Exhaust emission control system for internal combustion engine

摘要

An exhaust emission control system for an internal combustion engine having an exhaust system is disclosed. The control system may include an exhaust gas purifying device provided in the exhaust system and an oxygen concentration sensor provided downstream of the exhaust gas purifying device. The exhaust gas purifying device may include at least an oxygen storing ability or a nitrogen oxide storing ability. An air-fuel ratio of an air-fuel mixture supplied to the engine may be enriched with respect to the stoichiometric air-fuel ratio, so as to reduce the oxygen or nitrogen oxides stored in the exhaust gas purifying device. A predicted value of the output from the oxygen concentration sensor may be calculated using a predictor based on the fuzzy logic reasoning. The completion of the reduction of the oxygen or nitrogen oxides stored in said exhaust gas purifying device may be determined according to the predicted value.