Tesla on the Race Track

[bulls96]

Had this thought today.

I once owned a Camaro and was into muscle cars in general. If you look at the history of muscle cars, they built their reputation and "cred" on the Race track... Americans showing the world they can run with the Porsche 's and Ferraris of the world for less $$ with American ingenuity.

Why are we not seeing more Teslas on the Race tracks? That is one way to bring these cars to mass market, and build the reputation of Electric Cars the way Mustang and Canaria did for Muscle cars.

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[bwilson4web]

Why are we not seeing more Teslas on the Race tracks?

The Model S/X are showing up on the drag strips but after a couple of runs, they have to cool off.

The Model 3 has improved pack and motor cooling along with lower drag. It may not be a true track car although there are some modifiers who have made handling and performance improvements. Tesla has a 'track mode' that reports indicate will pre-chill the pack and motor.

The roadster is likely to be a serious track contender.

Bob Wilson

 

[bulls96]

The Model S/X are showing up on the drag strips but after a couple of runs, they have to cool off.

The Model 3 has improved pack and motor cooling along with lower drag. It may not be a true track car although there are some modifiers who have made handling and performance improvements. Tesla has a 'track mode' that reports indicate will pre-chill the pack and motor.

The roadster is likely to be a serious track contender.

Bob Wilson

Cool. That said, they have to put theme out there. [emoji106]

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[bwilson4web]

Cool. That said, they have to put them out there.

Now there is a gearing problem that has not yet been addressed. The Teslas have a fixed gear ratio but they run out of top end. To work on the track, the gearing needs to shift peak torque to higher speeds.

In an ideal world, a two speed transmission:

• 150 mph - current top speed
• +75 mph - second gear
• 225 mph - top end

However just changing the single gear ratio would work too. The initial acceleration would be reduced but at track speeds, the motor torque would be a distinct advantage. In a mixed gas-electric race, the EV would initially trail but at track speed, it would go from the back to behind the leader.

The other technical challenge is cooling. Ordinary gas cars dump their excess heat via exhaust and radiators but EV needs active cooling to keep them closer to ambient. One thought would be a hybrid turboexpander:
https://www.sciencedirect.com/science/article/pii/S1359431118304538

I would look at either CO{2} or NH{3} as the closed loop, refrigerant.

Bob Wilson

 

[Pushmi-Pullyu]

Now there is a gearing problem that has not yet been addressed. The Teslas have a fixed gear ratio but they run out of top end. To work on the track, the gearing needs to shift peak torque to higher speeds.

In an ideal world, a two speed transmission:

Long-time Tesla fans (like me) will remember Tesla's failure with a two-speed transmission in their first car, the 2008 Roadster. Tesla tried twice with transmissions from two different suppliers, but both failed to hold up under extended use from Tesla's high-torque motors. Tesla wound up making the first deliveries of its Roadster with the transmission locked into 2nd gear, with the promise (which was kept) of replacing those with the single-speed "drivetrain 1.5" when it went into production.

So it's understandable why Tesla would be quite leery of putting a two-speed transmission into its cars. If my understanding is correct, the next-generation (2020??) Roadster has only a single gear, also. If there is any Tesla car which is going to be engineered to perform well on a real racetrack, it's the next-gen Roadster.

That's not at all to say that a two-speed transmission is impossible, and in fact as I recall, the Formula E racers use... well, they started with a 5-speed transmission, but I think most of them are now down to 3 speeds. On the other hand, I don't know that those transmissions would stand up to extended use over time. After all, the systems on those race cars only have to last the length of a single race.

The other technical challenge is cooling. Ordinary gas cars dump their excess heat via exhaust and radiators but EV needs active cooling to keep them closer to ambient. [snippage of good stuff]

I would look at either CO{2} or NH{3} as the closed loop, refrigerant.

I'm going to disagree with you here, Bob. A gasmobile's ICEngine uses active cooling, too, with a water jacket surrounding the hottest parts of the engine, water pumps, and a radiator. That works on the same engineering principle as Tesla's battery/motor cooling system, which uses tubes to carry water/glycol coolant in loops circulating throughout the battery pack, one or more water pumps, and one or more radiators. Water is just about the ideal coolant for cooling gas engines and battery packs, with a high specific heat (the ability to absorb heat) as well as a very high heat of vaporization... meaning it absorbs a lot more heat when it turns to vapor.

