Mercedes-Benz SLR McLaren-Part two
SLR in depth
Bodyshell and safety: high-tech materials for exemplary occupant protection
Carbon fibre body, ceramic brake discs
- Rigidity and crash safety of the highest level
- Result of several years of successful materials research
- Adaptive front airbags and newly developed sidebags
When it comes to body and safety technology the new Mercedes-Benz SLR McLaren yet again lives up to its reputation as an innovative force among today's Gran Turismos. High-tech materials from the field of aeronautical technology make their debut in a series-produced car here: carbon fibre is used for manufacturing the body, lending it its low weight and an exemplary rigidity and strength previously only achieved in Formula 1 race cars. The crash safety standards achieved using this innovative material are equally high.
Carbon fibre has been used to great effect in the aeronautical industry for some time. The rudder unit, vertical rudder, landing flaps and other parts of most airbuses are made from this material, in the development and series use of which the scientists at DaimlerChrysler Research played a significant role. Their expertise and the extensive experience of the Mercedes-Benz and McLaren experts in the field of race car design can now, for the first time, be seen in a series-produced car: the entire bodyshell and the doors and bonnet of the SLR are made from cor-rosion-resistant carbon fibre composite.
While offering the same strength as their steel or aluminium counterparts, carbon fibre components weigh up to 50 percent less than comparable steel components and up to 30 percent less than aluminium components. This makes carbon fibre composite the material of choice for manufacturing high-performance cars, because lower weight not only means lower fuel consumption but also outstanding transfer of power to the road. The lower the mass to be accelerated and braked, the better the agility. In fact, thanks to the extensive use of carbon fibre composites, the primary structure of the Mercedes-Benz SLR McLaren is around 30 percent lighter than the conventional steel construction of a comparable front mid-engined vehicle.
Carbon fiber composite offers significantly higher energy absorption
On top of this, the state-of-the-art lightweight material is also characterised by very good energy absorption. The figures here for carbon fibre composites are around four to five times higher than those for metal materials. Formula 1 constructors have been exploiting this quality for several years, manufacturing the crash structure of their race cars from carbon fibre composite. The result has been a significant fall in the number of serious injuries incurred in high-speed accidents in this top motorsportdiscipline.
The monocoque – or, to put it another way, the passenger cell – of the new Mercedes-Benz SLR McLaren is also made entirely from this high-tech material. In the event of a head-on, side-on or rearend collision, it offers the passengers a highly rigid and hence safe survival zone.
Carbon fibre crash elements in the front structure
The innovative fibre composite demonstrates its safety advantages particularly impressively in the front structure of the SLR bodyshell. Here two conical carbon fibre composite elements, each approximately 620 millimetres in length and weighing just 3.4 kilograms, are enough to absorb the full energy of the crash in a defined frontal collision without exceeding tolerable deceleration values for the passengers. The carbon fibre composite members are bolted onto the aluminium structure of the engine mounts; at the front they are connected to the remaining bodyshell structure by means of a cross member and a horizontal sandwich panel made from carbon fibre composite. This makes the SLR the world's first series-produced car to have a front crash structure manufactured entirely from carbon fibre.
In a collision, the fibres of the carbon fibre composite elements shred from front to rear, absorbing the energy of the impact with constant deceleration. Thanks to this steady deformation behaviour, the energy absorption of the carbon fibre longitudinal members can be tuned to meet specific requirements. The engineers achieve this, for example, by creating a constantly changing cross-sectional area for the components. This fine tuning means that the deceleration values result not only in predictable energy absorption behaviour but also in a weight advantage, because this design uses only as much material as is actually needed.
Four-year development of carbon fibre composite longitudinal members
The two conical longitudinal members of the front crash structure are made up of a main body and an internal web – a basic configuration which proved to be the most successful during the four-year development of this SLR component. The aim of the engineers from the Advanced Design department at the Mercedes-Benz Technology Centre in Sindelfingen and of DaimlerChrysler Research was not only to develop longitudinal members which offered an unprecedented degree of passive safety, high rigidity, tremendous strength and as low a weight as possible, but also to draw up manufacturing concepts which involved a high degree of automation to enable series production. In doing so, the experts entered uncharted technological territory.
