Wondering about the feasability of engineering this device:
Take a turbocharger and add a high speed motor/alternator with
a high speed reduction gear directly to the turboshaft.
At wide open throttle, electricity is sent to the unit instantly speeding it up to produce INSTANT boost, and at part throttle the unit would draw off excess kinetic energy converting it back into electricity, reducing the load on the belt driven alternator.
Doesn’t sound like it would be impossible or even very hard to do. There are quite a few motor/generator combos out there.
Now, if you had asked if it would be WORTH it…
What advantage would this have over a mechanically driven supercharger? You mention using it to reduce load on the alternator (I assume as a move to save fuel). I think there would probably be enough loss in your system to make it not worthwhile. Not to mention the weight and complexity gain.
Unless you had other motives, in which case I will shut up. 
A gear driven supercharger has a fixed boost level determined by the drive ratio of the gears/pulleys.
A turbo can be dialed into any desired boost level.
Electrically accelerating the compressor eliminates lag.
Recovering electricity at part throttle is a side benefit.
While I have no specific knowledge of turbos, I believe that it actually takes quite a lot of energy to compress the air. I think I’ve seen figures stating that the added resistance in the exhaust system corresponds to several percent of the engine output. You would need a pretty heavy duty electric motor to generate that kind of power. I don’t know what power a normal starter is, but I would guess around 1kW. What you need here would be several times that.
I believe that the end result would be far too heavy to be usefull. (But it would indeed be cool!)
(If I’m talking out of my hat here, please correct me.)
I do know for a fact that these have been tried on some cars as early as the 1950’s, and that for some reason they just do not work very well. It seems to me, from a seat-of-the-pants estimate, that it should work. However, my friend from Chrysler who I asked yesterday was too pressed to give me a cite as to why it didn’t work.
Ah. I didn’t know what you were trying to do with this.
How about a supercharger with a continuously variable transmission?
Although a blower with CVT will produce instant boost without lag at a boost level you choose, it does not utilize and/or recover the useful pressure energy free for the taking in the exhaust manifold.
That thing is going to take a BUNCH of current. I see some drawings, have they even built one yet?
IIRC, turbochargers spin at roughly 20,000 RPM. Centrepital force at this speed would likely throw armature windings; gear reduction to slow the motor would probably quickly wear out.
The only reason you can dial up the boost you want with a turbo is the use of a waste gate which can be controllable. You can do the same thing with a supercharger if you want to, it just gets a little more complex in the plumbing since superchargers can be compactly mounted right on the intake itself. I haven’t really looked at the superchargers used on production cars but it’s likely they have some sort of pressure limitation circuitry.
It looks a lot of complexity with losses in both the alternator and motor, as well as the gearing required.
I would think that, on a diesel application, this would be the ideal power enhancement device. From what I’ve seen on the web, turbocompounding can recover horsepower from the pressure in the exhaust manifold…about 30% extra power.
I would assume that the device is engineered so that the armature windings favor alternator mode…I doubt that it would take massive amouts of current toassist the compressor to spool up, since the exhaust pressure is already acting on the turbine.
Ceramic turbines and composite compressors can drastically reduce the inertia, and variable geometry vanes can also spool up the turbo.
Furthermore, a multistage axial turbine bolted to and co-axial with the radial turbine would extract even more exhaust energy…however there is diminishing returns with this idea: more inertial mass and complexity extracting less and less energy.
Nevertheless, I am pleased that someone has actually created a working example of technology.
How could you do the same thing with a supercharger? The wastegate dumps exhaust gas before it even reaches the turbine. Where would it come into play on a mechanical supercharger that isn’t even driven by exhaust gas?
I suppose he means some sort of pop-off valve to bleed off evcess boost from the intake manifold, like what’s mandatory on CART engines…though they are turbo motors, the same logic applys.
Hmmm. So instead of using a wastegate to prevent the boost from being made in the first place, you just bleed off your excess from the upper deck. That just makes a supercharger even more inefficient than it already is. Lots of turbo engines can bleed off upper deck pressure also, but only as a last resort to prevent overboosting rather than the primary means of regulating boost pressure.
Yucky.
NASA has developed a “toothless” gear system that could be used to help eliminate this problem. No idea if it’s made it into widespread use as of yet. (It was intended for helicopters.)
Say, Una, you don’t suppose your friend would be kind enough to get me a ride in the Chrysler turbine car that they built in the 1960s, do you?