How Does Electric Vehicle Regenerative Braking Work
Regenerative Braking: How and Why It Works for Electric Cars
Regenerative braking allows an electric or hybrid-electric vehicle to collect electricity as it decelerates. Traditional braking results in a lot of lost energy, which in traffic leads to increased gas consumption and wear on brakes.
In electric vehicles (EVs), regenerative braking is performed by the electric motor, not by the brakes. This helps EV drivers use their brakes less.
How Regenerative Braking Works
In a gas-powered car, braking results in a lot of lost energy.
In regenerative braking, when an EV driver releases the accelerator pedal, the flow of electricity from the battery to the motor is stopped. Yet the spinning part of the motor (the rotor) still rotates along with the wheels of the still-moving car.
Without a continuous flow of electricity from the battery, the motor becomes a generator, sending the kinetic energy from the spinning rotor into the battery, while resistance to the rotor slows down the vehicle.
Electric vehicles still have disc brakes, but they are backups in situations like:
- In case of motor failures
- Below a certain speed, disk brakes supplement the generator since the torque (or rotational force) of the generator isn't strong enough to supply 100% of braking power
- At very higher speeds, when a short stop could break the motor.
Torque blending is how EVs find the appropriate balance between friction braking and regenerative braking. Like in an automatic car, EV drivers rarely notice the difference.
How Regenerative Are Electric Brakes?
Swiss companies are developing an electric truckthat can generate more electricity than it uses. But this isn't possible for ordinary electric vehicles.
While an electric vehicle is far more efficient than a gas-powered one in converting fuel to kinetic energy, some energy is lost as heat, as vibration, as sound energy, as aerodynamic drag, etc.
The same forces that take up energy during acceleration are also lost during deceleration, just as a car put in neutral on a flat surface will eventually stop.
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Other factors impact battery performance and how much braking energy it can save, including:
- The types of electronics and capacitors in the vehicle
- The temperature of the battery
- How full the battery already is.
Studies show that up to roughly 50% of the car's kinetic energy while braking can be used to accelerate the car again later. Anecdotal testimony from real-world driving, however, reports a range of 15% to 32% recapture of energy through regenerative braking.
History of Regenerative Braking
Regenerative braking is not new technology. In 1967, the American Motor Car Company introduced an ill-fated electric car, the AMC Amitron, with an impressive range of 150 miles and regenerative braking. Regenerative braking was also used on railways such as the Transcaucasus Railway and those in Scandinavia in the 1930s.
Today, Japan's highly efficient maglev trains and France's TGVs use regenerative braking, as do most electric trains and metro systems all around the world. Increasingly popular electric bicycles (e-bikes), scooters, and skateboards also use regenerative braking, with an efficiency of some 4% to 5%.
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The hybrid-electric Toyota Prius was the first commercially successful car to use regenerative braking, and the technology is almost exclusive to electric and hybrid vehicles.
The Mazda 3 is one of the few gas-powered vehicles that use regenerative braking, in this case merely to power the car's auxiliary electronic functions.
When Is Regenerative Braking Best?
Regenerative braking is most effective at higher speeds and on long downhills, since more kinetic energy is available to be converted.
Yet in stop-and-go urban traffic, the benefit of regenerative braking comes less in the amount of energy recaptured than in the reduced wear-and-tear on the friction brakes. This, in turn, reduces the emission of particulate matter pollution. At a societal level, the health outcomes from regenerative braking may even outweigh the financial or climate benefits.
The Future of Regenerative Braking
Regenerative braking is a mature technology with over a century of use, but research continues to refine its efficiency.
Battery improvements will increase the amount of energy that regenerative braking can store. Additional improvements to supercapacitors will also improve braking efficiency.
Continued research can reduce the energy loss in the braking process in order to make electric vehicles more efficient, more economical, and more environmentally friendly.
One-Pedal Driving
One-pedal driving takes getting used to, just as it takes drivers of standard transmission vehicles time to get used to the lack of a clutch in cars with automatic transmissions. But of all the benefits of regenerative brakingenvironmental and economicthe simplification that comes with using only a single pedal may be one that drivers enjoy the most.
Frequently Asked Questions
Do all electric vehicles have regenerative braking?
All hybrids and fully electric vehicles sold in the U.S. have regenerative braking. Even some conventional gasoline-powered cars have it. Of course, EVs also have conventional braking systems, too.
Why does regenerative braking not fully stop a car?
Most of the time, you can't stop an EV fully just with regenerative braking. Regenerative braking actually stops working as your speed dips below six mph. At such low speeds, the car is no longer drawing enough kinetic energy to bring the car to a complete stop.
How much range does regenerative braking add?
It's said that regenerative braking adds up to 15% more range in urban environments and almost no more range on highways. In situations where there's a lot of downhill driving, you might even find that regenerative braking adds up to 50% more range to your electric vehicle.
How can you maximize regenerative braking?
It's easy: Use the conventional braking system only when necessarily, such as at the very end of deceleration, when you're ready to stop the car. You should also make sure your settings are set to maximum regeneration.
Regenerative braking: what is it and how does it work?
Some cars also have an automatic cruise control system that uses brake regeneration. The car in front is monitored by sensors and brake regen is used to match that cars speed on the road.
