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Body: A model of strength, safety and lightweight design
OverviewAppointments and technical highlights of the new C-Class Estate*Body: A model of strength, safety and lightweight designChassis: A blend of agility and comfortDesign: Cast from a single mouldEngines and transmissions: Extra power coupled with far lower fuel consumptionInterior: Taking spaciousness and load capacity into a new dimensionModel range: As multifaceted as daily lifeSafety: Innovations borrowed from the luxury classTechnical dataThe new C-Class Estate: Unrivalled spaciousness, plus exemplary safety, optimum comfort and tangible agility
- 70 per cent of all bodyshell panels made from high-strength grades of steel
- Torsional stiffness increased by around 12 percent
- Panoramic sliding sunroof available for the Estate for the first time
- Intelligent Light System with five different lighting function
"The right material in the right place" - once again, the Mercedes principle for strength and lightweight construction proves to be a success in the new C-Class Estate. Using an intelligent mix of steel and aluminium, the engineers in Sindel-fingen were able to achieve a remarkable result: despite all of the extra measures implemented for the benefit of safety, spaciousness and comfort, the bodyshell now weighs four kilograms less than previously - all whilst complying with the stringent Mercedes demands in terms of durability.
Preference has been given to high-strength steel alloys, as these provide maximum strength in combination with minimal weight, which in turn translates into the greatest possible safety. Around 70 per cent of all the sheet metal panels in the bodyshell of the new Estate are made from these high-tech grades of steel. For around a fifth of all parts, the specialists at Mercedes deployed sophisticated, ultra-high-strength steels which have only been developed in recent years. Their tensile strength is three to four-fold greater than that of conventional steels. By way of comparison: these alloys only accounted for one per cent of the predecessor's bodyshell by weight.
Aluminium and plastics are the two other lightweight materials used by Mercedes-Benz wherever they offer the most benefits. Aluminium components in the new C-Class Estate include ...
- the front wings
- the front-end assembly including flexible cross member and crash boxes
- the cross member underneath the dashboard
- the door modules.
Apart from these high-tech steel alloys, the use of high-strength structural adhesives makes another major contribution to the strength of the bodyshell. The adhesive creates a flat bond between the sheet metal flanges, significantly increasing the load resistance and transfer of forces in zones critical to safety. In this way, the adhesive supplements conventional processes such as spot and laser welding. In total, there is around 60 metres of high-strength bonded seams in the bodyshell.
A low-stress joining technique and the latest spot or laser welding methods virtually eliminate the need for additional soldered connections and MAG (Metal Active Gas) welding seams at the joins between the sheet steel panels – likewise benefitting the body's durability. The sophisticated joining technique also guarantees a high level of dimensional accuracy. The flanges at the edges of the steel parts are designed in such a way that any tolerances are compensated for as soon as the panels are brought together, allowing them to be welded together at low stresses.
For the first time Mercedes-Benz has used the new "RobScan" joining process, which is based on the latest laser welding technology. It produces narrow welding flanges and even better crash characteristics at a high processing speed. This method is used for manufacturing the doors, sidewalls and rear end – with a total of around 640 welding seams.
Body structure: a further major improvement in rigidity
This intelligently designed bodyshell provides some of the key ingredients for the high level of ride comfort that distinguishes the new model from other estate cars in this market segment. Static torsional stiffness – an important indicator for the body's vibration characteristics – has improved by around twelve percent compared to the preceding model. The engineers in Sindelfingen paid particular attention to the connecting points between the chassis and body, which are required to withstand very high forces. These were specifically reinforced to ensure that road-induced vibrations are not transferred to the body at the expense of driving pleasure.
However, the structures have been made robust not least in the interests of safety too. For example, the subframe that is bolted rigidly to the body and to which the front axle, steering, engine and transmission are attached, acts as part of the front crumple zone. For this purpose it has been extended forward, forming an additional impact level at the bottom: in a severe frontal collision, this component made from high-strength steel is able to deform in a predetermined manner, absorbing energy and conducting forces directly into the floor structure by means of special support tubes.
The structure and integration of the front end is also new. It basically consists of a sturdy aluminium cross-member and two single-piece crash boxes, also made from aluminium, which are inserted into the side members and bolted to them at the sides. The other components of the front end are bolted together too, allowing them to be replaced cost-effectively following an accident.
Firewall: new, four-piece design with varying panel thicknesses
The firewall has a four-piece construction. This enables Mercedes engineers to vary the material thicknesses according to vulnerability in an accident, while making a further contribution to weight reduction. As the load acting on the firewall during a frontal collision is greatest in the lower section, the sheet metal used here is up to 56 per cent thicker than at the top.
