Electromagnetic Shock Absorber

ELECTROMAGNETIC SHOCK ABSORBER

PROJECT REPORT

Submitted by

AJITH ARAVIND (AXAKEME002)

JESBIN JOHNSON (AXAKEME018)

VINOD K J (AXAKEME035)

VISHNU T SAJEEVAN (AXAKEME038)

in partial fulfillment for the award of the degree

of

BACHELOR OF TECHNOLOGY

in

MECHANICAL ENGINEERING

AXIS COLLEGE OF ENGINEERING & TECHNOLOGY,

AMBANOLY

2014

Project ’14 Electromagnetic Shock Absorber

ii

Dept of Mechanical Engg AXISCET

DEPARTMENT OF MECHANICAL ENGINEERING

CERTIFICATE

This is to certify that the Project titled

ELECTROMAGNETIC SHOCK ABSORBER

was prepared and presented by

AJITH ARAVIND (AXAKEME002)

JESBIN JOHNSON (AXAKEME018)

VINOD K J (AXAKEME035)

VISHNU T SAJEEVAN (AXAKEME038)

of the Eighth Semester Mechanical Engineering

in partial fulfillment of requirement for the award of

Degree of Bachelor of Technology in Mechanical Engineering under the

University of Calicut during the year 2010-2014

PROJECT GUIDE HEAD OF THE DEPARTMENT


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ACKNOWLEDGEMENT

We express our deep sense of gratitude and indebtedness to Asst Prof. Manu

Mohan Nair, Head of Department, Mechanical Engineering for his valuable

advice, constant encouragement, for being our internal guide in the design and

implementation of our project, constructive criticism during the course of the

project and also during the preparation of this manuscript.

We are highly indebted to the staff members of Mechanical Department,

especially Asst.Professors Jineesh.V.V, Clint.K.S, Joffin Jose, Midhun Joy,

Ridhik Radh for their wholehearted support and co-operation.

We also express our indebt thanks to our Mechanical workshop

superintendent Mr.Velayudhan, and trade instructors Mr.Sooraj and Mr.Jacob, for

their helpful mind during the work.

We also express our sincere thanks to all the classmates for their support

and co-operation in completing the project work.

Above all, we should express our supreme gratitude to almighty God.


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ABSTRACT

A shock absorber in common parlance (or damper in technical use) is a

mechanical device designed to smooth out or damp sudden shock impulse and

dissipate kinetic energy. It is analogous to a resistor in an electric circuit. Shock

absorbers must absorb or dissipate energy. One design consideration, when

designing or choosing a shock absorber is where that energy will go.

Magnetic shock absorber is an advanced area that can be used to absorb

the heavy shock loads which will occur in automobiles. In magnetic shock

absorber, repulsive forces from same poles of permanent magnets/electro magnets

are used for absorbing the heavy shock loads. Two magnets are fixed permanently

in top and bottom end cover of the magnetic shock absorber. Another one magnet

is mounted on the movable rod. This magnet will move up and down vertical

direction with the rod. All magnets are fixed like same poles are facing each other.

This will help to create the repulsive force for absorbing the shock.

Top end cover is fixed with body of the vehicle by using bolt connections

and movable rod is fixed at the end with the axle of the vehicle. When the vehicle

experiences the sudden shock, movable rod slides vertically inside the cylinder

along with the magnet. The same poles of the fixed and movable magnets are

creating the strong repulsive force. This repulsive force is used for absorbing the

heavy shock load and magnetic shock absorber will act as a damping device for

vehicle. When the heavy shocking load decreases, the movable magnet comes into

the original position. The variable magnet movement depends on the magnitude of

the shock load. In this way, this magnetic shock absorber absorbs the heavy load

in the vehicle.

High grade “Neodymium” [NdFeB] materials are available, having good

magnetic property. Along with stainless steel can used for other components in

the magnetic shock absorber. This non magnetic stainless steel will not disturb the

magnetic field and magnets inside the shock absorber. The non-magnetic material

will hold the magnet in both the sides.


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TABLE OF CONTENT

CHAPTER TITLE PAGE

ACKNOWLEDGEMENT iii

ABSTRACT iv

LIST OF TABLES vii

LIST OF FIGURES vii

1 INTRODUCTION 1

1.1 Different shock absorbers in use 3

1.2 Types of suspension system 5

1.2.1 Rigid axle front suspension 5

1.2.2 Independent front suspension 6

1.2.3 Torque rod 8

1.2.4 Stabilizer 8

1.3 Permanent magnetic shock absorber 8

2 LITERATURE REVIEW 12

2.1 Investigations of shock absorber 12

2.2 MR Fluids 17

2.3 Concept & modelling eddy current damper 18

2.4 Design considerations 20

2.4.1 Manufacturability 20

2.4.2 Cost 20

2.4.3 Durability 21

2.4.4 Heat dissipation 21

2.4.5 Assembly/Disassembly considerations 21

2.4.6 Sealing 21

2.5 Theoretical Approaches 22

3 PROBLEM STATEMENT 25


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4 COMPONENTS AND DESCRIPTION 27

4.1 Mechanical components 27

4.1.1 Frame structure 27

4.1.2 Cylinder and piston 27

4.1.3 Permanent magnet 30

4.1.4 Coil spring 35

4.2 Electrical components 38

4.2.1 Battery 38

4.2.2 Electromagnet 40

5 RESULTS AND DISCUSSIONS 52

5.1 Electromagnetic force 53

5.2 Repulsive force between magnets 54

5.3 Critical damping coefficient 55

5.4 Design of shock absorber 55

5.5 Billing 57

6 SCOPE AND FUTURE OF PROJECT 58

REFERENCES 60


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LIST OF TABLES

Table Number TITLE PAGE

4.1 Physical properties of neodymium magnet 34

4.2 Battery specifications 39

5.1 Billing table 57

LIST OF FIGURES

Figure Number TITLE PAGE

1.1 Telescopic shock absorber 2

1.2 Schematic Representation 9

1.3 Magnetic Shock Absorber with Regeneration11

2.1 Force vs. Peak Velocity at A Constant

Frequency of 20 Hz 14

2.2 MR Effects 18

2.3 Velocity Profiles across the Annular Duct 18

2.4 Illustration of Arrangement

of Magnetic Field 19

4.1 Cylinder top view 28

4.2 Cylinder top and cover 28

4.3 Piston 29

4.4 Neodymium magnet 32

4.5 Coil spring 36

4.6 Battery 39

4.7 Magnetic wire 41

4.8 Typical EI lamination 46

4.9 Electromagnet 49

5.1 Shock absorber attached on frame 52

5.2 Repulsion of magnets 53

5.3 Piston and cylinder view 55

5.4 Damper 56


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CHAPTER I

INTRODUCTION

A shock absorber in common parlance (or damper in technical use) is a

mechanical device designed to smooth out or damp sudden shock impulse and

dissipate kinetic energy. It is analogous to a resistor in an electrical circuit.

Shock absorbers must absorb or dissipate energy. One design

consideration, when designing or choosing a shock absorber is where that energy

will go. In most dashpots, energy is converted to heat inside the viscous fluid. In

hydraulic cylinders, the hydraulic fluid will heat up. In air cylinders, the hot air is

usually exhausted to the atmosphere. In other types of dashpots, such as

electromagnetic ones, the dissipated energy can be stored and used later.

Shock absorbers are an important part of automobile and motorcycle

suspensions, aircraft landing gear, and the supports for many industrial machines.

Large shock absorbers have also been used in structural engineering to reduce the

susceptibility of structures to earthquake damage and resonance.

Shock absorbers, linear dampers, and dashpots are devices designed to

provide absorption of shock and smooth deceleration in linear motion

applications. They may be mechanical (e.g., elastomeric or coil spring) or rely on

a fluid (gas, air, hydraulic), which absorbs shock by allowing controlled flow from

outer to inner chamber of a cylinder during piston actuation. In conventional

shock absorbers the piston rod is typically returned to the unloaded position with a

spring. Shock absorbers typically contain either a fluid or mechanical dampening

system or a return mechanism to the unengaged position. They vary from small

device application to large industrial and civil engineering uses. Linear dampers is

an inclusive term that can be applied to many forms of dashpots and shock

absorbers; typically used for devices designed primarily for reciprocating motion

attenuation rather than absorption of large shock loads. Dashpots are typically

distinct in that while they use controlled fluid flow to dampen and decelerate

motion, they do not necessarily incorporate an integral return mechanism such as

a spring. Dashpots are often relatively small, precise devices used for applications.


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Fig No 1.1 Telescopic Shock Absorber

Shock absorbers or damper types for shock absorbers, linear dampers and

dashpots can be hydraulic, air, gas spring, or elastomeric. The absorption or

damping action can be compression or extension. Important parameters to

consider when searching for shock absorbers, linear dampers and dashpots include

absorber stroke, compressed length, extended length, maximum force, and

maximum cycles per minute. Absorber or spring stroke is difference between fully

extended and fully compressed position. Compressed length is the minimum

length of shock (compressed position). Extended length is the maximum length of

shock (extended position). The maximum rated force for shock absorber or

damper, referred to as the force. The maximum cycles per minute are the rated

frequency of compression or extension.

Important physical specifications to consider when searching shock

absorbers, linear dampers and dashpots include the cylinder diameter or maximum

width, the rod diameter, mounting, and body material. The cylinder diameter or

maximum width refers to the desired diameter of housing cylinder. The rod

diameter refers to the desired diameter of extending rod. Mounting choices

include ball and socket, rod end, clevis, eyelet, tapered end, threaded, and bumper


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or rod end unattached. Choices for body materials include aluminum, steel,

stainless steel, and thermoplastic.

Common features for shock absorbers, linear dampers and dashpots

include adjustable configuration, reducible, locking, and valve. An adjustable

configuration allows the user to fine tune desired damping, either continuously or

at discrete settings. A reducible shock absorber, linear damper or dashpot has an

adjustment style for gas shocks in which gas is let out to permanently reduce force

capacity. In a locking configuration the position can be locked at ends or in the

middle of stroke. Valves can be included for fluid absorbers, a valve or port,

which can be used to increase or decrease fluid volume or pressure.

1.1 DIFFERENT SHOCK ABSORBERS IN USE

1. There are several commonly-used approaches to shock absorption:

2. Hystersis of structural material, for example the compression of rubber

disks, stretching of rubber bands and cords, bending of steel springs, or

twisting of torsion bars. Hysteresis is the tendency for otherwise elastic

materials to rebound with less force than was required to deform them.

Simple vehicles with no separate shock absorbers are damped, to some

extent, by the hysteresis of their springs and frames.

3. Dry friction as used in wheel brakes, by using disks (classically made of

leather) at the pivot of a lever, with friction forced by springs. Used in

early automobiles. Although now considered obsolete, an advantage of this

system is its mechanical simplicity; the degree of damping can be easily

adjusted by tightening or loosening the screw clamping the disks, and it

can be easily rebuilt with simple hand tools. A disadvantage is that the

damping force tends not to increase with the speed of the vertical motion.

4. Solid state, tapered chain shock absorbers, using one or more tapered, axial

alignment(s) of granular spheres, typically made of metals such as nitinol,

in a casing.


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5. Fluid friction, for example the flow of fluid through a narrow orifice

(hydraulics), constitutes the vast majority of automotive shock absorbers.

