i

DESIGN AND CONSTRUCTION OF AN ELECTRO-RHEOLOGICAL VALVE ACTUATING SYSTEM

A MASTER’S THESIS

in

Mechanical Engineering University of Gaziantep

By Egemen Ramazan TOPÇU

December, 1997

ii

Approval of Graduate School of Natural and Applied Sciences. Assoc. Prof. Dr. Ali Rýza TEKÝN

Director I certify that I have read this thesis satisfies all the requirements as a thesis for

the degree of Master of Science. Assoc. Prof. Dr. Sedat BAYSEÇ

Chairman of the Department

I certify that I have read this thesis and that opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Science.

Assist. Prof. Dr. Sadettin KAPUCU Supervisor

Examining Committee in Charge: Assoc. Prof. Dr. Sedat BAYSEÇ (Chairman) Assist. Prof. Dr. A. İhsan KUTLAR Assist. Prof. Dr. Sadettin KAPUCU

iii

ABSTRACT

DESIGN AND CONSTRUCTION OF AN ELECTRO-RHEOLOGICAL

VALVE ACTUATING SYSTEM

TOPÇU, Egemen Ramazan M.S. in Mechanical Engineering

Supevisor: Assist. Prof. Dr. Sadettin KAPUCU December 1997, 63 pages

An Electro-Rheological fluid (ERF) is a mixture of finely divided particles

suspended in a non-conducting base fluid. The application of the sufficient electric

field causes polarisation of particles between electrodes and flow resistance is

increased in this way. The study presented here is about to finding out the

performance of shear and flow mode operations of ER fluids, and also to design and

construct an ER valve as an alternative conventional hydraulic valves. To achieve

this, firstly, mineral oil and transformer oil-based ER fluids were prepared by mixing

them with varying mass ratio of corn starch. Then, the effect of the applied electric

field and the concentration of the corn starch on rheological behaviour of these

mixtures were determined by using Rotational viscometer. Viscous behaviour of the

ER fluids were drawn, i.e., the change of yield stress with the applied electric field

was determined. Furthermore, ER valve dimensions were determined by using the

Rotational viscometer results on the basis of desired pressure drop analysis. Then, a

rectangular multi-plate ER valve was designed and manufactured. This ER valve was

directly connected to a hydraulic pump and pressure drops through the ER valve were

measured with respect to the varying pump flow rate as well as the intensity of the

electric fields. Finally, four ER valves were arranged as Wheatstone bridge in

hydraulic circuit to control the hydraulic piston regard in to start, stop and direction

of motion.

Keywords: Electro-rheological fluid, Wheatstone bridge, Rotational Viscometer.

iv

ÖZET

ELEKTRO-RHEOLOGICAL VALF İLE HAREKETLENDİRİLEN BİR SİSTEMİN

DİZAYNI VE YAPIMI

TOPÇU, Egemen Ramazan Yüksek Lisans Tezi, Makine Müh. Bölümü

Tez Yöneticisi: Yar. Doç. Dr. Sadettin KAPUCU Aralık 1997, 63 sayfa

Elektro-Rheological (ER) akışkan, iletken olmayan parçacıklarla bir temel

akışkanın karışımından oluşur. Yeterli elektrik alanın uygulanması elektrodlar

arasındaki parçacıkların polarize olmasına sebep olur ve böylece akışa karşı direnç

artırılır. Sunulan çalışma, ER akışkanların kesme gerilimi ve akış davranışlarının

tespit edilmesinin tanı sıra halihazırda kullanılan hidrolik valflerin yerini alabilecek

bir ER valfin tasarlanması ve üretilmesi hakkındadır. Bunu yapabilmek için de, İlk

olarak, farklı oranlarda mısır nişastası içeren madeni yağ ve trafo yağı bazlı ER

akışkanlar hazırlanmıştır. Daha sonra, uygulanan elektrik alan ve nişasta oranının, bu

karırışımların rheological davranışları üzerindeki etkileri döner viskosite ölçer

kullanılarak incelenmiştir. ER akışkanların uygulanan değişik elektrik alan altındaki

viskoz davranışları ve akma gerilimi üzerinde yarattığı değişimler grafiksel olarak

belirlenmiştir. Bunların ötesinde, ER valf’in ölçüleri, elde edilen viskosite

sonuçlarını kullanarak, gerçekleşmesi istenen basınç düşüleri analizi temel alınarak

belirlenmiştir. Daha sonra, birden fazla dikdörtgen şeklinde plakaları bulunan ER

valf tasarlanıp üretilmiştir. Hidrolik bir pompaya doğrudan bağlanılan ER valf

üzerinde oluşan düşümler, değişik debi ve elektrik alan şiddetleri uygulanarak

ölçülmüştür. Son olarak, ER valfler hidrolik devre içerisinde Wheatstone köprü

şeklinde dizilerek bir hidrolik pistonun hareketinin başlaması, durması ve hareket

yönü kontrol edilmiştir.

Anahtar Kelimeler: Electro-rheological Akışkan, Wheatstone Köprü,

Döner Viskosite Ölçer.

v

ACKNOWLEDGEMENTS

I wish to express my sincere appreciation to my supervisor Assist. Prof. Dr.

Sadettin KAPUCU, for his helpful encouragement throughout all experiments,

especially for his help making this thesis understandable and readable.

I wish to express my warmest gratitude to the Assoc. Prof. Dr. Sedat

BAYSEÇ, Dr. Oðuzhan Koca, Assistant Hüseyin OVAYOLU and all personnels of

the Mechanical Engineering Department.

This study would have never been completed without moral support,

continuous help and encouragement of my dearest family, Çiðdem HAZIR and

Assistant Bircan YILMAZ. Therefore, my special thanks are due to them.

vi

TABLE OF CONTENTS

Page

ABSTRACT ........................................................................................... iii

ÖZET ..................................................................................................... iv

ACKNOWLEDGEMENTS .................................................................... v

LIST OF TABLES ................................................................................. viii

