11-09-2014, 03:20 PM
Master Thesis
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Abstract
This thesis presents the nonlinear MR brake to a semi active suspension system (e.g. of a
vehicle suspension). Semi-active control has recently received considerable attention in
some years, because its strong potential to control devices without imposing heavy
power demands.
The dynamic response characteristics of the damper are captured in data collection,
random input signals were used for angular velocity and current input.
The relationship between the current and damping force in magneto-rheological brake
is nonlinear but in the reality it is possible to control the current of MR brake to reduce
the vibration of the system as much as possible, because the nonlinearity of the model
depends on the current and angular velocity.
The first part of this project describes the vibration suppression in passive, active and
semi active suspension. Subsequently several mathematical models are used to simulate
and analyze hysteresis behavior of magneto-rheological brake. The second part of this
work is devoted to derivation of the dynamic model equation of the experimental setup.
The last part presents the evaluation of the dynamic simulation modeling results with
the full-scale experimental data. In particular, special attention is paid to comparison
with the Bouc-Wen model analysis.
Introduction
The purpose of this project is to provide the reader with information regarding different
vibration suppression strategies, particularly SAS mechanical system’s description and
modeling. There are three main types of vehicle suspensions that have been proposed,
that is, passive, semi-active and active suspensions, which depend on the operation
mode to improve vehicle ride comfort, vehicle safety, road damage minimization and the
overall vehicle performance. Study of vehicle vibration reduction in this project was
made by simulating the dynamics of a semi active suspension system.
There are various mechanical systems in the world which provide isolation of a
structure from the effect of disturbances (e.g. vibrations). One example of such a device
is a rotational magneto-rheological brake (MR brake) which creates braking torque by
changing the viscosity of the MR fluid inside the brake. The magneto-rheological brakes
are used in many applications including prosthetics, automotive, vibration stabilization.
In this project, there is presented examination of the mechanical system equipped with
MR brake. The main aim of this thesis is to obtain the hysteresis plot by finding the
torque in MR brake dependent on different input current. A passive suspension has the
ability to store energy via a spring and to dissipate it via a damper. In the passive
suspension system, the sprung mass, spring and damper parameters are generally fixed,
and they already have been chosen in terms of the design requirements of this part of
experimental setup. All the physical and geometrical constants characterizing the real
experimental setup which is examined here were included and given in the SAS
manufacturer’s documentation.
Organization
This project presents some introduction of the vibration suppresion system in three
different strategy in chapter 2. Then the physical study of the Magnetor-rheological
brake is explained in the chapter 3. Chapter 4 describe the theory of SAS physical system
in geometrical and dynamic equation. In the chapter 5 the estimation and identification
parameters of experimental setup will be done. Chapter 6 explain the electronic setup of
each part of mechanical system. Chapter 7 explain about software setup, to shows how
different SAS (such as Real Experimental Data, RPM Stabilization, Real Time Data, SAS
Simulation) system works.
2 System description
The MR device designed in this research is a rotational damper through which an
electro-magnet rotates MR fluid. The semi-active suspension system consists of a
rocking lever that emulates the quarter of car body, whereas a spring and an MR damper
simulate the semiactive vibration control.
A DC motor coupled to an eccentric wheel due to the same shaft is used to simulate the
vibrations induced to the vehicle. A set of equations that model the dynamics of the
suspension system are given in this chapter, in which the detailed definitions of the
angles and distances are provided
8. Project conclusion
During this project it has been studied the vibration suppression systems, such as
passive, active and semi active.
The application of the physical device for the vibration control is studied. The dynamic
equation of the mechanical SAS system is derived together with the geometrical and
graphical description of the system. Equations of motion are established by using
Newton’s 2nd law. Some interesting observations are obtained and their physical
insights are explained.
The flexibility of shaping the closed-loop road excitation frequency responses of a
quarter-car model by feedback control was investigated.
Physical torque equation due to the MR brake has been investigated, and then
parameters of the different mathematical models have been estimated. Also, the
parameters identification has been done for the real experimental data. The estimated
hysteresis loops were compared in passive and semi active suspension with the real
experimental results. Furthermore, it was found that the disadvantage of the passive
damping strategy is that there is no control in this system, while the advantage for the
semi active damping control is the fact that the value of braking torque can be changed
by increasing or decreasing current.