Intake and exhaust apparatus of multi-cylinder engine

An intake and exhaust apparatus of a multi-cylinder engine provided with a plurality of cylinders having intake and exhaust valves for opening and closing intake and exhaust ports, respectively, the apparatus comprising:

• an intake system including intake ports of respective cylinders, independent intake passages connected with respective intake ports, a surge tank connected with upstream ends of the independent intake passages, and an air cleaner connected with the surge tank;
• and
• an exhaust system including independent exhaust passages connected with an exhaust port of one cylinder or exhaust ports of the plurality of cylinders that are not continuous in exhausting order, and a collecting pipe connected with downstream ends of the independent exhaust passages in a bundled manner, and for collecting exhaust gas ejected from the downstream ends of the independent exhaust passages,
• wherein, within a low engine speed range where an engine speed is below a predetermined first engine speed, open periods of the intake and exhaust valves of each cylinder have a predetermined overlap period, and the overlap period of the open period of the intake valve of one of the cylinders is set to overlap with an opening timing of the exhaust valve of another cylinder that is continuous in exhausting order,
• wherein both a pipe length and a pipe diameter of the intake system, or a volume of the intake system alone are set so that a synchronizing time point of intake air resonance in which a frequency of vibration caused by opening and closing the intake valve matches with a resonance frequency of the intake system is included within a middle engine speed range where the engine speed is between the first engine speed and a predetermined second engine speed higher than the first engine speed, and
• wherein a length of the independent intake passage is set so that an intake inertia effect based on a positive pressure wave is obtained within a high engine speed range where the engine speed is above the second engine speed, the positive pressure wave being obtained by a negative pressure wave of the intake air inverting in the surge tank, and the negative pressure wave being generated by opening the intake valve.