| 摘要 |
PROBLEM TO BE SOLVED: To avoid HC adhesion to inner wall surface of a cylinder when HC amount supplied to NOx catalyst increases, by closing an exhaust circulation valve, dividing a reducing agent of the amount to be supplied to exhaust branch tubes, and supplying it to the exhaust branch tubes. SOLUTION: An exhaust circulation tube 15 is connected with a forth exhaust branch tube 7d of a four-cylinders engine, and the forth exhaust branch tube 7d is confluent with first and second exhaust branch tubes 7a, 7b at upstream side confluent part 8. When NOx catalyst 12 interposed in an exhaust path 20 does not degraded, HC is supplied from a fuel injection valve 2c to only a third air-cylinder during expansion process and exhaust process of the third air-cylinder. On the other hand, when NOx catalyst 12 is degraded, degradation recovering HC amount more than cleaning HC is similarly supplied from the fuel injection valve 2c to recover catalyst degration. When the calculated degradation recovering HC amount is more than a set value, an exhaust circulation valve 16 is closed, and HC is divided and supplied from each fuel injection valve 2a-2d. |
