EXHAUST GAS PURIFYING SYSTEM FOR INTERNAL COMBUSTION ENGINE

摘要

This invention provides a technique which can complete SOx poisoning recovery control for an occlusion reduction-type NOx catalyst in a shorter time. During SOx poisoning recovery control, the level of lowering in SOx emission rate (the SOx emission rate lowering level Ddw), attributable to a reduction in SOx occlusion amount in the NOx catalyst, relative to the SOx emission rate at the start of the SOx poisoning recovery control is estimated. As the SOx emission rate lowering level Ddw increases, the catalyst bed temperature Tc is raised to a target temperature Tct on a higher temperature side. Further, the air-fuel ratio (A/F) in the exhaust gas is lowered to a target air-fuel ratio (A/Ft), which is on a richer side, to suppress the lowering in SOx emission rate Vsox during the SOx poisoning recovery control.