View Single Post
      11-16-2014, 06:32 AM   #64
Brigadier General
Boss330's Avatar

Drives: BMW
Join Date: Mar 2012
Location: Norway, Scandinavia

iTrader: (0)

Originally Posted by Torgus View Post
You Don't need a 90kw engine to spool a turbo up or a crank shaft.
You don't need a 90kW motor to spool up a turbo, that's correct.

However if you want to add the complexity and weight of a hybrid drivetrain to the engine (crank) you need sufficient battery capacity to make it work for more than a few seconds a time. The weight of the electric motor, and the necessary coupling/transmission to connect the electric motor to the crank, isn't that different if you have a 30kW or 90kW motor added.

And, if you choose to add a hybrid drivetrain then you want to make the most out of the weight penalty that follows from this.

For instance the McLaren P1 has a 130kW/177hp e-motor, the Porsche 918 a 94kW/128hp and the LaFerrari a 118kW/161hp e-motor. And even a Prius has a 49kW/67hp e-motor. Look at a Prius and you see that the hybrid drivetrain adds weight and complexity, even at that low power output... And with very little gain in performance...

Picture illustrating what's involved in the hybrid drivetrain, in addition to the combustion engine and transmission, on a Prius:

If you really want to add the weight and complexity of a hybrid drivetrain, you also want to add enough kW/hp from the e-motor to the drivetrain to make a noticeable difference in performance.

And, even a e-motor to spool up the turbo needs a separate high voltage battery system. For instance a modest 2kW output at 12V would need 167Amps... Studies from 2006 by Garret on the viability of a "e-turbo" showed that a single turbo was preferrable since that required a 2,1kW motor, while a twin turbo set up required two 1,4kW motors. The study also showed that under normal driving conditions there wasn't enough exhaust gas flow to sufficiently take advantage of the e-motor attached to the turbo as a generator. Implying that the batteries would need charging in addition to the charge available from the e-motor.

I personally find the e-turbo tech very fascinationg and hope to see that employed in road cars soon.

But, this is getting seriously off topic now. I suggest that the hybrid/turbo material/tech discussion is either closed now, or continues in a dedicated thread (like in one of the old threads that discussed hybrid turbo tech in depth).