OK that makes more sense now...
The Generator/Starter (smaller) electric motor is attached to the Sun gear, while the engine is attached to the Planet Carrier yoke. So when the Traction (larger) motor is spinning in EV-only mode, the Generator/Starter is spinning the sun gear backwards to force the planet gears to spin synchronous with the outer ring gear (which is linked to the traction & final drive) so the planet carrier yoke does not spin, thereby keeping the engine still.
Likewise when the engine is spinning, the rotational speed of the sun gear (Generator/Starter motor) determines whether the planet gears are locked so the engine synchronously transfers torque to the ring gear (to transfer gear & final drive, traction motor) or not... and if I'm understanding this correctly, the Generator/Starter motor might even spin its sun gear at a variable speed to modify the "gear ratio" between the engine & planet ring (final drive)? That's a crazy thought but it makes perfect sense now why it's called a "CVT" with that kind of computer-driven control, literally the phase & frequency of the 3-phase inverter signal going into/out of the generator/starter motor determines the effective gearing behavior dynamically (as opposed to static, which you see in a traditional automatic or manual, and to some extent even belt-driven CVTs maintain gear ratios "statically"). This requires a lot of accurate signalling and coordination which is probably where the "clutch damper" comes into play, it's the "mechanical fuse" to blow if somehow the engine's crank angle sensor or Generator/Starter motor's 3-phase wiring were damaged or just got out of alignment somehow (or heaven forbid, a firmware bug in the real-time control computer skipped a beat and its perception of the current motor location was out of whack).
Edited by spirilis, 21 February 2018 - 10:36 AM.