Patent ID: 6823658
Filing Date: 2004-11-30
Classification: F01N,F02D,Y02T

Abstract:
An exhaust gas purifying apparatus for an internal-combustion engine having an exhaust gas purifier provided in an exhaust system of the engine and an oxygen density sensor disposed downstream of the purifier, the purifier including a nitrogen oxide purifier for purifying nitrogen oxide contained in the exhaust gas during a lean operation in which air-fuel ratio of air-fuel mixture to be supplied to the engine is lean, the exhaust gas purifying apparatus comprising:a sulfur oxide detector for detecting density of sulfur oxide in the exhaust gas purifier; sulfur-poisoning recovery means for recovering the exhaust gas purifier from sulfur poisoning when it is determined by the sulfur oxide detector that the sulfur oxide density is high; a lean operation limiter for limiting lean operation of the engine to such operation region that is not influenced significantly by sulfur poisoning after the exhaust gas purifier recovery is done by the sulfur-poisoning recovery means; and means for determining deterioration of the exhaust gas purifier based on output of the oxygen density sensor only after the exhaust gas purifier has recovered from sulfur poisoning and during the lean operation of the engine.