On the left and right in front of the firewall, there are two compartments housing a number of assemblies, including the starter battery (right, on diesel models) and the central electrics unit (left). These areas are insulated from the engine compartment by a partition wall made of sheet steel and aluminium panelling. A special application of melamine resin foam on the inside of the partition ensures effective soundproofing and heat insulation.
Passenger compartment: continuous side members in floor structure
The passenger cell proves to be a structure which is virtually immune to deformation and which keeps the occupant space intact even at high impact speeds, regardless of whether the vehicle is involved in a collision from the front, the rear or the side, or rolls over. The use of ultra-high-strength grades of steel and panels made of thicker material plays as important a role here as the installation of additional load-bearing members. The main floor structure consists of three separate sheet metal blanks, which are laser-welded together and subsequently shaped into the right form. The centre blank, which is made from thick sheet metal, forms the tunnel, the actual backbone of the passenger cell.
Other new features which are very important for both occupant protection and the rigidity of the bodyshell include the continuous floor side members, the insides of which are further reinforced with extra sections. Their front faces connect to the side members, thereby lengthening the load-bearing paths along which forces can be distributed in the event of an impact. At the rear, the floor side members extend as far as the cross member beneath the rear seat unit to stabilise the entire floor structure, resulting in a considerable improvement in the body's vibration characteristics.
Mercedes engineers have also incorporated sturdy aluminium transverse sections – known as transmission tunnel braces – into the floor assembly. One is located beneath the transmission, and is designed to direct forces to the opposite side of the vehicle during an impact from the side. The second creates a connection between the two side members. It likewise braces the floor assembly and is able to direct impact forces into the floor structure at an early stage in a side-on collision. Diagonal struts between the side skirts and the side members also give added rigidity, as well as improving the vehicle’s cornering characteristics.
Side wall: extremely sturdy B-pillars as impact protection
The outer sidewalls of the new Estate have a one-piece construction. Individually welded inner shells and extra sheet-metal reinforcements ensure high levels of strength in the vicinity of the roof pillars. The B-pillars - which are required to absorb large forces and transfer them to the bodyshell structure during a side impact - consist of three sheet metal shells plus a large, reinforced area extending to the upper edge of the belt guide point. One of the shells as well as the reinforcement are made from hot-formed, ultra-high-strength steel.
When designing the doors, Mercedes engineers devoted particular attention to the door hinges, for which they developed special mounting plates with high load resilience. This creates a robust, integrated side structure which is able to provide effective occupant protection in the event of a collision. The inner door shells are made of high-strength steel blanks reinforced by sections in the area of the frame and beltline and at bumper level.
Additional members located in the lower area of the doors between the inner and outer shells supplement the design measures for side impact protection. Each of the rear doors has two of these sheet-metal sections.
Rear end: cross member made from flexibly rolled high-tech steel
Multi-piece side members of high-strength steel and a robust, flexible cross member form the key components of the rear-end structure. The rear side members are continuous, closed box sections with carefully graduated material thicknesses. These are able to absorb high forces, thereby making a decisive contribution to occupant safety in an impact from the rear. The bolt-on flexible cross member is manufactured using an innovative flexible rolling process which likewise allows the material thickness to be varied as required. Flexible means that the ultra-high-strength steel can be processed in such a way that areas with differing sheet metal thicknesses can be produced within a single component. Accordingly, the material thickness on the outside of the cross member – where impact loads are highest – is greater than on the inside.
The hinges and latches of the folding rear seat backrests are entirely encompassed within a supporting structure that is bolted to the sidewalls and the floor plate. This also contributes to the bodyshell's high torsional stiffness.
Long-term protection: fully galvanised body with tougher paintwork
Long-term protection against corrosion for the bodyshell 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.
Fully weather-sealing the welding seams also prevents the onset of corrosion. This seam sealing benefits not only the bonnet, doors, boot lid and rear wheel arches, but also a large proportion of the welded joints in the floor structure of the new C‑Class. Using laminated plastic for a large area of the underbody panelling has allowed Mercedes engineers to dispense with conventional PVC underseal. This underbody panelling protects the body from stone chippings, water and soiling. Axle components subject to severe stone impacts are also protected by a plastic lining.
Mercedes-Benz also makes a major contribution to exemplary long-term quality and value retention with a particularly scratch-resistant clearcoat. This innovative paint system, which celebrated its world debut at Mercedes-Benz at the end of 2003, is a standard feature of the new Estate and is used for both metallic and non-metallic finishes. The clearcoat triples the scratch resistance of the paint finish and ensures a visibly superior, long-lasting sheen.
Exterior mirrors: significantly larger glass surface
The exterior mirrors of the new C-Class make an important contribution to perceptual safety: the glass surfaces have been significantly enlarged, and thereby already comply with future legislation. With the new exterior mirrors, the driver is even able to spot smaller objects lying on the ground around four metres behind the vehicle.
