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MEE396: AUTOMOTIVE MINI PROJECT

PROJECT REPORT

SUBMITTED TO:PROF. T VIJAYKUMAR(PROGRAM MANAGER)

PROF. VENKATESHAN

PROF. SENTHUR PRABHU

REGENERATIVE BRAKING SYSTEM

GUIDE: PROF G. VENKATACHALAN

BY:

KRUTIK N RATHOD- 12BMA0013

ANGAD BANGA-12BMA0073

VAMSI VARMA-12BMA0066


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ABSTRACT:

Every time you step on your car's brakes, you're wasting energy. Physics tells usthat energy cannot be destroyed. So when your car slows down, the kinetic energy that was

propelling it forward has to go somewhere. Most of it simply dissipates as heat and

becomes useless. That energy, which could have been used to do work, is essentially wasted.

In most cars it's the inevitable byproduct of braking and there's no way you can drive a car

without occasionally hitting the brakes. But automotive engineers have given this problem

a lot of thought and have come up with a kind of braking system that can recapture much

of the car's kinetic energy and convert it into electricity, so that it can be used to recharge

the car's batteries. This system is called regenerative braking.

At present, these kinds of brakes are primarily found in hybrid vehicles like the

Toyota Prius , and in fully electric cars, like the Tesla Roadster. In vehicles like these,keeping the battery charged is of considerable importance. However, the technology was

first used in trolley cars and has subsequently found its way into such unlikely places as

electric bicycles and even Formula One race cars.

In a traditional braking system, brake pads produce friction with the brake rotors

to slow or stop the vehicle. Additional friction is produced between the slowed wheels and

the surface of the road. This friction is what turns the car's kinetic energy into heat. With


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regenerative brakes, on the other hand, the system that drives the vehicle does the majority

of the braking. When the driver steps on the brake pedal of an electric or hybrid vehicle,

these types of brakes put the vehicle's electric motor into reverse mode, causing it to run

backwards, thus slowing the car's wheels. While running backwards, the motor also acts as

an electric generator, producing electricity that's then fed into the vehicle's batteries. These

types of brakes work better at certain speeds than at others. In fact, they're most effectivein stop-and-go driving situations. However, hybrids and fully electric cars also have friction

brakes, as a kind of back-up system in situations where regenerative braking simply won't

supply enough stopping power. In these instances, its important for drivers to be aware of

the fact that the brake pedal might respond differently to pressure. The pedal will

sometimes depress farther towards the floor than it normally does and this sensation can

cause momentary panic in drivers.

In the following pages, we'll take a more detailed look at how a regenerative braking

system works, and we'll discuss reasons why regenerative braking is more efficient than a

typical friction brake system.

In the following pages, we'll take a more detailed look at how a regenerative braking

system works, and we'll discuss reasons why regenerative braking is more efficient than a

typical friction brake system.

INTRODUCTION:

When a conventional vehicle applies its brakes, kinetic energy is converted into heat

energy due to friction. This heat is further lost in the airstream, hence the energy is wasted.

The total amount of energy lost depends on

How often the brakes are applied. How hard the brakes are applied. For how long these brakes are applied

Regenerative braking refers to a process by which the kinetic energy of the vehicle is

stored by a short term storage system and re-used for further acceleration. Energy

normally dissipated by brakes is directed by the power transmission system to a energystore during deceleration. The energy is held until required again for accelerating the

vehicle(converted back to kinetic energy). The magnitude of the energy stored varies

according to type of storage, drive train efficiency, drive cycle and inertia weight. For

example: a lorry on a motorway would account for only a little saving even if the efficiency

is 100%. But driving in the city center involves higher frequency braking which increases

the potential saving of energy.


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A regenerative brake is an energy recovery mechanism which slows a vehicle or

object down by converting its kinetic energy into another form, which can be either used

immediately or stored until needed. This contrasts with conventional braking systems,

where the excess kinetic energy is converted to heat by friction in the brake linings and

therefore wasted.

Regenerative braking is a system in which the electric motor that normally drives a

hybrid or pure electric vehicle is essentially operated in reverse (electrically) during

braking or coasting. Instead of consuming energy to propel a vehicle, the motor acts as a

generator that charges the onboard batteries with electrical energy that would normally be

lost as heat through traditional mechanical friction brakes. As the motor acts in reverse,

it generates electricity. The accompanying friction (electrical resistance) assists the normal

brake pads in overcoming inertia and helps slow the vehicle.

We use super capacitors in regenerative braking systems to store energy. Though

super capacitors have energy densities that are approximately 10% of conventionalbatteries, their power density is generally 10 to 100 times greater. This results in much

shorter charge/discharge cycles than batteries. Additionally, they will tolerate many more

charge and discharge cycles than batteries. In these electrochemical capacitors, the

electrolyte is the conductive connection between the two electrodes. This distinguishes them

from electrolytic capacitors, in which the electrolyte is the cathode and thus forms the

second electrode.

