| 摘要 |
<p>A device for judging deterioration of a catalyst accurately by taking account of oxygen concentration in the downstream of exhaust emission purification catalyst. In case of catalyst active state, oxygen sensor output (VO2) and ammonia sensor output (VNH3) in the downstream of an NSR catalyst are read in (step 104). If the oxygen sensor output (VO2) thus read out is at a reference level (a) or higher and the ammonia sensor output (VNH3) is at a reference level (ß) or higher, it is estimated that oxidation reaction of ammonia does not take place in the NSR catalyst under existence of oxygen. In this case, a judgment is made that the NSR catalyst is deteriorated (steps 108, 11, 114).</p> |
