Volvo's new electric supercharger...turbocharger...what exactly is it?

New forced induction system uses electric motor to spin impeller

    Perhaps you saw the news last week about an experimental engine under development at Volvo. It’s a 2.0-liter gasoline-powered four-cylinder that cranks out an amazing 450 horsepower.

    At 225 horsepower per liter, it would be one of the most power-dense engines ever produced, if Volvo decides to build it.

    How Volvo engineers boosted the output of the engine is ingenious. Two turbochargers plumbed into the engine’s intake system are powered not by exhaust gases -- the traditional way -- but by air pressure generated by what I would call a third turbocharger.

    It’s not clear what that third device is -- a turbo or a supercharger. From its appearance, it looks like a turbocharger. But the turbine on the exhaust side has been replaced with an electric motor. Volvo calls the unit an “electrically powered turbo compressor.” But French supplier Valeo, which makes a similar device, calls theirs an “electric supercharger.”

    OK, engineers, gearheads and engine builders out there, I need some help with this. Here’s the question: If you change the power source of a turbocharger from exhaust gases to a high-revving electric motor, is the device still a turbocharger?

    Valeo calls its device, left, an electric supercharger. It uses an electric motor -- not exhaust gasses -- to spin the impeller. A traditional supercharger looks like the one from Eaton, middle. It is driven by a fan belt connected to the front of the engine. Turbocharges like the one made by Honeywell, right, have an exhaust gas driven turbine on one side and an impeller on the other.PHOTO BY VOLVO

    I say it is. What defines the turbocharger in my view is not its source of power but the method in which the air is pressurized.

    Superchargers are usually mounted directly to the intake side of the cylinder head, and air is blasted into the engine via rotors or air screws. Also, superchargers are connected to the engine mechanically, usually by a fan belt to the front of the crankshaft.

    Turbochargers have two vanes inside that look a bit like the fan you see on the front of a jet engine. One side of the turbine is driven by exhaust gases and powers the other side, the impeller, which compresses the air and pressurizes the engine’s intake.

    There’s no question that Volvo’s experimental engine uses two turbos to boost the air going into the engine. But is the device that is powered by the electric motor no longer a turbocharger because exhaust gas doesn’t power it?

    Here’s why this is important: We might be seeing something like this in production fairly soon. Valeo’s “electric supercharger” is being tested by Audi. The rumor mill around Detroit says that the Valeo device will be offered by Audi in a regular production vehicle, possibly as soon as next year.

    The thing is: The Valeo electric supercharger looks just like a turbocharger and nothing like a supercharger, as made by industry leader Eaton.

It’s not clear if Volvo is using Valeo’s device. My guess is yes, since Valeo leads in this technology.