In many EVs, when you lift off the pedal completely it feels like youve got your foot firmly on the brake. This is often referred to as one-pedal driving, as you need to modulate your right foot to speed up and slow down, rather than swapping it between the brake and accelerator pedals as with a combustion-engined car. In most cases, a cars brake lights will come on when lifting off the accelerator in the most aggressive regenerative braking setting, even if youre not touching the pedal.
In the Nissan Leaf, for example, this is referred to as the e-Pedal, and it can be switched on and off using a button on the dash. In the Polestar 2, there is an option located on the touchscreen infotainment system that allows you to set the One Pedal Drive system to off, low or standard. While the names of these systems can vary, they are all similar in operation.
One-pedal systems often produce enough braking power to reduce the need for and subsequent wear of traditional braking components. In some other models, though, the regenerative force isnt very strong, and these systems tend to feel more similar to engine braking in a petrol or diesel car.
In order to see how much power is being regenerated when youre braking, most cars have a gauge or readout on the dashboard which displays this information.
What are the pros and cons of regenerative braking?
As with any new technology, regenerative braking has its own pros and cons. Here are some of the main ones
Pros | Cons |
Ability to boost battery range | Can be an unusual sensation to get used to |
Reduced wear of braking components | Efficiency can vary |
One-pedal' systems can make driving easier and more relaxing if calibrated well | Not always easy to modulate braking force by using accelerator pedal |
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What is regenerative braking and how does it work?
The best electric cars come with a lot of impressive features, but one of the most interesting is the regenerative braking system. The idea is that you can recuperate some of the lost electricity, sending it back into the battery to be used later.
If youve never driven an electric car, or even a hybrid, then this concept might be completely new to you. Even if its not, you may not be aware of how regenerative braking works or the scope of what it can actually do. So what is regenerative braking exactly, and how does it work?
What is regenerative braking?
Regenerative braking is a system in which an electrified vehicle, be it a fully-fledged electric car or a hybrid, reclaims kinetic energy as the car slows down. That energy is then used to recharge the main battery, ready to be used later.
Some non-hybrid cars do offer some sort of regenerative braking. However it only happens in quantities that are barely noticeable, and the captured energy is pumped into your 12V battery. The majority of your kinetic energy is lost to heat as the brake pads slow your car down.
The regenerative braking in electrified cars is much more noticeable and beneficial. While you cant reclaim all the cars kinetic energy as you brake, the reclaimed power can make a difference to your overall battery level. That extra power can be utilized in the future, improving your gas mileage or electrical range in the process.
How does regenerative braking work?
When you hit the brakes in your car, hydraulic fluid squeezes your brake pads against the brake disc which is rotating with your wheels. The two coming together produces friction, which slows the car down or brings it to a halt. The regular brakes in an electric car work the same way, but regenerative braking is a different system.
Regenerative braking kicks in as soon as the driver takes their foot off the accelerator pedal. The electric motor, which powers your wheels, then switches directions and begins running in reverse sending power back into the battery.
In simple terms, the wheels become a miniature generator, producing electricity as the motors magnetic field rotates through the stationary stature. Its the same way the alternator in an internal combustion engine produces power for the 12V battery.
This process also produces resistance, which slows you down, and the stronger the regeneration the faster the deceleration will be. The benefits here are that it takes the pressure off the brake pads, extending their life and the life of the system as a whole. Its also the principle behind one-pedal driving systems, which is one of the best features electric cars have to offer.
How much energy can you get from regenerative braking?
The amount of energy a regenerative braking system will recoup varies from car to car and situation to situation. No system can offer 100% regeneration, since it would break the laws of physics.
The system will also be less effective if you have a full battery, since theres nowhere for the power to actually go. But done right, you will see an electric car's range estimate and battery percentage tick upwards from time to time.
Different cars offer different levels of regenerative braking, and different ways of customizing it. Some cars, like a Tesla or Jaguar I-Pace, only let you adjust the level of regenerative braking by doing a deep dive into the settings. So you have to set it up before you drive, and stick with it for the duration of the journey.
The likes of the Hyundai IONIQ 5 and Kia EV6 have paddles behind the steering wheel that shift the regeneration strength up and down on the fly. Meanwhile, the Nissan Leaf has two options, with the e-Pedal activating the one-pedal driving mode and the B gear that increases the level of regen while still requiring regular brake usage.
No matter the car, or how you set it up, physically hitting the brakes will kickstart the regenerative braking system adding power back to the battery automatically.
Bottom Line
Regenerative braking isnt going to add hundreds of miles of range to your car, nor will it be particularly useful on long interrupted stretches of highway. But it will make those shorter journeys more efficient than they would be otherwise, especially if youve managed to anger the traffic light gods.
Granted there are still a lot of things you need to do to maximize your EV range, especially if youre driving in cold weather. Likewise, hybrid drivers will find regenerative braking is a big help towards improving your gas mileage, but there are plenty more things you can do to lower your gas consumption. All in to make sure you spend less time on how to find cheap gas or to find an EV charging station.
But passive as it may be some of the time, its still a pretty useful feature to have in your car be it fully electric or some kind of hybrid. After all, the only alternative is to let all that energy go to waste, and whod want that?
