To effectively utilize a resonance effect and an inertia effect in a wide engine rotation speed area.
A surge tank 5 is composed of first intake volume chambers 7A, 7B, second intake volume chambers 8A, 8B and a communication chamber 9. Inlet pipes 31 to 36 for slidingly moving in and out are provided at inlets of branch pipes 21 to 26 provided at the surge tank 5. For these inlet pipes, valve plates 41A, 41B are attached to cylinder groups formed by grouping cylinders of which intake orders are non-consecutive. When the inlet pipes are at a most retreat-in position, communication holes 12X, 12Y of a second separation wall are closed by the valve plates 41A, 41B, when the inlet pipes are at most protrude-out positions, communication holes 11X, 11Y of a first separation wall are closed by the valve plates 41A, 41B and when the inlet pipes are at middle positions of the most protrude-out positions and the most protrude-out positions, communication holes 11X, 11Y of the first separation wall and the communication holes 12X, 12Y of the second separation wall are opened by the valve plates 41A, 41B.
Hiromichi Kobayashi
Tomioka Kiyoshi
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