Regenerative Braking

How it works:


The regenerative braking systems implemented on automobiles and other forms of transportation today consist of two forms. The electrical form of regenerative braking turns mechanical kinetic energy into electrical energy. The mechanical form of regenerative braking uses mechanical kinetic energy from the automobile and stores it for later use. Both systems utilize a clutch that switches between acceleration and braking so that the system can be recharged or release the energy to the drivetrain. When the automobile is accelerating the gas powered engine or electrical motor is driving the car forward. When the brakes are applied the clutch for the regenerative braking system releases and allows the mechanical kinetic energy to be restored and saved electrically or mechanically depending on the system in use.

Electrical System

Automobiles that utilize electric motors have the option to utilize regenerative braking. When the electric motor is driving the car, electrical energy is being converted to mechanical energy and the car moves forward. When the driver applies the brakes the electrical motor is connected to the drive shaft of the vehicle but the motor spins in the opposite direction of when the motor is being used to drive the car. When the electrical motor spins in the opposite direction the mechanical kinetic energy of the car gets converted into electrical energy and is stored back in the cars battery for later use when acceleration is needed. Not only does the regenerative braking restore energy to the battery it also helps slow the car down. The use of frictional braking is still essential but as the electrical motor is spinning in the opposite direction it is applying a torque in the opposite direction of forward movement, thus causing the car to slow down. Regenerative braking helps reduce wear and tear on the frictional braking system of the car which leads to less need for repairs. Although the regenerative braking system can only be used on the drive wheels of the car, which in most cases is only two, it is still very effective and efficient.


Mechanical System

The concept used in mechanical regenerative braking is very primitive. Use the energy from the momentum of the car moving in one direction to spin a mass that is connected to a shaft. The energy of the rotating mass is then stored and released later to power the car forward. The rotating mass is connected to a transmission which allows it to either absorb energy or release the energy back to the system. These rotating masses can be very dangerous because of the speeds that they are being rotated and can be very inefficient if the frictional losses are not reduced.


Current Applications:

Performance cars:

The concept of regenerative braking, also known to be kinetic energy recovery systems (KERS), is being utilized in Formula 1 Racing. The first of the systems invented for the racecar was called the Flybrid. These concepts are still in development for Formula 1 Racing and also for road vehicles. The Flybrid system utilizes a flywheel that spins up to 64,500 rpm. A light flywheel was desired so that not too much weight was added to the car, however to get the performance desired the flywheel needed spin at a much high speed. This flywheel is connected to the drivetrain through a contiuously variable transmission. The transmission either allows the flywheel to gain energy from the drivetrain or release the energy to the drivetrain. The energy is being stored to the flywheel when the brakes are being applied on the racecar and thus not only storing the energy but also helping to slow the car down. The complexities of the system came up when most of the energy being stored was being lost due to friction and heat because the mass was spinning at such high speeds. To solve this problem, the Flybrid system operates in a vacuum. The Flybrid system is rated to release a 60 – 80 horsepower gain when the energy is released to the drivetrain. This relates to an 10% increase in power for a typical F1 racecar.


Hybrid / Conventional Cars:

The use of regenerative braking is essential in hybrid cars and is also starting to be implemented in non-hybrid cars as well. The ability for hybrid cars to run electrically for so long without needing to physically be plugged into an outlet to charge is because of the regenerative braking systems that are installed on them.


The Toyota Prius is the leader in hybrid cars and utilizes regenerative braking. It was estimated that about 20% of the energy consumed by the Prius comes from the regenerative braking system. The 4 wheel drive hybrid cars have the capability to use regenerative braking on all four wheels thus leading to more energy restores back into the battery. The conventional 2 wheel drive car is only able to utilize 2 wheels for regenerative braking and must rely on the extremely energy inefficient frictional braking on the other 2 wheels.


Non-hybrid cars are starting to implement regenerative braking because of its effectiveness and ability to recharge the battery. These cars are starting to eliminate alternators, air compressors, and power steering pumps that typically run off of the main crankshaft of the engine. Eliminating these systems from the gas driven motor and making them electrical makes the gas engine much more efficient and powerful. BMW has already released a gas powered engine car that incorporates regenerative braking to recharge the battery, run the air conditioning and power steering systems on the car. BMW is planning to implement these systems on the 5-series, M3, and Mini Cooper. The Mini Cooper will soon be available as a hybrid utilizing the regenerative braking system to recharge the electric battery while the 5-series and M3 will be utilizing the regenerative braking system to relieve some of the work the gas engine must exert to extra systems on the car as discussed before.

Environmental and Economic Impact:

Regenerative braking is an extremely environmentally friendly system. The conventional friction braking system is extremely inefficient because all of the momentum the vehicle has is being turned into heat by the frictional brakes. The regenerative braking system is using the energy that is present and restoring it back into the system allowing for much less wasted energy. This system when incorporated in a hybrid vehicle allows for the gas powered engine to run less because the electric battery is charged more frequently. This in effect allows for fewer emissions in our environment and less of the available oil to be consumed. Regenerative braking is helping to preserve one of our natural resources and if implemented on more personal cars and public transportation vehicles could reduce the emissions in our environment. The effectiveness of the system in the Prius and other hybrids shows the potential for this technology to be utilized for more energy saving possibilities.








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