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A

MAJOR PROJECT REPORT

ON

REGENERATIVE BRAKING SYSTEM

Submitted in the partial fulfillment of the award of

Bachelor of Technology(Rajasthan Technical University, Kota)

In

MECHANICAL ENGINEERING

Session 20092013

Submitted To: - Submitted By:-

Mrs. Rajashree T.B. Imran Khan

(H. O. D.) Vikram Khan

Shakeel Khan

Nandkishore Sharma

Vishal Kumar Gupta

DEPARTMENT OF MECHANICAL ENGINEERING

SIDDHI VINAYAK COLLEGE OF SCIENCE & HIGHER

EDUCATION

ALWAR


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CERTIFICATE

This is to certify that Imran Khan, Vikram Khan, Shakeel Khan,

Nandkishore Sharma, Vishal Kumar Gupta are student of

B.Tech.(Mechanical Engineering) 8th

semester, Final Year have submitted

Their Project report entitled Fabrication of electricity generation byspeed braker under my guidance.

APPROVED BY:-

Mrs. Rajashree T.B. Anurag Dixit

(H.O.D) (Principal)


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FORWARDING LETTER

A PROJECT ONREGENERATIVE BRAKING SYSTEM

SUBMITTED BY:-

Imran Khan

Vikram Khan

Shakeel Khan

Nandkishore Sharma

Vishal Kumar Gupta

This dissertation is in partial fulfillment as prerequisite to the award of the

degree BACHELOR of TECHNOLOGY in Mechanical Engineering from

Rajasthan Technical University during the Academic session 2009-2013.

Mr. Asgar khan

Mr. Dinesh Jangid

Designation of Project Guide


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CANDIDATE DECLARATION

We hereby declare that the work presented in the report preparation

submitted in fulfillment of the award of the degree of Bachelor of

Technology in Mechanical Engineering in an authentic record of our on

work carried out under the able guidance of Mrs. Rajashree T.B. (H.O.D.)

department of mechanical engineering.

Imran Khan

Vikram Khan

Shakeel Khan

Nandkishore Sharma

Vishal Kumar Gupta


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ACKNOWLEDGEMENT

We express our sincere thanks to all faculties, teaching & non teaching staffs

of department of Mechanical Engineering for us kind help in completing our

project. It was due to us kind cooperation, valuable suggestions and effective

discussions.

We would like acknowledge Mr. Rajashree T.B. (H.O.D. Mech. Engg.) for

his constant encouragement for the completion of this project successfully.

(Name of the students) (Signature of the students)

Imran Khan

Vikram Khan

Shakeel Khan

Nandkishore Sharma

Vishal Kumar Gupta


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ABSTRACT

Regenerative Braking System is the way of slowing vehicle by using the motors as brakes.

Instead of the surplus energy of the vehicle being wasted as unwanted heat, the motors act

as generators and return some of it to the overhead wires as electricity.

The vehicle is primarily powered from the electrical energy generated from the generator,

which burns gasoline. This energy is stored in a large battery, and used by an electric

motor that provides motive force to the wheels. The regenerative barking taking place on

the vehicle is a way to obtain more efficiency; instead of converting kinetic energy to

thermal energy through frictional braking, the vehicle can convert a good fraction of its

kinetic energy back into charge in the battery, using the same principle as an alternator.


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CONTENTS

1. Introduction1.1 Need for regenerative brakes

2. Basic idea of Regenerative brakes2.1 The Motor as a generator

3. Basic elements of the system3.1 Energy Storage Unit (ESU)

3.2 Continuously Variable Transmission (CVT)

3.3 Controller

3.4 Regenerative Brake Controllers

4. Different types of Regenerative braking4.1. Electric Regenerative Braking4.2. Hydraulic Regenerative Brakes

4.3. Fly Wheels

4.4. Use in compressed air

4.5. Regenerative Braking Using Nitilon Spring

5. Applications

6. Comparisons6.1 Advantages of regenerative braking over conventional braking

6.2 Comparison of Dynamic brakes and Regenerative brakes

6.3 Why Regenerative Brakes are assisted with the Frictional Brake??

7. Conclusion


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I NTRODUCTION

Brake:-

A brake is a machine element and its principle object is to absorb energy during

deceleration. In vehicle brakes are used to absorb kinetic energy whereas in hoists or

elevators brakes are also used to absorb potential energy. By connecting the moving

member to stationary frame, normally brake converts kinetic energy to heat energy. This

causes wastage of energy and also wearing of frictional lining material.

