NOX PURIFICATION METHOD OF AN EXHAUST PURIFICATION SYSTEM OF AN INTERNAL COMBUSTION ENGINE

In an internal combustion engine, inside of an engine exhaust passage, a hydrocarbon feed valve (15) and an exhaust purification catalyst (13) are arranged. The concentration of hydrocarbons which flow into the exhaust purification catalyst (13) is made to vibrate by within 200 ppm or more predetermined amplitude and within a 5 second or more predetermined period. At this time, when a predetermined amount or more of NO x is stored in the exhaust purification catalyst (13) or can be stored, the concentration of hydrocarbons flowing into the exhaust purification catalyst (13) is temporarily increased to desorb NO x which is stored at the exhaust purification catalyst (13).