Mercedes Benz

OFFICIAL PRESS RELEASE

Stuttgart, Germany, Sep 07, 2010

Passive safety and bodywork: Sturdy structure, sensitive sensors

- PRE-SAFE®: early accident detection through anticipatory occupant protection
- Restraint systems: sensors ensure protection in keeping with the situation
- Body: high crashworthiness owing to high-tech steel alloys
- Aerodynamics: wind resistance and wind noise exemplary

Occupant protection in the new-generation CL already begins before an accident. The Mercedes-Benz invention PRE-SAFE®, a standard feature of the two-door car, sees to that. Much as living beings react instinctively and seek cover when danger threatens, when an accident threatens PRE-SAFE® is able to activate precautionary protective measures for the occupants so that the belts and airbags can protect them to best effect during a collision.


This early accident detection is possible because PRE-SAFE® is an intelligent synergy of active and passive safety. The anticipatory occupant protection system is linked to the Brake Assist and the Electronic Stability Program (ESP®), BAS PLUS (optional), DISTRONIC PLUS (optional), and the PRE-SAFE® Brake (optional), whose sensors detect potentially critical driving situations and send the relevant information to the electronic control units within a matter of milliseconds. PRE-SAFE® also uses this comprehensive sensor data.

If PRE-SAFE® recognises, for instance, that the car is about to go into a skid, the driver is forced to brake sharply or the PRE-SAFE® Brake is going into action, it brings the front-passenger seat into a more favourable position and, if necessary, begins to close the side windows and the sliding sunroof automatically, so that the occupants are not thrown out of the car in an accident and the windowbags find better support in a side collision or rollover. The positioning of the front-passenger seat prepares the occupants for the possible collision such that belts and airbags can protect them as best possible.

Active multicontour seats embrace the occupants

Another PRE-SAFE® measure: the active multicontour front seats in the CL 500 4MATIC BlueEFFICIENCY and CL 600 offer the possibility of seating the driver and front passenger even more securely, thereby limiting dangerous whiplash movements by the upper body. If PRE-SAFE® detects a critical driving situation, the system instantly activates the air chambers in the seat cushions and backrests. These then envelop the seat occupants and give them support. Tests at the Mercedes-Benz Technology Center have shown that this PRE-SAFE® function increases the distance between the shoulder and the inner door lining by up to 40 millimetres at a lateral acceleration of 0.6 g. This enables the sidebag to fulfil its protective function even more effectively.
All PRE-SAFE® protective measures are reversible: if the accident is averted, the occupants are able to reset all systems to the desired positions. The anticipatory occupant protection system is then ready for action again straightaway.

PRE-SAFE® functions during emergency braking

Electrically adjustable front-passenger seat is moved backwards or forwards into the optimum position whilst the cushion angle and backrest inclination are also optimised

The bolsters in the seat cushions and backrests of the active multicontour front seats* are inflated

PRE-SAFE® measures in the event high lateral acceleration is detected

The side windows at the front and rear are closed

The sliding sunroof is closed

*depending on equipment

Individual safety according to personal height and bodyweight

If the accident is unavoidable despite advanced assist systems, a powerful restraint system goes into action in the new-generation CL to protect the occupants in a way appropriate to the need and the situation. Using various sensors, a computer evaluates not only the seriousness of the accident, but also personal data describing the front-seat passenger. If the sensor in the seat cushion has identified a small passenger, depending on the type of accident it initially deploys only the first airbag stage so that the air cushion is less fully inflated. If it detects a larger passenger, however, both airbag stages are deployed.

In addition, on board is the proven automatic child seat identification feature that deactivates the front-passenger seat airbag when a special Mercedes-Benz rear-facing child seat with transponder has been recognised. If the front-passenger seat remains unoccupied, airbag, sidebag and belt tensioner on the front-passenger side are deactivated.

Sensitive: eleven sensors for accident detection

The CL has a total of eleven installed sensors that provide immediate data on the probable type and seriousness of a collision:

*
Frontal impact: In addition to the central sensor in the airbag control unit, the luxury coupé is equipped with "up-front" sensors. Because of their exposed position in the front module, they detect the anticipated strength of an impact even earlier and with even more precision, so that the time between the crash and the activation of airbags and seat-belt tensioners can be reduced even further.
*
Side impact: pressure sensors relay rapid, precise information to the control unit in the event of an impact from the side in the area of the doors. These sensors react when the air between the doors' outer skin and inner lining is compressed on impact. Additional side sensors are installed in the lower (not visible) B-pillars.
*
Rear end collision: if the central crash sensor in the interior detects a rear impact, it triggers the pyrotechnic front and rear belt tensioners to fix the occupants securely in their seats.
*
Rollover: in side rollovers, a rollover sensor integrated into the airbag control unit can activate the seat-belt tensioners and windowbags.

