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Exhaust gas purification device for an internal combustion engine

  • US 6,138,453 A
  • Filed: 09/10/1998
  • Issued: 10/31/2000
  • Est. Priority Date: 09/19/1997
  • Status: Expired due to Term
First Claim
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1. An exhaust gas purification device for an internal combustion engine, comprising:

  • a NOX occluding and reducing catalyst disposed in an exhaust gas passage of an internal combustion engine, the catalyst absorbing NOX in exhaust gas when an inflowinq air-fuel ratio of exhaust gas flowing into the catalyst is lean and releasing and reducing previously absorbed NOX when the inflowinq air-fuel ratio is one of a stoichiometric air-fuel ratio and a rich air-fuel ratio;

    an air-fuel ratio sensor disposed in the exhaust gas passage downstream of the catalyst and detecting an outflowing air-fuel ratio of exhaust gas flowing out of the catalyst;

    air-fuel ratio control means for switching the inflowing air-fuel ratio from a rich air-fuel ratio to a lean air-fuel ratio; and

    evaluating means for evaluating an ability of the catalyst based on length of time during which the outflowing air-fuel ratio is maintained at a stoichiometric air-fuel ratio after the inflowing air fuel ratio is switched by the air-fuel ratio control means.

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