Saab 9-3: Body Structure & Systems

Built on a Solid Foundation

• New standards in torsional rigidity
• New jointing technique adds strength
• Second-generation “crash boxes” prevent body damage
• Aluminum hood
• Unique halogen headlamps
• Bi-xenon headlamps
• Powerful windshield washing system

“This is the strongest structure we’ve ever produced. It was developed in close cooperation with the design, chassis and safety departments who all had their own specific requirements.”
– Kerry Andersson, Project Leader, body in white

The body structure of the new 9-3 Sport Sedan is the stiffest yet produced by Saab engineers and it is the solid foundation on which the car’s exemplary handling, ride and safety characteristics are built.

The use of high-grade steels, laser welding, and galvanizing of all external components and advanced joint techniques has produced an extremely strong and durable body. Effective “crash boxes” in the front bumper help to minimize body damage in low-speed impacts, up to approximately 9 mph.

The power of the lighting system, which includes the option of bi-xenon headlamps, as well as the efficiency of the windshield wipers and washing systems continue to uphold Saab’s reputation for safety.

Structural benefits
An exceptional level of structural stiffness was a top priority in the design of the new 9-3. It is high torsional rigidity that helps give that reassuring rock-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.

A stiff body is also a prerequisite for the work of chassis engineers. The car’s handling can only be effectively honed through its suspension and steering if the structure on which all these components exert force is solid and predictable.

Finally, but probably most importantly, 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 help prevent energy from reaching it.

Structural strength
A four-door sedan body is inherently stronger than a five-door hatchback format because there is no large rear tailgate opening. This design, and advances in technology, contributes to the 9-3’s exceptional torsional rigidity of 5,000 lbs. per degree of deflection, which is more than double that of its predecessor. To put that figure into perspective, the body structure is as strong as a meter-long rod, fixed at one end, that would bend just one degree under the weight of fully-laden large car – or a small elephant – placed on the other end!

The Saab design team has adopted unique bracings above the rear wheel housings to provide a structure that is more than a match for premium-class competitors, despite some potential loss of stiffness through having the versatility of a split/folding rear seat.

While 59 percent of the new 9-3’s body weight is composed of high-strength or ultra-high-strength steel, a far more important consideration is how all the elements – 332 structural body parts are used in the new 9-3 – are connected. In other words, how they interact in sharing the load-bearing task. The strength of a good design is far more than simply the sum of its parts.

The body of the new 9-3 is essentially a monocoque construction fabricated from beams and pressings. Saab structural engineers have used CAD techniques and finite element data models with a resolution of up to 500,000 cells representing the new 9-3’s structure.

Special attention was devoted to the design of seams and joints. It is pointless using high-strength steel for different sections if the technique used to join them together is not at least as strong. For example, there are no joints at any of the corners of the safety cage, where stresses are likely to be greatest. Instead, joints between beams are carefully welded in place with overlaps of at least 20 mm on straight sections.

In order to be sure that extra strength does not necessarily mean extra weight, Saab engineers have made great use of new technology in using “tailored blanks” for large structural components. For example, the two main bearers that extend from the front of the car to the rear bulkhead are made from pressings of high-strength steel. These are produced in different thicknesses, according to the localized loading demands at any point in the car’s structure. The extra strength or weight is located only where it is required.

Outer body
Both front and rear bumper assemblies are designed to be “self-repairing,” in that they can absorb impacts up to 5 mph, minimizing damage and the need for repair. The bumper “skin” is simple and quick to replace after a minor collision – a very practical benefit in minimizing the nuisance and cost of “parking lot” incidents.

For higher speeds, Saab was first to introduce deformable “crash boxes” behind the front bumper on the second generation Saab 900 in 1993. These are intended to absorb and contain relatively low-speed impact forces in order to prevent damage to more expensive bodywork components.

Other manufacturers have now adopted crash boxes, and in the new Saab 9-3 the technique is perfected still further. More than 100 computer simulations were carried out to ensure their effectiveness – a testimony to the extreme attention to detail that went into finalizing the new 9-3’s structures.

The finished design is a hexagon shape with a conical profile and “accordion” sections that are designed to protect the structure of the car, including its front body panels, from damage in impacts up to about 9 mph. The boxes are now also bolted, instead of welded, to the front beam to make their replacement even easier.

Where there are no structural demands, Saab engineers were able to consider the further use of weight-saving materials. For the new 9-3, they have adopted aluminum for the hood, saving 50 percent or 20 lbs. in weight compared to steel. It is also slightly stiffer and more resistant to dents.

The design of the trunk lid was also the subject of detailed research and the solution adopted is typically Saab. For users of the new 9-3 to be able to exploit the load carrying capabilities of a 60/40 folding seat, it was important that trunk opening be as large as possible. That is why the design team chose “swan neck” hinges for the once-piece trunk lid.

The use of a more conventional strut and multi-link pivot arrangement would have resulted in an unacceptable 4-inch, or 15 percent, reduction in opening width. The compact, spring-loaded “swan-neck” hinges, in fact, provide an even easier, almost weightless opening and closing action.

The doors are inset-mounted, as part of the monoside body pressing. With substantial ultra-high-strength steel reinforcements, they play an important occupant protection role. A particular feature of note is the way the bottom edge of the door frame overlaps and interlocks with the strong, reinforced side sills. This allows the doors to spread heavy impact forces by enlisting the support of stronger sections of the body.

Superior lighting
The strong lighting performance of Saab cars is widely acclaimed, serving as an integral element in Saab’s overall safety initiative.
The headlamps of the new 9-3 are housed within neatly integrated units. These are now molded clear plastic, which is lighter and less prone to stone chips, cracking and condensation than glass.

The standard equipment headlamps use halogen bulbs behind projector units for excellent illumination. In order to meet demanding Saab requirements, the reflector surfaces are uniquely made by the supplier, Hella, from magnesium, instead of the commonly used steel, which allows more complex shaping for better lighting performance.

New 9-3 customers can also go one step further by specifying exceptionally powerful bi-xenon lights, an option for all variants. These gas-discharge bulbs give an extremely bright, much whiter light than halogen units. Saab is among the first manufacturers to offer this technology for both low- and high-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 60 percent better spread of light.

The effective control of such a powerful beam is essential for the benefit of fellow road users, as well as the driver, which is why the bi-xenon lights have a dynamic, self-leveling function. 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 level.

The performance of the headlamps, no matter how powerful, is badly compromised if the lens becomes covered with dirt or road film. For the new 9-3, powerful spray jets with 50 psi (3.5 bar) of pressure are activated with the windshield washers, to help keep the plastic unitsclean. These automatically retract when not in use.

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, center-mount rear brake light is now an LED unit, as tests show this illuminates more quickly than a conventional bulb, giving a more efficient warning signal.

Cleaning power for visibility
Keeping a clear windshield is vital for driving safety. The 9-3’s large wipers are linked to three pairs of powerful washer jets, all working at 50 psi (3.5 bar) pressure, twice the power of most other systems on the market.

The wipers are two-speed with an infinitely variable intermittent wipe. An automatic rain-sensing operation is available as an option, including driver adjustment for sensitivity.

In true Saab tradition, the 1.3-gallon 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.