| 摘要 |
PROBLEM TO BE SOLVED: To accurately diagnose element-crack abnormality when occurring in a downstream side air-fuel ratio sensor.SOLUTION: An exhaust emission control device includes an exhaust emission control catalyst 20, a downstream side air-fuel ratio sensor 41, and a control device for controlling the air-fuel ratio of exhaust gas flowing into the exhaust emission control catalyst and diagnosing the abnormality of the downstream side air-fuel ratio sensor. When the air-fuel ratio of the exhaust gas flowing into the exhaust emission control catalyst is set to be a rich air-fuel ratio if an air-fuel ratio output by the downstream side air-fuel ratio sensor is kept not lower than a lean determined air-fuel ratio, the control device performs air-fuel ratio enriching control to change the air-fuel ratio of the exhaust gas flowing into the exhaust emission control catalyst into an air-fuel ratio richer than the previous air-fuel ratio. Besides, when performing the air-fuel ratio enriching control to change the air-fuel ratio of the exhaust gas flowing into the exhaust emission control catalyst into the air-fuel ratio richer, if the air-fuel ratio output by the downstream side air-fuel ratio sensor is changed to be leaner, the control device determines that abnormality occurs in the downstream side air-fuel ratio sensor.SELECTED DRAWING: Figure 15 |
