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KINETIC ENERGY RECOVERY SYSTEM

Aditya Bhavsar1, Dhaval Kothari

2, Abhijeet Ahire

3

1,2,3Dept. of Mechanical Engineering, Gokhale Education Society’s

R. H. Sapat College of Engineering, Management Studies and Research Centre, India

ABSTRACT

The world has vastly benefitted with the advancement of technology and knowledgebase which has brought

about enormous socio-economic progress and consequently raised the standard of living of humankind beyond

comprehension. Among the many resources which have played a major part in the growth, the role of fossil

fuels has been undeniably quite significant. But the reserves of these ‘non-renewable’ fossil fuels are rapidly

declining and at the rate of growth of the humankind, the exhaustion of these resources in near future is

inevitable. This has been the one of the major causes of concern in the recent past. The other major concern in

the present day has been declining state of environment. As a result, over the past 40-50 years, the focus has

shifted towards finding solutions which combat these issues, with the major areas of concentration being –

efficient usage of energy resources (fossil fuels) in various applications like industry, transportation etc., finding

alternative and/or renewable energy resources to supplement/replace the fossil fuel, better control strategies

and treatment techniques to reduce pollution.

An alternative for saving the energy, wasted in the case of decelerating or slowing down the speed of a

vehicle is KERS. KERS stands for Kinetic Energy Recovery System, the term of which explains about the

concept of energy conservation. The introduction of KERS is one of the most significant technical introductions

for the normal (non-hybrid) vehicles. KERS is an energy saving device fitted to the engines to convert some of

the waste energy produced during braking into more useful form of energy. The system stores the energy

produced under braking in a reservoir and then releases the stored energy under acceleration. The key purpose

of the introduction is to significantly improve the fuel economy without compromising with the performance of

the automobile.

Keywords: Braking, KERS, Fossil Fuels, Fuel Economy, Reservoir.

I. INTRODUCTION

The Age of Industrialization, since the late 1800‘s, has been nothing short of remarkable. The world has vastly

benefitted with the advancement of technology and knowledgebase which has brought about enormous socio-

economic progress and consequently raised the standard of living of humankind beyond comprehension. Among

the many resources which have played a major part in the growth, the role of fossil fuels has been undeniably

quite significant. But the reserves of these ‗non-renewable‘ fossil fuels are rapidly declining and at the rate of

growth of the humankind, the exhaustion of these resources in near future in inevitable. This has been the one of

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the major causes of concern in the recent past. The other major concern in the present day has been declining

state of environment.

The inefficient and excess usage of fossil fuels has caused the pollution of the environment, to the extent of its

breakdown. As a result, over the past 40-50 years, the focus has shifted towards finding solutions which combat

these issues, with the major areas of concentration being – efficient usage of energy resources (fossil fuels) in

various applications like industry, transportation etc., finding alternative and/or renewable energy resources to

supplement/replace the fossil fuel, better control strategies and treatment techniques to reduce pollution.

Automobiles are one of the major consumers of fossil fuels and therefore:

1. One of the major sectors responsible for their depletion to the extent of near exhaustion;

2. One of the major contributors to the escalating environmental pollution levels.

Due to these problems, in the recent past, the Auto Industry has come to an impasse where they are left with

no alternative but to find alternate solutions to conserve natural resources. Over the years, the efforts in this

direction have led to research and development in the following areas:

1. Improving engine efficiencies and performance – with the help of innovation in engine design and its

components, improved control strategies etc.;

2. Emission treatment and control technologies;

3. Vehicle design changes for reduction of thermal, aerodynamic and road losses;

4. Improvised transmission design to reduce losses;

5. Hybrid and Alternative Energy Propulsion systems e.g. the Hybrid Electric Vehicle (HEV), the Fuel

Cell Vehicle (FCV);

6. Recycling Braking energy – Storage and reuse of braking energy which is otherwise lost in the form of

heat energy – technology that achieves this purpose is termed as a Regenerative Braking System (RBS).

With legislations in place for strict emission standards, the automobile industry currently has embraced the new

development, by embedding one or more of the above mentioned technologies in commercial vehicles.

Additionally, as a long term alternative to fossil fuels, the research in ‗Alternative Energy Vehicles‘, especially

the field of ‗Hybrid Propulsion with Regenerative braking‘ has come to the forefront. ‗Hybrid Propulsion

Vehicles (HPV)‘ or ‗Hybrid Vehicles‘ are vehicles in which two or more power sources propel the vehicle, in

order to share the load and hence improve performance/improve fuel efficiency. Most of the current hybrid

vehicles use an internal combustion engine (ICE) as one of the power sources and an alternative energy source

(electrochemical battery, Fuel cell etc.) for the other source. By utilizing a hybrid power train, the load on the

ICE reduces, as a result of which the size of the ICE can be reduced. Reduction of an ICE implies better fuel

efficiency. Alternatively/additionally the ICE can be optimized to operate only in certain load conditions, which

also results in improved fuel efficiency. Overall, the result is a more efficient vehicle. As an additional tool to

improving efficiency, current hybrid vehicles also employ regenerative braking to capture and utilize braking

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energy. Regenerative Braking Systems (RBS) capture the energy that is usually lost while braking, store that

energy in an energy storage system (ESS) and the reuse it to start or accelerate the vehicle. In case of HEVs,

regenerative braking is easily implemented as the electrical technology used to run the wheels is modified to

also perform regenerative braking. Designing and testing such a regenerative braking system for the application

in a Formula racecar is the topic of this research. The later part of this chapter is as follows: In the next section,

the motivation for the thesis is explained followed by the problem statement, after which the aims for the

research and design are set and methodology used is explained. The chapter concludes with the thesis outline.

