a magnetorheologic semi-active isolator...

Smart Structures Bio-Nano Laboratory

A MAGNETORHEOLOGIC SEMI-ACTIVEISOLATOR TO REDUCE NOISE AND VIBRATION

TRANSMISSIBILITY IN AUTOMOBILES

Gregory J. StelzerDelphi Automotive Systems

Chassis Systems Test Center, Dayton, OH 45401-1245

Mark J. Schulz, Jay Kim, Randall J. AllemangDepartment of Mechanical Engineering

University of Cincinnati, Cincinnati, OH 45221-0072


OUTLINE1. INTRODUCTION1. INTRODUCTION

2. BACKGROUND2. BACKGROUND

3. MODELING OF RHEOLOGIC FLUIDS3. MODELING OF RHEOLOGIC FLUIDS

4. MODELING OF ISOLATION SYSTEMS4. MODELING OF ISOLATION SYSTEMS

5. RESULTS5. RESULTS

6. MR ISOLATOR COIL DESIGN6. MR ISOLATOR COIL DESIGN

7. CONCLUSIONS7. CONCLUSIONS

8. RECOMMENDATIONS OF FUTURE WORK8. RECOMMENDATIONS OF FUTURE WORK


11--1. INTRODUCTION1. INTRODUCTION

•• Passive vibration isolators are inexpensive and simple. For thePassive vibration isolators are inexpensive and simple. For these reasons, se reasons, most isolation systems in automobiles use passive isolators.most isolation systems in automobiles use passive isolators.

•• When using a passive vibration isolator, there is a tradeoff betWhen using a passive vibration isolator, there is a tradeoff between Noise, ween Noise, Vibration, and Harshness (NVH) performance and durability characVibration, and Harshness (NVH) performance and durability characteristics. teristics. Passive isolators cannot provide both optimal isolation and optiPassive isolators cannot provide both optimal isolation and optimal mal durability.durability.

•• The object of this thesis is to develop an advanced vibration isThe object of this thesis is to develop an advanced vibration isolator olator design for automotive components that can provide substantial andesign for automotive components that can provide substantial and costd cost--effective improvements in NVH performance.effective improvements in NVH performance.

•• The new work in this thesis will provide:The new work in this thesis will provide:

1.1. Information on the advantages and limitations of semiInformation on the advantages and limitations of semi--active isolation.active isolation.2.2. A detailed nonlinear model of the isolator.A detailed nonlinear model of the isolator.3.3. The results of extensive simulation studies of a practical desigThe results of extensive simulation studies of a practical design.n.



•• In the automotive industry, noise control expectations from the In the automotive industry, noise control expectations from the end user end user are becoming more strict, and consequently the Original Equipmenare becoming more strict, and consequently the Original Equipment t Manufacturer (OEM) has responded by placing higher expectations Manufacturer (OEM) has responded by placing higher expectations on the on the suppliers.suppliers.

•• Noise control specifications have now become standard on many ofNoise control specifications have now become standard on many of the the smallest components in the vehicle.smallest components in the vehicle.

•• A customer will now use component performance to develop a list A customer will now use component performance to develop a list of of acceptable candidates, and then use NVH to determine where the bacceptable candidates, and then use NVH to determine where the business usiness is awarded.is awarded.

•• This increased emphasis on noise reduction and operator comfort This increased emphasis on noise reduction and operator comfort is is requiring that more attention be paid to the use of vibration anrequiring that more attention be paid to the use of vibration and noise d noise isolation and attenuation systems in automobiles.isolation and attenuation systems in automobiles.



•• A compressor, used in an automobile’s leveling systems, will be A compressor, used in an automobile’s leveling systems, will be used as used as an example in this research.an example in this research.

•• A leveling system is used to keep a vehicle level with respect tA leveling system is used to keep a vehicle level with respect to road o road surface, surface, ieie, when a load is placed in the back of the truck, the rear , when a load is placed in the back of the truck, the rear suspension is compressed more than the front. A leveling systemsuspension is compressed more than the front. A leveling system will will raise the back end of the vehicle so that it is once again levelraise the back end of the vehicle so that it is once again level with the with the front.front.

•• The compressor pumps air into the vehicle shocks, and this is whThe compressor pumps air into the vehicle shocks, and this is what at raises the back end of the vehicle.raises the back end of the vehicle.

•• When the compressor runs, it generates high frequency vibration When the compressor runs, it generates high frequency vibration that is that is transmitted to the vehicle structure.transmitted to the vehicle structure.



•• In this research, the compressor will be modeled as a mass with In this research, the compressor will be modeled as a mass with a force a force that produces high frequency excitation. that produces high frequency excitation.

•• The isolator design will minimize the transmitted force from theThe isolator design will minimize the transmitted force from thecompressor to its structural base, a vehicle body. compressor to its structural base, a vehicle body.

•• From this point, the component generating the high frequency excFrom this point, the component generating the high frequency excitation itation will be referred to as a compressor.will be referred to as a compressor.


FIGURE 1.1. A compressor assembly with passive isolators.FIGURE 1.1. A compressor assembly with passive isolators.


22--1. VIBRATION ISOLATORS1. VIBRATION ISOLATORS

•• A vibration isolator is a flexible device that is used to attachA vibration isolator is a flexible device that is used to attach the the compressor to a mounting base.compressor to a mounting base.

•• The purpose of the isolator is to reduce the vibration or force The purpose of the isolator is to reduce the vibration or force transmitted between the compressor and the base.transmitted between the compressor and the base.

•• Different possible approaches for vibration isolation of automobDifferent possible approaches for vibration isolation of automobile ile components are described and compared. components are described and compared. The following systems are The following systems are discussed:discussed:

1.1. Passive isolation systems.Passive isolation systems.2.2. SemiSemi--active isolation systems.active isolation systems.3.3. Active isolation systems.Active isolation systems.4.4. Smart materials for actuators.Smart materials for actuators.


22--2. Passive Isolation Systems2. Passive Isolation Systems

•• In a passive isolation systems, no controls are needed for the iIn a passive isolation systems, no controls are needed for the isolator.solator.

•• The design consists of a simple natural rubber material, or a coThe design consists of a simple natural rubber material, or a comparable mparable synthetic material.synthetic material.

•• This is the cheapest option because it is the simplest design anThis is the cheapest option because it is the simplest design and the d the easiest to manufacture.easiest to manufacture.

•• The durability of the isolator can be improved by stiffening theThe durability of the isolator can be improved by stiffening the isolator. isolator. This can be done simply by increasing the This can be done simply by increasing the durometerdurometer hardness of the hardness of the material or by changing material.material or by changing material.

•• However, as the stiffness of the isolators is increased, the noiHowever, as the stiffness of the isolators is increased, the noise se performance of the compressor will be compromised, because a stiperformance of the compressor will be compromised, because a stiffer ffer isolator will generally transmit higher frequency vibration.isolator will generally transmit higher frequency vibration.



FIGURE 2.1. Design of a passive isolator.FIGURE 2.1. Design of a passive isolator.



•• A A hydromounthydromount is a more complex passive isolator. A fluid is is a more complex passive isolator. A fluid is incorporated into the design to provide extra damping.incorporated into the design to provide extra damping.

•• Fluid is forced through an orifice within the isolator. The resFluid is forced through an orifice within the isolator. The resistance istance provided by the orifice provides damping for the isolated compreprovided by the orifice provides damping for the isolated compressor.ssor.

•• The increased damping allows the isolator to be designed of a leThe increased damping allows the isolator to be designed of a less stiff ss stiff material. The combination of reduced stiffness and increased damaterial. The combination of reduced stiffness and increased damping mping allows the allows the hydromounthydromount to provide better isolation without compromising to provide better isolation without compromising durability.durability.

•• However, the added damping increases the transmitted force, and However, the added damping increases the transmitted force, and therefore, the system is not an optimal solution.therefore, the system is not an optimal solution.



FIGURE 2.2. Design of a passive FIGURE 2.2. Design of a passive hydromounthydromount..

FLUID

FLUID

ORIFICE ORIFICE

MOUNTING LOCATION

MOUNTING LOCATION

ELASTOMER SURROUNDING FLUID



•• A transmissibility model was developed to show some of these A transmissibility model was developed to show some of these concepts. It shows the compressor mounted to its structural basconcepts. It shows the compressor mounted to its structural base e through an isolator that has only passive stiffness and passive through an isolator that has only passive stiffness and passive damping damping components (k and c, respectively).components (k and c, respectively).

FIGURE 2.3. Transmissibility model.FIGURE 2.3. Transmissibility model.

c

Compressorx

yk

Base



•• The transmissibility model is used to create a ratio between forThe transmissibility model is used to create a ratio between force seen ce seen in the compressor due to rotation unbalance and force transmittein the compressor due to rotation unbalance and force transmitted d through the isolator into the base.through the isolator into the base.

•• The ratio is developed by summing the forces in the model.The ratio is developed by summing the forces in the model.

(2.1)(2.1)

•• Assuming x and y are sinusoidal displacements for the compressorAssuming x and y are sinusoidal displacements for the compressor and and base, respectively, velocity and acceleration can be calculated base, respectively, velocity and acceleration can be calculated by taking by taking the derivative of the displacement. The result is:the derivative of the displacement. The result is:

(2.2)(2.2)

where X and Y are amplitudes of vibration and where X and Y are amplitudes of vibration and ωω is the rotational speed is the rotational speed of the compressor.of the compressor.

( )

•• −+−=∑ ↑=+ xycxykxmF &&

cXjcYjkXkYXm ωωω −+−=− 2



•• The equation is rewritten as:The equation is rewritten as:

(2.3)(2.3)

•• Solving, the amplitude of the mass, X, divided by the amplitude Solving, the amplitude of the mass, X, divided by the amplitude of the of the base, Y, gives the transmissibility.base, Y, gives the transmissibility.

