Regenerative Braking in Cars

What is Regenerative Braking?

Regenerative Braking is a braking technology that re-captures kinetic energy normally dissipated by a vehicle as heat. It converts this captured energy into electrical energy which is used to charge the vehicle’s batteries or used for any other purpose.

The advantage of using Regenerative Braking systems is energy efficiency (in the context of kinetic energy) and fuel efficiency since the recaptured kinetic energy reduces dependency on fuel in certain situations like sudden acceleration.

Kinetic energy is the energy that is generated when an object is in motion and gets wasted due to dissipation as heat by conventional dynamic braking systems used normally in cars. This wasted energy can be utilized for other purposes and it is this reason that led automotive engineers to create regenerative braking systems.

How does Regenerative Braking work?

Electric motors run in one direction producing mechanical energy from electric energy but when run in reverse direction, they act as generators converting mechanical energy into electrical energy which can be stored for further use.

When a Regenerative Braking System is used, the brakes use the momentum of the vehicle as the required energy to drive the motor in the reverse direction. The reversed motor acts as a generator converting the kinetic energy into electricity which is stored in the batteries connected to the motor for future use, like accelerating the car again after stopping.

A brake controller is the most important device in the Regenerative Braking system which decides when and how quickly braking is done. The most important function of the controller is to decide whether regenerative braking can be used and if not, pass the control to friction brakes to do the job. It handles the storage of the produced electricity into the batteries or capacitors ensuring optimal storage.

Electric and hybrid cars also use friction brakes along with regenerative brakes for higher deceleration rates or as a back up in case of failure.

Types of Regenerative Braking Systems

Chemical battery based Regenerative Braking systems where the energy is stored in batteries.
Ultracapacitor based Regenerative Braking systems where the energy is stored in ultracapacitors (charging and recharging is fast).
Flywheel based Regenerative Braking systems where the flywheel is used as an alternative to batteries.
Hydraulic Regenerative Braking systems where the energy is stored and released by compression and expansion of a gas using hydraulic fluid.

Applications of Regenerative Braking

Regenerative braking is used in electric vehicles and hybrid vehicles.It is also found in electric trains and bicycles as well as in Formula One racing cars.

Formula One is a sport where performance is the sole objective. Issues like fuel efficiency normally take a backseat. However the sport has lately started taking notice of energy efficiency as a cost cutting measure. Some teams have developed and used a regenerative braking system called the Kinetic Energy Recovery System or KERS. The system is mainly used to provide sudden acceleration which can increase the straight-line speed of the car. The benefit of using the system is fuel efficiency since the driver doesn’t always have to depend on fuel to give that much needed sudden burst which enables him to overtake another car. The drawback of the KERS system is the reduction in the car’s balance which makes the car unpredictable on the turns. Another limitation is the high cost incurred to develop the system. Also safety issues on the track have to be dealt with before it finds its way into commercial vehicles. However since the system is in its nascent stage, there is a lot of scope for the KERS in the future.