Patent ID: 8056321

Claim:
An exhaust gas purification method for purifying exhaust gas when an air-fuel ratio of the exhaust gas is in a lean state, and recovering purification ability when in a rich state, comprising: conducting a rich control by conducting EGR and by supplying uncombusted fuel to the exhaust gas, so that the air-fuel ratio in the exhaust gas is brought to be in the rich state, adsorbing on an upstream side of an EGR cooler the uncombusted fuel in the exhaust gas that passes through an EGR passage during the rich control; calculating a cumulative adsorption amount of the uncombusted fuel adsorbed on the upstream side of the EGR cooler; and determining whether or not the cumulative adsorption amount has exceeded an adsorption tolerance amount of the uncombusted fuel adsorbed on the upstream side of the EGR cooler; and if the cumulative adsorption amount has exceeded the adsorption tolerance amount, terminating the rich control.