final year report: kinetic energy recovery system

SHELL ECO MARATHON: KINETIC ENERGY RECOVERY SYSTEM

(KERS)

SAM WING HONG

A project report submitted in partial fulfilment of the

requirements for the award of Bachelor of Engineering

(Hons.) Mechanical Engineering

Faculty of Engineering and Science

Universiti Tunku Abdul Rahman

April 2012

ii

DECLARATION

I hereby declare that this project report is based on my original work except for

citations and quotations which have been duly acknowledged. I also declare that it

has not been previously and concurrently submitted for any other degree or award at

UTAR or other institutions.

Signature : _________________________

Name : _________________________

ID No. : _________________________

Date : _________________________

iii

APPROVAL FOR SUBMISSION

I certify that this project report entitled “SHELL ECO MARATHON: KINETIC

ENERGY RECOEVERY SYSTEM (KERS)” was prepared by SAM WING

HONG has met the required standard for submission in partial fulfilment of the

requirements for the award of Bachelor of Engineering (Hons.) Mechanical

Engineering at Universiti Tunku Abdul Rahman.

Approved by,

Signature : _________________________

Supervisor : Mr. Wong Hong Mun

Date : _________________________

iv

The copyright of this report belongs to the author under the terms of the

Copyright Act 1987 as qualified by Intellectual Property Policy of University Tunku

Abdul Rahman. Due acknowledgement shall always be made of the use of any

material contained in, or derived from, this report.

© 2012, Sam Wing Hong. All right reserved.

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ACKNOWLEDGEMENT

I would like to thank everyone who had contributed to the successful completion of

this project. I would like to express my upmost gratitude to my research supervisor,

Mr Wong Hong Mun for his invaluable advice, superior guidance and his enormous

patience throughout the development of the research.

In addition, I would also like to express my gratitude to my loving parent and

friends who had helped and given me encouragement to complete my project.

vi

SHELL ECO MARATHON: KINETIC ENERGY RECOVERY SYSTEM

(KERS)

ABSTRACT

A KERS was used in Shell Eco Marathon competition as a strategy to minimize fuel

consumption. The performance of the system was not up to expectations. Therefor

experiments based on Taguchi’s Method for were conducted to analyse its problems.

A new design of KERS which had a different method of engagement and also

variable moment of inertia was also tested for improvement. However, from the

experiments conducted, the efficiency of the system was considerably low due to

losses of energy from the system.

vii

TABLE OF CONTENTS

DECLARATION ii

APPROVAL FOR SUBMISSION iii

ACKNOWLEDGEMENT v

ABSTRACT vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS / ABBREVIATIONS xiii

CHAPTER

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Aims and Objectives 2

1.4 Schedule 3

LITERATURE REVIEW 4

2.1 Kinetic Energy Recovery System (KERS) 4

2.1.1 Components of Kinetic Energy Recovery System

(KERS) 4

viii

2.1.2 Types of Kinetic Energy Recovery Systems

(KERS) 5

2.1.3 Engagement of KERS 9

2.2 Prototype 1 by UTAR M.E 11

2.2.1 Design of Kinetic Energy Recovery System for

Prototype 1 11

2.2.2 Technical Specification of KERS Model 14

2.3 Current Problem Faced 14

2.4 Findings 15

2.5 Possible Strategies 15

2.5.1 Reduce the Huge Relative Velocity Difference

between Roller and Wheel 15

2.5.2 Improve on Surface of Contact 16

2.5.3 Reducing the Moment of Inertia for the Flywheel

for Energy Storage 16

2.6 Alternative Solution 16

2.6.1 Friction 17

2.6.2 Jaw (tooth) 17

3 METHODOLOGY 19

3.1 Introduction 19

3.2 Project Flow Chart 20

3.2.1 Problem Definition 20

3.2.2 Literature Review 21

3.2.3 Components Design and Simulation 21

3.2.4 Experiment Verification 22

3.2.5 Data Analysis 22

3.2.6 Report 22

4 RESULTS AND DISCUSSIONS 23

4.1 Introduction 23

4.2 Introduction to Concept of Applying KERS in Shell Eco

Marathon 23

ix

4.3 Testing on existing KERS system 24

4.4 Development of New KERS Design 28

4.4.1 Concept 28

4.4.2 Evaluating the New KERS Design 30

4.4.3 Evaluating on the Practicality of New KERS

Design 40

4.5 Problems Encountered 42

5 CONCLUSION 46

5.1 Conclusion 46

5.2 Recommendations on KERS Generation 3 47

5.3 Future Improvements on KERS Generation 3 47

5 REFERENCES 49

Appendx A 51

Appendix B 69

x

LIST OF TABLES

TABLE TITLE PAGE

1-1 Project Gantt Chart 3

2-1 Technical Specification of KERS 14

4-1 Summary of Energy Transfer Efficiency for Charging Experiments 26

4-2 Summary of Energy Transfer Efficiency for Disharging Experiments 27

4-3 Moment of Inertias for Different Positions 33

4-4 Summary of Expected Mechanical Losses 33

4-5 Comparison of Angular Acceleration for Different Positions 35

4-6 Comparison of Percentage of Energy Transferred During Charging 35

4-7 Comparison of Percentage of Energy Transferred During Discharging 39

xi

LIST OF FIGURES

FIGURE TITLE PAGE

2-1 Charging of Electrical KERS 6

2-2 Discharging of Electrical KERS 7

2-3 Mechanical KERS System (Ramirez, 2011) 8

2-4 CFT Transmission by Flybrid® 10

2-5 KERS Isometric View 11

2-6 KERS Front View 12

2-7 KERS Side View 12

2-8 KERS Top View 13

2-9 Debris resulting from charging the KERS 14

3-1 Project Flow Chart 20

4-1 Existing KERS Testing Rig 24

4-2 New KERS Design (Isometric View) 30

4-3 New KERS Design (Real-time Isometric) 30

4-4 KERS at Position 1 31




4-8 Comparison of Energy Transfer Efficiency (Charging) 35

xii

4-9 Force Analysis on KERS 36

4-10 Comparison of Energy Transfer Efficiency (Discharging) 39

4-11 Graph of Deceleration of System 41

4-12 Energy Loss due to Slippage 43

xiii

LIST OF SYMBOLS / ABBREVIATIONS

cp specific heat capacity, J/(kgK)

v tangential velocity, m/s

I moment of inertia, kgm2

r radius, m

α angular acceleration, rad/s2

m mass, kg

ω angular velocity, rad/s

E energy, J

Τ torque, Nm

Ρ density, kg/m3

A cross sectional area, m2

F force, N

fdrag frictional drag, N

1

CHAPTER 1

INTRODUCTION

1.1 Background

With the growing demand for transportation from time to time, the number of

vehicles owned in this world has increased exponentially, which in turn raises the

demand for fuel. However, the supply for crude oil available on earth to provide fuel

is diminishing quickly. Therefore change is needed to decrease the global reliance on

oil and also to tackle the environmental problems caused by the usage of fuel, mainly

the green house effects.

Investigations on the efficiency of combustion engines show that about 75%

of the energy from fuel combustion generates heat rather than kinetic energy (John

Walsh, 2011). Therefore approaches have to be carried out to enhance the efficiency

of vehicle engines to reduce wasted energy. To deal with energy, a system called

Kinetic Energy Recovery System or KERS can be utilized to help in reduction of the

consumption of fuel in any vehicle.

Team UTAR M.E from the Faculty of Engineering and Science built a

prototype car to compete in the 2nd Shell Eco Marathon Asia competition. The aim of

the competition is to show how far a vehicle can go with just 1 litre of fuel.

Therefore to meet this target, a Kinetic Energy Recovery System was installed

aiming at saving the usage of fuel. However, there are several flaws that occurred

when the system was brought into usage.

2

1.2 Problem Statement

The KERS installed on Prototype 1 was found to be performing below expectations.

1.3 Aims and Objectives

To develop an efficient charging and discharging mechanism for a mechanical

Kinetic Energy Recovery System.

3

1.4 Schedule

The following shows the gantt chart for the entire project.

Table 1-1: Project Gantt Chart

UTAR Semester I

1 2 3 4 5 6 7 8 9 10 11 12 13 14Shell Eco Marathon CompetitionProblem StatementLiterature ReviewDesign and Simulations

UTAR Semester III

15

16 17 18 19 20 21 22 23 24 25 26 27 28

Experiment VerificationsData AnalysisCompletion of FYP ReportSubmission of FYP Report

4

CHAPTER 2

LITERATURE REVIEW

2.1 Kinetic Energy Recovery System (KERS)

Kinetic Energy Recovery System (KERS) is a regenerative braking that stores the

kinetic energy of a moving vehicle under deceleration. The main concept behind

KERS is to recover any energy loss during the deceleration process of a moving

vehicle for its acceleration which is supported by the basic principle of physics that

states “energy cannot be created or destroyed, but it can be endlessly converted”.

This reduces the amount of energy needed for the engine to deliver for the vehicle to

pick up which leads to better performance as well as fuel efficiency.

2.1.1 Components of Kinetic Energy Recovery System (KERS)

The whole system of Kinetic Energy Recovery System consists of 4 sub-systems

namely the braking system, energy storage system and the energy discharging

system.

5

Braking system

This is the part where the energy to be stored is collected. It also acts as

brakes for vehicles.

Energy storage system

This is the part where the energy collected form the braking system is stored.

Energy discharging system

This is the part where the energy stored is drawn to drive the vehicle.

Coupling and decoupling

This is the part where the KERS is engaged for charging or discharging

2.1.2 Types of Kinetic Energy Recovery Systems (KERS)

Generally, there are two types of KERS notably electrical (by battery) and

mechanical (by flywheel).

6

21.2.1 Electrical Type

For the electrical KERS, a motor generator in integrated in a car’s transmission so

that during braking, the system converts mechanical energy into electrical energy

which is then stored in a rechargeable battery. When needed, energy stored in the

battery will be released to assist in accelerating.

Charging phase

Figure 2-1: Charging of Electrical KERS

(Formula One Management Limited, 2009)

The kinetic energy from the rear brakes is captured by an electric

alternator/motor, controlled by a central processing unit (CPU), which then charges

the batteries.

Discharging Phase

7

Figure 2-2: Discharging of Electrical KERS

(Formula One Management Limited, 2009)

The electric alternator/motor gives the stored energy back to the engine in a

continuous stream when the driver presses a boost button on the steering wheel.

21.2.2 Mechanical Type

In a mechanical KERS, the concept of flywheel energy storage is used. The inertia

mass is accelerated to a very high rotational speed to maintain the energy in the

system as rotational energy. The energy is then converted back by slowing down the

flywheel. The performance of such technical approach depends heavily on the

moment of inertia effect and operation rotational speed.