Restraint systems: a series of eight airbags

With eight airbags fitted as standard, not to mention seat-belt tensioners and belt-force limiters, the new-generation CL offers an even more extensive package of safety equipment than its predecessor. The airbags, which deploy in a matter of milliseconds in the event of an accident, include two adaptive airbags for the driver and front passenger, two sidebags in the front-seat backrests, two sidebags in the rear compartment side panels, and two large windowbags which extend from the A-pillar to the C-pillar during a side impact.

All the occupants have three-point automatic seat belts with seat-belt tensioners and belt force limiters. The force limiter of the front belt straps is adaptive: after attaining a certain maximum level of force, the force limiters switch to a lower level of force – the belts are loosened so that front passengers can plunge deeper into the airbags. This reduces the loads acting on the chest area of the occupants.

The steering column serves the same purpose. During a front-end impact, it collapses telescopically by up to 80 millimetres.

The occupant restraint system of the CL at a glance:

System components / Front seats / Rear seats

3-point seat belts with automatic belt height adjustment / x With automatic comfort-fit function / x

Belt tensioners / x Buckle retractor / x Inertia-reel tensioners

Belt-force limiters / x Adaptive / x

Head restraint height and angle adjustable / x / x

Front airbags / x with adaptive control on the front passenger side incl. customisation / -

Sidebags / x / x

Windowbags / x / x

Automatic child seat detection / Optional on the front-passenger side for Mercedes-Benz child seats with transponder / -

x Standard

Mercedes safety after the accident too

The comprehensive Mercedes safety concept also takes into account the phase after the traffic accident. To prevent follow-on damage, the fuel supply of the engine is automatically blocked in the CL in accidents above a certain severity. The hazard warning signal also switches on to warn drivers approaching from behind and to prevent new accidents.

After an accident in which airbags are deployed, all the side windows open just enough to leave a narrow space through which the interior can be ventilated. Additionally, the door locks are automatically released so that injured passengers can be rescued more quickly. Specially designed crash joints prevent the doors from becoming blocked by the wings. The passengers can also open the doors after an accident, because Mercedes-Benz uses cables that remain intact after deformation for the internal activation of the door locks. Markings on the rear windows show the emergency services places where they can cut through the C-pillars in the event of a serious accident to quickly reach injured passengers and provide them with medical care.

Crashworthy thanks to high-tech steel: carefully designed body

The basis for the exemplary level of occupant protection in the CL is an intelligently designed bodyshell with large deformation zones at the front and rear ends. Around 44 percent of all the bodyshell components are made of high- or increased-strength high-tech steel alloys, which offer the maximum strength for the minimum weight. In addition, ultra high-strength high-tech alloys find use in the body areas important for occupant protection. In this top-of-the-range model with the star, the share of conventional deep-drawn steels is now only 26 percent. Mercedes-Benz manufactures the bonnet, front wings, door panels, front and rear module carriers as well as the rear panel behind the rear seat backrest from aluminium.

The boot lid and the spare wheel well likewise are made of a lightweight material: plastic.
The front module and the frame-type integral support, to which the engine, front axle and steering are attached, connect the front side members with the second side member plane above the wheel housings. During a frontal collision, this gives rise to two important paths along which forces and loads are transmitted, which is one of the major reasons for the exemplary passenger protection of the CL. Similarly, the solid, multi-layer side skirts can absorb large forces and divert the impact energy past the passenger compartment.

In the event of a one-sided frontal impact the continuous firewall cross member distributes the impact forces over a large area, into the centre tunnel and the longitudinal members at the sides. An additional upper member increases the rigidity of the firewall and reduces the extent to which the pedals are pushed into the passenger compartment.

The V engines of the CL make an important contribution to passenger safety as well. Because of their compact design, they allow greater deformation in the front-end structure, reducing the strains on the passengers. The propeller shaft has likewise been equipped with special deformation elements.

The distribution of the impact forces onto several vertical and horizontal planes specifically designed to carry certain amounts of load not only helps keep passengers safe; it also makes collisions with smaller vehicles less "uneven". The front-end structure of the big coupé is designed in such a way that it purposefully dissipates collision energy for the other vehicle, too.

Practically undeformable: the passenger compartment

The passenger cell is a structure virtually immune to deformation which keeps the passengers' survival space largely intact, even at high impact speeds, regardless of whether the collision is head-on, from the rear or from the side, or whether the vehicle rolls over. The use of high-strength steel and thicker panels plays as important a role here as the installation of additional load-bearing members.

A complex and carefully designed floor structure forms the sturdy foundation for comprehensive occupant protection. Eight side member sections, four cross members and a three-part tunnel reinforcement stabilise the passenger compartment in a crash, and ensure that impact forces are distributed over a large area.

Side structure: optimally prepared for collisions

The elegant lateral lines with the continuous expanse of glass and the delicately traced roof pillars were made possible by carefully designed bodywork features which help the coupé to meet the most stringent test conditions in regard to torsional stiffness and occupant protection even without upper B-pillars.

