Zirconia Oxygen Probe (Oxygen Sensor) (ZRO2-II)

Working principle of zirconia oxygen probe (oxygen sensor) (ZRO2-II)

The working principle of zirconia oxygen sensor is as follows: the ceramic body of the zirconia tube is a porous body, and oxygen can penetrate into the solid electrolyte of the porous body. When the temperature is high, oxygen undergoes ionization. As long as there is a difference in oxygen concentration between the inside (atmosphere) and outside (exhaust gas) sides of the zirconium tube, oxygen ions will diffuse from the atmosphere side to the exhaust side inside the solid electrolyte, forming a micro cell in the zirconium tube and generating voltage between the platinum electrodes of the zirconium tube. When the mixture is lean, the oxygen content in the exhaust is high, the difference in oxygen concentration on both sides is small, and the generated voltage is small; When the mixture is rich, the oxygen content in the exhaust is low, and the content of CO, CH, and NOx is high. These components react with oxygen under the catalytic action of platinum on the outer surface of the zirconium tube, consuming residual oxygen in the exhaust gas and reducing the oxygen concentration on the outer surface of the zirconium tube to zero. This suddenly increases the oxygen concentration difference between the inner and outer sides of the zirconium tube, and the voltage generated between the two poles also increases.

Therefore, the voltage generated by the oxygen sensor undergoes a sudden change around the excess air coefficient λ=1. When λ>1, the output voltage of the oxygen sensor is almost zero, and when λ<1, the output voltage of the oxygen sensor is close to 1V. In the closed-loop control process of the engine mixture, the oxygen sensor is equivalent to a concentration switch, which inputs a width changing electric pulse signal to the ECU according to the change of the air-fuel ratio of the mixture. The ECU controls the fuel injection amount based on the feedback signal of the oxygen sensor, so as to minimize the harmful gas components in the exhaust.