| 摘要 |
PROBLEM TO BE SOLVED: To provide an evaporating fuel discharge preventing device for an internal combustion engine to prevent worsening of operability and exhaust gas emission characteristics due to the rapid change of an air-fuel ratio of air-fuel mixture in an intake pipe when a pressure in a fuel tank is brought into a negative pressure state due to a negative pressure in an intake pipe. SOLUTION: During operation of an engine, the target duty ratio DRO of a control valve set according to the number NE of revolutions of engine and an absolute pressure PBA of an intake pipe is researched at a step S12. The duty ratio DR of the control valve is controlled to the researched target duty ratio DRO at a step S16. In this case, the duty ratio DR of the control valve is gradually increased by a given valueΔd at a time at intervals of a given time until the duty ratio reaches the target duty ratio DRO at steps S13-S17. This constitution prevents worsening of operability due to the occurrence of a shock as a result of evaporating fuel in a fuel tank being rapidly sucked in an intake pipe, and prevents worsening of exhaust emission characteristics due to a rapid change of an air-fuel ratio of air-fuel mixture in the intake pipe.
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