Importance

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Abstract

A device for detecting the air-fuel ratio in an engine comprises a limiting current type air-fuel ratio sensor 20, an air-fuel ratio sensor circuit 30, a detecting means 40, a determining means 50 and a correcting means 60. The air-fuel ratio sensor 20, which is arranged in an exhaust system of the engine 10, generates an electric current when a voltage is applied thereto and is made from solid electrolyte. The sensor circuit 30 applies a voltage to the sensor 20 within a range of the limiting current, detects a concurrent limiting current and outputs a signal proportional to the magnitude of the detected current. The detecting means 40 detects a change in the voltage output from the sensor circuit 30 when the voltage applied to the sensor 20 is changed from a voltage within the range of the limiting current to a voltage outside the range of the limiting current a predetermined time after the engine 10 is started. The determining means 50 determines whether the change in output voltage of the sensor circuit 30 is less than a predetermined and correcting means 60 corrects an output error of the sensor circuit 30 based on the voltage output from the sensor circuit 30 when it is determined that the output voltage change is less than the predetermined value.

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