| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control system capable of further improving emission, even when responsiveness of a downstream side air-fuel ratio sensor is not excellent. <P>SOLUTION: When an output value Voxs of the downstream side air-fuel ratio sensor arranged downstream of a catalyst reduces and the size ¾ΔVoxs¾ of a variation ΔVoxs per predetermined time of the output value Voxs becomes a lean determining threshold value ΔVLeanth or more, the target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich. When the output value Voxs increases and the size ¾ΔVoxs¾ of the variation ΔVoxs becomes a rich determining threshold value ΔVRichth or more, the target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean. As responsiveness of a change in the output value Voxs of the downstream side air-fuel ratio sensor 56 to a change in the air-fuel ratio of catalyst outflow gas becomes not excellent, the lean determining threshold value is changed so that the size of the lean determining threshold value becomes small, and the rich determining threshold value is changed so that the size of the rich determining threshold value becomes small. <P>COPYRIGHT: (C)2013,JPO&INPIT |
