| 摘要 |
<p>PURPOSE:To exactly detect the deterioration of a sensor in an engine having air-fuel ratio sensors provided on the upstream and the downstream side of an exhaust catalyst by, when the trouble of the sensor is detected in the domain of idling time or the like, detecting the deterioration of the sensor on the upstream side on the ratio of outputs of both the sensors. CONSTITUTION:The upstream and downstream sides of a catalyst 7 interposedly provided in the exhaust passage 6 of an engine 1 are provided with the first and second air-fuel ratio sensors 12, 13, and their output signals are inputted in a control unit 9, which controls the air-fuel ratio of the engine 1 in a feedback mode to a target air-fuel ratio on the output of the first air-fuel ratio sensor 12. A sensor trouble detecting means is actuated in a domain where engine intake air quantity detected by an air flowmeter 4 is below set up value at idling time or the like to detect the deterioration of the first air-fuel ratio sensor 12 on the ratio of outputs of the first and second air-fuel ratio sensors 12, 13. for instance the ratio of their frequencies. Namely, when the ratio of frequencies at off-idling time is 1, and that at the idling time is above threshold, the first air-fuel ratio sensor 12 is judged to be in a deteriorated state.</p> |
