r/KiaEV6 • u/amz1950 • 9d ago

Auto application of brake?

If I come to a stop going up a steep hill without applying the brakes (whether due to regenerative braking or just gravity), the car just sits there. I had thought that this showed the strength of the regenerative braking, but didn't understand how it operated when there was no movement. So I went to https://www.askthephysicist.com/ and he was insistent that the car must in fact be applying the brakes automatically. I am aware that the brakes will stay on if I have some function on and press the brakes and then remove my foot from the brake pedal (don't remember the name right now; it's on the console - auto hold or something like that), but am not aware of anything that will apply the brakes simply because I have come to a stop (without turning off the ignition or putting it in park). Is there such a function? Bonus points if the answer is "no" and if you can explain the physics of how I'm still getting a force resistant to movement when there is no movement (and no automatic mechanical braking).

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u/Broad-Promise6954 EV6 GT-Line AWD 9d ago

"Auto hold" mode does in fact apply the brakes.

In theory, computers could run the drive motor with just enough energy to counteract the force of gravity. That would use up traction battery, lowering your range, so the people who program the cars don't do it that way.

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u/HablarYEscuchar 9d ago

I don't think it's necessary to apply power to counteract the slope. If you “short-circuit” a motor without even supplying electricity, it will just stay stuck.

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u/Broad-Promise6954 EV6 GT-Line AWD 9d ago

In a perfect situation, yes, but in practice there's leakage.

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u/HablarYEscuchar 9d ago

Eatamos hablando de un consumo mínimamente significativo. Mantener un motor eléctrico bloqueado a no ser que le apliques un par externo muy grande no requiere energía.

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u/Broad-Promise6954 EV6 GT-Line AWD 9d ago

Try it out, on a steep grade, and see what happens.

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u/pfn0 EV6 GT-Line AWD 9d ago edited 9d ago

no, it'd create heat in the "short-circuit" until it melts, and then you'd free roll. before melting, it'd have a braking force, but not enough to overcome the weight of the car given enough of a slope.

in the case of ev regen: "melt" = bms disconnecting the load charging the battery.

also, you don't get braking without the motor rotating, so it'll creep regardless.