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      05-21-2012, 08:21 PM   #52
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Drives: A6 turbo, TR-8, 740il,
Join Date: Jan 2011
Location: Sacramento

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This idea goes back at least several decades.

The idea of an electric turbocharger goes back at least several decades. The Russians used an electric motor/alternator coupled to a standard turbocharger on an aircraft engine (diesel) back in the 80s. I don't believe that BMW has the patent on the idea of en electric turbo, just the specific setup using the various clutches. It may even be that the only reason for the clutches was to get around the Russian invention, or to allow BMW to give the impression that they had some important IP for electric turbos.

Ultimately the idea goes all the way back to the turbo compound aircraft engines used on post WW2 piston engine airliners. In these engines the turbo is actually used to convert some of the waste energy in the exhaust power back to the engine/propellor (and of course also to power the turbosupercharger). In the turbo compound engines they used gears to feed the power back to the engine rather than the motor generator used on the Russian and BMW systems. These gears were the Achilles heal of the turbo compound engine because it was very difficult to build gearing systems that could match the very high RPM of the turbo to the very low RPM of the big radial engines of the day. A single backfire could tear up the gears, but even barring such a failure the gears were constantly getting beaten by the huge power pulses of the slow turning engine. The Russian application was the first I have seen that used a motor generator to harness some of the waste energy (energy not used by the turbo itself). I am not sure why BMW needs all the clutches and other stuff but perhaps they found that they got somewhat better efficiency under the varying loads of a car vs. the much more constant load in an airplane that the Russian system was meant for.