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Title : Design and Development of a Flywheel-Based Regenerative Braking System for Bicycles
Author: Ravikiran Kammar Designation : Lecturer Dept. of Mechanical Engg. University: Visvesvaraya Technological University
ISSN :
Volume: 01 Issue: 01
Publication Year: June 2026
ABSTRACT
As the basic principle of conservation of energy “Energy can neither be created nor be destroyed, it can only be converted from one form to another” flywheel stores energy when torque is applied by the energy source, and it releases stored energy when the energy source is not applying torque to it. Flywheel bicycle which takes energy from braking and stores it in a revolutionary device. The flywheel is making a comeback and it is forcing innovators to re-investigate the accepted limitations of energy storage. It allows for energy to be stored kinetically. Flywheel Bicycle stores energy in a similar way as how hybrid automobiles absorb energy from braking. In a hybrid car, the kinetic energy which is normally wasted during the braking process is redirected into the battery. But instead of directing energy into a battery, Flywheel Bicycle takes braking energy and uses it to spin flywheel. Regenerative braking refers to a system in which the kinetic energy of the vehicle is stored temporarily, as an accumulative energy, during deceleration, and is reused as kinetic energy during acceleration or running. Regenerative braking is a small, yet very important, step toward our eventual independence from fossil fuels. These kinds of brakes allow batteries to be used for longer periods of time without the need to be plugged into an external charger.
Keywords: Regenerative Braking, Flywheel Energy Storage, Kinetic Energy Recovery System (KERS), Bicycle, Energy Conservation, Sustainable Transportation, Mechanical Energy Storage, Green Mobility.
1.0 INTRODUCTION
1.1 Introduction to Conventional Braking System
Braking in a moving vehicle means the application of the brakes to slow or stop its movement, usually by depressing a pedal. The braking distance is the distance between the time the brakes are applied and the time the vehicle comes to a complete stop. When brakes are applied to a vehicle using conventional braking system, kinetic energy is converted into heat due to the friction between the wheels and brake pads. This heat is carried away in the airstream and the energy is wasted. The total amount of energy lost in this process depends on how often, how hard and for how long the brakes are applied.
1.2 Introduction to Regenerative Braking System
Regenerative braking is one of the emerging technologies which can prove very beneficent. The use of regenerative braking in a vehicle not only results in the recovery of the energy but it also increases the efficiency of vehicle(in case of hybrid vehicles) and saves energy, which is stored in the auxiliary battery. Generally the electric motor, is actuated when electric current is passed through it. But, when some external force is used to actuate the motor (that is during the braking process) then it behaves as a generator and generates electricity. That is, whenever a motor is run in one direction the electric energy gets converted into Mechanical energy, which is used to accelerate the vehicle and whenever the motor is run in opposite direction it functions as a generator, which converts mechanical energy into electrical energy. This makes it possible to employ the rotational force of the driving axle to turn the electric motors, thus regenerating electric energy for storage in the battery and simultaneously slowing the car with the regenerative resistance of the electric motors.This electricity is then used for recharging the battery Energy is always lost as friction in the event of application of a brake. If a part of that energy can be recovered, it helps in improving fuel economy of a vehicle or any machine that consumes petroleum products, ranging from airplanes to drill rigs. This is a concept of regenerative braking. Kinetic Energy Recovery System (K.E.R.S) is one such method used for regenerative braking. It employs the use of motor generator set, coupled to a battery for energy recovery. The motor-generator set acts as a generator in the event of braking and as a motor in the event of acceleration. Thus energy is stored in battery through the generator and the motor runs on this energy generated. Hence energy can be saved during braking and released during acceleration, saving fuel consumption system that takes the energy from braking a car and transforms it into electricity to be used as an alternate electrical power source. It is much like a Hybrid vehicle where petrol/diesel will be used as the primary energy source, with the collected energy being used to supplement it.[1]
1.3 Purpose of energy recovery
During braking, a lot of energy is wasted as heat due to friction. If this energy can be stored and used again, it can reduce fuel consumption up to 20% Cost of running is reduced significantly. Cost of running is reduced significantly.
Lower emission of exhaust gases reduces pollution and Global Warming. Mechanical Braking results in wear and tear of the brake linings & tyres. Regenerative braking avoids such problems to an extent.
A DECREASED FUEL CONSUMPTION IS VERY MUCH IMPORTANT SINCE THE FUEL RESERVES OF NATURE ARE DECLINING RAPIDLY. [1]
2.0 LITERATURE SURVEY
The Age of Industrialization, since the late 1800’s, has been nothing short of remarkable. The world has vastly benefitted with the advancement of technology and knowledgebase which has brought about enormous socio-economic progress and consequently raised the standard of living of humankind beyond comprehension. Among the many resources which have played a major part in the growth, the role of fossil fuels has been undeniably quite significant. But the reserves of these ‘nonrenewable’ fossil fuels are rapidly declining and at the rate of growth of the humankind, the exhaustion of these resources in near future in inevitable. This has been the one of the major causes of concern in the recent past. The other major concern in the present day has been declining state of environment. The inefficient and excess usage of fossil fuels has caused the pollution of the environment, to the extent of its breakdown. As a result, over the past 40-50 years, the focus has shifted towards finding solutions which combat these issues, with the major areas of concentration being efficient usage of energy resources (fossil fuels) in various applications like industry, transportation etc., finding alternative and/or renewable energy resources to supplement/replace the fossil fuel, better control strategies and treatment techniques to reduce pollution.
Automobiles are one of the major consumers of fossil fuels and therefore:
One of the major sectors responsible for their depletion to the extent of near exhaustion;
One of the major contributors to the escalating environmental pollution levels.
