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signals fed back by the oxygen sensor, i.e. control injection pulse-width to let the mixed gas always maintain an approximately ideal air-fuel ratio (14.7:1). 7.2 Principle of the sensor: Sensing element of oxygen sensor is a kind of ceramic tube with holes, and outside of tube walls are surrounded by engine exhaust gas and inside is air. Ceramic sensor element is a kind of solid state electrolyte with electrical heating tube inside (as shown in the figure).
The operation of the oxygen sensor is achieved by converting the concentration difference of oxygen ion between inside and outside of the ceramic sensor element to the voltage signal output. It bears the characteristic of solid electrolyte once the temperature of the ceramic sensor element reaches 350 . Because of the particularity of its materials, the oxygen ion can pass the ceramic ℃ sensor element freely. Taking advantage of this characteristic, the concentration difference will be converted to electric potential difference to form electric signal output. If the mixed gas is comparatively thick, the oxygen ion thickness difference between inside and outside of the ceramic tube will be higher and the potential difference will also be higher, then a mass of oxygen ion will move from inside to outside, so, the output voltage is comparatively high (close to 800mV-1000mV); If the mixed gas is comparatively thin, the oxygen ion thickness difference between inside and outside of the ceramic tube will be smaller and the potential difference will also be smaller, then just a few of oxygen ion will move from inside to outside, so, the output voltage is comparatively low 1. Cable 2. Dish washer 3. Insulation bush 4. Protective bush 5. Clamp fitting of heating element 6. Heating rod 7. Contact pad 8. Sensor seat 9. Ceramic probe 10. Protection sleeve Cross-section view of oxygen sensor
Characteristic Curve of oxygen sensor at 600° C O u tp u t v o lt ag e V
Excessive air-fuel ratio λ |