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Lightening up is serious business at Audi
Neckarsulm, Germany–There's an old saying in horse racing: "Weight will stop a freight train." It refers to the fact that, in handicap races, faster horses are burdened with a heavier load on their backs to slow them down and even out the field.
Weight has a similar effect on automobiles, which is why race cars are engineered to be as light as possible. Along with speed, weight also affects fuel consumption and emissions, which is why Audi is spending so much time and money on lightweight construction.
It isn't the only automaker to do so, but it's at the forefront of the technology: it's been building cars based on its aluminum Audi Space Frame design for 15 years, and applied for 38 lightweight design patents in 2008.
It also helps to have customers who can afford cars such as the R8 and A8, along with the Lamborghini and Bugatti models that share the expertise. The materials and construction techniques are often very costly, and aren't yet at the volume production levels that help substantially bring down the price.
Just as air conditioning and power windows trickled down from prestige to economy cars, though, lightweight technology has the potential to eventually transform the auto industry, including alternative fuel vehicles.
"We are facing global trends, such as fuel prices, transportation and infrastructure," says Heinrich Timm, head of Audi's Aluminum and Lightweight Design Center. "The components of electric and hybrid vehicles are heavy, and will require lightweight technologies to balance them."
By reducing a vehicle's weight by 100 kilograms, Timm says, there can be a fuel economy improvement of 0.3 to 0.5 L/100 km, and a reduction of 8 to 11 g/km of CO2 in emissions. A lighter-weight car also handles better and stops sooner.
The company approaches the problem from several angles. It uses lightweight materials, including various steel alloys, aluminum, titanium, magnesium, carbon fibre and fibre-reinforced plastics. All have pros and cons, and can present special challenges, such as finding new ways to attach them together. Bolt aluminum to steel, and you'll eventually get corrosion as the metals interact. Audi isolates the two with coatings and adhesives.
Next up is how to use the materials. Most noticeable is that the parts are thin-walled, and reinforced inside with honeycomb-style braces. Audi got the idea from nature: bird bones and elephant skulls are constructed this way, and are incredibly light and strong.
Anything that doesn't bear a load is considered superfluous. "Use the best material at the right place, and as little of it as possible," Timm says. "We also look at the car and what it needs. The TT uses the Audi Space Frame, but it needs weight on the rear axle to balance it against the front aluminum structure. We use a steel sheet in the rear to produce the weight and also to reduce cost (over using other materials)."
And no weight loss is too small to be overlooked. At times it seems overly obsessive, but it all adds up: spray-on sound-deadening saves 1 kg per car over glue-in mats; aluminum engine bolts save 560 grams over steel ones; an aluminum battery cable drops 1.2 kg over a copper one; and a robot applying exactly enough adhesive to join two panels saves a gram or two of weight.
On a nearby test track, Audi sent me out to drive two A5 models, one a production model with V6 engine. The second, a prototype, used a four-cylinder engine and weighed 250 kg less, thanks to a carbon-fibre hood and wheel inserts, and mostly aluminum body construction. Even with a smaller engine, it accelerated faster, and also cornered sharper and took less distance to stop. Such a car would currently be impossible to produce at reasonable cost, but it's all part of the development process.
"Downsized engines and transmissions are possible when the car is lighter," says Heinz Hollerweger, head of Total Vehicle Technical Development. "A lighter car means short stopping distances, and cooler brakes with less fade. The reduction in unsprung weight allows for a gentler shock setting, for a more comfortable ride. The lower mass is less kinetic energy to be dissipated in a crash, for improved safety. The smaller engine means a smaller fuel tank, so it's lighter again. It takes less to produce and recycle the car. Nothing is too small to care. It will all come together to reduce weight."
Travel was provided to freelance writer Jil McIntosh by the automaker. jil@ca.inter.net
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