Due to these problems, in the recent past, the Auto Industry has come to an impasse where they are left with no alternative but to find alternate solutions to conserve natural resources.
Over the years, the efforts in this direction have led to research and development in the following areas:
1. Improving engine efficiencies and performance with the help of innovation in engine design and its components, improved control strategies etc.
2. Emission treatment and control technologies.
3. Vehicle design changes for reduction of thermal, aerodynamic and road losses.
4. Improvised Transmission design to reduce losses.
5. Hybrid and Alternative Energy Propulsion systems e.g. the Hybrid Electric Vehicle (HEV), the Fuel Cell Vehicle (FCV).
6. Recycling Braking energy – Storage and reuse of braking energy which is otherwise lost in the form of heat energy technology that achieves this purpose is termed as a Regenerative Braking System (RBS).
With legislations in place for strict emission standards, the automobile industry currently has embraced the new development, by embedding one or more of the above mentioned technologies in commercial vehicles. Additionally, as a long term alternative to fossil fuels, the research in ‘Alternative Energy Vehicles’, especially the field of ‘Hybrid Propulsion with Regenerative braking’ has come to the forefront. ‘Hybrid Propulsion Vehicles (HPV)’ or ‘Hybrid Vehicles’ are vehicles in which two or more power sources propel the vehicle, in order to share the load and hence improve performance/improve fuel efficiency. Most of the current hybrid vehicles use an internal combustion engine (ICE) as one of the power sources and an alternative energy source (electrochemical battery, Fuel cell etc.) for the other source. By utilizing a hybrid power train, the load on the ICE reduces, as a result of which the size of the ICE can be reduced. Reduction of an ICE implies better fuel efficiency. Alternatively/additionally the ICE can be optimized to operate only in certain load conditions, which also results in improved fuel efficiency. Overall, the result is a more efficient vehicle. As an additional tool to improving efficiency, current hybrid vehicles also employ regenerative braking to capture and utilize braking energy. Regenerative Braking Systems (RBS) capture the energy that is usually lost while braking, store that energy in an energy storage system (ESS) and the reuse it to start or accelerate the vehicle. In case of HEVs, regenerative braking is easily implemented as the electrical technology used to run the wheels is modified to also perform regenerative braking. Designing and testing such a regenerative braking system for the application in a Formula racecar is the topic of this research. The later part of this chapter is as follows: In the next section, the motivation for the thesis is explained followed by the problem statement, after which the aims for the research and design are set and methodology used is explained.
Jayhawk Motorsports, University of Kansas is a student run organization that designs, manufactures, and builds two race cars within the given school year. It has been participating in annual student design competition organized by SAE (Society of Automotive Engineers) – the Formula SAE for a little more than 20 years. The Formula SAE is a mainly a design, build and racing competition of mini-Indy type prototype racecars. These race cars are designed and manufactured by the students, in adherence to the guidelines/constraints set by SAE and with the intended market to be of nonprofessional weekend autocross racer. From 2011 onwards, Jayhawk Motorsports has decided to use its experience from Formula SAE and start participating in Formula Hybrid as well.Formula Hybrid is a competition similar to Formula SAE which involves designing, building and racing high performance hybrid and electric vehicles instead of conventional one. In Formula Hybrid, the guidelines allow the racecar to be fitted with a regenerative braking system. It was observed that firstly in an autocross style racing with frequent braking events there is a potential for a substantial amount of braking energy, secondly, fitting an RBS to the vehicle would not only capture the braking energy, increase energy efficiency, but it could also provide the edge in performance as long as the gain can outweigh the loss due to the extra weight addition and required power was calculated. The data was used in the design and selection of individual components of the Flywheel RBS.
One of the earliest major applications of FES in vehicles was the ‘Electrogyro’ bus. Around the end of 1940s, Oerlikon (Switzerland) developed the ‘Electrogyro’ bus which was a city bus with exclusively flywheel based propulsion system for short range of around 6 km. It had a huge 1500 kg steel flywheel which ran up to a top speed of 3000 rpm, was recharged at charging points by electric supply and the bus ran using a motor/generator setup. It was tested and it ran successfully first in Yverdon-les-baines, Switzerland. Due to the huge weight of the flywheel machine and the associated safety (gyroscopic, bearings etc.) and efficiency issues, although it was practically pollution free, the running of this bus was discontinued after a few years of service. Another instance was demonstrated by the Garrett Ai Research company, when in 1960s they produced a flywheel energy storage unit with electric motor/generator unit (electrical transmission) which was tested and implemented successfully on a prototype New York R32 Subway car. In the 70s, with the beginning of the energy crisis Garrett went on to design and test the same technology for other commercial applications like t transit bus, a concept train and commercial automobiles About the same time, there were several Government sponsored studies on the feasibility and different configurations for Flywheel and Flywheel Hybrid propulsion for commercial automobiles. As a culmination of these studies, during the end of 70s, General Electric (GE) came up with its own version of the Flywheel bus or the gyro bus using a 1.5 ton flywheel and electric motor/generator for transmission. Also, General Motors (GM) extensively studied the flywheel hybrid for their new concept commercial vehicle, which they designed and simulated in 1986. This system had a mechanical transmission (CVT), but after the simulation it was realized that the system (engine/flywheel hybrid) didn’t match the expected requirement, hence the project was discontinued. Leyland Bus in the U.K. successfully tested and demonstrated the mechanical regenerative braking system in their busses around the 80s. The system consisted of a composite flywheel (developed by British Petroleum) and the Leyland CVT for transmission.