LIST OF FIGURES ................................................................................ ix

1. INTRODUCTION ............................................................................. 1

1.1 Electro-Rheological Fluids .............................................................. 1

1.2 Electro-Rheological Effect .............................................................. 2

1.3 Literature Survey and Previous Works ........................................... 3

1.4 Content of This Work .................................................................... 9

2. ELECTRO-RHEOLOGICAL BEHAVIOUR .................................. 11

2.1 Introduction ................................................................................. 11

2.2 Idealised Behaviour of ER Fluids .................................................. 12

2.3 Electro-Rheological Fluids Used in this Study ................................ 13

2.4 Experimental Set-up ..................................................................... 14

2.5 Experimental Results .................................................................... 16

2.6 Conclusion ................................................................................... 22

vii

3. ELECTRO-RHEOLOGICAL SINGLE VALVE MODEL .......... 24

3.1 Introduction ............................................................................... 24

3.2 Design of an ER Valve ............................................................... 25

3.3 Pressure Analysis of ER Valve ................................................... 27

3.4 Conclusion ................................................................................. 31

4. ER VALVE HYDRAULIC WHEATSTONE BRIDGE

ARRANGEMENT ....................................................................... 33

4.1 Introduction ............................................................................... 33

4.2 ER Valve Wheatstone Bridge Arrangement ................................ 34

4.3 ER Valve Hydraulic Wheatstone Bridge ...................................... 35

5. CONCLUSIONS AND RECOMENDATIONS .......................... 38

5.1 Conclusion ................................................................................. 38

5.2 Recommendations ...................................................................... 40

REFERENCES ............................................................................ 42

APPENDICES

A- ASSEMBLY AND PART DRAWING OF THE DESIGNED

ER VALVE .............................................................................. 44

B- ASSEMBLY AND PART DRAWING OF THE DESIGNED

ROTATIONAL VISCOMETER ............................................... 52

viii

LIST OF TABLES

Table Page

1.1 Ingredients for ER Fluids ............................................................ 2

1.2 Available Load Pressure on Piston ............................................. 37

ix

LIST OF FIGURES

Figure Page

1.1 Rheological Effect ...................................................................... 3

1.2 Operation Modes of ER Fluids .................................................... 4

1.3 ER Valve Construction Types ..................................................... 6

1.4 Two Valve Arrangement ............................................................ 6

1.5 Wheatstone Bridge Arrangement ................................................ 7

1.6 Multi-Plate ER Valve .................................................................. 7

2.1 Ideal Behaviour of ER Fluid ...................................................... 12

2.2 Dynamic Viscosity of Mineral Oil-Based ER Fluids .................... 13

2.3 Dynamic Viscosity of Transformer Oil-Based ER Fluids ............. 14

2.4 Rotational Viscometer ................................................................ 15

2.5 Viscous Behaviour of Mineral Oil-Based ER Fluid

Contamining 20% Corn Starch by Weight .................................. 17

2.6 Viscous Behaviour of Mineral Oil-Based ER Fluid

Containing 30% Corn Starch by Weight ................................... 17

x

2.7 Viscous Behaviour of Mineral Oil-Based ER Fluid

Containing 40% Corn Starch by Weight .................................. 17

2.8 Viscous Behaviour of Mineral Oil-Based ER Fluid

Containing 50% Corn Starch by Weight ................................... 18

2.9 Viscous Behaviour of Transformer Oil-Based ER Fluid

Containing 20% Corn Starch by Weight .................................. 20

2.10 Viscous Behaviour of Transformer Oil-Based ER Fluid

Containing 30% Corn Starch by Weight .................................. 20

2.11 Viscous Behaviour of Transformer Oil-Based ER Fluid

Containing 40% Corn Starch by Weight ................................... 21

2.12 Viscous Behaviour of Transformer Oil-Based ER Fluid

Containing 50% Corn Starch by Weight .................................... 21

3.1 Parallel Plate Valve .................................................................... 25

3.2 Multi-Plate ER Valve ................................................................ 27

3.3 Single ERValve Pressure Analysis System ................................... 28

3.4.a Valve Pressure Drop Against Pump Flow Rate,

Transformer Oil-Based ER Fluid

Containing 20% Corn Starch by Weight ............ ....................... 29

3.4.b Valve Pressure Drop Against Pump Flow Rate,

Transformer Oil-Based ER Fluid

Containing 30% Corn Starch by Weight ............................... 30

xi

3.4.c Valve Pressure Drop Against Pump Flow Rate,

Transformer Oil-Based ER Fluid

Containing 40% Corn Starch by Weight ................................ 30

4.1 ER Valve Hydraulic Wheatstone Bridge Arrangement ............... 34

4.2 Valve Actuator System ............................................................... 36

A- Part List of ER Valve ................................................................. 44

Assembly Drawing of The ER Valve .......................................... 45

Nipple ......................................................................................... 46

Front Cover ................................................................................ 47

ER Valve Plate ........................................................................... 48

Isolator Plate ............................................................................... 49

Outer Cover ................................................................................ 50

Bolt ............................................................................................. 51

Isolator Ring ................................................................................ 51

B- Part List of Rotational Viscometer ............................................... 52

Assembly Drawing of The Rotational Viscometer ........................ 53

DC Motor Plate ........................................................................... 54

xii

Coupler ........................................................................................ 54

Plate Stick ................................................................................... 55

Top Plate Rice Ring .................................................................... 55

Main Top Plate Bearing ............................................................... 56

Isolating Fittings .......................................................................... 56

Main Top Plate ............................................................................ 57

Inner Cylinder ............................................................................... 58

Outer Cylinder ............................................................................. 59

Main Block Stick ......................................................................... 60

Outer Cylinder Isolator Cup ......................................................... 61

Outer Cylinder Fittings ................................................................ 61

Main Bottom Plate ...................................................................... 62

Top Plate Rice Ring ..................................................................... 63

Main Bottom Plate Bearing ......................................................... 63

1

CHAPTER 1

INTRODUCTION

1.1 Electro-Rheological Fluids

When a material dissolves in another material to form a bona-fide solution and

the size of the solute particles are greater than the size of the molecules of the

solvent, the system will term a colloidal dispersion which have a variety of

subgroups. These subgroups include sols which are dispersion of solids in solids, or

solids in liquid; emulsion which are dispersions of liquids in liquids; aerosols which

are dispersion of liquids in gases, or solids in gases; and foams which are dispersions

of gases in liquids, or gases in solids. Electro-rheological (ER) fluids belong to the

sols, [1].

The ingredients of ER fluids have a great diversity of solvent, solute and

additive category as indicated in Table 1.1. This diversity depends upon seven

criteries which must be considered when developing ER fluids. They are electro-

mechanical, electrical, thermal, stability, viscous, solvent and solute characteristics,

[1].

An ER fluid is a mixture of finely divided particles suspended in a non-

conducting base. The application of the sufficient electric field causes polarisation of

the particles which forming chains between the electrodes. When the electric field is

removed, these particle chains are breakdown. The mechanical properties of the ER

fluid in shear, tension, and compression are subject to dramatic variations with

applied electric field. It is often stated in the literature that ER fluids behave like a

Bingham plastic in which the yield strength is a function of the applied electric field,

[9].

The relationship between the shear stress and applied electric field is important

in the design of any ER device. High shear stress should be desired for a relatively

2

low electric field intensity and ER fluids to be characterised by a low viscosity in the

absence of an electric field and be characterised by a high viscosity when an electric

field applied upon the fluid. It should be low volatility, non-toxic, non-corrosive, and

non-flammable.

Table 1.1: Ingredients for ER Fluids.

SOLVENT SOLUTE ADDITIVE Silicone oils Sodium carboxymethyl

cellulose Water

Olive oil Gelatine none Mineral oil Aluminium dihydrogen Water

Transformer oil Carbon Water Dibutyl sebacate Iron oxide Water and surfactant

Mineral oil Lime none P-xylene Piezoceramic Water and glycerol oleates

Silicone oil Copper Phthalocyanine none Transformer oil Starch none

Kerosene Silica Water and detergents Polychlorinated biphenyls Sulphopropyl dextran Water and sorbitan

Hydrocarbon oil Zeolite none

1.2 Electro-Rheological Effect

Modern solid state devices and microprocessor systems meet the

performance/cost criterion of the logic aspect. The ER effect is a method of providing

high performance inexpensive output element that is interfacable with solid state

electronics.

The ER effect is known as the increasing of the resistance of the special fluids

under the applied electric field. When the elements of the ER fluid device are neutral

(no charge on the electrode) the solute particles are free to move in ER fluids. When

the voltage is applied, negative side of the particles are nearest the positive electrode,

positive side of the particles are nearest the negative electrode, at the same time they

attract each other and consequently arrange themselves into chains, thus forming

mechanical bridges across the electrodes, shown in Figure 1.1.

At low field strength the ER fluid is essentially in a liquid state. When the

electric field is 1 to 3 kV/mm, the ER fluid behave more like a solid, [2]. The effect

3

is reversible so that when the electric field removed the ER fluid reverts to begin a

fluid. Under the fast switching of the electric field, the change of the state quickly.

This electro-rheological phenomenon has been exploited in engineering practices for

the development of discrete devices and in hydraulic circuits. Such devices are

clutch, [3,4], damper, [5], beam, [6], valve, [2,7,11], brake, [15], etc.

Electrode

ER particle

V+

(a) (b)

Figure 1.1: Rheological Effect.

1.3 Literature Survey and Previous Works

The addition of the polarizable solid particles causes the resulting emulsion to

undergo a liquid-to-semi-solid phase change on the application of an electric field.

This was first discovered by Winslow who reported the variation of rheological

properties of some fluids when an electric field is applied. But the authorities can not

claim credit for his observation. They explained this effect to under the presence of

electric field, these fluids become solid. Recent reviews on the phenomenon of

electro-rheology and its applications has been presented by Jordan and Shaw, [8].