Regenerative Braking System:-

Regenerative Braking System is the way of slowing vehicle by using the motors as

brakes. Instead of the surplus energy of the vehicle being wasted as unwanted heat, the

motors act as generators and return some of it to the overhead wires as electricity.

The vehicle is primarily powered from the electrical energy generated from the generator,

which burns gasoline. This energy is stored in a large battery, and used by an electric

motor that provides motive force to the wheels. The regenerative barking taking place on

the vehicle is a way to obtain more efficiency; instead of converting kinetic energy to

thermal energy through frictional braking, the vehicle can convert a good fraction of its

kinetic energy back into charge in the battery, using the same principle as an alternator.Therefore, if you drive long distance without braking, youll be powering the

vehicle entirely from gasoline. The regenerative braking

Regenerative Braking System comes into its own when youre driving in the city, and

spending a good deal of your time braking.

You will still use more fuel in the city for each mile you drive than on the highway,

though. (Thermodynamics tells us that all inefficiency comes from heat generation. For

instance, when you brake, the brake pedals heat up and a quantity of heat, or energy, is lost

to the outside world. Friction in the engine produces heat in the same way.

Heat energy, also, has higher entropy than, say, electric, meaning that it is less ordered.)


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Definition:

Braking method in which the mechanical energy from the load is converted into

electric energy and regenerated back into the line is known as Regenerative

Braking. The Motor operates as generator.

Regenerative Braking For Hybrid Vehicle:

In most electric and hybrid electric vehicles on the road today, this is accomplished

by operating the traction motor as a generator, providing braking torque to the wheels and

recharging the traction batteries. The energy provided by regenerative braking can then be

used for propulsion or to power vehicle accessories.


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NECESSITY OF THE SYSTEM

The regenerative braking system delivers a number of significant advantages over

a car that only has friction brakes. In low-speed, stop-and-go traffic where little

deceleration is required; the regenerative braking system can provide the majority of the

total braking force. This vastly improves fuel economy with a vehicle, and further

enhances the attractiveness of vehicles using regenerative braking for city driving. At

higher speeds, too, regenerative braking has been shown to contribute to improved fuel

economyby as much as 20%.

Consider a heavy loaded truck having very few stops on the road. It is operated

near maximum engine efficiency. The 80% of the energy produced is utilized to

overcome the rolling and aerodynamic road forces. The energy wasted in applying brake

is about 2%. Also its brake specific fuel consumption is 5%.

Now consider a vehicle, which is operated in the main city where traffic is a major

problem here one has to apply brake frequently. For such vehicles the wastage of energy

by application of brake is about 60% to 65%. And also it is inefficient as its brake specific

fuel consumption is high.

HEAVY LOADED TRUCK CITY BUS

2.1 Graphical representation of energy usage between two vehicles.

In regenerative breaking system both these problems is solved i.e. Storage of energy and

efficient brake specific fuel consumption.

Some of the advantages of regenerative braking over conventional braking are as

follows:

Road 80%

Other

18%

Rake 65%

Road

26%

Brake 2% other 9%


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BASIC IDEA OF 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'sSwitched off.

That's because some of our peddling energy is being "stolen" by the dynamoAnd turnedinto 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 behindRegenerative 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.


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Fig. (c): Basic idea of Regenerative brakes


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ELEMENTS OF THE SYSTEM

There are three basic element required which are necessary for the working of regenerative

braking system, these are :

1.EnergyStorage Unit (ESU):

The ESU performs two primary functions

1.TO recover & store braking energy

2. TO absorb excess engine energy during light load operation

The selection criteria for an effective energy storage includes:-

1. High specific energy storage density

2. High energy transfer rate

3. Small space requirement

The energy recaptured by regenerative braking might be stored in one of three devices: an

electrochemical battery, a flywheel, in a regenerative fuel cell.

