Torque Shop

I drive an electric car. If I release the accelerator, the car will slow down to an eventual stop and then stays stationary. But if I apply the brakes before the car comes to a standstill, it will stop but will crawl once I release the brake pedal. Why is this so?

When electricity is supplied to a motor, its shaft will spin. Less commonly known is that if the motor shaft is made to spin by an external drive, electricity will be produced by the motor .

In an electric vehicle (EV), when the accelerator pedal is released, the car will decelerate because the motor switches its role to function as a generator (using the momentum of the vehicle to provide drive input to the shaft).

The system is said to be in "regenerative mode" then and the electricity generated is supplied to the batteries.

In this mode, the car will slow down and ultimately come to a stop.

However, the EV will disengage from regenerative mode once the brake pedal is depressed.

Hence, if the brake pedal is then released, the car will creep forward (or backwards if Reverse was engaged).

The creep or crawl is particularly necessary during parking or slow manoeuvres such as three-point turns.

A version of this article appeared in the print edition of The Straits Times on September 28, 2019, with the headline 'Torque Shop'. Print Edition | Subscribe