Bosch 6.5 urea pump is an airless urea pump launched by Bosch in response to the Asian post-processing market. Compared with the previously launched Bosch 2.2 urea pump, it reduces the working pressure of the urea pump (from 9bar to 5bar).
As shown in the figure, the urea pump sucks the urea solution from the urea tank into the urea pump when building pressure, and the urea solution passes through the suction connector → motor → filter element → pressure sensor → injection connector (→ return connector).
The reasons for the failure of the urea pump to build pressure can be summarized as leaks (seals), blockages (filter elements, filter screens), and old (rubber parts, sealing rings).
The liquid flow process in the pump with pre-injection and pressure build-up: suction connector filter screen → pressure balance unit → check valve plate (inlet) → motor diaphragm → check valve plate (outlet) → filter element → check valve, pressure balance Diaphragm, liquid return connector (pressure sensor, spray connector)
Let’s take a look at the parts that each liquid passes through in turn:
1. Suction connector
There is a filter in the suction connector, and the most prone fault is clogging, which leads to failure to build pressure. There is a filter in the suction connector to initially filter the impurities in the urea and protect the parts in the pump. After the pump is used for a long time, the filter screen will accumulate a lot of impurities, increase the suction resistance and pressure loss, affect the suction efficiency, and cause pressure build-up failure; at the same time, it will also accelerate the wear of the parts in the pump and need to be replaced on time. If the quality of the urea solution is poor and there are many impurities, it will accelerate the blockage of the joint and affect the efficiency of liquid absorption. The blockage cannot be directly observed from the appearance. If you feel that the suction is slow or the direct pressure building fails, you need to consider the blockage of the suction connector. In addition, if the suction connector is exposed to the outside, it will inevitably be bumped and damaged, and the sealing performance will decrease. If there are cracks and damages on the surface, there is also the possibility of liquid leakage and failure to build pressure.
A similar situation can happen when the spray joint leaks.
2. Check valve plate
The function of the one-way valve plate is to control the flow direction of the liquid during the pressure build-up process, and cooperate with the motor to realize the one-way flow of the urea solution.
The one-way function of the one-way valve plate mainly relies on the sealing effect of two rubber parts. The service life of the rubber part is closely related to its material, temperature and pressure. The long-term use of rubber parts or other failures will cause aging, which will cause the urea pump to reduce the liquid suction capacity, and in severe cases, it will fail to build pressure. In addition, if the suction connector and the filter screen in the urea tank are damaged, foreign particles will accumulate around the rubber parts, which will affect the sealing performance and the efficiency of liquid absorption. The one-way valve plate is prone to loose sealing and cannot play a one-way sealing role, and slow or unable to absorb liquid, resulting in failure to build pressure.
The motor is the most critical component of the urea pump. It consists of O-rings, eccentric wheels, connecting rods, main bearings, connecting rod bearings, elastic bearings, pump brackets, screws, motor stators (including PCB boards), motor rotors and driving diaphragms. (Diaphragm) composition. The mechanism is rotated by a brushless DC motor, so that the coaxially connected eccentric wheel drives the diaphragm to reciprocate, thereby controlling the pressure in the pipeline.
This mechanism is an intelligent actuator, and its control circuit can not only receive the speed signal from the ECU in the form of PWM to complete the driving function of the motor, but also can transmit temperature and fault signals to the ECU through the PWM signal.
The main faults of the motor are: bearing wear and aging, driving diaphragm aging and deformation, motor PCB board components aging or damage. Among them, the damage of the motor PCB board will cause the motor to work abnormally or stop, which is the most vulnerable part of the main pump. Since the PCB board does not have a protective shell, the installation location is very close to the top cover of the urea pump. Once the top cover is severely impacted or the environment in the pump is humid, it is easy to be damaged.
The motor-driven diaphragm is stretched, compressed, and rubbed against the bracket for a long time, and it will gradually age and deform, decrease its elasticity, increase the power loss of the motor, and reduce the liquid absorption capacity of the motor.
The motor is prone to short-circuit and burns when it is exposed to water. Therefore, after the urea pump is repaired, be sure to clean the water droplets in the pump, blow it clean with an air gun, and then install the upper and lower covers, because the internal moisture is not easy to volatilize after installation.
