Working Principle of Zirconia Oxygen Probe (Oxygen Sensor) (ZRO2-II)

The working principle of the zirconia oxygen sensor is as follows: the ceramic body of the zirconium tube is a porous body, and oxygen can penetrate into the solid electrolyte of the porous body. At higher temperatures, oxygen ionizes. As long as the oxygen content inside (atmosphere) and outside (exhaust gas) sides of the zirconium tube is different, and there is a difference in oxygen concentration, oxygen ions in the solid electrolyte diffuse from the atmosphere side to the exhaust side, so that the zirconium tube forms a micro-battery. A voltage is generated between the electrodes. When the mixture is lean, the oxygen content in the exhaust gas is high, the difference between the oxygen concentrations on both sides is small, and the voltage generated is small; when the mixture is rich, the oxygen content in the exhaust gas is small, and the contents of CO, CH, and NOx are high. Under the catalytic action of platinum on the outer surface of the zirconium tube, it reacts with oxygen and consumes the residual oxygen in the exhaust gas, so that the oxygen concentration on the outer surface of the zirconium tube becomes zero, so that the oxygen concentration difference between the inner and outer sides of the zirconium tube suddenly increases , the voltage developed between the two poles also increases.

Therefore, the voltage generated by the oxygen sensor has 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. According to the change of the air-fuel ratio of the mixture, an electrical pulse signal with varying width is input to the ECU, and the ECU controls the fuel injection amount according to the feedback signal of the oxygen sensor to make the exhaust gas The composition of harmful gases is reduced to the minimum.