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OverviewDesign - Love at first sightEngines and transmissions - Geared up for powerModel range and equipment - The allure of the roadster summed up in three lettersSafety - Safety takes a front seatSLK 55 AMG - Top of its classTechnical data SLK-ClassThe bodywork and vario-roof - Expertise and skillThe chassis - Leading the packThe interior - An experience for twoThe new Mercedes-Benz sports Roadster - The SLK-Class: More power, more safety, more driving pleasure
Mar 15, 2004
- A world first: AIRSCARF provides the warming effect of an invisible scarf
- Sensor-controlled heating and air conditioning systems
- Chronometer-style cockpit combines cutting-edge technology and aesthetics
- The latest audio/navigation systems guide drivers to destinations across Europe
Longer and more– that's the message sent out by the new SLK-Class to aficionados of open-top motoring. It means that even more trips can be made with the vario-roof down and that the open-air motoring season stretches into the colder times of the year courtesy of the sensational, sporty Mercedes Roadster. It is all thanks to a revolutionary new neck-level heating system for both driver and passenger which is now available as an option.
AIRSCARF is the name given by the Mercedes engineers to their world first. It works as follows: warm air which is emitted from special vents in the head restraints at the touch of a button acts as an invisible scarf by flowing around the neck, throat and head of the SLK's occupants.
With this innovation, the Stuttgart-based car manufacturer is once again helping to enhance "thermal comfort" a topic which has always played a prominent role throughout the development of open-top Mercedes cars. Their many years of experience in the development of this type of car have shown Mercedes engineers that open-top motoring alone cannot guarantee driving pleasure in the long term. Passenger comfort is no less important whilst driving with the roof down, and is often hampered as the result of a draught or a poor seating position.
It was with this consideration in mind that the developers of the AIRSCARF worked closely together with their colleagues from the aerodynamics department. During wind-tunnel testing they focused their attentions on maintaining a draught-free interior, as this was crucial to creating an effective system of neck-level heating. The result is a seating position which is matched to the height of the windscreen frame so that the airflow is directed over the heads of the SLK passengers; this means they are truly screened from the wind when seated in the car, making the journey a much more comfortable one. Thanks to these aerodynamic measures, the prerequisites for optimising thermal comfort whilst driving with the roof down had been fulfilled. However, the SLK developers had no intention of stopping there: as well as smoothing the airflow with the draught-stop, they wanted to warm the air up too. And after a development and testing phase which lasted several years, their efforts were rewarded with the creation of the AIRSCARF system.
AIRSCARF technology: heating element and blower in the seat backrest
Over the course of numerous test runs, the seat development team in Sindelfingen tried out a number of different ideas and concepts for the neck-level heating system, and soon came to the conclusion that only a system that was integrated into either the seat or the head restraint could achieve the desired level of heating. In other words, the technology used had to be both small enough to fit into the SLK seats and at the same time powerful enough to generate enough thermal energy to heat the air-flow in the roadster interior with the roof down.
The engineers at Mercedes were able to resolve these conflicting technical objectives using state-of-the-art, high-performance ceramic materials: various elements made of barium titanate and other metal oxides are energised, causing them to heat up in a matter of seconds and emit heat continuously. This does not drain the car's 12-volt power supply though, as once a certain temperature is reached the electrical resistance of the ceramic material suddenly jumps, thereby reducing power consumption; heat output remains unchanged, however. This produces an equilibrium between the electrical energy the ceramic material is fed with and the heat output it produces. The experts refer to this state as a "Positive Temperature Coefficient" or PTC for short. Meanwhile, the ceramic heating element is able to prevent itself from over-heating by monitoring its surface temperature and automatically reducing the output if necessary.
As well as the compact design, this technology's key benefits are its speed when heating up and the constant heat output.
The PTC air heater for the AIRSCARF system measures only a few centimetres in size, allowing it to fit into the backrest of the SLK seat. It consists of a number of rectangular ceramic elements with a total heat output of around 216 watts. The heat produced is dissipated into the air through aluminium fins which are positioned between the individual ceramic elements. A blower directs the air though a plastic duct until it reaches the head restraint where it flows out of a special vent to warm up the neck, throat and head of the seat occupant.
