Method and apparatus for regulating the fuel-air ratio in internal

Abstract

A method and an apparatus for regulating the fuel-air ratio of the operational mixture of an internal combustion engine and for monitoring the operational readiness of a .lambda. sensor controlling the regulating apparatus and functioning according to the principle of ionic conduction in fixed electrolytes. A constant reference voltage which approximately corresponds to the average sensor output voltage is connected opposite to the .lambda. sensor. The level of the resultant voltage thus established, the values of which are disposed symmetrically relative to the reference voltage, is utilized, along with the cooperation of a resultant electric current which causes a voltage drop across the temperature-dependent internal resistance of the .lambda. sensor as a gauge for the operational readiness of the .lambda. sensor. The pickup of the resultant voltage is accomplished by two comparison devices, whose logically evaluatable output signals are transformed via a logical linkage circuit into an operational readiness or unreadiness signal. A third comparison device serves the purpose of controlling the regulating apparatus. The third comparison device output is switched when the .lambda. sensor is not under the influence of any resultant electric current; as a result, no temperature-dependent shift of the switchover point relative to the internal sensor voltage occurs and regulation can be effected with the regulating apparatus in a temperature in dependent manner to a desired point in the sensor voltage curve or to a desired lambda value.