by Adrian-Liviu Dorofte

The C-Class Coupé: Pure fun at the wheel with the perfect coupé proportions - VII


Stuttgart, Germany, May 17, 2011

Passive safety, bodywork and manufacturing: Comprehensive protection for passengers

The C-Class Coupé safety concept has been optimised based on the analysis of real-life accidents. As part of the standard specification, nine airbags (front airbags and pelvisbags for the driver and front passenger, a kneebag on the driver's side, sidebags in the front, as well as windowbags for the driver and the front and rear passengers), belt tensioners, belt-force limiters and NECK-PRO crash-responsive head restraints in the front offer the occupants an extremely high level of protection should an accident occur. Sidebags in the rear are available as an option. The body structure has been designed to ensure that, in the event of a frontal collision, the impact forces are distributed over a wide area and on four independently acting impact levels, meaning that the occupant cell remains largely intact. Around 70 percent of all the bodyshell panels are made from state-of-the-art, high-strength steel alloys that minimise weight and maximise safety. An active bonnet is one of the measures designed to meet requirements to protect pedestrians.

The C-Class Coupé also features the anticipatory occupant protection system PRE-SAFE® as an option. This Mercedes-Benz innovation uses the time between detection of a potential accident situation and a possible collision to initiate preventive protective measures, thus reducing the loads exerted on the occupants in the event of a crash by up to 40 percent. Depending on equipment, the PRE-SAFE® system consists of reversible belt tensioners for the front seats, a closing function for power windows, a closing function for the electric panoramic sliding sunroof and a positioning function for the front passenger seat.

Being closely related to the other C-Class models means the safety concept can also be expected to do brilliantly in standardised rating crash tests. The renowned American Insurance Institute for Highway Safety (IIHS), for instance, declared the Mercedes-Benz C-Class Top Safety Pick three times in a row (in 2009, 2010 and 2011) – deeming it to be the best purchasing decision with regard to safety. The C-Class achieved good ratings in all the safety criteria which were examined.

Extensive crash-test simulations formed the basis for safety development work, particularly on coupé-specific components. This is a field which has made great leaps forward: at the beginning of the 1990s, Mercedes-Benz was performing around 200 computerised crash tests per annum. By the year 2000 this number had already increased to 1500 simulations, and in 2010 more than 50,000 were carried out. And this is by no means the only impressive set of statistics: for the tests on the W 201, the C-Class’s predecessor from the 1980s, the computer model consisted of 25,000 finite elements. Nowadays the level of detail is much greater – the digital replica of the current C-Class (W 204), for example, comprises around two million elements. And the planar grid of the virtual vehicle structure is now composed of tiny rectangles and triangles with an edge length of three millimetres. This facilitates a far more precise and detailed deformation analysis than previously, when, at 25 mm the elements were so much larger.

As well as the high development speed, the decisive advantage that computer simulation has over real crash tests lies not only in the fact that the vehicles are not destroyed; even more important than that is the ability which today’s engineers have to detect and follow what actually happens in an impact in great detail. As if with x-ray eyes the engineers can track the course of deformation in extreme slow motion and from any perspective they wish, thus delving further and further into the details every year.

The right material in the right place: in accordance with this principle, approximately 70 percent of all the sheet metal panels in the C-Class Coupé are made of high-strength steel alloys. With minimum weight, they offer maximum strength and thus the highest possible levels of safety. Today’s ultra-high-strength steel sheet panels deserve a special mention. They achieve a tensile strength that is three to four times higher than that of conventional steel grades, making them indispensable for meeting the stringent Mercedes requirements regarding durability and safety. These ultra-high-strength high-tech alloys account for around 20 percent of the weight of the bodyshell.

Aluminium and plastic are the other two lightweight materials which Mercedes-Benz uses where they offer maximum benefit. For example, the bonnet is made of aluminium. It weighs in at some 9.2 kg less than a comparable steel version, thus reducing the weight where this makes most sense in terms of driving dynamics. Other aluminium features on the coupé are the front wings, the front-end assembly including its flexible cross member and crash boxes, the sheet metal panel for the parcel shelf in the rear, and the door modules. The spare wheel recess is made of plastic.
The aerodynamics of the C-Class Coupé are the mark of the bodyshell’s efficiency. With a Cd figure of 0.26 it is not only exceptionally aerodynamic, but also glides through the wind better than most compact cars – and even small cars – with its wind resistance of Cd x A = 0.55 m2.

Long-term corrosion prevention for the bodywork is based on fully galvanised sheet metal panels. Structural areas of the body which are subjected to high stresses are protected with cavity-fill preserving agent. Sheet metal panel laminations and beads are completely filled with adhesive, whilst systematic sealing of the weld seams and edges with a PVC joint prevents corrosion from occurring. Generous underbody panelling composed of plastic laminate protects the bodywork and engine against stone chipping, moisture and dirt. Axle components, which are also subjected to a great deal of stone chipping damage, are protected by plastic panelling.

The C-Class Coupé is made at the Mercedes-Benz plant in Bremen. New for Daimler, it is the fourth model to be made on a single production line together with the Saloon and Estate versions and the GLK. This places high demands on production management and logistics, but gives the company the ability to respond to fluctuations in demand for specific models with exceptional flexibility.

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