Temperature control: adjusted according to the vehicle speed and outside temperature
AIRSCARF comes equipped with a three-speed switch and an electronic control module that adjusts heating at neck level to meet current requirements. A data bus keeps the micro-computer in contact with the speedometer, the temperature sensor in the centre console and the exterior thermometer of the Mercedes Roadster. The micro-computer then compares this up-to-the-minute data with the stored characteristic curves for particular ambient conditions and driving situations.
Pushing a button starts the system in switch position 3, after which it adjusts automatically depending on ambient temperature and road speed. The AIRSCARF system adapts the blower speed constantly in order to achieve optimal distribution of the warm air in all situations. This adaptive control based on stored characteristic data is active up to a speed of 120 km/h. At higher speeds, the system operates at a constant setting. Anyone preferring to regulate the heating effect individually can also select three different output settings manually via the buttons in the centre console.
Sports seats: newly developed design with rigid magnesium frame
As well as the AIRSCARF, the seat experts at the Mercedes-Benz Technology Centre (MTC) worked on the development of further special technical features which are geared towards boosting ride comfort and increasing practicality. The sports seats boast a number of distinguishing features, including core springing and a layer of foam which provides a precise level of cushioning. Both of these elements – the core springs and the layer of foam – are incorporated into a robust cushion shell made from fibre-reinforced plastic. When it came to the seat backrests, the engineers opted for magnesium. By combining low weight with high strength, this high-tech material helps to boost occupant safety by providing extra lateral bracing for the side wall in the event of a side-on collision, for example. In addition to this, the silver-painted magnesium frame provides a solid basis for attaching the standard head/thorax sidebags. The backrests' foam cushioning is applied directly onto cushion holders made from glass-fibre reinforced plastic. These are in turn supported by the magnesium frame.
The seats fitted in the SLK-Class feature fore-and-aft, height and squab-angle adjustment, allowing all occupants to find their ideal position. Compared to the predecessor model, the engineers at Mercedes have been able to increase the fore-and-aft adjustment range by nine millimetres to a total of 247 millimetres. Yet another novel feature is the facility for folding the driver's and passenger's seat backrests forwards. A coat hook can also be found on the rear of each seat backrest in the new SLK.
Dimensional concept: extra room for driver and passenger alike
The revolutionary new AIRSCARF system, sports seats which are also ideally suited for longer journeys, the broad scope of adjustment for individual seat positioning and the seats' increased fore-and-aft adjustment range all clearly demonstrate just how much progress has been made in the new SLK-Class when it comes to comfort and convenience compared to the previous model. The increase in the exterior body dimensions plays a crucial role in this respect, as the car's passengers also benefit from the additional length (+ 72 millimetres), width (+ 65 millimetres), height (+ 20 millimetres) and wheelbase length (+ 30 millimetres). The extra interior space means that passengers enjoy higher levels of comfort compared to the previous Roadster model. The width at shoulder height, one of the key criteria for assessing interior comfort, now measures 1326 millimetres, representing an increase of 13 millimetres compared to before. The greater overall height of the body translates into 965 millimetres of headroom for the vehicle's occupants, an extra 16 millimetres compared to the model it replaces.
Climate control: three systems available to choose from
Progress has also been made in terms of climate comfort in the new SLK-Class. There are now a total of three systems to choose from: the basic automatic heating system, THERMATIC and THERMOTRONIC.
Even the standard heating and ventilation system fitted by Mercedes-Benz, the automatic heating system, boasts an array of sophisticated microelectronics. The automatic heating system employs sensors which permanently monitor the temperature inside the car and maintain the temperature constantly at the settings selected by the driver and passenger. The automatic heating system's control panel in the centre console stands out by virtue of its attractive design, with all relevant functions clearly arranged using four ergonomically styled rotary switches: the temperature control for driver and passenger side, ten-speed blower control, air distribution, "Defrost" function, air recirculation and residual engine heat utilisation modes, plus the switch for the heated rear window.