During the early 1990s, Chrysler had developed the ‘Patriot’, a concept car for Le Mans 24 hour race. It was a gas turbine-electric hybrid vehicle with a Flywheel Regenerative Braking System used for the purpose of load leveling, with a composite flywheel. The project was dropped later due to issues in safety and packaging. With the development and usage of the composite materials for flywheels, the research in flywheels propulsion picked up immensely. One of the most significant events in recent times, was that FIA authorized the use of Hybrid drive trains for Formula 1 2009 season. Due to this development, various Regenerative Braking System “Kinetic Energy Recovery System (KERS)” options including flywheel systems were explored and devised.
2.1 Suchlike, N.A. (1986)
As a culmination of government sponsored, GM research and other studies in the fuel economy potential of flywheel hybrid vehicles, GM designed a concept engine-flywheel hybrid drive system for a compact car and predicted its performance using analytical tools. Initially, for the power train concept two versions were considered, one was a system which had two mode operation and the other with one mode operation. A CVT is used for transmission in both cases. The two mode drive discontinued due to high level of complexity in design and hence the simpler one mode drive was chosen. The one mode drive was a parallel drive system in which wheels or accessories (of the vehicle) were driven either by the engine or the flywheel and similarly, the energy recovered by regenerative braking charged the flywheel or the accessories. There was no method of charging the flywheel directly through the engine. All the flywheel energy was captured only through braking. The design of flywheel was based on the GM Cymbal Flywheel and had a maximum rotational speed of 12000 RPM, and energy storage of 60Wh. After laboratory tests and computer simulation, the performance was predicted to achieve a significant gain in urban fuel economy but the highway fuel economy could not meet the required efficiency levels and hence the project was discontinued.
2.2 Jefferson and Ackerman (1996)
The paper describes a flywheel based energy storage system designed as a standalone propulsion unit or the main propulsion unit in a hybrid setup, for a railcar application. The system comprised of a steel flywheel and a mechanical variation (i.e., CVT) for matching the speeds of output drive train and the flywheel and also in order to affect power transfer from/to the flywheel by the variation of the CVT ratio. The Flywheel of flywheel energy storage (FES) could be charged by an onboard or external power source (battery, engine etc.) en-route or at stops, and by regenerative braking and the charged FES was used to propel the railcar. The system was tested on a laboratory test rig and successfully demonstrated on a minitram. The test rig setup used a composite flywheel, a KOPP CVT and an induction motor as power source (simulating vehicle). Open and closed loop tests were used to understand CVT control and gauge system performance. The minitram system used a steel flywheel of 4 MJ storage capacity. The results from the Minitram system showed that on using ‘flywheel only’ propulsion, the energy savings were around 24%. It was concluded that having a hybrid powertrain with a flywheel variator system and a compact constant power source like an Internal Combustion Engine (ICE) or Fuel Cell would result in a fuel efficient vehicle of large range.
2.3 ETH -Hybrid III: Dietrich (1999)
The parallel hybrid drive train design of ETH – III hybrid vehicle project has been described. The design was successfully tested and implemented. An ICE, an electric motor, a flywheel, a CVT with a wide gear ratio and a battery (5 kWh capacities) are all part of the drive train. Three friction clutches control the power flow between the output and the sources. The drive train has the capability to operate in different drive modes, due to which the vehicle can be powered individually by the engine, flywheel or the motor, or the motor and flywheel can operate in a combined mode. The control of the drive modes was one the basis of the output load requirement. Flywheel could be charged by the engine or by regenerative braking, but the regenerative braking potential was limited. The entire power train system was tested on a dynamic test bench after the completion of individual component testing and then the system was integrated into a Multi-Utility Vehicle and tested on a chassis-dynamometer test bench.
2.4 Hayes et al (1999)
This paper describes the University of Texas-Center for Electro Mechanics (UT-CEM)’s Flywheel Battery (FWB) project for a hybrid electric transit bus. A Flywheel Battery (FWB) is common nomenclature for systems in which the transmission is an electric motor/generator but the energy is stored in rotational form in a flywheel. So when the FWB is used for regeneration, the rotational energy of the wheels is converted into electrical energy and back into rotational energy at the flywheel using an electrical motor/generator and vice versa for acceleration. UT-CEM developed computer models to simulate hybrid electric drive train with FWB to calculate the design requirement. The FWB used in this demonstration had a 2 kWh composite flywheel and a high speed permanent magnet motor/generator with magnetic bearings. The FWB was of “partially integrated topology” which means that the flywheel and motor/generator are separate components but ride on the same shaft and in a single housing. Initial testing was carried out using a titanium flywheel and the thermal analysis results obtained were included to optimize the design. All components are individually bench tested for safety and optimization. The paper describes the system in pre-vehicle integration testing phase.
2.5 Zero Inertia Power train at Eindhoven University (2001-06)
The Eco Drive project and related work done at the Eindhoven University of Technology presents an innovative power train concept called “the Zero Inertia power train (ZI)” with the aim of improve fuel efficiency of vehicle by efficient engine utilization methods and hybrid strategies to achieve load sharing. Optimal engine operation is ensured by the use of the CVT and additionally the flywheel power assist helps in load sharing. The Planetary Gear System (PGS) through its three degrees of freedom connects the primary shaft of Metal push belt CVT (engine side), the secondary shaft of the CVT and the flywheel. One application of the powertrain, called the “IdleStop and Go” (SG) powertrain, for use in start-stop operation of a vehicle, in presented. The system operates such that when the vehicle comes to a stop or to idle, the engine is shut off .When the vehicle needs to resume motion, the flywheel launches the vehicle as well restarts the engine. This way the fuel consumed during idling in conventional systems is saved. The flywheel is charged by the engine as well as through regenerative braking although that functionality is limited. [1]
3.0 FLYWHEEL Methodology
Flywheel is a simple rotating wheel used to store energy or stabilize something. The energy it stores is equal to its moment of inertia -- a physics term that basically means the mass of the object times the square of its distance from the axis of rotation -- times the square of its angular velocity divided by 2. Flywheels help stabilize drive shafts subject to alternating pressures, such as piston engines or piston pumps. The stabilizing effect comes from the flywheel resisting changes in its rotational speed.