An advantage of this type is that using special internal valving the absorber

may be made relatively soft to compression (allowing a soft response to a

bump) and relatively stiff to extension, controlling “jounce”, which is the

vehicle response to energy stored in the springs; similarly, a series of

valves controlled by springs can change the degree of stiffness according

to the velocity of the impact or rebound. Some shock absorbers allow

tuning of the ride via control of the valve by a manual adjustment provided

at the shock absorber. In more expensive vehicles the valves may be

remotely adjustable, offering the driver control of the ride at will while the

vehicle is operated. The ultimate control is provided by dynamic valve

control via computer in response to sensors, giving both a smooth ride and

a firm suspension when needed. Many shock absorbers contain

compressed nitrogen, to reduce the tendency for the oil to foam under

heavy use. Foaming temporarily reduces the damping ability of the unit.

Another variation is the magneto rheological damper which changes its

fluid characteristics through an electromagnet.

6. Compression of a gas, for example pneumatic shock absorbers, which can

act like springs as the air pressure is building to resist the force on it. Once

the air pressure reaches the necessary maximum, air dashpots will act like

hydraulic dashpots. In aircraft landing gear air dashpots may be combined

with hydraulic damping to reduce bounce. Such struts are called oleo struts

(combining oil and air).

7. Magnetic effects. Eddy current dampers are dashpots that are constructed

out of a large magnet inside of a non-magnetic, electrically conductive

tube.

8. Inertial resistance to acceleration, for example prior to 1966 the Citroen

2cv had shock absorbers that damp wheel bounce with no external moving

parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight

inside a vertical cylinder and are similar to, yet much smaller than versions

of the tuned mass dampers used on tall buildings


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9. Composite hydro-pneumatic devices which combine in a single device

spring action, shock absorption, and often also ride-height control, as in

some models of the Citroen automobile.

10. Conventional shock absorbers combined with composite pneumatic

springs with which allow ride height adjustment or even ride height

control, seen in some large trucks and luxury sedans such as certain lincoln

and most land rover automobiles. Ride height control is especially

desirable in highway vehicles intended for occasional rough road use, as a

means of improving handling and reducing aerodynamic drag by lowering

the vehicle when operating on improved high speed roads.

1.2 TYPES OF SUSPENSION SYSTEM

1.2.1 RIGID AXLE FRONT SUSPENSION

It shows a typical rigid axle font wheel suspension. This type of suspension was

universally used before the introduction of independent front wheel suspension. It

may use either two longitudinal leaf spring, or on transverse spring, usually in

conjunction with shock absorbers. These assemblies are mounted similarly to rear

leaf spring suspensions.

In this type of suspension, the front wheel hubs rotate on anti – fiction

bearings on steering spindles, which are attached to the steering knuckles. To

permit the wheels to be tuned by the steering gear, the steering spindle and the

steering knuckle assemblies are hinged on the axle ends. The pin that forms the

pivot of this hinge is usually referred to as the kingpin or steering knuckle pin.

Where the forked portion is integral with the steering knuckle and fits over the end

of the axle, the construction is known as reverse Elliot. In Elliot type construction,

the ends of the axle are forked to hold the steering knuckle extension between the

ends.


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1.2.2 INDEPENDENT FRONT SUSPENSION

In the independent type of front suspension, a coil, torsion bar or leaf spring

independently supports each front wheel. Almost all the passenger cars now use

the independent front suspension, in which the coil spring arrangement is the most

common.

There are three types of coil spring front suspension:

1. In the first type, the coil spring is located in between the upper and lower

control arms. The lower control arm has one point attachment to the car

frame.

2. In the second type, the coil spring is located in between the upper and

lower control arms. The lower arms have two points to attachment to the

car frame.

3. In the third type, the coil spring is between the upper control arm and

spring tower or housing that is part of the front – end sheet – metal work.

Other types of front suspension, besides coil spring type, are also in use.

The twin I – beam construction is another type, used on some models of Ford

trucks. Each front wheel is supported at the end by a separate I – beam. The ends

of the I – beams are attached to the frame by pivots.

The wheel ends of the two I – beams are attached to the frame by radius

arms, which prevent backward or forward movement of the wheels. This type of

suspension provides more flexibility. Single I – beam front suspension is used in

larger trucks. The I-beam has a hole in each end through which a kingpin is

assembled to hold the steering knuckle in place. Each end of the I-beam is

supported by a leaf spring.

In this type of suspension system, a steel rod, known as a torsion bar, act

as a spring to hold the upper and lower control arms parallel under load. The front

end of the rod is of hexagonal shape to fit tightly into an opening in the lower


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control arm. Its rear reaction is also of the hexagonal shape to fit tightly into an

opening in an anchor attached to the frame cross member.

A seal hides the hexagonal shaped end of the torsion bar. The torsion bar

twisted due to the forces on the wheel assembly outer end of the lower control

arm. The torsion bar is designed to balance these forces so that the lower arm is

kept at a designated height. The height can be adjusted by a tightening mechanism

at the anchor end, which twists the rod by means of an adjusting bolt and swivel.

A strut rod is used to keep the suspension in alignment.

This type of suspension is able to cushion road shocks by causing the

lower arm to twist the torsion bar. When the wheels are no larger under stress, the

arm returns to normal. It simplifies the independent front suspensions using coil,

torsion bar and leaf spring. Basically, the system is known as parallelogram type

independent front suspension. It consists of an upper and lower link connected by

the stub axle carrier. In general, the lower link is larger than the upper and they

may not be parallel. This arrangement maintains the track width as the wheel rise

and fall and so minimize tyre wear caused by the wheel scrubbing sideways.

Strut and link type suspension system is particularly for integral body

construction, because the loading points are widely spaced. The normal top link is

replaced by a flexible, mounting, and a telescopic damper acts as the kingpin. This

system, known as the Mac Pherson system has little rolling action and absorbs

shocks readily.

Trailing arm independent front suspension maintains constant track and

wheel attitude with a slight change in wheelbase and caster angle. A coil spring is

attached to the trailing arm which itself is attached to the shaft carrying the wheel

hub. When the wheel moves up and down, it winds and unwinds the spring. A

torsion bar has also been used in certain designs in place of the coil spring.

In sliding type suspension system, the stub axle can move up and down as

well as rotate in the frame members. Track, wheel attitude and wheelbase remain

unchanged throughout the rise and fall of the wheel.

In vertical guide suspension system, the kingpin is attached directly to the

cross member of the frame. It can slide up and down, thus compressing and

expanding the springs.


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1.2.3 TORQUE ROD

The torque rod is used to maintain correct alignment of the axle with the frame. It

also serves to remove all the stresses on the springs. One end of the torque rod is

rigidly fixed to the axle or axle housing, and the other end is attached to the frame

by means of a pivoted mounting. The torque rod is also known as torque rod.

1.2.4 STABILIZER

A stabilizer or a sway bar, is necessarily is used in all independent front-end

suspension. It reduces the tendency of the vehicle to roll or tip on either side when

taking a turn. This tendency has been increased due to the use of softer springs

and independent front-end suspension.

A stabilizer is simply a bar of alloy steel with arms at each end connected

to the lower wishbone of the independent suspension or axle. It is supported in

bush bearings fixed to the frame, and is parallel to the cross member.

When both the wheels deflect up or down by the same amount, the

stabilizer bar simply turns in the bearings. When only one wheel deflects, then

only one end of the stabilizer moves, thus twisting the stabilizer bar, which acts as

a spring between the two sides of the independent suspension. In this way, the

stabilizer reduces heeling or tipping of the vehicle on curves.

1.3 PERMANENT MAGNET SYSTEM SHOCK ABSORBER

A permanent magnetic suspension apparatus for maintaining a spaced

relationship between a first movable member and a second fixed member, wherein

the motion of the movable member requires dampening, cushioning, stabilizing,

harmonic balancing, and/ or reflexive re-centring.

The suspension apparatus includes a plurality of sets of permanent

magnets located within a case, which is coupled to one of the members. The sets

of permanent magnets are coupled to an elongated support member, which is


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couple to the second member. The support member extends within the case, with

the support member and the case being adapted for relative axial movement.

The sets of permanent magnets are arranged in bidirectional repulsion

configuration with additional magnet fixed within the case. The sets of permanent

magnets are being moved relative to the fixed permanent magnets, such that the

magnetic forces of repulsion produced by the permanent magnets are increased in

response to relative movement between the support member and the case, creating

dampening, cushioning, stabilizing, harmonic balancing, and/or re-centring forces.

Fig No 1.2 Schematic Representation

In one embodiment, the control mechanism is coupled between the frame

of a vehicle and a wheel support assembly. The permanent magnetic suspension

apparatus, however, is for use with any type of equipment or machinery having a

movable and non-movable, or fixed, member. This includes, but is not limited to,

cars, trucks, motorcycles, scooters, all terrain vehicles, semi-tractors, semi-trailers,

and the like, as well as, but not limited to, industrial equipment and machinery,

hospital and office machinery and equipment, such as being coupled between the

frame of an office chair and the chair seat.

A regenerative electromagnetic shock absorber comprising: a linear

electromagnetic generator comprised of a central magnet array assembly

comprising a central magnet array comprised of a plurality of axially-aligned,

stacked cylindrical magnets having like magnetic poles facing one another, a

plurality of high magnetic permeability, high saturation magnetization, central


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cylindrical spacers positioned at each end of stacked central magnet array and

between adjacent stacked central magnets, and a magnet array support for

mounting magnets and spacers. An inner coil array comprising a plurality of

concentric cylindrical coil windings positioned adjacent to central spacers and

magnetic poles of central magnets, inner coil windings surrounding an outside

perimeter of central spacers. The inner coil array mounted on a movable coil

support, movable coil support providing for reciprocating linear motion of coil

array relative to magnet array.

And an outer magnet array assembly comprising an outer magnet array

comprised of a plurality of axially-aligned, stacked concentric toroidal magnets

having like magnetic poles facing each other, outer magnet array surrounding

inner coil array, stacked outer concentric magnets being aligned and positioned

essentially coplanar with stacked central cylindrical magnets with the magnetic

poles of outer magnets aligned with and facing opposing magnetic poles of central

cylindrical magnets, and a plurality of high permeability, high saturation

magnetization, outer concentric toroidal spacers positioned at each end of stacked

outer magnet array and between adjacent stacked outer magnets, outer magnet

array assembly attached to magnet array support; wherein a predetermined

location, configuration and orientation of central magnet magnetic poles, central

spacers, inner coil windings, outer magnet magnetic poles and outer spacers

provide for superposition of a radial component of a magnetic flux density from a

plurality of central and outer magnets to produce a maximum average radial

magnetic flux density in the inner coil windings; and a voltage conditioning circuit

electrically connected to coil windings, voltage conditioning circuit providing an

output voltage and output current to an electrical load.


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Fig No 1.3 Magnetic Shock Absorber with Regeneration

http://4.bp.blogspot.com/-Z50iYZavBls/TtcVbilOrMI/AAAAAAAAAG8/sjR1j_eYE-c/s1600/clip_image002.jpg


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CHAPTER II

LITERATURE REVIEW

Andrzej Milecki , Miko" Aj Hauke, 2012,Application Of Magnetorheological

fluid In Industrial Shock Absorbers, discussed: Magnetorheological (MR) fluid,

which is capable of controlling the stopping process of moving objects, e.g. on

transportation lines. The proposed solution makes it possible to adjust the braking

force (by electronic controller) to the kinetic energy of the moving object . The

paper presents an overview of passive shock absorbers. Next, the design concept

of a semi- active shock absorber with the MR fluid is proposed. Theoretically the

optimal breaking process occurs when the breaking force is constant on the whole

stroke of the absorber.

