US Patent 7610906 Fuel vapor treatment system

A fuel vapor treatment system which has adsorbent, a purge passage for introducing a mixture gas of air and the fuel vapor desorbed from the adsorbent into the internal combustion engine, a detection passage which communicates to the purge passage, and a pump which generates gas flow so that the mixture gas flows into the detection passage from the purge passage. A pressure sensor detects fuel vapor concentration. An ECU and a purge control valve controls a purge of the mixture gas from the purge passage to the internal combustion engine based on a reference concentration of the fuel vapor. The ECU establishes the detection interval of the fuel vapor concentration in consideration of change in reference concentration.