This thesis has been performed at Öhlins Racing AB which is known world-wide for its high quality racing shock absorbers. Öhlins have been developing shock absorbers for more than 30 years and in addition to this they also develop a technology for semi-active suspension. Semi-active suspension technology makes it possible to achieve an intelligent and dynamic vehicle chassis control. Compared to standard passive suspensions, semiactive dampers allow improving vehicle cornering performance while still providing good comfort when cruising. This is achieved by a real time adjustment of the suspensions damping characteristics. Öhlins system for semi-active suspension is called CES (Continuously controlled Electronic Suspension). The systems consist of electronically controlled hydraulic valves for uniflow dampers. These valves are mounted on all four dampers of the vehicle and are controlled individually to provide the desired ride quality. The valves are configurable to suit many types of vehicles by changing internal parts. The first goal of this thesis project was to study the behaviour of the CES valve and uniflow damper. In order to achieve this a simulation model was created using Hopsan which is a 1-dimensional multi-domain modelling tool developed at the division of Fluid and Mechatronic Systems at Linköping University. The model considers mechanical forces from for example springs together with hydraulic forces. It was validated against static and dynamic measurements made in a flow bench and a dynamometer. The second goal was to use the simulation model as part of a tool that configures the CES valve according to a requirements specification. To achieve this goal a method of estimating the characteristics of the internal damper valves was developed. This estimation method, together with the simulation model, was used to choose the best valve configuration by using weighted least-squares. The result is presented in a Matlab-based graphical user interface.

Changes in the characteristics of the structure, such as damage, have not been considered in most of the active and semi-active control methods that have been used to control and optimize the response of civil engineering structures. In this dissertation, a direct adaptive control which can deal with the existence of measurement errors and changes in structural characteristics or load conditioning is used to control the performance of structures. A Simple Adaptive Control Method (SACM) is modified to control civil structures and improve their performance. The effectiveness of the SACM is verified by several numerical examples. The SACM is used to reduce the structural response such as drift and acceleration using active and semi-active devices, and its performance is compared with that of other control methods. Also, a probabilistic indirect adaptive control method is developed and its behavior is compared to the SACM using a simple numerical example. In addition to the simplicity of the SACM implementation, the results show that SACM is very effective to reduce the response of structures with linear and non-linear behavior in comparison with other control methods.

Ce travail concerne le développement de méthodes de commandes avancées pour les suspensions automobiles afin d'améliorer la tenue de route des véhicules et le confort des passagers, tout en respectant les contraintes technologiques liées aux actionneurs de suspension (passivité, non-linéarités, limite structurelle). Dans la 1ère partie, nous proposons deux schémas de commande par approche LPV polytopique (Linéaire à Paramètre Variant) et Stabilisation Forte (Strong Stabilization) avec optimisation par algorithme génétique pour résoudre les conflits confort/tenue de route et confort/débattement de suspension. Dans la 2ème partie, pour résoudre le problème complet de commande de suspensions semi-actives, nous développons d'abord une stratégie générique pour les systèmes LPV généraux soumis à la saturation des actionneurs et à des contraintes d'état. Le problème est étudié sous la forme de résolution d'inégalités linéaires matricielles (LMI) qui permettent de synthétiser un contrôleur LPV et un gain anti wind-up garantissant la stabilité et la performance du système en boucle fermée. Ensuite, cette stratégie est appliquée au cas de la commande des suspensions semi-actives. Les méthodes proposées sont validées par une évaluation basée sur un critère industriel et des simulations effectuées sur un modèle non-linéaire de quart de véhicule. / This work concerns the development of advanced control methods for automotive suspensions to improve road holding and passenger comfort, while satisfying the technological constraints related to the suspension actuators (passivity, nonlinearity, structural limit). In the first part, we propose two control schemes by polytopic LPV (Linear Parameter Varying) approach and by Strong Stabilization with genetic algorithm optimization to solve the comfort/handling and comfort/suspension travel conflits. In the second part, to solve the full semi-active suspension problem, we develop first a generic strategy for general LPV systems subject to actuator saturation and state constraints. The problem is studied in the form of resolution matrix of linear inequalities (LMI) that allows synthesizing an LPV controller and an anti-windup gain to ensure the stability and performance of the closed-loop system. Second, the theoretical result is applied to the case of semi-active suspension control. The proposed methods are validated by an evaluation based on an industrial standard and simulations on a nonlinear quarter vehicle model.

