Exhaust gas purifying apparatus for an internal-combustion engine

摘要

An exhaust gas purifying apparatus for an internal-combustion engine includes an exhaust gas purifier having a nitrogen oxide purifier for purifying nitrogen oxide contained in exhaust gases and an oxygen density sensor located downstream of the exhaust gas purifier. The apparatus further includes a sulfur oxide detector for detecting the density of sulfur oxide in the exhaust gas purifier, a sulfur-poisoning recovery apparatus for recovering the exhaust gas purifier from sulfur poisoning when the sulfur oxide detector determines the sulfur oxide density is high, a lean operation limiter for limiting the lean operation of the engine to such operation region that is not influenced so much by the sulfur poisoning after the exhaust gas purifier has been recovered from the sulfur poisoning, and a deterioration determiner for determining deterioration of the exhaust gas purifier based on the output of the oxygen density sensor during the lean operation of the engine.