Parameters Consideration in Designing a Magnetorheological Damper

I.M.Yazid1,a, S.A. Mazlan1,b, H. Zamzuri2,c, M.J. Mughni1,d and S. Chuprat3,e 1Malaysia-Japan International Institute of Technology, 2UTM-Proton Active Safety Laboratory,

3Advanced Informatics School,

Universiti Teknologi Malaysia, 54100 Jalan Semarak, Kuala Lumpur, Malaysia.

aiiryani3@live.utm.my, bamri@ic.utm.my, chairi@ic.utm.my, dmjamalullail2@live.utm.my, esuria@ic.utm.my.

Keywords: Magnetorheological Fluid, MR Damper, Simulation, Magnetic Circuit, Mixed Mode

Abstract. This paper presents a simulation study of electromagnetic circuit design for a mixed

mode Magnetorheological (MR) damper. The magnetic field generated by electromagnetic circuit

of the MR damper was simulated using Finite Element Method Magnetics (FEMM) software

package. All aspects of geometry parameters were considered and adjusted efficiently in order to

obtain the best MR damper performance. Eventually, six different parameters approach were

proposed; the selection of materials, the polarity of coils, the diameter of piston, piston rod and

core, the shear and squeeze gaps clearance, the piston pole length and the thickness of housing.

Introduction

Magnetorheological (MR) damper is a semi-active suspension that performs according to the

strength of magnetic field. The mechanical properties of the suspension can be controlled by

adjusting the critical yield stress of the MR fluid. In view of this benefit, the MR damper is capable

of producing a sufficient magnitude force for large-scale applications such as automobiles, heavy

trucks, bicycles, prosthetic limbs and gun recoil systems.

Recently, many researchers have conducted numerous studies on designing MR dampers to

enhance their performances. Most of them used the results of the magnetic field analysis to estimate

the performance of MR damper or to verify whether the magnetic saturation occurred or not in the

magnetic circuit. In addition, in order to predict the magnetic field strength in the MR damper, the

electromagnetic circuit has been simulated based on the finite element method (FEM) [1-2].

Nguyen and Choi [3] had proposed an optimal design using FEM to obtain a much better vibration

suppression performance of suspension systems. Significant work has been done on the geometrical

dimension optimization of the magnetic circuit to improve the damping performances [4]. Some

works have been performed on the magnetic design methods [5-6] and design optimization [7].

However, their researches focused more on the mechanical design parameters with minimal

considerations on the improvement of electromagnetic properties in the design phase. Other factors

such as the direction of magnetic polarity and combination of the working mode of MR fluid were

not getting much attention.

Consequently, this paper presents a simulation study of electromagnetic circuit design for a

mixed mode MR damper. The principal design parameters were analytically determined with

considering magnetic polarity of the electromagnetic circuit in order to obtain proper design

parameters for optimizing the damper performances. It is expected that the proposed design

procedures can be effectively utilized as fundamental design criteria in designing MR devices.

Material and Simulation Procedures

The MRF-132DG fluid produced by Lord Corporation was chosen in order to characterize the

mixed mode of MR damper under various conditions. The MR fluid was also used in other studies

and capable in producing a consistent result [8-9]. Besides MR fluid, electromagnetic circuit design

was very crucial to be considered in the new proposed MR damper. The coils would generate

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magnetic flux densities across the MR fluid. The magnetic field strength is proportionate to the

number of turns around the piston rod and the applied current. Thus an increase in the number of

turns or in the applied current, the magnetic flux density would be increased. Consequently, the flux

lines would also increase along the piston rod. However, an increase in the number of turns would

requires smaller diameter of wire which in turns, would only allowed small amount of applied

current.

Fig. 1(a) illustrates the conceptual design of the MR damper that previously done by Gavin et al

[7]. A modified version of the concept was made by introducing another electromagnetic circuit at

the bottom of the damper to create a squeeze mode. The copper (magnet) wire spools as indicated

by vertical-hatch marks, were used to produce magnetic fluxes along the steel piston. The direction

of magnetic polarity of the MR damper was represented by the three spools of the copper wire

wound in opposing direction to each other as shown in Fig. 1(b). The benefit of using three different

coils, instead of one single and long coil, was that the overall inductance of the circuit was much

lower and consequently the time response was shorter. The advantage of alternating the polarities

was to strengthen the magnetic field present between two adjacent cores through the piston poles. In

this design, the MR damper consisted of six different geometrical dimension parameters. They were

the polarity of coils, the diameter of piston, Dp, the diameter of piston rod, Dr, the thickness of shear

gap, S, the thickness of squeeze gap, S1, the piston pole length, Lp, and the thickness of housing, tw.

