EXHAUST GAS PURIFICATION APPARATUS FOR AN INTERNAL COMBUSTION ENGINE

摘要

The present invention has for its object to provide a technology in which in an exhaust gas purification apparatus for an internal combustion engine which is provided with a catalyst for NH3 generation, and a catalyst for removing or reducing NOx in an exhaust gas by using NH3 as a reducing agent, NOx in the exhaust gas can be reduced, even in cases where the NH3 generation capacity of the catalyst for NH3 generation has become low. In order to solve this object, the exhaust gas purification apparatus for an internal combustion engine of the invention is provided with a three-way catalyst and a storage reduction catalyst as catalysts for NH3 generation, wherein when the NH3 generation capacity of the storage reduction catalyst does not become low, NH3 is made to be generated in the storage reduction catalyst by adjusting the air fuel ratio of the exhaust gas flowing into the storage reduction catalyst to a first predetermined rich air fuel ratio, whereas when the NH3 generation capacity of the storage reduction catalyst becomes low, NH3 is made to be generated in the three-way catalyst by adjusting the air fuel ratio of the exhaust gas flowing into the three-way catalyst to a second rich air fuel ratio which is higher than the rich air fuel ratio and lower than a theoretical air fuel ratio.

主权项

1. An exhaust gas purification apparatus for an internal combustion engine comprising:
a storage reduction catalyst that is arranged in an exhaust passage of the internal combustion engine adapted to be operated in a lean burn state, and serves to reduce nitrogen oxides to ammonia when an air fuel ratio of an exhaust gas flowing thereinto is a first rich air fuel ratio which is lower than a theoretical air fuel ratio; a selective catalytic reduction catalyst that is arranged in the exhaust passage at a location downstream of said storage reduction catalyst, and serves to reduce nitrogen oxides in the exhaust gas by using ammonia as a reducing agent; a three-way catalyst that is arranged in the exhaust passage at a location upstream of said storage reduction catalyst; and a control unit that controls the air fuel ratio of the exhaust gas flowing into said three-way catalyst to a second rich air fuel ratio which is higher than said first rich air fuel ratio and lower than the theoretical air fuel ratio, when the ammonia generation capacity of said storage reduction catalyst has become low.