Regen and Batteries:

With this system, the electric motor of a car becomes a generator when the brake pedal isapplied. The kinetic energy of the car is used to generate electricity that is then used to

recharge the batteries. With this system, traditional friction brakes must also be used to

ensure that the car slows down as much as necessary. Thus, not all of the kinetic energy of

the car can be harnessed for the batteries because some of it is "lost" to waste heat. Some

energy is also lost to resistance as the energy travels from the wheel and axle, through the

drivetrain and electric motor, and into the battery. For example, the Toyota Prius can only

recapture about 30% of the vehicles kinetic energy.

The Honda Insight is another vehicle in addition to the Prius that is on the market and

currently uses regenerative braking. In the Insight there are two deceleration modes: When

the throttle is engaged, but the brake pedal is not, the vehicle slows down gradually, and

the battery receives a partial charge.

When the brake pedal is depressed, the battery receives a higher charge, whichslows the vehicle down faster. The further the brake pedal is depressed, the morethe conventional friction brakes are employed.


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In the Insight, the motor/generator produces AC, which is converted into DC, which is

then used to charge the Battery Module. The Insight, as well as all other regenerative

systems, must have an electric controller that regulates how much charge the battery

receives and how much the friction brakes are used.

Regen and Flywheels:

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.

Regen and Fuel Cells:

The third system uses what is known as a unitized regenerative fuel cell, which is designed

to both convert hydrogen and oxygen into energy and water, or be reversed to take the

energy from the wheels, combine it with water, and produce hydrogen and oxygen. The

system as a single unit is substantially lighter than a separate electrolyzer and generator,

which makes this system (known as a URFC) especially beneficial when weight is a

factor. When the URFC is paired up with lightweight hydrogen storage, it's energy density

of about 450 watt-hours per kilogram is ten times that of lead-acid batteries and twice as

much as any predictions for the energy density of forthcoming chemical batteries.

This means that not only will this technology make lighter hybrids available, it will also

give hybrids a driving range that is comparable to that of vehicles today that are equipped

with conventional engines. Further benefits of the URFC is that it will be more cost

effective than other vehicles because it will not need to be replaced, and it will provide the

additional power needed by an electric engine when accelerating onto a highway.

Although URFC technology is still in the labs and has not yet been tried out In the

electrolysis (charging) mode, electrical power from a residential or commercial charging

station supplies energy to produce hydrogen by electrolyzing water.


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The URFC-powered car can also recoup hydrogen and oxygen when the driver brakes or

descends a hill. This regenerative braking feature increases the vehicle's range by about

10% and could replenish a low-pressure (1.4-megapascal or 200-psi) oxygen tank about

the size of a football.

In the fuel-cell (discharge) mode, stored hydrogen is combined with air to generate

electrical power. The URFC can also be supercharged by operating from an oxygen tank

instead of atmospheric oxygen to accommodate peak power demands such as entering a

freeway. Supercharging allows the driver to accelerate the vehicle at a rate comparable to

that of a vehicle powered by an internal-combustion engine.

on the market, it should solve many of the problems with hybrid vehicles that

manufacturers are facing today when it becomes available.

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.

For the flywheel the continuously variable transmission and vehicle because flywheel

rotational speed increases when vehicle speed decreases and vice versa.

Flywheel can work well with either mechanical or hydrostatic continuously

variable transmission.

3. Control System:

An ON-OFF engine control system is used. That means that the engine is ON

until the energy storage unit has been reached the desired charge capacity and then is

decoupled and stopped until the energy storage unit charge fall below its minimum

requirement.


