| 摘要 |
A decrease in the NOx removal or reduction rate is suppressed, while suppressing the outflow of particulate matter from a filter after regeneration of the filter. To this end, in an exhaust passage of an internal combustion engine, there are provided a filter, an NOx storage reduction catalyst, and an NOx selective reduction catalyst which is arranged at the downstream side of the NOx storage reduction catalyst, wherein when a reducing agent is supplied to the NOx storage reduction catalyst or the NOx selective reduction catalyst, rich control in which an air fuel ratio of exhaust gas is controlled to a rich air fuel ratio is carried out, and the lowest value of the air fuel ratio of the exhaust gas, at the time of carrying out the rich control in a predetermined period of time from a point in time at which the regeneration of the filter has ended, is made higher than the lowest value or an average value of the air fuel ratio of the exhaust gas at the time of carrying out the rich control in a period of time from the lapse of the predetermined period of time until when the next regeneration of the filter is carried out. |
