| 摘要 |
PROBLEM TO BE SOLVED: To keep the high NOx purifying rate regardless of a reducer adsorbing capability by decreasing the quantity of a reducer when the reducer adsorbing capability of a NOx catalyst for purifying NOx by a reducer is lowered under the excess of oxygen, and increasing the quantity of a reducer when the reducer adsorbing capability is heightened. SOLUTION: During the operation of an engine, HC supplied to a NOx catalyst 10 in an exhaust passage 5 is adsorbed to the surface of a carrier of the NOx catalyst 10, and in here it is dissolved to HC with a lower boiling point, thereby heightening the activation of HC. The maximum HC adsorption quantity at the NOx catalyst 10 is decreased as the catalyst temperature becomes high, and when the catalyst temperature becomes high and the maximum HC adsorption quantity is decreased, in the case where the adsorption HC quantity is larger than the maximum HC adsorption quantity, some of the adsorption HC is separated from the surface of the NOx catalyst 10. The quantity of HC jetted by auxiliary injection is controlled to be decreased by the quantity of HC released from the surface of the NOx catalyst 10, whereby the NOx purifying rate is kept at a high level.
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