It's true that GM's EVs have a more complex cooling system, with a heat exchanger which uses an air conditioner/refrigerant loop to "supercool" the water/glycol coolant circulating thru the battery pack. But is that complexity really necessary? Or is that just an indication that the rate of flow thru the tiny tubes in a GM battery cooling system is inadequate to handle the highest demand on the cooling system?

* * * * *

The pertinent limitations here are:

1. How fast heat can be transferred out of the core of the battery pack... and out of the inverter, and the motor. If a faster rate of transfer is needed, all that needs to happen is to improve the heat transfer rate. I note the Model 3 has improved its rate by using a larger number of shorter coolant loops. Other possible solutions would be to increase the size of the tubes carrying the coolant, or to increase the rate of flow, or to increase the size of the radiator... or more precisely, increase the surface area of the cooling fins in the radiator. In no case is using refrigerant needed. For both lower cost and lower energy use, a water/glycol system would be preferred. Using a refrigerant coolant loop takes much more energy. (A/C compressors are notorious energy hogs; water pumps use much, much less energy.)

2. The heat gradient across the battery pack. EV batteries work best when they are all at the same temperature. If I recall correctly, GM tries to keep its EV batteries all operating within a 2 degree range; no more than 2 degrees difference between the hottest parts of the battery pack and the coldest. I'm not sure about the tolerance in Tesla's packs, but I assume it's similar. Again, this limitation can be dealt with by ensuring that the cooling system is able to transfer heat out of the core of the pack at an adequately fast rate.

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[bwilson4web]

My back-of-the envelope speculation.

The challenge is the battery pack needs to be at ambient temperature, ~70F (21C). To dump the heat, there needs to be a temperature difference. Then the captured heat needs to be dumped to the ambient air.

IMHO, a cold plate of ~32F (0C) or lower would be able to handle the heat load from the battery/motor with a fairly small (i.e., light weight) heat exchanger. Yet the waste heat needs to be dumped on a track that can easily be at ~100F (38C) so the hot side of the refrigeration unit needs to be in the ~212F (100C) range. I've used water temperature ranges to simplify the math. There are optimum temperature differences that minimize the weight.

The biggest salvation is we're likely to see only 10% of the battery/motor power needing to be dumped. Better still, the car isn't (shouldn't) be sized too small but needs 'passing' surge power. Once passed, the car can revert to a lower 'cruise' power.

These are general terms and a math model really needs to be developed and validated. I suspect Tesla already has a model and metrics from their existing cars. Then there are the e-racers and Formula E.


FYI, a dedicated race car could use superconductors and compete in longer distance races.

Bob Wilson

 

[Pushmi-Pullyu]

The challenge is the battery pack needs to be at ambient temperature, ~70F (21C). To dump the heat, there needs to be a temperature difference. Then the captured heat needs to be dumped to the ambient air.

Well now that's a very pertinent point, and one I had not considered. If the ambient air temperature is significantly above 70°F, then a normal radiator isn't going to be able to cool the coolant sufficiently. So there is a case to be made for including a refrigerant in the cooling system. However, I think the best way to do that would be what GM has done, by using water/glycol as the main coolant but having a heat exchanger to allow a refrigerant cooling loop to lower the temperature of the water/glycol coolant.

Using a refrigerant as your main coolant would be horrendously wasteful of energy, which is why I'm pretty sure that no plug-in EV is built that way.

FYI, a dedicated race car could use superconductors and compete in longer distance races.

So far as I know, superconductor material is still quite expensive, and still requires cryogenic cooling to function properly. There would be quite a weight, space, and energy penalty to using a cryogenic cooling system in a race car. (Mr. Google does find references to "cryo spray cooling" in a drag racer, but that would be using something like liquid nitrogen stored offboard and merely added to the car very shortly before the race. It wouldn't involve an onboard cryogenic cooling system.)

Is there any product in mass production that uses superconductors? Yeah, I realize that dedicated race cars are not mass produced, but I'd be interested to know if superconductors are being manufactured in sufficient quantity to use them in any mass produced product.

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