Mech Project

8/4/2019 Mech Project

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A PROJECT REPORT ON

DESIGN, ANALYSIS AND FABRICATION OF

CHASSIS AND SUSPENSION OF AN ATV

SUBMITTED BY

SANKHALA AMIT PRADEEPKUMAR

UNDER THE GUIDANCE OF

Prof. PAVAN B. CHAUDHARI

IN PARTIAL FULFILLMENT OF REQUIREMENT IN

BACHELORS DEGREE OF

MECHANICAL ENGINEERING

UNIVERSITY OF PUNE

DEPARTMENT OF MECHNICAL ENGINEERING

G.H.RAISONI COLLEGE OF ENGINEERING AND

MANAGEMENT WAGHOLI, PUNE-07


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G.H.RAISONI COLLEGE OF ENGINEERING AND

MANAGEMENT WAGHOLI, PUNE-07.

CERTIFICATE

This is to certify that the Project entitled

DESIGN, ANALYSIS AND FABRICATION OF

CHASSIS AND SUSPENSION OF AN ATV

Submitted by

1. SANKHALA AMIT PRADEEPKUMARis the bonafied work completed in the academic year 2009-10 under my supervisionand guidance in partial fulfillment for award of Bachelors Degree in MechanicalEngineering by the University of Pune.

Place:

Date:

(Prof. PAVAN B. CHAUDHARY) (Dr. D.D.SHAH)

GUIDE PRINCIPAL

(Prof. ABHAY A. PAWAR)

HOD EXTERNAL


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ACKNOWLEDGEMENT

This report is a collection of work done on Design and Fabrication of an

ATV, through the one year of our bachelors studies, and at the Department ofMechanical Engineering until the submission of this report.

I would like to thank some important people who have helped us during this

year.

One person who has inspired and guided us is our Faculty Advisor Prof.

Abhay A. Pawar, for his help and inspirations. Its always been a great pleasure

discussing with him, both our project and career goals. I are indebted to him for all

his suggestions and help in guiding the project, and for the huge support and

positive energy he has given to me. He has always been a great leader and for being

so modest and humble.

I would like to thank Prof. P. B. Choudhari for being a valuable guide, and

for providing the most valuable information for the completion of this report.

Without this information, the completion of report would not be possible. Thanks to

him for his timely guidance, and help in both academic and personal work. Thanksfor all his suggestions.

Other people whom I would like to say special thanks are: Prof. S.V. Patil,

Prof. V. Dange, Prof. Pratik, Prof. Abhijit Patil, and other staff members for their

valuable help and cooperation during the project, without you the work would not

be as fun and inspiring as it was.

My special thanks to Dr. D.D. Shah, Principal of our institute who had beenmeasure source of inspiration, motivation and for all needed support emotionally

and financially.

I would extent my thanks to all of my teammates who have also contributed

for this project and made the competition successful. I would also like to thank our

institute, G.H. Raisoni College Of Engineering And Management for granting funds

for this project and BAJA SAE INDIA organization for providing us valuable

guidelines for the design and testing of our project.


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ABSTRACT

This report explains the insight of dynamics of vehicles for its best

performance and the methodology required to be adopted for the design andfabrication of an All Terrain Vehicle (ATV). Also, it provides the prospects for

determining the appropriate parameters for better performance of an ATV in

rigorous conditions of sandy, muddy racetrack etc. without losing the stability. An

All-Terrain Vehicle (ATV) is defined by the American National Standards Institute

(ANSI) as a vehicle that travels on low pressure tyres, with a seat that is straddled

by the operator, along with handlebars for steering control. As the name suggests, it

is designed to negotiate a wider variety of terrain than most other vehicles.

This project is for study, analysis, design and fabrication of vehicle and to

identify the performance affecting parameters with respect to chassis, suspension,

driveline and its integration in the whole vehicle. It also incorporates the managing

of different manufacturing methodologies, within limited recourses of time,

equipment and money. The study explores the on ground manufacturing difficulties,

methods for identification and implementation of performance improving

parameters in vehicle systems of chassis, suspension and driveline. Also mention

has been made in the report for use of knowledge of basic subjects used in design,

fabrication and testing of the vehicle. ATV was made to run for about 100 km in

rough terrain and its performance found to be satisfactory.


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TABLE OF CONTENT

Acknowledgement iii

Abstract ivList of Figures viii

List of Images x

List of Tables x

Abbreviation xi

Chapter 1 Introduction

1.1. Background of A.T.V.s 011.2. Application of A.T.V.s 011.3. Comparison of A.T.V. and C.V. 021.4. Objective of the project 021.5. Project outline 02

Chapter 2 Literature Review

2.1 Chassis 04

2.1.1. Load on chassis 04

2.1.2. Vehicle and body C.G. 05

2.1.2.1. C.G. and handling properties 05

2.1.2.2. Calculating the vehicle C.G. 05

2.1.2.2.1. C.G. distance to front & rear axle 06

2.1.2.2.2. C.G. height 07

2.2. Suspension system 08

2.2.1. Basic consideration for suspension system 08

2.2.1.1. Vehicle loading 08

2.2.1.2. Rolling 08

2.2.1.3. Brake dip and Squat 08

2.2.1.4. Side thrust 08

2.2.1.5. Road holding 08


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2.2.1.6. Unsprung weight 09

2.2.2. Types of suspensions system used in automobiles 09

2.2.2.1. Dependent suspension system 09

2.2.2.2. Independent suspension system 10

2.2.3. Requirements of suspension system 10

2.2.4. Springs and Dampers 11

2.2.4.1. Important parameters in springs and dampers 11

2.2.4.1.1. Spring rate 11

2.2.4.1.2. Mathematics of the spring rate 12

2.2.5. Wheel rate 12

2.2.6. Roll couple center 13

2.2.7. Weight transfer 13

2.2.8. Unsprung weight transfer 13

2.2.9. Sprung weight transfer 13

2.2.10. Jacking force 14

2.2.11. Travel 14

2.2.12. Damping 14

2.2.13. Camber control 14

2.2.14. Roll center height 14

2.2.15. Instant center 14

2.2.16. Anti-dive and Anti-squat 15

2.2.17. Isolation from high frequency hook 15

2.2.18. Space occupied force distribution 15

2.2.19. Air resistance (Drag) 15

2.2.20. Cost 15

2.3. Tyre and wheels 16

2.3.1. Tyre design 16

2.3.2. Tyre pressure 17

2.4. Elastokinematics 17


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2.4.1. Wheelbase 18

2.4.2. Track 18

2.4.3. Roll center and roll axis 18

2.4.3.1. Roll center 18

2.4.3.2. Method of determining roll center for independent 19

suspension system

2.4.3.2.1. For double wishbone system 19

2.4.3.2.2. Mc. Pherson suspension system 21

2.4.3.3. Roll axis 22

2.4.4. Camber angles 23

2.4.4.1. Camber alteration 24

2.4.5. Caster angles 25

2.4.5.1. Caster and straight running 26

2.4.5.2. Kinematic caster alteration on front wheel travel 28

2.4.5.3. Resolution of vertical wheel force on caster 29

2.4.6. Kingpin inclination and kingpin offset at ground 31

2.4.7. Toe angle 34

2.5. Steering 35

2.6. Driveline 35

2.6.1. Driveline parts 36

2.6.1.1. Engine 36

2.6.1.2. Clutch 36

2.6.1.3. Manual gearbox 36

2.6.1.4. Propeller shaft 36

2.6.1.5. Drive shafts 37

2.6.1.6. Drive shafts 37

2.6.1.7. Brakes 37

2.6.1.8. Wheel 37

2.6.2. Types of drives preferable for A.T.V. 37


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2.6.2.1. Four wheel drive (4WD) 37

