Submitted by THIAGO GALBIATI LAGOIN null (thiagolagoin@yahoo.com.br) on 2017-10-26T18:00:51Z No. of bitstreams: 1 lagoin_tg_dr_ilha.pdf: 10803891 bytes, checksum: 11fc5487a11d931ddaa2432fe578288e (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-10-31T18:40:57Z (GMT) No. of bitstreams: 1 lagoin_tg_dr_ilha.pdf: 10803891 bytes, checksum: 11fc5487a11d931ddaa2432fe578288e (MD5) / Made available in DSpace on 2017-10-31T18:40:57Z (GMT). No. of bitstreams: 1 lagoin_tg_dr_ilha.pdf: 10803891 bytes, checksum: 11fc5487a11d931ddaa2432fe578288e (MD5) Previous issue date: 2017-09-28 / Fluidos magnetoreológicos (MR) são fluidos capazes de alterar suas propriedades reológicas quando um campo magnético é aplicado sobre ele. Uma das aplicações mais importantes do fluido MR é em amortecedores de vibrações, utilizados principalmente na construção civil, veículos automotivos e outros sistemas mecânicos sujeitos a excitações que provocam vibrações indesejáveis. Na indústria automobilística, atualmente a tecnologia dos amortecedores que utilizam fluido MR vem se destacando como uma solução que pode trazer benefícios de conforto e segurança aos usuários de veículos em geral. Este trabalho discute a modelagem não-linear de um veículo que considera a dinâmica vertical, lateral e longitudinal, simulado em diferentes condições de condução que buscam avaliar o conforto, a aderência à estrada, a dirigibilidade, a rolagem e a deflexão da suspensão. Pretende, também, contribuir com a área de controle de vibrações em suspensões veiculares que utilizam amortecedores MR, avaliando o desempenho dos controladores ótimo (LQR), nebuloso e FEB (Frequency-Estimation-Based ) projetados em 1/4 de veículo e aplicados ao modelo não-linear do veículo. O trabalho termina comentando as potencialidades da metodologia apresentada, discutindo as facilidades e dificuldades encontradas na sua implementação e aponta propostas para a sua continuidade. / Magnetorheological fluids (MR) are capable of changing their rheological properties when a magnetic field is applied. One of the most important applications of the MR fluid is in vibration dampers, mainly used in construction, automobiles and other mechanical systems subjected to excitations that cause unwanted vibrations. In the automotive industry, nowadays the technology of dampers using MR fluid has emerged as a solution which can bring benefits of comfort and safety to overall vehicle users. This work discusses the non-linear modeling of a vehicle which considers the vertical, lateral and longitudinal dynamics, simulated in different driving conditions aiming evaluate the comfort, the road holding, the handling, the roll and the suspension deflection. It also aims to contribute to the field of vibration control in vehicular suspensions that use magnetoreological dampers, evaluating the performance of controllers optimal (LQR), fuzzy and FEB (Frequency-Estimation-Based ) designed in 1/4 of vehicle and applied to the non-linear model of the vehicle. This work is concluded presenting the potentialities of the design methodology proposed and future developments to be implemented.

The purpose of this study is to mitigate the compromise between ride comfort and handling of a small single seat off-road vehicle known as a Baja. This has been achieved by semi-active control of the suspension system containing controllable magnetorheological (MR) dampers and passive hydro-pneumatic spring-damper units. MR fluid is a viscous fluid whose rheological properties depend on the strength of the magnetic field surrounding the fluid, and typically consists of iron particles suspended in silicone oil. When a magnetic field is applied to the fluid, the iron particles become aligned and change the effective viscosity of the fluid. The use of MR fluid in dampers provides variable damping that can be changed quickly by controlling the intensity of the magnetic field around the fluid. Various benefits associated with the use of MR dampers have led to their widespread implementation in automotive engineering. Many studies on conventional vehicles in the existing literature have demonstrated the conflicting suspension requirements for favourable ride comfort and handling. Generally, soft springs with low damping are ideal for improved ride comfort, while stiff springs with high damping are required for enhanced handling. This has resulted in the development of passive suspension systems that provide either an enhanced ride quality or good drivability, often targeting one at the expense of the other. The test vehicle used for this study is distinct in many ways with multiple characteristics that are not commonly observed in the existing literature. For instance, the absence of a differential in the test vehicle driveline causes drivability issues that are aggravated by increased damping. The majority of existing MR damper models in the literature are developed for uniform excitation and re-characterisation of model parameters is required for changes in input conditions. Although recursive models are more accurate and applicable to a wider range of input conditions, these models require measured force feedback which may not always be available due to limitations such as packaging constraints. These constraints required the development of alternative MR damper models that can be used to prescribe the current input to the damper. In this study parametric, nonparametric and recursive MR damper models have been developed and evaluated in terms of accuracy, invertibility and applicability to random excitation. The MR damper is used in parallel with passive damping as a certain amount of passive damping is always present in suspension systems due to friction and elastomeric parts. Most of the existing studies on suspension systems have been performed using linear two degree of freedom vehicle models that are constrained to specific conditions. Usually these models are implemented without an indication of the ability of these models to accurately represent the vehicles that these studies are intended for. For this study, a nonlinear, three-dimensional, 12 degrees of freedom vehicle model has been developed to represent the test vehicle. This model is validated against experimental results for ride comfort and handling. The MR damper models are combined with the model of the test vehicle, and used in ride comfort and handling simulations at various levels of passive damping and control gains in order to assess the potential impact of suspension control on the ride quality and drivability of the test vehicle. Simulation results show that lower passive damping levels can significantly improve the ride comfort as well as the handling characteristics of the test vehicle. Furthermore, it is observed that additional improvements that may be obtained by the implementation of continuous damping control may not be justifiable due to the associated cost and complexity. / Dissertation (MEng)--University of Pretoria, 2013. / Mechanical and Aeronautical Engineering / unrestricted

