Post-oxygen sensor

Nowadays, vehicles are equipped with two oxygen sensors, one in front of the three-way catalyst and one behind it. The function of the front is to detect the air-fuel ratio of the engine under different working conditions, and at the same time, the computer adjusts the fuel injection quantity and calculates the ignition time according to this signal. The rear is mainly to test the work of the three-way catalytic converter! I.e. the conversion rate of the catalyst. It is an important basis to test whether the three-way catalyst works normally (good or bad) by comparing with the data of the front oxygen sensor.

composition introduction

The oxygen sensor uses Nernst principle.

Its core element is a porous ZrO2 ceramic tube, which is a solid electrolyte, and its two sides are sintered with porous Pt electrodes. At a certain temperature, due to the different oxygen concentrations on both sides, oxygen molecules on the high-concentration side (inside 4 of the ceramic tube) are adsorbed on the platinum electrode and combined with electrons (4e) to form oxygen ions O2-, which makes the electrode positively charged, and O2- ions migrate to the low-oxygen concentration side (exhaust gas side) through oxygen ion vacancies in the electrolyte, which makes the electrode negatively charged, that is, a potential difference is generated.

When the air-fuel ratio is low (rich mixture), there is less oxygen in the exhaust gas, so there are fewer oxygen ions outside the ceramic tube, forming an electromotive force of about 1.0V;

When the air-fuel ratio is equal to 14.7, the electromotive force generated at the inner and outer sides of the ceramic tube is 0.4V~0.5V, which is the reference electromotive force;

When the air-fuel ratio is high (lean mixture), the oxygen content in the exhaust gas is high, and the concentration difference of oxygen ions inside and outside the ceramic tube is small, so the electromotive force is very low and close to zero.

Heated oxygen sensor:

-Heated oxygen sensor has strong lead resistance;

-It is less dependent on the exhaust temperature, and can function as usual under low load and low exhaust temperature;

-Quickly enter the closed-loop control after starting.