Patent ID: 7219535

Claim:
A leakage diagnosis apparatus for a fuel vapor purge system, in which fuel vapor generated in a fuel tank is trapped in a canister via an evaporation passage, and the fuel vapor trapped in said canister is purged, via a purge passage, into an intake passage of an internal combustion engine, comprising: a blocking device arranged for blocking a diagnosis zone containing at least one of said fuel tank, said evaporation passage, said canister and said purge passage; a pressure generator arranged for changing a pressure in said diagnosis zone; a pressure detector arranged for detecting the pressure in said diagnosis zone; a remaining quantity detector detecting a remaining fuel quantity in said fuel tank; and a diagnosis unit that blocks said diagnosis zone by said blocking device to change the pressure in said blocked diagnosis zone by said pressure generator, and diagnoses an occurrence of leakage in said diagnosis zone based on the pressure detected by said pressure detector, wherein said diagnosis unit calculates a pressure change acceleration based on the pressure detected by said pressure detector, and diagnoses, when said pressure change acceleration is greater than a threshold, an occurrence of leakage, and wherein said diagnosis unit sets said threshold according to the remaining fuel quantity in said fuel tank when the fuel tank is contained in said diagnosis zone.