Tesla Large Drive Unit (LDU) Motor Teardown and maintenance

[howardc64]

DELETED

[LunaticScientist]

- Larger diameter = higher surface speeds. 40mm over 30mm at 10k RPM is +5m/s (40mm = 20.9m/s 30mm = 15.7m/s) so there will be more frictional heat.

True, but have found several seal MFG that quote 40 m/s on dry lube PTFE within spec. Pushing to 40mm diameter @18k RPM puts as at 37.7 m/s surface speed.



A thermal paste would certainly help, but with the thermal diffusivity being 5x higher than 1045 steel (68 mm2/s for 6061 vs. 14 mm2/s for ASM 1045) and a surface area of 550mm2 (using a 40mm OD) on the wet side alone, conductivity to the shaft would be negligible compared to the face of the adapter ring. RTV would only be used to seal the potentially imperfect mating between the shaft and adapter ring.



Agreed, but much easier than complete disassembly for shaft reconditioning, metal deposition, or future tear-down like rotor or bearing replacement.

I haven't reached out to these guys yet, but it seems like their ATA/ATB lip seals would fit the bill, even potentially for OE shaft dims?

https://usseal.com/lip-shaft-seals/

Have we considered applying a high-temp silicone-ceramic lubricant between the multi-lip designs to aid in lubrication?

[howardc64]

DELETED

[LunaticScientist]

I've contacted US Seal with a design envelope and application information (without being 100% explicit to avoid potential CoI).

I also tore-down my 50k mile donor for my project. RevE (non-reman) had the triple seal, no inverter wetness and maybe a drop or two by the encoder. Blue G48 coolant.

There was heavy deposition on the shaft and black gunk buildup between the seal lips. I suspect maybe incorrect surface finish during installation or excessive lip pressure (incorrect ID spec)? Cannot confirm why, but it's hard to keep dry seals sealed...

[howardc64]

DELETED

[howardc64]

DELETED

[LunaticScientist]

Serial is T13, so 2013.

I haven't been able to clean up the shaft yet and my picture doesn't convey the thickness of the build up of the PTFE on the shaft.

It almost seems like the bond between the seal and seal body failed vs. wetness on the shaft or corrosion at the encoder. Have we seen any other failure modes before the seal gets destroyed during removal?

I'm curious if a solution might be an FKM or other flouro-compound, greased between the sealing lip and excluder, to be able to run sustained 10K or short-term 18k vs. 100% duty cycle 18k RPM. The thermal dissipation should be good as even 1045 is decent at conductivity, but thin walled and backed with moving coolant. Or, perhaps, too much thermal transfer into the steel-faced seal and causes expansion/excessive movement of the seal...

Tesla LDU Album

[howardc64]

DELETED

[WimV]

One would think no as its the same PTFE lip material and the lips has more energized pressure against the shaft from the very beginning. This makes cause of @WimV's shaft damage all that much more mysterious.

This was a rebuild DU, I wouldn't be surprized if the shaft had wear before the rebuild...

[howardc64]

DELETED

[LunaticScientist]

Shaft cleanup will happen later today, we'll see what it looks like.

I was able to pick some residue off the seal lips to reveal which looks like virgin material. Gray and black flakes, similar to graphite-impregnated material. But the lips are STIFF. Which I could see definitely being an issue as they age, imperfect seal, and stationary with hot coolant and higher pressure differential.

I've also reached out to AHP, who has a single lip, PTFE-lined, energizer-backed seal, rated for 35m/s and high pressure, who wanted more information (like production quantity, life cycle, etc), so maybe another option?

[howardc64]

DELETED

[LunaticScientist]

@dzolotnyuk bought the following from AHP. viewtopic.php?p=46191#p46191. Failed quickly with speedi-sleeve. Actually I don't understand the design of AHP's SB20 seal, its a classic asymmetric angle V shaped seal which relies on compression on v tip to provide pumping aid. Elastomers such as NBR and FKM is suitable for this compression. A completely PTFE seal is too hard and will prevents compression. So the design doesn't make sense to me.

PTFE "lined" seal with same design isn't the same. The thin PTFE lining should deform with the base seal material (NBR, FKM).

I saw that and wondered if that would be the best design for pure-PTFE designs... I was looking at the RB-series https://ahpseals.com/product/asrb/ with the PTFE-lined but flexible base with energizer.

Or even a single band PTFE seal. The multi-band seems to be problematic (with trapping wear particles between bands). I cleared out the area between the rings and pulled a ton of black gunk (likely a combination of PTFE dust and coolant), which I'm sure doesn't contribute to cooling nor flexibility. I also noticed quite a bit of lip deterioration on the second media lip. Odd that it doesn't match the primary lip's wear pattern.



The shaft was also pitted under the primary and excluder seals. Actual grooving at the second lip location, so I'm wondering if a speedi-sleeve might be a better option to restore surface finish (especially if AHP is requiring Ra 8-16 uin for PTFE materials) and maintain bore. I know it did not have high success in the last attempt, but that was with an OE style seal. Or, given the 0.020 in. tolerance the energizer allows, a slight bore reduction from a grind/polish job may be negligible.



I've added more pics too to the Google Album (Tesla LDU Album

[howardc64]

DELETED

[LunaticScientist]

Thats basically a PTFE lined seal on NBR or FKM. Good option for those that wants to try that.

