Intake port of internal combustion engine

Claim 1

An internal combustion engine including a combustion chamber in a cylinder, an exhaust port in communication with the combustion chamber at an upper portion of the cylinder, an intake port in communication with the combustion chamber at an upper portion of the cylinder, the intake port having an approach portion and a turning portion connected thereto which have an inner turning wall and an outer turning wall, respectively, an exhaust valve for controlling exhaust of combustion gases from the combustion chamber to the exhaust port, and an intake valve for controlling intake air which flows in a direction from the intake port into the combustion chamber, the intake valve having a valve shaft, the turning portion of the intake port turning around the valve shaft of the intake valve in a spiral shape so as to produce swirls in the cylinder, the axis of the intake valve shaft being positioned at a plane passing through a central axis of the cylinder, the improvement comprising: the intake port having an entrance portion preceding the approach portion, the entrance portion of the intake port being positioned completely out of the plane; the entrance portion of the intake port being so constructed and arranged that a major portion of the air flow entering the entrance portion forms a central axis, the central axis of the major air flow extending to intersect a fore section of the inner turning wall of the turning portion of the intake port; the fore section arranged in the direction of air flow and crossing the plane from one side of the plane to the other side of the plane and being inclined in a forward direction; the turning portion arranged in the direction of fluid flow to thereafter turn around the valve shaft of the intake valve and cross the plane again from said other side to said one side of the plane.