(2.4)(2.4)

YcjkXcjmk

+=+− ωωω 2

cjmkcjk

YX

ωωω+−

+= 2



FIGURE 2.4. Transmissibility as a function of the stiffness of FIGURE 2.4. Transmissibility as a function of the stiffness of the isolator.the isolator.

XX

YY



FIGURE 2.5. Transmissibility as a function of the damping of thFIGURE 2.5. Transmissibility as a function of the damping of the isolator.e isolator.

XX

YY


22--11. Semi11. Semi--Active Isolation SystemsActive Isolation Systems

•• A semiA semi--active isolator can only remove energy from the system.active isolator can only remove energy from the system.

•• However, a semiHowever, a semi--active isolator is capable of changing one or more active isolator is capable of changing one or more properties in response to a command signal.properties in response to a command signal.

•• The ability to change system properties gives the system designeThe ability to change system properties gives the system designer more r more control while using very little input power. control while using very little input power.

•• An example of a semiAn example of a semi--active system is a shock absorber with a variable active system is a shock absorber with a variable orifice that allows the damping coefficient to be changed as neeorifice that allows the damping coefficient to be changed as needed.ded.


22--12. Active Isolation Systems12. Active Isolation Systems

•• Active isolation systems can be controlled by computers through Active isolation systems can be controlled by computers through input input signals from sensors.signals from sensors.

•• Unlike passive and semiUnlike passive and semi--active systems, active systems are able to add active systems, active systems are able to add energy to the system.energy to the system.

•• The goal of active isolation is to provide energy equal in magniThe goal of active isolation is to provide energy equal in magnitude and tude and opposite in phase of the vibration input. In doing so, an activopposite in phase of the vibration input. In doing so, an active isolation e isolation system can improve noise performance and durability performance.system can improve noise performance and durability performance.

•• An example of an active system is an electromechanical actuator An example of an active system is an electromechanical actuator arranged to generate force by responding to a velocity or displaarranged to generate force by responding to a velocity or displacement cement feedback signal.feedback signal.


22--13. Active Isolation Systems13. Active Isolation Systems

•• However, active systems are very design intensive and require seHowever, active systems are very design intensive and require sensors nsors and processors to provide real time data to the isolator.and processors to provide real time data to the isolator.

•• Large amounts of power are also required to operate an active isLarge amounts of power are also required to operate an active isolator.olator.

•• These necessary features of the active isolation system make it These necessary features of the active isolation system make it the most the most expensive isolation design.expensive isolation design.

•• Because of the expense, active isolation systems are very uncommBecause of the expense, active isolation systems are very uncommon.on.


22--14. Smart Materials As Actuators14. Smart Materials As Actuators

•• Several different materials have been developed to allow designeSeveral different materials have been developed to allow designers to rs to use them as actuators in a system.use them as actuators in a system.

•• Piezoelectric materials experience a dimensional change when an Piezoelectric materials experience a dimensional change when an electrical voltage is applied to them.electrical voltage is applied to them.

•• Conversely, these materials produce an electrical charge when a Conversely, these materials produce an electrical charge when a pressure is applied to them.pressure is applied to them.

•• This rare property allows the piezoelectric material to be used This rare property allows the piezoelectric material to be used as a as a sensor or an actuator.sensor or an actuator.

•• The best known such material is leadThe best known such material is lead--zirconatezirconate--titanatetitanate (PZT).(PZT).

•• However, the use of PZT for vibration isolation is limited due tHowever, the use of PZT for vibration isolation is limited due to the small o the small strain capability of the material.strain capability of the material.


22--15. Smart Materials As Actuators15. Smart Materials As Actuators

•• Shape memory alloy (SMA) material possesses the interesting propShape memory alloy (SMA) material possesses the interesting property erty in that a metal “remembers” its original shape and size and chanin that a metal “remembers” its original shape and size and changes ges back to that shape and size at a characteristic transformation back to that shape and size at a characteristic transformation temperature.temperature.

•• Materials that exhibit these characteristics include: goldMaterials that exhibit these characteristics include: gold--cadmium, cadmium, brass, and nickelbrass, and nickel--titanium.titanium.

•• The alloys inherent properties have become very useful to the meThe alloys inherent properties have become very useful to the medical dical field.field.

•• The The SMA’sSMA’s ability to generate high forces at low frequency allows the ability to generate high forces at low frequency allows the material to be used as an actuator.material to be used as an actuator.

•• However, the use of SMA in engineering applications has been limHowever, the use of SMA in engineering applications has been limited ited because of slow response time and due to the limited temperaturebecause of slow response time and due to the limited temperature range range in which it can be effective.in which it can be effective.


33--1. MODELING OF RHEOLOGIC FLUIDS1. MODELING OF RHEOLOGIC FLUIDS

•• A A rheologicrheologic fluid changes properties as an external field is applied.fluid changes properties as an external field is applied.

•• These fluids can be used as controllable energy dissipaters.These fluids can be used as controllable energy dissipaters.

•• The control used is semiThe control used is semi--active, and with this approach small control active, and with this approach small control energy can produce large actuation forces.energy can produce large actuation forces.

•• The following characteristics of a The following characteristics of a rheologicrheologic fluid will be discussed:fluid will be discussed:

1.1. ER/MR fluid isolator systems.ER/MR fluid isolator systems.2.2. Bingham plastic model of MR fluids.Bingham plastic model of MR fluids.3.3. MR fluid isolator systems.MR fluid isolator systems.


33--2. ER/MR Fluid Isolator Systems2. ER/MR Fluid Isolator Systems

•• A great deal of research has been conducted on semiA great deal of research has been conducted on semi--active control active control to look for a compromise between passive and active isolation to look for a compromise between passive and active isolation systems.systems.

•• These systems can be used for vibration suppression or isolationThese systems can be used for vibration suppression or isolationand require minimal power as compared to an active system.and require minimal power as compared to an active system.

•• With a semi active system, noise performance can be improved With a semi active system, noise performance can be improved without dramatically hindering durability capabilities.without dramatically hindering durability capabilities.



•• Extensive studies have been conducted on ElectroExtensive studies have been conducted on Electro--RheologicRheologic (ER) (ER) and Magnetoand Magneto--RheologicRheologic (MR) fluids for use in semi(MR) fluids for use in semi--active systems active systems that are used for vibration suppression.that are used for vibration suppression.

•• The two materials were discovered in the late 1940’s.The two materials were discovered in the late 1940’s.

•• Jack Jack RabinowRabinow reported on a MR fluid experimental program at the reported on a MR fluid experimental program at the U.S. National Bureau of Standards for the Army’s Chief of U.S. National Bureau of Standards for the Army’s Chief of Ordinance in 1948.Ordinance in 1948.

•• Winslow published his account of a lengthy research program Winslow published his account of a lengthy research program investigating the properties and applications of ER fluid in 194investigating the properties and applications of ER fluid in 1949.9.



•• Initial testing with ER fluids showed problems with the fluid, nInitial testing with ER fluids showed problems with the fluid, namely amely operating temperature limitations and storage stability problemsoperating temperature limitations and storage stability problems..

•• Over time improvements have been made, but new problems have Over time improvements have been made, but new problems have arisen.arisen.

•• Today, ER fluids are considered to have low shear strengths. ThToday, ER fluids are considered to have low shear strengths. The e fluid provides shear strengths that are two to ten times lower tfluid provides shear strengths that are two to ten times lower than han needed for many practical applications.needed for many practical applications.

•• High voltages are required to operate ER fluids.High voltages are required to operate ER fluids.

•• There is a lack of universal fluid for ER technology.There is a lack of universal fluid for ER technology.

•• Because of these limitations, commercial success of ER fluids haBecause of these limitations, commercial success of ER fluids has s been elusive.been elusive.



•• MR fluids are more practical.MR fluids are more practical.

•• When compared to ER fluids, MR fluids offer higher order yield When compared to ER fluids, MR fluids offer higher order yield stresses and provide a better operating temperature range.stresses and provide a better operating temperature range.

•• At the same time, companies such as Lord Corporation have At the same time, companies such as Lord Corporation have commercial MR products.commercial MR products.

•• Because of the advantages of MR fluid over ER fluid, MR fluid wiBecause of the advantages of MR fluid over ER fluid, MR fluid will ll be considered from this point.be considered from this point.


33--6. Bingham Plastic Model Of MR Fluids6. Bingham Plastic Model Of MR Fluids

•• MR fluids are traditionally modeled as a Bingham plastic, where MR fluids are traditionally modeled as a Bingham plastic, where there is a passive and active component to the fluid. Wherethere is a passive and active component to the fluid. Where

(3.1)(3.1)

is the equation used to model the fluid.is the equation used to model the fluid.

•• The passive component is a function of the fluid rThe passive component is a function of the fluid resistance esistance from the viscosity, which is a property of the fluid and cannot from the viscosity, which is a property of the fluid and cannot be be controlled.controlled.

•• The active component is derived from the yield The active component is derived from the yield stress, stress, which changes proportionally with the applied magnetic field.which changes proportionally with the applied magnetic field.

••• +=⇔−+=

γηττ yMRyxMRcyieldfMRF

MRc

yieldf



•• Initial research showed the passive resistance could be modeled Initial research showed the passive resistance could be modeled as as a constant.a constant.

Figure 3.1. Shear stress versus shear strain rate for a Figure 3.1. Shear stress versus shear strain rate for a Bingham plastic material.Bingham plastic material.

Fo=0

F1

F2

F3

INCREASINGFIELDSTRENGTH

τy(F1)

τy(F2)

τy(F3)

00 •

γ

τ

η

η



•• However, further investigation showed that viscosity is a functiHowever, further investigation showed that viscosity is a function of on of shear rate, with the viscosity increasing dramatically at lower shear rate, with the viscosity increasing dramatically at lower shear shear rates. rates.

