| 摘要 |
PURPOSE:To utilize vaporizing fuel from a fuel tank so as to maintain a purifying factor of NOx always at a high value by introducing the vaporizing fuel into an exhaust pipe in the upstream of a lean NOx catalyst when an HC insufficient operation condition is judged. CONSTITUTION:A lean NOx catalyst 6, which is composed of zeolite carried with transition metals or noble metals to deoxidize NOx under presence of HC in the oxidizing atmosphere, is provided in an exhaust system 4 of an internal combustion engine 2. Vaporizing fuel pipes 12, 14, for guiding vaporizing fuel from a fuel tank 8 to a vaporizing fuel absorbing canister 10 and an upstream exhaust pipe 4a of the lean NOx catalyst 6, are provided. Here in an ECU30, a selector valve 16 is selected to a side of the vaporizing fuel pipe 12, when an operation condition of the internal combustion engine 2 detected by an operation condition detecting means is judged in an HC insufficient operation condition, and to a side of the vaporizing fuel pipe 14 when the operation condition is judged not in the HC insufficient operation condition. In this way, a purifying factor of NOx by the lean NOx catalyst 6 can be maintained always in a high value by holding a HC concentration of exhaust gas always in a high value. |
