Mercedes-Benz OM 651 Service Manual page 29

Charging
Boost pressure control during wide open throttle operation as of 2,800 rpm
The LRK is fully open as of an engine speed of
2,800 rpm. This causes almost the entire flow of
exhaust gas to be fed nearly without loss to the low-
pressure turbine via the bypass duct and limits the
level of exhaust back pressure.
This procedure means that the HD-Lader no longer
makes any contribution to increasing the boost pres-
sure. The HD-Lader has reached its choking limit. This
means that it can no longer generate boost pressure
and, in the event of further loading, the turbine speed
would drop off significantly.
Schematic illustration of boost pressure control during wide open throttle operation as of 2,800 rpm
A Intake air
B Exhaust flow
1 High-pressure turbocharger
2 Low-pressure turbocharger
3 Boost pressure control flap (LRK)
28
Introduction of New Generation of 4-Cylinder Inline Engines, OM 651
q
4 Wastegate
5 Charge air bypass flap
6 Air filter
7 Charge air cooler
8 Throttle valve actuator
9 Intake manifold
– This printout will not be recorded by the update service. Status: 09 / 2008 –
In order to prevent pressure loss and additional
warming of the charge air as it flows through the high-
pressure compressor, the charge air bypass flap is
opened so that the main part of the air flow is guided
to the charge air cooler along a direct, low-loss path.
The wastegate is used to regulate the turbine output
of the low-pressure turbine in the engine performance
map as required and depending on the load condition.
Depending on the load condition, the HD-Lader can
build up a high level of boost pressure at low engine
speeds and prevent overload of the ND-Lader at high
engine speeds.
10 Exhaust manifold
11 Exhaust gas recirculation (EGR)
pre-cooler
12 EGR actuator
13 EGR cooler
14 EGR bypass flap