Flywheels are used as power storage devices for high-power science experiments that would produce an unacceptable power spike if removing power from the electric grid. Such flywheel batteries might operate in a vacuum, to prevent energy loss due to air friction, and will be periodically sped up again to compensate for rotation speed lost due to energy dissipation from heat and vibration. Good flywheel designs will dissipate as little heat and vibration as possible, retaining energy for the target application.
A flywheel stores different quantities of energy depending on its mass and rotation speed. For instance, a bicycle wheel has a mass of about 1 kg (2.2 lb), diameter of about 70 cm (28 in), and a rotation speed of about 150 rpm (rotations per minute). This adds up to a stored energy of 15 J (joules). Next, consider a wheel on a train moving at 60 kph (37 mph), with a mass of 942 kg (2,076 lb), diameter of 1 m (3.3 ft), and a rotational speed of 318 rpm. This flywheel would have a rotational energy of about 64 kJ (kilojoules), roughly 43,000 times greater than the bike wheel.
Flywheel batteries dedicated to energy storage have energies much larger than both these previous examples, mainly due to extreme rotation speeds. One example made by a flywheel company in Ottawa boasts a 100 kg (220 lb) mass, diameter of 60 cm (27 in), and a rotation speed of 20,000 rpm. This flywheel battery can store about 10 MJ (mega joules), enough to light 100 100-watt light bulbs for 1,000 seconds. This flywheel battery design is not much larger than a refrigerator. An even larger flywheel, of the type used as an electric power backup, may hold 100 MJ of power. These types of flywheels may be used by casinos, hospitals, data centers, or in industry to maintain power in case of a failure or fluctuations in input.
3.1 Basic Concept of a Flywheel Bicycle:
Maxwell von Stein developed a Flywheel Bicycle which takes energy from braking and stores it in a revolutionary device. The flywheel is making a comeback and it is forcing innovators to re-investigate the accepted limitations of energy storage. This simple piece of technology has been used years ago in Victorian-era Europe. It allows for energy to be stored kinetically, instead of requiring chemicals as in modern lithium-ion or hydrogen fuel cell batteries.
Maxwell’s Flywheel Bicycle stores energy in a similar way as how hybrid automobiles absorb energy from braking. In a hybrid car, the kinetic energy which is normally wasted during the braking process is redirected into the battery. But instead of directing energy into a battery, Stein’s Flywheel Bicycle takes braking energy and uses it to spin a 15 pound flywheel. Since objects in motion tend to stay in motion, a well-constructed flywheel can keep spinning for a significant duration. If a person wants to extract energy from a flywheel, they can use gears to decrease the speed of the flywheel and redirect that energy to another wheel or gear. In the case of the Flywheel Bicycle, the energy is redirected to the rear wheel, which provides extra speed to the bike without needing to pedal.
This technology could come in very handy for a person who lives in a hilly city.Cyclists in need to use their brakes when going downhill. But when they want to go uphill on a street the extra power from the flywheel would be very beneficial.
3.2 Energy storage in flywheels
A flywheel stores energy in a rotating mass. Depending on the inertia and speed of the rotating mass, a given amount of kinetic energy is stored as rotational energy. The flywheel is placed inside a vacuum containment to eliminate friction-loss from the air and suspended by bearings for a stabile operation. Kinetic energy is transferred in and out of the flywheel with an electrical machine that can function either as a motor or generator depending on the load angle (phase angle). When acting as motor, electric energy supplied to the stator winding is converted to torque and applied to the rotor, causing it to spin faster and gain kinetic energy. In generator mode kinetic energy stored in the rotor applies a torque, which is converted to electric energy. Apart from the flywheel additional power electronics is required to control the power in- and output, speed, frequency etc.
The kinetic energy stored in a flywheel is proportional to the mass and to the square of its rotational speed according to Eq. (3.2.1)
Ek = 0.5Iω2……………………………………………………………………… (3.2.1)
Where,
Ek is kinetic energy stored in the flywheel,
I is moment of inertia and
ω is the angular velocity of the flywheel.
Table 1
Shape-factor K for different planar stress geometries
Table 3.2.1 Shape-factor K
Model
Fig3.2.1 Model of flywheel bicycle
3.3 FLYWHEEL CONSTRUCTION
Fig.3.3.1 Flywheel dimensions
The flywheel is made from steeel filament wrapped around a steel hub. The tensile strength of the steel prevents it from shattering under the G-loads at such high speeds.
Magnetization of the integrated magnetic particles generates the required field configuration forming the rotor. With no large metallic structures in the MLC flywheel rotor, eddy current losses are negligible resulting in very high electrical efficiencies.
The flywheel is kept in a robust housing. To avoid air resistance from slowing down the flywheel, the housing is made vacuum. It is so built that it can maintain a vacuum pressure of 10-7 bar virtually indefinitely.
3.4 Design Approach
There are two stages to the design of a flywheel.
First, the amount of energy required for the desired degree of smoothening must be found and the (mass) moment of inertia needed to absorb that energy determined.
Then flywheel geometry must be defined that caters the required moment of inertia in a reasonably sized package and is safe against failure at the designed speeds of operation.
