1. Sensor structure and startup process
Heating stage
After the ignition switch is turned on, the sensor starts the self-heating program, first heating to 100℃ to activate the basic function6.
Then wait for the ECU to send a "dew point temperature" (120℃) signal, and after confirming that there is no moisture in the exhaust system that damages the sensor, continue to heat up to 800℃ working temperature6.
Temperature control
The sensor needs to operate stably at a high temperature of 800℃. This temperature condition ensures its internal chemical reaction sensitivity and detection accuracy6.
2. Detection and signal transmission mechanism
Gas concentration detection
Through the principle of electrochemical or catalytic reaction, the sensitive element (such as solid electrolyte) in the sensor head reacts with NOx in the exhaust gas to generate a current or voltage signal proportional to the concentration6.
Signal processing and feedback
The control module converts the original signal into standardized data and transmits it to the ECU in real time through the CAN network for evaluating the efficiency of the SCR (selective catalytic reduction) system6.
3. System Application and Function
Emission Control Collaboration
In diesel National VI vehicles, the front NOx sensor (before DOC) monitors the original emission concentration, and the rear sensor (after SCR) verifies the concentration after treatment. The ECU adjusts the urea injection amount accordingly to optimize the NOx purification effect6.
Self-diagnosis and maintenance
The sensor has a self-diagnosis function and can report fault conditions (such as abnormal heating or signal distortion) to the ECU to ensure system reliability6.
4. Hardware Features
Integrated design: The sensor consists of a sensor head, a control module and a circuit, and components cannot be replaced separately6.
Pin configuration: Pin 1 distinguishes the front and rear sensors by grounding/open circuit status to ensure accurate ECU identification6.
Summary: The NOx sensor detects the concentration of nitrogen oxides through chemical reactions under high temperature conditions, and combines intelligent signal processing with ECU linkage to achieve closed-loop control of diesel vehicle exhaust emissions6.
Electrochemical Reaction Mechanism
- Electrode reactions:
- Pt electrode: Reduction of O₂ to O²⁻ ions:
O2+4e−→2O2− 7
- NiO electrode: Oxidation of NO to NO₂:
NO+O2−−2e−→NO2 7
- Ion migration: O²⁻ ions pass through the ZrO₂ electrolyte under high temperature (800°C), generating a current proportional to NOx concentration
Website:www.enginenoxsensor.com
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