MR dampers

1. M-TECH (DESIGN ENGINEERING), K.L.E.C.E.T,
BELGAUM
A Seminar on
MAGNETORHEOLOGICAL DAMPING FOR
SEMI- ACTIVE SUSPENSION
By
ADIVEPPA DARUR
UNDER THE GUIDANCE OF
Dr.M.A .KAMOJI

2. INTRODUCTION
• Suspension is the term given to the system of springs, shock absorbers, and
linkages that connects a vehicle to its wheels.
• Suspension systems serves vehicle’s road holding/handling and braking for
safety and keeping vehicle occupants comfortable and reasonably well
isolated from road noise, bumps, and vibrations, etc.
• It has been found that magneto-rheological (MR) fluids can be designed to
be very effective vibration control actuators. The MR fluid damper is a semi-
active control device that uses MR fluids to produce a controllable damping
force.
• The semi-active suspension have been greatly improved, compared with the
passive suspension and there is a certain adaptability to the disturbance of
outside.

3. SUSPENSION SYSTEMS
• Passive Suspensions
Traditional springs and dampers are referred to as
passive suspensions - most vehicles are suspended in this manner.
• Semi-active and active suspensions
If the suspension is externally controlled then it is a semi-active or active
suspension.
Magnetorheological shock absorber has several applications, most notably in
semi-active vehicle suspensions which may adapt to road conditions, as they are
monitored through sensors in the vehicle, and in prosthetic limbs.

4. 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
• So, MR fluid having unique ability to transform from liquid to solid and from solid to
liquid quicker than blinking of an eye.
 MR FLUID STATE
A MR fluid usually consists of 20-40 percent Carbonyl iron particles, suspended
in mineral oil, synthetic oil, water or glycol. The fluid also contains a substance which
prevents the iron particles from setting.

5.  HOW IT WORKS
The magnetic particles, which are typically micrometer or nanometer scale
spheres or ellipsoids, are suspended within the carrier oil are distributed randomly and
in suspension under normal circumstances, as below.
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 see below.
When the fluid is contained between two poles (typically of separation 0.5–2 mm in
the majority of devices), the resulting chains of particles restrict the movement of the
fluid, perpendicular to the direction of flux, effectively increasing its viscosity.

6.  MODES OF OPERATIONS
An MR fluid is used in one of three main modes of operation. These modes involve,
respectively, fluid flowing as a result of pressure gradient between two stationary plates;
fluid between two plates moving relative to one another; and fluid between two plates
moving in the direction perpendicular to their planes. In all cases the magnetic field is
perpendicular to the planes of the plates, so as to restrict fluid in the direction parallel to
the plates.
Flow mode
The MR fluid flow from one reservoir to another, in a small diameter passage. If the
passage is subjected to a variable intensity magnetic field, the amount of fluid that is
able to flow will be altered.

7. Shear mode
A very thin layer of MR fluid is placed between two electro-magnetic plates - and
then the plates are slid relative to one another - the MR fluid is said to be operating in
'shear mode'.
Squeeze-flow mode
A similar set-up - but this time with the plates being pushed towards one another - is
termed 'squeeze mode'. This approach can be used for damping very small movements.
• Flow mode can be used in dampers and shock absorbers, by using the movement to be
controlled to force the fluid through channels, across which a magnetic field is applied.
• Shear mode is particularly useful in clutches and brakes - in places where rotational
motion must be controlled.
• Squeeze-flow mode, on the other hand, is most suitable for applications controlling small,
millimeter-order movements but involving large forces.

8. MR DAMPERS:SHOCKABSORBERS
• A Magnetorheological damper or shockabsorber is a damper filled with
magnetorheological fluid, which is controlled by a magnetic field, usually using an
electromagnet.
• This allows the damping characteristics of the shock absorber to be continuously
controlled by varying the power of the electromagnet.
• This type of shock absorber has several applications, most notably in semi-active
vehicle suspensions which may adapt to road conditions, as they are monitored through
sensors in the vehicle, and in prosthetic limbs.
• As with conventional damper designs, MR dampers can be constructed in three types.
• These are the mono tube, the twin tube, and the double-ended MR damper.

