25-01-2013, 03:45 PM
REGENERATIVE BRAKING SYSTEM
REGENERATIVE BRAKIN.pdf (Size: 445.37 KB / Downloads: 89)
ABSTRACT
Regenerat i ve Brak ing System i s the way of slowing vehi cle by
using the motor s as brakes. Instead of the surplus energy of the
vehi c le being wasted as unwanted heat , the motor s act as
generators and return some of i t to the overhead wi res as
elec t r i c i t y.
The vehi cle i s pr imarily powered f rom the elect r ical energy
generated f rom the generator , which burns gasol ine. Thi s energy
i s stored in a large bat ter y, and used by an elec t r i c motor that
provides mot i ve force to the wheel s . The regenerat i ve bark ing
tak ing place on the vehicle is a way to obtain more ef f ic iency;
ins tead of conver t ing kinet ic energy to thermal energy through
f rictional brak ing, the vehic le can conver t a good f ract ion of i ts
kinet i c energy bac k into charge in the battery, us ing the same
principle as an al ternator .
INTRODUCTION
Brake: -
A brake i s a machine element and i t s pr inciple object i s to
absorb energy dur ing decelerat ion. In vehi c le brakes are used to
absorb kinet ic energy whereas in hois ts or elevator s brakes are
also used to absorb potent ial energy. By connect ing the moving
member to stat ionar y f rame, normal l y brake conver ts k inet i c
energy to heat energy. Thi s causes wastage of energy and also
wearing of frictional lining mater ial .
Regenerative Braking System: -
Regenerat i ve Brak ing System is the way of s lowing vehi cle
by us ing the motors as brakes. Instead of the surplus energy of
the vehic le being was ted as unwanted heat , the motor s ac t as
generators and return some of it to the overhead wi res as
electricity.
The vehi cle i s pr imar i l y powered f rom the elect r ical energy
generated f rom the generator , which burns gasol ine. Thi s energy
i s stored in a large bat ter y, and used by an elec t r i c motor that
provides mot i ve force to the wheel s . The regenerat i ve bark ing
tak ing place on the vehi cle is a way to obtain more ef f ic iency;
ins tead of conver t ing kinet ic energy to thermal energy through
f r ic t ional brak ing, the vehic le can conver t a good f ract ion of i ts
k inet i c energy bac k into charge in the bat ter y, us ing the same
pr inc iple as an al ternator .
Therefore, i f you dr i ve long dis tance wi thout braking, you’ l l
be power ing the vehi c le ent i rel y f rom gasol ine. The regenerat i ve
braking
Regenerat i ve Brak ing System comes into i t s own when you’ re
driving in the c i t y, and spending a good deal of your t ime brak ing.
You will still use more fuel in the ci t y for each mile you dr i ve than
on the highway, though. (Thermodynamic s tel ls us that al l
inef f icienc y comes f rom heat generat ion. For instance, when you
brake, the brake pedal s heat up and a quant i t y of heat , or energy,
i s lost to the outside wor ld. Fr ict ion in the engine produces heat
in the same way.
Heat energy, al so, has higher ent ropy than, say, elect r ic,
meaning that i t is les s ordered. )
Def ini t ion:
Braking method in which the mechani cal energy f rom the
load is conver ted into elec t r i c energy and regenerated back
into the l ine is known as Regenerat i ve Brak ing. The Motor
operates as generator .
Regenerat ive Braking For Hybr id Vehicle:
In most elect r ic and hybr id elect r i c vehic les on the road
today, thi s i s ac compl i shed by operat ing the t ract ion motor as a
generator , providing braking torque to the wheel s and recharging
the t ract ion bat ter ies . The energy provided by regenerat i ve
braking can then be used for propul sion or to power vehic le
accessor ies.
NECESSITY OF THE SYSTEM
The regenerat i ve braking s ys tem del i ver s a number of
s igni f i cant advantages over a car that onl y has f r ict ion brakes. In
low- speed, s top-and-go t raf f i c where l i t t le decelerat ion is
requi red; the regenerat i ve brak ing sys tem can provide the major i t y
of the total brak ing force. This vast l y improves fuel economy wi th
a vehic le, and fur ther enhances the at t ract i veness of vehic les
using regenerat i ve brak ing for ci t y dr i ving. At higher speeds, too,
regenerat i ve braking has been shown to cont r ibute to improved
fuel economy – by as much as 20%.
Cons ider a heavy loaded t ruck having very few s tops on the
road. I t i s operated near maximum engine ef f i ciency. The 80% of
the energy produced i s utilized to overcome the rol l ing and
aerodynamic road forces. The energy was ted in appl ying brake is
about 2%. Also its brake specific fuel consumpt ion is 5%.
Now cons ider a vehic le, whi ch is operated in the main ci ty
where t raf f ic is a major problem here one has to appl y brake
f requently. For such vehic les the wastage of energy by
appl icat ion of brake is about 60% to 65%. And al so i t is
inef f icient as i t s brake spec i f ic fuel consumpt ion is high.
Some of the advantages of regenerat ive braking over
convent ional braking are as fol lows:
Energy Conservat ion:
The f l ywheel absorbs energy when brak ing via a c lutch s ystem
s lowing the car down and speeding up the wheel . To accelerate,
another clutch s ys tem connects the f l ywheel to the dr i ve t rain,
speeding up the car and s lowing down the f l ywheel . Energy is
therefore conser ved rather than was ted as heat and l ight which is
what normal l y happens in the contemporar y shoe/dis c s ystem.
Wear Reduct ion:
An elect r i c dr i ve t rain al so al lows for regenerat i ve breaking which
inc reases Ef f ic ienc y and reduces wear on the vehic le brakes. In
regenerat i ve rak ing, when the motor is not recei ving power f rom
the bat ter y pac k, i t res is ts the turning of the wheels , captur ing
some of the energy of mot ion as i f i t were a generator and
returning that energy to the bat tery pac k. In mechanical brakes;
les sening wear and extending brake l i fe is not poss ible. This
reduces the use of use the brake.
Fuel Consumpt ion:
The fuel consumpt ion of the convent ional vehi c les and
regenerat i ve braking s ystem vehic les was evaluated over a course
of var ious f i xed urban dr i ving s chedules. The resul ts are
compared as shown in f igure. Represent ing the signi f icant cost
saying to i t s owner , i t has been proved the regenerat i ve brak ing is
ver y fuel -ef f ic ient .
Braking is not total loss:
Convent ional brakes appl y f r ic t ion to conver t a vehic le’s k inet ic
energy into heat . In energy terms, therefore, brak ing is a total
los s: once heat is generated, i t is ver y di f f icul t to reuse. The
regenerat i ve braking s ystem, however , slows a vehic le down in a
di f ferent way.