Saab 9-5 MY 2004
Safety through Real-life experience
Highlights:
* Excellent driving (active) safety - superb driver’s
environment and forgiving chassis
* Crash safety based on real-life data from 6,000
accident investigations
* More than 40 different crash test configurations,
including truck-to-car impacts Front structure channels
impact forces along three separate load paths
* Five progressive frontal deformation zones
* Side impact protection features ‘pendulum’ B-pillar
* Saab Active Head Restraints (SAHR) to minimise
whiplash neck injury
* Protection from ‘shifting loads’
* Adaptive front airbags
* Maximum 5-star EuroNCAP crash test rating
Driving
safety – avoiding an accident
Saab engineers have regarded occupant
safety as a vital feature since the first Saab cars
were designed in the 1940s. The primary goal is to
avoid getting involved in a road accident, known as
driving - or active - safety. A high level of driving
safety ensures the driver’s environment is conducive to
allowing full control and that the vehicle’s handling
is highly responsive and predictable.
The driver’s environment within the car is becoming
increasingly congested. Research shows there are now
more than 100 functions requiring manual control from
the driver and more than 150 information inputs being
given out. Increasing traffic densities also adds
further to an already heavy workload for the driver.
To make life easier, the instruments and controls of
the Saab 9-5 are logically arranged, according to
functionality and frequency of use. And to reduce the
risk of distraction for the driver at night, Saab first
developed the 'Black Panel' instrument display and this
feature is enhanced on the 9-5 as 'Night Panel'. (see
Comfort and Convenience section).
A clean interior air supply makes for a clear head and
this is another facet of driver control that receives a
high priority. All specifications have a combined
electrostatically-charged pollen and gas and odour
absorbing charcoal filter. The dual zone, automatic
climate control, another standard feature, allows the
driver to select a temperature setting inside the car
independent from the passengers.
For secure handling, the 9-5 follows Saab tradition in
being front wheel drive and providing consistent and
very ‘forgiving’ behavior. The chassis is relatively
insensitive to driver error, allowing ample safety
margins and always conveys clear and relevant signals
to the driver: how near the limit he or she is
travelling through bends and how slippery is the road
surface. Steering precision and feel are always
consistent and stable. Saab engineers work on the basic
premise that the more the driver feels in control, the
more safely he or she drives.
In addition sound chassis dynamics, a full range of
electronic aids are also available. These include ABS
and Electronic brake force distribution (EBD) as
standard. A traction control system (TCS) and a
progressive, Saab-developed electronic stability
program (ESP) can also be specified. (These features
are described in more detail in the Chassis, Suspension
and Brakes section).
Crash
safety
As every road accident is unique, each new
product development begins with studies of actual road
accidents. For 30 years, Saab has been continually
investigating Swedish road accidents in which Saab cars
are involved. The results of the investigations are
analysed by Saab medical experts together with
engineers to pinpoint precisely which part of the car
was, for example, responsible for an injury or how
structural features behaved. By this means, engineers
receive constant feedback about how their designs
perform in real life, which they can then incorporate
in their crash, or passive, safety work.
The Saab databank of statistics now covers more than
6,000 accidents, providing a unique insight into what
really happens out on the road, not just under
laboratory crash test conditions. Saab calls its
approach ‘Real Life Safety’ because it uses information
from real world experience to help protect drivers and
passengers in Saab cars.
More than 40 different types of crash test were also
carried out during the development of the Saab 9-5,
including 18 different frontal impacts, 10 different
side impacts, three rear impacts and a number of high
g-force and other non-destructive sled tests.
Other tests included car-to-car crashes with 50 per
cent overlap at speeds of up to 65 km/h for each
vehicle (a closing speed of around 130 km/h) using Saab
production cars and competitor models from other
manufacturers. “These crashes were extremely severe and
a good example of how we reproduce real-life
situations,” says Per Lenhof, Head of Crash Safety
Development at Saab Automobile. “Car-to-car crashes are
vital in developing structures that behave predictably
in the real world.”
Not content with real car-to-car side impacts and the
various proposed side test standards for Europe and the
US, which are different from each other, Saab has also
tested the new 9-5 in car-to-truck crashes.
Crash
safety systems
As the steering column is directly
connected to the front structure, it has a unique
collapsible element above, rather than below, its main
attachment support. This allows the safety feature to
function without first breaking away, increasing its
effectiveness.
