iss regenrative brakes

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INDEPENDE

NT

STUDYSEMINAR


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A

SEMINAR REPORT

ON

REGENRATIVE BRAKES

IN PARTIAL FULFILLMENT OF REQUIREMENTS FOR THE DEGREE OF

BACHELOR IN TECHNOLOGY

IN

MECHANICAL ENGINEERING

SUBMITTED BY:

RAVI KUMAR(07-ME-440)

DEPARTMENT OF MECHANICAL ENGINEERING


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GURGAON INSTITUTE OF TECHNOLOGY AND

MANAGEMENT

BILASPUR, GURGAON

2010-2011

CERTIFICATE

This is to certify that the seminar entitled regenerativebrakes has been submitted by Ravi Kumar ( 07-ME-440), for

the partial fulfilment of the degree of bachelor of technology in

mechanical engineering from gurgaon institute of technology

and management, gurgaon. Affiliated to the maharishi

dayanand university, rohtak, during the academic session

2010-2011( 8th semester).

Date:12th april 2011

Place: Bilaspur , Gurgaon

Department of mechanical engineering

Gurgaon institute of technology and management


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DECLARATION

I hereby declare that the work presented

here in this seminar report submitted to the

Department of Mechanical Engineering,

Gurgaon Institute of Technology &Management, Gurgaon, is an authentic

record of my own work.

Name: Ravi kumar

Roll No.: 07-ME-440

Branch: Mechanical

Semester: 8th


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ACKNOWLEDGEMENT

I would like to take the opportunity to thank Mr.

R.K.Gupta for his valuable guidance and co-operation

at every step of the project, without which, it would not

have been possible for me to explore this subject.

I pay a vote of thanks to our faculty Mr.Bharat

Bhushan and Mr.Imran Siraj for providing

necessary facilities, support, motivation and

understanding enabling me to understand the subject

deeply, throughout the process of this study.

I would like to take this opportunity to thank the

organization and each & everyone of you from the core

of my heart for all the support and encouragement

extended to me to learn, grow and contribute in this

organization.


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Regenerative brakes

A regenerative brake is an energy recovery mechanismwhich slows a vehicle by converting its kinetic energy intoanother form, which can be either used immediately or storeduntil needed. This contrasts with conventional braking systems,where the excess kinetic energy is converted to heat by frictionin the brake linings and therefore wasted.

The most common form of regenerative brake involves usingan electric motor as an electric generator. In electric railwaysthe generated electricity is fed back into the supply system,whereas in battery electric and hybrid electric vehicles, theenergy is stored in a battery or bank of capacitors for later use.Energy may also be stored via pneumatics, hydraulics or thekinetic energy of a rotating flywheel.


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Every time you step on your car's brakes, you're wastingenergy. Physics tells us that energy cannot be destroyed. Sowhen your car slows down, the kinetic energy that waspropelling it forward has to go somewhere. Most of it simply

dissipates as heat and becomes useless. That energy, whichcould have been used to do work, is essentially wasted. Isthere anything that you, the driver, can do to stop wasting thisenergy? Not really. In most cars it's the inevitable by product ofbraking and there's no way you can drive a car withoutoccasionally hitting the brakes. But automotive engineers havegiven this problem a lot of thought and have come up with akind of braking system that can recapture much of the car'skinetic energy and convert it into electricity, so that it can beused to recharge the car's batteries. This system is calledregenerative braking.

At present, these kinds of brakes are primarily found in hybridvehicles like the Toyota Prius, and in fully electric cars, like theTesla Roadster. In vehicles like these, keeping the batterycharged is of considerable importance. However, thetechnology was first used in trolley cars and has subsequentlyfound its way into such unlikely places as electric bicycles andeven Formula One race cars.


