Tesla P85D does sub 9 minute BTG run at Nurburgring

[Doug_G]

I reckon rotor cooling is the limiting factor. It seems (in my estimation) to be relatively easy to efficiently liquid cool the inverter IGBTs, motor windings and battery cells compared to cooling a spinning copper drum being heated by eddy currents inside a sealed metal oven.

I did read somewhere that the new drive unit has liquid cooling of the rotor; not sure if this is true, or if so how it is accomplished. Fluid could only enter through the shaft, whereas it's the copper outer that needs to be cooled.

I'm pretty sure the inner rotor is the biggest heat issue.

It's been posted on the forum that this is in fact true - coolant runs through the shaft. Still, it's gonna be hard to extract all that heat quickly. The Roadster's motor is the first to overheat on the track, so it's almost certainly true for the Model S as well. The big difference is that the Model S cools down much faster when you pull into the pits.

 

[Ingineer]

Keep in mind the rotor is made of copper and steel, and copper is one of the best thermal conductors. That's also what needs to stay cool, and since there aren't any other heat sensitive materials in there, I suspect a little coolant in the shaft goes a long way. They definitely couple it on the tail end. You can see this easily on the back of the motor if you look at any picture of the drive unit.

I would think the inverter is the most sensitive to heat. You don't want the IGBTs exceeding a 80C junction temp if you want them to be reliable.

 

[Doug_G]

Copper is an excellent heat conductor, but steel is not nearly as good, and only the wiring itself is copper.

From my experience with solid state sensor cooling systems, the bottleneck will be getting the heat from the windings into the water. From there it's a piece of cake.

 

[Ingineer]

The rotor is a copper "squirrel cage" surrounded by steel laminations. The copper in the rotor is what needs to be kept from getting too hot and melting.

In the stator, it's the copper motor windings that need to be kept from melting. Copper melts at at little over 1000C, so a delta of even half that should allow decent transfer from the rotor coils to the coolant.