Audi Lightens Up (Structurally)

Columns From: 5/16/2011 Automotive Design & Production,

One of the subtle ways that having a collection of luxury brands can really help a car company became apparent when I recently visited Audi’s Neckarsulm factory, where it builds its Audi Space Frame (ASF) vehicles.

The Audi Space Frame (ASF) for the current-generation A8. The ASF was first deployed on the ’94 A8 and has since been used on a number of other vehicles in the company’s lineup. While it may not be a tech that finds its way to cars made by other Volkswagen Group brands, the learnings achieved for the ASF is important as regards light weighting going forward.

One of the subtle ways that having a collection of luxury brands can really help a car company became apparent when I recently visited Audi’s Neckarsulm factory, where it builds its Audi Space Frame (ASF) vehicles. Audi is part of the Volkswagen Group, which also owns marques including Lamborghini and Bentley, so it is among the premier producers of high-end models. Because luxury vehicles demand extra margins, manufacturers can try out more expensive technologies on them, and then potentially move those technologies or techniques to the mass-market brands. An area where that trickle-down effect is going to be important in the future is materials, specifically to reduce weight. Not only does Audi realize the dynamic benefits of lower weight—better braking, acceleration, and road holding—but reducing mass is vital to meeting impending CO2 and gas mileage regulations and for electric vehicles. According to Lutz-Eike Eland, head of the Audi Lightweight Design Center, a major challenge is: “Joining materials that haven’t been joined before and doing it in a way that can be repaired. We have to use the right materials in the right places and use as little material as possible.”

ASF is an example of a trickle-down technology. As introduced on the 1994 A8 (D2), the structure was all aluminum, but Audi has since expanded the concept to use differing material mixes. The current D4 A8 is still essentially an aluminum structure, although high-strength steel is used in some areas. The structure is casting intensive, which gives high stiffness and thus good ride comfort. By contrast, the Audi R8’s ASF structure uses a lot of extruded sections that are production intensive but have low capital costs. Audi has now applied the ASF structure to the less-expensive A6, mixing aluminum components with steel parts. According to Audi, cold-formed steel gives freedom of design because it’s easy to shape and hot-formed steel gives good crash performance. Aluminum structural castings are said to improve functional integration and body rigidity; extrusions have good energy absorption; and sheet panels are light. Overall, Audi says that the new A6’s body-in white is 67 lb. lighter than the previous model’s conventional structure.

More Audis in the future will be underpinned by the ASF structure, with materials such as magnesium alloy, glass-fiber reinforced polymer (GFRP), and carbon-fiber reinforced polymer (CFRP) joined to steel and aluminum using techniques such as bonding, flow drill screwing, and riveting as well as welding. Audi says that the MLB Evo platform that will underpin the next A5 and A4 will be an ASF structure. We saw a prototype body-in-white for what we assumed was an A4 that mixed aluminum panels, including the rockers, with localized sections of ultra-high strength steel, joined by rivets. Audi says this body shell will weigh 221 lb. less than the old car’s.

I had an opportunity to experience how this weight reduction can affect the way a car drives. I drove an A5 with an aluminum ASF frame and carbon fiber hood and trunk lid—essentially a mule for the upcoming Quattro Coupe—that had a 402-hp, 2.5-liter in-line five-cylinder engine. Light on its feet and agile, it felt better balanced and faster than the 444-hp, 4.2-liter V8 powered RS5 that I also sampled. Thanks to a weight difference of 665 lb. over the RS5, which Audi claims weighs in at 3,804 lb., the A5 mule achieves more with less.

Of course, it’s highly unlikely that we’ll see VW Jettas with carbon fiber panels in the near future, but Audi’s experience with lightweight materials and construction can only help it build more efficient vehicles across all its brands. There are few car companies with the bandwidth that allows them to do this.