Exhaust gas purifying method of internal combustion engine

摘要

An air-fuel ratio of exhaust gas flowing into a NOx absorber catalyst is compulsorily changed from a lean side to a rich side to release NOx absorbed by the NOx absorber catalyst. The Nox is reduced at the same time. If temperature of the NOx absorber catalyst is lower than a first predetermined temperature T1, temporaral change of the air-fuel ratio of the exhaust gas to the rich side for the purpose of releasing and reducing NOx is inhibited, and if temperature of the NOx absorber catalyst is higher than the first predetermined temperature T1 and lower than a second predetermined temperature T2, at the time of changing temporarily the air-fuel ratio of the exhaust gas to the rich side for the purpose of releasing and reducing NOx, timing of changing the air-fuel ratio and the set air-fuel ratio are changed depending on the temperature of the NOx absorber catalyst.