The purpose of this thesis is to implement and test a semi-active damping system based on a concept from an earlier thesis. The project includes implementation of mechanical, hydraulic and electronic hardware, aswell as controller software. The idea is to measure the movements of the vehicle chassis and based on these measurements set the damping torque using hydraulics. To be able to develop, test and evaluate the system, realistic input data must be available. To acquire such data, driving trials have been conducted on a variety of tracks. The first part of the system is the sensors that measure chassis movements. Both accelerometers and a gyro has been used. To remove drift and high frequency vibrations, the signals are filtered. The suggested controller from the earlier thesis requests damping torque based on the dampers vertical velocity. When accelerometer signals are integrated, measurement and rounding errors causes drift in the velocity. To compensate for this, a floating average is calculated and used. The main hydraulic component is a pressure reduction valve that controls the pressure inside the damper. Higher pressure will give higher damping torque. The reaction speed of the system is mostly depending on the hydraulic components. It is important to know the time delay from a change in the valve control signal, to when the actual pressure in the damper has been reached. Tests have shown that a large step, going from 10 Bar to 60 Bar takes approximately 46ms, and that a small step from 1 Bar to 20 Bar takes 63ms. The valve is faster when higher pressure levels are requested. In addition to the hydraulic response time the delay through the signal filters, measured to about 14ms, must be added. The sensors are affected by vibrations. If these can be reduced, the digital filters can be made less sharp with a lower filter delay as result. It is also important to have a good control computer so that large rounding errors in the filter calculations can be avoided. This would greatly decrease drift in the integrated velocity.

Abstract Over recent years the progress in actuator and microelectronics technology has made intelligent suspension systems feasible. These systems are designed to reduce the drivers' exposure to harmful vibration, as well as to improve the handling properties of the vehicle. Due to widespread use of vehicles as an example of a true MIMO-system, a myriad of different control schemes and algorithms can be found in the literature for these systems. Linearized models are commonly used when the control algorithms are derived. This thesis describes the development of a new analytical full vehicle model, which takes the essential kinematics of the suspension system into account, as well as a new approach to controlling the full vehicle vibration problem. The method of calculating the desired damping forces for each of the semi-active actuators is based on the skyhook theory and this new model is introduced. The performance of the control schemes is evaluated with simulations in a virtual environment. For the excitation to the vehicle, standardized ISO-tracks, washboard tracks and single bump tracks were used. The performance between the two different semi-active control systems and the passive system are compared in terms of damping the vibration, variation of the dynamic tire load and demand for rattlespace. The damping of vibration evaluates both the ability to suppress the vibration on heave, pitch and roll degrees of freedom and ability to reduce the drivers' exposure to harmful whole body vibration. The frequency distribution of the vibration was also reviewed. Variation of dynamic tire contact force is evaluated as an RMS-value and the demand for rattlespace is evaluated as a percentage value of the used rattlespace compared to the maximum free stroke provided by the suspension hardware. As a result from this work, the theory and simulation results are presented. Also a new vehicle model, which takes the essential non-linearity caused by suspension kinematics into account, is presented including all the mathematics needed. The comparison between the passive and the semi-active concepts has been performed on the basis of simulation results. These results show that the novel semi-active concept reduces the driver's exposure to vibration induced by terrain undulations better than any earlier proposed version. Also variation of dynamic tire load is reduced with a novel concept, while it suffers a drawback in the demand for the rattlespace.

