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Lightweight design as a priority

The body

Audi's design engineers have also made considerable progress regarding the supporting structure of the new A4. The new body is no less than 45 percent more rigid than that of its predecessor. The car's acoustic quality is consequently just as outstanding as its dynamic behaviour. And last but not least, the A4's crash safety also benefits from the particular rigidity of the structure.

Lightweight construction index: high rigidity, low weight

Revolutionary vehicle concepts like the aluminium Audi Space Frame have demonstrated the importance Audi attaches to lightweight design. But weight can also be reduced effectively using a modern steel construction. The term "lightweight construction index" indicates just how frugal - and efficient - the new Audi A4 is when it comes to saving weight.

This category describes the relationship between body structure weight and the product of tyre contact area and torsional rigidity.

In other words, the lower the absolute value, the more efficiently a body structure translates weight into rigidity. And this is one area in which the new A4 clearly outshines the competition. It has a lightweight classification of 2.91 - the previous best value was 3.02.

Rigid structures for maximum safety

The use of special material grades also makes a vital difference. The body of the new Audi A4 is based on a unitary steel structure with integrated aluminium components. The percentage by weight of the lightweight materials aluminium and magnesium and of plastics has risen significantly; the proportion of steel and iron on the new A4 has been cut by as much as 7.5 percent compared with its predecessor.

A further decisive measure for weight reduction is the expansive use of high-strength and very high-strength sheet-metal panels, which make up a total of 45 percent of the bodyshell weight - an outstanding achievement, not just in this vehicle category. These special sheet panels are used primarily in the front end of the new A4 where the main priority is to absorb impact energy as effectively as possible in a frontal crash.

As a protective cage, the occupant cell must also make sure that deformation and intrusion are minimised in a crash. Three large tailored blanks in the floor area perform part of this task.

The advantage of this special technology is that the generally large-format tailored blanks can be structured in such a way that high wall thicknesses are only used in areas subjected to particularly high loads; a reduction in weight and a rigid structure can thus be effectively combined. In all, ten large tailored-blank components are used on the new Audi A4.

Aerodynamics and aeroacoustics

Shaped by the wind

In the field of aerodynamics, absolute drag coefficient records are no longer the sole measure of all things. But Audi vehicles still abide by the motto that optimum aerodynamics improves economy like virtually no other factor.

With a drag coefficient of 0.28, the new Audi A4 also fulfils this requirement, bettering its predecessor by a factor of 0.02.

The aerodynamic underbody

Faired underbodies have already proven just how effective they are, particularly in motor sport. However, considerable detailed development has to be carried out before they can be used on production vehicles, especially as conventional wind tunnel technology does not offer the appropriate testing capabilities.

Hardly any wind tunnel was previously able to include the rotation of the wheels and moving belts under the vehicle to simulate the road in its analysis. Things are different at the new Audi wind tunnel centre in Ingolstadt, where innovative test rigs, some of which are equipped with a glass floor, enable detailed analyses of the flow of air under the vehicle.

The aerodynamics engineers were thus actually able to develop a predominantly smooth, low-drag underbody.

The aerodynamic underbody also helps to reduce wind noise: the overall level in the interior has been cut by no less than 3 dB (A).


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