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A traditional braking system, brake pads produce friction withthe brake rotors to slow or stop the vehicle. Additional frictionis produced between the slowed wheels and the surface of theroad. This friction is what turns the car's kinetic energy into

heat. With regenerative brakes, on the other hand, the systemthat drives the vehicle does the majority of the braking. Whenthe driver steps on the brake pedal of an electric or hybridvehicle, these types of brakes put the vehicle's electric motorinto reverse mode, causing it to run backwards, thus slowingthe car's wheels. While running backwards, the motor also actsas an electric generator, producing electricity that's then fedinto the vehicle's batteries. These types of brakes work betterat certain speeds than at others. In fact, they're most effective

in stop-and-go driving situations. However, hybrids and fullyelectric cars also have friction brakes, as a kind of back-upsystem in situations where regenerative braking simply won'tsupply enough stopping power. In these instances, itsimportant for drivers to be aware of the fact that the brakepedal might respond differently to pressure. The pedal willsometimes depress farther towards the floor than it normallydoes and this sensation can cause momentary panic in drivers.

In the following pages, we'll take a more detailed look at how aregenerative braking system works, and we'll discuss reasonswhy regenerative braking is more efficient than a typicalfriction brake system.

The motor as a generator

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.

Early examples of this system were the front-wheeldrive conversions of horse-drawn cabs by Louis Antoine Krieger


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(18681951). The Krieger electric landaulet had a drive motor

in each front wheel with a second set of parallel windings

(bifilar coil) for regenerative braking. In England, the Raworth

system of "regenerative control" was introduced by tramway

operators in the early 1900s, since it offered them economic

and operational benefits as explained by A. Raworth of Leeds in

some detail.These included tramway systems at Devonport

(1903), Rawtenstall, Birmingham, Crystal Palace-Croydon

(1906) and many others. Slowing down the speed of the cars or

keeping it in hand on descending gradients, the motors worked

as generators and braked the vehicles. The tram cars also had

wheel brakes and track slipper brakes which could stop the

tram should the electric braking systems fail. In several casesthe tram car motors were shunt wound instead of series

wound, and the systems on the Crystal Palace line utilized

series-parallel controllers. Following a serious accident at

Rawtenstall, an embargo was placed on this form of traction in

1911. Twenty years later, the regenerative braking system was

reintroduced.

Regenerative braking has been in extensive use on railways for

many decades. The Baku-Tbilisi-Batumi railway(Transcaucasian railway or Georgian railway) started utilizing

regenerative braking in the early 1930s. This was especially

effective on the steep and dangerous Surami Pass. In

Scandinavia the Kiruna to Narvik railway carries iron ore from

the mines in Kiruna in the north of Sweden down to the port of

Narvik in Norway to this day. The rail cars are full of thousands

of tons of iron ore on the way down to Narvik, and these trains

generate large amounts of electricity by their regenerativebraking. From Riksgrnsen on the national border to the Port of

Narvik, the trains use only a fifth of the power they regenerate.

The regenerated energy is sufficient to power the empty trains

back up to the national border. Any excess energy from the

railway is pumped into the power grid to supply homes and

businesses in the region, and the railway is a net generator of

electricity.


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An Energy Regeneration Brake was developed in 1967 for

the AMC Amitron. This was a completely battery powered

urban concept car whose batteries were recharged by

regenerative braking, thus increasing the range of the

automobile.

Many modern hybrid and electric vehicles use this technique to

extend the range of the battery pack. Examples include

the Toyota Prius, Honda Insight, the Vectrix electric maxi-

scooter, and the Chevrolet Volt.

Electric railway vehicle operation


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During braking, the traction motor connections are altered to

turn them into electrical generators. The motor fields are

connected across the main traction generator (MG) and the

motor armatures are connected across the load. The MG now

excites the motor fields. The rolling locomotive or multiple unit

wheels turn the motor armatures, and the motors act as

generators, either sending the generated current through

onboard resistors (dynamic braking) or back into the supply

(regenerative braking).

For a given direction of travel, current flow through the motor

armatures during braking will be opposite to that during

motoring. Therefore, the motor exerts torque in a direction that

is opposite from the rolling direction.

