Patent ID: 7418953

Claim:
A fuel vapor treatment apparatus for an internal combustion engine, comprising: a canister that temporarily adsorbs fuel vapor developed in a fuel tank; a purge pipe that introduces the fuel vapor purged from the canister into an intake pipe of the internal combustion engine; a purge control valve that is arranged in the purge pipe and controls a purge flow rate from the purge pipe to the intake pipe; an air-fuel ratio sensor that is provided in an exhaust pipe of the internal combustion engine and measures an air-fuel ratio; a first fuel state determination means that determines a state of fuel of an air-fuel mixture containing the fuel vapor purged from the canister on the basis of an amount of deviation from a target air-fuel ratio of an air-fuel ratio detected by the air-fuel ratio sensor when the purge control valve is opened; and an air-fuel ratio control means that controls a fuel injection quantity to the internal combustion engine so as to bring an air-fuel ratio to the target air-fuel ratio on the basis of the state of fuel of the air-fuel mixture purged from the canister; and a second fuel state determination means that determines the state of fuel of the air-fuel mixture purged from the canister when the purge control valve is closed, wherein the air-fuel ratio control means switches a state of fuel for controlling the fuel injection quantity between the state of fuel determined by the first fuel state determination means and the state of fuel determined by the second fuel state determination means on the basis of an operating state of a vehicle.