Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Topics concerning the Tesla front and rear drive unit drop-in board
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

WimV wrote: Sun Oct 02, 2022 8:38 am I just removed the seal. Started cutting it, but then I noticed the steel was pretty thic. Tapped two holes in it and pushed it out with two bolts. Works perfectly, seal is removed within 5 minutes.

The lip at coolant side was, as expected in best shape. Other two rings were very worn and had a lot of black sticky mess on them (probably ptfe dust mixed with coolant).
Yeah, kind of expected. Everyone believes triple lipped seal (2 lip + excluder lip) is better over single (maybe evangelized by QC Charge?) but lacking hydrodynamic effect on the 2 dry lips would suggest the dry contact surface would get burned up quickly. Wonder if this will cause damage to the shaft.

Maybe the PTFE dust from the middle lip adds material to the coolant facing lip? Who knows haha.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

WimV wrote: Sun Oct 02, 2022 4:58 pm I used a wiring harness sleeve to pull the temp sensor wires through the tunnel, worked very well.
How did you prevent coolant from traveling through those sensor wires in future?

WimV wrote: Sun Oct 02, 2022 4:58 pm How do you guys purge the cooling system? Is it necessary to fill the motor before connecting the cooling system in the car? Or will it purge itself while driving?
I intend to fill mine -- when I have to DIY -- using an air evacuation tool that I use for all my other vehicles. It uses shop compressed air to generate a vacuum on the cooling system.

viewtopic.php?p=44254#p44254

I used to use an Airlift II, but I recently obtained a Snap-On RADKITPLUSA Cooling System Vacuum Filler set, thinking it might be an upgrade.

I've also got (for my Toyota RAV4 EV) a cracked install of Tesla Powertrain Diagnostics, which will command the pumps to run and valve to cycle, running the pumps for 50 minutes or something, which is the official method for my vehicle that came with a factory-installed customized version of the Tesla LDU (runs backwards, has electric Park mode, etc.).

Anecdotally, another RAV4 EV owner did not use either of those methods, and shortly after reinstalling his LDU, he received an overtemp warning at the dash, and found the reservoir low. I assume that running it around for a few minutes and topping up -- lather, rinse, repeat -- may get you to a stable situation, but I do not know if there are high spots in the Model S cooling system that can trap air. That's the advantage (and the whole purpose) of the vacuum tool: no air pockets are left, unless a valve is closed during evacuation of the air.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by WimV »

I don't have a vacuum tool, so I'm just going to try to let it purge itself. There are temp sensors everywhere, so I don't think anything can go wrong when there's an air lock.

I drained about 2 litres, so I’ll be driving and charging slowly till I’ve topped the reservoir with 2 litres.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by WimV »

Immediately after connecting the 12 V battery, the coolant pumps started running and the coolant level was lowering. I added about a litre before I started driving. I drove 20 minutes, the level was lowered again. Added again about a litre, so level should be the same as before.

Until now, everything looks fine :)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by WimV »

asavage wrote: Sun Oct 02, 2022 11:06 pm How did you prevent coolant from traveling through those sensor wires in future?
It looked like the white sleeve is embedded in the stator, so I don't expect water to leak in the sleeve.

If my seal is going to leak again in the future, I'm thinking about opening up the reluctor housing. There should be room enough to mill some slots and holes. Is there any reason why not to do this? The reluctor wheel and sensor are robust enough, they don't care about some dust.
If it would leak, it would just leak to the outside.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

WimV wrote: Tue Oct 04, 2022 10:46 am If my seal is going to leak again in the future, I'm thinking about opening up the reluctor housing. There should be room enough to mill some slots and holes. Is there any reason why not to do this? The reluctor wheel and sensor are robust enough, they don't care about some dust.
If it would leak, it would just leak to the outside.
Worried reluctor chamber drain tap at bottom not enough? With that drain, won't get a pool of coolant for the reluctor wheel to agitate and aerosolize? I suppose no pool is great step with drain tap. Your thought if we can get to no collateral damage from leak so no need to repair leaky seal. Even better.

