Regenerative Braking System

A SEMINAR REPORT ON REGENERATIVE BRAKING SYSTEM

SUBMITTED BY:

GUIDED BY: -

ACKNOWLEDGEMENT This acknowledgement is a humble attempt to earnestly thank all those who were directly or indirectly involved in preparation of this seminar report. In particular I am thankful to my guide Mr. Kalpesh D. Mania who guide me in my seminar work. I am thankful to him for taking active part in the preparation of my seminar report. It was impossible to present this report without his co-operation and suggestion.

Last but not least I would like to express out deep sense of gratitude

to

all

the

faculty

members

of

Mechanical

Engineering

Department and also my friends who help me to accomplish what I have started for.

DEPARTMENT OF MECHANICAL ENGINEERING THE SEMINAR REPORT ON :

REGENERATIVE BRAKING SYSTEM PREPARED BY: GUIDED BY: EXAMINER

H.O.D

(1) ___________________ (2) ___________________ (3) ___________________ (4) ___________________

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.

LIST OF FIGURES Fig. 1

G r a p h i c a l r e p r e s e n t a t i o n o f e n e r g y u s a g e b e t w e e n t w o v e h i c l e s.

Fig. 2

Mercury Hybrid Mariner

Fig. 3

Regenerative Braking System Using Nitinol Spring .

CONTENTS

1. INTRODUCTION 2. NECESSITY OF THE SYSTEM 3. REGENRATIVE BRAKE 4. ELEMENTS OF THE SYSTEM 5. DESCRIPTION & OPERATION 6. RESULTS 7. CONCLUSION

CHAPTER 1: INTRODUCTION

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

stationary energy.

frame,

energy. normally

By

connecting

the

brake converts

moving

kinetic

member

energy

to

to

heat

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, you’ll be powering the vehicle entirely from gasoline. The regenerative braking Regenerative Braking System comes into its own when you’re 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.) 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.

CHAPTER 2: 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, stopand-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 economy – by 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.

Road 80%

Rake 65% Other 18%

Brake 2%

HEAVY LOADED TRUCK

Road 26% other 9%

CITY BUS

2.1 Graphical representation of energy usage between two vehicles.

Some

of

the

advantages

of

regenerative

braking

over

c o n v e n t i o n a l b r a k i n g a r e a s f ol l o w s : 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. Wear Reduction: An electric drive train also allows for regenerative breaking which increases Efficiency and reduces wear on the vehicle brakes.

In

regenerative raking, 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. 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. 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.

CHAPTER 3 :REGENERATIVE BRAKING SYSTEM . A regenerative brake is an apparatus, a device or system which allows a vehicle to recapture and store part of the kinetic energy that would otherwise be 'lost' to heat when braking.

The IMA operating principle

Honda's patented IMA concept is quite simple - use an efficient Otto engine supplemented by an electric motor when additional power is needed. Also referred to as a 'hybrid' system because it uses two power sources, the IMA concept allows the Civic Hybrid to use a smaller gasoline engine without any significant loss in performance.

This system is especially effective due to the fact that acceleration requires a significantly higher power than needed for cruising on a level road (where vehicles spend most of their time). An engine more powerful than needed has to work under low load most of the time, condition where its efficiency is lower than under high loads, thus worsening the vehicle's fuel economy..

The electric motor-generator positioned between the engine and transmission assists the engine when accelerating and recovers energy to store in batteries when braking or decelerating (regenerative braking), allowing it to operate independently without the need for a grid power supply. When the Civic Hybrid is coasting or its brakes are applied, its electric motor becomes a generator, converting forward momentum (kinetic energy) into electrical energy, instead of wasting it as heat during conventional braking. Energy is stored in a battery pack located behind the rear seat in the trunk. If the state of charge of the batteries is low, the motor-generator will also recharge them while the Civic Hybrid is cruising.

CHAPTER 4: ELEMENTS OF THE SYSTEM There are three basic element required which are necessary for the working of regenerative braking system, these are : 1.Energy Storage 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 is applied. 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, which slows the vehicle down faster. The further the brake pedal is depressed, the more the conventional friction brakes are employed.

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

output of the small engine that hybrid vehicles are equipped with.

power

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. continuously

variable

transmission

and

For the flywheel the

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.

C H A P T E R 5 : 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. accelerator pedal is not being depressed.

And the

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 vehicle’s kinetic energy into a reusable formelectrical 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 pedal – in 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. the driver will typically shift into neutral.

