| 摘要 |
PROBLEM TO BE SOLVED: To provide an air/fuel ratio-detecting device for avoiding the decrease in detection accuracy by temperature change. SOLUTION: A detection part 101 of the air/fuel ratio-detecting device is provided with a zirconia solid electrolyte 102, an atmosphere-side electrode 104, an exhaust-side electrode 105, and a diffusion resistor 106. An inversion amplifier 17 consisting of an operational amplifier 16 and resistors R21 and R22 amplifies voltages V1 and V2 across a resistor R1 and generates a voltage V3. An A/D converter 84 converts the voltages V1-V3 from analog to digital before outputting to a microcomputer 85. The computer 85 calculates a sensor current Ip between the electrodes 104 and 105 based on the voltages V2 and V3 and the resistors R1, R21, and R22 when detecting an air/fuel ratio and calculates a sensor current Ip based on the values of the voltages V1 and V2 and the resistor R1 when detecting the internal impedance of the detection part 101. Then, a heater 103 is turned on or off so that internal impedance becomes constant, and the temperature of the zirconia solid electrolyte 102 is maintained constantly. |
