Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

asavage wrote: Fri Sep 23, 2022 2:24 pm Lots of people are not fans of waterless coolants for that reason: with water being "1", glycols typically have a thermal capacity of around .68-.72. In the ICE world so very many people seem to be chasing cures for overheating, and waterless coolant just isn't the right fix for almost all those situations, so it's gotten a bad rep.

However, in the LDU I don't think we need a whole lot of heat-moving capacity; there's just not a lot of heat to be moved, and unlike a legacy ICE situation, the pump capacity is not limited by the idle speed of the ICE; Tesla's thermal management can push the fluid as fast as is needed regardless of other conditions.

I assume that most people are not going to go this route, but it's a valid idea for harm reduction of the expensive bits.
Ah yes, good point regarding the electric pump decoupling the flow from the motor rpm. I'm assuming the pump speed will be dependent on the temperature?
An extreme case - but on here someone reported running into thermal limiting issues in their track driven Cobra with LDU, just unable to remove heat from the rotor quick enough - so in that 'extreme' case waterless coolant would not be a good idea but on a road car could be valid.

As a thought experiment? how about the opposite - no coolant through the rotor? on a road car does the rotor actually need cooling? if you're not drag racing/high speed/towing etc..? there are no magnets to worry about - the copper rotor should be quite resilient to higher temps.?
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

I can't recall: On the Model S, does the A/C-assisted heat-exchanger operate with the LDU, or only with the battery cooling loop?

I would think the BTU-moving ability of the A/C system would be good, because it can push the temperature of the hot fluid (refrigerant and/or coolant) in the radiator to a higher temperature, yielding a better ΔT than perhaps the coolant alone could do, working with only the heat of the LDU. Put another way, the hotter the hot side, the more BTUs that can be moved into the air.

I really haven't looked at this, it's only a thought.

[later]
I had it wrong: the A/C system apparently only cools the batteries on the Tesla, and not the LDU.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

SuperV8 wrote: Fri Sep 23, 2022 3:44 pm As a thought experiment? how about the opposite - no coolant through the rotor? on a road car does the rotor actually need cooling? if you're not drag racing/high speed/towing etc..? there are no magnets to worry about - the copper rotor should be quite resilient to higher temps.?
Interesting thought. Googled "AC Induction Motor Rotor Temperature" and came up with a bunch of stuff including Tesla patent. My background is computer science engineering and have reviewed many patents in my career. Patent tech info can be tricky as patent goal is to make the idea as big and encompassing as possible (with lawyer's help) so it can expand quickly beyond reality/practicality. Regardless, its good info source for this conversation and may not be the case in this specific topic.

In general, my short non expert research found the following

- Stator temp and insulation material degradation from temperature is a concern in AC induction motors. This is easy to measure with a sensor mounting to the stator.

https://www.machinedesign.com/automatio ... emperature

- Rotor temp is hard to measure (no direct contact) This seems to be a huge research area including many tech papers and patents filed to estimate. Tesla's 2010 patent ( https://patents.google.com/patent/US877 ... 0120007532 actual invention might be a couple of years before patent filing effort that starts a bit after engineering) in rotor temp estimation claim while rotor temp can be very high, the bearings temp rating is usually far lower. This paragraph in the patent is particularly interesting

"For instance, while the components of an AC induction squirrel cage rotor can operate at high temperatures (i.e., shaft, magnetic steel, bars/aluminum), there are bearings that are thermally well-coupled to the rotor shaft and these bearings typically have a much lower operating temperature limit than the other components. In this AC induction motor, it is extremely hard to measure directly the temperature of the rotor or the bearings. Additionally, many methods of directed rotor and bearing cooling come with efficiency penalties or mechanical design challenges. Thus, in such a system where a primary thermal rejection path for the rotor is via convection across an air gap to the stator, it is critical to have some quantification of the temperature of the thermally limiting component (e.g., the bearing(s))."

I suppose the rotor coolant circulation can serve as both 1) rotor/bearing cooling and 2) index rotor/bearing temp to coolant temp. Anyhow, info for those more well versed in AC Induction motors to chime in
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

SuperV8 wrote: Fri Sep 23, 2022 8:34 am Not sure I understand your point here regarding ratios?
Many ICE drivetrains can have 10-15:1 total gear reduction in the 1st & 2nd gears.
True but the ICE drivetrain ratio is quickly reduced via transmission shifting as the car gets moving, So not staying at this ratio for long.

