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Shock therapy: Merc’s electric SLS

TopGear does the morning rounds in the world’s fastest milk-float: the all-electric Mercedes SLS E-cell

  1. There’s an episode of Father Ted called ‘Speed 3’ which lampoons the Keanu Reeves action flick by stranding the idiot priest Dougal on a runaway milk-float. Milk-floats are intrinsically funny because they are the dullest form of transport known to man, noiseless, pitifully slow, emasculated. They’re also electric, which is why the milk-float is the pejorative that haunts the notion of the all-electric car.

    Can we really learn to love the electric car? Internal combustion is explosive and exciting, a thrilling collision between fuel and air, and regulated by fast-moving pistons and cylinders. Electricity comes out of the wall when you flick a switch. Yes, I know it’s more complicated than that, but still, electricity is the stuff that makes your fridge work. 

    Words: Jason Barlow

  2. Not in the AMG Mercedes’ SLS E-cell, it isn’t. Push the over-long accelerator pedal once you’re rolling, and three things happen simultaneously. The first sees the release of a big, beautiful hit of pure energy that will warp you up the road in a way utterly unlike anything you’ve ever experienced before. This prompts the second response, an expletive-laden outburst we can’t reproduce here. The third is the realisation that you are sampling the Future. With a capital F.

    Not that electric vehicles are a new concept. In fact, electric propulsion was more popular than internal combustion when the car was in its infancy. But industry realpolitik, particularly in the US, not to mention the greater range and flexibility that petrol-powered vehicles soon provided, conspired to drive the EV up a philosophical cul-de-sac. And there it stayed for most of the stupidly oil-happy 20th century.

  3. Climate change and other inconvenient truths have put EVs back into the mainstream. Silicon Valley upstart Tesla you’ll know. Vauxhall’s Ampera is almost with us. Renault-Nissan boss Carlos Ghosn has plunged his company into a game-changing strategy, a suite of new all-electric models generating 10 per cent of overall sales by 2020.

  4. But the big prize - if only symbolically - is the all-electric supercar. Audi’s R8 make-over, the E-tron, was a bold play but still felt more conceptual than feasible. AMG’s SLS E-cell aims to be the real deal: 528bhp and 649lb ft of torque of real deal, produced by four synchronous electric motors, and capable of reaching 125mph from a standstill in 11 seconds. AMG? There’s irony for you. 

    Merc’s performance wing is arguably the king of internal combustion, yet it has served up the most complete zero-emission electric powertrain so far. A year ago, I drove a prototype of the SLS at the Nürburgring, four months before its launch. Even then it was clear that AMG’s then-boss Volker Mornhinweg was just as charged by the e-drive version. “We wanted to make the big jump,” he told me. “As an industry, we need to be more proactive.”

  5. Though not on sale until 2013, AMG wanted to showcase its electric proactivity. So here I am standing beside the sole SLS E-cell prototype on a runway outside Kristiansund, a town in north-west Norway with strong connections to the oil industry. Norway’s a clever country: 99 per cent of its electricity is sustainable, generated mostly hydro-electrically with some solar input too. It shows what’s possible. The SLS E-cell does too.

  6. Visually, it’s almost identical to the existing car, but the E-cell has some big aero changes to make it 10 per cent more slippery. The front apron has been re-profiled and brought forward to optimise airflow along the car’s underbody. An extendable front splitter tilts downwards above 75mph and helps accelerate air under the car. Because the E-cell doesn’t need an exhaust system, the rear diffuser is bigger and more aggressively angled to generate extra downforce. The lightweight wheels are new, and look like the moon discs you see on Bonneville salt flat record breakers.

    There’s an E-cell badge on each front wing and the special ‘lumi-electric magno’ mustard-yellow paintjob is memorably lysergic, but other than that it looks like a stock SLS.

  7. Doesn’t sound like one, though. In fact, it doesn’t sound like anything. Standing right beside the E-cell, you can just make out a low, pulsing hum, the sort of sonic vibration most domestic appliances emit if you listen hard. It’s weird, then disturbing, and then kind of cool. This is a 528bhp, 3.9 seconds-to-62mph supercar, yet it’s… near-silent.

    Though the novelty of the SLS’s gullwing doors never fades, on this particular car there are more important things to note as you slide into it. For a one-off prototype, it’s finished to an incredibly high standard. The seats, dash and trim are all immaculate. Run your eye around the cabin and you’ll notice a unique set of instruments above the wheel, and a brand-new 10in touchscreen in the centre console. This is unique to the E-cell, and the interface is very similar to an iPhone’s. Chances are that what we’re looking at here is an early version of Mercedes’ next-generation telematics. Works well, too.