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DIFFERENT TYPES OF REGENERATIVE BRAKING

Based on the mode of storage of energy some of the system developed can be listed they

are:-

Electric Regenerative braking:

In an electric system which is driven only by means of electric motor the system consists

of an electric motor which acts both as generator and motor. Initially when the system is

cruising the power is supplied by the motor and when the there is a necessity for braking

depending upon drivers applied force on the brake pedal the electronic unit controls the

charge flowing through the motor and due to the resistance offered motor rotates back to

act as a generator and the energy is energy is stored in a battery or bank of twinlayercapacitors for later use.

In hybrid system motor will be coupled to another power source normally I.C

Engines as shown in the fig (1)


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The main components of this system Engine

Motor/Generator

Batteries

Electronic control system

During acceleration, the Motor/generator unit acts as electric motor drawing electricalenergy from the batteries to provide extra driving force to move the car as(Shown in fig

2). With this help from the motor, the cars internal combustion engine that is smaller

and with lower peak power can achieve high efficiency. During braking electric supply

from the battery is cut off by the electronic system. As the car is still moving forward,

the Motor/ Generator unit is acts as electric generator converting cars kinetic energy

into electrical and store in the batteries (shown in fig 3) for later use.

Fig (2) showing energy consumption from battery .


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Fig (3) showing charging of battery when brake applied.


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Hydraulic Regenerative Brakes:

Hydrostatic Regenerative Braking (HRB) system uses electrical/electronic Components as

well as hydraulics to improve vehicle fuel economy. An alternative regenerative brakingsystem is being developed by the Ford Motor Company and the Eaton Corporation.

It's called Hydraulic Power Assist or HPA. With HPA, when the driver steps on the

brake, the vehicle's kinetic energy is used to power a reversible pump, which sends

hydraulic fluid from a low pressure accumulator (a kind of storage tank) Inside the vehicle

into a high pressure accumulator. The pressure is created by nitrogen Gas in the

accumulator, which is compressed as the fluid is pumped into the space the gas Formerly

occupied. This slows the vehicle and helps bring it to a stop. The fluid remains Under

pressure in the accumulator until the driver pushes the accelerator again, at which Point

the pump is reversed and the pressurized fluid is used to accelerate the vehicle, Effectively

translating the kinetic energy that the car had before braking into the Mechanical energy

that helps get the vehicle back up to speed. It's predicted that a system Like this couldstore 80 percent of the momentum lost by a vehicle during deceleration And use it to get

the vehicle moving again. Bosch Rexroth has a regenerative braking system that does not

require a hybrid Vehicle. In fact, it does not involve electrical storage. The Hydrostatic

Regenerative Braking (HRB) system is intended for commercial vehicles and mobile

equipment. The Company says that initial measurements show that the HRB system

reduces the fuel Consumption in these vehicles by up to 25%.

In the HRB system, braking energy is converted to hydraulic pressure and stored in a high-

pressure hydraulic accumulator. When the vehicle accelerates, the stored hydraulic energy

is applied to the transmission reducing the energy that the combustion engine has toprovide. An electronic controller and a hydraulic valve manifold control the process.

At present, these hydraulic regenerative brakes are noisy and prone to leaks; however,

once all of the details are ironed out, such systems will probably be most useful

in large trucks.


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Fig. (d) Hydraulic Regenerative Brake (HRB)

Fly Wheels:Regenerative brakes may seem very hi-tech, but the idea of having "energy-saving

Reservoirs" in machines is nothing new. Engines have been using energy-storing

Devices called flywheels virtually since they were invented.

The basic idea is that the rotating part of the engine incorporates a wheel with a very

heavy metal rim, and this drives whatever machine or device the engine is connected

to. It takes much more time to get a flywheel-engineturning but, once it's up to speed,

the flywheel stores a huge amount of rotational energy. A heavy spinning flywheel is

a bit like a truck going at speed: it has huge momentum so it takes a great deal of

stopping and changing its speed takes a lot of effort. That may sound like a drawback,but it's actually very useful. If an engine supplies power erratically, , absorbing extra

power and making up for temporary lulls, so the machine or equipment it's connected

to is driven more smoothly.

It's easy to see how a flywheel could be used for regenerative braking. In something

like a bus or a truck, you could have a heavy flywheel that could be engaged or from

the transmission at different times. You could engage the flywheel everytime you

want to brake so it soaked up some of your kinetic energy and brought you to a halt.

