| 摘要 |
An object of this invention is to accurately determine deterioration of a catalyst and enhance reliability in an internal combustion engine with a turbo also. An engine 10 includes an exhaust purification catalyst 26, a turbo-supercharger 36, a bypass passage 38, and a waste gate valve 40. An ECU 60 alternatively changes a target air-fuel ratio At to a rich side and a lean side by active air-fuel ratio control, and changes an actual air-fuel ratio Ar in accompaniment therewith. The ECU 60 measures an oxygen storage capacity OSC of the exhaust purification catalyst 26 based on an oscillation period of the target air-fuel ratio At and the target air-fuel ratio At while executing the active air-fuel ratio control, and executes a deterioration determination with respect to the exhaust purification catalyst 26 based on the measurement value. When executing the deterioration determination, the ECU 60 closes the waste gate valve 40 to prevent a decrease in the accuracy of the deterioration determination that is caused by two kinds of exhaust gas whose flow paths are different from each other arriving at the area surrounding the air-fuel ratio sensor 56.
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