In the early development phase they had succeeded for the first time in using a specially developed algorithm to carry out dynamic crash calculations for carbon fibre composites. The sophisticated computer simulations were crucial when it came to optimising the design of the longitudinal members for the front crash structure.
In a parallel operation, materials experts tested the calculated findings in practice using models which they exposed to precisely defined stresses in drop tests. As a result of this process, the exemplary deceleration and deformation behaviour of the carbon fibre composite longitudinal members in the front structure of the new Mercedes-Benz SLR McLaren was gradually defined.
The first automated production of carbon fibre composite components
To date, carbon fibre composite components for racing cars and for the aeronautical and space industries have been manufactured by hand – a time-consuming process. The challenge for the Mercedes engineers was to use their experience in this field to develop automated methods of series production. To do this they divided the manufacturing process into separate stages, manufacturing of the preform being followed by impregnation with resin and hardening.
In order to allow extensive automation of the preform manufacturing process (the preform also being made from carbon fibre), the materials experts at Mercedes-Benz cast a glance at the work of their colleagues in the textile industry and adapted traditional manufacturing methods used in this sector, such as sewing, knitting, weaving and braiding, for the processing of high-performance carbon fibres.
To take an example, the web of the SLR's longitudinal members is formed from several layers of carbon fibre placed on top of one another and sewed together by machine. Once the piece has been cut to shape and the ends folded up to form a double T profile, the web blank is inserted in a polystyrene braiding core. This core element is clamped into a specially developed braiding machine, which braids together the longitudinal members from 25,000 extremely fine, individual carbon filaments, these being unwound simultaneously from 48 reels. This technology allows the fibre material to be braided around the core at a precisely cal-culated angle to create the required contour. Several layers are even laid on top of one another in certain areas, depending on the required thickness. An innovative method was developed for this process too.
In a further manufacturing process, a computer-controlled tufting machine joins the inner web to the braid of the longitudinal member. The braid core is removed and the preform of the longitudinal member is cut to the correct size. The preform is then injected with resin. Several, now patented, solutions had to be developed and tested in order to ensure short cycle times and high repeat precision for this manufacturing process – crucial qualities in series production. The manufacture of the complex fibre struc-ture of the longitudinal members using a braiding machine requires a cycle time of just twelve minutes, which illustrates the unit potential that this innovative manufacturing technology offers.
New method for manufacturing rear shelf
The rear shelf of the new SLR provides a further example of the new production techniques used by Mercedes-Benz for carbon fibre processing. It has a very complex form with several apertures, yet it is automatically manufactured as a single part. To achieve this, Mercedes-Benz and its collaborative partners adapted the SMC method (SMC – Sheet Moulding Compound) to create "Advanced SMC". Its advantage is that the carbon fibre mats are no longer manufactured by hand but by machine.
Here a handling system positions individual carbon fibre composite layers at precalculated angles and in preset positions which correspond to the principal form of the component, thereby creating the blank. Under heat this blank is then pressed, and in the process it takes on the precisely calculated form of the rear shelf. No subsequent reworking is required.
In the new SLR, Mercedes-Benz is the first car manufacturer to use components which are manufactured using the "Advanced SMC" method.
The British company McLaren Composites also manufactures over 50 carbon fibre and fibreglass components for the high-performance sports car. Here too familiar processes from the aeronautical industry were adapted and developed. The degree of integration achieved in the manufacture of the bodyshell is remarkable. The entire floor assembly, for example, including all support members and securing elements, are made in one piece. The cavities of the carbon fibre composite roof frame structure (also manufactured as a single piece) are automatically filled with foam before the resin injection, creating a particularly crashproof sandwich structure. High-strength bonding and riveting techniques ensure a reliable connection between the individual carbon components of the chassis and the body-shell. The aluminium engine mounts are bolted to the carbon fibre composite bulkhead and also bonded in place. The carbon structure includes integral metal link points for the aluminium and steel rear axle.
