An exhaust gas purifying device including a first O.sub.2 sensor, a first three-way catalyst, a secondary air feed port, a second O.sub.2 sensor, and a second three-way catalyst, which are arranged in the exhaust passage in that order. When not increasing the fuel supplied, the feeding of secondary air...http://www.google.fr/patents/US5271223?utm_source=gb-gplus-shareBrevet US5271223 - Exhaust gas purifying device of an engine
