The purpose of this work is to design a semi-active magnetorheological (MR) hydraulic bushing. The semi-active bushing is intended to be used to isolate a cylinder deactivating engine. Cylinder deactivation causes high transient torsional loading in addition to changing the magnitude and mode of engine vibrations requiring an adaptive or controllable isolator. <br /><br /> Practical and simple semi-active control strategies are inspired by investigating the optimization of linear and slightly cubic nonlinear single degree of freedom isolators. Experimental verification of the optimization technique, which minimizes the root mean square (RMS) of engine acceleration frequency response and RMS of the force transmitted frequency response, shows that this method can be implemented on real linear systems to isolate the engine from harmonic inputs. This optimization technique is also applied to tune selected model parameters of existing two degree of freedom hydraulic bushings. <br /><br /> This thesis also details the development of a MR hydraulic bushing. The MR bushing design retrofits an existing bushing with a pressure driven flow mode valve on the inertia track. A new efficient valve design is selected and developed for the application. The MR hydraulic bushing is designed, mathematically modeled, and numerically simulated. The simulation results show that the MR bushing tends to increase the low frequency dynamic stiffness magnitude while simultaneously decreasing the phase. The next stage of the project is fabrication and testing of the semi-active bushing. The performance of the manufactured MR bushing is tested on a base excitation apparatus. Varying the current input to the MR valve was found to have a small effect on the response of the suspended mass. The results are in agreement with the effects demonstrated by the dynamic stiffness numerical simulation.

<p>Magnetorheological (MR) rubber materials are the solid analogue of magnetorheological fluids; i.e. their rheological properties can be controlled continously, rapidly, and reversibly by an applied magnetic field. They consist of magnetically polarisable particles in an elastomer matrix and they can be made to respond to changes in their environment; hence, they are considered as "smart" materials. Examples of potential applications for these materials are adaptive tuned vibration absorbers, stiffness-tuneable mounts and suspensions, and automotive bushings.</p><p>The purpose of this work was to increase the knowledge relating to magnetorheological materials for damping applications. The materials should exhibit a large response to an applied magnetic field, and have good mechanical and long-term properties.</p><p>MR rubber materials were made from nitrile, natural and silicone rubber, with irregularly shaped iron particles several micrometres in size. The particles were not aligned by a magnetic field prior to the vulcanisation; hence, the materials can be considered to be isotropic. These materials show a large MR effect, i.e. an increase in the shear modulus when a magnetic field is applied, although the particles are not aligned within the material. This is explained by the low critical particle volume concentration (CPVC) of such particles. Similar behaviour can be obtained with materials containing carbonyl iron, if the particles are aggregated so that they behave like large irregular particles. The iron particle concentration must be very close to the CPVC in order to obtain a large MR effect without alignment of the particles.</p><p>The absolute MR effect (MPa) in an isotropic MR rubber material with large irregular iron particles is independent of the matrix material, and the relative MR effect (%) can thus be increased by the addition of plasticisers. However, the obtainable effect is limited by the reinforcement of the particles and by friction between the particles. Therefore, it is very difficult, if not impossible, to achieve an MR effect larger than 60%.</p><p>Other ways of increasing the MR effect are to increase the strength of the magnetic field, although the materials saturate magnetically at high field strengths, or to use small strain amplitudes. The strong strain amplitude dependence of the MR effect suggests that MR rubber materials are most suitable for low amplitude applications, such as sound and vibration insulation. Measurements at frequencies within the audible frequency range show that this is a promising application for MR rubber materials.</p><p>The incorporation of large amounts of iron into the rubber matrix decreases the oxidative stability dramatically. This is probably due to iron oxides on the surface of the particles, and to the fact that the oxidation rate is enhanced by iron ions, which are able to diffuse into the matrix. Standard antioxidants do not provide sufficient stabilisation for MR rubbers. Thus, proper stabilisation systems have to be found in order for these materials to be successful in applications.</p>

