The first A8 shows its Space Frame, 1993-2003; photo by Jil McIntosh. Click image to enlarge

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By Jil McIntosh

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Audi’s Aluminum and Lightweight Design Center

Neckarsulm, Germany – When it comes to automobiles, weight is the enemy. It affects acceleration, handling and fuel economy, but as buyers demand more safety and convenience features and cars get bigger, vehicle weight has been creeping up.

Audi isn’t the only automaker tackling the problem, but it’s a leader in the technology, which it showcased to a group of international journalists at its Aluminum and Lightweight Design Center, and its A8/R8 assembly facility in Germany. The company’s lightweight aluminum Audi Space Frame (ASF) has been an essential tool in its vehicle construction for 15 years, and last year alone, it applied for 38 lightweight patent designs. Some of its design work is purely experimental, and some is too expensive to be used on anything in the near future, but much is being continually incorporated into new designs. From the A2 and A3 right up to the R8, the company’s cars have reached a point that would make Weight Watchers proud.

Braces make a plastic pedal as strong as a metal one; photo courtesy Audi (top); Lightweight components are crushed to test their strength; photo courtesy Audi. Click image to enlarge

Tackling the problem becomes very involved, with numerous departments coming together to approach it. Lightweight materials play a major role, and the company is constantly experimenting with components made of aluminum, new steel alloys, titanium, magnesium, carbon fibre, and fibre-reinforced plastic. But it simply isn’t enough to just make a part out of aluminum instead of steel, and leave it at that. The new materials have an effect on all aspects of building a car. They will require new methods of shaping and fastening, their costs will have to be taken into consideration, and their lighter weight will affect how the vehicle is balanced. “The designers take the overall weight into account right from the beginning, and then the compounds are examined,” said Heinz Hollerweger, Head of Development, Total Vehicle. “Volume production creates challenges, and active safety items add weight. The weight will also increase as we add electric or hybrid powertrains, because the batteries are very heavy, and the weight affects the cruising range.”

While fuel economy is generally most important to people who buy inexpensive vehicles, the reality is that the know-how needs to start with premium automakers such as Audi: its customers can afford vehicles such as the Audi A8 and R8, and the Lamborghini and Bugatti models that also use the technology at its earliest stages. Those driving A2 and A3 models benefit from materials and production techniques that trickled down from far more expensive models as economies of scale and volume assembly brought down the price, just as features such as air conditioning and power amenities were once restricted to higher-end vehicles and are now found in almost every vehicle around the globe.

The company’s primary objective is to use the best material, and to use as little of it as possible, at exactly the places where it’s needed. If any part doesn’t bear a load, it doesn’t have a place in the car. Audi went to nature to learn the trick of lightweight strength: just as bird bones and elephant skulls are hollow, with bracing inside them to provide rigidity, so are Audi’s parts. A thin-walled aluminum strut with interior bracing is far stronger than a thick-walled piece of steel – the company slams them with several tons of pressure just to be sure – yet is a fraction of the weight, while a clutch pedal made of braced plastic outperforms a similar model made of metal. By reducing a vehicle by 100 kilograms, fuel economy can be improved by 0.3 to 0.5 L/100 km, and CO2 emissions drop by 8 to 11 g/km.

At times, the attention paid to tiny increments of weight seems almost obsessive. But just as one hundred pennies make a dollar, every gram adds up over the huge number of parts incorporated into each vehicle. The steel bolts attaching the engine to the transmission are swapped out for aluminum, at a savings of 560 grams; spray-on sound-deadening drops up to 12 kilograms over glue-in mats on some cars; an aluminum battery cable is 1.2 kilos lighter than a copper one. Laser welding, instead of spot welding, permits the use of narrower flanges, which save 250 grams per body, while a robot applying exactly the amount of glue needed to bond two panels means no excess weight, and also no extra step in cleaning off anything that seeps out.

Much of the assembly line is automated (top); The prototype lightweight brake disc is still too expensive but is paving the way (middle); Comparing production and lightweight prototype models; photos courtesy Audi. Click image to enlarge

How lightweight materials are used is also considered in the final design of the vehicle, the vehicle’s retail cost, and the customer’s expectations. For the Audi TT, a steel sheet at the rear balances the lightweight front suspension, giving the car its characteristic weight distribution and also keeping down the cost on this relatively high-volume car. On the considerably lower-volume and higher-priced R8, which leaves the factory at the rate of 25 cars per day, cost isn’t as much of an issue with its pricier, all-aluminum construction. There’s also the visual impact of some of its lightweight components: making the side blade out of carbon fibre reduces weight by 45 per cent, but also makes it very pleasing to the eye, and many customers more likely to order the featherweight carbon fabric throughout the vehicle for its high-end appearance than they are for how it ultimately tips the scales.