Survey of the literature on ER fluids reveals there are three possible modes of

operations which are shear, flow and squeeze- flow modes, shown in Figure 1.2.

4

Motion Direction ER Plate

ER Fluid

SHEAR MODE

ER Plate

Flow ER Fluid

FLOW MODE

Fixed Plate

ER Fluid

Moving Plate

Motion Direction

SQUEEZE-FLOW MODE

Figure 1.2: Operation Modes of ER Fluids.

In shear mode, the electrodes of the ER fluid devices are free to rotate or

translate in relation to each other. Control of the shear properties of the fluid leads to

application torque transmission such as clutches, brakes, shock absorbers and

vibration dampers, etc. Increasing of the shear stress with the applied electric field is

the important performance characteristics of the ER fluids and it was detected by

using Rotational viscometer and Oscillatory viscometer. Donalds L. Klass and

Thomas W. Martinek have used Rotational viscometer to observ the increase in

5

viscosity with electric field, [12]. But the stiffening and consequent ability of ER

fluids to transmit forces is due to rheological characteristics and not due to a viscosity

change. Detailed discussions of these rheometers are undertaken by many

researchers, [8].

N.G. Stevens, J.L. Sproston and R. Stanway designed ER clutches for torque

transmission by using shear mode principle, [10]. They describe the test facility and

presents the results of a series of experiments to determine the torque transmission

characteristics as a function of voltage and fluid temperature. They designed first

clutch in 1984. It had a vertical shaft with the ER fluid contained in an open reservoir

and the clutch plate was fixed. The transmission torque obtained was 0.007 Nm

upon the application of 1 kV/mm electric field. Second clutch was designed by these

researchers in 1988 [3]. This new design involved a horizontal shaft with a totally

enclosed reservoir for the ER fluid and the clutch plates were easily adjustable which

allowed opportunity to study the effect of the clutch plates distance.

N. Martis, S. A. Burton, D. Hill and M. Jordan investigated the mechanical

behaviour of a silicon oil based ER fluid by using oscillatory viscometer and

designed an ER damper, [5]. The modification of the damping resistance is obtained

by varying the mechanical properties of the ER fluid within the damper by applying

an electric field. Their damper consists of an outer cylinder and a double-ended

piston rod that pushes the ER fluid through a stationary annular duct.

In the flow mode, the electrodes of the ER devices are assumed fixed. The ER

devices can be constructed in which the flow rate-pressure characteristic is controlled

by varying the applied electric field. This leads to the concept of ER actuators in

which ER valves control the fluid flow in a hydraulic circuit.

D.A. Brooks explained the ER valve and different types of constructions

which are cylindrical and rectangular, shown in Fig 1.3, [11]. His rectangular valve

consist of pair of flat electrodes which are isolated with insulator material. The yield

stress obtained is 7 kPa when 3 kV/mm electric field is applied. The yield value is

6

controllable from 0 to 7 kPa by voltage from 0-1.5 kV and the no-field pressure loss

can be reduced by having multiple flow paths or increasing the gap.

Flow Flow insulator length length

width plate electrode width

(a) (b)

Figure 1.3: ER Valve Construction Types.

Two valve arrangement of the Brooks is shown in Figure 1.4. If a voltage

applied across the valves, the resulting differential pressure can cause the ram to

move.

Supply Pressure

ER Valve

Exhaust

Figure1.4: Two valve arrangement

Single valve has limited uses in itself. Four ER valves are arranged to form a

Wheatstone bridge by Brooks, shown in Figure 1.5. Opposing valves are connected

to the same power supply and bi-directional movement effected by upsetting the

balance of the bridge. The flow resistance to one side of the ram is raised and the

7

other side reduced and fluid flows into the ram chamber. The available thrust is a

product of the ER pressure drop and the piston area and the ram speed as a function

of the flow rate.

Supply Pressure

ER Valve

Exhaust

Figure 1.5: Wheatstone Bridge Arrangement.

A. J. Simmonds designed ER valve which operate in flow mode operation, [2].

His valve plate geometry is similar to the Brooks’s valve plate, but he uses multi-

plate in a valve to increase the surface area, shown in Figure 1.6.

ER Fluid Length

Flow Width

Length

Flow

HV

8

Figure 1.6: Multi-plate ER valve.

The ER fluid which is used in his experiments obtained by mixing of the 40%

cornflour and 60% silicon oil by weight. It has advantages in that it is cheap,

available in quantity and it is not biologically hazardous etc.

Firstly, he explained the pressure drop characteristics of the single valve with

the electric field and the flow rate of the fluid . Maximum pressure drop obtained

was 160 kPa with the application of 3.2 kV/mm as 19.3 lt/min from his single valve

was flowing.

Another ER valve study was presented by S. B. Choi, C. C. Cheong, J. M. Jung

and Y. T. Choi, [7]. They tested the Bingham property of the silicone oil-based ER

fluid as a function of electric field. The ER valve with multi-channel plates is

manufactured. Pressure drops of the ER valve are evaluated with respect to the

number of electrodes and the intensity of the electric field. The ER valve-cylinder

system is formulated and equations of motion for the system are derived to achieve

the position control of the cylinder system.

In squeeze-flow mode, the ER fluid is sandwiched between two electrodes, one

fixed and one moving in a direction normal to its own plate. In this mode, the

variation of the transmitted pressure with the applied electric field on the upper plate

are investigated.

J.L. Sproston, S.G. Rigby, E.W. Williams and R. Stanway have investigated

the compressive squeeze performance of an ER fluid sandwiched between two

circular electrodes,[13]. They explained the variation of transmitted force through the

ER fluid on the upper plate with the electrode distance, frequency of oscillation and

applied electric field.

9

1.4 Content of This Work

Electrohydraulic servovalves have been used in hydraulic control systems.

However, this type valves are complex and expensive, [16]. ER valves are designed

instead of servovalves to control the hydraulic system by using the ER effect. They

are desirable to introduce an alternative means of reversible and fast control since

they have no moving parts.

The aim of this work is to find out the rheological characteristics of the ER

fluids and to manufacture a valve by using this phenomenon. Mineral oil and

transformer oil-based ER fluids were produced by mixing with corn starch in

different weight ratios. Shear mode and flow mode operations of this ER fluids were

investigated.

Rotational viscometer was designed and constructed. Bingham property of the

ER fluids were tested as a function of electric field intensity. The relationship

between shear stress, shear rate and electric-field magnitude on such a devices was

obtained in order to determine geometrical dimensions of an ER valve.

After setting the dimensions, an ER valve was manufactured. Single ER valve

was connected directly to a pump. Then, pressure against flow characteristics under

the electric field for a Bingham plastic flow through an ER valve was obtained.

Four ER valves were arranged to form a hydraulic wheatstone bridge. Pump

and hydraulic actuator were connected to this bridge. Opposing pairs of valves were

connected to the same voltage supply and bi-directional movement effected by

upsetting the balance of the bridge.

• Chapter 2 presents the concentrations of the ER fluids and relationship

between shear stress, shear rate and electric-field magnitude on ER fluids. This part

of the investigation shear mode type of operation of the ER fluids.

10

• Chapter 3 presents the method of determination of the multi-plate ER valve

dimensions and pressure against flow characteristics of the multi-plate single ER

valve. This part of study is flow mode type of operation of the ER fluid.

• Chapter 4 describes wheatstone bridge arrangement of the multi-plate ER

valves. The performance characteristics of the bridge in hydraulic circuit was

explained and available load on piston were determined.

• Chapter 5 presents conclusions and recommendations for future research.

