Patent ID: 6474147
Filing Date: 2002-11-05
Classification: F01N,F02D,Y02T

Abstract:
An exhaust-gas purification device for an exhaust system of an internal combustion engine, comprising:nitrogen oxide purifying means for absorbing nitrogen oxide in exhaust gases during a lean exhaust-gas condition; a three-way catalyst disposed upstream of said nitrogen oxide purifying means; a first oxygen sensor, disposed between said nitrogen oxide purifying means and said three-way catalyst, for detecting a first oxygen density in said exhaust gases; a second oxygen sensor, disposed downstream of said nitrogen oxygen purifying means, for detecting a second oxygen density in said exhaust gas; first deterioration determination means, for determining a degree of deterioration of said three-way catalyst; and second deterioration determination means, for evaluating deterioration of said nitrogen oxide purifying means, from the degree of deterioration of said three-way catalyst determined by said first deterioration determination means and a first determination time period, said first determination time period being after a lean air-fuel ratio of the exhaust gases has been shifted to a rich air-fuel ratio by an decrease in the air-fuel ratio of a mixture to be supplied to the internal combustion engine, said first determination time period being from a time when a value output by first oxygen sensor changes to a value indicating a rich air-fuel ratio until a time when a value output by said second oxygen sensor changes to a value indicating a rich air-fuel ratio.