| 摘要 |
PROBLEM TO BE SOLVED: To provide an air-fuel ratio control system for an internal combustion engine in which an appropriate perturbation control is executed, when an abnormal output is produced at "A/F shift" or O2 sensor, so as to improve exhaust emission purification performance of a three-way catalyst.SOLUTION: An "A/F shift" or abnormal output of O2 sensor is detected in reference to an output of the O2 sensor installed at a downstream side of a three-way catalyst, and on the basis of this detected state, an amplitude or period, or period and amplitude of air-fuel ratio under a control of perturbation are changed in such a direction as one in which exhaust emission purification performance of three-way catalyst is not deteriorated. With the foregoing arrangement, when the air-fuel ratio shift or O2 sensor abnormal output occurs, it is possible to execute an appropriate perturbation control and improve exhaust emission purification performance of the three-way catalyst.SELECTED DRAWING: Figure 8A |
