EXHAUST GAS PURIFICATION APPARATUS FOR AN INTERNAL COMBUSTION ENGINE

摘要

An amount of ammonia flowing out from an SCR catalyst is reduced at the time of carrying out rich spike control to reduce an amount of NOx stored in an NSR catalyst. The NSR catalyst and the SCR catalyst are arranged in order in an exhaust passage of an internal combustion engine which is able to be operated at a lean air fuel ratio, wherein a target air fuel ratio of exhaust gas flowing into the NSR catalyst during the rich spike control is made higher within the range of a rich air fuel ratio, in the case where the outflow of ammonia from the SCR catalyst in accompany with the rich spike control is estimated or detected, than in the case where it is not estimated or detected.

主权项

1. An exhaust gas purification apparatus for an internal combustion engine which is able to be operated at a lean air fuel ratio, said apparatus comprising:
an NOx storage reduction catalyst that is arranged in an exhaust passage of said internal combustion engine, and serves to store NOx when an air fuel ratio of exhaust gas is a lean air fuel ratio, and to reduce the NOx thus stored when the air fuel ratio of the exhaust gas is equal to or less than a stoichiometric air fuel ratio, wherein ammonia is produced in a reducing atmosphere in which a predetermined amount of a reducing agent exists; an NOx selective catalytic reduction catalyst that is arranged in said exhaust passage at a location downstream of said NOx storage reduction catalyst, and serves to adsorb ammonia and to reduce the NOx by using the ammonia thus adsorbed as a reducing agent; an ammonia outflow detector configured to estimate or detect an outflow of ammonia from said NOx selective catalytic reduction catalyst; and a controller comprising at least one processor configured to carry out rich spike control in which an air fuel ratio of exhaust gas flowing into said NOx storage reduction catalyst is controlled to a rich air fuel ratio; wherein said controller farther configured to carry out air fuel ratio raising control in which a target air fuel ratio of the exhaust gas flowing into said NOx storage reduction catalyst during said rich spike control is made higher within the range of the rich air fuel ratio, in the case where the outflow of ammonia from said NOx selective catalytic reduction catalyst in accompany with the rich spike control is estimated or detected by said ammonia outflow detector, than in the case where it is not estimated or detected.