AIR-FUEL RATIO CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

An air-fuel ratio control device is provided with a constant current circuit that changes the output characteristics of an upstream oxygen sensor (25) by supplying a constant current between sensor electrodes of the upstream oxygen sensor (25). When the output of a downstream oxygen sensor (26) is more on the rich side than a target voltage, the output characteristics of the upstream oxygen sensor (25) are shifted to the lean direction. Thus, the control center for the air-fuel ratio feedback control based on the output of the upstream oxygen sensor (25) is changed in the lean direction and the control region for the air-fuel ratio of the catalyst inlet gas is expanded in the lean direction. When the output of a downstream oxygen sensor (26) is more on the lean side than a target voltage, the output characteristics of the upstream oxygen sensor (25) are shifted to the rich direction. Thus, the control center for the air-fuel ratio feedback control is changed in the rich direction and the control region for the air-fuel ratio of the catalyst inlet gas is expanded in the rich direction.