In any case, curious the source of LDU's gears mud production and weather its any worse than typically gearboxes which has clutch material wear as well (less metallic?)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

howardc64 wrote: Fri Sep 23, 2022 5:26 pm
- Rotor temp is hard to measure (no direct contact) This seems to be a huge research area including many tech papers and patents filed to estimate. Tesla's 2010 patent ( https://patents.google.com/patent/US877 ... 0120007532 actual invention might be a couple of years before patent filing effort that starts a bit after engineering) in rotor temp estimation claim while rotor temp can be very high, the bearings temp rating is usually far lower. This paragraph in the patent is particularly interesting

"For instance, while the components of an AC induction squirrel cage rotor can operate at high temperatures (i.e., shaft, magnetic steel, bars/aluminum), there are bearings that are thermally well-coupled to the rotor shaft and these bearings typically have a much lower operating temperature limit than the other components. In this AC induction motor, it is extremely hard to measure directly the temperature of the rotor or the bearings. Additionally, many methods of directed rotor and bearing cooling come with efficiency penalties or mechanical design challenges. Thus, in such a system where a primary thermal rejection path for the rotor is via convection across an air gap to the stator, it is critical to have some quantification of the temperature of the thermally limiting component (e.g., the bearing(s))."
Interesting links - yes Patents are very difficult to read!
Thinking more on this even cruising and say using 30kw you'd still need to dissipate 1.5kw if 95% efficient and most of this goes into the rotor on an induction motor, and presumably fitting the Large drive unit you want to use the power :D
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

howardc64 wrote: Fri Sep 23, 2022 6:00 pm True but the ICE drivetrain ratio is quickly reduced via transmission shifting as the car gets moving, So not staying at this ratio for long.

In any case, curious the source of LDU's gears mud production and weather its any worse than typically gearboxes which has clutch material wear as well (less metallic?)
By 'mud' do you mean the metallic particles stuck to the magnet?

These are just from the gears - when new they will be bedding in to each other on the micro level. I would expect if you were to clean off the magnet and check again in 20-30k there would be much less. Not something I would worry about. Manual gearboxes I have re-built had this metallic 'Christmas tree' on the magnet and is quite normal.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

SuperV8 wrote: Fri Sep 23, 2022 6:13 pm Interesting links - yes Patents are very difficult to read!
Thinking more on this even cruising and say using 30kw you'd still need to dissipate 1.5kw if 95% efficient and most of this goes into the rotor on an induction motor, and presumably fitting the Large drive unit you want to use the power :D
This 1980 patent seems to be the first to propose a hollow rotor shaft to run coolant with a sealing band to keep the liquid out of rotor/stator cavity haha. No details on design and reliability of the sealing band. It does cite improvement over the 1970 patent where cooling liquid is permitted to fill the gap between rotor+stator

https://patents.google.com/patent/US4311932A/en

Here is a water cooled induction motors running water in the mounting head where the rotor's bearing sleeves in.

https://static.weg.net/medias/downloadc ... nglish.pdf
SuperV8 wrote: Fri Sep 23, 2022 6:21 pm By 'mud' do you mean the metallic particles stuck to the magnet?

These are just from the gears - when new they will be bedding in to each other on the micro level. I would expect if you were to clean off the magnet and check again in 20-30k there would be much less. Not something I would worry about. Manual gearboxes I have re-built had this metallic 'Christmas tree' on the magnet and is quite normal.
Yes so far found in 5 places and 4 are metallic for sure

- magnetic fill+drain plug, small magnet, small volume of 1-2mm of mud

- huge magnet next to oil pump pickup screen just below diff's ring gear splash guard. Lots of mud on here. Here are closeups
IMG_2753.jpeg
IMG_2752.jpeg
- seal between motor and gearbox chamber where rotor's shaft goes through. Its a lipped seal and have a gap in the middle. Mud filled the gap and have a bead pattern which probably shows the motor's flux field lines. Pic in this post ( viewtopic.php?p=45912#p45912 ) No wear signs on the rotor spline end shaft. Here is the amount of mud removed. Pretty much filled the entire volume between the 2 seal lips.
IMG_2738.jpeg
- mud on inside bottom of gearbox casing. Don't know if these are metallic.

My 32k mile RevQ is a reman. Don't know what are the new/renewed parts during Tesla reman process. QC Charge replace 2 bearings every time gearbox is opened. I'm guessing its the 2 on the highest speed primary shaft. Anyhow, coolant seal will surely leak again < 30-50k miles. Will catch it very early with coolant drain mods so probably even sooner. Tesla LDU is buried in the rear subframe so changing the coolant seal = LDU fully out so might as well crack open the gear box to take a look. May have next mud data in a couple of years (actually hoping it will last that long haha)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Another useful note on researching seals. The PTFE manufacturer told me they were working with a tier 2 supplier a few years back making a seal that didn't leak. Google shows tier 2 is component supplier and tier 1 is assembled parts supplier in automotive supply chain.

So for all we know, the seal got changed via supply chain cost cutting pressure and Tesla's final integrator auditing didn't catch it. For this aggressive application, auditing would have required experienced engineering. Not saying this is what happened but we are talking about 3 layers of horizontal industry layers along with design to supply chain's naturally large timeline stagger (Silicon valley engineering probably long gone by the time auditing suppliers a few years after product release). Easily could see how not all the right decisions were made.