The passive shock absorbers which are in use now do not guarantee this.

The braking force of these absorbersis not constant, and, as a result, the stopping

process is not optimal. Therefore there is a need for improvement. Recently, semi-

active devices, also called ‘‘intelligent’’ devices, have been proposed for the

damping of vibrations and oscillations.The parameters of these devices, like the

movement opposite force, can be continuously changed with minimal energy

requirements. They utilise electrorheological (ER) or magnetorheological (MR)

fluids. Such fluids can be quite attractive for industrial applications in the stopping

of moving elements on production lines. Compared to conventional

electrorheological solutions, MR devices are stronger and can be operated directly

from low-voltage power supplies this is why MR fluids are much more often used.

2.1 INVESTIGATIONS OF SHOCK ABSORBER WITH

MAGNETORHEOLOGICAL FLUID

A bypass valve with a cylindrical gap was mounted on the interface plate. The

complete shock absorber is approximately 310 mm long and contains

approximately 0.05 dm3 of the MR fluid. An electro-hydraulic servo drive was

applied to control the velocity of the piston. The MR shock absorber and the drive

were attached to a plate that was mounted on a strong floor. A Linear Variable


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Differential Transducer (LVDT) was used to measure the displacement (linearity

0.5%) and an HBM 5 kN transducer was used to measure the braking force. The

measured signals (force and displacement) were transformed into a digital form by

a 16-bit analogue/digital (ADC0 and ADC1) converter placed in an input/output

card, and then sent to the computer and recorded in its memory. The displacement

signal was differentiated in order to obtain the piston velocity. The same computer

was used to control the electro-hydraulic servo system velocity (DAC1) and the

MR shock absorber coils current (DAC0).

Babak Ebrahimi , Mir Behrad Khamesee , M. Farid Golnaraghi, 2008,Design And

Modeling Of A Magnetic Shock Absorber Based On Eddy Current Damping

Effect, studied: Eddy currents are generated in a conductor in a time-varying

magnetic field. They are induced either by the movement of the conductor in the

static field or by changing the strength of the magnetic field, initiating motional

and transformer electromotive forces (emfs), respectively. Since the generated

eddy currents create a repulsive force that is proportional to the velocity of the

conductor, the moving magnet and conductor behave like a viscous damper.

Graves et al have derived a mathematical representation for eddy current dampers,

based on the motional and transformer emf, and have developed an analytical

approach to compare the efficiency of the dampers in terms of these two sources.

For more than two decades, the application of eddy currents for damping purposes

has been investigated, including magnetic braking systems , vibration. Control of

rotary machinery, structural vibration suppression , and vibration isolation

enhancement in levitation systems. The newly developed analytical model is used

to design high-performance dampers for a variety of applications.

The damping characteristic of the proposed system can be easily changed

by either re-positioning the conductor or choosing the appropriate conductor size

and the air-gap distance between the magnets. The novel magnetic spring–damper

described in this article is a non-contact device with adjustable damping

characteristics,no external power supply requirement and suitable for different

vibrational structures for high accuracy and simple implementation. The proposed

magnetic spring damper can be modified in terms of size, material , and

topological design for different applications. Future work might involve extending


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the magnetic spring–damper design for vehicle suspension systems, since the

damper is oil free, inexpensive, requires no external power, and is simple to

manufacture.

Fig No 2.1 Peak Force vs. Peak Velocity at A Constant Frequency of 20 Hz

Alberdi-Muniain , N. Gil-Negrete , L. Kari, 2012,Direct Energy flow

Measurement In Magneto-Sensitive Vibration Isolator Systems, learned: The

effectiveness of highly non-linear, frequency, amplitude and magnetic field

dependent magneto-sensitive natural rubber components applied in a vibration

isolation system is experimentally investigated by measuring the energy flow into

the foundation. The energy flow, including both force and velocity of the

foundation, is a suitable measure of the effectiveness of a real vibration isolation

system where the foundation is not perfectly rigid. The vibration isolation system

in this study consist s of a solid aluminium mass supported on four magneto-

sensitive rubber components and is excited by an electro-dynamic shaker while

applying various excitation signals, amplitudes and positions in the frequency

range of 20–200 Hz and using magneto sensitive components at zero-field and at

magnetic saturation. The energy flow through th e magneto-sensitive rubber

isolators is directly measured by inserting a force transducer below each isolator

and an accelerometer on the foundation close to each isolator.

Bart.L.J.Gysen, Johannes.J.H.Paulides, Jeroen.L.G.Janssen, 2010, Active

Electromagnetic Suspension System For Improved Vehicle Dynamics studied:


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Due to the change in vehicle concepts to the more electric car, the suspension

system becomes ever more important due to changes in the sprung and unsprung

masses. Active electromagnetic suspension systems can maintain the required

stability and comfort due to the ability of adaptation in correspondence with the

state of the vehicle. Specifications are drawn from on-and off road measurements

on a passive suspension system, and it can be concluded that, for ARC, a peak

force of 4kN and an RMS force of 2kN (dutycycleof100%) are necessary for th

front actuators. Furthermore, the necessary peak damping power is around 2kW;

however, the RMS damping power is only 16W during normal city driving. The

maximum bound and rebound strokes are 80 and 58mm, respectively. The on road

measurements, which are mimicked on a quarter car setup by means of

electromagnetic actuation, a good tracking response, and measurement of the

frequency response of the tubular actuator, prove the dynamic performance of the

electromagnetic suspension system

Georgios Tsampardoukas, Charles W.Stammers, Emanuele Guglielmino, 2008,

Hybrid Balance Control Of A Magnetorheological Truck Suspension, discussed:

The paper concerns an investigation into the use of controlled magnetorheological

dampers for a semi active truck suspension. A control strategy targeted to reduce

road damage without penalizing driver comfort is presented. A half truck model is

employed and system performance investigated via numerical simulation. A

balance control algorithm (variable structure type algorithm) based on dynamic

tyre force tracking has been devised. Algorithm robustness to parametric

variations as well as to real life implementation issues such as feedback signals

noises are investigated as well. The magnitude of total road damage reduction

(over three axles)on a simulated random road varies with vehicle speed. The

reduction was found to be 6% at 7.5m/s, 19% at 17.5m/s and 9% at 25m/s.

Kirk T. McDonald, Joseph Henry Laboratories, Princeton University, Princeton,

NJ08544 (April14,2012)Magnetic Damping discussed: When a conductor moves

through a non uniform, external magnetic field, the magnetic flux varies through

loops fixed inside the conductor, so an electromotive force is induced around the

loops, according to Faraday’s law (in the rest frame of the conductor), and eddy


16


currents flow. The Lorentz force on these eddy currents, due to the external

magnetic field, opposes the motion, and one speaks of magnetic braking/damping.

This effect is (ultra) relativistic, being of order v2/c2, where v is the speed of the

conductor and c is the speed of light in vacuum. While such relativistic effects are

generally small for “ordinary” velocities, the eddy current density obeys J=σE,

where the conductivity σf or good conductors approaches c2/v2 when measured in

Gaussian units, such that eddy current braking is a rare example of an important

(ultra) relativistic correction at low velocities. In the present problem the magnetic

field is spatially uniform, so the magnetic flux through a moving loop does not

change, and no eddy currents develop. Yet, there exists a very weak magnetic

damping effect.

Zekeriya Parlak, Tahsin Engin, Ismail Çallı, 2012, Optimal Design Of MR

Damper Via Finite Element Analyses Of Fluid Dynamic And Magnetic Field,

studied: The purpose of the study was to optimize MR damper geometrically in

accordance with two objectives, target damper force as 1000N and maximum

magnetic flux density. The optimization studies were carried out by finite element

method using electromagnetic and CFD tools of ANSYSv12.1. The FEM analyses

were employed to get desired optimal values in ANSYS Goal Driven

Optimization tool. Values of optimal of the design parameters of the MR damper

were searched between lower and upper boundaries in both electromagnetic and

CFD analyses. The parameters were geometrical magnitudes, current excitation

and yield stress. In the electromagnetic analysis gap width, flange length, gap

length, piston head housing thickness, radius of piston core, the number of coil

turns and the applied current were selected as design parameters to be able to get

maximum magnetic flux density. The values were used in CFD analysis to obtain

damper force under optimal conditions


17


2.2 MR FLUIDS

When a magnetic field is applied to the fluid, particles in the fluid form

chains, and the suspension becomes like a semi-solid material in a few

millisecond. Under the magnetic field, an MR fluid behaves as a non-Newtonian

fluid with controllable viscosity. However, if the magnetic field is removed, the

suspension turns to a Newtonian fluid and the transition between these two phases

is highly reversible, which provides a unique feature of magnetic field

controllability of the flow of MR fluids. The chains form causes about 50 kPa of

yield stress depending on type of MR fluids in a few millisecond, the case creates

a resistance against the fluid flow. If a force is applied on the chains form, the

shape of the form changes in terms of magnitudes of the force and magnetic field.

The pressure reaction on MR fluid is called ‘‘MR effect’’. In figure as can be seen

that the particles are scattered randomly in the liquid carrier, when magnetic field

applied, the particle array in the direction of the magnetic flux lines to resist the

flow, and the chains form is changed in term of force applied to the particles.

Fig No 2.2 MR Effect

Magnetic field in the gap, the fluid acts like a rigid body below dynamic

yield stress considering the Bingham plastic model. This plug region is called the

pre-yield. In the pre-yield region, the local shear stresses have not yet exceeded


18


the dynamic yield stress. When the local shear stresses exceed the dynamic yield

stress, these regions are called the post-yield region and then the fluid acts like a

viscous fluid. The pre- and post-yield regions are shown in figure with the

velocity profile. As can be seen in figure, the velocity profile is divided into three

regions.

Fig No 2.3 Velocity Profiles Across the Annular Duct

Lei Zuo, Xiaoming Chen, Samir Nayfeh, 2011,Design And Analysis Of A New

Type Of Electromagnetic Damper With Increased Energy Density, learned:

2.3 CONCEPT AND MODELLING OF A NEW EDDY CURRENT

DAMPER

In this section, we first present the concept of the proposed eddy current dampers,

and then derive an analytical model for its damping coefficient.

Concept Illustration: Alternative Arrangement of Magnetic Poles.

It is a common practice in the design o transformers or electromagnetic

motors to use laminated steel to reduce the eddy current losses. The reason is that

by splitting the conductor, we can increase the electrical resistance of the current

loops. In an eddy current damper, we would like to reduce the loop electrical

resistance; that is why the area of conductors is usually several times larger than

the area of the magnetic field. Inspired by the approach of “splitting the

conductor” to reduce the eddy current in transformer design, we can “split the

magnets” to increase the eddy current via alternating the magnetic poles. To

illustrate this idea, consider two extreme cases as follows. Figure1 as how’s a

moving conductor in a uniform magnetic field of the same width. In figure the

magnetic field is split into two with alternative pole directions. When the


19


conductor is moving at position as shown in the figure, instantaneous electric

charges are induced in both cases, as indicated in figure. However, eddy current

loop and damping exist only in second case, but not in first case. It is similar to

two identical batteries connected

Fig No 2.4 Illustration of two types of arrangements of magnetic field for eddy

current dampers: case a uniform magnetic field and case b alternating magnetic

field

R. Zalewski , J. Nachman , M. Shillor , J. Bajkowski, 2013, Dynamic Model For

A Magnetorheological Damper, discussed: Lumped mass thermo-mechanical

model for the dynamics of a damper filled with a magnetorheological fluid is

described, analyzed, and numerically simulated. The model includes friction and

temperature effects, and consists of a differential inclusion for the piston

displacements coupled with the energy balance equation for the temperature. The

fluid viscosity is assumed to be a function the temperature and electrical current,

which in practice may be used as the control variable. Numerical simulations of

the system behaviour are presented. In particular, the simulations of an initial

impact show how the subsequent oscillations can be effectively damped.


