PURPOSE: To prevent overthinning of fuel-air mixture, by a method wherein an air control valve and an on-off valve are respectively located in two intake secondary air feed passages placed in a manner to be extended around a throttle valve, and the air control valve is rapidly closed during low temperature running of an engine and under a brake operating state.
CONSTITUTION: An air cleaner 2 is communicated with a suction manifold 10, located down a line from a throttle valve 5, through a suction secondary air feed passage 11. The passage 11 is branched at the middle into two air control passages 11a and 11b, and an on-off valve 15, opened only when an air-fuel ratio is rich, is located in the air control passage 11a, and an air control valve 16 in the air control passage 11b. A negative pressure chamber 16a of the air control valve 16 is communicated with the downstream of a throttle valve 5 through a negative pressure feed passage 17 in which an electromagnetic valve 18, a constant negative pressure control valve 21, and a check valve 23 are situated, and is communicated with the open air through an atmospheric pressure feed passage 49 in which an electromagnetic valve 50 is situated. The electromagnetic valve 50 is controlled so as to be opened during low temperature driving of an engine and under a brake operating state.
ASAKURA MASAHIKO
KIMURA KATSUHIKO
SEKI YASUNARI
