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Efficiency, Performance From Audi's Electric Turbo Prototype

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Audi RS 5 TDI concept

Audi RS 5 TDI concept

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"Turbo" was the word to have on your car in the 1980s. Preferably in huge, bright script, completely out of correlation with the car's actual performance.

Now, it's more often used as an indication of efficiency--take Ford's Ecoboost brand, for example.

Audi has used them for many years on its gasoline and diesel models, and has now put its latest innovation--electric turbochargers--in a fully-working prototype vehicle.

Based on the firm's RS5 performance coupe, Audi's turbocharged tech could legitimately wear bright 80s-style turbo stickers. And in fact, it does--in a sort of restrained, Germanic way.

But while normal RS5s motor down the road with a V-8 gasoline engine, the RS5 prototype uses Audi's 3.0-liter TDI-badged V-6 turbodiesel, equipped with a brace of turbochargers.

The smaller of these, writes Motor Authority, is spooled up using a compact electric motor, rather than relying on the passage of exhaust gases.

ALSO READ: BMW Pairs Electric And Traditional Turbos To Boost Efficiency

Since an electric motor can spin turbine much quicker than exhaust gases can, the smaller turbo can then do its job of spooling up the larger turbo--for extra power--much more efficiently.

The electric motor spins the small turbo up to 3,000 rpm, after which point it's bypassed--Audi's engineers figured out that an electric motor alone isn't as efficient as mixing electric power and exhaust gases.

The concept develops 553 lb-ft of torque from just 1,250 rpm--111 lb-ft more than Audi's normal twin-turbo 3.0 TDI. Power has increased too, rising from 272 hp to a 385 hp maximum output.

The benefits for performance are obvious: The familiar sensation of "turbo lag"--waiting for exhaust gases to spool up the turbo--is largely eliminated, and boost can be maintained even when engine revs drop, making the car more responsive when you roll back onto the gas pedal.

MORE: Electric Supercharger Boosts Gasoline Engines To Diesel Efficiency

But we can see economy benefits too.

A responsive engine is one that can be driven in its most efficient range much more often. A driver may be less inclined to venture higher up the rev range--using more fuel--if their car is equally responsive and powerful lower down.

And at highway speeds, where diesels in particular traditionally excel, an engine with ample low-revs urge requires fewer fuel-wasting changes to lower gears.

Audi hasn't announced when its electrically-turbocharged engine might reach production, but if the technology is as usable as it seems, it may not be that long at all.

As more vehicles use turbocharging as a way to boost performance in downsized engines, electric turbochargers could become as familiar as the turbocharged engines themselves.

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