The exhaust gas purifying method

PROBLEM TO BE SOLVED : To prevent a particulate filter from eroded or thermally deteriorated by combustion heat of particles accumulated on the surface of the particulate filter. SOLUTION : The particulate filter having oxidation function is made to carry NOX absorbing and emitting agent thereon. In a case where the quantity of the accumulated particles is less than a prescribed quantity when the NOX absorbing and emitting agent is poisoned by a sulfur component, the air-fuel ratio of exhaust gas is set to a first rate richness. On the other hand, where the quantity of the accumulated particles is more than the prescribed value, the air-fuel ratio of the exhaust gas is set to a second rate richness larger than the first rate richness.