Next time you started off, you'd use the flywheel to return the energy and get you

Moving again, before disengaging it during normal driving. The main drawback of

using flywheels in moving vehicles is, of course, their extra weight.


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They save you energy by storing power you'd otherwise squander in brakes, but they also

cost you energy because you have to carry them around all the time.The transfer of energy

in both directions (captured from the driveline during coasting andbraking, and released to

the driveline for boost) is managed through a CVT (Continuously Variable Transmission)

gear box. Packaged inside a single housing is a shaft mounted flywheel that is connected

via a chain or belt/pulley drive to a series of discs and rollers (the CVT). During braking

and coasting, the flywheel spools-up (accelerates as it spins) and absorbs a storehouse ofotherwise wasted energy (heat from friction brakes). During power delivery, as the vehicle

begins to accelerate, the pent-up energy in the flywheel is released and it turns the shaft.

The rollers within the CVT can change position across the discs either retard or augment

the torque of the spinning flywheel shaft much like a conventional step-up or step-down

gear box.This gearing is necessary because unlike aircraft & to a certain extent watercraft,

which travel at arelatively constant load and speed, earth-bound vehicles travel at regularly

and greatly varying speeds and loads as they negotiate traffic and to pography. It is this

variable output velocity that allows for smooth power transmission from the flywheel to

the driveline as the vehicle travels over the roadway.

Advanced transmissions that incorporate hi-tech flywheels are now being used as

regenerative systems in such things as formula-1 cars, where they're typically referred to

as Kinetic Energy Recovery Systems (KERS).

Pros of flywheel systems:

Compact weight and size -- The entire system (the CVT, the flywheel andthe housing) is roughly half the weight and packaging of a battery hybrid

system.

Twice as efficient -- Battery-electric structures lose kinetic potential duringThe conversion of energy from mechanical to electrical to chemical, and then

back again.

Its a fundamental of the Second Law of Thermodynamics: transforming energy

from one form to another introduces losses. Batteryelectrics are approximately

34 percent efficient. Flywheel drives are allmechanical and suffer no conversion

losses. Most of the energy loss that does occur comes from normal friction

between moving parts. These systems are about 70 percent efficient.

Lower cost -- Smaller size and weight and reduced complexity make thesearrangements about one quarter the cost of a battery-electric system.

4.4. Use in compressed airRegenerative brakes could be employed in compressed air cars to refill the air tank

During braking. By absorbing the kinetic energy (necessary for braking), using the

same for compressing the air and reuse these compressed air while powering the car.

4.5. Regenerative Braking Using Nitilon SpringFrom fig it is clear that while braking the kinetic energy is stored in form of potential

energy in spring. When the system actually demands for the acceleration this potentialenergy stored is given back to the wheels to power them.


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Fig (e) Regenerative braking using Nitilon Spring

APPLICATIONS

Some of vehicles using regenerative brake:-

Fig (f): Toyota Prius


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Fig.(g): Ford FUSION

Fig.(h):Tesla Roadster Electric Car


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Fig(i). Truck using Hydraulic Regenerative Brake (HRB)

Fig.(j): Vectrix Electric Maxi-Scooter


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Fig: KERS is used in F1 cars from 2009


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COMPARISIONS

Advantages of regenerative braking over conventional braking

Energy Conservation:

The flywheel absorbs energy when braking via a clutch system slowing the car down andspeeding up the wheel. To accelerate, another clutch system connects the flywheel to the

drive train, speeding up the car 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.

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 a returning that energy to the battery pack. In mechanical brakes; lessening wearand extending brake life is not possible. This reduces the use of use the brake.

Fuel Consumption:The fuel consumption of the conventional vehicles & 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 ofcarbon dioxide from being released into the atmosphere by regenerating

112,500 megawatt hours of electricity through the use of regenerative braking systems b/w

2004 and 2007. It is expected that the Delhi Metrowill save over 100,000 tons of CO2 from

being emitted per year once its phase is complete through the use of regenerative braking.

