Air-fuel ratio control system for internal combustion engines

摘要

An air-fuel ratio control system for an internal combustion engine having a catalytic converter arranged in the exhaust system, has an upstream oxygen sensor and a downstream oxygen sensor arranged in the exhaust system at locations upstream and downstream of the catalytic converter, respectively. An ECU determines a feedback control constant, based on an output from the downstream oxygen sensor, and determines an air-fuel ratio control amount, based on the determined feedback control constant and an output from the upstream oxygen sensor. The ECU carries out feedback-control of the air-fuel ratio of a mixture supplied to the engine by means of the determined air-fuel ratio control amount. The updating rate of the feedback control constant is set based on the temperature of the catalyst of the catalytic converter.