The new Mercedes-Benz SLK: Passion meets efficiency ~ IV


Stuttgart, Germany, Mar 08, 2011

Vario-roof and body: Innovative technology with a unique roof concept

Driving a roadster is a wonderful emotional experience. Gliding through the landscape and its many sounds and smells at the wheel of an agile sports car, with the top down and the sun shining, awakens intensive and joyous feelings. In a Mercedes-Benz SLK, even rainy weather does little to mar this pleasure. Ever since the launch of the first SLK in 1996, this has been ensured by a vario-roof which converts the roadster into a coupé with a fixed roof at the touch of a button, and in just a few seconds. Since then, Mercedes-Benz engineers have constantly refined the vario-roof even further and maintained the SLK's pioneering role in this technology.

Unique item of equipment: MAGIC SKY CONTROL

For the first time, Mercedes-Benz is offering a choice between three variants of the lightweight vario-roof for the new SLK:

- The base version is a roof painted in the vehicle colour
- Alternatively there is the option of a panoramic vario-roof with tinted polycarbonate.
- The third variant is a world premiere – the panoramic vario-roof with MAGIC SKY CONTROL. This glass roof switches to light or dark as required at the press of a button. When light it is virtually transparent, offering an open-air experience even in cold weather. In its dark state the roof provides welcome shade and prevents the interior from heating up when the sun’s rays are very intense. In other words: a feel-good atmosphere at the touch of a button

The operating principle is based on the physics of a plate condenser: if the glass structure is subjected to an electrical voltage, particles in the structure position themselves so that light is able to pass through the glass. If the voltage remains switched off, however, the particles position themselves randomly. This partially blocks the light, and the glass remains dark. The control unit and converter are integrated into the front section of the roof, and the switch is in the overhead control console.

In addition to the unique panoramic effect and transparency at the touch of a button, MAGIC SKY CONTROL also provides a top-class feel-good atmosphere. UV and infrared light are also effectively blocked in transparent mode, while insulation increases even more significantly and noticeably in darkened mode, thereby helping to keep the temperature on interior parts such as armrests cooler by up to 10 degrees Celsius compared with conventional tinted glass.

Measurements using a device called a star pyranometer in Death Valley, one of the world's hottest places, impressively demonstrated the effect. This device measures the intensity of exposure to sunlight. With an open roof, the thermal load from the sun in the heat of Death Valley reached 1000 to 1100 W per square metre. With the transparent glass roof it dropped to 200 W, and when the roof was switched to darkened mode with MAGIC SKY CONTROL, it dropped to 40 to 50 W – one 20th of the original value and less than a 60 watt bulb.

Since the innovative glass also shields against the sun's rays far more effectively than conventional thermal insulation glass or sunblinds, the occupants of the new SLK also enjoy the highest level of climatic comfort. When driving with the roof open would be unpleasant owing to intense heat, the driver and front passenger are able to relax under the MAGIC SKY CONTROL roof – an important contribution to onboard comfort and the driver-fitness safety typical of a Mercedes. Even when the vehicle is at a standstill the interior does not overheat, since the roof is switched to darkened mode when powered off.

But MAGIC SKY CONTROL not only benefits passengers. Some of the strain is also taken off the air-conditioning system, thereby saving on CO2 emissions.

In addition, the frame of the three roof variants is now of magnesium. This makes each roof around six kilograms lighter than in the previous model, giving the car a lower centre of gravity.

The engineers have also refined the operating mechanism for the roof and boot lid. It now takes less than 20 seconds to open or close the roof completely. The improved mechanism mainly benefits the boot capacity.

Boot fully suitable for everyday use

The luggage capacity with the vario-roof closed is 335 litres (in conjunction with TIREFIT). This is enough to accommodate two crates of soft drinks and two crates of beer, or four of either, without difficulty. A golf bag or a large suitcase are also no problem.
When the roof is opened, the capacity is reduced by 110 to 225 litres. This includes 51 litres of luggage box capacity under a reversible floor (the box is omitted if a collapsible spare wheel is chosen instead of TIREFIT). In any case there is sufficient space for two large sports bags, for example with tennis equipment.

The luggage box or collapsible spare wheel is accessible if the variably usable reversible floor is removed. Depending on the application, it provides a level surface or a recess for carrying e.g. high drinks crates. The draught-stop or an umbrella can be secured with elastic straps on either side of the reversible floor.

To prevent luggage items from colliding with the roof components while these are being deposited in the boot, there is a luggage cover in the boot which can be pivoted longitudinally. The vario-roof can only be opened if this cover is pivoted to the rear, and when the roof is closed the cover can be easily pivoted forward by hand. This facilitates loading and unloading, and makes the full boot capacity available.

