A specific eCVT transaxle question

[mamboman777]

Yeah....I watched this again. I think I am wrong. It looks like it's possible to get power to the wheels from all motors.

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[FriscoTXJoe]

THANK YOU! I have a better handle but will leave it to you all inclined to understand it better than I.

 

[mamboman777]

THANK YOU! I have a better handle but will leave it to you all inclined to understand it better than I.

I have as much handle on this as I do a greased pig.

That being said...I have, since first learning the difference between CVT and eCVT, learned that it appears to be a beautifully simple system. No shifting, no clutches. Less moving parts. I've also learned that when though the Mavs transmission is "new" it's really an evolution of something that has been around for over a decade and has been in cars that have seen 200,000+

I hope it can prove just as reliable in the Mav.

 

[DryHeat]

We know the ICE turns the planet carrier, and we know MG1 applies torque to the planet carrier to start the ICE. I see no reason MG1 can't use the same torque path as the ICE, looking like a boost in ICE power through the ring gear to the road.

I think you are right about that. MG1 is a "motor-generator" and can run in either mode. As I understand it (and my understanding is limited), it's roughly like this:

• MG1 runs as a motor, drawing power from the battery, when it is starting the ICE.
• MG1 typically runs as a generator. So it is drawing power off the ICE, not adding power.
• MG1 could run as a motor when ICE is running, adding power to the ICE.

The question for me is, "When could the "additive motor" condition exist? And does it?"

I've found one source that implies that it happens in overdrive conditions when power is applied to MG1 to slow its rotational speed relative to ICE. It seems logical that MG1's power could translate to the wheels, but it's primarily designed to change the ICE gear ratio. FWIW, I've heard that it doesn't take that much power to change the ratios. Figuring out how much power goes where is beyond me.

See: Hybrid Synergy Drive - Wikipedia

On the other hand, this article doesn't describe any driving function to MG1.

See: http://www.ae.pwr.wroc.pl/filez/20110606092430_HEV_Toyota.pdf

My guess is that it could be programmed to perform a significant additive function, or not, depending on what the engineers think is best.

 

[clavicus]

I think you are right about that. MG1 is a "motor-generator" and can run in either mode. As I understand it (and my understanding is limited), it's roughly like this:

• MG1 runs as a motor, drawing power from the battery, when it is starting the ICE.
• MG1 typically runs as a generator. So it is drawing power off the ICE, not adding power.
• MG1 could run as a motor when ICE is running, adding power to the ICE.

The question for me is, "When could the "additive motor" condition exist? And does it?"

I've found one source that implies that it happens in overdrive conditions when power is applied to MG1 to slow its rotational speed relative to ICE. It seems logical that MG1's power could translate to the wheels, but it's primarily designed to change the ICE gear ratio. FWIW, I've heard that it doesn't take that much power to change the ratios. Figuring out how much power goes where is beyond me.

See: Hybrid Synergy Drive - Wikipedia

On the other hand, this article doesn't describe any driving function to MG1.

See: http://www.ae.pwr.wroc.pl/filez/20110606092430_HEV_Toyota.pdf

My guess is that it could be programmed to perform a significant additive function, or not, depending on what the engineers think is best.

If my (lack of) understand holds, adding more speed for MG1 in the same direction the ICE is spinning will force the ICE crankshaft to turn (if the sungear is spinning faster than the ring gear at the time I guess also?), but wouldn't that be bad or less than worthless, since the crankshaft relies on accurately timed combustion to turn itself once it's started? Hmm well I guess it has to coordinate with MG1 to start its combustion anyway. But basically, isn't it wasted effort since MG2 should be the only additive electric drive power? Why use battery power to use MG1 to turn the crankshaft more when you can just apply that power directly to the wheels with MG2. And also if MG1 (sun gear) isn't slowed down, the planetary gears won't be pushing on the ring gear?

The more I ask these questions the less I feel like I understand it lol

 

[DryHeat]

Take all this with a grain of salt. It’s my best current understanding.

adding more speed for MG1 in the same direction the ICE is spinning will force the ICE crankshaft to turn (if the sungear is spinning faster than the ring gear at the time I guess also?)

Increasing MG1 speed in the same rotational direction as ICE alters the gear ratio toward “underdrive,” allowing the ICE to turn faster relative to a given final drive speed. Essentially a “lower gear.”

but wouldn't that be bad or less than worthless, since the crankshaft relies on accurately timed combustion to turn itself once it's started?

No, it’s just a lower gear. It doesn’t directly affect combustion timing, which is controlled by the computer.

But basically, isn't it wasted effort since MG2 should be the only additive electric drive power? Why use battery power to use MG1 to turn the crankshaft more when you can just apply that power directly to the wheels with MG2.

