System for detection of air/fuel ratio in IC engine by using oxygen sensor operated with supply of current.

摘要

An air/fuel ratio detection system for an IC engine, using an oxygen sensor element (30) of the concentration cell type which has a laminate of a measurement electrode layer (42) exposed to the exhaust gas, a porous layer (40) of oxygen ion conductive solid electrolyte and a reference electrode layer (38) and requires the supply of a small DC current (is) thereto to produce a reference oxygen partial pressure at the reference electrode (38) by a balance between migration of oxygen ions to the reference electrode (38) and diffusion of oxygen molecules therefrom. To prevent excessive rise in the reference oxygen partial pressure even when the engine continues to discharge exhaust gas high in the content of oxygen, the detection system has a control circuit which controls the intensity and flow direction of the current (Is) for the sensor element (30) with reference to a voltage (V.) which is produced by adding a definite voltage (ΔV) to, or aubtacting the definite voltage from, the sensor output voltage (Vs) depending on the level of oxygen content in the exhaust gas indicated by the sensor output voltage and smoothing the voltage resulting from the addition or subtraction.