A specific eCVT transaxle question

[clavicus]

I'm trying to wrap my head around how the Hybrid ICE engine connects to the final drive gear in the CVT housing. Note I am a mechanical newby, I don't know how any of this stuff works, but I'm trying to learn some stuff.

From John Kelly's video about Ford's hybrid transaxle is awesome, but also difficult for me to digest.

Here's where I'm stuck: There's a planetary carrier that connects to the ICE engine directly, housed within the generator motor group. It goes ICE engine > crankshaft > flywheel > clutch dampener > planetary carrier in the generator motor group.

But how does the planetary carrier (A) allow the ICE engine power to engage/disengage with whatever connects to the the final input gear (B), such that it could allow the option to charge the generator motor without turning (B) and hence the transfer gear (C) and final drive gear (not shown) [D]?

Here's the video I'm referencing, showing Ford's 3rd generation of their parallel hybrid transaxle. I probably have all the direction arrows wrong for drive direction but hopefully you get my point.

https://youtu.be/hHU5xFOBcsU?t=974

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[clavicus]

Darnon gave an answer here:

It's like an open differential. Power will flow to whichever path has the least resistance. Say you're stationary and the ICE engine is running. If there's more holding force from the traction motor/brakes/inertia than the resistance of the starter/generator field then that is the only part that will be rotating.

 

[Rivers90]

Here is a video for the toyota ecvt

at the 9:30 time mark it shows the engine turning just the smaller motor generator and the vehicle not moving.
I think the ford one is kinda like this and would work the same way.

 

[clavicus]

I still don't inherently understand how the planetary gears work, but at least Darnon's other linked video gives me a better concept of the idea of how varying the generator motor resistance will change how the ICE engine power is applied as driving force.

 

[Rivers90]

For having so few moving parts it really is hard to understand. But I think i am getting it.

 

[The Speaker Guy]

I think of it this way: the Starter Charger (SC)motor can run forward or reverse, it don't care. The ICE has a sweet spot, let's say 3kRPM. When not moving, engine running, you hit the "gas" the engine jumps to a sweet spot in RPM, and the SC motor runs at -3kRPM, and the wheels are not moving yet. As the wheels start to turn forward, the SC motor reduces its negative RPM towards zero as the planetary output moves from 0 to 3kRPM (ignoring any gear gain or reduction)

 

[Rivers90]

It looks like there are not a lot of parts to wear out or break, so that is good.

 

[clavicus]

Ok going one further tumble down the rabbit hole... how is resistance applied to the starter generator motor, to enable the ICE engine to apply its force, through it's planetary gears, through the ring gear around those planetary gears, to the final drive input? Does it take power to make power, so to speak (relative to the ICE engine driving the wheels forward)?

 

[Darnon]

More John Kelly videos for that. Generating power creates an induction field which applies a resistive load to the spinning permanent magnet rotor. Rotational kinetic energy is thus turned into electricity. Same principal as the automotive alternator we're familiar with except because the motors in a hybrid are more powerful they're able to generate enough load to brake the vehicle.

 

[fbov]

Ok going one further tumble down the rabbit hole... how is resistance applied to the starter generator motor, ...? Does it take power to make power,

Yes

More John Kelly videos for that.

Indeed there are! But here's a subtle point that might be lost on the non-EE's in the group.

These are AC Synchronous motors. Their speed is governed by the AC frequency. The inverter turns DC from the HVB into AC for the motor(s), but it can do so at any frequency desired to achieve a target MG speed. And it can vary that speed without creating torque or charge, beyond the force required to change rotor RPM, in either clockwise or counterclockwise directions.

That's how "resistance" is applied at arbitrary RPM. It takes power, but very little compared with moving the vehicle.

 

[clavicus]

Another video from a Toyota hybrid transaxle that is similar to Ford's, but more discussion of the power split:

This is the video I needed

 

[FirstFord]

And where's the CVT in all this? It's gotta be on the ICE side, right? The Traction Motor output doesn't pass through the transmission.

 

[clavicus]

And where's the CVT in all this? It's gotta be on the ICE side, right? The Traction Motor output doesn't pass through the transmission.

I'm questioning everything I wrote lol, just watch this.

EDIT: I've edited this a thousand times now. It reflects my current understanding now...

Hm I wonder if you may need to re-map your image of the whole model the engine and transaxle (eCVT). The following will be an over-simplification, but you can watch the linked videos above to get the full range of information about what is happening. I was also confused about how the ICE connects to the transaxle. It goes [ICE > crankshaft > flywheel > safety clutch torque dampener] outside the transaxle to > [ planetary carrier spindle doohickey > planetary gearset (power split)] inside the transaxle. There's no good graphic illustrating all of these together that I've found so far. Forgive me if I'm wrong in anything because I'm a total newb to this but I've been trying to learn.

