PURPOSE: To obtain the stable combustion of an extremely dilute air-fuel mixture and suppress torque variations by controlling the air-fuel ratio of the air- fuel mixture properly in response to the number of engine revolutions and the negative pressure in a suction passage and by forming a suction port in a helical shape.
CONSTITUTION: A helical suction port 6 is formed in a cylinder head 3, and the port 6 is connected to a common surge tank 24 through a branch pipe 23, then is connected to an air cleaner 26 through an air duct 25. A fuel injection valve 27 is fitted to the branch pipe 23 and the valve 27 is controlled by an electronic control unit 50. That is, when the number of engine revolutions detected by a revolution number sensor 61 is about 1,400rpm or more and the suction negative pressure detected by a negative pressure sensor 58 is approximately -50W -350mmHg, the injection valve 27 is controlled so as to form a dilute air-fuel mixture with a constant air-fuel ratio. When the number of engine revolutions is about 1,400rpm or less or the suction negative pressure is about -50mmHg or less, the valve is controlled so as to lower the air-fuel ratio as these values are decreased.
MATSUSHITA SOUICHI
KATOU KENJI
