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