Σκοπός της παρούσας εργασίας είναι η μελέτη και κατασκευή ενός μετατροπέα ισχύος για την οδήγηση αναρτήσεως αποτελούμενης από μαγνητορεολογικό υγρό. Στην αρχή, γίνεται μία ιστορική αναδρομή στις εξελίξεις στο χώρο των αναρτήσεων. Κατόπιν, αναφέρονται τα χαρακτηριστικά των μαγνητορεολογικών υγρών και των αντίστοιχων αναρτήσεων, με παραδείγματα εφαρμογής τους στην αυτοκινητοβιομηχανία. Στη συνέχεια, παρουσιάζονται τα βασικά χαρακτηριστικά των τροφοδοτικών ισχύος, καθώς και τα συγκριτικά πλεονεκτήματα και μειονεκτήματά τους. Έπειτα παρουσιάζονται οι βασικότερες διατάξεις μετατροπέων ισχύος και τα χαρακτηριστικά τους, τα οποία θα χρησιμεύσουν στην επιλογή της κατάλληλης διάταξης για την παρούσα εφαρμογή. Ακολουθεί η παρουσίαση της θεωρητικής μελέτης της διάταξης forward, η οποία και επιλέχθηκε, ως καταλληλότερη και οι προσομοιώσεις στο πρόγραμμα Matlab, με τις αντίστοιχες εικόνες και πειραματικές τιμές. Τέλος, περιγράφεται η διαδικασία σχεδιασμού και κατασκευής της πλακέτας ισχύος. / The purpose of this diploma thesis is the design and construction of a power converter to drive a magnetorheological suspension. At the beginning, historical developments in the field of suspension are presented. Then, the characteristics of magnetorheological fluids and related suspension systems are described, with examples of their application in the automotive indusrty. Afterwards, it follows an analysis of the key features of the power supplies, along with their comparative advantages and disadvantages. Subsequently, the main power converters and their characteristics are discussed, which will be used in selecting the appropriate device for this application. In the followin paragraphs, the theoretical study of the device forward, which was selected as appropriate, is analyzed and simulated with Matlab application. The corresponding images and experimental values are presented also. Finally, the design and construction of the power converter board circuit is prsented.

Le but principal de ce travail est la présentation de la formulation mathématique et l’analyse des propriétés viscoplastiques du fluide magnétorhéologique dans des conditions d’exploitation d’amortisseur ainsi que la détermination des dimensions optimum de l’orifice d’écoulement du fluide MR dans le dispositif de ce type. Une analyse particulière de la littérature a été effectuée. Nous nous sommes limités à deux types d’amortisseurs: l’amortisseur LORD RD 1005-3 et le prototype d’amortisseur T-MR SiMR 132 DG. Les résultats expérimentaux ont permis de déterminer la limite élastique et la contrainte maximale de cisaillement du fluide MR sous tension en fonction de différentes vitesses de cisaillement, différentes intensités du courant, températures et hauteurs d’orifice d’écoulement. Les modèles viscoplastiques identifiés ont permis de simuler le comportement du fluide MR et de comparer les résultats numériques avec ceux obtenus par des mesures. On a constaté une bonne concordance des courbes tracées dans ces deux cas, ce qui permet de conclure qu’il est possible d’utiliser les modèles viscoplastiques des métaux pour décrire le comportement du fluide magnétorhéologique. / The main goal of this dissertation is a mathematical description and an analysis of viscoplasticproperties of magnetorheological fluid, in operational conditions of the damper’s work, as well as the determining the optimum, in view of indicated values of parameters, size of the gap for the MR fluid to flow, in these devices. A detailed analysis of literature was made. The scope of research work has been limited to two types of magnetorheological devices: the shock absorber LORD RD 1005-3 and the MR damper prototype T-MR SiMR -132 DG. On the basis of performed experiments, it has been estimated i.e.: conventional yield point and the maximum shear stress of analyzed MR fluid, including variable shear rate, intensity of current flowing in a solenoid, liquid’s temperature and the gap height. Identified viscoplastic models were used to develop a simulation that verifies the proposed mathematical model which describes the behaviour of MR fluid in operating gap of machine’s head, with data derived from performed experiments.