Also looked up more on PTFE seal info. Found 3 additional really interesting info. Seals don't burn up @ these high speeds from hydrodynamics (media gets in between the sealing surface and shaft to reduce contact once its spinning) And they can add "rib" shapes to help push the media back in the sump side in case of low viscosity. Below are some links. This company also showed testing process and equipment for rotational shaft seal testing. It is kind of what one might expect. Ability to use media of choice, adjust pressure, change temperature, add contaminants, measure power consumed from friction etc. An more aggressive test parameter than real life usage is probably used to accelerate wear. Probably some high precision inspection equipment etc. Its increasingly doubtful someone other than Tesla+supply chain actually made this level of effort to make a new seal. Seems much more likely one of the already designed seals that got some statistics in enough car volume is being used. Have no proof, just thinking through whats actually involved in the effort and its not trivial before installing them into a bunch of cars.

https://www.espint.com/engineering/tech ... mic-effect
https://www.espint.com/engineering/tech ... /viscosity
https://www.espint.com/esp-blog/ptfe-rotary-seals
https://www.espint.com/engineering/radi ... al-testing

Interesting to think about double or triple lipped seals with respect to hydrodynamics. The dry lip(s) probably need to be designed differently than the wet one?

Of course this part change theory is all conjecture. But since we are in a info vacuum, need to think "whats more and less likely" to make DIY part decisions where Tesla isn't supplying any.

BTW, just discovered Audi e-tron has coolant cooled rotor. Many reports of coolant leaking into electronics. Not much details yet (fairly new car so mostly warrantee motor replacements) and dealers describe problem as a failed "gasket". More mechanically inclined are chiming in the rotary shaft seal is suspect. I was curious to see what seals others use to solve this problem.

https://electrichasgoneaudi.net/models/ ... ain/motor/

One diagram shows the motor (1 of 3, looks like not exact same design) uses 2 slip ring seal (presumably PTFE) on both sides of the rotor shaft coolant tube. Don't know if that has better longevity. The motor could also be unidirectional if gear box provides reverse. This would probably give the seal better chance at preventing leak.

Here is a paper reviewing all EV motor cooling methods. Table 1 listed e-tron and Mercedes EQC as coolant/water cooled rotor.

https://d-nb.info/1232812978/34
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Link to someone else thinking around using non-conductive coolant (sparse on info, though):
https://www.evcreate.nl/shop/cooling-sy ... e-coolant/
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Didja know that Nissan/Subaru O2 sensor connectors fit this Tesla Model S coolant pump. I just received one from Amazon, $11, and it snaps right in place.

https://smile.amazon.com/dp/B07Z5ZRBY5
Amazon: Nissan/Subaru O2 sensor connector/harness.
Amazon: Nissan/Subaru O2 sensor connector/harness.
Tesla Coolant Pump w/Nissan/Subaru O2 connector/harness.
Tesla Coolant Pump w/Nissan/Subaru O2 connector/harness.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

A couple of questions for those with bearing wear experience and electric motor rotor rust cleanup

Bearing Wear

Looking at the angle teeth between the primary and intermediate shaft. I think the load side bearing on accel is(intermediate shaft bearing on motor side (not pressed in. Primary shaft bearing on motor side pressed in) and regen primary shaft bearing on inverter side. These 2 bearings and their cups/shafts are exactly where wear can be seen.

For reference, we have a right handed pinion gear and I believe the car's forward direction is CCW and reverse CW on the primary shaft.

https://khkgears.net/new/gear_knowledge ... orces.html

On the intermediate shaft bearing, we can see scores on the cup and bearing's outer ring face where it seats. Posted pic before but here again for reference
IMG_2642.jpeg
IMG_2643.jpeg

On the primary shaft bearing, we can see brownish streaks in the center of the mating surfaces (but not at the edge) If we think about how the primary shaft bearing radially tilt on accel and regen, the shaft will push against the inner or outer edge of that bearing surface. Middle of the bearing where everyone's teardown shows scoring streaks is where the biggest gap is. Furthermore, this primary shaft bearing inner ring is a small diameter with a long moment arm (length of primary shaft before the next anchor point at the pressed in bearing on the motor side) Any tilt on the primary shaft will be magnified particularly at the edges of the contact surface. Perhaps this bearing is one that should consider replacement. And maybe its the source of my downhill regen whine... Don't know.
IMG_2650.jpeg
IMG_2651.jpeg
Rotor cleanup

On a small patch of the rotor, used a little rust remover (chemical reaction) wiped it off followed by acetone and the area became hazy compared to rest of the shiny rotor. I've seen QC Charge's post with completely rusty rotor coming out completely shiny.

https://teslamotorsclub.com/tmc/posts/5312706/

Seems should be able to just knock rust off mechanically (protect the bearings, o-ring, and the cooling holes at the edge of the rotor) and probably spray clear coat on it (avoid the shaft's sealing surfaces of course) for future rust protection? Wonder if any concerns for balance issues? Probably no more so than weight distribution changes from the rust and knocking it off.

