The new Mercedes-Benz SL 55 AMG

COVER STORY Mercedes-Benz SL 55 AMG

2 ATZ worldwide 4/2002 Volume 104

The new SL 55 AMG – from Mercedes-AMG GmbH based in Affalterbach near Stuttgart– represents the ultimate in the high-performance roadster segment. Combining thedynamic characteristics of a thoroughbred sports car with the comfort, safety and every-

day practicality of a genuine Mercedes-Benz, it features themost powerful engine that the brand has ever offered in a

production car. A newly developed brake systemwith Sensotronic Brake ControlTM and the sporty

Active Body Control suspension provide superlativehandling and stopping power. Exclusive exteriorstyling elements and interior appointments which arecomplemented by a comprehensive range of stan-dard equipment emphasise the exceptional charac-ter of the Mercedes-Benz SL 55 AMG.

1 Introduction

As a member of the DaimlerChryslerGroup, Mercedes-AMG is linked into thedevelopment of Mercedes-Benz passengercars right from the early specificationstage on. Throughout the developmentprocess, the engineering departments atMercedes-AMG work closely with the rele-vant groups within the development, pur-chasing, production and sales divisions atDaimlerChrysler. Beyond this, the Mer-cedes-AMG project management team isalso responsible for coordinating coopera-tion with systems partners and, once de-velopment is complete, overseeing the

transfer to the production plant – the Mer-cedes-Benz SL 55 AMG is produced along-side the SL 500 at the DaimlerChryslerplant in Bremen.

An AMG Mercedes has to satisfy thesame exacting Mercedes-Benz standardswhich apply to any vehicle which bears thethree-pointed star. That is why, during adevelopment period of more than twoyears, the SL 55 AMG, like the SL 500, wassubjected to several hundred thousandkilometres of testing – from the Swabianmountains near Stuttgart to the Nardòhigh-speed test track in Italy; from wintertesting in Sweden to summer testing inDeath Valley and South Africa.

By Ulrich Bruhnke,

Wolf Zimmermann,

Ralf Wörner,

Hartmut Buchfink,

Tobias Moers and

Bernd M. Baumann

Der neue Mercedes-Benz

SL 55 AMG

You will find the figures mentioned in this article in the German issue of ATZ 4/2002 beginning on page 316.

The New Mercedes-Benz

SL 55 AMG

3ATZ worldwide 4/2002 Volume 104

Finally, the SL 55 AMG was handed overto the DaimlerChrysler plant in Bremenwhere the process of providing the assem-bly teams with thorough on-vehicle train-ing and co-ordinating the high qualitystandards of DaimlerChrysler and Mer-cedes-AMG began more than a year beforethe first car rolled off the line.

The launch of the AMG versions of theexisting R 170 and W/S 203 series – alsoknown as SLK 32 AMG and C 32 AMG withan engine output of 260 kW/354 bhp and450 Nm of torque – set a precedent for su-percharged power plants within the AMGfamily of engines. The development of theV6 engine was accompanied by the firstmoves to explore the possibilities of a V8with high-pressure supercharging. It waspossible to apply the existing "V6 with ascrew-type supercharger and charge-aircooler integrated in the V" layout to the V8engine with only minor modifications. Thetarget output values, which were set atover 330 kW and 700 Nm, were attainedduring the subsequent developmentprocess, the figure for the maximum poweroutput even being exceeded by some 20kW.

These figures meant that the target val-ues for the overall vehicle – such as a 0-100km/h acceleration time of < 4.9 seconds –could be attained with ease. But this was tocall for a degree of in-house developmentwork, both for the engine and the entire ve-hicle, which represented an exceptionalchallenge for the whole Mercedes-AMG de-velopment team. At the end of the develop-ment process, the vehicle's 0-100 km/h ac-celeration time was 4.7 seconds. The SL 55AMG reaches the 300 km/h mark in justover 32 seconds, although the productionvehicles are electronically limited to 250km/h. The technical data of the SL 55 AMGis shown in Table 1.

