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.

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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) 2.1.1

4

Components of Kinetic Energy Recovery System (KERS)

4

viii

2.1.2

2.1.3 2.2

Types of Kinetic Energy Recovery Systems (KERS)

5

Engagement of KERS

9

Prototype 1 by UTAR M.E 2.2.1

2.2.2

Design of Kinetic Energy Recovery System for Prototype 1

11

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

2.6

3

4

11

16

Alternative Solution

16

2.6.1

Friction

17

2.6.2

Jaw (tooth)

17

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

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

4.5

5

5

Problems Encountered

40 42

CONCLUSION

46

5.1

Conclusion

46

5.2

Recommendations on KERS Generation 3

47

5.3

Future Improvements on KERS Generation 3

47

REFERENCES

49

Appendx A

51

Appendix B

69

x

LIST OF TABLES

TABLE

TITLE

PAGE

1-1

Project Gantt Chart

2-1

Technical Specification of KERS

14

4-1

Summary of Energy Transfer Efficiency for Charging Experiments

26

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

Comparison of Percentage of Energy Transferred During Charging

35

Comparison of Percentage of Energy Transferred During Discharging

39

4-2

4-6

4-7

3

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

4-5

KERS at Position 2

31

4-6

KERS at Position 3

32

4-7

KERS at Position 4

32

4-8

Comparison (Charging)

of

Energy

Transfer

Efficiency 35

xii

4-9

Force Analysis on KERS

4-10

Comparison of (Discharging)

Energy

36 Transfer

Efficiency 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/(kgK)

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

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 14

Shell Eco Marathon Competition Problem Statement Literature Review Design and Simulations UTAR Semester III 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Experiment Verifications Data Analysis Completion of FYP Report Submission 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

2.1.2.1 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.

2.1.2.2 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

2.1.2.3 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 2-1: 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.

2.6.1.1 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.

2.6.2.1 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

2.6.2.2

Disadvantages of Jaw Engagement

a. Too much chock when applied suddenly

19

CHAPTER 3

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

Start

Problem Definition

Literature Review

Component Design and Simulation


Data Analysis

Report

End

Figure 3-1: 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

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

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

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 4-1: 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 4-1: Summary of Energy Transfer Efficiency for Charging Experiments Charging Experiment

Control Factors

Percentage of Energy

Flywheel

Gear Ratio

Contact Surface

Transferred, %

1

1

0.75

With grip

18.50

2

1

1.33

Without grip

33.86

3

2

0.75

Without grip

26.72

4

2

1.33

With grip

11.13

27

Table 4-2: Summary of Energy Transfer Efficiency for Disharging Experiments Discharging Experiment

Control Factors

Percentage of Energy

Flywheel

Gear Ratio

Contact Surface

Transferred, %

1

1

0.75

With grip

5.54

2

1

1.33

Without grip

6.40

3

2

0.75

Without grip

4.93

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)

E = 0.5 I ω2

(4.2)

I = 0.5 m r2

(4.3)

where τ : torque, Nm I : moment of inertia, kgm2 Α : angular acceleration, rad/s2

where E : energy, J I : moment of inertia, kgm2 ω : angular velocity, rad/s

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 4-2: New KERS Design (Isometric View)

Figure 4-3: 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 4-4: KERS at Position 1


32



33

Table 4-3: 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 4-4: Summary of Expected Mechanical Losses Losses due to:

Support bearings

Position bearing

-0.016295

Nm

-0.026824

Nm

34

Flywheel mass bushing

Total mechanical loss

-0.038022

Nm

-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.

4.4.2.1 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 4-5: 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 4-6: 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

40 35

Percentage %

30 25

Existing KERS Design

20

New KERS Design

15

New KERS Design Neglecting Mechanical Losses

10 5 0 Position 1

Position 2

Position 3

Position 4

Figure 4-8: 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.

(4.4) where Fc : centrifugal force, N m : mass, kg v : velocity, m/s r : radius, m

Fc θ Axial Force Figure 4-9: Force Analysis on KERS

(4.5) where Fc : centrifugal force, N

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.

(4.6) where v : tangential velocity, m/s r : radius, m ω : angular velocity, rad/s

(4.7) where fdrag : frictional drag, N C

: numerical constant

ρ

: air density, kg/m3

A

: cross sectional area, m2

v

: velocity, m/s

(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.

