PURPOSE: To prevent the output from being lowered under an intermediate or higher load and contrive to reduce vibration at the time of idling, by a method wherein a main passage and an sub-passage are provided, and an auxiliary throttle valve is fully opened at the time of fully closing a main throttle valve.
CONSTITUTION: An intake pipe 10 is provided with the main passage 10a having a larger cross-sectional area and the sub-passage 10b having a smaller cross- sectional area. The main throttle valve 11a is provided in the main passage 10a, and the auxiliary throttle valve 11b is provided in the sub-passage 10b. An introducing pipe 16 for heated air is connected with a shielding plate 14 and the sub-passage 10b. At the time of idling the engine, the main throttle valve 11a is fully closed, while the auxiliary throttle valve 11b is fully opened. At this time, the heated air is supplied to the engine through the pipe 16. An accelerator pedal 8 is stepped in to open the main throttle valve 11a and fully close the auxiliary throttle valve 11b, and the supply of the heated air is stopped. Accordingly, the increase in the amount of smoke and the lowering of the output due to a shortage of air under a intermediate or higher load are prevented, and vibration and noise at the time of idling are reduced.
ITOU TOSHIHIKO
TANAKA TAKESHI
