| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect element resistance by use of an element resistance detecting device detecting the element resistance from temporary changes in voltage and current. SOLUTION: An A/F(air/fuel ratio) sensor 10 has a sensor element part using a solid electrolyte and outputs a current signal (element current) matching the concentration of oxygen in exhaust gas with the application of a voltage. During the detection of element resistance, the voltage applied to the sensor element part in order to detect air/fuel ratio is temporarily changed to a voltage for detection of the element resistance at a frequency matching sensor characteristics, and the element resistance value is detected from the changes in voltage and current at that time. The detected value of the element current is inputted to an S/H(sample hold) circuit 30 and a P/H(peak hold) circuit 31. The S/H circuit 30 samples the element current and outputs it sequentially during the detection of the air/fuel ratio. The P/H circuit 31 holds the peak of the element current during the detection of the element resistance. An S/H circuit 32 samples the peak value held by the P/H circuit 31 and holds the value until the next detection of the element resistance. |
