Lightweight construction pioneer highlights its technological lead
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.
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.
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.
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.
NSU built the Type 8/24, featuring a body made entirely of aluminium, in 1913, and 10 years later, the Audi Type K wore an experimental streamlined skin of this same material. In the 1930s, specialists from the Racing department of Auto Union manufactured aluminium panels by hand and used them to build the bodies and streamlining panels for their spectacular racing cars and land speed record cars.
Lightweight design advanced to the level of a strategic project at Audi in 1982 to invent a self-supporting body with a material roughly two-thirds lighter than conventional steel and also with a new geometry tailored to this material – the Audi Space Frame.
In 1985, Audi presented the body of an Audi 100 made of aluminium but still using a conventional monocoque design. The legendary concept sports cars of 1991, the Audi Avus quattro and the Audi quattro Spyder, had skins of the light metal but underneath were still supporting frames.
The new technology was ready for series production in 1993. A shining silver showcar with an unpainted body of polished aluminium was on display at the Frankfurt Motor Show. The predecessor to the A8 bore the designation ASF, the abbreviation for Audi Space Frame. The production model that debuted the following year was a milestone – the first large-volume production car with a self-supporting aluminium body.
The A8 paved the way for Audi into the premium league and it also sparked new developments for the traditional material of steel. The principle embodied by the first A8 still applies today: Die castings and extruded sections form a framework-like skeleton that incorporates aluminium panels as co-supporting elements. The components with their various cross-sections and shapes combine optimal function with low weight.
Audi established a special Aluminium Centre in Neckarsulm for development, production planning and quality assurance in 1994. The Aluminium and Lightweight Design Centre experiments with high-strength steels, tailored blanks, fibre-reinforced plastics and magnesium.
Heinrich Timm, the Head of the Aluminium and Lightweight Design Centre, says: “Aluminium remains the primary material, but we are intensively investigating the other materials, with our primary focus on fibre-reinforced composites.”
The lessons learned at the Aluminium and Lightweight Design Centre innovation foundry, which employs 150, have already served as the basis for a three-digit number of patents in development and production – a balance they can be proud of. The European Patent Office named Audi “European Inventor of the Year 2008” for its achievements with the ASF technology.
Audi also makes systematic use of lightweight design in the drive chain and the chassis. Many engines uses aluminium and vermicular graphite cast iron, which is the result of a high-tech production process, to reduce the weight of the crankcase. Many models have chassis with predominately aluminium parts.
Carbon fibre-ceramic brake discs are available as an option in the high-performance models. Other highlights of lightweight design include brake callipers, bonnets and boot lids, side panels or cover components made of aluminium and steering wheel rims or instrument panel mounts made of magnesium.
Experience from the world of motor sports flows back into the development work – the reduction and distribution of weight are extremely important for Audi’s pioneering diesel-engined Le Mans sports-prototypes and its DTM (touring) cars. The race cars provide the production development engineers with important information about carbon and its combination with metal.
Research continues into new materials and alloys, with the focus on minimal weight with maximum durability as well as design and fabrication compatible with the materials.
Article source: www.audi.co.uk