Among the technologies it is developing to improve the fuel
consumption of gasoline and diesel engines, Audi is working on an electric
biturbo system in which a secondary compressor boosts the main turbocharger at
lower engine speeds.
Turbochargers are typically driven by energy from the
exhaust—i.e., starting from very low revs, the rise in boost pressure and
therefore torque becomes gradually greater only as the exhaust energy
increases.