Audi developed the “Audi Space Frame” body using aluminium, reducing the weight of the vehicles even further with components such as bionic honeycomb structures, magnesium components and fiber-reinforced plastics. This is not a new development, however, as the carmaker has been researching low-weight engines, brakes and gearboxes for years, thereby bolstering its position as a pioneer in the field of lightweight construction.
FETHERWEIGHT SKELETON CONSTRUCTION – The aluminium frame of the Audi A8 weighs just 231 kilograms.
At the Boxberg test track in the Main-Tauber district of Northern Baden-Württemberg, two Audi A5s are lined up at the start. The similarity between the two, though, is only superficial. One is a prototype that weighs in at 230 kilograms less than its series-produced counterpart – with an aluminium body, fiber-reinforced plastic hood, ultra-light brakes and a more refined suspension. Even the engine is smaller and lighter: Rather than the 265 PS engine found in the production version, 211 PS is enough for the prototype – after all, it is the power/weight ratio that counts here. Both contenders rev up. And although they are equally powerful in theory, the lightweight prototype exploits its dynamic advantages to the full. The slightest pressure applied to the gas pedal propels the slimmed-down Audi A5 forwards effortlessly. The car corners more tightly and hardly jounces at all when braking – not even when it comes to an abrupt halt. “Lightweight construction is positive in all regards, including driving dynamics,” says Michael Dick, the member of the Audi Board of Management responsible for Technical Development, who is observing the test drive from the side of the track.
REVERSAL OF THE WEIGHT SPIRAL
The Audi A5 prototype brings together virtually all the sophisticated lightweight construction technology developed by Audi engineers in recent years. The German carmaker has long been a pioneer in this field: As far back as 1985, the company unveiled the prototype of an Audi 100 with an aluminium body. “Modern vehicles are getting heavier and heavier as a result of more powerful engines, new safety technology and increased comfort features,” explains Michael Dick, “but Audi has been bucking the trend for decades.” With the advent of hybrid and electric cars with massive batteries, the weight problem is likely to get worse. “Because of this, we take a holistic approach in our lightweight construction design, too,” explains Dick. “An aluminium tailgate permits a lighter gas strut. Lightweight axle components transfer less force to the body, thereby permitting a lighter superstructure.” This in turn paves the way for more compact brakes, a smaller engine and a correspondingly streamlined exhaust system. “We are reversing the weight spiral,” declares Dick.
But there is more to lightweight construction than merely enhancing sportiness and driving dynamics. There are ecological benefits, too, because lightweight construction has a more favorable life cycle analysis than conventional cars – even though more energy is required to produce aluminium than steel. This is because lower weight goes hand in hand with lower fuel consumption and emissions. 100 kilograms less weight cuts fuel consumption by 0.35 liters and CO2 emissions by up to eight grams per kilometer. As a result, the higher costs associated with the new construction technique are amortized after a short time. Another important factor is that the lightweight vehicle bodies can be recycled more effectively and using less energy.
TECHNOLOGY FOLLOWING NATURE’S LEAD
When he talks to his colleagues, it seems like Heinrich Timm, Head of the Audi Lightweight Construction Center in Neckarsulm, has a mental list on which he is constantly crossing off weight-related elements – a few grams here, a few grams there. At Audi’s location in Swabia, a total of 150 lightweight construction specialists work on developing materials and joining technologies, optimizing production robot routines and recording the plasma welding processes with high-speed cameras. In the entrance area, the plastics responsible for winning three European Car Body Awards bear testimony to Audi’s lightweight construction expertise. Since 1994, more than 550,000 cars have been produced using the Audi Space Frame design. Applying lightweight construction principles to vehicle production is anything but easy. Cast components, sheet aluminium and other key elements must be produced, and equipment and tools constructed. “We have the entire process chain down to a fine art. Each step requires the highest precision and we have a highly qualified team at our disposal,” explains Frank Dreves, Member of the Audi Board of Management responsible for Production. His team plans production processes, develops innovative technologies, adapts the press shop to new requirements, ensures corrosion protection and paintwork – and puts all the components together at the end.