3.4.1 Speed fluctuation
The change in the shaft speed during a cycle is called the speed fluctuation and is equal to speed fluctuation =ωmax- ω min
Fl=ωmax –ωmin…………………………………........................................... (3.4.1.1)
Where ωavg is nominal angular velocity
3.4.2 Co-efficient of speed fluctuation
Coefficient of speed fluctuation Cf and it is defined as
C f= ωmax−ωmin/ω………………………….……… (3.4.2.1)
Where ω is nominal angular velocity, and ωave the average or mean shaft speed desired. This coefficient is a design parameter to be chosen by the designer.
The smaller this chosen value, the larger the flywheel have to be and more the cost and weight to be added to the system. However the smaller this value more smoother the operation of the device
It is typically set to a value between 0.01 to 0.05 for precision machinery and as high as 0.20 for applications like crusher hammering machinery.
3.4.3 Design Equation
The kinetic energy Ek in a rotating system
Ek = 0.5Iω2 (from Eq.…..3.2.1)
Hence the change in kinetic energy of a system can be given as,
Ek=0.5Im (ω2max−ω2min)………………………………………… (3.4.3.1)
Thus the mass moment of inertia Im needed in the entire rotating system in order to obtain selected coefficient of speed fluctuation is determined using the relation
Machine
The above equation can be used to obtain appropriate flywheel inertia Im corresponding to the known energy change Ek for a specific value coefficient of speed fluctuation Cf, [2]
4.0 Design Selection(Methodology in design)
The final design selection of the system is based on the following three criterions.
1. Energy Storage
2. Mounting
3. Manual Control
Several designs were considered for each system, with the best being selected based on safety, cost, practicality, and simplicity
4.1 Energy Storage
Three designs were considered for storing the braking energy of the bicycle:
4.1.1 Flywheel
A flywheel is a standard method of retaining rotational energy. The heavy disc is brought up to speed, along with the bicycle, and maintains its angular speed even when the bicycle has slowed. It maintains its rotational energy for later use with minimal losses to bearing friction.
4.1.2 Spiral Torsion Spring
A spiral tensional spring stores energy from being wound around its center axis. The amount of energy stored depends on the spring constant of the spring and the rotational distance the spring is moved from its original position.
4.1.3 Selection
The final selection is to store mechanical energy using a torsion spring. The spring provides the greatest potential to design a lightweight, efficient, durable, and reliable system. It provides a high enough torque to accelerate comfortably from stop. Although the tensional spring charges and discharges in opposite directions, it has been determined that it is possible to charge from the outside and release from the inside, or vice versa.
4.2 Mathematical Calculations
Formula
Wt. of flywheel= Diameter *diameter*length/162179
Size= 200*200*32/162179=7.8 kgs weight [3]
Design Equation
The kinetic energy EK in a rotating system
EK = I ( )………………………………………………..(4.2.1)
Hence the change in kinetic energy of a system can be given as,
EK = Im ( )
EK = E2 – E1
)
EK = Is ( )( )……………………………(4.2.2)
E2 – E1 =
Is =
EK = Is ( ) ( )
Is = …………………………………………..(4.2.3)
Thus the mass moment of inertia Im needed in the entire rotating system in order to obtain selected coefficient of speed fluctuation is determined using the relation
EK = Is ( ) ( )
Is =
The above equation can be used to obtain appropriate flywheel inertia I m corresponding to the known energy change EK for a specific value coefficient of speed fluctuation
Worked out Example
A 2.2 kw, 960 rpm motor powers the cam driven ram of a press through a gearing of 6:1 ratio. The rated capacity of the press is 20kN and has a stroke of 200 mm assuming that the cam driven ram is capable of delivering the rated load at a constant velocity during the last 15% of a constant velocity stroke. Design a suitable flywheel that can maintain a coefficient of Speed fluctuation of 0.02. Assume that the maximum diameter
of the flywheel is not to exceed 0.6m.
Work done by the press = 20*103*0.2*0.15
= 600 Nm
Work done by the press = Energy absorbed=600 Nm
Mean torque on the shaft :
= 21.88 Nm
Energy supplied =work done per cycle
= 2 *21.88*6
= 825 Nm
Thus mechanical efficiency of the system (η)
η = = 0.727 = 72%
Therefore the fluctuation in the energy is =
EK= Energy absorbed –Energy supplied
600 – 825 * 0.075 (21.88 * 6 * * 0.15)
538.125 Nm
I = =
= 2.6622 kg m2
I = ( + ) t
Assuming = 0.8
2.6622 = * ( ) t
= 59.805t
t = = 0.0445
or
45 mm
t = ( ) ( + - r2)
t = ( ) (0.242+ 0.32 - * 0.242)
t = 0.543 * (
= 55667N/m2
= 0.556MPa
or if t = 150 MPa
150 * 106 = 7961.4 (0.4125) (0.0376) (0.090) (0.0331)
= 0.548
= 16544 rad/sec2
NOS = = = 164.65
5.0 MECHANISM
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. Regenerative braking is used on hybrid gas/electric automobiles to recoup some of the energy lost during stopping. This energy is saved in a storage battery and used later to power the motor whenever the car is in electric mode.
5.1 Chain drive with sprockets
This is one of the most important parts of a chain drive which gives the final push or motion to the wheels and makes the vehicle move.
A sprocket is a toothed wheel upon which a chain rides. Contrary to popular opinion, a sprocket is not a gear.
Fig 5.1.1 Chain drive with spockets
5.2 Chain Construction
Chains have a surprising number of parts. The roller turns freely on the bushing, which is attached on each end to the inner plate. A pin passes through the bushing, and is attached at each end to the outer plate. Bicycle chains omit the bushing, instead using the circular ridge formed around the pin hole of the inner plate.
