[Yaggo]

That does not make sense. Electric cars don't really have a concept of neutral, because they have no gears or clutch (with few exceptions, such as two-gear Taycan). Yes, the "gear selector" has N as well, but that's just software trick (like all R/N/D "gears") which lets the car to roll when you lift your foot from power pedal, instead of applying regenerative braking.

If the car detects a problem in power supply circuit, it's perfectly rationale action to engage the electric parking brake as "last wish" when the car has stopped, because there are no other mechanism to prevent the car from rolling. In most cases that's the safest option, because freely rolling car is very dangerous.

A side note: Tesla has a sort-of reduntant 12V power supply, because it has a traditional 12V battery and also a 12V DC-DC converter from the high-voltage battery pack. So in theory you can lose either of those and still safely drive the car to a stop. But there can also be a problem with the 12V circuitry itself, e.g. in chassis grounding, which can cause all kind of weird problems and even total failure. This is not an unheard problem especially among older Model S cars such the one in the picture.

[pengaru]

> because freely rolling car is very dangerous

Practically every single car has a freely rolling mode the operator can easily select, despite being, according to you, "very dangerous".

For an EV like a Tesla neutral would be just not energizing the motor and letting it turn freely. There are hydraulic brakes on the car, are there not? These should always be available, even when non-boosted it's just a matter of standing on the pedal. Most vehicles in addition to this have a mechanical "emergency" or "parking" brake for actuating the rear calipers mechanically. There's nothing about a Tesla precluding the same manual brake methods practically every car has had since before I was born, which are the primary ways you stop the car from rolling when in neutral. At least this way you're always able to roll a vehicle when needed, even if it's inoperable for whatever reason.

Teslas are just annoying.

[Toutouxc]

> Most vehicles in addition to this have a mechanical "emergency" or "parking" brake for actuating the rear calipers mechanically.

> Teslas are just annoying.

Well, not any more, electric parking brakes have been a thing for some time and nowadays you can find them in very mainstream cars (like the latest Škoda Octavia). So it's not just Teslas that are annoying.

[Yaggo]

> Practically every single car has a freely rolling mode the operator can easily select, despite being, according to you, "very dangerous".

Yes, because traditional cars are not free rolling by default due to their mechanics, unlike electric cars.

Tesla does the only sensible thing in the scenario of possible power failure, it applies the electronic parking brakes when the car has stopped. Yes, you may not be able to push the car, but that's less dangerous than freely rolling car. The thing with power failure is that the car must prepare for a total lost of power in any moment.

And yes, Tesla has hydraulic brakes which works without power just like in any car, but that does not help in the emergency situation when the car has parked been without power. No one wants to sit in the car keeping the brakes pressed while waiting for the towing.

[pengaru]

> Yes, because traditional cars are not free rolling by default due to their mechanics, unlike electric cars.

What are you talking about?

Traditional cars have a neutral and yes it is free rolling by default.

If I don't personally set the hand brake in my mx-5 it will happily roll away, factory stock.

Edit:

And it gets even worse for an automatic transmission left in drive with the engine off. The torque converter hydraulics won't have pressure; it effectively becomes neutral. At least my manual mx-5 I can leave in 1st when off and it'll resist rolling a bit, not enough to park on an SF hill, but on level ground it'll generally hold still. But neutral in all cars is potential runaway car territory, completely unimpeded without manually setting the parking brake or for an auto explicitly putting the trans in park.

[Yaggo]

I mean that the traditional cars have either an automatic transmission with locking mechanism, or manual transmission which has significant resistance when coupled with the engine with a small gear. The traditional car is truly freely rolling only in specific configuration (neutral engaged).

Electric cars have none of that. The wheels are connected to the motor with a fixed gear, and the electric motor without power can't prevent the car from rolling. Thus you can say the system is "free rolling" by default. There are no mechanical configurations, just a fixed single one.

[pengaru]

An automatic transmission is effectively decoupled when the engine is off despite being left in drive. Without the engine spinning, there's no functioning torque converter. So the most ubiquitous ICE configuration, the auto with a torque converter, defaults to a neutral equivalent when the engine is off and the operator doesn't explicitly put the trans in park.

[Yaggo]

Yeah, we can argue about the semantics of "by default", but the point is that the traditional drivetrain has more backup options than electric car, which must solely rely on (parking) brakes.

[seanmcdirmid]

The axels are directly connected to the motor(s). To have a free wheeling mode, you’d have to disconnect them somehow, and I’m not sure how you would do that at all, definitely not without lots of extra parts. That problem isn’t unique to Tesla’s.

[Yaggo]

The electric drivetrain, including the motor, is in free wheeling mode by default, i.e. it has not much mechanical resistance, at least not enough to keep the car from rolling. So no need to disconnect anything. That's somewhat unique "problem" of electric cars, and it's the reason why it's critical to automatically apply the parking brake if the car may lose all the power.

[pengaru]

The motor will simply turn freely without power, there's no need to disconnect them. Tesla is literally going out of their way to prevent the neutral equivalent from being accessible.

But should we really expect anything else from a company so desperate to eliminate steering wheels from its cars?

[Toutouxc]

In the case of emergency, the car can either lock the brakes up and die, or do nothing and die. There's no other option, there's no mechanical backup, no braking pawl, no gear to shift in. Do you consider "being unable to secure the car in one place" the safer option?

[pengaru]

Why is there not a hand lever pulling a cable attached to the rear brake calipers? There's nothing about an EV precluding this mechanism we've used forever.

[Yaggo]

I don't think most modern premium cars have parking brake systems with hand lever anymore, even ICE cars?

[option]

Nissan Leaf has this problem too, not just Teslas

[yread]

eNiro has a (not very well documented) P release button

https://www.speakev.com/threads/p-release.139750/

[Yaggo]

Teslas also have a similar "tow mode" in menu settings.

But the case in the original post was a power failure condition, i.e. highly critical error mode.

[yread]

The eNiro button is a fully mechanical switch that you need a screwdriver to access and engage

[noptd]

>If the car detects a problem in power supply circuit, it's perfectly rationale action to engage the electric parking brake as "last wish" when the car has stopped

Perfectly rational as the default action perhaps, but Tesla should still provide a way to manually override that behavior. We have the technology.

[Yaggo]

No. If the car is in power failure mode, it means that all systems may shutdown in any moment. So if you let the user to override the very important safety feature (of applying the electronic parking brake), there's a high risk that the car would die in free-rolling mode in dangerous situation. As a manufacturer you have to make this kind of trade-offs. I'm sure Tesla has put lot of thinking into this to minimize the risks in worst-case situation (power failure). It's easy to comment in internet without knowing/seeing all the details. Many commenters here seem not to have much knowledge of the basics of electric drivetrains or Teslas.

[mft_]

I get the point you’re making in the context of not having a traditional gearbox with a clutch which would support neutral, but for completeness it’s worth mentioning that Teslas do have gearboxes - one for every electric motor.

[Yaggo]

That's technically correct. There's even serviceable transmission fluid and filter.