Bosch 2.2 post treatment system, urea pump, urea pipe and urea tank need heating. At present, the commonly used schemes are electric heating of urea pump and urea pipe and cooling water heating of urea tank of burn urea.
One Jiefang J6 is equipped with Bosch 2.2 post-processing system, the fault light is on, and the read fault code is as follows of burn urea.:
Water heating is also used for urea pumps of some systems. For example, Hino engine adopts water heating urea pumps. We focus on the electric heating system of burn urea..
The urea tank is heated by water, and the coolant solenoid valve controls whether the engine coolant flows for heating. When the temperature sensor in the urea tank detects that the temperature is lower than a certain limit, start heating. When the temperature is higher than a certain limit, stop heating. Generally, when the temperature is lower than 0 ℃, ECU opens the solenoid valve to heat the urea solution to 5 ℃, and closes the solenoid valve (different items) of burn urea.
The urea pipe is electrically heated. The urea pipe is wrapped with resistance wire, which generates heat when powered on, just like the household electric blanket. Judge whether heating is required according to the ambient temperature and control it through the heating relay. The resistance generally ranges from tens of ohms to hundreds of ohms of burn urea.
The urea pump is electrically heated, and there is a heating resistance wire inside the pump, which is covered on the filter and flat plate. 2.2 pins 5 and 6 of urea pump are heating pins. The resistance of 24V system is about 6 ohms, and that of 12V system is about 1.5 ohms. Generally, judge whether heating is needed according to the temperature in the pump (temperature signal is transmitted through the speed control line of the pump motor), and control it through the relay of burn urea.
In order to prevent overheating, there are two protective resistors on the heating circuit of the pump. When the temperature is higher than 110 ℃, the resistance becomes infinite of burn urea.
To understand heating related faults, first understand the heating circuit diagram. The following figure is the schematic diagram of the heating circuit. The post-treatment heating circuit has five relays in total, one main relay, and the live wire controlling the heating of urea pipe and urea pump of burn urea.
Four auxiliary relays, namely pressure pipe heating relay, return pipe heating relay, inlet pipe heating relay and urea pump heating relay, control the corresponding pipeline and the negative pole of urea pump heating. Simply understand that the main relay controls the heating live wire and the auxiliary relay controls the grounding of burn urea.
The following figure shows the post-treatment heating relay of Jiefang J6, which is located on the left side of the passenger’s safety box in the cab. Compare it with the above figure of burn urea.
The working principle of the relay will not be repeated. Just remember one sentence: the condition for the pull-in of the relay is that there is a voltage difference between the two control lines. Simply put, the relay is pulled in when there are two pins 85 and 86, one is 24V and the other is 0V of burn urea.