2 Exterior and Design

Throughout the design process, great em-phasis was placed on maximising the dy-namic appearance of the car without devi-ating from the characteristic AMG designline. The aim was to give the vehicle a mus-cular, distinctive look which would empha-sise its high-performance capability at firstglance. As it was out of the question tomodify the body-in-white, the desired visu-al impact is created exclusively throughspecial AMG body styling elements, 18-inchwheels and tyres, and the exhaust system.The characteristic features of the new SL 55AMG are:■ front air dam and rear apron as well asmore pronounced left and right side-skirtpanels

■ black expanded metal grilles in the air in-takes in the front air dam■ clear-lens foglamps■ radiator grille finished in “rough silver”paint■ four oval chrome-plated tail pipes withcharacteristic AMG styling■ black expanded metal grille in the rearapron between the tail pipes■ dark tinted lenses for rear indicators andreversing lights■ 18-inch AMG multi-spoke wheels■ “V8-Kompressor” legend on both frontwings.

The special AMG front apron/rear apronand side-skirt panels are made of polyure-thane RIM technology (material: Bayflex180) and are formed in front-cast moulds.Key features of this process, which Mer-cedes-AMG has developed in partnershipwith leading mould specialists, are theshort mould production times and a moulddurability which is significantly higherthan that usually associated with frontcasting. The components are manufacturedby a long-standing system partner whohandles the entire sequence of processesfrom production of the raw parts to just-in-sequence delivery of the fully assembledcomponents to DaimlerChrysler's Bremenplant.

3 Interior

The particularly sporty character of the SL55 AMG also finds expression in its distinc-tive interior appointments. The seats, steer-ing wheel and trim design have all beenspecially developed for the SL 55 AMG, Fig-ure 1.

The decorative stitching which runsround the dashboard, the centre consoleand door trims is finished in a contrastingcolour, while the appearance of the instru-ment cluster and selector lever has beenmodified. The clean lines of the rolled alu-minium trim elements with their anodisedcoating contribute greatly to the sporty ap-pearance, not least because they are madefrom the same metal – with the same lookand feel – as that used for the superchargerhousing and the boost air distribution line,both of them being key components of thesupercharged V8 engine.

A sporty yet ergonomic design charac-terises the steering wheel, which featuresintegral buttons on the back of the spokesfor operating the wheel-mounted gearshift. The buttons are positioned in such away that optimum ergonomic accessibilityis assured in all driving situations. The sim-ple concept (right-hand button shifts up,left-hand button shifts down) is the sameas that used in competition racing cars.

Like all AMG vehicles, the SL 55 AMG fea-tures a redesigned instrument cluster. Thespeedometer is graduated in 30 km/h inter-vals with a maximum reading of 300 km/h.As a consequence of the higher maximumengine speed, the rev counter has been de-signed for a maximum reading of 7000rpm. The speedometer features the legend"AMG" while the "V8 Kompressor" legendon the rev counter attests to the remark-ably powerful engine fitted in this perfor-mance roadster. Another new feature is thebright white instrument lighting.

Although the basic structure of the seatsis the same as that used for the integralseats in the SL 500, the design and er-gonomics are unique to the SL 55 AMG. Sig-nificantly greater contouring of the seatcushion and backrest provides improvedlateral support during sporty driving. Theexclusive leather upholstery has the char-acteristic AMG look and features an inlayedsilver-plated badge bearing the AMG logoin order to underline its Mercedes-AMGheritage. Smooth or embossed, the leatheritself has the special AMG perforation pat-tern and is available in the following rangeof appointment colours: black/graphite,dark alpaka grey/alpaka grey andblack/berry red, Figure 2.

Standard equipment includes not onlyseat heating for the driver and passenger,but also multi-contour functionality com-prising pneumatic adjustment of the lum-bar supports, seat cushion length adjust-ment and side bolsters with adjustable con-touring.

4 Chassis

4.1 Springing and DampingSystem As is the case with the SL 500, the standardequipment of the SL 55 AMG includes theActive Body Control (ABC) active suspen-sion system. However, modifications havebeen made both on the passive side – in theform of a significantly firmer damper set-up – and with regard to the active suspen-sion characteristics, whose parametershave been adjusted to provide a sportierroll response. This ensures highly respon-sive steering and significantly reducesbody roll when cornering.