This thesis deals with the design of the magnetorheological (MR) clutch. The extensive literature research with particular conclusions to each design variant of MR clutches or brakes has been done in the first part of the thesis. The second part of the thesis describes the design of the actual MR clutch based on the results of the analytical calculation of the magnetic circuit. Finally, the experiments verifying the function of the key segments of the clutch, and the whole clutch are summarized in the third part of the thesis.

This study evaluates and provides solutions to the problem of poor subjective feel of seat suspensions that employ magnetorheological (MR) dampers and skyhook control. An Isringhausen seat suspension that had been modified to replace the stock passive damper with a controllable MR damper was used to evaluate the problems and potential solutions. A seat suspension tester was built using materials from 80/20 Incorporated and a hydraulic actuation system from MTS. An HP Dynamic Signal Analyzer was used as the main piece of data acquisition equipment, along with a Pentium PC and National Instruments Data Acquisition card. All of the hardware is installed in a controlled laboratory facility at Virginia Tech's Advanced Vehicle Dynamics Lab. The first task was to analyze the source of the unexpected peak in the acceleration spectrum of the suspended seat. This analysis was accomplished using a combination of pure tone inputs and a Fourier analysis of a simple model of the system. This analysis indicated that the peak is actually three times the resonant frequency of the seat suspension. The analysis also indicates that the frequency components continue at odd multiples of the resonant frequency, however, the third peak is the most noticeable. The third multiple is in the resonant frequency range (4-8 Hz) of the human body, so it was initially blamed for the poor subjective feel of the seat. However, solutions to remove this harmonic were tested without success. The work progressed to a time domain analysis, which eventually led to determining the source of the poor subjective feel. The seat suspension was excited with a variety of inputs. The seat acceleration and damper control current were examined in the time domain to show that the cause of the poor subjective feel is the control signal discontinuities. The control policy was modified to remove the control signal discontinuities and was found to improve the subjective feel of the seat. Finally, several two-degree-of-freedom control policies were implemented and tested. Although the results from this testing are inconclusive, they generated several recommendations for future research. / Master of Science

<p dir="ltr">Magnetorheological elastomers (MREs) are a type of smart material composed of ferrous particles suspended in a solid elastic matrix [5, 6]. When an external magnetic field is applied to an MRE, the ferrous particles tend to align with the field, causing either deformation and/or a change in the mechanical properties of the system. MREs are utilized in applications such as soft robotics, actuators, sensors, vibration control systems, and mechanical metamaterials[20, 19, 27, 5, 6, 13]. Recent demand for theses technologies has motivated an increasing focus on the material properties of MRE’s over the last 20 years [6]. Multiple authors have proposed a variety of hyperelastic mechanical and magnetomechanical models to describe these materials [16, 12, 15, 25, 14, 38, 2, 6, 8, 24]. The research presented in this dissertation focuses on the modeling and characterization of MRE’s using a systematic development of the conservation and balance laws, Maxwell’s equations, and constitutive equations needed to describe the MRE as a multi-constituent system. The material parameters resulting from the derived constitutive equations are estimated using data collected from a series of compression experiments coupled with an externally applied magnetic field. The multi-constituent constitutive equations predicted the stress of the MRE in these compression experiments for a variety of ferrous particle concentrations.</p>

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Semi-active dampers utilizing various working principles have been developed for a variety of vehicles. These semi-active dampers have been designed to resolve the ride and handling compromise associated with conventional passive dampers, and increase vehicle stability. This thesis briefly reviews existing semi-active damper designs, including but not limited to MR dampers, before presenting two new prototype semi-active hydraulic dampers. Both prototype dampers are designed to provide a large force range while maintaining easily controllable valve characteristics. The first of these dampers served primarily as a proof of concept and a means of understanding the dynamics of a disc valve housed inside the main piston. The valve design is presented, along with other information concerning the fabrication of the Initial Prototype damper. Test results are presented and analyzed, and a second iteration of the valve is designed. The Final Prototype damper is a scaled up version of the initial design, with refinements made in piston geometry, internal disc profile, and dynamic seals. This large force range damper is tested and results are compared with existing MR dampers. The Final Prototype damper provides a significantly larger force range when compared with typical MR dampers. Finally, to conclude this research, the vehicle dynamics implications of the Final Prototype damper are discussed and recommendations for further study are made. / Master of Science