PURPOSE: To improve the combustion efficiency of an engine having two intake valves of a front valve and a rear valve in its cylinder head, by disposing an ON-OFF valve in an intake port having the rear valve so that the swirl ratio can be set at a proper value according to the engine speed and the engine load.
CONSTITUTION: A partition wall 11 is formed in the vicinity of the inlet of a cylinder head where intake ports 21, 31 are formed, in the manner that the two intake ports 21, 31 are separated completely from each other. Further, a butterfly valve 5 is disposed at a portion of the intake port 31 having a rear valve 30, and the top of a lever 52 fixed to a shaft 51 of the butterfly valve 5 is connected to an actuator 54 via an actuator rod 53. The butterfly valve 5 is opened and closed by detecting the injection quantity of fuel and the turning speed of a governor 7 attached to a fuel injection pump 6 by means of a sensor 56 and controlling the actuator 54 by a control unit 55 according to the output signal of the sensor 56. That is, when the engine speed is lowered, combustion is promoted by closing the butterfly valve 5 gradually and increasing the mixing energy of air by raising the swirl ratio.
YAGI YASUO
MINE KANETOSHI
