Mercedes-Benz CL-Coupé 2006

Highlight generates full success
With the new CL class Mercedes-Benz crowned its more than 50-year-old coupe tradition in autumn, 2006. The big Mercedes coupes are a perfect example for elegance and exclusivity in car design since decades. They put standards in design and features; unite exemplary security with the highest comfort and sovereign driving experience. A demanding car assumes demanding development. The long-standing collaboration qualified Bertrandt for the responsibility for the complete body-in-white development.

Comprehensive Competency

The project CL Coupe was incredible for Bertrandt with regards to the scope as well as the demands. Engineers from different competence centres in the Bertrandt Engineering Network co-developed in the new superlatives of Mercedes-Benz. In coordination with DaimlerChrysler, Bertrandt assumed the responsibility for the complete body-in-white development with the entire security process. Among others, it entailed single areas like project management, supplier's management, documentation and calculation. In particular, two areas show innovation strength: the columns and the rear.

Fire crash test

The challenge for every design is the crash tests, because success or failure of the whole development work depends thereon. To also fulfil the high of the US market, for the CL coupe it was a matter of passing through tough tests. On the following page the explained five crash tests were the fire test for the CL coupe. The entire know-how    was introduced optimally to master hurdles like the roof case test or side impact. Thus it was relocated in the complete joining of the side panel. Also the rear and the columns received a general overhaul of a special kind.

The columns

Because in the rear lid a lot of electronics is accommodated and therefore an electromagnetic compatibility must be guaranteed, plastic was ideal for the body-in-white. In the development the engineers, therefore used, pressed fibreglass reinforced plastic instead of the often used aluminium. This plastic also had a big advantage with regards to weight. The used Light SMC plastic (Sheet Moulding Compound) has a considerably lower density than the usual SMC plastic. The original plan to use carbon could be renounced with the design of the rear lid as it became evident in the rear impact.
 
The slight rejuvenated column configuration is a typical characteristic of the big Mercedes coupes whose roots go back to the fifties. The design requirements planned to rejuvenate the general look of the new CL coupe: The stretch-roof curve was substantially widened and flattened by what underlines the elegant character of the coupe. However, the transfer resulting there from - the C column of about 200 mms released to the back is a small revolution: New ways had to be found to guarantee the aimed stability.

Through the more complicated requirements concerning the stability in the side impact also changes emerged for the B column. The planned adjusting column was put on the sidebar. The A column likewise experienced a change. At the beginning of the development a USIBOR deep drawn component design existed. A steel kind which is transformed with approx. 800 °C and has a tensile strength from up to 1,300 Mega Pascal. However, the first crashes with the vehicle prototype in particular with the roof case; a need for test optimisation became evident, because USIBOR only has a limited stretching capacity. An ultrahigh-strength pipe concept was developed and implemented in the side panel as well as the material concept of the A column and the lateral roof frame. After all, a trivalve design emerged: The A column outside and inside plus the strengthening pipe lend the desired elasticity and stability.

Calculating safety

Beside the implementation of the crash test results into the body-in-white development, other main focuses in the calculation and attempt range were the interior security and head impact calculation.. Bertrandt carried out distance calculations and testing and validation for the pedestrian's safety internally. To lead all data and results without delay in the project, the Bertrandt employees were integrated with the calculation at DaimlerChrysler and were integrated into the whole vehicle integration team.

Way to pilot production
A huge step towards increased efficiency was the overleaping of the phase "Design-Vehicle". Switching from the configuration to the validation vehicle, the pilot production, was possible due to an absolute digital validation quality and parameters of the configuration vehicle. By this means the development time could be considerably abbreviated. After project take-over in May 2003, in October 2004 Bertrandt was already able to produce production release as well as several instrument and milling approvals. Close to Whitsuntide 2005 Bertrandt could present the pilot production.

A question of synchronisation
The project management of Bertrandt was responsible for the entire coordination of this gigantic project. A qualitative and efficient car can originate only from the perfect teamwork within the complicated project structures and the company internal processes of DaimlerChrysler and Bertrandt. To visualise these interfaces and to reiterate the entire scope, the scope of the CL coupe project is illustrated.


Conclusion

With about 80 experts in development, data management, quality management, release as well as change management, the project could be finalised within three years. For Bertrandt a milestone which encouraged the engineers once more in its competency and evened the way for other extensive collaborative projects. We are glad to have had the opportunity to contribute to the most popular luxury coupe in the world.