The SL 55 AMG is always equipped ex-works with 18-inch wheels, customers hav-ing a choice of two exclusive AMG wheeldesigns. The attractive light-alloy "multi-spoke" wheels for mixed tyres (255/40 R 18at the front and 285/35 R 18 at the rear) are anew design. When winter tyres are fitted,only 255/40 R 18 tyres (same size for frontand rear) will be used.



4.2 Brake System The SL 55 AMG is equipped with four inter-nally ventilated and perforated brakes (360 x36 mm at the front, 330 x 26 mm at the rear)and is the first production vehicle to feature8-piston compound calipers (at the frontaxle) which combine low weight with an ex-tremely large pad surface of 220 cm2 – al-most twice that of the corresponding surfacein the SL 500. As well as reducing the ther-mal load on the individual brake pads, thesubstantial dimensions make for a brakesystem with excellent resistance to fading,Figure 3. The rear wheels are equipped withaluminium 4-piston fixed calipers.

5 Cooling

5.1 Charge-Air CoolingAs in the AMG supercharged V6 engine, thecharge-air cooling system is based on anair/water heat exchanger which makes op-timum use of the available space as it is fit-ted in the "V" of the engine where it is di-rectly integrated with the screw-type su-percharger. For use with the V8, the super-charger underwent further airflow optimi-sation and was adapted to the specific re-quirements of the engine. The thermal con-version capacity of the system is well in ex-cess of 20 kW. Although the water circuit isdesigned as an independent low-tempera-ture circuit, it is filled via the existing ex-pansion tank which it shares with the mainengine coolant circuit. It is also equippedwith an electric water pump which is acti-vated on the basis of the intake air temper-ature, Figure 4.

The cooling module was redesigned inorder to permit the integration of the low-temperature water cooler. Compared to anair/air system, the great advantage of thewater-based system is that water offers agreater storage capacity when used as acoolant. As a result, even temperaturepeaks resulting from repeated full-throttleaccelerations can be absorbed and ironedout without incurring any power lossthrough high intake air temperatures.

5.2 Water and Oil CoolingThe engine cooling system is identical tothat found in the SL 500 but features a morepowerful 850 watt electric suction-type fan.Because of the modified design and the in-tegration of the low-temperature watercooler for the charge-air cooling system, theair-conditioning condenser and the steer-ing oil cooler are separated from each otherin the SL 55 AMG. The position of the ABC oilcooler was also changed. Optimum airflowis ensured by means of specially designedplastic elements to which plasticised rub-ber lips are riveted.

A separate engine oil cooler – in the formof an oil/air heat exchanger – is fitted in thefront apron, where it is able to benefit fromoptimum air flow characteristics. The ex-haust air is channelled off through a specialplastic air duct in front of the cooling mod-ule. In order to ensure that the oil is main-tained at the optimum temperature, the lu-bricating oil circuit is equipped with a ther-mostat mounted on the oil filter lines.

6 Fuel Supply

Thanks to close cooperation involving thesystem partner Pierburg and the relevantMercedes-Benz car development depart-ments, the SL 55 AMG is able to boast aworld first in the form of an electronicallycontrolled fuel-supply system featuring anewly developed helical spindle pump op-erating with a system pressure of 5.1 bar.This on-demand fuel supply system con-sists of the following components: electricfuel pump, pump controller, electric pres-sure sensor, fuel filter and mechanical pres-sure regulator, Figure 5.

When the engine is idling, the fuelpump delivers a minimum volume, whichis fed back to the tank by a nozzle adjustedto a constant flow rate. The return volumerefills the catch tank with the assistance ofa jet pump. Any increase in the fuel beingdrawn by the engine leads to a reduction inthe system pressure and is detected by thepressure sensor, which sends an electricalsignal to the pump controller. The con-troller processes this signal and sends apulse-width modulation signal which trig-gers the power electronics to increase thepower to the fuel pump.

The benefits of this system are to befound in the higher volumetric rate of de-livery combined with the high pressure ofthe fuel system which, in turn, has a posi-tive effect on the injection process. Further-more, the current consumption of the fuelpump and the noise level from the pumpassembly are lower than those for non-reg-ulated systems operating at the same nom-inal pressure and with the same flow rate.

