http://european-aluminium.eu/media/1543/1_aam_body-structures.pdf
Interesting info regards the body shell materials design of the S-class.
Aluminium hybrid bodyshell of the Mercedes-Benz S class (W222)
Mercedes-Benz describes the body of the 2013 S class model (W222) as a third-generation aluminium hybrid bodyshell. The body consists of 50% aluminium in combination with high- and ultra-high strength steels. A lightweight design concept by material and geometrical optimisation coupled with a highly complex joining technology (specifically the application of additional mechanical joining technologies) allows the new S class model to further raise the bar in the demanding luxury saloon segment – without adding weight. The lightweight index, the torsional stiffness in relation to weight and vehicle size, has been improved by 50% compared to the predecessor model. A further design goal was a better NVH performance than the already very good preceding model.
The entire outer skin of the S class model, including the roof and the front section of the body, consists of aluminium. In the case of detachable body parts such as the wings, bonnet and boot lid, the use of aluminium adopted for the previous model series was continued. A new development is, however, the lightweight aluminium front section which also greatly enhances crash and NVH performance. Cast aluminium and extruded aluminium sections are used in addition to sheet aluminium. Die-cast aluminium was chosen for the shock absorber strut bracket because of its good integration properties. In this way, it was possible to connect the front module without additional holders. In order to improve the safety system as a whole, a cross-functional load path was conceived. Additional support is provided by the aluminium struts running in X-direction from the shock absorber strut bracket to the cowl. Supplemented by a multi-piece framework, these struts also help to suppress the Y-movement of the side members. This design allowed the incorporation of a new load path into the limited package installation space in the front section. The forces are applied to the bodyshell structure in the three-piece cowl, which has been configured as a cast aluminium component in the centre section. The casting allows a functionally perfect connection with distinct advantages in terms of weight and installation space. The firewall area is a sheet steel design which also allowed the integration of the complex hybrid joint between the aluminium front section and the steel cell.
In addition to the front section, the integral carriers are also made of aluminium. As well as acting as a component carrier for numerous components (i.e. the complete cooling module in addition to the engine, steering, torsion bar and front axle), the integral carrier is a central component of the front-end structure when it comes to performing crash and NVH functions. The integral carrier's side members also form the third crash load path in the front section. In order to meet these multiple requirements, a complex aluminium mix comprising die castings/permanent mould castings, extruded sections and sheet metal parts was also required here.
The side members have been designed as combined aluminium extruded sections/castings to optimise crash performance, rigidity and component integration. The protrusions of the extruded aluminium sections of the side members required for package reasons have been designed to also have a positive effect on folding behaviour in the event of a crash. The side members are connected to the steel passenger cell by means of cast aluminium components that allow a very rigid connection and integration of the integral carrier connection.
The aluminium roof is another key area for lightweight design as reducing weight here has a positive effect on the vehicle's centre of gravity and on NVH characteristics. A major challenge here was integrating the roof into a steel structure. This was achieved by implementing an efficient and simple assembly solution in the bodyshop, which involves the roof being fixed to the bodyshell structure using shackles with defined spacing for the purpose of production in the factory.
The safety passenger cell is made using an extremely high percentage of high-strength steel, including roll-formed boron steel in critical load path areas. The rear panel and cockpit cross- member are designed as hybrid metal/plastic constructions.In addition to this, structural
foams sections are used in the A/B/C-pillars to increase bodyshell rigidity and ensure high NVH performance.
In order to reduce the loads exerted on a pedestrian if their head hits the bonnet of the vehicle, the deformation space between the bonnet and the components beneath it has been optimised. This was achieved in part by appropriate positioning of components such as control units or fluid reservoirs in the engine compartment. Furthermore, the S class model features an active aluminium bonnet with a homogenously reinforced inside face. In the event of a collision with a pedestrian, sophisticated sensors combined with intelligent algorithms trigger pyrotechnic actuators in the area of the bonnet hinges which raise the bonnet by around 80 mm.