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A lightweight Audi A5 Coupe prototype
has jettisoned over 100kg by swapping steel for advanced aluminium and
carbon fibre construction in the interest of fuel economy, emissions
reduction and handling agility. The A5 project is the latest example of
the pioneering work undertaken by the Vorsprung durch Technik brand to
extend efficiency optimisation measures well beyond the engine bay.
Taking an existing steel-bodied
production car as its basis, the A5 project car clearly demonstrates the
benefits of the aluminium Audi Space Frame (ASF) concept with which Audi
broke new ground 15 years ago, and which test beds of this kind help to
evolve and improve. Use of the ASF principle reduces the weight of a car
body by at least 40 per cent compared with conventional steel
construction, and this shows in a kerb weight of 1,310kg for the
aluminium A5 prototype, versus a total of 1,420kg for the equivalent
steel-bodied series production model.
Thanks to the significant weight loss,
achieved by mounting aluminium and carbon fibre-reinforced plastics onto
the aluminium Audi Space Frame (ASF), the A5 prototype is able to use a
four-cylinder engine with its attendant economy and emissions advantages
to deliver the performance of a higher output V6.
With the acclaimed 2.0-litre, 211PS
Turbo FSI engine, the A5 achieves a power-to-weight ratio of 161PS per
tonne. For comparison, the ‘standard’ A5 3.2 FSI V6 quattro with 265PS,
which tips the scales at 1,540kg, shades it only by a fraction at 172PS
per tonne.
The lightweight design of the test car
not only enables a smaller engine to supplement a larger one with no
impact on performance and gains in economy and emissions, but also has a
knock-on effect on ancillaries such as the brakes and transmission,
which can also be reduced in size and weight. It also enables the car to
change direction noticeably more keenly and nimbly and, thanks to the
reduction in unsprung weight, to ride with even more refinement.
15 years of lightweight
construction experience
Over the past 15 years, Audi has employed the ASF principle in two
generations of A8 luxury saloon, in the hyper-efficient,
ahead-of-its-time A2 compact hatchback and in the celebrated R8 super
car. ASF has also been re-interpreted in the creation of the latest TT
Coupe and Roadster, which feature advanced steel and aluminium ‘hybrid’
construction that allows for outstanding weight distribution.
“One of our most enduring aims for the
future is to reverse the weight spiral,” says Michael Dick, Member of
the Board of Management of AUDI AG responsible for Technical
Development. “Lightweight design is the foundation of our entire
approach to improving efficiency.”
Lightweight design is a strategic
responsibility at Audi. It makes a significant contribution to dynamic
potential and efficiency, helping to conserve resources and reduce
operating costs. The electric drives of the future will add additional
weight to the car and will initially only offer a limited range, making
systematic lightweight design all the more important.
ASF: the reversal of the
weight spiral
The reversal of the weight spiral that Audi initiated with the ASF
principle which began with the Audi A8 of 1993 has major efficiency
advantages. Every 100kg saved reduces fuel consumption by 0.3 to 0.5
litres per 100 kilometres, corresponding to a reduction of 8 to 11 grams
of CO2 per kilometre. A lighter body is also the starting point for
weight reductions on other parts of the car, such as the chassis or the
fuel tank.
Meanwhile lightweight bodies are an
absolute prerequisite for the electric drive systems of the future with
their heavy batteries. The performance and range expected by customers
cannot be achieved without them.
Audi has already built more than
550,000 vehicles with an aluminium body. Added to this are roughly 9,000
Lamborghinis – no other manufacturer in the world can even come close in
terms of the number of vehicles or their diversity.
The ASF technology is an unparalleled
success story. Audi has increased its lead step by step: in alloys, in
the reduction of the number of parts and in production efficiency.
Numerous innovations in development and production have raised the level
of automation from 25 to over 80 percent, which is nearly on par with
steel body construction.
In fabrication, traditional spot
welding is being replaced by joining methods developed by Audi,
including punch riveting, bonding or laser-MIG hybrid welding. In the TT
and the R8, self-tapping screws are used to join many of the components.
Another innovation is the laser-welded invisible seam on the roof of the
TT.
A8, R8, TT and TT Roadster:
the state of the art
The second generation of the A8 and the R8, TT Coupé and TT Roadster
sports cars document the current state of the ASF technology. The
superstructure of the current A8 weighs 218kg while the aluminium body
of the R8, whose co-supporting engine frame is made of ultra light
magnesium, tips the scales at 210 kg.
The TT Coupé and Roadster bodies weigh
206 kg and 251 kg respectively while the TT “family” also features an
additional innovation. To ideally balance the axle loads between the
front and back, Audi developed an innovative hybrid construction for its
compact sports cars: Most of the body is made of aluminium, but steel is
used in the rear.
Depending on the model, the kerb weight
of the TT has been reduced by between 20 and 90 kg compared to the
previous model which had an all-steel body. At the same time, the static
torsional rigidity of the Coupé increased by 50 percent and that of the
Roadster by an even more impressive 100 per cent.
The ASF provides the foundation for
precise handling and a high level of passive safety. A lighter car has
to dissipate less kinetic energy and is also does less damage to others
involved in an accident. The lightweight design combines chassis
responsiveness and efficiency in typical Audi fashion.
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