Patent ID: 8015800

Claim:
An internal combustion engine comprising: an exhaust passage; a post-treatment system arranged in the exhaust passage, the post-treatment system including at least an upstream side exhaust purification catalyst and a downstream side exhaust purification catalyst arranged in series in the exhaust passage; and a control device that controls the post-treatment system such that when the upstream side exhaust purification catalyst has a degree of degradation exceeding a predetermined degree of degradation, a method of feeding fuel is reset to a fuel feed method so that the fuel required for purification of exhaust gas in the exhaust passage can be fed into the downstream side exhaust purification catalyst to make an air-fuel ratio of the exhaust gas entering the downstream side exhaust purification catalyst temporarily rich so that the downstream side exhaust purification catalyst can handle a purification action of the exhaust gas, wherein: the upstream side exhaust purification catalyst and the downstream side exhaust purification catalyst arranged in series in the exhaust passage are comprised of NO x storing/reducing catalysts storing NO x contained in the exhaust gas when an air-fuel ratio of inflowing exhaust gas is lean and releasing the stored NO x when the air-fuel ratio of the inflowing exhaust gas becomes a stoichiometric air-fuel ratio or rich, when making the air-fuel ratio of the exhaust gas flowing into a NO x storing/reducing catalyst rich so that the NO x storing-reducing catalyst releases NO x , post-treatment fuel is fed in a combustion chamber or in the exhaust passage upstream of the NO x storing/reducing catalyst positioned at the most upstream side, and the further downstream a catalyst with a lowest degree of degradation is positioned, a higher a degree of richness the air-fuel ratio of the exhaust gas is made.