20


Michael James Atherden,2004, Formula Sae Shock Absorber Design, The

University Of Queensland, discussed:

2.4 DESIGN CONSIDERATIONS

To form accurate conclusions as to the feasibility of the production of a

customised set of dampers, certain design issues must first be taken into account.

The factors which require consideration include manufacturability, cost,

durability, heat dissipation, assembly and disassembly procedures and sealing.

2.4.1 Manufacturability

For the design of the new damper to be feasible, the design must be such that it

can be manufactured, preferably in house at the university. As expressed

previously, dampers require exacting tolerances to be adhered to if quality items

are to be produced. The mechanical engineering workshop has the ability to

machine parts to average accuracy, such that I believe it would be possible to

manufacture a set of dampers with the current tooling.

2.4.2 Cost

The overall cost of the dampers can be reduced if careful consideration is given to

the component designs. One area where potential savings exist over purchased

dampers is in assembly, with students being able to assemble to units when the

components have been manufactured. An actual costing analysis of the damper

production will be performed after the design has been presented.

In Formula SAE competition, teams are required to complete a cost report

based on the competition rules. To summarize, purchased items must be costed at

recommended retail price, regardless if the team received a discount from the

supplier. For a manufactured item however, the cost of the item includes the raw

cost of the material, the machining operations included and the labour to machine

and assemble the component. If the team were to manufacture its own set of

dampers, significant savings could be made to the final cost of the car, a figure

worth 30/100 points for the cost event.


21


2.4.3 Durability

Dampers need to be designed with durability in mind as they from the compliant

link between the suspension and the chassis. As dampers are usually one of the

most expensive items on the vehicle, it is beneficial to be able to re-use them. To

be able to reuse the dampers, they should be designed such that major components

do not wear to the point where replacement is necessary. This may mean

increasing the weight of some components to extend their fatigue life and exerting

higher tolerances on machined parts, both of which increase the cost of the

damper.

2.4.4 Heat Dissipation

Dampers produce a resistive force by passing oil through narrow passages. As

time passes, frictional forces within the fluid and damper mechanisms generate

heat which raises the temperature of the oil. Short term temperature variations will

affect the viscosity of the damper oil, in some cases drastically altering the

performance of the damper. Long term thermal cycling of oil eventually degrades

its performance as its chemical properties change, thus good heat dissipation

prolongs the life of the damper, requiring less frequent maintenance. Heat

dissipation away from dampers is usually left to the vehicle designer, who must

provide adequate airflow around the unit.

2.4.5 Assembly / Disassembly Considerations

As the damper consists of many smaller components, due consideration must be

given as to how the damper is going to be assembled or disassembled. Most

components are circular by nature and hence threads are prolific. Accessing these

threads, by virtue of being able to apply enough torque to tighten or loosen them,

must be considered.

2.4.6 Sealing

Dampers generate resistive forces by generate large internal pressures. To contain

the contents of the damper under these pressures, adequate sealing must be


22


provided. Static seals usually consist of rubber O-rings fitting into machined

groves with specific dimensions as to provide sufficient ‘squish’ to form a seal.

Another type of seal often found in dampers is the sliding seal. Sliding seals are

used around the piston, the main shaft and possibly in the external reservoir.

These sliding seals usually perform dual functions, providing both a sealing

surface and axial support for the particular component.

2.5 THEORETICAL APPROACHES

There are several commonly used approaches to shock absorption:

1. Hysteresis of structural material, for eg.

the compression of rubber disks stretching of rubber bands and

cords, bending of steel springs, or twisting of torsion bars. Hysteresis is

the tendency for otherwise elastic materials to rebound with less force than

was required to deform them. Simple vehicles with no separate shock

absorbers are damped, to some extent, by the hysteresis of their springs

and frames.

2. Dry friction as used in wheel brakes, by using disks (classically made

of leather) at the pivot of a lever, with friction forced by springs. Used in

early automobiles such as the Ford Model T, up through some British cars

of the 1940s. Although now considered obsolete, an advantage of this

system is its mechanical simplicity; the degree of damping can be easily

adjusted by tightening or loosening the screw clamping the disks, and it

can be easily rebuilt with simple hand tools. A disadvantage is that the

damping force tends not to increase with the speed of the vertical motion.

3. Solid state, tapered chain shock absorbers, using one or more tapered,

axial alignment(s) of granular spheres, typically made of metals such

as nitinol, in a casing.

4. Fluid friction, for example the flow of fluid through a narrow orifice

(hydraulics), constitutes the vast majority of automotive shock absorbers.

This design first appeared on Morsracing cars in 1902. One advantage of

this type is, by using special internal valving, the absorber may be made

relatively soft to compression (allowing a soft response to a bump) and

http://en.wikipedia.org/wiki/Hysteresis

http://en.wikipedia.org/wiki/Compression_(physical)

http://en.wikipedia.org/wiki/Rubber

http://en.wikipedia.org/wiki/Stretching

http://en.wikipedia.org/wiki/Bending

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Spring_(device)

http://en.wikipedia.org/wiki/Torsion_spring

http://en.wikipedia.org/wiki/Elasticity_(physics)

http://en.wikipedia.org/wiki/Friction

http://en.wikipedia.org/wiki/Brake

http://en.wikipedia.org/wiki/Leather

http://en.wikipedia.org/wiki/Ford_Model_T

http://en.wikipedia.org/wiki/Granular

http://en.wikipedia.org/wiki/Nitinol

http://en.wikipedia.org/wiki/Fluid

http://en.wikipedia.org/wiki/Hydraulic

http://en.wikipedia.org/wiki/Mors_(automobile)

http://en.wikipedia.org/wiki/Mors_(automobile)


23


relatively stiff to extension, controlling "rebound", which is the vehicle

response to energy stored in the springs; similarly, a series of valves

controlled by springs can change the degree of stiffness according to the

velocity of the impact or rebound. Specialized shock absorbers for racing

purposes may allow the front end of a dragster to rise with minimal

resistance under acceleration, then strongly resist letting it settle, thereby

maintaining a desirable rearward weight distribution for enhanced traction.

Some shock absorbers allow tuning of the ride via control of the valve by

a manual adjustment provided at the shock absorber. In more expensive

vehicles the valves may be remotely adjustable, offering the driver control

of the ride at will while the vehicle is operated. The ultimate control is

provided by dynamic valve control via computer in response to sensors,

giving both a smooth ride and a firm suspension when needed. Many

shock absorbers are pressurized with compressed nitrogen, to reduce the

tendency for the oil to cavitate under heavy use. This causes foaming

which temporarily reduces the damping ability of the unit. In very heavy

duty units used for racing or off-road use, there may even be a secondary

cylinder connected to the shock absorber to act as a reservoir for the oil

and pressurized gas.

5. In electrorheological fluid damper, an electric field changes the viscosity

of the oil. This principle allows semi-active dampers application in

automotive and various industries.

6. Other principles use magnetic field variation magneto rheological

damper which changes its fluid characteristics through an electromagnet.

7. Compression of a gas, for example pneumatic shock absorbers, which can

act like springs as the air pressure is building to resist the force on it. Once

the air pressure reaches the necessary maximum, air shock absorbers will

act like hydraulic shock absorbers. In aircraft landing gear air shock

absorbers may be combined with hydraulic damping to reduce bounce.

Such struts are called oleo struts (combining oil and air).

8. Inertial resistance to acceleration, for example prior to 1966 the Citroën

2CV had shock absorbers that damp wheel bounce with no external

http://en.wikipedia.org/wiki/Drag_racing

http://en.wikipedia.org/wiki/Nitrogen

http://en.wikipedia.org/wiki/Cavitate

http://en.wikipedia.org/wiki/Electrorheological_fluid

http://en.wikipedia.org/wiki/Magneto_rheological_damper

http://en.wikipedia.org/wiki/Magneto_rheological_damper

http://en.wikipedia.org/wiki/Electromagnet

http://en.wikipedia.org/wiki/Pneumatic

http://en.wikipedia.org/wiki/Aircraft

http://en.wikipedia.org/wiki/Oleo_strut_(aircraft_suspension)

http://en.wikipedia.org/wiki/Inertia

http://en.wikipedia.org/wiki/Citro%C3%ABn_2CV

http://en.wikipedia.org/wiki/Citro%C3%ABn_2CV


24


moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron

weight inside a vertical cylinder and are similar to, yet much smaller than

versions of the tuned mass dampers used on tall buildings.

9. Composite hydropneumatic devices which combine in a single device

spring action, shock absorption, and often also ride-height control, as in

some models of the Citroën automobile.

10. Conventional shock absorbers combined with composite pneumatic

springs which allow ride height adjustment or even ride height control,

seen in some large trucks and luxury sedans such as certain Lincoln and

most Land Rover automobiles. Ride height control is especially desirable

in highway vehicles intended for occasional rough road use, as a means of

improving handling and reducing aerodynamic drag by lowering the

vehicle when operating on improved high speed roads.

http://en.wikipedia.org/wiki/Tuned_mass_damper

http://en.wikipedia.org/wiki/Hydropneumatic

http://en.wikipedia.org/wiki/Citro%C3%ABn

http://en.wikipedia.org/wiki/Lincoln_(automobile)

http://en.wikipedia.org/wiki/Land_Rover

http://en.wikipedia.org/wiki/Car_handling


25


CHAPTER 3

PROBLEM STATEMENT

The automobile chassis is mounted on the axles, not direct but through some form

of springs. This is done to isolate the vehicle body from the road shocks which

may be in the form of bounce, pitch, roll or sway. These tendencies give rise to an

uncomfortable ride and also cause additional stress in the automobile frame and

body. All the parts which perform the function of isolating the automobile from

the road shocks are collectively called a suspension system. It includes the

springing device used and various mountings for the same.

Broadly speaking, suspension system consists of a spring and a damper.

The energy of road shock causes the spring to oscillate. These oscillations are

restricted to a reasonable level by the damper, which is more commonly called a

shock absorber.

A springing device must be a compromise between flexibility and

stiffness. Springs are placed between the road wheels and the body. When the

wheel comes across a bump on the road, it rises and deflects the spring, thereby

storing energy therein. On releasing, due to the elasticity of the spring material, it

rebounds thereby expending the stored energy. In this way springs starts vibrating,

of course, with amplitude decreasing gradually on account of internal friction of

the spring material and friction of the suspension joints, till vibrations die down.

The name Shock absorber is rather misleading since it is the spring and not

the shock absorber that initially absorbs the shocks. The ‘Shock Absorber’ absorbs

the energy of shock converted into vertical movement of the axle by providing

damping and dissipating the same into heat. Thus it merely serves to control the

amplitude and frequency of spring vibrations. It cannot support weight and has

zero resilience. Therefore, ‘Damper’ is a better term technically to describe the

‘Shock Absorber’.