8

Figure 2-3: Mechanical KERS System (Ramirez, 2011)

Charging Phase

The energy captured from the driveshaft is transferred to the flywheel through a

Continuous Variable Transmission (CVT) system. The CVT system allows a variety

of gear ratios in order to charge the flywheel up to 60,000pm smoothly and

efficiently.

Discharging Phase

Energy stored in the flywheel is drawn out to the drive shaft through the CVT which

is also connected to an output gear train to drive the vehicle. The CVT controls the

rate of energy release from the flywheel through multple gear ratios.

9

21.2.3 Electrical KERS versus Mechanical KERS

Between the two types of KERS, the mechanical approach is believed to be more

efficient when compared to the electrical approach. According to Jon Hilton (2007),

managing partner of Flybrid Systems, the overall in-out efficiency of a mechanical

drivetrain feeding energy into a flywheel and back out to the vehicle again via an

ancillary transmission system is approximately 65-70 per cent compared with 35-45

per cent for a hybrid battery-electric system. Fundamentally, this is because a purely

mechanical system doesn't have to convert the kinetic energy into electrical and

chemical energy as with a battery system where the energy transferred within the

system does not change state.

Furthermore, Cross & Hilton (2008) commented that mechanical KERS has

longer lifespan as compared to an electrical KERS which runs on batteries. In terms

of safety, a mechanical KERS is safer as flywheels are established technology and

guaranteed safe with the implementation of technologies provided by Flybrid. Unlike

mechanical KERS, Electrical KERS which runs on Li-ion batteries occasionally

experience thermal run-away, resulting in melting or bursting of batteries.

2.1.3 Engagement of KERS

With reference to Flybrid® CFT KERS, the CFT transmission uses a number of

discrete gears and special Flybrid-developed high-speed clutches that perform a

controlled slip to transmit the drive, as shown in Figure 2-4.

10

Figure 2-4: CFT Transmission by Flybrid®

When connected to an engine speed shaft within the vehicle transmission the three

gears in the CFT KERS are multiplied by the number of gears in the main vehicle

transmission to provide a large number of available overall ratios between flywheel

and wheels. The efficiency of a slipping clutch depends upon the speed across it and

with so many gears to choose from a high efficiency option is always available.

When the system is in use, a computer controller selects the most appropriate

gear by partially engaging the high-speed clutch associated with that gear. The

control system uses hydraulic pressure to close the normally open clutches and

transmit the drive, seamlessly changing from one gear to another with no torque

interruption as the speed across the engaged clutch reduces to near zero.

However, there are currently limited references regarding the performance

and operation of the clutch system used.

11

2.2 Prototype 1 by UTAR M.E

For Prototype 1 by team UTAR M.E that participated in Shell Eco Marathon Asia

2011, a KERS system was implemented onto the vehicle aiming at saving fuel to

improve the performance of the vehicle. The KERS was design to have two

flywheels to store energy when the vehicle decelerates, and to assist in the

acceleration motion of the vehicle. In the design, the two flywheels were charged and

discharged by means of two separate rollers contacting directly on the rear wheel.

2.2.1 Design of Kinetic Energy Recovery System for Prototype 1

The design of the KERS system applied onto Prototype 1 is shown as below:

Figure 2-5: KERS Isometric View

12

Figure 2-6: KERS Front View

Figure 2-7: KERS Side View

13

Figure 2-8: KERS Top View

As shown in the figures above, the method used for charging and discharging

of the flywheel are through two separate rollers that connect to the wheels. When the

driver initiates charging, the charging roller will be brought into contact with the

wheel. This will result in creating a braking effect onto to vehicle which slows it

down. In the meantime, the roller brought into contact with the wheel will charge the

flywheel at a train value of 1.60. When the driver intends to draw energy out from

the flywheel to assist in pick-up, he initiates the discharging which the other roller

(discharging roller) will be brought into contact with the wheel. Here, the roller will

drag the wheels to cause the vehicle to move forward therefore helping in pushing

the vehicle forward.

The design of the KERS system was aimed at saving 22kJ of energy when the

vehicle brakes and to supply the stored energy to assist in acceleration. This can be

achieved by accelerating the two flywheels up to 5000rpm.

14

The rollers used for charging and discharging the KERS were knurled during

machining to provide a rough surface. This was aimed at providing sufficient grip for

the rollers when brought into contact with the wheel.

2.2.2 Technical Specification of KERS Model

Table 2-2: Technical Specification of KERS

Diameter of flywheels 320 mm

Total inertia masses of flywheels 0.167409894 kg m2

Maximum energy stored 22000 J

Maximum speed of flywheels 4500 rpm

Diameter of rollers 25 mm

Gear ratio for charging KERS 1.34

Gear ratio for discharging KERS 1.34

2.3 Current Problem Faced

Figure 2-9: Debris resulting from charging the KERS

15

When Prototype 1 was on track, the KERS was brought into usage. A serious

problem occurred where the tyre experienced serious wear when the KERS was

charging. This problem could lead to tyre puncture if the KERS was engaged for a

period of time. Figure 2-9 shows the resultant debris produced from the operation of

KERS left on the engine. The debris created might be suck into the carburettor of the

engine and might lead to damaging the engine, affecting its performance. Therefore

approaches have to be made to improve and overcome the current situation.

2.4 Findings

Due to the regulation of Shell Eco Marathon Asia 2011 stated that the vehicle has to

start the race with zero energy, both flywheels were stationary. Therefore when the

KERS was engage while the vehicle was travelling at high speed, a huge relative

velocity difference occurred between the tyre and the charging roller. The inertia of

the flywheels resisted the rollers from rolling when the rollers are in contact with the

tyre. This in turn resulted in a situation where the metal rollers shredded the tyre

instead of rolling.

2.5 Possible Strategies

2.5.1 Reduce the Huge Relative Velocity Difference between Roller and

Wheel

In my opinion, in order to improve on current design focusing on reducing the

damage to the tyre caused during KERS charging and discharging, the relative

velocity difference between the charging roller and the tyre has to be reduced. The

reduction can be done by increasing the diameter of the roller to a desirable size to

reduce the force required to create torque for accelerating the roller thus reducing the

friction force experienced by the tyre. This results in introducing less destruction to

the tyre by the steel roller.

16

2.5.2 Improve on Surface of Contact

Apart from enlarging the size of the rollers, I would suggest to add-on rubber pads on

to the rollers as rubber pads can be used to increase grip and reduce wear of the tyre.

When knurled metal surfaces were used to provide gripping, the hardness of the

metal surfaces caused damage to the relatively soft material of the tyre. Therefore

through providing a softer material as a contact surface with the tyre, performance

might improve while damage could be reduced.

2.5.3 Reducing the Moment of Inertia for the Flywheel for Energy Storage

As the existing KERS design equipped with two flywheels made of mild steel as

energy storage was found to possess too much moment of inertia for acceleration,

alternative materials of lower density could be considered as replacement for easier

acceleration. This would reduce the energy wasted to accelerate the flywheels during

the charging phase.

2.6 Alternative Solution

Power transfer through two rotating devices can be performed by friction or jaw

(tooth) (How power transfers through a clutch or brake and the method by which the

energy is transferred from one rotating device to a second non-rotating device). This

can be accomplished in a form of mechanical clutch system.

17

2.6.1 Friction

When friction is concerned, friction clutches and brakes utilize friction plates to

transmit power from one rotating device to another. The friction on the contact

surfaces of both members allows torque transmission.

For friction clutches, the sequence and type of friction surface and the load

presented onto the friction surface determine the size of friction surface required to

transmit torque. Friction discs may be made up of various materials depending on the

application or purposes.

Friction clutch will slip when the torque capacity of the disc turning friction

surfaces in exceeded. Therefore during the engagement and disengagement period,

the clutch will slip as the friction discs are being squeezed together gradually. The

slip allows smooth transfer of torque from one device to another, which permits

gradual starts.

26.1.1 Advantages of Friction Engagement

a. Allows soft engagement of the two devices to be coupled;

b. Engagement speed is not limited

2.6.2 Jaw (tooth)

Jaw clutches make use of a serrated tooth design to transfer or absorb energy from a

primary rotating device to a secondary rotating device. The friction between the

surfaces of teeth of the rotating and non-rotating device allows the clutch to transmit

torque.

18

There are various tooth forms as well as different physical numbers of teeth

available depending on the field of application. The designs of the tooth forms will

determine the torque capacity for a particular jaw clutch. Different designs of tooth

forms allow the device to slip or disengage at a predetermined point as determined

by the application requirements.

Like friction clutches, once the torque capacity of the jaw teeth is exceeded,

the jaws will disengage dragging the teeth of one rotating device along the surface of

the teeth of another rotating device. However, this is not the desired use of a jaw

teeth clutch.

26.2.1 Advantages of Jaw Engagement

a. High torque capacity with relatively small size;

b. Indexing or registration of input to output capable;

c. Positive engagement of teeth allowing virtually zero backlash

26.2.2 Disadvantages of Jaw Engagement

a. Too much chock when applied suddenly

19

CHAPTER 3

METHODOLOGY

3.1 Introduction

This chapter studies the approach to be used to study on the improvement of KERS

charging and discharging.

20

3.2 Project Flow Chart

Figure 3-10: Project Flow Chart

3.2.1 Problem Definition

The whole project started at identifying the problem being faced in the application of

Kinetic Energy Recovery System in Prototype 1. In this case, the problem was

identified as the method of charging and discharging the KERS. As mentioned in the

Start

Problem Definition

Literature Review

Component Design and Simulation

Experiment Verification

Data Analysis

Report

End

21

previous part, the roller used for charging the flywheels caused undesirable damage

to the wheel of the vehicle which led to inefficient charging of the KERS. The tyre

shredded off at a high rate where it might cause safety problems. Therefore

alternative methods were developed to encounter it.

3.2.2 Literature Review

Having the problem known, literature reviews have been carried out to review on

available information related to overcoming the problem. Sources either electronic or

printed sources has been reviewed for reference in proposing a workable solution for

the current situation.

3.2.3 Components Design and Simulation

When the literature review was completed, every useful findings were highlighted.

With reference to available resources, workable solutions were proposed to

overcome the problem. In this case, three main solutions were proposed:

1. Enlarging the diameter of the roller

2. Applying rubber coating on the roller

3. Redesigning the entire KERS

Designs for each solution were established in CAD drawings. Simulations

will also be applied onto the design to provide first insight in testing the design.

22

3.2.4 Experiment Verification

After proposing the solutions, experiments were carried out for verifications. In this

part, experimental jigs were built to perform try-out. Any relevant data were

recorded for justification and reference. The goal of carrying out experiments was to

test out the proposed solutions and assess the functionality of each method. Here,

every expected problem that would occur was taken into account for reliable data

analysis.