The ICE engine block is slightly centered toward the passenger side under the hood, and the transaxle 'bell housing' is attached to the driver side of the ICE block. The ICE is not connected to the wheels in any way except through the transaxle, there is no path for the ICE to do anything in terms of moving the car or charging the battery except through the transaxle.

Think of the transaxle (eCVT) itself as the place where the "final drive gear" is. This is gear is always tied to the wheels, whether forward or backward, it's a direct connection. All power to turn the wheels comes from the final drive gear, inside the transaxle housing. There is no 'changing of gears' inside the transaxle, everything is fixed, but there is some magic happening where the ICE comes into the transaxle (through the planetary carrier spindle boi) with the planetary gears (aka power split device), but I'm getting ahead of myself.

The transaxle has two electric motors. One is the larger traction/generator motor (MG2 in Toyota's terminology), which can provide driving force (or be a generator for the battery when regenerative braking); MG2 is always turning when the wheels are turning, they are physically connected. MG2 provides continuously variable power since it's electric, that's how it be. MG2 is also the only thing that can provide reverse driving power, by the way; it just spins in the opposite direction.

The other is a smaller starter/generator motor (MG1), which can freely spin when final drive gear is turning, but it can be easily stopped or even reversed independent of MG2/final drive gear/wheels. MG1 is part of the power split system in the transaxle. The power split is a planetary gearset made of 3 gear components, each of which is physically tied to a different component. MG1 is tied to the sun gear, which is the center of the planetary gearset; it's surrounded by the planetary gears which are physically connected to the ICE crankshaft, essentially. And those planetary gears are surrounded by the ring gear. The ring gear is physically connected to the final drive gear. Confusion?

So how can the sun gear and ring gear turn without spinning up the ICE crankshaft? That's the magic of this engineering marvel, which I can't actually comprehend myself. But that's how it works.

Q: So when DOES the planetary gear turn, and hence turn the crankshaft and 'turn over' the ICE?
A: When the sun gear (MG1) spins faster than the ring gear, the sun gear forces the planetary gears to turn, starting the ICE. When you're driving on MG2 (battery power only), this can be done if battery power is used to spin MG1 faster. When you're parked on a full battery, nothing at all is spinning, but if you have low battery you can provide power to MG1 to spin it (faster than the ring gear, which isn't moving at all in this case) to start the ICE.

Once the ICE crankshaft (planetary gears) are spinning, this is where my ability to explain breaks down... the ICE (planetary gears) are now turning MG1 (sun gear), independent of what's happening with the ring gear/wheels turning, but if MG1's rotational speed is forced to slow down relative to the planetary gears via electromagnetic magical resistance, the planetary gears now begin to apply force to the ring gear. Depending on how much MG1 relative rotation opposes the ICE, that's the continuously variable power provided to drive power (planetary gear > ring gear > transfer gears > final drive gear > differential > wheels > pothole oh sh**). Not only can the MG1 rotation be varied, but also the engine RPM can be varied, in order to stay in the most appropriate fuel-efficient or performance RPM for the given situation.

So, to reiterate, all these gears in the transaxle are fixed, there are no clutches or 'shifting'. There are no belts or chains like on the Nissan/Subaru CVT. But it is a continuously variable transmission of power I guess, so it's a CVT, eh?

Anybody correct me where I'm wrong I'm sure I forked something up. But hopefully you get the gist and I didn't totally misinterpret your question.

 

[FirstFord]

So where's the lightbulb emoji?

I didn't appreciate how fundamentally different an eCVT is from a CVT. While, like you, I still don't get it all, at least I know where to look now.

I'm an EE, so I get all the magnetic and PWM magic. I've disassembled heads and carburetors, but transmissions are still Pandora's Box to me. i think I have to get my hands on one of these and turn the shafts myself before I can really get it!

thanks for the effort you put into the explanation.

 

[clavicus]

So where's the lightbulb emoji?

I didn't appreciate how fundamentally different an eCVT is from a CVT. While, like you, I still don't get it all, at least I know where to look now.

I'm an EE, so I get all the magnetic and PWM magic. I've disassembled heads and carburetors, but transmissions are still Pandora's Box to me. i think I have to get my hands on one of these and turn the shafts myself before I can really get it!

thanks for the effort you put into the explanation.

Well after a couple hours it benefitted me also. I kept writing more and more because I realized I had to write it out to see that I didn't really understand some things. I finally understand now that there is not a clutch that engages the ICE with the power split, it's always connected. I'm still sitting here flailing around in the dark, both metaphorically and literally in this chair, trying to see in my minds eye how the sun gear, planetary gears, and ring gear can all be rotating at different (or the same!) speed, and somehow these three rotation speeds make so many different things happen. I just can't visualize it!

Off, underdrive, constant drive, overdrive... rotation... rotation... rota... eh, one day it'll make sense.

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