4. Filter element
The filter element is the last port that blocks the flow of urea impurities to the nozzle and the liquid return valve. If the filter paper is damaged or falls off, the filter element itself will easily block the nozzle and the liquid return throttle valve.
After a long time of filtering and soaking, the blockage of the filter element will become more and more serious, the pressure loss will increase, and the pressure build-up time will be prolonged. In severe cases, the pressure build-up will fail. Even if the quality of the urea used is qualified, the filter chip will be clogged after long-term use, and it needs to be replaced every 3 months.
5. Pressure sensor
If the pressure value of the pressure sensor stops at a certain value and there is no change during the test, it means that the pressure sensor has a problem. The pressure value (or the signal pin voltage value) continues to increase and maintains above 500kPa to build the pressure successfully, so In the process of building pressure, it is necessary to observe the change of the pressure value. It only takes about 30s. If the pressure does not reach 500kPa, it will fail.
There is a vent hole on the front of the pressure sensor, which is directly connected to the outside air (in the pump). If the hole is blocked or the top cover vent plug is blocked, the pressure signal will be affected to a certain extent, and the normal pressure signal cannot be fed back. In severe cases, abnormal pressure will be reported. The urea pump failed to build pressure.
The internal electronic components of the pressure sensor are prone to failure, and the pressure sensor cannot correctly measure the urea pressure, which leads to the failure of pressure building.
6. One-way throttle valve (return valve) and emptying pump (solenoid valve)
The one-way throttle valve is located in the liquid return pipeline of the housing, and works in coordination with the emptying solenoid valve to divide the liquid circuit into a high-pressure circuit and a low-pressure circuit. In the pressure building stage, the urea is released from the pressure through the one-way throttle valve, and flows into the urea tank after passing through the liquid return joint and the urea tube.
In the pressure build-up phase, the spring of the empty solenoid valve will drive the diaphragm against the upper cover of the diaphragm, closing the low-pressure circuit. Due to the small fit gap between the drive diaphragm and the valve body, once rusted, stuck or improperly installed, it will cause loose sealing, fail to build up urea pressure, and cause liquid leakage or failure to build pressure.
The function of the positioning sleeve is to limit the position of the one-way throttle valve and prevent the sealing failure caused by the leakage of the sealing ring.
The small filter screen of the one-way throttle valve can block the impurities in the pump. If the small filter screen is severely blocked, the pressure in the pump will soar; in severe cases, the urea pressure overcomes the spring resistance to release the pressure, and flows into the return line through the low-pressure circuit, which affects the urea pump. The housing and electrical components are protected.
When the vehicle is parked, the urea pump will enter the emptying stage to release the pressure and empty the urea solution in the pump. If the driver operates improperly or cuts off the power prematurely, the urea pump will not be completely emptied. Urea crystals are formed in the one-way throttle valve, causing blockage and unsuccessful pressure building. After the one-way throttle valve is blocked, it can be soaked in warm water to dissolve the urea and continue to be used; if the crystallization is serious, the one-way throttle valve needs to be replaced decisively.
7. Heating plate
The heating plate is responsible for thawing and controlling the temperature in the pump. The electric heating is efficient and stable, and has good controllability of the urea temperature. In cold areas or low-temperature weather, if the heating plate is damaged or the heating efficiency is reduced, the urea pump will not be completely defrosted and the pressure will not be successfully built.
There is an overheating protection device on the heating plate, which can protect the heating resistance to a certain extent to prevent the influence of high temperature on the service life of the heating plate. If the heating protection device fails, the urea pump will overheat and the urea temperature will be high. (The motor can monitor the temperature of the heating resistance wire).
Before testing the urea pump, observe whether the pins of the lead frame are broken or connected. If there is a problem, it needs to be replaced immediately. The virtual connection of the pins will cause large or abnormal motor speed fluctuations and unstable pressure signals, which will affect the normal operation of the urea pump; during the running of the vehicle or under heavy load (heating or high injection volume), it may cause electric sparks or high temperature burns. Danger occurs. The most prone fault of the pins is fracture or rust, which may cause the urea pump to fail to build pressure.