Exhaust gas purification system for an internal combustion engine

摘要

The present invention is intended to improve a SOx reduction rate which is a ratio of an amount of SOx reduction with respect to an amount of SOx occlusion in SOx poisoning recovery processing. In the present invention, in the SOx poisoning recovery processing in which the SOx occluded in an NOx storage reduction catalyst is reduced by decreasing the air fuel ratio of an exhaust gas flowing into the NOx storage reduction catalyst to a predetermined air fuel ratio in a repeated manner, the length of a period in which the air fuel ratio of an exhaust gas flowing into the NOx storage reduction catalyst is decreased is made longer in a relatively early time during the processing than in a relatively late time during the processing.