Patent ID: 6167695
Filing Date: 2001-01-02
Classification: B01D,F01N,Y02A,Y02T

Abstract:
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.