Air intake structure of internal combustion engine

Abstract

To provide an internal combustion engine in which one intake valve port and one exhaust valve port are mounted on a ceiling surface of a combustion chamber to which a top portion of a piston which is slidably fitted in a cylinder block faces and an intake valve which opens or closes the intake valve port and an exhaust valve which opens or closes the exhaust valve port are arranged on a cylinder head in an approximately V shape in a state that the intake valve and the exhaust valve are capable of performing an open / close operation, wherein the internal combustion engine can effectively stir a gas flow in the inside of a combustion chamber while minimizing the disturbance of the gas flow at the intake valve port thus contributing to the enhancement of an engine output and the reduction of fuel consumption. [Means for Resolution] An intake port 60 which is formed in the cylinder head 25 in communication with the intake valve port 47 is constituted of an upstream-side passage portion 60a which extends substantially linearly to the vicinity of the intake valve port 47 from a side surface of the cylinder head 25 and a downstream-side passage portion 60b which is curved in projection toward a plane orthogonal to an axis of the piston and connects the upstream-side passage portion 60a and the intake valve port 47, and the ceiling surface 46 of the combustion chamber is formed in a dome shape having an elliptical transverse cross-sectional shape with a direction which connects the center of the intake valve port 47 and the center of the exhaust valve port 48 directed in the major-axis direction.