Figure 3.2. Viscosity of a MR fluid is a function of shear rateFigure 3.2. Viscosity of a MR fluid is a function of shear rate..

0 50 100 150-1

0

1

2

3

4

5MR Fluid Characteristics - MRF 132LD - Lord Corporation

Shear Rate (1/s)

Vis

cosi

ty (

Pas

)



•• The active component is derived from resistance due to yield The active component is derived from resistance due to yield stress, which is a function of the magnetic field created by a cstress, which is a function of the magnetic field created by a coil oil that is incorporated into the isolator. that is incorporated into the isolator.

Figure 3.3. Yield stress as a function of magnetic field.Figure 3.3. Yield stress as a function of magnetic field.

0 0.5 1 1.5 2 2.5 3

x 105

0

1

2

3

4

5x 104

H (Amp/m)

Yie

ld S

tress

(Pa)

MR Fluid Characteristics -- MRF 132 LD - Lord Corporation


33--10. MR Fluid Working Modes10. MR Fluid Working Modes

•• MR fluid has three different types of working modes, depending oMR fluid has three different types of working modes, depending on n how the fluid is loaded. The modes include:how the fluid is loaded. The modes include:

1.1. Shear mode.Shear mode.2.2. Flow mode.Flow mode.3.3. Squeeze mode.Squeeze mode.

•• Different equations are used to calculate resistive force for eaDifferent equations are used to calculate resistive force for each of ch of the different modes.the different modes.



Figure 3.4. Three working modes of a MR fluid (a) shear, (b) flFigure 3.4. Three working modes of a MR fluid (a) shear, (b) flow,ow,and (c) squeeze. B is the magnetic flux direction.and (c) squeeze. B is the magnetic flux direction.

B

Flux Guide

Moving Surface

B

TensionCompression

COIL

Flux Guide

Moving Surface

v

F

COIL

Flux Guide

Bp1 p2

COIL

(a) (b) (c)



•• The shear mode works when one surface moves through the fluid wiThe shear mode works when one surface moves through the fluid with th respect to another surface.respect to another surface.

•• The magnetic field is perpendicular to the direction of motion.The magnetic field is perpendicular to the direction of motion.

•• A MR based clutch is a good example of working the fluid in the A MR based clutch is a good example of working the fluid in the shear shear mode.mode.

•• The equation corresponding to the shear mode is:The equation corresponding to the shear mode is:

(3.2)(3.2)

where f is the resultant force based on the plate area, and S, Lwhere f is the resultant force based on the plate area, and S, L, b, and h , b, and h are the surface area, length, width, and height, respectively. are the surface area, length, width, and height, respectively. Is the Is the viscosity of the fluid and is the yield strength of thviscosity of the fluid and is the yield strength of the fluid.e fluid.

yLbhSLbf τη +=

ηyτ



•• The flow mode is characterized by two static flux guides with thThe flow mode is characterized by two static flux guides with the e magnetic field normal to the flow.magnetic field normal to the flow.

•• The magnetic field can be used to control flow resistance and prThe magnetic field can be used to control flow resistance and pressure essure drop across the valve.drop across the valve.

•• Automotive shock absorbers work in the flow mode.Automotive shock absorbers work in the flow mode.

•• The equation corresponding to the flow mode is:The equation corresponding to the flow mode is:

(3.3)(3.3)

where Q is the flow rate of the fluid.where Q is the flow rate of the fluid.

yhL

bhQL

HFERPHFPP τη 3312

,,0 +=∆+∆=∆



•• The squeeze mode works when two parallel surfaces are used to The squeeze mode works when two parallel surfaces are used to compress the fluid.compress the fluid.

•• The magnetic field is parallel to the motion of the surfaces.The magnetic field is parallel to the motion of the surfaces.

•• The magnetic flux density can be used to adjust the normal forceThe magnetic flux density can be used to adjust the normal force to to resist the motion.resist the motion.

•• The squeeze mode has been shown to damp vibrations with high forThe squeeze mode has been shown to damp vibrations with high forces ces and low amplitudes.and low amplitudes.

•• The equation corresponding to the squeeze mode is:The equation corresponding to the squeeze mode is:

(3.4)(3.4))()(0

302

xthha

F Φ−

=πτ


44--1. MODELING THE ISOLATION SYSTEM1. MODELING THE ISOLATION SYSTEM

•• A single degree of freedom model is used to model the compressorA single degree of freedom model is used to model the compressorsystem.system.

•• The model simulates a compressor mounted to a vehicle body.The model simulates a compressor mounted to a vehicle body.

•• To simplify the model, the motion of the vehicle body is modeledTo simplify the model, the motion of the vehicle body is modeled as a 1 as a 1 Hz sine wave. This simulates the vehicle body bouncing at the nHz sine wave. This simulates the vehicle body bouncing at the natural atural frequency of the suspension system.frequency of the suspension system.

•• Two seconds of data are simulated.Two seconds of data are simulated.

•• Halfway through the model, a speed bump is introduced. The speeHalfway through the model, a speed bump is introduced. The speed d bump is a severe test of the isolator’s durability.bump is a severe test of the isolator’s durability.


44--2. MODELING THE ISOLATION SYSTEM2. MODELING THE ISOLATION SYSTEM

•• Two models are created. One for the passive system and the otheTwo models are created. One for the passive system and the other for r for the semithe semi--active system.active system.

•• The following discussion is included:The following discussion is included:

1.1. Simulation of the passive isolator.Simulation of the passive isolator.2.2. Simulation of the semiSimulation of the semi--active isolator.active isolator.3.3. NewmarkNewmark--Beta explicit time integration.Beta explicit time integration.4.4. Filter design.Filter design.5.5. Control law design.Control law design.6.6. System inputs.System inputs.7.7. System outputs.System outputs.8.8. Detailed design of the MR isolator.Detailed design of the MR isolator.


44--3. Simulation Of The Passive Isolator3. Simulation Of The Passive Isolator

•• The passive model was used to create baseline performance standaThe passive model was used to create baseline performance standards rds for the existing isolator, and to show trend lines when stiffnesfor the existing isolator, and to show trend lines when stiffness and s and damping parameters are changed.damping parameters are changed.

•• The passive model can be seen in Figure 4.1. The model shows thThe passive model can be seen in Figure 4.1. The model shows the e compressor mounted to the vehicle body through an isolator that compressor mounted to the vehicle body through an isolator that has has only passive stiffness and passive damping components (only passive stiffness and passive damping components (kkpassivepassive and and ccpassivepassive, respectively)., respectively).

1.1. The free body diagram for the passive system can be seen in FiguThe free body diagram for the passive system can be seen in Figure 4.2. re 4.2. This diagram helps show how the equation of motion and the equatThis diagram helps show how the equation of motion and the equation ion for transmitted force are developed.for transmitted force are developed.



Figure 4.1. Passive model.Figure 4.1. Passive model. Figure 4.2. Passive free body diagram.Figure 4.2. Passive free body diagram.

cPASSIVEkPASSIVE

VEHICLE BODY

COMPRESSOR

x(t)

y(t)

F COMPRESSOR

COMPRESSOR

F COMPRESSOR ASSUME x>y

VEHICLE BODY

)( yxkPASSIVE − )(••

− yxcPASSIVE



•• The equation of motion is created by summing the forces seen in The equation of motion is created by summing the forces seen in the the free body diagram, given by:free body diagram, given by:

(4.1)(4.1)

•• This summation of forces is:This summation of forces is:

(4.2)(4.2)

•• Rearranging gives:Rearranging gives:

(4.3)(4.3)

•• The acceleration of the compressor, The acceleration of the compressor, , is then calculated as:, is then calculated as:

(4.4)(4.4)

∑ =↑+ ••xmF

( ) COMPRESSORFyxPASSIVEcyxPASSIVEkxm +−−−−=

••••

COMPRESSORFxPASSIVEcyPASSIVEcxPASSIVEkyPASSIVEkxm +−+−=••••

( )

+−+−=

••••

COMPRESSORFxyPASSIVEcxyPASSIVEkmx 1

••x



•• The force transmitted into the vehicle body is also seen in the The force transmitted into the vehicle body is also seen in the free body free body diagram. A transmitted force is considered any force created frdiagram. A transmitted force is considered any force created from the om the relative motion between the vehicle body and the compressor thatrelative motion between the vehicle body and the compressor that acts acts upon the vehicle body.upon the vehicle body.

•• The transmitted force is computed using:The transmitted force is computed using:

(4.5)(4.5)

•• Including the spring and damper force in (4.5) gives:Including the spring and damper force in (4.5) gives:

(4.6)(4.6)

∑ =↑+ TRANSFF

( )

••

−+−=∑ =↑+ yxPASSIVEcyxPASSIVEkTRANSFF



•• The compressor assembly consists of three baseline isolators andThe compressor assembly consists of three baseline isolators and the the compressor.compressor.

•• Each isolator is a simple passive isolator with the following prEach isolator is a simple passive isolator with the following properties:operties:

•• Synthetic rubber material of 60 Synthetic rubber material of 60 durometerdurometer..•• Rated to withstand temperatures up to 110 C.Rated to withstand temperatures up to 110 C.•• Measured stiffness of k=50,000 N/m and damping ratio of zeta=0.1Measured stiffness of k=50,000 N/m and damping ratio of zeta=0.1..•• Height of 20 mm, outer diameter of 14 mm, and mass of 6.8 grams.Height of 20 mm, outer diameter of 14 mm, and mass of 6.8 grams.

•• The compressor has the following properties:The compressor has the following properties:

•• 230 mm long, 180 mm wide, and 110 mm tall.230 mm long, 180 mm wide, and 110 mm tall.•• Mass of 3 kg (6.6 lbs.)Mass of 3 kg (6.6 lbs.)