The magnetic fluxes generated by the electromagnetic circuit flew axially through the steel piston

beneath the windings, radially along the piston pole, penetrated MR fluid that located at the gap

thickness and axially through the housing.

(a) (b)

Fig. 1. (a) Diagram of the conceptual design of MR damper [7] and (b) flux path illustration for the

flow of flux around three coils,whose windings orientations alternate for each coil.

Results and Discussion

The asymmetrical model of magnetic circuit design for the mixed mode MR damper has been

altered and simulated using FEMM software package [8]. This software package covered the

geometrical dimension input including component’s materials, coil’s turn and type, and applied

current. These parameters were very crucial to produce the best value for the magnetic field

intensity H, which was correlated with the magnetic flux density B. For any changes study in the

dimension, the number of coil turns, the clearance at the effective area and the electric current value

supplied to the coil were kept constant. Furthermore, the magnetic properties of the non magnetic

materials were assumed to be linear, whilst the magnetic properties of the magnetic materials were

assumed to follow the B-H curves given in the software package or provided by the manufacturer.

The dimension of the coils at shear and squeeze areas were selected based on the highest values

of magnetic field intensity, H that could be achieved by varying the applied current. The dimension

parameters were limited the area for both shear and squeeze, in which the copper wire could be

wound. The average value of magnetic field intensity, H for each wire gauge is shown in Fig. 2.

Thus, the most tolerated type of wire was 26AWG, which has 0.40mm diameter and 675 turns with

maximum current allowable at about 0.4 Amps.

488 Materials and Applications for Sensors and Transducers II

Fig. 2. Magnetic field intensity of wire gauge, 26AWG copper wire has a high value of magnetic

field intensity H with th eaverage value was 7400 H.

Analyses of the magnetic field strengths at the effective area at shear area and squeeze area was

performed in the software and the results are shown in Fig. 3. The relationship between the

magnetomotive force generated in the magnetic circuit by applying the coil current and the

corresponding magnetic field intensity is given by Ampere’s law:

∲�. �� � � � (1)

where � is the magnetic field intensity (Am-1

), �� is the infinitesimal element of path length (m), �

is the magnetomotive force (mmf), is the number of coil turns and is the value of electrical

current (A).

Fig. 3. Magnetic flux distribution in mixed mode MR damper with the average of magnetic flux

density in (a) shear area and (b) squeeze area.

After the most tolerable design of the damper was predicted by FEMM, some modifications have

been made based on the conceptual damper. The final component of the MR damper was consisted

of nine parts that could be divided into three categories; magnetic materials, non magnetic materials

and an electromagnetic circuit. High magnetic permeability was used for the housing, piston rod,

piston pole, electromagnetic circuit cover and core, whereas the piston cover was made from non

magnetic stainless steel. The simulation results were based on the middle half of the damper, while

the average values of the magnetic flux density were pointed out by the red circle line on shear and

squeeze area as shown in Fig. 3.

Key Engineering Materials Vol. 543 489

After several design modifications of MR damper have been considered in the selection of

materials, the polarity of coils, the diameter of piston rod, the diameter of piston, the diameter of

core, the piston pole length, the thickness of housing, the shear gap thickness and the squeeze gap

thickness, the optimum value of magnetic flux density was achieved in the MR damper. Eventually,

the geometrical dimension of mixed mode MR damper with considering all the parameters as

shown in Fig. 4, were L1 = 156, Lp = 6, Dp = 46, Dr = 8, S = 1, S1 = 2 and T = 5mm.

Fig. 4. Middle half of the final design of the proposed MR damper.

Conclusion

An electromagnetic circuit simulation and design parameters procedures for the mixed mode MR

damper was proposed in this study. The new concept of MR damper design could generate higher

magnetic field at the effective area, hence capable to improve the damper performance.

Furthermore, alternate polarities of coil also help to strengthen the magnetic field in shear and

squeeze area. It is expected that the concept of a mixed MR damper could be generalized to other

applications especially in sensors and actuators.

Acknowledgment

This research is supported by Ministry of High Education Malaysia and Universiti Teknologi

Malaysia under research university grant (Vote 01H20).

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Materials and Applications for Sensors and Transducers II 10.4028/www.scientific.net/KEM.543 Parameters Consideration in Designing a Magnetorheological Damper 10.4028/www.scientific.net/KEM.543.487

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http://dx.doi.org/10.1016/j.matdes.2008.09.009