Without knowing how and when the leak occurs. Kind of hard to judge what happens next. I was also curious about reluctor wheel chamber air circulation pattern while running. What happens when minute drop seeps out at say top of the seal during high speed forward rotation (seems like it could get aerosolized right away before getting to the drain), or slow speed reverse, or stationary parked. And if the minute leak sticks to the walls and not vacated by gravity right away during parking/reverse. What happens when reluctor wheel starts spinning up at high speeds with these small droplets on the walls? These thoughts were also motivated by.. just let it leak if no collateral damage (if possible)

I suppose more opening exposes the sealed hybrid bearing and excluder lip as well. But that lip might be making PTFE residue anyways?
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by Johan »

WimV wrote: Tue Oct 04, 2022 10:46 am It looked like the white sleeve is embedded in the stator, so I don't expect water to leak in the sleeve.
Yes, the brown stator potting resin encapsulates the white sleeve in my LDU too.
Disclaimer: Despite all efforts, all (which I write) should be conservatively interpreted as a poorly informed, error-prone, non-expert opinion that is subject to continuous change, especially in this age of hyper-specialization and newly gained insights.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Thanks for clarifying that stray coolant should not be able to travel along with the temp sensing harness.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by WimV »

howardc64 wrote: Tue Oct 04, 2022 2:49 pm Worried reluctor chamber drain tap at bottom not enough? With that drain, won't get a pool of coolant for the reluctor wheel to agitate and aerosolize? I suppose no pool is great step with drain tap. Your thought if we can get to no collateral damage from leak so no need to repair leaky seal. Even better.

Without knowing how and when the leak occurs. Kind of hard to judge what happens next. I was also curious about reluctor wheel chamber air circulation pattern while running. What happens when minute drop seeps out at say top of the seal during high speed forward rotation (seems like it could get aerosolized right away before getting to the drain), or slow speed reverse, or stationary parked. And if the minute leak sticks to the walls and not vacated by gravity right away during parking/reverse. What happens when reluctor wheel starts spinning up at high speeds with these small droplets on the walls? These thoughts were also motivated by.. just let it leak if no collateral damage (if possible)

I suppose more opening exposes the sealed hybrid bearing and excluder lip as well. But that lip might be making PTFE residue anyways?
Yeah, it probably won't form a puddle, but I do think it will be wet inside when the seal leaks.

I’ve had and tractor engine with a cylinder block rusted stuck because there was a little bit of water in the exhaust damper after standing still for a few days. During the day, the exhaust warmed faster than the cylinder block. Causing water to evaporate in the exhaust, travel through the exhaust and valves to condense in the cylinder block.

I wouldn’t be surprised if some moisture still manages to travel trough the stator.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Decided to look at what a basic water pump does to seal the coolant. The design seems quite a bit more sophisticated than a lipped PTFE seal.

https://www.agcoauto.com/content/news/p2_articleid/190

I'd imagine any cheap water pump seals surely have to handle at least 3-4k RPM for endured periods.

There are more advanced dry gas seals cartridges for industrial applications. But the principle seems similar just more advanced : 2 rings, mating ring fixed to the shaft and the primary ring to the stationary body that forms the sealing surface. Dry gas seals then pump gas between the ring gaps to maintain sealing properties.

https://www.pumpsandsystems.com/sealing ... omachinery

Should we be thinking about pressing on a water pump type seal cartridge where the current PTFE seal goes? Probably press water tight onto the shaft and maybe o-ringed case against the coolant neck seal sleeve? Also e-tron's seal looks a lot like 2 rings mating against each other. But of course that motor has a leak as well, just don't know much details on where. Maybe time to consult water pump seal design expertise?

Here is an example supply from a Japanese company to the water pump industry. Need more surface speed and not sure how one would fit it into our application. Also some basic background info on these type of seals

https://www.ekkeagle.com/en/product/mec ... ater-pumps
https://www.ekkeagle.com/en/technology/mechanical/

Fundamentally, assembling the sealing surface on high precision machines allows the seal designer to tightly control mechanical tolerances which leads to broader material choice, applying micro structures, and deploy more sealing techniques.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Yes, I mentioned water pump cartridge seals as being in use for automotive water pumps forever (upthread? one of the other threads?).

At one time, I had to rebuild a Hillman 1390cc water pump (see my avatar), around 40 years ago, and OEM parts were NLA even then. I sourced a cartridge ceramic face seal and re-faced the back of the impeller to fit. Fitted a new WP bearing cartridge (a separate unit).

I can only assume the ceramic face seals won't work with the RPM requirement of the rotor for some reason, but I don't have the engineering to know. Also, they take up a lot of axial space (for the tension spring and bellows).
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

asavage wrote: Wed Oct 05, 2022 8:03 pm Yes, I mentioned water pump cartridge seals as being in use for automotive water pumps forever (upthread? one of the other threads?).

