EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To accurately detect sulfur poisoning of a three-way catalyst.SOLUTION: After the air-fuel ratio of exhaust gas flowing into a three-way catalyst is changed from a rich air-fuel ratio into a lean air-fuel ratio but before the air-fuel ratio of the exhaust gas flowing out of the three-way catalyst is changed into the lean air-fuel ratio, an exhaust emission control device for an internal combustion engine determines whether to restore the sulfur poisoning of the three-way catalyst or not, on the basis of a NOx concentration downstream of the three-way catalyst, or determines that the degree of the sulfur poisoning of the three-way catalyst is higher when the NOx concentration detected by a NOx sensor is high, than when it is low.SELECTED DRAWING: Figure 6