  8. But the thing that really knocks you sideways is what happens when you do that instinctive driver thing and try to blip the throttle pedal. In the SLS you get the expected AMG V8 thunder and a ripple of torque reversal along the driveline. In the E-cell you get nothing at all. Yet the glowing instruments and that low hum tell you that the car is good to go. As with all electric cars, it’s up to you how fast and how far you’re prepared to recalibrate your personal expectations.

  9. So how does it actually work? The heart of the E-cell is its drive system. There are four electric motors, one close to each wheel to provide what is effectively four-wheel drive, and each revving to 12,000rpm. There is one transmission on each axle (effectively a gearbox for each pair of electric motors).

    The power source is a high voltage lithium ion battery with an energy content of 48kWh and a 40Ah capacity. That’s made up of 324 lithium-ion polymer cells, and because an all-electric powertrain was part of the SLS battleplan from day one, the battery’s modules are cleverly packaged under the bonnet, in what would normally be the transmission tunnel, and behind the seats. So the car’s centre of gravity is actually 25mm lower, its weight distribution isn’t compromised, and the aluminium spaceframe is unchanged.

  10. The battery’s direct current is converted into a three-phase alternating current and fed to the four motors by an electronic control unit. Two low-temperature cooling circuits regulate the motors’ and electronics’ operating temperature; in cold conditions an electric heating element warms things up, in hot ones the aircon system can help cool things down. The batteries weigh 450kg, and the E-cell’s overall weight is 2.1 tonnes, around 300kg more than the standard SLS.

    A few other things: because the E-cell gains front-wheel drive, it swaps its double wishbone set-up for a multi-link suspension configuration. The steering is now electro-hydraulic. Though it features ABS and ESP, there’s no traction control. The E-cell’s four-motor system also allows for torque vectoring, but it’s not yet operational on the car we’re driving. Braking is by ceramic composites - a whopping 402mm in diameter at the front, 360 at the rear.

  11. There’s no escaping the sheer oddness of the driving experience. Strictly speaking, nothing is easier than pushing a pedal to go, then another to stop. Yet the E-cell’s sensory parameters are so different, and the mechanisms by which the you interacts with it so alien, that it’s all a bit… discombobulating. Tyre rumble predominates, and not only do you feel the suspension working, you can also hear it. I don’t like CVTs much, either, and the E-cell’s fixed ratio transmission is similarly remote. It feels more ponderous than the regular car, and the steering is initially rather nervous.

  12. But by the time we reach the Atlanterhavstunnelen - a 5.7km engineering masterpiece that spears 250m beneath the sea - it’s starting to feel more natural. There are four modes to choose from - C (comfort or city), S (sport), S+ (sport plus) and M (manual), and flicking from one to the other gives you different levels of control and throttle response. Go for kickdown in any mode, though, and you’re rewarded with the sort of forward thrust that’s not far off Veyron velocity. Not bad for a milk-float, eh? Under full acceleration it starts to sound like a commercial jet engine on initial descent. 

  13. Then there’s the E-cell’s regenerative braking system. The standard car’s column paddleshift remains, but as the car runs a fixed ratio, they’re relieved of transmission duties. Instead, if you pull and hold the left-hand downshift paddle, a strip of green appears in one of the dials ahead of you and you get maximum regen braking. In fact, it’s the equivalent to a fairly hefty push on the brake pedal. Another paddle prod puts you in ‘sailing’ mode, and you just surf along on all those electrically generated torques in near-silence. 

    It handles, too. Four-wheel drive gives it great traction from corners, and though it’s much less nimble than its petrol brother it’s still a lot of fun. When the torque vectoring tech is on-line, the electric SLS will be quite something. 

  14. E-cell engineer Daniel Semmler admits that there is still lots to do. Battery technology is ever-evolving, so their energy and power density can only improve. They’ll get lighter too, which will help the car’s balance. A range of 60-130 miles is another limiting factor, and though the E-cell can be quick-charged in under an hour, standard re-charging procedure is nearer eight hours. Assuming the infrastructure is in place. And because we don’t live in Norway, there’s the small matter of where our electricity comes from. Britain’s coal-fired power stations aren’t that clean, and we don’t have the funds to pay for all the nuclear powerplants we need. Or the stomach.

    Not that AMG is selling the SLS E-cell as the Holy Grail. It’s one answer of many. It not only demonstrates what can be done, it shows that it works. These guys are very clever and very committed. Imagine where they’ll be in five years’ time.

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