I don't have much rust so probably do something minimal if anything at all.
IMG_2757.jpeg
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

howardc64 wrote: Sat Sep 24, 2022 3:58 am BTW, just discovered Audi e-tron has coolant cooled rotor. Many reports of coolant leaking into electronics. Not much details yet (fairly new car so mostly warrantee motor replacements) and dealers describe problem as a failed "gasket". More mechanically inclined are chiming in the rotary shaft seal is suspect. I was curious to see what seals others use to solve this problem.

https://electrichasgoneaudi.net/models/ ... ain/motor/

One diagram shows the motor (1 of 3, looks like not exact same design) uses 2 slip ring seal (presumably PTFE) on both sides of the rotor shaft coolant tube. Don't know if that has better longevity. The motor could also be unidirectional if gear box provides reverse. This would probably give the seal better chance at preventing leak.

Here is a paper reviewing all EV motor cooling methods. Table 1 listed e-tron and Mercedes EQC as coolant/water cooled rotor.

https://d-nb.info/1232812978/34
Interesting that the E-tron also used a cooled rotor induction motor. Can't see anywhere that this special 'laser' seal is available separately - many other seals are available but it looks like it would be a new drive unit if this seal ever failed! These are between £3,000-4,000.
Also interesting to note that Audi specifically say "however a small amount of leakage cannot be prevented"! and also designed a small reservoir in the resolver housing - with a drain plug!!
I have also found that this 'drip container' has a 24 month service requirement!
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

The EQC also used induction motors.
seems they also have some issues with coolant sealing (only recalled in China though!)
https://www.autoevolution.com/news/merc ... 81994.html
https://www.laitimes.com/en/article/34nq8_3ld7t.html

surprised by the low RRP for a new ELECTRIC DRIVE - which includes the inverter and reduction box!:
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

SuperV8 wrote: Mon Sep 26, 2022 9:46 am Interesting that the E-tron also used a cooled rotor induction motor. Can't see anywhere that this special 'laser' seal is available separately - many other seals are available but it looks like it would be a new drive unit if this seal ever failed! These are between £3,000-4,000.
Also interesting to note that Audi specifically say "however a small amount of leakage cannot be prevented"! and also designed a small reservoir in the resolver housing - with a drain plug!!
I have also found that this 'drip container' has a 24 month service requirement!
SuperV8 wrote: Mon Sep 26, 2022 10:34 am The EQC also used induction motors.
seems they also have some issues with coolant sealing (only recalled in China though!)
https://www.autoevolution.com/news/merc ... 81994.html
https://www.laitimes.com/en/article/34nq8_3ld7t.html

surprised by the low RRP for a new ELECTRIC DRIVE - which includes the inverter and reduction box!:

3 designs 3 failures

Nice find! 3 fails on 3 different attempts by 3 different teams on keeping back the coolant. On the e-tron seal, pink color is probably PTFE seal. Wonder what the dark grey material with the laser etching is?

Other diagrams also say its a slip ring seal. My understanding is such seal is in 2 parts. Each part pressed onto the shaft and the round tunnel respectively and they mate in the middle with the sealing material. But looks like no better than keeping back the coolant.

Failure Modes

So far, haven't found/heard any info on failure modes. Is the leak during rotation? while sitting? reverse spin direction? This rebuilder claims its the axial play on the bearings (I presume then suggest the shaft axial movement) is causing the leak in the video's comments



This doesn't quite make sense since LDU has a pair of disc springs next to the outer rotor bearing. This suggest rotor axial movement is present and need to prevent the rotor from slamming side to side.

Thinking about how failure mode can be discovered/confirmed? If leak is suspected to occur under high speed rotation, would need use a high speed camera and data store to film the dry side of the seal and likely operate very long time to capture the leak mechanism (10k RPM = 150Hz camera+data store, commonly available professional tool). This observation would then feed back into hydrodynamic pump aid design (see below)

QC Charge tech's comment on teslamotorclub on statistics is perhaps a hint. There is high occurrence of lower mileage LDUs that leaks. His guess (just a guess of course) is seal could be sticking while sitting. I'm also wondering about reverse spin direction since thats usually what happens after parking. Hydrodynamics effect explanation by ESP Engineering says structures can be built into the seal to aid pumping the media back to the sump side. They showed such a structure in unidirectional spinning shafts. Also noted its possible for bidirectional. But I imagine bidirectional aid can't be quite as optimal as unidirectional. Anyhow, e-tron's laser etching seems to be just fancier way to build more complex aid patterns.

https://www.espint.com/engineering/tech ... mic-effect

Probably never get to a detailed understanding of the leak mechanism and failure mechanisms will remains all conjecture.

How to get rid of coolant that leaked?

Adding drain hole in the reluctor chamber is definitely a lot better than a mostly sealed washing machine. And also sealing up as much of the path to stator and inverter cavity as possible with proper air pressure eq.