In a side impact, the main elements that come into play to stabilise the passenger compartment are the sturdy side skirts, the lower B-pillars, the four cross members in the floor area and a solid steel section below the dashboard. Mercedes-Benz produces the sills and B-pillars using increased-strength steel alloys, which are far superior to all other materials in terms of their tensile strength. Side impact protection is also provided by steel reinforcing sections with a high tensile strength in the doors.

High-strength fastening surfaces for the door hinges additionally provide sturdy tensile bracing in the area of the side structure that can effectively protect the occupants in a side collision.
In addition to a high level of safety, the doors of the CL have functions which make access and egress more convenient. A hydraulic system ensures that from an opening angle of 15 degrees the doors are arrested in any position – even on gradients or in strong winds. An electric servo-locking mechanism closes all the doors (and the boot lid).

Rear-end structure has successfully passed the toughest of crash tests

At the rear the passenger compartment is protected by a meticulously designed deformation zone. In addition to the aluminium transverse section and the steel crash boxes of the bolted rear module, this consists of two sturdy side members and a cross member in the area of the boot floor. The suspension sub-frame of the rear axle likewise forms an energy-absorbing plane in the event of an impact.

The fuel tank is located in the protected area in front of the rear axle. Even with respect to rear-end protection, this means that the CL meets the world's most stringent crash test standards such as the US test according to FMVSS301 at 80 km/h.

Easy repair: the front and rear modules

In accidents involving low collision speeds, the proven module design for the front and rear sections protects the vehicle from major damage. The bumper cross members of the modules consist of high-strength extruded aluminium sections. They are connected to the side members via steel crashboxes and designed in such a way that the energy of impact is first absorbed by the aluminium sections and the crash boxes. The portions of the body shell behind them thus remain undamaged. In addition, the sturdy cross members take on the job of transferring energy to the non-stressed side of the body structure during an offset frontal impact.

The front and rear modules are bolted to the body and can be replaced without elaborate and costly welding work during accident repairs. The individual components within the modules are likewise connected to one another by bolts.

Long-term protection: fully galvanised body and paint with nanoparticles

Mercedes-Benz has developed an effective package of measures for long-term protection against corrosion for the CL bodyshell. It is based on fully galvanised body panels, some of which have an additional organic coating on both sides depending on their location – on the doors for instance or on the side members at the front, sides and rear. This coating contains rust-inhibiting zinc pigments too. Mercedes-Benz also protects the most vulnerable structural areas of the bodywork – for example the front side members, the front end structure's upper side member level, the side skirts and the rear wheel arches – with a cavity-fill preserving agent.

In addition, sealed welds prevent corrosion from developing. Seam sealing is applied to a great many of the welded connections of the floor structure along with the bonnet, doors, boot lid, rear wheel arches and tank flap. Extensive underfloor panelling made of a plastic laminate protects the body from flying stones, moisture and dirt.

An important contribution to exemplary long-term quality and value retention is also made by a scratch-resistant clear coat employing nanotechnology. It is part of the standard specification of the CL and is used both on metallic and non-metallic paints. It features tiny ceramic particles less than a millionth of a millimetre in diameter which are integrated into the molecular structure of the paint binding agent. These particles improve the paint's scratch resistance by a factor of three and lastingly ensure a noticeably better gloss.

Aerodynamics: an example among the luxury coupés

The previous model with a drag coefficient of 0.27 was the most aerodynamic vehicle in its class on its debut. In the successor the Mercedes-Benz specialists further improved this figure through meticulous attention to details like the new exterior mirror housings, a spoiler lip on the lower engine compartment covering and various design modifications. The redesigned front bumper, for example, deflects airflow around the front wheel even more efficiently. The design of the radiator grille also helps improve aerodynamic efficiency. Result: the new model generation impresses with a top cd figure of 0.26 in the CL 500 BlueEFFICIENCY. The flagship model of the brand with the star thus remains a model of aerodynamics among the luxury coupés.

The better the airflow around the vehicle body, the less wind noise there will be. The good aerodynamics of the CL therefore also benefit acoustics. Well-targeted aero-acoustic measures include reinforced outer skin surfaces, noise-insulating door seals, six-millimetre thick side windows, windscreen wipers positioned beneath the stream of air, a special rubber seal between rear window and boot lid, and serrated draught deflectors on the tilting/sliding sunroof.

The aerodynamic data of the Mercedes-Benz CL - CL new / Preceding model
Drag coefficient (cd) - 0.26–0.27 / 0.27-0.28
Frontal area (A) m² - 2.32-2.33 / 2.28-2.30
Wind resistance (cd × A) m² - 0.603–0.629 / 0.616–0.644

Apart from wind noise, the Mercedes developers managed to further reduce driving noise and tyre noise in the new-generation CL. They achieved this with additional damping foils in the rear wheel arches which absorb noises and vibrations just as effectively as the boot floor, heavier compared with the previous model, and the increased insulation of the rear panel in front of the boot. To reduce engine noises, the coupé was given new underfloor panelling in the area of the engine compartment along with a redesigned insulating panel for the bulkhead in front of the cockpit.

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