At one time, I had to rebuild a Hillman 1390cc water pump (see my avatar), around 40 years ago, and OEM parts were NLA even then. I sourced a cartridge ceramic face seal and re-faced the back of the impeller to fit. Fitted a new WP bearing cartridge (a separate unit).

I can only assume the ceramic face seals won't work with the RPM requirement of the rotor for some reason, but I don't have the engineering to know. Also, they take up a lot of axial space (for the tension spring and bellows).
Cool, didn't catch your prior thoughts on this. A lot to read and learn. I seem to be the type that need multiple passes even with structured info much less internet scattered ones haha.

Trying to reach EKK's subsidiaries and talk to application engineering to point in the right direction. EKK (Japanese public company started 1965) seems to be in the "sealing" business with every kind of advanced sealing tech serving industry from auto water pumps all the way to high end industrial machines.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Back of the envelop design calculation on 2 ring water pump seals with Johan (CAD credit below) and arrived at... Audi e-tron seal haha.

There is only ~12mm of space for a seal. Maybe another 2-3mm if follow shaft contour and butt up against the reluctor. So it'd have to be thin.

1665008268298.png
2 ring water pump seals likes to be wide (or long along the shaft axis) because

- have 2 rings
- need a spring to apply pressure to the 2 ring's face to seal. Simple spring make the seal longer in the shaft axis direction

So need a special spring design where its really compressed. The then arrives at the e-tron seal design

Image

EKK has solutions for this application. Probably custom for OEM customers only. I guess we have to live with Flintstone seal haha.

https://www.ekkeagle.com/en/product/aut ... ic_vehicle



https://www.ekkeagle.com/en/technology/texturing

Could extend the shaft length by extending everything outwards but a lot of mods + still need to clear the wrap around subframe on Tesla.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by mjc506 »

I used to sell components for the heavy commercial and industrial refrigeration industry - massive surge vessels, valves, pumps etc for fairly nasty refrigerants like ammonia, R22 (before it was banned), Co2...

Valve spindles were sealed with two o-rings, a gap between them filled with refrigeration oil. Think thinking being that any leaking refrigerant had to push past the first o-ring, and also displace a volume of thick oil past the second o-ring. Very effective seal, and as a backup you have a valve cap over the top of the whole lot with a third o-ring - any leaks through the stem seal would become obvious as you undid the cap, exposing a hole drilled through the theads, which would make a whistling noise if any pressured gas would escape.

For higher pressures (over 40bar, for CO2) a different stem seal was needed(!) - two PTFE cones that fit inside each other, pressed together with a very strong spring, plus the pressure of the refrigerant (the spring was required for pressures below ambient). Again, the valve cap was a backup.

Despite sealing well enough that you couldn't smell ammonia through them, they weren't 100% effective (after several months, you'd still get a 'whistle' when removing the valve cap), and are of course entirely unsuitable for this application (only designed for very low turning speeds, and quite bulky)...

The pumps we sold were of two types. There was an 'open' type, where the pump and motor were separate. These needed shaft seals to seal against the refrigerant, and experienced quite high pressures. PTFE rings (similar to the waterpump layout about), springs, and actual fibrous 'packing', so an effective seal, but it was accepted that there would be some 'seepage' (similar to auto waterpumps - they all have a drain hole, and all say 'some seepage is normal').

There was of course a desire to develop a pump that was completely refrigerant tight so could be used inside buildings (you wouldn't want a pump that seeped ammonia inside the same building that stored your food... so 'traditional' solutions were to have a separate plant building and pipe the refrigerant around the site. Caused problems with insulation and energy loss, and everything was outdoors (and had to be well ventilated) so did deteriorate relatively quickly). The engineers spent years on testing different designs. Low speeds were easy, the PTFE cone design was good for up to around 100rpm, but much above that the sealing surfaces basically overheated at a very small scale - they would appear polished, but the material basically became porous through that fraction-millimeter layer (so it wasn't just a case of 'seeps while above xxx rpm', the seal would become degraded once the surface speed exceeded some threshold). The two-o-rings-with-oil-between design nearly worked (some refrigerant would get through the first o-ring, displacing a small volume of oil through the second, but became so diluted in the oil it was barely detectable) but needed frequent replacement, which then of course opened the system. I suspect it would be no good at all at the very high surface speeds experienced in the LDU - melty o-rings! These topped out around 3600rpm, and were usually ran slower.

