Pump module, component description

 Since December 2006, on engines 900.917/918/919 in model 668.###, 670.### ## to 126250, only the modified metering device with heating element (R28) is installed as standard, and is supplied as a replacement part by the Global Logistics Center (GLC).

 In the case of repairs, the metering device without heating element is replaced by a metering device with heating element, and the following operations are also required:

 Routing a wiring harness for power supply of heating element.

 Update the software release in the MR control unit (A38) by downloading V07

 Parameterize the heating element using Star Diagnosis.

 Below is a description of the system with a metering device without heating element.

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4 AdBlue supply unit

4p Pump module

Location

The AdBlue supply unit with integrated pump module is located on the inner side of the RH longitudinal frame member at the AdBlue tank.

Task

The AdBlue supply unit with integrated pump module draws the AdBlue reducing agent out of the AdBlue tank, filters it and pumps it to the AdBlue metering unit.

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Design

41 Pressure filter

42 Line fitting (AdBlue feed line)

43 Line fitting (AdBlue return line)

44 Pneumatic switching valve

45 Connector (compressed air)

46 Pressure reservoir

47 Pressure filter and pressure reservoir housing

48 Line fitting (coolant outlet)

49 Pressure reservoir filling valve

50 Filler connection for pressure reservoir

51 Line fitting (coolant inlet)

52 Pump housing

53 Housing cover

54 Electrical connector

55 Cover vent membrane

56 AdBlue line fitting (intake)

57 Suction filter

M26/1 SCR AdBlue pump

The AdBlue supply unit with integrated pump module consists of a plastic housing with splash protection, pump housing screwed onto an aluminum block, and a pressure filter and pressure reservoir housing. The SCR AdBlue pump is located in the pump housing, an electrical 3-chamber diaphragm pump.

The pressure filter/pressure reservoir housing also contains a pneumatic switching valve, located beside the pressure filter and pressure reservoir. It also has a channel through which the coolant flows, and connections for the following coolant lines:

 Coolant feed line (from engine) at the line connection fitting (coolant inlet)

 Coolant feed line (to AdBlue tank) at the AdBlue line connection fitting (intake)

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Function

When the SCR AdBlue pump receives the switch-on signal from the MR control unit, it pumps the AdBlue reducing agent from the AdBlue tank. The AdBlue is prefiltered by the intake filter integrated in the AdBlue line connection fitting (intake), which has a mesh size of 100 μm.

The SCR AdBlue pump brings the AdBlue reducing agent up to an operating pressure of about 6 bar, and pumps it into the pressure filter and pressure reservoir housing. There, the AdBlue is passed through another filter (with mesh size 30 m) to remove the finer dirt particles,μ then pumped toward the AdBlue metering unit. The pressure reservoir is usually a gas-filled reservoir bladder made of rubber, and it's purpose is to compensate for pressure surges and reduce the cut-in frequency of the SCR AdBlue pump. It has a volume of approx. 0.13 l. It is filled with nitrogen (N2) ex-works. It can be refilled with oil and grease free air.

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Air admission

The pneumatic switching valve and line fitting (AdBlue feed line) are used for automatic ventilation of the pump module integrated in the AdBlue supply unit during operation or at startup. The pneumatic switching valve closes when compressed air is applied.

The SCR AdBlue pump does not normally function when "dry", as it switches off if the fill level sensor in the SCR AdBlue combination fill level and temperature sensor (B103) in the AdBlue tank falls below the defined limit value. However, it may run briefly in the "dry" state, if the AdBlue reducing agent is swashing around in the AdBlue tank. If the SCR AdBlue pump runs for more than 10 s when dry, the MR control unit detects it and starts automatic ventilation.

AdBlue pressure reduction

To prevent damage to the pump module integrated in the AdBlue-supply unit due to freezing of the AdBlue reducing agent, after the ignition is switched off ("circuit 15 OFF"), the pressure of the AdBlue is reduced in the pump module and in the AdBlue pressure feed line between the pump module and the AdBlue metering unit. This is done by ventilating the compressed air controller unit. This causes the pneumatic switching valve to open and allow the AdBlue to flow back through the AdBlue return line to the AdBlue tank.

AdBlue heater

A channel is provided in the pressure filter and pressure reservoir housing, through which coolant flows for heating and de-icing. The MR control unit controls the flow of coolant with the SCR feed line tank heater solenoid valve (Y107) attached to the engine, according to temperature.