Patent ID: 7159580
Filing Date: 2007-01-09
Classification: F02M

Abstract:
1. A failure diagnosis apparatus for diagnosing a failure of an evaporative fuel processing system that includes a fuel tank, a canister having adsorbent for adsorbing evaporative fuel generated in said fuel tank, an air passage connected to said canister for communicating said canister communicates with the atmosphere, a first passage for connecting said canister and said fuel tank, a second passage for connecting said canister and an intake system of an internal combustion engine, a vent shut valve for opening and closing said air passage, and a purge control valve provided in said second passage, said failure diagnosis apparatus comprising: pressure detecting means for detecting a pressure in said evaporative fuel processing system; engine stoppage detecting means for detecting stoppage of said engine; first determining means for closing said purge control valve and said vent shut valve when stoppage of said engine is detected by said engine stoppage detecting means, and for determining whether there is a leak in said evaporative fuel processing system based on a determination parameter corresponding to a second-order derivative value of the pressure detected by said pressure detecting means during a first predetermined determination period after closing of said purge control valve and said vent shut valve; second determining means for determining whether the leak is present in said evaporative fuel processing system based on a relationship between the pressure detected by said pressure detecting means and a staying time period in which the detected pressure stays at a substantially constant value, during a second predetermined determination period which is longer than the first predetermined determination period after closing of said purge control valve and said vent shut valve; evaporative fuel parameter calculating means for calculating an evaporative fuel parameter indicative of an amount of evaporative fuel generated in said fuel tank after stoppage of said engine; and final determining means for selecting one of the determination results of said first determining means and said second determining means, according to the evaporative fuel parameter calculated by said evaporative fuel parameter calculating means.