11

CHAPTER 2

ELECTRO-RHEOLOGICAL BEHAVIOUR

2.1 Introduction

The influence of the electric field on the deformation of the materials has

been investigated by many researchers over the years. Electro-rheological effect is

main part of these studies. If an external electric field applied on an ER fluid, the

particles of the ER fluid is charged and arrange themselves like chains, between

electrodes. In this way, flow resistance and applied stress on electrodes can be

increased. This effect is proportional to the electric field applied, and it is reversible

and fast acting.

This special characteristic of the ER fluids allow some potential applications.

Flow, squeeze-flow and shear modes are three major application methods of the ER

effect in practical devices. The fluid is pumped through a valve which consists of

fixed electrodes in flow modes. The ER fluid is sandwiched between two electrodes

in squeeze-flow mode. In shear mode, shearing the fluid by moving one electrode

relative to another. Rotational viscometer test is the type of shear mode operation.

D. L. Klass and T. W. Martinek presented the influence of shear rate, field

strength, composition and temperature on rheological behaviour of special fluids in

1966, [12]. They plotted the apparent viscosity against shear rate under the electric

field and temperature by using rotational viscometer. Since that time, numerous

investigators have studied rheological behaviour by same method.

In this chapter, the shear mode application of ER fluids is presented.

Ingredients of the ER fluid and different mixture ratios are explained. Experimental

results showing the relations between shear stress, shear rate and electric field

12

magnitude are given in graphical form. Besides, Bingham property of the ER fluids is

briefly explained.

2.2 Idealised Behaviour of ER Fluids

Understanding of the ER fluid’s behaviour is the key to design ER devices.

The relationship between shear stress and shear rate is the most important parameter

in understanding this behaviour and it depends on some criteria. Increasing weight

ratio of the polarised particles, field strength and temperature increase ER effect, but

increasing shear rate and frequency decrease this effect, [12].

ER fluids have been modelled as Bingham plastics which means that flow is

observed only after exceeding a minimum yield stress. Idealised behaviour of the ER

fluid is shown in Figure 2.1.

Shear Stress

b η p

τ y

Newtonian Fluid

a ηN

Shear Rate

Figure 2.1: Ideal Behaviour of ER Fluid.

Line “a” shows the characteristics of Newtonian fluids and line “b” shows

the characteristics of Bingham plastics. Slopes of these lines are the dynamic

viscosities of fluids. With no electric field applied an ER fluid behaves like a

Newtonian fluid and the applied stress will cause the liquid to flow. Eq.2.1 is a first

order model approximating the behaviour of a Newtonian fluid.

τ µ ∂ ∂= N u y/ (2.1)

13

Where µ N is the Newtonian viscosity in Pa.s, ∂ ∂u y/ is the shear rate in s-1 and the τ

is the shear stress in Pa.

Flow only occurs for a stress greater than the yield stress in Bingham plastics.

Below the yield stress, applied stress will strain the plastic but not cause it to flow.

The equation for a Bingham body is:

τ τ µ ∂ ∂= +y p u y/ (2.2)

Where τ is the shear stress in Pa, τ y is the yield stress in Pa, µ p is the plastic

viscosity in Pa.s. The yield stress increases proportional to the applied electric field

while the plastic viscosity unchanged, [2].

2.3 Electro-Rheological Fluids Used in This Study

The ER fluids used in rotational viscometer tests comprised of mineral oil and

transformer oil containing corn starch. Dynamic viscosity and density of mineral oil

are 0.041 Pa.s and 900 kg/m3, respectively. 0.0074 Pa.s is the dynamic viscosity and

840 kg/m3 is the density of transformer oil. These fluids are mixed with corn starch in

different weight ratios. Figure 2.2 and Figure 2.3 show the effect of mixing ratios on

dynamic viscosity of mineral oil and transformer oil-based ER fluids, respectively.

0

0,2

0,4

0,6

0,8

0 20 30 40 50% of Polarised Particles by Weight

Dynamic Viscosity ( Pa.s)

Figure 2.2: Dynamic Viscosity of Mineral Oil-Based ER Fluids.

14

0

0,2

0,4

0,6

0,8

0 20 30 40 50% of Polarised Particles by Weight

Dyamic Viscosity (Pa.s)

Figure 2.3: Dynamic Viscosity of Transformer Oil-Based ER Fluids.

The comparison is rather good for weight ratios up to about 50% both mineral

oil-based and transformer oil-based ER fluids. The dynamic viscosities increase

drastically above 50%, even ER fluids lose their fluid properties. Increasing the

weight ratio of particles increases the electro-rheological effect. That is why ER

particle should be maximum in possible range.

2.4 Experimental Set-up

Viscous behaviour of the ER fluids can clearly be seen by plotting the change

in shear stress with respect to shear rate. And this curve are clearly describe the

rheological behaviour of the ER fluids in detail. Flow curves are obtained by using

rotational viscometer which comprises of two concentric cylinders with 0.8 mm

radial separation of two faces as shown in Figure 2.4. An ER fluid is filled in this

space. With no electric field present, rotating the inner cylinder creates the shear

stress but littler or no motion and torque on the outer cylinder. When the electric field

is applied, the ER fluid stiffen with field strength and stress is transferred to the outer

cylinder as a torque. When the electric field great enough, the ER fluid turns out to

be like a solid and the cylinders behave as tough, they were pressed together with no

fluid between them.

15

Figure 2.4: Rotational Viscometer.

The electric field between two concentric cylinders is obtained from a high

voltage power supply capable of providing voltages from 0-1000 Volts. Outer

cylinder of the viscometer is connected to a cantilever beam on which two strain

gauge were stuck. Transmitted stress is determined by using a strain indicator. The

flow curves of the ER fluid were drawn by using a plotter. X direction on the plotter

DC motor

Inner cylinder

Plotter

Outer cylinderER fluid

Strain Gauge

High voltage Pover S l

Power supply

Strain indicator

16

corresponds to the DC motor speed which is proportional to the shear rate and Y

direction corresponds to the voltage of the strain indicator which is proportional to

the transmitted stress. The speed of the inner cylinder is transformed to the shear rate

and the voltage of the strain indicator is transformed to the shear stress. Thus, the

output graph of the plotter is arranged with these new values.

2.5 Experimental Results

The variation of the transmitted torque or shear stress with electric field was

investigated in these experiments. The effect of mixture ratios on ER behaviour was

examined. Increase of the yield stress under the application of different electric

fields on mineral oil and transformer oil-based ER fluids which contain corn starch in

different weight ratios are presented.

Rotational viscometer results of the mineral oil-based ER fluids are given in

Figures 2.5 to 2.8. The shear stress was measured by applying the electric Voltages

from 250 to 1000 V, while the shear rate up to 160 s-1. In order for the experimental

data to be credible, measurement was repeated four or five times at the same

operating conditions.

These graphs present both Newtonian and Bingham property of the ER fluids

and the effect of concentration of polarised particles together with the intensity of

applied electric field on ER behaviour.

17

18

Investigation of Figures 2.5 to 2.8 under the application of electric field show

the effect of concentration of the corn starch on the shear stress. These curves reflect

Bingham plastic characteristics, i.e. under an applied electric field flow only occurs

for a stress greater than the yield stress. Application of 1 kV can cause an increase in

yield stress approximately 6 Pa, 10 Pa, 18 Pa and 110 Pa corresponding to the weight

ratios of 20%, 30%, 40% and 50% corn starch in mineral oil, respectively. It is clear

19

that yield stress increases exponentially depending on the concentration of cornstarch

in mineral oil. Slopes of viscous behaviour curves for the mineral oil-corn starch ER

fluid under the applied different electric fields are almost the same with the slope of

curve for the ER fluid without no electric field applied. Also, it can be deducted from

these curves that shear stress difference between with and without electric field does

not change at any shear rate. It has a constant value which is approximately equal to

the yield stress.

