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Ford hybrid drivetrain teardown/detailed informational videos


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13 replies to this topic

#1 OFFLINE   cr08

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Posted 20 February 2018 - 01:18 PM

So I have been watching this particular Youtube channel off and on for a while now called Weber Auto. Essentially lecture-like informational videos created by Professor John Kelly at Weber State University for their Advanced Automotive Technology course. And they have some videos specifically for the Ford hybrid drivetrain. Very educational.
 
https://www.youtube.com/user/WeberAuto
 

 

 
https://www.youtube.com/watch?v=MZf_BUuW5Qg
 
https://www.youtube.com/watch?v=UddAfkFfXuU


Edited by cr08, 20 February 2018 - 01:21 PM.

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#2 OFFLINE   spirilis

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Posted 20 February 2018 - 04:01 PM

I saw that a week or 2 ago. Awesome detail. I am not quite clear how the engine/generator is coupled to the planet carrier for engaging the engine to the drivetrain (is there a clutch somewhere? Any other options for gearing I missed in there?)

#3 OFFLINE   cr08

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Posted 21 February 2018 - 03:58 AM

Based on a number of things including what he mentioned in the transmission teardown video as well as some searches including a post related to the Escape hybrid, appears to be a clutch damper there. So an always engaged clutched and its primary use is to disengage in case of shock or exceeded torque on the ICE side input shaft.

 

EDIT: Should add as additional clarification on these findings is the damper has no control mechanisms. It is merely used as a breakaway in extreme situations.


Edited by cr08, 21 February 2018 - 04:26 AM.


#4 OFFLINE   spirilis

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Posted 21 February 2018 - 06:01 AM

Yeah so that wouldn't be the thing I'm thinking of... since the C-Max can have its engine completely shut down while the output gear (can't recall the names offhand, been a week or so since I watched) is spinning or propelled via the traction motor.


Edited by spirilis, 21 February 2018 - 06:43 AM.


#5 OFFLINE   cr08

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Posted 21 February 2018 - 06:22 AM

I'll have to re-review that video later after work. I watched it again late last night and specifically recall he mentioned a mechanism inside the transmission that allows the starter/generator to spin while the ICE remains stationary, potentially allowing it to provide additional motive power as required. I want to say this was brought up when discussing the HF-35 (2013-2016) but not 100% certain.


Edited by cr08, 21 February 2018 - 06:37 AM.

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#6 OFFLINE   stolenmoment

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Posted 21 February 2018 - 08:49 AM

As I understand it (and it took me awhile), the main traction motor is connected to the ring gear, which is directly connected to the wheels.  The second electric motor is connected to the yoke connecting the planetary gears (spinning the yoke, not the gears themselves), and the ICE is connected to the sun gear.  The second motor serves as clutch and transmission; its rotation controls the power transfer between ICE (sun) and wheels (ring).  All three motors can contribute to traction power.

 

The planetary gear motor is the real trick, and controlling that motor allows control of power and regen.


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#7 OFFLINE   cr08

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Posted 21 February 2018 - 09:51 AM

Now that you mention it and jog my memory, that is the case. Work's been frying my brain this morning. :p The biggest bit to be reminded of is the fact the traction motor is directly attached to the final drive with no gearing (other than the diff ratio). That leaves the other two 'inputs' of the planetary gearset for the starter/generator and the ICE. If moving in EV only, the starter/generator needs to spin in the opposite direction of the traction motor at essentially the same ratio to keep the ICE in a stationary position. And I seem to recall via Torque (once again, memory a bit hazy and I can verify this later on) seeing the starter/generator showing an equal but negative RPM to the traction motor in EV mode. And there is likely very little effort needed to be maintained on the starter/generator in this scenario as the ICE is going to have a lot more friction to get spinning versus a freely movable rotor in the starter/generator.

 

What I think I'm actually recalling is the sprag clutch mentioned in the early 2005-2008 Escape transmissions which allows the starter/generator to spin in one direction without engaging the ICE. As assumed by Mr. Kelly this was likely to allow the starter/generator to provide a little extra traction assistance if needed and with the lower HP rating of the traction motor it may have been needed.