Braking effort is proportional to the product of the magnetic

strength of the field windings, times that of the armature

windings.

Savings of 17% are claimed for Virgin Trains Pendolinos. There

is also less wear on friction braking components. The Delhi

Metro saved around 90,000 tons of carbon dioxide (CO2) from

being released into the atmosphere by regenerating 112,500megawatt 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.

Another form of simple, yet effective regenerative braking is

used on the London Underground which is achieved by having

small slopes leading up and down from stations. The train isslowed by the climb, and then leaves down a slope, so kinetic

energy is converted to "stored" potential energy in the station.

Electricity generated by regenerative braking may be fed back

into the traction power supply; either offset against other

electrical demand on the network at that instant, or stored in

line side storage systems for later use.


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Regenerative Braking Circuits

Regenerative braking is used in vehicles that make use ofelectric motors, primarily fully electric vehicles and hybridelectric vehicles. One of the more interesting properties of anelectric motor is that, when it's run in one direction, it convertselectrical energy into mechanical energy that can be used toperform work (such as turning the wheels of a car), but whenthe motor is run in the opposite direction, a properly designed

motor becomes an electric generator, converting mechanicalenergy into electrical energy. This electrical energy can thenbe fed into a charging system for the car's batteries.

In a regenerative braking system, the trick to getting the motorto run backwards is to use the vehicle's momentum as themechanical energy that puts the motor into reverse.Momentum is the property that keeps the vehicle movingforward once it's been brought up to speed. Once the motorhas been reversed, the electricity generated by the motor isfed back into the batteries, where it can be used to acceleratethe car again after it stops. Sophisticated electronic circuitry isnecessary to decide when the motor should reverse, whilespecialized electric circuits route the electricity generated bythe motor into the vehicle's batteries. In some cases, theenergy produced by these types of brakes is stored in a seriesof capacitors for later use. In addition, since vehicles usingthese kinds of brakes also have a standard friction brakingsystem, the vehicle's electronics must decide which braking

system is appropriate at which time. Because so much iscontrolled electronically in a regenerative braking system, it'seven possible for the driver to select certain presets thatdetermine how the vehicle reacts in different situations. Forinstance, in some vehicles a driver can select whetherregenerative braking should begin immediately whenever thedriver's foot comes off the accelerator pedal and whether thebraking system will take the car all the way to 0 mph (0kilometres per hour) or will let the car coast slightly.


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There's a general movement in the automotive industry towardso-called brake-by-wire systems where many of the functionsof brakes that have traditionally been performed mechanicallywill be performed electronically. Hybrids and electric cars will

probably be early adopters of these brake types. At present,different automotive engineers have come up with differingcircuit designs to handle the complexities of regenerativebraking; however, in all cases, the single most important partof the braking circuitry is the braking controller, which we'lldiscuss in the next section.

Regenerative Braking Controllers

Brake controllers are electronic devices that can control brakesremotely, deciding when braking begins, ends, and how quicklythe brakes need to be applied. In towing situations, forinstance, brake controllers can provide a means of coordinatingthe brakes on a trailer with the brakes on the vehicle doing thetowing.

Regenerative braking is implemented in conjunction with anti-lock braking systems (ABS), so the regenerative brakingcontroller is similar to an ABS controller, which monitors therotational speed of the wheels and the difference in that speedfrom one wheel to another. In vehicles that use these kinds ofbrakes, the brake controller not only monitors the speed of thewheels, but it can calculate how much torque -- rotational force-- is available to generate electricity to be fed back into thebatteries. During the braking operation, the brake controller

directs the electricity produced by the motor into the batteriesor capacitors. It makes sure that an optimal amount of power isreceived by the batteries, but also ensures that the inflow ofelectricity isn't more than the batteries can handle.

