PURPOSE: To make it possible to exercise feedback control over an air fuel ratio, by suppressing a relative drop of a sensor output due to a secular change by increasing its inflow current.
CONSTITUTION: A sensor output signal, after being amplified by amplifier 21, is passed through diode 22 and capacitor 23 to obtain the peak value of a signal that shows the magnitude of the sensor output signal. Next, this peak value is compared to prescribed reference level B by comparator 24 and on the basis of its comparison signal, the resistance value across resistance 17 is brought under control via transistor 25 to control electric current flowed into sensor element part 15 so that reference level B and peak value signal may become equal. Thus, the sensor output signal is maintained at fixed magnitude.
OKAMURA KENJI
NAKAGAWA TOYOAKI
