After the gullwing
version, the open-top variant is the second car to be independently
developed by AMG. The Coupe and Roadster concepts were created in
parallel - which brought decisive advantages during the development
process. During this approx. 3-year period for the SLS AMG Roadster, the
engineers devoted particular attention to the aspects of bodyshell
rigidity, driving dynamics, the soft top and NVH.
Greater Stuttgart area, spring 2011: the new SLS AMG Roadsters are
slightly disguised as they cover their test routes. Easily identified by
those in the know, others only see these two-seaters with a fabric soft
top as some prototype or other: there are no Mercedes stars or model
designations to be seen, just black adhesive foil at the front, rear and
along the sides. The proportions speak for themselves, however: a long
bonnet, large wheels and a short rear end indicate that this is a sports
car of breathtaking design.
There are still several months to go before the world premiere at
the International Automobile Show in Frankfurt/Main in September 2011.
Enough time to verify the maturity of the new SLS AMG Roadster. The
personnel responsible at AMG have already completed most of the work
involved, as the Coupe and Roadster were created in parallel. The
development and testing of a new AMG high-performance car is based on
the digital prototype (DPT). Extensive investigations help to achieve
specific objectives. Whether these concern the bodyshell design, weight
distribution, engine position, centre of gravity or axle design, or of
course the handling dynamics, aerodynamics, ergonomics, crash behavior
and production process - the very latest simulation programs allow the
very realistic representation of a vehicle and all its characteristics.
The digital prototype is therefore a complete, virtual automobile.
In the process AMG also uses the extensive know-how of colleagues
at Mercedes-Benz: as in the case of the Coupe, networked development
with selected Mercedes-Benz development departments at the Mercedes
Technology Center (MTC) in Sindelfingen was intensified.
The latest simulation software and extensive test drives on all
continents make the 420 kW (571 hp) Roadster fit for its market launch
in autumn 2011. The focus of the specialists in Affalterbach was
particularly on bodyshell rigidity, handling dynamics, the soft top and
NVH (Noise, Vibration and Harshness).
Synthesis: rigidity, performance and a close-fitting soft top
Naturally all these development aspects are closely linked, as
Tobias Moers (44), head of overall development and member of the
Executive Board at Mercedes-AMG, explains: "Without bodyshell rigidity
there are no handling dynamics, and neither can the close fit of the
soft top be guaranteed." As the Roadster variant was already taken into
consideration during the conceptual phase for the SLS AMG, the
lightweight and extremely rigid aluminum spaceframe was specified at a
correspondingly early stage. Owing to the omission of a fixed roof and
gullwing doors, it was necessary to design the side sills more robustly.
But not primarily to meet the legal requirements in the event of a
crash - in principle the Roadster would also manage this with the side
sills of the Coupe. Studies and test drives showed that the driving
dynamics could be improved even further with this measure, therefore
side sills with greater wall thicknesses and chambers were developed for
the open-top SLS AMG. Tobias Moers: "The SLS AMG Roadster is a
super-sportscar - just like the Coupe. It goes without saying that AMG
is also determined to achieve superior driving dynamics with this
open-top variant."
In order to achieve handling dynamics identical to those of the
Coupe, despite the lack of a fixed roof, the Roadster has two features
designed to increase the rigidity of the bodyshell: the cross-member
carrying the dashboard has additional supporting struts at the
windscreen frame and at the centre tunnel, and a strut mounting stay
between the soft top and the fuel tank makes the rear axle even more
rigid. These features prevent unwanted vibrations from the start, and
make the use of additional, weight-increasing vibration dampers such as
those often employed by competitors unnecessary. As another important
aspect, it is only if the bodyshell has the requisite rigidity that the
soft top can be safely and reliably opened and closed electro
hydraulically while on the move at up to 50 km/h. The side members of
the front and rear modules in both SLS AMG models are identical. The
bodyshell of the Roadster tips the scales at only 243 kilograms - which
is comparable to the low, 241-kilogram weight of the SLS AMG Coupe's
bodyshell.
A few specific modifications to the aluminum spaceframe
Owing to the omission of the coupe roof and gullwing doors, the
open-top SLS AMG has a reinforcing cross-member behind the seats which
supports the fixed rollover protection system. Not forgetting the
250-watt subwoofer of the Bang&Olufsen BeoSound AMG high-end sound
system: This is accommodated in the cross-member, as the Coupe-specific
location on the parcel shelf is not available owing to the Roadster's
soft top. One particular challenge was acoustic insulation of the
cross-member, which acts as a subwoofer housing for the two
165-millimetre speakers connected in series. Numerous improvements
became necessary before the required listening pleasure was achieved. It
was only with the help of a special bulkhead within the aluminum
cross-member that all audiophile standards could be satisfied.
The three-layered fabric soft top of the SLS AMG Roadster, which is
deposited behind the seats in a Z-formation to save space, is also an
aspect relevant to handling dynamics. This weight-optimized, combined
magnesium/steel/ aluminum construction ensures a low centre of gravity
and is designed for speeds up to the maximum of 317 km/h (electronically
limited). Whether open or closed, even at top speed there must be no
intrusive flapping, booming, hissing, clattering, whistling or howling.