Retention system with adaptive airbags, sidebags and kneebags
A cutting-edge retention system with six airbags, belt tensioners and belt force limiters completes the SLR's sophisticated safety concept, ensuring that it meets all Mercedes standards.
In the event of a head-on collision of a specific severity, the electronic control unit first triggers the high-performance belt tensions, which pull up to 15 centimetres of loose belt taut in fractions of a second, reducing the forward displacement of the occupants as a result of the impact. The Mercedes-Benz SLR McLaren is also fitted with kneebags, which – together with the two-stage driver and front-passenger airbags – provide a large protective cushion for the driver and front passenger, supporting the effect of the seat belts and belt tensioners.
Upfront sensors for rapid airbag deployment
The belt tensioners are also activated if a roll-over situation is detected. A roll-over sensor reliably recognises this type of accident and supplies its data at lightning speed to the central control unit for the retention systems. The sensor is located on the centre tunnel.
Sophisticated sensors also allow adaptive control of the front airbags, which de-ploy according to the severity of the accident. If the sensors register a light head-on collision, they each trigger just one chamber of the two-stage gas generators, and the 64-litre driver airbag and 125-litre front passenger airbag are deployed with lower internal pressure. If the sensors register a higher severity of accident, the electronics also trigger the second chamber of the gas generators and the airbags fill with higher pressure.Two upfront sensors on the radiator cross member also assist this adaptive deployment of the retention systems. Thanks to their exposed installation position in the front structure, they detect the severity of the impact even earlier and more precisely. The deployment algorithm uses both this signal and the signal from the central crash sensor on the centre tunnel.
While the occupants sink safely into the airbags, the belt force limiters reduce the force of the belt on the upper body, decreasing even further the risk of light chest and shoulder injuries.
Sidebags provide extra protection for the head
Protection in the event of a side impact is optimised by integral sidebags in the doors. These cushion both the head and the upper torso and are sometimes, therefore, referred to as "head/thorax bags". In a side-on collision, this specially developed side airbag rips open a seam above the armrest and inflates in milliseconds to form an asymmetrical airbag, the upper edge of which, when inflated, extends higher than that of the familiar sidebag. This design means that the air cushion reduces the risk of the head hitting the side windows or any object which may penetrate the interior. It also holds back glass shards and other objects which could enter the interior in a collision.
The automatic child seat recognition system, developed by Mercedes-Benz, is also part of the SLR's standard equipment. It deactivates the front passenger airbag if a special child seat from the Mercedes-Benz accessories range is installed on the front passenger seat. These child seats have a transponder system which receives and responds to signals from two antennae in the seat upholstery. As a result of the exchange of data, the airbag electronics recognise that a child seat is fitted and deactivate the airbag on the front passenger side since its deployment is not desirable in these circumstances. The belt tensioner and sidebag remain activated, offering the young passenger additional protection in the event of an accident.
Swing-wing doors with large angle of opening
If there is one distinctive feature that the new Gran Turismo has adopted from the Uhlenhaut Coupé, the 1955 coupé version of the legendary SLR race car, it is the doors. In their modern interpretation, however, they are attached to the front roof pillars rather than to the roof itself and swing forwards and upwards at a 107-degree angle. This new concept ensures greater safety, an exciting look and, because of the large opening angle, allows comfortable access to the interior for the driver and front passenger.
The high-performance sports car's luggage capacity is equally striking. The leather and velour-trimmed boot holds a total of 272 litres (using the VDA measuring method). Flaps below it provide easy access to stowage compartments for the washer and brake fluid reservoirs, the two batteries and tools. The designers opted for this unusual arrangement in order to achieve sports car-style weight distribution with a low centre of gravity close to the centre of the vehicle.