The most important function of the brake controller, however,may be deciding whether the motor is currently capable ofhandling the force necessary for stopping the car. If it isn't, thebrake controller turns the job over to the friction brakes,averting possible catastrophe. In vehicles that use these typesof brakes, as much as any other piece of electronics on board a


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hybrid or electric car, the brake controller makes the entireregenerative braking process possible.

Hybrid Regenerative Braking

Hybrid electric vehicles use both an electric motor and aninternal combustion engine to provide a best-of-both-worldsdriving experience. They combine the driving range of aninternal combustion engine with the fuel efficiency andemissions-free characteristics of an electric motor. If a hybrid isto have maximum fuel efficiency and produce as few carbon

emissions as possible, it's important that the battery remaincharged as long as possible. If a hybrid vehicle battery were tolose its charge, the internal combustion engine would beentirely responsible for powering the vehicle. At that point, thevehicle is no longer acting as a hybrid but rather just anothercar burning fossil fuels.

Automotive engineers have come up with a number of tricks towring the maximum efficiency out of hybrids, like aerodynamic

streamlining of the bodies and use of lightweight materials, butarguably, one the most important is regenerative braking. In ahybrid setup, however, these types of brakes can providepower only to the electric motor part of the drivetrain via thevehicle's battery. The internal combustion engine gains noadvantage from these kinds of brakes.

In part, these efficiencies are necessary due to the extreme

difficulty in finding a place to recharge a hybrid. This makeslonger trips difficult without relying on the hybrid's internal
http://auto.howstuffworks.com/engine.htmhttp://auto.howstuffworks.com/engine.htm


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combustion engine, which actually cancels out some of theadvantage of owning a hybrid.

Hydraulic Regenerative Braking

An alternative regenerative braking system is being developedby the Ford Motor Company and the Eaton Corporation. It's

called Hydraulic Power Assist or HPA. With HPA, when thedriver steps on the brake, the vehicle's kinetic energy is usedto power a reversible pump, which sends hydraulic fluid from alow pressure accumulator (a kind of storage tank) inside thevehicle into a high pressure accumulator. The pressure iscreated by nitrogen gas in the accumulator, which iscompressed as the fluid is pumped into the space the gasformerly occupied. This slows the vehicle and helps bring it to astop. The fluid remains under pressure in the accumulator until

the driver pushes the accelerator again, at which point thepump is reversed and the pressurized fluid is used toaccelerate the vehicle, effectively translating the kineticenergy that the car had before braking into the mechanicalenergy that helps get the vehicle back up to speed. It'spredicted that a system like this could store 80 percent of themomentum lost by a vehicle during deceleration and use it toget the vehicle moving again [source: HybridCars.com]. Thispercentage represents an even more impressive gain than

what is produced by current regenerative braking systems.Like electronic regenerative braking, these kinds of brakes --


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HPA systems -- are best used for city driving, where stop-and-go traffic is common.

So far, HPA systems have been used primarily as proofs of

concept and in demonstration projects only. They aren't quiteready for production models just yet. At present,these hydraulic brakes are noisy and prone to leaks; however,once all of the details are ironed out, such systems willprobably be most useful in large trucks weighing 10,000pounds (4,536 kilograms) or more, where these types of brakesmay prove to be a more optimal system than electronicallycontrolled regenerative brakes.

Eventually, this technology may trickle down to smallervehicles. One company, Hybrid-Drive Systems, LLC, ofMichigan, has retrofitted a 1968 Volkswagen Beetle with ahydraulic regenerative braking system. However, theaccumulators take up a considerable amount of space, andfuture production plans are focused more on using thetechnology in larger vehicles, like vans. Meanwhile, the U.S.Environmental Protection Agency (EPA) has partnered withEaton Corporation to install hydraulic regenerative braking

systems on UPS delivery trucks.

