| 摘要 |
An exhaust gas purifying apparatus for an internal combustion engine is provided. The apparatus includes a first catalyst and a second catalyst. The first catalyst is provided in an exhaust passage of the engine, and can remove NOx in exhaust gases from the engine when an air-fuel ratio of an air-fuel mixture burning in the engine is in the vicinity of the stoichiometric ratio. The second catalyst is provided downstream of the first catalyst, an can remove NOx in the exhaust gases using a reducing agent. An execution condition of a lean operation in which the air-fuel ratio is set to a lean air-fuel ratio which is leaner than the stoichiometric ratio, is determined. When switching the air-fuel ratio from an air-fuel ratio in the vicinity of the stoichiometric ratio to the lean air-fuel ratio, the air-fuel ratio is controlled to a rich air-fuel ratio which is richer than the stoichiometric ratio, during a lean transition period from the time the execution condition is satisfied. The air-fuel ratio is controlled to the lean air-fuel ratio after the lean transition period has elapsed. |
