Intake system for an internal combustion engine

摘要

A dual induction type intake system for an internal combustion engine has a primary intake passageway for light load operation of the engine and a secondary intake passageway for heavy load operation of the engine. The downstream side open end of each intake passageway opens toward the intake port of the cylinder of the engine. The secondary intake passageway is provided with a controllable valve therein. The load on the engine is detected and the controllable valve is opened when the load on the engine is heavier than a predetermined value so that the intake gas is introduced into the combustion chamber through both the primary and secondary intake passageways, while otherwise the controllable valve is closed so that the intake gas is introduced into the combustion chamber only through the primary intake passageway. The primary intake passageway has a flat cross sectional configuration with its longer axis extending substantially in parallel to the lower end surface of the cylinder head, and at the same time the primary intake passageway is throated by narrowing its width, as measured in the horizontal direction, from upstream toward downstream in the direction of the flow of the intake gas. The downstream side open end of the primary intake passageway is offset from the center of the cylinder bore.