In Magneto-rheological fluid type suspension system, fluid passes through

an orifice, which can be restricted by applying an electrical field across it. The

fluid consists of magnetically soft particles suspended in a synthetic fluid. When

current is applied to an electromagnetic coil inside the shock absorbers piston, the


26


resulting magnetic field changes the resistance of flow (rheology) of the fluid

which produces a very responsive and controllable damping action without any

valves. In the Magneto-suspension system, the damping effect is produced by the

theory of magnetic repulsion.

The fluidized damping system in the ‘Telescopic- shock absorbers’, is

replaced by the introduction of magnetic field. The magnets are placed in such a

way that, the mating surfaces are fitted with the same poles of magnet, thereby

producing the repulsive effect on the damper system


27


CHAPTER 4

COMPONENTS AND DESCRIPTION

The components of Electromagnetic shock absorbers are mainly categorized in to

two;

1. Mechanical Component

2. Electrical Component

4.1 MECHANICAL COMPONENTS

1. Frame Structure

2. Cylinder and Piston

3. Permanent Magnet

4. Coil Spring

4.1.1Frame Structure

It is just to support the shock absorber arrangement. The whole parts are fixed in

to this frame stand with suitable arrangement. It is made up of hollow MS pipes

which are cut and welded at desired positions.

4.1.2 Cylinder and Piston

A cylinder is the central working part of space in which a piston travels. It has two

heads. The top head accommodate the electromagnetic coil and core, which will

produce the repulsive force when excited. At the top head its just bored to increase

diameter, that will help to accommodate the electromagnet. Connection to the coil

is passed through the top hole that is drilled at the top.The material of cylinder is

usually mild steel, due to easy for machining

http://en.wikipedia.org/wiki/Piston


28


Fig.No 4.1 Cylinder top view

Fig. No 4.2 Cylinder and top cover


29


The piston is a cylindrical member of certain length which reciprocates

inside the cylinder. The diameter of the piston is slightly less than that of the

cylinder bore diameter and it is fitted to the top of the piston rod. It is one of the

important part which converts the pressure energy into repulsive force in this

shock absorber.

The piston is equipped with a ring suitably proportioned and it is relatively

soft rubber which is capable of providing good sealing with low friction at the

operating pressure. The purpose of piston is to provide means of conveying the

pressure.

Generally piston is made up of

1. Aluminium alloy-light and medium work.

2. Brass or bronze or CI-Heavy duty.

The piston is double acting type. The piston moves forward when the high-

pressure air is turned from the right side of cylinder. The piston moves backward

when high pressure acts on the piston from the left side of the cylinder. The

piston should be as strong and rigid as possible.

The efficiency and economy of the machine primarily depends on the

working of the piston. It must operate in the cylinder with a minimum of friction

and should be able to withstand the high compressor force developed in the

cylinder and also the shock load during operation.

The piston should posses the following qualities.

1. The movement of the piston not creates much noise.

2. It should be frictionless.

3. It should withstand high pressure.

Fig. No 4.3 Piston


30


4.1.3 Permanent Magnet

A magnet is a material or object that produces a magnetic field. This magnetic

field is invisible but is responsible for the most notable property of a magnet: a

force that pulls on other ferromagnetic materials like iron and attracts or repels

other magnets.

A permanent magnet is an object made from a material that is magnetized and

creates its own persistent magnetic field. An everyday example is a refrigerator

magnet used to hold notes on a refrigerator door. Materials that can be

magnetized, which are also the ones that are strongly attracted to a magnet are

called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some

alloys of rare earth metals, and some naturally occurring minerals such as

lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones

attracted to a magnet strongly enough to be commonly considered magnetic, all

other substances respond weakly to a magnetic field, by one of several other types

of magnetism. Ferromagnetic materials can be divided into magnetically "soft"

materials like annealed iron which can be magnetized but don't tend to stay

magnetized, and magnetically "hard" materials, which do. Permanent magnets are

made from "hard" ferromagnetic materials which are subjected to special

processing in a powerful magnetic field during manufacture, to align their internal

microcrystalline structure, making them very hard to demagnetize.

To demagnetize a saturated magnet, a certain magnetic field must be applied

and this threshold depends on coercivity of the respective material. "Hard"

materials have high coercivity whereas "soft" materials have low coercivity. An

electromagnet is made from a coil of wire which acts as a magnet when an electric

current passes through it, but stops being a magnet when the current stops. Often

an electromagnet is wrapped around a core of ferromagnetic material like steel,

which enhances the magnetic field produced by the coil.

The overall strength of a magnet is measured by its magnetic moment, or

alternately the total magnetic flux it produces. The local strength of the magnetism

in a material is measured by its magnetization

http://en.wikipedia.org/wiki/Magnetic_field

http://en.wikipedia.org/wiki/Ferromagnetic

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Magnetize

http://en.wikipedia.org/wiki/Refrigerator_magnet

http://en.wikipedia.org/wiki/Refrigerator_magnet

http://en.wikipedia.org/wiki/Ferrimagnetic


http://en.wikipedia.org/wiki/Nickel

http://en.wikipedia.org/wiki/Cobalt

http://en.wikipedia.org/wiki/Rare_earth_element

http://en.wikipedia.org/wiki/Lodestone

http://en.wikipedia.org/wiki/Magnetism

http://en.wikipedia.org/wiki/Annealing_(metallurgy)


http://en.wikipedia.org/wiki/Crystallite

http://en.wikipedia.org/wiki/Coercivity


http://en.wikipedia.org/wiki/Electric_current


http://en.wikipedia.org/wiki/Magnetic_moment

http://en.wikipedia.org/wiki/Magnetic_flux

http://en.wikipedia.org/wiki/Magnetization


31


Magnetic field: The magnetic field (usually denoted B) is a vector field. The

magnetic field vector at a given point in space is specified by two properties:

1. Its direction, which is along the orientation of a compass needle.

2. Its magnitude (also called strength), which is proportional to how strongly

the compass needle orients along that direction.

In SI units, the strength of the magnetic field is given in teslas.

Magnetic moment: A magnet's magnetic moment (also called magnetic dipole

moment, and usually denoted μ) is a vector that characterizes the magnet's overall

magnetic properties. For a bar magnet, the direction of the magnetic moment

points from the magnet's south pole to its north pole, and the magnitude relates to

how strong and how far apart these poles are. In SI units, the magnetic moment is

specified in terms of A·m.

A magnet both produces its own magnetic field and it responds to

magnetic fields. The strength of the magnetic field it produces is at any given

point proportional to the magnitude of its magnetic moment. In addition, when the

magnet is put into an external magnetic field, produced by a different source, it is

subject to a torque tending to orient the magnetic moment parallel to the field. The

amount of this torque is proportional both to the magnetic moment and the

external field.

A magnet may also be subject to a force driving it in one direction or

another, according to the positions and orientations of the magnet and source. If

the field is uniform in space, the magnet is subject to no net force, although it is

subject to a torque.A wire in the shape of a circle with area A and carrying current

I is a magnet, with a magnetic moment of magnitude equal to IA.

Magnetization: The magnetization of a magnetized material is the local value of

its magnetic moment per unit volume, usually denoted M, with units A/m. It is a

vector field, rather than just a vector (like the magnetic moment), because

different areas in a magnet can be magnetized with different directions and

strengths (for example, because of domains, see below). A good bar magnet may

http://en.wikipedia.org/wiki/Vector_field

http://en.wikipedia.org/wiki/Euclidean_vector

http://en.wikipedia.org/wiki/Compass

http://en.wikipedia.org/wiki/SI

http://en.wikipedia.org/wiki/Tesla_(unit)

http://en.wikipedia.org/wiki/Vector_(geometry)

http://en.wikipedia.org/wiki/SI

http://en.wikipedia.org/wiki/Torque


http://en.wikipedia.org/wiki/Ampere

http://en.wikipedia.org/wiki/Meter

http://en.wikipedia.org/wiki/Vector_field


32


have a magnetic moment of magnitude 0.1 A·m2 and a volume of 1 cm

3, or

1×10−6

m3, and therefore an average magnetization magnitude is 100,000 A/m.

Iron can have a magnetization of around a million amperes per meter. Such a large

value explains why iron magnets are so effective at producing magnetic fields.

The permanent magnet used in this shock absorber is Neodymium magnet.

A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most

widely used type of rare-earth magnet, is a permanent magnet made from

an alloy of neodymium, iron and boron to form the

Nd2Fe14B tetragonal crystalline structure. Developed in 1982 by General

Motors and Sumitomo Special Metals, neodymium magnets are the strongest type

of permanent magnet commercially available. They have replaced other types of

magnet in the many applications in modern products that require strong permanent

magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners.

Some important properties used to compare permanent magnets

are: remanence (Br), which measures the strength of the magnetic

field; coercivity (Hci), the material's resistance to becoming demagnetized; energy

product (BHmax), the density of magnetic energy; and Curie temperature (TC), the

temperature at which the material loses its magnetism. Neodymium magnets have

higher remanence, much higher coercivity and energy product, but often lower

Curie temperature than other types. Neodymium is alloyed

with terbium and dysprosium in order to preserve its magnetic properties at high

temperatures. The table below compares the magnetic performance of neodymium

magnets with other types of permanent magnets.

Fig. No 4.4 Neodymium magnet

http://en.wikipedia.org/wiki/Rare-earth_magnet

http://en.wikipedia.org/wiki/Magnet

http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Neodymium


http://en.wikipedia.org/wiki/Boron

http://en.wikipedia.org/wiki/Tetragonal_crystal_system

http://en.wikipedia.org/wiki/General_Motors

http://en.wikipedia.org/wiki/General_Motors

http://en.wikipedia.org/wiki/Sumitomo_Metal_Industries

http://en.wikipedia.org/wiki/Cordless

http://en.wikipedia.org/wiki/Hard_disk_drive

http://en.wikipedia.org/wiki/Remanence


http://en.wikipedia.org/wiki/Curie_temperature

http://en.wikipedia.org/wiki/Terbium

http://en.wikipedia.org/wiki/Dysprosium


33


Neodymium magnets are graded according to their maximum energy product,

which relates to the magnetic flux output per unit volume. Higher values indicate

stronger magnets and range from N35 up to N52. Letters following the grade

indicate maximum operating temperatures.

Grades of Neodymium magnets:

1. N35-N52

2. 33M-48M

3. 30H-45H

4. 30SH-42SH

5. 30UH-35UH

6. 28EH-35EH

Neodymium magnet used is N4518, the easy availability and desirable

properties are the reason to choose it.

Property Neodymium

Remanence (T) 1–1.3

Coercivity (MA/m) 0.875–1.99

http://en.wikipedia.org/wiki/Oersted


http://en.wikipedia.org/wiki/Remanence



34


Relative permeability 1.05

Temperature coefficient of remanence (%/K) −0.12

Temperature coefficient of coercivity (%/K) −0.55..–0.65

Curie temperature (°C) 320

Density (g/cm3) 7.3–7.5

CTE, magnetizing direction (1/K) 5.2×10−6

CTE, normal to magnetizing direction (1/K) −0.8×10−6

Flexural strength (N/mm2) 250

Compressive strength (N/mm2) 1100

Tensile strength (N/mm2) 75

Vickers hardness (HV) 550–650

Electrical resistivity (Ω·cm) (110–170)×10−6

Table No 4.1 Physical properties of neodymium magnet

http://en.wikipedia.org/wiki/Permeability_(electromagnetism)

http://en.wikipedia.org/wiki/Curie_temperature

http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion

http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion

http://en.wikipedia.org/wiki/Flexural_strength

http://en.wikipedia.org/wiki/Compressive_strength

http://en.wikipedia.org/wiki/Tensile_strength

http://en.wikipedia.org/wiki/Vickers_hardness

http://en.wikipedia.org/wiki/Resistivity


35


4.1.4 Coil Spring

A coil spring, also known as a helical spring, is a mechanical device, which is

typically used to store energy due to resilience and subsequently release it, to

absorb shock, or to maintain a force between contacting surfaces. They are made

of an elastic material formed into the shape of a helix which returns to its natural

length when unloaded.

