| 摘要 |
PURPOSE:To prevent destruction of sensor element certainly by using an air-fuel ratio sensor of linear output type and Z-characteristic output type, stopping the air-fuel ratio feedback control when the voltage impressed on the sensor increases, and by putting off the impression voltage. CONSTITUTION:According to the engine operating condition, the reference value corresponding to the target air-fuel ratio is calculated A, and the voltage impressed on an air-fuel ratio sensor 13 is selected B in accordance with the engine operating condition. The selected impression voltage is impressed on the air-fuel ratio sensor 13 of linear output type with Z-characteristic. The output from the air-fuel ratio sensor 13 as the one of linear output type is compared C with the reference value, and the air-fuel ratio according to the comparative result is feedback controlled D. When increase in the impression voltage is judged E, a voltage impressing means F and feedback controlling means D are stopped, and the output of air-fuel sensor 13 as the one of Z- characteristic type is compared G with specific value. When output of the air- fuel ratio sensor lines on the leaner side than the specific value, the means F, D are resumed.
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