As is the case with many of the heating functions, the automatic heating system's standard air recirculation mode is also governed electronically. In order to prevent the windows from misting up, the duration of the recirculation mode is adjusted as a function of the ambient temperature, and is limited to a maximum of five minutes at temperatures below seven degrees Celsius. Once this period of time has elapsed, the air recirculation flap is opened by the system automatically, allowing fresh air to enter the interior of the car. The standard-fit interior filter remains active permanently, regardless of whether the automatic heating system is operating in fresh-air or air recirculation mode. As well as filtering out all particles of dust and diesel particulates larger than five micrometres in size, the filter also purifies the air by removing allergenic substances such as flower or grass pollen.
By conducting extensive airflow and climate-control simulations, the engineers at Mercedes have succeeded in optimising the air-intake and heating-duct cross sections. This has led to an audible difference, with the ventilation system now running far more quietly and even more effectively than before. The various ventilation outlets in the dashboard have also been increased in size and number with the intention of achieving a more pleasant ventilation of the interior which is free of draughts.
It was with this important consideration in mind that a system of indirect ventilation was developed. Featuring an air vent which is positioned beneath the perforated grille in the centre of the dashboard and is directed towards the windscreen, this method of indirect ventilation distributes cool air over a large area to prevent any draughts from forming on SLK models fitted with the THERMOTRONIC system. The majority of the other ventilation outlets in the dashboard are also fitted with individual adjustment wheels which can be used to reduce or even cut off the airflow from the outlet in question, or to direct it upwards, downwards or to the side.
THERMATIC air conditioning with humidity sensor
THERMATIC represents a practical extension to the automatic heating system. Although the basic heating and ventilation system is equipped with sensors and an electronic control for maintaining the desired interior temperature at a constant level, this system reaches its limits during the hot summer months as it lacks the necessary refrigeration unit. This gave rise to the development of the THERMATIC system that is fitted as standard on SLK 350 and SLK 55 AMG models. This system cools down the air flowing into the car from the outside whilst also removing any moisture. At high ambient temperatures, the unit also automatically governs the proportion of recirculated air used in order to cool down the interior of the car more quickly.
The THERMATIC system fitted in the SLK-Class basically works using the same reheat principle featured by many of the Mercedes-Benz air conditioning systems. This means that the unit operates permanently, even at low ambient temperatures, in order to first cool the in-flowing air and to then dry it, thereby preventing the windows from misting up. Following this, the air is then reheated to the desired temperature. The system uses the current air humidity for doing this: a dew-point sensor monitors the air humidity constantly and supplies the air conditioning's micro-computer with the data required for governing the reheat function to match requirements. Consequently, the in-flowing air is cooled down depending on the air's moisture content and then reheated. The advantage of this approach is that the air conditioning works far more economically than conventional systems, as well as offering greater comfort.
This intelligent system of control is made possible by a refrigerant compressor which is governed by the electronics to produce the exact cooling output required. Whereas air conditioning compressors used to cut in and out by means of an electromagnetic clutch, the compressors on the latest Mercedes systems are connected to the engine by means of a belt drive, keeping them running permanently and removing the need for a clutch. The smooth adjustment of the air conditioning compressor is the task of a solenoid valve which varies the compressor's swept volume.
The "Defrost" and residual engine heat utilisation modes are part of the THERMATIC system's standard specification, as is a combined dust and activated charcoal filter which is capable of absorbing pollutants and odours in the air, as well as particulate matter.
Luxury automatic climate control meets even the most exacting requirements
THERMOTRONIC represents the very ultimate in climate control for the new SLK-Class, and offers S-Class standards of climate comfort in a sports car. The scope of functions includes automatically regulating the temperature separately for the driver and passenger sides, as well as using additional sensor signals for controlling the system. The clearly set-out display in the control panel in the centre console indicates the current temperature settings.
The system reaches its full potential in automatic mode which SLK passengers can activate by pressing the "Auto" button. Once they have done this, there is no need to worry about adjusting the climate control settings as the system will then cool or heat the air automatically based on various sensor information:
- A multifunction sensor monitors the air humidity, ambient temperature and pollutant content of the air. It reacts particularly sensitively to the carbon monoxide and nitrogen oxides contained in exhaust fumes, and automatically activates the air recirculation flap the instant it detects any sudden increase in these pollutants. As a result, contaminated air is kept out of the vehicle interior.
