Mercedes-Benz OM 651 Service Manual page 27

Charging
Boost pressure control during wide open throttle operation up to 1,200 rpm
The boost pressure control flap (LRK) is almost closed
up to an engine speed of 1,200 rpm during wide open
throttle operation. In this state, the entire exhaust flow
flows over the turbine wheel of the high-pressure
turbocharger (HD-Lader) to the turbine wheel of the
low-pressure turbocharger (ND-Lader) and then to the
exhaust system.
The majority of the exhaust energy acts on the turbine
wheel of the HD-Lader, which generates the main part
of the required boost pressure. Despite the low
exhaust flow, this produces a high boost pressure
which builds up very quickly.
Schematic illustration of boost pressure control during wide open throttle operation up to 1,200 rpm
A Intake air
B Exhaust flow
1 High-pressure turbocharger
2 Low-pressure turbocharger
3 Boost pressure control flap (LRK)
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Introduction of New Generation of 4-Cylinder Inline Engines, OM 651
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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 –
The remaining exhaust energy acts on the turbine
wheel of the ND-Lader, which drives the compressor
impeller via the supercharger shaft. The ND-Lader
thus does not act as a hydrodynamic retarder. The
wastegate and charge air bypass flap are closed in this
operating condition.
10 Exhaust manifold
11 Exhaust gas recirculation (EGR)
pre-cooler
12 EGR actuator
13 EGR cooler
14 EGR bypass flap