| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent a waste of fuel by suppressing the degradation of exhaust emission attributable to impairment of the catalyst reaction of a NOx occlusion reduction catalyst by hydrocarbon. <P>SOLUTION: When it is determined that a flow-in HC concentration thccl into the NOx occlusion reduction catalyst is larger than an excessive concentration determination value thmax ('YES' in S116), HC control by the NOx occlusion reduction catalyst cannot be achieved, and NOx control can be impaired by HC heavily covering a catalyst surface. Accordingly, the implementation of a rich spike is prohibited in advance, or stopped in the way by implementing rich spike prohibition (S120). Since a situation that the catalyst surface is heavily covered by HC can be prevented, the degradation of the exhaust emission attributable to the impairment of the catalyst reaction of the NOx occlusion reduction catalyst by HC can be suppressed, and a waste of fuel can be prevented. <P>COPYRIGHT: (C)2003,JPO |
