Fuel vapor treatment system for internal combustion engine

摘要

A butterfly valve restricts flow passage areas of a purge passage and a blow-by gas passage by the same degree. A first pressure sensor detects variation in pressure of the purge gas, which is generated by the butterfly valve. A second pressure sensor detects variation in pressure of the blow-by gas, which is generated by the butterfly valve. Since a fuel vapor concentration of the blow-by gas is lower than that of the purge gas, the blow-by gas can be treated as air of 100%. Hence, the fuel vapor concentration is calculated based on the variations in pressure detected by the first pressure sensor and the second pressure sensor.