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Introduction of NOx Sensor

The N0x sensor is one of the most critical components in the aftertreatment system. During the operation of the engine, the N0x concentration in the exhaust gas of the engine exhaust pipe is constantly detected, so as to detect whether the N0x emission meets the regulatory requirements.
The N0x sensor is a completed part consisting of an induction probe, a control module and a wiring harness. There is a self-diagnosis function inside, and the monitoring information is reported to the ECU through CAN bus communication.
1. Physical installation of nitrogen oxide sensor:
1. N0x sensor installation temperature requirements: The installation of the N0x sensor should be careful not to install it in a place where the temperature is too high. It is recommended to stay away from the exhaust pipe and the surface of the SCR box, and a heat shield and insulation cotton must be installed during installation. And evaluate the temperature around the sensor ECU installation, it is recommended that the optimal working temperature of the N0x sensor should not be higher than 85 degrees.
2. Wire harness and connector installation requirements: do a good job of fixing and waterproofing the wire harness, keep the line loose during the installation and use of the N0x sensor, and the entire wire harness cannot be bent too much to prevent the wire harness from falling off due to excessive external force or shock force, and try to avoid the wire harness and The N0x sensor is exposed. If there are metal wires exposed, they should be wrapped with tape respectively, and the wire joints should not be affected by oil, debris, mud and other magazines, and waterproof. Otherwise, the sensor will fail due to water in the wiring harness.
2. Appearance style of N0x nitrogen oxide sensor: 2.1 generation and 2.8 generation
1. The NOx sensor has 12V and 24V.
2. The NOx sensor has 4-pin and 5-pin plugs.
3. The brands of nitrogen oxide application models are: Cummins, Weichai, Yuchai, Sinotruk, etc.
3. The working process of the nitrogen oxide sensor is explained in detail:
The main function of the N0x sensor is to detect whether the N0x concentration value in the exhaust gas exceeds the limit, and diagnose whether the catalytic converter muffler is aging or dismantled.
The N0x sensor communicates with the control unit via the CAN bus and has its own diagnostic function. After the sensor self-checks without fault, the control unit instructs the heater to heat the N0x sensor. During the heating process, if the sensor signal is not received after the maximum heating time limit is exceeded, it is determined that the sensor heating is unreliable.
1. “No Power State”:
A. In this state, 24V power is not supplied to the sensor.
B. This is the normal state of the sensor when the ignition switch of the body is turned off.
C. At this time, the sensor has no output.
2. “Powered – sensor inactive”:
A. At this time, the power has been supplied to the sensor through the ignition switch.
B. The sensor enters the preheating stage. The purpose of preheating is to evaporate all the moisture on the sensor head.
C. The preheating stage will last about 60 seconds.
3. When the ignition switch is turned on, the N0x sensor will heat up to 100°C.
4. Then wait for the ECM to issue a “dew point” temperature signal (Dew point):
The “dew point” temperature is the temperature at which there will be no moisture in the exhaust system that could damage the N0x sensor. The dew point temperature is currently set to 120°C, and the temperature value is the value measured by the outlet temperature sensor of the reference EGP.
5. After the sensor receives the dew point temperature signal from the ECM, the sensor will heat itself to a certain temperature (maximum 800°C) – Note: If the sensor head comes into contact with water at this time, the sensor will be damaged.
6. After heating to the working temperature, the sensor starts to measure normally.
7. The nitrogen oxygen sensor sends the measured nitrogen oxide value to the ECM through the CAN bus, and the engine ECM monitors the nitrogen oxide emission from time to time through this information.
4. the working principle of nitrogen oxide sensor:
Working principle: The core element of the nitrogen and oxygen sensor is the Zr02 zirconia ceramic tube of the ferry, which is a solid electrolyte, and porous platinum (Pt) electrodes are sintered on both sides. When heated to a certain temperature (600-700°C), due to the difference in oxygen concentration on both sides, zirconia will undergo a chemical reaction, charge movement will occur on both sides of the electrode, and the moving charge will generate current. According to the size of the generated current, the oxygen concentration is reflected, and the oxygen concentration is fed back to the controller to calculate the current nitrogen oxygen concentration and transmit it to the ECU through the CAN bus.
5. sensor probe self-protection function and precautions:
When the ignition is switched on, the N0x sensor will heat up to 100°C. Then wait for the DCU to send a “dew point” temperature signal. When the sensor receives the dew point temperature signal sent by the DCU, the sensor will heat itself to a certain temperature (maximum 800°C. Note: If the sensor comes into contact with water at this time, it will cause damaged sensor)
Dew point protection function: Because the nitrogen oxygen sensor itself needs a higher temperature when the electrode works, the nitrogen oxygen sensor has a ceramic structure inside. The ceramic will burst when it encounters water at high temperature, so the nitrogen oxygen sensor will set a dew point protection function. The function of this function is to wait for a period of time after the detection of the exhaust temperature reaches a certain temperature. The computer version believes that at such a high temperature, even if there is water on the sensor after such a long time, it can be blown dry by the hot exhaust gas.
6. Other knowledge of nitrogen and oxygen sensor:
A material called “Gortex”* is applied to the NOx sensor to ensure that fresh air enters the reference comparison space inside the sensor. Therefore, it is very important to ensure that this vent is unobstructed, and it is necessary to avoid foreign matter blocking or covering this vent during installation. In addition, try to ensure that the sensor is installed after the body is painted and painted. If the body painting and painting work must be carried out after the sensor is installed, the vents of the sensor must be properly protected, and the protective material must be removed after the painting and painting work is completed to ensure the normal operation of the sensor.

Post time: Jul-09-2022