•• For the model, it was assumed that oneFor the model, it was assumed that one--third of the mass (1 kg) was on third of the mass (1 kg) was on each isolator.each isolator.


44--8. Simulation Of The Semi8. Simulation Of The Semi--Active IsolatorActive Isolator

•• The semiThe semi--active isolator was modeled to replace the passive isolator.active isolator was modeled to replace the passive isolator.

•• The fluid was modeled as a Bingham plastic, where there is a pasThe fluid was modeled as a Bingham plastic, where there is a passive sive and active component to the fluid.and active component to the fluid.

•• The equations used to model the fluid are as follows:The equations used to model the fluid are as follows:

(4.7)(4.7)

(4.8)(4.8)

••

−+= yxMRcyieldfMRF

•

+= γηττ yMR



•• The The ccMRMR component of the fluid is the passive part of the fluid.component of the fluid is the passive part of the fluid.

•• It is a function of the viscosity of the fluid, , the shear raIt is a function of the viscosity of the fluid, , the shear rate of the fluid, , te of the fluid, , and the geometry of the flow path.and the geometry of the flow path.

•• The shear rate of the fluid is a function of the relative velociThe shear rate of the fluid is a function of the relative velocity and the ty and the fluid gap width. The viscosity of the fluid is a function of thfluid gap width. The viscosity of the fluid is a function of the shear rate.e shear rate.

•• The The ffyieldyield is the active isolation component of the MR fluid.is the active isolation component of the MR fluid.

•• It is a function of the yield strength of the fluid, .It is a function of the yield strength of the fluid, .

•• The yield strength of the MR fluid is related to the resistance The yield strength of the MR fluid is related to the resistance force force through the gap area of the isolator’s flow channels and the strthrough the gap area of the isolator’s flow channels and the strength of ength of the magnetic field surrounding it.the magnetic field surrounding it.

yτ

•γη



Figure 4.3. SemiFigure 4.3. Semi--active model of the MR isolator.active model of the MR isolator.

Processor WithControl Law

ControlFilterIntegratorVehicle Body

Compressor

Amplifier ForMR Coil

MR cpassivekpassive

y(t)

x(t)

Fcomponent



Figure 4.4. SemiFigure 4.4. Semi--active free body diagram.active free body diagram.

COMPRESSOR

F COMPRESSOR ASSUME x>y

VEHICLE BODY

FMR)( yxkPASSIVE − )(••

− yxcPASSIVE



•• The equation of motion is created by summing the forces seen in The equation of motion is created by summing the forces seen in the the free body diagram, given by:free body diagram, given by:

(4.9)(4.9)

•• However, in the semiHowever, in the semi--active system, forces created by the MR fluid are active system, forces created by the MR fluid are included in the equation of motion.included in the equation of motion.

(4.10)(4.10)

•• Rearranging gives:Rearranging gives:

(4.11)(4.11)

•• The acceleration of the compressor, , is then calculated asThe acceleration of the compressor, , is then calculated as::

(4.12)(4.12)

∑ =↑+ ••xmF

( ) COMPRESSORFMRFyxPASSIVEcyxPASSIVEkxmF +−−−−−=∑ =↑+

••••

COMPRESSORFMRFxPASSIVEcyPASSIVEcxPASSIVEkyPASSIVEkxm +−−+−=••••

( )

+−−+−=

••••

COMPRESSORFMRFxyPASSIVEcxyPASSIVEkmx 1

••x



•• The transmitted force equation for the semiThe transmitted force equation for the semi--active system is very similar active system is very similar to the passive equation.to the passive equation.

•• The transmitted force is computed using:The transmitted force is computed using:

(4.13)(4.13)

•• But once again, the forces generated by the MR fluid need to be But once again, the forces generated by the MR fluid need to be considered.considered.

(4.14)(4.14)

•• It is important to note that the MR force is transmitted into thIt is important to note that the MR force is transmitted into the vehicle e vehicle body. For this reason, the control of the MR fluid is very impobody. For this reason, the control of the MR fluid is very important.rtant.

∑ =↑+ TRANSFF

( ) MRFyxPASSIVEcyxPASSIVEkTRANSFF +−+−=∑ =↑+

••



•• To generate the passive and active force components from the MR To generate the passive and active force components from the MR fluid, fluid, the pressure drop through the isolator must be analyzed.the pressure drop through the isolator must be analyzed.

(4.15)(4.15)

•• From (4.15), the force components can be derived using the area From (4.15), the force components can be derived using the area of the of the flow channel, flow channel, AAgapgap, and the area of the isolator plunger, A, and the area of the isolator plunger, Aii..

•• The derivation of the active component follows:The derivation of the active component follows:

(4.16)(4.16)

•• It is important to note that the active component of the MR fluiIt is important to note that the active component of the MR fluid is d is directly proportional to the yield stress of the fluid. directly proportional to the yield stress of the fluid.

3123bhQL

yhLP ητ +=∆

yhL

iroryhL

gapAyieldf τπτ

−== 2233



•• The derivation of the passive component is a little more complicThe derivation of the passive component is a little more complicated. ated. The passive force is related to the viscosity and flow rate.The passive force is related to the viscosity and flow rate.

(4.17)(4.17)

•• However, the flow rate is a function of relative velocity.However, the flow rate is a function of relative velocity.

(4.18)(4.18)

•• When the velocity is factored out, the passive component is seenWhen the velocity is factored out, the passive component is seen as as being proportional to the viscosity of the fluid and the geometrbeing proportional to the viscosity of the fluid and the geometry of the y of the isolator.isolator.

(4.19)(4.19)

312bhQLyxMRc η=−

••

3

22212312312

bh

Lyxirirorbh

LyxiAgapA

bhQL

gapAyxMRc

••••

••−

−=−

==−ηπ

πηη

3222123

22212

bhL

irorirbh

LirirorMRc ηππ

ηππ

−=−=



•• Simplifying, the equation for the passive component of the MR flSimplifying, the equation for the passive component of the MR fluid is uid is found.found.

(4.20)(4.20)

•• Combining the passive rubber components and the MR components ofCombining the passive rubber components and the MR components ofthe isolator, the MR based isolator is modeled as follows:the isolator, the MR based isolator is modeled as follows:

(4.21)(4.21)

312bhL

gapAiAMRc η=

( ) ( ) yieldfyxMRccyxkIsolatorF +−++−=

••



•• The control of the The control of the ffyieldyield component is very important.component is very important.

•• The goal of the The goal of the ffyieldyield term is to control road input frequencies without term is to control road input frequencies without transmitting higher frequencies created by the compressor.transmitting higher frequencies created by the compressor.

•• This done by controlling the active MR component to model the paThis done by controlling the active MR component to model the passive ssive damping provided by the isolator, but using a low pass filter todamping provided by the isolator, but using a low pass filter to eliminate eliminate the higher frequencies created by the compressor.the higher frequencies created by the compressor.


44--18. 18. NewmarkNewmark--Beta Explicit Time Integration MethodBeta Explicit Time Integration Method

•• This is an integration method with force balance iteration used This is an integration method with force balance iteration used to move to move from one time point to the next because the equations of the isofrom one time point to the next because the equations of the isolator lator system are nonlinear and cannot be solved in closed form.system are nonlinear and cannot be solved in closed form.

•• The integration method requires initial displacement, velocity, The integration method requires initial displacement, velocity, and and acceleration components. It then calculates displacement and veacceleration components. It then calculates displacement and velocity locity for the next time point, and inputs them into the equation of mofor the next time point, and inputs them into the equation of motion. tion.

•• Ten iterations are run for each point, allowing the calculationsTen iterations are run for each point, allowing the calculations to to converge.converge.

•• This is an accurate, flexible, and simple method for solving nonThis is an accurate, flexible, and simple method for solving nonlinear linear equations. However, a small time step is required.equations. However, a small time step is required.


44--19. Filter Design19. Filter Design

•• The lowThe low--pass filter was designed as a second order Butterworth filter.pass filter was designed as a second order Butterworth filter.

•• The filter was designed with a cutoff frequency of 30 Hz in ordeThe filter was designed with a cutoff frequency of 30 Hz in order to “turn r to “turn off” the actuator at 50 Hz so the compressor vibration is not troff” the actuator at 50 Hz so the compressor vibration is not transmitted ansmitted to the automobile frame.to the automobile frame.

•• Figure 4.5 shows how the filter introduces amplitude distortion Figure 4.5 shows how the filter introduces amplitude distortion based on based on frequency.frequency.

•• It also shows how the filter introduces phase lag into the respoIt also shows how the filter introduces phase lag into the response of the nse of the active MR component.active MR component.



Figure 4.5. Characteristics of a second order Butterworth filteFigure 4.5. Characteristics of a second order Butterworth filter.r.

0 20 40 60 80 100 120 140 160 180 2000

0.2

0.4

0.6

0.8

1Second Order Butterworth Low Pass Filter Properties -- 30 Hz

Frequency (Hz)

Mag

nitu

de

0 20 40 60 80 100 120 140 160 180 200-200

-150

-100

-50

0

Frequency (Hz)

Pha

se (

deg)



•• The following shows how the lowThe following shows how the low--pass filter works:pass filter works:

•• The active variable v is set equal to the relative velocity betwThe active variable v is set equal to the relative velocity between the een the compressor and the structural base. compressor and the structural base.

•• It is then filtered, producing a variable z with the compressor It is then filtered, producing a variable z with the compressor excitation excitation content removed.content removed.

•• The variable z is then scaled to produce the yield stress of theThe variable z is then scaled to produce the yield stress of the fluid.fluid.

v = relative velocityv = relative velocity vv FilterFilter zz yield stress=z*scaleyield stress=z*scale



•• The variable v is exactly in phase with the passive isolation foThe variable v is exactly in phase with the passive isolation force.rce.