Vibrations caused by rough road excitations influence tracked vehicle dynamic performance. Good capabilities of such vehicles like high mobility, manoeuvrability and comfort are guaranteed by optimal suspension systems. The suspension systems of tracked vehicles are exposed to extreme operating conditions. This creates a conflict between ride comfort and handling that is even greater than the conflict between ride comfort and handling for general road vehicles. Tracked vehicles must be able to traverse not only rough roads but also smooth terrains. The challenges in developing an optimized suspension system for tracked vehicles include the high and changeable damping forces required for tracked vehicles crossing rough terrains. The use of active or semi-active suspension systems overcomes the limitations inherent in the conventional passive suspension. However, active suspension systems are expensive, complicated to design and have high power demand. Thus, semi-active suspension systems have emerged as a good compromise between active and passive suspension system. There is considerable current research on the applications of magnetorheological (MR) fluid dampers for semi-active suspensions of executive brand of some cars. However, there is very little research on semi-active devices for tracked vehicle suspension. In fact, currently, there is no commercially available large scale MR dampers in the market that produce the high damping force to suit such applications. In response to these requirements, this research proposes a novel semi-active tracked vehicle suspension system that uses MR dampers to improve the ride comfort and handling characteristics of tracked vehicles. It also assesses the dynamics of the new suspension with various semi-active control methods. This study is conducted in four phases. The first phase provides a numerical investigation on the dynamic performance of a seven-degrees-of-freedom (7-DOF) passive suspension model of the armour personnel carrier (APC) M113 tracked vehicle. The numerical investigation considers the influence of variation of five suspension design parameters on the vehicle dynamic performance. These parameters include number, locations of hydraulic shock absorber, damping coefficient, suspension and wheel stiffnesses. The results indicate that the optimal suspension performance is attained by using two or three dampers. The best locations for these dampers are at the extreme road wheels i.e. the first, second and last road wheel stations. Moreover, the vehicle performance is reduced when the damping coefficient is increased. Additionally, low suspension stiffness offers better vehicle ride while high wheel stiffness degrades the vehicle performance. These results identify the limitations inherent in the conventional passive suspension. For the second phase, the dynamic characteristics of the hydraulic, hydro-gas and MR dampers are experimentally measured and fitted using the Chebyshev orthogonal functions to produce the restoring force surfaces for each damper, which are compared. On one hand, the restoring force surfaces of the hydraulic and hydro-gas dampers show fixed properties at specified frequencies. On the other hand, the restoring force surfaces of the MR dampers show properties that can be controlled at the same specified frequencies by the variation of the applied current levels. Thus, the potential and the effectiveness of the controllable properties of MR dampers for semi-active vibration control is demonstrated. Also, in this phase, the best set of parameters to use in the modified Bouc-Wen model to characterise the MR dampers, has been derived. The third phase of the project is also experimentally based. A new and novel test rig which represents the 7-DOF scaled suspension model of the tracked vehicle is designed and fabricated. The primary purpose of the test rig is to evaluate the performance of the proposed suspension with MR dampers. Furthermore, experiments are conducted on the test rig to evaluate some semi-active control methods and their effectiveness in reducing suspension vibration. The results show that the use of two or three MR dampers at the extreme wheels offers optimal suspension performance. This confirms the numerical results that are derived from the full scale passive suspension system with hydraulic dampers. The experimental results also show that skyhook control and hybrid control (which combines groundhook and skyhook controls) of the semi-active suspension are more effective in reducing the road-induced vibration and improving the suspension dynamic behaviours. Also, validations of the predicted responses of the semi-active scaled MR suspension model with the measured responses have been presented. The fourth and final phase provides a numerical simulation on the development and evaluation of the semi-active control methods for a full scale tracked vehicle suspension with MR dampers using the validated suspension model. Three semi-active control strategies are proposed. The first two controllers are the skyhook and hybrid controls which provide better suspension performance. In addition, the third controller, which is an intelligent fuzzy-hybrid control system, is used to optimize the suspension performance. The results from this intelligent system are compared with the two traditional control methods (skyhook and hybrid controls) under bump, sinusoidal and random excitations. It is shown that the proposed controller can enhance simultaneously the vehicle ride and handling characteristics.