4.4.2.2 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 4-7: Comparison of Percentage of Energy Transferred During Discharging Percentage of Energy Transferred During Charging, % Existing

New Design (w/o mech loss)

Design

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

-

-

14 12

Percentage %

10 Existing KERS Design 8 New KERS Design 6 New KERS Design Neglecting Mechanical Losses

4 2 0 Position 1

Position 2

Position 3

Position 4

Figure 4-10: 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

4.4.3.1 Charging up the New Design KERS

RPM vs Time (s) 600

Deceleration of Combined System at Position 4

500 y = -40x + 527.33

Deceleration of Combined System with Increasing Moment of Inertia of KERS Linear (Deceleration of Combined System at Position 1)

RPM

400 300 y = -78x + 380.83 200 y = -52.988x + 262.98 100

Linear (Deceleration of Combined System at Position 4)

0 0

Deceleration of Combined System at Position 1

2

4 Time, s

6

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

Figure 4-11: 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

4.4.3.2 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 4-12: 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 nonmaximum 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.

46

CHAPTER 5

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

5 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-recoverysystem/

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-flywheelkinetic-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-work2815.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-reducirconsumos

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=&arn umber=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 Flywheel inertia

550 mm 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 Factors A

Flywheel pieces

B

Gear Ratio

C

Contact Surface

Level 1

2

1

2

0.75

1.33

With Grip

Without Grip

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

53

Table A-3: Experimental Design Experiment

Factors

Result (Energy, J)

A

B

C

1

1

1

1

2

1

2

2

3

2

1

2

4

2

2

1

1

2

3

Mean

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

Moment of inertia

1-flywheel

2-flywheels

0.00872538 kgm2

0.017556 kgm2

Charging

Experiment 1

Table A- 5: Results for Charging Experiment 1 Attempts

Result 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 Attempts

Result 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 Attempts

Result 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 Attempts

Result 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 Attempts

Result 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


Result 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


Result 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


Result 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 Experiment

Factors

Result (Energy, J)

Mean

A

B

C

1

2

3

1

1

1

1

29.3315

28.0351

2

1

2

2

51.7461

50.5589

49.8727

3

2

1

2

42.2495

41.6395

40.5327

4

2

2

1

17.1508

17.0939

17.4774

28.6315

28.6660 50.7259 41.4739 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

Larger the Better 50 45 40

Energy, J

35 30 25 20 15 10 5 0 A1

A2

B1

B2

C1

C2

Figure A-2: Response Graph for Charging

Table A-15: ANOVA for Charging of KERS Source

Pool

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

C

0.0000

1607.2863

1.0000

Error

1.0000

4.2395

9.0000

Pooled

3.5425

St

1935.7339

11.0000

Sm

14305.0592

1.0000

ST

16240.7930 12.0000

0.0000

1607.2863 1606.9642

83.0158

0.4711 0.3220 175.9758

8.4261

0.4353

1935.7339 100.0000

Discharging

Table A-16: Overall Results for Discharging Experiment

Factors A

B

Result (Energy, J) C

1

2

3

Mean

59

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

Larger the Better 10 9 8

Energy, J

7 6 5 4 3 2 1 0 A1

A2

B1

B2

Figure A-3: Response Table for Discharging

C1

C2

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

St

65.5578

11.0000

Sm

568.0450

1.0000

ST

633.6029 12.0000

0.5192

8.5558

5.9598

65.5578 100.0000

Investigations on Energy Transfer Efficiency

Charging Experiment 1 to Experiment 4

13.0508

61

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 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

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

63

Initial energy content of flywheel mass @200rpm

156.00 J

Energy loss from flywheel mass:

154.98 J

Percentage of energy transferred:

18.50 %

Experiment 2:


1029.67 rpm


50.73 J


39.77 rpm


6.17 J

Initial energy content of flywheel mass @200rpm:

156.00 J

Energy loss by flywheel mass:

149.83 J


33.86 %

Experiment 3:


656.37 rpm


41.47 J


14.26 rpm


0.79 J


156.00 J

Energy loss by flywheel mass:

155.21 J


26.72 %

Experiment 4:


423.20 rpm

64

Energy gained by KERS flywheel @656.3667rpm

17.24 J


16.34 rpm


1.04 J


156.00 J

Energy loss from flywheel mass:

154.96 J


Discharging Experiment 1 to Experiment 4

11.13 %

65

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 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

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: Energy gained by flywheel [email protected]:

43.22 rpm 7.29 J

67

Rotational speed of KERS flywheel:

1119.11 rpm

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


5.54 %

Experiment 2:

Table A-24: Discharging Experiment 2 Energy Loss Max rotational speed of flywheel mass: Energy gained by flywheel [email protected]: Rotational speed of KERS flywheel:

34.33 rpm 4.60 J 1580.71 rpm


119.54 J


191.37 J

Energy loss from KERS flywheel: Percentage of energy transferred:

71.83 J 6.40 %

Experiment 3:

Table A-25: Discharging Experiment 3 Energy Loss Max rotational speed of flywheel mass:

51.76 rpm

Energy gained by flywheel [email protected]:

10.46 J

Rotational speed of KERS flywheel:

1340.32 rpm


172.93 J


385.04 J


212.11 J


Experiment 4:

4.93 %

68

Table A-26: Discharging Experiment 4 Energy Loss Max rotational speed of flywheel mass: Energy gained by flywheel mass @36.33rpm: Rotational speed of KERS flywheel:

36.33 rpm 5.16 J 1672.65 rpm


269.32 J

Initial energy content of KERS flywheel mass @2000rpm:

385.04 J


115.73 J


4.46 %

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 KERS 2. The moment of inertia of the wooden rotating mass 3. 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. 2. 3. 4.

The KERS was set up according to Figure B-3 The KERS was given an initial rotational speed of 200rpm. The time taken for the system to drop to 100rpm was recorded. 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-4 2. 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. 2. 3. 4.

The KERS was set up according to Figure B-5 The KERS was given an initial rotational speed of 200rpm. The time taken for the system to drop to 100rpm was recorded. 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 Time, s

Max speed, rpm


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


Max speed, rpm


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


Max speed, rpm


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 Time, s

Max speed, rpm


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


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


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

Support Bearing Losses Positioning Bearing Losses Bushing Losses

Deceleration,

Moment of

Torque loss,

rad/s2

inertia, kgm2

Nm

3.17

0.008483

0.016295

1.63

0.008483

0.026824

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,

Torque loss,

Net Torque,

Moment of

rad/s2

Nm

Nm

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).

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 overall efficiency of energy transferred

Calculate for efficiency of energy transferred if mechanical loss was eliminated Figure B-8: Steps in Data Analysis

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 =Iα = (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 – ω12) = 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 – ω02) = 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 20.97 rad/s2

Average Acceleration of KERS 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 %




Time, s

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


625.0 rpm


469.0 rpm

82

Average Time Taken

1.8 s

Average Acceleration of KERS

24.179 rad/s2

Average Torque on KERS

0.1494 Nm


0.0811 Nm


0.2305 Nm


37.31 rad/s2

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


8.438 J


37.0669 J


12.02 %


18.54 %




Time, s

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


649.6 rpm


469.0 rpm

Average Time Taken

1.5 s

83

32.74 rad/s2

Average Acceleration of KERS Average Torque on KERS

0.1234 Nm


0.0811 Nm


0.2048 Nm 54.2693 rad/s2

Compensated Acceleration of KERS Energy Loss by Rotating Mass in 1.3s

40.11 J

Energy Gained by KERS in 1.5s

4.55 J


36.84 rads


7.54 J


32.57 J


11.34 %


18.79 %




Time, s

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


671.0 rpm


607.0 rpm

Average Time Taken Average Acceleration of KERS

1.3 s 45.26 rad/s2

84

Average Torque on KERS

0.0668 Nm


0.05811 Nm


0.1479 Nm


100.22 rad/s2

Energy Loss by Rotating Mass in 1.3 Energy Gained by KERS in 1.3s Total Radians Covered in 1.3s KERS Energy Gained Inclusive Mech Losses Energy Loss Due to Slippage and Wind Percentage of Energy Successfully Transferred Observed Percentage of Compensated Energy Transferred

27.01 J 2.42 J 36.21 rads 5.36 J 21.65 J 8.95 % 19.83 %

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.

Test for Deceleration of Combined System at Position 4 2.1 The KERS was engaged all the time at Position 4 to the wooden rotating 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. 2.4 Steps 2.1 to 2.3 were repeated for 3 times to obtain reliable data.

85

Test for Deceleration of Combined System at with Increasing Moment of Inertia of KERS 3.1 The KERS was engaged all the time at Position 4 to the wooden rotating 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. 3.4 Steps 3.1 to 3.3 were repeated for 3 times to obtain reliable data.