In the experiments carried out, the percentage of energy transfer for each

condition was measured. The most important values obtained for analysis were time

and revolution speed. The findings were compared to obtain for the best solution.

3.2.5 Data Analysis

Data collected from the experiments were evaluated and compared with the

theoretical results. Other than that, every data obtained from the experiments were

compared to obtain the best solution for the problem.

3.2.6 Report

The whole project was documented as a report for submission and also for future

references.

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CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 Introduction

In this chapter, the testing on the existing KERS was conducted using Taguchi

Method to determine the efficiency in terms of energy transfer. Then a new design of

KERS was also tested for its efficiency in terms of energy transfer and was compared

to the previous version for improvements.

4.2 Introduction to Concept of Applying KERS in Shell Eco Marathon

The concept of the KERS system in the Prototype 1 was aimed at recycling the

energy of the vehicle during the race. It was planned to be brought into engagement

for charging when Prototype 1 rolled downwards a hill. Having the KERS system

charged, the driver would engage it for discharging going uphill in order to assist in

fuel consumption.

24

4.3 Testing on existing KERS system

Figure 4-11: Existing KERS Testing Rig

A test rig was developed in the performance evaluation of KERS as shown in Figure

4-1. It was conducted to investigate the influence of 3 variables in affecting its

performance. In real life applications, when the driver wishes to decelerate his

vehicle, he engages the KERS for charging. During charging, the charging roller will

be brought into contact with the wheel to decelerate it at the same time converts the

vehicle’s kinetic energy into rotational energy in at the rotating flywheels. When the

driver requires additional energy for acceleration, he engages the KERS for

discharging where the discharging roller will be brought into contact with the wheel

and transfers its rotational energy into the vehicle’s kinetic energy to provide boost.

The study was conducted using Taguchi’s method. In this method,

combinations of 3 control factors (moment of inertia of flywheel, gear ratio for

charging and discharging and the condition for surface of contact) with 2 levels of

factor of study were applied to investigate the best combination that provides the best

efficiency.

25

When the experiment was initially carried out, the original KERS system

used on the Prototype 1 was installed on to the testing rig. However, the original

KERS system which its energy storage system consisted of mild steel was found to

be not suitable for the investigation in the experiments. When the experiment

procedures were applied on charging the KERS, it was noticed that the KERS did not

charge up. Instead, the energy was lost in accelerating the high inertia of the mild

steel flywheels. Therefore, flywheels made of lighter material with lower moment of

inertias were used in the Design of Experiment. Eventually, flywheels made of

plywood were used to replace the mild steel flywheels.

Referring to Appendix A, the following was observed:

1. For charging purposes, referring to Appendix A Table A-13, the optimum

combination of the control factor is to have one flywheel, charging at a gear

ratio of 0.75 without grip attached to the charging roller. While for

discharging purposes, according to Table A-16, the better combination is to

have 2 flywheels, discharging at a gear ratio of 0.75 without grip attached to

the discharging roller.

2. Referring to Table A-15, the greatest factor that influences the charging

efficiency of the KERS system on the testing rig was the contact surface of

the roller with the wheel. The result shows that without grip attached to the

roller, the system had a greater efficiency in terms of charging. This could be

due to the greater friction that existed between the knurled roller and the

wheel when compared to the contact between the grip and the wheel.

Although the performance without the grip is better, the contact between the

knurled roller and the wheel was not ideal as the roller shredded the wheel

when contact was made. This situation is not desirable for long term usage as

it would eventually damage the wheel.

3. For the case of discharging, gear ratio was the most significant factor the

affected the efficiency of discharging the KERS according to Table A-18.

26

With a gear ratio of 0.75, energy stored in the KERS was able to be released

more effectively compared to the usage of gear ratio of 1.33.

For further understandings on the 8 experiments conducted with different

combinations of variables, analysis was performed to investigate the efficiency of

energy transfer for each experiment. Refer to Appendix A, Tables A-19 to A-26.

Initially, for the charging case, the energy contained in the rotating mass was

156J. An investigation of the loss of energy is conducted by calculating theoretically

the total energy contained in the entire system when the wooden flywheels were

charged to maximum rotational speed. At the maximum rotational speed, the

tangential velocity of the charging roller and the wheel are equal at a synchronised

speed.

The sample calculations for energy transfer efficiency are shown in Appendix

A. The summary of the analysis is shown below:

Table 4-3: Summary of Energy Transfer Efficiency for Charging Experiments

Charging

ExperimentControl Factors Percentage of Energy

Transferred, %Flywheel Gear Ratio Contact Surface

1 1 0.75 With grip 18.50

2 1 1.33 Without grip 33.86


4 2 1.33 With grip 11.13

27

Table 4-4: Summary of Energy Transfer Efficiency for Disharging Experiments

Discharging

ExperimentControl Factors Percentage of Energy

Transferred, %Flywheel Gear Ratio Contact Surface

1 1 0.75 With grip 5.54



4 2 1.33 With grip 4.46

Referring to Table 4-1 and Table 4-2, from the 8 experiments carried out to test on

energy transfer efficiency, it was observed that the best configuration for the

charging was to have the configuration as in Experiment 2 which has an efficiency of

33.86% of energy transfer. On the other hand, the best configuration for discharging

was to have the configuration as in Experiment 2, which had an efficiency of 6.4%.

Thus, the combination of these two would generate an overall efficiency of 2.17% of

energy recovery. This was undesirable to be used on Prototype 1 as the percentage of

energy recoverable did not compensate the weight penalty induced by installing the

KERS system on the vehicle to participate in a fuel save competition.

Referring Appendix A, from Tables A-19 to A-26, there are energy losses

which lead to inefficiency of the KERS. For the charging cases, great amount of

energy was used to accelerate the flywheel of the KERS to spin from idle state to

maximum achievable rotational speed. Other than that, energy was also lost when

slip occurred at the moment where the roller was brought into contact with the wheel

during charging due to great difference in relative velocity. Furthermore, energy was

also lost due to mechanical efficiency of the overall testing system.

From observation, according to Figure A-2, the better combination for

charging was to have a single flywheel, charging with a gear ratio of 0.75 and the

contacting roller without grip. According to Figure A-3, the better setting for

discharging was to have two flywheels, discharging at a gear ratio of 0.75 and having

a contacting roller without grip.

28

The outcome of the experiments was not satisfying. Therefore another contact

method for the operation of KERS was proposed and tested to seek for

improvements.

4.4 Development of New KERS Design

4.4.1 Concept

As mentioned in the previous section where the existing KERS design had failed to

deliver a desirable efficiency of energy transferred, another approach in designing

the KERS was initiated. This led to an idea of designing a different KERS that

performs the same duty but at better performance and efficiency in terms of energy

transfer. First of all, the new design had a different method of contact than that of the

previous version’s where its concept was similar to a clutch (friction engagement).

Also, with reference to the commercially available KERS system (Flywheel KERS

by Volvo) which uses a CVT to charge and discharge the energy storage flywheels, a

similar concept was adopted with the combination of the following combinations:

τ = Iα (4.1)

where τ : torque, Nm

I : moment of inertia, kgm2

Α : angular acceleration, rad/s2

E = 0.5 I ω2 (4.2)

where E : energy, J

I : moment of inertia, kgm2

ω : angular velocity, rad/s

I = 0.5 m r2 (4.3)

where I : moment of inertia, kgm2

m : mass, kg

r : radius, m

29

Equation (4.1) shows that the torque required to accelerate a body is directly

proportional to the moment of inertia of that particular body and also its angular

acceleration. Therefore it is desirable to have the KERS system to accelerate at

shortest time to avoid slip when it is engaged. Meanwhile, Equation (4.2) shows that

energy stored in a rotating mass is proportional to the moment of inertia of the body

itself and also the rotational velocity it spins at. Subsequently, Equation (4.3) shows

that the moment of inertia of a round disc along the rotation axis is dependent on its

mass and also its radius.

In this new design, the main idea was to have a rotating mass for the KERS

which has a variable moment of inertia. The variable moment of inertia functions in a

way that it can be accelerated under lower torque to minimize slip at the contact

surface and also to increase its ability to absorb more energy with a greater moment

of inertia at the same time decelerating the whole vehicle. This concept was based on

the theory of conservation of energy, where at the same energy, a mass with greater

diameter rotates slower than a mass with a smaller diameter which is illustrated in

Equation (4.3).

For its application, when the driver would like to decelerate his vehicle, he

would engage the KERS at its lowest moment of inertia to start for deceleration. If he

would like to further increase his deceleration, he would increase the moment of

inertia of the KERS to further decelerate his vehicle. On the discharging end, when

the driver would like to release energy stored in the KERS to assist in acceleration,

he would engage the KERS for discharging at its highest moment of inertia and

gradually decrease its moment of inertia to further draw energy from the KERS.

30

Figure 4-12: New KERS Design (Isometric View)

Figure 4-13: New KERS Design (Real-time Isometric)

4.4.2 Evaluating the New KERS Design

In order to achieve a good understanding on how well the new design of KERS,

experiment were run to test on its performance. The experiments were conducted by

31

assigning 4 different positions of the KERS storage as demonstrated in Figure 4-4 to

Figure 4-7. Then the moment of inertia was determined experimentally for each

position as shown in Appendix B and listed in summary in Table 4-3. Then the

influence of moment of inertia towards its energy transfer efficiency was tested.

Figure 4-14: KERS at Position 1


32



33

Table 4-5: Moment of Inertias for Different Positions

Moment of inertia, kgm2

Position 1 0.008483

Position 2 0.006179

Position 3 0.003770

Position 4 0.001476

Before proceeding with the energy transfer experiments, expected losses

especially friction forces were first determined experimentally. In this design, the

determined friction forces were mechanical loss due to the two support bearings, the

positioning bearing and the bushing of the flywheel mass. The details of data

collection for friction losses are shown in Appendix B (Table B-6 to Table B-9) and

are summarized as follows:

Table 4-6: Summary of Expected Mechanical Losses

Losses due to:

Support

bearings-0.016295 Nm

Position

bearing-0.026824 Nm

34

Flywheel mass

bushing-0.038022 Nm

Total

mechanical loss-0.081141 Nm

The losses shown in Table 4-4 are accounted into the investigation of energy transfer

efficiency of the prototype of the new KERS design. The reason behind this was to

study how efficient could the new system perform by eliminating such mechanical

losses. The mechanical losses listed in Table 4-4 can be minimized through improved

design and material selection.

44.2.1 Charging

Table 4-4 below shows the summary of the results from the investigations carried out

for charging. The results are also compared to the existing KERS design to check for

improvements in terms of energy transfer efficiency.

