Torque Shop: How do brakes of EVs work?

The initial braking function is created by the electric motor harnessing the car's momentum for regeneration. ST PHOTO: EUGENE GOH

SINGAPORE - If conventional cars use a vacuum-assisted booster for the brakes, how do hybrid and electric cars perform the same function? Electric vehicles (EVs) have no engine to produce a vacuum, while hybrids do have engine-off moments. How do their brakes work?

Traditional power-brake systems employ a sealed chamber which uses a vacuum to assist the force applied by the driver's foot on the brake pedal.

In a petrol-engined car, the vacuum is tapped off the intake manifold, while in a diesel car, a small belt-driven pump generates the necessary vacuum. Commonly known as the brake servo, the booster's function is to assist the brake pedal operation so the driver needs less effort to apply the brakes.

In a hybrid or electric vehicle, the power brake system is far more complex. The initial braking function is created by the electric motor harnessing the car's momentum for regeneration. Hence, the brake pedal mechanism consists of sensors to measure force and pedal angle.

A hydraulic brake actuation is initiated automatically when higher levels of deceleration are demanded by the driver based mainly on the applied pedal pressure.

Some EVs use an electric vacuum pump, but others use electric motor-driven actuators which assist the driver's brake pedal input.

In all motor vehicles, regardless of the type of brake booster, there is always a direct mechanical link between the brake pedal and master pump. Even if the power assistance is disabled for whatever reason, the hydraulic braking will still be available, although this alone will require far greater foot pressure on the pedal.

Join ST's Telegram channel and get the latest breaking news delivered to you.