- Penetration by the sun's rays is registered by a sensor positioned behind the windscreen which comprises two photodiodes. These diodes relay precise information on the angle of incidence as well as the intensity of the sun’s rays. Using this data, the computer is able to first calculate a mean value for the current background brightness, which it then compares with the brightness values for the two sensor zones. In this way, the system is able to determine if the sun is shining particularly intensely on one of the two seats and then adjust the temperature control and blower setting in this zone accordingly.
- The interior temperature is measured by means of a temperature pick-up in the air conditioning's control panel.
Once again, the THERMOTRONIC luxury automatic climate control features a residual engine heat utilisation mode, a defrost function and a combined dust and activated charcoal filter. The individual temperature settings, meanwhile, are stored in the electronic ignition key that comes with the SLK-Class.
Dashboard: top marks for form and function
The attractively styled heating and air conditioning controls exemplify the design concept applied throughout the SLK interior. Stimulating colour contrasts and high-grade materials have been used to create an ambience of sporty practicality which represents a novel reinterpretation of the roadster philosophy. The cockpit and dashboard offer a number of technical and stylistic highlights:
The compact three-spoke steering wheel (diameter 380 millimetres), sporting integral, silver-painted multifunction buttons and a Mercedes star with a chrome finish, is adjustable for both rake and height.
The striking design of the instrument cluster, with silver-coloured cylindrical tubes housing the speedometer and clock on the left as well as the rev counter and the fuel gauge on the right, very much recalls the cockpit design of racing cars from bygone times. The tubes are both turned slightly inwards and sloped at the front, to ensure that the driver has no problems reading the dial-type gauges. The styling of the white-lit dials is in keeping with that of high-quality instrumentation, producing an impression of supreme precision. The indicator and warning lamps are distributed over the faces of the two gauges and only become visible when the ignition is switched on or a malfunction is detected.
Positioned between the dial-type gauges is a two-section central display which indicates the mileage (top) and the ambient temperature. On SLK-Class models fitted with an automatic transmission, information on the current selector lever position and drive mode also appears in the bottom display.
The central display is coupled with the buttons on the multifunction steering wheel, which can be used by the driver to call up further information depending on the Roadster's specification, such as trip computer data, navigation information or the phone book, or to programme up to 50 individual settings.
The centre console blends smoothly into the dashboard, while the semi-oval air outlets mirror the bonnet's styling, fusing the exterior and interior to form a harmonious whole. Beneath the two pivoting louvred outlets there is room for a compartment, which is ideal for storing smaller travel items. Alternatively, a twin cup holder can be fitted here on request. Below this is positioned the in-car radio or COMAND system whose display is flanked by silver-painted buttons on the left and right. The same silver finish is used for the horizontal panel of switches, producing a vivid contrast with the basic black trim of the centre console. The rotary controls for the heating or air conditioning system, the shift lever, the handbrake handle, as well as the controls for the vario-roof and for adjusting the exterior mirrors likewise have a silver finish that contrasts with the black background of the transmission tunnel trim.
The armrest between the seats doubles as the cover for a stowage compartment which can be specified with a socket for connecting a mobile phone. The cover is linked up to the central locking system. A second stowage compartment with a cover is fitted to the rear wall of the interior.
A silver-coloured trim strip adorns the passenger side of the dashboard. With a capacity of 6.3 litres, the glove compartment offers some 30 percent more room than the predecessor model. As a result, it is now able to accommodate the six-disc CD changer which is available as a factory-fitted option. The glove compartment lid is integrated into the standard-fit central locking system of the SLK-Class, meaning that it is automatically locked whenever the Roadster is locked using the electronic ignition key's remote control.
The dashboard is made from injection-moulded polyurethane film. This method permits precision moulding of edges and rounded corners, while a foamed plastic backing as much as ten millimetres thick helps to produce a pleasantly soft surface finish. As a result, both the looks and feel of the dashboard mirror the exacting standards of the Mercedes sports car in terms of high-class appeal and design.
