Mercedes-Benz gullwing returns

  • 21-Sep-2009 03:40 EDT
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The Mercedes-Benz SLS-AMG features lightweight aluminum construction technology, a front/mid-positioned 6.2-L V8 engine, and gullwing doors.

The Mercedes-Benz gullwing is back, but now the classic 300SL has become the modern day SLS AMG—and an electric version is in development. The production car uses lightweight technology including aluminum double wishbone suspension, aerodynamic downforce, a high power output of 420 kW (563 hp) from its 6.2-L (Mercedes categorizes it as a 6.3-L) front/mid V8 engine, a transaxle gearbox, and of course, distinctive gullwing doors.

The SLS AMG weighs in at a relatively modest 1620 kg (3571 lb) with a front/rear weight distribution percentage of 47/53. Its wheelbase is 2680 mm (105.5 in), while tracks are 1682 mm (66.2 in) in front and 1653 mm (65.1 in) in the rear.

“This exceptional car is far from being a nostalgic glimpse backwards," said Dr. Dieter Zetsche, Chairman of the Daimler Board and Head of Mercedes-Benz Cars, speaking at the SLS’s global premiere at the Frankfurt Motor Show. "It is a determined step into the future. As of 2013, it will be available with an electric-only driveline. This makes the SLS perhaps the best looking proof that driving fun has a great future at Mercedes-Benz.”

Performance claims for the gasoline-fueled car include a 0-100 km/h (0-62 mph) time of 3.8 s and a top speed electronically limited to 317 km/h (197 mph), with a combined fuel consumption of 13.2 L/100 km.

A chassis and body of aluminum represent a production first for Mercedes. An aluminum spaceframe is used and light aluminum profiles combine the "force nodes" to create a stable structure, and the large, low-lying cross sections of those profiles are said to exhibit high resistance torque figures. The spaceframe comprises 45% aluminum profiles, 31% aluminum paneling, 20% cast aluminum, and 4% steel. The A-pillars use ultrahigh-tensile, hot-rolled steel. The BIW (body-in-white) mass is 241 kg (531 lb).

Mercedes designed the SLS to have what it terms “the lowest possible center of gravity,” and the car’s V8 engine, mounted behind the front axle, has dry-sump lubrication to help achieve that. The engine gives the SLS a weight/power ratio of 2.84 kg/hp. Naturally aspirated, it achieves maximum torque at 4750 rpm.

Based on the Mercedes-AMG M156 unit, the 6208-cm³ engine has been so extensively changed that it has been given a new designation: M159. As well as the dry sump, those changes include new intake manifold, valve gear, camshaft, and exhaust system, forged pistons, a strengthened crankshaft mounting, optimized crankcase structure, smart generator management, and improved lubrication. A brake energy regeneration system is fitted. Dry mass of the M159 is 205 kg (452 lb), giving an engine a weight/power ratio of 0.36 kg/hp.

The driveline includes a rear-mounted dual-clutch transmission (DCT), lightweight driveshafts similar to those used on the DTM (motorsport) C-Class touring car, and a torque tube. Shift time for the transmission can be as short as 100 ms. Drive programs include Controlled Efficiency, Sport, Manual, and Race Start. And the SLS has a mechanical differential lock.

The double wishbone suspension also incorporates dual A-arms with a track rod to each wheel. The A-arms, steering knuckles, and hub carriers are of forged aluminum, reducing unsprung mass.

Carbon ceramic front brakes and the AMG light alloy wheels are 9.5 x 19 in front and 11 x 20 in rear, shod with 265/35R-19 front and 295/30R-20 tires.

Demonstrating its broad program of alternative zero-emissions powertrains, Mercedes decided to develop an electric version of the SLS. It has an individual electric motor for each wheel in total, providing 392 kW output and 880 N·m (649 lb·ft) and two transmission systems.

For what Mercedes describes as the car’s “first pilot stage,” the electric SLS has a modular liquid-cooled high-voltage lithium-ion battery with an energy content of 48 kW·h and a 40-A·h capacity at 400 V. Battery modules are positioned ahead of the firewall, in the chassis’ center tunnel, and behind the seats.

The electric STS, with its virtually instant maximum torque delivery, reaches 100 km/h (62 mph) in 4 s, only 0.2 s longer than the gasoline SLS.

Mercedes planned the electric version of the SLS from the car’s concept stage, and no changes to the spaceframe were needed. Deutsche Accumotive, a joint venture between Daimler and Evonik Industries, is to provide the car’s future battery technology. Daimler is taking the lead role for the development and production of batteries and battery systems.

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