PURPOSE: To restrain the difference in the air-fuel ratio at the time when fuel is changed over between a liquid fuel and a gas fuel by delaying the fuel supply stopping time and the fuel supply starting time in both fuels by a prescribed time.
CONSTITUTION: The intake port of an engine 11 is provided with a fuel injection valve 15 for injectedly supplying gasoline fuel as a liquid fuel. The engine 11 is provided with a CNG fuel supply device 41 for supplying CNG fuel as a gas fuel. The changeover of fuel is carried out by opening or closing a fuel cut valve 45 on the basis of the signal from a control unit 50. When gasoline fuel is changed over to CNG fuel, the fuel supply stopping time of the liquid fuel supply system is delayed later than the fuel supply starting time of the gas fuel supply system by a prescribed time. When CNG fuel is changed over to gasoline fuel, the fuel supply starting time of the liquid fuel supply system is delayed later than the fuel supply stopping time of the gas fuel supply system by a prescribed time. Thereby, the fluctuation in air-fuel ratio can be restrained.
INADA EIJI
HAMAI KYUGO
