| 摘要 |
<p>PROBLEM TO BE SOLVED: To restrain degradation of exhaust emission and fuel economy due to deterioration of a NOx absorbing catalyst and an engine, and to diagnose degradation of the NOx absorbing catalyst with high accuracy, in the engine provided with the NOx absorbing catalyst. SOLUTION: A rich spike control is carried out such that an air-fuel ratio is temporarily made rich every time the NOx absorbing catalyst becomes saturated, to reduce and purify NOx. A frequency of the rich spike control is more than a first threshold (S23), an exhaust reflux amount is corrected to be increased (S24), and an ignition timing is corrected in order to maintain combustion stability (S25). When the frequency of the rich spike control is more than a second threshold (>first threshold) (S29) in a state in which the exhaust recirculated amount and/or the ignition timing is corrected to reach the limit (S26), the degradation of the NOx absorbing catalyst is diagnosed (S30).</p> |
