The Audi A3 Sportback: Body

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July 19, 2004

Like its three-door counterpart, the five-door Audi A3 Sportback is a paragon of what is possible in a modern steel body. It combines a high degree of rigidity – and therefore excellent vibrational comfort – with excellent occupant cell stability and efficient weight-saving design.

This synthesis is made possible by the specific use of high-strength and ultra-high-strength body panels, tailored blanks (where the thickness varies within the panel itself) and the most advanced and sophisticated joining technologies. High-strength and ultra-high-strength steel components account for over 60 percent of the Sportback’s panels.

The result is lower weight coupled with superior rigidity. And although the previous A3 was most definitely one of the best cars in its class in terms of body rigidity, the new model offers an overall improvement in dynamic flexural and torsional rigidity. A sound basis for high passive safety as well as outstanding acoustic and vibrational comfort.

Excellent vibrational comfort

A high level of local and overall dynamic rigidity in the body of the car is essential to superior vibrational comfort. The objective is to keep vibration amplitudes to a minimum at all points of the car that are relevant to comfort, such as the footwells, the area beneath the seats, and the area around the steering wheel.

The body-in-white of the A3 Sportback plays a significant role in achieving this goal. Cross-sections designed to cope with varying loads, consistently uninterrupted profiles throughout the body, and optimised structural intersections all combine in providing an optimum all-round concept. Tailored blanks are used on the body to guarantee efficient use of materials.

Modern adhesive is also used in conjunction with welding spots and laser seams together with spot-welded connections to assure firm connections between the individual components. More than three metres of laser seams serve to connect the roof and the side frame alone.

Integrated assembly components such as the hybrid front end, aluminium subframes and an aluminium cockpit support integrated in the overall structure of the body serve to enhance all-round body rigidity to an even higher level.

Stable structures for passive safety

A high standard of occupant safety is one of the obvious goals in developing an Audi – this applies equally to head-on, side or rear-end collisions, as well as to passenger safety in a rollover.

The Euro-NCAP crash striking a deformable barrier at 64 km/h and with 40 per cent overlap of the front end is an important criterion for determining the safety of a car in the most common type of accident, a head-on collision. The structure of the Audi A3 Sportback is protected in such a case by a multi-chamber aluminium cross-member with deformation elements positioned slightly further back.

Interacting with the longitudinal arms or “chassis legs”, as they are often called, the bumpers correspondingly absorb energy acting on the forward structure, to relieve the load on the passenger cell and, in particular, the footwells.

This effect is supported by the aluminium subframe bolted to the front of the car at six points, spreading out forces efficiently throughout the extra-strong floor and tunnel structure.

Within the passenger compartment, the exact coordination of all restraint systems as well as the kinematic action of the steering column and pedals keep forces acting on the occupants to a minimum. Two-stage full-size front airbags for the driver and front passenger as well as belt tensioners and belt-force limiters reduce the forces acting on the occupants’ bodies in a head-on collision. Special padding on the steering column and in the footwells as well as the foot rest and the bottom-hinged accelerator pedal protect the driver’s lower extremities, particularly the sensitive ankle and knee joints.

In a collision from the side, the occupants of the Sportback benefit from the particularly rigid structure of the bodyshell. A homogeneous contour and cross-sectional design assure a deformation characteristic that minimises the load on the occupants, especially in the area of the B-post and sill.

The central sill profile prevents any major deformation and, together with the extra-large seat cross members, provides very good support. This is particularly helpful under very substantial local loads, in a pole impact for example.

In the doors, hybrid carrier systems consisting of aluminium impact members with bolted-on steel aprons assure additional safety. In a side-on collision the carrier system rests on the sill along its full length, thus transmitting forces to the lower structure of the car with maximum efficiency.

Inside the car, side airbags enhance safety. The sideguard head airbag system, which covers almost the entire window area from the A-post to the D-post and thus significantly enhances protection for the occupants against harsh impact between the head and objects outside the car, is standard in all Audi A3 models in Western Europe.

With the airbags being rapidly filled by a hybrid gas generator and maintaining their pressure for a protracted period, passenger safety is assured rapidly and consistently, with ample safety potential also in secondary collisions.

A comprehensive sensing system with a total of six satellite crash sensors on the B- and C-posts and in the front-end support serves to activate the restraint systems with the same standard of efficiency. This ensures on-demand detection of accidents, with the occupants being efficiently protected by decelerating together with the car itself.

Over and above these benefits, the crash sensors in the Audi A3 Sportback offer additional safety in an accident by opening the central locking, switching on the hazard warning lights and interrupting the supply of fuel to the engine.

Active head restraints in the front seats reduce the risk in a rear-end collision. Activated mechanically, they move forward whenever required to reduce the gap with the occupant’s head as rapidly as possible.

The compact Audi is also protected with maximum efficiency against the effects of an impact from the rear at higher impact speed. Indeed, the A3 Sportback already meets the requirements of future standards. In other words, it withstands impact with a deformable barrier at 80 km/h and 70 percent overlap. The passenger compartment and fuel tank are located outside the primary deformation zone in this test constellation. The entire rear structure of the car undergoes deformation according to a defined pattern with the aid of extra-large support arms, and thus absorbs impact energy for extra safety.

Fine-tuning in the wind tunnel

A longer wheelbase and wider track as well as greater overall length and width than the predecessor, coupled with wider basic tyres: these modified dimensions produce a completely new aerodynamic profile for the new Audi A3 Sportback.

The number one challenge in designing the car was to maintain the very good drag coefficient despite the larger frontal area.

The most significant change made to this end was the fine-tuning of the underfloor, with its full panel extending from front to rear. Developing this kind of aerodynamic cover was of course the ideal task for Audi’s wind tunnel in Ingolstadt, with the simulation of ground effect conditions provided by belts running beneath the car, to permit highly realistic assessment of air flow below.

A spoiler fitted on the lower edge of the front bumper serves to guide the flow of air entering the underfloor area efficiently. Spoilers on all four wheels ensure that the airflow to the wheels and brake system is controlled ideally and that the brake discs are simultaneously kept largely clear of dirt.

Two large underfloor panels around the middle of the car maintain a smooth flow of air with virtually no turbulence. So-called heel-plate spoilers on the panel’s rear edge then block the flow of air beneath the body so effectively that the air flow at the car’s rear end is favourably altered.

With its drag coefficient of 0.32, the new A3 Sportback again offers advantages in terms of performance, driving dynamics and fuel economy.

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