| 摘要 |
PURPOSE: To monitor the aged state of an oxygen sensor disposed forward of a catalyst without using the signal of the sensor disposed rear of the catalyst. CONSTITUTION: The aged state of an oxygen sensor 11 for supplying an actual voltage U-IST to the lambda controller 12 of an internal combustion engine disposed forward of a catalyst 10 is monitored. The time average value (|U- IST-U-SOLL|)' of the absolute vale of the deviation U-IST-U-SOLL from the target voltage U-SOLL of the actual voltage is calculated, and when the value becomes a threshold value or less, it is decided that the sensor is remarkably aged. To enhance the S/N ratio, the quotient of the average value (|FR-IST-FR- SOLL|)' of the absolute value of the deviation from the target value of the output signal of the controller by the mean value is formed.
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