| 摘要 |
PROBLEM TO BE SOLVED: To realize an excellent purification performance by circulating necessary and sufficient amount of exhaust gas irrespective of the operating conditions. SOLUTION: An exhaust path 2 is merged on the upstream side from a main catalyst 3 provided in the exhaust path 2 of an engine 1 after it is branched into a main path 6 and a bypass path 4, and a lean NOx catalyst 5 is provided in the bypass path 4. Also a valve 7 and a valve 8 are installed at the inlets of the main path 6 and the bypass path 4, respectively, and an ECU12 controls the valves 7 and 8 so that exhaust gas is introduced to the bypass path 4 in lean combustion and to the main path 6 in combustion at a theoretical air/fuel ratio. In addition, a flow path cross-sectional area of the inlet part of the bypass path 4 is set smaller than that of the main path 6. Thus, because the pressure of the exhaust gas from the exhaust path 2 is increased in lean combustion, the amount of circulation of the exhaust gas to the sucking path 14 through an exhaust gas circulating path 13 is increased more than that in the combustion at the theoretical air/fuel ratio. |