Saab engineers work on the basic principle that in the
event of a crash, the car’s structure must behave in a
predictable way, independent of the precise point of
impact. Variables such as the crash velocity and the
stiffness and shape of the object impacted should have
as little effect as possible on the outcome of the
accident.
Saab research shows that in a frontal impact there are
three criteria which must be fulfilled to achieve the
crash performance needed to provide Real Life Safety.
These involve stable deformation behaviour; the
adoption of wide longitudinal members; and the
provision of three integrated crash load paths between
the front elements and the strong safety cage behind.
Front
structure with three load paths
The front structure of the new Saab 9-5
therefore incorporates three robust impact load bearers
that are connected to each other in a unique way to
optimise and distribute crash loads efficiently,
according to a predetermined pattern.
At the front, which is the point of contact in the vast
majority of accidents, there is an exceptionally wide
and robust beam, to spread the initial forces of an
offset impact to as much of the supporting structure as
possible. At high angular impacts the shape of this
beam even causes the car to be deflected from direct
contact, further reducing the intensity of the crash
forces. This beam effectively eliminates localised high
stresses, reducing the risk of structural penetration
and increasing the time before crash pulses reach the
cabin.
The wide front beam ensures that both sides of the car
share in the deformation process regardless of which
side is actually hit, significantly increasing the
effectiveness of the total system in offset crashes.
Behind the beam are two widely-spaced longitudinal
beams with large cross-sections. They ensure that the
energy from any kind of sharp localised impact, such as
a collision with tree or lamp post, can be adequately
absorbed.
The principal load path is formed by these
exceptionally wide and long longitudinal side members
that form the front section of the body frame. They
have a wide distance between them and pass around the
sides of the engine bay to the main front bulkhead just
above floor level. The second path transmits loads at a
higher level via the wheelarch reinforcements to the
A-pillars at waistline height, where the structure is
heavily reinforced to carry the main door hinges. The
third path uses the front sub-frame to direct crash
forces to another part of the safety cage via its
reinforced and widely spaced mounting points.
“The idea behind this arose from our accident
investigations where we have seen several cases of
severe wheel contact collapsing the passenger
compartment,” says Per Lenhof. “Although it is
impossible to predict the type of crash before it
happens, we can at least predict how the front
structure will deform. The more load paths between the
point of contact and the rigid safety cage, the easier
it is to absorb the energy of the impact.”
Five progressive frontal deformation zones
The structural crash performance of Saab 9-5 has been
developed to progressively absorb the energy from
impacts at the following approximate speeds:
0-8 km/h: The self-repairing moulded plastic bumpers
absorb low speed impacts and normally need no repair.
8-15 km/h: Short, front ‘crash boxes’ supporting the
bumper deform in a controlled way with minimal body
damage. They are made from thinner gauge metal and
incorporate special pressings designed to act as
folding points.
15-30 km/h: At higher impact speeds, the load boxes
behind take progressively more of the total crash
energy, collapsing in a controlled way so relatively
little damage is caused to the body structure.
30-65 km/h: The total system starts to work,
dissipating and absorbing the crash energy through all
three load paths to dilute the intensity of the impact
when it reaches the cabin and the occupants inside.
Above 65 km/h: At high speeds, the total car will be
deformed with even the safety cage starting to be
deformed in a predetermined way that absorbs the higher
energy levels involved.
All the speeds mentioned above relate to impacts
against solid, immovable objects. When other vehicles
are involved the intensity of the crash forces is
usually about half that against a fixed barrier at the
same speed. Accidents involving actual impacts against
rigid objects at speeds above 65 km/h (equivalent to
about 139 km/h car to car) are extremely rare.
Rigid
safety cage
The safety cage provides an effective
survival space within an extremely strong structural
frame that is designed to deform in a predetermined
way, withstanding the crash forces in the most severe
accidents and never breaking apart or collapsing in on
itself.
It is an extremely rigid system of steel members that
pass around and over the front and rear seats. The
parts likely to be subjected to the highest forces are
reinforced by high-tensile steel and extra metal
thickness and all the joints are carefully designed to
resist tearing. The A and B-pillars are formed from
several layers of high strength steel and a unique
jointing process is used where the pillars meet the
roof rails. This provides very good protection in the
rare event of a rollover accident.
