PURPOSE: To improve combustion efficiency, by providing two intake ports, using one of the ports at low loaded operation to increase an inflow speed of air into a combustion chamber while using the two ports at high loaded operation to decrease intake air resistance.
CONSTITUTION: The first intake port 2, having the first intake valve 10, and the second intake port 4, having the second intake valve 12 equipped with a valve action stopper mechanism 44 closing the valve in a range of low loaded operation, are provided. When an engine is in low loaded operation, the valve action mechanism 44 is operated to allow the second intake valve 12 to close the second intake port 4, and an inflow speed of air into a combustion chamber is fully held, then a suitable swirl can be caused, when the engine is in high loaded operation, the both intake ports 2, 4 are opened to increase sectional area for intake air and decrease intake air resistance, and an intake air quantity can be increased. In this way, good efficiency of combustion is always obtained, and output of the engine can be improved.
ITOU TADAHIKO
ISOMOTO ATSUSHI
