| 摘要 |
In an internal combustion engine including an EGR device with an EGR catalyst in some of exhaust systems, an oxygen occlusion capacity of a catalyst disposed in an exhaust collecting pipe of it is obtained with high precision, and based on the result, deterioration of the catalyst can be accurately diagnosed. A catalyst deterioration diagnostic device for an internal combustion engine of the present invention implements active air-fuel ratio control which forcefully changes an air-fuel ratio of an exhaust gas which flows into a main catalyst between a lean side and a rich side with stoichiometry as a center. The catalyst deterioration diagnostic device measures an oxygen occlusion capacity of the main catalyst by using signals outputted from an air-fuel ratio sensor upstream from the main catalyst and an oxygen sensor downstream from the main catalyst at a time of implementation of the active air-fuel ratio control, and diagnoses deterioration of the main catalyst from the measurement result of the oxygen occlusion capacity. In the active air-fuel ratio control according to the catalyst deterioration diagnostic device of the present invention, when the EGR device with the EGR catalyst is stopped, a target air-fuel ratio of a cylinder group with the EGR device not provided in an exhaust system is changed with a large amplitude between the lean side and the rich side with stoichiometry as a center, and a target air-fuel ratio of a cylinder group with the EGR device provided in an exhaust system is kept stoichiometric. |
