|The Mercedes-AMG SLS AMG E-CELL. Click to enlarge.
Mercedes-AMG, the performance brand within Mercedes-Benz Cars, provided an update on its development of an electric version of the SLS AMG, the development of which it announced last July. (Earlier post.)
With a power output of 392 kW (526 hp) and 880 N·m (649 lb-ft) of torque, the gullwing with electric drive is part of the company strategy entitled “AMG Performance 2015” which aims to continually reduce fuel consumption and emissions. The SLS AMG E-CELL may see a limited production run, the company says.
Traction is provided by four synchronous electric motors each achieving a maximum 12,000/rpm and positioned near to the wheels. Compared with wheel-hub motors the unsprung masses are substantially reduced. One transmission per axle transmits the power.
|Powertrain components of the E-CELL. Click to enlarge.
The electric model accelerates from zero to 100 km/h in 4 seconds—which almost puts it on the same high level as the SLS AMG with 6.3-liter V8 engine developing 420 kW (571 hp), which can accelerate to 100 km/h in 3.8 seconds. However, unlike the combustion engine, torque build-up with an electric motor is instantaneous—maximum torque is available virtually from a standstill.
The SLS AMG E-CELL drive incorporates a liquid-cooled high-voltage lithium-ion battery featuring a modular design with an energy content of 48 kWh and a capacity of 40 Ah. The maximum electric load potential of the battery, which consists of 324 lithium-ion polymer cells, is 480 kW.
The intelligent parallel circuit of the individual battery modules helps to maximize the safety, reliability and service life of the battery. The 400-volt battery is also charged 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.
|Another perspective on Mercedes-Benz SLS AMG E-CELL powertrain components. Click to enlarge.
A separate low-temperature circuit is responsible for cooling the high-voltage lithium-ion battery. In low external temperatures, the battery is quickly brought up to operating temperature with the aid of an electric heating element. This helps to preserve the overall service life of the battery. In extremely high external temperatures, the cooling circuit for the battery can be additionally boosted with the aid of the air conditioning system.
Battery pack modules are located in front of the firewall, in the center tunnel and behind the seats. Advantages of this solution include the vehicle’s low centre of gravity and balanced weight distribution. The installation of the drive components required no changes to the model’s weight-optimized aluminium spaceframe.
The additional front-wheel drive called for a newly designed front axle: unlike the series production vehicle with AMG V8 engine, which has a double wishbone axle, the SLS AMG E-CELL features an independent multilink suspension with pushrod damper struts. This is because the vertically-arranged damper struts in the series SLS had to make way for the additional drive shafts. As is usual in a wide variety of racing vehicles, horizontal damper struts are now used, which are operated via separate push rods and transfer levers.
This front-axle design, already tried and tested in motorsport, enables the agility and driving dynamics of the electrically-powered SLS AMG to attain the same high levels as the V8 variant. Another feature is the speed-sensitive power steering with rack-and-pinion steering gear: the power assistance is implemented electrohydraulically rather than just hydraulically.
The technology vehicle is slowed with the aid of AMG ceramic composite brakes, available as an optional extra for the series production model, which feature extremely short stopping distances, a precise actuation point and outstanding fade resistance, even in extreme operating conditions.
The over-sized discs—measuring 402 x 39 mm at the front and 360 x 32 mm at the rear—are made of carbon fibre-strengthened ceramic, feature an integral design all round and are connected to an aluminium bowl in a radially floating arrangement.
The ceramic brake discs are 40% 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 tire grip. The lower rotating masses at the front axle also ensure a more direct steering response—particularly noticeable when taking highway 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 air outlet openings on the hood and the vehicle sides have been modified for enhanced aerodynamics. The front apron has not only been brought further forward, but also helps to guarantee an optimized airflow in the area of the underbody. This improves air resistance while reducing downforce.
An extendable front splitter enhances this effect: in parallel with the automatic rear spoiler, it extends downwards by seven centimeters at speeds above 120 km/h (75 mph) and helps to further accelerate the air which travels beneath the car. When it reaches the area of the rear axle, the air enters the rear diffusor which, due to the lack of an exhaust system, features a steeper angle, thus increasing downforce at the rear axle and in turn further enhancing the aerodynamic balance.
The AMG instrument cluster and center console both feature a new design. The new AMG instrument cluster provides information on speed, charge status of the battery and the estimated range. The newly designed center console now houses a 25 cm touchscreen, which driver and passenger can use to conveniently operate all of the audio, climate and navigation functions, and also obtain information on the flow of power from the four electric motors.
The AMG Drive Unit, which is angled towards the driver, houses buttons for starting the motor, and the ESP functions, the AMG memory function and the extendable front splitter and rear spoiler. Using three new buttons, the driver can switch simply between P, R and D. The park setting is also enabled automatically by switching the electric motors off.