What is Regenerative Braking?

Jessica Shea Choksey | Jan 25, 2021

Hybrid and electric vehicles apply battery technology, aerodynamics, and other engineering advancements to achieve efficiency in driving. One such feature employed by these energy-saving vehicles is regenerative braking. Regenerative braking captures energy that is otherwise lost during braking and then uses this power to help recharge the vehicle's battery.

Regenerative Braking System

How Regenerative Braking Works

Understanding how regenerative braking works first requires knowledge of how a conventional braking system operates. When you step on a vehicle's brake pedal, the discs and the brake pads create friction as they meet. In turn, the friction creates kinetic energy that dissipates into the environment in the form of heat. 

Regenerative braking recovers some of the kinetic energy that would otherwise turn into heat and instead converts it into electricity. In this system, the motor drives the wheels during acceleration or cruising, but the wheels drive the motor while decelerating. This two-way energy flow allows the motor to act as a generator, resisting the rotation of the wheels and creating electricity to recharge the vehicle's battery.

There are two conditions when regeneration occurs: 

1. When the driver applies the brake pedal

2. When the driver releases the accelerator pedal, and the vehicle is coasting

In both cases, the system creates electricity to recharge the battery. Drivers can view this regenerative effect on the vehicle's charging gauge, which shows it as energy flowing from the wheels to the battery.

The amount of electricity the system generates is proportional to the level of braking force. That means the stronger the braking force, the greater the electrical current. Ultimately, the amount of energy the system captures is dependent on the vehicle's speed and the duration of brake application.

When braking, the system automatically allocates some portion of the braking force to energy regeneration and some to the conventional brake system. This way, the system simultaneously achieves the dual purpose of slowing the vehicle down and recharging the battery for improved efficiency and greater electric driving range.

Regenerative Braking System Efficiency

Each year, new hybrid or EV models arrive with increasingly sophisticated regenerative braking systems, improving the amount of energy these systems can capture. In some cases, the latest regenerative braking systems can recover up to 70% of the kinetic energy otherwise lost during braking. 

Depending on how much an owner drives their vehicle, this can add up to hundreds of miles of extra electric range throughout the year. It reduces trips to the fuel pump for hybrids and lessens the need for pure EVs to plug into the power grid.

Disadvantages of Regenerative Braking

Like anything else, regenerative braking has its drawbacks. The most obvious is a decrease in effectiveness at low speeds. In slow-moving stop-and-go traffic, regenerative braking cannot capture much energy and feed it back to the battery, significantly reducing system benefits for many commuters during rush hour.

Another downside to some regenerative braking systems is how it changes brake pedal feel and modulation. Depending on the vehicle and the design, regenerative brakes can feel momentarily unresponsive or difficult to modulate for smooth, clean braking and stopping. These sensations may not inspire driver confidence or comfort.

Regenerative brakes may not have the same stopping power as conventional brakes, requiring drivers to step harder on the brake pedal. Drivers should be aware of this possibility and adjust their driving style accordingly.

Many newer regenerative braking systems perform much better than early examples of the technology, feeling more natural to the driver and offering the same level of effectiveness as a conventional system. When test-driving hybrid and electric vehicles, be sure to pay close attention to how the brakes feel and work. You might not notice any difference at all.

Summary

Hybrid and electric cars integrate various systems to optimize efficiency, and regenerative braking is a vital component of that overall equation. Besides minimizing energy loss and extending electric range, regenerative braking systems lengthen brake life due to their low wear and tear characteristics. The benefits of this technology are evident and help make green vehicles ever more appealing to consumers.

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