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Method and system for diagnosing deterioration of NOx catalyst

  • US 6,167,695 B1
  • Filed: 02/12/1999
  • Issued: 01/02/2001
  • Est. Priority Date: 02/12/1998
  • Status: Expired due to Term
First Claim
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1. A system for diagnosing deterioration of a nitrogen oxide catalyst coupled to an internal combustion engine, said catalyst being capable of absorbing nitrogen oxides present in exhaust gas emitted from the engine during lean-burn operation and releasing the nitrogen oxides absorbed when an air/fuel ratio is less than a stoichiometric air/fuel ratio, comprising:

  • a nitrogen oxide sensor arranged downstream of the nitrogen oxide catalyst to detect concentration of the nitrogen oxides in the exhaust gas passing through the nitrogen oxide catalyst and generate a signal indicative of the detected concentration of the nitrogen oxides; and

    a controller operative, in response to said signal generated from said nitrogen oxide sensor, to calculate a rate of change in the detected concentration of the nitrogen oxides at any point in time during a predetermined period after the air/fuel ratio becomes less than the stoichiometric air/fuel ratio, compare said rate of change in the detected concentration of the nitrogen oxides with a predetermined reference value and determine, in response to the comparison result, that the nitrogen oxide catalyst is deteriorated.

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