In the end, the only way they managed it was to design a hermetic pump, where the shaft itself wasn't sealed, but the whole pump and motor were within a complete sealed case (which was disassembleable for maintenance, but static seals are relatively easy!). The pump was expensive, as the motor had to be custom made to cope with various refrigerants moving through it, and actually used the refrigerant to cool the rotor, stator and bearings. But it didn't leak refrigerant! Sold very well...

That's a lot of text to say I think you'll always get some seepage through any moving seal, it's just a case of finding a method of dealing with it to some workable level. The drains would hopefully help, but probably won't drain away single droplets (surface tension stronger than gravity). Hopefully a single droplet won't do any damage, and that'll be 'good enough'. Eventually that shaft seal will wear enough that it's letting through more than one droplet, at which points the drains will really start working and give time to notice and repair the problem. The only 'forever' solution I can think of is finding some coolant that won't hurt the rotor/stator/inverter and just flood the motor (or sealing the path between inverter and motor, and just flooding the motor) but this will be chemically difficult, and a rotor spinning in a liquid won't be as happy as one spinning in gas...

A possible alternative, however... Rather than trying to seal completely, why not try making it leak in the other direction? Pressurise the 'dry' side to some low amount about the coolant loop pressure, and the worst you'll have to do with is small bubbles in the coolant, which should eventually end up in a reservior (or more likely, just get absorbed into the coolant) This will require the motor/inverter to be air tight, and a 'vent' to be installed somewhere (probably near the seal), but that's probably less difficult than trying to keep that rotating seal perfect.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Incredibly informative @mjc506.

Your examples of 2-3x o-ring chambers and hermetic pump are interesting solutions. With more chamber(s) and space, more techniques can be used to vacate the escapees. Been thinking similar but LDU just don't have the space. Also been wondering why 3 lip LDU seal would work better than 1 if 2 dry lips are quickly worn without coolant hydrodynamic buffer during high RPM. Perhaps also benefitting from this multiple chamber concept in some way. As the chamber between lips get filled, can act as back pressure until chamber's pressure is lost by seeping through the dry side. In any case, there are 3 doors and 2 rooms to go through instead of a single door even if 2 doors don't work quite as well.

The increased porosity of seal surface above RPM limit is interesting. LDU seal failures rate seems directly proportional to time rather than mileage suggesting leak maybe occurring when the vehicle is mostly parked than many miles of rotation. We see vastly different mileage LDUs all leaking after about the same time period (what that time period is to initial inconsequential leak isn't clear, more aggressive monitoring just started. Tesla may have data but unpublished if they do).

Also been thinking air flow/pressure solution (air pressure gradient). Surface tension weeping when vehicle is parked offers a challenge so may need 24/7 active operation. Bearing and its seal performance need to be considered of course. Not sure temperature gradient offers any solutions. Media viscosity gradient may have potential. Don't know how can mount a grease line of defense after coolant seal lips. Can't just shooting thicker grease into reluctor chamber and clog the drain haha (and probably centrifugally spun to the edge anyways). Air moisture gradient would need to pump dehumidified air. Anyway, passive solutions are probably preferred over active for simplicity.

Looking at EKK's entire business line as a public company focused on "sealing" science. Seems quite clear sealing perfectly or even well is a challenge with low viscosity or even worse gaseous media. High viscosity media like oil would probably last longer. LDU would need more mods and operational testing.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by asavage »

Good story, MJC.

O-rings are limited to low shaft RPM (ft/min.) in most applications; they'll neither seal well nor wear well. Decent service life for low-movement assemblies.

---

Perhaps maintain a very slight vacuum on the entire cooling system? I wonder how leaky the system as a whole is, under a slight vacuum. I wonder if I have any decent small vacuum pumps left around here (besides my Vacu-Vin, which I won't sacrifice for Science).
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Pics of coolant seal lip from my cheap Aliexpress USB microscope. All pics similar magnification. Ignore the smudge in lower left corner (inside camera lens)

22 ID x 4mm CS O-Ring for reference

IMG_2845.jpeg
S20221006_009.jpg

Coolant seal lip (wet side)

2nd pic's dark black on the right side is the rubber suction cup used to stand up the seal for pic of sealing lip
IMG_2843.jpeg
S20221006_007.jpg
S20221006_003.jpeg
Looks like some pitting on the sealing lip.

Each "rib" pattern you see on the left is ~ 1mm. This PTFE hydrodynamic overview shows ribbed pump aid on the air side forcing escaped oil back under the lip.

