Audi electric turbo 2013: First drive

Tall, folding himself carefully into the A6’s ample door frame and eyes creased from squinting at data, Axel Schwarz bids us to roll the Audi prototype normally out of the driveway.

We do. It’s a normal A6 biturbo diesel, as far as we can tell. Even from the standing start sprint Herr Schwarz encourages us to do, it feels like a normal twin-turbocharged oil-burning Audi.

There’s the initial half-second of softness as the car’s acceleration climbs Mount Soggy while the engine tries to build its turbo pressure, then a thumping wave of unbroken punch from around 1800rpm. The biturbo is one of the better ones, yet this step-off lag is one of the few remaining problems turbocharged engines have.

Yet it’s Mount Soggy that Mr Schwarz and his team have been working on, and this is their solution.

We stop again, he flicks a switch hidden in a cupholder and we go again. This time, the A6 pauses for about a tenth of a second and then just leaps away, fizzing with a light whine before the bigger turbocharger chimes in and begins to hammer away in its familiar, strong guise.

What on earth has Mr Schwarz just done? Simply put, he’s flicked the switch to turn on an electric turbocharger. Technically, it’s not a turbocharger unless it’s driven by exhaust gases, but most car buyers won’t see the difference between a turbocharger and this.

Effectively, it’s an electric compressor and it’s designed to do the job of a small, mechanical turbocharger. And it’s designed to do it instantly on demand and it’s designed to fill in any gaps that traditional turbocharging can’t fill.

It’s enough, he says, to slash two full car-lengths out of the A6’s first three seconds of acceleration from a standing start and also helps out on the road when exiting low-speed corners.

Fitted to the Biturbo V6 diesel, the electrically powered compressor looks like a stack of dinner plates with a hose on one end and weighs less than 5kg, though the bigger battery it requires adds a few more at the back-end of the car.

Audi will call it the Electric Biturbo system when it, perhaps, goes on sale in late 2013 in the new Q7, but the real secret to the system is that the electricity it needs to spin up comes directly from capturing waste energy from braking and coasting down to lights or down hills.

Up until now, that energy has been refocused, stored in a 12-volt battery and spent turning things like air-conditioning compressors, power-steering pumps and oil pumps.

Not anymore. This system spends electricity so rapidly that it needs a full 48-volt wiring harness and a bigger battery, yet its brake and coasting regeneration means it’s effectively energy neutral and uses no extra fuel.

“The turbocharger is traditionally driven by the energy of the exhaust gases,” Mr Schwarz explained. “At lower revs, the exhaust gas sometimes gives problems for acceleration with larger vehicles, simply because there isn’t enough of it yet.

“We have a turbocharger and an electric compressor that we added to it. This compressor makes it possible to build up charge or boost pressure independent of the driving situation.

“The strength is a spontaneous build-up of torque. It means you build up the charge pressure quicker and achieve higher values of torque at whatever rpm. The engine speed or revs won’t matter in turbocharged engines of the future.”

“We are at an early stage of development (could have fooled us – MT). It’s some years for production because the wiring harness is 12 volts and this needs 48 volts.”

But Audi wouldn’t be pressed for more details. The boost pressure it generates is an Ingolstadt secret, the amps it draws is an Ingolstadt secret and the suppliers it is working with are Ingolstadt secrets.

Another Ingolstadt secret, according to Mr Schwarz, is what machinery we’re likely to see it in first, but other Audi sources are not so reticent.

“It’s a little over a year away and most likely to come first with a V6 turbo-diesel,” one source admitted.

“It would be at its most helpful in an SUV because of their extra weight and because that would help them overcome it better.

“It’s not decided in what or when, though we have a good idea it’s going to be a big SUV. Realistically, we have to wait until our new board members understand and decide on their strategies, but late 2013 is likely,” the source said.

Effectively, the Electric Biturbo does the job that the smaller turbos do in most biturbo engines today – it just does it better, faster and more efficiently. Most such engines have one small turbocharger to build boost pressure quickly and then a larger turbocharger that hits hard higher in the rev range to deliver maximum power.

Audi places its conventional, larger turbo-charger closest to the exhaust gases to maximise its boosting potential and sites its electric “turbo”, which doesn’t need exhaust gases at all, downstream of it.

The electric “turbo” actually doesn’t work all that often. It is usually bypassed via a valve, leaving the mechanical turbocharger to do most of the boosting work, chiming in only when the engine needs its extra strength.

“It will also raise the fun of driving this car, but it’s also more efficient as well,” Mr Schwarz said.

“There is only one mechanical turbocharger, not two, so there is more space inside the engine bay. Currently, the Biturbo’s particle filters are under the seats, but this is smaller and that means they will move inside the engine bay and use the same filter as the single-turbo diesel.

“Besides being cheaper and easier to build that way, it also has the gas arriving at the particle filters around 10-15 degrees hotter than the current system, so that’s added efficiency.”

Read the latest news and reviews on your mobile, iPhone or PDA at carsales' mobile site…