Patent ID: 8661789

Claim:
An exhaust purification system for an internal combustion engine capable of lean-burn driving, the system comprising: a NOx storage reduction (NSR) catalyst disposed in an exhaust passageway of the internal combustion engine; a NOx selective catalytic reduction (SCR) catalyst disposed downstream of the NSR catalyst; an exhaust sensor, disposed downstream of the SCR catalyst, for producing output in response to NOx concentration; and an electronic control unit programmed to cause a rich-spike at a particular timing during the lean-burn driving, increase the amount of NOx contained in exhaust gas discharged during the rich-spike, in the event that the exhaust sensor has produced output indicative of a NOx concentration higher than a given NOx concentration, and increase the amount of exhaust gas during the rich-spike, in the event that the internal combustion engine is being operated under a given low-load condition.