| 摘要 |
When determining a maximum storable oxygen amount of a catalyst disposed in an exhaust passage, a target air-fuel ratio of the gas upstream of the catalyst is set to a predetermined lean air-fuel ratio upon determining that the output of a downstream-side air-fuel ratio sensor indicating a lean air-fuel ratio has changed to indicate a rich air-fuel ratio. Then, a feedback correction amount is calculated such that the air-fuel ratio detected by an upstream-side air-fuel ratio sensor matches the target air-fuel ratio, and a feed-forward amount required for the gas, to be supplied into the internal combustion engine, to become lean is determined. A final injection amount is determined by correcting the feed-forward amount by the feedback correction amount.
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