Boost Pressure Control (Via Wastegate); Turbocharger Protection Function - Mercedes-Benz OM 471 Introduction Into Service Manual

Functions
Boost pressure control and turbocharger
protection function, shown code (M5Z)
Engine version Euro VI
A4 Engine management control unit
(MCM)
B608 Charge air pressure and
temperature sensor in charge air
pipe
B610 Rpm sensor for turbine wheel
(only for code (M5Z) Engine version
Euro VI)
B611 Temperature sensor downstream of
air filter (only for code (M5Z) Engine
version Euro VI)
Y636 Charge pressure positioner

Boost pressure control (via wastegate)

The engine management (MCM) control unit (A4) determines the
current boost pressure via the charge air pressure and
temperature sensor in the charge air pipe (B608).
If the engine management (MCM) control unit (A4) recognizes
that the current boost pressure is too high, it limits the boost
pressure in that it actuates the boost pressure regulator (Y636)
with an appropriate pulse width modulated signal. The engine
management (MCM) control unit (A4) can use the duty cycle of
this signal to influence the pressure (up to 2.8 bar) which should
be applied to the vacuum cell (4). The valve (7) is opened over a
linkage according to this pressure, so that more or less exhaust (D)
is passed over the bypass opening (8) on the turbine wheel (3)
depending on how far it is opened.
Since only part of the exhaust (D) hits the turbine wheel (3) the
acceleration is not so strong anymore and the boost pressure
drops.
Component description for engine
management (MCM) control unit
Charge air pressure and temperature
sensor in charge air pipe, component
description
Turbine wheel rpm sensor, component
description
Component description for temperature
sensor downstream of air filter
Component description for boost pressure
regulator
Component description for turbocharger
36
– This printout will not be recorded by the update service. Status: 09 / 2011 –

Turbocharger protection function

For vehicles with code (M5Z) Engine version Euro VI the rotor
speed of the turbocharger (1) as well as the temperature of the
intake air are monitored by the air filter (A) on the compressor
inlet to protect the turbocharger.
This occurs with the aid of the turbine wheel rpm sensor (B610)
and the temperature sensor downstream of air filter (B611).
Since these sensors for vehicles with code (M5R) Engine version
EEV and vehicles with code (M5Y) Engine version Euro VI are not
installed, the engine management (MCM) control unit (A4)
orients itself on the ambient temperature and on the altitude the
vehicle is at. The latter is determined using the installed
atmospheric pressure sensor.
Dependent on the determined values and values stored in the
characteristics maps for the turbocharger protection function the
engine management (MCM) control unit (A4) adapts the injection
which leads to a lowering of the combustion temperature.
One indirect effect of actuation of the boost pressure regulator
(Y636) can be reduction of the rotor speed of the turbocharger.
A4
B608
B610
i Only for vehicles with code (M5Z)
Engine version Euro VI.
B611
i Only for vehicles with code (M5Z)
Engine version Euro VI.
Y636
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