At this point,

EXAMPLE

Mercury Hybrid Mariner 1. Mercury Mariner Hybrid • Production Pull ahead: Production begins a year ahead of schedule • Growing the Mercury Brand: New models and goals • Distinctive Design: Mariner features clean lines, careful craftsmanship • Power Play: Full-hybrid gasoline and electric powertrain • Dynamic Chassis: Nimble handling and a smooth, quiet ride • Distinguished Safety: Full array of safety features • Green Mission: Ford Motor Company's strategy for sustainability in vehicles The Mercury Mariner Hybrid offers a uniquely satisfying transportation choice for an ever-increasing segment of the population concerned about the environment. It's a stylish, upscale sport-utility vehicle with nimble handling and impressive performance, as well as ample cargo and towing capacity. In addition, it's an environmentally conscious SUV with remarkable fuel economy – an estimated 33 miles per gallon (mpg) city, 29 mpg highway – and is expected to meet the cleanest emissions rating achievable by a fossil-fuel vehicle (California's Advanced Technology Partial Zero Emissions Vehicle standard).

Engineers placed the additional hybrid powertrain components low and to the rear, to lower the center of gravity and improve the conventional Mariner's front-rear weight distribution. The rack-and-pinion steering is electrically assisted, rather than using the traditional hydraulic steering pump for consistent steering efforts and control whether the gasoline engine is stopped or running. Regenerative braking uses the traction motor to assist the four-wheel disc brakes in slowing Mariner Hybrid while simultaneously generating electricity for charging the battery.

•

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 vehicle’s speed when braking is initiated.

The

remaining braking force is provided by the vehicle’s friction brakes. To maximize fuel economy, of course, the regenerative braking system is made to do as much of the braking work as possible.

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. pressure

on

the

pedal

Next, the master cylinder exerts hydraulic

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.

CHAPTER 6: RESULT Regenerative

braking

technology

is

one

more

positive

step

forward in Toyota’s quest to realize the ultimate ecocar. By working in concert with previously developed electric motor technologies, its application

helps

Toyota’s

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 while enjoying the same firm braking feel found in conventionally equipped vehicles.

Wheel Rotating Device.

Wheel – A Rotating Device – B Shafts – C.D. Gearbox –E Clutch – G Spring - H

Shafts.

Gearbox

Clutch

Spring

7.1 Regenerative braking system using Nitinol Spring

A hydraulic regenerative braking system improves the fuel economy of Ford's F-350 Tonka 25-35% during stop-andgo driving. The system provides power during initial acceleration when demand peaks.

The HLA system consists of a reversible hydraulic pump/motor from Eaton's Fluid Power Group (Eden Prairie, MN) coupled to the drive shaft through a clutch and two accumulators. As the driver steps on the brake, the pump/motor forces hydraulic fluid out of a low-pressure accumulator and into a high-pressure accumulator, increasing the pressure of nitrogen gas stored there to 5,000 psi. During acceleration, the HLA system switches from the pump mode to the motor mode, the nitrogen gas forces the hydraulic fluid back into the low-pressure accumulator, and the pump/motor applies torque to the driveshaft through the clutch. If quick acceleration is required, the F350's diesel engine works with the HLA system

The hydraulic launch assist system in the F-350 Tonka functions as a secondary source of energy during peak power demand. It consists of a low-pressure accumulator in blue, and a high-pressure accumulator in red. The system captures energy normally dissipated as heat during breaking, stores it, and uses it later during periods of peak power demand. Eighty percent of the initial kinetic energy is returned to the vehicle. "The system stores approximately 380 kJ of energy," says Brad Bohlmann, a mechanical engineer and business development coordinator in Advanced Technology at Eaton's Fluid Power Group. "With that much energy, we can accelerate a 10,000-lb vehicle from a dead stop to between 25 and 30 miles per hour with no assistance from the vehicle's combustion engine." "Ford thinks that both electric and hydraulic regenerative systems have a future," says John Brevick, a Ford mechanical engineer working on the HLA system. "But for heavy vehicles like our 10,000-lb F-350 trucks, hydraulics are better at capturing lost energy than electric systems." Eaton's Bohlmann explains that the real advantage of hydraulics is in its power density. "Hydraulics is capable of transferring energy very quickly," says Bohlmann. "The rate of energy transfer is in a hybrid electric system of a similar size is much lower." Bohlmann adds that the specific vocation or driving cycle of the vehicle determines whether a hybrid hydraulic or hybrid electric system is best suited for the vehicle. "Think of hydraulics as a sprinter,