The fuel tank has also been revised andequipped with an electric pre-deliverypump, which guarantees a sufficient deliv-ery volume – regardless of the operatingconditions – even when the engine is run-ning at high load. The capacity of the fueltank is unchanged at 80 litres.

7 Exhaust System

The twin-pipe exhaust system of the SL 55AMG is entirely new. Emission control ishandled by two catalytic converters – locat-ed near the bulkhead – with Pd/Rh-coated

ceramic monoliths as well as by two under-floor catalytic converters using thin-filmtechnology with a Pt/Rh coating. As a re-sult, the SL 55 AMG already complies withthe EU4 emission standard which does notcome into force until 2005. Stainless steelpipes with a diameter of 70 mm are usedbecause the high air throughput of the su-percharged AMG engine requires thelargest possible pipe diameters in order tominimise exhaust gas backpressure.

The SL 55 AMG owes its sporty sound totwo centre and two rear mufflers as well asa connecting pipe between the left and theright exhaust pipes, Figure 6. The design ofthe system has been optimised to empha-sise the throaty sound of the superchargedengine without being intrusive during part-throttle operation, at high revs or when dri-ving with the top down. In keeping with thehigh standards of the SL 55 AMG, all thesound engineering activities were conduct-ed with the actual vehicle in order to avoidattaching too much significance to artificialsound patterns which are removed from thereality of the real driving experience.

The four oval tail pipes are equippedwith characteristic AMG chrome ends andenhance the sporty look of the SL 55 AMG.

8 Powertrain/Rear Axle

8.1 TransmissionAcknowledged as a model of perfection, theMercedes-Benz five-speed automatic trans-mission with touch shift is also used in theSL 55 AMG. However, the engine's hightorque and higher maximum speed meantthat modifications had to be made in orderto optimise the clutch action and the trans-mission's capability to handle high enginespeeds.

The SL 55 AMG is the first AMG Mercedesfor which a “manual transmission mode”with a steering-wheel gear shift has beendeveloped. This gives the driver the optionof shifting gear directly by means of thetwo buttons on the backside of the two up-per steering-wheel spokes as soon as the"manual transmission mode" is selected.The familiar basic functions of the W5A 580automatic transmission – i.e. automaticgear shifting, touch-shift selection of the Dmode and gears 4 to 1, and the choice ofstandard and winter transmission modes –remain fully available.

The mode selector button next to the se-lector lever is used in order to switch be-tween the manual "M", standard "S" andwinter "W" transmission modes. The cur-rent gear and the currently active transmis-sion mode are displayed in the instrumentcluster. In manual transmission mode, thegears can only be shifted when the driver


5ATZ worldwide 4/2002 Volume 104

wishes to do so. Pressing the right-handbutton on the back of the steering wheelcauses the transmission to upshift, whilepressing the left-hand button shifts down agear. In this mode, automatic shifting willnevertheless still take place in the follow-ing situations: if the engine speed limit hasbeen reached, the transmission automati-cally upshifts; if the vehicle comes to astandstill, first gear is engaged automati-cally. Gear shifting in the manual transmis-sion mode can also be performed with theselector lever. The steering-wheel buttonsare disabled when the "S" and "W" trans-mission modes are active.

8.2 Propshaft/Rear Axle andWheel SuspensionThe radically upgraded capabilities of thedrive train set-up and the entire rear axleattest to the fact that the engine develops a

formidable 700 Nm of torque from just2650 rpm. Compared with the basic model,the torsional stiffness of the propshaft issome 50 percent greater and the boltedflanges on the gearbox and rear axle arelarger, as are the Hardy disks.

As a consequence of load simulationswhich were conducted with the expectedengine performance data, the idea of usinga reinforced version of the aluminium rearcross member from the SL 500 was aban-doned. The SL 55 AMG is now equippedwith a high-strength welded steel designwhich was developed jointly with the re-sponsible engineering department at Mer-cedes-Benz. Because of the high level oftorque, an additional torsional supportmounting for the differential was integrat-ed into the rear cross member.