The methods for quantifying are as follows:

1. The wooden flywheel was initially driven at a certain speed.2. The KERS at each position was allowed to charge to obtain maximum speed.3. The times taken and the maximum speeds of KERS were recorded and

analysed.

35

Table 4-7: Comparison of Angular Acceleration for Different Positions

Moment of Inertia, kgm2 Angular Acceleration, rad/s2

Position 1 0.008483 20.97

Position 2 0.006179 24.18

Position 3 0.003770 32.74

Position 4 0.001476 45.26

Table 4-8: Comparison of Percentage of Energy Transferred During Charging

Percentage of Energy Transferred During Charging, %

Existing Design New Design New Design (w/o mech loss)

Position 1 33.86 14.18 20.64

Position 2 33.86 12.02 18.54

Position 3 33.86 11.34 18.79

Position 4 33.86 8.96 19.84

Position 1 Position 2 Position 3 Position 40

5

10

15

20

25

30

35

40

Existing KERS DesignNew KERS DesignNew KERS Design Neglecting Mechanical Losses

Perc

enta

ge %

Figure 4-18: Comparison of Energy Transfer Efficiency (Charging)

Referring to both Table 4-6 and Figure 4-8, the efficiency of the new KERS design

in terms of energy successfully transferred was found to be lower compared to the

36

previous design. From the result, with decreasing of the moment inertia of the KERS,

less efficiency was observed. Theoretically, with decreasing moment of inertia,

efficiency of energy transfer should be increasing as less torque was required to

accelerate an object with lower moment of inertia. For the acceleration of an object

with high moment of inertia, for instance at Position 1, greater torque is needed to

accelerate the system from idle state thus more energy losses were expected

especially due to slippage during engagement. In contrast, when the KERS was set at

Position 4 having the least moment of inertia, needing the least torque for

acceleration, should have delivered greater efficiency of energy transfer. Analysis

was done to study the reason why the experiment outcomes did not comply with

what was expected. Other than the losses listed in Table 4-4, the whole test also lost

energy due to vibration and also wind resistance. Whereas for the KERS set in

Position 2, Position 3 and Position 4 where the KERS had not expanded to maximum

achievable diameter, the positioning bearing experienced extra axial load to maintain

the KERS’s position.

F c=mv2

r(4.4)

where Fc : centrifugal force, N

m : mass, kg

v : velocity, m/s

r : radius, m

Figure 4-19: Force Analysis on KERS

Axial Force=Fc

tan θ(4.5)

where Fc : centrifugal force, N

θ

Arm of KERS

Axial Force

Fc

37

Referring to Equation (4.4), the centrifugal force increases with increasing velocity

and decreasing radius. And the axial force is related to the centrifugal force as shown

in Equation (4.5). Thus when the axial force exerted on the position bearing increases

from Position 2 to Position 4. As the positioning bearing was at a poor initial

condition, extra axial load could worsen its performance. Thus more energy loss was

expected to the positioning bearing to withstand the axial load subjected to it.

Also, the power loss of bearing is related to the rotational speed it runs at (M.

Deligant, 2012). In their research, power loss of a bearing due to friction is also

contributed by rotational speed. In other words, with an increase in rotational speed,

the bearing experiences more power loss. Therefore when the KERS was charged at

higher speed, more power loss had to be accounted for the bearing losses. This in

turn reduced the efficiency of energy transferred at higher revolution speed as shown

in the trend in Figure 4-8.

v=rω (4.6)

where v : tangential velocity, m/s

r : radius, m

ω : angular velocity, rad/s

f drag=12

CρA v2(4.7)

where fdrag : frictional drag, N

C : numerical constant

ρ : air density, kg/m3

A : cross sectional area, m2

v : velocity, m/s

τ=Fr (4.8)

where τ : torque, Nm

F : tangential force, N

r : radius, m

38

When the KERS was expanded to obtain its maximum moment of inertia, it achieved

its maximum radius. From Equation (4.5) and Equation (4.6), the effective wind

resistance experienced is related to the angular velocity and its radius. Thus when the

KERS was set at Position 1, wind resistance exerted on the KERS was thought to be

significant at the maximum speed it was charged at. However, since the wind drag is

also a function of velocity, it also influenced the performance of KERS to be charged

at Positions 2 to 4 (as shown in Appendix B Tables B-12, B-14, B16 and B-18)

where the maximum speed of KERS charged at these positions were increasing with

decreasing moment of inertia. This could lead to greater wind resistance.

44.2.2 Discharging

Table 4-7 below shows the summary of the results from the investigations carried out

for discharging. The results are also compared to the existing KERS design to check

for improvements in terms of energy transfer efficiency.

The methods for quantifying are as follows:

1. The KERS was initially driven at a certain speed at each position.2. The wooden flywheel was allowed to discharge the system to obtain a

maximum speed.3. The times taken and the maximum speeds of the wooden flywheel was

recorded and analysed.

39

Table 4-9: Comparison of Percentage of Energy Transferred During Discharging

Percentage of Energy Transferred During Charging, %

Existing

Design

New Design (w/o mech loss) New Design

(Actual)

Position 1 6.40 10.19 8.14

Position 2 6.40 11.55 8.89

Position 3 6.40 7.55 5.39

Position 4 6.40 - -

Position 1 Position 2 Position 3 Position 40

2

4

6

8

10

12

14

Existing KERS DesignNew KERS DesignNew KERS Design Neglecting Mechanical Losses

Perc

enta

ge %

Figure 4-20: Comparison of Energy Transfer Efficiency (Discharging)

Referring to Table 4-7 and Figure 4-10 to compare improvements in discharging, it

was noticed that the percentage of energy transferred in the new KERS design was

greater than the previous version. In the new design, percentage of energy transferred

was peak at Position 2 at about 11.55% which outperformed the effective output of

the previous design. During discharging, it was expected that the KERS having the

maximum moment of inertia should provide the maximum efficiency in terms of

energy transfer efficiency. This was because the KERS set at Position 1 had the

40

greatest moment of inertia among all as it had the largest radius. Thus it supposed to

have the sufficient energy to accelerate the wooden rotating mass.

However in the experiment conducted, the efficiency of energy transfer of

KERS set at Position 1 was slightly less compared to the efficiency of energy

transfer of KERS set at Position 2. This could be due to the greater resistive torque

that arose from wind resistance. This was because at greater radius, the effective

torque introduced by wind resistance was greater. On the other hand, wind resistance

turned to be increasingly significant at increasing velocity. When the system was set

at its largest radius, the velocity at the edge of the radius travelled the fastest

according to Equation (4.7). Thus, when the KERS was set to discharge at Position 1,

it experienced the largest opposing wind resistance according to Equation (4.5),

causing it to lose more energy on overcoming wind friction than accelerating the

wooden rotating mass. Therefore, certain improvements have to be made to

overcome such flaw.

It was noticed that when the KERS was set at Position 4, which had the least

radius and moment of inertia among all 4 pre-set positions, the system halted once it

was engaged for discharging. This was because at the pre-set rotational speed, it did

not possess sufficient energy to accelerate the idling wooden rotating mass.

For experiments on both charging and discharging, slippage occurred at the

interface where the KERS was connected to the wooden flywheel.

4.4.3 Evaluating on the Practicality of New KERS Design

Experiments were also conducted aiming at studying the practicality of the new

KERS design. The experiments are listed in Appendix B.

41

44.3.1 Charging up the New Design KERS

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

100

200

300

400

500

600

f(x) = − 78 x + 380.83

f(x) = − 40 x + 527.33

f(x) = − 52.98828125 x + 262.98

RPM vs Time (s) Deceleration of Com-bined System at Posi-tion 1

Linear (Deceleration of Combined System at Position 1)

Deceleration of Com-bined System at Posi-tion 4

Linear (Deceleration of Combined System at Position 4)

Deceleration of Com-bined System with In-creasing Moment of Inertia of KERS

Linear (Deceleration of Combined System with Increasing Moment of Inertia of KERS)Time, s

RPM

Figure 4-21: Graph of Deceleration of System

From Figure 4-10, it was noticed that the gradient (deceleration, rad/s2) for the KERS

can decelerate the wooden rotating mass by increasing its moment of inertia. When

the KERS was fixed at either Position 1 or Position 4, the gradient was not as steep

as in the process of increasing the moment of inertia of KERS. This showed that the

KERS can function as a braking system to a rotating object. During the braking

process, energy contained in the wooden rotating flywheel was shifted to the KERS,

thus its rotational speed reduced. For the self-deceleration of KERS at Position 1, it

was found to be slightly steeper compared to the self-deceleration of KERS at

Position 4. This was due to the greater influence of wind resistance that introduced

extra friction on the KERS.

Referring to Appendix B Table B-23, although the charging effect was

observed where the KERS was able to decelerate the rotating mass, the study on its

energy transferred showed low efficiency, at 17.75%. Despite accounting in the

findings on known mechanical losses into the study, results still proved that there

were still unknown losses the lead to low efficiency in energy transferred.

42

44.3.2 Discharging the New Design KERS

Referring to Appendix B Table B-30, it was observed that by discharging the KERS

from maximum moment of inertia to least moment of inertia, it was able to accelerate

the wooden rotating mass. From Table B-31, the study on its efficiency for energy

transferred was determined to be 45% after accounting in the findings on known

losses.

This proved that energy stored in the KERS was able to be transferred back to

the master system. In Table B-32, the experiment conducted showed that when the

wooden rotating mass had an initial rotational speed, it could provide a greater

acceleration to the wooden rotation mass as less torque was required to accelerate it

from a given initial speed compared to accelerating from idle. Also, due to the low

relative velocity difference that existed between the surfaces of contact, slippage was

also minimized. This condition was similar to a real-time application of KERS in

assisting Prototype 1 to gain extra power for acceleration.

4.5 Problems Encountered

In the testing on the new KERS design, there are mechanical losses that could

deviate the experimental outcomes. Hence, effort was put in to determine

discoverable losses through experiments. As mentioned in Table 4-4, the losses

included losses due to support bearings, losses due to position bearings and losses

due to bushing. However, there were still two unquantifiable losses which were wind

losses and losses due to slippage. Therefore in the experiments carried out, these two

losses were grouped together as one.

43

Figure 4-22: Energy Loss due to Slippage

From Figure 4-12, it showed that the contact between the metal plate and the

wooden flywheel was not at maximum where. Only part of the metal plate had made

contact with the wooden flywheel. This was due to flaws in the manufacturing

process where welding introduced deformation on the metal plate. Where non-

maximum area was allowed for contact, less grip was present which lead to slippage.

Another issue that also significantly influenced the performance of the third

generation KERS was vibration. When the system was charged to high rotational

speed, the whole rig started to vibrate. This was caused by the rotational imbalance

of the prototype. As the wooden rotating mass was made of pieces of plywood, the

pores within the plywood layers caused the centre of gravity of the rotating mass to

be shifted away from its rotating axis, creating rotating unbalance when rotating.

