Intake system construction for internal combustion engine and manufacturing process of intake passage section of internal combustion engine

摘要

An intake system construction for an internal combustion engine includes a combustion chamber formed with upper and lower extremities thereof defined by a lower wall of a cylinder head and a top wall of a piston, an intake open end formed in the lower wall in opposition to the combustion chamber on one side of a reference plane which contains a central axis of the cylinder, an intake port formed in communication with the combustion chamber via the intake open end and extending upwardly from the intake open end so that a vertical swirl of inducted air is formed in the combustion chamber, an intake valve having a head portion for opening or closing the intake open end and a stem portion extending from the head portion to an upstream side of the intake port through the cylinder head, and a straightening member arranged in the intake port on a downstream side of the stem portion so that an inducted air flow is straightened on the downstream side of the stem portion.