Mercedes-Benz OM 471 Introduction Into Service Manual page 125

System components
Function
5 AdBlue" inlet
7 Injection nozzle
11 Temperature sensor
12 Pressure sensor
13 Heating element
14 Injector
15 Filter
When the engine is started and at an operating pressure of
approx. 10 bar, the AdBlue" metering device (A67) has AdBlue"
pumped constantly through it by the pump module.
This happens irrespective of whether AdBlue" is injected or not,
because the AdBlue" metering device (A67) is protected against
overheating at the installation location on the EATU (1) and the
prevailing high temperatures by this recirculation cooling.
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Injection
The AdBlue" metering device (A67) receives the signals from the
SCR control unit (A58) for the currently delivered AdBlue"
quantity. The pressure sensor (12) and temperature sensor (11)
integrated into the AdBlue" metering device (A67) supply the
values for the basis on which the opening duration and opening
period of the injection valve (14) are calculated.
The AdBlue" metering device (A67) is actuated by the SCR control
unit (A58) > the computation however takes place in the exhaust
aftertreatment (ACM) control unit (A60).
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The AdBlue" that is not required or not injected flows back
through the return line to the AdBlue" container. This cooling is
absolutely necessary, and it continues for a specific period in a
run>on phase, even when the engine is switched off.
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The injection valve (14) opens in pulsed intervals and injects > due
to the atomized effect produced by the injection nozzle (7) >
AdBlue" as a superfine spray straight into the exhaust flow, or put
more accurately into the hydrolysis path of the EATU (1)
Heating
At low ambient temperatures the AdBlue" metering device (A67)
is heated by the integrated heating element (13).
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