| 摘要 |
<p>PURPOSE:To provide the air-fuel ratio control device of an internal combustion engine which can control an air-fuel ratio based on the output of two air-fuel ratio sensors installed in the up/down stream part of a three dimension catalyzer and judge whether a purification rate is dropped to the degree requiring the replacement of the catalyzer. CONSTITUTION:This device can feedback control so that the air-fuel ratio of an engine can be a prescribed center air-fuel ratio corresponding to the output of the upstream side sensor 13 of a three dimension catalyzer 12. By shifting the center air-fuel ratio of the feedback control from the prescribed center air-fuel ratio, whether the purification rate of the catalyzer 12 is dropped down or not is judged based on the output of the air-fuel ratio sensor 15 in the downstream part of the three dimension catalyzer 12. Also, whether a catalyzer deterioration diagnosis is necessary or not in the air-fuel ratio feedback control by the upstream sensor 13 is judged by the output of the downstream sensor 15. When the diagnosis is judged necessary, the air-fuel ratio control center is shifted and judge whether the catalyzer 12 is deteriorated to such a degree that the replacement of the catalyzer 12 is necessary or not.</p> |
