DOUBLE AIR-FUEL RATIO SENSOR SYSTEM HAVING IMPROVED EXHAUST EMISSION CHARACTERISTICS

In a double air-fuel sensor system including two air-fuel ratio sensors upstream and downstream of a catalyst converter provided in an exhaust gas passage, an air-fuel ratio correction amount is calculated in accordance with the outputs of the upstream-side and downstream-side air-fuel ratio sensors, thereby obtaining an actual air-fuel ratio. When all of the feedback control conditions for the downstream-side air-fuel ratio sensor are satisfied, a speed of renewal of the air-fuel ratio correction amount in accordance with the output of the downstream-side air-fuel ratio sensor is lowered before the output of the downstream-side air-fuel ratio sensor is reversed or for a predetermined time period.