This diploma thesis investigates the accelerated sedimentation of the magnetorheological fuids (MRFs) using centrifuge. Experiments are carried out at room temperature as well as at higher temperatures (40°C, 60°C and 80°C). The development of the new improved measuring device for the sedimentation evaulation is described. Magnetic components of the device were designed using FEM analysis. Newly designed device is verified. To accomplish the experiments at the high temperatures the new heated chamber for experimental centrifuge is designed and constructed. In the next part of the work full experiment of the accelerated sedimentation is performed. At final the empirical model of the sedimetation velocity for various accelerations and temperatures is synthesized.

This diploma thesis deals with development of a new generation of magnetic circuits of fast magnetoreological (MR) dampers that will not use problematic ferrite materials. To ensure a short response time, eddy currents must be avoided. Using the Finite Element Method, 2 solutions were proposed - the use of soft magnetic composites with high electrical resistance and the cutting of grooves in metallic material. Subsequently, 2 magnetic circuits were produced - one from Sintex SMC prototyping material composite and one from 11SMn30 steel with 48 deep grooves 0,35 mm wide. Both were implemented into the MR damper and tested on a hydraulic pulsator. The results of the experiments were compared with 2 different MR dampers: one with 11SMn30 magnetic circuit without grooves and another with the Epcos N87 ferrite magnetic core. It has been found that both new circuits have ensured an equally short response of the damper force to the change of electric current like ferrite. At the same time, a much larger dynamic range was ensured. Compared to 11SMn30 without grooves, the new circuits provided approximately 7x faster response.

The diploma thesis deals with the development of the magnetic circuit of Magnetoreological (MR) dampers with a short time response. To achieve a short response time, a shape approach was chosen whereby the geometry of the magnetic circuit was chosen to significantly eliminate the occurrence of eddy currents. The influence of structures on magnetic properties was first examined on a simpler toroidal core and then the optimization was subjected to the magnetic circuit of the MR damper itself. Geometry optimization was done using FEM simulations. The resulting geometry was made of pure iron using Selective Laser Melting technology (SLM). In addition, a MR damper was completed and its properties on air and with MR fluid were measured, which were then compared with previously developed rapid MR dampers. It has been found that the newly designed magnetic circuit achieves similar time responses as all other compared fast MR dampers and reaches a higher dynamic range than most of the compared variants. The proposed magnetic circuit also has a significantly reduced weight.

This diploma thesis deals with an engineering design of a fail-safe magnetorheological (MR) damper capable of semi-active control. The first part of the thesis is devoted to the current state of knowledge of fail-safe MR dampers and permanent magnets contained in these dampers. The next part contains an engineering design of a fail-safe MR damper, made using FEM simulations, and its subsequent testing in terms of magnetic and hydraulic properties. Finally, a design of a fail-safe MR damper with fast response time was made and simulated using verified FEM analysis. Fast response time is ensured by limiting the generation of eddy currents in the piston core by grooving.

This paper is focused on MR dampers and its critical parts in term of damper`s durability, which seems to be a piston-rod seals, and it should find an ideal material combination of seal and MR fluid for increasing the damper`s life. The tests were conducted in modified pin-on-flat configuration, which was supposed to be more suitable for laboratory testing. There was tested and compared a suitable material for seals, like PTFE, NBR, SBR of polyurethanes. The article is also focused on MR fluids and its contribution to seal`s wear. The impact of particle concentration, wear of MR fluid and effect of modification of MR fluid was tested. It showed up, that the best material for seal is H-PU95FDA. The effect of particle concentration is negligible on seal`s wear, while effect of modification and wear of MR fluids are significantly higher.

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