AIR-FUEL RATIO CONTROLLING APPARATUS FOR INTERNAL-COMBUSTION ENGINE

PURPOSE:To prevent contamination of the exhaust emission of an engine, by providing a chopper means which cuts off a lean air-fuel ratio signal intermittently when the lean air-fuel ratio signal is produced continuously for more than a predetermined period. CONSTITUTION:An O2-sensor 66 detects the concentration of oxygen contained in the exhaust gas for an engine and produces a rich air-fuel ratio signal and a lean air-fuel ratio signal according to the detected concentration of oxygen. A by-pass flow control valve 70 and a valve 76 for controlling recirculation of exhaust gas are opened and closed by a control unit. In a control circuit 132, there is provided a chopper means which cuts off the lean air-fuel ratio signal intermittently when the lean air-fuel ratio signal is produced continuously for more than a predetermined period. By employing such an arrangement, it is enabled to prevent contamination of the exhaust emission of an engine when the control move is shifted to feedback control after a gas sensor is inactivated at the time of decelerating the engine.