Suspension: top performance for the race track and the motorway
- Aluminium double wishbone suspension with 18-inch wheels
- Highly-performance brake discs made from carbon fibre-reinforced ceramic
- Electrohydraulic brake system (SBC™) plus ESP®
- Automatically adaptable airbrake in boot lid
Highly developed motor racing technology, high-performance control systems and cutting-edge materials – a unique combination which propels the Mercedes-Benz SLR McLaren into a new dimension in sports car dynamics, helping it to achieve top figures in three key areas: agility, active safety and comfort. In the process, the SLR suspension meets every criteria a discerning car driver would expect to find in a Gran Turismo with a Mercedes star.
The axle design bears the signature of experienced racing car developers, with double wishbone suspension at the front and rear. The lower struts are arranged so that, as the springs compress and when cornering at speed, the wheels have a negative camber. This ensures the best possible contact with the road in every situation. At the same time the axle technology prevents the front of the car from diving when braking heavily and the rear from diving when accelerating.
Aluminium was the key material for the developers of the new Mercedes-Benz SLR McLaren's suspension. The wishbones are made from forged aluminium, while the wheel mounts are cast in aluminium. In addition to a whole series of other advantages over conventional steel designs, the lightweight nature of the material allows the suspension to react significantly faster and to respond more sensitively.
The relatively long wheelbase (at 2700 millimetres) also contributes to the SLR's exemplary handling and makes itself noticed above all in the car's exemplary directional stability, while the large track width, combined with the low centre of gravity, allows high cornering speeds.
Springing/damping combinations at the front and rear axle and an anti-roll bar at the front complete the suspension structure. The anti-roll bar is positioned above the front axle and – as in Formula 1 – is controlled via rocker arms. This means that it does not take up any installation space which could impair the smooth line of the underbody – a vital factor when it comes to the sports car's outstanding aerodynamic properties.
The speed-sensitive rack-and-pinion power steering also corresponds with the in-telligent lightweight concept. In comparison with other steering systems, this design is characterised by a significantly lower weight. Thanks to its low installation position in front of the engine and the gear ratio of 12.6, the steering system re-sponds directly to the driver's commands and carries them out with high precision. The three-spoke steering wheel has a diameter of 380 millimetres and is fitted with an electric motor which allows it to be positioned to suit the individual driver. It can be adjusted by 60 millimetres for reach, and the height of the steering wheel can be varied by 2.7 degrees.
SBC™ and ESP® for sporty dynamic handling with high level of active safety
The electrohydraulic braking system, Sensotronic Brake Control, a milestone in car technology, forms part of the standard equipment of the Mercedes-Benz SLR McLaren. It processes data from various sensors regarding the current status of the vehicle and can use this to calculate and apportion the optimum brake pressure for each wheel at lightning speed. A high-pressure accumulator holds the brake fluid, which flows into the system at a pressure of 140 to 160 bar. This also optimises the function of the Electronic Stability Program (ESP®), which keeps the SLR safely on track by applying targeted brake impulses to the individual wheels and/or reducing the engine torque. Here too SBC™ offers the advantage of higher dynamism and precision: thanks to even faster and even more finely metered brake impulses from the SBC™ high-pressure accumulator, ESP® can stabilise a swerving vehicle comfortably at an early stage.
The coordination of this system with the Electronic Stability Program (ESP®) was a particular challenge for the engineers of the high-performance sports car. Their aim was to adapt the dynamic handling control system to the vehicle's distinctly sporty performance yet maintain the usual safety standards, achieving an ideal compromise between outstanding dynamic handling and exemplary directional stability. Here too SBC™ demonstrated its strengths, being able to deliver adequate braking power at lightning speed in every on-road situation, thanks to its sophisticated sensors and the high-pressure accumulator, making a key contribution to the precision handling of the SLR. It was therefore possible to allow a very sporty driving style with controlled side-slip angles in keeping with the character of the high-performance car without compromising active safety. On top of this, SBC™ significantly enhances active safety in critical situations:
- Emergency braking: SBC™ recognises the driver's sudden switch from the accelerator to the brake as an indication of an emergency situation and is able to react automatically. With the aid of the high-pressure accumulator, the system increases the pressure in the brake lines and positions the brake pads against the brake discs so that they can grip with full force the moment the driver steps on the brake.
