Editorial: Tri Turbo and Electrical Assist

Interesting | July 9th, 2011 by 15
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The triple turbo talk continues unabated, this time with a bit of a twist, electric turbo. Not so fast! Electric turbo? If a turbo was …

The triple turbo talk continues unabated, this time with a bit of a twist, electric turbo. Not so fast! Electric turbo? If a turbo was powered electrically (rather than with exhaust gases) it would be a centrifugal supercharger.

And a quick interwebs search on ‘electric supercharger’ will bring up the same level of snake oil stupidity since ‘high mileage’ magnets. But if you look for ‘electrically assisted turbochargers’, a completely different set of information comes up.

What the electrical assist does is spin the turbine up to speed in very light to no load conditions. And the term ‘light to no load’ is the critical piece. Under load, you have to supply massive quantities of
amps to the electric motor to generate the boost levels needed. But if all that is required is for the turbine to be spun up then an existing automotive electrical system will work just fine.

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A random electric supercharger featured here

Knowing that, where the electrical assist in a tri-turbo setup resides is just a matter of deduction (as opposed to ‘induction’). The speculation is that the engine would continue to use two small turbos (one for cylinders 1-3, the other for cylinders 4-6) as the N54B30 does. They have minimal lag, and provide decent performance right off idle. But they suffer at higher engine RPMS. It’s at this juncture that the third turbo would be employed, picking up the compression of air at higher RPM/load tan the two smaller turbos won’t handle as efficiently.

It’s that third turbo that would benefit from electrical assist. As engine RPM rose, the circuit to spin the third turbine with the small electric motor would kick in and the turbo would be ready to provide
boost with virtually no lag. (Even more fun is grabbing the electrical output from the motor when under boost and applying that to the battery.)

In thinking about how that would be accomplished, I imagined a pancake motor housed between the turbine and compressor side of the turbocharger. Et voila, electrical assist! But, Garrett has been down this road before with their e-Turbo, and I suspect electrically assisting the turbine was conceived prior to 2005.

But before jumping on the band wagon, there is one major caveat. What it boils down to (all puns intended) is how do you protect the electric assist motor, living on the shaft that joins the turbine and compressor, from the intense heat produced by the turbocharger.

I suspect they have an answer to that, and that’s why they are titled engineers and I’m a scribbler. Regardless, chalk another new thing up as EfficientDynamics.

15 responses to “Editorial: Tri Turbo and Electrical Assist”

  1. Petkunterä says:

    Correct me if I’m wrong but I think BMW advertises the current twin-scroll turbocharged I6 as TwinPower turbo.
    My guess would be that the M3 will have a TriPower turbo and not a tri-turbo engine. The TriPower turbo would combine a twin-scroll turbo with that electrically assisted turbo mentioned in the article. Three separate turbos sounds expensive, large and heavy to me.

    • Hugo Becker says:

      BMW has gone to some great pains in press conferences I’ve attended to explain that ‘TwinPower’ indicates the presence of VALVETRONIC and direct injection in the cylinder head. Theysay it hasn’t any bearing on the number of turbos employed. To prove that point they call the new four cylinder with a single turbo (the ‘N20’) a TwinPower Turbo.

      Yeah it’s a bit of a stretch – but that’s what they’re saying. ;-)

  2. Otto says:

    Used to be a time where BMW increased the number of cylinders.
    My guess is that soon we’ll get engines with more turbos than cylinders.

  3. Jimmy G says:

    Our distinguished author is mistaken. What the e-turbo affords is the ability to install larger, free-breating high boost pressure conventional twin-turbos for mid and high rpm applications, as the e-turbo handles the low rpm, low load applications, TOTALLY eliminating turbo lag (not virtually eliminating as is the talk with BMW’s current generation of turbocharged engines, n20, n54, n55, n63, s63 and s63tu).
    This setup, e-turbo for low-rpm/load, conventional for mid to high rpm will mean potential for high revving massive hp/L engines as each turbo class can be optimized for it’s own setting. Be prepared to be awed. A final application, is rather than venting excess boost pressure, a part of the exhaust gases kinetic energy can be harnessed in reverse mode by the e-turbo to recharge the battery.

    • Nnnn says:

      I would think that the “e-turbo” would be far less responsive than a small turbocharger – for essentially the reasons Hugo stated – it would require a *lot* of current to compete with exhaust gasses.   However, I could see a “sport mode” maintaining a fixed compressor speed for some increased nominal system pressure (+3 psi ?).

  4. Bry says:

    I can’t help but wonder if a tri-turbo setup with an electrical assist turbo will be good or bad for tuners. While tuners will certainly find some way to get more power out of the setup, the amount of R&D required to develop aftermarket parts will make them significantly more expensive.

  5. Nnnn says:

    interesting idea. 

    The picture is baffling – i can’t figure out what any of those ducts are doing.

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