Examples: All hybrid and electric vehicles use regenerative braking to generate electricity

to help recharge their batteries.

Hybrids and all-electric vehicles create their own power for battery recharging

through a process known as regenerative braking (regen. mode). We've explained what

regenerative braking is and how the process works in general terms. We understand that in

a hybrid or all-electric vehicle the word "regenerative," in terms of regenerative braking,

means capturing the vehicle's momentum (kinetic energy) and turning it into electricity

that recharges (regenerates) the onboard battery as the vehicle is slowing down and/or

stopping. It is this charged battery that in turn powers the vehicle's electric traction motor.

In an all-electric vehicle, this motor is the sole source of locomotion. In a hybrid, the motor

works in partnership with an internal combustion engine. But that motor is not just a

source of propulsion, it's also a generator.

So How Does a Motor/Generator Work in an Hybrid Vehicle:

Any permanent magnet motor can operate as either a motor or generator. In all-

electrics and hybrids, they are more precisely called a motor/generator (M/G). No matter


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the vehicle design, there must be a mechanical connection between the M/G and the

drivetrain. In an all-electric vehicle there could be an individual M/G at each wheel or a

central M/G connected to the drive train through a gearbox. In a hybrid, the

motor/generator could be an individual component that is driven by an accessory belt from

the engine (much like an alternator on a conventional vehicle--this is how the GM Braking

system works), it could be a pancake M/G that is bolted between the engine and

transmission (this is the most common setup--the Prius, for example), or it could be

multiple M/Gs mounted inside the transmission (this is how the two-modes work). In any

case, the M/G has to be able to propel the vehicle as well as be driven by the vehicle in

regen. mode.

Regenerative Braking: Slowing the Vehicle and Generating Electricity

This is really what the regeneration mode is all about. With the electronic throttle

closed and the vehicle still moving, all of its kinetic energy can be captured to both slow the

vehicle and recharge its battery. As the onboard computer signals the battery to stop

sending electricity (via the controller relay) and start receiving it (through a charge

controller), the M/G simultaneously stops receiving electricity for powering the vehicle and

starts sending current back to the battery for charging.

However, the above technology (regenerative braking systems in hybrids) has its

limitations and therefore does not stand on its own, but is always assisted with conventional

hydraulic brakes

We look forward to remove this limitation and allowing a vehicle to fully rely on

regenerative braking technology to deal with any braking situation ranging from simpleslow down to emergency stops. To enable this, multiple generators with different gear

ratios are used. . The additional benefit of this construction is that, by introducing the

appropriate control circuit, the generators can be used as electrical engines. Since these

motors are connected with different gear ratios there is a more consistent acceleration at

any speed. The paper shows that the overall efficiency of the system is very close to the

efficiency of the generators used while achieving braking performance similar to

conventional braking mechanisms.


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How does regenerative braking system work(in electric vehicles):


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The vehicle controller determines the regenerative braking torque and the EMB torque

according to various driving conditions such as driver input, vehicle velocity, battery State

of Charge (SOC), and motor characteristics. The Motor Control Unit (MCU) controls the

regenerative braking torque through command signals from the vehicle controller. The

Brake Control Unit (BCU) receives input from the driver via an electronic pedal, thentransmits the braking command signals to each EMB. This is determined by the

regenerative braking control algorithm from the value of remaining braking torque minus

the regenerative braking torque. The braking friction torque is generated when the EMB

in each wheel creates a suitable braking torque for the motor; the torque is then

transmitted through the gear mechanism to the calliper.

Advantages:


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Improved fuel economy dependent on duty cycle, powertrain design, controlstrategy and the efficiency of the individual components

Emission reduction engine emissions reduced but engines decoupling, reducingtotal engine revolutions and total time of engine operation (engine on off strategy)

Improved performance Reduction in break wear reducing cost of replacement brake linings, cost of labor

to install them and vehicles down time.

Smaller accessories-hybrid power train offers potential for eliminating (electricstarter) or downsizing(fuel tank) some accessoriues, thus partially offsetting the

increased vehicle weight and cost due to hybrid hardware additions.

Operating range is comparable with conventional vehicles-a problem not yetovercome by electric vehicles.

Limitations:

The regenerative braking effect drops off at lower speeds; therefore the frictionbrake is still required in order to bring the vehicle to a complete halt. Physical

locking of the rotor is also required to prevent vehicles from rolling down hills.

The friction brake is a necessary back-up in the event of failure of the regenerativebrake.

The amount of electrical energy capable of dissipation is limited by either thecapacity of the supply system to absorb this energy or on the state of charge of the

battery or capacitors. Regenerative braking can only occur if no other electrical

component on the same supply system is drawing power and only if the battery orcapacitors are not fully charged. For this reason, it is normal to also incorporate

dynamic braking to absorb the excess energy.