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

Strange debris field in one spot along circumference of seal and shaft

Most of my shaft circumference looks like first pic. But one spot likes like 2nd pic where hazy cloudy part extends further (not just shiny metal lens effect). 3rd pic is just close up. The hazy cloudy pattern is on the wet side before the seal lip.
IMG_2817.jpeg
IMG_2819.jpeg
S20220920_004.jpg
My seal has a debris field on the wet side. Don't think its from me destructively removing the seal (can't be certain unfortunately) Maybe its the part of the seal that sat at the bottom of the sleeve collecting sediments? See diagram ( https://sites.google.com/view/teslaldu/failure-symptoms )
S20221006_001.jpg
S20221006_004.jpeg
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Have an observation from my seal and a potential theory on failure mode.

My seal's debris field is in 1 spot on the seal lip circumference (of course 1/3 of the seal is destroyed and missing), just behind the lip edge, on the seal surface and cage on the wet side. Here are the pics
IMG_2851.jpeg
S20221006_011.jpg
Have been suspecting failure mode is related to time rather than mileage for awhile from 3 data points

- QC Charge tech (Alex) indicated low mileage LDU fails just as much as high mileage LDU if not more. Nothing quantified but he sees a lot of LDUs w/coolant seal failure.

- In the small database sample we've collected, we have 6k mi/year (me) 10k mi/yr (wimV) and 20k+ mi/yr (Dimitri). me/wimV discovered leak at 4-5 year mark. wimV had triple lip seal so leak progression less than mine (single lip seal) Dimitri's car stopped in 3yr (Rev R, no speed sensor air eq hole so stator took all the coolant leak and isolation error)

- my MS does 6k mi/year and often not driven for multiple days at a stretch. Mostly parked and mostly short trips. I'm retired and mostly staying home fixing stuff haha.

If primary related to time, then most of the time the car is actually parked and not moving.

Debris field could be related to sediment when parked. And clearly debris is accumulating on the seal just beyond the lip's edge. The pattern on the lip and the cage doesn't appear to be an accidental smudge from oily gearbox disassembly (kept the seal in a drawer with all other small parts laid out individually)

Forensics suggest the destroyed part of the seal is facing downwards so debris field is ~12 o'clock. I don't know why not 6 o'clock? Or maybe my forensics is wrong. Would be good for future efforts to mark gravity vector and look for existence of debris field and orientation. One challenge is no easy way for non destructive removal. Perhaps tapping 2 bolt holes at 9 and 3 o'clock is best for inspection at 12 and 6 ( download/file.php?id=18842&mode=view ) cage is double layer metal sandwiching the PTFE seal.
IMG_2621.jpeg
I guess the logic is debris field near seal lip is not a good thing. Anyway, its an observation and a theory to be affirmed, modified or debunked :)
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by beastman »

Howard, are you thinking the debris are causing the seal failures at this point? It would seem that the triple lip might hold back some of the debris floating around the du, including the dirt and grease. even though i dont appear to have coolant failure, this grease is quite thick from the bearings and i would think this grease would prevent the seal from doing its job. Makes me think the drains once again would allow us to get contaminants out of the system and prevent those small pores on the seal from getting clogged and misshape the seal. maybe all we need is a way to clean or flush contaminants annuallly and clean the speed sensor too as it catches some grease... i very much appreciate your efforts on this and think drains are the solution w a detector as the triple lip just gives us some failure redundancy for a while. I still also believe that any high voltage transients may use the coolant seal path as a discharge point further electrolysing the coolant and possible damage to the lip over time since hybrid ceramic bearings are no longer going to be the preferred discharge path.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

beastman wrote: Sat Oct 08, 2022 5:50 pm even though i dont appear to have coolant failure, this grease is quite thick from the bearings and i would think this grease would prevent the seal from doing its job.
The reluctor chamber and speed sensor dirt and grease is on the dry side of the seal. Maybe it can affect the sealing. Don't really know. The debris observed on my seal lip is on the wet side.
beastman wrote: Sat Oct 08, 2022 5:50 pm are you thinking the debris are causing the seal failures at this point?
Debris theory is just a theory.. A lot of variables. @asavage was over yesterday to help getting a bearing out with general advice on various rebuild step methods. He also had a look at the seal under 10x loupe also. Here is a summary

- Certainly hard to be conclusive. Was the debris/smudge just from handling in a dirty environment? Don't really know. Didn't know had to be ultra careful for magnified inspection until much later.

- The bead of RTV under the seal cage was visible during destructive seal removal. Pulled up on it a little. Could have scraped the seal lip in the smudge area.

