Patent ID: 6467463
Filing Date: 2002-10-22
Classification: F02M

Abstract:
An abnormality diagnosis apparatus for an evaporative emission control system which includes a fuel tank, a canister for adsorbing evaporative fuel generated in said fuel tank, a charging passage for connecting said canister and said fuel tank, a purge passage for connecting said canister and an intake system of an internal combustion engine, a vent passage for opening said canister to atmospheric air, an evaporative fuel passage for connecting said fuel tank and said intake system, a first control valve interposed in said charging passage for opening and closing said charging passage, a second control valve interposed in said purge passage for opening and closing said purge passage, a third control valve interposed in said vent passage for opening and closing said vent passage, a fourth control valve interposed in said evaporative fuel passage for opening and closing said evaporative fuel passage, and control means for controlling an opening of said fourth control valve so that a pressure in said fuel tank may be maintained at a predetermined pressure lower than atmospheric pressure at least during operation of said internal combustion engine, said abnormality diagnosis apparatus comprising:tank pressure detecting means for detecting the pressure in said fuel tank; and abnormality diagnosis means for diagnosing abnormality of said evaporative emission control system based on an output of said tank pressure detecting means; wherein said controlling means outputs a control signal for maintaining said fourth control valve in a closed state while an abnormality diagnosis is performed by said abnormality diagnosis means, and said abnormality diagnosis means performs an abnormality diagnosis by outputting a control signal for changing an open or closed state of at least one of said first, second and third control valves without opening said first and third control valves simultaneously.