Under emergency braking it is desirable that the braking force exerted be themaximum 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 dissipate the surplus energy in

order to allow an acceptable emergency braking performance.

Complexity-depends on control necessary for operation of regenerative brakingsystem.


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generated pollutants can be controlled and reduced more easily than the disturbed

pollution sources of individual vehicles.

Most American motor vehicle manufacturers believe that hybrid systems are the way toachieve more flexibility and range out of electric vehicles until better batteries are

available. this would allow them to meet again the stringent Californian exhaust emission

standers being phased in for passengers cars over the next few years. Ultra Low Emission

Vehicles(ULEV)standards are expected to provide a niche for hybrid vehicles which is why

manufacturers interest is heightened at present. It is widely specifically for local

commuting and not needing to provide the same all round performance as conventional

cars.

European manufacturers believe hybrid vehicles are a way to achieve high fuel efficiency

and very low emissions from liquid fuelled vehicles. This differing view is due to fact that

in the LA basin the air pollution problem extends over a vast area requiring a vehicle with

good range and zero emission capability. In Europe pollution tends to be a localized event

concentrated in urban areas, this combines with the fact that fewer Europe families have

two or more cars means manufacturers need to provide a car that can deal with local air

quality but also travel at higher speed for interurban and long distance driving

REQUIRED VEHICLE PERFORMANCE

The amount of stored energy and maximum power extraction depends on vehicle

performance specifications, the conversion efficiency and the efficiencies of the components

in the drive train. Performance specifications should be similar to existing automobiles to

obtain acceptance in the market place. Typically specifications are:

Mass Vehicle (inc. fuel) 1600kg

Passengers 400kg

Luggage 200kg

Total 2200kg


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Range 250km at constant speed of 48kmph

200km at constant speed of 88kmph

10km 10% slope constant speed of 48kmph

Speed Maximum 120kmph

Acceleration From 0-96kmph in 10s

Deceleration From 96-0 kmph in 7s

Rapid recharge Fully charged in less than 40 min

Slow recharge Fully charged in 8h

Aux. power Air-conditioning/heating 3kW

Windscreen wipers 0.1kW

Lights 1kW

Radio/hi-fi 0.2kW

Electric windows 0.2 kW

Cooling pump and fan 1.5kW

Total 6kW

Efficiencies Motors 95%

Gearboxes 99%

Controllers 97%

Controlled rectifiers 98%

Flywheel generator 95%

Batteries 92%

A minimum energy storage of 78kWh is required to give the automobile a range of 200-

250km.this is based on a total vehicle weight of 2200kg and is significantly less if a lighter


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vehicle and the allowable time to recharge the batteries or flywheels minim um power of

92kW is required to meet the specified acceleration/deceleration rates.

METHDOLOGY:

After a lot of research work being done on this topic, we have decided to up with a working

model of Regenerative Braking Systems. On our next review, we will be ready with the

exact methodology of the working model. Meanwhile what we were able to find out are the

various working methods of Regenerative Breaking Systems. One of them is discussed

below.

In a regenerative braking system, the objective is to recapture the energy byproduct that

results when the brakes are applied.

In electric or hybrid automobiles, the electric motor that drives the car's wheels plays a

major part during braking. When the brake pedal is pressed, the regenerative braking

circuit switches the motor so that it now operates in reverse to counter the direction of the

wheels. This reversal actually makes it perform like a power generator or dynamo that

produces electrical energy. The electricity developed is routed towards the car's storage

batteries to recharge them.

At higher speeds, regenerative brakes still require the assistance of traditional brake

system to be applied as a backup.

This recapturing and storing of electrical energy may be likened to "trickle" charging of

the batteries. This is because most of the time, the electric motor runs in torque producing

mode to drive the vehicle. The recommended battery charging method still has to be

performed to charge the batteries fully, although regenerative braking does translate to an

increase in vehicle range


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FUTURE WORKS:

We will be putting more research efforts in our next review regarding various aspects of

Regenerative Breaking Systems. Moreover, efforts on finding a basic, simple and

economically feasible working model are still going on. In our next report we will be

coming up with the pros and cons of Regenerative Breaking Systems. Further research will

also include a detailed study of the working principle of the project.

REFRENCES:

Mar 30, 2007 - Clegg, S.J. (1996) A Review of Regenerative Braking Systems.Working Paper. Institute of Transport Studies, University of Leeds , Leeds, UK.

S.J. Clegg (1996) A Review of Regenerative Braking Systems. Institute of. TransportStudies, University of Leeds, Working Paper 471.

The World Electric Vehicle Journal, Vol 2, Issue 4.

International Journal of Sustainable Energy Development (IJSED), Volume 2,Issues 1 and 2, March/June 2013

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