| 摘要 |
PURPOSE: To prevent a lowering of NOx purifying efficiency of a catalyst by providing a lean NOx catalyst for purifying NOx in exhaust in a lean atmosphere, and injecting fuel in the vicinity of the intake top dead center at the time of detecting the NOx conversion efficiency lowered state of the catalyst during lean control. CONSTITUTION: During the driving of a vehicle, the reference fuel injection quantity Tp is computed in a control unit 5 from the intake air flow Qa and engine speed Ne. In the case of the engine 1 being in the warming-up state, the time change of vehicle speed obtained from a vehicle speed sensor 18 is computed, and whether to be a lean operating condition is judged. Whether to be a steady state is further judged. In the case of the steady state, the moving quantity ΔT of injection timing is obtained from Ne and Tp, and injection start timing is delayed by ΔT from the normal operating time. Fuel is thereby injected in the vicinity of the intake top dead center at the time of steady lean operation where the conversion efficiency of a lean NOx catalyst 15 is apt to be lowered, so that HC concentration in exhaust is increased, and the conversion efficiency of the lean NOx catalyst 15 is heightened. |
