What Is Regenerative Braking?
Regenerative braking allows your vehicle to capture energy during braking and use that energy to recharge the vehicle's battery.
Regenerative braking is a mechanism through which an all-electric or hybrid vehicle's powertrain captures energy as your car slows down or goes downhill, then uses that energy to recharge the vehicle's battery. Since this kinetic energy would otherwise be lost as heat, regenerative braking helps maximize your vehicle’s electric efficiency. Regenerative braking does not replace the need for braking with friction brakes, but it can help maximize your vehicle’s electric range.
If, in researching electric or hybrid vehicles, you ran across the terms regenerative braking or just “regen” but weren’t sure what they meant, this guide is for you. Let’s walk you through what the definition above really means, how regenerative braking works, how drivers can use regenerative braking effectively, and more.
How does regenerative braking work?
1. Electric motor draws power from the battery to turn the wheels, creating the kinetic energy it needs to move.
2. When braking the process is reversed using the kinetic energy previously created to propel the vehicle.
3. Instead of consuming electricity, the motor starts to produce it using kinetic energy. This is stored in a high voltage battery where it is used again to propel the vehicle.
In the “standard” braking procedure, when a driver applies the brakes in their vehicle to slow or stop its momentum, the shift toward inertia creates kinetic energy in the form of heat. This occurs when friction — caused by applying brake pads or shoes to a brake disc or drum — creates heat and slows down your car. The collective braking system described here, commonly called friction brakes, is found within every vehicle on the highway, including electric vehicles of all types.
Vehicles with electric motors that contribute to propulsion — most types of EVs — add regenerative braking to this process. In regenerative braking, the kinetic energy of the car in motion is captured and converted into electrical energy, rather than it dissipating entirely as heat. The electric motor is responsible for these actions; in reversing the processes it uses to propel the car, the motor becomes a generator. The power it produces is then fed to the onboard battery pack.
Regenerative braking may be initiated in several ways:
• When you lift your foot off the accelerator
• When you touch the brake pedal
• When you’re going down a hill (sometimes called a “downgrade”) and the gravitational pull on your vehicle increases its speed without adding more pressure to the accelerator
Putting this all together, the same electric motor that provides your vehicle with propulsion under throttle becomes a generator when the vehicle is slowing down or on a downgrade, thereby recapturing some of the energy that got the vehicle moving in the first place.
All of this occurs automatically, but there are ways the driver can maximize the efficiency of their vehicle’s regenerative braking system.
Understanding the role of the driver in regenerative braking
Maximizing regenerative braking efficiency
The key to maximizing the efficiency of regenerative braking is to use only as much brake pedal pressure as needed to maintain maximum regeneration — without exceeding that point. As you’d guess, the further ahead you can determine you’ll have to slow or stop, the more energy you can recover in regeneration.
Once you’ve reached maximum regeneration, any more brake pedal pressure will cue your friction braking system to initiate. This transition point is frequently referred to as the handoff and may result in a different brake pedal feel.
Many vehicles with regenerative braking have a graphic or gauge displayed on the dashboard that shows this energy flow to or from the battery. In the Mazda CX-90 PHEV, for example, drivers can see the Deceleration Regeneration Charge Display in the gauge on the vehicle’s dashboard. You can monitor for handoffs by using this gauge on your dash (if available), but you’ll also build familiarity with this threshold over time.
Finally, you may also notice a handoff from regenerative braking to friction braking as you come to a stop, as the motor’s ability to convert energy becomes limited as your car reaches lower speeds. More on this below.
Regardless of whether your car has regenerative braking or not, braking in emergencies should be handled the same way: hit the brake pedal and the car will stop in the shortest distance possible. You should always prioritize braking at a safe distance.
Vehicles with additional regenerative braking capabilities
While regenerative braking is primarily an automatic process, in some vehicles, the default rate of regeneration can be adjusted by the driver. This can be done by selecting a different mode (e.g., Sport, Normal, Eco), shifter position (e.g., B, L, 3), and/or by pulling a dedicated steering wheel paddle that activates quicker regenerative braking while slowing.
