Ignition system
58
Electrical and electronic systems
Introduction of the New V12 Biturbo Engine, M 279 AMG
b
Ignition system
The ME-SFI control unit transmits the signal for the
dwell time of the relevant operating point to the
ignition coil over the actuation line (circuit 3). The
corresponding ignition coil interrupts the primary
circuit by means of an integrated fuse when the
dwell time has elapsed. From the ignition coil the
ignition voltage travels to the two spark plugs at
each cylinder and causes arcing in the gap between
the center and ground electrodes.
Operating modes of the ignition coil
Singlespark – Single-spark ignition
Usually the ignition coil is charged and an ignition
spark is generated once in each ignition cycle when
the engine is warm.
In order to reliably ignite the mixture during a cold
st
art, hi
gh-energy ignition coils are used which
provide a long spark duration.
It is also possible to use several sparks per ignition
cycle instead of just one. This system is
referred to
as multi-spark ignition.
Multispark – Multiple-spark ignition
In contrast to the single-spark mode, several sparks
are generated in multi-spark operation. Rather than
producing a succession of sparks by the single-
spark method, the coil is recharged in the mean-
time in order to provide sufficient energy for more
spar
ks.
i Note
The ignition angles can only be checked using
Xentry Diagnostics.
A multi-spark ignition cycle begins in the same way
as a sing
le-spark cycle. The coil is initially charged
to a desired target primary current. At the firing
point the charging current is switched off,
producing the ignition spark. However, in multi-
spark mode the coil is not discharged completely.
The secondary current, which is directly dependent
on the charge level of the coil, is measured
in the
coil. If it drops below the secondary current
threshold, the coil's electronic control reopens the
power amplifier and the charging current flows
again. The level of the primary current is also moni-
tored. When the primary current threshold is
reached, the power amplifier opens the primary
circuit and high
voltage is generated once more.
This causes another spark to be produced. Subse-
quent sparks are generated in the same way.
– This printout will not be recorded by the update service. Status: 06 / 2012 –
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