Turbochargers always used to be about performance, but in recent years they've become very popular as a way of improving the efficiency of regular engines.
Forced induction by turbocharging is still a good way of developing power, and many performance cars take just such a route.
But using the same theory, you can build a smaller, more efficient engine, and turbocharge it to maintain the performance offered by its larger, gas-guzzling predecessor.
Now, German automaker Audi has previewed a way in which turbocharging technology itself can be improved--electric turbocharging.
Audi electric biturbo
The technology is demonstrated on Audi's twin-turbo, or biturbo 3.0-liter TDI diesel.
This engine already has twin turbochargers. A small turbocharger works on the lower half of the rev range, able to spool up quickly to start boosting engine power at lower revs, while a larger turbocharger takes over at higher revs to boost top-end power.
Despite this setup, and in common with many other turbocharged engines, there's always a little 'turbo lag'--a period where not enough exhaust gas is spinning the turbo to enable it to boost intake gases--leading to slow responses.
The electric biturbo changes this. The smaller, first turbocharger is replaced by a separate turbine placed after the main turbocharger. During normal operation, the turbine is bypassed.
However, it's equipped with a small electric motor. When required, the motor spins the turbine, replicating the effects of exhaust gases--but can be operated at any engine speed. When in use, it boosts low-revs power and torque.
Power to the small electric motor is regenerated during coasting, meaning very little energy is required to run the technology.
Efficiency, as well as power
So what does this mean for fuel efficiency?
Well firstly, the technology could potentially be used for any turbocharged engine, allowing for smaller engines with larger turbochargers to maintain power, without running the risk of huge, lag-prone turbos such as those often found in 1980s performance cars.
But also, greater response at low engine revs will mean drivers could be less inclined to drive hard to achieve their desired performance.
Gutless-feeling engines are typically overworked as drivers try to compensate, but an engine that really pulls from low revs, even in smaller applications, gives drivers real-world performance without having to burn loads of gas.
Provided the technology can be made inexpensive and reliable, it seems like the best of both worlds--power when you need it, and efficiency all the time.