|Mercedes-Benz SLK 55 AMG|
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The Mercedes-Benz SLK 55 AMG is the most powerful SLK of all time. Its newly developed AMG 5.5-litre V8 engine featuring cylinder shut-off combines the ultimate in performance with the best possible fuel consumption. With a peak output of 422 hp and maximum torque of 540 Nm, the SLK 55 AMG outperforms all of its direct competitors. Its fuel consumption of 33.6 mpg on the combined cycle and CO2 emissions of 195 grams per kilometre are around a 30 percent improvement of that of its predecessor. High levels of driving dynamics are ensured thanks to the AMG sports suspension with Direct-Steer system, Torque Vectoring Brakes and 3-stage ESP, as well as the AMG high-performance braking system.
Forming part of the third-generation of the SLK launched in March, the new top-of-the range AMG model already demonstrates its individuality even at first glance: distinctive AMG light-alloy wheels, specific AMG bodystyling with AMG spoiler lip and two chrome-plated twin tailpipes at the rear complement the classic roadster proportions, while adding a markedly athletic touch. The expressive design of the SLK 55 AMG is both eye-catching and unmistakable.
The SLK 55 AMG is the perfect embodiment of the new AMG brand claim of "Driving Performance": in the compact high-performance roadster segment there is nothing to compare to its combination of tangible driving dynamics, superior sportiness, unique high-technology and low fuel consumption. The SLK 55 AMG accelerates from 0-62 mph in 4.6 seconds, and reaches a top speed of 155 mph (electronically limited).
The world's most fuel-efficient V8 engine combines the lowest consumption figures with the superior power delivery and the typical sound experience which only a large-displacement eight-cylinder engine can provide.
In line with its "AMG Performance 2015" strategy, with the new V8 unit Mercedes-AMG is meeting its promise to continue to reduce both the fuel consumption and emissions of new models over the next few years - while reaching new heights with the central brand claim of "Driving Performance". At the same time, AMG is also demonstrating its social responsibility with the M152.
The new M152 is based on the AMG M157 5.5-litre V8 biturbo engine presented in 2010, which powers the E 63 AMG, CLS 63 AMG, S 63 AMG and CL 63 AMG. Numerous design features are identical, such as the displacement, bore/stroke, distance between cylinders, start/stop system and direct petrol injection technology. Distinguishing features versus the M157 include the new intake air ducting, new cylinder heads, the modified valve drive, an adapted oil supply system and an optimised crankcase.
The high-tech M152 powerpack enthrals with a combination of advanced technologies which is unequalled anywhere in the world. No other petrol engine features direct injection at a pressure of 200 bar, spray-guided combustion and piezo injectors, all in conjunction with map-controlled cylinder shut-off, an all-aluminium crankcase with "spectacle" honing, four-valve technology with continuous camshaft adjustment, a high compression ratio of 12.6 : 1, a start/stop system and generator management - while revving to a maximum speed of over 7000 rpm. All of these measures lead to high thermodynamic efficiency, which is a precondition for high fuel efficiency and low exhaust emissions. Moreover, deciding in favour of a large-displacement, naturally-aspirated eight-cylinder unit with cylinder shut-off resolves the conflict of aims between high output/torque delivery and improved fuel consumption figures.
It is the AMG Cylinder Management cylinder shut-off system in particular - completely newly developed by Mercedes-AMG - that significantly improves efficiency: cylinders two, three, five and eight are cut off under partial load, which lowers fuel consumption considerably. In similar form this technology is also used in the approx. 750 hp V8 engines used in Formula 1. As efficiency also plays a major role at the pinnacle of motor racing, two or four of the eight cylinders are cut off e.g. when cornering at slow speed, in the Safety Car phases or for pit stops. With a fuel consumption of 33.6 mpg and CO2 emissions of 195 grams per kilometre (NEDC combined), the naturally-aspirated AMG V8 engine comes in at or below the level of its competitors, however these are unable to match either the output or torque of the SLK 55 AMG - and above all, they do not use large-displacement eight-cylinder engines.
The cylinder shut-off function is available over a wide engine speed range from 800 to 3600 rpm if the driver has selected transmission mode "C" - Controlled Efficiency. The AMG main menu in the instrument cluster informs the driver whether cylinder shut-off is active, and whether the engine is currently running in four or eight-cylinder mode. No less than 230 Nm of torque is still available in four-cylinder mode - enough power to ensure plenty of acceleration in most driving situations. As soon as the driver has a need for more power and leaves the partial load range, cylinders two, three, five and eight are activated. The switch from four to eight-cylinder operation is immediate and imperceptible, leading to no loss of occupant comfort whatsoever. At an engine speed of 3600 rpm the activation process takes no more than 30 milliseconds.
