Model S motor

[Mycroft]

Every time I see that magic drive train, my heart beats faster. A true work of art, both aesthetically and technologically!

 

[qwk]

Thanks for the pic.

Yes, you could remove the rotor that way, but what about the stator/case?

From the pic you posted, it looks like both motor bearings are lubricated by gear oil from the differential.

 

[NigelM]

For some reason I cannot imbed the pic in the link.

This one?

 

[Tommy]

Thanks for the pic.

Yes, you could remove the rotor that way, but what about the stator/case?

From the pic you posted, it looks like both motor bearings are lubricated by gear oil from the differential.

Just a guess from my experience with ICE alternators, starters, the stator/case case might be the equivalent of the "core" to these ICE parts. In other words, failure rate is extremely low as the part itself is stationary and therefore not prone to wear.

 

[neroden]

While looking at the pics of the drivetrain from the skateboard mule, I have noticed something interesting. The Model S motor case seems to be integrated(welded) onto the differential case. That can't be a very service friendly proposition, as you would almost certainly need to disassemble the differential to do any work on the motor. I wonder if the production motor would be the same setup?

Does anyone ever have to service the motor?!? To be more specific, I would expect the motor to need servicing about as often as the differential (a very long interval), so I don't see this as an issue.

Another thing I noticed from the very first pic in this thread of the Model S motor is, Tesla seems to be using a front motor bearing that is oil lubricated by the differential oil. Not that that is a very bad thing, but don't sealed motor bearings have much longer longevity?

That is an interesting question, because yes, I believe sealed motor bearings have longer longevity. I wonder if this is related to cooling.

I wonder if these are cost cutting measures?
Discuss.

 

[TEG]

Every time I see that magic drive train, my heart beats faster. A true work of art, both aesthetically and technologically!

What he said... (+1)

 

[ElSupreme]

That is an interesting question, because yes, I believe sealed motor bearings have longer longevity. I wonder if this is related to cooling.

It does look like it is sharing lubrication. I would imagine it is for cooling. That is all I can think of. The motor will have sustained speeds much higher than standard motors. And automotive duty is probably worse than pretty much but marine duty, and some chemical applications. Plus even with that fluid line the bearing could still be equally 'sealed' as I doubt the differential fluid is open to atmosphere.

 

[qwk]

Does anyone ever have to service the motor?!? To be more specific, I would expect the motor to need servicing about as often as the differential (a very long interval), so I don't see this as an issue.

It usually isn't an issue, but sharing fluid with the differential has two downsides.

1- metal flakes from the gears can contaminate the bearings that otherwise would not be able to be contaminated.

2- a leaky seal in the differential not only can take the differential out if ran low on fluid, but the motor bearings also.

These above issues usually don't become a concern until higher mileage, so everything would be out of warranty by then.

 

[JRP3]

Think about this, sealed wheel bearings usually need changing more often than oil lubed differential bearings, which are usually good for the life of the vehicle, and beyond. Also, some differential housings have a small magnet embedded in the bottom of the housing, trapping small gear particles.

 

[doug]

Tesla seems to be using a front motor bearing that is oil lubricated by the differential oil.

... it looks like both motor bearings are lubricated by gear oil from the differential.

Could you describe what specifically gives you that impression?

 

[qwk]

Could you describe what specifically gives you that impression?

If you look at the pic of the motor input shaft, the front bearing is of the oil lubricated variety(you can visually see the ball bearings).

In the skateboard model s pic,there is a gear-lube line going from the diff to the rear motor bearing.

Now don't get me wrong, high quality lubed bearings can and do last a couple hundred thousand miles, but there are many reasons why sealed bearings are better for an electric motor application.

The only reason I think Tesla went with lubricated bearings is cost. I would bet that a high rpm, high quality sealed bearing is substantially more than a lubed one.

 

[Lloyd]

If you look at the pic of the motor input shaft, the front bearing is of the oil lubricated variety(you can visually see the ball bearings).

In the skateboard model s pic,there is a gear-lube line going from the diff to the rear motor bearing.

Now don't get me wrong, high quality lubed bearings can and do last a couple hundred thousand miles, but there are many reasons why sealed bearings are better for an electric motor application.

The only reason I think Tesla went with lubricated bearings is cost. I would bet that a high rpm, high quality sealed bearing is substantially more than a lubed one.

Cooling also!

 

[qwk]

The model s motor is already water cooled.

 

[Doug_G]

The model s motor is already water cooled.

Yes, but you can't run water through the bearing to cool it. It needs to be lubricant.

 

[doug]

In the skateboard model s pic,there is a gear-lube line going from the diff to the rear motor bearing.

I assume you mean the thin metal tube with the Swagelok like fittings. I was told that's a coolant line.

Coolant enters from this hose nozzle (viewed from below) on the motor side.


It flows through the motor casing, but some amount (~10% ??) is split off through that tube to cool the diff oil.

Coolant somehow flows through the inverter and exits from this nozzle on the other side of the diff.

At least that's how I understand it. Would be nice to know the flow path inside that casing.


I guess it's still an open question on whether or not the rotor is liquid cooled. This image of the Alpha drivetrain shows the coolant inlet right near the rotor.

Tesla Model S Development Facility Photo Gallery - Autoblog

The black hose it teed upstream with the blue one that goes to the diff.

 

[qwk]

I guess that is possible. I wonder why they have that coolant line going through what looks like the differential case? There are very few differential or transmissions that are liquid cooled, and those are used primarily in sustained high speed applications. An EV is clearly not going to be sustaining high speeds for any length of time.

Ford used motor bearings cooled by gear oil in the EV ranger. Here are some pics of the rotor/bearings( forgive me for not embedding the pics, as I cannot seem to get them to work from my phone).

The Electric Passat

 

[richkae]

Maybe its one of these two things:
1) They have the coolant right there anyway, so why not cool the diff.
2) A bunch of metal components bolted together, cooling one and not the other might cause stresses from the different temperatures and expansion rates.

 

[Mycroft]

Ack! More drive train porn! Youse guys are killin' me! :scared:

 

[doug]

Maybe its one of these two things:
1) They have the coolant right there anyway, so why not cool the diff.
2) A bunch of metal components bolted together, cooling one and not the other might cause stresses from the different temperatures and expansion rates.

I was told 1, no mention of 2.

 

[doug]

If you look at the pic of the motor input shaft, the front bearing is of the oil lubricated variety(you can visually see the ball bearings).

That's a good observation, though it might just be for display. I assume you mean the image above. When I asked JB about rotor cooling back in 2009 he did mention the bearings as a possible path to get heat out.

This photo of the motor in an Alpha shows some mystery orange hose connecting the diff to itself.