In the overall project carried out to study on the efficiency of two KERS

designs, there were certain factors that limited the reliability on the data obtained.

Several improvements can be made to have a better study on this topic:

1. The handheld tachometer used is not good enough for this application. This is

because the handheld tachometer could not provide the instantaneous

44

revolutionary speed and have it recorded from time to time. It only showed

the reading when the sensor sensed the reflection paper and it possessed

certain lag. Its memory is only limited to show the maximum and average

revolutionary speed. If a computer tachometer could be used, instantaneous

data logging was possible together with chart could be displayed in the

computer for better analysis of the performance.

2. The design for testing the KERS system can also be modified to improve the

performance. In this design, the self-made bearing housing for the KERS can

be replaced by commercially available standard housings. However, in the

experiment conducted for the new KERS design, effort was put into

determining the known losses to obtain a better understanding on its overall

performance.

3. The recorded timing might had certain influence towards the outcome of the

experiments. As the tachometers are operated by man, the response time

although could be considered insignificant, it still had the potential to affect

the accuracy of the result. As a recommendation, computer software

associated with appropriate equipment should be used to obtain accurate

timing throughout the experiments.

In overall, from the tests performed, the original KERS installed on Prototype 1 was

found to possess too high of moment of inertia where too much of energy was lost to

accelerate the system. Thus, the second generation of KERS with its flywheels made

of lighter material (plywood) was tested. This KERS was found to be performing

better than its predecessor. However, in order to further improve the performance of

KERS, and to eliminate the destruction that occurred during charging and

discharging, another concept of KERS (Figure 4-2) was tested. The third generation

of KERS was proved to perform better than the existing design in terms of energy

transfer efficiency during discharging. For charging, the results shown that the third

generation KERS performed worse. In terms of overall performance, the third

generation KERS had an overall efficiency of 2.3% which slightly outperformed the

existing version of delivering an overall of 2.17%. An absolute advantage of the third

45

generation over the previous two was that it had a different channel of charging and

discharging energy, was not as detrimental as the method adopted in the previous

versions.

Comparing to Flywheel KERS by Volvo, the first and second generation of

KERS did not have the CVT that the model in Volvo has. This turned out to be a

disadvantage of the two generations of KERS where there was only one gear ratio for

charging and another for discharging, and this limited to maximum achievable speed

of the flywheel mass to store and deliver energy efficiently. Unlike the first two

generations of KERS tested, the CVT in Flywheel KERS has a wide range of gear

ratio that enables it to charge and deliver energy efficiently. For the third generation

of KERS test, although it has a variable moment of inertia that aimed at improving

its ability in absorbing and releasing energy, its capacity of energy storage was

limited by its maximum achievable speed, which is the synchronized speed between

the wooden flywheel and the KERS. Thus when compared to Flywheel KERS of

having a CVT, the CVT allows great gear ratio where the flywheel can be

accelerated to high rpm even though the synchronized speed between the

engagement interface is relatively low.

Besides that, Flywheel KERS has its flywheel made of carbon fibre which is

relatively light in weight compared to the flywheels used in the 3 generations of

KERS. Thus, the flywheel can be easily accelerated via the CVT to achieve

60,000rpm as claimed by Volvo. Derek Crabb, Volvo's Vice President for Powertrain

Engineering explained that the carbon-fibre flywheel that rotates at 60,000rpm

travels at Mach2 so the wheel has to be contained in a vacuum chamber to minimize

friction. Whereas in the three generations of KERS tested in this project, the KERS

was exposed to open air and thus a lot of friction occurred and limited its

performance.

4.

46

CHAPTER 5

CONCLUSION

5.1 Conclusion

Due to the inefficiency of the existing KERS which was mainly due to the contact

slippage, a different concept of KERS was designed and tested for improvements. In

the third generation KERS, it has the ability to increase its moment of inertia to

provide smoother acceleration of flywheel and more energy can be stored at lower

rotational velocity which at the same time decelerates the vehicle.

The third generation of KERS was proved to provide a more practical method

for charging and discharging where it was not as destructive as the second

generation. Nonetheless, from the results of the project, there were new problems

that arose from the experiments, where the reason for the results obtained to be

deviated from theoretical expectations. Other than unquantifiable losses that affected

the performance of the KERS tested, the scale of the KERS models tested were not

according to the actual scale of the prototype vehicle. Thus, the comparison for the

second and third generation of KERS required further studies to distinguish the better

of the two.

47

5.2 Recommendations on KERS Generation 3

However, for this new design to be implemented in Prototype 1, certain

modifications have to be made in order to accommodate the entire KERS as its

configuration was totally different. This KERS can be connected to the rear wheel of

the prototype vehicle via chain rather than having a direct contact to the wheels as in

the previous version:

5.3 Future Improvements on KERS Generation 3

As obtained from the results in Section 4.5, it was noticed that energy still lost due to

two main factors: slippage and wind resistance.

The contact surface used in this prototype consisted of a metal plate and

plywood. This was due to the relatively low coefficient of friction that exists between

wood and clean metal is estimated to range from 0.2 to 0.6 (The Engineering

Toolbox). Therefore in order to minimize slippage at the contact surface, alternative

materials which has a greater coefficient of friction can be installed to provide better

traction during contact. A proposed material to suit this purpose is rubber which has

a coefficient of friction of 1.16 (The Physics Hypertextbook).

As wind resistance is proportional to the rotational velocity of the system,

therefore when the system was charged at high initial rotational velocity to test for its

discharging capability, a great amount of energy was lost to wind energy which

caused the system to decelerate at a high rate. Also, as wind resistance was

concerned, the larger the diameter of the rotating system, the greater the effect of the

wind resistance was observed. This was due to at larger diameter, the effective

counter-torque felt by the rotating system was larger. Referring to Equation 4.5, the

frictional drag is also a function of the shape of the object. Thus, as a proposal to

overcome such disadvantage introduced by the wind, an improved design of the

system with a better aerodynamic approach should be adopted to reduce wind drag to

the minimum. Furthermore, with reference to commercially available mechanical

48

KERS that allows its flywheel to rotate in a vacuum chamber for minimal air

resistance, another proposal to reduce wind friction in the later KERS design is to

have a chamber to cover the rotating system to avoid the influence of external wind.

49

REFERENCES

Rubber Friction. (2004, January 27). Retrieved August 17, 2011, from Inside Racing

Technology: http://insideracingtechnology.com/tirebkexerpt1.htm

CFT Transmission. (2010). Retrieved May 3, 2012, from CFT KERS:

http://www.cftkers.com/CFTtransmission.html

Ashley, S. (2011, July 12). Volvo to test flywheel-KERS hybrid cars. Retrieved April

19, 2012, from SAE International: http://ev.sae.org/article/9925

Friction. (n.d.). Retrieved April 14, 2012, from The Physics Hypertextbook:

http://physics.info/friction/

Friction and Coefficients of Friction. (n.d.). Retrieved April 14, 2012, from The

Engineering Toolbox: http://www.engineeringtoolbox.com/friction-

coefficients-d_778.html

How power transfers through a clutch or brake and the method by which the energy

is transferred from one rotating device to a second non-rotating device.

(n.d.). Retrieved August 22, 2011, from The Carlyle Johnson Machine

Company L.L.C.: http://www.cjmco.com/power_transfer.htm

John Walsh, T. M. (2011). Design and analysis of kinetic energy recovery system for

automobiles: Case study for commuters in Edinburgh. Journal of Renewable

and Sustainable Energy 3.

Kinetic Energy Recovery System | KERS | Formula One (F1) KERS | How It Works .

(n.d.). Retrieved August 9, 2011, from Mechanical Engineering A Complete

Online Guide for Every Mechanical Engineer:

http://www.mechanicalengineeringblog.com/tag/kinetic-energy-recovery-

system/

50

M. Deligant, P. P. (2012). Experimental identification of turbocharger mechanical

friction losses. Energy 39, 388-394.

Navarro, X. (n.d.). More details about the flywheel 'kinetic energy recovery system.

Retrieved August 7, 2011, from autoblog-green:

http://green.autoblog.com/2007/10/31/more-details-about-the-flywheel-

kinetic-energy-recovery-system/

Panzariu, O. (2008, December 20). How KERS Works. Retrieved August 19, 2011,

from Auto Evolution: http://www.autoevolution.com/news/how-kers-work-

2815.html

Ramirez, D. (2011, May 27). Volvo thinks of a KERS to reduce consumption.

Retrieved August 21, 2011 , from Wikinoticia:

http://motorfull.com/2011/05/volvo-piensa-en-un-kers-para-reducir-

consumos

Ward, W. (n.d.). RET-MOTOR.COM. Retrieved August 8, 2011, from Mechanical

KERS: http://www.ret-monitor.com/articles/1604/mechanical-kers/

Cross, D.; Hilton, J.; , "High Speed Flywheel Based Hybrid Systems for Low Carbon

Vehicles," Hybrid and Eco-Friendly Vehicle Conference, 2008. IET HEVC

2008 , vol., no., pp.1-5, 8-9 Dec. 2008

URL: http://ieeexplore.ieee.org.libezp.utar.edu.my/stamp/stamp.jsp?

tp=&arnumber=4784374&isnumber=4784367

http://ieeexplore.ieee.org.libezp.utar.edu.my/stamp/stamp.jsp?tp=&arnumber=4784374&isnumber=4784367

http://ieeexplore.ieee.org.libezp.utar.edu.my/stamp/stamp.jsp?tp=&arnumber=4784374&isnumber=4784367

51

Appendices

APPENDIX A: Test on Existing KERS

Experiment Preparation

A testing rig for the KERS system used in Shell Eco Marathon Asia 2011

competition was built (Figure 4-1 and Figure A-1):

This testing rig has the following specification:

Table A-1: Testing Rig Specification

Flywheel dimension 550 mm

Flywheel inertia 0.711502 kgm2

Energy stored @ 200rpm 156 J

Gear ratio between flywheel and wheel 0.29

52

Figure A- 1: Testing Rig

Data Collection

To collect data for analysis for the KERS system, an L4 array of Taguchi’s method

of quality optimization was opted. In this design of experiment, three variables have

been set to assess for the efficiency of charging and discharging of the KERS system:

1. The inertia of storage flywheel

2. The contact surface of the roller

3. The gear ratio for charging and discharging of KERS

The design of experiment was done according to the following factors of study:

Table A- 2: Factors of Study

FactorsLevel

1 2

A Flywheel pieces 1 2

B Gear Ratio 0.75 1.33

C Contact Surface With Grip Without Grip

The experiment template for the L4 array is as the following:

53

Table A-3: Experimental Design

ExperimentFactors Result (Energy, J)

MeanA B C 1 2 3

1 1 1 1

2 1 2 2

3 2 1 2

4 2 2 1

Mean

Procedures in Conducting Experiments

Charging

1. The flywheel mass was rotated manually to achieve a rotational speed of

200rpm.