Springs can be classified depending on how the load force is applied to

them:

1. Tension/Extension spring – the spring is designed to operate with

a tension load, so the spring stretches as the load is applied to it.

2. Compression spring – is designed to operate with a compression load, so

the spring gets shorter as the load is applied to it.

3. Torsion spring – unlike the above types in which the load is an axial force,

the load applied to a torsion spring is a torque or twisting force, and the

end of the spring rotates through an angle as the load is applied.

4. Constant spring - supported load will remain the same throughout

deflection cycle

5. Variable spring - resistance of the coil to load varies during compression

The suspension coil springs combined with shock absorbers prevent

undesired vertical movement of the vehicle and suppress jolts and vibrations. An

optimum design, an improved production process and a new type of primary

material make it possible to reduce the suspension coil spring weight by up to

50%.

One type of coil spring is a torsion spring: the material of the spring acts in

torsion when the spring is compressed or extended. The quality of spring is judged

from the energy it can absorb. The spring which is capable of absorbing the

greatest amount of energy for the given stress is the best one. Metal coil springs


http://en.wikipedia.org/wiki/Helix

http://en.wikipedia.org/wiki/Tension_(physics)


http://en.wikipedia.org/wiki/Torque


http://en.wikipedia.org/wiki/Spring_(device)


36


are made by winding a wire around a shaped former - a cylinder is used to form

cylindrical coil springs.

A spring is an elastic object used to store mechanical energy. Springs are

usually made out of spring steel. Small springs can be wound from pre-hardened

stock, while larger ones are made from annealed steel and hardened after

fabrication. Some non-ferrous metals are also used including phosphor

bronze and titanium for parts requiring corrosion resistance

Fig. No 4.5 Coil Spring


http://en.wikipedia.org/wiki/Energy

http://en.wikipedia.org/wiki/Spring_steel


http://en.wikipedia.org/wiki/Ferrous

http://en.wikipedia.org/wiki/Phosphor_bronze

http://en.wikipedia.org/wiki/Phosphor_bronze

http://en.wikipedia.org/wiki/Titanium


37


This spring is obtained from a dismantled fluid shock absorber. Two end

caps are made with sheets two cover the ends and attach with the piston rod. The

properties of the spring taken are follows:

Material: spring steel

Wire dia= 10mm

Outer dia= 70mm

Inner dia= 50mm

Pitch= 23.2mm

No.of turns= 11

Length= 230mm

Stiffness of spring= 41.72×10^3 N/m


38


4.2 ELECTRICAL COMPONENTS

Electrical components are the other important parts of this system. These include:

1. Battery

2. Electromagnet

4.2.1 Battery

In isolated systems away from the grid, batteries are used for storage of

excess solar energy converted into electrical energy. The only exceptions are

isolated sunshine load such as irrigation pumps or drinking water supplies for

storage. In fact for small units with output less than one kilowatt. Batteries seem

to be the only technically and economically available storage means. Since both

the photo-voltaic system and batteries are high in capital costs. It is necessary that

the overall system be optimized with respect to available energy and local demand

pattern. To be economically attractive the storage of solar electricity requires a

battery with a particular combination of properties:

1. Low cost

2. Long life

3. High reliability

4. High overall efficiency

5. Low discharge

6. Minimum maintenance

a. Ampere hour efficiency

b. Watt hour efficiency

We use lead acid battery for storing the electrical energy from the solar

panel for lighting the street and so about the lead acid cells are explained below.

Since the shock absorber is installed in automobile, the easy power source

will be the rechargeable battery. It will recharge automatically when engine is on.

Usually 12V batteries are available for the use. And current will vary. Two

wheelers have 7A and four wheelers have 40A. We use a 7a battery for this

demonstration purpose.


39


Fig. No 4.6 Battery

Feature Data

Voltage 12V

Current 40A

Type 50B20R

Table No 4.2 Battery Specifications


40


4.2.2 Electromagnet

An electromagnet is a type of magnet in which the magnetic field is produced

by electric current. The magnetic field disappears when the current is turned off.

Electromagnets are widely used as components of other electrical devices, such

as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific

instruments, and magnetic separation equipment, as well as being employed as

industrial lifting electromagnets for picking up and moving heavy iron objects like

scrap iron.

An electric current flowing in a wire creates a magnetic field around the

wire, due to law. To concentrate the magnetic field, in an electromagnet the wire

is wound into a coil with many turns of wire lying side by side. The magnetic field

of all the turns of wire passes through the center of the coil, creating a strong

magnetic field there. A coil forming the shape of a straight tube (a helix) is called

a solenoid. Much stronger magnetic fields can be produced if a "core"

of ferromagnetic material, such as soft iron, is placed inside the coil. The

ferromagnetic core increases the magnetic field to thousands of times the strength

of the field of the coil alone, due to the high magnetic permeability μ of the

ferromagnetic material. This is called a ferromagnetic-core or iron-core

electromagnet.

The direction of the magnetic field through a coil of wire can be found

from a form of the right-hand rule. If the fingers of the right hand are curled

around the coil in the direction of current flow (conventional current, flow

of positive charge) through the windings, the thumb points in the direction of the

field inside the coil. The side of the magnet that the field lines emerge from is

defined to be the North Pole.

The main advantage of an electromagnet over a permanent magnet is that

the magnetic field can be rapidly manipulated over a wide range by controlling the

amount of electric current. However, a continuous supply of electrical energy is

required to maintain the field.

http://en.wikipedia.org/wiki/Magnet



http://en.wikipedia.org/wiki/Electric_motor

http://en.wikipedia.org/wiki/Electric_generator

http://en.wikipedia.org/wiki/Hard_disk

http://en.wikipedia.org/wiki/Magnetic_resonance_imaging

http://en.wikipedia.org/wiki/Magnetic_separation

http://en.wikipedia.org/wiki/Electromagnetic_coil

http://en.wikipedia.org/wiki/Helix

http://en.wikipedia.org/wiki/Solenoid

http://en.wikipedia.org/wiki/Magnetic_core

http://en.wikipedia.org/wiki/Ferromagnetism



http://en.wikipedia.org/wiki/Right_hand_grip_rule

http://en.wikipedia.org/wiki/Conventional_current

http://en.wikipedia.org/wiki/Positive_charge

http://en.wikipedia.org/wiki/Permanent_magnet


41


The cost of an electric machine depends upon its size and weight and

primarily on the weight of magnetic and conducting materials as these being most

costly ones. The weight of the magnetic materials is influenced by the size of the

magnetic circuit of the machine. To a great extent, the size and the weighty of the

machine depends upon the assigned values of specific magnetic loading, which is

limited by the saturation and core losses of the magnetic materials used in the

machine. However an increased value of specific magnetic loading could be

assigned for designing an electrical machine, provided the magnetic materials has

a comparatively higher saturation limit and lower core losses per kg of the

material.

The main components of electromagnets are insulated magnet wire and a

soft iron core. Magnet wire or enameled wire is

a copper or aluminium wire coated with a very thin layer of insulation. It is used

in the construction of transformers, inductors, motors, speakers, hard disk, head

actuators, potentiometers, electromagnets and other applications which require

tight coils of wire.

Fig No 4.7 Magnetic wire

The wire itself is most often fully annealed, electrolytically refined copper.

Aluminium magnet wire is sometimes used for large transformers and motors. An

aluminium wire must have 1.6 times the cross sectional area as a copper wire to

http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Aluminium

http://en.wikipedia.org/wiki/Wire

http://en.wikipedia.org/wiki/Electrical_insulation

http://en.wikipedia.org/wiki/Transformer

http://en.wikipedia.org/wiki/Inductors


http://en.wikipedia.org/wiki/Loudspeaker

http://en.wikipedia.org/wiki/Hard_disk_drive#Components

http://en.wikipedia.org/wiki/Hard_disk_drive#Components

http://en.wikipedia.org/wiki/Potentiometer




42


achieve comparable DC resistance. Due to this, copper magnet wires contribute to

improving energy efficiency in equipment such as electric motors. Smaller

diameter magnet wire usually has a round cross section. This kind of wire is used

for things such as electric guitar pickups. Thicker magnet wire is often square or

rectangular (with rounded corners) to provide more current flow per coil length.

Although described as "enameled", enameled wire is not, in fact, coated with

either a layer of enamel paint nor with vitreous enamel made of fused glass

powder. Modern magnet wire typically uses one to four layers (in the case of

quad-film type wire) of polymer film insulation, often of two different

compositions, to provide a tough, continuous insulating layer. Magnet wire

insulating films use (in order of increasing temperature range) polyvinyl formal

(Formvar), polyurethane, polyamide, polyester, polyester-polyimide, polyamide-

polyimide (or amide-imide), and polyimide. Polyimide insulated magnet wire is

capable of operation at up to 250°C. The insulation of thicker square or

rectangular magnet wire is often augmented by wrapping it with a high-

temperature polyimide or fiberglass tape, and completed windings are often

vacuum impregnated with an insulating varnish to improve insulation strength and

long-term reliability of the winding.

Other types of insulation such as fiberglass yarn with

varnish, aramid paper, kraft paper, mica, and polyester film are also widely used

across the world for various applications like transformers and reactors. In the

audio sector, a wire of silver construction, and various other insulators, such as

cotton (sometimes permeated with some kind of coagulating agent/thickener, such

as beeswax) and polytetrafluoroethylene (Teflon) can be found. Older insulation

materials included cotton, paper, or silk, but these are only useful for low-

temperature applications (up to 105°C).

For ease of manufacturing, most new magnet wire has insulation that acts

as a flux (metallurgy) when burnt during soldering. [1]

This means that the

electrical connections at the ends can be made without stripping off

the insulation first. Older magnet wire is normally not like this, and requires

sandpapering or scraping to remove the insulation before soldering.

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Electrical_resistance

http://en.wikipedia.org/wiki/Enamel_paint

http://en.wikipedia.org/wiki/Vitreous_enamel

http://en.wikipedia.org/wiki/Polymer

http://en.wikipedia.org/wiki/Polyurethane

http://en.wikipedia.org/wiki/Polyamide

http://en.wikipedia.org/wiki/Polyester

http://en.wikipedia.org/wiki/Polyimide

http://en.wikipedia.org/wiki/Fiberglass

http://en.wikipedia.org/wiki/Aramid

http://en.wikipedia.org/wiki/Kraft_paper

http://en.wikipedia.org/wiki/Mica

http://en.wikipedia.org/wiki/Beeswax

http://en.wikipedia.org/wiki/Polytetrafluoroethylene

http://en.wikipedia.org/wiki/Flux_(metallurgy)

http://en.wikipedia.org/wiki/Soldering

http://en.wikipedia.org/wiki/Magnet_wire#cite_note-1



43


Why must use an insulated copper wire for coils of an electromagnet? A

single coil of wire produces an electromagnetic field. Multiple coils add their

electromagnetic fields together for a stronger field. Using uninsulated copper wire

in the coils would resemble a single large coil because current would not flow

evenly through all the copper wires. Also, without insulation the resistance to the

flow of electricity would be reduced to near zero drawing too much current and

perhaps blowing a fuse or tripping a circuit breaker. E = IR and I = E/R, I

(current) is equal to E (voltage)/R(resistance) and I is large if R is small for a

given voltage.

