I have been reading this thread with interest, and it seems to me that you are zeroing in on a correct description of what the FEH's transmission does. Perhaps you'll allow me (as a TCH owner) to interject a few comments on recent posts:

stevewa (post #83) — I believe that the original Prius had the traction motor (MG2) directly on the ring-gear shaft, with no intermediate reduction gearing. Hence it was relatively slow-turning, and was designed for low-speed operation. Later Prius's and subsequent Toyota hybrids (such as my TCH) have a reduction gear between MG2 and the ring gear. In the latest designs, a second planetary-gear set, with its planetary-carrier pinned, performs the MG2 reduction function. In the FEH, the traction motor drives the output shaft to the wheels through a reduction gear — this is, of course, equivalent to driving the ring-gear as above.

gpsman1 (post#99) — Perhaps the limiting factor on the allowable speed of the generator (MG1), which restricts the maximum speed allowed in pure-EV mode (ICE not rotating), is the open-circuit voltage (not power) generated by MG1 when spinning really fast. Since it would be open-circuit in this situation, there could be a danger of voltage-breakdown. This is, I believe, also a danger during high-speed towing in 'N'. Just a thought.

GaryG

• (post #104) — The rotational kinetic energy stored in the MGs is very small compared with the translational kinetic energy of the moving vehicle. It plays no significant role in their coasting behavior.
• (post #107) — It's possible that what the Manual means by the ICE being "disengaged" from the wheels in Neutral towing is simply that, since the generator (MG1) spins freely in this situation, there's no torque exerted on the ICE's output shaft during such towing — it is effectively disconnected. That is, I don't read this as implying that there's a physical disconnect between the ICE and the planetary-gear set, and indeed we now know that there isn't.

GaryG (post #107, 109, 116) and gpsman1 (post #108) — The ICE's output shaft is permanently connected to the planetary-gear set. The OWC does not disconnect the output shaft from the planetary-gear under any circumstances. It acts solely between the output shaft and the housing to allow rotation of the ICE in the positive direction only ("one way"), and it automatically and purely mechanically locks the shaft to the housing to prevent the shaft from rotating rotating backwards if it tries to do so. There's never any disconnect. There's no "free-wheeling" either. I therefore don't think that the ratchet analogy is a good one, and I think you've also come to this conclusion.

During engine braking the ICE is being spun in the forwards direction, of course, and the OWC plays absolutely no role. During engine starting, the ICE is spun up in the forwards direction too, of course, and again the OWC plays no role, whether it's the generator or the car's kinetic energy that cranks the ICE. By the way, you don't get "both electromagnetic slowing, and engine compression braking at the same time." The power to spin the ICE during fuel-cut engine braking is sent electrically from MG2 to MG1, and is thus an indirect transfer of the car's retarding torque to the ICE. The "electromagnetic slowing" and the "compression braking" are one and the same thing! The two effects are not cumulative — in this situation you can't have the one without the other.

It is not necessary to have the Parking pawl or the brakes engaged in order to prevent the traction motor (MG2) from rotating, in order to start the engine. Even if the pawl is engaged, there'd still be an undesirable "jolt" felt because of play in the ratchet. And indeed, you'd still feel an undesirable jolt even if the vehicle was moving when the ICE was started. What Toyota do is to apply a torque to MG2 to oppose the jolt caused by MG1 cranking the engine. Even if the car is stationary or barely moving in 'D,' say, with the parking brake "off," there's normally no jolt when MG1 starts the ICE. By driving MG2 appropriately electrically, one can "lock" its rotor or apply a reverse torque to counteract the starting torque transmitted through the planetary-gear set.

Stan

 

Stan, you are always welcome to post outside your "niche" anytime.
I encourage you to do so here. You made a very thorough post as always.
Thanks. I agree with most of your statements, but not all. I will be brief, because I have said a lot already.

When slowing in "L" or "B", then traction motor, acting as a generator, provides resistance to slow the car. YES?

When slowing in "L" or "B" the electrical energy generated by said traction motor can be sent to the battery, or sent into the generator motor, which can speed up the ICE. YES?

When slowing in "L" or "B" and the ICE is sped up to higher RPM, the ICE creates additional friction, which can aid slowing even more. YES?

I think everything I stated was correct. Maybe you didn't like my particular wording the last time I said it.