1.1. Regenerative Braking System

Regenerative Braking is one of the emerging technologies which can prove very beneficent. The use of

regenerative braking in a vehicle not only results in the recovery of the energy but it also increases the efficiency

of vehicle (in case of hybrid vehicles) and saves energy, which is stored in the auxiliary battery. Regenerative

braking refers to a process in which a portion of the kinetic energy of the vehicle is stored by a short term

storage system. Energy normally dissipated in the brakes is directed by a power transmission system to the

auxiliary battery during deceleration. The energy that is stored by the vehicle is converted back into kinetic

energy and used whenever the vehicle is to be accelerated. The magnitude of the portion available for energy

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

In order to understand the concept of a RBS and its impact on vehicle energy performance, a simple example is

presented: Consider a 300 kg (nearly 661 lbs.) vehicle moving at an initial speed of 72 km/hr (nearly 45 mph).

Now, on stopping the vehicle to a speed of 32 km/hr (nearly 20 mph) the amount of energy spent is around 47.8

kJ using the equation given below:

= * * …(1)

where,

Ek: Kinetic Energy of the vehicle;

m: Mass of the vehicle;

v: Velocity of the vehicle.

Ideally, this is the amount of energy available for capturing at each instance of braking. If regenerative braking

was used on such a vehicle it would be able to capture this amount of energy and reuse this same energy which

would otherwise have been lost in the form of heat, sound etc. Now, even if we suppose that the efficiency of

the brake is 25% of this, there would still be an amount of 11.85 kJ (25% of 47.8kJ) of energy available at each

braking instance, which shows the amount of energy that can be utilized for beneficial causes.

The energy that has been harnessed from the braking action of the vehicle will be converted to torsional energy

of the spring. The use of helical torsion spring ensures that the mechanical energy is stored when it is twisted

and the amount of force that is exerted is proportional to the amount by which it has been twisted.

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This energy is roughly, neglecting all losses, enough to accelerate a car from 0 km/h to around 32 km/h (using

equation 1). This stored energy using RBS can be reutilized for different purposes, either to help improve

performance or fuel efficiency, in either case assisting in ‗Load Sharing‘.

1.2. Problem Statement (Conventional Braking)

Braking in a moving vehicle means the application of the brakes to slow or stop its movement, usually by

pressing pedal. The braking distance is the distance between the time the brakes are applied and the time the

vehicle comes to a complete stop. When brakes are applied to a vehicle using conventional braking system,

kinetic energy is converted into heat due to the friction between the wheels and brake pads. This heat is carried

away in the airstream and the energy is wasted. The total amount of energy lost in this process depends on how

often, how hard and for how long the brakes are applied. Conventional methods uses friction brakes for

retarding the vehicle which is a total loss of momentum of vehicle.

1.3. Objectives

The objectives based on which the project is manufactured are as:

To design and manufacture the KERS components.

To construct a Test Rig, for demonstrating KERS.

1.4. Methodology

This project will progress as per by providing firstly an in-depth review of Regenerative Braking System (RBS),

and explaining its types. Then deal is with the design and selection of various components. The gears and shafts

needs to be selected based on the calculations, after which the bearing will be chosen. With the progress of the

design of various components, assembly is to be done. After the manufacturing of the complete rig, it will be

run for a specific period, which will notify its success.

II. REGENERATIVE BRAKING SYSTEM

2.1. Introduction

Regenerative braking is one of the emerging technologies which can prove very beneficent. The use of

regenerative braking in a vehicle not only results in the recovery of the energy but it also increases the efficiency

of vehicle (in case of hybrid vehicles) and saves energy, which is stored in the auxiliary battery. Regenerative

braking refers to a process in which a portion of the kinetic energy of the vehicle is stored by a short term

storage system. Energy normally dissipated in the brakes is directed by a power transmission system to the

auxiliary battery during deceleration. The energy that is stored by the vehicle is converted back into kinetic

energy and used whenever the vehicle is to be accelerated. The magnitude of the portion available for energy

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

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2.2. Types of Regenerative Braking Systems:

There are many ways by which the energy can be saved, depending upon the components used in it. There are

basically three types of the Regenerative Braking Systems, which are described as follows:

2.2.1. Mechanical Regenerative Braking

Regenerative brakes may seem very hi-tech, but the idea of having ‗Energy Storing Reservoirs‘ in machines is

nothing new. Engines have been using energy storage devices as flywheels virtually since they were invented.

The basic idea is that the rotating part of the engine incorporates a wheel with a very heavy metal rim, and this

drives whatever machine or device the engine is connected to.

When the braking force is required than the flywheel is connected to the drive train and the momentum of the

vehicle is stored in the flywheel. Hence the flywheel starts rotating at higher speed. Whenever the extra driving

force is required, the flywheel is again connected to the system and the energy from the flywheel is transferred

to the drive train through CVT. Flywheels are extremely versatile devices such that, they can be used to

seamlessly feed power back into the power train, reducing the work done by the engine, saving fuel and

reducing CO2 emissions. The high power density and long life potential of Flywheel technology results from its

inherent simplicity and effectiveness offering a robust, compact and lightweight package. The simplicity of its

design also yields comparatively very low projected production costs, thus opening the door to a wide range of

potential applications.

