85009935 Regenerative Braking System

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A SEMINAR ON REGENERATIVE BRAKING SYSTEM ASWIN SANKAR J S ROLL NO:12

Transcript of 85009935 Regenerative Braking System

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A SEMINAR ON

REGENERATIVE BRAKING SYSTEM

ASWIN SANKAR J S

ROLL NO:12

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Abstract Regenerative Braking System is the way of slowing vehicle by using

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.

This energy is stored in a large battery, and used by an electric motor that

provides motive force to the wheels.

The regenerative braking 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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Brake:-

A brake is a machine element and its principle object is to

absorb energy during deceleration. In vehicles 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.

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Regenerative Braking System:-

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

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.

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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 a generator.

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NECESSITY OF THE SYSTEM

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 of the 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%.

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Advantages of Regenerative braking over Conventional

braking:-

Energy Conservation The energy efficiency of a conventional car is only about 20 percent,

with the remaining 80 percent of its energy being converted to heat

through friction. The miraculous thing about regenerative braking is

that it may be able to capture as much as half of that wasted energy

and put it back to work. This could reduce fuel consumption by 10

to 25 percent.

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Wear Reduction:

An electric drive train also allows for regenerative breaking

which increases efficiency and reduces wear on the vehicle

brakes. Traditional friction based braking is used in

conjunction with mechanical regenerative braking. 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. Since both are used together the

wear of friction brakes is lesser.

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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. With regenerative brakes, on the other hand, the

system that drives the vehicle does the majority of the

braking.

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The Integrated Motor Assist(IMA) operating principle

Integrated Motor Assist (commonly

abbreviated as IMA) is Honda's hybrid car

technology. The theory behind IMA is to use

regenerative braking to recapture some of the

energy lost through deceleration, and reuse

that energy later on to help accelerate the

vehicle. This has two effects: it increases the

rate of acceleration, and it reduces the work

required of the petrol engine. The acceleration

boost is important as it allows the engine to be

scaled down to a smaller but more fuel-

efficient variant without rendering the vehicle

overly slow or weak. This smaller engine is the

primary reason cars equipped with IMA get

better highway mileage than their more

conventional counterparts.

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Additionally, vehicles equipped with IMA can

shut off their engine when the vehicle stops

and use the electric motor to rapidly spin it

back up when the driver releases the brake

pedal. They also have a conventional starter as

a backup, making it the only production hybrid

system which can operate with its high voltage

electric system disabled, using only its engine

like a traditional vehicle. However, since the

IMA also acts as the vehicle's alternator,

eventually the 12 volt accessory battery would

require an external charge.

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The Honda Civic Hybrid runs on two power source which is the

petrol engine and the electric motor. Other than the Integrated

Motor Assist (IMA) the Civic Hybrid features a 3 stage i-vtec

system which will give plenty of power throughout the rpm

range. The combination of IMA and 3 stage i-Vtec will gives the

car higher engine output , better fuel efficiency and lower

emissions without compromising the power.

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ELEMENTS OF THE SYSTEM Energy Storage Unit (ESU):

The ESU performs two primary functions

To recover & store braking energy

To absorb excess engine energy during light load operation

The selection criteria for an effective energy storage includes:-

High specific energy storage density

High energy transfer rate

Small space requirement

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

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

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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.

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.

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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.

Using a continuously variable transmission (CVT), energy is recovered from the drive train during braking and

stored in a flywheel. This stored energy is then used during acceleration by altering the ratio of the CVT.

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.

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Continuously Variable Transmission (CVT):

The energy storage unit requires a transmission that can handle

torque and speed demands in a stepless manner and smoothly

control energy flow to and from the vehicle wheels. It can use

separate power inputs to produce one output.

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Regenerative Braking Controllers

Brake controllers are electronic devices that can control

brakes remotely, deciding when braking begins, ends, and

how quickly the brakes need to be applied.

Regenerative braking is implemented in conjunction with

anti-lock braking systems (ABS), so the regenerative braking

controller is similar to an ABS controller, which monitors the

rotational speed of the wheels and the difference in that

speed from one wheel to another.

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In vehicles that use these kinds of brakes, the brake controller not

only monitors the speed of the wheels, but it can calculate how

much torque -- rotational force -- is available to generate electricity

to be fed back into the batteries.

During the braking operation, the brake controller directs the

electricity produced by the motor into the batteries or capacitors. It

makes sure that an optimal amount of power is received by the

batteries, but also ensures that the inflow of electricity 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 of handling the

force necessary for stopping the car. If it isn't, the brake controller

turns the job over to the friction brakes, averting possible

catastrophe.

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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.

There are two deceleration modes:

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.

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

the vehicle will slow more rapidly

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Why Regenerative Brakes are assisted with the Frictional Brake??

Traditional friction-based braking is used in conjunction with mechanical

regenerative braking for the following reasons:

The regenerative braking effect drops off at lower speeds; therefore the

friction brake is still required in order to bring the vehicle to a complete halt.

Physical locking of the rotor is also required to prevent vehicles from rolling

down hills.

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

regenerative brake.

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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, so in order to provide controlled braking under

difficult conditions (such as in wet roads) friction based braking is necessary

on the other wheels.

The amount of electrical energy capable of dissipation is limited by either

the capacity of the supply system to absorb this energy or on the state of

charge of the battery or capacitors. No regenerative braking effect can occur

if another electrical component on the same supply system is not currently

drawing power and if the battery or capacitors are already charged. For this

reason, it is normal to also incorporate dynamic braking to absorb the

excess energy.

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Some of the cars using Regenerative Braking:-

Toyota Prius

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Honda Civic Hybrid

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Tesla Roadster

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Nissan Leaf

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CONCLUSION

In a century that may see the end of the vast fossil fuel reserves that have provided us

with energy for automotive and other technologies for many years, and in which fears

about carbon emissions are coming to a peak, this added efficiency is becoming

increasingly important

Regenerative braking is a small, yet very important, step toward our eventual

independence from fossil fuels.

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 a few years time.

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. 

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