2.6.2.1.1. Part-time four wheel drive 37

2.6.2.1.2. All wheel drive 38

2.6.2.2. Two wheel drive (2WD) 38

Chapter 3 Design

3.1. Tyre selection for A.T.V. design 39

3.2. Chassis 40

3.2.1. Determination of center of gravity distance to front 40

and rear axle

3.2.2. Determination of C.G. 41

3.3. Suspension systems 42

3.3.1. Designing of front suspension system 42

3.3.1.1. Determination of length of wishbone 42

3.3.1.2. Calculation of spring 44

3.3.1.3. Shocker mounting support beam 45

3.3.2. Designing of rear suspension system 47

3.3.2.1. Calculation for rear suspension system 47

3.3.2.2. Calculation of spring 49

3.4. Driveline 51

3.4.1. Engine 51

3.4.2. Manual gear box 53

3.4.3. Calculation for traction force and different velocities 54

3.4.4. Drive shafts 57

Chapter 4 Fabrication

4.1. Chassis and roll cage 59

4.2. Front suspension 62

4.2.1. Front wheel hubs 63


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4.2.2. Wishbones 64

4.2.3. Shock absorbers 65

4.3. Engine mounting 66

4.4. Rear engine 67

4.4.1. Rear wheel hubs 67

4.5. Safety accessories 68

4.5.1. Seat mounting 68

4.5.2. Belly Pan 68

4.5.3. Fire wall 68

Chapter 5 Testing analysis

Chapter 6 Cost analysis

Chapter 7 Conclusion & Scope of future work

7.1. Results 76

7.2. Conclusion 78

7.3. Problems noted in the system 78

7.4. Scope for future work 79

References 81


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LIST OF FIGURES

2.1. Determining C.G. of the overall vehicle 05

2.2. Vehicle on weighbridge 07

2.3. Dependent suspension system using leaf spring 09

2.4. Independent suspension system using double wishbone 10

2.5. Design of diagonal ply tubeless car tire 17

2.6. Tyre dimension specified in standard and directives 17

2.7. Path designation on the front axle 18

2.8. Determination of the paths hRo andp by drawing 20

and calculation

2.9. Determination of the body roll centre on parallel 20

double wishbone

2.10. Determination of virtual roll centre of rotation when 21

viewed from the rear

2.11. The body roll centre Ro in Mc Pherson strut 21

2.12. Calculation ofhRo andp in the standard configuration of 22

Mc Pherson strut and strut damper

2.13. Camber angles 23

2.14. Inclination of wheel with the body using independent wheel 24

inclination

2.15. Construction for determination of camber and kingpin 25

inclination on double wishbone

2.16. Construction for determination of camber and kingpin 25

inclination on Mc Pherson strut

2.17. Caster angles 25

2.18. Direction of tractive power 26

2.19. Stabilizing effects of caster 27

2.20. Lateral forces caused by uneven ground 27


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2.21. Caster effect on wind sensitivity of a vehicle 28

2.22. Effect of loading on rear part of vehicle 28

2.23. Effect of parallel axes of rotation on caster 29

2.24. Position of wheel centre when spring is supported 29

2.25. Shift of vertical forces for static observation 30

2.26. Resolving vertical force FZ, W in rear view 30

2.27. Generation of force FT in the rods 31

2.28. Effect of caster on location of force FZ, Wsin 31

2.29. Precise positioning of steer-axis 32

2.30. Inclination angle of kingpin 332.31. Toe angles 34

2.32. Driveline for a rear-drive vehicle 36

3.1. Position of C.G. from front and rear axle 40

3.2. Determination of C.G. height from ground 41

3.3. Graphical determination of roll centre for front double 42

wishbone suspension

3.4. Angular geometry for determination of roll centre height 43

by analytical method

3.5. Cross section of shocker mounting beam 46

3.6. Graphical determination of roll centre for front double 48

wishbone suspension system

3.7. Angular geometry for determination of roll centre by 49

analytical method

3.8. Roll axis position of designed vehicle 49

3.9. Overall dimension of engine 53

3.10. Overall dimension of manual gear box 54

3.11. Schematic layout of clutch and transmission 54

4.1. Drawing for base structure 61

4.2. Drawing for FBM, overhead member of roll cage 62


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4.3. Drawing for RRH of roll cage 62

4.4 Drawing for front axle 63

4.5. Drawing for upper wishbone 64

4.6. Drawing for lower wishbone 64

4.7. Drawing for spring mounting plate and guide 65

4.8. Drawing for fabrication of engine mounting 66

4.9. Drawing for rear wheel hub 67

4.10. Drawing of drive shaft 68


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LIST OF IMAGES

3.1. Tire profile 39

3.2. Lombardini LGA 340 OHC engine 52

4.1. Testing certificate of selected material ASTM 106 Grade B 60

4.2. CATIA model of entire roll cage 62

4.3. Machining of hub on lath machine 63

4.4. CATIA model of helical spring front shocker 65

4.5. Assembly of front suspension system after manufacturing 66

4.6. Assembly of rear suspension, engine and gear box 67

5.1. FEA analysis of roll cage 69

5.2. FEA analysis of front stub axle 70

5.3. FEA analysis of front upper wishbone 70

5.4. Possible deformation of upper wishbone due to forces 71

5.5. FEA possible shocker spring 71

5.6. FEA analysis of shocker mounting bar 726.1. Vehicle before testing 75

6.2. Vehicle after testing 75


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LIST OF TABLES

3.1. Final values obtained for front double wishbone suspension 44

3.2. Final values obtained for front suspension spring 47

3.3. Final values obtained for rear suspension spring 51

3.4. Specification of LGA 340 OHC 51

6.1. Cost Estimation of ATV model 74

7.1. General specification 77


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ABBRIVATIONS

Bo Body centre of gravity

Ro Roll centre

Ufor U r Wheel centre point, front or rear

CG Vehicle centre of gravity

mV, t Gross weight of the vehicle

W Center of tyre contact

Inclination angle of lower control arm (double wishbone orMcPherson axles)

Inclination angle of upper control arm (double wishbone)

q Force lever of vertical force

SUFFIXES

dyn Dynamic

X or x Longitudinal direction

Y or y Lateral direction

Z or z Vertical direction

Ro Body roll center

LENGTHS & DISTANCES

Cr Dynamic rolling circumference at 60 kmh-1

hv Height of the vehicle center of gravity

hRo Height of roll center

r Transverse offset at ground, static

Kingpin inclination angle

Camber angle

Caster angle

Efficiency

d Distance of lower wishbone ball joint from ground

c Length of kingpin

p distance of roll pole from ground


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CHAPTER 1

INTRODUCTION

1.1. BACKGROUND OF ATVS

An All-Terrain Vehicle (ATV) is defined by the American National Standards

Institute (ANSI) as a vehicle that travels on low pressure tires, with a seat that is straddled

by the operator, along with handlebars for steering control. In some vehicles steering

wheel similar to passenger cars is also used. As the name suggests, it is designed to

negotiate a wider variety of terrain than most other vehicles. Although it is a street-legal

vehicle in some countries, it is not legal within most states and provinces of Australia, the

United States and Canada and definitely not in India. By the current ANSI definition, it is

intended for use by a single operator, although a change to include 2-seaters is under

consideration. [9]

The All Terrain Vehicle (ATV) was initially developed in the 1960s as a farm-to-

town vehicle in isolated, mountainous areas. During spring thaws and rainy seasons, steep

mountainous roads were often impassable with conventional vehicles. It soon became a

recreational vehicle however, providing transportation to areas inaccessible by othermotorized transport. Royal Enfield CO built and put on sale a powered Quadra cycle in

1893 that worked in the same way as, and resembles, a modern quad-bike. ATVs were

made in the United States a decade before 3- and 4-wheeled vehicles were introduced by

Honda and other Japanese companies. During the 1960s, numerous manufacturers

offered similar small off-road vehicles that were designed to float and were capable of

traversing swamps, ponds and streams, as well as dry land.

The early ATVs were mainly used for agricultural purpose only. But now thedefinition of ATV is changing. Many countries are allowing ATVs as commercial

vehicle, though with the regulations on its use and safety. Now days, ATVs are generally

used in defense and sports application redefining the ATV. Now the ATVs are also

coming with durable roll cages, added safety of seat and shoulder belts and higher ground

clearance making it more rugged vehicle. The rear cargo deck is more useful for hauling

camping gear, bales of hay, tools and supplies making it suitable for exploring back

country, riding sand dunes, hunting, fishing and camping. ATVs Sport models are builtwith performance, rather than utility, in mind. To be successful at fast trail riding, an


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ATV must have light weight, high power, good suspension and a low center of gravity.

These machines can be modified for such racing disciplines as motocross, woods racing,

desert racing, hill climbing, ice racing, speedway, tourist trophy, flat track, drag racing

and others.

1.2. APPLICATION OF ATVs

Initially the ATVs were solely used for the transportation through the inaccessible

areas, but now these vehicles have found their application in different areas as mentioned

below:

a. In Defense Services like army and air force etc to carry and transport guns, ammunitionand other supplies to remote areas of rough and varied terrain.

b. By railways during construction of railway tracks on mountain or on other rough terrain.c. By police force.d. In sport also like golf for traveling one place to other place.e. In Antarctic bases for research things where use of conventional vehicle is impossible.f. Now a days ATVs are also used in adventuring like mountaineering, in dirt and in snow.

1.3. COMPARISON BETWEEN ATV AND CVAn ATV is made for rough terrain whereas a Conventional Vehicle (CV) is made

for a metal road or may be used on village roads. Hence, an ATV requires a sturdy and

stable design compared to any CV. Although the basic automotive concepts and types of

different subsystems used in an ATV and a CV are similar, these vehicles are

distinguished by the values of different parameters of automobile suspension system, their

steering geometry etc.

