| 摘要 |
PROBLEM TO BE SOLVED: To estimate change with the lapse of time an air/fuel ratio sensor and correct its output. SOLUTION: When fuel is cut off and oxygen concentration in the exhaust gas is not lower than a prescribed value (S1-4), the output voltage Vr of an element part in an air/fuel ratio sensor is sampled for a prescribed time (S5-7). At the time of the initial use of the air/fuel ratio sensor, the peak value of the sampled output voltage is stored in the ring buffer of the first storage area, and an average value or a standard deviation of (n) numbers of peak values is calculated and stored (S10, 18, 19). At the time of estimating change with the lapse of time of the air/fuel ratio sensor, the peak value of the sampled output voltage is stored in the ring buffer of the second storage area and the average value or the standard deviation of (n) numbers of peak values is calculated and stored (S10-12). An air/fuel ratioλis corrected with a set correction factor Ks based on the deviation Dsigm of the average value or the standard deviation which are stored in the first storage area or the second storage area, and air/fuel ratio feedback control is conducted based on the corrected air/fuel ratioλ(S14-17) at the time of estimating the change with the lapse of time.
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