| 摘要 |
<p>PROBLEM TO BE SOLVED: To hold the frequency of S poisoned recovering operation of a NOx storage reduction catalyst without deteriorating fuel consumption. SOLUTION: A NOx storage reduction catalyst 7 is arranged in an exhaust passage 2 in an internal combustion engine, for absorbing NOx in exhaust gas when an exhaust air-fuel ratio is in a lean condition, and for discharging and reduction-purifying NOx absorbed when the exhaust air-fuel ratio is in a rich condition. A recovering operation is carried out only in a specified operating condition of an engine for discharging SOx absorbed together with NOx in the NOx storage reduction catalyst by heating the NOx storage reduction catalyst. In preventing deterioration of fuel consumption in the engine, the more the SOx holding rate of the NOx storage reduction catalyst is increased, the more an engine operating condition is increased for carrying out the recovering operation. Accordingly, the more the SOx holding rate increases the easier the recovering operation is carried out therefore it is possible to prevent a condition in which the SOx holding rate of the NOx storage reduction catalyst is increased from continuing for a long time.</p> |