A magnetic core is a piece of magnetic material with a

high permeability used to confine and guide magnetic fields in

electrical, electromechanical and magnetic devices such as

electromagnets, transformers, electric motors, generators, inductors,

magnetic recording heads, and magnetic assemblies. It is made

of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites.

The high permeability, relative to the surrounding air, causes the magnetic field

lines to be concentrated in the core material. The magnetic field is often created

by a coil of wire around the core that carries a current. The presence of the core

can increase the magnetic field of a coil by a factor of several thousand over what

it would be without the core.

The use of a magnetic core can enormously concentrate the strength and

increase the effect of magnetic fields produced by electric currents and permanent

magnets. The properties of a device will depend crucially on the following factors:

1. The geometry of the magnetic core.

2. The amount of air gap in the magnetic circuit.

3. The properties of the core material

(especially permeability and hysteresis).

4. The operating temperature of the core.

5. Whether the core is laminated to reduce eddy currents.

In many applications it is undesirable for the core to retain magnetization

when the applied field is removed. This property, called hysteresis can cause

http://en.wikipedia.org/wiki/Magnetism

http://en.wikipedia.org/wiki/Magnetic_permeability


http://en.wikipedia.org/wiki/Electromechanical



http://en.wikipedia.org/wiki/Electric_generator

http://en.wikipedia.org/wiki/Inductor

http://en.wikipedia.org/wiki/Recording_head



http://en.wikipedia.org/wiki/Ferrite_(magnet)

http://en.wikipedia.org/wiki/Magnetic_field_line

http://en.wikipedia.org/wiki/Magnetic_field_line

http://en.wikipedia.org/wiki/Magnetic_fields

http://en.wikipedia.org/wiki/Electric_currents



http://en.wikipedia.org/wiki/Geometry

http://en.wikipedia.org/wiki/Magnetic_circuit


http://en.wikipedia.org/wiki/Hysteresis

http://en.wikipedia.org/wiki/Operating_temperature

http://en.wikipedia.org/wiki/Laminated

http://en.wikipedia.org/wiki/Eddy_currents


44


energy losses in applications such as transformers. Therefore 'soft' magnetic

materials with low hysteresis, such as silicon steel, rather than the 'hard' magnetic

materials used for permanent magnets, are usually used in cores.

Commonly used core structures are:

Air core: A coil not containing a magnetic core is called an air core coil. This

includes coils wound on a plastic or ceramic form in addition to those made of

stiff wire that are self-supporting and have air inside them. Air core coils generally

have a much lower inductance than similarly sized ferromagnetic core coils, but

are used in radio frequency circuits to prevent energy losses called core losses that

occur in magnetic cores. The absence of normal core losses permits a higher Q

factor, so air core coils are used in high frequency resonant circuits, such as up to

a few megahertz. However, losses such as proximity effect and dielectric

losses are still present.

Straight cylindrical core: Most commonly made of ferrite or a similar material,

and used in radios especially for tuning an inductor. The rod sits in the middle of

the coil, and small adjustments of the rod's position will fine tune the inductance.

Often the rod is threaded to allow adjustment with a screwdriver. In radio circuits,

a blob of wax or resin is used once the inductor has been tuned to prevent the core

from moving.

The presence of the high permeability core increases the inductance but

the field must still spread into the air at the ends of the rod. The path through the

air ensures that the inductor remains linear. In this type of

inductor radiation occurs at the end of the rod and electromagnetic

interference may be a problem in some circumstances.

Single "I" core: Like a cylindrical rod but square, rarely used on its own. This type

of core is most likely to be found in car ignition coils.

"C" or "U" core: U and C-shaped cores are used with I or another C or U core to

make a square closed core, the simplest closed core shape. Windings may be put

on one or both legs of the core.

"E" core: E-shaped core are more symmetric solutions to form a closed magnetic

system. Most of the time, the electric circuit is wound around the center leg,

http://en.wikipedia.org/wiki/Hysteresis_loss

http://en.wikipedia.org/wiki/Silicon_steel

http://en.wikipedia.org/wiki/Inductance

http://en.wikipedia.org/wiki/Radio_frequency

http://en.wikipedia.org/wiki/Core_loss

http://en.wikipedia.org/wiki/Q_factor


http://en.wikipedia.org/wiki/Resonant_circuit

http://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)

http://en.wikipedia.org/wiki/Dielectric_losses

http://en.wikipedia.org/wiki/Dielectric_losses

http://en.wikipedia.org/wiki/Ferrite_(iron)

http://en.wikipedia.org/wiki/Radio



http://en.wikipedia.org/wiki/Screw_thread

http://en.wikipedia.org/wiki/Wax

http://en.wikipedia.org/wiki/Resin


http://en.wikipedia.org/wiki/Air


http://en.wikipedia.org/wiki/Linear

http://en.wikipedia.org/wiki/Radiation

http://en.wikipedia.org/wiki/Electromagnetic_interference



45


whose section area is twice that of each individual outer leg. A core shape derived

from E shape is used in this model.

When the core is subjected to a changing magnetic field, as it is in devices that

use AC current such as transformers, inductors, and AC motors and alternators,

some of the power that would ideally be transferred through the device is lost in

the core, dissipated as heat and sometimes noise. This is due primarily to two

processes:

1. Hysteresis - When the magnetic field through the core changes,

the magnetization of the core material changes by expansion and

contraction of the tiny magnetic domains it is composed of, due to

movement of the domain walls. This process causes losses, because the

domain walls get "snagged" on defects in the crystal structure and then

"snap" past them, dissipating energy as heat. This is called hysteresis loss.

It can be seen in the graph of the B field versus the H field for the material,

which has the form of a closed loop. The amount of energy lost in the

material in one cycle of the applied field is proportional to the area inside

the hysteresis loop. Since the energy lost in each cycle is constant,

hysteresis power losses increase proportionally with frequency.

2. Eddy currents - If the core is electrically conductive, the changing

magnetic field induces circulating loops of current in it, called eddy

currents, due to electromagnetic induction. The loops flow perpendicular

to the magnetic field axis. The energy of the currents is dissipated as heat

in the resistance of the core material. The power loss is proportional to the

area of the loops and inversely proportional to the resistivity of the core

material. Eddy current losses can be reduced by making the core out of

thin laminations which have an insulating coating, or alternately, making

the core of a nonconductive magnetic material, like ferrite.



http://en.wikipedia.org/wiki/AC_motor

http://en.wikipedia.org/wiki/Alternator

http://en.wikipedia.org/wiki/Heat

http://en.wikipedia.org/wiki/Noise

http://en.wikipedia.org/wiki/Magnetization

http://en.wikipedia.org/wiki/Magnetic_domain

http://en.wikipedia.org/wiki/Domain_wall_(magnetism)

http://en.wikipedia.org/wiki/Hysteresis_loss

http://en.wikipedia.org/wiki/Hysteresis_loop

http://en.wikipedia.org/wiki/Frequency

http://en.wikipedia.org/wiki/Electrical_conductivity

http://en.wikipedia.org/wiki/Eddy_current


http://en.wikipedia.org/wiki/Electromagnetic_induction

http://en.wikipedia.org/wiki/Lamination

http://en.wikipedia.org/wiki/Ferrite_(magnetic_core)


46


Having no magnetically active core material (an "air core") provides very low

inductance in most situations, so a wide range of high-permeability materials are

used to concentrate the field. Most high-permeability material

are ferromagnetic or ferrimagnetic. The most common core materials are follows:

Soft iron:"Soft" (annealed) iron is used in magnetic assemblies, electromagnets

and in some electric motors; and it can create a concentrated field that is as much

as 50,000 times more intense than an air core. Iron is desirable to make magnetic

cores, as it can withstand high levels of magnetic field without saturating (up to

2.16 tesla at ambient temperature)

It is also used because, unlike "hard" iron, it does not remain magnetized

when the field is removed, which is often important in applications where the

magnetic field is required to be repeatedly switched. Unfortunately, due to the

electrical conductivity of the metal, at AC frequencies a bulk block or rod of soft

iron can often suffer from large eddy currents circulating within it that waste

energy and cause undesirable heating of the iron.

Laminated silicon steel: Because iron is a relatively good conductor, it cannot be

used in bulk form with a rapidly changing field, such as in a transformer, as

intense eddy currents would appear due to the magnetic field, resulting in huge

losses (this is used in induction heating).

Two techniques are commonly used together to increase the resistivity of iron:

lamination and alloying of the iron with silicon.

Lamination:

Fig No 4.8 Typical EI Lamination







http://en.wikipedia.org/wiki/Saturation_(magnetic)


http://en.wikipedia.org/wiki/Induction_heating

http://en.wikipedia.org/wiki/File:EI_Lam.jpg


47


Laminated magnetic cores are made of thin, insulated iron sheets, lying, as much

as possible, parallel with the lines of flux. Using this technique, the magnetic core

is equivalent to many individual magnetic circuits, each one receiving only a

small fraction of the magnetic flux (because their section is a fraction of the whole

core section). Because eddy currents flow around lines of flux, the laminations

prevent most of the eddy currents from flowing at all, restricting any flow to much

smaller and thinner and thus higher resistance regions. From this, it can be seen

that the thinner the laminations, the lower the eddy currents. This type of plates

are used here to make the core materials.

Silicon alloying: A small addition of silicon to iron (around 3%) results in a

dramatic increase of the resistivity, up to four times higher. Further increase in

silicon concentration impairs the steel's mechanical properties, causing difficulties

for rolling due to brittleness.

Among the two types of silicon steel, grain-oriented (GO) and grain non-

oriented (GNO), GO is most desirable for magnetic cores. It is anisotropic,

offering better magnetic properties than GNO in one direction. As the magnetic

field in inductor and transformer cores is static (compared to that in electric

motors), it is possible to use GO steel in the preferred orientation.

Carbonyl iron: Powdered cores made of carbonyl iron, a highly pure iron, have

high stability of parameters across a wide range of temperatures and magnetic

flux levels, with excellent Q factors between 50 kHz and 200 MHz. Carbonyl iron

powders are basically constituted of micrometer-size spheres of iron coated in a

thin layer of electrical insulation. This is equivalent to a microscopic laminated

magnetic circuit (see silicon steel, above), hence reducing the eddy currents,

particularly at very high frequencies.

A popular application of carbonyl iron-based magnetic cores is in high-

frequency and broadband inductors and transformers.

Iron powder: Powdered cores made of hydrogen reduced iron have higher

permeability but lower Q. They are used mostly for electromagnetic

http://en.wikipedia.org/wiki/Lamination

http://en.wikipedia.org/wiki/Silicon

http://en.wikipedia.org/wiki/Silicon_steel

http://en.wikipedia.org/wiki/Anisotropic

http://en.wikipedia.org/wiki/Carbonyl_iron

http://en.wikipedia.org/wiki/Temperature




http://en.wikipedia.org/wiki/Sphere


http://en.wikipedia.org/wiki/Eddy_currents



http://en.wikipedia.org/w/index.php?title=Hydrogen_reduced_iron&action=edit&redlink=1



48


interference filters and low-frequency chokes, mainly in switched-mode power

supplies.

