PURPOSE: To stabilize combustion, by opening a intake-air control valve in an engine in which a helical passage and a straight passage are formed, upon rich mixture operation in addition to operation at a predetermined opening degree to prevent swirl from occurring.
CONSTITUTION: An intake-air control valve 13 disposed in the vicinity of an intake-valve 6 in an intake-air port 7, is opened when the opening degree of a throttle valve exceeds a predetermined opening degree, in accordance with the output of a control device 30 which receives a detection value from a throttle valve opening sensor 32, in order to carry out a normal intake-air operation ranging from a low load operation in which swirl is created by a helical passage to a high load operation in which a straight passage is also used. Meanwhile, a control device 31 drives a fuel injection nozzle 27 in accordance with a rotational speed signal from a distributor 29, an intake-air pressure signal from an intake-air pipe pressure sensor 31, etc. to carry out a mixture control having a predetermined air-fuel ratio. However, if a rich mixture control is carried out upon starting, etc., the intake-air control valve 13 is opened to eliminate the creation of swirl to carry out a normal combustion.
KAMIOKA RIYUUICHIROU
TAURA MITSUHARU