Likewise the push-on glass draught-stop and the paneling in the
interior, on the soft top and along the beltline must be vibration-free.
Nothing must be allowed to compromise the open-air enjoyment. The basis
for verified, customer-compatible results in extreme conditions is
provided by precisely defined test drives on the high-speed tracks in
Papenburg, Nardo (Italy) and Idiada (Spain).
The excellent acoustics - which AMG engineers have naturally also
verified with sophisticated measuring technology - also benefit from
another special feature, namely the seamless, bonded-in rear window of
single-layer safety glass. A special production process not only ensures
a smooth transition between the outer skin of the soft top and the
glass, as the sum of these design measures also leads to low wind noise
when the roof is closed - at any speed.
125 years of experience with innovations in open-top vehicles
Ensuring that the soft top is wind and waterproof is a complex
undertaking, and AMG and Mercedes-Benz have used the enormous experience
gained during 125 years of innovation. There have always been open-top
vehicles in the history of Mercedes-Benz - and unlike in the case of
many competitors, in an uninterrupted sequence.
Every soft top is different, however, and even objectives already
defined become more ambitious over time. The five challenges to which
the AMG developers of the SLS AMG Roadster gave great attention and
commitment were water, sand, dust, heat and cold. One special feature of
the compact soft top is the continuous water pocket: this is attached
below the soft top to catch rainwater and direct it down to the
underbody via two apertures on each side.
All the development aspects of a vehicle which involve flexible
deformation are always very complex. Simulations can sometimes lead to
false conclusions, and do not always provide the most cost-effective
solution. Classic test procedures often help to achieve rapid results.
Development project manager Holger Strahl (34): "In this field it is
not possible to simulate everything with CAD, and it becomes a matter
of trying out, driving, testing and improving. The solution finally
approved must also be suitable for series production, of course. Our
specialist departments and the overall development team work together
very closely in their common search for the perfect solution." He also adds: "There is no such thing as the second-best alternative for AMG."
Endurance test with 16 criteria: the "Sindelfingen rain test"
The rain test at the Mercedes Technology Center (MTC) in
Sindelfingen is particularly demanding, and every new vehicle bearing
the Mercedes star is required to pass it - whether it has a fixed roof, a
soft top or a vario-roof. Extreme quantities of water are used to
ensure that the result of the development work is watertight - which is a
particular challenge in the case of roadsters or cabriolets. 16 tests
must be successfully absolved before approval is granted.
Whether during the hose test, when all soft top, door and flap
seals are sprayed with a water-hose, the continuous, overnight rain
test, the fording test, the icing, swirl and high-pressure tests, or the
final session in an automatic car wash - the rain test simulates every
conceivable situation that can occur on any continent.
Bench testing and practical trials in all climatic zones
In addition to various test facilities such as the water chamber
and the climate/ wind tunnel, the AMG specialists have recourse to test
drives in all climatic regions of the world, where problems can be
identified and solutions sought. In Laredo, Texas, for example, there is
a particularly fine dust which finds its way into practically any gap -
and tests the seals to the absolute limit.
The compact fabric soft top, which can be conveniently opened and
closed in just 11 seconds at the touch of a button, even at speeds up to
50 km/h, must also submit to various tortures. One of these is the
standardized soft top endurance test used for all new Mercedes roadsters
or Mercedes cabriolets: 20,000 closing cycles on a stationary test rig
must present no problem for the hydraulic cylinders, electric motors and
joints. There are also 2500 closing cycles while on the move, whether
in great heat, icy cold, high humidity or dry desert winds. In this area
too, nothing is left to chance - and for excellent reasons: the aim of
this enormous effort is to give the customer limitless driving pleasure
in their SLS AMG Roadster.
Endurance trial as a final quality check
All the optimization stages have been absolved, and the production
tests at the Mercedes-Benz plant in Sindelfingen have been successful,
but the developers have still not reached their goal. The quality of the
overall vehicle is now the focus of the accompanying endurance trials.
These simulate an entire vehicle life under the toughest conditions in
accelerated test cycles. The aim is to verify the level of maturity
before production of customer vehicles commences.
The endurance testing at a glance:
Long-term testing on a variety of different roads:
All the components and systems are tested together in everyday
operation. Loaded up to their permitted gross vehicle weight, the test
cars are put through a precisely defined test programme on country
roads, on motorways and in city traffic.
Endurance testing on heathland:
In this case, the developers focus on the durability of the chassis
and suspension components, the entire bodyshell and the integral
subframe on which the front axle, steering and engine are mounted. The
test cars are loaded up to their permitted gross vehicle weight.
Accelerated endurance testing:
Testing of the entire vehicle, focusing on the powertrain, chassis
and suspension. Special features of the AMG program include 10,000
kilometers on the Nurburgring's North Loop and 10,000 kilometers in city
traffic.
Full-load endurance testing:
Extreme acceleration and braking maneuvers with a high proportion
of full-load operation, making extreme demands on the cooling,
fuel-delivery and braking systems.
Long-term corrosion testing:
Corrosion testing of the entire vehicle simulates the toughest dynamic and climatic environmental influences.
Final board approval:
All-inclusive verification of the degree of development and production maturity.
World premiere on 13 September 2011, at the International Motor Show (IAA) in Frankfurt/Main 
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