•• If the filter was a perfect filter, there would be no phase lag If the filter was a perfect filter, there would be no phase lag in variable z, in variable z, and it too would be exactly in phase with the passive isolation and it too would be exactly in phase with the passive isolation force.force.

•• However, as seen in Figure 4.6, when the vehicle hits the bump, However, as seen in Figure 4.6, when the vehicle hits the bump, the the response of the active component lags behind the passive componeresponse of the active component lags behind the passive component nt by roughly ninety degrees.by roughly ninety degrees.

•• Because the active component lags, it cannot be as effective as Because the active component lags, it cannot be as effective as possible.possible.

•• If the amplitude of the active MR component is scaled too high, If the amplitude of the active MR component is scaled too high, this this phase lag can cause a phase lag induced instability in the modelphase lag can cause a phase lag induced instability in the model..



Figure 4.6. Showing the phase lag with a Butterworth low pass fFigure 4.6. Showing the phase lag with a Butterworth low pass filter.ilter.

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3-15

-10

-5

0

5

10

15

Time (s)

Active component lags behind the passive component.

Dam

ping

For

ce (

N)

pass iveactive



•• Several ideas were explored to resolve this phase lag issue and Several ideas were explored to resolve this phase lag issue and improve improve results.results.

•• A phase lag compensator can be used to correct the phase lag.A phase lag compensator can be used to correct the phase lag.

•• Displacement and velocity feedback control with phase lag can beDisplacement and velocity feedback control with phase lag can beresolved into corrected displacement and velocity components.resolved into corrected displacement and velocity components.

•• This feedback can be used in a linear control law.This feedback can be used in a linear control law.•• The limitation of this technique is that both position and velocThe limitation of this technique is that both position and velocity ity

feedback are needed.feedback are needed.

•• Another idea is the concept of an ideal filter, as seen in FigurAnother idea is the concept of an ideal filter, as seen in Figure 4.7.e 4.7.

•• This filter would have no phase lag at any frequency.This filter would have no phase lag at any frequency.•• The amplitude cutThe amplitude cut--off is perfect at the cutoff frequency.off is perfect at the cutoff frequency.



Figure 4.7. Characteristics of an ideal lowFigure 4.7. Characteristics of an ideal low--pass filter.pass filter.Frequency (Hz)

Frequency (Hz)

0

180

1800 ∞

1

0

-1∞0 30

Phase

Magnitude

Ideal Low Pass Filter



•• To get the desired results for this type of control system, reseTo get the desired results for this type of control system, research arch showed that the design of the low pass filter is a very importanshowed that the design of the low pass filter is a very important factor.t factor.

•• Research also showed that compensating for phase lag is very Research also showed that compensating for phase lag is very complicated.complicated.

•• While this subject needs further research, a simpler approach waWhile this subject needs further research, a simpler approach was taken s taken for this model.for this model.

•• To illustrate the adverse affects of the low pass filter, the fiTo illustrate the adverse affects of the low pass filter, the filter was lter was simply turned off when the compressor was off.simply turned off when the compressor was off.

•• The filter was there for the sole purpose of taking out the compThe filter was there for the sole purpose of taking out the component in onent in the relative velocity response due to the compressor.the relative velocity response due to the compressor.

•• If the compressor is not running, there is no reason to have theIf the compressor is not running, there is no reason to have the filter on.filter on.


44--27. Control Law Design27. Control Law Design

•• A skyhook control algorithm was considered for the control of thA skyhook control algorithm was considered for the control of the e isolator.isolator. It was based on the following logic:It was based on the following logic:

Figure 4.9. Diagram of skyhook control law.Figure 4.9. Diagram of skyhook control law.

Positive absolute velocity (+)

Negative absolute velocity (-)

Negative relative velocity (-)

Positive relative velocity (+)

Negative relative velocity (-)

Positive relative velocity (+) Controller ON

Controller OFF

Controller ON



•• A careful evaluation of the results showed that the active MR coA careful evaluation of the results showed that the active MR component mponent would not react immediately to the bump in the model.would not react immediately to the bump in the model.

Figure 4.10. Skyhook control law does not allow theFigure 4.10. Skyhook control law does not allow theisolator to react properly to a bump.isolator to react properly to a bump.

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3-15

-10

-5

0

5

10

15

Time (s)

Skyhook control does not allow the active component to react properly .

Dam

ping

For

ce (

N)

passiveactive



•• A relative skyhook control algorithm was investigated. It was bA relative skyhook control algorithm was investigated. It was based on ased on the logic below. It was quickly noted that this control was thethe logic below. It was quickly noted that this control was the same as same as always having the control on.always having the control on.

Figure 4.11. Diagram of relative skyhook control law.Figure 4.11. Diagram of relative skyhook control law.

Positive relative velocity (+)

Negative relative velocity (-) Negative relative velocity (-)

Positive relative velocity (+) Controller ON

Controller ON



•• With no skyhook control, the isolator is able to react properly.With no skyhook control, the isolator is able to react properly.

Figure 4.12. No skyhook control allows the isolator to react prFigure 4.12. No skyhook control allows the isolator to react properly.operly.

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3-15

-10

-5

0

5

10

15

Time (s)

No skyhook control allows the active component to react properly .

Dam

ping

For

ce (

N)

passiveactive



•• In the control system shown in Figure 4.3, an accelerometer is lIn the control system shown in Figure 4.3, an accelerometer is located ocated on the compressor and another accelerometer is located on the veon the compressor and another accelerometer is located on the vehicle hicle body.body.

•• The acceleration signals can be integrated and then subtracted tThe acceleration signals can be integrated and then subtracted to give o give the velocity of the compressor relative to the vehicle body.the velocity of the compressor relative to the vehicle body.

•• This relative velocity is used as a feedback signal in the contrThis relative velocity is used as a feedback signal in the control ol algorithm.algorithm.

•• While this approach is feasible, the two channels of data acquisWhile this approach is feasible, the two channels of data acquisition and ition and the signal processing would add complication and cost to the isothe signal processing would add complication and cost to the isolator lator system.system.



•• Another approach is to design a direct relative velocity sensor Another approach is to design a direct relative velocity sensor that is that is built into the isolator. built into the isolator.

•• The velocity of the piston in the isolator with respect to the bThe velocity of the piston in the isolator with respect to the base is the ase is the relative velocity that must be measured.relative velocity that must be measured.

•• It may be possible to have a magnet built into the piston rod anIt may be possible to have a magnet built into the piston rod and a small d a small coil of wire attached to the isolator housing which is attached coil of wire attached to the isolator housing which is attached to the to the base.base.

•• The magnet moving through the coil of wire around the piston rodThe magnet moving through the coil of wire around the piston rod will will produce a voltage in the coil that will be proportional to the vproduce a voltage in the coil that will be proportional to the velocity of elocity of the magnet relative to the coil.the magnet relative to the coil.



•• Another possible approach is to use a Linear Variable DifferentiAnother possible approach is to use a Linear Variable Differential al Transformer.Transformer.

•• These devices are used to measure relative displacement and may These devices are used to measure relative displacement and may be be adapted to measure velocity, or the derivative of the relative adapted to measure velocity, or the derivative of the relative displacement may be taken to obtain relative velocity. displacement may be taken to obtain relative velocity.

•• A design with a sensor in each isolator would have the added posA design with a sensor in each isolator would have the added possibility sibility and advantage of individually controlling each isolator. This wand advantage of individually controlling each isolator. This would ould provide rotational isolation for the component and is a potentiaprovide rotational isolation for the component and is a potentially simple lly simple approach to achieve multiapproach to achieve multi--degreedegree--ofof--freedom control.freedom control.

•• The development of such a sensor should be investigated in futurThe development of such a sensor should be investigated in future e work.work.


44--34. System Inputs34. System Inputs

•• The unbalance force due to the compressor rotation is simulated The unbalance force due to the compressor rotation is simulated as a as a sinusoidal force input to the compressor mass.sinusoidal force input to the compressor mass. As discussed earlier, As discussed earlier, the compressor is turned on and off during the simulation.the compressor is turned on and off during the simulation.

•• The vehicle body motion is modeled as a body heave mode, with a The vehicle body motion is modeled as a body heave mode, with a speed bump input midway through the simulation.speed bump input midway through the simulation.

•• Both inputs can be seen in Figure 4.13.Both inputs can be seen in Figure 4.13.


44--35. System Inputs35. System Inputs

Figure 4.13. Model inputs for the compressor and vehicle body.Figure 4.13. Model inputs for the compressor and vehicle body.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-20

-10

0

10

20

Noi

se S

ourc

e In

put

(N)

Model Inputs

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.05

0

0.05

Veh

icle

Bod

y M

otio

n (m

)

Time (s)


44--36. System Outputs36. System Outputs

•• The main outputs from the simulation are:The main outputs from the simulation are:

•• Power spectral density of the transmitted force at 50 Hz, the Power spectral density of the transmitted force at 50 Hz, the frequency of the compressor.frequency of the compressor. The PSD is calculated during the time The PSD is calculated during the time period that the compressor is on. An example of the PSD is seenperiod that the compressor is on. An example of the PSD is seen in in Figure 4.14.Figure 4.14.

•• Maximum relative displacement between the compressor and the Maximum relative displacement between the compressor and the vehicle body.vehicle body. This occurs shortly after the bump. This is This occurs shortly after the bump. This is considered a measure of durability of the isolator.considered a measure of durability of the isolator.


44--37. System Outputs37. System Outputs

Figure 4.14. Example of a power spectral density plot.Figure 4.14. Example of a power spectral density plot.