The slope of the flow curves indicate the Newtonian viscosity of mixtures. To

validate the results obtained from Rotational viscometer, some are cross checked

with the results obtained from a saybolt viscometer. It is seen that slope of the fluid

under consideration is about 0.057 in Fig. 2.5 and saybolt viscometer result is the

0.052 Pa.s. This difference may be emerged from the measurement errors and it may

be tolerable according to the nature of the work, but nevertheless, a consistent

method is set to determine viscous behaviour of ER fluids.

Figures 2.7 and 2.8, depicting viscous behaviour under the electric field show

humps within the small region of shear rate around 2 s-1. Where the fluid behaves as

a solid. It is realised that the torque motor used to rotate the inner cylinder of the

viscometer can not overcome the yield stress created by the ER fluid resistance and

the bearing friction force. When the inner cylinder starts its motion initially formed

chains break suddenly. This phenomenon causes a sudden in shear stress. This region

can be assumed as a transitional region and the results obtained within this small

region should not be relied on. Figure 2.8 indicates also that with increasing the

electric field, yield stress increases linearly. Obviously, there is a directly

proportional relationship between them.

Figures 2.9 to 2.12 show the mechanical stress/strain relationship for

transformer oil-based ER fluids. These curves are obtained by using the same

experimental set-up and measurement techniques.

20

21

The curves which are obtained under 0 V/mm electric field have Newtonian

fluid characteristics. When the slope of this curves are investigated, it is seen that

they are approximately the same with Saybolt viscometer measurements given in

Figure 2.3. For example, Newtonian viscosity of the ER fluid which contains 30%

corn starch and 70% Transformer oil is 0.02 Pa.s and the slope of the flow curve of

this ER fluid is 0.02. Under the application of an electric field, these fluids behave

like a Bingham body. When the viscous behaviour of transformer oil-corn starch ER

fluids given in Figures 2.9 to 2.12 are examined, it is seen that the slopes of the

curves under electric field are not parallel to the slopes of the curves without

electrical field. It can be stated that shear stress difference between the with and

without electric field is reduced by increasing the shear rate. At certain shear rate it

would be very small or zero. The yield stress of the fluids in the same figures are 7,

18, 62 and 158 Pa for the weight ratios of 20, 30, 40 and 50% corn starch particle in

transformer oil respectively. As in the case of mineral oil-starch ER fluid, yield stress

22

increases exponentially depending on the concentration of corn starch in transformer

oil. And also yield stress is linearly proportional to the applied electric field.

2.6 Conclusion

Selection of a suitable base fluid and a mixture ratio can be made on the basis

of observation of the rheological characteristic of a mixture. The experimental results

show that ER properties of the both base fluid under consideration are these:

� Yield stress increases linearly with increasing the electric field.

� Increase of concentration of dielectric particles causes the exponential yield stress

increase.

� Newtonian viscosity exponentially increases with increasing the concentration of

dielectric particles

Transformer oil-based ER fluid have some advantages over the mineral oil-

based ER fluid. These are:

� Newtonian viscosity of the transformer oil-based ER fluid is low. Low no-field

viscosity property of this fluid provides low pressure drop passing through an

orifice.

� The sedimentation of the dielectric particles in transformer oil takes long time.

� Increase of yield stress of the transformer oil-based ER fluids under the applied

electric field is always higher than mineral oil-based ER fluids yield stresses at all

weight ratios.

One of the major disadvantage of the transformer oil is the decrease of the shear

stress between the no-electrical field and under electrical field, while increasing the

shear rate.

24

CHAPTER 3

ELECTRO-RHEOLOGICAL VALVE

SINGLE MODEL

3.1 Introduction

Directional control valves are important elements of an hydraulic system. The

task of the control valve is to connect various hydraulic lines to one another, and

continuously make a variety of cross linkage connection between different hydraulic

lines. Using such valves, it is possible to influence the direction of the effect of

pressure and volumetric flow, and therefore to control the cylinders or hydraulic

motors regard in to start, stop and direction of motion. In order to increase both

accuracy and speed of the system response, servovalves have been used in hydraulic

control systems, but they are highly non-linear, complex, expensive and their

response is limited by moving parts. ER valves are desirable to introduce an

alternative means of fast and simple control since they have no moving parts.

While designing an ER valve, a common requirement is that the ER fluid

have a high ratio between applied field shear stress and no-field shear stress. Power

requirement and solid content of the ER fluids should be known before designing ER

devices. Since, they are important controlling factor of yield strength. Other fluid

characteristics for the device design are the dispersion stability to sedimentation and

no-field viscosity.

Previous chapter presents the performance characteristics of mineral oil and

transformer oil-based ER fluids. Bingham property of the ER fluids were tested as a

function of applied electric field in order to determine geometrical parameters of the

ER valve. The main objective of this study is to determine the controlling factors of

the pressure drop on ER valve and the possibility of using the ER valve for

25

controllable hydraulic systems. The valve dimensions were determined on the basis

of desired pressure drop analysis by using the Rotational viscometer results. Then, a

rectangular multi-plate ER valve was designed and manufactured. This valve was

directly connected to a hydraulic pump and pressure drop over ER valve was

measured with respect to the pump flow rate as well as the intensity of the electric

fields.

3.2 Design of an ER Valve

To analyse an ER valve it is necessary to have some understanding of an ER

fluid’s idealised behaviour. This can be done by using the stress against shear rate

diagram obtained from Rotational viscometer.

When we consider an ER valve which has a single flow path, in the absence

of the electric field the pressure drop produced only by the Newtonian viscosity of

the ER fluid and it is proportional to the flow rate of the ER fluid pumped through

the gap. Assuming that the flow between two plates is laminar, then the pressure drop

becomes, [2,7];

P lQ whN N G= 12 3µ / ( ) (3.1)

where QG is the flow passing through a single gap valve without electric field, in

m3/s,

µ N is the Newtonian viscosity, in Pa.s,

l is the length of valve electrode, in m,

w is width of the valve electrode, in m,

h is the gap between two plates, in m.

w l

h

26

Figure 3.1: Parallel Plate Valve.

Upon applying electric field, a pressure drop due to the yield stress of the ER

fluid is additionally generated. Resistance force on a single plate caused by yield

stress can be written as;

F lwy Y= τ (3.2) Where τ y is the yield stress, in Pa.s. Since there are two plates, this equation must be multiplied by 2 .

F lwy Y= 2τ (3.3) This resistance yields a pressure drop across the gap then, force on the fluid body

contained between the plates becomes;

F P hwf ER= ∆ (3.4)

Equating these forces each other; the pressure drop due to the yield stress becomes;

∆P l hER y= 2τ / (3.5)

Total pressure drop of the ER valve with single path in the presence of the electric

field is obtained by adding the pressure drop due to the Plastic viscosity to the

pressure drop due to the yield stress. This is given by,

∆P lQ wh l hP y= +12 23µ τ/ ( ) / (3.6)

When we consider the ER valve which has a multi-flow path, the contribution

of shear resistance and the pressure drop due to the yield stress increase with number

of flow path. The total pressure drop of the ER valve with multi-channels under the

application of applied electric field can be obtained as:

∆P m l h m Q l why P G= +2 12 3τ µ/ / ( ) (3.7)

27

where m is the number of energised paths by electric field.

Eq. 3.7 reveals that the total pressure drop over an ER valve increases directly

as the number of the energised paths increases. In the absence of electric field,

number of energised paths are zero so that the total pressure drop of the ER valve is

produced by only the Newtonian viscosity of the ER fluid. Eq. 3.7 also implies that

the performance of the ER valve is dependent on the number of energised paths,

rheological behaviour of the ER fluid and design parameters such as the electrode

width, w, length, l , and height, h . Rheological behaviour of ER fluids are controlled

with the electric field intensity applied and the concentration of polarised particles.

Consequently, they directly affect the ER valve performance.

