Patent ID: 6892696

Claim:
An internal combustion engine comprising: a cylinder in which a piston is reciprocably fitted, the cylinder having a cylinder axis; a cylinder head formed with an intake port having a first port and a second port including, respectively, a first inlet slot and a second inlet slot opening into a combustion chamber; a valve mechanism for opening and closing a first intake valve and a second intake valve for opening and closing the first port and the second port, respectively, the first valve and the second valve each having a longitudinal axis; and intake air control means for generating a swirl in the combustion chamber by intake air flowing from the first port; and a camshaft provided with a valve motion cam for opening and closing the first intake valve, the camshaft having a rotational centerline perpendicular the cylinder axis, wherein a perpendicular line orthogonal to a first plane, which is a plane including the first inlet slot, the perpendicular line being either parallel to or coincident with the longitudinal axis of the first intake valve, that a plane including the cylinder axis and extending in parallel with the rotational centerline of the camshaft is a first reference plane, that a plane including the cylinder axis and extending orthogonally to the rotational centerline is a second reference plane, and that a plane extending in parallel with the first reference plan is a first orthogonal plane, that a line of intersection n 1 between the first plane which includes the first inlet slot and the first orthogonal plane inclines upwardly as it approaches from a position near an outer periphery of the combustion chamber toward the second reference plane, wherein the first port includes a first port section having a passage shape which extends substantially along the perpendicular line from the first inlet slot in an upstream direction by a predetermined length of the first port in a plan view, and wherein the first port section having the passage shape has a cross section which gradually and smoothly increases in size as it extends from the first inlet slot in the upstream direction.