It is very essential for an ATV to have very strong and flexible suspension system

in order to sustain the tremendous dynamic forces acting on the vehicle which is quite

large compared to a CV.The main difference that can be observed in an ATV and a CV is

the tires used. These tires are specially meant for ATVs to provide greater amount of

traction to the vehicle in case of sandy, muddy or gravelly terrain. As the ATVs are


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mostly used in places like farms and mountains where large amount of torque is required

rather than mere speed, hence, ATVs are designed for larger torque, less speed and high

ground clearance whereas CVs are designed for speed and passenger comfort for their

transportation through metal roads. The ATVs also possess the ability to travel through

terrains like desert, dirt, sandy and muddy areas unlike any other CV.

1.4. OBJECTIVE OF THE PROJECTThe objective of our project work was to study the static and dynamic parameter

of the chassis, suspension system and driveline of an ATV by determining and analyzing

the dynamics of the vehicle when driving on an off road racetrack. Though, there are

many parameters which affect the performance of the ATV, the scope of this project work

is limited to optimization, determination, design and fabrication of following systems and

to integrate them into whole vehicle systems for best results.

The scope of the project was limited to study, analyze, design, manufacture and

integrate the following systems into main vehicle for best performance.

a. Chassisb. Suspensionc. Driveline

The goals were to identify and optimize the parameters affecting the dynamic

performance above systems within limitations of time, equipment and data from

manufacturer. For better performance a fast, light weight and reliable vehicle is required.

The project was sponsored by BAJA SAE INDIA, under Society of Automotive

Engineers (SAE).

The objective of the project includes:

a. Study the static and dynamic parameters of the chassis.b. Workout the parameters by analysis, design, optimization, fabrication, integration and

testing of chassis.

c. Study of existing suspension systems and parameters affecting its performance.


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d. Determination of design parameters for suspension system, its design, selection of othercomponents, manufacturing, integration and testing of suspension system.

e. Study of driveline, its design, selection, manufacture, integration and testing of driveline.f. Testing vehicle system in rough terrain for about 200 km.

1.5. PROJECT OUTLINEThis section outlines the material presented in each chapter of the report and

provides a general overview of the work. This chapter intends to provide the vision and

objectives which have guided our efforts to build an ATV. All in all, our intentions are to

set the scenario for automotive designing, fabrication and testing procedures.

Chapter two providesgeneral background about vehicle systems. An introduction

to chassis, suspension and driveline design and the important parameters or design factors

that affect them are presented in this chapter. The purpose of this section is to collect

adequate information to understand the working of different systems in the vehicle and

parameters affecting their performance. Some of the important concepts that will be

important to this work will be introduced.

Chapter three outlines the important design constraints and requirements of

important dimensions for manufacturing. Detailed calculations for these constraints are

presented. Chapter 3 also identifies and selects values of parameters which affect the

vehicle performance.

Chapter four summarizes the manufacturing methods and discusses the

fabrication of the vehicle.

Chapter five is a summary of the results of testing of the project vehicle.

Chapter six presents the cost analysis the project. It also provides the overview on

method employed for cost reduction.

Chapter seven presents the conclusions.


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CHAPTER 2

LITERATURE REVIEW

An Automobile has different components, also called as main units. These units

further comprise of subassemblies. They are as follows:

a. The Basic Structure: It consists of the frame, the suspension system, axels, wheels andtires.

b. The Power Plant: The power plant (engine) provides the motive power for all thefunctions which the vehicle or any part of it, may be called upon to perform.

c. The Transmission System: It consists of a clutch, a gear box giving four or even sixdifferent ratios of torque output to torque input, driving shafts to transmit torque to

wheels.

d. The Auxiliaries: It is consists of battery, generator, the starter, ignition system etc.e. The Controls: The controls consist of Steering system and Brakes.f. The Superstructure: It is the body attached to the frame, which prevents intrusion of

foreign particles inside. [6]

2.1. CHASSIS

The chassis of an automobile consists of following components suitably mounted:

a. Engineb. Transmission systemc. Suspension systemd. Road wheelse. Steering systemf. Brakes


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2.1.1. Loads on the Chassis

a. Weight of the vehicle and driver, which causes vertical bending of the side members.b. Vertical loads when the vehicle comes across a bump or hollow, which result in

longitudinal torsion due to one wheel lifted (or lowered) with other wheels at the usual

road level.

c. Loads due to road camber, side wind, cornering force while taking a turn which result inlateral bending of side members.

d. Load due to wheel impact with road obstacles may cause that particular wheel to remainobstructed while the other wheel tends to move forward, distorting the frame to

parallelogram shape.

e. Engine torque and braking torque tending to bend the side members in the vertical plane.2.1.2. Vehicle and Body Centre of Gravity

2.1.2.1. Centre Of Gravity And Handling Properties

The following are important variables considered in chassis design in vehicle

engineering:

a. Vehicle centre of gravity CGb. Body (sprung-mass) centre of gravity Boc. Axle (unsprung mass) centers of gravity Ufor Ur

Low centers of gravity are always desirable, as they are associated with fewer

driving dynamic problems and increased vehicle performance during cornering andbraking, but in practice the design options are relatively restricted. [2]

2.1.2.2 Calculating the Vehicle Centre Of GravityCalculating the position of the centre of gravity is likely to be possible only with

great difficulty and considerable effort. If the vehicle and all its individual components

are shown on a computer in the form of a digital model including body surfaces and

properties (digital surfaced model), modern CAE tools make it possible to calculate the

position of the centers of gravity of the components and the whole vehicle.


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Figure 2. 1: Designation of the paths for determining the centers of gravity CG of the overall vehicle and B o

of the body. The centers of gravity Uf and Ur of the front and rear axles can be regarded as being in the

centers of the wheels.

It is much simpler to determine the position experimentally by weighing. For this,

the empty vehicle should be observed and when it is occupied by driver (approximately

170 cm tall and weighing around 68 kg).

2.1.2.2.1 Centre of Gravity Distance to Front and Rear AxleFigure 2.1 contains the paths and angles necessary for calculating the centers of

gravity. When the vehicle is weighed, it must be standing on a completely horizontal

plane and with each axle on a weighbridge. So as not to distort the weighbridge, it must

be possible to turn the wheels freely. The weighed front axle load mV, f and the rear axle

load mV, r give the total weight mV, t of the vehicle:

(2.1)The balance of moments around mV, for mV, r, in conjunction with the wheelbase l

in the longitudinal direction, gives the centre of gravity distances lf to the frontand lr to

the rear axle:

(2.2)


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If the lateral distance of the centre of gravity (y-direction) from the vehicle centre-

line is required, the wheel loads must be weighed to be able to calculate first of all the

lateral offset of the centers of the front and rear axles from the centre-line via similar

equations made up from the rear view, and then similarly for the vehicle centre of gravity

from the top view. [2]

2.1.2.2.2. Centre of Gravity HeightTo calculate height of center of gravity (hV), first the front and then the rear axle

must be lifted as high as possible (by the amount h) with an elevating mechanism (auto

hoist, jack, crane), with the other axle standing in the centre of a weighbridge (Fig. 2.2).

The following would need to be ensured:

a. The vehicle must be prevented from falling off by inserting wedges from the outside onthe axle to be raised. The brake must be released and the gearbox must be in neutral. It

must be possible to turn the wheels on the platform easily; the platform would otherwise

distort and the result will be imprecise.

b. The wheels are held still on the centre of the platform; the vehicle forward movementmust be even when the vehicle is raised, in order to prevent wrong measured values as a

result of different force application positions on the horizontal surface.

c. If the change in axle load during lifting is measured by means of a crane over a load cell,it is possible to ensure that the direction of lifting is completely vertical.

d. The vehicle should be in the on-road condition, i.e. full tank, tools, spare wheel, etc.e. Both axles must be prevented from compressing or rebounding before the vehicle is

raised.

f. To eliminate tire springing during the measurement, it is recommended that the tirepressure on both axles be increased to 3.0 to 3.5 bar.

Mathematical observation of the measurement is as follows (Fig. 2.2):

The angle is known; but is sought, whereby


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To be able to determine lr, the equation of moments produced around the centre

of the front axle is set up:

( ) ( )Eliminating cos

( ) whereas

Therefore,

Hence

Figure 2. 2:Vehicle on a weighbridge with forces and paths for deriving the equation for vehicle centre of

gravity height hV included.