0 50 100 150 200 250 300 350 400 450 50010-6

10-4

10-2

100

102

Frequency (Hz)

Power Spectral Density(N2/Hz)

Power spectral density of the transmitted force.


44--38. Detailed Design Of The MR Isolator38. Detailed Design Of The MR Isolator

•• Once the control and filter issues were resolved, a fluid was chOnce the control and filter issues were resolved, a fluid was chosen.osen.

•• Lord Corporation’s web site was used to get fluid properties on Lord Corporation’s web site was used to get fluid properties on their their product MRF 132LD. This fluid was chosen because it had low visproduct MRF 132LD. This fluid was chosen because it had low viscosity cosity properties.properties.

•• The properties of MRF 132LD can be seen in Figure 4.15.The properties of MRF 132LD can be seen in Figure 4.15.



Figure 4.15. Properties of MRF 132LD.Figure 4.15. Properties of MRF 132LD.

0 50 100 150

0

2

4

MR Fluid Characteristics - MRF 132LD - Lord Corporation

Shear Rate (1/s)V

isco

sity

(P

as)

0 0.5 1 1.5 2 2.5 3

x 105

0

1

2

3

4

5x 10

4

H (Amp/m)

Yie

ld S

tres

s (P

a)

0 0.5 1 1.5 2 2.5 3

x 105

0

0.5

1

H (Amp/m)

B (

Tesl

a)



•• Using the fluid properties, the size of the isolator needed to oUsing the fluid properties, the size of the isolator needed to obtain the btain the performance necessary was determined.performance necessary was determined.

•• The power capability and coil design needed to generate the poweThe power capability and coil design needed to generate the power was r was also determined.also determined.

•• Final design parameters, such as weight, size, fluid volume, coiFinal design parameters, such as weight, size, fluid volume, coil l length,etc., were determined.length,etc., were determined.

•• Results are compared.Results are compared.

•• The goal is to show that the semiThe goal is to show that the semi--active design can give the same active design can give the same maximum relative displacement as the passive baseline, but, in amaximum relative displacement as the passive baseline, but, in addition, ddition, provide a significant reduction in noise transmission.provide a significant reduction in noise transmission.


55--1. RESULTS1. RESULTS

•• The results of the passive and semiThe results of the passive and semi--active models are plotted. The active models are plotted. The maximum relative displacement and transmitted force seen with thmaximum relative displacement and transmitted force seen with the e passive system are plotted. These results are used to develop tpassive system are plotted. These results are used to develop the he baseline performance of the passive isolator.baseline performance of the passive isolator.

•• The following four designs are discussedThe following four designs are discussed::

•• Design Case 1Design Case 1 Passive rubber isolator.Passive rubber isolator.•• Design Case 2Design Case 2 Passive rubber isolator with passive MR fluid.Passive rubber isolator with passive MR fluid.•• Design Case 3Design Case 3 Passive rubber isolator with active MR fluid withPassive rubber isolator with active MR fluid with

Butterworth filter.Butterworth filter.•• Design Case 4Design Case 4 Passive rubber isolator with active MR fluid withPassive rubber isolator with active MR fluid with

filter off.filter off.

•• The forces seen in the different isolator components are evaluatThe forces seen in the different isolator components are evaluated.ed.

•• The change in viscosity of the fluid is analyzed. The change in viscosity of the fluid is analyzed.


55--2. Results For The Passive Isolator Design2. Results For The Passive Isolator Design

•• The power spectrum of the transmitted noise at 50 Hz is seen to The power spectrum of the transmitted noise at 50 Hz is seen to increase increase as the stiffness of the isolator increases.as the stiffness of the isolator increases.

Figure 5.1. The effect of passive stiffness seen on transmittedFigure 5.1. The effect of passive stiffness seen on transmitted force.force.

Power Spectrum Of Transmitted Noise @ 50 Hz

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

0 10000 20000 30000 40000 50000

Stiffness (N/m)

PS O

f Tra

nsm

itted

Noi

se (N

^2/H

z)

PASSIVE RESULTS

Baseline Transmission



•• The maximum relative displacement is seen to decrease as the stiThe maximum relative displacement is seen to decrease as the stiffness ffness of the isolator increases.of the isolator increases.

Figure 5.2. The effect of passive stiffness seen onFigure 5.2. The effect of passive stiffness seen onmaximum relative displacement.maximum relative displacement.

Maximum Relative Displacement

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 10000 20000 30000 40000 50000

Stiffness (N/m)

Max

Rel

Dis

p (m

m)

PASSIVE RESULTS

Baseline Displacement



•• From the previous two figures, the baseline performance of the iFrom the previous two figures, the baseline performance of the isolator solator is determined. This is seen below.is determined. This is seen below.

(i)(i) Maximum relative displacement of 2.3 mm.Maximum relative displacement of 2.3 mm.

(ii)(ii) Maximum transmitted force from the compressor of 6.3 NMaximum transmitted force from the compressor of 6.3 N22/Hz./Hz.


55--5. Results For The Semi5. Results For The Semi--Active Isolator DesignActive Isolator Design

•• The power spectrum of the transmitted noise at 50 Hz is seen to The power spectrum of the transmitted noise at 50 Hz is seen to increase increase as the stiffness of the isolator increases.as the stiffness of the isolator increases.

Figure 5.3. The effect of passive stiffness seen on transmittedFigure 5.3. The effect of passive stiffness seen on transmitted force.force.

Power Spectrum Of Transmitted Noise @ 50 Hz

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

0 10000 20000 30000 40000 50000

Stiffness (N/m)

PS O

f Tra

nsm

itted

Noi

se (N

^2/H

z)

PASSIVE RESULTS

MR INACTIVE RESULTS

MR ACTIVE RESULTS -- Butterworth Lowpass Filter

MR ACTIVE RESULTS -- Ideal Low Pass Filter

Baseline Transmission



•• The maximum relative displacement is seen to decrease as the stiThe maximum relative displacement is seen to decrease as the stiffness ffness of the isolator increases.of the isolator increases.

Figure 5.4. The effect of passive stiffness seen onFigure 5.4. The effect of passive stiffness seen onmaximum relative displacement.maximum relative displacement.

Maximum Relative Displacement

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 10000 20000 30000 40000 50000

Stiffness (N/m)

Max

Rel

Dis

p (m

m)

PASSIVE RESULTS

MR INACTIVE RESULTS

MR ACTIVE RESULTS -- Butterworth Lowpass Filter

MR ACTIVE RESULTS -- Ideal Low Pass Filter

Baseline Displacement



•• The results show the passive component of the MR fluid has a The results show the passive component of the MR fluid has a significant affect on results.significant affect on results.

•• As expected, the maximum relative displacement is reduced, and tAs expected, the maximum relative displacement is reduced, and the he transmitted force increases.transmitted force increases.

•• The following effects were seen when the active component of theThe following effects were seen when the active component of the MR MR fluid is introduced with the Butterworth filter.fluid is introduced with the Butterworth filter.

•• The maximum relative displacement at low stiffness is reduced.The maximum relative displacement at low stiffness is reduced.•• However, there is little effect at higher stiffness.However, there is little effect at higher stiffness.•• The transmitted noise is not affected much by the active componeThe transmitted noise is not affected much by the active component.nt.



•• When the filter is turned off, the active fluid is in phase and When the filter is turned off, the active fluid is in phase and the results the results improve significantly.improve significantly.

•• With the filter turned off, the following effects are seen in thWith the filter turned off, the following effects are seen in the results:e results:

•• The transmitted force is not affected.The transmitted force is not affected.•• The maximum relative displacement is reduced at each stiffness.The maximum relative displacement is reduced at each stiffness.



Figure 5.5. Improvement to relative displacement with MR fluid.Figure 5.5. Improvement to relative displacement with MR fluid.

0.9 1 1.1 1.2 1.3 1.4 1.5 1.6-8

-6

-4

-2

0

2

4

6

8x 10

-3

Time (s)

Rel

ativ

e D

ispl

acem

ent

(m)

Passive Passive MRActive MR



•• The results can be seen in Table 5.1.The results can be seen in Table 5.1.

•• Shown in the table are the following properties:Shown in the table are the following properties:

(i)(i) Isolator stiffness.Isolator stiffness.(ii)(ii) Isolator passive damping ratio.Isolator passive damping ratio.(iii)(iii) Compressor mass per isolator.Compressor mass per isolator.(iv)(iv) Natural frequency of the isolator.Natural frequency of the isolator.(v)(v) Maximum relative displacement.Maximum relative displacement.(vi)(vi) Compressor transmitted force.Compressor transmitted force.(vii)(vii) Maximum forces seen by the isolator components.Maximum forces seen by the isolator components.



Table 5.1. Summary of simulation results.Table 5.1. Summary of simulation results.