Figure 3.2 shows a rectangular multi-plate ER valve, which was designed on

the basis of desired pressure drop analysis. The material of the electrode is carbon

steel and is isolated from each other by rubber plates. The fluid gasket is applied

between the valve and rubber plates to prevent the leakage of the ER fluid. The

number of electrodes is 6 and they form five flow paths. The gap spacing is 0.7 mm.

The length and width of each electrode is 100 and 25 mm, respectively.

Figure 3.2: Multi-Plate ER valve.

28

3.3 Pressure Analysis of ER Valve

While designing an ER valve-actuating system, it is necessary to known the

pressure drop characteristics of an ER valve. The experimental set-up used in this

study is shown in Figure 3.2.

4 3 2

5

1

8

9

6

7

1- Multi- plate ER Valve 6- Personal Computer

2- 0-1000 V High Power Voltage Supply 7- Pump Driver

3- 0-1000 Psi Pressure Transducer 8- Hydraulic Pump

4- Multimetre 9- ER Fluid Reservoir

5- Amplifier

Figure 3.3: Single ER Valve Pressure Analysis System.

29

Multi-plate ER valve is connected directly to a pump which has the

proportional flow rate with pump speed. The nominal displacement of the pump is

50 10 6 3× − m rev/ and it is driven between 0-100 rpm. Pressure transducers which

have the range of 0-1000 Psi were calibrated by using Dead Weight Tester and

mounted at the inlet and outlet of the ER valve. Transducer signals are conditioned

by a 5 kHz frequency amplifier. 0-1000 Volt high power voltage supply was used to

create electric field between valve plates.

Experimental results are given in Figure 3.4.a-3.4.c which present the field-

dependent pressure drop with respect to the pump flow rate. The agreement between

measured and theoretical values is important for valve design, thus the validation of

the proposed pressure analysis is proved.

30

The pressure drop characteristics of a single valve with respect to the flow rate is

given in Figures 3.4.a, b and c under the applied 1 kV electric voltage. As it can be

seen from these figures, pressure drop due to yield stress shows similar trend as the

shear stress curves obtained from the rotational viscometer. The electro-rheological

pressure drop decreases with the pump flow rate, when using ER fluids containing

20% and 30% corn starch, shown in Figures 3.4.a and b. Shear rate increases with the

31

pump flow the valve effects the yield stress. The particle chains are destroyed, when

the fluid flow exceeds the 4 l/min and the effect of the yield stress on the rheological

pressure drop disappeares. Increase of the concentration of the dielectric particles in

mixtures partially prevent the chain breakdown. And the pressure drop due to yield

stress are additionally generated up to high fluid flow, shown in Figure 3.4.c.

The pressure drop due to yield stress is approximately 85 kPa at a flow of 5

l/min under the application of the 1 kV high voltage and the total pressure drop is

approximately 850 kPa, when using the ER fluid contaminated 40% dielectric

particles by weight, Figure 3.4.c and the theoretical pressure drop due to yield stress

is 75 kPa at the same conditions. Considering the pressure drop due to concentration

of the polarised particles in Fig. 3.4, the pressure drop increases with the

concentration of the corn starch. This results and conclusions are observed some

researchers before that. Brooks designed an ER valve which has the length is 100

mm, electrode spacing is 0.5 mm, width is 155 mm and number of flow path is 1,

[11]. The pressure drop due to Newtonian viscosity is 5.2 bar at a flow of 10 l/min.

Maximum yield stress is 7 kPa and additional pressure drop is 30 bar when the

application of 3 kV/mm. Simmonds designed a multi-flow ER valve, [2]. His valve

has seventeen valve plates, the width of each being 36 mm, length of 102 mm and

gap height 1mm. The maximum pressure drop is obtained 160 kPa when the

application of 3200 V/mm and the pump flow rate is 19.3 l/min. S.B. Choi, C.C.

Cheong, J.M. Jung and Y.T. Choi developed a valve which has five pairs of flow

paths, [7]. Geometrical dimensions of the gap, length and width of each electrode

space are 0.8, 200 and 20 mm, respectively. They obtain the 400 kPa pressure drop

across the valve upon the application of 4 kV/mm when all gaps are energised.

3.4 Conclusion

This chapter presented the flow mode operation of the ER fluids. Design

parameters of the ER valve was determined. A multi-channel plate for the ER valve

was designed and manufactured on the basis of the field depended Bingham model.

The pressure drop of the ER valve was evaluated experimentally and theoretically

32

with respect to the intensity of the electric field and the concentration of polarised

particles.

Eq. 3.7 implies that the performance of the ER valve dependent on the

number of energised paths, rheological behaviour of the ER fluid and design

parameters such as the electrode width, w, length, l , and gap height, h . No-field

viscosity effects can be reduced by increasing the gap between the electrodes, but

required voltage must be very high. Figure 3.7 presents the effect of concentration of

polarised particles and intensity of applied electric field on valve pressure drop.

These results are proved each other and they are verified with the other researches

from literature. Experimental results also shows that the pressure drop due to yield

stress decreases with the increase of the pump flow rate which is directly affected by

the shear rate in the ER valve. The reason for this behaviour is the yield stress

decrease by increasing of the shear rate.

33

CHAPTER 4

ER VALVE HYDRAULIC WHEATSTONE BRIDGE

ARRANGEMENT

4.1 Introduction

The basic concepts behind the hydraulic power and hydraulic control systems

have changed little over the past decades. In designing a hydraulic control system, the

limiting element in performance is often the mechanical stage. The performance of

dynamic system is characterised by the dynamic response. It is largely governed by

the mass, stiffness and energy dissipation characteristics of the system. The electro-

rheological effect is a new method of providing high performance element that is

directly interfecable with solid state electronics. ER phenomena results from the

effect of a electrical field over the contaminated fluid across two electrodes. Thus,

dielectric particles form chains to produce a force that resist the fluid motion.

Single ER valve and two valve actuator system have limited performance for

controlling the load pressure on hydraulic actuators. This type of constructions are

estimated in Reference 11. Four identical ER valves should be arranged to form a

Wheatstone bridge to control the fluid flow in hydraulic circuits. A. J. Simmonds and

D. A. Brooks have used Wheatstone bridge arrangement to control the fluid flow in

an hydraulic circuit, [2,11]. They present the effects on flow resistance of ER fluid in

this circuit.

34

In this study, four identical multi-plate ER valves were designed and they are

arranged to form a Wheatstone bridge. The performance characteristics of this bridge

on fluid flow control are presented. Moreover, the control factors of the available

thrust on hydraulic piston are explained.

4.2 ER Valve Wheatstone Bridge Arrangement

A wheatstone bridge circuit adapted for ER fluids is shown in Figure 4.1.

Four identical ER valves are arranged in pairs 1 through 4 and they are normally

open. Opposing pairs of the valves (1-4 and 2-3) are connected to the same voltage

supply and bi-directional movement effected by upsetting the balance of the bridge.

The flow resistance to one side of the ram is raised and the other side reduced and

fluid flows into the actuator. The available thrust is the product of the pressure drop

and the piston area. Actuator speed depends on the flow rate into the chamber.

P Qp P,

P1,Q1 P2 ,Q2 1 2 3 4 P2 P1

PL ,QL

Figure 4.1: ER Valve Hydraulic Wheatstone Bridge Arrangement.

When a high voltage applied on the valve pairs which are valves in 1 and 4,

available pressure drop P1 is obtained by adding the pressure drop due to the plastic

viscosity to the pressure drop due to the yield stress, P2 is the pressure drop due to

35

Newtonian viscosity. Thus, P1 is greater than P2 and the flow rate Q1 is less than the

Q2. Using the equivalent hydraulic law’s, the following equations can be written,

P P PP P PQ Q QQ Q Q

L

p

L

p

= −= +

= −= +

1 2

1 2

2 1

1 2

(4.1)

Flow rate through the valves can be found,

Q Q QQ Q Q

p L

p L

2

1

22

= +

= −

( ) /( ) /

(4.2)

Eqs. 4.1 and 4.2 hold true for any hydraulic valve. Pump pressure and load pressure

on actuator for ER valve bridge is calculated by using Eq. 4.3, given below

P lQ wh lQ wh m l h

P m l h lQ wh lQ wh

p p N y

L y p N

= + +

= + −

12 12 2

4 12 12

13

23

13

23

µ µ τ

τ µ µ

/ ( ) / ( ) /

/ / ( ) / ( ) (4.3)

Eq. 4.3 implies that, the load pressure decrease with increasing load flow. This is

because as, when the application of applied electric field is increased; P1 is increased

across the valve pairs 1 and 4, P2 is decreased across the valve pairs 2 and 3.

