A key to improving efficiency in the latest cars and trucks is using electricity to make them go. As part of the process, there’s a simple way to produce some of that electricity when the vehicles stop. The technology is called “regenerative braking,” and it was first patented in 1908. The first car with regenerative braking was the 1967 AMC Amitron concept. Toyota introduced the technology to the mainstream 30 years later, with the Toyota Prius in 1997. Today, it’s standard on all hybrid and electric vehicles. Tomorrow? Regenerative braking may mean the end of brake pedals entirely.
How Does Regenerative Braking Work?
Typical electric and hybrid vehicles work in much the same way. They store electricity in special battery packs, then rely on that electricity to drive one or more electric motors. Pure electric vehicles use only those motors, while hybrids get most of their power from gasoline engines. Plug-in hybrids split the difference. They have batteries and electric driving capabilities that fall between traditional hybrids and EVs. In any case, regenerative braking is a way of switching the flow of electricity. Instead of going from the batteries to the motors, it goes from the motors to the batteries.
For example, in an electric car, pressing on the accelerator basically tells the electric motors to begin spinning the driving wheels. Taking your foot off the pedal puts the powertrain into sort of “generator” mode. Then, the kinetic energy of the wheels ends up spinning the electric motors. Imagine trying to stop a spinning bicycle wheel with your hand. When you grab it, you’ll feel a jerk as the inertia of the spinning wheel tries to pull your hand along. The same force in a regenerative-braking system acts on the electric motors in a similar way. The difference is that the car wheels have enough continuing force to keep the electric motors turning for while.
On another level, as those motors turn, coils of conductive metal are moving in and out of a magnetic field. This creates an electric current thanks to the wonders of physics.
The motors don’t just turn freely, though. They put up some resistance to the spinning force of the wheels. It’s this drag that helps slow the car. Now, in most vehicles, the mechanical brakes are still providing a lot of the stopping power. But some regenerative-braking systems also let you dial in higher levels of resistance. With these setups, the electric motors generate more electricity as they do more of the braking work. And yes, some systems can deliver so much resistance that you don’t have to touch the brake pedal at all.
What Is ‘One-Pedal’ Driving?
The newest generation of electric cars, such as the 2018 Chevrolet Bolt and Nissan Leaf, take things to the next level. They have dedicated modes for “one-pedal” driving. That technology was specifically engineered so that you can you can drive and stop with only the gas pedal. The regenerative-braking system kicks in as soon as you begin to lift up on the accelerator, supplying resistance that can completely stop the vehicle. According to Nissan, the Leaf “lets drivers use a single pedal for more than 90 percent of their driving needs.”
Do Any Non-hybrids Have Regenerative Braking?
A few automakers have adapted regenerative braking to improve fuel economy for their non-hybrid, non-electric vehicles. This includes BMW, which offers the technology for the 2018 BMW 3 Series and many other cars and SUVs. Here, an important difference is that when you press the accelerator, the generator units are automatically disengaged from the drivetrain. As a result, even if they’re not helping spin the vehicle’s wheels, they’re at least not creating any drag. The entry-level 320i shows the effect of the system with EPA ratings of 24/35 mpg city/highway.
Regenerative braking also was available in recent models of the Mazda3 and Mazda6. Though neither is expected to provide the technology for 2018, a car like the 2015 Mazda6 is rated at 28/39 mpg city/highway with the company’s advanced braking system. That’s a midsize sedan with better EPA grades than many compacts.