PURPOSE: To improve the durability and efficiency of an engine, by advancing the open time of a second exhaust port with respect to the open time of a first exhaust port and disabling a stop means under high rotation and heavy load.
CONSTITUTION: Under high rotation and heavy load operation of an engine E, the pulsating high pressure exhaust gas being produced during blowdown bypasses a turbine 12c and then discharged through a second exhaust port 4, second branch exhaust path 15 and second exhaust path 17. In order to prevent increase of the exhaust pressure and to smooth the fluctuation of exhaust pressure caused by blowdown gas, a second exhaust valve 3 is arranged to function. The open-valve timing of the second exhaust valve 3 is set to the quicker than that of a first exhaust valve 1.
HITOMI MITSUO
HITASE FUMIO
