| 摘要 |
PURPOSE:To always control an air-fuel ratio to a prescribed said ratio by varying a reference voltage for judging whether the air-fuel ratio is higher or lower than the prescribed air fuel ratio basing on an inner resistance of an oxygen sensor. CONSTITUTION:The oxygen sensor 11 has the inner resistance RS varying with a temp. under a fixed correlation, and outputs a voltage signal VS determined by the resistance RS and an electromotive force E. A bias voltage VB changed over to voltages VB(H) and VB(L) at a prescribed period (frequency, several HZ- several hundreds HZ) is impressed to the output terminal from a bias voltage generator 12 through a resistance RB. A voltage signal VO after this impression is inputted to a circuit 14 for detecting oxygen concn. signal and a circuit 15 for determining reference voltage through a buffer amplifier 13. The circuit 14 takes out the output signal (signal corresponding to oxygen concn.) VS of the sensor 11 from the input signal VO, and outputs the signal VS to a plus terminal of a comparator 16. Consequently, even at low temp., the actual variation of the air- fuel ratio is judged exactly, and the judgement shifted to diluted or condensed side is prevented. |