(2.3)In Equation 2.3 the angle can be expressed through the easily measurable

vehicle stroke height h and so the equation can be simplified:

(2.4)


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Where, rdyn is dynamic rolling radius given by,

rdyn = Cr/2

With m/h or m/tan there is a constant in the equation. When it is weighed, in

each instance, only the changes caused by the vehicle lifting on one side, namely m and

the raised dimension h, need to be determined. The other values such as wheelbase l,

vehicle weight mV,t and the dynamic rolling radius rdyn remain the same. The centre of

gravity height is required for calculating various vehicle conditions, i.e. for the travelling

vehicle, so the dynamic rolling radius rdyn of the tyre must be added to hV and not the

somewhat lower static rolling radius that only applies to the standing vehicle. [2, 3]

2.2. SUSPENSION SYSTEMThe suspension of vehicles needs to satisfy a number of requirements which

depend on different operating conditions of the vehicle (loaded/unloaded,

acceleration/braking, level/uneven road, straight running/ cornering). Suspension systems

serve a dual purpose contributing to the vehicle's handling and braking for good active

safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably

well isolated from road noise, bumps, and vibrations. The suspension also protects the

vehicle itself and mounted systems from damage and wear.

Suspension is the term given to the system comprise of springs, shock absorbers

and linkages that connects a vehicle to its wheels. The design of front and rear suspension

of a vehicle may be different.

2.2.1. Basic Consideration for Suspension System

2.2.1.1. Vertical Loading

When the road wheel comes across the bump or a pit on the road it is subjected to

vertical forces (tensile or compressive) depending on the load irregularity which are

absorbed by the elastic compression, shear, bending, twisting properties of spring. To

reduce the pitching tendency of the vehicle, the front system should be less springing than

the rear suspension system.


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2.2.1.2.Rolling

The center of gravity (C.G.) of the vehicle is considerably above the ground. As a

result while taking turns the centrifugal force acts outwards on the C.G. of vehicle, while

the load resistance acts inwards at the wheels. This give rise to a couple turning the

vehicle about the longitudinal axis called rolling.

2.2.1.3.Brake Dip and Squat

On applying brakes the nose of the vehicle dips which depends on the position of

C.G. relative to the ground, wheel base and other suspension characteristics. This

phenomenon is called as dip. In the same way the torque loads during acceleration tend to

lift the front of vehicle. This effect is called as squat.

2.2.1.4.Side Thrust

Centrifugal force during cornering, crosswinds, cambering of the road causes side

thrust.

2.2.1.5.Road Holding

The degree to which vehicle maintains the contact with the road surface in various

types of directional changes as well as in straight line motion is called as road holding.

2.2.1.6.Unsprung Weight

Unsprung weight is the weight of the vehicle components between suspension and

road surface (Rear axle assembly, steering knuckle, front axle, wheels). [6]

2.2.2. Types of Suspension System used in AutomobilesSuspension systems can be broadly classified into two subgroupsDependent and

Independent.

2.2.2.1. Dependent Suspension System

A dependent suspension normally has a beam or live axle that holds wheels

parallel to each other and perpendicular to the axle with the help of leaf springs to it. In

dependent suspension system when the camber of one wheel changes, the camber of the

opposite wheel changes in the same way (by convention, on one side this is a positivechange in camber and on the other side this a negative change). Depending on the


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location of system of linkages, the dependent suspension systems have various

configurations as:

a. Satchell linkb. Panhard rodc. Watt's linkaged. WOBLinke. Mumford linkagef. Live axleg. Twist beamh. Beam axle

Dependent suspension system assures constant camber, it is most commonly used

in vehicles that need to carry large loads.

Figure 2. 3:Dependent suspension system using leaf spring

2.2.2.2. Independent Suspension System

In an independent suspension system wheels are allowed to rise and fall on their

own without affecting the opposite wheel by using kinematic linkages and coil springs.

Suspensions with other devices, such as anti-roll bars that link the wheels are also


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classified in independent suspension system. The various independent suspension systems

are:

a. Double wishbone suspensionsb. McPherson struts and strut dampersc. Rear axle trailing-arm suspensiond. Semi-trailing-arm rear axlese. Multi-link suspension

In this type of suspension system, the wheels are not constrained to remain

perpendicular to a flat road surface in turning, braking and varying load conditions;

control of the wheel camber is an important issue.

In double wishbone and multi-link system we can have more control over the

geometry of system than swing axle, McPherson strut or swinging arm because of the

cost and space requirements. [2]

Figure 2. 4: Independent suspension system using Double wishbone

2.2.3. Requirements of Suspension Systema. Independent movement of each of the wheels on an axle


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b. Small, unsparing masses of the suspension in order to keep wheel load fluctuation as lowas possible

c. The introduction of wheel forces into the body in a manner favorable to the flow of forcesd. The necessary room and expenditure for construction purposes, bearing in mind the

necessary tolerances with regard to geometry and stability, ease of use

e. Behavior with regard to the passive safety of passengers and other road usersf. To preserve stability of the vehicle in pitching and rolling while in motiong. Cost

2.2.4. Spring and DampersMost suspensions use springs to absorb impacts and dampers (or shock absorbers)

to control spring motions. Traditional springs and dampers are referred to as passive

suspensions. If the suspension is externally controlled then it is a semi-active or active

suspension.

Semi-active suspensions include devices such as air springs and switchable shock

absorbers, various self-leveling solutions, as well as systems like Hydro pneumatic,

Hydromantic, and Hydra gas suspensions. Mitsubishi developed the worlds first

production semi-active electronically controlled suspension system in passenger cars; the

system was first incorporated in the 1987 Gallant model.

Fully active suspension systems use electronic monitoring of vehicle conditions,

coupled with the means to impact vehicle suspension and behavior in real time to directly

control the motion of the car.

With the help of control system, various semi-active/active suspensions could

realize an improved design compromise among different vibrations modes of the vehicle,

namely bounce, roll, pitch and warp modes. However, the applications of these advanced

suspensions are constrained by the cost, packaging, weight, reliability, and/or the other

challenges.

Interconnected suspension, unlike semi-active/active suspensions, could easily

decouple different vehicle vibration modes in a passive manner. The interconnections can

be realized by various means, such as mechanical, hydraulic and pneumatic. Anti-rollbars are one of the typical examples of mechanical interconnections, while it has been


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stated that fluidic interconnections offer greater potential and flexibility in improving

both the stiffness and damping properties.

The leading / trailing swinging arm, fore-aft linked suspension system together

with inboard front brakes had a much smaller unsprung weight than existing coil spring or

leaf designs. The interconnection transmitted some of the force deflecting a front wheel

up over a bump, to push the rear wheel down on the same side. When the rear wheel met

that bump a moment later, it did the same in reverse, keeping the car level front to rear.

The springing balance (which expresses how well the front and rear axles are

matched to one another) also needs to be taken into consideration. If a vehicle does not

pitch when it goes over bumps in the ground, but instead moves up and down in parallel

translation, it has a good springing balance. [1]

2.2.4.1.Important Parameters in Spring and Dampers

2.2.4.1.1. Spring RateThe spring rate (or suspension rate) is a component in setting the vehicle's ride

height or its location in the suspension stroke. Vehicles which carry heavy loads will

often have heavier springs to compensate for the additional weight that would otherwise

collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used inperformance applications when the suspension is constantly forced to the bottom of its

stroke causing a reduction in the useful amount of suspension travel which may also lead

to harsh bottoming.

Springs that are too hard or too soft will both effectively cause the vehicle to have

no suspension at all. Vehicles that commonly experience suspension loads heavier than

normal have heavy or hard springs with a spring rate close to the upper limit for that

vehicle's weight. This allows the vehicle to perform properly under a heavy load when

control is limited by the inertia of the load. Riding in an empty truck used for carrying

loads can be uncomfortable for passengers because of its high spring rate relative to the

weight of the vehicle. A race car would also be described as having heavy springs and

would also be uncomfortably bumpy. A luxury car, taxi, or passenger bus would be

described as having soft springs. Vehicles with worn out or damaged springs ride lower to

the ground which reduces the overall amount of compression available to the suspension

and increases the amount of body lean. Performance vehicles can sometimes have spring

rate requirements other than vehicle weight and load. [1]


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2.2.4.1.2. Mathematics of the Spring RateSpring rate is a ratio used to measure how resistant a spring is to being

compressed or expanded during the spring's deflection. The magnitude of the spring force

increases as deflection increases according to Hooke's Law. Briefly, this can be stated as,

Where,

Fis the force the spring exerts

kis the spring rate of the spring.

x is the displacement from equilibrium length i.e. the length at which the spring is

neither compressed or stretched.

Spring rate is confined to a narrow interval by the weight of the vehicle, the load

the vehicle will carry, and to a lesser extent by suspension geometry and performance

desires.