This is made possible by intelligent interaction within the highly effective engine management system, with 16 hydraulically compensating elements and a complex oil supply system in the cylinder head. The compensating elements are integrated into the cylinder head, and keep the intake and exhaust valves of cylinders two, three, five and eight closed when cylinder shut-off is active. At the same time their fuel supply and ignition are deactivated. This not only enables the load-change losses of the four deactivated cylinders to be reduced, but also increases the efficiency of the four remaining cylinders. This is because the operating point is transferred to the higher load range. The compensating elements are compact and lightweight, allowing taut valve train operation and engine speeds up to 7,200 rpm.
The crankcase of the new AMG 5.5-litre V8 engine features a diecast all-aluminium construction. The low (dry) engine weight of just 187 kilograms is the result of uncompromising lightweight construction methods. The bearing covers for the main crankshaft bearings are of grey cast iron, and are bolted to the crankcase, as well as on the sides, for high rigidity.
The piston rings are carbon-coated to minimise internal friction and optimise the wearing characteristics. Cast-in Silitec cylinder liners ensure low friction for the eight pistons. So-called "spectacle" honing is another measure to reduce friction and therefore fuel consumption: in this sophisticated and complex process, the cylinder liners receive their mechanical surface treatment when already bolted in place. As honing would no longer be possible with the cylinder head installed, a jig resembling spectacles is bolted to the crankcase. The cylinder liners distort as if the cylinder head were in place, and are only then given their mechanical surface treatment. As a result, any static distortion of the cylinder liners caused by tightening the cylinder head bolts can be completely eliminated.
Perfect charging of the combustion chambers is ensured by large intake and exhaust valves, of which there are four per cylinder. The exhaust valves, which are subject to high thermal loads, are hollow and sodium-cooled. Four overhead camshafts operate the 32 valves via low-maintenance, low-friction cam followers. The infinitely variable camshaft adjustment within a range of 40 degrees on the intake and exhaust sides depends on the engine load and engine speed, leading to high output and torque values. This also results in consistent idling at a low speed. Depending on the engine speed, valve overlap can be varied for the best possible fuel/air supply to the combustion chambers and efficient removal of the exhaust gases. The variable camshaft adjustment is carried out hydraulically via four pivoting actuators. These are electromagnetically actuated and controlled by the engine control unit. The camshafts are driven by three high-performance silent chains, which have considerable advantages in terms of noise comfort compared with cylinder roller chains.
The Controlled Efficiency start/stop function further contributes to the low fuel consumption. This system is standard equipment on the SLK 55 AMG, and active in the fuel economy transmission mode "C". Once the driver comes to a halt e.g. at a red traffic light, the V8 engine is automatically switched off. Once the brake pedal is released or the accelerator is depressed, the engine is immediately restarted and the car is able to move off quickly. Intelligent technology guarantees a comfortable and immediate starting procedure: a crankshaft sensor which recognises the direction of rotation registers the resting position of all eight pistons. For an automatic engine start, the cylinder with the most favourable piston position receives an injection of fuel into its combustion chamber. The precise piezo-electric injectors greatly assist this process, as they make particularly fast starts possible. The M152 always starts in eight-cylinder operation.
A framed "ECO" symbol in the AMG main menu shows the driver that the Controlled Efficiency start/stop function is active. When cylinder shut-off is active, the driver is informed by the symbol "ECO4", while "ECO8" stands for eight-cylinder operation. In the two more performance-oriented driving modes "S" (Sport) and "M" (Manual), the start/stop function is always deactivated. If required, the driver can also switch it off while in "C" mode as well. In this case neither a "start/stop" nor an "ECO" symbol appears.
A generator management system makes a further contribution to fuel economy: whenever the V8 engine is on the overrun or when braking, kinetic energy is used to charge the battery rather than being wasted as heat in the usual way. In all other operating modes a combination of onboard network and generator management enables the generator to be kept at a low voltage. This reduces the load on the engine and enhances fuel efficiency in city traffic with its frequent overrun and braking phases.