PASSIVE RESULTS POWER SPECTRUMstiffness mass zeta nat. freq. scale max. rel. displacement comp. transmitted spring damper passive fluid active fluid total

(N/m) (kg) (Hz) (mm) (N^2/Hz) (N) (N) (N) (N) (N)50000 1 0.1 35.6 0 2.3 6.300 113.7 26.6 0 0 116.030000 1 0.1 27.6 0 3.0 1.300 91.4 21.7 0 0 93.310000 1 0.1 15.9 0 6.2 0.100 62.0 11.9 0 0 62.95000 1 0.1 11.3 0 12.8 0.030 63.8 14.7 0 0 65.11000 1 0.1 5.0 0 26.3 0.003 26.3 5.0 0 0 27.7

MR INACTIVE RESULTS POWER SPECTRUMstiffness mass zeta nat. freq. scale max. rel. displacement comp. transmitted spring damper passive fluid active fluid total

(N/m) (kg) (Hz) (mm) (N^2/Hz) (N) (N) (N) (N) (N)50000 1 0.1 35.6 0 2.1 6.50 105.0 27.6 15.7 0 110.530000 1 0.1 27.6 0 2.6 2.10 79.2 21.1 15.5 0 84.510000 1 0.1 15.9 0 4.3 0.70 42.5 12.0 15.3 0 47.05000 1 0.1 11.3 0 7.1 0.54 35.5 11.5 20.9 0 42.01000 1 0.1 5.0 0 15.6 0.43 15.6 3.8 15.2 0 21.4

MR ACTIVE RESULTS -- Butterworth Lowpass Filter POWER SPECTRUMstiffness mass zeta nat. freq. scale max. rel. displacement comp. transmitted spring damper passive fluid active fluid total

(N/m) (kg) (Hz) (mm) (N^2/Hz) (N) (N) (N) (N) (N)50000 1 0.1 35.6 10000 2.1 6.75 104.4 27.4 15.6 7.4 112.430000 1 0.1 27.6 10000 2.6 2.06 78.4 21.5 15.8 8.8 88.010000 1 0.1 15.9 10000 4.0 0.66 40.2 13.4 15.2 50.4 56.75000 1 0.1 11.3 30000 5.0 0.43 24.8 11.5 20.6 56.4 80.51000 1 0.1 5.0 30000 6.0 0.32 6.0 3.8 17.1 13.7 57.8

MR ACTIVE RESULTS -- Ideal Low Pass Filter POWER SPECTRUMstiffness mass zeta nat. freq. scale max. rel. displacement comp. transmitted spring damper passive fluid active fluid total

(N/m) (kg) (Hz) (mm) (N^2/Hz) (N) (N) (N) (N) (N)50000 1 0.1 35.6 45000 1.5 7.70 75.7 26.7 15.2 121.6 158.530000 1 0.1 27.6 45000 1.7 2.10 49.6 20.9 15.3 122.5 152.910000 1 0.1 15.9 45000 2.5 0.60 25.2 12.2 15.5 124.1 144.75000 1 0.1 11.3 45000 3.2 0.40 15.7 8.5 15.2 121.7 141.41000 1 0.1 5.0 45000 3.6 0.30 3.6 3.7 14.8 118.4 136.9

MAXIMUM FORCES

MAXIMUM FORCES

MAXIMUM FORCES

MAXIMUM FORCES



•• The maximum forces are shown in the right columns of Table 5.1. The maximum forces are shown in the right columns of Table 5.1. They They give an indication of how the forces seen by the different compogive an indication of how the forces seen by the different components of nents of the isolator compare to each other.the isolator compare to each other.

•• The columns are linked to the following forces:The columns are linked to the following forces:

(i)(i) Spring force resulting from the passive stiffness component k.Spring force resulting from the passive stiffness component k.(ii)(ii) Damper force resulting from the passive damping component c.Damper force resulting from the passive damping component c.(iii)(iii) Fluid force resulting from the passive component of the MR fluidFluid force resulting from the passive component of the MR fluid..(iv)(iv) Fluid force resulting from the active component of the MR fluid.Fluid force resulting from the active component of the MR fluid.(v)(v) Total force resulting from the sum of all the isolator forces.Total force resulting from the sum of all the isolator forces.



•• The results show the force resulting from the passive stiffness The results show the force resulting from the passive stiffness and and damping components decreases as the passive stiffness of the isodamping components decreases as the passive stiffness of the isolator lator decreases.decreases.

•• This explains why transmitted noise decreases when stiffness andThis explains why transmitted noise decreases when stiffness anddamping decrease.damping decrease.

•• Also, the results show the negative affect on relative displacemAlso, the results show the negative affect on relative displacement, and ent, and thus durability, when the stiffness decreases.thus durability, when the stiffness decreases.



•• The active results show why turning the filter off is necessary.The active results show why turning the filter off is necessary.

•• When the Butterworth low pass filter is used, the active componeWhen the Butterworth low pass filter is used, the active component of nt of the MR fluid is roughly the same size as the passive component othe MR fluid is roughly the same size as the passive component of the f the MR fluid. If the active force is scaled higher than this, the iMR fluid. If the active force is scaled higher than this, the isolator solator becomes inefficient.becomes inefficient.

•• When the filter is turned off, the semiWhen the filter is turned off, the semi--active force of the MR fluid is active force of the MR fluid is nearly eight times the force from the passive component. Becausnearly eight times the force from the passive component. Because e there is no phase lag, the active component can efficiently be sthere is no phase lag, the active component can efficiently be scaled caled very high.very high.

•• The percentage of noise reduction for each case is seen below:The percentage of noise reduction for each case is seen below:

Inactive control with MR fluid.Inactive control with MR fluid. 50%50%SemiSemi--Active control with Butterworth low pass filterActive control with Butterworth low pass filter 55%55%SemiSemi--Active control with filter offActive control with filter off 83%83%



•• Figure 5.6 shows all four isolator components with the filter tuFigure 5.6 shows all four isolator components with the filter turned off, rned off, along with the relative displacement of the compressor.along with the relative displacement of the compressor.

Figure 5.6. Relative displacement and isolator components with Figure 5.6. Relative displacement and isolator components with the filter off.the filter off.

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3-3

-2

-1

0

1

2

3Four Isolator Components -- Filter Off

Rel

ativ

e D

ispl

acem

ent

(mm

)

0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3

-100

-50

0

Res

ista

nce

For

ce (

N)

Time (s)

Passive Damping Passive StiffnessPassive MR Fluid Active MR Fluid



•• A look at the MR fluid viscosity yields another interesting resuA look at the MR fluid viscosity yields another interesting result.lt. A plot A plot of the viscosity shows that it varies significantly during the mof the viscosity shows that it varies significantly during the model.odel.

•• This contradicts the assumption of a constant passive MR componeThis contradicts the assumption of a constant passive MR component, nt, as seen in a Bingham plastic model.as seen in a Bingham plastic model.

•• The plot showing the viscosity is dependent on relative velocityThe plot showing the viscosity is dependent on relative velocity is seen is seen in Figure 5.7.in Figure 5.7.



Figure 5.7. Viscosity is dependent on relative velocity.Figure 5.7. Viscosity is dependent on relative velocity.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-1

-0.5

0

0.5Viscosity is dependant on relative velocity.

Rel

ativ

e V

eloc

ity (

m/s

)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

1

2

3

4

Vis

cosi

ty (

Pa

s)

Time (s)


66--1. MR ISOLATOR COIL DESIGN1. MR ISOLATOR COIL DESIGN

•• A detailed design of an isolator that can be used for the compreA detailed design of an isolator that can be used for the compressor ssor application will be presented.application will be presented.

•• The isolator could not be built within the scope of this thesis,The isolator could not be built within the scope of this thesis, but all the but all the design information is presented to allow construction of the isodesign information is presented to allow construction of the isolator.lator.

•• The following requirements of the design will be investigated:The following requirements of the design will be investigated:

1.1. Determining the necessary yield stress.Determining the necessary yield stress.2.2. An electromagnetic model of the isolator.An electromagnetic model of the isolator.3.3. Isolator coil properties.Isolator coil properties.4.4. Final design of the optimal isolator based on research.Final design of the optimal isolator based on research.


66--2. Determining The Necessary Yield Stress2. Determining The Necessary Yield Stress

•• Once the necessary yield stress needed for results was determineOnce the necessary yield stress needed for results was determined, the d, the strength of the magnetic field needed to generate that yield strstrength of the magnetic field needed to generate that yield stress is ess is determined.determined.

Figure 6.1. Yield stress and magnetic flux in the model.Figure 6.1. Yield stress and magnetic flux in the model.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

2000

4000

6000

8000

Yie

ld S

tres

s (P

a)Y ield Stress And Magnetic Flux

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.05

0.1

0.15

0.2

Mag

netic

Flu

x (T

esla

)

Time (s)


66--3. Electromagnetic Model Of The Isolator3. Electromagnetic Model Of The Isolator

•• A electromagnetic model was created to develop a coil design thaA electromagnetic model was created to develop a coil design that will t will produce the necessary magnetic flux.produce the necessary magnetic flux.

•• In discussions, MR engine mount designers stated that a well desIn discussions, MR engine mount designers stated that a well designed igned coil will produce five hundred ampcoil will produce five hundred amp--turns. However, the efficiency of the turns. However, the efficiency of the coil begins to decrease when the coil is designed to produce morcoil begins to decrease when the coil is designed to produce more than e than this.this.

•• Figure 6.2 shows the coil design that provided the flux necessarFigure 6.2 shows the coil design that provided the flux necessary. The y. The arrows indicate the intended flux pattern.arrows indicate the intended flux pattern.

•• The results of the electromagnetic model are seen in Figure 6.3.The results of the electromagnetic model are seen in Figure 6.3.



Figure 6.2. Coil design with the intended flux pattern.Figure 6.2. Coil design with the intended flux pattern.

+

++

+

-- COILS

STEEL 1020A

MR FLUID (20%)

STEEL CASTING

PISTON



Figure 6.3. Finite element results showing flux in the isolatorFigure 6.3. Finite element results showing flux in the isolator..