Fig. 1: Sectional View of Flywheel

2.2.2. Electrical Regenerative Braking

In an electric system, which is driven only by means of electric motor also acts as generator and motor. Initially

when the system is cruising the power is supplied by the motor and when there is a necessity for braking

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depending upon driver‘s applied force on the brake pedal the electronic unit controls the charge flowing through

the motor and due to the resistance offered, motor rotates back to act as a generator and the energy is stored in a

battery or bank of twin layer capacitors for later use. In hybrid system, motor will be coupled to another power

source normally I.C. Engines.

The main components of this system are:-

Engine,

Motor/Generator,

Batteries,

Electronic Control System.

During acceleration, the MGU acts as an electric motor to draw electrical energy from the batteries to

provide extra driving force for moving the car as shown in fig. 3.2.1(a). With this help from the motor, the car‘s

internal combustion engine which is smaller having lower peak power can achieve high efficiency. During

braking, electric supply from the battery is cut off by the electronic system.

As the car is still moving forward, the MGU acts as an electric generator to convert car‘s kinetic energy into

electrical energy and store it in the batteries as shown in fig 3.2.1(b) for later use.

This stored energy is available at the time of acceleration; whenever extra driving torque is required the

electrical energy from battery runs the motor to supply power.

Fig. 2: Recalling stored energy from battery during acceleration

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Fig. 3: Storing of energy in batteries during braking

2.2.3. Hydrostatic Regenerative Braking

Hydrostatic Regenerative Braking (HRB) system uses electrical/electronic components as well as hydraulics to

improve vehicle fuel economy. An alternative regenerative braking system is being developed by the Ford

Motor Company and the Eaton Corporation. It is called Hydraulic Power Assist (HPA).

With HPA when the driver applies brakes, the vehicles kinetic energy is used to power a reversible pump, which

sends hydraulic fluid from a low pressure accumulator (a kind of storage tank) inside the vehicle into a high

pressure accumulator. The pressure is created by nitrogen gas in the accumulator, which is compressed as the

fluid is pumped into the space where the gas was stored formerly. This slows down the vehicle and helps to

bring it to a stop. The fluid remains under pressure in the accumulator until the driver pushes the accelerator

pedal again, the point at which the pump is reversed and the pressurized fluid is used to accelerate the vehicle,

effectively translating the kinetic energy that the car had before applying brakes, into the mechanical energy

which helps to get the vehicle to recover the initial speed. It is a prediction, that a system like this could store

about 80% of the lost momentum by a vehicle during deceleration and use it to get back the lost momentum of

the vehicle. Bosch Rexroth has an RBS that does not require a vehicle to be hybrid. In fact, it does not involve

electrical storage. In the HRB system, braking energy is converted to hydraulic pressure and stored in a high-

pressure hydraulic accumulator. When the vehicle accelerates, the stored hydraulic energy is applied to the

transmission reducing the energy that the combustion engine has to provide.

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Fig. 4: Hydrostatic Regenerative Braking

2.3. Gap Identification

In the hydraulic braking the components increases the weight of vehicle, due to which the efficiency is affected

and also they require considerable space. This problem is overcome by using flywheel and by electrical method

but the cost increases dramatically. The major area of developing system is in storage of Kinetic Energy and

then utilization of this stored energy in mechanical form or electrical form as per requirement with safety and

enough braking effort. This can be achieved by using which is light in weight and conversion of this mechanical

energy in electrical by means of an alternator.

2.4. Limitations of existing braking systems

Being advantageous doesn‘t mean that there may not be any limitations to the system. There are certain

limitations to the braking systems, described above. Some of the limitations are listed below:

1. Existing systems aim at converting basically the momentum of the vehicle to the mechanical energy, which

is further converted to electrical energy by dynamo, for it to be stored in the batteries. Considering battery

to be Li-ion, it has a far charging time and thus proves to be inefficient for storing such large amount of

energy in such small time.

2. There is a possibility for there to be conversion losses at each stage due to inefficiency of each component

of system viz. the dynamo, battery and the electric motor.

3. The components of the above discussed systems, with flywheel and CVT added are extremely costly,

thereby making implementation of technology close to impossible.

4. Computers and electronic controls are absolutely essential to run the system. Hence the running cost of such

system is considerably high.

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Hence there is need for a simpler system to be used for converting and storing the momentum (Kinetic Energy)

into pure mechanical form and put to use the same energy back in mechanical energy form, thereby reducing the

conversion losses and keep the system production, installation and running cost to minimum level.

2.5. Alternative for existing braking systems

After analyzing other types of KERS, it seems that there is a need for the braking system or KERS to be

efficient and reliable at all times (without loss of energy). Thus, the present project circulates about an idea of

storing and recovering the lost energy by means of spring.

This spring based KERS or Mechanical Regenerative type braking system, has a basic concept of using spring

as an Energy Storage System (ESS), which can be used later for summing up the momentum to the wheel or a

shaft offering more torque.

Next Chapter aims at introduction and evaluation of the spring based KERS and the components, used in this

system.

III. SPRING BASED KERS

3.1. Basic Concept

It all starts with the introduction of an axle, on which a planetary gear system is fitted along with disc brake

arrangement. When the axle starts rotating, wheel also rotates along with the components described above.