Side
impact protection
In side impacts, the body structure is
designed to distribute the stresses over as large an
area as possible, using all parts of the body sides and
most of the safety cage. There are strong beams in all
the doors, which also have large sill overlaps to
prevent them caving in. The side sills themselves are
reinforced and the steel used for the door beams is
four times the strength of normal steel, produced in a
special patented process.
The B pillars are designed with a predetermined
deformation behaviour that helps protect the parts of
an occupant’s body nearest to the impact. “The side
structure is designed to behave like a pendulum,” says
Lenhof. “This mechanism, together with our side airbag,
provides the optimal protection for the more sensitive
parts of the human body, such as ribs, head and chest.
We allow more deformation in the lower part of the
B-pillar to channel most of the forces down to the more
robust parts of the body.
“The upper part of the B-pillar acts like of hinge
point, so that it stays in place and allows the lower
part to move inwards. That way you get the best effect
from the side airbag which only works well if there is
a strong section for it to react against.”
Cross-members in the floor under the front and rear
seats are designed to prevent the body from being
compressed sideways and help distribute side impact
forces into more of the safety cage structure.
Saab
Active Head Restraint
Neck injuries are one of the most common
results of rear-end collisions, even at relatively low
speeds, and the front seats of the 9-5 are fitted with
Saab Active Head Restraints (SAHR), a unique safety
system pioneered by Saab which reduces the risk of
whiplash injury.
In the event of a rear-end collision, the SAHR system
effectively limits the head movement of the occupant
during the impact sequence. The SAHR system is entirely
mechanical and is based on a lever principle. The head
restraint is connected by a linkage to a pressure plate
in the backrest of the seat. In a rear impact, inertia
forces the occupant's body into the backrest against
the pressure plate which triggers a mechanism to push
the head restraint upwards and forward, catching the
head and minimising any dangerous neck movement.
The system is designed to come into operation in
rear-end collisions from speeds equivalent to a barrier
impact of 15-18 km/h. The precise activation of the
system is determined by the force with which the
occupant's back is forced against the backrest, the
magnitude of the collision forces and by the occupant's
weight. Its performance is always optimised
automatically to match the occupant in the seat at the
time and the conditions of the crash.
As the SAHR system is entirely mechanical, it needs no
repairs to restore it to operational condition, unlike
pyrotechnic systems such as air bags. After deployment,
it automatically reverts to its initial position ready
of use again.
Rear
impact and shifting load protection
The rear body provides an outstanding
level of crash protection, thanks to the same kind of
collapsible elements and reinforcements as seen at the
front. A shield around the fuel filler neck is designed
to protect it from breaking away, while the tank itself
is in the safest possible place, low down just ahead of
the rear axle.
Under conditions of severe deceleration, seemingly
innocent items stowed on-board can became dangerous. It
is, therefore, insufficient to engineer substantial
front impact resistance if those inside the car are
vulnerable to a shifting load bursting through the rear
seat from the trunk or cargo load space.
For example, in a 50 kph frontal collision with a fixed
barrier an 80 kilo load, equivalent to two full
suitcases, undergoes 30g deceleration – in effect,
weighing some 2,400 kilos, or the size of a small
elephant. Both the 9-5 sedan and wagon, therefore, have
extremely rigid seat-backs which can withstand such
forces.
Restraint systems: Adaptive airbags and five
three-point seat- belts
All five seating positions are provided with
three-point seat-belts, those for front occupants
having pyrotechnic pre-tensioners and load limiters
fitted.
The ‘adaptive’ deployment of both 65-liter driver and
145-liter front passenger airbags utilises a system of
on-board crash impulse sensing together with switches
that detect the seating position and whether or not a
seat-belt is being worn. In this way, the force of
inflation may be level 1 or level 2, depending on the
severity of the crash. Likewise, the force of inflation
can take account of how close the occupant is sitting
to the steering wheel or fascia and if a seat-belt is
being worn. Some-one sitting close to the wheel, for
example, would be better protected by a lower pressure
inflation, or level 1, and anyone not wearing a
seat-belt would always benefit from the higher
pressure, or level 2, activation.
For side impact protection, double action head/thorax
airbags are mounted in the side of the backrest of each
front seat. These 20-litre airbags have two sections –
one protecting the rib cage, which is activated first,
and the other providing head protection.
As well as placing the ignition key in the centre
console, well away from the driver's knee contact zone,
further protection is provided by an aluminium section
behind the plastic foam padding under the fascia which
gives way in high speed impacts to absorb energy and
reduce the risk of injury