What Is Regenerative Braking?
Hybrids and EVs boost their efficiency by using their electric motors to slow down.
Braking technology has come a long way, from drums to discs, mechanical linkages to hydraulic lines, anti-lock brakes to automated emergency systems that sense and mitigate impending collisions. As automakers build and sell more hybrid, plug-in hybrid, and electric vehicles (EVs), the process of slowing a vehicle is changing again with the rise of regenerative braking: a technology that makes vehicles more efficient and saves the friction brakes from unnecessary wear.
How Does Regenerative Braking Work?
With regenerative braking, the same electric motors that power a hybrid or EV essentially work in reverse, acting as generators while slowing the car. To understand why that’s significant, first consider how conventional friction brakes operate. To bring a vehicle to a stop with friction brakes, brake pads clamp down on discs and convert the kinetic energy of a vehicle in motion to heat that dissipates into the ambient air. In other words, the energy that was used to accelerate and maintain the vehicle’s speed is rapidly scrubbed off and thrown away to the atmosphere.
Regenerative braking recoups some (but not all) of the vehicle’s kinetic energy and converts it into electricity that charges the battery. This helps boost the efficiency and increase the range of EVs. It’s also one reason why hybrids and EVs perform better on the Environmental Protection Agency’s (EPA’s) city testing cycle than on the highway — with so much stopping and starting, the vehicle has plenty of opportunities to use regenerative braking and boost its energy efficiency. Using an electric motor to slow the car also reduces the wear on the brake pads and discs, meaning those components won’t need to be replaced as often.
Regenerative Braking In Electric Vehicles
Some automakers provide various regenerative-brake settings, allowing drivers to choose between gentle or aggressive deceleration once they lift off the accelerator. Some EVs can even come to a stop without the assistance of traditional friction brakes. This is known as one-pedal driving, although drivers still need to use the brake pedal in some scenarios. Whether the vehicle in front of you does something unexpected or the car’s battery can’t accept any more recouped energy, there will come a time when an EV driver needs to use those friction brakes. This presents manufacturers with a challenge: how to transition between regenerative braking and traditional friction braking smoothly.
Most hybrids and electrics use brake-by-wire technology with a portion of the brake pedal’s travel activating the regenerative-braking function, after which point the friction brakes start to bite. In the early days of the technology, automakers struggled to make this hand-off gracefully leading to grabby, touchy, or inconsistent brake feel. As engineers became more experienced calibrating these systems, that’s largely a thing of the past with most modern systems operating seamlessly.