| 摘要 |
PURPOSE:To prevent drivability and exhaust characteristics from deteriorating, by stopping the operation of a control constant by an oxygen sensor at the downstrem side when this oxygen sensor at the downstream side is deteriorated and its output amplitude comes smaller, in a device provided with each oxygen sensor at both upstream and downstream sides of a catalyzer. CONSTITUTION:A first oxygen sensor 13 is installed at the upstream of a catalytic converter 12 and a second oxygen sensor 15 at the downstream, respectively, and inputted into a control circuit 10 together with an air flow meter 3 and crank angle sensors 5 and 6. The control circuit 10 secures an air-fuel ratio signal for rich-lean discrimination on the basis of detection value of the oxygen sensor at the upstream side at time of the specified driving state, and sets a control constant including a skip quantity, an integration constant or the like on the basis of full force of the oxygen sensor 15 at the downstream side, setting it down to an air-fuel ratio feedback control signal. The control circuit 10 stops the operation of the control constant on the basis of the oxygen sensor at the downstream side when amplitude of the control constant based on the oxygen sensor 15 at the downstream side is less than the specified value.
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