- In the wet: through brief, regular application of the brakes, Sensotronic Brake Control ensures that the film of water on the brake discs is stripped away so that the brakes can always operate to full effect. This automatic drying function is activated whenever the windscreen wipers have been operat-ing for a certain length of time. The finely metered brake impulses are not no-ticeable to the driver.
- Braking on bends: thanks to variable brake force distribution, SBC™ is able to exert an active influence over the sports car's self-steering behaviour. While conventional braking systems always apply the braking pressure to the wheels on the inside and the wheels on the outside of the bend in the same ratio, SBC™ can distribute the brake forces to suit the situation. The system automatically increases the brake force at the wheels on the outside of the bend because, thanks to the higher wheel contact forces, they are able to transmit greater braking forces. At the same time the braking forces at the wheels on the inside of the bend are reduced to benefit lateral traction, which is so important to directional stability. The result is more stable braking behaviour and excellent deceleration figures.
Sensotronic Brake Control also offers special additional functions for even greater safety and comfort:
- The Soft-Stop function allows the vehicle to come to a particularly gentle stop, which will be much appreciated in city traffic, involving frequent stops at traffic lights. It is made possible by finely metered pressure control. The Soft-Stop function is permanently activated; only on emergency braking and when manoeuvring does the system ensure that priority is given to rapid deceleration.
- Start-Off Assist (SBC™ Hold) prevents the car from unintentionally creeping forwards or rolling backwards on hills and steep gradients. A brief but firm ap-plication of the brake pedal is all it takes to activate this function.
- Tailback Assist (SBC™ Stop) can be activated using the cruise control lever when the vehicle is at a standstill or travelling at a maximum of 15 km/h. The advantage of this is that in stop/go traffic the driver only needs to use the accelerator; when the driver takes his or her foot off the accelerator, SBC™ brakes the SLR to a standstill with constant deceleration. Tailback Assist can remain active up to a speed of 60 km/h. It is automatically deactivated at higher speeds. When Tailback Assist is activated, the letters "SBC S" appear in the instrument cluster.
Ceramic brake discs for top performance
Mercedes-Benz has optimised the outstanding properties of the Sensotronic Brake Control system in the new SLR with a braking system which also marks a technological high-point in a high-performance car: at the front and rear axle of the cutting-edge swing-wing door vehicle, brake discs made from fibre-reinforced ceramic ensure reliable deceleration. Their development is based on the one hand on the results of DaimlerChrysler materials research and on the other on Mercedes-AMG's experience of high-tech brakes in touring cars and GT sport. Here Mercedes-Benz yet again underlines its leading role in the development of groundbreaking technologies for car production.
In manufacturing the brake discs, the carbon fibre, powdered carbon and resin are pressed into shape at high pressure and baked with a silicon infiltration at temperatures of around 1500 Celsius to form the ceramic. The advantages of this composite material are considerable: in addition to being characterised by an extremely sensitive response, the Mercedes-Benz SLR McLaren's brake discs demonstrate a high temperature-resistance of up to 1000 Celsius, which produces a fade-resistance when braking at high speed never before achieved in a series-produced car. The result is brake power of up to 2000 hp.
Further advantages of the new brake material include...
- ... the long life of the brake discs – up to 300,000 kilometres.
- ... the low maintenance requirements of the corrosion-free brake discs.
- ... the lower weight – up to 60 percent less than conventional brake discs – a further bonus in terms of dynamic handling and ride comfort.
- ... even more comfortable braking – the low thermal expansion of the ceramic discs means reduced heat friction under high stress. Cold friction, familiar from cast iron brake discs, is also significantly reduced with ceramic brakes.
Brake pad area of 440 cm2 at the front axle
The design of the callipers was specially adapted to the fibre-reinforced ceramic brake discs. Mercedes-Benz developed eight-piston fixed callipers especially for this fast Gran Turismo, allowing excellent deceleration at the front axle. Special channels, which actively feed the cooling air to the outside of the brake callipers, ensure optimum cooling of the brakes. The braking data at a glance:
|
Front axle
|
Rear axle
|
Calliper
Piston diameter
|
8-piston fixed calliper
28/32 mm
|
4-piston fixed calliper 28/30 mm
|
Brake disc
Disc diameter
Disc thickness
Brake pad area
|
Internally ventilated
370 mm
36 mm
4 x 55 cm²
|
Solid
360 mm
26 mm
2 x 47 cm²
|
Tyres
|
Wheels
|
Wheel design
|
Front: 245/40 ZR 18 Rear: 295/35 ZR 18
|
9.0 J x 18 ET 45 11.5 J x 18 ET 44
|
10-spoke design
(standard)
|
Front: 245/40 ZR 18 Rear: 295/35 ZR 18
|
9.0 J x 18 ET 45 11.5 J x 18 ET 44
|
5-spoke design
(option at no extra charge)
|
Front: 245/35 ZR 19 Rear: 295/30 ZR 19
|
9.0 J x 19 ET 45 11.5 J x 19 ET 44
|
Turbine design
(optional extra)
|
Overall in the Mercedes-Benz SLR McLaren there is a total brake pad area of 440 square centimetres at the front axle alone – a top value which, in combination with the extremely robust high-tech material of the brake discs, allows maximum deceleration of up to 1.3 g. This results in outstanding stopping distances: on emergency braking from 100 km/h the Mercedes-Benz SLR McLaren comes to a standstill after an average of 34.9 metres.
Adaptable rear spoiler as airbrake
The outstanding performance of the SLR is also aided by the adaptable spoiler – known as the airbrake – in the boot lid. If the driver steps heavily on the brake pedal, the rear spoiler rises to an angle of 65 degrees, boosting the braking effect by producing greater aerodynamic drag. When braking from high speeds, it lends the SLR outstanding stability.
In most situations the electronics control the airbrake as required. However, the driver can also opt to take control of the adjustments using the switch in the centre console, manually raising the rear spoiler up to an angle of 30 degrees.
18-inch wheels as standard
Attractive 18-inch light-alloy wheels are part of the standard equipment of the Mercedes-Benz SLR McLaren. The sporty, 10-spoke wheels are fitted with different widths of tyres at the front and rear. 5-spoke wheels are available as an option at no extra cost. 19-inch turbine-design wheels, which particularly emphasise the dynamic character of the Gran Turismo, are available as an optional extra.
Tyres
|
Wheels
|
Wheel design
|
Front: 245/40 ZR 18 Rear: 295/35 ZR 18
|
9.0 J x 18 ET 45 11.5 J x 18 ET 44
|
10-spoke design
(standard)
|
Front: 245/40 ZR 18 Rear: 295/35 ZR 18
|
9.0 J x 18 ET 45 11.5 J x 18 ET 44
|
5-spoke design
(option at no extra charge)
|
Front: 245/35 ZR 19 Rear: 295/30 ZR 19
|
9.0 J x 19 ET 45 11.5 J x 19 ET 44
|
Turbine design
(optional extra)
|
An electronic system monitors the air pressure in the tyres of the Mercedes-Benz SLR McLaren. Its sensors are situated in the tyre valves and measure both air pressure and air temperature inside the tyre. Since it is not possible to install cable connections to the wheels, the information is transmitted by radio. Each sensor sends its data readings around once per minute to special antennae in the wheel arches which pass the information on to a control unit. This unit uses individual identifiers to distinguish between the signals from the four wheels and is able to inform the driver of the air pressure in each tyre via the central display in the cockpit.
email andre: avoglezon@mbzlongbeach.com
|