But it seems quite natural some coolant will get aerosolized and attack the nearby sealed rotor bearing. Don't know of bearing seal will keep it out. Even if the leak occurs when shaft is stationary, any tiny drops doesn't drain probably gets airborne from spinning motion AND potentially heat (see below). It seems to truly get all leaked coolant out, shaft need to include structures to spin coolant away from the bearing and collect it (baffled passages for condensation?) or circulate air to draw out the moisture... On temperature, here are pics of motor and inverter side temps

https://teslamotorsclub.com/tmc/posts/7069127/
https://teslamotorsclub.com/tmc/threads ... ion.88055/

This is a diagnostic mode display on Model S/X's 17" screen. Need Tesla tech's daily changing security code to gain access. There are hacker 3rd party tools (scanmytesla https://teslamotorsclub.com/tmc/threads ... id.112636/) that may get these temps. Will check when my LDU is back in the Model S.

But anyway, a drain hole + cavity seals is a huge improvement to current design. Just thinking through what it takes to improve longevity.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

I'll venture that the presence of aerosolized coolant is not a significant factor to lubricant washout on the end-cap rotor bearing. You can look up SKF's spec on the bearing's seal's capability, but that's my guess: unless there's a pressure differential, a bunch of axial movement, or even more likely enough bearing wear to render the bearing's seal ineffective, the presence of coolant just running down the seal's face isn't going to want to get into the bearing. The bearing's internal grease/seal interface is an effective incidental moisture barrier all by itself, until other forces act on it. IOW, look elsewhere for greater bearing longevity. That's my guess for now.

A bit of a rant . . . As I mentioned above, providing a weep hole between the pump seal and bearing was standard practice for lowly water pumps on pretty much everybody's automotive and industrial engines for a century. I don't know why any engineer would have reason to assume that a seal would operate with 100% efficacy for any significant length of time in this type of application, and I'm surprised that these engineering youngins with their fancy-pants 3D modelling haven't looked backward a bit to see how this type of engineering problem had been resolved by others.

Do they really think it's so disposable now that it just doesn't matter if the thing leaks and becomes the cause of a significant repair? IDK, I've worked in an Engineering department where we were trailing-edge and overbuilt everything, because everything we built was pretty much one-off, so trying to wring every penny out of a design wasn't worth hardly any engineering time, and after building one-off equipment for 50 years, the business had a model of engineering that worked very well, within those limitations (ie don't try too hard to reduce costs to build; stay within our engineering talents' lane).

---

For centuries, one reason that bearings of nearly all types were fitted with external lubrication mechanisms was to provide a way to remove excess contaminants from the bearing that had made their way in to the moving bits. "Sealed" bearings aren't; they're only sealed to a certain percentage of ingress, for a certain range of size of particulates or viscosity of liquids, and only within a certain pressure differential. In the quest to reduce costs, reduce drag (increase bearing efficiency), reduce service attention intervals, etc., this is where we've come: it's "good enough".

All anything has to do is make it out of warranty; the next owner be-damned.

Sorry, I'm having a grumpy old man moment; you get old and know things, and nobody wants to listen. Quoting Vonnegut, "Everyone wants to build, nobody wants to maintain."
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

asavage wrote: Mon Sep 26, 2022 6:58 pm I'll venture that the presence of aerosolized coolant is not a significant factor to lubricant washout on the end-cap rotor bearing. You can look up SKF's spec on the bearing's seal's capability, but that's my guess: unless there's a pressure differential, a bunch of axial movement, or even more likely enough bearing wear to render the bearing's seal ineffective, the presence of coolant just running down the seal's face isn't going to want to get into the bearing. The bearing's internal grease/seal interface is an effective incidental moisture barrier all by itself, until other forces act on it. IOW, look elsewhere for greater bearing longevity. That's my guess for now.
Sensible. Having taking apart the bearing seal, to clean off inside, the seal's rubberized surface and seams seems to be in perfect condition. Here is a pic and the -1 post shows the fully trashed grease from washing machine spin cycle haha.

https://teslamotorsclub.com/tmc/posts/7069409/
asavage wrote: Mon Sep 26, 2022 6:58 pm A bit of a rant . . . As I mentioned above, providing a weep hole between the pump seal and bearing was standard practice for lowly water pumps on pretty much everybody's automotive and industrial engines for a century. I don't know why any engineer would have reason to assume that a seal would operate with 100% efficacy for any significant length of time in this type of application, and I'm surprised that these engineering youngins with their fancy-pants 3D modelling haven't looked backward a bit to see how this type of engineering problem had been resolved by others.

Do they really think it's so disposable now that it just doesn't matter if the thing leaks and becomes the cause of a significant repair? IDK, I've worked in an Engineering department where we were trailing-edge and overbuilt everything, because everything we built was pretty much one-off, so trying to wring every penny out of a design wasn't worth hardly any engineering time, and after building one-off equipment for 50 years, the business had a model of engineering that worked very well, within those limitations (ie don't try too hard to reduce costs to build; stay within our engineering talents' lane).