It is required to have the ParkingPawl when starting in Park.
This particular design does not have the play or "jolt" you may be used to in other cars. I have been told this by someone in very high authority at Ford.

When starting at speed, there is a "jolt" and you can feel it.
Ford spent a lot of time, effort and money to make the jolt as minimal as possible. One reason, a very big reason, and perhaps the only reason why they will not hold EV higher than 40 miles per hour is the jolt, or "harshness" when starting at speeds faster than 40 MPH exceeded industry standards for harshness. I was told this by a designer of the FEH on my visit to Dearborn in 2005.

For some time, myself included, have believed, mostly from relying on Toyota data, that there was a EV speed limit due to RPM speed limits. This is FALSE! Now that I can directly measure generator speeds, they are pretty slow at 40 MPH in EV mode. Only 6000 RPM at 40 MPH EV, and only 9000 RPM at 60 MPH EV. The allowed limit is 12,000 RPM, which would occur at just before 80 MPH EV.

This is probably why the FEH can be towed with 4 wheels down, and other hybrids cannot. Rotation speed is not an issue. Like you said, the motor mass and "inertia" is also relatively small.

 

gpsman1 — I have a problem with your third "YES?" This is the one:
"When slowing in "L" or "B" and the ICE is sped up to higher RPM, the ICE creates additional friction, which can aid slowing even more. YES?"
Assuming that the battery is fully charged, so that all the power generated by the traction motor (MG2) is sent to the generator (MG1), and assuming no losses, there is no ICE "friction" directly felt by MG2 (i.e., the wheels), only the load of MG1. MG1 spins the ICE, thus transferring all the work done by MG2 (i.e., the wheels) to work done turning the ICE over. There's no direct mechanical connection between the wheels and the ICE here. It's all via the MG2-to-MG1 path. So, the ICE doesn't create additional friction (i.e., drag). It creates all the friction (i.e., drag)!

Stan

P.S. This turns out to be incorrect! Please see my post #125 below.

 

I meant that more engine friction was felt by MG1 at high RPM, than low, which put more load on MG1, which means more power would be taken out of MG2 now generating power, which means the wheels would feel more resistance, aiding in slowing the car down.
So I think we are both right, just using different words.
I don't feel we need further discussion, unless it is over a new topic.

 

gpsman1 — Mea culpa! Further discussion isn't really needed, but I do want to correct an error I made in my post #123 in commenting on your post #122. Yes, I was correct in what I said in the sense that all the energy being transferred from the car during fuel-cut engine braking is dissipated only in the ICE. The MGs don't dissipate any power, at least in principle, while shuttling energy around. However, I was not correct when I implied that all the braking power flowed through the MGs, and that none flowed directly from the wheels to the ICE through the planetary-gear set. What you said was indeed closer to the truth. Sorry!

The following is what my formulas say about this (see my posts # 27 and 34 in the thread "Heretical Mode" in the TCH forum).

Assuming, as I did before, that no battery charging is taking place (it's "full" say), and that the MGs are 100% efficient in their energy conversion (this isn't seriously wrong — they are apparently ~95% efficient at each conversion between mechanical and electrical energy, so that their back-to-back conversion efficiency is ~90%), then using the TCH's planetary-gear ratios as an example, I can calculate the energy flow in say the fuel-cut coasting scenario shown in my Figure I (in the post #34 cited above). We have:

Transmission in 'B' (= 'L');
Car travelling at 100 km/h (~62 mph) (this is the Road Speed RS);
ICE spinning at 3000 rpm (this is Ne);
Ring-gear spinning at 2822 rpm (this is Nr);
Sun-gear (i.e., MG1 = generator) spinning at +3463 rpm (this is Ns);

and I compute that, of the total braking power flowing from the wheels to the ICE, fully 67.9% flows mechanically directly through the planetary-gear set from the ring-gear to the planetary-carrier (i.e., the ICE), while only 32.1% flows electrically from the ring-gear through MG2 (= the traction motor) to the sun-gear (i.e., MG1). [I won't bore you with the calculations!] So, I was certainly wrong when I said that all the engine-braking power flowed to the ICE "via the MG2-to-MG1 path." The ICE creates all the drag, but its effect is felt by the wheels partially directly through the planetary-gear set and partially indirectly through the electrical path of the MGs.

Stan