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Automotive Industry Completely New Bodyshell for Upcoming Mercedes-AMG SL

| Updated on 27.05.2021Editor: Nicole Kareta

The new roadster architecture consists of the combination of an aluminum space frame with a self-supporting structure. It was created - as with the first SL in 1952 - literally on a blank sheet of paper: not a single component was taken over from the preceding SL model or, for example, from the AMG GT Roadster.

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The new roadster architecture consists of the combination of an aluminum space frame with a self-supporting structure.
The new roadster architecture consists of the combination of an aluminum space frame with a self-supporting structure.
(Source: © Mercedes-Benz AG)

Roadster Architecture with a Composite Aluminum Structure for Maximum Rigidity

Affalterbach. It began in 1952 with a filigree space frame, which in the first SL combined low weight with the highest possible torsional rigidity. This construction was conceived for its original use in motorsport and further developed to provide the backbone for the later production model in coupé and roadster form. When the all new roadster icon takes to the stage this year, its basis will be a completely new vehicle architecture developed by Mercedes-AMG. The lightweight composite aluminum chassis provides the basis for precise driving dynamics, high comfort, optimal packaging and sporty body proportions.

The new roadster architecture consists of the combination of an aluminum space frame with a self-supporting structure. It was created - as with the first SL in 1952 - literally on a blank sheet of paper: not a single component was taken over from the preceding SL model or, for example, from the AMG GT Roadster.

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"The development team in our bodyshell design area was faced with an extremely appealing, but also challenging task: when we were commissioned to undertake the overall development of the new SL, we started from scratch, so to speak, without building on any existing structure. We can be justifiably proud of the result, which proves, once again, the high level of development competence in Affalterbach. On the one hand we have managed to reconcile the high package demands, while on the other we have been able to achieve excellent rigidity values in all areas in conjunction with a favourable weight, so providing the basis for agile driving dynamics and exceptional comfort." says Jochen Hermann, Chief Technical Officer of Mercedes-AMG GmbH.

The requirements for the bodyshell architecture of the new luxury roadster were considerable: the specifications demanded a much more comprehensive scope of services than for the predecessor model series. In particular, the basic layout with 2+2 seats and the potential to accommodate a wide range of drive systems were realized here for the first time in an SL, a task that presented the developers with completely new challenges in terms of complexity. The aim was to present the Driving Performance characteristic of the brand with a focus on lateral and longitudinal dynamics, as well as to meet the high expectations in terms of comfort and safety.

Fondital as part of the challenge

Fondital S.p.A. is producing HPDC aluminum components for the Body-in-white of the Mercedes-AMG SL (R232). For the production of aluminum components, Fondital is using alloys directly produced by their sister company Raffmetal, first European producer of aluminum alloys from recycling.
Raffmetal has recently started with the production of SILVAL, a new range of primary aluminum alloys from recycling, thanks to the 40-years know-how in the treatment and selection of scrap, in addition to the strict control of the production process that guarantees a constant high quality. The company has conducted a LCA study of its recycled aluminum alloys with the support of a prestigious Italian university. The result of its commitment to sustainability and energy efficiency is a carbon footprint much lower than usual structural alloys.
The SILVAL alloy used by Fondital for the components of the AMG SL contains 90 % recycled aluminum with a carbon footprint cradle to gate of 1.58 kg CO2eq/kg aluminum produced. In this way Fondital can guarantee to its customers a fully in-house process with closed loop and low-carbon circular products with high quality.

As was already the case in 1952: the space frame, the basis of the SL's success almost 70 years ago, is very light and yet has very high torsional rigidity. However, it is built so high in the entrance area that regular doors are not possible - the famous gullwing doors are the outcome of this design. The frame construction, designed specifically to cope with tensile and compressive stress, allows for small tube diameters. Stability is ensured by numerous closed triangles, which transfer the occurring forces to a tubular pyramid at the end of the engine compartment.

Intelligent Material Composition with High Aluminum Content and New Fibre Composites

In the new SL, on the other hand, the intelligent material composition of aluminum, steel, magnesium and fibre composites ensures the highest possible rigidity in conjunction with low weight. Optimized material cross-sections and sophisticated component shaping create space for the required comfort and safety features, the sophisticated technology and the soft top. Other targeted measures include aluminum thrust panels on the underbody and function-integrated struts at the front and rear. The instrument panel support made of magnesium, along with part of the front module cover bridge made out of a fibre composite material with a mixture of glass fibres and carbon, also demonstrate the engineers' efforts to achieve the best possible, customized use of the most diverse materials. This also applies to the windscreen frame made of high-strength, hot-formed tubular steel. This, in conjunction with a system behind the rear seats that extends at lightning speed if necessary, serves as rollover protection.

Cast Components with Tailor-Made Wall Thicknesses

Cast aluminum components are used at the nodal points where forces come together or where functions are highly integrated, i.e. where large forces have to be transferred. Cast components have the advantage of enabling the specific discharge of forces, and make it possible to vary wall thicknesses locally according to the loads encountered. Areas of greater rigidity can therefore be realised where required, for example at the chassis connections. Moreover, only the necessary wall thickness is provided at any point of the component, which saves weight in the areas subject to low forces.

Compared to the previous model series, the torsional stiffness of the bodyshell structure increased by 18 %. The transverse rigidity is 50 % higher than that of the AMG GT Roadster, while the longitudinal rigidity is 40 % higher. The likewise improved introduction rigidity for the chassis connection ensures sporty driving performance with precise handling and high agility. The weight of the pure bodyshell without doors, bonnet and boot lid, as well as without add-on assembly parts, is around 270 kilograms.

The entire vehicle concept is geared towards the lowest possible centre of gravity. This applies both to the low connection points for the powertrain and axles and to the lowest possible arrangement of the rigidity-relevant bodyshell structure. Examples of this are the connections between the front and rear sections and the passenger safety cell, with their high flexural strength and torque rigidity, systematically realized via force paths that are as low as possible.

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