---

For centuries, one reason that bearings of nearly all types were fitted with external lubrication mechanisms was to provide a way to remove excess contaminants from the bearing that had made their way in to the moving bits. "Sealed" bearings aren't; they're only sealed to a certain percentage of ingress, for a certain range of size of particulates or viscosity of liquids, and only within a certain pressure differential. In the quest to reduce costs, reduce drag (increase bearing efficiency), reduce service attention intervals, etc., this is where we've come: it's "good enough".

All anything has to do is make it out of warranty; the next owner be-damned.

Sorry, I'm having a grumpy old man moment; you get old and know things, and nobody wants to listen. Quoting Vonnegut, "Everyone wants to build, nobody wants to maintain."
I think a completely fair observation besides rant. I've worked in silicon valley for one of these companies that pioneered the computers for 3D CAD (Silicon Graphics, and my tech background is 3D gfx chips) These companies are fly by night (come and go in 10+ years) with respect to a car's service cycle. All the design team disappears after stock vesting... Perhaps okay for solid state semiconductors but for something mechanically complex like a car... far from the necessary continuity of existing car manufacturers.

Tesla's biggest problem going forward is fundamentally maxed out stock price... The secret key word in any silicon valley company is "stock exits" Its on the mind of every employee with stock based compensation and every layer of investors.

- Design team cycles in and out quickly from stock vesting period. Those doing it for green/futurism (self driving) quickly sees the reality.
- Institutional investors like Blackrock looking to exit Tesla holdings. Probably lobbying gov for EV purchase tax rebates to help the exit.
- Tesla's Chinese factory (probably close to 50% of global sales volume) is owned by Chinese gov owned companies. Likely same for the German factory. These factories can be shifted to manufacture any EV quickly.
- Finally, Elon is sleeping in a tiny home at SpaceX TX. Probably no body is home that drives hard at anything at Tesla HQ these days. He has basically "exited"

LDU might be pain for us currently but the battery failure and replacement is a far bigger problem for all EVs. US market has killed off the low capacity cars (24kw cars : original leaf, e500, focus EV, golf EV, etc...) and now are all >= 60kw expensive batteries. Historical data on rebuilding battery pack by mixing cells/submodules isn't very good (Prius rebuilds last 1-3 years as compared to new) 057 posted on TMC anything short of completely set of matched aged modules doesn't work for very long and they've gone through hundreds of packs. So basically when cell failure occurs (anode cathode bridge gets built over that tiny gap and cause a short from repeated recharge/discharge cycles) The whole battery is toast for use @ same capacity. >=60kw means $15k-$30k+ for a new battery pack which exceeds the residual value of the car. Hence... battery failure = disposable/salvage status. EVs are great to drive and have no service (if no dumb coolant cooled rotor seal design haha) until the battery pack failure death sentence.

I think as post warranty battery failure expense word get more prominent, EV buyers will shift towards leasing to stay in warranty honeymoon the whole time. This is how today's premium German car segment works (>50% sales = lease) > 100k mile German car residual value is sustained by parts/independents/cloned diag tool availability along with army of average DIYers. Tesla's DNA disables all of these via draconian HQ process control. Can't even order common OTC parts (not coolant seal) through proper process as of today. Basically unbelievable for > 1M car shipped/year!

Arguably to be greener (lower mining, salvaging, and recycling difficulty pressure), smaller battery pack EVs makes much more sense. This is happening in mass in China but doesn't work in US population distribution.

So personally, I've got to decide what to do once LDU seal leak is repaired and staring at the $25k battery pack failure replacement death sentence... 057 offers a $2k/2year extended warranty plan. Great service but the solution doesn't scale... I'd imagine they must be hoarding lots of crashed vehicle battery packs (cheapest way to get batteries haha) Maybe I'll sell the repaired+modded LDU and battery pack to 057 and call this guy haha

Ok my rants done. Back to engineering and solution finding :)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

You've typed lots of things I nodded along with.

wk057 says he can't reliably get multi-year service life from battery packs in which only modules were replaced (I think I have that right).

Gruber (the ones who have had two separate shop fires burn up many irreplaceable Roadsters) says wk057 just haven't figured out how to do (module? brick?) replacement right, and that Gruber have.

Rich Rebuilds is replacing modules (though not bricks) and thinks they're getting away with it.
https://www.youtube.com/watch?v=T7Q0nNkQTCo

This hasn't shaken out yet, and as you say even with all these people working on it, it can't scale, because prominently Tesla won't help (generalized and summarized). I'm hopeful that the obstacles (ie Tesla) will be worked around before I have to contemplate my own pack repair; I'm at 106k and on a "refurb" pack since Aug2019/73k, which might mean I have updated contactors; I assume ALL the RAV4 EV packs in existence were assembled before 2015. I don't think that Model S modules fit in RAV4 EV packs, they're the same tech but different physical form factor. So, I either find modules from another pre-2015 (ie OLD) RAV4 EV pack, try to determine if Model S bricks can be retrofitted into the RAV4 EV modules, or branch off into experimental land by replacing the OEM modules with someone else's cells (and therefore having to ditch pretty much ALL the Tesla<->Toyota integration, as the Tesla Gateway won't likely work with anybody else's BMS, etc.

