EXHAUST PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

The purpose is to prevent ammonia from flowing out of a NOx selective reduction catalyst when an air-fuel ratio of exhaust gas flowing into a NOx storage/reduction catalyst decreases. An NSR catalyst, a NOx sensor, and an SCR catalyst are provided in an exhaust passage in sequence from an upstream side, and a control apparatus is further provided to determine an amount of ammonia supplied to the NOx selective catalytic reduction catalyst on the basis of a detection value of the NOx sensor. When the air-fuel ratio of the exhaust gas flowing into the NOx storage/reduction catalyst is set at or below a stoichiometric air-fuel ratio, an amount of ammonia supplied from an ammonia supply apparatus relative to the detection value of the NOx sensor is decreased so as to be smaller than when the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio.