MB SL 55 AMG Technology

Press Release

• V8 engine with high-performance motorsport components
  
• New screw-type compressor for 30 percent higher charge pressure
  
• Electronically controlled fuel supply in use for the first time
  
• Cutting-edge chassis technology with SBC and ABC

Traditionally the "sports badge" worn by the Mercedes-Benz brand has three letters: AMG. Cars displaying this badge on the boot lid have always been among the most powerful, most innovative and safest in their class. And the new SL-Class is no exception. Taking the SL 500 as their starting point, the engineers at Mercedes-AMG GmbH have developed a sports car which, in terms of power delivery and torque characteristics, sets new standards in the eight-cylinder roadster class: the SL 55 AMG. The markedly dynamic bodystyling, muscular side skirts and classic AMG-style bumpers are not the only clear indications of the phenomenal power contained within this car. The sporty sound produced by the newly developed engine, even when idling, is also a clear give-away that the eight cylinders form a powerpack of immense proportions. A quick touch of the accelerator is all it takes to feel and experience this power. At a mere 1500 rpm, the driver can elicit no less than 500 Newton metres of torque from the V8 engine, rising to 650 Newton metres at 2000 rpm and 690 Newton metres at 2500 rpm. The rev counter still only displays 2650 rpm when maximum torque is reached: a massive 700 Newton metres. The power curve is just as steep, reaching its peak of 350 kW/476 hp at 6100 rpm. No other Mercedes passenger car can match the new SL 55 AMG in terms of pure power. 0 to 100 km/h in 4.7 seconds On-the-road performance is equally impressive: it takes the new AMG Roadster just 4.7 seconds to accelerate to 100 km/h from a standing start. And only a little over 15 seconds for the red speedometer needle to reach the 200-km/h mark. The speed is piled on until the engine's microcomputer cuts in at precisely 250 km/h to electronically limit the power delivery. The scale on the speedometer goes up to 300 km/h, showing just what this exhilarating high-performance sports car is theoretically capable of. Powerful supercharger between the cylinder banks The impressive power development in the eight-cylinder engine is largely down to a newly developed belt-driven supercharger enthroned between the cylinder banks. It works on the principle of a "Lysholm" compressor and achieves about 30 percent more charge pressure than other comparable belt-driven supercharging systems. The compressor screws - Teflon-coated aluminium castings - rotate at over 23,000 rpm (equivalent to an engine speed of 6500 rpm) and, in doing so, press 1850 kilograms of air per hour into the engine's combustion chambers. The maximum charge pressure is 0.8 bar. The engine management unit calculates whether to use the screw-type compressor depending on the engine speed and load. With lightning speed, the electronic system actuates an electromagnetic clutch which drives the compressor by means of a separate poly-V-belt. The advantage of this direct link to the crankshaft is that the supercharger can spontaneously react when the driver presses the accelerator and provide powerful thrust at an engine speed barely above idle. Separate low-temperature circuit for charge air Besides the compressor, the supercharger module houses an intercooler between the cylinder banks. This charge air cooler operates as an air-to-water heat exchanger, extracting heat from the compressed air and transferring it to the coolant. A pump allows the water to flow through a special low-temperature cooler which is located in the cooling module, between the air-conditioning condenser and the radiator. The actual water circuit in the 5.5-litre engine works independently of the low-temperature system for the charge air. An electrical suction-type fan uprated to 850 watts takes the greater cooling requirements of the supercharged engine into account. The oil cooling system is another example of the innovation shown by the AMG engineers: a separate oil cooler is installed in the front apron of the high-performance sports car, from which dissipated air is bled upstream of the cooling module. Special technical features in the new V8 supercharged engine also include the fuel system which, for the first time in a Mercedes-Benz, is controlled by a computer. This ensures that the right amount of fuel is delivered every time, according to the engine speed and load. Emissions meet future EU-4 requirements The AMG engine's exhaust system is just as sophisticated as its supercharger, cooling system and fuel supply. The system has twin pipes throughout (pipe diameter 70 mm). It also has two firewall catalytic converters with extremely thin-walled ceramic monoliths as well as two powerful metal catalytic converters on the Roadster's underbody. A total of four lambda probes in front of and behind the firewall catalytic converters establish the exhaust gas composition and forward the data to the engine management unit. This means the SL 55 AMG meets strict EU-4 emissions requirements, even though they are not due to come into force until 2005. Two centre and rear mufflers with a switchover valve between the two exhaust pipes lend the new AMG Roadster its sporty sound. The entire exhaust system is made of stainless steel and, with its four chromed tailpipes, emphasises the extremely powerful character of this top-of-the-range sports car. Nearly all the mechanical components in the original SL 500 engine had to be modified when developing the V8 power plant. The AMG engineers' vast experience of developing high-performance engines for motorsport stood them in good stead during this phase. Components they modified included:

... the crankcase which they adapted by using special transverse screw connections. Measuring 97 mm, the bore is the same as in the standard production engine.

... the crankshaft, adapted to the high torque of the supercharged engine using modified bearings and more durable material. The stroke was increased from 84 to 92 millimetres.

... the pistons which are made of a special material that is extremely resistant to heat and pressure.

... the oil supply which differs from the V8 engine in the SL 500 in that it has a modified oil sump with oil catch tray and front sump as well as a more powerful oil pump.

... the cylinder head with optimised intake and exhaust ducts to take account of the higher air flow rate.

... the camshafts which have longer valve opening times and thus improve charging of the combustion chambers.

... the valve train with a double spring assembly, enabling the rated engine speed to be increased from 5600 to 6100 rpm.

... the engine ECU which performs additional tasks for the AMG engine, such as using electronic maps to activate the compressor. The new bore/stroke ratio (92 : 97 mm) means the displacement of the AMG engine is now exactly 5439 cc; 473 cc more than the engine in the SL 500. The following chart contains a summary of the most important engine and performance data:

ÂÂÂÂ	SL 55 AMG
Cylinders/valves per cylinder	V8/3
Displacement cc	5439
Stroke/bore mm	92/97
Power Output kW/hp at rpm	350/476 6100
Torque Nm at rpm	700 2650- 4500
0 - 100 km/h s	4.7
Top speed km/h*	250
NEDC overall consumption l/100 km	14.2

