Saab 9-5 MY 2004
Design and Aerodynamics
Highlights:
* Distinctive bodystyling gives clear Saab brand
identity
* Sedan and Wagon developed as parallel but separate
projects
* Typical Saab ‘cockpit-like’ driving environment
* Exceptionally low levels of NVH (noise, vibration,
harshness)
* Wagon offers same comfort levels as Sedan
* Three specifications or ‘forms’: Linear, Arc, Vector,
plus range-topping Aero
* Highly competitive drag co-efficients: Sedan - Cd
0.29, Wagon - 0.32
Design
concept
The strong and sporty character of the
9-5’s exterior design immediately identifies it as a
Saab. Whilst the sedan and wagon models share the same
frontal styling, they were developed as separate,
parallel projects and have their own identities.
The overall visual concept is a modern interpretation
of traditional and distinctive Saab styling themes.
Essentially, the Saab design team wanted the 9-5 range
to have a strong, dynamic stance. “It had to be more
than just a good looking car, it had to have a soul,”
says Simon Padian, Head of Project Design. “The world
is full of look-alike cars. We didn't need another
one.”
The range exudes a robust, sporty character, reflecting
its all-turbo powertrain, with a greater emphasis on
multi-dynamic qualities for the wagon. It is positioned
towards the top of the European large car segment with
a wheelbase of 2703 mm and an overall length of 4827
and 4828 mm, respectively for the sedan and wagon.
Exterior design
In its frontal appearance, the new Saab
9-5 looks wide and low with the grille, headlamps and
bumper flowing smoothly together. The shape of the
headlamps and side indicator lenses and the adoption of
a ‘clamshell’ hood design, echo design details from
earlier Saab models.
In side elevation, the body and window lines rise
upwards to create a typically-Saab, wedge-like profile,
including the ‘teardrop’ shape of the side windows. The
curvature of the ‘C’ pillar, which is also a prominent
feature in the wagon, is another key Saab identifier.
At the rear, the ‘D’ shape of the sedan’s back window
is again reminiscent of earlier Saab designs. The boot
lid, with a subtle rear lip, is relatively short but
high enough to prevent the airflow detaching too early,
reducing drag and increasing the height of the luggage
compartment. The ‘cut out’ shape of the rear light
clusters is another classic Saab styling cue.
From the B-pillar rearwards, the wagon’s styling is
unique. This includes the roof and rear doors and it
was an essential requirement in order to give the wagon
its own identity, without any compromises. “Whilst
there is a strong link between the two models, it was
important that the wagon should not just be seen as
simply an add-on variant,” says chief designer Simon
Padian. “ That would have been impossible if we had
retained the rear doors and roof line of the sedan, as
many manufacturers are inclined to do. There are no
awkward angles or add-on solutions with our wagon.”
To emphasis its sporty character, the wagon adopts a
markedly raked rear window. And to break up the length
of the car and to give it a strong waistline, the
prominence of the ‘C’ pillar is further emphasised by
the distinctive ‘wraparound’ rear window, which appears
to merge with the side windows by concealing the ‘D’
pillars. “To do justice to the fine qualities of the
chassis, it was essential to move away from the
traditional box-like shape of a load-carrier,” explains
Padian.
Interior design
The spacious interior of the new Saab 9-5
has been designed to give the driver a feeling of being
totally in command and to offer passengers exceptional
standards of comfort. The soft curves and fluid
‘organic’ shapes complement the exterior styling and
the overall effect is very different from the
relatively cold and clinical interior design themes
adopted by Saab’s premium class competitors.
The cockpit-like main instrument console curves around
driver and downwards towards the ignition key,
handbrake and electric window controls. The scalloped
door panels and sweeping curves of the interior
upholstery echo the shape of the fascia. The low-level
cinema style interior lighting creates a warm and
welcoming atmosphere. The quality of materials and
their fit and finish is everything you would expect in
a car of this class. The tactile satisfaction in simply
operating the controls and the great attention to
detail - as evidenced by the superbly designed fascia
air vents – follows a fine Saab tradition.
To produce an adaptable and comfortable driving
position, the interior designers started from a single
fixed point of reference - the heel of the right foot.
Numerous computer simulations then developed the most
natural and comfortable operating arcs and reach zones
for different-sized driver, in combination with all
possible seat locations and positions for the steering
wheel, which adjusts for reach and height.
