PURPOSE: To prevent air-fuel ratio of a fuel mixture from being rendered over- rich and maintain combustion characteristics under good condition, by stopping purging of vapor fuel during transition from an engine idling operation to an engine load operation.
CONSTITUTION: When an accelerator pedal is depressed at an engine idling operation, an opening degree of a throttle valve 3 is enlarged and a vacuum generated at a vacuum induction port 20 starts acting to a vacuum chamber 17 of a purge control valve 7. At this time, an idle siwtch 10 is turned on. Accordingly, a control signal is outputted from a monostable multivibrator 11 in a control circuit 22 by a predetermined time, and a three-way selector valve 9 is switched from a first valve position to a second valve position where a vacuum induction passage 8 is closed. As a result, atmospheric air is introduced to the vacuum chamber 17 and the purge control valve 7 is closed, thereby stopping purging of vapor fuel as adsorbed to a canister 4. After a predetermined time is elapsed, the three-way selector valve 9 is returned to the first valve position, and the purge control valve 7 is opened to effect purging of the vapor fuel.
NAKAO SHINJI
OOIZUMI YUTAKA
