25-09-2014, 04:34 PM
DESIGN AND ANALYSIS OF KINETIC
ENERGY RECOVERY SYSTEM IN
BICYCLES
1408158606-42DESIGN.pdf (Size: 1.03 MB / Downloads: 106)
I. INTRODUCTION
KERS is a collection of parts which takes some of the kinetic energy of a vehicle under deceleration, stores this energy
and then releases this stored energy back into the drive train of the vehicle, providing a power boost to that vehicle. For
the driver, it is like having two power sources at his disposal, one of the power sources is the engine while the other is
the stored kinetic energy. Kinetic energy recovery systems (KERS) store energy when the vehicle is braking and return
it when accelerating. During braking, energy is wasted because kinetic energy is mostly converted into heat energy or
sometimes sound energy that is dissipated into the environment. Vehicles with KERS are able to harness some of this
kinetic energy and in doing so will assist in braking. By a proper mechanism, this stored energy is converted back into
kinetic energy giving the vehicle extra boost of power.There are two basic types of KERS systems i.e. Electrical and
Mechanical. The main difference between them is in the way they convert the energy and how that energy is stored
within the vehicle. Battery-based electric KERS systems require a number of energy conversions each with
corresponding efficiency losses. On reapplication of the energy to the driveline, the global energy conversion efficiency
is 31–34%. The mechanical KERS system storing energy mechanically in a rotating fly wheel eliminates the various
energy conversions and provides a global energy conversion efficiency exceeding 70%, more than twice the efficiency
of an electric system.
This design of KERS bicycle was motivated by a desire to build a flywheel energy storage unit as a proof of concept.
On a flat road, the cyclist can maintain a fixed cruising speed to get from point to point. Globally all roads are flat with
impediments such as intersections, cars, and turns that force the cyclist to reduce speed, then accelerate.
KERS BICYCLE WORKING
A crank wheel connected to the rear wheels always rotates the clutch plate, connected in the flywheel axle. This is
being achieved by using chain transmission at a specified gear ratio, crank to clutch sprocket helps us to increase the
overall speed of flywheel. Now at a time when a speed reduction is required, clutch is applied which makes the contact
between the clutch and flywheel. Then the flywheel starts rotating, also the speed of bicycle is decreased. Thus a
regenerative braking system is achieved. On course energy is stored in flywheel. In case the brake has to be applied
fully then after flywheel rotations clutch is disengaged and the brake is applied. Now when we again rides the bicycle
during which we would apply clutches at this time as rear wheel rotation is lesser compared to flywheel the energy gets
transmitted from the flywheel to the wheels. Now also we can reduce the overall pedalling power required in course of
overrides by having clutch fully engaged. We can reduce overall pedalling power by 10 per cent. Also situation arises
such as traffic jam, down climbing a hill where we do not intend to apply brake fully. For such cases we can apply our
smart braking system which would allow us to decelerate and allow us to boost acceleration after this during normal
riding and distance that can be covered by pedalling can also improve.
During normal rides situations may arise we need to reduce the speed without braking fully such as traffic jams taking
turns etc. we can store the energy that would normally be wasted due to speed reduction by the application of clutch.
When the clutch is engaged that time due to initial engage the flywheel rotation consumes energy which would result in
speed reduction thus a braking effect. After some instances the energy is being stored in the flywheel this can be
reused by the engage of clutch plate and energy transfer from the flywheel occurs whenever the rotation is high enough
to rotate rear wheel. Thus if sudden braking then applied we can disengage the flywheel connections so that flywheel
energy is not wasted and going to take ride the speed of rear wheel is null and hence engage would help in returning the
energy from the flywheel to rear wheel. While riding downhill we always use braking for allowing slowdown. This is
the best case where we can store maximum amount of energy in our flywheel. The flywheel can be engaged for full
downhill ride and after all for some distance we need not ride the bicycle which would be done by the flywheel. This is
the main advantage area of KERS bicycle. During long drive the engage can be made full time. This will help in
reducing the overall pedalling effort. It has been found that the pedalling power can be reduced by 10 per cent during
long drives. Also this would help in avoiding pedalling effort at some points of ride. The complete KERS bicycle is
shown in figure 2 below.
FABRICATION PROCESS
A. Frame Modification
The frame modification is the first part of the fabrication that has to be done. The frame has to be modified by adding
steel tube. One end has to be welded at the handle end and the other at the rear wheel centre. The frame should have
enough strength so as to carry the flywheel and the additional forces that comes to play. The modification should not
hinder normal riding. Also the modified frame should have enough space in order to accommodate flywheel and clutch
RESULT AND ANALYSIS
The flywheel bicycle increases efficiency on rides where the rider slows often. The additional weight is outweighed by
the ability to recover energy normally lost during braking. Thus the addition of extra weight does not make it difficult
for the rider. Also clutch provided helps in deciding the time period of activity. The overall result is that KERS system
is efficient in storing the energy normally lost in braking and returns it for boosting.
A. Weight And Performance
Normally energy stored in the flywheel is directly proportional to the weight and radius. Hence increase in weight
proves to improve the performance. But as we know that the maximum safe weight that can be used is limited due to
frame properties and rider compatibility. And also after some extent the radius can‟t be increased and the energy
storage thus seems to be limited to some particular extend. This is also because of the fact that the total running speed
is being reduced due to weight. Energy storage capacity increases with increase in weight but limitation seems to be the
speed driving the flywheel. And performance of system is directly linked with the energy stored. Thus a graph can be
plotted between performance and weight. Optimum value lies between 5 and 8 kg.
Energy stored in flywheel, Ek=
1
2
?ω2
Where, „I‟ is the moment of inertia
„ω‟ is the rotational velocity (rpm)
Moment of inertia, I = ?
2
Where, „k‟ is inertial constant (depends on shape)
„m‟ is mass of the disc
„r‟ is the radius
Thus Ek is directly proportional to the mass of the disc
The flywheel and transmission add weight to the bicycle. The increased weight will add to the energy required to
accelerate the bicycle and to ride it uphill. However, once the rider has provided the energy to reach a cruising speed,
the flywheel reduces the energy cost of slowing down from this speed since it aids in subsequent acceleration. Roads
are optimal environment for the flywheel bicycle because it‟s flat and there are lots of reasons for the cyclist to slow
CONCLUSION
KERS system used in the vehicles satisfies the purpose of saving a part of the energy lost during braking. Also it can be
operated at high temperature range and are efficient as compared to conventional braking system. The results from
some of the test conducted show that around 30% of the energy delivered can be recovered by the system. KERS
system has a wide scope for further development and the energy savings. The use of more efficient systems could lead
to huge savings in the economy of any country. Here we are concluding that the topic KERS got a wide scope in
engineering field to minimize the energy loss. As now a day‟s energy conservation is very necessary thing. Here we
implemented KERS system in a bicycle with an engaging and disengaging clutch mechanism for gaining much more
efficiency. As many mating parts is present large amount of friction loss is found in this system which can be improved.
Boost is reduced because of friction. Continuously variable transmission can be implemented to this system which
would prove in drastic improvement in energy transmissions.