| 摘要 |
PROBLEM TO BE SOLVED: To surely determine deterioration of an exhaust purification catalyst based on OSC.SOLUTION: A catalyst deterioration determining device includes first detecting means for detecting an air-fuel ratio of exhaust gas flowing into an exhaust purification catalyst, second detecting means for detecting an air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst, control means for providing a period to control the air-fuel ratio of the exhaust gas to an intermediate air-fuel ratio between a stoichiometric air-fuel ratio and a lean air-fuel ratio on the returning way to the lean air-fuel ratio from a rich air-fuel ratio in rich spike control, estimating means for estimating OSC of the exhaust purification catalyst on the basis of a detection value of the first detecting means and a detection value of the second detecting means changing in accompany with switching of the air-fuel ratio of the exhaust gas from the rich air-fuel ratio to the intermediate air-fuel ratio in the rich spike control, and deterioration determining means for determining the deterioration of the exhaust purification catalyst on the basis of OSC. |