If you decide ahead of time that “MG2 should be the only additive electric drive power” then, sure, using MG1 to add power is wrong. Kind of like “Since it’s wrong to eat snails, isn’t it bad to eat snails?”

But... MG2 has a certain maximum amount of power it can apply. So does MG1. The question was whether MG1 can (or ever does) add its power to that of MG2.

And also if MG1 (sun gear) isn't slowed down, the planetary gears won't be pushing on the ring gear?

Right. If MG1 spins freely without any resistance up to any RPM, then no force would be exerted on the ring gear. There has to be resistance on the sun gear for the planetary gears to exert force on the ring gear. Resistance can be provided, for example, by using MG1 as a generator.

In the end, it’s a matter of relative component speed and gear ratios.

• If MG1 (sun gear) spins faster than the ring gear, ICE (planet carrier) spins faster than the ring gear (thus underdrive).
• If MG1 (sun gear) spins slower than the ring gear, stops, or spins backwards, then ICE (planet carrier) spins slower than the ring gear (thus overdrive).

 

[clavicus]

Take all this with a grain of salt. It’s my best current understanding.


Increasing MG1 speed in the same rotational direction as ICE alters the gear ratio toward “underdrive,” allowing the ICE to turn faster relative to a given final drive speed. Essentially a “lower gear.”


No, it’s just a lower gear. It doesn’t directly affect combustion timing, which is controlled by the computer.


If you decide ahead of time that “MG2 should be the only additive electric drive power” then, sure, using MG1 to add power is wrong. Kind of like “Since it’s wrong to eat snails, isn’t it bad to eat snails?”

But... MG2 has a certain maximum amount of power it can apply. So does MG1. The question was whether MG1 can (or ever does) add its power to that of MG2.


Right. If MG1 spins freely without any resistance up to any RPM, then no force would be exerted on the ring gear. There has to be resistance on the sun gear for the planetary gears to exert force on the ring gear. Resistance can be provided, for example, by using MG1 as a generator.

In the end, it’s a matter of relative component speed and gear ratios.

• If MG1 (sun gear) spins faster than the ring gear, ICE (planet carrier) spins faster than the ring gear (thus underdrive).
• If MG1 (sun gear) spins slower than the ring gear, stops, or spins backwards, then ICE (planet carrier) spins slower than the ring gear (thus overdrive).

I feel there's some hole in my mental model that I'm still trying to fill.

Alright here's where I'm hung up. Say we're stopped, MG1 cranks up the ICE, the ICE starts running, and if MG1 provides no resistance for electricity generation, is the sun gear / MG1 is freely spinning at the same rotational speed (or whatever their natural gear ratio is) as the planet carrier? The ICE is just spinnin' that baby and no 'work' is being done aside from negligible friction?

Then the computer sets up MG1 stator to induce current, which creates physical resistance, but we're parked so we're not moving and the ring gear is stationary. But since it requires resistance to charge the battery, is that causing the planets to apply some amount of force to the ring gear and, would the car theoretically try to move forward if we were on flat ground in neutral gear? I.e. is that technically underdrive?

 

[DryHeat]

Again, take my answers with a grain of salt.

Alright here's where I'm hung up. Say we're stopped, MG1 cranks up the ICE, the ICE starts running, and if MG1 provides no resistance for electricity generation, is the sun gear / MG1 is freely spinning at the same rotational speed (or whatever their natural gear ratio is) as the planet carrier? The ICE is just spinnin' that baby and no 'work' is being done aside from negligible friction?

That's pretty much right. With the ring gear held stationary, the running ICE transfers its force to MG1. I guess the MG1 could "freely spin" at that time, but it seems more likely that it would generate at least some power to top up the high voltage battery (HVB) so it can top up the 12V battery as the rest of the car's systems draw it down. Pretty much like an ICE car idling and spinning the alternator.

Then the computer sets up MG1 stator to induce current, which creates physical resistance, but we're parked so we're not moving and the ring gear is stationary. But since it requires resistance to charge the battery, is that causing the planets to apply some amount of force to the ring gear and, would the car theoretically try to move forward if we were on flat ground in neutral gear? I.e. is that technically underdrive?

If you're holding the ring gear stationary the planets would apply force to it but would not move it. That would provide ring gear resistance, so the planet gears would move MG1 instead -- generating electricity.

Is that technically underdrive? Given that the final drive isn't turning, the gear ratio is ICE-RPM:0, which is meaningless (i.e., not a number). So I wouldn't know what to call it.

(BTW, I'm not sure how neutral works in these cars. I read something about it a while ago but it didn't stick with me. I think it said something about it turning off (1) regenerative braking and (2) charging below a certain speed.)

