| 摘要 |
PROBLEM TO BE SOLVED: To enhance NOx reduction purification ability when a oxidation catalyst 22a and a NOx trap catalyst 22b are respectively arranged at an upstream side and a downstream side of an exhaust passage 20. SOLUTION: When NOx is released from the NOx trap catalyst 22a, concentration of oxygen in an exhaust gas is reduced by carrying out a post fuel injection in addition to a main fuel injection. Further, the amount of the post fuel injection is increased or decreased every predetermined time, whereby HC in the exhaust gas blows through the oxidation catalyst 22a at the upstream side to thereby making easy for HC to reach the NOx trap catalyst 22b at the downstream side.
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