| 摘要 |
PROBLEM TO BE SOLVED: To reliably detect element cracking of an air-fuel ratio sensor.SOLUTION: An abnormality diagnostic device for an air-fuel ratio sensor includes: a current detection section for detecting an output current of the air-fuel ratio sensor; a sensor temperature control section for controlling an element temperature of the air-fuel ratio sensor; and an imbalance degree estimation section for estimating an imbalance degree that is nonuniformity of an air-fuel ratio between cylinders. In the case where a target air-fuel ratio of exhaust gas is set to be a rich air-fuel ratio, when the output current of the air-fuel ratio sensor reaches or exceeds a predetermined threshold value corresponding to a lean air-fuel ratio, the abnormality diagnostic device determines that element cracking occurs in the air-fuel ratio sensor Yes in S18. When an abnormality of the air-fuel ratio sensor should be detected, in the case where the imbalance degree estimated by the imbalance degree estimation section S14 becomes a predetermined reference value or larger, control is performed by the sensor temperature control section so that an element temperature of the air-fuel ratio sensor becomes higher compared to the case where the imbalance degree is smaller than the reference value S15, and the threshold value is set to be high S16.SELECTED DRAWING: Figure 19 |