9. DESIGN CONFIGURATION
• The design also based upon type of MR fluid used in the damper.
• Fig. illustrates the conceptual design of the MR damper.
• Spool of magnet wire, Shown with the vertical hash marks, generate magnetic flux
within the steel piston.
• The flux in the magnetic circuit flows axially through the piston core of diameter Dc,
beneath the winding, radially through the piston poles of length Lp, through a gap of
thickness tg, in which the MR fluid flows, and axially through the cylinder wall of
thickness tw.

10. Construction of twin tube MR damper
 In this configuration, the damper has an inner and outer housing.
 The inner housing guides the piston rod assembly, in exactly the same manner as in a
mono tube damper.
 The volume enclosed by the inner housing is referred to as the inner reservoir. Likewise,
the volume that is defined by the space between the inner housing and the outer housing
is referred to as the outer reservoir.
 The inner reservoir is filled with MR fluid so that no
air pockets exist.

11. Working of twin tube MR shockabsorber
 In a twin tube design, the inner tube is called the pressure tube and the outer tube is
called the reserve tube. The reserve tube stores excess MR fluid.
 valves allows the fluid to leak through as piston moves up and down in the pressure tube.
 Because the valves are relatively
tiny only a small amount of fluid
under great pressure passes through.
 This slows down the piston
which in turn slows down the spring.

12.  Above fig. shows that Shock absorbers work in two cycles’ compression cycle and
extension cycle.
 Compression cycle occurs as the piston moves downwards compressing the
magntorheological fluid in the chamber below the piston.
 The extension cycle occurs as the piston moves toward s the top of the pressure tube,
compressing the fluid in the chamber above the piston.
Magnetorheological suspension system in Ferrari 599 GTB

13. This technology has enormous potential in improving suspension systems
 MR suspensions are velocity sensitive – the faster the suspension moves the more
resistance the shock absorber provides. This enables shocks to adjust to road conditions
and to control all the unwanted motions that can occur in moving vehicles including
bounce and brake drive.
 The semi active suspension has a maximum response time of just 10 milliseconds 4
times faster than a conventional one.
 The movement of each individual wheel is controlled by a damper which contains the
fluid the viscosity of which is modified by applying an electronically controlled
magnetic field
 It Can be easily introduced to cars without changing the current basic design of
automotive suspension systems.
 Is able to be controlled electronically.
 Can be easily interfaced with other automotive

14. APPLICATIONS OF MR DAMPERS
 These dampers are mainly used in heavy industry with applications such as heavy motor
damping, operator seat/cab damping in construction vehicles, and more.
 Many car manufactures are applying this technology , such as BMW Audi and Ferrari
599GTB
 MR dampers for use in military and commercial helicopter cockpit seats, as safety
devices in the event of a crash, are under development.
 MR dampers are utilized in semi-active human prosthetic legs

15. ADVANTAGESAND DISADVANTAGES
 Unequaled shock and vibration control.
 MR suspension has no small moving parts (valves), less manufacturing complexity.
 Low power consumption.
 Fast response time - MR dampers can switch between conditions in milliseconds.
 Low damping levels when not subjected to the magnetic field.
 Quieter operation. MR dampers are also quieter in operation than those based on
conventional servo-valve technology.
The biggest disadvantage with an MR suspension system is the cost.
• The current cost for MR fluid is US$595 per liter.

16. CONCLUSION
The MR damper was tested and its results were obtained. The study of rheology as
such, the theory behind rheological fluids, their properties and their application to
vibration control. MR dampers use a technology that is very attractive in its apparent
simplicity. The design and fabrication of MR damper suited to vehicle suspensions were
carried out.

17. REFERENCES
1. Carlson, J.D. and Spencer Jr., B.F. “Magneto-Rheological Fluid Dampers for Semi-
Active Seismic Control”, Proc. of the 3rd Int. Conf. on Motion and Vibr. Control, Chiba,
Japan, Vol. 3, pp. 35–40.
2. Jolly, M. R., J. D. Carlson and B. C. Muñoz “A Model of the Behaviour of
Magnetorheological Materials, Proc. of the 2nd Intl. Workshop on Struc. Control, Hong
Kong, pp. 163–173.
3. Weiss, K.D., J.D. Carlson and D.A. Nixon “Viscoelastic Properties of Magneto- and
Electro-Rheological Fluids,”
4. www.mrfluid.com
5. www.autospeeddrive.com
6. www.howstuffworks.com