Fast and frugal

Using an electric motor for each of its wheels, the Mercedes-AMG SLS E-cell is a silent supercar with a conscience, writes DAVE MOORE.

With its conventional drivetrain removed, the SLS gullwing AMG Mercedes-Benz has been turned into something equally quick, but a whole lot easier on the environment.

Boasting a power output of 400kW and 880Nm of torque, this development vehicle from AMG is able to offer exceptional performance. Effectively a gullwing with electric drive, it's part of a company strategy labelled 'AMG Performance 2015' whose aim is to continually improve fuel consumption and lower emissions.

Finished in fluorescent 'AMG lumilectric magno' paint, this special gullwing even offers the prospect of a possible small production run, at the same time reflecting the Mercedes-Benz AMG performance brand.

The drive system is provided by four synchronous electric motors which can each achieve a maximum rotational speed rpm of 12,000rpm. By positioning them close to, rather directly upon, the drive hubs, the car's unsprung masses are substantially reduced. One transmission per axle transmits the power which can realise 100km/h in just four almost silent seconds. This almost puts it on the same evel as the SLS AMG with a conventional petrol-powered 426kW 6.3-litre V8 engine which can accelerate to the same velocity in 3.8 seconds.

Unlike the combustion engine, torque build-up with an electric motor is instantaneous so maximum torque is available virtually from a standstill. The spontaneous torque build-up and confident power delivery - which does not suffer from any interruption of tractive power - are combined with engine running characteristics which are totally free of vibration. Four motors, four wheels the resulting all-wheel drive offers driving dynamics at the highest level, while providing the best possible traction and active safety.

The SLS AMG E-cell drive incorporates a liquid-cooled high-voltage lithium-ion battery featuring a modular design with an energy content of 48kWh and a capacity of 40Ah. The maximum electric load potential of the battery, which consists of 324 lithium-ion polymer cells, is 480kW, which is an absolute best value in the automotive sector.

The 400-volt battery is constantly recharged by means of targeted recuperation during braking while the car is being driven.

A high-performance electronic control system converts the direct current from the high-voltage battery into three-phase alternating current which is required for the synchronous motors and regulates the energy flow for all operating conditions. Two low-temperature cooling circuits ensure that the four electric motors and the power electronics are maintained at an even operating temperature. A separate low-temperature circuit is responsible for cooling the lithium-ion battery.

The installation of the drive components required no changes whatsoever to the gullwing model's weight-optimised aluminium spaceframe. And there were just as few constraints when it came to maintaining the excellent level of passive safety and high degree of long-distance comfort that are hallmarks of Mercedes cars.

Unlike the series production vehicle with AMG V8 petrol engine, which has a double wishbone axle, the SLS AMG E-cell features an independent multilink suspension with pushrod damper struts, because the previously vertically-arranged damper struts in the series SLS had to make way for drive shafts. As is usual in a wide variety of racing vehicles, horizontal damper struts are now used, which are operated via push rods and transfer levers.

The car's ceramic brake discs are 40 per cent lighter in weight than the conventional, grey cast iron brake discs. The reduction in unsprung masses not only improves handling dynamics and agility, but also ride comfort and tyre grip. The lower rotating masses at the front axle also ensure a more direct steering response which is particularly noticeable when taking motorway bends at high speed. The ABS and ESP systems have been adapted to match the special application spectrum of the permanent all-wheel drive.

The E-cell car's air outlet openings on the bonnet and the vehicle sides have been modified for enhanced aerodynamics. All trim and detachable parts, which are finished in chrome or silver shadow on the standard SLS AMG, are now finished in matt black.

No price has been quoted for the production version of the AMG SLS E-cell car, nor how much it will cost to have a man with a red flag in front of the car to warn of its imminent arrival. Being so quiet, it might be best to just use it on the track where no cyclists and pedestrians can be hurt.

- © Fairfax NZ News