85009935 Regenerative Braking System
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Transcript of 85009935 Regenerative Braking System
A SEMINAR ON
REGENERATIVE BRAKING SYSTEM
ASWIN SANKAR J S
ROLL NO:12
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
Some of the cars using Regenerative Braking:-
Toyota Prius
Honda Civic Hybrid
Tesla Roadster
Nissan Leaf
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.
THANK YOU