Spring rates typically have units of N/mm. A non-linear spring rate is one for

which the relation between the spring's compression and the force exerted cannot be fitted

adequately to a linear model. The spring rate of a coil spring may be calculated by a

simple algebraic equation or it may be measured in a spring testing machine. The spring

constant kcan be calculated as follows:

Where, dis the wire diameter, G is the spring's shear modulus (e.g., about 80 GPa

for steel), andNis the number of wraps andD is the diameter of the coil. [11]

2.2.5. Wheel RateWheel rate is the effective spring rate when measured at the wheel. Wheel rate is

usually equal to or considerably less than the spring rate. Commonly, springs are mounted

on control arms, swing arms or some other pivoting suspension member. The wheel rate

is calculated by taking the square of the ratio (0.5625) times the spring rate. Squaring the

ratio is because the ratio has two effects on the wheel rate. The ratio applies to both the

force and distance traveled.


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Wheel rate on independent suspension is fairly straight-forward. However, special

consideration must be taken with some non-independent suspension designs. Yet because

the wheels are not independent, when viewed from the side under acceleration or braking

the pivot point is at infinity (because both wheels have moved) and the spring is directly

in line with the wheel contact patch. The result is often that the effective wheel rate under

cornering is different from what it is under acceleration and braking. This variation in

wheel rate may be minimized by locating the spring as close to the wheel as possible.

2.2.6. Roll Couple PercentageRoll couple percentage is the effective wheel rates, in roll, of each axle of the

vehicle as a ratio of the vehicle's total roll rate. Roll Couple Percentage is critical in

accurately balancing the handling of a vehicle.

A vehicle with a roll couple percentage of 70% will transfer 70% of its sprung

weight at the front of the vehicle during cornering.

2.2.7. Weight TransferWeight transfer during cornering, acceleration or braking is usually calculated per

individual wheel and compared with the static weights for the same wheels. Cornering

wheel weights requires knowing the static wheel weights and adding or subtracting the

unsprung, sprung and jacking forces at each wheel.

2.2.8. Unsprung Weight TransferUnsprung weight transfer is calculated based on the weight of the vehicle's

components that are not supported by the springs. This includes tires, wheels, brakes,

spindles, half the control arm's weight and other components. These components are then

(for calculation purposes) assumed to be connected to a vehicle with zero sprung weight.

They are then put through the same dynamic loads. The weight transfer for cornering in

the front would be equal to the total unsprung front weight times the G-Force times the

front unsprung center of gravity height divided by the front track width. The same is true

for the rear.


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2.2.9. Sprung Weight TransferSprung Weight Transfer is the weight transferred by only the weight of the vehicle

resting on the springs not the total vehicle weight. Calculating this requires knowing the

vehicles sprung weight (total weight less the unsprung weight), the front and rear roll

center heights and the sprung center of gravity height (used to calculate the roll moment

arm length). Calculating the front and rear sprung weight transfer will also require

knowing the roll couple percentage.

The roll axis is the line through the front and rear roll centers that the vehicle rolls

around during cornering. The distance from this axis to the sprung center of gravity

height is the roll moment arm length. The total sprung weight transfer is equal to the G-

force times the sprung weight times the roll moment arm length divided by the effective

track width. The front sprung weight transfer is calculated by multiplying the roll couple

percentage times the total sprung weight transfer.

2.2.10.Jacking ForcesJacking forces can be thought of as the centripetal force pushing diagonally

upward from the tire contact patch into the suspension roll center. The front jacking force

is calculated by taking the front sprung weight times the G-force times the front rollcenter height divided by the front track width. The rear is calculated the same way except

at the rear.

2.2.11.TravelTravel is the measure of distance from the bottom of the suspension stroke to the

top of the suspension stroke. Bottoming or lifting a wheel can cause serious control

problems or directly cause damage. "Bottoming" can be the suspension, tires, fenders, etc.running out of space to move the body or other components of the car hitting the road.

The control problems caused by lifting a wheel are less severe if the wheel lifts when the

spring reaches its unloaded shape than they are if travel is limited by contact of

suspension members.

2.2.12.DampingDamping is the control of motion or oscillation, as seen with the use of hydraulic

gates and valves in a vehicles shock absorber. This may also vary, intentionally or


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unintentionally. Like spring rate, the optimal damping for comfort may be less than for

control.

Damping controls the travel speed and resistance of the vehicles suspension. An

undamped car will oscillate up and down. With proper damping levels, the car will settleback to a normal state in a minimal amount of time. Most damping in modern vehicles

can be controlled by increasing or decreasing the resistance to fluid flow in the shock

absorber.

2.2.13.Camber ControlA tire wears and brakes best at -1 to -2 degrees of camber from vertical.

Depending on the tire, it may hold the road best at a slightly different angle. Small

changes in camber, front and rear, are used to tune handling.

2.2.14.Roll Center HeightThis is important to body roll and to front to rear roll moment distribution.

However, the roll moment distribution in most cars is set more by the antiroll bars than

the RCH. It may affect the tendency to roll over.

2.2.15.Instant CenterA tire's force vector points from the contact patch of the tire through a point

referred to as the "instant center". This imaginary point is the effective geometric point at

which the suspension force vectors are transmitted to the chassis. Another way of looking

at this is to imagine each suspension control arm mounted only at the frame. The axis that

the arm rotates around creates an imaginary line running through the vehicle. Forces, as

far as suspension geometry are concerned, are transmitted either along this axis (usually

front to rear) or through this axis at a right angle (usually right to left and intersects the

ball joint). When force lines of the upper and lower control arms intersect, where they

cross is the Instant Center. The Instant Centers when viewed from the front or side may

not seem to have much of a relation to each other until you imagine the points in three

dimensions. Sometimes the Instant Center is at ground level or at a distant point due to

parallel control arms.

The instant center can also be thought of as having the effect of converting

multilink suspension into a single control arm which pivots at the Instant Center. This is


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only true at a given suspension deflection, because an unequal length, multi-link system

has an instant center that moves as the suspension is deflected.

2.2.16.Anti-Dive and Anti-SquatAnti-dive and anti-squat are expressed in terms of percentage and refer to the front

diving under braking and the rear squatting under acceleration. They can be thought of as

the counterparts for braking and acceleration as jacking forces are to cornering. The main

reason for the difference is due to the different design goals between front and rear

suspension, whereas suspension is usually symmetrical between the left and right of the

vehicle.

Anti-dive and anti-squat percentage are always calculated with respect to a

vertical plane that intersects the vehicle's center of gravity The anti-dive is the ratio

between the height of where the tire force vector crosses the center of gravity plane

expressed as a percentage. An anti-dive ratio of 50% would mean the force vector under

braking crosses half way between the ground and the center of gravity. Anti-squat is the

counterpart to anti-dive and is for the rear suspension under acceleration. Anti-dive and

anti-squat may or may not be desirable depending on the suspension design.

2.2.17.Isolation from High Frequency Shock

For most purposes, the weight of the suspension components is unimportant, but

at high frequencies, caused by road surface roughness, the parts isolated by rubber

bushings act as a multistage filter to suppress noise and vibration better than can be done

with only the tires and springs.

2.2.18.Space Occupied Force DistributionDesigns differ as to how much space they take up and where it is located. It is

generally accepted that MacPherson struts are the most compact arrangement for front-

engine vehicles, where the wheels is required to place the engine.

2.2.19.Air Resistance (Drag)Certain modern vehicles have height adjustable suspension in order to improve

aerodynamics and fuel efficiency. And modern formula cars, that have exposed wheels

and suspension, typically use streamlined tubing rather than simple round tubing for theirsuspension arms to reduce drag. Also typical is the use of rocker arm, push rod, or pull


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rod type suspensions, that among other things, places the spring/damper unit inboard and

out of the air stream to further reduce air resistance.

2.2.20.CostProduction methods improve, but cost is always a factor. The continued use of the

solid rear axle, with unsprung differential, especially on heavy vehicles, seems to be the

most obvious example. [5]

2.3. TIRES AND WHEELSThe tires are crucial functional elements for the transmission of longitudinal,

lateral and vertical forces between the vehicle and road. The tire properties should be as

constant as possible and hence predictable by the driver. As well as their static and

dynamic force transmission properties, the requirements described below depending on

the intended use of the vehicleare also to be satisfied.

Selecting the right tires for the ATV is not difficult if we know what we are

looking for, there are some important things to consider in order to make the best

selection, doing a wrong selection can kill the fuel economy, decrease performance and

possibly damage the vehicle.Tread pattern is one of the most important things to consider, there are several

patterns like mud tires, trail tires, sand tires and race tires. It is needed to analyze first

what type of terrain the vehicle will drive in most, in order to select best performing tires

for that particular terrain. Since, the ATV is meant to drive in all kinds of terrains, an

aggressive all terrain tires should be the best.

The all terrain tires come in two patterns, flat and round. Flat tires have more

treads to the ground, and in the other hand round tires can increase the vehicle speed. But

the round tires also have a tendency to roll under during hard cornering, while the flat tire

"puts more rubber to the track".

