EXHAUST PURIFYING DEVICE FOR INTERNAL COMBUSTION ENGINE

In an internal combustion engine, an SO x trap catalyst (13) which traps SO x contained in the exhaust gas is arranged upstream of an NO x storing catalyst (15) in an engine exhaust passage. When the NO x storing catalyst (15) should release NO x , auxiliary fuel is injected into a combustion chamber (2) at a combustible timing after the completion of injection of fuel into the combustion chamber (2) for generating the engine output. At this time, the auxiliary fuel is injected so that the air-fuel ratio A/F of the combustion gas in the combustion chamber (2) does not become below a minimum allowable air-fuel ratio M where SO x trapped at the SO x trap catalyst (13) will not be released.