US Patent 7392800 Fuel vapor treatment

A fuel vapor treatment system includes a canister containing an adsorbent, a detector detecting a concentration of a fuel vapor, a purge passage for introducing the mixture gas into an engine, and an ECU which controls a purge based on a detected fuel vapor condition quantity and learns a fuel vapor concentration. If a difference between a learned concentration and a detection concentration is not less than a specified value, the ECU performs a purge control based on the learned concentration prior to a purge control based on the detection concentration.