Then comes the problem with the choice between the tall tire and the short tire,

the a tall tire will lift the ATV higher off the ground and give a softer ride, but on the

other hand a tall tire has more sidewall flex which will give the ATV a feeling of being

loose during hard cornering. Whereas a short tire gives more stability during hard


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cornering and high speeds, but gives less ground clearance and makes the ride a little

bumpier.

Things to remember while selecting ATV tires:

a. Ride Comfort: These tires ride exceptionally smooth on pavement and dirt roads. Theyalso absorb the impact of rocks and other obstacles very well. The driver should feel

comfortable and safe while driving the vehicle.

b. Steering/Handling: These tires steer effortlessly and track well over the trail, but theyare a little sensitive to uneven surfaces, tending to follow small ruts and grooves etc.

c. Puncture Resistance: Puncture resistance should be very high as this vehicle is going torun through rough terrains, water, mud and many such adverse conditions. Also small bitsof gravel caught between the tire bead and rim should be cleaned periodically as it causes

to lose all air minimizing life of the tire.

d. Mud Traction: Mud traction is as expected, pretty good for a multi-purpose tire.e. Sand/loose dirt track traction: This is where these tires really shine, especially in very

steep terrain. The soft tread cleats that wrap around the tire shoulders and flexible tire

construction combine to grab nicely on to most dirt/rocky trail conditions i.e. it should

have very high sand tracks in order to deal with the muddy tracks. [2, 6]

2.3.1. Tire DesignCross-ply tires consist of the substructure (also known as the tire carcass, Fig. 2.5)

which, as the supporting framework has at least two layers of rubberized cord fibers,

which have a zenith or bias angle of between 20 and 40 to the centre plane of the tire.

Rayon (an artificial silk cord), nylon or even steel cord may be used, depending on the

strength requirements. This represents the frictional connection to the rim. On tubeless

tires the bead must provide the airtight seal.


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Figure 2. 5: Design of a diagonal ply tubeless car tire with a normal drop rim and pressed-in inflating valve

2.3.2. Tire Pressures. Since, ATVs are intended to ride on muddy and sandy areas, where the grip

provided by the road surface is relatively less; the tire pressure recommended is in the

range 15 PSI to 20 PSI. Sometimes depending on the terrain, the tire pressure of 13 PSI is

also recommended by the manufacturers.

Figure 2. 6: Tyre dimensions specified in standards and directives. B is the cross-section width of the new

tire; the tread molding is not included in the dimension. The tire radius, dependent on the speed, is

designated r.


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2.4. ELASTOKINEMATICSElastokinematics defines the alterations in the position of the wheels caused by

forces and moments between the tires and the road or the longitudinal movement of the

wheel, against suspension anchorage required to prevent compliance, kinematics changes.

2.4.1. WheelbaseThe wheelbase l, measured from the centre of the front to the centre of the rear

axle (Fig 2.1), is an important variable in the vehicles ride and handling properties.

The short body overhangs to the front and rear, reduce the tendency to pitch

oscillations and make it possible to fit soft springing, normally associated with a high

level of ride comfort. A short wheelbase, on the other hand, makes cornering easier, i.e.

gives a smaller swept turning circle for the same steering input.

2.4.2. TrackThe track bfis measure of centre distance between two front wheels or two rear

wheels.

When the wheels travel in bump and rebound-travel direction, the track changeson almost all independent wheel suspensions, which may be unavoidable if a higher body

roll centre is necessary. However, the track size alteration causes the rolling tire to slip

and, on flat cross-sections in particular, causes lateral forces, higher rolling resistance and

deterioration in the directional stability of the vehicle, and may even influence the

steering.

When the wheels travel in bump and rebound-travel direction, the track changes

on almost all independent wheel suspensions, which may be unavoidable if a higher body

roll centre is necessary. However, the track size alteration causes the rolling tire to slip

and, on flat cross-sections in particular, causes lateral forces, higher rolling resistance and

deterioration in the directional stability of the vehicle, and may even influence the

steering.


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Figure 2. 7: Path designations on the front axel

2.4.3. Roll Centre and Roll Axis2.4.3.1.Roll Centre

The roll center of a vehicle is the imaginary point at which the cornering forces in

the suspension are reacted to the vehicle body.

There are two definitions of roll center. The most commonly used is the geometric

(or kinematics) roll center, whereas the Society of Automotive Engineers uses a forcebased definition.

"The point in the transverse vertical plane through any pair of wheel centers at

which lateral forces may be applied to the sprung mass without producing suspension

roll".

The roll centers are also defined as the instant center of rotation of the chassis

relative to the ground when both suspensions of the same axle are regarded as planar

mechanisms.

Load transfer is of critical importance for vehicle stability in vehicle such as

ATVs. Ideally in high performance applications load transfer tends to be minimized as a

tires performance is directly affected by the amount of load that it has to transmit. In a

steady state turn the final load transfer, summed across all the axles, is only related to the

position of the center of mass above the ground, the track width and the lateral

acceleration. ATVs must shift their center of mass lower level or decrease their lateral

acceleration to avoid tipping. To keep them from tipping the tires used are with lower grip


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which reduces the vehicles cornering capacity, or another option is altering the roll

stiffness balance from front to rear, to encourage under steer or over steer as necessary to

limit the maximum lateral acceleration of the vehicle.

The geometric roll center of the vehicle can be found by following basic

geometrical procedures when the vehicle is static. However, when the vehicle rolls the

roll centers migrate. The rapid movement of roll centers when the system experiences

small displacements can lead to stability problems with the vehicle. The roll center height

has been shown to affect behavior at the initiation of turns such as nimbleness and initial

roll control.

2.4.3.2.Method of Determining the Roll Center for Independent Suspension System

2.4.3.2.1. For Double Wishbone SystemThe height of the (instantaneous centre of rotation) P determines the position of

the body roll centre Ro (Figure 2.8)

From figure 2.8, the roll center height can be calculated by formula, [2]

Where,

As it can be seen in figure 2.8, for double wishbone suspension only the position

of the control arms is important. The lines connecting the inner and outer control arm

pivots need to be extended to fix virtual centre of rotation P and, at the same time, its

height p.


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Figure 2. 8: Determination by drawing and calculation of the paths hRo and p on double wishbonesuspensions and a multi-link as well as longitudinal transverse axes.

Figure 2. 9:Determination of the body roll centre on parallel double wishbones; the virtual centre of rotation

is at infinity.

P linked with the centre of tire contact W gives the body roll centre Ro in the

intersection with the vehicle centre plane. In the case ofparallel control arms, P is at

and a line parallel to them needs to be drawn through W (Figure 2.9). Where the virtual

centre of rotation is a long way from the wheel centre of contact, it is recommended that

the distances p and hRo be calculated using the formulae listed above.

Steering control arm axes of rotation, which are sloped when viewed from theside, need E1 and G1 to be moved perpendicularly up or down (Figure 2.10). The points


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E2 and G2 obtained in this way linked with E1 and G1 when viewed from the rear

give the virtual centre of rotation P, and the line from this axis to the centre of tire contact

(as shown in Figure 2.8) gives the body roll centre.

Figure 2. 10: If the suspension control arm axes of rotation are at an angle to one another when viewed from

the side, a vertical should first be drawn to the ground through the points E 1 and G1; the intersections with

the axes of rotation C1C2 and D1D2 yield the points E2 and G2, needed for determining the virtual centre of

rotation when viewed from the rear.

2.4.3.2.2. For McPherson Suspension SystemOn McPherson struts, or strut dampers, a vertical must be created in the body side

fixing point E to the centre line of the shock absorber piston rod, and the lower steeringcontrol arm must be extended. The intersection of the two lines will then give point P. [8]

On the McPherson strut, the height of the body roll centre can only be influenced

by placing the lower suspension control arm at an angle and only marginally by changing

the angle between steering axis EG and the McPherson strut centre line (Figure 2.12),

which is a disadvantage of this type of suspension.

Figure 2. 11: The body roll center Ro in McPherson strut


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The Roll Center Height can be calculated as, [2]

Where,

Figure 2. 12: Calculation of the paths hRo andp in the standard configuration of a McPherson strut and strut

damper

2.4.3.3.Roll Axis

Traditionally the vehicle has been assumed to roll about a roll axis which has

been defined as an axis joining two imaginary points, the roll centers of the front and

rear suspensions.

The roll axis is the line about which the chassis (or car body) rolls when a force

(or a pure rolling moment) acts on the car body from the side (which is what happens, for

instance, when the car enters a turn). Or the roll axis is the set of the chassis points where

a lateral force can be applied without producing any roll movement of the chassis itself.


