Failure diagnosis device of fuel evaporation preventive apparatus

A failure diagnosis device of the fuel evaporation preventive apparatus, comprising:

• a fuel evaporation prevention apparatus having a canister having an atmospheric hole communicating with outside air and installed in a purge passage connecting a fuel tank with an intake pipe, for preventing evaporation of fuel by adsorbing fuel gas generated in the fuel tank by an adsorber incorporated in the canister and pertinently introducing the adsorbed fuel gas into the intake pipe by controlling a purge control valve in accordance with a running state of an internal combustion engine;
• initializing means for controlling an inner pressure of the fuel tank to a predetermined initial pressure;
• pressure controlling means for changing the initial pressure to a predetermined target pressure and controlling a purge amount at that time to a constant flow rate by closing the atmospheric hole and driving the purge control valve;
• hermetically enclosing means for forming a hermetically enclosed section in the fuel evaporation preventive apparatus by closing both the purge control valve and the atmospheric hole when the inner pressure of the fuel tank reaches the target pressure, wherein the constant flow rate is set such that the inner pressure in the hermetically enclosed section overshoots the target pressure during a period of pressure overshoot occurring after the purge control valve and atmospheric hole are closed;
• pressure detecting means installed in the hermetically enclosed section for detecting the inner pressure of the hermetically enclosed section;
• and
• failure diagnosing means for diagnosing failure of the fuel evaporation preventive apparatus, wherein the failure diagnosing means diagnoses failure by comparing the inner pressure of the hermetically enclosed section with a predetermined reference value at a point in time during the period of pressure overshoot.