Function Of The Eats (Overall System); Reduction Of Nox In The Scr Catalytic Converter - Mercedes-Benz OM 471 Introduction Into Service Manual

Functions
A4 Engine management control unit
(MCM)
A57 NOx sensor control unit outlet of
EATU
A57 b1 NOx sensor outlet of EATU
A58 SCR control unit
A60 Exhaust aftertreatment (ACM)
control unit

Function of the EATS (overall system)

The basic functionalities of the whole EATS are monitored and
regulated over the engine management (MCM) control unit (A4)
and the exhaust aftertreatment (ACM) control unit (A60).
After an engine start the engine management (MCM) control unit
(A4) starts an automatic test routine automatically in the
background which checks the operational readiness of the EATS.
The SCR control unit (A58) integrated in the pump module (1) is
actuated after successful release of the system. This switches on
the SCR delivery pump (M25) contained in the pump module (1)
which now suctions up AdBlue" out of the AdBlue" container (5)
and delivers it over the AdBlue" feed line to the AdBlue"
metering device (A67).
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Reduction of NOx in the SCR catalytic converter

The AdBlue" injection into the exhaust flow is calculated by the
engine management (MCM) control unit (A4). If AdBlue" should
be injected this first of all sends a signal to the exhaust
aftertreatment (ACM) control unit (A60) which processes the data
and afterwards actuates the SCR control unit (A58) integrated on
the pump module.
The injection timing point and the injection quantity are now
calculated there and the AdBlue" metering device (A67) is
appropriately actuated.
The following occurs if AdBlue" is injected:
the AdBlue" metering device (A67) injects AdBlue" into the so>
called hydrolysis segment in the EATU (2) directly into the exhaust
flow.
70
A67 AdBlue" metering device
A70 b1 NOx sensor control unit inlet of
EATU
A70 NOx sensor inlet of EATU
B72 Exhaust temperature sensor
upstream of SCR catalytic
converter
– This printout will not be recorded by the update service. Status: 09 / 2011 –
B73
B74
CAN 4
CAN 13 NOx>CAN
M25
Since the AdBlue" injection does take place continuously in the
exhaust flow the AdBlue" flows back again over the AdBlue"
return line into the AdBlue" container. This circulation
continuously takes place independently of whether AdBlue" is
injected or not. So recirculation cooling is achieved which protects
the AdBlue" metering device (A67) directly attached to the EATU
(2) against damage due to overheating.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The AdBlue" mixes here with the already precleaned exhaust and
breaks down in a first process step into ammonia (NH
with the nitrogen oxide molecules (NOx) generated during
combustion the ammonia (NH ) so created flows on in the exhaust
3
flow to the SCR catalytic converter (4). Its honeycomb structure
has a special coating which allows conversion of NH
harmless nitrogen (N ) and water vapor (H
2
W14.40>1598>79
Exhaust temperature sensor
downstream of SCR catalytic
converter
AdBlue" fill level
sensor/temperature sensor
Drive train CAN
SCR delivery pump
). Along
3
and NOx into
3
O).
2