| 摘要 |
PROBLEM TO BE SOLVED: To provide an air-fuel ratio sensor by which air-fuel ratio can be detected with good accuracy irrespective of the change in power-supply voltage or in the ambient temperature. SOLUTION: The air-fuel ratio sensor is provided with a current control circuit 20, by which a pumping current Ip flowing to a pumping element 7 is controlled bidirectionally in such a way that the output voltage Vs of a battery element 11 becomes a prescribed value corresponding to a theoretical air-fuel ratio, a first output circuit 22 which is constituted as a well-known differential amplifier circuit by making use of an operational amplifier OP3 as the center and which corresponds to a voltage across both ends of a detecting resistance Rd installed in the route of the pumping current Ip , and a second output circuit 24 which outputs a second air-fuel ratio signal Do , whose signal level is changed according to the magnitude relationship of the voltage across both ends of the detecting resistance Rd . The signal level of a first air-fuel ratio signal Vo corresponding to the theoretical air-fuel ratio can be measured on the basis of a timing at which the second air-fuel ratio signal Do is inverted. As a result, an air-fuel ratio can be reset correctly even when the relationship is changed due to the influence of a power-supply voltage and an ambient temperature. |
