| 摘要 |
<p>With respect to an internal combustion engine, SO<SUB>X</SUB> trap catalyst (11) capable of trapping SO<SUB>X</SUB> contained in an emission gas is disposed in an engine exhaust passage upstream of NO<SUB>X</SUB> occlusion catalyst (12). When whether or not the SO<SUB>X</SUB> trap catalyst (11) has been deteriorated is to be judged, the temperature of the SO<SUB>X</SUB> trap catalyst (11) is raised while keeping lean the air/fuel ratio of emission gas flowing into the SO<SUB>X</SUB> trap catalyst (11). At that time, the level of NO<SUB>X</SUB> having been released from the SO<SUB>X</SUB> trap catalyst (11) is detected by means of NO<SUB>X</SUB> level sensor (24), and when the NO<SUB>X</SUB> level is a set value or below, the deterioration thereof is determined.</p> |
