Regenerative braking in EVs

How does regenerative braking work?

While driving a vehicle with a regenerative braking system, the electric motor draws power from the battery to turn the wheels, creating the kinetic energy it needs to move. When the brakes are applied, however, the process switches into reverse mode. Now the kinetic energy that was initially used to propel the vehicle, makes the wheels rotate the electric motor, turning it into a generator. Instead of consuming electricity, the motor/generator starts producing it, using the vehicle’s kinetic energy. The electrical energy is then stored in a high voltage battery, where it is used again to help propel the vehicle. Since regenerative braking converts the vehicle’s kinetic energy into electricity, it is also able to slow it, in the same way hydraulic brakes do with friction.

In most cases, the electric motor/generator will provide sufficient braking power to slow the vehicle. Yet, when it's traveling at high or very low speeds, is stationary or the battery is fully charged, too hot or too cold, the electric motor cannot provide enough braking torque on its own and will need the support of a hydraulic braking system. To what extent will largely depend on the vehicle.

What regenerative braking feels like?

Regenerative braking really feels like endless braking, with no fade or change. It gives a huge amount of control to the vehicle once the driver has become used to the effect. In some vehicles it is possible to drive with one pedal – coming right off the accelerator will give full regenerative braking, partially pressing down allows the vehicle to coast, and pressing further provides acceleration in the usual way.

Types of regenerative braking systems

The size of the motor and size of the battery will affect how much regenerative braking can be used. As a general rule, the larger the motor and battery, the more available energy there is from regenerative braking. This means it’s usually the case that fully electric vehicles recover more energy from regenerative braking than hybrid vehicles. Hybrid systems have many different configurations yet each features a regenerative braking function.

Advantages of regenerative braking 

Perhaps the biggest advantage of regenerative braking is the energy efficiency that it provides, recycling energy and reducing the need for recharging. On fully electric vehicles Delphi tested, around 20% of the energy the vehicle used was from regenerative braking. 

It also provides better control of braking, reducing reaction times, as the system kicks in as soon as the accelerator is released. Having two braking systems also provides greater braking power. However, as regenerative braking does not use the hydraulic brakes, there is far less wear and tear on the system. Disadvantages of regenerative braking 

Disadvantages of regenerative braking

There are pros and cons when it comes to regenerative braking. As it’s unavailable when the battery is fully charged and, in some instances, when too hot or too cold, this inconsistent feel of the pedal can be difficult to get used to.   Corrosion of the hydraulic braking system is also common as they are underused. Regenerative braking solutions from Delphi

Regenerative braking solutions from Delphi

At Delphi, our innovative EV brake pad range has been designed to meet the challenges that regenerative braking brings. An advanced coating on the pads optimises friction performance, giving reliable braking power from the first press. It eliminates the need for bedding in which most new brakes require. As with all Delphi products, they’re always manufactured to OE spec or above. Controlling and adjusting regenerative braking in EVs

Controlling and adjusting regenerative braking in EVs

Most vehicles with regenerative braking allow you to adjust how much braking power it gives you. The number of settings and how you change them varies from vehicle to vehicle. For example, Tesla allows you to select low or standard on the main screen whereas Mercedes has paddles behind the steering wheel. The adjustments can be useful for different types of driving, such as switching from motorway to urban roads. Brake lights and regenerative braking.

Brake lights and regenerative braking

A common question is whether the brake lights come on with regenerative braking, as the hydraulic brakes are not used. Brake lights will come on to meet the deceleration limit of 1.3m/s set by EU regulations, whether that deceleration comes from hydraulic or regenerative braking.Learn more about EVs

Learn more about EVs

• Changing the brake fluid on a Tesla
• Tesla Model S: Bedding in new brakes
• Three key differences with EV brakes

An overview of regenerative braking 

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