Active tank and SCR delivery module

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The following are permanently integrated in the SCR delivery module:

Pump block with delivery pump and return pump
Fuel level sensor with temperature sensor
Tank heating

Fig 1: Identifying Pressure Line Connection, Active Tank, Heating Element And Plug Connection
Courtesy of BMW OF NORTH AMERICA, INC.

Item	Explanation
1	Active tank
2	Pump block with pre-supply pump and return pump
3	Heating element
4	Fill level sensor with temperature sensor
5	five-pin plug connection
6	Pressure line connection
7	4-pin plug connection

Fill level sensors with temperature sensor

The fluid level is measured by ultrasound.

The evaluation electronics transmit ultrasonic pulses. These ultrasonic pulses are reflected at the transition from AdBlue to air (echo impulse). The evaluation electronics receive and amplify these echo impulses. The amplified echo pulses are then converted into a digital signal.

NOTE: On extreme inclines or if the active/passive tank is froze, the signal is 15 mm. This is the same as the signal for an empty active tank or passive tank.
The fill level sensor is installed in both the active tank and the passive tank.

A temperature sensor is integrated as part of the fill level sensor. A temperature-dependent electrical resistor is used for temperature sensing. The circuit contains a voltage divider where the resistance can be measured depending on the temperature. A temperature is converted using a characteristic curve specific to the sensor. The measuring range is from -40 °C to 80 °C.

Tank level and temperature values are sent via pulse-width-modulated signals to the SCR control unit.

Delivery pump and return pump

A pump block is integrated into the SCR delivery module. A delivery pump and return pump are housed in the pump block. The pumps are activated by the SCR control unit through a four-pin plug connection.

Fig 2: Identifying Pump Block, Pressure Line And Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.

Item	Explanation
1	Pump block
2	Pressure line connection
3	4-pin plug connection

The delivery pump sends the AdBlue to the SCR metering module. The delivery pump operates at a system pressure of between 4.5 and 8.5 bar.

The return pump drains the pressure line. Partial draining of the pressure line is needed to avoid ice damaging the SCR metering module in freezing conditions.

Active tank heating

The tank heating is also activated by the SCR control unit through the five-pin plug connection. AdBlue freezes at -11 °C.

After the following maximum heating periods, enough AdBlue must have been thawed in order to guarantee sustained injection:

-15 °C: 20 minutes
-25 °C: 45 minutes

The delivery rate is restricted to 150 g/h when the active tank is frozen. A higher delivery rate endangers the sustained withdrawal of liquid AdBlue from the active tank and could cause a malfunction in the SCR system.

Pressure line heating

An additional heating element is located at the start of the pressure line. This heating element is also activated by the SCR control unit. It too contributes to keeping the AdBlue in a liquid state.

The ground connection for the heating element is to the body (load earth).

Filter element

A filter element in the SCR delivery module filters the AdBlue.