When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
hm that is very interesting, transmission is sealed off from the motor no? or motor housing acts as the other side of the transmission case? so your transmission was overfilled then with mix of gear fluid and coolant, was it making any kind of noises?
I think these motors get hot under load (100 C +) - lot of power going through them so air cooling might be non-starter...
I'm not planning, or thinking about air cooling the entire motor. Just the rotor. I can't find any other EV motor on the planet that uses through rotor cooling. So unless this motor in particular is incredibly inefficient I question its usefulness.
For reference, Audi considers rotor temp so unimportant the motor coolant temperature sensor is upstream of it.
And hopefully this diagram helps explain where the coolant leaks from, and where it goes
So the one thing this diagram doesn't capture is the two leak paths (red arrows) are connected to eachother, not isolated like this diagram will lead you to believe.
There is no meaningful seal between that driveshaft going through the motor and the internals of the transmission, They did a few things to prevent trans fluid from escaping down the shaft but nothing that would hold back water intrusion if things started leaking.
My plan is the following
Design a new rotor cover that will use conventional high RPM seals (bit in pink) and pump oil into that sealed void cooling the rotor and dumping oil into the transmission. pass it through a small heat exchanger and jobs done. I'll have increased fluid in the trans which is good for its lifetime, and probably better rotor cooling than it had before.
The biggest challenge to this will be machining a part with a tight enough concentricity to not damage the seal. Which is a benefit to the pool pump seals Audi was using, things don't have to be perfectly concentric to work. big cost reduction.
Originally Posted by Tronification
Would you say there's anything in this design that is (more) prone to failure due to prolonged running time? Both of mine failed during or right after long drives and I've been wondering whether having less frequent cool-downs can somehow induce failure. I would think there should not be much in the way of temperature variation, with the coolant running past these seals.
Do you know what exactly is failing? Is it the rubber ring or the ceramic-to-graphite interface? I would think there's no way there would not be some seepage between those two surfaces and over time a bit of build-up would develop, destroying the seal.
I'm not sure whats leading to the seal failure. I'm an Automotive engineer but i don't specialize in sealing things (and neither does Audi to be fair)
I'd hypothesize that debris that normally shows up in the coolant system as time goes by is getting caught between the two ceramic/graphite faces and tearing things up.
The transmission cooling loop sounds fun, but bench validating the seal system, plumbing in a pump and heat exchanger into the back of the car seems like alot of work.
So we're going to let the rotor think about what it's done and self soothe.
I will be jamming a thermocouple all up in the rotors business to see what temps it's hitting and will revisit the oil cooling if I don't like what I see. But for now I've either got the most reliable Etron motor on the planet, or the least reliable Etron motor on the planet.
Reinstall later this week, and straight into a 120 degree summer trial by fire.
if the operating motor temperatures are what your motor cross-section diagram shows/audi measured and what necessitated the need for cooling in the first place then this might be very short experiment. If I am not mistaken, we could monitor motor temps via obd reader - there are motor temperature sensors already in each motor - see page 25 MC-10155750-9999.pdf (nhtsa.gov)
but they also say this: Electric drive cooling system Front axle Rear axle The electric drive motors for the front and rear axles are cooled by a low-temperature cooling fluid circuit. The coolant stream flows through both the stator and the rotor. The additional internal rotor cooling has significant benefits in terms of continuous power output and reproducible peak output. The complete coolant circuit was moved into the electric drive motor to facilitate service work.
so you might be able to get away with it as long as you don't use full power repeatedly
Last edited by nadrealista; 04-17-2024 at 09:48 AM.
if the operating motor temperatures are what your motor cross-section diagram shows/audi measured and what necessitated the need for cooling in the first place then this might be very short experiment. If I am not mistaken, we could monitor motor temps via obd reader - there are motor temperature sensors already in each motor - see page 25 MC-10155750-9999.pdf (nhtsa.gov)
but they also say this: Electric drive cooling system Front axle Rear axle The electric drive motors for the front and rear axles are cooled by a low-temperature cooling fluid circuit. The coolant stream flows through both the stator and the rotor. The additional internal rotor cooling has significant benefits in terms of continuous power output and reproducible peak output. The complete coolant circuit was moved into the electric drive motor to facilitate service work.
so you might be able to get away with it as long as you don't use full power repeatedly
that's the hope. I don't tow with my Etron anymore so I just need enough power to cruise the highway and perform passing maneuvers without fuss.
If I start observing rotor temps in excess of ~120C from my own sensors during normal driving I'll be back in to do the annoying work of making a proper cooling circuit.
Things went together great! rotor temps were about ~160F after 45 miles at highway speeds. (thermocouple is what's sticking out)
and then disaster. HV isolation fault. Gonna pull the motor back apart, completely this time and see if there's anything obvious wrong.
and then for good measure the tow truck driver decided to put his hook through my rear air suspension. Or he pulled the car so tight something popped. Delightful.
04-06-2024, 02:38 PM
