Patent ID: 7707989

Claim:
An intake port structure for an engine, comprising: first and second intake ports extending in a direction perpendicular to a cylinder line and communicating in a combustion chamber of the engine and respective first and second intake valve holes opening in the combustion chamber, wherein the first intake port is a straight port in which a throat portion is formed in a linear shape and opens in a tangential direction of an inner periphery of a cylinder wall, the first intake port being generally perpendicular to the cylinder line, the first intake port generating a first swirl, and the second intake port is a helical port in which a throat portion is formed in a helical shape, the second intake port generating a second swirl inside the first swirl in the same direction as that of the first swirl and further wherein, the second intake port comprises a helical outer wall formed along a peripheral edge of the second intake valve hole, a helical inner wall formed inside of said helical outer wall and radially outside a valve stem positioned at the center of the second intake valve hole, a first guide wall connected to the helical outer wall and extending in a direction tangential to the second intake valve hole and substantially perpendicular to the cylinder line, and a second guide wall connected continuously to the helical inner wall from a state in which it is substantially parallel to the first guide wall, and is formed so that as a first interwall distance of the first and second guide walls decreases toward the downstream side in the intake air flow direction, a second interwall distance, in a direction perpendicular to the first interwall distance, increases.