Audi’s e-tron doesn’t have just one electric motor – it has four, one for each wheel. But this prototype has limitations…
By Andrew Frankel
They closed the Pacific Highway the day I drove the Audi e-tron. Which was nice of them. With all the trucks, pick-ups and SUVs stacked up behind the troopers positioned at either end of a several-mile stretch, I was able to waft up and down the Malibu coastline untroubled by anything other than the nagging doubt that something other than the traffic was missing.
It didn’t take much to figure out what. I was sitting in a supercar, a mid-engined coupé that will hit 60mph from rest in under 4sec, and yet even under full acceleration it made barely a sound. There were no gears to flick through, either manually or automatically, no rev-counter needle soaring towards the red paint, no engine to hear. It was performance stripped back to its barest bones. It could almost have been a conveyor belt.
I had felt this before. I remember the same sense of sensory deprivation when gunning an inaudible Tesla Roadster up the Goodwood hill, but that was somehow different – the car an esoteric curiosity. This was an Audi for goodness sake: this is the main event. If this is the future for fast cars, is it a future worth having?
Do not doubt Audi’s commitment to the e-tron. What you are looking at is not so much a concept car as a first working prototype. There will be others, some displayed to the public and some not, throughout the course of 2010 and then, at some stage in 2011, either it or something very like it will go on sale.
What ‘it’ is exactly takes a little explaining, even to those with an understanding of electric cars. It is not, for instance, any kind of hybrid, a technology Audi regards as a mere bridge from the internally combusted present to an all-electric future. Inside that sleek shape there is nothing you or I might recognise as an engine.
But there is a motor. In fact there are four. Even the Tesla stops way short of this approach, relying on a single electric motor driving through a transmission to power both rear wheels. By stark contrast, the e-tron has a motor at each corner, so each wheel has its own power supply. And if that makes you see new meaning in the term ‘four-wheel drive’ that is exactly what Audi is hoping. One of the purposes of the e-tron is to show how Audi’s Quattro philosophy can be redefined for the modern world.
Where the e-tron shares common ground with the Tesla, but no other electric car on sale, is in the lithium-ion battery technology that is the source of such power. But even here the e-tron goes its own way: while the Tesla relies quite literally upon nearly 5000 laptop batteries for its power, the e-tron has just 100 lithium-ion cells, specifically developed for it by Sanyo.
These batteries allow the motors to direct up to 313bhp to the wheels and, electric motors being what they are, maximum torque the instant you put the accelerator to the floor. As this concept actually started life as a prototype Audi R8 (though it now shares not a single significant dimension with the donor vehicle), the batteries are placed within the wheelbase, directly behind the cabin, which is just as well considering that, at 470kg, the battery pack alone weighs more than a Caterham.
Nevertheless by careful use of composite materials and Audi’s aluminium spaceframe, the e-tron’s weight has been pegged back to 1600kg, or about the same as the R8. Whether such a slimline figure will be achievable for a production version that will have to be built down to a commercially viable price remains to be seen.
There is more cleverness everywhere you look. There is not enough residual heat created by the motors to warm the interior, so instead of using an electrically-powered heater that eats into power reserves, the e-tron comes with a heat pump – a common enough device in a building but never before used in a car. Moreover three independent cooling systems are used because the battery, electronics and motors all operate in different temperature ranges.
But perhaps most impressive is the e-tron’s electronic brake-by-wire system. In all normal driving, when you put your foot on the brake you’re not actually making use of its ceramic discs at all, but merely the massive engine braking afforded by those motors. Better still, while you do, the e-tron is able to recover all the energy that would otherwise be lost during braking and use it to charge the battery. Only when your braking requirements go beyond what the motors are able to offer are the discs used, but when you drive the e-tron it is not possible to discern when the car slips from one mode to the other.
Yet there are issues inherent within the design of any electric car, e-tron included, and it is impossible to escape the feeling that it is how successful Audi is in addressing them over the next two years that will eventually decide the success or otherwise of this project. Audi says it has conquered entirely the cooling issues of lithium batteries (the e-tron is water-cooled unlike the air-cooled Tesla), but cites a range of just 155 miles on a full charge. And be assured if you drove an e-tron with anything other than saintly restraint – which must surely be part of its point – it wouldn’t take much to drop the real world range down into double figures. It is hard to see people paying £100,000 for an e-tron (which is the least it will cost) and tolerating a limitation like that. Moreover, recharging the battery can take up to eight hours, depending on available voltage. They may baulk too at being limited to a top speed of just 125mph, because electric motors use disproportionately more power the faster you go.
Yet it’s hard to see Audi going so public with such a car as to put the press behind its wheel without first having a good idea of how these problems are to be resolved. When you quiz its engineers they just smile and say ‘wait and see’, but are keen that you appreciate this e-tron is just their first effort, their practice car if you like. In the two years that have passed since they started work on it, further substantial and still unseen technological leaps have been made.
But even if they manage to extend the range, preserve the performance and reduce the charge time, Audi is still left with a silent supercar.
I suggested they could synthesise various soundtracks to play in the cabin according to throttle opening and load – an unsilenced flat-eight for the track, a silken smooth straight-six for the road – but was returned only a rather old-fashioned look. Audi’s view is that by removing external noise sources and distractions like the need to change gear, what results is actually a purer driving experience. I wasn’t able to drive the e-tron hard enough up the coast road to put this to the test, though I don’t discount entirely the possibility. I was amazed by the e-tron, encouraged by the rate of progress it represents and awestruck by some of the technology it contains. But enthralled? That will have to wait for another day.