Air-fuel ratio control system for internal combustion engines

摘要

An air-fuel ratio control system for an internal combustion engine having first and second catalytic converters arranged in the exhaust passage comprises first to third exhaust gas component concentration sensors arranged in the exhaust passage, the first one being arranged upstream of the first catalytic converter, the second one at a location intermediate between the first and second catalytic converters, and the third one downstream of the second catalytic converter. An ECU carries out feedback control of the air-fuel ratio of a mixture supplied to the engine to a desired air-fuel ratio in response to an output from the first exhaust gas component concentration sensor. A first feedback control parameter for use in the feedback control is calculated, based on an output from the second exhaust gas component concentration sensor. A second feedback control parameter for use in the calculation of the first feedback control parameter is calculated, based on an output from the third exhaust gas component concentration sensor.