Exhaust gas purification device for internal combustion engine

摘要

An exhaust gas purification device senses an air-fuel ratio of exhaust gas flowing into a catalyst and performs rich purge control for supplying fuel for reduction to the catalyst. The device calculates a total reducing agent amount consumed for the reduction during the rich purge control based on the air-fuel ratio and a fresh air amount as of the rich purge control. The device sets a specified air-fuel ratio state for controlling the air-fuel ratio in a certain range enabling more precise measurement of the air-fuel ratio than in the rich purge control. The device corrects the total reducing agent amount based on a difference between an injection amount command value as of the rich purge control and the injection amount command value in the specified air-fuel ratio state and the air-fuel ratio sensed in the specified air-fuel ratio state.