Fuel supply control device of an engine

A fuel supply control device of an engine having an exhaust passage and an intake passage which has a throttle valve therein, said device comprising:

• a charcoal canister temporarily storing fuel vapor therein;
• a purge passage connecting said charcoal canister to the intake passage downstream of the throttle valve;
• a purge control valve arranged in said purge passage to control an amount of the fuel vapor purged into the intake passage;
• reference purge rate calculating means for calculating a reference purge rate which is a ratio of the amount of the fuel vapor purged into the intake passage to an amount of air fed into the engine and is determined by an engine operating state for the same degree of opening of said purge control valve;
• target purge rate setting means for determining a target purge rate;
• opening operation control means for controlling a rate of the opening operation of said purge control valve on the basis of a ratio of said target purge rate to said reference purge rate;
• fuel amount calculating means for calculating an amount of fuel fed into the engine;
• air-fuel ratio detecting means arranged in the exhaust passage to detect an air-fuel ratio;
• first fuel amount correcting means for correcting the amount of fuel by a feedback correction coefficient on the basis of an output signal of said air-fuel ratio detecting means to make an air-fuel ratio equal to a target air-fuel ratio;
• vapor concentration calculating means for calculating a concentration of the fuel vapor in an air fed into the engine on the basis of a deviation of said feedback correction coefficient from a reference value, which deviation is caused when the fuel vapor is purged into the intake passage;
• and
• second fuel amount correcting means for reducing the amount of fuel on the basis of said concentration of the fuel vapor when the fuel vapor is purged into the intake passage.