Gas containing fuel vapor is purged as purge gas from a canister to an intake passage of an engine through a purge line. An ECU renews a vapor concentration value representing the concentration of fuel vapor contained in the purge gas by a predetermined renew amount at a time in response to a deviation...http://www.google.com/patents/US6779512?utm_source=gb-gplus-sharePatent US6779512 - Apparatus and method for controlling internal combustion engine
