PRESENTED BY:-PAWAN KUMAR

16ME62R07

Magneto-Rheological Dampers

CONTENTS

IntroductionNeed of MR damping devices.Magneto-rheological fluids.MR DampersTypes of MR DampersModeling of MR DampersLimitationsCurrent and Future ScopeConcluding Remarks

Introduction

The main purpose of this presentation is to-

Introduce the topic of magneto-rheological dampers.The mechanism of working of MR fluid. Objectives and future prospects of MR damper devices.

Need of MR damping devices

• Automobile suspension mostly influence the vehicle ride quality and safety.

• Need of real-time performance adjustment based on road situation and vehicle operation state.

• Conventional dampers such as hydraulic and spring dampers have constant setting throughout their life.

• MR dampers due to the apparent viscosity of magnetic fluids can operate in semi-active conditions.

Magneto-rheological fluids

A Magnetorheological fluid (MR fluid) is a type of smart fluid in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid

Composition : Oil (having low permeability) with varying percentage of micron-sized (µ) iron particles coated with anti-coagulant material.

Active state : When fluid is exposed to magnetic field, can be said in the active state and its viscosity can be varied by varying the strength of magnetic field.

Un-active state : In the absence of magnetic field it is in un-active state and behaves like normal fluid.

Apparent viscosity : It has constant viscosity in its un-active state but in active state, due to alignment of iron particles along the magnetic-flux lines, it possesses some apparent viscosity. This viscosity can be controlled by controlling the magnetic field.

Shear yield stress : The strength of MR fluid can be described by shear yield stress.

INTRODUCTION

Magneto-rheological fluids

Characteristics :• Under a strong magnetic field its viscosity can be

increased by more than two orders of magnitude in a very short time (milliseconds) Hence, very low response time.

• The change in viscosity is continuous and highly reversible.

• Yield strength of up to 50-100 kPa.• Insensitivity to contaminants.• Low voltage (12-24 V) required for operation.• Broad working temperature range : -40º C to 150º

C.

Working Principle of MR Fluids

WORKING: .

• The magnetic particles which are typically micrometer or nano meter scale When a magnetic field is applied, however, the microscopic particles (usually in the 0.1–10 µm range) align themselves along the lines of magnetic flux

• Due to this magnetic flux viscosity of magneto rheological fluid gets increases and helps to reduce shock.

• Thus it acts as a Bingham plastic.

Modes of Operation

MR fluid can be used in three different ways : Squeeze, valve and shear.

Squeeze mode (or compression mode) : Squeeze mode has a thin film (on the order of 0.5 mm) of MR fluid that is sandwiched between paramagnetic pole surfaces as shown in Figure-

1. The distance between the parallel pole plates changes, which causes a squeeze flow.

2. Suitable for relatively high dynamic forces with small amplitudes (few mm).

Modes of Operation

• Shear mode : It differs in operation from squeeze mode due to moving paramagnetic sliding or rotating surfaces. It has thin layer( 0.3 mm) of MR fluid sandwiched between paramagnetic surfaces.

1. Magnetic field is perpendicular to the direction of motion of these moving surfaces.

2. Examples of shear mode include clutches, breaks, chucking and locking devices, dampers and structural composites.

3. Suitable for relatively small force applications.

Modes of Operation

Valve mode : It is the most widely used of three modes. Here the two reservoirs of MR fluid are used and magnetic field is used to impede the flow of MR fluid from one reservoir to another. Here the flow can be achieved by pressure drop between reservoirs and flow resistance can be controlled by magnetic field.

MR Dampers

These devices generally operate in the valve mode.Having structure of piston and cylinder with flow control

valves either incorporated in piston end or cylinder (bypass).

MR dampers were introduced by first Lord Corporation in 1980’s in truck seat damping system under trademark ‘Motion Master’

General Motors in partnership with Delphi corporation (branch of GM) has developed dampers for automotive suspensions. It made its debut in Cadillac (2002) as MagneRide and on Chevrolet passenger vehicles (2003) as Magnetic Selective Ride Control (MSRC).

BMW uses it’s own proprietary version of this device while Audi and Ferrari offer Delphi’s MageRide on various models.

