This is about to change...
The first question is obvious, why an electric turbo?
The answer is downsizing (remember that this concept refers to maintainin
g or increasing the power of engines at a lower energy cost).
Since new turbocharged engines were started to be used in the world of competition, this technology has progressed considerably.
For the engines of single seater Formula 1 cars, a hybrid turbo is used called MGU-H (Motor Generator Unit-Heat). This turbo is still similar to conventional turbos as it uses a turbine accelerated by the exhaust gas to compress the intake gas. The big difference from the traditional turbo is that between the turbines there is an electric motor that can accelerate the intake turbine.
This electric motor eliminates turbo lag, which is the time that elapses from the moment the accelerator is pressed until the pressure in the intake manifold increases.
This system allows the turbine to be accelerated and braked depending on the power demand, therefore the turbo control solenoid valve and the variable geometry vanes are not required, although to achieve rapid deceleration it still incorporates a blow-off valve.
As with all the successful advances that give good results in competition, electric turbo technology is arriving in street cars. The first make to develop and to adapt these systems to their vehicles was the Audi-VW group which presented the RS5 TDI Concept, a prototype equipped with a V6 diesel engine with double turbo and 385 horsepower that achieved an approved average consumption of 5.3 l/100 km and CO2 emissions under 140 gr/km.
Others have followed this prototype, such as the Audi A6 3.0TDI Concept or the more recent VW Passat 2.0 TDI Bi-Turbo, the latter is the closest to going on the market. It also rumoured that the new Audi Q7 will incorporate this technology in 2016.
All these cars have the same base technology, although they are fitted with engines of different capacities, derived from the Audi R18 e-tron, winner of the 24 hours of Le Mans in 2014.
Two turbos in series are installed in these engines, one conventional activated by the exhaust gas and the other fully electric.
The conventional turbo cannot be dispensed with entirely as 55% of the fuel energy escapes through the exhaust and it is very efficient in accelerating the intake turbine.
Then why a second electric turbo?
The answer to this question is that it is complementary to the first, when the engine rpm is low, the conventional turbine takes a time to reach its optimal working rpm range (around 60,000 rpm).
To eliminate this turbo-lag, the intake gases are made to pass through the electric turbo which rapidly accelerates the turbine and starts to raise the pressure first, as it does not depend on the engine rpm.
Once a certain rpm is reached at which the conventional turbo enters into its working phase, the gas bypass to the electric turbo is closed and they go directly to the engine. This system improves thrust at low engine rpm and achieves maximum torque over a wider rpm range.
The electric turbo reduces consumption and improves the dynamic performance of the car, but when operating at full speed it constitutes a large electrical load for the vehicle, in fact to be able to reach its working range it uses electric motors supplied with 48 V.
This characteristic means that it is necessary to strengthen the car's electrical system, and the use of capacitors and one or more large capacity batteries.
This technology appears attainable and effective for engine manufacturers, and it is only a question of time before it is generally extended in the car world.