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Diagnosis apparatus for fuel vapor purge system

  • US 6,523,398 B1
  • Filed: 11/30/1999
  • Issued: 02/25/2003
  • Est. Priority Date: 12/04/1998
  • Status: Expired due to Fees
First Claim
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1. A diagnosis apparatus for a fuel vapor purge system that includes a fuel tank for storing fuel and supplies fuel vapor from the rank to an air-intake passage of an engine, wherein the diagnosis apparatus determines whether the fuel vapor purge system has a malfunction, the apparatus comprising:

  • a pressure sensor for detecting purge system pressure in the fuel vapor purge system;

    a pressure changing means for changing the purge system pressure to a predetermined level; and

    a diagnosis means for diagnosing the fuel vapor purge system, wherein the diagnosis means closes the fuel vapor purge system after the purge system pressure has been changed by using the pressure changing means, measuring a first rate of pressure change when the purge system pressure approaches a predetermined first reference pressure, and for measuring a second rate of pressure change when the purge system pressure approaches a predetermined second reference pressure, wherein the second reference pressure differs from the first reference pressure, and the second reference pressure value is closer to the purge system pressure before the purge system pressure was changed by the pressure changing means than the first reference pressure, and wherein the diagnosis means judges whether the fuel vapor purge system has a malfunction based on the ratio of the first rate to the second rate.

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