| 摘要 |
PURPOSE:To detect an air/fuel ratio from a lean range to a rich range by forming a constant voltage circuit for holding the potential difference between a pair of electrodes of an oxygen concentration sensor at a prescribed voltage and setting up the prescribed voltage lower than a voltage to be generated in the oxygen sensor at the time of a rich air/furl ratio. CONSTITUTION:The oxygen concentration sensor 10 is fitted to an exhaust pipe 14 of an internal combustion engine 12. The sensor 10 is provided with the constant voltage circuit for holding the voltage between the electrodes of the sensor 10 at the prescribed voltage and a limited current detecting circuit for detecting current flowing into the sensor 10. The current is detected by an electronic circuit 16 and the detected signal is sent to an air/fuel ratio control circuit 18 to control the air/fuel ratio. In case of a rich air/fuel ratio, electromotive voltage is generated in the oxygen sensor 10 and the prescribed voltage of the constant voltage circuit is held lower than the generated voltage. Consequently, the rich air/fuel ratio and the limited current at the time of rich air/fuel ratio can be detected. Since the holding voltage of the constant voltage circuit is held lower than the generated voltage at the time of a rich air/fuel ratio, the air/fuel ratio can be detected with a simple constitution over a wide range from a lean ratio to a rich ratio. |
