Quote:
Originally Posted by freebeard
The BMW patent shows something that should work, but it is intended as a [third?] turbo to supplement others. So it isn't a total solution.
The problem comes in when you are essentially driving the turbo with the alternator. Losses accumulate. What might be feasible would be to use a conventional turbo to drive a generator/alternator to recharge the battery.
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That's why you have the turbine and compressor and motor all on the same shaft. The motor accelerates the turbo so there's no lag, and when the turbine is spinning at high speed it is more efficient and can be entirely exhaust powered.
Instead of using a wastegate on a smaller turbine to build boost at low rpm, you use a big turbine and slow it down to optimal speed using the motor as a generator. At very low speed, the turbine might need help from the electric motor, but that's not a big deal as the compressor power requirements are also lower. At high speed is when the power requirement is high and you want to tap into the exhaust to avoid the need for massive electrical power draw.
It's simple and seemingly compromised but actually works pretty well.