The oxygen sensor utilizes the Nernst principle.
The core element is a porous ZrO2 ceramic tube, which is a solid electrolyte with porous platinum (Pt) electrodes sintered on both sides. 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 to combine with electrons (4e) to form oxygen ions O2-, making the electrode positively charged, O2 -The ions migrate to the low oxygen concentration side (exhaust gas side) through the oxygen ion vacancies in the electrolyte, making the electrode negatively charged, that is, a potential difference is generated.
When the air-fuel ratio is relatively low (rich mixture), there is less oxygen in the exhaust gas, so there are less 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 on the inner and outer sides of the ceramic tube is 0.4V ~ 0.5V, and the electromotive force is the reference electromotive force
When the air-fuel ratio is relatively high (lean mixture), the oxygen content in the exhaust gas is high, and the oxygen ion concentration difference between the inside and outside of the ceramic tube is small, so the generated electromotive force is very low, close to zero.
Heated oxygen sensor:
-Heated oxygen sensor has strong anti-lead ability;
-Less dependence on exhaust temperature, can function as usual under low load and low exhaust temperature;
-Quickly enter closed loop control after starting