During the run time of the vehicle, spur gear starts rotating in the same direction as that of wheel, causing the

planetary gear to complete a rotation around the spur gear. During this time, recovery ring is stationary. Disc

brake has a connection with the planetary gear, which rotates along with the planetary gear system.

When the brakes are applied, disc brake ceases the rotation of the planetary gear around the sun gear and

recovery ring starts rotating. The position of spring is such that, its inner end is attached to the recovery ring hub

and outer end is attached to the scroll spring case. When the recovery ring rotates, it rotates in opposite direction

as that of wheel, causing the spring attached on it to wound more, thereby increasing the torsion of spring. This

leads to the energy storage in the spring. A one-directional clutch is brought in use in this system, for the

purpose of recovering energy.

During acceleration, when the pedal is pressed, this one-directional clutch gets fitted against the scroll spring

case hub. This action results in the un-wounding of the spring, thereby returning the stored energy to the axle, in

the same amount of fuel consumption. This method is a perfect solution to the conservation of energy without

conversion losses. After the initial amount of energy is gained by the system, the spring stops its wounding and

the clutch comes to normally-off position.

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3.1 Test Rig Concept

The previous types of KERS were installed in automobiles, as they succeeded in conserving energy of the

vehicle. These systems proved beneficial for the performance of the vehicle, as these increased the fuel

economy under same amount of fuel consumption.

Now, the spring based KERS also aims at conserving kinetic energy, but firstly testing needs to be done. So, a

test rig needs to be designed for the purpose of analysis of this type of KERS. The actual working and its

operation is stated here as follows.

The whole process of energy conservation starts with the introduction of the motor. This motor or a prime

mover (general reference) drives an engine through the shaft. Gear Box is thus operated due to shaft, and the

whole setup starts working like an automobile engine. Speed of the motor is varied and fuel is also fed time to

time for its smoother operation. Clutch lever being attached to the engine itself, fulfills engagement or

disengagement, as per demand of the operator. This gear box is further extended to the spring case.

When the clutch lever is pressed, the output shaft of the engine and the input shaft of the Gear Box are

disengaged, which eventually leads to the shaft from the gearbox to rotate freely. Gear Box operates the gear

and thus the springs in the spring case starts rotating and thus stores the kinetic energy. Now when the clutch

comes to an off-position or when it engages the shafts, the spring rotates in such a manner that it un-wounds and

gives more energy (torque) to the engine shaft, with the load on the motor being same. In this way, the spring

after returning the stored amount of energy stops un-wounding further more.

Fig. 5: Schematic Representation of Mechanical Regenerative Type KERS

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Fig. 6: Test Rig Conceptual Representation

3.2 Components of KERS

Test Rig for demonstrating KERS concept deals with a lot of spare parts. It is the combination of all the

transmission devices and power transmission devices that results into the energy saving machine.

The list of all the components used here are:

Motor,

Frame,

Crank Case,

Belt Drive,

Shaft,

Gears,

Single Plate Clutch,

Plummer Block,

Spiral Spring,

Alternator.

3.2.1 Motor

An induction or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to

produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding. An

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induction motor therefore does not require mechanical commutation, separate-excitation or self-excitation for all

or part of the energy transferred from stator to rotor, as in universal, DC and large synchronous motors. An

induction motor's rotor can be either wound type or squirrel-cage type.

Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans.

Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-

frequency drives (VFDs) in variable-speed service. VFDs offer especially important energy savings

opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump and

compressor load applications. Squirrel cage induction motors are very widely used in both fixed-speed and VFD

applications.

A motor of the following specifications is used for the rig:

Single Phase Induction Motor

Power: 0.5 HP

Voltage: 220-230 volts

Frequency: 50 Hz

Speed: 1440 rpm

3.2.2 Frame

A frame is a supporting structure. The whole assembly is mounted on the frame, including motor, crank case,

gears, Plummer block, etc. Hence it should robust enough to support the whole system and damp the vibrations

as far as possible.

For the frame to be used in the test rig, the dimensions of the frame are as:

Length= 1000

Breadth= 520

Height= 490

3.2.3 Crank Case

An engine is a machine designed to convert one form of energy into mechanical energy. Heat engines, including

Internal Combustion and External Combustion Engines (such as steam engines), burns the fuel to create heat,

which then creates a force. Electric motors convert electrical energy into mechanical motion; pneumatic motors

use compressed air and others- such as clockwork motors in wind-up toys – use elastic energy. In biological

systems, molecular motors, like myosins in muscles, use chemical energy to create forces and eventually

motion. Here, we have just used an engine as a crank case in order to be run by the motor.

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The actual use of engine in KERS is to give the required amount of torque to the shafts on which gears are

mounted, which follows to the spring. For this purpose, a provision of a Maruti 800 engine has been made,

which will be used as torque generating device.

The specifications of the motor are as:

Displacement: 796 cc (49 cu in)

Valves per cylinder: 2

Numbers of cylinder: 3 (In-line)

Fuel Type: Petrol

Power: 37 bhp @ 5000 rpm

Torque: 59 Nm @ 2500 rpm

3.2.4 Belt Drive

For the purpose of transmitting power from motor to the crank case, belt drive is used. The belt is mounted over

the shaft of the motor and over the pulley near the crank case.