The energy efficiency of aconventional 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 towork. 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.

Braking is not total loss:

Conventional brakes apply friction to convert a vehicles kinetic energy into heat.

In energy terms, therefore, braking is a total loss: once heat is generated, it is verydifficult to reuse. The regenerative braking system, however slows a vehicle down

in a different way.


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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 streetcars.

This heat can be used to warm the vehicle interior, dissipated externally by large radiator-

like cowls to house the resistor banks.The main disadvantage of regenerative brakes whencompared 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 the voltage be closely controlled. Only with the development of powerelectronics

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.

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 necessary

back-up in the event of failure of the regenerativebrake.

Most road vehicles with regenerative braking only have power on some wheels (as in two-

wheel drive car) and regenerative braking power only applies to suchwheels, 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 ,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 theexcess energy.

Under emergency braking it is desirable that the braking force exerted be the 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 energyin order to allow an acceptable emergency braking performance.


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DESCRIPTION & OPERATION

How regenerative braking system works?

Regenerative (or Dynamic Braking) occurs when the vehicle is in motion, such as

coasting, traveling downhill or braking. And the accelerator pedal is not being depressed.

During Regent, the motor becomes a generator and sends energy back to the batteries.

It is explained as follows, because the wheels of a decelerating vehicle are still

moving forward, they can be made to turn the electric motor, which then feeds energy to

the batteries for storage. The system becomes, in effect, a generator, which provides

braking force while it converts the vehicles kinetic energy into a reusable form- electrical

energy.

When the accelerator pedal is released, the absence of pressure triggers a response

from the Energy Storage Unit (ESU). Regenerative braking begins, and the batteries are

re-charged by the motor, which is turned by the wheels. In this case, the friction brakes are

not engaged. If more vigorous deceleration is required, and the brake pedal is depressed,

this engages both sets of brakes. However, to maximize energy efficiency, it is

advantageous to apply the regenerative brake as such as possible it therefore tends to do

more of its total work in the first part of the braking motion.

There are two deceleration modes:1. Foot off throttle but not on brake pedalin this mode, the charge/assist gauge will show

partial charge, and the vehicle will slow down gradually.

2. Foot on brake pedal - In this mode, a higher amount of regeneration will be allowed,

and the vehicle will slow more rapidly. During light brake pedal application, only the

IMA motor//generator is slowing the car. With heavier brake pedal application, the

conventional friction brakes also come into play. When decelerating, regeneration will

continue u8ntil engine speed falls to about 1000 rpm. At this point, the driver will

typically shift into neutral.

In this way braking of the vehicle is obtained.


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EXAMPLE

Regenerative braking of Toyota Prius:

Toyota realized that one way to achieve longer vehicle range was to conserve and

reuse some of the energy that a vehicle normally loses as heat caused by braking friction.

This idea led engineers to apply the principles of regenerative braking.

In all Toyota vehicles that feature the regenerative braking system, the regenerative

brake is only responsible for a part of the deceleration necessary to stop the vehicle. In an

EV, this fraction is determined by the vehicles speed when braking is initiated. The

remaining braking force is provided by the vehicles friction brakes. To maximize fuel

economy, of course, the regenerative braking system is made to do as much of the braking

work as possible.

Technology Used in Toyota Prius:

The next phase of regenerative breaking technologys development came in its

application to the Prius, the platform for the Toyota Hybrid System. Whit the Prius, too,

the fraction of breaking torque supplied by the regenerative break is proportional to the

vehicles speed when the breaks are applied. Because the Prius battery pack is less than a

fifth the size of that of a pure EV, however, regenerative capacity is considerably lower.Squeezing the greatest energy savings out of the Prius regenerative breaking system

meant devising a new way to control the interplay of the friction and regenerative breaking

systems throughout the breaking action.