Bodyshell structure with aluminium components

The bodyshell structure already proved highly successful in the preceding model, and was weight-optimised still further for the new SLK. Accordingly the bonnet and front wings are of aluminium for the first time, as are the dashboard cross-members and the rear end. The rear bulkhead module of fibre-reinforced plastic is a new feature. The torsional rigidity of this optimised lightweight steel construction was improved even further compared to the already very rigid preceding series. Thanks to the intelligent use of lightweight construction methods, the bodyshell weight was reduced by around 13 kilograms.

The doors are a completely new development, with reinforcement at the beltline and at the lower edge. A section of high-strength steel ensures good side impact protection. The well-proven A-pillars with welded-in oval tubes of hot-formed ultra-high-strength steel and a robust nodular connection to the side members remain unchanged.

To keep the cost of minor damage caused by a frontal impact at speeds up to 15 km/h reasonable, the front side members have a prescribed cutting point for a sectional repair, and their shape causes them to bend ahead of this area in the event of a collision.

Exemplary aerodynamics

Despite the more striking, steeper front and the just under three percent larger frontal area compared to the previous model, the Cd value for the new SLK has been cut to just 0.30 – a very good figure for a roadster (the preceding model had a Cd value of 0.32). This improvement has enabled CO2 emissions to be reduced by roughly one to two grams per kilometre. Once again this shows that the engineers at Mercedes-Benz have made good use of many possibilities to enable SLK owners to enjoy the fun factor in the new roadster with an easy conscience - thanks to its high environmental compatibility.

The aerodynamic data for the new SLK-Class

In addition to familiar features such as a spoiler lip on the upper edge of the boot lid, wheel spoilers in front of the front and rear wheels, and a full engine compartment and underbody cladding concept, the excellent drag coefficient is especially due to:

- A radiator shutter for demand-related control of the cooling airflow,
- highly aerodynamic tyres,
- newly designed exterior mirrors and
- painstaking modifications to the A-pillar cladding.

The A-pillar cladding is a good example of meticulous development work. It took more than one year to develop a plastic cover that would combine high design requirements with exemplary functioning perfection. The result is a pillar cover with a fine front edge and a drainage channel on the upper surface. This ensures a very close airflow and therefore a significant reduction in air resistance, as well as very good results in terms of draught protection, aeroacoustics and reduced soiling of the exterior mirrors and side windows.

Innovative draught-stop system AIRGUIDE

To reduce draughts when driving with the roof open, the SLK can be fitted with a draught-stop. This consists of a net with a fixed frame which is installed between the head restraints. When not in use it can be stowed in the boot, where it occupies little space.

A comfortable alternative to the conventional draught-stop is a new pivoting draught-stop for the new SLK which has been invented by Mercedes-Benz aerodynamics engineers. It consists of pivoting transparent plastic layers which are attached to the reverse of the roll-over bars. This is the world's first draught protection system that enables different comfort levels to be selected for two occupants, as the driver and passenger can individually pivot the units to the centre of the vehicle in a flash, thus taming turbulent air flow from the rear. Advantage: no installation or removal effort is required.

Modern headlamp technology and LED daytime running lamps

In the base version the new Mercedes-Benz SLK is equipped with single-tube H7 headlamps. These are combined with round daytime running lamps with chromed surrounds in the bumper. On request, horizontally arranged, elongated LED daytime running lamps with four LEDs can be fitted in a chrome clasp to give the SLK an even more striking front. If the vehicle is equipped with the Intelligent Light System or the AMG Sports package, these LED daytime running lamps are included. A manually operated and electrically activated headlight beam control system is standard equipment with halogen headlamps. The Intelligent Light System has automatic headlight beam control.

Alternatively the new SLK can be equipped with the Intelligent Light System (ILS) developed by Mercedes-Benz.The Intelligent Light System provides five lighting functions (cornering light function, country mode, motorway mode, active light function and enhanced fog lamps), which are activated depending on the driving conditions. In this case the main headlamps are twin-tub units, and for the first time the indicators and position lights are in LED technology.

The ILS headlamps automatically feature dynamic headlamp range control. This automatically adjusts the angle of the light beam to changes in the car's attitude – for example pitching movements when braking and accelerating – and when the attitude changes if a load is carried.

The wide tail lights of the new SLK are for the first time in full-LED technology. This not only ensures an unmistakable night design, but also enables LEDs to shine with different intensities in specific areas of the tail light cluster, depending on their lighting function. LED technology has other advantages: compared to conventional bulbs they light up around 150 milliseconds faster, and also have a considerably longer operating life – a safety aspect that should not be underestimated.

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