The specifications of the belt drive used in test rig are as:

Input pulley diameter (d): 75 mm

Output Pulley diameter (D): 300 mm

N1: 1440 rpm

N2: 350 rpm

Speed reduction ratio (G1): 4.11

3.2.5 Gears

A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to

transmit torque. Geared devices can change the speed, torque, and direction of a power source. Gears almost

always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be

considered a simple machine. The teeth on the two meshing gears all have the same shape. Two or more

meshing gears, working in a sequence, are called a gear train or a transmission. A gear can mesh with a linear

toothed part, called a rack, thereby producing translation instead of rotation.

The gears in a transmission are analogous to the wheels in a crossed belt pulley system. An advantage of gears is

that the teeth of a gear prevent slippage.

When two gears mesh, if one gear is bigger than the other, a mechanical advantage is produced, with the

rotational speeds, and the torques, of the two gears differing in proportion to their diameters.

In transmissions with multiple gear ratios—such as bicycles, motorcycles, and cars—the term "gear" as in "first

gear" refers to a gear ratio rather than an actual physical gear. The term describes similar devices, even when the

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gear ratio is continuous rather than discrete, or when the device does not actually contain gears, as in a

continuously variable transmission.

There are various types of gears depending upon the position, of which some are listed as follows

3.2.5.1 External vs. Internal Gears

An external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal

gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is

one with the pitch angle exceeding 90 degrees. Internal gears do not cause output shaft direction reversal.

3.2.5.2 Spur Gears

Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with teeth

projecting radially. Though the teeth are not straight-sided (but usually of special form to achieve a constant

drive ratio, mainly involute but less commonly cycloidal), the edge of each tooth is straight and aligned parallel

to the axis of rotation. These gears mesh together correctly only if fitted to parallel shafts.

3.2.5.3 Helical Gears

Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to

the axis of rotation, but are set at an angle. Since the gear is curved, this angling makes the tooth shape a

segment of a helix. Helical gears can be meshed in parallel or crossed orientations. The former refers to when

the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel,

and in this configuration the gears are sometimes known as "skew gears".

The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and

quietly. With parallel helical gears, each pair of teeth first make contact at a single point at one side of the gear

wheel; a moving curve of contact then grows gradually across the tooth face to a maximum then recedes until

the teeth break contact at a single point on the opposite side. In skew gears, teeth suddenly meet at a line contact

across their entire width causing stress and noise. Spur gears make a characteristic whine at high speeds.

Whereas spur gears are used for low speed applications and those situations where noise control is not a

problem, the use of helical gears is indicated when the application involves high speeds, large power

transmission, or where noise abatement is important. The speed is considered high when the pitch line velocity

exceeds 25 m/s.

A disadvantage of helical gears is a resultant thrust along the axis of the gear, which must be accommodated by

appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth—often addressed

with additives in the lubricant.

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3.2.5.4 Skew Gears

For a 'crossed' or 'skew' configuration, the gears must have the same pressure angle and normal pitch; however,

the helix angle and handedness can be different. The relationship between the two shafts is actually defined by

the helix angle(s) of the two shafts and the handedness, as defined:

, for gears of the same handedness

, for gears of opposite handedness

Where is the helix angle for the gear. The crossed configuration is less mechanically sound because there is

only a point contact between the gears, whereas in the parallel configuration there is a line contact.

Quite commonly, helical gears are used with the helix angle of one having the negative of the helix angle of the

other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal

angles. The two equal but opposite angles add to zero: the angle between shafts is zero—that is, the shafts

are parallel. Where the sum or the difference (as described in the equations above) is not zero the shafts

are crossed. For shafts crossed at right angles, the helix angles are of the same hand because they must add to 90

degrees.

3.2.5.5 Double Helical Gears

Double helical gears and herringbone gears are similar but the difference is that herringbone gears don't have a

groove in the middle like double helical gears do. Double helical gears overcome the problem of axial thrust

presented by "single" helical gears, by having two sets of teeth that are set in a V shape. A double helical gear

can be thought of as two mirrored helical gears joined together. This arrangement cancels out the net axial

thrust, since each half of the gear thrusts in the opposite direction resulting in a net axial force of zero. This

arrangement can remove the need for thrust bearings. However, double helical gears are more difficult to

manufacture due to their more complicated shape.

For both possible rotational directions, there exist two possible arrangements for the oppositely-oriented helical

gears or gear faces. One arrangement is stable, and the other is unstable. In a stable orientation, the helical gear

faces are oriented so that each axial force is directed toward the centre of the gear. In an unstable orientation,

both axial forces are directed away from the centre of the gear. In both arrangements, the total (or net) axial

force on each gear is zero when the gears are aligned correctly. If the gears become misaligned in the axial

direction, the unstable arrangement generates a net force that may lead to disassembly of the gear train, while

the stable arrangement generates a net corrective force. If the direction of rotation is reversed, the direction of

the axial thrusts is also reversed, so a stable configuration becomes unstable, and vice versa.

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3.2.5.6 Bevel Gears

A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears mesh, their

imaginary vertices must occupy the same point. Their shaft axes also intersect at this point, forming an arbitrary

non-straight angle between the shafts. The angle between the shafts can be anything except zero or 180 degrees.

Bevel gears with equal numbers of teeth and shaft axes at 90 degrees are called mitre gears.