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The roll axis is determined as the line going through the front and rear roll centers

of a car. In the general, the roll axis is determined by introducing the ensuing

simplifications:

a. The front and rear parts of the car are considered separately. Each semi-vehicle iscomposed of a part (front or rear) of the chassis, together with the suspensions of the

corresponding axle.

b. Any pitch rotation of the chassis of a semi-vehicle is neglected, so that a transversevertical plane pt fixed to the chassis of the semi-vehicle and going through the centers of

the wheels at the reference configuration of the vehicle keeps vertical when the chassis

moves with respect to the ground.

c. The spatial kinematic chains of the suspensions connecting the chassis to the two hubcarriers of any semi-vehicle are considered as planar (even though they are actually not),

the plane of motion being pt.

d. The two wheels of any semi-vehicle are supposed as rigid and of infinitesimal thickness.e. The toe and steering angles of the wheels are neglected, so that the points of contact

between the two wheels of a semi-vehicle and the ground always lie on plane pt.

f. The mutual distance of the contact points between the two wheels of a semi-vehicle andthe ground is considered as constant.

2.4.4. Camber AngleCamber angle is the angle made by the wheel of an automobile; that is, it is the

angle between the vertical axis of the wheel and the vertical axis of the vehicle when

viewed from the front or rear. If the top of the wheel is farther out than the bottom (that

is, away from the axle), it is called positive camber; if the bottom of the wheel is farther

out than the top, it is called negative camber.

Camber angle alters the handling qualities of a particular suspension design.

Negative camber improves grip when cornering. This is because it places the tire at a

more optimal angle to the road, transmitting the forces through the vertical plane of the

tire, rather than through a shear force across it. Another reason for negative camber is that

a rubber tire tends to roll on itself while cornering. If the tire had zero camber, the inside


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edge of the contact patch would begin to lift off of the ground, thereby reducing the area

of the contact patch. By applying negative camber, this effect is reduced, thereby

maximizing the contact patch area. Note that this is only true for the outside tire during

the turn; the inside tire would benefit most from positive camber.

Figure 2. 13: Camber Angle

On the other hand, for maximum straight-line acceleration, the greatest traction

will be attained when the camber angle is zero and the tread is flat on the road. Proper

management of camber angle is a major factor in suspension design, and must incorporate

not only idealized geometric models, but also real-life behavior of the components; flex

distortion, elasticity, etc.

In cars with double wishbone suspensions, camber angle was usually adjustable,

but in newer with McPherson strut suspensions, it is normally fixed. While this may

reduce maintenance requirements, if the car is lowered by use of shortened springs, this

changes the camber angle (as described in McPherson strut) and can lead to increased tire

wear and impaired handling. For this reason, for better handling the car should not only

lower the body, but also modify the mounting point of the top of the struts to the body to

allow some inward/outward (relative to longitudinal centerline the of vehicle) movement

for camber adjustment. Aftermarket plates with slots for strut mounts instead of just holes

are available for most of the commonly modified models of cars. Off-Road vehicles such

as agricultural tractors, ATVs generally use positive camber. In such vehicles, the

positive camber angle helps to achieve a lower steering effort.


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2.4.4.1. Camber alteration

The designers tend to design the suspension on cars such that the wheels go into

negative camber as they travel in bump and into positive camber as they rebound.

From a construction point of view, the camber alteration on the front wheels can

easily be determined as a function of the wheel travel over the angle of alteration of

the kingpin inclination if elasticitys are ignored. On double wishbone suspensions, arcs

with the suspension control arm lengths e andfmust be drawn around the points C and D

(in other words the suspension control arm axes of rotation) and, in the normal position,

the centers of the outer ball joints marked as points 1 and 2 (Figure 2.15). A point 3 is

determined on the upper arc and an arc with the path 1, 2 drawn around it to give point 4.

The line connecting them, 3, 4 then has the alteration angle to the path 1, 2 if the

wheel compresses by the path s1. If it goes into negative camber (as in the example), then

must be subtracted from the camber angle wo, in the normal position, i.e.

In the case of positive camber, would have to be added:

Figure 2. 14: In independent wheel suspensions, the wheels incline with the body when the vehicle is

cornering. To even this out, the wheels, in bump travel, should go into negative camber and the rebounding

ones into positive camber.

On McPherson struts and strut dampers, the distance 1, 2 is shortened when thewheel is in bump travel; the upper mounting point is in the wheel house and only the


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lower point 2 moves to 3. are again the angle between the two connecting lines.

Figure 2. 15:Construction determination of the kingpin inclination alteration on double wishbones which

is equal to the camber alteration.

Figure 2. 16:Construction for determining the camber and kingpin inclination alteration on the McPherson

struts and strut damper

2.4.5. Caster AngleCaster angle is the angular displacement from the vertical axis of the suspension

of a steered wheel in a vehicle, measured in the longitudinal direction. It is the angle

between the pivot line (in a car - an imaginary line that runs through the center of the

upper ball joint to the center of the lower ball joint) and vertical.


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Figure 2. 17: Caster Angle

As shows in figure, caster angle is angle between center plane of wheel (AA) and

line joining two pivot points E and G.

The pivot points of the steering are angled such that a line drawn through them

intersects the road surface slightly ahead of the contact point of the wheel. The purpose of

this is to provide a degree of self-centering for the steering - the wheel casters around so

as to trail behind the axis of steering. This makes a car easier to drive and improves its

directional stability (reducing its tendency to wander). Excessive caster angle will make

the steering heavier and less responsive, although, in racing, large caster angles are used

to improve camber gain in cornering. Caster angles over 10 degrees with radial tires are

common. Power steering is usually necessary to overcome the jacking effect from the

high caster angle.

The steering axis (the dotted line in the diagram above) does not have to pass

through the center of the wheel, so the caster can be set independently of the mechanical

trail, which is the distance between where the steering axis hits the ground, in side view,

and the point directly below the axle. The interaction between caster angle and trail is

complex, but roughly speaking they both aid steering, caster tends to add damping, while

trail adds 'feel', and return ability. In the extreme case the system is undamped but stable,

as the wheel oscillates around the 'correct' path. Complicating this still further is that the

lateral forces at the tire do not act at the center of the contact patch, but at a distance

behind the nominal contact patch. This distance is called the pneumatic trail and varies

with speed, load, steer angle, surface, tire type, tire pressure and time. A good starting

point for this is 30 mm behind the nominal contact patch.


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2.4.5.1.Caster and straight running

Caster can be compared with the tea trolley effect, where the pulled wheel takes

on the direction of pull and the wheel centre adopts a position behind the axis of rotation

1 (Figure 2.18). The tensile force and the opposed force FR generated by the rolling

resistance are on an effective line, in other words in a stable ratio to one another because

the guiding and wheel axis lie behind one another. The same effect also exists (despite

kingpin offset and kingpin inclination) on the wheels of a vehicle if these can be rotated

around axes. The wheels are set to caster on both sides and are linked by tie rods.

Figure 2. 18: If the rolling resistance force FR acts behind the steering axis 1, the wheel follows in a stable

manner in the direction in which it is pulled.

Figure 2. 19: When the vehicle is travelling in a straight line, caster has a stabilizing effect.


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Figure 2. 20: Lateral forces FY,W,fcaused by uneven ground, in conjunction with the caster moment-arm n,k

cause the forces FT in the tie rods.

If unevenness in the road surface or a steering input pushes the wheels out from

the straight-ahead direction, by the angle , the rolling resistance components FRsin (as

shown in Figure 2.19) move both wheels back via the force lever n,k(or the overall lateral

force lever n,t) until they roll in a straight line again. The components FRcos (left and

right) compensate and only subject the tie rods to pressure.

On a vehicle moving in a straight line, caster would not only have advantages but

also disadvantages. Uneven road surfaces cause alternating lateral forces on the centers of

tire contact and these, together with the lever in n,k (orn,t) cause moments around the

steering axis (Figure 2.20), which are supported on the tie rods and can cause steering

disturbances and vibrations.


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Figure 2. 21: Caster can increase the wind sensitivity of a vehicle. The point at which the wind acts is usually

in front of the centre of gravity V, a moment arises which seeks to turn the vehicle and causes the wheels to

steer in the same direction.

Furthermore, there is increased wind sensitivity due to the fact that a wind force

acting on the body (Figure 2.21) causes lateral forces FY, W in the opposite direction, on

the centers of tire contact. In addition, the front forces FY,W,f together with the caster

moment-arm n,k (or n,t) result in moments that turn the vehicle in the direction of the

wind, i.e. further in the direction in which the body is already being pushed by the wind.

This also applies to driving on (diagonally) inclined roads and leads to increased steering

moment.

2.4.5.2. Kinematic caster alteration on front-wheel travel

If two or three people are seated in the back, or the boot at the back of the vehicle

is loaded, it is a very different story. The rear axle springing complies more strongly than

that of the front axle and the bodys position, which was almost parallel to the ground,

alters by Bo, t = 1 to 2 (Figure 2.22). The caster angle increases by the same amount

something which designers should bear in mind when specifying axle settings. Theincrease in the caster angle under load is likely to be the main reason why the steering is

heavier on a fully laden vehicle even though this sometimes causes the front axle load to

be reduced. An alteration in caster has its disadvantages, as this in turn causes the self-

righting torque to alter, but it is unavoidable if the brake dive on the front axle is to be

kept within limits by means of vehicle pitch poles.


