Body structure,
Electrical and Lighting systems
Structured Approach
• Excellent torsional rigidity
• Unique supplementary platform
• Firm foundation for improved refinement and chassis
dynamics
• Second-generation ‘crash boxes’ help prevent body
damage
• Multiplex digital signal network for fast control of
all major functions
• Powerful screen washing system
The body structure of the 9-3 Convertible is
essentially an open ‘uni-body’ fabricated from steel
beams and pressings with all external parts galvanized.
Structural engineers used CAD techniques and finite
element data models with a resolution of up to 500,000
cells to represent the car’s structure.
About 50 per cent of its 383 structural body parts are
unique to the Convertible, and 60 per cent of its body
weight is composed of high or ultra high strength
steel. However, a more important consideration is how
all the elements interact in sharing the load-bearing
task. The strength of a good design is far more than
simply the sum of its parts.
When work began on the latest Saab 9-3 product range,
designers and engineers were for the first time able to
ensure that the needs of a Convertible variant were
given the same priority as those of a sedan.
In particular, they took up the challenge of
engineering an open top car that concedes little or
nothing to the structural losses implicit in foregoing
a fixed roof. The result is a convertible that shares
the Sport Sedan’s much improved, ‘fun to drive’
handling; its solid, vibration-free running refinement
and, of course, its impressive crashworthiness. A
strong body, stiff in torsion, was an absolute
pre-requisite.
The 9-3 Convertible's body structure is exceptionally
stiff and among the strongest in its class, with a
torsional rigidity of 11,500 Nm/degree of deflection.
It is high torsional rigidity that helps give that
reassuring ‘hewn for solid’ feel, which is communicated
every time a door is closed or the car negotiates a
poor road surface. And it makes a major contribution to
eliminating squeaks and rattles, vibrations and
resonances.
Chassis engineers also demand a stiff body because the
car’s handling can only be effectively honed through
the control of its suspension, wheel and steering
movements if the structure, on which these components
exert loadings, is solid and predictable.
Finally, the car’s ability to withstand a heavy impact
is largely due to the strength of its passenger
compartment and the ability of the structure’s crumple
zones to prevent energy reaching it.
‘Twin’ chassis architecture
To achieve their goals for the
Convertible, engineers have successfully installed what
is, in effect, a second or ‘parallel’ structure within
the car's platform: an additional, completely linked
‘ring of steel’, extending from the front to the rear
of the car.
The most important element of this new structure is a
large closed casing, known as the ‘torsion box’,
located between the rear wheel housings, immediately
behind the rear seat and ahead of the soft-top stowage
compartment. It helps compensate for the loss of
rigidity as the ‘C’-pillars are no longer connected by
the beams of a fixed roof.
The bottom of the torsion box is welded to another
completely new large pressing, a combined rear seat
beam and floor which also forms the boot well. This is
another important link in the structure and, like the
torsion box, is welded at each side to the first of two
rear inner side panels which, in turn, connect with the
lower B-pillar and side sills.
Enlarged side sills, unique to the Convertible, are
further major components of this ‘second chassis’. They
are 32 mm higher and 8 mm wider, with a 25 per cent
larger cross-section, than those of the sedan. They are
made even stronger by the addition of an internal
longitudinal plate running the whole length of the box
section. The three cross bracings are also good for
impact resistance.
Forward of the side sills is another crucial area,
connecting the sill, the base of the A-pillar, the
bottom of the front bulkhead, the sub-frame mountings
and the floor. This is heavily reinforced through a
structure of four carefully shaped steel pressings.
The upper A-pillars, together with the windshield
header rail, provide rollover protection as well as
structural strength and are made from no less than four
longitudinal steel members with short, strategic cross
bracings. The header rail is also reinforced,
consisting of three layers of steel. The whole combined
structure can withstand a loading of 2.2 times the
weight of the car, about 3.5 tonnes.
As the final pieces of the ‘second chassis’ jigsaw,
both the front and rear sub-frames are now bolted
directly to the body with steel collars, for extra
stiffness, instead of polymer bushes. At the rear, two
diagonal ‘V-rods’ are also bolted in position as
bracings, linking the sub-frame on each side to the
mounting of the trailing arm in the rear suspension.
A novel ‘off-set’ spot-welding technique has been
developed which can bridge a gap of 40 mm, eliminating
any potential weak links or connections where more than
two thicknesses of steel are welded together.
Outer Body
The front and rear bodywork is protected
by ‘self-repairing’ bumper assemblies, which can absorb
impacts up to 8 kph in order to minimize damage and the
need for repair. The bumper ‘skins’ are easy and quick
to replace after a minor collision. A very practical
benefit in minimizing the nuisance and cost of those
little ‘supermarket car park’ incidents.
For higher speed impacts, Saab was first to introduce
deformable ‘crash boxes’ behind the front bumper
(introduced on the second generation Saab 900 in 1993).
These are intended to absorb and contain relatively
‘low speed’ impact forces, preventing damage to more
expensive bodywork components.