3.2.5.7 Hypoid Gears

Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear

conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution. Hypoid gears are almost

always designed to operate with shafts at 90 degrees. Depending on which side the shaft is offset to, relative to

the angling of the teeth, contact between hypoid gear teeth may be even smoother and more gradual than with

spiral bevel gear teeth, but also have a sliding action along the meshing teeth as it rotates and therefore usually

require some of the most viscous types of gear oil to avoid it being extruded from the mating tooth faces, the oil

is normally designated HP (for hypoid) followed by a number denoting the viscosity. Also, the pinion can be

designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and higher are

feasible using a single set of hypoid gears. This style of gear is most common in motor vehicle drive trains, in

concert with a differential. Whereas a regular (non-hypoid) ring-and-pinion gear set is suitable for many

applications, it is not ideal for vehicle drive trains because it generates more noise and vibration than a hypoid

does. Bringing hypoid gears to market for mass-production applications was an engineering improvement of the

1920s.

3.2.5.8 Worm Gears

Worms resemble screws. A worm is meshed with a worm wheel, which looks similar to a spur gear. Worm-and-

gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical

gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1. A

disadvantage is the potential for considerable sliding action, leading to low efficiency.

A worm gear is a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and

its body is usually fairly long in the axial direction. These attributes give it screw like qualities. The distinction

between a worm and a helical gear is that at least one tooth persists for a full rotation around the helix. If this

occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. If that tooth persists for

several turns around the helix, the worm appears, superficially, to have more than one tooth, but what one in fact

sees is the same tooth reappearing at intervals along the length of the worm. The usual screw nomenclature

applies: a one-toothed worm is called single thread or single start; a worm with more than one tooth is

called multiple threaded or of multiple start. The helix angle of a worm is not usually specified. Instead, the lead

angle, which is equal to 90 degrees minus the helix angle, is given.

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In a worm-and-gear set, the worm can always drive the gear. However, if the gear attempts to drive the worm, it

may or may not succeed. Particularly if the lead angle is small, the gear's teeth may simply lock against the

worm's teeth, because the force component circumferential to the worm is not sufficient to overcome friction.

Worm-and-gear sets that do lock are called self locking, which can be used to advantage, as for instance when it

is desired to set the position of a mechanism by turning the worm and then have the mechanism hold that

position. An example is the machine head found on some types of stringed instruments.

If the gear in a worm-and-gear set is an ordinary helical gear only a single point of contact is achieved. If

medium to high power transmission is desired, the tooth shape of the gear is modified to achieve more intimate

contact by making both gears partially envelop each other. This is done by making both concave and joining

them at a saddle point; this is called a cone-drive or "Double enveloping". Worm gears can be right or left-

handed, following the long-established practice for screw threads.

3.2.5.9 Rack and Pinion Gears

A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely large radius of curvature.

Torque can be converted to linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a

straight line. Such a mechanism is used in automobiles to convert the rotation of the steering wheel into the left-

to-right motion of the tie rod(s). Racks also feature in the theory of gear geometry, where, for instance, the tooth

shape of an interchangeable set of gears may be specified for the rack (infinite radius), and the tooth shapes for

gears of particular actual radii are then derived from that. The rack and pinion gear type is employed in a rack

railway.

3.2.5.10 Materials for Gears

Numerous nonferrous alloys, cast irons, powder-metallurgy and plastics are used in the manufacture of gears.

However, steels are most commonly used because of their high strength-to-weight ratio and low cost. Plastic is

commonly used where cost or weight is a concern. A properly designed plastic gear can replace steel in many

cases because it has many desirable properties, including dirt tolerance, low speed meshing, the ability to "skip"

quite well and the ability to be made with materials that don't need additional lubrication. Manufacturers have

used plastic gears to reduce costs in consumer items including copy machines, optical storage devices, cheap

dynamos, consumer audio equipment, servo motors, and printers. Another advantage of the use of plastics,

formerly (such as in the 1980s), was the reduction of repair costs for certain expensive machines. In cases of

severe jamming (as of the paper in a printer), the plastic gear teeth would be torn free of their substrate, allowing

the drive mechanism to then spin freely (instead of damaging itself by straining against the jam). This use of

"sacrificial" gear teeth avoided destroying the much more expensive motor and related parts. This method has

been superseded, in more recent designs, by the use of clutches and torque- or current-limited motors.

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3.2.6 Shaft

A shaft is a rotating element which is used to transmit power from one place to another. The power is delivered

to the shaft by some tangential force and the resultant torque set up within the shaft permits the power to be

transferred to various machines linked up to the shaft. In order to transfer the power from one shaft to other, the

various members such as pulleys, gears, etc. are mounted on it. These members along with the forces exerted

upon them causes the shaft bending.

These are mainly classified into two types:

1. Transmission shafts are used to transmit power between the source and the machine absorbing power; e.g.

counter shafts and line shafts.

2. Machine shafts are the integral part of the machine itself; e.g. crankshaft.

3.2.6.1 Materials

The material used for ordinary shafts is mild steel. When high strength is required, the alloy steel such as nickel,

nickel-chromium or chromium-vanadium steel is used. Shafts are generally formed by hot rolling and finished

to size by cold drawing or turning and grinding.

The materials used for shaft should have:

1. High strength,

2. Good machine ability,

3. Good heat treatment properties,

4. High wear resistance properties.

3.2.6.2 Stresses

The various stresses induced in shafts during operation are as:

1. Shear stress due to transmission of torque (i.e. due to torsional load).

2. Bending stresses (tensile or compressive) due to the forces acting on the machine elements like gears,

pulleys etc. as well as due to the self-weight of the shaft.

