Improve cooling of drivetrain

Interesting. What needs cooling? The battery, the inverter or the AC motor?

L@urens said:

Interesting. What needs cooling? The battery, the inverter or the AC motor?

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Yes.

skills said:

Cant seem to find any EDIT button here?

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Some functions only appear when you've become an established member. As a new member there's a time lag on your posts appearing (part of our anti-spam measures) so there's a tendency for new members to duplicate post, I deleted one of your duplicates but don't worry about it. Keep posting and you'll be approved soon enough.

If I remember correctly the track experiences reported by others, there are two main limitations at work. First, the rotor of the electric motor is really hard to cool. Tesla has some secret sauce there, e.g. an oil loop running thru the axis. Second, the power output is limited as soon as the remaining range falls below a certain threshold e.g. 30 miles. It is easy to approach 30 miles of RR while lapping the car with a nearly full battery.

VolkerP said:

. Second, the power output is limited as soon as the remaining range falls below a certain threshold e.g. 30 miles. It is easy to approach 30 miles of RR while lapping the car with a nearly full battery.

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That theory was disproven.

Based on others experience with the roadster, collective wisdom points to the motor (esp the rotor) getting hot.

Someone suggested (sorry I forget your forum name) using a CO2 cooling system.....

I theorize that turning off regen would help with this issue on the track.
Use only friction brakes to slow so that you aren't wasting cooling capacity on removing the heat from regen.
Unfortunately you can only turn regen to low- not off.

The rotor is the weak link. The liquid cooling system does a fairly good job of managing the battery and inverter temperatures. The motor has a liquid cooling jacket around it, but the rotor itself is air cooled.

It's very difficult to transfer heat away from the rotor without introducing drag. Hydrogen or helium gas is used to cool rotors in industrial motors, but would be an expensive mod for a Model S.

I agree setting regen to low will help a bit by reducing power demands on the motor.

richkae said:

I theorize that turning off regen would help with this issue on the track.
Use only friction brakes to slow so that you aren't wasting cooling capacity on removing the heat from regen.
Unfortunately you can only turn regen to low- not off.

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I've explored with this theory somewhat. For most of my car's life, it's been on Standard. For two days thus far I've had it on Low. It didn't seem to help much with the acceleration limiting under "high load".

What's "high load"? Averaging > 1000 Wh/mi for 20 minutes.


And yes, 160 kW acceleration is torturously slow for a car that normally offers 320+ kW.

When Isaw the discussion here turning to the rotor I thought I had heard/seen that the rotor was actively cooled along with the the rest of the drivetrain. VolkerP mentions similar (although I don't think it's oil, but rather coolant).

In any case, I didn't have time to do any digging until now... here's the Tesla Patent describing the cooled rotor assembly.

Also the picture below from THIS THREAD shows the hollow rotor, which would allow coolant flow:


So... while this doesn't necessarily mean that the motor isn't the most significant factor in the drivetrain limiting power output over time due to heat buildup (and I suspect it or the inverter may be), it does indicate Tesla is doing more than just cooling the outer motor housing...

Has anyone investigated heat buildup in the motor area? Given the entire assembly (pictured in skills' first attachment) essentially sits under the superficial rear seats, I wonder if there might be some benefit to removing them for track days.

Certainly improvements to the liquid cooling system would probably be more effective, but that's not as easy as pulling out the seats. Plus, weight loss helps!

If the weakness is the rotor, though, reducing the ambient temperature probably won't have a huge impact.

haha, I'm so lazy I'm lucky if I remove the child seats for an evening at the track.

However, maybe next time I'll look into pulling the seat out and setting the AC to low.

Gizmotoy said:

Has anyone investigated heat buildup in the motor area? Given the entire assembly (pictured in skills' first attachment) essentially sits under the superficial rear seats, I wonder if there might be some benefit to removing them for track days.

Certainly improvements to the liquid cooling system would probably be more effective, but that's not as easy as pulling out the seats. Plus, weight loss helps!

If the weakness is the rotor, though, reducing the ambient temperature probably won't have a huge impact.

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brianman said:

I've explored with this theory somewhat. For most of my car's life, it's been on Standard. For two days thus far I've had it on Low. It didn't seem to help much with the acceleration limiting under "high load".

What's "high load"? Averaging > 1000 Wh/mi for 20 minutes.


And yes, 160 kW acceleration is torturously slow for a car that normally offers 320+ kW.

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I'm talking about a racetrack scenario where you are spending lots of your time either full throttle or full braking.
Under full throttle you are pushing 320kW through the motor and generating heat.
Under regen braking you are pulling 60kW through the motor and generating heat.
Back of the napkin - if you alternated accelerating 0-100-0 over and over again without friction braking, I would expect turning off regen to reduce the amount of heat generated by 50% ( you've got to slow the same mass, it just takes longer )
But if you add heavy friction braking you will slow a lot faster - since friction braking is much much stronger than the regen, regen may only contribute a tiny amount of heat. So eliminating regen might remove something in the ballpark of 5-10% of the heat endured by the drivetrain to do the 0-100-0 when using friction braking - depending on how hard you use the brakes.

You'd need to do some careful measuring on the racetrack to see if you get a slightly longer time on the track before your drivetrain became power limited due to heat. I don't think it would be perceptible without measuring down to the second.

scaesare said:

When Isaw the discussion here turning to the rotor I thought I had heard/seen that the rotor was actively cooled along with the the rest of the drivetrain. VolkerP mentions similar (although I don't think it's oil, but rather coolant).

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I haven't seen any solid evidence that Tesla is using the patent in production, the hollow rotor could simply a weight saving feature. It's not easy to pump fluid through a shaft spinning at 14,000 rpm!

skills said:

Thanks for the input guys! Now we are going somewhere i think my next move will be pulling the nosecone, and see if i can buy another one to open up and give more air to the drivetrain radiator.

Talked to two of my friends that are mechanics at the local tesla store, and they say that the code is almost impossible to get hold of. Changes every day, and unique to each VIN.

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Why not get a few temperature sensors and run them to a data logging box and gather some data?
Try to find the coolant lines and put a sensor on the motor, and on the coolant lines into and out of the motor, and into and out of the radiator.