providing fast bursts of power," he says. "An electric hybrid is more like a marathon runner." "The challenge now is to make use of the regenerative braking system seamless to the customer," says Ford's Brevick. "We still have room for improvements and feel the HLA system has a lot of potential." As for the future, Ford, Eaton, and the U.S. Environmental Protection Agency (EPA) are jointly conducting research on hydraulic hybrid vehicles, including internal combustion engines that would produce hydraulic pressure to drive the vehicle. Eaton signed both a technology license agreement and a cooperative research and development agreement with the EPA for the development of future generation systems. Inertia, Force and Mass Everything has inertia; if it has a mass, it has inertia. A hybrid reclaims energy through the fundamentals of physics. Do you remember any high school or college physics? You apply a force to move an object. The equation for this is: F=ma “F” being the force, “m” being the mass and “a” being the acceleration The faster you want an object to accelerate, the more force you have to apply. Let’s just look at the electric motor for now. Energy from the battery (Watts) is applied to the coil windings in the motor. These windings then produce a magnetic force on the rotor of the motor, which produces torque on the output shaft. This torque is then applied to the wheels of the car via a coupling of gears and shafts. When the wheel turns, it applies a force to the ground, which due to friction between the wheel and the ground causes the vehicle to move along the surface. This is like if you were in a boat at a dock, and you grabbed the dock and pushed with your arm. The force you are generating is moving the boat relative to the location of the dock. The more force you apply, the fast you get the boat to move. Friction in Hybrids There is friction everywhere in the hybrid system. There is electrical friction between the atoms and electrons moving in the wires between the battery and the motor and through the motor itself. There is magnetic friction in the metal laminations that make up the magnetic

circuit of the motor, as well as in the magnets again on the atomic level. Then, there is mechanical friction between every moving part, such as the bearings, seals, gears, chains and so on. The by-product of friction is heat. Take your hands rub them together and your palms get warm. The faster you do it, the faster they heat up. Also, the harder they are pressed together, the faster they will heat. Friction is energy lost to heat. When all of these losses are added up, that is what determines the efficiency of the vehicle. Frictional Losses in Conventional Cars A standard car generates torque to move the wheels to drive the vehicle down the road. During this time, it is generating friction and losses. When you apply standard brakes, it is just another friction device that has specially designed material to handle the heat from friction, which is applied to the drums and rotors that stop the wheel from turning. The friction between the wheel and the ground stops the vehicle. This standard vehicle has frictional losses to move the vehicle—and uses the fundamental behind frictional losses to stop the vehicle. So it’s a loselose situation. Transferring Torque Back to the Motor This inertia is the fundamental property of physics that is used to reclaim energy from the vehicle. Instead of using 100% of the foundation brakes of the vehicle, which are the friction brakes, we now let the linkages back to the motor such as the drive shafts, chains, and gears transfer the torque from the wheels back into the motor shaft. One of the unique things about most electric motors is that electrical energy can be transferred into mechanical energy and also mechanical energy can be transferred back into electrical energy. In both cases, this can be done very efficiently. Thus, through the technology of the motor and motor controller, the force at the wheels becomes torque on the electric motor shaft. The magnets on the shaft of the motor (called the rotor—the moving part of the motor) move past the electric coils on the stator (the stationary part of the motor) passing the magnetic fields of the magnets through the coils producing electricity. This electricity becomes electrical energy, which is pumped back to the battery. This, in turn, charges the hybrid battery pack. This is where the comment “regeneration” or “reclaiming energy” comes from. That is the basics of how regeneration works. How much energy you can reclaim depends on a lot of factors. There are different regeneration theories and designs, which fall into two groups: one being called parallel regen and the other called series regen, which are different from the parallel and series hybrids. These regen groups

strictly are design topologies for braking systems. It also matters how many wheels you are using to reclaim energy. Most vehicles to date are front wheel drive so you can only reclaim energy from the front wheels. The back wheels still waste energy to standard friction brakes unless they are somehow connected back to the electric motor. The other factor is battery state of charge and how hard can you drive that energy back into the battery.

C H A P T E R 7 : 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.

BIBLIOGRAPHY 1) G e n e r a l M o t o r s W e b s i t e ( w w w . g m . c o m ) . 2) www.sae.org 3) www.google.com