Patent ID: 7316228

Claim:
An evaporated fuel treatment system for an internal combustion engine that introduces evaporated fuel in a fuel tank into a canister via an evaporated fuel passage to make an adsorbing material in the canister adsorb the evaporated fuel temporarily and purges the evaporated fuel adsorbed by the adsorbing material into an intake pipe of the combustion engine when the internal combustion engine is operated, the system comprising: a first pressure detection means for detecting an amount of change in pressure of an air-fuel mixture caused by a restriction in a first measurement state in which the fuel tank, the canister, and the restriction communicates with each other and in which the air-fuel mixture flows through the restriction, the air-fuel mixture containing evaporated fuel purged from the canister; a flow rate control means for controlling a flow rate of the air-fuel mixture introduced into the intake pipe from the canister on a basis of an amount of change in pressure detected by the first pressure detection means and an amount of change in pressure of an air flowing through the restriction; and a fuel swing determination means for determining whether a fuel in the fuel tank swings, wherein when the fuel swing determination means determines that the fuel swings, the flow rate control means stops the control of a flow rate of the air-fuel mixture based on an amount of change in pressure of the air-fuel mixture.