Characteristics of ZrO2-Type Oxygen Sensors for Automotive Applications

The characteristics of ZrO₂-type oxygen sensors for closed-loop control of the air-fuel mixture for automotive engines were investigated. New sensors, sensors tested in dynamometers and road vehicles, and lead-poisoned sensors were characterized as to their performance in terms of voltage output, switching response, internal resistance and voltage-λ switching behavior. New sensors behaved as ideal sensors at temperatures above 400°C, and behaved non-ideally at temperatures below 350°C. Sensors subjected to dynamometer and vehicle tests showed a gradual degradation in output voltage and steepness of their voltage-λ switch. Their internal resistances and lean-to-rich switching times increased with use while the rich-to-lean switching times decreased. Self-recovery of a sensor from lead poisoning occurred during subsequent vehicle operation with lead-free fuel.