| 摘要 |
PURPOSE:To obtain a detection output free from voltage drop of an internal resistance in an oxygen sensor varying with the temperature of exhaust gas by selectively connecting a capacitor to an oxygen sensor and an amplifier with a given repetition cycle. CONSTITUTION:Synchronizing a specified frequency output of an oscillator 8, a changeover switch 7 alternately connects a capacitor 6 to input terminals of an oxygen sensor 1 and an amplifier 2. When the capacitor 6 is connected to the oxygen sensor 1, it is charged to attain the electromotive foce of the oxygen sensor 1 itself eliminating voltage drop due to an internal resistance r of 1. When the capacitor 6 thus charged is connected to the input terminal of the amplifier 2, the minimum value of the output voltage V01 from the amplifier 2 is stable free from the internal resistance r of the oxygen sensor 1 both at the high temperature and the low temperature of the exhaust gas. Setting the reference voltage Vref slightly higher than this constant minimum value enables a comparator 5 to generate an output corresponding to the theoretical air/fuel ratio. |
