I see the flywheel has a clutch disk on it. Why??? From my understanding of how you are using the planetary gear setup I see no real need to ever disengage the engine
It seem to slip if the engine vibrations would be an out of round stress on the HSD. (It is not a clutch, as there is no throwout bearing to ever make it slip intentionally, it is the transaxle damper) http://www.autoshop101.com/forms/Hybrid02.pdf Page 6
Think of it less as a clutch and more of a torque limiter. If the torque going into or out of the engine is higher than "yea", then the clutch disk slips. That's it. It makes the starting and stopping of the ICE less jerky to the rest of the car and the drivetrain. As the other poster mentioned, there's no clutch release bearing or similar mechanism of any kind, so even though it kinda looks like a clutch, it's not one. KBeck.
I've never heard of it failing. I suspect is doesn't slip in normal operation. It's there to absorb the damaging shocks to the drivetrain. Such as a transition from ice to pavement.
From the look of it, short (pun intended) of motor failures, the trasaxle should be more durable than traditional auto, belt CVT, or even manual transmissions.
Here is my untintellegent question. Why does a HSD need a flywheel? Isn't MG1 acting like a flywheel? Definitely as others have said, the flywheel should be able to slip if there is one, and that's what you are seeing.
MG1 is on a different shaft. Over various operating conditions, it can be spinning fast, or slow, or even be stalled, so it doesn't make a good flywheel for the ICE.
The ICE needs a flywheel -and- a "damper" on the crankshaft. One on each end. These help absorb the oscillations induced by each cylinder firing and driving the crankshaft vigorously. They need to be physically connected as close as possible to the bearings on each end of the crankshaft. Curiously, the MG's are the reason the "plate dampener" (that looks like a clutch) is needed. The MG's are large inertial loads and the shafts and gears connecting them to the ICE would be in danger if the plate dampener weren't there.
