Audi brings its electric turbocharger closer to production with RS 5 TDI concept


June 20, 2014

Audi's RS 5 TDI concept

Audi's RS 5 TDI concept

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Audi has been developing an electric turbocharger for several years and seems close to launching it on a production car. The new RS 5 TDI concept adds an e-turbo to its biturbo V6 to provide an immediate boost in power that doesn't wait around for exhaust gas.

"Twenty-five years ago, Audi launched the first TDI on the market, writing the first chapter of an enduring success story," says Prof. Dr. Ulrich Hackenberg, Audi board member for technical development. "Our latest innovation is the electric turbocharger, which further improves not just sprint times and pulling power, but also efficiency. This technology illustrates the possibilities harbored by 48-volt electrical systems, which we are currently developing for use in production vehicles."

Electric turbocharging is a bit of a misnomer since turbos rely on exhaust gas-powered turbines by definition, but Audi's been in the habit of calling it that since revealing it several years ago. Since then, it's been applied to the R18 e-tron quattro LMP1 car and now the new RS 5 TDI concept, which shows what it could do in a more road-friendly application.

The RS 5 TDI concept loses the 4.2-liter V8 engine of the production RS 5 Coupe for a 3.0-liter V6 TDI with triple turbos – the e-turbocharger supplements the two traditional turbos. Replacing the typical exhaust-powered turbine wheel, the electric turbo's motor spins the compressor wheel to over 70,000 rpm in a few hundredths of a second. This action essentially eliminates turbo lag and provides a powerful boost right off the line.

"What all turbocharged engines have in common is that the turbocharger is driven by energy from the exhaust," Audi explained when it discussed its electric turbo technology in 2012. "This means that starting from very low revs, the rise in boost pressure and therefore torque becomes gradually greater only as the exhaust energy increases.

A new development stage is the electric biturbo. This makes it possible – independently of the exhaust energy available – to build up charge pressure quickly and achieve high levels of torque even at very low revs."

The RS 5 TDI Concept has a dedicated 48-volt power system providing the large quantities of energy needed to feed the electric turbo. The system is energized by brake recuperation, storing electricity in a lithium-ion battery.

The tri-turbo set-up gives the RS 5 TDI a bank of 385 hp (287 kW) and 553 lb-ft (750 Nm) of torque, firing it to 62 mph (100 km/h) in four seconds (more than half a second faster than the 450-hp production RS 5) and 124 mph (200 km/h) in under 16 seconds. The car's top speed is listed at 174 mph (280 km/h). Meanwhile, it rolls for more than 44 miles for every gallon of diesel (5.3cL/100 km), another large improvement over its production sibling, which combines for 18 mpg (13 L/100 km).

Audi doesn't make any hints at RS 5 TDI production, but the e-turbo seems likely to find its way into dealerships. A report in Drive this week suggests that the Q7 SUV will be the first production model with the technology when it debuts at this year's Paris Motor Show.

Source: Audi

About the Author
C.C. Weiss Upon graduating college with a poli sci degree, Chris toiled in the political world for several years. Realizing he was better off making cynical comments from afar than actually getting involved in all that mess, he turned away from matters of government and news to cover the things that really matter: outdoor recreation, cool cars, technology, wild gadgets and all forms of other toys. He's happily following the wisdom of his father who told him that if you find something you love to do, it won't really be work. All articles by C.C. Weiss

So Audi is taking an approach similar what Ford and Mazda are planning by using regenerative braking to power things around the car other than a hybrid/electric motor.

I wouldn't be surprised to see more companies looking to replace the standard 12v 40lb lead acid battery with something more suited to work with regenerative braking (like 48v Li-Ion).

One thing I'm not sure of though, aren't regenerative braking systems in hybrids just using the motor itself to recoup energy in braking? If so the only thing preventing the motor from also helping to power the car is essentially just a larger battery right? Is there anything else that separates non-hybrid regenerative braking systems from the ones in hybrids or are the costs to build it about the same?


and this is precisely why i love Audi. They seem to be one of the few makers on the market developing cars that are fuel efficient, fun to drive, and actually look like something the average person would want to buy.

I cannot wait until this hits the market!

Michael Wilson

brings back memories of the e-turbo you could buy for 99 bux lol.

i like Audi too...but the cash for it? In my neck of the woods Audi means you have cash and no brains... (Toronto..Yonge/ know the deal). R8's with automatic shifters where the drivers bounce the car up and down the street anyway with absolutely no clue what they are doing.

had a few Audis (6).... i'll stick to vw diesel and let the others spend spend.


I want!

Jon Smith

I would say that this is more like what was done in the new F1 engines.

TC Cramer

I think TC Cramer is right on the money, this is like the motor/generator system that F1 uses on their turbos this year. It eliminates turbo lag and also can generate electricity instead of using the traditional waste gate. This is a completely separate system from regenerative braking, btw, those are generators/motors connected to the wheels (which is also used in F1).

There's a lot of interesting side effects and benefits that can be gained purely through software. For example, if the batteries are low, the engine can burn a little more fuel to generate more electricity by some slight dragging of the generators, and vice-versa, without the driver noticing any change.

There's also some old designs being resurrected to remove a lot of the moving parts in these hybrids, like making the pistons be magnets and the cylinder containing a generative coil, eliminating all the rotational components.

Fill Fill

If they were smart, they'd couple a big honkin' electric motor to the turbine shaft via a centrifugal clutch from a go-kart, or use a sprag type clutch from a transmission or starter drive, and then they'd have their cake and be able to eat it too!! A switch at the bottom of the travel of the loud pedal (WOT) would energize a relay when full, quick boost is wanted, and then when you back out of it, the turbo is in normal operation mode again. What's not to like here? Or, behind door number two, have a cylinder charged up with air that dumps its contents into the turbine side when it's needed at WOT. That will spin the turbine up quickly and not lean out the mixture. A small air compressor run off the drive line could keep the cylinder charged up with a couple of hundred PSI for use when you get down to business.


Expanded Viewpoint

Isn't this e-turbo thing just a supercharger that gets switched on and off? Can someone 'splain the difference?

(I'll admit I'm not a true-mechanic type gearhead - I love cars, love to drive them, but not so handy at taking apart an engine to do a valve job. In 12th grade I replaced brakes in Auto-tech class, and I've replaced a radiator and alternator on my own!)


I hope this trickles down soon. While small cars are fun to drive, the lack of grunt at low RPM can be scary, especially when pulling into traffic. So if this helps, and can feather in and out depending on need at other speeds and paired with proper fuel control, it might be a real boon to efficiency.

Bruce H. Anderson

I say use a smaller battery pack and but a generator on an exhaust gas turbine.


If they need high voltage for the "turbo" a hybrid seems like the way to go. My Lexus GS450h has a 288 volt battery just sitting there. That would be plenty to spool up an electric turbo when you want a power blast.

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