Patent ID: 8683852

Claim:
A leakage diagnosis device for diagnosing leakage from a fuel vapor processing apparatus having a fuel tank, a fuel pump, a canister adsorbing fuel vapor produced within the fuel tank, a fuel vapor desorbing device for desorbing fuel vapor from the canister by applying a negative pressure to the canister, the leakage diagnosis device comprising: a pressure applying device comprising the fuel vapor desorbing device and capable of applying a pressure to a process system of the fuel vapor processing apparatus; a pressure detecting device detecting an internal pressure of the process system when the pressure applying device applies a pressure to the process system; a fuel vapor pressure determining device for determining a fuel vapor pressure, and a leakage determining device determining leakage based on a result of detection of the internal pressure of the process system with reference to a diagnosis reference and capable of correcting the diagnosis reference according to the fuel vapor pressure determined by the fuel vapor pressure determining device, wherein the fuel vapor pressure determining device comprises: an aspirator having a decompression chamber in which a part of fuel discharged from the fuel pump is introduced for producing a negative pressure; a negative pressure detecting device for detecting the negative pressure produced by the aspirator, and a fuel vapor pressure calculating device calculating the fuel vapor pressure based on at least the negative pressure detected by the negative pressure detecting device; wherein the aspirator communicates with the fuel pump via a branch passage that is branched off from a fuel supply passage through which pressurized fuel is fed from the fuel pump to an engine, so that surplus fuel other than the fuel that is introduced into the aspirator via the fuel pump is released into the fuel tank; wherein a branch passage valve is provided in the branch passage and is configured to open and close the branch passage; wherein the decompression chamber of the aspirator communicates with the outside of the fuel tank; and wherein the aspirator also serves as the pressure applying device, so that the negative pressure produced by the aspirator is used for introducing an atmospheric air into the fuel tank in order to apply a positive pressure to inside of the fuel tank for diagnosing leakage.