Pics shows the pitted shaft surface has already been sleeved. Was that a prior DIY rebuild? If so, what sleeve was used and is any material hardness info known?

Mine has not been rebuilt, as far as I can tell. No sleeve installed (although the tool marks on the interior of the rotor shaft are interesting....

Reading some various literature on PTFE seals, it looks like the preferred surface finish is Ra 0.2-0.6 um(micron). However, it seems to widely vary on how that finish is best achieved. P600 paper? 1000 grit AlO2 paper? Medium polish #2? Electropolishing?

Regardless, refinishing the shaft surface without complete disassembly seems daunting, but could be doable. I imagine a lathe bar-type setup could be used to true and turn the rotor shaft (team it with a shop-vac to minimize debris) for more extreme cases. A Dremel with a polishing wheel would likely still fit (thinking of these "repair in place" people).

[howardc64]

DELETED

[WimV]

By the way: I’ve checked the speed sensor after driving 400 km with the new seal (Ceimin CTLBDYW). Well, that wasn’t what I hoped. There was condensation on the sensor. The drain was still dry (was plugged, so I would know how much it leaked). I collected about one drop of coolant when using some compressed air to flush the reluctor chamber.

I don’t think the speedi sleeves are usable with PTFE seals. I think the seal is stretched too much cause of the increase in diameter.

I’m going to keep driving for a while and keep checking the leak. If it get worse, I’ll pull the rotor to get it welded and grinded to the correct diameter and try with a new seal.

Just did another check after 4.000 km. There was a drop or two collected in the drain tube (flushed the reluctor housing with compressed air). A little bit of small droplets on the sensor. I would say it doesn't leak more than the first 400 km.

I dried the reluctor housing with compressed air and will check again in the future.

[howardc64]

DELETED

[howardc64]

DELETED

[Johan]

Here's my rotor shaft end measurement in millimeters (sorry British people and their colonies, no inches today). The resulting chamfer angle is ~9°, based on two measured diameters plus the shown 1.5mm chamfer length in axial direction. Of course maybe I made a measurement mistake. Could someone repeat this? Also note, to make things more fun, that there could be different revisions and different numbers due to (my guess) "quality control issues". You could stick a smooth plastic pipe of 30mm outer diameter in the seal until just before final assembly to try to reduce damage.

[asavage]

Opinion from what I've read thus far, regarding the triple-lip PTFE seal . . .

I feel that the excluder lip is non-funtional: it doesn't do anything, doesn't add any value. It's not designed to seal anything smaller than a threshold that is much larger than liquid, its place is to exclude larger particles than we need to be concerned with in this cooling system.

The non-wetted lip on the other end of the triple-lip seal is also useless: the pics you've shown of examples removed from service show a non-functional seal (gunk, wear, overheat, whatever). I think it has a place in a proper application, but not this one.

A single-lip PTFE seal will have sufficient heat transfer via the coolant, so thermal transfer properties of sleeves can be ignored for a single lip.

In fitting Teflon (PTFE) seals, it has been common practice to use a resizing tool during installation (random link for such a toolset). From memory, and from the handful of times I've had to handle and install Teflon seals, using the resizing tool to maintain a temporary larger diameter whilst installing is preferred, but it's also possible to use the tool and then rapidly remove it and perform the assembly, without the tool in place -- which would be necessary for our LDUs.

Below is a representation of the type of tool I'm thinking would be appropriate to reduce single-lip PTFE seal damage during assembly.

Tesla Teflon Seal Resizing/Installation Tool 02

I'm not aware of a cone install tool of these dimensions being available off-the-shelf -- and I'm not convinced the dimensions I've picked are ones I'd settle on -- but it would certainly be easy to fabricate. Certainly for less than $200 for a prototype, probably less then $100 ea. for qty. (50) or so (rough guess using eMachineshop for fab and based on a lot of stuff I've had them prototype for me over the past 16 years). A local facility could possibly be more cost effective, as EM typically has a cost-effecdtive place for only a small range of quantities.

Temporarily changing (deforming) the seal lip reduces reliance on chamfer angle and surface finish during installation.

[howardc64]

DELETED

[Boxster EV]

This will be a quick write-up and update, but Howard kindly sent me a PTFE lined rubber seal (over steel frame). It's made by a company called Peach Motor Parts in the US. I understand its application is for Snowmobiles but it almost has the required dimensions of the Tesla OE seal, albeit with a large unwanted outer lip.

The critical feature is the PTFE lined characteristic which I'm hoping will play nicely with the SKF Speedi sleave installed in my LDU.

Here's the lip preventing it from fitting in the manifold

Even when incorrectly installed in the opposite direction, it wont fit flush

However the frame of the seal is made from steel so I carefully removed the outer lip, seemingly without compromising the rigidity of the frame

Decent quality gasket maker placed around the edge

The seal can then be carefully pressed into the enclosure.

I'm waiting on some translucent plastic pipe to improve my manifold drain set-up and then I'll place this back in the car for testing.


Edit 20th January 2023: I am yet to fit this seal to the car. The reason is explained in my edited post here:

viewtopic.php?p=49499#p49499

[howardc64]

DELETED

[howardc64]

DELETED