| 摘要 |
PURPOSE:To obtain expected exhaust gas purifying performance reducing the size of a catalyst device by arranging a small-sized catalyst device at a position on the upper stream side of the section junctioning with an exhaust by-path on the down stream side of the turbine of a small-sized turbocharger. CONSTITUTION:A large-sized low pressure stage turbocharger 17 and small-sized high pressure stage turbocharger 18 are arranged in series in the gas flow direction, and an exhaust cut-off poppet valve 38 is provided in an exhaust by-path 36 making a detour of the turbocharger 18. Each working area of the turbochargers 17 and 18 is changed-over by opening and closing the exhaust cut-off poppet valve 38. A small-sized catalyst device 84 is arranged at a position on the upper stream side of the section junctioning with the exhaust by-path 36 on the down stream side of the turbine 28 of the turbocharger 18, and a large-sized catalyst device 86 is arranged at a position in the downstream of the turbine 22 of the turbocharger 17. Owing to this constitution, exhaust gas is effectively purified by the catalyst device 84 in the rotation at a low speed and low load by 2 stage supercharging and by the catalyst device 86 in the rotation at a high speed and high load by 1 stage supercharging respectively. |
