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Over
the past ten years or so, electronic systems have
proliferated in all
aspects of vehicle design, including mechanical
systems (engines,
automatic gearboxes, suspension, ABS, etc.), safety
systems (airbags,
transponders, etc.) and passenger comfort systems (air
conditioning,
radio, etc.). At the same time, a need has
developed for on-board
systems to be able to communicate with each other.
This has made the
use of multiplex electrics essential.
Introduced
on a trial basis with the XM in 1994, multiplex
electrics were first
applied on the Xsara Picasso. The C5 takes the concept
one stage
further with four separate and interdependent networks
in which twenty
modules and the built-in systems interface (BSI) are
linked by
harnesses referred to as “buses”.
Multiplexing
brings the following major advantages :
-
Greater
reliability and simplification of the electrical
system, through the
reduction in the number of connecting wires (-30 %
compared with an
individually wired system).
-
Greater user
functionality, through permanent dialogue between
all the units concerned and the BSI.
The
built-in systems interface (BSI) controls the entire
system through
software running on a microprocessor. This unit
centralises incoming
data, decodes it and executes the corresponding orders
by sending out
messages in binary format. These messages are coded so
that they can
only be read by the unit to which they are addressed.
The unit also
provides a bridge between the various networks and
transmits diagnostic
information from other units.
In
addition, the built-in systems interface reduces
energy consumption by
running all the multiplexed controller units in
low-power mode whenever
possible. The bus carries data between the
built-in systems interface
and the other modules in both directions over a single
communication
link.
The twenty
modules (electronic control units) are interconnected
by the following four networks :
-
The
Controller Area Network (CAN) carries short
messages at high speed
(e.g. engine speed and vehicle speed data for
engine, automatic
gearbox, suspension and ABS / ASR modules).
-
The
passenger comfort Vehicle Area Network (VAN)
transmits long messages at
medium speed for the instrument cluster, display,
radio, CD
autochanger, air conditioning system, navigation
system and parking
assistance system.
-
The
bodywork VAN (consisting of two distinct networks)
controls reliable
operation of eight modules : the steering column
controls, lighting and
signalling indicators, airbags, left and right
electric windows, alarm,
sunroof and particle filter.
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