Finally Understand! Inside The Mysterious Urea Pump

After the implementation of the fourth national emission, most domestic tractors adopt SCR technology route. The most obvious feature of SCR system is that the vehicle is equipped with a urea tank, which stores the urea solution used to inject into the tail gas.
If the aftertreatment system fails, the ECU will reduce the fuel injection to ensure that the exhaust emission does not exceed the standard. At this time, the vehicle will show insufficient power, which is what we card friends often call torque limit. Although the current truck has implemented the national five emission, many people are still unfamiliar with the post-treatment system of urea and feel that it is very mysterious.
Most of the daily aftertreatment failures are caused by the aftertreatment injection system. Bosch 2.2 aftertreatment system is widely used in all kinds of trucks. Today, we will take the urea pump of Bosch 2.2 aftertreatment system as an example to explain the internal structure of the urea pump.
● the structure is not complex

In fact, the interior of the urea pump is not complex. It is mainly composed of diaphragm pump, electromagnetic directional valve, pressure sensor, urea filter element, electric heating system, lead frame and other components.

There are three urea solution pipelines on the outside of the urea pump. The liquid injection pipe is on the left, the liquid return pipe is in the middle, and the liquid inlet pipe is on the right.

It is a diaphragm pump that provides power for the pressure building of the system. The speed of the diaphragm pump will change according to the exhaust volume of the engine. The maximum pump pressure can reach 9BAR. After reaching the pressure, the excess urea solution will be discharged back to the urea tank through the return pipe.

The main function of electromagnetic directional valve is to change the positive and negative absorption of urea. Some people will ask, why is it designed like this? Positive suction, as we all know, builds pressure through diaphragm pump and injects urea solution through urea nozzle. If the vehicle stalls, urea solution will remain in the pipeline. As we all know, urea solution will crystallize below minus 11 ℃. The design of suction and emptying is to solve this problem.
During shutdown, the system will automatically suck back, empty the urea solution in the pipeline, and suck back the urea solution in the pipeline to the urea tank. Because the urea tank has a water heating system, the urea can be heated in winter. After the urea solution is heated, the whole system can work normally.
In order to solve the problem of low-temperature urea crystallization in the urea pump, there are two heaters on the filter element and in the lead frame to heat the urea pump at low temperature to prevent low-temperature urea crystallization.

The urea nozzle is installed at the front end of the silencer, and the urea pump with pressure is injected into the tail gas through it. There is a solenoid valve on the urea nozzle. The solenoid valve will adjust the pulse according to the ECU signal to adjust the injection frequency.

Let’s talk about the key point. This part is the urea filter element. Many people will ask, does the urea pump also have a filter element? Yes, in order to ensure the normal operation of the urea system, both Bosch and Cummins post-treatment have urea filter elements. The urea filter elements of Bosch 2.2 system are in the urea pump.

At the lower end of the urea pump filter element is a pressure sensor, which is used to detect the pressure of the urea pump and provide a pressure signal for the SCR electronic control unit to ensure the normal injection of urea.

Urea pump needs to pay attention to these two points

It is understood that post-processing is prone to problems, mainly caused by the injection part, so we need to pay attention to these two points.
1. Use genuine urea solution. The quality of inferior urea solution is not up to standard and the purity is not enough. The urea solution contains impurities and is easy to crystallize, resulting in nozzle blockage. At this time, the urea nozzle can be disassembled, boiled with boiling water, the urea is dissolved, and the nozzle returns to normal.
2. Replace the urea filter element regularly. The dirt holding capacity of urea filter element is limited. Even if you use genuine urea solution, you need to replace it regularly. Once the filter element loses its filtering effect, the impurities in urea will cause system failure. The replacement mileage of urea filter element is generally 50000 km.
Through the introduction, you will find that the urea injection system is not so mysterious. The internal structure is very simple. The reason why you feel mysterious is that you don’t understand it. It is recommended that you use genuine urea solution and replace the urea filter element regularly, so as to ensure the normal operation of post-treatment, the engine is not limited to torque, and the vehicle can run normally.