Really, that makes a great case for scrapping the vehicle.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

asavage wrote: Mon Sep 26, 2022 6:58 pm A bit of a rant . . . As I mentioned above, providing a weep hole between the pump seal and bearing was standard practice for lowly water pumps on pretty much everybody's automotive and industrial engines for a century. I don't know why any engineer would have reason to assume that a seal would operate with 100% efficacy for any significant length of time in this type of application, and I'm surprised that these engineering youngins with their fancy-pants 3D modelling haven't looked backward a bit to see how this type of engineering problem had been resolved by others.
Agreed, especially considering the consequences of any leak - if your coolant pump seal leaked no big deal, just fit a new water pump; If your coolant seal leaks on your induction motor that can result in total drive unit failure/replacement!
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by SuperV8 »

howardc64 wrote: Mon Sep 26, 2022 6:08 pm
So far, haven't found/heard any info on failure modes. Is the leak during rotation? while sitting? reverse spin direction? This rebuilder claims its the axial play on the bearings (I presume then suggest the shaft axial movement) is causing the leak in the video's comments

This doesn't quite make sense since LDU has a pair of disc springs next to the outer rotor bearing. This suggest rotor axial movement is present and need to prevent the rotor from slamming side to side.
Very high speed bearings (like on the LDU rotor) have more clearance than standard bearings required due to thermal & centrifugal forces.
From one of Prof John Kelly's videos - one of the bearings is constrained - while the other is allowed to float axially to compensate for rotor thermal expansion.
The belleville or wave washers are often used in high speed machines fitted with these high speed bearings (which have more clearance) to 'gently' pre-load the bearings. This helps with running accuracy, and prevent skidding.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

"skidding" in this instance meaning the balls do not rotate, but slide on the races; I want to differentiate this from the effect Howard thinks he sees, with the outer race's OD fretting the gear case's counterbore.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

SuperV8 wrote: Tue Sep 27, 2022 8:48 am Very high speed bearings (like on the LDU rotor) have more clearance than standard bearings required due to thermal & centrifugal forces.
From one of Prof John Kelly's videos - one of the bearings is constrained - while the other is allowed to float axially to compensate for rotor thermal expansion.
The belleville or wave washers are often used in high speed machines fitted with these high speed bearings (which have more clearance) to 'gently' pre-load the bearings. This helps with running accuracy, and prevent skidding.
asavage wrote: Tue Sep 27, 2022 4:05 pm "skidding" in this instance meaning the balls do not rotate, but slide on the races; I want to differentiate this from the effect Howard thinks he sees, with the outer race's OD fretting the gear case's counterbore.
Thanks for both comments and clarification. Very helpful. Here is another mystery on the rotor hybrid (non conductive) bearings. Mine have different PN on each one

Coolant Seal Side : BB1-3793 16 352 N USA SKF
Gear Side : BB1-1107 14 337N USA SKF
IMG_2805.jpeg
IMG_2804.jpeg
IMG_2803.jpeg
IMG_2802.jpeg
Both look identical including cage shape/color. Measures 62mm OD, 35mm ID and 14mm wide (D/d/B respectively in SKF spec). ID measurement on gear side is approx as shaft diameter is nearly completely buried under the installed seal.

On SFK website. Only 6007-2RZTN9-HC5C3WT has a cage that looks like both of mine. I would have thought the 14 and 16 marking are dimension B in SKF but clearly not ( my coolant seal side is 14mm actual measurement ) Nathan used this bearing in his Rav4 EV LDU rebuild ( pg 6 https://docs.google.com/document/d/1A6n ... 2qzGA/edit )

https://www.skf.com/us/products/rolling ... d-bearings
https://www.skf.com/us/products/rolling ... %2FHC5C3WT
https://www.skf.com/us/products/rolling ... 07%2FHC5C3
https://www.motionindustries.com/products/sku/06006940

Also looked for primary shaft inverter side bearing and SKF has a million PNs that seems to match

SKF EXPLORER 6207/C3VC4521 09 313N USA SKF
IMG_2729.jpeg
SKF website closest one have a non metal cage (mine looks metal from pic)

https://www.skf.com/sg/productinfo/prod ... 2FC3VC4521

Could go Nathan's route and use FAG compatible bearings ( pg 11 https://docs.google.com/document/d/1A6n ... 2qzGA/edit )

Haven't decided to change these bearings yet but good to have a source of course. Never purchased bearings before so am unfamiliar with SFK markings and what they mean. 6007-2RZTN9-HC5C3WT spec does explain C3=clearance, TN9=glass fiber cage, 2RS=NBR non-contact seal on both sides. None of these markings are on my hybrid bearing. Contacted SFK but they replied not answering to non business emails due to international conflict at the moment.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Regarding battery failure with mixed cells/modules. There is another basic statistical factor. Once a cell fails, another one can't be far behind.

