition discriminating circuit 8A where the operating condition is discriminated, and a target air-fuel ratio comparing circuit 8B selects the target air-fuel ratio corresponding to the discrimination and delivers it to a comparator 8C which produces a deviation between the set target value and the output of an O2 sensor 6. Further an arithmetic circuit 8D calculates a fuel supply in accordance with the signal of the deviation and delivers a control signal to a fuel supply device 12 for controlling the air-fuel ratio. Accordingly, the air-fuel ratio of mixture may be controlled to the target value even when the target air fuel ratio varies in dependence upon operating conditions during vehicle running.