Mercedes-Benz SLS AMG E-CellEnlarge Photo
They're certainly not suitable for everyone, but that's not to say there aren't aspects we can appreciate.
649 pounds-feet of torque from a standstill is an appreciable quality, as is 525 horsepower. Those are the figures produced by the Mercedes-Benz SLS AMG E-Cell, the exceedingly yellow electric car you may have seen at several auto shows over the last year or so.
The E-Cell isn't a half-hearted attempt at putting an electric drivetrain in a regular SLS body, but an in-depth engineering project that has roots in the world of Formula One.
While the aluminum and carbon-fiber body is standard SLS, the technology is anything but.
Torque vectoring electric motors
Central to the SLS E-Cell are the four synchronous electric motors, mounted in the chassis near each wheel. Powering all four wheels has traction benefits, and torque vectoring from the individually-driven wheels means cornering characteristics can be adjusted almost infinitely - and reduces the reliance on electronic stability controls, useful for the keen driver.
Light weight helps achieve the high standards of performance implied by the AMG badge. Carbon-fiber reinforced plastic (CFRP) has been used extensively, as well as aluminum. Benefits of CFRP include a weight saving of around 30 percent over aluminum, but high strength too.
The car's battery is mounted inside the carbon-fiber monocoque, which increases safety, but also allows the center of gravity to remain low and the weight distribution to remain even. Mercedes is keen to point out that you can expect the very highest standards of safety from the E-Cell.
And just how light are the fibers themselves? Mercedes uses a fascinating--if arbitrary--yardstick. Each fiber is a tenth the thickness of human hair, and if one were long enough to reach the moon, it would weigh only 25 grams--less than one ounce.
Formula 1 technology
Many carmakers claim their cars are infused with technology from the racetrack, but in many cases the link is tenuous.
Not so the SLS AMG E-Cell, and not just in its carbon fiber unibody structure. The carbon ceramic brake rotors take a leaf from the racing world, with massive power and resistance to fading, even when used very hard.
They also help keep the car's weight down, at 40 percent lighter than regular gray cast-iron rotors. That has benefits for handling too--offering lower unsprung weight, to the benefit of steering response.
Racing-style pushrod shocks replace the vertically-arranged system in the regular SLS, as the electric drive system--and the now driven front wheels--required a different axle setup.
Owing even more to Formula One racing is the battery system. Kinetic Energy Recovery Systems, or KERS, are familiar to F1 now. Kinetic energy is turned into heat, and electric energy when braking, which is then used to provide a boost of power at certain points during each lap.
Similar technology has featured in hybrid vehicles for many years, but Mercedes-Benz has used its F1 expertise in the 48 kWh battery fitted to the SLS E-Cell. The battery is liquid-cooled, lithium-ion and high voltage. Just like the F1 KERS, energy is recuperated when braking.
On sale in 2013
Most important for some is that all this technology isn't even going to waste. Mercedes-Benz expects a market launch in 2013, as part of a small series-production run.
In the greater scheme of things the E-Cell's contribution to the world of electric cars may be small, but as with the Tesla Roadster, benefits to the concept's image may be invaluable.