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Diagnostic apparatus and method for fuel vapor purge system

  • US 6,564,780 B2
  • Filed: 05/18/2001
  • Issued: 05/20/2003
  • Est. Priority Date: 06/23/2000
  • Status: Expired due to Fees
First Claim
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1. A diagnostic apparatus for a fuel vapor purge system in which fuel vapor generated in a fuel tank is trapped in a chamber, and the fuel vapor trapped in the chamber is purged into an intake passage of an internal combustion engine through a purge path that includes the fuel tank, the apparatus comprising:

  • a controller that;

    measures a first change in an internal pressure of the purge path after creating a pressure difference between an inside and an outside of the purge path and sealing the purge path;

    measures a second change in the internal pressure that varies with an amount of fuel vapor generated in the fuel tank, which second change is measured while the purge path is sealed for a first predetermined period of time after an atmospheric pressure is introduced into the purge path in which the pressure difference was created;

    performs leakage diagnosis to determine whether leakage is present in the purge path, based on the first change and the second change in the internal pressure of the purge path;

    measures a third change in the internal pressure that varies with an amount of fuel vapor generated in the fuel tank, prior to measurement of the first change and measurement of the second change, the third change in the internal pressure being measured while the purge path is sealed for a second predetermined period of time after an atmospheric pressure is introduced into the purge path before the pressure difference is created; and

    inhibits the leakage diagnosis when a result of measurement of the third change in the internal pressure is greater than a predetermined value, and permits the leakage diagnosis when the result of measurement of the third change is equal to or less than the predetermined value.

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