To ensure that the mirrors always provide the clearest possible view to the rear, they are electrically heated as standard. The mirror heating comes on automatically, depending on the outside temperature and humidity. Both exterior mirrors are electrically adjustable, and fold inwards at the touch of a button. A number of different mirror settings can be stored on models with the memory package (optional).
Sliding sunroofs: panoramic effect now available for Estate passengers too
In addition to the tilting/sliding glass sunroof, Mercedes-Benz is offering an optional extra for the new C-Class Estate which guarantees a very special sort of open-air motoring pleasure: the panoramic sliding sunroof, which is now making its debut in an estate model. Its glass surface covers almost twice the area of the tilting/sliding sunroof, extending from the windscreen right back to the load compartment. At the touch of a button, the front section of the glass roof rises up and slides to the rear over the fixed section, while a wind deflector pops up at the front. The moving section of the panoramic sliding sunroof can also be moved into a tilted position.
Remote control using the electronic ignition key also works with the panoramic sliding sunroof. On models equipped with PRE-SAFE®, both the tilting/sliding roof and the panoramic sliding sunroof are integrated into the anticipatory occupant protection system and close automatically before an imminent accident. If it is linked up to the rain sensor, the panoramic sliding sunroof also closes automatically then rises into the tilted position when it rains.
The Estate's standard roof rails are made from aluminium. On the CLASSIC line the rails have a black anodised finish, while on the ELEGANCE and AVANTGARDE models they are silver-coloured.
Tailgate: EASY-PACK system for power opening and closing
The tailgate is composed of one inner and two outer shells which are joined to one another using a special method (brazing combined with laser welding). This elaborate design makes the tailgate extremely rigid.
For particular ease and convenience when opening and closing the tailgate, Mercedes customers may opt for the EASY-PACK tailgate. A touch of a button is all that is required to set the tailgate in motion. This is made possible by an electronically controlled electric drive system, whose motor is located beneath the roof liner in the load compartment. The torque required for operating the tailgate is transmitted to the left-hand hinge. The automatic closing procedure concludes with the electrical power closing aid pulling the tailgate securely into the lock.
The EASY-PACK power tailgate can be opened by either pressing a switch located on the interior panel of the driver's door, pulling the handle above the rear number plate or pressing a button on the electronic key, i.e. by radio remote control. It can be closed by means of either a button on the inside of the tailgate or the switch in the driver's door panel.
Aerodynamics: cd value reduced by three per cent
On the basis of their tremendous know-how, and with the help of the latest development methods, Mercedes engineers achieved another triumph where the aerodynamics are concerned. Despite a less tapered rear end, larger rear radii, larger exterior mirrors and smaller front overhangs, the Estate achieves a cd value of 0.30, an improvement of some three per cent compared to its predecessor. Key aerodynamic figures at a glance:
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New Estate *
Coefficient of drag cd
Frontal area (A)
Air resistance (Cd x A)
* Example of C 200 CDI
These figures are the result of several months of development work on the computer and in the wind tunnel, that already began during the early conceptual phase. Based on the key exterior dimensions and the fundamental stylistic concept, 1: 4-scale models were initially produced and subjected to numerous wind tunnel tests in order to create the basic conditions required for excellent aerodynamics. This experimental work was supplemented with flow simulations: using the latest CFD (computational fluid dynamics) software, it is possible to calculate and optimise the aerodynamic conditions beneath the bonnet, along the underbody or around individual areas of the bodywork. Doing so enabled the Mercedes engineers to identify any potential for further improvements at an early stage.
The streamlined styling of the front and rear aprons and of the A-pillars, along with the optimum sealing of the area around the radiator, the full underbody panelling and the aerodynamically effective diffuser on the underside of the spare wheel well, are just a few of the results of the development work which together contribute to the new Estate's impressive coefficient of drag.
Dirt-repellent: water deflectors on A-pillars
Keeping the exterior mirrors and side windows free of dirt in poor weather conditions is of crucial importance for driving safety. Accordingly Mercedes-Benz has always given this topic a great deal of attention, and has now made yet further progress:
- The A-pillars feature special twin drainage channels in which rainwater striking the windscreen is collected, before being conducted downwards or to the rear along the roof with the help of the airflow. This largely prevents any build-up of dirt on the side windows.
- The housings of the exterior mirrors are designed in such a way that rainwater flows to the outside along a slender, continuous channel then drains away. A small spoiler assists this defined drainage process, which keeps the side windows, mirror surfaces and door handles clean.
Aero-acoustics: detailed adjustments for audible comfort
Wind noises caused by the flow of air around the body and its detachable parts, or by vibrations induced in the sheet metal surfaces, can soon take the pleasure out of a journey. In the new C-Class Estate, the more rigid bodyshell with its continuous floor side members, the reinforced outer skin and newly designed doors all help to keep vibrations at a very low level. A new gap-sealing concept is also employed: the doors of the C-Class feature a continuous double seal - and in the most important areas even a triple seal. For the new panoramic sliding sunroof, Mercedes specialists have developed an air-deflecting mesh which is erected automatically. This suppresses the annoying booming sound that is heard when travelling with the sunroof open.
