Wouldn't it be nice to have a couple hundred pounds of flywheel in your vehicle for regenerative braking and the occasional bit of acceleration, *without* actually having to have an extra couple hundred pounds of flywheel in the vehicle ? Well now you can:
Pop the hood and take a look; there's a
metre-wide, soundproofed, round aluminum shell underneath; take the top of that off and inside is a freewheeling(ish) air-cooled radial engine.
HOW IT WORKS! :
At the front of the downwards-facing engine the crankshaft enters the transmission assembly. But we want to take power from the actual engine spinning 'round like a (Gnome) rotary as well, so we have a second shaft also entering the transmission. This is the "flywheel" PTO which is connected to a toothed wheel fixed to the engine, encircling (but not connected to) the crankshaft. The transmission contains a not too complicated set of 3 CVT's, planetary gear and brakes. The driveshaft emerges and connects to the rest of the drivetrain (differentials, wheels).
Inside the transmission, the planetary gear, and a CVT(/brake) on each of the shafts (crank, fly, drive) allow any source(s) of power to be routed to any destination(s) in any ratio. No clutching is necessary since a CVT can gear down to almost a standstill (at which point the brake engages).
So all 3 sources of energy: engine proper, engine flywheel motion, and driveshaft (kinetic energy of the vehicle) can be routed to any of the others.
Engine power and/or flywheel power can be routed to the wheels, flywheel-braking and acceleration can be applied, you can bump-start the stopped engine from the flywheel-motion or driveshaft ("bump-starting"), or any reasonable combination of the above.
ETC. :
Starter Motor / Electrics - A motor/generator is mounted clutched onto the driveshaft. This is used to start the car, run electrics and power Reverse (all at the same time if necessary).
Airflow - a crankshaft mounted fan on top draws air into the aluminium shell to provide cooling and intake air. Exhaust entering the shell from the cylinders is pushed out the bottom into a tailpipe and a small muffler. The aluminum shell is soundproofed which takes care of some of the noise.
Exhaust Fanjet :) - The exhaust port of each cylinder has its own little fanjet/turbine, which as well as pulling air over the cylinder head for cooling purposes, pushes the cylinder to increase flywheel RPM.
Air, Fuel and Exhaust flow are further managed depending on the specific requirements of the engine (2 or 4 stroke, carbureted/injection, DI, turbocharged, etc.)
Precession - the engine/gearbox assembly should have a few degrees of movement in most directions to allow for hill climbing/descending etc... and/or counter-rotating cylinder banks.
ETC. ETC.:
It's not in a vacuum but we're talking a few hundred pounds of flywheel here and anyways air needs to stream over the engine for cooling.
For clarity's sake I'll mention that only the engine spins around: the gearbox is fixed (possibly excepting any arrangements to mitigate precession).
Oddly enough I have no clue if the engine and crankshaft should be rotating (relative to each other) in the same or opposite direction. If they go in the same direction power from the crankshaft has to be returned through the flyshaft; if they counter-rotate then power has to be drawn from the flyshaft as well to compensate (no biggie, but it limits the flywheel to whatever RPM is being used or something like that).
[I stuffed this into engines:rotary because of a not entirely superficial similarity to rotary engines from a century or so ago]