| 摘要 |
PROBLEM TO BE SOLVED: To effectively reduce the NOx occluding quantity of a catalyst by judging whether an HC fluctuation type NOx reduction catalyst is within an active temperature range or not at the time of deceleration, and fluctuating (increasing or decreasing) the HC concentration in the exhaust air flowing into the catalyst when the judgment result is YES. SOLUTION: When an engine 51 having a catalyst 1 containing an HC fluctuation type NOx reduction catalyst and an HC adsorptive catalyst in an exhaust system is operated, it is judged in a control unit whether the HC fluctuation type NOx reduction catalyst is in an active temperature area or not at the time of deceleration just after steady operation and just after acceleration operation. When YES is judged, an HC concentration fluctuating means is operated to secondarily supply HC. According to this, the HC concentration at the catalyst inlet is fluctuated, and the NOx occluded by the catalyst is desorbed and reduced by the fluctuation of the HC concentration to reduce the NOx occluding quantity of the catalyst. Thus, when the catalyst is in the active temperature area every deceleration, the NOx occluding quantity of the catalyst is reduced to delay its regeneration timing. |
