Mercedes-Benz OM 471 Introduction Into Service Manual page 67

Functions
Brake stage III
14 Cylinder 1...3 oil duct
15 Cylinder 4...6 oil duct
In brake stage III the brake power is reached by all cylinders and
through an additional increase in the internal pressure of the
cylinder.
As soon as the brake stage III is activated by the driver over the
engine brake switch the initial reaction is for the same processes
as for brake stage II to be triggered. In addition to the now fully
switched>in decompression brake also the wastegate valve on the
turbocharger (17) as well as the exhaust gas recirculation
positioner (Y621) are actuated.
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Additional functions of the engine brake system
Providing support during shift operations
The engine brake is automatically activated for all normal shift
operations without the driver having to do anything. Activation
of the engine brake significantly lowers the rotational speed
between the individual shift operations whereby more rapid
synchronization is achieved, which in turn leads to a more rapid
acceleration of the vehicle.
The engine management (MCM) control unit (A4) uses the
following parameters as a controlled variable:
f Oil temperature
f Differential speed
f Boost pressure
The brake stages I...III are activated based on these.
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17 Turbocharger
Y621 Exhaust gas recirculation positioner
– This printout will not be recorded by the update service. Status: 09 / 2011 –
Y624 Engine brake solenoid valve, stage 1
Y625 Engine brake solenoid valve, stage 2
In this way a situation is achieved whereby the internal pressure of
the cylinder is increased during the compression stroke > which
results in a higher braking torque.
The engine management (MCM) control unit (A4) uses the boost
pressure and the turborcharger speed as controlled variables.
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Supporting stopping the engine
If the ignition is switched off and the injected fuel quantity = 0,
the engine brake is automatically activated without any action on
the part of the driver. The compression is strongly reduced
through opening the exhaust valve so the engine can "slowly
come to a halt" and not be shifted between two ignition TDCs by
the compression.
This function is only effective for oil temperatures below about
70∞C. In the case of a warm engine it is, therefore, possible that
the engine tangibly "shakes" when stopping.
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