| 摘要 |
PROBLEM TO BE SOLVED: To simplify a control system for an air-fuel ratio based on a stored oxygen amount by estimating the stored oxygen amount of a catalyst by use of an oxygen sensor. SOLUTION: When an output value Es of the oxygen sensor in the upstream of the catalyst is within a prescribed range including a theoretical air-fuel ratio corresponding value (S401), the oxygen amount is estimated on the basis of an air-fuel ratio found by converting the output value Es (S402). When the output value Es is out of the prescribed range, and when a rich/lean state detected by the oxygen sensor in the downstream of the catalyst is maintained, the oxygen amount is estimated according to a target air-fuel ratio (S404). When the output value Es is out of the prescribed range, and when reversion of the rich/lean state is detected by the oxygen sensor on the downstream side of the catalyst, the oxygen amount is rest to a maximum amount in the case of the reversion to the lean state (S407), and is reset to a minimum amount in the case of the reversion to the rich state (S408).
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