Importance

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Abstract

An exhaust gas purification system including a catalyst device configured to recover a purification capacity of a catalyst by an air-fuel ratio richness control, based on a richness control permission range where the air-fuel ratio richness control is permitted to be performed, and a richness control prohibition range where the air-fuel ratio richness control is prohibited from being performed. A catalyst temperature of the catalyst device and an air intake amount of an internal combustion engine are parameters for determining the richness control permission range or the richness control prohibition range. The richness control prohibition range is set as a range where the catalyst temperature of the catalyst device is lower than a preset lower limit catalyst temperature and the air intake amount is larger than a preset upper limit air intake amount. The lower limit catalyst temperature is set to a temperature lower than a catalyst activation temperature. This makes it possible to reduce HC and NOx slip amounts and raise the catalyst temperature when the temperature is low.

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First Claim