Headlamps: intelligent lighting according to the driving situation
The new C-Class quite literally shows the way ahead with its ultra-sophisticated and supremely effective headlamp system, and the Intelligent Light System developed by Mercedes-Benz is optionally available for the Estate too. It includes five different lighting functions:
- The familiar low-beam headlamps are replaced by the new country mode, which illuminates the road verge on the driver’s side more broadly and brightly than before. This enables drivers to orientate themselves even more easily in the dark, and respond more rapidly when other road users cross the road.
- Motorway mode , which comes on automatically when driving above 90 km/h, increases the driver’s range of vision by up to 60 per cent. This lighting function is activated in two stages: the Intelligent Light System first increases the output of the bi-xenon bulbs from 35 to 38 watts, thereby increasing the light intensity and providing noticeably better illumination of the road ahead and the side verges. The second stage of motorway mode is triggered at 110 km/h, when the beam of the bi-xenon module on the driver’s side is elevated slightly. Motorway mode has a range of around 120 metres, and the driver is able to see about 50 metres further at the centre of this cone of light than with conventional low-beam headlamps.
- With the enhanced fog lamps, which are also new, Mercedes-Benz improves driver orientation when visibility is poor too. This lighting function is activated at speeds below 70 km/h, as soon as the rear fog lamp is switched on. The variable headlamp technology deployed by the Intelligent Light System makes it possible to pivot the bi-xenon headlamp on the driver’s side outwards by eight degrees, while lowering its beam of light at the same time. This illuminates the inner half of the road more brightly and reduces the degree of glare from light reflected back by the fog.
- Depending on the steering angle, yaw rate and vehicle speed, the active light function pivots the headlamps sideways by up to 15 degrees in fractions of a second to greatly improve road illumination. On a long sweeping bend with a radius of 190 metres, the driver is able to see 25 metres further than with conventional low-beam headlamps thanks to the active light function, which, incidentally, operates with both low and high beam.
- The cornering light function integrated into the fog lamps in the bumper improves safety at junctions, when turning into side roads and on tight bends. The function is activated automatically when the driver operates the indicators or turns the steering wheel at a speed below 40 km/h. The fog lamps then swivel to illuminate the area diagonally in front of the vehicle for a distance of around 30 metres, with an angle of coverage of 65 degrees.
The Intelligent Light System is based on powerful bi-xenon headlamps. These permit variable control and are networked with other electronic control units on board the Estate, from which the headlamps obtain information about the current driving situation and then distribute their beam patterns accordingly. A headlamp cleaning system supplements the technology of the Intelligent Light System. It is linked to the windscreen washer system, and is automatically activated every tenth time the washer system is operated. The advantage of this is that the headlamp cleaning system no longer needs to be operated manually.
Powerful bi-xenon systems with around 50 per cent more lighting power are optionally available as an alternative to the halogen headlamp units. Apart from the headlamp cleaning system, tail light clusters with yellow LED indicator bulbs are also included if Mercedes customers opt for the Intelligent Light System and/or bi-xenon headlamps.
In standard trim, the new C-Class Estate leaves the factory equipped with low-beam projector headlamps and separate reflector headlamps for high beam; halogen bulbs are fitted in both. Two parking lamp bulbs shine out from the flat, upper area of the headlamp units where they meet the bonnet. The standard front fog lamps are integrated into the bumper lining, placing them in a favourable, low position for their purpose.
The Headlamp Assist function, which turns on the lights automatically when darkness falls or the vehicle enters a tunnel, is included as standard on the new Estate. It is activated by turning the light switch in the dashboard to the "Auto" position.
Flashing brake lights: effective warning when danger threatens
Mercedes-Benz has developed flashing brake lights to help prevent rear-end collisions. These, too, are standard equipment in the new Estate. If the driver is obliged to brake sharply from a speed of over 50 km/h, or if Brake Assist comes to the driver's aid in an emergency situation, the brake lights flash rapidly to warn traffic behind. If the C-Class comes to a halt after such an emergency braking manoeuvre, the brake lights revert to continuous operation plus, if the speed when emergency braking commenced was greater than 70 km/h, the hazard warning lamps are switched on at the same time.
Studies show that drivers’ braking reaction time can be shortened by up to 0.2 seconds on average if a flashing red warning light is substituted for a conventional brake light in emergency braking situations. As a result, the stopping distance is reduced by approximately 4.40 metres at a speed of 80 km/h, and by a whole 5.50 metres at 100 km/h.