Development of the new 2012 Mercedes-Benz SLS AMG Roadster
05/05/2011
Mercedes-Benz
The convertible SLS AMG Roadster is the second car to be developed independently by AMG. The Coupe and Roadster concepts were created in parallel - very advantageous during the development process. During this 3-year development period for the 2012 SLS AMG Roadster, the engineers devoted particular attention to bodyshell rigidity, driving dynamics, the soft top and NVH.
Currently undergoing testing in Stuttgart, the 2012 SLS AMG Roadsters are minimally disguised as they cover their test routes. Easily identified by enthusiasts, these two-seaters with a fabric soft top have 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 with a long hood, large wheels and a short rear unified by breathtaking design.
There are still six months to go before the world premiere at the International Automobile Show in Frankfurt in September 2011. Time enough to verify the maturity of the new SLS AMG Roadster. The personnel responsible at AMG have already completed most of the work involved since 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 such as the bodyshell design, weight distribution, engine position, center of gravity or axle design. The very latest simulation programs allow engineers to test handling dynamics, aerodynamics, ergonomics, crash behavior and production process. The digital prototype is therefore a complete, virtual automobile.
In the process AMG also uses the extensive know-how of colleagues at Mercedes-Benz, working with select Mercedes-Benz development departments at the Mercedes Technology Center (MTC) in Sindelfingen.
The latest simulation software and extensive test drives on all continents make the 563 hp Roadster fit for its U.S. market launch in late 2011. The specialists in Affalterbach particularly focused 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. Due to the lack of a fixed roof and gullwing doors, it was necessary to design the side skirts more robustly, not just for crash performance, but because test drives showed that the driving dynamics could be improved even further by strengthening this area. 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 convertible variant."
In order to achieve handling dynamics identical to the Coupe - without 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 windshield frame and at the center tunnel, and a structure between the soft top and the tank stiffens the rear axle. These features prevent unwanted vibrations from the start and dispose of additional weight-increasing vibration dampers often employed by competitors. Because of this rigidity, the soft top can be reliably opened and closed electrohydraulically at speeds up to while on the move at up to 31 mph. The bodyshell of the Roadster tips the scales at only 536 pounds - which is comparable to the low, 531 pounds of the SLS AMG Coupes bodyshell.
A few specific modifications to the aluminum spaceframe
Without a fixed roof and gullwing doors, the convertible SLS AMG has a reinforcing cross-member behind the seats which supports the fixed rollover protection system. The 250-watt subwoofer of the Bang&Olufsen BeoSound AMG high-end sound system is located in the cross-member rather than the parcel shelf of the Coupe. One particular challenge was acoustic insulation of the cross-member, which acts as a subwoofer housing for the two 6.5-inch speakers connected in series. Numerous improvements became necessary before the required listening pleasure was met. It was only with the help of a special bulkhead within the aluminum cross-member that the system was deemed ready.
The three-layer fabric soft top of the SLS AMG Roadster, which is stored behind the seats in a Z-formation to save space, is also relevant to handling dynamics. This weight-optimized magnesium/steel/ aluminum construction provides a low center of gravity and is designed for speeds up to the maximum of 197 mph (electronically limited). Engineers stressed that whether open or closed, even at top speed there must be no intrusive flapping, booming, hissing, clattering, whistling or howling. Likewise the plexi-glass windstop and the paneling in the interior, on the soft top and along the beltline must be vibration-free. These precisely defined tests were conducted on the high-speed tracks in Papenburg, Nardo (Italy) and Idiada (Spain).
The superior acoustics, which AMG engineers verified with sophisticated measuring technology, also benefit from another special feature - the seamless, bonded-in rear window made of single-layer safety glass. A special production process not only provides a smooth transition between the outer skin of the soft top and the glass but also leads to low wind noise when the roof is closed - at any speed.
125 years of experience with innovations in convertible vehicles
Ensuring that the soft top is wind and water-proof is a complex undertaking, and AMG and Mercedes-Benz have used the enormous experience gained during 125 years of innovation. There have always been convertible vehicles throughout Mercedes-Benz history.
AMG developers of the 2012 SLS AMG Roadster paid great attention to 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 openings on each side.
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 retractable hardtop. Extreme amounts 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 convertibles. 16 tests must be successfully passed before approval is granted.
Tests include 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, and a 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 conduct test drives in all climatic regions of the world. In Laredo, Texas, for example, there is a particularly fine dust which finds its way into practically any gap, testing the absolute limits of the seals.
The compact fabric soft top, which can be conveniently opened and closed in just 11 seconds at the touch of a button at speeds up to 31 mph, must also submit to various tortures. One of these is the standardized soft top endurance test used for all new Mercedes roadsters and convertibles: 20,000 closing cycles on a stationary test rig, followed by 2,500 closing cycles while on the move (whether in extreme heat, icy cold, high humidity or dry desert winds).
Endurance trial as a final quality check
Even though all the development tests have been passed, and the production tests at the Mercedes-Benz plant in Sindelfingen have been successful, the developers still haven't reached their goal. The focus now turns to the quality of the overall vehicle during endurance trials. These simulate an entire vehicle life under the toughest conditions in accelerated test cycles.
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 program on country roads, highways and in city traffic.
Endurance testing on unpaved surfaces:
-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 6,200 miles on both the Nürburgring's North Loop and in city traffic.
Full-load endurance testing:
-extreme acceleration and braking maneuvers with a frequent full-load operation, which place 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 finished product.
World premiere on September 13, 2011, at the Frankfurt International Motor Show
This is an extensive and tightly scheduled program which for many AMG engineers will only be complete once the 2012 SLS AMG Roadster makes its world debut before the media at the Frankfurt International Motor Show on September 13, 2011.