| 摘要 |
PROBLEM TO BE SOLVED: To obtain HC purification effect to the maximum extent while suppressing NOx exhaust by providing lean NOx catalyst and HC adsorption catalyst in the order from the upstream side in an exhaust passage and controlling an air-fuel ratio of mixed air to a lean state while lean NOx catalyst is active and HC is removed from an HC adsorption material. SOLUTION: In an exhaust manifold of an air exhaust passage 17, an oxygen sensor 18 detecting rich or lean state of an air-fuel ratio is provided, a lean NOx catalyst 19 is provided on the downstream side thereof, and an HC adsorption catalyst 20 provided with a ternary catalyst layer on an upper layer of an HC adsorption material is provided on the downstream side furthermore. This HC adsorption catalyst 20 absorbs HC in exhaust air into the HC adsorption material when an internal combustion engine is cold and removes HC from the HC adsorption material upon completion of warming up the engine to purify the removed HC by oxygen in the ternary catalyst layer. In this case, an air-fuel ratio of mixed air is controlled to a lean state while lean NOx catalyst 19 is activated and HC is removed from the HC adsorption material. Consequently, it is possible to securely supply oxygen required for HC purification to the ternary catalyst layer and increase the purification efficiency of HC.
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