Creep, hold, and the last few km/h
Regen torque fades out near a stop, and something else has to hold the car once it's stationary.
- Explain creep, hold, and the last few km/h at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real braking system
Overview
A motor generating at very low speed produces very little back-EMF and therefore very little usable regen torque, so no EV can regen all the way to a perfect standstill. The last fraction of a km/h and holding the car stationary both need a different mechanism.
In depth
Why regen fades near zero speed
Generated voltage is proportional to rotor speed, so as the wheels slow toward a stop the available electrical power — and with it, controllable regen torque — collapses toward zero. Engineers blend in a small amount of friction braking during the final metre or two of a one-pedal stop specifically to mask this fade.
| Speed range | Dominant deceleration source | Why |
|---|---|---|
| High/medium speed | Regen torque | Strong back-EMF gives the motor full authority to generate |
| Last few km/h | Blended friction + fading regen | Regen torque collapses as back-EMF approaches zero |
| Standstill | Electronic parking brake or hold function | Zero speed means zero back-EMF and zero regen torque |
Because regen torque is zero at zero speed, any one-pedal system that appears to 'hold' a car on a hill is doing so with the friction brakes or the parking brake, never with the motor.
Key takeaways
- Regen torque authority collapses toward zero as speed approaches zero, because back-EMF collapses with it.
- The final portion of a one-pedal stop is blended with a small amount of friction braking.
- Standstill hold is always a friction-brake function, never a regen function.
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