Thanks to the top-grade materials used and their dimensional accuracy, the top sec-tion of the dashboard forms a single visual unit together with the door trim panels – the two components blend almost seamlessly with one another and seem to form an integral whole.
Interior lighting: discreet interior lighting out on the road
To ensure that occupants aboard the new SLK-Class continue to feel completely at ease after nightfall and have no difficulty finding their way around the controls, Mercedes-Benz has developed a sophisticated lighting system for the interior, which even makes up part of the standard specification on SLK 350 and SLK 55 AMG models. A number of the lamps and LEDs remain illuminated whilst the vehicle is on the move, producing a pleasant interior glow and making it easier to find things in the dark. The interior lighting package comprises:
- An ambient light, directed downwards, in the rear-view mirror casing
- Lights in the footwells
- Entry/exit lights in the doors
- Additional reading lights in the rear-view mirror casing
- Vanity lights in the trim at the top of the windscreen frame
- Lights in the stowage compartments underneath the centre armrest and along the rear wall of the interior.
The standard specification of all SLK models includes two interior and reading lights in the overhead control panel, a glove compartment light, illumination of the ashtray and cigarette lighter, illumination of the controls in the dashboard, centre console and door trim panels, plus boot lamps.
Car radios: high-tech information and communications technology
Mercedes-Benz offers three state-of-the-art units to keep the SLK's passengers both informed and entertained. As well as being able to receive radio stations and play CDs, each is also able to serve as a command centre for a mobile phone. Apart from this, a great many of the functions can be controlled using the keys in the multifunction steering wheel, meaning that motorists do not need to take their hands off the wheel.
The Audio 20 CD unit features an FM/MW/LW receiver and allows up to ten station presets to be stored per waveband. The unit's four-channel amplifier produces an output of 4 x 25 watts. The integral CD player is also capable of playing CDs which have been burned at home. Further features of this unit include automatic station search, RDS Radio Data System (for FM stations) and a station scan function.
The Audio 50 APS offered for the SLK-Class by Mercedes-Benz is a powerful system which combines a twin-tuner FM receiver, CD drive as well as an arrow-based navigation system with dynamic route guidance based on RDS-TMC into a single unit. Information appears on a 4.9-inch colour display with graphics capability. The road network of the main European countries is stored on the navigation CD, while the integral CD drive is also capable of playing music CDs whilst the navigation function is activated.
The sophisticated COMAND APS control and display system, which has already proved extremely successful in top-of-the-range Mercedes-Benz models, is now to be made available for the SLK-Class for the first time. Boasting the latest TFT technology, the large, 6.5-inch colour display offers outstanding brilliancy and colour reproduction, whilst the 16:9 picture format is also suitable for watching films. DVD videos, as well as audio and MP3 CDs can all be played in the DVD player, although safety considerations mean that it is not possible to play DVD films while the vehicle is moving. To allow it to receive radio stations, the unit is equipped with an RDS FM twin tuner as well as an aerial diversity function. The system is also capable of receiving long-wave, medium-wave and short-wave stations. Passengers aboard the SLK are also able to read SMS text messages on the COMAND screen and reply to them using the unit's control keys.
Sound system: surround sound from eleven speakers
New SLK-Class models which are factory-fitted with one of the three available radio units come equipped with a total of nine speakers: three in each door, a centre-fill speaker in the top section of the dashboard, plus two speakers in the rear.
An even more effective acoustic experience is available by opting for the newly developed multi-channel sound system. With a maximum output of 380 watts, this system is harmonised perfectly with the acoustic conditions in the interior of the SLK. A microphone inside the car detects current noise levels, allowing the micro-computer to precisely adjust volume and sound, even with the vario-roof down. The result is sheer listening pleasure at all times. Each and every stereo signal is converted by the system into a surround sound, producing a peerless acoustic experience on both the driver's side and the passenger side. The surround effect is achieved using two extra speakers which are positioned above the stowage compartment on the rear wall. The sound system can be combined with either the Audio 50 APS or the COMAND APS unit.