Networking Of Control Units; Function Of Exhaust Aftertreatment System (Overall System) - Mercedes-Benz OM 471 Introduction Into Service Manual

Functions

Networking of control units

A3 Drive control (CPC) control unit
A4 Engine management control unit
(MCM)
A57 NOx sensor control unit output for
exhaust aftertreatment unit
A58 SCR control unit (in pump module)
A60 Exhaust aftertreatment (ACM)
control unit
A70 NOx sensor control unit input for
exhaust aftertreatment unit

Function of exhaust aftertreatment system (overall system)

The basic functionalities of the overall EATS are monitored and
controlled by the engine management (MCM) control unit (A4)
and the exhaust aftertreatment (ACM) control unit (A60).
After the engine is started, the engine management (MCM)
control unit (A4) automatically starts an automatic test routine in
the background, which checks the operational readiness of the
EATS. Once the system has been enabled, the SCR control unit
(A58) integrated into the pump module (2) is actuated. This
switches on the SCR delivery pump (M25) in the pump module (2),
which then sucks in AdBlue" from the AdBlue" container (3) and
pumps it over the AdBlue" feed line to the AdBlue" metering
device (A67).
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Phase 1: Conversion of CO and HC in the diesel oxidation catalytic
converter
The exhaust gas coming from the exhaust manifold initially flows
through the EATU (4) into the diesel oxidation catalytic converter
(7). In it, the given hydrocarbons (HC) and the carbon monoxide
(CO) are converted to carbon dioxide (CO
Apart from this, a part of the nitric oxide (NO) is oxidized to form
nitrogen dioxide (NO ).
2
Phase 2: Reduction of particulate mass in the diesel particulate
filter
The diesel particulate filter (8) is connected in series after the
diesel oxidation catalytic converter (7). In its porous filter structure
the particles are separated through adhesion and then collected.
Phase 3: Reduction of NOx in SCR catalytic converter
The AdBlue" injection into the exhaust flow is calculated by the
engine management (MCM) control unit (A4). If AdBlue" is to be
injected, then this initially sends a signal to the exhaust
aftertreatment (ACM) control unit (A60), which processes the data
and then actuates the SCR control unit (A58) integrated into the
pump module.
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) and water (H O).
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Because the AdBlue" injection into the exhaust flow is not
continuous, the AdBlue" flows over the AdBlue" return line back
into the AdBlue" container (3). This circulation is continuous, and
irrespective of whether AdBlue" is injected or not. This enables
recirculation cooling to be achieved, which prevents the AdBlue"
metering device (A67), which is installed on the EATU (4) itself
against damage due to overheating.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The injection timing point and the injection quantity are now
calculated here and the AdBlue" metering device (A67) actuated
accordingly.
If AdBlue" is injected, the following happens:
The AdBlue" metering device (A67) located in the exhaust path
downstream of the diesel oxidation catalytic converter (7) and
diesel particulate filter (8) injects AdBlue" straight into the
exhaust flow.
The AdBlue" is mixed here with the previously precleaned exhaust
and decomposes in an initial process step to form ammonia (NH
Along with the nitrogen oxide molecules generated during
combustion (NOx), the resulting ammonia (NH
the exhaust flow towards the SCR catalytic converter (6). Its
honeycomb core has a special coating, which enables a conversion
of NH and NOx into harmless nitrogen (N
3
(H O).
2
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).
3
) flows through
3
) and water vapor
2