2. Once the rotational speed of 200rpm was achieved, the KERS was engaged

by allowing the roller to contact with the wheel.

3. The maximum rotational speed of the KERS flywheel was recorded and

converted into energy.

4. Steps 1 to 3 were repeated for 5 times to obtain more reliable results.

5. Steps 1 to 4 were repeated for each experiment 1, 2, 3 and 4.

Discharging

1. The KERS flywheel was charged to rotate at 2000rpm.

2. Once the rotational speed of 2000rpm was achieved, the discharging of

KERS was engaged by contacting the discharging roller onto the wheel.

3. The maximum rotational speed of the flywheel mass was recorded and

converted into energy.

4. Steps 1 to 3 were repeated for 5 times to obtain more reliable results.

5. Steps 1 to 4 were repeated for each experiment 1, 2 ,3 and 4.

54

Results

The initial parameters of the KERS flywheel are as follows:

Table A- 4: Parameters of KERS Flywheel

1-flywheel 2-flywheels

Moment of inertia 0.00872538 kgm2 0.017556 kgm2

Charging

Experiment 1

Table A- 5: Results for Charging Experiment 1

AttemptsResult

rpm rad/s Energy, J

1 783.0000 81.9956 29.3315

2 765.5000 80.1630 28.0351

3 773.6000 81.0112 28.6315

Average 774.0333 81.0566 28.6660

Experiment 2

Table A- 6: Results for Charging Experiment 2

AttemptsResult

Rpm rad/s Energy, J

1 1040.0000 108.9085 51.7461

2 1028.0000 107.6519 50.5589

3 1021.0000 106.9189 49.8727

Average 1029.6667 107.8264 50.7259

55

Experiment 3

Table A-7: Results for Charging Experiment 3

AttemptsResult

rpm rad/s Energy, J

1 662.5000 69.3768 42.2495

2 657.7000 68.8742 41.6395

3 648.9000 67.9526 40.5327

Average 656.3667 68.7346 41.4739

Experiment 4

Table A-8: Results for Charging Experiment 4

AttemptsResult

rpm rad/s Energy, J

1 422.1000 44.2022 17.1508

2 421.4000 44.1289 17.0939

3 426.1000 44.6211 17.4774

Average 423.2000 44.3174 17.2407

Discharging

Experiment 1

Table A-9: Results for Discharging Experiment 1

AttemptsResult

rpm rad/s Energy, J

1 43.4700 4.5522 7.3719

2 42.4100 4.4412 7.0168

3 43.7800 4.5846 7.4775

56

Average 43.2200 4.5260 7.2887

Experiment 2


AttemptsResult

Rpm rad/s Energy, J

1 37.3200 3.9081 5.4336

2 33.0700 3.4631 4.2665

3 32.6100 3.4149 4.1486

Average 34.3333 3.5954 4.6162

Experiment 3


AttemptsResult

Rpm rad/s Energy, J

1 53.4400 5.5962 11.1413

2 51.5500 5.3983 10.3672

3 50.3000 5.2674 9.8705

Average 51.7633 5.4206 10.4597

Experiment 4


AttemptsResult

Rpm rad/s Energy, J

1 38.0000 3.9794 5.6334

2 36.0000 3.7699 5.0560

3 35.0000 3.6652 4.7790

57

Average 36.3333 3.8048 5.1561

Overall Results

Charging

Table A-13: Overall Results for Charging


MeanA B C 1 2 3

1 1 1 1 29.3315 28.0351 28.6315 28.6660

2 1 2 2 51.7461 50.5589 49.8727 50.7259

3 2 1 2 42.2495 41.6395 40.5327 41.4739

4 2 2 1 17.1508 17.0939 17.4774 17.2407

Mean 34.5266

Table A-14: Response Table for Charging

A B C

Level 1 39.6960 35.0700 22.9534

Level 2 29.3573 33.9833 46.0999

Difference 10.3387 1.0867 23.1465

SSQ 320.6656 3.5425 1607.2863

Rank 2 3 1

Optimum 1 1 2

58

A1 A2 B1 B2 C1 C20

5

10

15

20

25

30

35

40

45

50

Larger the Better

Ener

gy, J

Figure A-2: Response Graph for Charging

Table A-15: ANOVA for Charging of KERS

Sourc

ePool SSQ Dof Var SSq Rho

A 0.0000 320.6656 1.0000 320.6656 320.3436 16.5489

B 1.0000 3.5425 1.0000 3.5425 0.0000

C 0.0000 1607.2863 1.0000 1607.28631606.964

283.0158

Error 1.0000 4.2395 9.0000 0.4711

Pooled 3.5425 0.3220 8.4261 0.4353

St 1935.7339 11.0000 175.97581935.733

9100.0000

Sm 14305.0592 1.0000

ST 16240.7930 12.0000

Discharging

59

Table A-16: Overall Results for Discharging


MeanA B C 1 2 3

1 1 1 1 7.3719 7.0168 7.4775 7.2887

2 1 2 2 5.4336 4.2665 4.1486 4.6162

3 2 1 2 11.1413 10.3672 9.8705 10.4597

4 2 2 1 5.6334 5.0560 4.7790 5.1561

Mean 6.8802

Table A-17: Response Table for Discharging

A B C

Level 1 5.9525 8.8742 6.2224

Level 2 7.8079 4.8862 7.5379

Difference 1.8554 3.9880 1.3155

SSQ 10.3277 47.7127 5.1917

Rank 2 1 3

Optimum 2 1 2

A1 A2 B1 B2 C1 C20

1

2

3

4

5

6

7

8

9

10

Larger the Better

Ener

gy, J

Figure A-3: Response Table for Discharging

60

Table A-18: ANOVA for Discharging KERS

Source Pool SSQ Dof Var SSq Rho

A 0.0000 10.3277 1.0000 10.3277 9.8085 14.9616

B 0.0000 47.7127 1.0000 47.7127 47.1935 71.9876

C 1.0000 5.1917 1.0000 5.1917

Error 1.0000 2.3258 9.0000 0.2584

Pooled 1.0000 5.1917 0.5192 8.5558 13.0508

St 65.5578 11.0000 5.9598 65.5578 100.0000

Sm 568.0450 1.0000

ST 633.6029 12.0000

Investigations on Energy Transfer Efficiency

Charging Experiment 1 to Experiment 4

61

Figure A-4: Flow Chart of Data Analysis

For example, take Charging Experiment 1:

Maximum rotational speed of KERS flywheel

= 774.03 rpm

= 81.06 rad/s

Energy gained by KERS flywheel @ 81.06 rad/s

= 0.5 I ω2

= 0.5 (0.00872538 kgm2) (81.06 rad/s)2

=28.67 J

Record maximum achievable rotational speed of KERS

flywheel in each experiment

Calculate for energy gained by KERS flywheel

Reverse calculations on the rotational speed of flywheel

mass at the synchonized speed

Calculate for energy left in flywheel mass at that particular

speed

Calculate for initial energy contained in flywheel mass

Calculate for energy loss from flywheel mass

Calculate overall efficiency of energy transferred

62

Rotational speed of flywheel mass

= (774.03 rpm) (0.02172)

= 16.16 rpm

= 1.69 rad/s

Energy contained in flywheel mass @ 16.16 rpm

= 0.5 I ω2

= 0.5 (0.711502 kgm2) (1.69 rad/s)2

= 1.02 J

Initial energy content of flywheel mass @ 200 rpm

= 0.5 I ω2

= 0.5 (0.711502 kgm2) (20.94 rad/s)2

= 156 J

Energy loss from flywheel mass

= 156 J – 1.02 J

=154.98 J

Percentage of energy successfully transferred

= (energy gained by KERS flywheel) / (energy loss from flywheel mass)

= 28.67 J / 154.98 J

=18.50 %

Experiment 1:

Table A-19: Charging Experiment 1 Energy Loss

Max rotational speed of KERS flywheel: 774.03 rpm

Energy gained by KERS flywheel @774.0333rpm: 28.67 J

Rotational speed of flywheel mass: 16.16 rpm

Energy contained in flywheel mass @16.16rpm: 1.02 J

Initial energy content of flywheel mass @200rpm 156.00 J

63

Energy loss from flywheel mass: 154.98 J

Percentage of energy transferred: 18.50 %

Experiment 2:






Initial energy content of flywheel mass @200rpm: 156.00 J

Energy loss by flywheel mass: 149.83 J


Experiment 3:







Energy loss by flywheel mass: 155.21 J


Experiment 4:



64

Energy gained by KERS flywheel @656.3667rpm 17.24 J




Energy loss from flywheel mass: 154.96 J


Discharging Experiment 1 to Experiment 4

65

Figure A-5: Flow Chart for Data Analysis

For example, take Discharging Experiment 1:

Maximum rotational speed of flywheel mass

= 43.22 rpm

= 4.53 rad/s

Energy gained by flywheel @ 43.33 rpm

Record maximum achievable rotational speed of flywheel

mass in each experiment

Calculate for energy gained by flywheel mass

Reverse calculations on the rotational speed of KERS

flywheel at synchronized speed

Calculate for energy left in KERS flywheel at that

particular speed

Calculate for initial energy contained in flywheel mass

Calculate for energy lost from KERS flywheel

Calculate for overall efficiency of energy transferred

66

= 0.5 I ω2

= 0.5 (0.00872538 kgm2) (4.53 rad/s)2

= 7.29 J

Rotational speed of KERS flywheel

= (43.22 rpm) / (0.03862)

= 1119.11 rpm

= 117.19 rad/s

Energy contained in KERS flywheel @ 1119.11 rpm

= 0.5 I ω2

= 0.5 (0.00872538 kgm2) (117.19 rad/s)2

= 59.92 J

Initial energy content of KERS flywheel @ 2000 rpm

= 0.5 I ω2

= 0.5 (0.00872538 kgm2) (209.44 rad/s)2

= 191.37 J

Energy loss from KERS flywheel

= 191.37 J – 59.92 J

= 131.45 J

Percentage of energy successfully transferred

= (7.29 J) / (131.45 J)

= 5.54 %

Experiment 1:

Table A-23: Discharging Experiment 1 Energy Loss

Max rotational speed of flywheel mass: 43.22 rpm

Energy gained by flywheel [email protected]: 7.29 J

Rotational speed of KERS flywheel: 1119.11 rpm

67

Energy contained in KERS flywheel @1119.11rpm: 59.92 J

Initial energy content of KERS flywheel @2000rpm: 191.37 J

Energy loss from KERS flywheel: 131.45 J


Experiment 2:









Experiment 3:









Experiment 4:

68



Energy gained by flywheel mass @36.33rpm: 5.16 J



Initial energy content of KERS flywheel mass @2000rpm: 385.04 J



69

Appendices

APPENDIX B: New Design KERS

Experimental Preparation

Before any investigations on the performance of the new KERS design, the initial

parameters of the prototype listed below were first determined experimentally.