Consequently, the flow Q1 decreased as Q2 increased.

4.3 ER Valve Hydraulic Wheatstone Bridge

Valve-actuator system is shown in Fig. 4.2. This circuit can be operated as a

symmetrical balanced bridge. Each pair of valves must be similar and they are

controlled by a high voltage power supply. When operated of this bridge, the constant

flow is required from the pump. The fluid in the pipe from tank to actuator does not

36

need to be accelerated. Only small reservoir tank is required. Pipes from tank to

bridge and bridge to actuator should be as short as possible. Some care has to be

taken in choosing circuit components because of nature of the fluid mixture.

Polarised particles can cause same problems on sliding seals. That is why the solid

particles should be wholly solute in base fluids. Double acting hydraulic cylinder

should be taken to obtain similar thrusts on both sides of the actuator.

1

2

1 2 3

3 4 4

5

6

7 8

1- Hydraulic Actuator 5- Amplifier

2- ER Valve Wheatstone Bridge 6- ER Fluid Reservoir

3- Pressure Transducer 7- Hydraulic Pump

4- Multimeter 8- Pump Driver

Figure 4.2: Valve Actuator System.

37

The ER valves used were the same as the prototype used to determine the

experimental results. Double acting cylinder has a low coefficient of friction and the

effective actuator area of both sides is 2 34 10 3 2. × − m . Pressure transducers were

located at the input and output of the actuator to determine the load pressure under

the application of 1 kV/mm. The nominal pump displacement is 50 10 6 3× − m rev/ and

it produces constant flow.

The ER fluid used in these tests comprised of a transformer oil containing

corn starch particles. The weight fraction of the particles was about 40 % and there

was no any other additive material. The Newtonian viscosity of this mixture is

approximately 0.042 Pa.s.

Experiments were carried out with different pump flow rates under the

application of 1 kV voltage. The results are shown in Table 4.1. It indicates that the

load pressure on the both sides of the piston are not the same. It means that valves are

not identical and pressure drop are not identical and for this reason it is drastically

effected.

Table 4.1: Available Load Pressures on Piston.

Q Load Pressure (kPa) l/min First Pairs Second Pairs

1.6 35.53 179.72

2.1 30.72 141.27

2.6 25.92 122.05

3.1 25.02 102.82

In spite of these inconsistent results of the load pressure, hydraulic actuator

motion was controlled by the application of the electric field on the valve pair 1-4

cylinder was moved to leftwards. Removing electric field from this pair and applying

to the other pair it was moved to the rightwards.

38

CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

The mechanical properties of the ER fluids in shear, tension, and compression

are subject to dramatic variations with applied electric field. If the intensity of

electric field is 1-3 kV/mm, an ER fluid turns to a solid, [2]. This effect is fast and

fully reversible.

This electro-rheological phenomenon has been exploited in engineering

practices for the development of discrete devices. The ER devices can be constructed

in which the flow rate-pressure characteristic is controlled by varying the applied

electric field in flow mode. This leads to the concept of ER actuators in which ER

valves control the fluid flow in a hydraulic circuit. In shear mode, the electrodes of

the ER fluid devices are free to rotate and/or translate in relation to each other.

Control of the shear properties of the fluid leads to torque transmission applications

such as clutches, brakes, shock absorbers, and vibration dampers, etc.

The study presented here is investigated the shear and flow mode operations

of ER fluids. The aim of this study was to make the initial step in gathering the

knowledge and the technology of an ER effect in actuating systems which will lead to

design of an ER valve as an ultimate purpose of this study. Firstly, the effect of the

applied electric field and the concentration of the polarised particles on rheological

behaviour were investigated by using Rotational viscometer. Flow curves of the ER

fluids were drawn and the increase of the yield stress with the applied electric field

was determined. Secondly, The valve dimensions were determined on the basis of

desired pressure drop analysis. Then, rectangular multi-plates ER valve was designed

and it was directly connected to a hydraulic pump. Pressure drop over an ER valve

was determined with respect to the pump flow rates and applied electric fields.

39

Finally, the ER valves to form a Wheatstone bridge in a hydraulic circuit and the

available thrust on actuator was determined.

ER fluids which used in hydraulic circuits should be available in quantity,

non-corrosive and biologically non-hazardous. In this study, mineral oil and

transformer oil are used as base fluids and corn starch as an additive. The Bingham

property of the mineral oil and transformer oil-based ER fluids were investigated by

using Rotational viscometer. Experimental results of these fluids show that

concentration of the polarised particles and the intensity of the electric field are the

most important controlling factors. Yield stress increase with the increase of the

applied electric field and the concentration of the corn starch. Experimental results

also show that transformer oil-based ER fluids have some advantages over the

mineral oil-based ER fluids. Newtonian viscosity of the transformer oil-based ER

fluids are low and the sedimentation time of the polarised particles is high. Low

no-field viscosity property of this fluid provides low pressure drop due to Newtonian

viscosity in ER valve. Other advantage of this fluid is the increase of in yield stress

with applied electric field under the same electric field. Consequently, these two

important properties provide a high available thrust force in a hydraulic circuit.

To illustrate the interplay between fluid characteristics and design of an ER

device, an ER fluid must have a high ratio between applied-field stress and no-field

stress. Control factors of the ER effect which are power requirement and solid

content must be determined before designing of an ER device. Under these

considerations, ER devices designed and their dimensions were determined.

Examination of Eq. 3.7 shows that the performance of an ER valve is dependent on

the number of energised paths, rheological behaviour of the ER fluid and dimensions

of valve gap. The pressure drop increases with increasing electrode length and

decreasing electrode height. The pressure drop due to Newtonian viscosity decreases

with increasing of the gap height. Pressure drop-flow rate characteristics show the

effects of rheological behaviour on valve pressure drop. The pressure drop due to

yield stress increase with increasing applied electric field and concentration of

40

polarised particles. It is decrease with increasing pump flow rate. Because, the yield

stress decrease with increasing shear rate.

Single valve has limited uses in itself. Four ER valves were arranged to form

a Wheatstone bridge for controlling actuator in hydraulic circuit. Opposing valves are

connected to the same power supply and bi-directional movement is affected by

upsetting the balance of the bridge. The available thrust is a product of the ER fluid

pressure drop and the piston area. Experimental results show that, the available thrust

on both sides of the actuator are not same. This results from the difference of valve

dimensions and flow in wheatstone bridge. To obtain similar pressure drop the

valve dimensions must have been identical.

5.2 Recommendations

1. ER fluid used in hydraulic circuit must be available in quantity and non-

corrosive. It must have low-no field viscosity for low pressure drop due to

Newtonian viscosity on ER valve. Sedimentation of the polarised particles

must be prevented.

2. Increase of the yield stress under the application of the electric field must

be maximum. The ER fluids must have a high ratio between

applied-field stress and no-field stress.

3. Materials of the circuit component must be selected carefully. Fluid

composition can cause some problems on sliding seals. That’s why, the

solid particles must be wholly solute in base fluids.

4. During the design, manufacturing methods to be used must be kept in

mind. The shape and dimensions of the valve must be determined due to

desired pressure drop. Dimensions and pressure drop of the ER valves

must be similar which used in wheatstone bridge arrangement to obtain

41

similar pressure drop on both sides of the actuators. Only small dimension

differences between the valves can cause unbalanced thrust on hydraulic

piston.

