Abstract: An internal combustion engine is provided in which an intake valve, which opens and closes an intake valve hole formed in a cylinder head facing a combustion chamber has a hollow structure. An exhaust valve hole formed in the intake valve is made to open and close by an exhaust valve coaxially housed within the intake valve. The intake valve hole communicates directly with an intake port, and the exhaust valve hole coniniunicates with an exhaust port via an exhaust passage formed within the hollow intake valve. This ensures that the intake valve has a large opening area, thus increasing the intake charging efficiency. Furthermore, since exhaust gas coming out of the combustion chamber does not make direct contact with the cylinder head, which has a large heat capacity, any decrease in temperature of the exhaust gas can be minimized, thereby utilizing waste heat effectively.

Abstract: Intake passage in cylinder heads of an opposed six-cylinder engine. The cylinder heads are disposed on opposite sides of a crankcase including cylinder blocks.Three cylinders in each cylinder head are arranged in firing order. Intake valves and exhaust valves in each cylinder are disposed in the same arrangement at every cylinder so that the distance between the intake valves are equal to each other, and an intake passage in each cylinder head is so formed as to communicate intake valves with an opening. The opening is located at a position between two cylinders which are faster in firing order than the other cylinder.