Patent ID: 6698187
Filing Date: 2004-03-02
Classification: F01N,Y02A,Y02T

Abstract:
An exhaust gas purifying apparatus for an internal-combustion engine, comprising:a three-way catalyst disposed in an exhaust system of the engine; a nitrogen oxide purifier disposed downstream of the three-way catalyst to clean nitrogen oxide contained in the exhaust gas when air fuel ratio of the exhaust gas is lean; an upstream oxygen sensor disposed between the three-way catalyst and the nitrogen oxide purifier; a downstream oxygen sensor disposed downstream of the nitrogen oxide purifier; determining means for determining abnormality of the nitrogen oxide purifier based on change in the output of the downstream oxygen sensor when air-fuel ratio is altered from lean to rich; and correcting means for correcting criterion for determining abnormality of the nitrogen oxide purifier by said determining means in relation to a manner the output of the upstream oxygen sensor changes, wherein said criterion is defined in terms of the delay time from reversal of the output of the upstream oxygen sensor to reversal of the output of the downstream oxygen sensor when air-fuel ratio is turned from lean to rich, the determining means determining abnormality of the nitrogen oxide purifier when the output of the downstream oxygen sensor reverses before the delay time as defined by the criterion elapses, and wherein the correcting means correct the criterion based on the speed that the output of the upstream oxygen sensor changes when air-fuel ratio is turned from lean to rich.