Regenerative Braking Efficiency

The energy efficiency of a conventional car is only about 20percent, with the remaining 80 percent of its energy beingconverted to heat through friction. The miraculous thing aboutregenerative braking is that it may be able to capture as muchas half of that wasted energy and put it back to work. Thiscould reduce fuel consumption by 10 to 25 percent. Hydraulicregenerative braking systems could provide even moreimpressive gains, potentially reducing fuel use by 25 to 45percent [source: HybridCars.com]. In a century that may seethe end of the vast fossil fuel reserves that have provided uswith energy for automotive and other technologies for manyyears, and in which fears about carbon emissions are comingto a peak, this added efficiency is becoming increasingly

important.


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The beginning of the 21st century could very well mark thefinal period in which internal combustion engines arecommonly used in cars. Already automakers are moving

toward alternative energy carriers,such as electric batteries, hydrogen fuel and even compressedair. Regenerative braking is a small, yet very important, steptoward our eventual independence from fossil fuels. Thesekinds of brakes allow batteries to be used for longer periods oftime without the need to be plugged into an external charger.These types of brakes also extend the driving range of fullyelectric vehicles. In fact, this technology has already helpedbring us cars like the Tesla Roadster, which runs entirely on

battery power. Sure, these cars may use fossil fuels at therecharging stage -- that is, if the source of the electricity comesfrom a fossil fuel such as coal -- but when they're out there onthe road, they can operate with no use of fossil fuels at all, andthat's a big step forward.

The added efficiency of regenerative braking also means lesspain at the pump, since hybrids with electric motors andregenerative brakes can travel considerably farther on a gallonof gas, some achieving more than 50 miles per gallon at this

point. And that's something that most drivers can reallyappreciate.

Regenerative Braking Diagram

This simple diagram shows how a regenerative braking system is able to recapture some ofthe vehicle's kinetic energy and convert it into electricity. This electricity is then used torecharge the vehicle's batteries.


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Limitations

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


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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 (as in a two-wheel drive car) and

regenerative braking power only applies to such wheels

because they are the only wheels linked to the drive motor,

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 islimited 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 brakingforce 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 powerwhich 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

dissipate the surplus energy in order to allow an acceptable

emergency braking performance.


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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. The

GM EV-1was the first commercial car to do this. Engineers

Abraham Farag and Loren Majersik were issued two patents for

this brake-by-wire technology.[


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Sources

BrakeByWire.com. (Jan. 13, 2009)

http://www.brakebywire.com/

Cantwell, Katie. "Regeneration Overview." Rockwell Automation Allen-Bradley. May 7,2002. (Jan. 13, 2009)

http://www.ab.com/drives/techpapers/RegenOverview01.pdf

Chen, Jason. "Panasonic Makes Electric Bike with Regenerative Braking." Gizmodo.

July 7, 2008. (Jan. 13, 2009)

http://gizmodo.com/5022587/panasonic-makes-electric-bike-with-regenerative-braking

Continental Corporation. "ISAD and EHB Make Cars More Economical and More

Environmentally Friendly." March 17, 2002. (Jan. 13, 2009)

http://www.conti-online.com/generator/www/com/en/continental/portal/themes/

press_services/press_releases/products/automotive_systems/brakesystems/

pr_2002_03_17_7_en.html

Gitlin, Jonathan M. "McLaren and Freescale partner up for regenerative braking."

Ars Technica. Nov. 5, 2008. (Jan. 13, 2009)

http://arstechnica.com/news.ars/post/20081113-mclaren-and-freescale-partner-

up-for-regenerative-braking.html

HybridCars.com. "Hydraulic Hybrids." April 3, 2006. (Jan. 13, 2009)

http://www.hybridcars.com/related-technologies/hydraulic-hybrids.html

Torrens, Richard. "Regen Braking." 4QD. Nov. 3, 2008. (Jan. 13, 2009)

http://www.4qd.co.uk/fea/regen.html

Tur, Okan, et al. "Application Note on Regenerative Braking of Electric Vehicles as

Anti-Lock Braking System." Ansoft, LLC. April 11, 2006. (Jan. 13, 2009)

http://www.ansoft.com/news/articles/RegenBrakingAsABS.pdf

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