- When pulling off the coolant neck during disassembly, the seal will act as a squeegy to scrape off anything that is on the shaft while coming out

smudge/debris is just suspicious so leaving this observation out there for others to observe upon removing seal. Seal removal will have some level of destruction. Perhaps tap bolt holes at 9 and 3 o'clock is the gentlest for magnified inspection at 6 and 12 o'clock. Anyway, would be good to more carefully handle the seal for close up in the future.

Got higher magnifications from my cheap aliexpress microscope. Not sure what it tells us, just posting for reference

- cut a small piece of seal for better observation under microscope
- removed barrier on microscope preventing higher mag
- used external lighting for better imaging
IMG_2860.jpeg
Small O-Ring reference pic
S20221008_006.jpg
Seal lip contact surface with shaft (taken from dry side). Grids are 0.5mm
S20221008_004.jpg
Seal lip edge (taken from wet side)
S20221008_005.jpg
One note on lighting methodology. Microscope has a ring of LED lights so its harder to see depth using this lighting (and generally appears washed out). Using an external light source is directional so tends to look moonscape which give better sense of depth. Here is the same shot of seal lip in contact with shaft from the dry side in the 2 different lighting methodology
IMG_2861.jpeg
IMG_2862.jpeg
S20221008_007.jpg
S20221008_008.jpg
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Same shot from different angle external lights. Changes the picture quite a bit. Seal lip contact surface from dry side
IMG_2863.jpeg
S20221008_015.jpg
S20221008_016.jpg
S20221008_012.jpg
S20221008_013.jpg
S20221008_014.jpg
Tesla LDU rebuild website https://sites.google.com/view/teslaldu
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by beastman »

those last few pics looks like elecyrolyzed coolant to me. the minerals appear to make paths and lots of pitting like water spots. if you can get a good multimeter, you could test some spots for conductivity under the scope. the dry side vs wet side really tells a story. i would think an aegis ring may help prevent this as well as using non conductive coolant if we can get one that still works w some contaminants.
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

beastman wrote: Sat Oct 08, 2022 7:39 pm those last few pics looks like elecyrolyzed coolant to me. the minerals appear to make paths and lots of pitting like water spots. if you can get a good multimeter, you could test some spots for conductivity under the scope. the dry side vs wet side really tells a story. i would think an aegis ring may help prevent this as well as using non conductive coolant if we can get one that still works w some contaminants.
Unfortunately no control to do conductivity testing of this white coating of particles. But did find out the seal cage has a non conductive surface. But where ever it has scapes/damages, conductive beneath the surface.

Scraped off a tiny bit of this whitish coating (completely coats the wet side of the seal and cage surface. Ruler on the microscope base in mm and cm for reference. My 13 MS never had coolant changed. DU replaced 2x and last time in 17 (thought Tesla would flush the coolant then but now realize during LDU rebuild probably only small amount was refilled). My 11 Prius has 2 coolant circuits. ICE/tranny/electric motor circuit is 10 year 100k mi interval, inverter circuit is 150k interval.
IMG_2864.jpeg
S20221008_017.jpg
S20221008_018.jpg
S20221008_019.jpg
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2013 Model S85 3rd (Reman RevQ) LDU on 2017 @40k. Coolant seal leak discovered in 8/2022 @ 72k miles
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Re: Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

Post by howardc64 »

Coolant seal updates on suppliers, design, and choices

Supplier

Heard from a 2nd US manufacturer that have quoted this seal to Tesla in 18-19 time frame. Presumably Tesla and tiered suppliers are still trying to find a solution to the leak issue. Will be getting some design info (have single lip and a cartridge type design, NDA required) Buyer asked for hydrodynamic pump aid in the spec (see below)

Contacted Saint-Gobain's custom seal division in Southern California. Provided initial seal spec and application. Received an email reply after 2 days saying "after careful management review, can't bid on quote due to proprietary application" Maybe a hint they are OEM supplier but not much help to us if no aftermarket. If you want to contact without revealing Tesla application. Send email to GardenGroveQuoteTeam@saint-gobain.com but maybe they've been alert now. But they do have worldwide locations so maybe try your luck somewhere else.

Design handbook link here https://www.omniseal-solutions.com/comp ... -lip-seals (p16 series 71)
WW offices here https://www.omniseal-solutions.com/locations

Anyway, looks like coolant leak saga continues at Tesla with high volume of LDU replacements.

