Patent ID: 7418952

Claim:
A evaporative fuel treatment system, comprising: a canister into which an evaporative fuel is adsorbed and from which the evaporative fuel is purged into an intake air passage of an internal combustion engine; a detection passage having a reduced area portion; a switching device that switches among communication of the reduced area portion and an atmosphere, communication of the reduced area portion and the canister, and shutoff of communication between the reduced area portion, the atmosphere, and the canister; a depressurizing device coupled to the detection passage on a side of the reduced area portion opposite to the switching device, the depressurizing device operable for depressurizing the detection passage; a pressure detecting device for detecting a pressure in the detection passage; and an evaporative fuel state calculating device for calculating an evaporative fuel state in the mixture based on a cutoff pressure detected by the pressure detecting device when the depressurizing device is in operation and when the switching device shuts off communication between the atmosphere and the canister, an air pressure detected by the pressure detecting device when the reduced area portion and the atmosphere are in communication and when the switching device shuts off communication between the reduced area portion and the canister, and a mixture pressure of a mixture of air and the evaporative fuel detected by the pressure detecting device when the switching device shuts off communication between the reduced area portion and the atmosphere and the reduced area portion and the canister are in communication during purge stop of the evaporative fuel from the canister to the intake air passage, wherein the cutoff pressure, the air pressure, and the mixture pressure are detected independently and discontinuously.