Some engineers tell us that we will start seeing electric turbochargers on production vehicles within the next five years. Image via Valeo.com

It doesn’t matter who you talk with, most everyone will agree that once a turbo spools up, they are actually a good way to generate more horsepower. However, spooling up is one of the main problems many people have with them. Their “lag” is something that most feel is the only downfall.

How Turbos Work

On a standard turbo, the drive impeller is driven solely by exhaust gases, which can reduce efficiency of the system. Image via aeristech.co.uk

There are two basic-types of forced induction systems that are available for automotive use-supercharging and turbocharging. Both force more air into the combustion chamber. The difference is how they do it. Superchargers are belt driven, while turbos are exhaust driven.

A turbo consists of two impellers that are connected by a shaft. As the hot exhaust gases hit the impeller in the exhaust stream, the impeller is spun, spinning the connecting driveshaft which drives the compressor impeller. While they do help create extra power, they also steal some of that power.

This image from Aeristech helps illustrate how the gains from an electric turbo are achieved.

The drive impeller in the exhaust stream creates an obstruction to the smooth and speedy flow of exhaust gases out of the combustion chamber. We know that in order to produce maximum power, your engine has to breathe, and that impeller in the exhaust stream acts like a hand over your mouth. While it doesn’t block the flow completely, it restricts it.

Enter the Electric Turbocharger

The Aeristech electric turbo/electric supercharger.

Word hit the automotive press last week that we’re soon going to be seeing electric versions of turbochargers. However, calling them a turbo is technically incorrect. Since they aren’t driven by exhaust gases shouldn’t they be referred to as superchargers. It would be technically correct to call them a compound turbo/electric supercharger system. These systems promise to deliver increased fuel economy, better throttle response, and better top-end performance, because they don’t impede the flow of the exhaust.

How It Works

Cut-away of the Valeo electric turbocharger showing the compressor section and the electric motor windings. Valeo.com.

An electric motor is coupled to the turbo driveshaft. When acceleration is required while at low speeds, the electric motor instantly spins the turbo up to speed. Once the engine is up to speed, the electric motor kicks off and is decoupled from the driveshaft.

Until recently supplying enough voltage and current to spin the turbo to full speed immediately was an obstacle. Engineers have surmounted that obstacle by using a large capacitor. The shot of energy is fed through a DC-DC conditioner, and from there to the motor.

Full Power Finally Unleashed!

Engine power output depends on the density of the air charge. This graph shows the improvements gained in testing. Image via Valeo.com

For years, automakers have tried to overcome turbo lag by building smaller turbos that spool up much faster than larger turbos. However, the trade-off is less power being generated by the smaller turbo. The development of electric turbochargers would allow automakers and engine builders to install much larger turbos so their engines can develop more power.

One automaker is quoted as saying their standard 3.0 TDi engine produces around 240 hp and 428 lb-ft. of torque, while their electric turbo-equipped 3.0 TDi produces 326 hp and 428 lb-ft. respectively. This means that engines can be scaled down in size, while their power output can be increased. This will help with fuel efficiency.

Thank You Hybrid Vehicle Technology

Aeristech’s All-Electric Turbo/Supercharger looks a little different from the Valeo offering.

Electric turbo technology has been in use since roughly the year 2000. However, it was out of the reach of most everyone except high-end racing teams and labs. This was due to the cost of delivering enough voltage.

Enter hybrid-car battery technology. With these 40 to 50-volt batteries, the current required drops significantly, thus making the system more stable and less dangerous. Another cool part is that hybrid technology also allows us to include circuitry inside the drive motor that turns it into a generator under deceleration, allowing us to recover some of the power that was used to spool up the electric motor.