The turbocharger is a very efficient way for automakers to take a smaller displacement engine, and increase both engine performance and reduce fuel consumption. But turbochargers can have a lag in power as they wait for the exhaust gasses to build up. Audi has developed an electric biturbo that will revolutionize the turbocharged engine by completely eliminating turbo lag.
Turbocharging makes a lot of sense because automakers can downsize engine displacement and achieve the same power and efficiency compared with larger naturally aspirated engines. Audi says that their TDI diesel engines have realized power gains of over 100 percent and torque gains of 70 percent since 1989. Over the same time period, emissions have been reduced by 95 percent with the use of turbochargers.
Audi's electric biturbo technology
In advanced diesel development at Audi’s site in Neckarsulm, engineers developed this new electric biturbo technology that uses a secondary compressor that boosts the main turbocharger at lower engine speeds. All turbochargers use energy from the exhaust to drive the turbo. The problem with conventional turbo’s is the torque needed for power becomes gradually greater only as the exhaust energy increases.
Audi’s new electric biturbo 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 rpm’s. This eliminates turbo lag and offers an instant increase in torque and power. The biturbo uses both a turbine wheel driven by the exhaust gas stream, and an electrically driven turbine that accelerates to very high speeds in an extremely short time.
Audi says, the electrically driven compressor is placed after the main turbocharger and intercooler in the charge air path. And when the main turbocharger’s energy output is low, the air is directed into the electric compressor and is compressed there a second time thus boosting the power at low revs.
The results of the new Audi electric biturbo are impressive. In preliminary testing, torque buildup occurs significantly earlier, and the driver experiences a distinct boost in performance immediately. Both BMW and Subaru have also been developing their own electric turbochargers with Subaru looking to put the new technology on the next generation WRX engines.
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