1. Moment of inertia for each of the 4 preset positions of the KERS2. The moment of inertia of the wooden rotating mass3. Mechanical losses

Figure B-1: Setup for Measuring Moment of Inertia of KERS Experimentally

Test 1: Experimental method to determine moment of inertia of KERS:

70

1. The KERS was set up as Figure B-1 and to Position 1 (Figure 4.3)2. A load of 0.46kg was placed along the perimeter of the shaft (d = 0.0158m)

of the rotating KERS system and was allowed to drop freely.3. Both the maximum speed and the time taken for the system to achieve

maximum speed were recorded.4. Steps 1 to 3 were repeated for 3 times to obtain reliable data. 5. Steps 1 to 4 were repeated for Position 2 (Figure 4.4), Position 3 (Figure 4.5)

and Position 4 (Figure 4.6).

Figure B-2: Determine for Moment of Inertia of Wooden Flywheel

Test 2: Experimental method to determine moment of inertia of wooden rotating

mass:

1. A load of 0.175kg was placed along the perimeter of the wooden rotating mass (d = 0.287m) and was allowed to drop freely.

2. Both the maximum speed and time taken to achieve maximum speed were recorded.

3. Steps 1 and 2 were repeated for 4 times to obtain reliable data.

71

Figure B-3: Determine for Support Bearing Losses

Test 3: Experimental method to determine for support bearing losses:

1. The KERS was set up according to Figure B-32. The KERS was given an initial rotational speed of 200rpm.3. The time taken for the system to drop to 100rpm was recorded.4. Steps 1 to 3 were repeated for 3 times to obtain reliable data.

Figure B-4: Determine for Positioning Bearing Losses

Test 4: Experimental method to determine for position bearing losses:

1. The KERS was set up according to Figure B-42. The KERS was given an initial rotational speed of 200rpm.3. The time taken for the system to drop to 100rpm was recorded.

72

4. Steps 1 to 3 were repeated for 3 times to obtain reliable data.

Figure B-5: Determine for Bushing Losses

Experimental method to determine for bushing losses:

1. The KERS was set up according to Figure B-52. The KERS was given an initial rotational speed of 200rpm.3. The time taken for the system to drop to 100rpm was recorded.4. Steps 1 to 3 were repeated for 3 times to obtain reliable data.

Results

Test 1:

Table B- 1: Data for Moment of Inertia at Position 1

Position 1

Time, s Max speed, rpm Angular acceleration, rad/s2

1 9.40 193.40 2.15

2 9.14 190.10 2.18

3 8.84 200.40 2.37

4 8.60 200.00 2.44

Average 9.00 195.98 2.28

73

Table B-2: Data for Moment of Inertia at Position 2

Position 2


1 5.75 173.80 3.17

2 5.48 170.10 3.25

3 6.06 170.50 2.95

4 5.80 176.30 3.18

Average 5.77 172.68 3.13


Position 3


1 4.58 231.60 5.30

2 4.50 230.90 5.37

3 5.56 252.60 4.76

4 5.27 261.10 5.19

Average 4.98 244.05 5.13


Position 4


1 3.28 405.50 12.95

2 3.22 410.60 13.35

3 3.13 405.60 13.57

4 3.38 407.20 12.62

Average 3.25 407.23 13.11

Test 2:

74

Table B-5: Data for Moment of Inertia of Rotating Wooden Mass

Rotating Wooden Mass


1 0.80 50.23 6.57

2 0.80 51.45 6.73

3 0.80 51.95 6.80

4 0.77 52.35 7.12

Average 0.79 51.49 6.80

Test 3:

Table B-6: Data for Determining Support Bearing Losses

Support Bearing Losses

Start speed, rpm Time, s Angular deceleration, rad/s2

1 217.00 10.44 2.18

2 200.40 11.50 1.82

3 192.30 11.30 1.78

Average 203.23 11.08 1.92

Test 4:

Table B-7: Data for Determining Support Bearing Losses and Positioning Bearing

Losses

Support Bearing Losses + Position Bearing Losses

Start speed, rpm Time, s Angular acceleration, rad/s2

1 210.40 4.28 5.15

2 199.20 4.20 4.97

3 201.00 4.10 5.13

Average 203.53 4.20 5.08

75

Test 5:

Table B-8: Data for Determining Support Bearing Losses and Bushing Losses

Support Bearing Losses + Bushing

Start speed, rpm Time, s Angular acceleration, rad/s2

1 243.00 4.00 6.36

2 248.00 4.10 6.33

3 258.00 4.15 6.51

Average 249.67 4.08 6.40

Calculations for moment of inertia of the KERS at Position 1:

When the test for moment of inertia was conducted, consider only support

bearing losses:

(0.45 kg) (9.81 m/s2) (0.0075 m) Nm – (1.921 I) Nm = (2.28154 I) Nm

(4.2 I) Nm = 0.0357 Nm

I = 0.008483 kgm2

Having the moment of inertia for Position 1 known, the losses can be

calculated:

Table B-9: Torque Loss due to Each Factor

Deceleration,

rad/s2

Moment of

inertia, kgm2

Torque loss,

Nm

Support Bearing

Losses3.17 0.008483 0.016295

Positioning

Bearing Losses1.63 0.008483 0.026824

Bushing Losses 2.64 0.008483 0.038022

76

Thus the moment of inertia for the Position 2, Position 3 and Position 4 can

be calculated:

Table B-10: Moment of Inertia for Various Positions

Acceleration,

rad/s2

Torque loss,

Nm

Net Torque,

Nm

Moment of

inertia, kgm2

Position 2 3.13 0.016295 0.019355 0.006179

Position 3 5.13 0.016295 0.019355 0.003770

Position 4 13.11 0.016295 0.019355 0.001476

Refer Test 2 for the moment of inertia for the rotating wooden flywheel:

Table B-11: Moment of Inertia of Rotating Wooden Mass

Acceleration, rad/s2 Net Torque, Nm Moment of inertia, kgm2

6.80 0.246354 0.03621

Test for KERS Performance

77

The testing was separated into charging and discharging. Each of the tests was

conducted at the 4 pre-set moment of inertia determined in the previous section.

Figure B-6: Method for Taking Wooden Rotating Mass RPM

Figure B-7: Method for Taking KERS RPM

78

Experimental method for Charging:

1. The KERS was set up according to Figure 4.3 for Position 1.2. The wooden mass was given an initial velocity of 650rpm.3. The KERS was engaged. The maximum achievable speed and the time taken

to achieve maximum speed was recorded.4. Steps 1 to 3 were repeated for 4 times to obtain reliable data.5. Steps 1 to 4 were repeated for KERS set up at Position 2 (Figure 4.4),

Position 3 (Figure 4.5) and Position 4 (Figure 4.6).

Figure B-8: Steps in Data Analysis

Record rotational speed of wooden rotating mass when KERS started to engage

Record maximum achievable rotational speed of KERS

Reverse calculations on the rotational speed of wooden rotating mass at synchronized speed

Calculate for energy loss in wooden rotating mass at that particular speed

Calculate for energy gained by KERS at that particular speed

Calculate for energy gained by KERS without mechanical losses


Calculate for efficiency of energy transferred if mechanical loss was eliminated

79

Results

Charging at Position 1:

Table B-12: Data for Charging at Position 1

Rotating Mass, rpm KERS Maximum Charged, rpm Time, s

1 643.6 391.2 2.0

2 650.5 407.1 2.0

3 654.8 406.3 2.7

4 659.8 397.0 2.7

Average 652.2 400.4 2.4

Sample Calculations:

Average Torque on KERS

= I α

= (0.006825 kgm2) (17.84 rad/s2)

= 0.1228 Nm

Compensated Torque on KERS

= average torque + mech loss

= 0.1228 Nm + 0.0508 Nm

= 0.1726 Nm

Compensated Acceleration of KERS

= (compensated torque) / (moment of inertia)

= (0.1726 Nm) / (0.006825 kgm2)

= 25.2906 rad/s2

Energy Loss by Rotating Mass in 2.4s

= 0.5 I (ω02 – ω1

2)

= 0.5 (0.031298 kgm2) [(652.2 rpm) (2π/60 rad/rpm)]2 - [(400.4 rpm) (2π/60

rad/rpm)]2

= 52.61 J

80

Energy Gained by KERS in 2.4s

= 0.5 I (ω12 – ω0

2)

= 0.5 (0.006825 kgm2) ](400.4 rpm) (2π/60 rad/rpm)]2

= 7.4573J

Total Radians Covered in 2.4s

= ω0 t + 0.5 α t2

= 0 + 0.5 (17.84 rad/s2) (2.4 s)2

= 49.2675 rads

KERS Energy Gained Inclusive of Mech Loss

= (compensated torque) (radians covered)

= (0.2325 Nm) (49.2675 rads)

= 11.4549J

Energy Loss due to Slippage and Wind

= 52.61 J – 11.4549 J

= 41.1551 J

Percentage of Energy Successfully Transferred

= 7.4573 J / 52.61 J

= 14.18 %

Percentage of Compensated Energy Transferred

= 11.4549 J / 52.61 J

= 21.77 %

Table B-13: Summary of Data for Charging at Position 1

Average Rotating Mass RPM 652.2 rpm

81

KERS Charged to Maximum RPM 400.4 rpm

Average Time Taken 2.0 s

Average Acceleration of KERS 20.97 rad/s2

Average Torque on KERS 0.1779 Nm

Expected Mechanical Loss 0.0811 Nm

Compensated Torque on KERS 0.2590 Nm

Compensated Acceleration of KERS 30.5297 rad/s2

Energy Loss by Rotating Mass in 2s 52.6099 J

Energy Gained by KERS in 2s 7.4572 J

Total Radians Covered in 2s 41.9298 rads

KERS Energy Gained Inclusive Mech Losses 10.8595 J

Energy Loss Due to Slippage and Wind 41.7505 J

Percentage of Energy Successfully Transferred Observed 14.17 %

Percentage of Compensated Energy Transferred 20.64 %




1 617.5 396.6 1.8

2 633.5 408.5 1.7

3 619.0 401.9 1.9

4 630.0 400.0 1.7

Average 625.0 407.8 1.8




82







Energy Loss by Rotating Mass in 2.4s 45.50 J

Energy Gained by KERS in 2.35s 5.47 J

Total Radians Covered in 2.35s 36.60 rads








1 631.5 483.7 1.4

2 657.0 464.5 1.6

3 650.0 470.8 1.5

4 660.0 457.1 1.5

Average 649.6 469.0 1.5





83






Energy Loss by Rotating Mass in 1.3s 40.11 J










1 671.0 607.0 1.2

2 656.0 529.1 1.2

3 656.0 521.3 1.3

4 655.0 529.4 1.5

Average 659.5 546.7 1.3






84





Energy Loss by Rotating Mass in 1.3 27.01 J







Practicality of the New KERS Design:

Method:

Test for Deceleration of Combined System at Position 1

1.1 The KERS was engaged all the time at Position 1 to the wooden rotating

mass.