MR Dampers

Typical MR damper • Choking Points : The

areas where MR fluid is exposed to magnetic flux lines.

• Fluid restricts the flow when it is in vicinity of chocking points and in active state.

• With increase in magnetic flux increase in apparent viscosity(damper resistance) occurs up to

some ‘saturation point’ after which damper resistance cannot be increased.

Types of MR dampers

Mono tube Twin tube Double ended MR damper MR-Hydraulic hybrid damper

Types of MR dampers

Mono tube MR damper :

• Has only one reservoir for MR fluid.• Gas accumulator (nitrogen) is used to compensate for

the change in the volume due to piston rod movements.

Types of MR dampers

Twin tube MR damper :

• Has two fluid reservoirs, one inside of the other.

• The inner housing filled with MR fluid guides the piston/piston rod assembly.

• The outer housing partially filled with MR fluid serves the purpose of reservoir.

Types of MR dampers

Types of MR dampers

• ‘Foot Valve Assembly’ is attached to the bottom of the inner housing to regulate the flow of fluid between two reservoirs.

• Foot Valve Assembly includes – Compression valve that guides flow from inner to outer housing during compression stroke while return valve for exact opposite function during piston retraction.

• For proper functioning, compression valve must be stiff relative to the pressure differential that exists on both the sides. While the return valve must be very unrestrictive.

Conditions for proper functioning :• The valving is set up properly.• MR fluid settling is not a problem.• The damper is used in an upright position.

Types of MR dampers

Types of MR dampers

Double Ended MR damper :

• It has 2 piston rods of equal diameter protruding through both ends of damper.

• Does not require an accumulator or similar arrangements.• Have been used for bicycle applications, gun recoil applications,

and for stabilizing buildings during earthquakes.

Types of MR dampers

MR-Hydraulic Hybrid damper :

• These are dampers in which a small MR damper controls a valve that, in turn, is used to regulate the flow of hydraulic fluid.

• It has been used in military applications and seismic applications.

Modeling of MR dampers

Modeling MR dampers is difficult and complex task due to their non-linear and hysteretic dynamics.

Currently there are different modelling techniques for MR dampers. Modified Bouc-Wen Model by Spencer for MR devices, is widely used for this purpose.

Limitations

1. Settling stability of MR fluid : Heavy particles tend to settle in static fluid. But using proper anti-coagulant can prevent such settling and fluid can be used without any adverse effect in its operation.

2. Relative Costs : This is very important factor while making choice between MR dampers and conventional passive devices. To reduce the cost use of absorbent matrix method is used. Due to this, volume of MR fluid is reduced to great extent, requirement of highly finished surfaces, precision tolerances and seals is negated.Absorbent matrix method uses sponge like structures that keeps MR fluid in active(choking) regions.

3. Durability of devices : MR fluids are inherently somewhat abrasive. To tackle the problem, dynamic seal design, material selection and proper MR fluid chemistry are required.

Current and Future Scope

Vehicular suspension, breaks, clutch systems.Military applications such as gun recoil

system, naval gun turrets. Magneto-rheological finishing techniques.Prosthetic limbs and tremor suppression. MR fluid fixtures.

Concluding Remarks

MR fluids and MR fluid devices have been greatly advanced in the last decade and there are some commercial products have been developed.

This technique has been developing competitively in the main industrialized countries, especially in the United States, Belarus, France, Germany and Japan.

It can be seen that the MR fluid devices introduced in this seminar will continue to be the subject of extensive research and applications in various field as mentioned before

REFRENCES

"Study on the mechanism of the squeeze-strengthen effect in magnetorheological fluids " X. Z. Zhang, X. L. Gong, P. Q. Zhang, and Q. M. Wang, J. Appl. Phys. 96, 2359 (2004).

A. Spaggiari, E. Dragoni "Effect of Pressure on the Flow Properties of Magnetorheological Fluids" J. Fluids Eng. Volume 134, Issue 9, 091103 (2012).

How Stuff Works "How Smart Structures Will Work"

Wikipedia” Magnetorheological fluid” https://en.wikipedia.org/wiki/Magnetorheological_fluid

Thank You