Current Single Lipped Seal in the LDU

The current removed single lip seal from mine/Johan's LDU shows the following

- 2+mm of smooth contact region on the lip where it mates to the shaft
- concentric cuts on the dry side. Seal manufacturer told me this is to help the hard PTFE material seal lip to bend.
- microscope inspection of seal lip AND cross section cuts shows embedded granules of additives blended into the PTFE material. I read these granules are softer than the shaft but harder than PTFE material so they wear against the shaft and become like standoffs to increase durability.
IMG_2885 (2).jpeg
Seal Design Info

Spent quite a bit of time learning about the coolant seal design from academia (seal text book, German univ seal lab papers) and manufacturer's published info (which usually list pros and no cons haha). Found many answers but also many additional unknowns.

Hydrodynamics

If the seal runs on the shaft surface dry, it will blister and fail (PTFE is more tolerant) This is why they tell you not to run the ICE water and power steering pump with the system dry. Its a must to have a thin film of fluid get in between the seal and shaft surface for lubrication.

This is achieved with asperities on the shaft (micron scale ridges). These score the seal with micron scale ridges where fluid flim gets in and shaft starts hydroplaning when it rotates. Imagine driving fast down a road with tires that lock in lubricants on its surface.

Then its important to create pressure towards the fluid side of the seal to constantly push fluid flim back towards the wet side. Method to create this pressure is called dynamic pumping aid.

Fluoro Rubber Seal (SKF HMS5 V and HMSA10 V - incl dust lip)

1. FKM material (standard's material abbreviation) Dupont trade marked it as Viton. There are multiple variations of FKM. No idea what SKF's FKM is.
2. Higher temperature resistance than NBR. BUT this is against hydrocarbons (eg oil). FKM's temperature resistance is much lower (100C) with highly polar molecule like water so not great for coolant application. This is noted in text book and also in SKF spec ( https://www.skf.com/binaries/pub12/Imag ... 318140.pdf )
3. Parker does claim to have a CR FKM (Coolant Resistant) with higher coolant temperature heat resistance. ( https://www.parker.com/literature/TechS ... G_5040.pdf )

The 2 SKF seals have the classical V shaped lip cross section where the angle on the dry side is shallower than the wet side. This cross section design has been around for multiple decades. The different angle along with elastomer compression and shaft asperities (tiny micron scale holes/grooves from surface prep) produces a pressure gradient towards to wet side. pg 106 of this link shows how this works

https://elib.uni-stuttgart.de/bitstream ... _Bauer.pdf

Highly elastic rubber provides great static (when shaft not turning) and dynamic (when shaft is turning) sealing property. Would have been a good choice except lower water thermal resistance. Static sealing is important. 12k miles/year @ avg of 30mph means the shaft spends 20x more time sitting idle than rotating.

PTFE seal lips

Much harder material than elastomers. Like plastic and therefore requires tighter fitting tolerances. Can handle high temps and inert to most chemicals including water/coolant. High temp tolerance is desirable with high surface speed generating high heat over the small lip shaft contact area. Here are some info I've been able to find

- Hard material lacking elasticity makes it harder to seal statically as compared to elastomers. Thus lips with 2+mm contact area probably desired for this reason. For reference, the V shaped elastomer lip contact area is ~0.25mm.
- A smooth lip will leak oil at 1mL/hr (30W oil, 120C, 10+m/s surface speed)
- Ceimin seal 3 lips are all smooth. (except for lathe cutting rings) 2 lips face wet side and 3rd is an dust/debris excluder facing the dry side. All manufacturers of this type of seal say the "backup" lip is there to increase sealing but no explanation how it works. I think likely back pressure. As the chamber between 2 lips fill up, there will be back pressure against leaking past the main lip in contact with coolant. So in a way, its a pumping aid. This is just my conjecture. There are no literature on this mechanism. There are more advanced mulit-lip PTFE seals for industrial applications including tapping the in between lip chambers to aid sealing somehow.
- smooth lip is best for static sealing. As noted above, its the most dominant scenario for auto use.
- there are decades old literature on helix pattern micro grooves on PTFE lips for unidirectional pumping aid. Also many recent attempts to include micro structures on sealing lips for bi-directional rotation pumping aid (this motor spins backwards for reverse. Furthermore, Rav4 EV's motor rotation is opposite of Tesla Model S for same car travel direction). Its not clear how practical these micro structures are for longevity due to wear and clogging (pumping aid can actually pump air back to the wet side and oxidize the media to form particulates to clog micro structures)

On mounting this hard seal material. Most seal and shaft mount onto the same block. This seal is press fitted onto a coolant manifold that is bolted onto the block the shaft mounts on. Careful manifold assembly to minimize eccentricity is probably desirable. Imagine the mounting precision challenge if the seal lips had micro machined patterns on them for pumping aid...