1.2 The whole system was charged at a specified speed.

1.3 The time taken for the whole rotating system stop was recorded to get

deceleration.

1.4 Steps 1.1 to 1.3 were repeated for 3 times to obtain reliable data.



mass.

2.2 The whole system was charged at a specified speed.

2.3 The time taken for the whole rotating system to drop to a specified speed was

recorded to get deceleration.


85

Test for Deceleration of Combined System at with Increasing Moment of

Inertia of KERS


mass.

3.2 Once the external torque applied on the system was taken off, the KERS was

adjusted gradually from Position 4 to Position 1.

3.3 The time taken for the whole stroke and the rotational speed at the end of the

stroke were recorded.


Table B-20: Test for Deceleration of Combined System at Position 1


1 2 3 Average

Initial Speed of Whole System, rpm

258.90 257.30

272.7

5 262.98

Final Speed of Whole System, rpm

128.50 126.00

127.5

0 127.33

Time Taken, s 5.18 5.44 6.01 5.54

Whole System Deceleration, rad/s2 2.64 2.53 2.53 2.56

Initial Energy Contained in Combination, J 16.94659

Energy Content in Combination Eventually, J 3.972922

Energy Loss to Friction, J 12.97367

Power Loss to Friction, watt 2.340409

Table B-21: Test for Deceleration of Combined System at Position 4


1 2 3 Average

86

Initial Speed of Whole System, rpm 106.75 107.65 112.50 108.97

Final Speed of Whole System, rpm 0.00 0.00 0.00 0.00

Time Taken, s 4.16 4.25 3.94 4.12


Initial Energy Contained in Combination, J 2.453271

Energy Content in Combination Eventually, J 0

Energy Loss to Friction, J 2.453271

Power Loss to Friction, watt 0.595936

Table B-22: Test for Deceleration of Combined System at with Increasing Moment

of Inertia of KERS

Test for Deceleration of Combined System at with Increasing Moment of Inertia of

KERS

1 2 3 Average

Initial Speed of Whole System, rpm 379.50 388.50 374.50 380.83

Final Speed of Whole System, rpm 242.10 271.50 252.15 255.25

Time Taken, s 1.75 1.48 1.60 1.61


Table B-23: Study on Energy Transfer in System

Wooden Flywheel KERS

Initial Energy Content, J 28.79203 1.173928

Final Energy Content, J 12.93403 3.030545

87

Energy Difference, J 15.858 1.856617

Mech Energy Loss, J (refer Table B-21) 0.959457

Energy Gained including Friction, J 2.816074

Percentage of Energy Transfer Observed, % 11.71

Percentage of Energy Transferred after Compensation for Mech Loss,

%17.76

Experimental method for Discharging:

1. The KERS was set up according to Figure 4.3 for Position 1.

2. The KERS was given an initial velocity of 750rpm.

3. The KERS was engaged. The maximum achievable speed of the wooden

rotating mass and the time taken for it to achieve maximum speed was

recorded.

4. Steps 1 to 3 were repeated for 4 times to obtain reliable data.

5. Steps 1 to 4 were repeated for KERS set up at Position 2 (Figure 4.4),

Position 3 (Figure 4.5) and Position 4 (Figure 4.6).

88

Figure B-9: Steps for Data Analysis

Record rotational speed of KERS when started to engage for discharging

Record maximum achievable rotational speed of wooden rotating

flywheel

Reverse calculations on the rotational speed of KERS at synchronized speed

Calculate for energy loss in KERS at that particular

speed

Calculate for energy loss by KERS without mechanical

losses

Calculate for energy gained by wooden rotating flywheel at that

particular speed


Calculate for efficiency of energy transferred if mechanical loss was

eliminated

89

Discharging at Position 1:

Table B-24: Data for Discharging at Position 1

KERS Charged, rpm Rotating Mass Maximum, rpm Time, s

1 768.1 107.2 2.0

2 710.7 121.2 1.6

3 752.1 127.1 1.5

4 750.0 105.0 2.0

Average 745.2 115.1 1.8

Sample Calculations

Energy Loss by KERS Observed

= 0.5 I (ω02 – ω1

2)

= 0.5 (0.006825 kgm2) [(745.2 rpm) (2π/60 rad/rpm)2 – (115.1 rpm) (2π/60

rad/rpm)2]

= 25.2159 J

Energy Gained by Rotating Mass in 1.8s

= 0.5 I (ω12 – ω0

2)

= 0.5 (0.036206 kgm2) [(115.125 rpm) (2π/60 rad/rpm)]2

= 2.6311 J

Total Radians Covered by KERS in 1.8s

= ω0 t + 0.5 α t2

= (745.225 rpm) (2π/60 rad/rpm) (1.8 s) + 0.5 (-37.174 rad/s2) (1.8 s)2

= 79.9599 rads

Negative Torque to Decelerate KERS from Observation

= (Energy Loss by KERS in 1.8s) / (Total Radians Covered by KERS in 1.8s)

= (25.2159 J) / (79.9599 rads)

= 0.3231 Nm

Summation of Negative Torque

90

= Negative Torque to Decelerate KERS from Observation + Mech Loss

= 0.3231 Nm + 0.0811 Nm

= 0.4042 Nm

Energy Loss by KERS Including Mech Loss

= (Summation of Negative Torque) (Total Radians Covered by KERS in

1.8s)

= (0.4042 Nm) (79.9599 rads)

= 32.3204 J

Percentage of Observed Energy Successfully Transferred

= (Energy Gained by Rotating Mass) / (Energy Loss by KERS Observed)

= (2.6311 J) / (25.2159 J)

= 10.44 %

Percentage of Compensated Energy Transferred

= (Energy Gained by Rotating Mass) / (Energy Loss by KERS incl. Mech

Loss)

= (2.6311 J) / (32.3204J)

=8.14%

91

Table B-25: Summary of Data for Discharging at Position 1

Average KERS RPM 745.225 rpm

Rotating Mass Maximum RPM 115.125 rpm


Average Acceleration of Rotating Mass 6.8 rad/s2

Average Deceleration of KERS 37.174 rad/s2

Energy Loss by KERS Observed in 1.8s 25.2159 J

Energy Gained by Rotating Mass in 1.8s 2.6311 J


Negative Torque to Decelerate KERS Observed 0.3231 Nm

Summation of Negative Torque 0.4042 Nm

Energy Loss by KERS Including Mech Loss 32.3204 J






1 843.9 116.7 1.6

2 848.9 112.7 1.9

3 781.9 125.1 1.7

4 851.0 112.5 1.8

Average 831.4 116.8 1.7

92


Average KERS RPM 831.4 Rpm

Rotating Mass Maximum RPM 116.8 Rpm




Energy Loss by KERS Observed in 1.7s 22.9573 J



Negative Torque to Decelerate KERS Observed 0.2703 Nm








1 880.0 74.7 1.7

2 903.6 75.8 1.6

3 894.8 82.7 1.6

4 912.9 85.1 1.5

Average 897.8 79.6 1.6

93


Average KERS RPM 897.8 Rpm

Rotating Mass Maximum RPM 79.6 Rpm




Energy Loss by KERS observed in 1.6s 16.5302 J



Negative Torque to Decelerate KERS from Observation 0.2035 Nm





Practicality of New Design KERS in Discharging

Method:

Test for Discharging with Decreasing Moment of Inertia of KERS


mass.

1.2 The entire system was charged at a specified rotational speed.

1.3 Once the external torque was removed, the KERS was adjusted from Position

1 to Position 4. The time taken for the adjustment and the maximum

rotational speed achieved by the rotating mass was recorded.


Test for Discharging with Decreasing Moment of Inertia of KERS onto

Rotating Wooden Mass with Initial Rotational Speed

2.1 The KERS and rotating wooden mass were charged up to a specified speed.

2.2 Once the KERS was engaged for discharging, the KERS was adjusted from

Position 1 to Position 4. The time taken for the transition was recorded

94

together with the rotational speed of the rotating wooden mass right before

engagement and the maximum rotational speed it achieved.


Table B-30: Test for Discharging with Decreasing Moment of Inertia of KERS

Test for Discharging with Decreasing Moment of Inertia of KERS

1 2 3 Average

Initial Speed of Entire System, rpm 221.00 225.00 219.00 221.67

Maximum Rotational Speed Achieve after

Discharging, rpm227.50 230.50 227.00 228.33

Time taken 0.44 0.36 0.45 0.42

Acceleration 1.55 1.60 1.86 1.67

Table B-31: Study on Energy Transfer in System

Wooden Flywheel KERS Total

Initial Energy Content, J 9.75 2.29 12.04

Final Energy Content, J 10.35 0.42 10.77

Energy Difference, J 0.60 -1.86 -1.27

Percentage of Energy Transfer

Observed, %31.96

Mech Energy Loss, J

(refer Table B-21)0.25

Percentage of Energy Transferred

after Compensation for Mech Loss,

%

0.45

95

Table B-32: Test for Discharging with Decreasing Moment of Inertia of KERS onto


Test for Discharging with Decreasing Moment of Inertia of KERS onto


1 2 3 Average

Wooden Rotating Mass Speed before

Engage, rpm51.50 56.50 49.80 52.60

Maximum Speed of Wooden Rotating Mass

after Discharged, rpm97.50 112.00 112.00 107.17

Time Taken, s 1.20 1.43 1.50 1.38

KERS Initial Rotational Speed, rpm 457.00 467.00 460.00 461.33

Acceleration Introduced by KERS on

Wooden Rotation Mass, rad/ss4.01 4.06 4.34 4.15

Initial Energy Content in KERS, J 9.90

Initial Energy Content in Wooden Rotating

Mass, J0.55

Maximum Energy Content in Wooden

Rotating Mass after Discharged, J2.28

Energy Gained by Mass, J 1.73

Percentage of Energy Transferred, % 17.48

final year report: kinetic energy recovery system

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initial energy content

final energy content

maximum achievable speed

wooden rotation mass

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