This cutaway diagram of General Motors’ 2005 Sequel hydrogen fuel cell concept car showcases the regenerative braking system. (Picture / GM)

When battery electric vehicles (BEVs) and hybrid electric cars really started to emerge in the early 21st century, they brought a term that many gearboxes were not familiar with: regenerative braking.

And while the concept of regenerative braking is new to many automotive enthusiasts, the technology and its application have been around for a long time. In fact, the basic principle behind regenerative braking goes hand in hand with the first electric motor ever built.

But first …

What is Regenerative Braking?

In the context of a hybrid or electric vehicleRegenerative braking describes the ability of a vehicle to convert kinetic energy (AKA motion) into electrical energy. This energy is then used to recharge an electric vehicle battery while driving.

In other words, when you take your foot off the accelerator pedal in an electric vehicle, the regenerative braking system is activated to automatically charge the EV’s battery.

This means that a regenerative braking system essentially extends the usable range of an electric or hybrid vehicle and has a significant impact on the viability of an electric powertrain.

How Does the Regenerative Braking System Work?

While we can devote a few thousand words to the basics of electrical engineering, we’ll boil it down to this: an electric motor and an electric generator are basically the same thing.

In short, if you apply electrical power to an EV’s electric motor, the output shaft will start to spin and push the vehicle. But when you stop supplying power, the vehicle pulls up and the wheels manually spin the same shaft that now becomes an electric generator.

Or another way, in deceleration, manual rotation from the wheels of the vehicle now turns the engine, essentially turning it into a generator, which creates electricity to charge the battery.

Again, this is a very, very simplified explanation. If you really want to get into weed on the electromagnetic principles behind how all this works, you might want to start with a guy named. Michael faraday.

Say you want to slow down from 45 mph. You take your foot off the accelerator pedal, and the flow of electricity to the vehicle’s electric motor (s) stops. But obviously the car won’t stop suddenly. Since the car still has momentum, until the kinetic energy flows slowly (from friction, air entrainment, etc.)

This is where the regenerative braking system comes into play. It turns the vehicle’s electric motor into an electric generator driven by the vehicle’s wheels and then starts sending a charge to the electric vehicle’s battery.

Regenerative braking systems continue to evolve. Nissan’s e-Pedal technology is a good example. Essentially it lets you use the accelerator pedal to accelerate AND slow down. Click here to see how it works. (Image / Nissan)

Better still, this system typically slows the vehicle down faster than the normal slowdown. This means less wear on conventional brake components such as the vehicle’s pads and rotors.

… This brings us to another good point.

Can Regenerative Braking System Replace a Traditional Friction Brake System??

No. While regenerative braking can positively affect an electric vehicle’s ability to slow down, you will eventually need to depress the brake pedal to bring the vehicle to a complete (or sudden) stop.

Normal hydraulic friction brake system takes action.

An electric vehicle with regenerative braking still has a conventional friction brake system – meaning it has brake rotors (perhaps drums on the rear), brake calipers, pads or shoes, a master cylinder, and hydraulic DOT-spec brake fluid.

In other words, an electric vehicle can essentially have two braking systems. So perhaps in the context of just slowing down and stopping, it’s easiest to think of a regenerative braking system as a complement to the hydraulic friction braking system we all know and love.

Advantages of Regenerative Brake System

We mentioned two main benefits above. A regenerative braking system can:

  1. Charge an electric vehicle battery while driving
  2. Slow down a vehicle faster to reduce wear of traditional brake system components

Although not all regenerative braking systems work the same (each part of the respective manufacturer’s EV “secret sauce”), they typically offer the same benefits.

However, there is another important point to note here. Today, a regenerative braking system works automatically. In most cases, a driver barely notices that it is working; The system smoothly turns the regenerative mode on and off without any effort or intervention from the vehicle operator. You may only notice that the vehicle slows down a little faster.

Cadillac introduced “Regen-On-Demand” in its hybrid-electric ELR. Thanks to paddle shifting, it allows the rider to temporarily control the regenerative braking system. Read more about it here. (Image / Cadillac)

Regenerative braking is very important, especially with regard to battery charging. Battery range is at the forefront of these efforts, as every electric vehicle manufacturer is in a constant search to improve the applicability and practicality of electric vehicles.

Given the ability of regenerative braking to charge an electric vehicle battery through normal driving (this results in a significantly increased range of electric vehicles), it has become a basic system in seemingly every EV produced today.

Author: Paul Sakalas
Paul is editor of OnAllCylinders. When he’s not writing, you’ll likely find him throwing tools at his unfortunate day-to-day driver or tampering with an old Jeep CJ-5. An ambitious motorcyclist spends the rest of his time synchronizing the carburetors and removing grease from his left trouser leg.