| 摘要 |
During deterioration detection of a catalyst, exhaust gas of a lean air/fuel ratio and exhaust gas of a rich air/fuel ratio are alternately supplied to the catalyst, and decrease of the O<SUB>2 </SUB>storage function is detected by obtaining the oxygen occlusion amount in the catalyst, based upon the timing at which, after changeover of the air/fuel ratio of the exhaust gas flowing into the catalyst, the air/fuel ratio of the exhaust gas passed through the catalyst changes to track that air/fuel ratio of the exhaust gas flowing into the catalyst. At this time, the rich air/fuel ratio of the exhaust gas and the lean air/fuel ratio of the exhaust gas supplied to the catalyst are set closer to the stoichiometric air/fuel ratio, the larger is the exhaust flow amount.
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