HEATED OXYGEN SENSOR (HO2S) CONSTRUCTION/OPERATION [MZI-3.7]

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Construction

• Installed on the rear side of the WU-TWC.

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• A heater is built into the sensor to facilitate the activation of the HO2S at engine startup (when the exhaust gas temperature is low).

Operation

• A zirconium element is used on the sensor. When there is a difference between the oxygen concentration inside and outside the element, electromotive force is generated by the movement of oxygen ions (inside of the zirconium element: atmosphere, outside: exhaust gas). The electromotive force changes significantly at the boundary of the stoichiometric air/fuel ratio (A/F=14.7).
• When the temperature of the zirconium element is low, electromotive force is not generated. Therefore the HO2S is heated by a built-in heater, facilitating the oxygen sensor activation. Due to this, the sensor is efficiently activated even immediately after cold-engine startup, and a stable sensor output can be obtained.
• The output voltage from the HO2S is used for aged deterioration determination of the catalytic converter and fuel injection control.

HO2S characteristic

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