| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve accuracy for diagnosing the degree of deterioration by judging the degree of deterioration of an NOx storage catalyst from an NOx concentration ratio between NOx concentration of an output part and an input part in a period from an engine operating time when an exhaust air-fuel ratio becomes in a rich condition to an engine operating time when the exhaust air-fuel ratio becomes in a rich condition. SOLUTION: An estimate map is referred on the basis of engine rotating speed and an engine torque during operation of an internal combustion engine, concentration of NOx in an inlet part of an NOx storage catalyst 11 is estimated, and concentration of NOx in an output part of the catalyst is detected by an output part NOx concentration sensor 14. In a controller 9, an degree of deterioration is detected from a map for detecting a degree of deterioration on the basis of a ratioεbetween concentration of NOx in an inlet part and an outlet part of the NOx storage catalyst 11 and a minimum value of concentration of NOx in the inlet part, in a period from an engine operating time when an exhaust air-fuel ratio becomes in a rich condition to an engine operating time when the exhaust air-fuel ratio becomes in a rich condition. In the case where the degree of concentration is a prescribed value and less, a maximum storage rate of the NOx storage catalyst 11 is corrected.</p> |
