Mercedes-Benz OM 471 Introduction Into Service Manual page 70

Function
The EGR rate describes the relationship of recycled quantity of
exhaust to the quantity of fresh air. It is determined over the
engine management (MCM) control unit (A4) that the mass of
actually suctioned in or supercharged fresh air and the mass of
actually recycled exhaust are correlated with one another.
Regulation of the EGR rate takes place over the exhaust gas
recirculation positioner (Y621) which opens or closes the throttle
valve (5) in the EGR line (6) over the adjustment lever (4) and
therefore regulates which quantity of exhaust is added.
The branched off exhaust initially flows through the exhaust gas
recirculation cooler (1) attached to the coolant circuit. Here
cooling takes place from a temperature of about 650∞C down to
about 170∞C.
Component description for engine
management (MCM) control unit
Component description for charge air
pressure and temperature sensor in charge
air pipe
Component description for charge
temperature sensor in charge air housing
Component description for EGR
differential pressure sensor
Component description for exhaust gas
recirculation controller
Component description for exhaust gas
recirculation cooler
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >
– This printout will not be recorded by the update service. Status: 09 / 2011 –
The AGR rate can be increased by the cooling since the density
and therefore the mass of the recycled exhaust is increased.
Furthermore the added quantity of cooled exhaust causes a
reduction in the NOx emissions by the lowering of the combustion
temperature.
Once the exhaust has passed through the exhaust gas
recirculation cooler (1), it passes through the EGR line (6) into the
charge air pipe (7). It is mixed here with the fresh air coming out
of the charge air cooler and then led to the individual cylinders for
combustion.
A4
B608
B617
B621
Y621
Functions
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