For example, some battery-electric vehicles (BEVs) have a “one-pedal mode” that helps maximize regeneration. This mode can bring the vehicle to a stop using regenerative braking, or nearly so — some models use the friction brakes for the very last few mph of slowing, but without requiring the driver to press on the brake pedal. One-pedal mode is particularly useful in urban areas, where the driver needs to frequently switch between accelerating and braking.
What are the advantages of regenerative braking?
• Maximized range: Regenerative braking can help maximize your vehicle’s range by recapturing energy that is otherwise lost in friction braking and using it to partially recharge your vehicle’s battery.
• Reduced brake wear: When used regularly and efficiently, regenerative braking can save wear and tear on your vehicle’s friction braking system, including brake pads, discs, and drums.
• Improved driver efficiency: Drivers who use the vehicle-provided data regarding regenerative braking and energy flow (if available) effectively can improve the efficiency of their driving.
What are the disadvantages of regenerative braking?
• Driver adjustment: Regenerative braking creates a different brake pedal feel and response from that of a standard internal combustion vehicle. In a car with regenerative braking, the driver may feel like pressing on the brake pedal requires less effort than in a friction-brakes-only vehicle. It may also feel as though the pedal needs to move only a few millimeters to initiate deceleration.
• It cannot replace friction brakes: At 60 mph on dry ground, most modern vehicles can stop a vehicle in about three seconds with a professional driver using friction brake systems. Road planners allow closer to seven seconds, including one second of reaction time. Currently, no form of regenerative braking can adequately handle the force required for emergency braking at higher speeds. The two types of braking are intended to work together.
• It loses effectiveness at lower speeds: The benefits of regenerative braking are diminished at parking lot speeds or when driving at a stop-and-go crawl.
What types of EVs have a regenerative braking system?
Virtually every vehicle with a battery that contributes to propulsion has some degree of regenerative braking. Battery-electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and traditional, full hybrid electric vehicles (HEVs) apply the energy stored and saved via regenerative braking to propel the vehicle. Mild hybrids (MHEVs) typically use the energy recouped by regenerative braking to help power ancillary systems like climate control, power steering assistant, and more.
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Numerous variables make this difficult to even generalize. Most decelerations of more than a few miles per hour at low speeds or downgrades of a few hundred feet offer regeneration opportunity; how much is recovered depends on both vehicle and driver efficiency. For example, an interstate trip across dead-flat plains on cruise control will likely invoke regeneration only when you exit and slow down.
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The U.S. Department of Energy estimates regenerative braking energy recovery at 5-9% for hybrids and 22% for electric vehicles in combined city/highway driving. As with gasoline consumption estimates, energy recovery depends on many factors, including the driver.
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The U.S. has no standard requirement for brake light illumination for all types of regenerative braking (in Europe, any deceleration rate greater than 1.3 meters per second squared requires brake lights). This means that during regeneration when driving at faster speeds, the brake lights may illuminate but you’ll want to check your owner’s manual for specifics about your car’s model. Regardless, If the accelerator pedal has even the slightest pressure on it, some vehicles will not illuminate the brake lights. This is especially important for people who use their left foot to brake while keeping their right foot on or over the accelerator.
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The exact speed at which a handoff at low speed occurs varies by vehicle, but regenerative braking typically operates best at speeds greater than 9 mph. Below these speeds, the energy needed to set up the magnetic field needed for an induction motor to engage regeneration is greater than the energy that can be recovered at such slow speeds.
Regenerate your interest in EVs with the Mazda CX-90 PHEV and the Mazda CX-70 PHEV
The Mazda CX-90 PHEV, and the CX-70 PHEV are crossover SUVs that blends powerful efficiency and luxurious style. Featuring an electric motor (with regenerative braking capabilities) and an all-new powertrain, the CX-90 PHEV, and the CX-70 PHEV was crafted with flexibility, responsiveness, and our planet in mind.
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