Regenerative braking system By P.VenugopalRaju 3pg07me029

Contents: Introduction Conventional Breaking System Regenerative Breaking & Its Working Kinetic Energy Recovery System(K.E.R.S) Discharge mode of K. E. R. S Benefits of Regenerative Breaking System Limitations of Regenerative Breaking System Conclusion Reference

What are brakes? A brake is a device that decelerates a moving object / prevents an object from accelerating. Brakes use friction to convert kinetic energy into heat Guiding principle- kinetic energy increases quadratic ally with velocity -K = mv2 / 2 When the brake is pushed the caliper containing piston pushes the pad towards the brake disc which slows the wheel down.

Convectional braking system Conventional braking systems use friction to counteract the forward momentum of a moving car. As the brake pads rub against the wheels, excessive heat energy is created. This heat energy dissipates into the air, wasting up to 30% of the car's generated power

Regenerative braking Regenerative braking technology funnels the energy created by the braking process back into the system in the form of charging the battery for further use In a regenerative braking system the energy normally lost in the braking process is transferred to the generator from the rotating axel and then transferred to the battery, thus saving energy

How does it work The system that drives the vehicle does the majority of the braking. When the driver steps on the brake pedal of an electric or hybrid vehicle, these types of brakes put the vehicle's electric motor into reverse mode, causing it to run backwards, thus slowing the car's wheels. While running backwards, the motor also acts as an electric generator, producing electricity that's then fed into the vehicle's batteries.

Vehicles driven by electric motors use the motor as a generator when using regenerative braking: it is operated as a generator during braking and its output is supplied to an electrical load; the transfer of energy to the load provides the braking effect. Many modern hybrid and electric vehicles use this technique to extend the range of the battery pack.

Over view v v Wheel Wheel IC Engine IC Engine Generator Battery Transmission Generator Battery Motor Motor Wheel Wheel Scenario 2: Braking – Kinetic energy is converted to electric energy during regenerative braking by electric motor and supplied to battery. Scenario 1: Low speed - Power is provided by electric motor using energy supplied by the DC battery Scenario 3: High speed – Power is provided by IC engine and electric motor via generator. Generator also charge battery during high speed. Wheel IC Engine Transmission Generator Battery Motor Wheel

Kinetic energy recovery system The device recovers the kinetic energy that is present in the waste heat created by the car’s braking process. The concept of transferring the vehicle’s kinetic energy using Flywheel energy storage was postulated by physicist Richard Feynman in the 1950s

How does K. E.R. S work

When the driver brakes most of the kinetic energy is still converted to heat energy but a portion is treated differently and is stored up in the car. When the driver presses his boost button that stored energy is converted back into kinetic energy The mechanical KERS system utilises flywheel technology to recover and store a moving vehicle’s kinetic energy which is otherwise wasted when the vehicle is decelerated.

Flywheel of K. E . R. S Made of steel and carbon fibre which rotates at over 60,000 RPM. 60 kW power transmission in either storage or recovery 400 kJ of usable storage

Discharge mode of K. E. R. S

During this stage when the driver pushes the boost button the flywheel acts as a propulsion motor and discharges the energy to the wheels The Flywheel rotor is decelerated during boost discharge mode and the energy is converted back. Flywheel acts as a generator and sending energy back to electric motor, which works as propulsion motor.

Benefits of regenerative braking Reduction of pollution Increase in engine life Breaking is not total loss Wear Reduction

Reduction in pollution Railway vehicle – The Delhi Metro saved around 90,000 tons of carbon dioxide (CO2) from being released into the atmosphere by regenerating 112,500 megawatt hours of electricity through the use of regenerative braking systems Increase engine efficiency Regenerative brakes have been able to improve the performance of engines. This has been exhibited in the Motor sport industry –The system used by F! cars is called K. E. R. S (Kinetic Energy Recovery System)

Breaking is not total loss Conventional brakes apply friction to convert a vehicle’s kinetic energy into heat. In energy terms, therefore, braking is a total loss: once heat is generated, it is very difficult to reuse. The regenerative braking system, however, slows a vehicle down in a different way. Wear Reduction An electric drive train also allows for regenerative breaking which increases Efficiency and reduces wear on the vehicle brakes.

Limitations of regenerative braking system The regenerative braking effect drops off at lower speeds, therefore the friction brake is still required in order to bring the vehicle to a complete halt. The friction brake is a necessary back-up in the event of failure of the regenerative brake. Most road vehicles with regenerative braking only have power on some wheels (as in a 2WD car) and regenerative braking power only applies to such wheels, so in order to provide controlled braking under difficult conditions (such as in wet roads) friction based braking is necessary on the other wheels

Conclusion The energy efficiency of a conventional brake is only about 20 percent, with the remaining 80 percent of its energy being converted to heat through friction. The miraculous thing about regenerative braking is that it may be able to capture as much as half of that wasted energy and put it back to work. This reduces fuel consumption by 10 to 25 percent. Hence regenerative braking plays an important role in fuel consumption and also in the field of speed

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