An intake system for an internal combustion engine

摘要

According to the present invention, each of the cylinders (1) of an engine is provided with a first (10) and a second swirl ports (20) for generating a swirl of intake air in the cylinder. The second swirl port is located at the position downstream of the first swirl port (10) with respect to the direction of swirl generated by the first intake port. The helical air passages of the first and the second intake port have a bottom which opens to the cylinder and an upper wall facing the bottom and an end wall defining the end of the helical air passage. The angle &thetas;1 between the upper wall and the end wall of the helical air passage of the first (upstream) intake port is formed smaller than the same (the angle &thetas;2) of the helical air passage of the second (downstream) intake port. By forming the angle &thetas;1 small, intake air flowing through the first intake port rotates a large amount before it flows into the cylinder and a strong swirl is formed by the intake air from the first intake port. On the other hand, since the angle &thetas;2 is relatively large, intake air flowing through the second intake port flows into the cylinder before it rotates sufficiently. Therefore, the intake air from the second intake port flows into the cylinder without interfering with the swirl in the cylinder. Thus, the flow resistance of the second intake port decreases. <IMAGE>