Exhaust emission control device for internal combustion engine, method of controlling the exhaust emission control device, and engine control unit

摘要

An exhaust emission control device for an internal combustion engine, which is capable of terminating reduction control in proper timing when a NOx cleaning catalyst includes an auxiliary catalyst having an oxygen storage capacity, thereby making it possible to reduce exhaust emissions and improve fuel economy. The exhaust emission control device includes the NOx cleaning catalyst and an ECU. The NOx cleaning catalyst includes the auxiliary catalyst having an oxygen storage capacity. The ECU executes reduction control when predetermined conditions for executing the reduction control are satisfied. During execution of the reduction control, when exhaust gas temperature is higher than a predetermined value, if a second excess air ratio is lower than a predetermined value, the ECU determines that the reduction control should be terminated. When the exhaust gas temperature is not higher than the predetermined value, if the remaining NOx amount is not larger than a predetermined value, the ECU determines that the reduction control should be terminated.