Audi – The Leader in Lightweight Design
Aluminum was an interesting material for bodies even back in the pioneering days of the automobile, and important inspiration was drawn from aeronautical engineering. In 1913, NSU built the Type 8/24, a model having a body made entirely of aluminum. Ten 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 aluminum panels by hand and used them to build the bodies and streamlining panels for their spectacular racing cars and land speed record cars.
825 kilograms: the 1936 Auto Union Type C According to the Grand Prix rules for the years 1934 to 1937, the cars were not permitted to weigh more than 750 kilograms (1653.47 lb) without operating fluids, wheels and tires. The radical lightweight design that resulted drove performance to breathtaking heights. The 1936 Auto Union Type C, which tipped the scales at 825 kilograms (1818.81 lb) ready to race, had a V16 supercharged engine producing a good 380 kW (520 hp) mounted in front of the rear axle. Each horsepower had to propel just 1.6 kilograms (3.53 lb), hardly more than with a modern Le Mans sports prototype.
Lightweight design advanced to the level of a strategic project at Audi in 1982, at which time the company established a joint venture with an aluminum company from the United States. The mission was nothing more and nothing less than to once again reinvent the self-supporting body, but this time with a material that is roughly two-thirds lighter than conventional steel and also with a new geometry tailored to this material – the Audi Space Frame.
The development work was organized as an integrated project. A process that generated more than 40 patents and patent applications also developed a broad base of expertise in all areas – alloys, casting, shaping and joining of the parts. In 1985, Audi presented the body of an Audi 100 made of aluminum but still using a conventional monocoque design. The legendary concept sports cars from the fall of 1991, the Audi Avus quattro and the Audi quattro Spyder, had skins of the light metal but underneath were still supporting frames.
1993: The ASF technology study The new technology was ready for series production in 1993: A shining silver showcar with an unpainted body of polished aluminum was on display at the International Motor Show in Frankfurt am Main, Germany. 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 in the history of the automobile: the first large-volume production car with a self-supporting aluminum 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: Diecastings and extruded sections form a framework-like skeleton that incorporates aluminum panels as co-supporting elements. The components with their various cross-sections and shapes combine optimal function with low weight.
Compared to steel, an ASF body is at least 40 percent lighter. The body of the first A8 weighed only 249 kilograms (548.95 lb); that of the A2 compact (from 1999) weighed only 156 kilograms (343.92 lb). The superstructure of the A2 1.2 TDI – the world’s first four-door, three-liter car – weighed in at only 135 kilograms (297.62 lb), which was a decisive factor in the sensational average fuel consumption of 2.99 liters of diesel fuel per 100 kilometers (78.67 US mpg).
A8, R8, TT and TT Roadster: the state of the art Today’s models – 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 weights 218 kilograms (350.84 lb). The aluminum body of the R8, whose co-supporting engine frame is made of ultra light magnesium, tips the scales at 210 kilograms (462.97 lb). With the V10 engine producing 368 kW (525 hp), the entire car weighs only 1,620 kilograms (3,571.49 lb). Its specific weight is 3.1 kilograms (6.83 lb) per hp – the same as that of a well-trained athlete without a single gram of fat on his frame.
The body of the TT Coupé weighs in at 206 kilograms (454.15 lb); that of the TT Roadster at 251 kilograms (553.36 lb). 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 aluminum, but steel is used in the rear.
Depending on the model, the curb weight of the TT has been reduced by between 20 and 90 kilograms (44.09 and 198.42 lb) compared to the previous model, which still 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 percent. The ASF provides the foundation for the precise handling, the driving dynamics and the high level of passive safety. A lighter car has to dissipate less kinetic energy and is also does less damage to others involved in the accident.
The lightweight design combines sportiness and efficiency in typical Audi fashion. The TT 2.0 TDI quattro – a sports car with 125 kW (170 hp), 350 Nm (258.15 lb-ft) of torque and all-wheel drive – contents itself with 5.3 liters of diesel fuel per 100 kilometers (44.38 lb-ft) and emits just 139 grams of CO2 per kilometer (223.70 g/mile). Its dynamic driving performance – it accelerates from zero to 100 km/h in 7.5 seconds and has a top speed of 226 km/h (140.43 mph) – are the result of the intelligent application of lightweight design. Audi uses lightweight design as an integrated approach to resolving the former paradox between driving pleasure and efficiency.
ASF: the reversal of the weight spiral The reversal of the weight spiral that Audi initiated with the ASF principle has major secondary effects. A lighter body is the starting point for weight reductions on other parts of the car, such as the chassis or the fuel tank. Every 100 kilograms (220.46 lb) saved reduces fuel consumption by 0.3 to 0.5 liters per 100 kilometers, corresponding to a reduction of 8 to 11 grams of CO2 per kilometer (12.87 to 17.70 g/mile).
A low body weight already harmonizes ideally with the Audi principle of downsizing, according to which turbocharging replaces displacement. The highly efficient engines make further significant contribution to lowering fuel consumption. Lightweight bodies are even an absolute prerequisite for the electric drive systems of the future with their heavy batteries. The performance and range expected by the customers cannot be achieved without them.
Audi has already built more than 550,000 vehicles with an aluminum 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 perfect interplay throughout the entire process chain – from development and planning, the building of the machines, fixtures and tools to the press shop, body shop and the paint shop to assembly – culminates in the utmost precision. The ideas of the designers are implemented to within a tenth of a millimeter in accordance with Audi’s stringent quality standards.
The Aluminum and Lightweight Design Center in Neckarsulm In 1994, Audi established a special Aluminum Center at the Neckarsulm site for development, production planning and quality assurance. This facility was renamed the Aluminum and Lightweight Design Center in 2003. High-strength steels, tailored blanks, fiber-reinforced plastics and magnesium play an increasingly important role here. The head of the Aluminum and Lightweight Design Center, Heinrich Timm, says, “Aluminum remains the primary material, but we are intensively investigating the other materials, with our primary focus on fiber-reinforced composites.”
The lessons learned at the Aluminum and Lightweight Design Center 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.
Prestigious award: The Euro Car Body Award Audi won another prestigious trophy in 2006 for the TT hybrid construction – the Euro Car Body Award presented by the renowned Automotive Circle International. Audi had previously won this important innovation prize for body construction in 2003 in recognition of the A8.
A third award followed in 2008 for the Q5 – lightweight design is also a top priority for bodies made of steel panels. At only 355 kilograms (782.64 lb), the mid-size SUV has the lightest body in its class. Hot-shaped, ultra-high-strength steels form the strong backbone of its superstructure. They achieve their extremely high strength by being heated in a pass-through furnace to roughly 920 degrees Celsius (1688° Fahrenheit) and then subsequently cooled to approximately 180 degrees Celsius (356° Fahrenheit) in chilled press tools.
Lightweight design in the rest of the vehicle Audi also makes systematic use of lightweight design in the drive chain and the chassis. Many engines uses aluminum 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 aluminum parts. Carbon fiber-ceramic brake discs are available as an option in the high-performance models. Other highlights of lightweight design include brake calipers, hoods and trunk lids, side panels or cover components made of aluminum 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 the Le Mans sports prototypes and the 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. Audi will continue to expand its leadership role – the Vorsprung durch Technik in lightweight design.