 

[fbov]

And this part of a simplified hybrid model video here.

Very good video. Listen to the narrator at 4:20: "Each one of these three components can be an input, a reactionary member, or an output, depending on the drive mode that we are using."

I'm saying exactly the same thing. The PSD allows all components to push, spin or pull. They can drive, freewheel or generate. It's up to the control system engineers to figure out which ones to use when.

Think of it this way. MG1 can spin up the ICE to start it. With the ICE running, what happens if MG1 tries to increase speed - provide drive torque - as if it were starting the ICE. That's the path for MG1 to provide drive torque.

 

[clavicus]

Ok this is helping me again thanks guys. I think I wasn't considering that the ring gear is the other side of the resistance that causes/allows the planets to spin the sun gear and vice versa. I can't say I totally get it but I can at least throw out some magical theories that were incorrect in my mind.

Can you throw me another bone -- at a low speed in essentially electric MG2 drive mode, let's say we're going 15 mph on flat ground with a low HV battery state of charge -- can the battery can be charging through MG1 resistance (or power being directed back to MG2 through MG1) but ICE is not applying drive force? Or is it going to be applying a little bit of drive force theoretically but the inertia of the heavy vehicle is so relatively large (ring gear is hard to push) that it essentially isn't moving it much -- and the force flows to the path of least resistance (sun gear/MG1)?

 

[Darnon]

Can you throw me another bone -- at a low speed in essentially electric MG2 drive mode, let's say we're going 15 mph on flat ground with a low HV battery state of charge -- can the battery can be charging through MG1 resistance (or power being directed back to MG2 through MG1) but ICE is not applying drive force? Or is it going to be applying a little bit of drive force theoretically but the inertia of the heavy vehicle is so relatively large (ring gear is hard to push) that it essentially isn't moving it much -- and the force flows to the path of least resistance (sun gear/MG1)?

You're overcomplicating it a bit. If the ICE is running it's what's providing driving power with the electric drive motor pitching in under higher load circumstances. Otherwise if it's driving in EV mode the only charging is regen when braking or no-throttle coasting.

 

[clavicus]

You're overcomplicating it a bit. If the ICE is running it's what's providing driving power with the electric drive motor pitching in under higher load circumstances. Otherwise if it's driving in EV mode the only charging is regen when braking or no-throttle coasting.

I thought electricity is capable of being generated at any time through ICE and MG1, not just when in park? Aka "Series Hybrid operation".

Mode 4: Low load cruising with low HV battery state of charge.

Mode 6: Steady state cruising with low HV battery state of charge

 

[Darnon]

I thought electricity is capable of being generated at any time through ICE and MG1, not just when in park? Aka "Series Hybrid operation".

I didn't say it doesn't generate when driving with the ICE. Maybe it's just the way the instrument cluster displays it but I've never seen low ICE power and EV motor power indicating that the ICE is generating but the traction motor is doing the driving. Usually only a mix when going up hills.

 

[fbov]

The question for me is, "When could the "additive motor" condition exist? And does it?"
... Figuring out how much power goes where is beyond me.

This is a job for Control System Engineers. Yes, what they do is beyond most mortals.

... can the battery can be charging through MG1 resistance (or power being directed back to MG2 through MG1) but ICE is not applying drive force?

MG1 regen braking? I can't see why. The system is limited to 35kW regen braking. MG2 is rated for far more power, so there's no need for that kind of complexity, even if there is a combination that would do it.

Maybe it's just the way the instrument cluster displays it

I also see no information displayed in my Escape on what MG1 is doing, only MG2.

Food for Thought - where does the current come from?

The traction motor, MG2, will be rated for 94kW in Maverick. With a 211V HVB, that's 94/0.211 = 445A current draw at rated output. If Maverick is true to form, you'll get 35kW regen braking (166A)and 20kW EV (95A) before ICE comes on. Presumably, the higher power levels are available in hybrid mode, when ICE is generating AC power directly, bypassing the AC-DC converter in the HVB power path.

Using ICE to solely to generate electricity from MG1 to run the traction motor MG2 is "series hybrid mode." MG1 output isn't shown on the dash display. I am starting to wonder if the dash display is driven only by HVB power usage/charging, and ignores MG1. It would explain the 0-60 videos.

 

[MakinDoForNow]

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)?

Ok this is by memory without reviewing the video yet again. There is a shaft from the ice damper which passes through or is the same shaft as the armature of the starter/generator which winds up turning with the final output shaft to wheels. John Kelley mentions this shaft when he is stacking the gears near the s/g motor. I will look at video and see if I can get time it happens in video for you. ( N th time viewing ).

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