For the first time AMG is using a sports exhaust system featuring an exhaust flap on each side. This technology resolves the conflict of aims between an emotional sound when driving in a sporty manner and a more discreet engine note in the partial load range. The main focus of the sound design was on achieving a perfect synthesis of perceptible dynamism and the long-distance comfort that is a hallmark of Mercedes.
Each of the two rear silencers has a flap which is variably activated on a logic-controlled basis depending on the driver's power requirement and the engine speed. At low loads and engine speeds below 2000 rpm the flaps remain closed. This causes the exhaust gases to cover a longer distance and flow through an additional damping element, so that the engine sound is pleasantly subdued and irritating frequencies are effectively suppressed - resulting in a harmonious sound impression especially in four-cylinder operation when cylinder shut-off is active.
When the driver accelerates, the flaps open at an angle of 15, then 30 and up to 50 degrees so that some of the exhaust gases cover the longer, acoustically dampened distance and some the shorter distance. This produces a sonorous engine note. Under full load at higher engine speeds in eight-cylinder mode, both flaps are fully opened so that the occupants are able to enjoy the decidedly muscular sound typical of an AMG V8. In short, they are left in no doubt about the performance potential of the 422 hp naturally aspirated AMG eight-cylinder engine.
The two-pipe AMG sports exhaust system with two chromed twin tailpipes has a pipe diameter of 65 millimetres from the manifolds to the pre-silencer. The diameter is reduced to 60 millimetres from the pre-silencer to the rear silencers.
The AMG sports suspension with Torque Vectoring Brakes and AMG Direct-Steer system provides both impressive lateral dynamics as well as agile handling. Looking for a highly dynamic driving style or comfortable cruising? The new SLK 55 AMG is able to offer both. Independent suspension struts with stiffer spring/damper tuning, torque strut bearings on the front axle featuring higher rigidity, stiffer stabilisers all round as well as a more negative camber on the rear axle result in high cornering speeds and a low body roll in fast S-shaped bends.
In critical cornering conditions, the Torque Vectoring Brakes produce a defined rotational movement of the vehicle about the vertical axis in fractions of seconds, through selective brake actuation at the rear wheel on the inside of the bend. This results in the SLK 55 AMG steering into the bend precisely and under full control, without any compromises where dynamism is concerned. Complementing this feature perfectly is the AMG Direct-Steer system: it enhances handling and agility compared with the standard steering, whilst also reducing the amount of physical effort required when parking. A new power steering pump helps to improve fuel consumption. The reason behind this: the power assistance for the steering only requires energy when the driver is actually steering. In addition, the AMG Direct-Steer system has a parameter function adapted to match the AMG sports suspension. This results in optimum response from the central position, outstanding road feel and dynamic handling in all driving situations.
The optionally available AMG Handling package enhances the vehicle's sportiness even further. It comprises an AMG Performance suspension with stiffer tuning, an AMG rear axle differential lock, composite brake discs at the front and a three-spoke AMG Performance steering wheel finished in nappa leather with Alcantara inserts in the grip areas.
Classic roadster proportions with typical AMG design characteristics as well as a hint of the SLS AMG - these are the striking visual highlights of the new SLK 55 AMG. The AMG designers have complemented the exciting basic forms of the long bonnet, the greenhouse positioned well to the rear and crisp rear section with typical AMG styling at the front, sides and rear. The new AMG front apron has large air inlets and AMG-specific LED daytime driving lights. Inspired by the SLS AMG super sports car, the wide radiator grille features a large, centrally-positioned Mercedes star. In the case of the SLK 55 AMG, the slats in the radiator grille and the lower cross strut on the front apron are painted in a high-gloss black finish. Darkened clear-lens headlamps and darkened bicolour tail lamps also come as standard exclusively on the top-of-the-range V8 model. The Intelligent Light System (ILS) is also available as an optional extra.
The vent grilles with chrome-plated fins in the front wings are not only reminiscent of the SLS AMG, but also evoke memories of the famous Mercedes-Benz 300 SL Roadster from the 1950s. The "V8 AMG" lettering beneath the grilles points to the top-of-the-range eight-cylinder model from the SLK model series. AMG-specific, distinctively styled side sill panels continue the design of the front apron through to the new rear apron. With its own unique shape, black diffuser insert with three fins as well as the two chrome-plated twin tailpipes of the AMG sports exhaust system, it gives a distinctive finishing touch to the vehicle. The spoiler lip on the boot lid, painted in the vehicle body colour, reduces lift at the rear axle and thereby increases driving stability at high speeds.
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|Article||Image gallery (12)||Specifications|