 

Again, I'm going to re-review the video later this afternoon and try to verify some of this.



#8 OFFLINE   spirilis

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Posted 21 February 2018 - 10:32 AM

OK that makes more sense now...

 

https://youtu.be/hHU5xFOBcsU?t=772

 

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.

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#9 OFFLINE   cr08

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Posted 21 February 2018 - 10:51 AM

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)?

 

Yep. This is exactly it. It's why the more accurate terminology used is 'eCVT'. Simple but effective system and is generally why they are pretty bulletproof. Constantly meshed gearing with no clutches or gear changes. Just electric motors doing all the work in managing the transmission operation.



#10 OFFLINE   spirilis

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Posted 21 February 2018 - 10:58 AM

I have heard it said before that parallel hybrid CVTs are not suitable for towing or heavy hauling, and I would wager a guess that the small size and strength of those planetary gears, and especially that sun gear, might be a limiting factor given the amount of leverage they have to handle.  Too much weight & resistance could really crack some teeth in the extreme sense.  But the solution for that would be to make the gears much bigger, right?



#11 OFFLINE   cr08

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Posted 21 February 2018 - 11:12 AM

Couldn't exactly tell you on that topic. But I'd guess they aren't terribly weak and the lack of approved tow rating might be more lawyerish protection than anything. A small handful of people over on another forum I've lurked over some years ago towed over 1500lb with the first gen Escape hybrids with no issue. Where I think the lawyer-ese comes and was guessed by those members was the reduced braking efficiency in hybrids primarily to greatly reduced engine braking with Atkinson cycle engines. Plug-ins have a big benefit of being able to recharge a pretty large battery and use that for braking but once that is fully charged you either have to rely on the limited engine braking or the friction brakes which can fail pretty easily if ridden for long enough especially if driving in mountainous areas. Additionally those vehicles with actual tow ratings are likely over-engineered with a larger margin of capability than what is officially permitted. Likely with the C-Max you might be able to get away with 1500lb but that would legitimately be the limit.

 

Once again I'm not a mechanical engineer so take that above wall of text with a grain of salt but there's at least been some first hand towing experience to go off of. I believe it was on the GreenHybrid forums. They seem to have a pretty good repository of Escape content.

 

EDIT: Forgot also that in not only Ford hybrids but Toyota's as well with the planetary gearset based eCVT, there is no ICE assistance in reverse. It is all EV. So that is an additional concern when towing if having to back up an incline for example.


Edited by cr08, 21 February 2018 - 11:20 AM.

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#12 OFFLINE   spirilis

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Posted 21 February 2018 - 11:46 AM

That's just such a neat system the more I think about it.  It's also probably not practical without the use of high-speed real-time microcontrollers calling the shots on the 3-phase motors, to keep the Generator/Starter motor's speed super accurate relative to the engine and final drive gears, as it requires reacting in realtime to any disturbance in the rotational speed introduced by outside factors (car suddenly going over a bump or up hill, etc).



#13 OFFLINE   cr08

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Posted 21 February 2018 - 12:39 PM

So about 7:00 into that video covers operation of the Sprag clutch which was just in the first gen 2005-2008 Escape hybrids and just brief assumptions on its use due to lack of information from Ford. And about 20:40 in starts a brief operational explanation of the modern HF-35 (2013-2016) which is confirmed there is no special mechanism to keep the ICE stationary. Just relying on the two motors to counteract to equate to 0 rotation on the ICE end.



#14 OFFLINE   viajero

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Posted 24 February 2018 - 04:19 PM

This site has a good animation of the Prius power split transmission, which is the same basic architecture as the Ford system. You can move the sliders up and down to get a feel for how it works. It’s a very simple and elegant mechanical system; all the complexity is in the firmware controlling the motors. It has to run them at the right speed, and start/stop them smoothly enough that the drivetrain isn’t jerky.

The site requires Flash, so it won’t work on many mobile devices.

http://eahart.com/prius/psd/

Edited by viajero, 24 February 2018 - 04:19 PM.

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