Air-fuel ratio control device of an internal combustion engine

Claim 1

An internal combustion engine having at least one cylinder, an intake passage and an exhaust passage, said engine comprising: a carburetor arranged in the intake passage and having a fuel passage which is open to the intake passage; an electric air-fuel ratio control valve controlling an air-fuel ratio of an air-fuel mixture fed into the cylinder in response to an electric control signal, said air-fuel ratio of the air-fuel mixture increasing as a level of said electric control signal rises; an oxygen concentration detector arranged in the exhaust passage to produce a lean signal when said air-fuel ratio of air-fuel mixture fed into the cylinder is larger than a predetermined air-fuel ratio and to produce a rich signal when said air-fuel ratio of air-fuel mixture is smaller than the predetermined air-fuel ratio; first control means controlling the level of said electric control signal in response to said lean signal and said rich signal to raise the level of said electric control signal when said rich signal is produced and lower the level of said electric control signal when said lean signal is produced; a charcoal canister containing activated carbon therein; a purge control valve arranged between said charcoal canister and the intake passage to control the supply of purge gas fed into the intake passage from said charcoal canister; and second control means controlling the level of said electric control signal in response to both a rate of rising of the level of said electric control signal and an opening operation of said purge control valve to instantaneously raise the level of said electric control signal by a predetermined level when said rate of rising exceeds a predetermined rate and when said purge control valve is open.