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Mercedes-Benz reveals SLS E-Cell performance data

Fri, 09 Mar 2012 00:00:00 -0800

Mercedes-Benz has lifted the veil of secrecy on the plug-in-electric propulsion system of its upcoming SLS E-Cell, first revealed in concept form at the 2009 Frankfurt auto show.

Set to go into limited production in early 2013, the zero-emission version of the German carmaker's signature gullwing coupe is set to rival a raft of new high-priced electric or hybrid supercars due out in the not-too-distant future, including the Audi E-tron, the BMW i8, the Jaguar C-X75 and the Porsche 918.

The car is undergoing development at Mercedes-Benz's performance-car AMG unit and its British-based sister company, AMG High Performance Powertrains--the company behind Mercedes' latest 2.4-liter V6 Formula One race engine.

The SLS E-Cell eschews the naturally aspirated 6.2-liter V8 gasoline engine of its standard sibling for a quartet of synchronous electric motors--one mounted at each corner of its carbon-fiber-and-aluminum body structure and driving all four wheels--for a combined output of 526 hp and a heady 649 lb-ft of torque.

The motors, supplied by Bosch, are capable of reaching a rotational speed of up to 12,000 rpm and drive through two separate fixed-gear transmissions--one mounted on each axle and both featuring torque vectoring to provide selective distribution of drive forces to the wheels possessing the most traction. AMG claims that design ensures only minimal electronic-stability-program intervention, even on wet and/or slippery road surfaces. By comparison, the standard SLS uses a six-speed dual clutch gearbox and rear-wheel drive.

Energy for the SLS E-Cell's electric motors is provided by a 400-volt lithium-ion battery pack mounted within the space usually reserved for the SLS's transmission tunnel and fuel tank behind the driver and passenger seats. It consists of 864 individual cells provided by Korean battery specialist SK Innovations. They are arranged in 12 individual modules, each consisting of 72 cells and providing an overall energy density of 48 kilowatt-hours and a maximum load of 480 kilowatts, which AMG boss Ola Kaellenius describes as “an absolute best in the automotive sector.”

By mounting the four electric motors low at each corner and the battery wholly within the wheelbase, AMG claims to have achieved a weight distribution of 46:54 front-to-rear and a center of gravity nearly 1 inch lower than that of the gasoline-powered SLS coupe.

In addition to plug-in recharging, the SLS E-Cell uses a multistage variable kinetic-energy-recuperation system (KERS) operated via steering-wheel-mounted paddles. The recharging technology was first developed by AMG High Performance Powertrains for the KERS system used on McLaren's Mercedes-Benz-engined car during the 2009 F1 season and subsequently improved for use on this year's Mercedes-Benz-engined F1 race cars.

Unlike the standard SLS coupe, which uses an all-aluminum body, the SLS E-Cell employs a more complex carbon-fiber-reinforced plastic (CFRP) and aluminum structure revealed at last year's Frankfurt motor show. Its key element is a transmission tunnel fashioned out of CFRP, which is structurally integrated into the existing aluminum structure.

The stiff, high-strength CFRP component helps reduce weight while creating a zero-intrusion cell that protects the batteries from damage in the event of a crash. The use of carbon fiber means that the SLS AMG E-Cell's transmission tunnel is about 30 percent lighter than the transmission tunnel in a standard SLS, which goes some way to offsetting the extra weight of the batteries.

Mercedes-Benz has not revealed a weight figure for the production version of the SLS E-Cell just yet, but its high-tech propulsion system is claimed to provide it with a 0-to-62-mph time of 4.0 seconds, just 0.2 second more than the standard SLS coupe, and a top speed that is likely to be limited to 155 mph.

By Greg Kable