The solution that Toyotas engineers found was to have the prius regenerative brake

supply a continuously varying amount of braking torque as the vehicle decelerates. A pure

EV, with its greater battery capacity, can achieve substantial energy saving without

modifying the regenerative brakes contr4ibution throughout the braking action. This was

not the case for the prius. So Toyota engineers developed a new type of control value to

regulate the interplay between the two systems. These values allow continuous variation,

so the maximum possible energy is extracted from the vehicles deceleration.


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Demand curve (1) most of the gracing is regenerative. For fast & powerful

braking Demand Curve (2). Friction brakes do most of the work.

Two Brake, One Natural Banking Experience:

The final step was to make sure that the two brake systems worked smoothly

togetherso that the driver would experience a natural braking feel when the brake pedal

was depressed.

The hydraulic brakes and the regenerative brake are essentially two separate systems.

Integrating them required the construction of two dedicated computer systems that keep

the brakes coordinated at all times. They call these the electronic control units, or ECUs.

They continuously control the braking forces being generated by the friction and

regenerative systems, ensuring that the total force produced matches the force signaled by

the driver. This design gives the brakes a very smooth feel as far as the driver is

concerned the brakes work like conventional brakes.

In the prius, the Toyota Hybrid System accounts for an 80% gain in fuel efficiency

compared to vehicles equipped with conventional gasoline engines. The regenerative

braking system adds and additional 20% to this, making the prius one of the worlds most

fuel-efficient vehicles.


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Component Used in Toyota Prius for Regenerative Braking System:

Brake Pedal:

It is used to apply braking force by the driver.

Hydraulic Booster Unit:

It is composed of the master cylinder and the regulator, responds in two steps. First it

signals electronically to the brake ECU that braking force has been demanded. Next, the

master cylinder exerts hydraulic pressure on the pedal stroke simulator, and the regulator

feeds hydraulic fluid to the hydraulic pressure control unit.

Brake ECU:

The brake ECU senses the braking demand and sends a fraction of this demand to the

THSECU for regenerative braking.

It also calculates the force necessary to fulfill remaining braking demand and instruct the

hydraulic pressure control unit to pass on a corresponding amount of hydraulic fluid

Pedal Stroke Simulator:

It absorbs an amount of hydraulic pressure from master cylinder that corresponds to the

amount of braking force applied by the regenerative braking system.

As hydraulic pressure is fed back to the pedal, the pedal, the pedal stroke simulator

feeds back to the master cylinder.

THS (Toyota Hybrid System) ECU:

It induces regenerative braking, and returns a signal that indicates braking force output

back to the brake ECU.

Hydraulic Pressure Control Unit:

It passes on a corresponding amount of hydraulic fluid to a four way cylinder.Result:

Regenerative braking technology is one more positive step forward in Toyotas

quest to realize the ultimate ecocar. By working in concert with previously developed

electric motor technologies, its application helps Toyotas electric vehicles and hybrid

vehicles (including the recently released prius) to achieve extended ranges and to be

friendlier to the environment than ever before. At the same time, this new technology

remains unobtrusively in the background; drivers benefit from regenerative braking whileenjoying the same firm braking feel found in conventionally equipped vehicles.


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7.1 Regenerative braking system using Nitinol Spring

Wheel

Rotating Device.

Shafts.

Gearbox

Clutch Spring

WheelA

Rotating DeviceB

ShaftsC.D.

GearboxE

ClutchG

Spring - H


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CONCLUSION

Theoretical investigations of a regenerative braking system show about 25% saving in fuel

consumption.

The lower operating and environment costs of a vehicle with regenerative braking

system should make it more attractive than a conventional one. The traditional cost of the

system could be recovered in the few years only.

The exhaust emission of vehicle using the regenerative braking concept would be much

less than equivalent conventional vehicles as less fuel are used for consumption.

These systems are particularly suitable in developing countries such as India where buses

are the preferred means of transportation within the cities.


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REFERENCES

1) Automotive Abstracts , ARAI Pune.2) General Motors Website (www.gm.com).3) www.sae.org
http://www.gm.com/http://www.gm.com/http://www.gm.com/http://www.sae.org/http://www.sae.org/http://www.sae.org/http://www.gm.com/

vikram khan 1

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