42

LIST OF REFERENCES

1. M. V. Gandhi and B. S. Thompson, 1992, “ Electro-Rheological Fluids”,

Smart Materials & Structures, Chapman and Hall Ltd., pp 137-173.

2. A. J. Simmonds, 1991, “Electro-Rheological Valves in a Hydraulic

Circuit”, IEE Proceedings-D, Vol. 138, No. 4, pp 400-404.

3. N. G. Stevens, J. L. Sproston, R. Stanway, 1988, “ An Experimental Study

Of Electro-Rheological Torque Transmission”, Transactions of the

ASME, Vol. 110, pp 182-188.

4. G. J. Monkman, 1997, “ Exploitation Of Compressive Stress In

Electrorheological Coupling”, Mechatronics, Vol. 7, No. 1, pp 27-36.

5. N. Markis, S. A. Burton, D. Hill and M. Jordan, 1996, “Analysis And

Design Of ER Damper For Seismic Protection Of Structures”, Journal of

Engineering Mechanics, Vol. 122, No. 10, pp 1003-1001.

6. S. B. Choi and Y. K. Park, 1994, “ Active Vibration Control Of A

Cantilevered Beam Containing An Electro-Rheological Fluid”, Journal of

Sound and Vibration, Vol. 173, pp 428-430.

7. S. B. Choi, C. C. Cheong, J. M. Jung and Y. T. Choi, 1996, “ Position

Control Of An ER Valve-Cylinder System Via Neural Network

Controller”, Mechatronics, Vol. 7, No. 1, pp 37-52.

43

8. Therese C. Jordan and Montgomery T. Shaw, 1989, “ Electrorheology”,

IEEE Transactions on Electrical Insulation, Vol. 2, No. 5, pp 849-879.

9. R. Stanway and J. L. Sproston, 1994, “ Electro-Rheological Fluids: A

Systematic Approach to Classifying Modes of Operation”, Transactions of

the ASME, Vol. 116, pp 498-504.

10. N. G. Stevens, J. L. Sproston and R. Stanway, 1985, “ The Influence Of

Pulsed D.C. Input Signals On Electrorheological Fluids”, Journal of

Electrostatics, Vol. 17, pp 181-191.

11. D.A. Brooks, 1982,“ Electro-Rheological Devices”, Chart Mechanical

Engineering, pp 91-93.

12. D. L. Klass and Thomas W. Martinek, 1967,“ Electroviscous Fluids. I.

Rheological Properties”, Journal of Applied Physics, Vol. 38, pp 67-74.

13. J. L. Sproston, S. G. Rigby, E. W. Williams and R. Stanway, 1994, “ A

Numerical Simulation of Electrorheological Fluids in Oscillatory

Compressive Squeeze-Flow”, J. Phys. D: Applied Physics, Vol. 27, pp

338- 343.

14. S. B. Choi, C. C. Cheong, J. M. Jung and G. W. Kim, 1997, “Feedback

Control Of Tension In A Moving Tape Using An ER Brake Actuator”,

Mechatronics, Vol. 7, No. 1, pp 53-66.

15. T. G. Duclos, Debra N. Acker and J. David Carlson, 1988, “ Fluids That

Thicken Electrically”, Machine Design, vol. 1000, pp 56-61.

16. S. Kapucu, “ Design and Construction of a Two Stage Electrohydraulic

Servovalve With Force Feedback ”, M.S. Thesis, METU.

44

PART LIST OF ER VALVE Name of Part Quantity Materials Drawing No 1- Nipple 2 Iron 2

2- Front Cover 2 Iron 3

3- ER Valve Plate 6 Stainless Steel 4

4- Isolator Plate 10 Rubber 5

5- Outer Cover 2 Iron 6

6- Bolt 16 Iron 7

7- Isolator Plate 8 Rubber 8

45

A A

1 2 3 4 5 6 7

SECTION A-A

Drawing Name ASSEMBLY DRAWING OF THE ER VALVE GAZIANTEP

Drawn By Egemen Ramazan Topçu Drawing No 1 UNIVERSITY

46

M14 D5 D24

16 22 16

Drawing Name NIPPLE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 2 UNIVERSITY

47

60 15 30

16 14 12 5 30 Drawing Name FRONT COVER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 3 UNIVERSITY

48

100 20 20 20 20 20 45 60 6 D8 Thickness 2 mm. Drawing Name ER VALVE PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 4 UNIVERSITY

49

20 80 7 11 D8 Thickness 0.7 mm Drawing Name ISOLATOR PLATE GAZIANTEP

Drawn By Egemen Ramazan Topçu Drawing No 5 UNIVERSITY

50

100 45 20 20 20 20 20 60 D8 8 Drawing Name OUTER COVER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 6 UNIVERSITY

51

M8 45 Drawing Name BOLT GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 7 UNIVERSITY 5 D8 30 Drawing Name ISOLATOR RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 8 UNIVERSITY

PART LIST OF ROTATIONAL VISCOMETER

52

Name of Part Quantity Materials Drawing No

1- DC Motor 1 ---- ----

2- DC Motor Plate 1 Iron 2

3- Coupler 1 Rubber 3

4- Plate Stick 4 Iron 4

5- Top Plate Rice Ring 1 Rice 5

6- Main Top Plate Bearing 2 Steel 6

7- Isolator Fittings 1 Rubber 7

8- Main Top Plate 1 Iron 8

9- Inner Cylinder 1 Aluminium 9

10- Outer Cylinder 1 Aluminium 10

11- Main Stick 4 Iron 11

12- Outer Cylinder Isolator Cup 1 Fiberglass 12

13- Outer Cylinder Fittings 1 Iron 13

14- Main Bottom Plate 1 Iron 14

15- Strain Gauge 2 --- ----

16- Main Bottom Plate Bearing 2 Steel 15

17- Main Bottom Plate Rice Ring 1 Rice 16

53

1 2 3 4 6 5 7 8 9 10 11 12 13 14 15 16 17 Drawing Name ASSEMBLY DRAWING OF THE ROTATIONAL VISCOMETER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 1 UNIVERSITY

54

D5 15 55 75 8 Drawing Name DC MOTOR PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 2 UNIVERSITY D5 25 D25 Drawing Name COUPLER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 3 UNIVERSITY

55

M8 D10 15 45 Drawing Name PLATE STICK GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 4 UNIVERSITY D20 D12 18 Drawing Name TOP PLATE RICE RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 5 UNIVERSITY

56

D12 D6 6 Drawing Name MAIN TOP PLATE BEARING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 6 UNIVERSITY M20 40 10 20 D20 D5 Drawing Name ISOLATING FITTINGS GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 7 UNIVERSITY D10

57

110 D20 135 18 20 95 Drawing Name MAIN TOP PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 8 UNIVERSITY 5 10

58

15 45 20 D45 D35 D40 M20 Drawing Name INNER CYLINDER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 9 UNIVERSITY

59

45 3 D50 D41.4 Drawing Name OUTER CYLINDER GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 10 UNIVERSITY 20

60

68 D25 M8 Drawing Name MAIN BLOK STICK GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 11 UNIVERSITY D60 D50 5 10 5

61

30 Drawing Name OUTER CYLINDER ISOLATOR CUP GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 12 UNIVERSITY 20 5 D30 D6 Drawing Name OUTER CYLINDER FITTINGS GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 13 UNIVERSITY D10 110

62

D20 145 20 25 95 Drawing Name MAIN BOTTOM PLATE GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 14 UNIVERSITY

63

D20 D12 20 Drawing Name TOP PLATE RICE RING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 15 UNIVERSITY D12 D6 6 Drawing Name MAIN BOTTOM PLATE BEARING GAZIANTEP Drawn By Egemen Ramazan Topçu Drawing No 16 UNIVERSITY