All controls are black, except the door release levers,
which are chrome so that they are easier to find in the
dark. Most of the other controls are illuminated and
identified by easily-understood graphic symbols.
The layout of the instruments and controls is
straightforward and logical. Those most commonly used
are nearest the driver to view or operate. All dials
are white on black and green instrument illumination is
preferred at night as this is more restful for the
driver.
The ignition switch is mounted just where you would
expect to find it in a Saab - down between the front
seats alongside the handbrake. It is located there for
good reason: it cannot damage the driver’s knee in the
event of a heavy crash; it makes good ergonomic sense
because the handbrake is nearby and it also serves as a
reverse gear lock for additional security.
Seating
Comfort
Saab cars are widely-acclaimed for their
supportive and comfortable seats and the 9-5 follows
this tradition.
The front seat structure provides good back and under
thigh support for long journeys, as well as high levels
of crash protection. Seating comfort is one of the main
reasons why Saab cars have earned a reputation among
drivers as superb long distance tourers. The padding is
soft enough for good comfort, but firm enough to
support occupants securely. Extremely high quality trim
materials, a textile fabric weave or leather, are used
to combine comfort with long-term wear resistance.
Electrical heating is available for rear as well as
front seat occupants.
he driver’s seat has a wide range of adjustments for
reach, height and back-rest rake. Electrically-operated
adjustment is also available for both front seats, with
three memories that record all the adjustments chosen
for the driver’s seat, including the door mirror
settings. This is a useful feature when more than one
person regularly drives the same car. The front seats
are also fitted with Saab Active Head Restraints
(SAHR), a unique Saab-developed safety feature that
automatically reduces the risk of neck injury in a
severe rear-end crash (see Safety Section).
Cabin
Refinement
The new Saab 9-5 benefits from extremely
low interior noise levels. This has been achieved
through the excellent aerodynamic properties of the
body, its fine structural properties and the scientific
application of sound deadening materials and special
door seals.
Almost all the unwanted noise, vibration and harshness
is attenuated by the design of the engine and
suspension mounts, while the turbocharger fitted to all
engines helps reduce exhaust noise. Porous sound
absorbent pads are applied to the engine compartment
bulkhead, hood, floor and wheel housings before the
body is painted. Extra sound insulating materials are
also applied to all sheet-metal surfaces that might be
susceptible to vibration.
To minimise road and wind noise, as perceived by those
inside, triple rubber seals are fitted to the upper
door frames and double seals lower down. All are
tubular in section to ensure they work consistently,
irrespective of any differences in air pressure inside
or outside of the car.
In the interests of cabin refinement, a great deal of
attention was devoted to the installation of the
sub-frames and the engine mounting system. The Saab 9-5
is the first Saab to use a torque-roll axis engine
installation where the vertical loads of the powertrain
assembly are separated from the torque reactions. An
additional tuned rubber-in-metal mass damper is also
installed in the steering wheel assembly to absorb
vibrations when the engine is at idle.
The wagon is designed to offer occupants the same level
of comfort as the sedan, despite the open load area
behind the rear seats, which in some cars is prone to
resonance or ‘booming’. This has been achieved by
careful attenuation of noise and vibration at the rear,
as well as the use of a substantial, foldable rear
parcel shelf, which was preferred to the more common,
but far less effective, ‘roller blind’ partitions.
Interior
specifications
There is a choice of three interior
specification levels, or ‘forms’: Linear, Arc and
Vector. The terms are drawn from the world of
architecture and each ‘form’ creates its own
distinctive ambience or atmosphere, reflecting a
typically Scandinavian flair for simple yet elegant
design. These forms are available in a ‘light room’
theme, with sand beige upholstery and carpet, or as a
‘dark room’, with zinc gray furnishings. The Aero
designation is reserved strictly for the 250 bhp
sporting flagship of the range, in sedan or wagon
format.
Linear, a straight line or base element in
architecture, communicates simple, understated
functionality and is probably closest to the design
essence of Saab. The fabric upholstery features
contrasting weaves, with thicker material for the seat
cushions, and the fascia is presented in a natural
black, anthracite color.
Arc is a modern interpretation of classic design and
adopts a natural leather theme for the seats and door
panels, with a light burr walnut veneer fascia insert.
Externally, it is distinguished by the addition of
16-inch, 5 spoke alloy wheels.
