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Exhaust gas purification device for an internal combustion engine

  • US 5,970,707 A
  • Filed: 09/09/1998
  • Issued: 10/26/1999
  • 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 three-way catalyst disposed in the exhaust gas passage of an internal combustion engine;

    a NOX occluding and reducing catalyst disposed in the exhaust gas passage downstream of the three-way catalyst and absorbing NOX in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the NOX occluding and reducing catalyst is at a lean air-fuel ratio and releasing and reducing the absorbed NOX when the air-fuel ratio of the exhaust gas flowing into the NOX occluding and reducing catalyst is at a stoichiometric or a rich air-fuel ratio;

    a first air-fuel ratio sensor disposed in the exhaust gas passage at the position between the three-way catalyst and the NOX occluding and reducing catalyst;

    a second air-fuel ratio sensor disposed in the exhaust gas passage downstream of the NOX occluding and reducing catalyst;

    air-fuel ratio control means for switching the air-fuel ratio of the exhaust gas flowing into the three-way catalyst either from a rich air-fuel ratio to a lean air-fuel ratio or from a lean air-fuel ratio to a rich air-fuel ratio; and

    evaluating means for evaluating the abilities of both of the three-way catalyst and the NOX occluding and reducing catalyst when the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas either from a rich air-fuel ratio to a lean air-fuel ratio or from a lean air-fuel ratio to a rich air-fuel ratio, wherein the evaluating means evaluates the ability of the three-way catalyst based on the output signal of the first air-fuel ratio sensor and evaluates the ability of the NOX occluding and reducing catalyst based on the output signals of both the first and the second air-fuel ratio sensors.

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