Page 370 - Mechatronics for Safety, Security and Dependability in a New Era

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behavior and performance of systems consisting of rigid or flexible parts undergoing large
displacement motions [Ozdalyan, B. and Blundell M.V. (1998)].

PURPOSE

Vibration control of vehicle suspensions systems has been a very active subject of research, since it
can provide a very good performance for drivers and passengers [Yao, G.Z. (2002)]. Recently, many
researchers have investigated the application of magnetorheological (MR) fluids in the controllable
dampers for semi-active suspensions. This work has the purpose of characterize, identify the
mathematical model and simulate the behavior of a magnetorheological fluid in car suspension
systems.

METHODOLOGY

To reach the purpose previously pointed out, firstly, the characterization is made by means of
experimentation and by using a prototype damper. The displacement of the damper is measured by
stages meanwhile known compression forces are applied under the influence of different magnetic
fields. Subsequently, the constitutive model is developed throughout the mathematical identification of
the relationships Force-Displacement, and Equivalent Damping Coefficient-Displacement. Polynomial
expressions are derived in function of electrical current as independent variable and displacement,
force and velocity as dependent variables. Finally, the simulation is carried out in two parts. Part one;
uses a program in which the constitutive model is used in order to adjust the damper resistance based
on the necessary current and according to different modes of behavior that can simulate several kinds
of road. And part two; the damper resistance is read by the module ADAMSVTEW of MSC ADAMS
software in which a suspension system has been modeled for describing the damper displacements at
different virtual road conditions.

SYSTEM DESCRIPTION

The MR fluid used for this analysis, shown in Figure 1, is mainly a dispersion of iron powder 99.9%,
as the soft magnetic material, in a carrier oil, and it was developed at ITESM, Campus Monterrey. The
iron particles size distribution has a mean value of 15.53um with standard deviation of 2.624um. The
particles are irregularly shaped and the mass fraction of the solid phase is 60%. The kind of oil used is
commercial engine oil. The total period of precipitation exceeds 40 days, without movement. The
viscosity of the MR fluid varies from 800 cP to 150,000 cP according to magnetic field applied. And,
under the influence of a magnetic field the liquid phase separates from particles after more than 24
hours. The system used for the experiments is composed by the following components and presented
in Figure 2.The damper is aprototype made of aluminum with 0.112 m of length, 0.014 m of diameter
and 3.6 xlO" 6 m 3 of capacity. The common oil used inside the damper has been replaced with the
magnetorheological fluid, which under no current presents a similar behavior as the original fluid.

(a) (b)
(b)
Figure 1: (a) Magnetorheological fluid and (b) prototype damper.