While semi-active suspensions help improve the ride comfort and road holding capacity of the vehicle, they tend to be reactive in nature and thus leave a lot of room for improvement. Incorporating road preview data allows these suspensions to become more proactive rather than reactive and helps achieve a higher level of performance. A lot of preview-based control algorithms in literature tend to require high computational effort to arrive at the optimal parameters thus making it difficult to implement in real time. Other algorithms tend to be based upon lookup tables which classify the road input into different categories and hence lose their effectiveness when mixed types of road profiles are encountered that are difficult to classify. Thus a novel control algorithm is developed which is easy to implement online and more responsive to the varying road profiles that are encountered by the vehicle. A numerical methods-based semi-active suspension control algorithm and a Model Predictive Control(MPC)-based semi-active suspension control algorithm are developed that can leverage the data from the upcoming road profile to increase the ride comfort of the vehicle. The numerical methods-based algorithm is developed for the sole purpose of determining the maximum possible ride comfort that can be achieved using semi-active dampers capable of altering their damping characteristics every 0.01 seconds. The MPC-based algorithm is a more realistic algorithm that can be implemented in real-time and achieves on average 70% of the ride comfort that the numerical methods-based algorithm can with minimal computational effort. / Master of Science / Semi-active suspensions help cars ride more smoothly and handle better on the road. However, they often react to bumps and potholes only after hitting them, which means there's room for improvement. By using information about the road ahead, these suspensions can adjust before reaching rough spots, making the ride even better. To make this work, a new control system was developed. This system includes two parts. The first part uses detailed calculations to find the best possible comfort level, adjusting the suspension every 0.01 seconds. This method shows the highest comfort that can be achieved but is too complex for everyday use. The second part uses a simpler method called Model Predictive Control (MPC). This part is practical for real-time driving and achieves about 70% of the best possible comfort. It doesn't need as much computing power and can quickly adapt to different road conditions, making it ideal for normal driving. This new system improves driving comfort and safety by making suspensions smarter and more efficient.

The main focus of this study is on the active and semi-active control of civil engineering structures subjected to seismic excitations. Among different candidate control strategies, the sliding mode control approach emerges as a convenient alternative, because of its superb robustness under parametric and input uncertainties. The analytical developments and numerical results presented in this dissertation are directed to investigate the feasibility of application of the sliding mode control approach to civil structures. In the first part of this study, a unified treatment of active and semi-active sliding mode controllers for civil structures is presented. A systematic procedure, based on a special state transformation, is also presented to obtain the regular form of the state equations which facilitates the design of the control system. The conditions under which this can be achieved in the general case of control redundancy are also defined. The importance of the regular form resides in the fact that it allows to separate the design process in two basic steps: (a) selection of a target sliding surface and (b) determination of the corresponding control actions. Several controllers are proposed and extensive numerical results are presented to investigate the performance of both active and semi-active schemes, examining in particular the feasibility of application to real size civil structures. These numerical studies show that the selection of the sliding surface constitutes a crucial step in the implementation of an efficient control design. To improve this design process, a generalized sliding surface definition is used which is based on the incorporation of two auxiliary dynamical systems. Numerical simulations show that this definition renders a controller design which is more flexible, facilitating its tuning to meet different performance specifications. This study also considers the situation in which not all the state information is available for control purposes. In practical situations, only a subset of the physical variables, such as displacements and velocities, can be directly measured. A general approach is formulated to eliminate the explicit effect of the unmeasured states on the design of the sliding surface and the associated controller. This approach, based on a modified regular form transformation, permits the utilization of arbitrary combinations of measured and unmeasured states. The resulting sliding surface design problem is discussed within the framework of the classical optimal output feedback theory, and an efficient algorithm is proposed to solve the corresponding matrix nonlinear equations. A continuous active controller is proposed based only on bounding values of the unmeasured states and the input ground motion. Both active and semi-active schemes are evaluated by numerical simulations, which show the applicability and performance of the proposed approach. / Ph. D.

This experimental study evaluates the dynamic response of five semi-active control policies as tested on a single suspension quarter-car system. Incorporating a magneto-rheological damper, the full-scale 2DOF quarter-car system was used to evaluate skyhook, groundhook, and hybrid control. Two alternative skyhook policies were also considered, namely displacement skyhook and relative displacement skyhook. As well as exploring the relative benefits of each of these controllers, the performance of each semi-active controller was compared to the performance of conventional passive damping. Each control policy is evaluated for its control performance under three different base excitations: chirp, step, and pure tone. Corresponding to the chirp input, transmissibilities and auto spectrums are considered for each control policy. Specifically, transmissibilities between the sprung mass displacement and the unsprung mass displacement are generated relative to the input displacement. Further, the ratio between the relative displacement across the damper and the input displacement is evaluated for each control technique. The chirp input also reveals the results of the auto spectrums of the sprung and unsprung mass accelerations. Both the step input and the pure tone input were used to generate time domain values of RMS and peak-to-peak displacements and accelerations. This study shows that semi-active control offers benefits beyond those of conventional passive damping. Further, traditional skyhook control is shown to outperform the less conventional alternative skyhook policies. / Master of Science

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