Used rechargeable batteries are not same as new after they age even if they still work. Internal chemistry and physical structures has degraded through repeated charge/discharge cycles and statistically will reach a failure point. In Tesla's 7000 cell design, this manifest as a single small cell failure. But statistics would suggest another failure is on the way. In large cell designs like pouch. There is much higher surface area for anode/cathode per cell. So each cell should have higher statistical failure rate based on ionic exchange surface area.

Learned about lithium ion battery dendrites in the past. Its basically a bridge (tree branch structure) that starts on the cathode and build towards anode. Common knowledge amongst battery developers is dendrites grow during rapid charge < 20C (Tesla over the air updated my Model S to charge slower at home (30A limit instead of 40A 240V at home AND dropped my supercharge rate significantly. So much for that short stop at supercharger haha)

https://www.batterypoweronline.com/news ... ites-grow/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8510069/
https://www.designnews.com/electronics- ... rites-grow

So even when mixing older cells/modules to rebuild a pack. Its starting with chemically and physically degraded cells (at molecular level) further along the statistical failure curve. By definition can't last as long.

Anyway, fundamental ionic chemistry and parasitic reactions suggest as ions migrate back and forth... it doesn't go 100% efficient according to the ideal reaction equation. Sounds like solid state lithium ion battery are trying to combat dendrites. This paper says... still dendrite problems in solid state

https://www.sciencedirect.com/science/a ... 8520301284

At the atomic level, I know ordinary glass and semiconductor industry chips (both silicon) are at 2 ends of spectrum on the silicon atomic crystalline structure which impacts electron movement. Chips have the most perfect crystalline structure and fastest electron mobility. Ordinary glass are amorphous (without structure) and LCD panels are somewhere in between (LTPS and HTPS (Low and High Temperature PolySilicon) Sharp used laser annealing method to increase crystalline structure on glass surface for 400 dots/inch screens back in the mid 2000s) Camera sensors also need higher crystalline structure. Not saying its all related but there is real and complex atomic level chemistry and physics actions that is happening inside Lithium Ion batteries.

I'm no battery experts but there are lots of first principle considerations on fundamental chemistry that are being ignored in consumer media. How does Lithium Ion batteries fail (or for that matter all rechargeable batteries) isn't summarized much to the consumers handing over $$$ on a large consumer and discretionary spending item.

In simple speak, I'd imagine for 057, new low mile crashed Tesla battery packs is more valuable than those still working at higher mileage :)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Well, there are no new low-mileage packs for my RAV4 EV :(

Interesting about the OTAU reducing your 240v at-home charge rate. I've got a 40A EVSE at home and no DCFC on the car at all, so when I charge, it bulk charges at ~38.2A AC input to the OBC.

Off the top of my head, I recall the BB1-3793 being sold by various sources ($150 (counterfeit?) - $450 ea.) as the brg to use for both ends of the rotor. I have no idea how appropriate that is.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by dzolotnyuk »

thought I would add one more 2013 tesla model SP85 to the list of dead rear drive units my car has 137K miles when seal leaked again on a unit that was replaced some time in april of 2019 under warranty when car had 65K miles by the way my unit that failed is an R version had a single lip seal. I have been looking for a solution lake everybody else. I should be receiving a seal form https://ahpseals.com/product/sb20/ $175 is what i paid for it. it was about 3 weeks wait time now i need to machine an adapter plate hopefully some time later this week or next week. I am not an engineer of any kind just desperate to get my car back on the road so i thought i would get an opinion of a professional on the forum about that seal if it fail i will be modifying coolant manifold and adding water to oil cooler
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Thinking more abstractly on chemical energy storage and conversion. Rechargeable batteries are quite amazing already in comparison

- Ionic reactions are quite aggressive. Imagine presence of any impurities
- Humans and ICE take in fuel with plenty of impurities (O2 mixed in air, food mix, hydrocarbons mix) But we also produce waste products that gets rid of them to reduce long term damage to the energy conversion system.
- Rechargeable batteries doesn't get rid of waste so any unwanted chemical products are cumulative.

IBM researched a technology called Lithium Air battery for a couple of decades before pulling the plug. It was 10x energy/weight density than current Lithium Ion battery. In part from getting one of the reagents (oxygen) out of the air rather than carrying all reagents with you all the time like current lithium batteries. Pulling oxygen for its oxidization energy is of course what biology and ICE does. Combining it with C-H bonds energy from sugar and hydrocarbons (I think, am no chemist haha)

https://www.zurich.ibm.com/news/12/battery500.html

IBM eventually pulled the plug. Imagine the impurities filtering required. I recall keeping water vapor away from Lithium was a challenge.

So building a rechargeable battery that can't eliminate accumulating harmful products for longevity is quite the challenge and an amazing feat already :)

Ok, back to seal and bearing land haha.
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