0.000.25

0.500.75

1.001.25

1.501.75

Flux DensityB (T)


66--6. Coil Properties6. Coil Properties

•• The electromagnetic model defined the following parameters:The electromagnetic model defined the following parameters:

•• The number of ampThe number of amp--turns in the coilturns in the coil•• The area of the coilsThe area of the coils•• Design of flux guidesDesign of flux guides

•• Once the model was completed, the specifics of the coil could beOnce the model was completed, the specifics of the coil could becalculated. This included:calculated. This included:

•• Coil gageCoil gage•• Coil lengthCoil length•• Coil massCoil mass•• Voltage applied to the wireVoltage applied to the wire•• Current through the wireCurrent through the wire•• Resistance from the wireResistance from the wire



•• The following parameters were used to determine coil volume:The following parameters were used to determine coil volume:

•• Coil inner diameterCoil inner diameter•• Coil maximum outer diameterCoil maximum outer diameter•• Coil widthCoil width

•• The following parameters were determined by wire gage:The following parameters were determined by wire gage:

•• Copper diameterCopper diameter•• Insulation thicknessInsulation thickness•• Insulated diameter (which is equivalent to the copper diameterInsulated diameter (which is equivalent to the copper diameter

plus twice the insulation thickness)plus twice the insulation thickness)



•• The following equations were used to calculate the coil propertiThe following equations were used to calculate the coil properties:es:

Determining the number of turns.Determining the number of turns.

Coil physical propertiesCoil physical properties

Coil electrical propertiesCoil electrical properties

iameterInsulatedDCoilWidth

layerturns

=#

))((2)(#

ghtPackingHeiiameterInsulatedDCoilODCoilIDlayers −

=

)(### layersINTlayerturnsINTturns

=

))(#)()(( layersINTghtPackingHeiiameterInsulatedDCoilIDODCoilActual +=

2ODCoilActualCoilIDeDiameterCoilAverag +

=

))(#( turnseDiameterCoilAveragCoilLength π=

CoilLengthCoilMassCoilLengthCoilMass =

CoilLengthCcesisCoilCoilLengthCcesisCoil )(@tanRe)(@tanRe °

=°

cesisVoltageCurrent

tanRe=

))((# CurrentturnsAmpTurns =



•• The following dimensions were used for the modeling of the coilsThe following dimensions were used for the modeling of the coils. This . This geometry limited the area in which the coil could be wound.geometry limited the area in which the coil could be wound.

•• Coil inner diameterCoil inner diameter 17 mm17 mm•• Coil maximum outer diameterCoil maximum outer diameter 19 mm19 mm•• Coil widthCoil width 13 mm13 mm

•• The number of turns that could fit into this area jumped signifiThe number of turns that could fit into this area jumped significantly cantly when the wire gage was increased from 24 to 25.when the wire gage was increased from 24 to 25.

•• With 24 gage wire, the wire is too thick to allow for a second lWith 24 gage wire, the wire is too thick to allow for a second layer of ayer of coils.coils.

•• This can be seen in Figure 6.4This can be seen in Figure 6.4



Figure 6.4. Number of coil turns and coil mass as a function ofFigure 6.4. Number of coil turns and coil mass as a function of wire gage.wire gage.

19 20 21 22 23 24 25 26 27 28 290

20

40

60

80

100

120

140

Wire Gage Number

Coil Properties Of Different Wire Gages

Number Of TurnsCoil Mass (g)



Figure 6.5. Coil length and resistance as a function of wire gaFigure 6.5. Coil length and resistance as a function of wire gage.ge.

19 20 21 22 23 24 25 26 27 28 290

1

2

3

4

5

6

7

Wire Gage Number

Coil Properties Of Different Wire Gages

Coil Length (m) Coil Resistance (Ohms)



Figure 6.6. Voltage and current needed to achieve 500 amp turnsFigure 6.6. Voltage and current needed to achieve 500 amp turns..

19 20 21 22 23 24 25 26 27 28 290

5

10

15

20

25

30

35

40

Wire Gage Number

Electrical Properties To Achieve 500 Amp Turns

Voltage (V) Current (Amps)


66--13. Final Design13. Final Design

•• The final design of the optimal isolator is seen below.The final design of the optimal isolator is seen below.

Figure 6.7. Proposed design of a MR based semiFigure 6.7. Proposed design of a MR based semi--active isolator.active isolator.

COILS

STEEL 1020A

MR FLUID

STEEL CASTING

PISTON

PASSIVE RUBBER

3520

4

131921

Measurements in millimeters.



•• The final design parameters are seen below.The final design parameters are seen below.

Table 6.1. Final design parameters. Table 6.1. Final design parameters.

Coil ID 17 mm Plunger Diameter 13 mmCoil OD 19 mm Gap Width 1 mm

Coil Length 3.2 m Channel Length 20 mmWire Gage 25 Fluid Volume 13 cc

Voltage 10 V



•• The power requirements of the semiThe power requirements of the semi--active isolator increase as the active isolator increase as the relative velocity between the vehicle and the compressor increasrelative velocity between the vehicle and the compressor increase.e.

•• The maximum power requirement for each isolator is 0.04 W. ThisThe maximum power requirement for each isolator is 0.04 W. Thisoccurs when the vehicle hits the bump. Therefore, the maximum pooccurs when the vehicle hits the bump. Therefore, the maximum power wer needed for the entire isolation system (assuming 3 isolators) isneeded for the entire isolation system (assuming 3 isolators) is 0.12 W.0.12 W.

•• A plot showing the power requirements throughout the model are sA plot showing the power requirements throughout the model are seen een in Figure 6.8.in Figure 6.8.



Figure 6.8. Power requirements of the semiFigure 6.8. Power requirements of the semi--active isolator.active isolator.

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.005

0.01

0.015

0.02

0.025

0.03

0.035P

ower

(W

)

Time (s)

Power requirements of the isolator.



•• The overall mass of each isolator comes to 238.2 grams, or 8.4 oThe overall mass of each isolator comes to 238.2 grams, or 8.4 oz. This z. This is significantly larger than the baseline isolator, which has a is significantly larger than the baseline isolator, which has a mass of 7.0 mass of 7.0 grams, or 0.25 oz.grams, or 0.25 oz.

Table 6.2. Mass of semiTable 6.2. Mass of semi--active isolator.active isolator.

Component Density Volume Mass (g)

Rubber and Piston 7.3 (1)

MR Fluid 3.005 g/cc 13 cc 39.1

Coils 4 (2)

Steel Casting 7900 kg/m3 1.71E-5 m3 135.1

Flux Guide (Steel) 7900 kg/m3 6.67E-6 m3 52.7

Total 238.2



•• Studies can be done to reduce mass.Studies can be done to reduce mass.

•• A simple analysis of the mass breakdown shows that the steel parA simple analysis of the mass breakdown shows that the steel parts of ts of the isolator contribute most of the mass. The steel could possithe isolator contribute most of the mass. The steel could possibly be bly be replaced with aluminum or graphite to reduce mass.replaced with aluminum or graphite to reduce mass.

•• Also, a less dense fluid will lower the mass of the isolator.Also, a less dense fluid will lower the mass of the isolator.


77--1. Conclusions1. Conclusions

•• The MR fluid based semiThe MR fluid based semi--active isolator should have the following active isolator should have the following characteristics:characteristics:

•• Very soft rubber component.Very soft rubber component.•• Fluid should work in flow mode.Fluid should work in flow mode.•• MR fluid should have low viscosity and high yield stress.MR fluid should have low viscosity and high yield stress.•• The control algorithm should scale the active component of the MThe control algorithm should scale the active component of the MR R

fluid proportional to the relative velocity.fluid proportional to the relative velocity.•• The control algorithm should include an improved low pass filterThe control algorithm should include an improved low pass filter..•• The coil design needs to be sufficient to generate the necessaryThe coil design needs to be sufficient to generate the necessary

magnetic field.magnetic field.•• Use a small enough diameter wire that multiple layers of coils cUse a small enough diameter wire that multiple layers of coils can an

be wound, in this case, wire gage of 25. be wound, in this case, wire gage of 25. •• The semiThe semi--active isolator has significantly more mass than the active isolator has significantly more mass than the

baseline isolator. baseline isolator.


77--2. Conclusions2. Conclusions

•• The MR fluid based semiThe MR fluid based semi--active isolator can give the same durability active isolator can give the same durability performance of a stiff passive isolator.performance of a stiff passive isolator.

•• The MR fluid based semiThe MR fluid based semi--active isolator can reduce transmitted noise by active isolator can reduce transmitted noise by as much as 83%.as much as 83%.

•• Without mass reduction measures, the MR fluid based semiWithout mass reduction measures, the MR fluid based semi--active active isolator will have 34 times more mass than the stiff passive isoisolator will have 34 times more mass than the stiff passive isolator.lator.

•• The vibration isolator designed here can be used for other appliThe vibration isolator designed here can be used for other applications. cations. Independent control of the each isolator also allows for use in Independent control of the each isolator also allows for use in multiple multiple degree of freedom systems.degree of freedom systems.


88--1. Recommendations For Future Work1. Recommendations For Future Work

•• An algorithm could be developed to more effectively control to aAn algorithm could be developed to more effectively control to a relative relative plane. This would allow more efficient use of energy, by reduciplane. This would allow more efficient use of energy, by reducing the ng the amount of power required for the isolator. amount of power required for the isolator.

•• The filter used with the control algorithm needs to be improved.The filter used with the control algorithm needs to be improved.

•• A fluid that has low viscosity and a high shear stress can be deA fluid that has low viscosity and a high shear stress can be developed.veloped.

•• Optimization of the coil design would allow the isolator to moreOptimization of the coil design would allow the isolator to moreeffectively use the unique characteristics of the MR fluid, whileffectively use the unique characteristics of the MR fluid, while requiring e requiring less input power.less input power.

•• Building and testing of a prototype isolator is needed to validaBuilding and testing of a prototype isolator is needed to validate te performance.performance.


88--2. Recommendations For Future Work2. Recommendations For Future Work

•• Cost and weight improvement studies will need to be conducted onCost and weight improvement studies will need to be conducted once ce the performance of the isolator is validated.the performance of the isolator is validated.

•• The design of a simple relative velocity sensor will simplify thThe design of a simple relative velocity sensor will simplify the control e control of the isolator and dramatically reduce cost.of the isolator and dramatically reduce cost.

a magnetorheologic semi-active isolator...

Documents