Field-dependent Damping Forces Research Articles

Comparative Study on Wear Characteristics between Flow Mode and Shear Mode Magnetorheological Dampers

ABSTRACTThis comparative study experimentally examines the wear characteristics of magnetorheological (MR) dampers operated in flow mode and shear mode. First, electromagnetic coil structures are designed for two different MR dampers to maximize the field-dependent damping force. Two MR dampers are also designed to have the same volume of MR fluid for reasonable comparison. After identifying the field-dependent damping force at the initial state, the two dampers are operated up to 60,000 cycles using a reciprocating-type wear durability tester. The field-dependent damping forces are then evaluated before and after operation. The wear properties of the MR fluid are investigated using scanning electron microscope (SEM) images that show the changes in the MR fluid particles' size and shape. The surface roughness of the MR damper's piston areas are also measured. In addition, the effects of the permeability of the piston sleeve materials on the wear properties are investigated by selecting three different sleeve materials that have different permeability values: 0.2% carbon steel (S20C), 0.45% carbon steel (S45C), and tool die casting steel (STD-11). The surface roughness of each case is tested and the atomic spectrum is investigated after long operation using energy-dispersive X-ray spectroscopy (EDS) inside the piston. The experimental results obtained from this work indicate that the motion of the operating mode significantly affects the wear characteristics of the MR fluid itself as well as the magnetic effective areas of the MR dampers.

Design and Evaluation of a Semi-Active Magneto-rheological Mount for a Wheel Loader Cabin

In this study, a semi-active magneto-rheological (MR) mount is designed and manufactured to minimize unwanted vibrations for the cabin of heavy vehicles. Normally, working conditions in heavy vehicles are extremely rugged. Usually, the heavy vehicles use passive rubber mounts for the reduction of vibrations from road. However, the passive mount has definite performance limitations because the passive mount has a fixed resonance frequency when the design is finished. An MR application is one of the solutions because the viscosity of MR fluid can be controlled. As a first step, an experimental apparatus was established for performance evaluation of the mounts. The apparatus has hydraulic excitatory, force, and displacement sensors. Performance of two different passive mounts used in industrial fields were evaluated. The passive mount data of force-displacement, force-velocity, and displacement transmissibility were collected and tested. After that, an MR mount was designed and manufactured that provides better performance using the passive mount data. The MR mount uses two different flow paths, annular duct and radial channels, for generating the required damping force. The field-dependent damping forces were then evaluated with respect to the moving stroke and input current. In this work, in order to control the damping force, an on-off controller associated with the fast Fourier transform (FFT) was used. The control results of the MR mount were compared with the results of passive rubber mounts. It was shown that the semi-active MR mount can attenuate vibrations more effectively at all frequency ranges compared with the passive rubber mount.

The field-dependent shock profiles of a magnetorhelogical damper due to high impact: an experimental investigation

This work proposes a new damper featuring magnetorheological fluid (MR damper) and presents its field-dependent damping forces due to high impact. To achieve this goal, a large MR damper, which can produce a damping force of 100 kN at 6 A, is designed and manufactured based on the analysis of the magnetic flux intensity of the damper. After identifying the field-dependent damping force levels of the manufactured MR damper, a hydraulic horizontal shock tester is established. This shock testing system consists of a velocity generator, impact mass, shock programmer, and test mass. The MR damper is installed at the end of the wall in the shock tester and tested under four different experimental conditions. The shock profile characteristics of the MR damper due to different impact velocities are investigated at various input current levels. In addition, the inner pressure of the MR damper during impact, which depends on the input’s current level, is evaluated at two positions that can represent the pressure drop that generates the damping force of the MR damper. It is demonstrated from this impact testing that the shock profiles can be changed by the magnitude of the input current applied to the MR damper. It directly indicates that a desired shock profile can be achieved by installing the MR damper associated with appropriate control logics to adjust the magnitude of the input current.

A low sedimentation magnetorheological fluid based on plate-like iron particles, and verification using a damper test

This study presents a new kind of low sedimentation magnetorheological fluid (MRF). Its salient properties are evaluated using a small-sized damper. The proposed MRF is characterized to investigate the effect of plate-like iron particles on rheological properties such as yield stress and flow behavior. Plate-like micron size iron particles play an important role in improving stability against rapid sedimentation as well as in enhancing the value of the yield stress. This study also considers a bidisperse MRF because this can produce a higher yield stress compared with a monodisperse suspension. Since the field-dependent yield stress is the key factor in mechanical applications, the physical properties of the MRF proposed in this work are evaluated and applied to the design of a small-sized damper which can be used for vibration control in washing machines. In order to verify the smaller effect on the damping force due to the particle sedimentation, the field-dependent damping forces are measured under two different operating conditions; one is just after filling the MRF and another after operating for 48 h. The proposed MRF is shown to be very effective in reducing adverse effects due to particle sedimentation.

MR 댐퍼를 이용한 전자제어 현가장치의 승차감 평가

This paper presents design and control of electronic control suspension(ECS) equipped with controllable magnetorheological(MR) damper for passenger vehicle. In order to achieve this goal, a cylindrical type MR fluid damper that satisfies design specification of a middle-sized commercial passenger vehicle is proposed. After manufacturing the MR damper with design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of a conventional damper. A quarter-vehicle MR ECS system consisting of sprung mass, spring, tire, controller and the MR damper is established in order to investigate the ride comfort performances. On the basis of the governing equation of motion of the suspension system, five control strategies(soft, hard, comfort, sport and optimal mode) are formulated. The proposed control strategies are then experimentally realized with the quarter-vehicle MR ECS system. Control performances such as vertical acceleration of the car body and tire deflection are evaluated in frequency domains on random road condition. In addition, performance comparison of WRMS(weighted root mean square) of the quarter-vehicle MR ECS system on random road are undertaken in order to investigate ride comfort characteristics.