Additional strength is ensured by the re-vised rear wheel suspension set-up with re-

inforced wheel suspension struts and strutmounting bolts, welded-steel spring linksand nodular cast-iron wheel carriers. As theouter ring joints on the half-shafts are alsosignificantly larger, the wheel carriers hadto be redesigned in order to accommodatethem, Figure 7. The rigidity of the rear crossmember mounts – which comprise bothhydro-mounts and rubber mounts – hasalso been increased to a significant extentin all degrees of freedom.

9 Engine

Mercedes-AMG engines power high-perfor-mance vehicles which offer a superb dri-ving experience combined with everydaypracticality and excellent emissions. Devel-oped on the basis of AMG's proven M 113 E55 naturally aspirated 5.5-litre V8 engine,the power plant which is equipping thenew SL 55 AMG worldwide is a V8 super-charged engine with an output of 350kW/476 hp and 700 Nm of torque, Figure 8and Table 2.

As well as employing supercharger tech-nology and increasing the sheer thermody-namic performance of the power plant, thedevelopment team made a large number ofmodifications to the entire engine in orderto ensure that it enjoys the long service lifecharacteristic of Mercedes-Benz products.Although the new unit shares its basic de-sign with the M 113 E 55 naturally aspiratedengine, it was possible to carry over only alimited number of parts such as valves,auxiliary units, the cylinder head cover andthe crankshaft end cover, Figure 9.

9.1 Crank MechanismIncreasing the torque by some 30 percentand the rated speed by 500 rpm meant thatit was necessary to make fundamentalchanges to the crankcase with its 90 degreeV angle. However, it was possible to retainthe "open-deck" design, despite the factthat the brake mean effective pressure wasincreased by about 30 percent. Reinforcedand additional stiffening ribs on thecrankcase improve torque flows from thescrew bosses into the main structure of thecrankcase. With bearing caps 1 and 5 boltedto the side of the crankcase, it was also pos-sible to reinforce the main bearing assem-bly.

An extensively modified timing casecover was required as the supercharger isdriven by a separate 8-groove belt driveand both belt drives needed additional fas-tening points for guide pulleys. Further-more, it was necessary to provide space forthe supercharger drive. Because of thegreater loads involved, the geometry of thecrankshaft and the choice of materials from

MATERIALSTitanium

The fuel supply system of the SL 55 AMG

6 Fuel Supply

The exhaust system of the SL 55 AMG


which it is made had to be optimised. In-ductive hardening of all the fillet radii andbearing surfaces of the crankshaft journalsand crankpins guarantees lasting structur-al integrity.

The crankshaft has been redesigned toallow for piston clearance and two-masstorsional vibration dampers. Masses arebalanced optimally thanks to the use ofprecision balancing weights and heavy-metal plugs in the crank webs.

At 64 mm and 48 mm respectively, thediameters of the main bearings and theconnecting rod bearings were taken overunchanged from the M 113 E 55, althoughthe entry and exit geometry of the oil ductswas optimised. In another departure fromthe M 113 E 55, the supercharged engine fea-tures newly developed forged and cracked-steel connecting rods. The outer edge of theforged contour of the small connecting rodeye has also been machined to produce aprecisely defined contour to optimise clear-ance with regard to the piston crown andits pin boss. G-81 three-compound bearingsare used for the main bearings and lowerconnecting rod bearing shells while high-quality lead-free G-188 three-compoundbearings are used for the upper connectingrod bearing shells.

As the connecting rods do not have anoil riser duct, a new connecting rod bushwith new duct geometry was developed tosupply oil to the piston pin. The design andcharacteristics of the piston rings representthe best possible compromise betweenthermal load, service life, oil consumptionand blow-by characteristics.

A new piston material (142S) was devel-oped, tested and approved for use in pro-duction of the aluminium pistons. The formof the piston was reviewed and refinedcontinuously throughout the entire devel-opment period. All endurance tests demon-strated that, when used in conjunctionwith the Silitec 5 piston wall, the "HA andFerrostan II" piston coating provides reli-able wear protection throughout the entireservice life of the engine.

9.2 Oil SupplyThe newly developed rear oil sump of theMercedes-Benz SL 500, and the oil catchtray and oil pump in particular, were com-pletely redesigned to cater for the differentgeometry and volumetric characteristics ofthe M 113 E 55 ML power plant, the most no-table changes being the inclusion of an ad-ditional front sump and a revised oil returnsystem, Figure 11.

