On-board electrical system
Networking
77
Introduction of the New E-Class, Model Series 212 Sedan
b
Consumer shutoff
In order to prevent complete discharge of the on-
board electrical system battery in all driving cycles,
the on-board electrical system voltage is continuously
monitored by the battery sensor and evaluated by the
rear SAM control unit. The operating rate of the alter-
nator is also monitored.
In phases where the alternator can no longer supply
the demands for electrical power, the on-board elec-
trical system management system employs a dynamic
load management function to reduce the load on the
electrical system by successively shutting down
convenience functions (consumer shutoff).
This guarantees a positive charge balance and
ensures that starting ability is preserved. As soon as
the power supply is sufficient, the consumer shutoff is
revoked accordingly.
Dynamic idle speed increase
The dynamic rpm increase is intended to adjust the
idle speed of the engine so that no power is drawn
from the on-board electrical system battery while
idling. Accordingly, when consumer load is high, a high
idle speed is set. In contrast to the previous rpm
increase function, which takes effect when the voltage
drops below a given limit or when a certain consumer
shutoff stage is reached, the dynamic idle speed
control acts preventively. Therefore it does not react
to a lack of electrical energy, but determines in
advance the necessary idle speed for the current load.
The required idle speed increase is computed via the
on-board electrical system control in the rear SAM
control unit and forwarded to the CDI or ME-SFI
control unit. This calculates the idle speed that is actu-
ally required, taking into account various engine char-
acteristics.
P54.10-3112-00
Main components of on-board electrical system, shown on the E 250 CDI
B95
Battery sensor
F32
Front prefuse box
G1
On-board electrical system battery
G2
Alternator
N3 / 9 CDI control unit
N10 / 2 Rear SAM control unit with fuse and relay
module
– This printout will not be recorded by the update service. Status: 01 / 2009 –