자기유변유체를 이용한 승용차량 쇽 업소버의 유한요소 최적설계

This paper presents optimal design of controllable magnetorheological(MR) shock absorbers for passenger vehicle. In order to achieve this goal, two MR shock absorbers (one for front suspension; one for rear suspension) are designed using an optimization methodology based on design specifications for a commercial passenger vehicle. The optimization problem is to find optimal geometric dimensions of the magnetic circuits for the front and rear MR shock absorbers in order to improve the performance such as damping force as an objective function. The first order optimization method using commercial finite element method(FEM) software is adopted for the constrained optimization algorithm. After manufacturing the MR shock absorbers with optimally obtained design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of conventional shock absorbers. In addition, vibration control performances of the full-vehicle installed with the proposed MR shock absorbers are evaluated under bump road condition and obstacle avoidance test.

PERFORMANCE COMPARISON OF MR DAMPERS WITH THREE DIFFERENT WORKING MODES: SHEAR, FLOW AND MIXED MODE

In this work, three different magneto-rheological(MR) dampers, which are applicable for vibration control of a multi-story structure, are devised and their performance characteristics are compared. As a first step, the schematic configurations of the shear, flow, and mixed mode MR dampers are described with design constraints. The analytical models to predict the field-dependent damping forces are derived for each type and their damping forces are evaluated. The field-dependent damping forces are compared in terms of the damping force magnitude and the mixed-mode type of MR damper is chosen as an optimal candidate for the vibration control of the multi-story structure. An appropriate size of the mixed mode MR damper is manufactured and its field-dependent damping characteristics are evaluated in time domain. In addition, the displacement vs. damping force cycles of the piston are observed at various field intensities.

Non-dimensional analysis for effective design of semi-active electrorheological damping control systems

This paper presents a non-dimensional analysis for effective design of semi-active electro- rheological (ER) damping control systems. The non-dimensional equations consist of the Bingham number, the non-dimensional damping force, the dynamic range and the non-dimensional geometric parameter. After showing the effectiveness of the proposed analysis scheme through a comparative examination of predictions and measured values of the non-dimensional damping force, sequential steps for the ER damper design have been developed. A flow mode type ER damper, considering control performance of a semi-active quarter-car system, has been designed on the basis of the proposed non-dimensional design steps. To assess the effectiveness of the proposed non-dimensional design methodology, the field-dependent damping forces of an ER damper have been experimentally evaluated and compared with those obtained from the non-dimensional analysis.

Performance comparison of vehicle suspensions featuring two different electrorheological shock absorbers

This paper proposes a novel type of semi-active electrorheological (ER) shock absorber for a small-sized passenger vehicle. The field-dependent damping forces of the proposed orifice type of ER shock absorber are experimentally evaluated and compared with those of a conventional cylinder type of ER shock absorber. The governing equations of motion for a vehicle suspension system equipped with ER shock absorbers are derived and an optimal controller is designed to attenuate vibration due to bump and random road excitations. Control responses such as vertical acceleration of the vehicle body are evaluated in time and frequency domains, and comparative work is done between the orifice type and cylinder type of ER shock absorbers.

Vibration control of a flexible beam structure using squeeze-mode ER mount

This paper presents vibration control of a flexible beam structure supported by squeeze-mode electro-rheological (ER) mounts. After devising an appropriate size of the squeeze-mode ER mount, its field-dependent damping forces are evaluated at various exciting frequencies. The damping force controllability of the ER mount is also demonstrated by implementing a proportional integral derivative (PID) controller. The ER mounts are then incorporated with a flexible beam structure subjected to external excitations. The governing equation of the structural system is obtained and an optimal controller which consists of the position and velocity components of the beam structure as feedback signals is designed to attenuate the imposed vibrations. The controller is empirically realized and control responses such as beam acceleration are evaluated in time and frequency domains. In addition, the forces transmitted from the input point (exciting position) to the base plate (mount position) are investigated by applying control voltage and constant voltage.

Vibration Isolation of Structural Systems Using Squeeze Mode ER Mounts

This paper presents vibration control of flexible structures using squeeze mode ER mounts. After devising the squeeze mode ER mount, its field-dependent damping forces are evaluated at various exciting frequencies. The ER mounts are then incorporated with a flexible beam structure. The governing equation of motion is obtained and an optimal controller which represents controllable damping force is designed to attenuate unwanted structural vibration. The controller is experimentally realized and control responses are presented in the frequency domain. In addition, vibration control responses of a flexible frame structure integrating with the proposed ER mounts are investigated by experiment.

Performance Evaluation of a Semi-Active ER Damper with Free Piston and Spring

This paper presents a novel type of a semiactive damper featuring an electro-rheological(ER) fluid. Unlike conventional cylindrical ER damper, the proposed one has controllable orifices by the intensity of electric fields (We call it orifice type). The dynamic model of the orifice type ER damper is formulated by incorporating field-dependent Bingham properties of an arabic gum-based ER fluid. Design parameters such as electrode gap are subsequently determined on the basis of the dynamic model. After manufacturing the orifice type ER damper, field-dependent damping forces and damping force controllability are empirically evaluated. In the evaluation procedure, conventional cylindrical ER damper is adopted and its performance characteristics are compared with those of the orifice type ER damper. In addition, the proposed one is installed with a full-car model and its vibration control performance associated with a skyhook controller is investigated