3. Stresses due to combined torsional and bending loads.

3.2.6.3. Design Stresses

The maximum permissible (design) stresses in bending (tension or compression) may be taken as:

1. 112 N/mm2 for shafts with allowance for keyways.

2. 84 N/mm2 for shafts without allowance for keyways.

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The maximum permissible (design) shear stresses may be taken as:

1. 56 N/mm2 for shafts with allowance for keyways.

2. 42 N/mm2 for shafts without allowance for keyways.

3.2.6.4. Parameters for designing Shaft

N=1440 rpm

T = 4.645 x 103

F.O.S = 5

Gear thickness = 20

3.2.7Single Plate Clutch

A clutch is a mechanical device that engages and disengages the power transmission, especially from driving

shaft to driven shaft. Clutches are used whenever the transmission of power or motion must be controlled either

in amount or over time (e.g., electric screwdrivers limit how much torque is transmitted through use of a clutch;

clutches control whether automobiles transmit engine power to the wheels).

In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). In

these devices, one shaft is typically attached to an engine or other power unit (the driving member) while the

other shaft (the driven member) provides output power for work. While typically the motions involved are

rotary, linear clutches are also possible. In a torque-controlled drill, for instance, one shaft is driven by a motor

and the other drives a drill chuck. The clutch connects the two shafts so they may be locked together and spin at

the same speed (engaged), locked together but spinning at different speeds (slipping), or unlocked and spinning

at different speeds (disengaged).

Stationary idle, transition to motion and interruption of power flow are all made possible by the clutch. The

clutch slips to compensate for the difference in the rotational speeds of the engine the drive train when the

vehicle is being set to motion. When a change in operating conditions makes it necessary to change gears, the

clutch disengages the engine from the drive train for the duration of the procedure.

The clutch is intended for general starting of the automobile from rest, disconnecting the engine form the

transmission in order to shift gears, and for avoiding the effect of large dynamic loads on the transmission which

appear in transient conditions and on moving on the different types of roads. A standard clutch of Maruti 800

has been selected.

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3.3.8 Bearing

A cylindrical hole formed in a cast iron machine member to receive the shaft which makes a running fit is the

simplest type of solid journal bearing. Its rectangular base plate has two holes drilled in it for bolting down the

bearing in its position as shown in the figure. An oil hole is provided at the top to lubricate the bearing. There is

no means of adjustment for wear and the shaft must be introduced into the bearing endwise. It is therefore used

for shafts, which carry light loads and rotate at moderate speeds.

Specifications of Plummer Block used for test rig:

Unit Number: 6205

Inside Diameter: 20mm

Length(L):127mm

Bolt Size:10mm

Weight: 0.49kg

Material: Gray Cast Iron

H: 50 mm

H1: 22 mm

H2: 90 mm

Quantity: 5

3.3.9 Spring

Springs are elastic bodies (generally metal) that can be twisted, pulled, or stretched by some force. They can

return to their original shape when the force is released. In other words it is also termed as a resilient member.

A flat spring is a long thin strip of elastic material wound like a spiral as shown in figure. When the outer or

inner end of this type of spring is wound up in such a way that there is a tendency in increase of number of

spirals of the spring, the strain energy is stored into its spirals. This energy is utilized in any useful way the

spirals. This energy is utilized when spiral opens. The inner end is clamped on shaft and outer end is kept fixed.

Since the radius of curvature of every spiral decreases when the spring is wound up, therefore the material of the

spring is in a state of pure bending.

3.3.10 Alternator

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of

alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a

stationary armature, but occasionally, a rotating armature is used with a stationary magnetic field; or a linear

alternator is used. In principle, any AC electrical generator can be called an alternator, but usually the term

refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that

uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by

steam turbines are called turbo-alternators.

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A conductor moving relative to a magnetic field develops an electromotive force (EMF) in it, (Faraday's Law).

This emf reverses its polarity when it moves under magnetic poles of opposite polarity. Typically, a rotating

magnet, called the rotor turns within a stationary set of conductors wound in coils on an iron core, called the

stator. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical

input causes the rotor to turn.

The rotating magnetic field induces an AC voltage in the stator windings. Since the currents in the stator

windings vary in step with the position of the rotor, an alternator is a synchronous generator.

The rotor's magnetic field may be produced by permanent magnets, or by a field coil electromagnet. Automotive

alternators use a rotor winding which allows control of the alternator's generated voltage by varying the current

in the rotor field winding. Permanent magnet machines avoid the loss due to magnetizing current in the rotor,

but are restricted in size, due to the cost of the magnet material. Since the permanent magnet field is constant,

the terminal voltage varies directly with the speed of the generator. Brushless AC generators are usually larger

machines than those used in automotive applications.

An automatic voltage control device controls the field current to keep output voltage constant. If the output

voltage from the stationary armature coils drops due to an increase in demand, more current is fed into the

rotating field coils through the voltage regulator (VR). This increases the magnetic field around the field coils

which induces a greater voltage in the armature coils. Thus, the output voltage is brought back up to its original

value.

Alternators used in central power stations also control the field current to regulate reactive power and to help

stabilize the power system against the effects of momentary faults. Often there are three sets of stator windings,

physically offset so that the rotating magnetic field produces a three phase current, displaced by one-third of a

period with respect to each other.