Diagram of SKF's triple lip PTFE (probably OEM only). Ceimin is very similar.

https://www.skf.com/binaries/pub12/Imag ... 459856.png

2 Choices. Both with strength and weakness

So SKF FKM seal or Ceimin triple lip seal? Quite the dilemma.

SKF FKM seal has all great properties except the low heat resistance to watered coolant as noted above. Have a speedi sleeve for pitted shafts or achieve a consistent machined surface asperity critical for hydrodynamics (no idea if waterless coolant helps... yet another variable.. need to evaluate how polar is the coolant molecule, consult SKM chemical sensitivity table)

Triple lipped PTFE seal is rumored to be better than single lip. Only source is Ceimin with 3 smooth lips (maybe more? see below). Leak control mechanism is unknown other than the guessed reason above. I'm planning to follow Johan's choice with Ceimin. Others (@Boxster EV) are using SKF FKM. If you have pitted shaft or not confident with shaft surface prep, then potentially need to follow @WinV's double speedi-sleeve effort ( viewtopic.php?p=46364#p46364 ) to achieve full surface coverage for the triple lip seal.

Ceimin seals comes with the risk of AliExpress transaction and questionable quality. 1 of 3 gearbox seal I received can't pass the naked eye QC inspection despite the attached signed QC paperwork so just for show. But no alternatives for 30x55 PTFE lipped seal at this time.

Other 30x55 PTFE seals besides Ceimin

Don't know how real these are. Don't have one in hand to inspect.

- https://www.athena.eu/en-us/oil-seal-wi ... P15357.htm
- PM-SEAL-0065A (pg 59, FTPE is presumed to be typo on PTFE) http://peachmarine.com/files/PeachMotorPartsCatalog.pdf

Still probing seal manufacturers for customs of course. Best bet is probably find ones already quoted Tesla and hopefully even prototyped. Then if confident with our seal midterm cramming knowledge, buy initial small manufacturing run. No way to pay for even a basic lab test ($10k?) So probably best keep it simple. Maybe just a high quality PTFE material triple plain lip seal with concentric bend assist grooves would be best. If can get a custom SKF speedi-sleeve with wider width (12? instead of 8mm?). Then we'd have a consistent precision assembly kit. Maybe someone in Europe would be interested to check with SKF on a custom speedi-sleeve.

References

Can provide gory details/links for all the literature. And much thanks to @Johan for his engineering rigor and comments. Don't have all the answers and many new questions appeared. Just putting it out here for reference and invite more knowledge.

Industrial vs Consumer application

Looking at the manufacturers large and small. They provide a specification template and willing to supply tiny volumes. Even big companies have custom seal efforts. Very clear they are supporting the industrial market where machines are operated for income producing activities and regularly disassembled for maintenance (bearings and seals must be a main maintenance activity). Some machine manufacturers have probably long stopped producing replacement parts or not even in business anymore requiring remanufacturing of the wearable part. Saint-Gobain even sell a seal that can be disassembled by customer just to change lips for "more cost effective maintenance". This is very different than the LDU application which is high volume consumer buried it for 100k miles application. Thus, all the leak sealing techniques need to be practically considered. A sealing solution lasting 500 hours before maintenance isn't very good for EV usage scenario (we'd probably be happy with even this now haha). A lot of literature and historical techniques seems to have been pioneered for the industrial machine market with its acceptable high maintenance levels.

Where is the Design Heading?

For consumer EVs, need tighter tolerance to use micro machining techniques to improve sealing characteristics. Evolution of the 2 ring seal seems to be the direction (e-tron, EKK). 2 ring's sealing face is perpendicular to the shaft, tension from a spring, and a more sealed cartridge structure. All high precision assembly is controlled at the seal factory and sealed rather than tight tolerance on final motor assembly. Too late for the LDU. Maybe the latest Tesla DUs are using EKK judging from this video

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

Post by asavage »

That EKK vid is fun. The seal's moveable face floats away from the fixed face at higher RPM to achieve frictionless sealing. Neat trick, and not at all how the legacy water pump seals I worked with 40 years ago worked; they had two smooth ceramic faces and AFAICT never separated, regardless of RPM.
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