| 摘要 |
An occluded oxygen quantity in a catalyst is estimated when fuel cut is executed. Then, upon return from the fuel cut, a target air-fuel ratio is set to significantly richer value. When it is detected on the basis of an output of an oxygen sensor that oxygen occluded by an upstream-side catalyst has been consumed, the target air-fuel ratio is switched to slightly richer value. Lastly, when the occluded oxygen quantity has become 0, a return is made to a normal air-fuel ratio feedback control. It is possible to consume the oxygen occluded by the catalyst quickly, and simultaneously it is possible to diminish emission released to the atmosphere even if an estimated value of the occluded oxygen quantity is deviated from an actual value.
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