Audi shaves power-to-weight ratios via high-tech engineering
These days, a ‘lightweight’ vehicle can deliver structural integrity, performance
The Audi Space Frame (ASF) arrived in the company’s then all-new 1994 A8 saloon. The reason for it was simple: The aluminum construction reduced the curb weight dramatically, which brought better performance while improving fuel economy.
Since then, Audi has expanded the use of this technology through three generations of A8 and applied its lightweight philosophy to the R8 V10 supercar. The company has also teased with concepts such as the all-aluminum Avus Quattro concept car and its 509-horsepower V12 engine.
The latest expression of the ASF will arrive in the 2019 A8. The thrust, again, is to reduce mass, which brings a better power-to-weight ratio. It is a win/win situation. However, with changing tastes and the need to increase the level of luxury and convenience to meet today’s demands, along with the ever increasing difficulty of the crash-test standards all manufacturers must meet, have forced the ASF concept to adapt to the times.
Enter the hybrid Audi Space Frame. This concept is not new, as the TT embraced the advantage of blending different materials to arrive at a lighter, but strong structure. In simple terms, it puts the right amount of the right material in the right place.
In the case of the new A8 platform, the multi-material theme is taken to a new level. In this case, 58 per cent of the body is aluminum and it’s found in the form of sheet aluminum, extruded sections and cast components (this does not include the aluminum front fenders, hood and rear deck lid). Other portions of the body are composed of 24 per cent regular steel and 16.5 per cent hot-formed, ultra-high-strength steel. The latter is featured heavily in the A- and B-pillars and firewall cross brace, where side impacts are the issue.
The balance of the new A8’s makeup is composed of a magnesium cross brace between the shock towers and a carbon fibrereinforced plastic (CFRP) rear firewall-cum-parcel shelf. The latter may seem superfluous to need, but it improves the stiffness of this area of the A8 by 33 per cent.
Overall, the new multi-material body ups the torsional rigidity by 24 per cent when compared to the current car, and this in spite of the inclusion of a new panoramic moonroof that consumes most of the roof panel. As with a convertible, a large opening tends to hurt torsional rigidity, but no fear here, thanks to the bracing.
The adoption of the hybrid ASF yields the lightweight advantages despite the increased presence of steel components; the next-gen A8’s makeup brings a body-in-white mass of just 282 kg, which is the lightest of any full-bodied sedan, says Audi.
Beyond its inherent strength, the light-makes-might philosophy does a number of good things; key among them is the improvement in the power-to-weight ratio. This not only betters performance, it improves fuel economy and lowers the centre of gravity, which brings sharper handling. What goes unspoken is the fact that dropping the curb weight allows the adoption of lighter components in other key areas. For example, the mass reduction allows a smaller engine to be used without hurting performance, which has obvious fuel-economy benefits. It also allows for a smaller brake package, which shaves off more precious grams. And on it goes.
Conversely, maintaining the engine size sees a dramatic improvement in performance, as witnessed with the audacious R8 V10 Plus. Audi managed to shave the body-in-white weight to just 200 kg. As with the next-gen A8, a big part of the diet boiled down to the inclusion of CFRP components for the rear firewall, central tunnel and three-piece B-pillars.
The R8 V10 Plus’s numbers reveal the true advantages of blending lightweight construction with a monster 610-horsepower, 5.2-litre V10 engine. With a curb weight of just 1,655 kg, the R8 V10 Plus boasts a world-class power-to-weight ratio of 2.71 kg of car for each of its stampeding stallions.
This equates to stunning performance: it runs from rest to 100 km/h in 3.2 seconds, flashes through 200 km/h in 9.4 seconds and goes on to a top speed of 330 km/h. Remarkably, this thoroughbred still manages to return a combined average fuel economy of 14.1 L/100 km. These numbers are a testament to Audi’s lightweight philosophy.