Ferrite: Ferrite ceramics are used for high-frequency applications. The ferrite

materials can be engineered with a wide range of parameters. As ceramics, they

are essentially insulators, which prevents eddy currents, although losses such as

hysteresis losses can still occur.

Vitreous Metal: Amorphous metal is a variety of alloys that are non-crystalline or

glassy. These are being used to create high efficiency transformers. The materials

can be highly responsive to magnetic fields for low hysteresis losses and they can

also have lower conductivity to reduce eddy current losses. China is currently

making wide spread industrial and power grid usage of these transformers for new

installations.

Soft iron has a far greater magnetic permeability than steel. Meaning it

provides a stronger magnetic field for a given magnetization current (up to

saturation).

It has a much lower retentivity than steel - when the current is switched off the

remaining field strength is very weak (objects held by iron will be released , but

probably held by the significant 'permanent' field retained by steel). That’s why

soft iron core is used for core material.

During the last few years, considerable developments have place in the

field of magnetic materials. Presently magnetic materials having very high

permeability’s and low specific iron losses are available. These materials are

much superior and result into a reduced size of the machine with a lower overall

cost. As such they are replacing the poor magnetic materials previously used in

electrical machines. The most suitable magnetic materials for electrical machines,

which give a considerable reduction in size and cost, are silicon steel of various

grades.


http://en.wikipedia.org/wiki/Electronic_filter

http://en.wikipedia.org/wiki/Switched-mode_power_supply

http://en.wikipedia.org/wiki/Switched-mode_power_supply

http://en.wikipedia.org/wiki/Ferrite_(magnet)

http://en.wikipedia.org/wiki/Amorphous_metal


49


Fig No 4.9 Electromagnet

The force exerted by an electromagnet on a section of core material is:

F= (B²A)/ (2μₒ)

The magnetic field created by an electromagnet is proportional to both the

number of turns in the winding, N, and the current in the wire, I, hence this

product, NI, in ampere-turns, is given the name magneto motive force. For an

electromagnet with a single magnetic circuit, of which length Lcore of the magnetic

field path is in the core material and length Lgap is in air gaps, Ampere's Law

reduces to:

Where

is the permeability of free space (or air)

For a closed magnetic circuit (no air gap), such as would be found in an

electromagnet lifting a piece of iron bridged across its poles, equation becomes:

B= (NIμ)/L

http://en.wikipedia.org/wiki/Ampere_(unit)

http://en.wikipedia.org/wiki/Magnetomotive_force

http://en.wikipedia.org/wiki/Magnetic_circuit


50


F= (μ²N²I²A)/(2μₒL²)

The above methods are inapplicable when most of the magnetic field path

is outside the core. For electromagnets (or permanent magnets) with well defined

'poles' where the field lines emerge from the core, the force between two

electromagnets can be found using the 'Gilbert model' which assumes the

magnetic field is produced by fictitious 'magnetic charges' on the surface of the

poles, with pole strength m and units of Ampere-turn meter. Magnetic pole

strength of electromagnets can be found from:

The force between two poles is:

The variables of the electromagnet are:

Permeability,μ =1.2567×10^-6 H/m

Number of turns,N =250

Current,I =7amp

Radius of core ,R =3cm

Area of cross section, A =Πd²/4

= 7.06×10^-4 m²

Permeability of free space,μₒ = 4Π×10^-7 N/A²

Length of core,L = 6cm

http://en.wikipedia.org/wiki/Ampere_(unit)


51


Calculating the attractive or repulsive force between two magnets is, in the

general case, an extremely complex operation, as it depends on the shape,

magnetization, orientation and separation of the magnets. The Gilbert model does

depend on some knowledge of how the 'magnetic charge' is distributed over the

magnetic poles. It is only truly useful for simple configurations even then.

Fortunately, this restriction covers many useful cases.

For two cylindrical magnets with radius , and height , with their

magnetic dipole aligned and the distance between them greater than a certain

limit, the force can be well approximated (even at distances of the order of ) by,

Where is the magnetization of the magnets and is the distance

between them. For small values of , the results are erroneous as the force

becomes large for close-to-zero distance.


52


CHAPTER 5

RESULTS AND DISCUSSIONS

Electromagnet is made by winding the insulated copper coil around the soft iron

piece. To end of the coil is leads to connections. The permanent magnet is

attached at the centre of piston head, with adhesives. According to the outside

pole of the permanent magnet electromagnet is connected to the battery, such that

the poles are identical and repel each other when comes closer. After that cylinder

and piston are arranged. Then the spring is aligned on the piston rod with end

covers. And fixed on the frame.

Fig. No 5.1 Shock absorber attached on frame


53


Since we have no exact equation to find the repulsive force between two

non identical magnet, its assumed that both magnets have shape, size, magnetic

force approximately same. For two cylindrical magnets with radius , and

height , with their magnetic dipole aligned and the distance between them

greater than a certain limit, the force can be well approximated (even at distances

of the order of ) by,

Fig No. 5.2 Repulsion of magnets

5.1 ELECTROMAGNETIC FORCE

The magnetic force generated by the electromagnet is calculated by formula

F= (μ²N²I²A)/(2μₒL²)

Permeability,μ =1.2567×10^-6 H/m

Number of turns, N =250

Current, I =7amp

Diameter of core ,d =3cm

Area of cross section, A =Πd²/4

= 7.06×10^-4 m²



54


Length of core, L = 6cm

Force, F = 300.48N

5.2 REPULSIVE FORCE BETWEEN MAGNETS

Radius of electromagnet, R = 3cm


Height of magnet, H =6cm

At normal condition the permanent magnet rest at distance of 10cm from

the core, and the minimum distance when it comes during shock is 3cm. So there

is a maximum and a minimum force, between these repulsion forces varies. As the

distance between magnets decreases the force will increase. But when it comes

closer the magnet will attract. So in order to avoid such situation a rubber bush is

placed over the electromagnet.

Magnetisation, M =Nm/V, m-unit vector in that direction

=(250/54)*m

= 4.62 A/m

Therefore Repulsive force,

When x =x1

i.e., x =3cm, Repulsive force will be maximum

Fmax = 4.23×10^-6 N

When x =x2

i.e., x =10 cm, Repulsive force will be minimum

Fmin = 3.748×10^-7 N


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5.3 CRITICAL DAMPING COEFFICIENT

Stiffness of spring, K = 41720 N/m

Mass of spring, m = 0.650kg

Linear resonance frequency, fres =127Hz

Angular natural frequency, ωn = 797.96 rad/s

Critical damping coefficient, Cc =2 ( )

= 2 ( )

=329.35

5.4 DESIGN OF SHOCK ABSORBER

Fig No 5.3 Piston and cylinder view


56


Fig No 5.4 Damper


57


5.5 BILLING

No

ITEM

No. of ITEMS

COST ₹

1

Cylinder & Piston

1

650

2

Coil Spring

1

250

3

Neodymium Magnet

1

350

4

Copper Coil

10mtrs

100

5

Insulated plate

15

30

6

Wire

3mtrs

20

7

Machining cost

100

Total, ₹

1500

Table 5.1 Billing table


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CHAPTER 6

SCOPE AND FUTURE OF PROJECT

The riding comfort ability is one of the main factors that considered in designing.

Shock absorbers, linear dampers, and dashpots are devices designed to provide

absorption of shock and smooth deceleration in linear motion applications. The

road conditions are different at places. An automobile is designed to perform best

at all places. Suspension system will help to maintain better stability at any state.

Hydraulic and gas charged shock absorbers are commonly used now a days. But at

severe shock load the hydraulic shock absorbers may fail. The fluids get leaked.

So in introducing magnets in the shock absorber to provide damping effect is an

efficient method.

During the shock loads the damper will absorbs the energy, in case of the

fluidic type it take time. These create an unstable condition. And the passengers

want to suffer its after effects. In case of racing cars, the loads are suddenly

fluctuating type and the vibrations wants to remove as soon as possible. General

principle similar poles deflect; can be applied to absorb the damping effect by

providing the magnets. And there is no contact between parts inside the damper,

so the friction is negligible.

The absence of conductive medium will also help to remove hysteresis

effect. The design can be varied to the required conditions and the component

such as electromagnets are available on the requirement. While considering the

additional cost for fabrication it’s not large when compared with the performance.

The levitation based researches are presently takes place. So more improved

magnetic parts will be available easily in future.

Actually now it’s a conceptual model. We are not included the features

such as sensor to detect the deflection of the coil spring. Depending on the

deflection magnetic field with required strength can be induced, that will help to

make the repulsive force to dampen the shock loads in few seconds. During this

project we had studied various method of suspension system, using the magnetic

properties.


59


We had noticed that when any two leads of the three phase induction

motor were shorted then we had to apply more force to rotate the shaft. If it is

coupled with the suspension system like a torque arm suspension system, we can

damper the force without any expenditure of energy. The only requirement will be

the shorting circuit. We hope these high performance suspension systems will

incorporate in coming generation vehicles, which will remove the defects caused

by the current models.


60


REFERENCES

1. Andrzej Milecki , Miko Aj Hauke,2012, Application Of

Magnetorheological fluid In Industrial Shock Absorbers, Mechanical

Systems And Signal Processing 28,528–541

2. Babak Ebrahimi , Mir Behrad Khamesee , M. Farid Golnaraghi,2008,

Design And Modeling Of A Magnetic Shock Absorber Based On Eddy

Current Damping Effect, Journal Of Sound And Vibration 315, 875–889.

3. Alberdi-Muniain , N. Gil-Negrete , L. Kari, 2012,Direct Energy flow

Measurement In Magneto-Sensitive Vibration Isolator Systems, Journal Of

Sound And Vibration 331,1994–2006

4. Bart.L.J.Gysen, Johannes.J.H.Paulides, Jeroen.L.G.Janssen, 2010, Active

Electromagnetic Suspension System For Improved Vehicle Dynamics,

IEEE Transactions On Vehicular Technology, Vol.59.No.3

5. Georgios Tsampardoukas, Charles W.Stammers, Emanuele Guglielmino,

2008,Hybrid Balance Control Of A Magnetorheological Truck

Suspension, Journal Of Sound And Vibration31.7 ,514-536

6. Kirk T. Mcdonald, Joseph Henry Laboratories, Princeton University,

Princeton, NJ08544,2012, Magnetic Damping

7. Zekeriya Parlak, Tahsin Engin, Ismail Çallı, 2012,Optimal Design Of MR

Damper Via Finite Element Analyses Of Fluid Dynamic And Magnetic

Field, Mechatronics 22, 890–903

8. Lei Zuo, Xiaoming Chen, Samir Nayfeh, 2011,Design And Analysis Of A

New Type Of Electromagnetic Damper With Increased Energy Density,

Journal Of Vibration And Acoustics, Vol.133/041006-1

9. R. Zalewski , J. Nachman , M. Shillor , J. Bajkowski,2013, Dynamic

Model For A Magnetorheological Damper, Applied Mathematical

Modelling

10. Pinjarla.Poornamohan, Lakshmana Kishore.T,2012, Design And Analysis

Of A Shock Absorber,IJRET,Vol 1,Issue 4, 578-592


61


11. Michael James Atherden,2004, Formula Sae Shock Absorber Design, The

University Of Queensland, BE thesis, 51-54

12. Bogdan Sapinski,2009, Magnetorheological Damper in Vibrational

Control of Mechanical Structures, Mechanics,Vol 1, No 1,18-25

Automotive

Electromagnetic Shock Absorber