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

2

3

Average

Initial Speed of Whole System, rpm

258.90 257.30 272.75

262.98

Final Speed of Whole System, rpm

128.50 126.00 127.50

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 Test for Deceleration of Combined System at Position 4 1 Initial Speed of Whole System, rpm

2

3

106.75 107.65 112.50

Average 108.97

86


0.00

0.00

0.00

0.00

Time Taken, s

4.16

4.25

3.94

4.12


2.69

2.65

2.99

2.78

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


242.10 271.50 252.15

255.25

Time Taken, s

1.75

1.48

1.60

1.61


8.22

8.28

8.01

8.17

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

15.858

1.856617

Energy Difference, J

87

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

0.959457

Energy Gained including Friction, J

2.816074

Percentage of Energy Transfer Observed, % Percentage of Energy Transferred after Compensation for Mech Loss, %

11.71 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

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 overall efficiency of energy transferred

Calculate for efficiency of energy transferred if mechanical loss was eliminated Figure B-9: Steps for Data Analysis

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 – ω12) = 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 – ω02) = 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 Time Taken

1.8 s

Average Acceleration of Rotating Mass

6.8 rad/s2 37.174 rad/s2

Average Deceleration of KERS Energy Loss by KERS Observed in 1.8s

25.2159 J

Energy Gained by Rotating Mass in 1.8s

2.6311 J


79.9599 rads

Negative Torque to Decelerate KERS Observed

0.3231 Nm


0.4042 Nm

Energy Loss by KERS Including Mech Loss

32.3204 J

Percentage of Energy Successfully Transferred Observed Percentage of Compensated Energy Transferred

10.44 % 8.14 %




Time, s

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


831.4 Rpm


116.8 Rpm

Average Time Taken

1.7 s

Average Acceleration of Rotating Mass

7.006 rad/s2

Average Deceleration of KERS

42.89 rad/s2

Energy Loss by KERS Observed in 1.7s

22.9573 J


2.7059 J


86.63 rads

Negative Torque to Decelerate KERS Observed

0.2703 Nm


0.3515 Nm


30.4486 J

Percentage of Energy Successfully Transferred Observed Percentage of Compensated Energy Transferred

11.79 % 8.89 %




Time, s

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


897.8 Rpm


79.6 Rpm

Average Time Taken Average Acceleration of Rotating Mass

1.6 s 5.2085 rad/s2

Average Deceleration of KERS

53.5540 rad/s2

Energy Loss by KERS observed in 1.6s

16.5302 J


1.2572 J


81.8829 rads

Negative Torque to Decelerate KERS from Observation

0.2035 Nm


0.2846 Nm


23.3052 J


7.60 %


5.39 %

Practicality of New Design KERS in Discharging

Method:

Test for Discharging with Decreasing Moment of Inertia of KERS 1.1 The KERS was engaged all the time at Position 1 to the wooden rotating 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. 1.4 Steps 1.1 to 1.3 were repeated for 3 times to obtain reliable data. 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. 2.3 Steps 2.1 to 2.2 were repeated for 3 times to obtain reliable data.

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

221.00

225.00

219.00

221.67

227.50

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

Initial Speed of Entire System, rpm Maximum Rotational Speed Achieve after Discharging, rpm

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

31.96

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 Rotating Wooden Mass with Initial Rotational Speed Test for Discharging with Decreasing Moment of Inertia of KERS onto Rotating Wooden Mass with Initial Rotational Speed

Wooden Rotating Mass Speed before Engage, rpm Maximum Speed of Wooden Rotating Mass after Discharged, rpm Time Taken, s KERS Initial Rotational Speed, rpm Acceleration Introduced by KERS on Wooden Rotation Mass, rad/ss Initial Energy Content in KERS, J Initial Energy Content in Wooden Rotating Mass, J Maximum Energy Content in Wooden Rotating Mass after Discharged, J

1

2

3

Average

51.50

56.50

49.80

52.60

97.50

112.00

112.00

107.17

1.20

1.43

1.50

1.38

457.00

467.00

460.00

461.33

4.01

4.06

4.34

4.15 9.90 0.55

2.28

Energy Gained by Mass, J

1.73

Percentage of Energy Transferred, %

17.48

Final Year Report: Kinetic Energy Recovery System

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