* electronically limited Manual transmission mode with sporty gearshift on the steering wheel In the SL 55 AMG, the standard-fitted automatic transmission as used in the new SL-Class is extended to include a "steering wheel gearshift" and an additional manual transmission mode. This means that, for the first time in a series-produced Mercedes-Benz passenger car, the sportier motorist can opt for a Formula-1-style gearshift with two selector switches located behind the top two steering wheel spokes. To enable the system, the driver must first activate the manual mode by pressing the program select button on the automatic selector lever. The selector switch on the right of the steering wheel is used for upshifts whilst the one on the left is for downshifts. The transmission only intervenes of its own accord and changes gear if the maximum permitted engine speed is reached. If the SL 55 AMG comes to a stop, first gear is selected automatically. A display on the instrument cluster tells the driver which transmission mode is active and which gear is selected. Besides manual transmission mode, the five-speed automatic in the SL 55 AMG offers all the familiar functions such as the practical touchshift feature on the selector lever - also active in manual transmission mode - or the special winter program. New SBC high-pressure brake for exemplary active safety The interaction of state-of-the-art systems such as new Sensotronic Brake Control and Active Body Control allows the chassis of the new S-Class to deliver maximum directional stability, driving safety and agility. The AMG engineers adapted this technology to their new high-performance Roadster, to provide an even more dynamic sports car experience. The Sensotronic Brake Control (SBC) high-pressure brake, fitted as standard in the SL 55 AMG, ushers in a new era in brake technology. It pushes open the door to the future world of "by-wire" systems. This technology communicates the driver's commands electronically via cable, rather than mechanically or hydraulically, as has traditionally been the case. A powerful microcomputer, which is integrated into the data network of the car and processes information from a series of electronic control units, oversees the operation of the system. The voluminous vacuum-powered brake booster is no longer required and the brake pedal and main brake cylinder merge into a single "activation unit". This unit is hydraulically de-coupled from the remaining parts of the system by valves and serves merely to register the braking command. Among the foremost performance characteristics of Sensotronic Brake Control are the extremely fast build-up of pressure and the precise monitoring of driver and vehicle behaviour by a sophisticated sensory system. Emergency braking is a good example of where the benefits lie: if the driver switches quickly from accelerator to brake pedal, SBC recognises the early signs of an emergency situation and reacts automatically. With the help of the high-pressure reservoir, the system raises the pressure in the brake connectors and instantaneously presses the pads onto the brake discs, which can then be applied with full force the moment the brake pedal is pressed. Taking emergency braking at a speed of 120 km/h as an example, this "priming" of the braking system reduces the stopping distance by some three percent. ESP® functions benefit from new dynamism and precision Sensotronic Brake Control doesn't just prove itself under emergency braking, but also in other critical situations - when the vehicle is in danger of skidding, for example. Here the system works in tandem with the Electronic Stability Program (ESP®), which keeps the sports car safely on track by applying precise brake impulses at individual wheels and/or by reducing the engine torque. This is another situation where SBC capitalises on the greater dynamics and precision: ESP® uses the even faster and more precisely measured brake impulses to stabilise a swerving car both quickly and comfortably. SBC also offers higher levels of safety than a conventional system when braking through corners. Here, the brake force distribution - varied according to the situation in hand - can prove particularly helpful in actively influencing the car's self-steer effect. Whilst conventional braking systems apply the same brake pressure ratio to the outer and inner wheels when cornering, SBC allows the brake force to be distributed according to the situation in hand. Consequently, the system automatically increases the brake pressure on the outer wheels when cornering, as they produce more brake force by virtue of their greater contact forces. At the same time, the brake force on the inner wheels is reduced. This alters the lateral force exerted on the car, which also plays an important role in keeping it on track. The result is more stable braking and optimum stopping distances. Sensotronic Brake Control offers further benefits on wet roads. In wet weather, the system injects regular, short brake impulses to ensure that the film of water on the brake discs is wiped off and SBC can work as effectively as possible at all times. This automatic dry braking function is activated in intervals whenever the car's windscreen wipers have been running for a certain time. The brake impulses are precisely calculated so that the driver is not aware of them. The de-coupling of the SBC pedal from the rest of the braking system and the proportional pressure control improves braking comfort - particularly when braking heavily or when the Anti-lock Braking System cuts in. The vibrations which are normally felt through the brake pedal when ABS intervenes are eliminated. Mercedes engineers have found that this is not just a comfort-enhancing feature of the new system, but also beneficial from a safety point of view. Active Body Control for superb cornering dynamics Active Body Control - a Mercedes-Benz development - is also fitted as standard on the new SL 55 AMG. This high-tech system provides the answer to the traditional sixty-four-thousand-dollar question in the world of passenger car suspension settings: should the engineers keep the wheel vibrations caused by the road surface as low as possible by using sporty, taught shock absorbers, or should the damping be made as soft and therefore comfortable as possible, but to the detriment of driving safety and driving dynamics? Active Body Control resolves this conflict of interests: the system adapts the suspension setting automatically to the driving situation in hand. The driver and passengers can enjoy greater comfort and enhanced driving dynamics at the same time. The most prominent components in the active suspension system are hydraulically controlled servo cylinders, which are located together with passive shock absorbers and coil springs in the suspension struts, where they work together as a suspension control system: the actively controlled elements reduce body vibrations of up to five hertz occurring, for example, on uneven road surfaces as a result of body lift and roll, when cornering, if the car leans heavily to the side, or through the typical pitching of the car body when braking. Compared with steel suspension systems, Active Body Control can greatly reduce vibrations of this kind. Passive gas-filled shock absorbers and coil springs absorb wheel vibrations of higher frequencies (6 to 20 hertz), and their damping force can be selected at a lower level than is possible in conventional suspension systems. The result is enhanced ride comfort and lower vibration levels. The torsion bar stabilisers fitted in standard suspension systems are not required thanks to the active roll stabilisation. Online calculation of actual vehicle weight The engineers at Mercedes have made further advances in the active suspension for the new SL-Class, including the addition of a load adjustment element. This means that the system can now calculate the actual load in the vehicle and use this figure in the calculation processes for the active suspension. A change in the weight of the vehicle, due to luggage being removed from the boot or because a passenger has got out, automatically triggers a further online calculation of the vehicle weight and the system then adapts the suspension characteristics to the new load level. Reinforced axles and perforated brake discs on all wheels The AMG engineers built on this innovative chassis technology used in the new SL-Class to develop their high-performance Roadster, adding special ABC suspension struts with sporty, stiffer damper settings for even more spontaneous steering characteristics. They also reset the algorithms for the active suspension and other control systems (ESP®, Brake Assist, DISTRONIC). Further special features of the AMG chassis include:

... the rear axle with reinforced wheel location components, steel sub-frame and spring links, made using an extremely robust welded steel construction.

... the brakes with internally ventilated and perforated brake discs (diameter 360 or 330 mm) on both axles. At the front there are powerful 8-piston fixed-calliper brakes fitted with four pads, to ensure safe braking. The front pad face is almost twice as large as it is in the SL 500: 220 square centimetres in all.

... the 18-inch wheels with new multi-spoke design (8.5 J x 18 at the front and 9.5 J x 18 at the rear). One-piece five-spoke wheels are optionally available in the same sizes.

... the wide-profile tires, size 255/40 R 18 at the front and 285/35 R 18 at the rear.