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Figure 2. 22: When loaded, the body tail sinks further than the front; the caster angle increases by its angle

alteration Bo,t

Figure 2. 23: On most double wishbone suspensions, the axes of rotation 1 and 2 are parallel to one another;

in such cases, caster does not change when the wheels compress and rebound.

On double wishbone suspensions, the axes of rotation 1 and 2 of the two

suspension control arms are usually parallel to one another (Figure 2.23); in the standard

configuration of the McPherson strut and strut damper there is a right angle between the

centre line of the damping part and suspension control arm. In such cases regardless of

the position of the compressed or rebounded wheel the caster is retained. This is not the

case where there are different angles between the suspension control arm axes of rotation,

or the damper centre and suspension control arm.

2.4.5.3. Resolution of the vertical wheel force on caster

If the steering axis EG on a double wishbone suspension is angled by the caster

angle , the lower ball joint lies in front of the wheel centre and the upper one behind it. If

the spring is supported on the lower suspension control arm, its force FG,z may be the


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same size as the vertical wheel force less the weight of the axle side (Figure 2.24), but the

momentMZ = FG,z (f- e) occurs, causing the forces FE,x and FG,x. The compliance present

causes the caster angle to reduce. If the spring were on the top, it would increase.

Figure 2. 24: If the spring is supported on the lower suspension control arm and if the front axle has caster,

the supporting ball joint will be in front of the wheel centre.

Figure 2. 25: For static observation, the vertical force FZ, W must be shifted to the wheel axis and resolved into

its components. The distance to the steering axis is equivalent to the vertical force lever q, the size of which

depends on the kingpin offset rand the angle .


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Figure 2. 26: If the steering axis is at the caster angle in the side view, the vertical force component FZ,W

cos calculated in the rear view in Fig. 2.25 must be further resolved.

Where there is caster (Case 1), the vertical force component FZ,W cos , shown in

Figure 2.25, would be further resolved by the angle , i.e. in FZ,W cos cos and FZ,W cos

sin (Figure 2.26). The last component tensions the wheels via the lever q at the front

(Figure 2.27). If the caster angles on the left and right wheels are different, the same will

apply to the tensioning forces, i.e. the vehicle could deviate from the direction of travel if

the steering wheel were let go, and would pull to one side when held. A 2 difference

means that there is a 3040 N higher tie rod force on the side with the greater angle . If

the caster is achieved by relocating the wheel centre to the back (Case 2), the component

FZ,W sin pushes the wheels together at the front via the force lever n (Figure 2.28), i.e.

even here the parallel position of the left and right steering axes to one another plays a

role.


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Figure 2. 27: The forces FZ,Wcos sin push the front wheels together at the front via the levers q (i.e. into

toe-in) both when the vehicle is in a stationary position and moving in a straight line, and generate the

forces FTin the tie rods.

Figure 2. 28: With caster achieved by setting the wheel centre back, the vertical force component FZ, Wsin

comes to be located behind the steering axis.

2.4.6. Kingpin Inclination and Kingpin Offset at GroundAccording to ISO 8855, the kingpin inclination is the angle which arises

between the steering axis EG and a vertical to the road (Figure 2.29). The kingpin offset

is the horizontal distance r from the steering axis to the intersecting point of line NN in

the wheel centre plane with the road.

Larger kingpin inclination angles are necessary to give the vehicle a small or

negative kingpin offset. In commercial vehicles, tractors and building-site Lorries, the

inclination of the kingpin is often equivalent to the angle , whereas the wheels are

controlled by ball joints on the front axles of passenger cars. On double wishbone

suspensions, the steering axis therefore goes through the centers of the ball sockets E and

G indicated (Figure 2.29); the engineering detail drawing must show the total angle of

camber and kingpin inclination.

The McPherson strut and strut damper have a greater effective distance between

the lower ball joint G and the upper mounting point E in the wheel house; however, the

upper axle parts are next to the wheel, so attention should be paid to creating enough

clearance for the rotating tire (possibly for snow chains). As a result, a higher inclination

of the steering axis and a higher angle has to be accepted. In addition, as can be seen in

the illustrations, point G has been shifted to the wheel to obtain a negative kingpin offset.The steering axis then no longer matches the centre line of the suspension strut. Due to


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the relationship between camber and kingpin inclination shown in Figure 2.29, the angle

does not need to be tolerance on double wishbone suspensions.

Figure 2. 29: The precise position of the steer axis also known as kingpin inclination axis can only be

determined if the centre points E and G of the two ball joints are known. The total angle of kingpin

inclination and camber ( + w) must also be included when dimensioning the steering knuckle as an

individual part.

The permissible deviations on the overall angle W+ are given in the detailed

drawing of the steering knuckle. If the camber has been set correctly on this type of

suspension, the kingpin inclination angle will also be correct.

However, the important thing is (as specified in the camber tolerance) that the

deviation between left and right does not exceed 30, otherwise the steering could pull to

one side if the caster angle on the left- and right-hand sides.

On McPherson struts and strut dampers, the steering knuckle is usually bolted to

the damping unit. In this case there may be play between the bolts and holes or the

position may even be used for setting the camber. In this case it is sensible to tolerance

the kingpin inclination angle because, provided the camber is correct, the kingpin

inclination does not have to be.


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There is also a direct correlation between the alteration to camber and kingpin

inclination when the wheels bump and rebound. The aim is to make the compressing

wheel go into negative camber, as this leads to small changes in camber at body roll, but

an increase in kingpin inclination by the same angle. Strictly speaking, the calculation by

drawing of the camber alteration, shown in Figure 2.15 relates to the kingpin inclination,

and for this reason the angle alteration is also entered.

To obtain the self-aligning torque MZ,W,Z which is important for righting, the

vertical force FZ,W, which is always present on the centre of tire contact, must, for static

consideration, be shifted up to the wheel axis and resolved there in the direction of the

steering axis:

FZ, W cos and, vertical to it, FZ,W sin (Figure 2.25 and 2.30)

The steering lever or vertical force lever q at the resolution point is:

(2.5)The equation will apply provided that cos W = 1, a condition that applies to

normal camber angles. If the vehicle has caster, the force components FZ,W sin must be

further resolved by the angle . The parameterrdyn can be calculated using Equation,

rdyn = Cr/2

When the wheels are turned, the force FZ,Wsin is at the angle to the wheel axis

and the component FZ,W sin sin will, with smaller steering angles, give the

approximate righting moment based on the whole axle;


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Figure 2. 30: The negative kingpin offset reduces the vertical force lever q. However, its length is one of the

determining factors in the self-aligning torque MZ,W,Z. To maintain its level, the kingpin inclination angle

would have to be increased.

Mean steering angle,

and The exact solution has to take the changing kingpin inclination angle (due to

lateral forces when the wheels are turned and due to the body roll) into account as well as

the positive and negative caster that occurs. The influence of the paths r , T and rT in the

tire contact area also has to be considered. Both can have a significant influence on the

size of MZ, W, Z during cornering. On the outside of the bend, the lateral force FY,W,O

reduces the kingpin offset by rT(or causes it to become more negative) whereas on the

inside of the bend, it increases or becomes less negative.

There is also a load alteration during cornering, whereby FZ,W,f,o > FZ,W,f,i and also

i and o are not always of the same size, so that different moments always occur on

individual wheels. The kingpin offset r, which appears in Equation 2.5, influences the

level of the self-aligning torque MZ,W,Z; if this offset is large, the righting increases, if r

decreases or even becomes negative (owing to the shorter lever q), the moment reduces

(Figure 2.30). The moreMZ,W,Z increases, the more the front axle becomes longitudinally


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sensitive. There is, therefore, a clear tendency towards a small positive or negative

kingpin offset.

IfMZ,W,Z is to remain at the same level, the kingpin inclination angle has to be

enlarged with the disadvantage that, when the wheels are turned, the wheel on the outside

of the bend goes in the more positive camber direction, which makes more space

necessary because the brake disc has to be shifted into the disc wheel. With a given path

r 1, the necessary angle 1 can be calculated from the existing values r(in mm) and 0;

Where,

2.4.7. Toe Angle

In automotive engineering, toe is the symmetric angle that each wheel makes with

the longitudinal axis of the vehicle, as a function of static geometry, and kinematic and

compliant effects.

Positive toe, or toe in, is the front of the wheel pointing in towards the centerline

of the vehicle. Negative toe, or toe out, is the front of the wheel pointing away from the

centerline of the vehicle. Toe can be measured in linear uni

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