Such a variety of materials comes with its own set of headaches, including how to shape the parts, and then how to join them to each other. Bolting steel to aluminum will cause a reaction that eventually leads to corrosion; Audi must isolate the two metals by using coatings and adhesives. Special lightweight self-tapping screws and rivets are drilled in by robots. Remote laser beam welding creates an almost imperceptible seam, and the automated system moves the laser head continuously, working much faster and more accurately than a human welder could. The new materials and techniques also allow for simplification in some areas: the side frame of the first-generation A8 was eight pieces, while it’s now a single piece, eliminating the task of joining the parts together.

In the technical centre, a display of conventional parts and their lightweight equivalents show the differences that can be achieved. There are large pieces such as lightweight glass panels, wheels, and SUV cargo floor covers for more pronounced differences, and tiny weight savings in turbocharger turbines and fasteners. Of special interest is a “hybrid” brake disc, so-called because it combines several materials, and can be easily lifted with one hand versus a traditional rotor. It’s still far too expensive and difficult to manufacture to be a large-volume unit, but its design has led to a new pin connector, integrated into the cast iron friction ring on a conventional rotor, that quickly dissipates heat and displaces water. The pin is now in the prototype stage with the aim of using it in production. Components such as brakes and flywheels are of special interest because of the effect of their rotational force: shaving a kilogram off a part that spins is the equivalent of saving 16 kg on one that doesn’t.

The result of all this attention to paring the slightest bit of flab became evident as I headed out to the proving grounds. Three courses were set up, two of them comparative events. In one, a production A5 Quattro coupe with 3.2-litre V6 squared off against a prototype lightweight A5 with 2.0-litre four-cylinder, but with a body made mostly of aluminum, carbon fibre hood, and other weight-saving tricks, including carbon fibre inserts in the wheels. The difference was 230 kg in favour of the four-cylinder. Although it had only 211 horsepower to the V6’s 265 horses, its acceleration felt much stronger. It also cornered sharper, stopped faster, and simply felt more “tossable” all around. It wouldn’t be possible to currently produce such a relatively high-volume car at a price consumers would pay, but these prototypes are all essential pieces of the development process.

The second course was simply about having fun. On hand was the Audi A3 24th Street, a street-legal version of the A3 race car that took part in a 24-hour race at Nürburgring. The car carries a 2.0-litre TFSI engine producing 300 horsepower and 287 lb-ft of torque. Put that into a car that weighs a mere 1,190 kg, and hang on tight.

Laser welding creates an almost imperceptible seam (top); Workers weld an A8 floor (photo two); Interior structure of a Q5 (photo three); Internal braces allow for thinner walls but with superior strength; photos one, two and four courtesy Audi; photo three by Jil McIntosh. Click image to enlarge

Finally, I approached the fuel efficiency test, between two TT Coupes. The one equipped with a 2.0-litre four-cylinder weighed 1,360 kg, versus a V6-powered one at 1,500 kg. Both cars were equipped with fuel efficiency meters mounted on the dash; the idea was to accelerate so as to keep the car’s progress consistent with a series of acceleration and braking movements, indicated by a line on the screen, simulating a cycle in city traffic. It proved difficult to match it exactly, and it took a couple of turns around the course to get the hang of it, but the difference was noticeable when the computer did the math. The smaller engine and lighter weight resulted in fuel savings of 2.0 to 2.5 L/100 km.

That was to be expected with a smaller engine and lighter car, but it’s all part of the company’s philosophy in the face of an automotive world that has changed drastically since Audi was formed a century ago. In days past, big, powerful engines were needed to move heavy automobile bodies. Today, fuel prices — €1.35 per litre for gasoline advertised at a station I passed, or about $2.13 – and tightening emissions standards are moving all manufacturers toward smaller and more efficient engines. Many customers are unwilling to sacrifice performance, especially those who drive premium brands. The solution becomes one of balancing several options: improving the engines and transmissions to get more power out of smaller displacement, and making the structure lighter, with less mass to move around.

“Downsized engines and transmissions are possible when the car is lighter,” Hollerweger said. It all comes together: a smaller engine requires a smaller fuel tank; lower weight means dampers don’t have to be as stiff, giving a smoother ride; brakes stop faster, up to six metres at 100 km/h when the car weighs 100 kg less; and with less kinetic energy to be dissipated in the event of a crash, the car can be safer. The environmental effects also go beyond fuel and emissions: it takes fewer resources to produce the car, and at the end of its lifespan, its aluminum is easier to recycle than steel.

Still, it isn’t all just full speed ahead. Every promising solution also comes with challenges that must be overcome. Cost is a primary factor, of course, but it’s hardly the only one. Smaller engines are noisier, and so the vehicle’s acoustics must be modified to overcome the problem. Unconventional materials must be sourced in sufficient quantities and with timely delivery to the factory. Workers must be trained in the skills needed to work with new techniques and materials, and the assembly line may have to be modified to handle the new procedures. And a part that comes together perfectly when hand-assembled in the lab might be too complex to be viable on the factory floor. It’s all part of the reason why Audi will send out each new model as strong and as lightweight as it can be – and then go right back to the drawing board to see what can be done next.

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