Control device for an air-fuel ratio sensor

摘要

A control device detects a characteristic change of an air-fuel ratio sensor indicative of deterioration of the air-fuel ratio sensor. The control device determines deterioration due to aging of the air-fuel ratio sensor accurately and calculates an air-fuel ratio from the air-fuel ratio sensor highly accurately. Then, the control device detects a current proportional to the concentration of oxygen in the detected gas from a sensor element by applying a voltage to the sensor element of the air-fuel ratio sensor. By applying AC voltages at high and low frequencies to the element, an AC impedance is detected. The temperature of the element is controlled to a target temperature according to the high frequency impedance and a characteristic change of the element is detected in accordance with the low frequency impedance. <IMAGE>