Vector is more progressive, reflecting a sportier, more
performance-orientated ethos. The interior leather
upholstery features deeply bolstered, sports front
seats in cloth/leather and the fascia is finished in
aluminum. Externally, the sporty, high-tech look is
complemented by a deeper front air dam, extended side
sills and larger, 17-inch, 6- spoke alloy wheels.
The ultimate expression of Saab turbocharged
performance is the 250 bhp Aero model. It shares the
same sports seats as the Vector, but upholstered
throughout in two-tone leather. Externally, it has
distinctive sports bodystyling; 17-inch, 5-spoke alloy
wheels inspired by the 9X concept car and a chassis
lowered by 10 mm. A stainless steel exhaust and ‘Aero’
badging on the trunk lid completes the look.
Aerodynamics
Low drag coefficients
The teardrop-shaped first Saab 92,
revealed more than 50 years ago, had a Cd value of only
0.31 but required partially covered front and rear
wheel housings to achieve it and was powered by a small
engine with minimal cooling requirements. The Saab 9-5
sedan and wagon each has a highly competitive Cd of
only 0.29 and 0.32 respectively, even though they are
much larger vehicles.
The aerodynamic development of the new 9-5 range was
such a high priority that the process started with
discussions about body shapes and styling details as
soon as the first sketches of the design proposals had
been drawn. A number of one-fifth scale models were
built in the design studios and taken to the wind
tunnel at Stuttgart University for concept testing. The
results of these preliminary investigations were then
fed back to the design team, so they could continue
finalising the shape and design details of the new car
from a sound technical base.
Unusually for the automotive industry, these early clay
models incorporated a fully detailed underbody. “Taking
the trouble to model the floorpan and suspension
components meant the initial aerodynamic values were
much closer to those we measured later on full-scale
cars,” says Håkan Danielsson, head of aerodynamic
development at Saab.
The shapes were only ‘frozen’ after a series of eight
one-third scale models were subjected to design studies
and static aerodynamic assessment. “At that stage I
walked around with the designers and discussed the
consequences of various details, not just for their
influence on the drag coefficient but for the effect on
wind noise, stability and contamination by road grime,
rain water and spray,” he explains. “We selected the
best four proposals, then merged their best features
into just two that were remodelled and taken back to
the wind tunnel to start the optimisation process.”
This air flow work focused on the breakaway points,
where the turbulent wake or localised eddies leave the
body surface, which are very important in allowing the
designer to optimise features like the windshield
angle, the height of the rear trunk lid or the shape of
the tailgate, as well as determining the most efficient
basic form.
Scale effects fully
considered
The models were then rotated by up to 30
degrees to the direction of the air flow, to reproduce
the effects of cross winds. “It is essential for us to
know the lift forces front and rear under these
conditions because we must provide stability in cross
winds as well as in still air,” adds Danielsson.
The next stage after optimisation, about 12 months
ahead of the first engineering prototypes, was to build
a full-size aerodynamic model for further wind tunnel
testing. “That way we built an early model that
included a fully representative and operational engine
bay with cooling air flow.”
This model was then taken to the Motor Industry
Research Association’s closed-section wind tunnel in
the UK for the further development of functional
features like door mirrors, spoilers, mud flaps and
noise shields and to obtain the first real values for
drag and lift coefficients.
In total, some 16 different body details were
optimised, including: the raised rear edge of hood; the
rear edge of the front wings; the windshield;
A-pillars; door mirrors;side windows; the teardrop
shaped roof profile; retracted C-pillars; D-pillars;
the rear body sides; the rear window and integrated
rear spoiler
“We spent a lot of time refining the front corners to
find the best radius to keep the air flow attached all
along the body sides,” he adds, “as well as trying to
find the best form for the C-pillar profile for the
sedan, because that’s one of the points which has a
major effect on stability. This area acts as a kind of
rudder while a distinct separation of the flow at the
rear spoiler at high yaw angles also aids stability in
cross winds.”
Under body airflow and
contamination effects
The 9-5 generates progressively less drag
as more air is allowed to flow under the floor. “We
utilised shields under the engine compartment to
maintain attached flow in this area,” explains Håkan,
“but we found it better to provide air dams instead of
shields at the sides underneath the front bumper.” A
flat plate about 100 mm long was added under the rear
bumper so the flow is reattached before it breaks off
into the rear wake, reducing contamination of the rear
end.