Patent ID: 6971375
Filing Date: 2005-12-06
Classification: F02M

Abstract:
1. A fuel vapor treatment system for an internal combustion engine comprising: a canister containing an adsorbing material for temporarily adsorbing fuel vapor conducted thereto from the interior of a fuel tank through an inlet passage; a purging passage for conducting an air-fuel mixture containing fuel vapor desorbed from the adsorbing material into an intake pipe of the internal combustion engine and purging the fuel vapor; a purge control valve disposed in the purging passage to adjust the purge flow rate based on the result of measurement of a fuel vapor concentration in the air-fuel mixture; a measurement passage having an orifice; gas flow producing means for producing a gas flow within and along a measurement passage; measurement passage switching means for switching the measurement passage between a first concentration measurement state in which the measurement passage is open to the atmosphere at both ends thereof, allowing an air to flow through the measurement passage, and a second concentration measurement state in which the measurement passage is put in communication at both ends thereof with the canister, allowing the air-fuel mixture fed from the canister to flow through the measurement passage; differential pressure detecting means for detecting a pressure at both ends of the orifice; and fuel vapor concentration calculating means for calculating a fuel vapor concentration based on a pressure difference detected in the first concentration measurement state and a pressure difference detected in the second concentration measurement state.