There are two main ways to produce the magnetic field used in the alternators, by using permanent magnets

which create their own persistent magnetic field or by using field coils. The alternators that use permanent

magnets are specifically called magnetos. In other alternators, wound field coils form an electromagnet to

produce the rotating magnetic field.

All devices that use permanent magnets and produce alternating current are called PMA or permanent magnet

alternator. A "permanent magnet generator" (PMG) may produce either alternating current, or direct current if it

has a commutator. If the permanent magnet device makes only AC current, it is correctly called a PMA.

Synchronous Speeds:-

One cycle of alternating current is produced each time a pair of field poles passes over a point on the stationary

winding. The relation between speed and frequency is N=120f/P , where f is the frequency in Hz (cycles per

second). P is the number of poles (2,4,6...). N is the rotational speed in revolutions per minute (RPM). Very old

descriptions of alternating current systems sometimes give the frequency in terms of alternations per minute,

counting each half-cycle as one alternation; so 12,000 alternations per minute correspond to 100 Hz.

The output frequency of an alternator depends on the number of poles and the rotational speed. The speed

corresponding to a particular frequency is called the synchronous speed for that frequency.

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IV. CONCLUSION

As studied earlier, it has been made clear that, due to extinction of the natural reserves & fossil fuels, the

alternatives used for conserving these resources rather than finding new fuels (probably a beneficial mean) is

KERS. Energy conservation is the most important issue that needs to be solved as soon as possible. Using

energy from fossil fuels is not always convenient, as it is limited in quantity and dependence on it may cause its

extinction with no other sources left for energy. Hence, utilising the energy in an effective way is a new

challenge. One such method for utilising the energy or reusing the energy is KERS. There are various types of

KERS till the present time, viz. Mechanical KERS, Electrical KERS, Hydro-static KERS. But these types

proved to be non-beneficial for energy efficiency, due to lack of energy in process of conversion. Also, the

components used in the system are quite costly, which may be only affordable for installation in the racing cars

(non-normal vehicles).

There is an alternative for these KERS‘s too, called Mechanical Regenerative Type KERS. This system uses

much cost effective components proving to be economical & beneficial. It all deals with the energy storage by

means of a Flat Spiral Spring. By using this system, it is an idea that energy will be stored in normal vehicles

too.

In this project, we successfully demonstrated the recovery of energy with the help of a spiral spring. The

energy stored in the spring was given back to the input shaft through a series of gears, from spring to the shaft.

With the detailed study of the topic and some more financial expenditure on the components and concepts to be

applied practically, it may be possible to drive the engine with the help of energy stored in the spring. This

energy saved in the spring can be used in many ways, like as to generate electrical power by using an alternator

or any other way.

In this project, the spring used has a very low torsion capacity with less number of wounds. For this reason,

the rig is run for a very short time; say 3 to 5 sec. or the spring will break under tension. Being entry level

concept, normal spiral spring is used. With the success of the project, it will be of great attention to use this

concept on big scale and the required modifications will be taken care of. For the spring to be safe, de-coupler

may be used for big scale project.

Following are points regarding the future scope, modification and development of the machine:

Microprocessor can be used to calculate the braking effort required to stop in specific distance to effectively

control the speed.

The excess amount of energy stored in spring can be converted into electricity by alternator during long run.

Spring and alternator can be used as a combined unit to reduce the size of unit.

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REFERENCES

1. Mayuresh Thombre, Prajyot Borkar, et. al., ―Kinetic Energy Recovery System using Spring‖, World

Academy of Science, Engineering and Technology, International Journal of Mechanical, Aerospace,

Industrial, Mechatronics and Manufacturing Engineering Vol:8, No:4, 2014.

2. Cibulka, J., ―Kinetic Energy by means of Flywheel Energy Storage‖, Advanced Engineering, 3(2009)1,

ISSN 1846-5900.

3. Pottabattini naveen, Mamidi ranga rao, et. al., ―Kinetic Energy Recovery System‖, International Journal of

Scientific & Engineering Research, Volume 5, Issue 1, January-2014, ISSN 2229-5518.

4. Radhika Kapoor, C. Mallika Parveen, ―Comparative Studies on Various KERS‖, Proceedings of the World

Congress on Engineering 2013 Vol. III, WCE 2013, July 3-5, 2013, London, U.K.

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System (KERS) in Bicycle‖, IJMET, Dept. of Mechanical Engineering, Sinhgad College of Engineering,

Pune, Maharashtra, India.

6. William M. Yates, Benjamin T. Ingram, ―Front Wheel Energy Recovery System‖, United States Patent,

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7. M. M. Tehrani, M. R. Hairi – Yazdi, et. al., ―Design of an Anti-Lock Regenerative Braking System for a

Series Hybrid Electric Vehicle‖, IJAE, Tehran, Iran.

8. Quinn Lai, ―Compact Car Regenerative Drive Systems: Electrical or Hydraulic‖, School of Mechanical

Engineering, Georgia Institute of Technology.

9. Siddharth Dave, Aneesh Bhardwaj, ―Kinetic Energy Regeneration System for Fuel Efficiency and

Performance Enhancement‖, IJSER, April 2013.

10. Susan Rebecca Cikanek, Kathleen Ellen Bailey, ―Regenerative Braking System for a Hybrid Electric

Vehicle‖, United States Patent, Oct. 2013.

11. http://en.wikipedia.org

12. http://www.formula-hybrid.org/

13. http://auto.howstuffworks.com/cvt2.htm