US Patent 7290535 Leak diagnostic device for fuel vapor treatment device

A lag time is set in a period from the time when a leak down is finished to the time when measurement of the amount of fuel vapor is started for the purpose of returning a deformed fuel tank to its original shape. A fuel vapor amount estimating means is provided that estimates the amount of fuel vapor produced in the fuel tank during the time of the leak down. This means is so set as to make the lag time shorter as the amount of fuel vapor increases. With this, undesired precision in measuring the amount of fuel vapor produced under a condition wherein the amount of fuel vapor is large can be avoided.