EXHAUST CLEANING SYSTEM OF INTERNAL COMBUSTION ENGINE

Concerning an internal combustion engine equipped with an NSR catalyst and an SCR, this invention is intended to provide an exhaust gas purification system for an internal combustion engine, the system being used to suppress degradation of emissions due to blow-through of NOx. The exhaust gas purification system, used for the internal combustion engine 10 susceptible of lean-burn operation, includes an NSR catalyst 16 disposed in an exhaust passageway 12 of the internal combustion engine 10, an SCR 18 disposed on a downstream side relative to the NSR catalyst 16, and an element for executing rich-spike control at a predetermined interval during lean-burn operation. On the basis of a first rule as a relationship between the time interval and the amount of NH 3 generated in the NSR catalyst 16 during rich-spike control, and a second rule as a relationship between the time interval and the amount of NOx blown through the NSR catalyst 16 to the downstream side thereof during rich-spike control, the time interval is set to stay in a period during which a total of the amount of NOx blown through will be reduced and purified in the SCR 18. Preferably, the time interval is set so that a ratio of the amount of NH 3 generation to that of NOx blow-through is greater than a predetermined ratio.