Other manufacturers have now adopted crash boxes but
for the new 9-3 program, Saab has perfected the
technique still further. No less than 103 computer
simulations were carried out to ensure their
effectiveness. The finished design is an octagon shape
with a conical profile and ‘concertina’ sections that
will protect the structure of the car, including its
front body panels, from damage in impact s up to 15
kph. The boxes are bolted and lightly welded to the
front beam to make their replacement simple.
For the 9-3 series, an aluminum hood has been adopted,
saving 50 per cent, or 9 kilos, in weight compared to
steel. It is also slightly stiffer and more resistant
to dents.
Electrical architecture
All major mechanical and electrical
functions in the 9-3 Convertible, including numerous
driver and passenger comfort features, are precisely
and reliably controlled through an advanced digital
signal network.
The entire electronic and electrical network uses
databus transmission – often referred to a
‘multiplexing’ – to connect groups of electrical
sub-systems and to pass on signals from all the car’s
sensors. In this way, a CANBUS (Controller Area
Network) uses just one or two wires with
microprocessors, transistors and LEDs (Light Emitting
Diodes) to replace a complicated wiring harness and all
its associated relays, switches and bulbs.
CANBUS technology offers great benefits in weight
saving, reliability and data transmission capacity. It
is used to connect all the main subsystems: powertrain,
chassis, body, ‘infotainment’, telematics, navigation
and climate and comfort.
Fast networking
A battery of sensors are the ‘nerve
endings’ of the new 9-3 Convertible and the data they
provide is dispatched as packages of digital signals,
or ‘buses’, along three information ‘highways’,
stopping where required at 44 sub-stations, or
microprocessors, for analysis and subsequent action.
A powerful control module governs each of these
highways and their substations; all three integrated
with each other to ensure there are no ‘traffic jams’
or conflicting requirements. If all this functionality
were achieved using a traditional, complex wiring
harness, it would weigh twice as much, more than 40
kilos, and be twice as long, at 1,600 meters!
A single wire highway, or ‘low speed’ Bus, with a
capacity of 33 kbits per second, connects functions
within the car: the ignition switch, steering column
lock, airbags, the main instrument panel, interior
lighting, doors, mirrors, windows, the soft-top, the
security alarm, gear shift position and, where fitted,
electrically-operated seats and parking assistance.
Powertrain control, engine management systems, ABS,
TCS, ESP® and related functions are all connected by a
dual wire, ‘high speed’ Bus, with a transmission
capacity 15 times greater at 500 kbits per second.
The third highway is utilized by all three audio system
options, the GPS navigation system with DVD reader and
the advanced voice recognition (AVR) function. These
systems are described further in the ‘Interior Design
and Features’ section.
The fast moving world of information technology is
likely to place increasing demands on the ‘in-car’ time
of drivers and passengers and the latest Saab 9-3
series is configured to accommodate all likely future
developments in digital communication to and from the
car.
Superior Lighting
The strong lighting performance of Saab
cars is almost as widely acclaimed as their reputation
for safety. Hardly surprising, as good night-time
visibility is, of course, an essential element of
driving safety.
The headlights of the 9-3 Convertible are housed within
neatly integrated units made from molded clear plastic,
which is lighter and less prone to damage from stone
chips, cracking and condensation than glass.
The standard equipment headlights use halogen bulbs
behind projector units to give excellent illumination,
while customers can also go one step further by
specifying exceptionally powerful bi-xenon lights..
These gas discharge bulbs give an extremely bright,
much whiter light than halogen units and Saab was among
the first to offer this technology for both dipped and
main beam – hence the term, bi-xenon. Where a normal
halogen bulb will emit 1,500 lumens of lighting, a
xenon unit will give 3,200 lumens, more than twice as
much power, giving a spread of light 60 per cent
better.
The effective control of such a powerful beam is
essential for the benefit of fellow road users, as well
as the driver, and bi-xenon lights have a dynamic,
self-leveling function as standard. Under acceleration
or braking, sensors detect body motion at the front of
the car and electric motors in the headlamp units
automatically adjust the height of the beam to
compensate for any changes in attitude of the body. As
a further refinement, steering linked bi-xenon lights
can also be specified to give an improved field of
vision when cornering.
The performance of the headlamps, no matter how
powerful, is badly compromised if the lens becomes
caked in grime. Powerful spray jets, working at 3.5 bar
pressure, keep the plastic units clean.
At the rear of the car, the single fog light
automatically disconnects when the ignition is switched
off, an added precaution to prevent it being
inadvertently left on when no longer necessary.
The high level brake light on the top edge of the trunk
lid is an LED unit, which illuminates more quickly than
a conventional bulb, thus giving a more efficient
warning signal.
High powered cleaning
Keeping a clear windscreen is vital for
driving safety and the large wipers are linked to a
powerful battery of three pairs of washer jets, all
working under high pressure with twice the power of
other systems on the market. It is cleaning power
designed to shift the most stubborn of deposits.
The wipers are two speed with an infinitely variable
intermittent wipe. An automatic rain-sensing function
is available as an option, including driver adjustment
for sensitivity.
In true Saab tradition, the 5.0 liter washer reservoir
is exceptionally large, with two liters more capacity
than normal. User trials show that jets working at such
high pressure do not, in fact, require more washer
fluid because they are generally used in shorter
bursts.
Next page: Safety