Fig 5.2.1 over view of the chain construction
5.3 Chain Dimensions
Chain types are identified by number; i.e. a number 40 chain. The rightmost digit is 0 for chain of the standard dimensions; 1 for lightweight chain; and 5 for roller less bushing chain. The digits to the left indicate the pitch of the chain in eighths of an inch. For example, a number 40 chain would have a pitch of four-eighths of an inch, or 1/2", and would be of the standard dimensions in width, roller diameter, etc.
The roller diameter is "nearest binary fraction" (32nd of an inch) to 5/8ths of the pitch; pin diameter is half of roller diameter. The width of the chain, for "standard" (0 series) chain, is the nearest binary fraction to 5/8ths of the pitch; for narrow chains (1 series) width is 41% of the pitch. Sprocket thickness is approximately 85-90% of the roller width.
5.4 Sprockets
There are four types of sprocket;
• Type A: Plain Plate sprockets
• Type B: Hub on one side
• Type C: Hub on both sides
• Type D: Detachable hub
Sprockets should be as large as possible given the application. The larger a sprocket is, the less the working load for a given amount of transmitted power, allowing the use of a smaller-pitch chain. However, chain speeds should be kept less than 1200 feet per minute.
The dimensions of a sprocket can be calculated as follows, where P is the pitch of the chain, and N is the number of teeth on the sprocket;
Pitch Diameter = P ÷ sin (180° ÷ N)
Outside Diameter = P × (0.6 + cot (180° ÷ N))
Sprocket thickness = 0.93 × Roller Width - 0.006
5.5 Application of Sprockets
Sprockets should be accurately aligned in a common vertical plane, with their axes parallel. Chain should be kept clean and well lubricated with thin, light-bodied oil that will penetrate the small clearances between pins and bushings. [3]
6.0 REGENERATIVE BRAKES
Concept of this regenerative brake is better understood from bicycle fitted with dynamo. If our bicycle has a dynamo (a small electricity generator) on it for powering the lights, we'll know it's harder to peddle when the dynamo is engaged than when it's switched off. That's because some of our peddling energy is being "stolen" by the dynamo and turned into electrical energy in the lights. If we're going along at speed and we suddenly stop peddling and turn on the dynamo, it'll bring us to a stop more quickly than we would normally, for the same reason: it's stealing our kinetic energy. Now imagine a bicycle with a dynamo that's 100 times bigger and more powerful. In theory, it could bring our bike to a halt relatively quickly by converting our kinetic energy into electricity, which we could store in a battery and use again later. And that's the basic idea behind regenerative brakes! Electric trains, cars, and other electric vehicles are powered by electric motors connected to batteries. When we're driving along, energy flows from the batteries to the motors, turning the wheels and providing us with the kinetic energy we need to move.
When we stop and hit the brakes, the whole process goes into reverse: electronic circuits cut the power to the motors. Now, our kinetic energy and momentum makes the wheels turn the motors, so the motors work like generators and start producing electricity instead of consuming it. Power flows back from these motor-generators to the batteries, charging them up. So a good proportion of the energy we lose by braking is returned to the batteries and can be reused when we start off again. In practice, regenerative brakes take time to slow things down, so most vehicles that use them also have ordinary (friction) brakes working alongside (that's also a good idea in case the regenerative brakes fail).
That's one reason why regenerative brakes don't save 100 percent of our braking energy.
A regenerative brake is an energy recovery mechanism which slows a vehicle or object down by converting its kinetic energy into another form, which can be either used immediately or stored until needed. This contrasts with conventional braking systems, where the excess kinetic energy is converted to heat by friction in the brake linings and therefore wasted.
The most common form of regenerative brake involves using an electric motor as an electric generator. In electric railways the generated electricity is fed back into the supply system, whereas in battery electric and hybrid electric vehicles, the energy is stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic motors and store energy in form of compressed air.
Concept of this regenerative brake is better understood from bicycle fitted with dynamo. If our bicycle has a dynamo (a small electricity generator) on it for powering the lights, we'll know it's harder to peddle when the dynamo is engaged than when it's switched off. That's because some of our peddling energy is being "stolen" by the dynamo and turned into electrical energy in the lights. If we're going along at speed and we suddenly stop peddling and turn on the dynamo, it'll bring us to a stop more quickly than we would normally, for the same reason: it's stealing our kinetic energy. Now imagine a bicycle with a dynamo that's 100 times bigger and more powerful. In theory, it could bring our bike to a halt relatively quickly by converting our kinetic energy into electricity, which we could store in a battery and use again later. And that's the basic idea behind regenerative brakes!
Electric trains, cars, and other electric vehicles are powered by electric motors connected to batteries. When we're driving along, energy flows from the batteries to the motors, turning the wheels and providing us with the kinetic energy we need to move.
When we stop and hit the brakes, the whole process goes into reverse: electronic circuits cut the power to the motors. Now, our kinetic energy and momentum makes the wheels turn the motors, so the motors work like generators and start producing electricity instead of consuming it. Power flows back from these motor-generators to the batteries, charging them up. So a good proportion of the energy we lose by braking is returned to the batteries and can be reused when we start off again. In practice, regenerative brakes take time to slow things down, so most vehicles that use them also have ordinary (friction) brakes working alongside (that's also a good idea in case the regenerative brakes fail).
That's one reason why regenerative brakes don't save 100 percent of our braking energy.
6.1 Advantages of Regenerative Braking
The device works by applying to the electric motor-generator the recovered electrical energy captured from the vehicle during braking events.
