| 摘要 |
PROBLEM TO BE SOLVED: To expand a control region of an air fuel ratio of catalyst inflow gas while reducing a control amplitude of an air fuel ratio F/B (feedback) control on the basis of output from an upstream side oxygen sensor.SOLUTION: An air fuel ratio control device for an internal combustion engine includes a constant current circuit for changing output characteristics of an upstream side oxygen sensor 25 by making a constant current flow between sensor electrodes of the upstream side oxygen sensor 25. When output from a downstream side oxygen sensor 26 is on the rich side of target voltage, the output characteristics of the upstream side oxygen sensor 25 are switched to the lean direction. Thus, a control center of air fuel ratio F/B control on the basis of the output from the upstream side oxygen sensor 25 is changed to the lean direction and a control region of an air fuel ratio of catalyst inflow gas is expanded in the lean direction. In contrast, when the output from the downstream side oxygen sensor 26 is on the lean side of the target voltage, the output characteristics of the upstream side oxygen sensor 25 are switched to the rich direction. Thus, the control center of the air fuel ratio F/B control is changed to the rich direction and the control region of the air fuel ratio of the catalyst inflow gas is expanded in the rich direction. |
