Detailed explanation of the position and working principle of the urea pump sensor

Urea tank liquid level temperature sensor

Location: The urea level and temperature sensors are installed inside the urea tank, and the two sensors are generally integrated together.
Function: Used to measure the urea level and temperature inside the urea tank. A few have integrated engine cooling water heating pipes. When the urea temperature is too low, the ECU or DCU controls the cooling water solenoid valve to open and heat the urea.

Classification:

1. From a functional perspective, it can be divided into heated and non heated types. The main difference can be seen from the number of joints. Non heated types generally have 2 joints, while heated types typically have 4-5 joints;
2. From the perspective of installation method, it can be divided into canned and non canned types. Canned type refers to the urea pump directly placed on the liquid level temperature sensor, eliminating the urea pipeline between the urea pump and the urea pipe. Currently, this installation method is mainly used by Cummins and CNHTC’s independently developed pneumatic urea pump.

Fault: When the urea level is too low, the indicator light is turned on to remind the driver to add urea.

Attention: During liquid level detection, the urea level and temperature sensors at full level, zero level, and empty tank will send different alarm signals to the ECU. The detection float will float according to the level of urea, and the percentage of urea will be displayed on the instrument panel.

Exhaust temperature sensor

Location: Two are located at the front and rear of the SCR box. Weichai, Xichai, and other supporting Bosch 2.2 systems (such as non gas assisted SCR systems such as Yuchai and Cummins) are generally only equipped with upstream exhaust temperature sensors.
Function: ECU/DCU controls whether urea is injected under pressure and corrects the amount of urea injection based on the feedback signal from the exhaust temperature sensor.
Principle: There are two structures for the upstream exhaust temperature sensor, one with a 90 degree right angle bend at the end of the sensor, and the other with a straight structure. The shape and structure depend on the actual situation. The exhaust temperature sensors are all positive temperature coefficient resistors, meaning that the higher the temperature, the greater the resistance value.
Additional note: Measure the exhaust temperature as a condition for urea pressure building and injection. The installation depth of the exhaust temperature sensor to the exhaust pipe varies, and the measured exhaust temperature also varies, which can have varying degrees of impact on urea consumption.

Ambient Temperature Sensor

Location: Generally installed away from heat sources and away from direct sunlight.
Function: The ambient temperature sensor is used to measure the ambient temperature, judge the rationality of the SCR system, monitor OBD interruption, and control urea heating.
Working principle: The environmental temperature sensor and water temperature sensor are the same, and are ordinary NTC thermistor sensors. Changes in external temperature cause changes in the sensor resistance value, which in turn causes changes in the voltage at both ends of the sensor. By calibrating the corresponding electrical pressure values at different temperatures, the external environmental temperature is measured.
Attention: The installation position of the ambient temperature sensor should be away from heat sources, avoid direct sunlight, and avoid areas with heavy sludge pollution. It is recommended to install it in areas such as the chassis of the frame, the front crossbeam of the frame, the rear of the frame, the engine air inlet, or near the intercooler.

NOx nitrogen oxygen sensor

Location: The NOx sensor is installed at the outlet of the SCR catalyst in the exhaust system.
Function: The NOx nitrogen oxygen sensor is used to detect the concentration of NOx in the processed exhaust gas during operation, serving as an OBD monitoring signal to correct the urea injection amount.
Working principle: When the NOx concentration reaches 5g/(KW • h), the MIL light will be activated; When the concentration reaches 7g/(KW • h), the torque limiter will be activated, and the maximum torque of the vehicle will be limited to the original 60%; When the NOx sensor is removed or communication with the ECU fails, the torque limiter will be activated after 50 hours.
Attention: The NOx sensor is an intelligent sensor that communicates with the engine ECU through the CAN bus and can perform internal fault self diagnosis. The NOX sensor and NOX control module are connected together and are a complete component that cannot be partially replaced, and there are rain plugs at the wiring harness end.

NOX sensor operating conditions

After receiving the dew point temperature signal from the ECU/DCU, the NOx sensor will heat itself to a certain temperature (up to 800 ℃).
Dew point temperature refers to the temperature at which there will be no moisture present in the exhaust system that can damage the NOx sensor. At present, the dew point temperature is set to 140 ℃, and the temperature value is measured by the exhaust temperature sensor of the reference catalyst.
Attention: If the sensor head comes into contact with water at this time, it will cause damage to the sensor.
2. After heating to the working temperature, the sensor begins normal measurement work.
3. The sensor sends nitrogen oxide values to the CAN bus, and the engine post-processing unit monitors the emissions of nitrogen oxides through this information.
Fault symptoms: 1. No urea burning 2. No refueling 3. Insufficient power 4. CAN line communication failure

Urea pressure sensor

Location: The urea pressure sensor is integrated into the urea pump, consisting of a stainless steel casing and materials that are resistant to high alkali environments. It can operate for long periods of time in urea solutions at -8~85 ℃.
Working principle: Used to monitor the liquid flow pressure in the urea system pipeline and provide real-time pressure signal feedback to ECU/DCU. This signal can be used to control the motor speed, achieve stability of working pressure, and monitor the urea injection amount, ensuring that the urea injection amount is the key to the entire SCR system. The control of pressure sensor directly determines the urea injection amount, It will also further affect the effectiveness of urea catalytic reduction.
Parameter: After successful normal pressure building, when injecting urea, the urea pressure stabilizes at around 9 kilograms. The power supply voltage of the pressure sensor is 5V, the output voltage of the signal line is 0.5V-4.5V, and the range is 0-13bar.
Precautions: The foam sheath inside the sensor can absorb the expansion volume of frozen urea solution to protect the pressure sensing element.