With the completely redeveloped SL, Mercedes-Benz continues a tradition that began 60 years ago. The letters “SL” have ever since been synonymous with a symbiosis of sportiness, style and comfort – and with groundbreaking innovations. The new SL has been produced for the first time almost entirely from aluminium and weighs up to 140 kilograms (309 lbs) less than its predecessor. Its highly rigid all-aluminium bodyshell provides the basis for agile, sporty handling that has been taken to an entirely new level, coupled with exemplary roll characteristics and ride comfort. Even better driving dynamics come courtesy of the new BlueDIRECT engines; they are more powerful yet at the same time up to 29 percent more economical than the engines in the outgoing generation. Other new features include the unique FrontBass system, which turns the luxury sports car into a concert hall regardless of whether the top is open or closed, and the highly efficient adaptive windscreen wipe/wash system MAGIC VISION CONTROL; it supplies water from the wiper blade as required and depending on the direction of wipe.
Compared with its successful predecessor, the new Mercedes-Benz SL offers considerably more comfort and sportiness, setting new standards in the luxury roadster class. Added to which is uncompromising day-to-day suitability, which turns the SL into an incomparable all-rounder among sports cars. In short, anyone that talks about the new SL is bound to be talking about the ultimate in passionate, refined motoring.
Dr Dieter Zetsche, Chairman of the Board of Management of Daimler AG and Head of Mercedes-Benz Cars: “There are around 900 million cars in the world and thousands of models. But there are only a handful of automotive icons. Our SL is one of them: it has class, it has style, it is the ultimate in comfort and luxury. But it combines all that with incredible sportiness and dynamism. You would struggle to find a car that embodies Gottlieb Daimler’s aspiration more perfectly than our new SL: the best or nothing.”
The new-generation Mercedes-Benz SL takes the meaning of the famous letters “SL” – super-light – literally. Consistent weight reduction is one of the most outstanding design characteristics in the new SL as was the case in its namesake, the original SL of 1952 with its lightweight tubular frame. For the first time Mercedes-Benz has implemented an all-aluminium bodyshell in a series-production model.
The greater part of the weight-reduction “diet” is hidden from the eyes of the observer of the SL. Under the aluminium outer skin there is a bodyshell made almost entirely from aluminium, only very few components being made from other materials. The even lighter magnesium is used in part for the cover behind the tank. The A-pillars and the roof frame are of steel sheet metal incorporating high-strength steel tubing. For these elements steel is the best solution to provide survival space for occupants in the event of the vehicle overturning.
The new aluminium bodyshell weighs around 110 kilograms (243 lbs) less than it would using the steel technology from the predecessor. “The effect is rather as if a heavyweight-class passenger had got out of the car” says Dr Thomas Rudlaff, responsible for the aluminium bodyshell at Mercedes-Benz. “The result is perceptible and measurable. Less weight means more dynamism and less consumption. In other words: the motoring enjoyment increases, the environmental burden sinks.”
The aluminium structure is not only lighter but also proves superior to the predecessor’s steel construction in terms of rigidity, safety and comfort. This is achieved thanks, among other things, to its intelligent lightweight construction with components optimised for their specific task. Thus, diverse processes are used to make different kinds of aluminium depending on the use the component is to be given: the parts are made by chill casting or vacuum die-casting, worked into extruded aluminium sections or into aluminium panels of different thicknesses. The result: high rigidity, high safety levels and better vibration characteristics.
The developers at Mercedes-Benz did not rest content achieving weight benefits alone. The aluminium structure had to be superior to a steel construction in terms of rigidity and comfort as well. In order to attain this high objective, developers consistently went for an intelligent lightweight construction, and explored many new paths to do this. Every single component of the aluminium bodyshell was specifically optimised for its particular function and expected loads. Thus, diverse processes are used to make different kinds of aluminium depending on the use the component is to be given: the parts are made by chill casting or vacuum die casting, worked into extruded aluminium sections or into aluminium plates of thicknesses that vary within one and the same component; these are what are known as the tailored welded blanks. Expressed in numbers, the bodyshell weight is made up of: 44 percent cast aluminium, 17 percent aluminium sections, 28 percent aluminium sheet metal, 8 percent steel and 3 percent of other materials.
At the Bremen production facilities the parts are assembled using diverse load-adequate joining methods, some of which are innovative processes. Secure joints are ensured, for example, by MIG welding, hemming, bonding, self-piercing rivets, flow hole bolting, or friction stir welding – a joining method by which a highly resistant weld seam is produced by means of friction heat; a method particularly well-suited to aluminium on account of its low melting point.
Particular highlights of the bodyshell:
- The firewall is at present the largest aluminium cast component made in large series for vehicle bodywork
- Many sheet metal parts are designed in such a way that for the first time they can be made from 100-percent recycled aluminium, saving 80 percent of the energy used in their production.
- The main floorpan consists of a 3-layer shaped panel made from thin, extrusion-moulded hollow sections, welded together by friction stir welding.
- The longitudinal members in the vehicle front end are made using high-pressure hydroforming (IHU) technology, which enables the creation of highly complex and robust components, permitting optimum use of reduced installation spaces.
- The door sills (longitudinal members) consist of 1.7 metre-long, 7-chamber extrusion-moulded aluminium sections; these provide rigidity in the lateral sectors and safety in the event of a collision. Flexible chamber distribution makes possible a minimum component weight coupled with optimum characteristics.
- The tunnel is made of aluminium sheet metal with a reinforcement of varying thickness (3 different thicknesses depending on the sector, a so-called tailored welded blank, TWB).
- The rear sector floor is a MIG welded frame with a hollow chilled cast longitudinal member as its central element. This technique is employed in the SL for the very first time in automotive bodyshell
- The rear sector floor frame structure is closed by floor sheet metal panels and the boot tub made by vacuum die-casting.
- The boot recess is made from recycled sheet metal.
- The central member connects the front end with the rear sector floor. The mounting points for the drive shaft, the transmission cross beam, the transmission tunnel braces and the seat bolting points on the tunnel side are all integrated into a single element. The wall thicknesses and rib distribution are oriented bionically towards the requirements and loads.
- Many other components were optimised bionically, i.e. based on examples from the natural environment. These structures reduce the vehicle weight compared to a classic design even further.
The sum total of all the design measures leads to a lightweight, torsionally and flexurally rigid bodyshell with an optimum rigidity/weight ratio. It was possible to increase the bodywork’s torsional rigidity by more than 20 percent over the already highly rigid preceding model series. This is confirmed by measurements of the new SL’s torsional strength – at 19400 Nm per degree the roadster achieves an absolute top value (its predecessor already reached 16400 Nm per degree).