A generator is coupled onto the same shaft as that of the power train. The shaft rotates as long as vehicle is under throttle. When brake is applied, a micro-controller is employed to magnetize the poles of generator. Thus the generator is on and it reduces the torque on the shaft, utilizing it to generate energy.
The energy generated is stored into the Flywheel Capacitor by speeding up the flywheel. This is by using a special flywheel - “Magnetically loaded composite flywheel”
It may also be stored onto a battery in case a battery operated K.E.R.S is being employed. [4]
7.0 COMPONENTS IN DETAIL
7.1 Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. Energy is transferred to a flywheel by applying torque to it, thereby increasing its rotational speed, and hence its stored energy. Conversely, a flywheel releases stored energy by applying torque to a mechanical load, thereby decreasing its rotational speed.
Three common uses of a flywheel include:
• They provide continuous energy when the energy source is discontinuous. For example, flywheels are used in reciprocating engines because the energy source, torque from the engine, is intermittent.
• They deliver energy at rates beyond the ability of a continuous energy source. This is achieved by collecting energy in the flywheel over time and then releasing the energy quickly, at rates that exceed the abilities of the energy source.
• They control the orientation of a mechanical system. In such applications, the angular momentum of a flywheel is purposely transferred to a load when energy is transferred to or from the flywheel.
Flywheels are typically made of steel and rotate on conventional bearings; these are generally limited to a revolution rate of a few thousand RPM. Some modern flywheels are made of carbon fiber materials and employ magnetic bearings, enabling them to revolve at speeds up to 60,000 RPM [4]
8.0 BASIC ELEMENTS OF THE SYSTEM
There are four elements required which are necessary for the working of regenerative braking system, these are:
8.1 Energy Storage Unit (ESU)
The ESU performs two primary functions
1) To recover & store braking energy
2) To absorb excess energy during light load operation
The selection criteria for effective energy storage include:
I. High specific energy storage density
II. High energy transfer rate
III. Small space requirement
Fly wheels
In this system, the translational energy of the vehicle is transferred into rotational energy in the flywheel, which stores the energy until it is needed to accelerate the vehicle.
The benefit of using flywheel technology is that more of the forward inertial energy of the car can be captured than in batteries, because the flywheel can be engaged even during relatively short intervals of braking and acceleration. In the case of batteries, they are not able to accept charge at these rapid intervals, and thus more energy is lost to friction.Another advantage of flywheel technology is that the additional power supplied by the flywheel during acceleration substantially supplements the power output of the small engine that hybrid vehicles are equipped with.
8.2 Continuously Variable Transmission (CVT)
The energy storage unit requires a transmission that can handle torque and speed demands in a steeples manner and smoothly control energy flow to and from the vehicle wheels.
8.3 Components Specifications
8.3.1Bearing
Fig 8.3.1.1 Bearing
Dimensions
Center-ball bearings=ID=80mm
OD=100mm
Materials: Steel
8.3.2 Connecting Chain
Fig 8.3.2.2: chain [5]
9.0 COMPARISIONS
9.1 Advantages of regenerative braking over conventional braking
9.1.1 Energy Conservation
The flywheel absorbs energy when braking via a clutch system slowing the car down and speeding up the wheel. To accelerate, another clutch system connects the flywheel to the drive train, speeding up the car and slowing down the flywheel. Energy Is therefore conserved rather than wasted as heat and light which is what normally happens in the contemporary shoe/disc system.
9.1.2 Wear Reduction
An electric drive train also allows for regenerative breaking which increases Efficiency and reduces wear on the vehicle brakes.
In regenerative braking, when the motor is not receiving power from the battery pack, it resists the turning of the wheels, capturing some of the energy of motion as if it were a generator and returning that energy to the battery pack. In mechanical brakes; lessening wear and extending brake life is not possible. This reduces the use of use the brake.
9.1.3 Fuel Consumption
The fuel consumption of the conventional vehicles and regenerative braking system vehicles was evaluated over a course of various fixed urban driving schedules.
The results are compared as shown in figure. Representing the significant cost saying to its owner, it has been proved the regenerative braking is very fuel-efficient. 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 between 2004 and 2007. It is expected that the Delhi Metro will save over 100,000 tons of CO2 from being emitted per year once its phase II is complete through the use of regenerative braking. The energy efficiency of a conventional car 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 could reduce fuel consumption by 10 to 25 percent. Hydraulic regenerative braking systems could provide even more impressive gains, potentially reducing fuel use by 25 to 45 percent.
9.1.4 Braking 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.
9.2 Comparison of Dynamic brakes and Regenerative brakes
Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes,dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use dynamic brakes include forklifts, Diesel-electric locomotives, and streetcars. This heat can be used to warm the vehicle interior, or dissipated externally by large radiator-like cowls to house the resistor banks.
The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics and increased maintenance cost of the lines. With DC supplies, this requires that the voltage be closely controlled. Only with the development of power electronics has this been possible with AC supplies, where the supply frequency must also be matched (this mainly applies to locomotives where an AC supply is rectified for DC motors).
A small number of mountain railways have used 3-phase power supplies and 3-phase induction motors. This results in a near constant speed for all trains as the motors rotate with the supply frequency both when motoring and braking.
9.3 Why Regenerative Brakes are assisted with the Frictional Brake??
Traditional friction-based braking is used in conjunction with mechanical regenerative
Braking for the following reasons:
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. Physical locking of the rotor is also required to prevent vehicles from rolling down hills.
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 (in a two-wheel drive 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.
The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power and if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.
