| abstract |
A decrease in an NOx removal or reduction rate at the time of filter regeneration is suppressed. To this end, provision is made for an NOx selective reduction catalyst, a filter arranged at the upstream side of the NOx selective reduction catalyst, an NH 3 generation catalyst arranged at the upstream side of the NOx selective reduction catalyst to generate NH 3 when the air fuel ratio of an exhaust gas is equal to or less than a stoichiometric air fuel ratio, a regeneration unit to carry out regeneration of the filter, and a generation unit to make the air fuel ratio of the exhaust gas equal to or less than the stoichiometric air fuel ratio, thereby causing NH 3 to be generated in the NH 3 generation catalyst, wherein the regeneration unit inhibits the regeneration of the filter until the generation of NH 3 by the generation unit is completed. |