Lightweight Garage #7 Aluminium space frame @ Audi A8 D2 (4D)

The Vehicle

This time, the legendary successor to the Audi V8, the first Audi A8, is behind our garage door. With an unladen weight of 1.46 to 1.75 t and engine output of up to 309 kW and 550 Nm for the W12 engine, the Audi A8 was the flagship of the product portfolio at the time.

©AUDI AG, CC BY-NC-ND 2.0, Audi A8 D2

In addition to all-wheel drive, the aluminium body was a unique feature of the chassis of the time and paved the way for multi-material lightweight construction and the design of complex aluminium structures.

The Technology

This aluminium space frame - also known as the Audi Space Frame - offers advantages from a lightweight design point of view. The basic idea behind it is a clear function separation of each individual component. The frame is provided by the economically producible extruded aluminium profiles, which are connected via aluminium cast nodes. These are clad with aluminium sheets, although presumably due to the crash requirements for the entire chassis, these only make a minor contribution to the overall rigidity.

In addition to the redesign of the vehicle architecture, the production side has also been redesigned in 12 years. The specially developed alloys and manufacturing and joining techniques offered not only fulfilment of the mechanical requirements, such as ductile cast nodes using vacuum casting, but also resistance to contact corrosion between aluminium and plastics. Components were also glued, welded, or riveted.

The Lightweighting Effect

With this design principle, the aluminium properties can be exploited, and individual components designed to withstand their specific loads. Worth mentioning is the inherent stiffness of the aluminium profiles with several chambers. Further components, such as planking and doors, have been added to this aluminium skeleton. In current vehicles, this still results in weight savings of up to 40 % compared to a steel version of current Audi models. Nowadays also other materials are used in addition to aluminium.

©Jens from AudiStory, Audi A8 D2

At 1,750 kg, the 1994 Audi A8 weighed less than the Mercedes W140 S420 at 1,900 kg or the BMW E38 740i at 1,755 kg, despite its all-wheel drive. And the cast nodes certainly sharpened the ideas for subsequent carbon applications in automobiles.

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