Under emergency braking it is desirable that the braking force exerted be maximum allowed by the friction between the wheels and the surface without slipping, over the entire speed range from the vehicle's maximum speed down to zero. The maximum force available for acceleration is typically much less than this except in the case of extreme high-performance vehicles. Therefore, the power required to be dissipated by the braking system under emergency braking conditions may be many times the maximum power which is delivered under acceleration. Traction motors sized to handle the drive power may not be able to cope with the extra load and the battery may not be able to accept charge at a sufficiently high rate. Friction braking is required to absorb the surplus energy in order to allow an acceptable emergency braking performance.
For these reasons there is typically the need to control the regenerative braking and match the friction and regenerative braking to produce the desired total braking output.
9.4 Comparison between Flywheel and Battery
The conversion of energy from mechanical to electrical to chemical energy, in a battery based KERS results in a lot of energy wastage. The efficiency of a battery based KERS system is only 35% compared to a Mechanical system with a efficiency of 70% Battery operated KERS is costlier and heavier than flywheel based Construction of a highly rigid vacuum housing is required to place the flywheel in order to sustain the high speed in it.[6]
10.0 APPLICATIONS
Flywheels are often used to provide continuous energy in systems where the energy source is not continuous. In such cases, the flywheel stores energy when torque is applied by the energy source and it releases stored energy when the energy source is not applying torque to it., a In this case, the flywheel—which is mounted on the crankshaft—stores energy when torque is exerted on it by a firing piston, and it releases energy to its mechanical loads when no piston is exerting torque on it. Other examples of this are friction motors, which use flywheel energy to power devices such as toy cars.
A flywheel may also be used to supply intermittent pulses of energy at transfer rates that exceed the abilities of its energy source, or when such pulses would disrupt the energy supply (e.g., public electric network). This is achieved by accumulating stored energy in the flywheel over a period of time, at a rate that is compatible with the energy source, and then releasing that energy at a much higher rate over a relatively short time. For example, flywheels are used in punching machines and riveting machines, where they store energy from the motor and release it during the punching or riveting operation.
The phenomenon of precession has to be considered when using flywheels in vehicles. A rotating flywheel responds to any momentum that tends to change the direction of its axis of rotation by a resulting precession rotation. A vehicle with a vertical-axis flywheel would experience a lateral momentum when passing the top of a hill or the bottom of a valley (roll momentum in response to a pitch change). Two counter-rotating flywheels may be needed to eliminate this effect. This effect is leveraged in momentum wheels, a type of flywheel employed in satellites in which the flywheel is used to orient the satellite's instruments without thruster rockets. [6]
11.0 FUTURE SCOPE
• Incorporation of the actuator mechanism in the CVTs for external control of the transmission if necessary.
• Vacuum and Containment Design for the flywheel for reduction of wind age losses.
• Bearing and clutch selection to reduce friction losses.
• Incorporation of Carbon Fiber or other composite material for high speed flywheel design
• Instead of metal low speed with the appropriate transmission-CVT for improving safety from shattering of flywheels.
• Rotational Dynamics analysis from the vehicle standpoint as to how inclusion of two
• Rotating counter-rotating flywheels from two f-RBS systems can affect the dynamics of the moving race car.
• A more comprehensive failure and fatigue analysis for safety of the system
• Control system design for the f-RBS operation in conjunction with the vehicle.
• Cooling system design if required.
• Physical/Experimental testing on a Rig and vehicle.
On the front of the virtual test rig, it can be developed further more to incorporate all the possible applications mentioned above. The current model needs to be run manually and individually for every acceleration and deceleration event. Instead, it can be modified to run a complete cycle with a few simple inputs with the help Solver scripts, sensors, Macros and GUI developing tools. Also road, bearing and clutch losses need to be incorporated for a complete dynamic analysis of the f-RBS system.
12.0 CONCLUSION
Using flywheel Bicycle results in:
1. Reduced fuel consumption
2. Reduced running costs
3. The Flywheel Based KERS is the more commonly used form since:
4. It is twice as efficient
5. Lighter
6. Cheaper
7. It provides a more stable output
8. KERS is now primarily used in Formula1 Motorsports.
Already automakers are moving toward alternative energy carriers, such as electric batteries, hydrogen fuel and even compressed air. Regenerative braking is a small, yet very important, step toward our eventual independence from fossil fuels. These kinds of brakes allow batteries to be used for longer periods of time without the need to be plugged into an external charger. These types of brakes also extend the driving range of fully electric vehicles. [7]
REFERENCES
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2. Brockbank, C. (n.d.). Development of full-toroidal traction drives in flywheel based mechanical hybrids (Bachelor's dissertation).
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4. Draz, A., Ashraf, H., & Makeen, P. (2024). Artificial intelligence computational techniques of flywheel energy storage systems integrated with green energy: A comprehensive review. e-Prime: Advances in Electrical Engineering, Electronics and Energy, 10, 100801.
5. Hewko, L. O. (1986). Automotive traction drive CVTs: An overview (SAE Technical Paper No. 861355). SAE International.
6. Jin, Y., Huang, X., Zhong, Z., Lin, F., & Yang, Z. (2026). Review of the key technologies and development of flywheel energy storage in urban rail transit. Urban Rail Transit.
7. Li, X., & Palazzolo, A. (2021). A review of flywheel energy storage systems: State of the art and opportunities. Energy Storage Review.
8. Mandona, M., & Chilanga, M. (2026). Design and development of a kinetic energy recovery system (KERS) using a flywheel in bicycles. International Journal of Advanced Multidisciplinary Research and Studies, 6(2), 900–906.
9. Nkomo, N. Z., & Alugongo, A. A. (2024). Flywheel energy storage systems and their applications: A review. International Journal of Engineering Trends and Technology, 72(4), 209–215.
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