Extensive trials on the tilting test standshowed that the oil returns from the cylin-der heads and the de-aerated oil reservoir,as well as those resulting from direct and

deflected oil waves, had to be separated.This was achieved through the use of bulk-heads in conjunction with an oil catch trayand baffle plate. The oil pump takes theform of a triple pump configuration andthe position of the suction cup on the in-take side was adapted for the new frontsump. A reliable and sufficient supply of oilis assured by an additional pressure stageas part of a two-stage feed process. As theincreased thermal gain at the piston crowncounteracts the cooling effect of the oilspray nozzles, the throughput volume ofeach of the existing twin oil sprayers wasincreased by 50 percent.

9.3 Cylinder HeadThe basic design of the 3-valve cylinderhead from the Mercedes-Benz M 113 engineseries was carried over to a large extent,Table 3. The increased air consumption ne-cessitated the adaptation of the intake andexhaust ports while the greater thermalgain called for a modified water jacket.

Newly developed spark plugs with alonger thread (26.5 mm instead of 19 mm)are making their debut in the superchargedV8 engine after successfully completing allthe tests and endurance trials. As well asmatching the valve timing to the specificcharacteristics of the supercharged engine,the development team equipped the powerplant with twin valve springs to ensure re-liable operation right up to the maximumspeed of 6500 rpm.

9.4 Supercharger ModuleThe supercharger module (see Fig. 12) com-prises the supercharger, the charge air cool-er, the air intake with the electronic accel-erator adjusting motor as well as the fuelsupply rail with the injection valves. Basedon the patented principle of the screw-typesupercharger, the newly developed IHI-S120 BA1 supercharger has an internal com-pression ratio of 1.6:1 and is equipped witha parameter-controlled electromagneticclutch. The drive gearing for the super-charger has an internal step-up gear and islubricated for life.

The air ducting is entirely new with at-mospheric and clean air being routedthrough two resized engine-mounted airfilters. After passing through the charge aircooler, the intake air is divided between theboost air distribution lines of the cylinderbanks and cylinders. The new fuel supplyrail has a damper to prevent system-gener-ated pressure waves.

9.5 Engine ManagementTaking an engine management systemwhich had been specially designed to meetthe requirements of DaimlerChrysler as

their starting point, the AMG team workedwith system partners from Daimler-Chrysler and Bosch to create a completelyrevised engine control system for the M 113E 55 ML. The principal objective was toadapt the engine management system tothe actuator/sensor principle associatedwith the supercharger while taking ac-count of the current country-specific re-quirements concerning emissions and self-diagnosis capability (EOBD, OBDII). As wellas adapting the controller hardware bymeans of new components, the team im-plemented a comprehensive upgrade pro-gramme for the control algorithms whichinvolved more than 900 modulus changes.Core elements, such as those governing su-percharger engagement, were protected bypatents.

In summary, the AMG-specific enginemanagement unit is characterised by thefollowing outstanding features: pressure-based load detection with injection volumetiming adjusted for each cylinder in orderto provide dynamic performance of thehighest standard; parameter-based controlof the intake temperature/coolant circuitfor optimum efficiency and lowest possibledemand on the vehicle’s electrical system;knock detection/control for each cylinderbased on structure-borne sound with inno-vative component protection functionalityfor exhaust-side components; a dynamicadaptive drive control system installed up-stream of the enlarged electronic accelera-tor adjusting motor in order to improvemodulability for different driving situa-tions and driver reactions; a pioneeringtorque-based engagement model for thesupercharger for optimum efficiency andsmooth response with minimal switchingtime between operating modes. This re-sults in the supercharger engaging at givenoperating points and in response to the dri-ver's wishes and so leads to a drastic reduc-tion in power loss levels compared withthose associated with running the super-charger permanently during partial-loadoperation.

By combining these measures concern-ing the engine and its management systemwith the appropriate exhaust system set-up, it has been possible to remain wellwithin the European (EU4) and NorthAmerican (LEV) emissions limits. ■


Documents

The new Mercedes-Benz SL 55 AMG