Magneto-rheological dampers use magneto-rheological fluid that can rapidly change viscosity when exposed to a magnetic field, allowing damper resistance to be varied in real-time. The document discusses the need for variable dampers, how MR fluids work, types of MR dampers including mono tube and twin tube, modeling challenges, limitations around cost and durability, and applications in vehicle suspensions, prosthetics, and military equipment. MR dampers offer semi-active damping control to improve ride quality and safety.

1. Magneto-rheological
Dampers
Ameya Sanjay Dahale
College of Engineering, Pune
B. Tech Mechanical Engineering
MIS 111010040

2. Contents
• Introduction
• Need of MR damping devices.
• Magneto-rheological fluids.
• MR Dampers
• Types of MR Dampers
• Modeling of MR Dampers
• Limitations
• Current and Future Scope
• Concluding Remarks

3. Introduction
The main purpose of this presentation is to
• Introduce the topic of magneto-rheological dampers to the audience.
• The mechanism of working of MR fluid.
• Objectives and future prospects of MR damper devices.

4. Need of MR damping devices
1. Automobile suspension mostly influence the vehicle ride quality and safety
2. Need of real-time performance adjustment based on road situation and vehicle
operation state.
3. Conventional dampers such as hydraulic and spring dampers have constant
setting throughout their life.
4. MR dampers due to the apparent viscosity of magnetic fluids can operate in
semi-active conditions.

5. Magneto-rheological Fluid
• 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.

6. • Characteristics :
1. 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.
2. The change in viscosity is continuous and highly reversible.
3. Yield strength of up to 50-100 kPa.
4. Insensitivity to contaminants.
5. Low voltage (12-24 V) required for operation.
6. Broad working temperature range : -40º C to 150º C.

7. • 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 0.020 in.) 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).

8. • Shear mode : It differs in operation from squeeze mode due to moving
paramagnetic sliding or rotating surfaces. It has thin layer( 0.015 in.) 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, breakes, chucking and
locking devices, dampers and
structural composites.
3. Suitable for relatively small force
applications.

9. • 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.

10. 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.

11. • Typical MR damper :
1. Choking Points : The
areas where MR fluid is
exposed to magnetic flux
lines.
2. Fluid restricts the flow
when it is in vicinity of
chocking points and in
active state.
3. With increase in magnetic
flux increase in apparent
viscosity(damper
resistance) occurs up to
some ‘saturation point’ after which damper resistance cannot be increased.

12. Types of MR dampers :
1. Mono tube
2. Twin tube
3. Double ended MR damper
4. MR-Hydraulic hybrid dmper

13. • Mono tube MR damper :
1. Has only one reservoir for MR fluid.
2. Gas accumulator (nitrogen) is used to compensate for the change in the
volume due to piston rod movements.

14. • Twin tube MR damper :
1. Has two fluid reservoirs, one inside of the other.
2. The inner housing filled with MR fluid guides the piston/piston rod assembly.
3. The outer housing partially filled with MR fluid serves the purpose of reservoir.

15. • Twin tube MR dampers (contd..) :
4. ‘Foot Valve Assembly’ is attached to the bottom of the inner housing to
regulate the flow of fluid between two reservoirs.
5. 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.
6. 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 :
1. The valving is set up properly.
2. MR fluid settling is not a problem.
3. The damper is used in an upright position.

17. • Double Ended MR damper :
1. It has 2 piston rods of equal diameter protruding through both ends of damper.
2. Does not require an accumulator or similar arrangments.
3. Have been used for bicycle applications, gun recoil applications, and for
stabilizing buildings during earthquakes.

18. • MR-Hydraulic Hybrid damper :
1. These are dampers in which a small MR damper controls a valve that, in turn,
is used to regulate the flow of hydraulic fluid.
2. It has been used in military applications and seismic applications.

19. 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. Following
are well known-
1. Modified Bouc-Wen Model by Spencer for MR devices.
2. Recursive Lazy Learning based on neural networks

20. 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.

21. 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.

22. 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.

23. Thank You