Dissertations / Theses on the topic 'Lateral Stability Control'

Características de dirigibilidade de um veículo automotivo foram estudadas com o auxílio de uma ferramenta computacional para simulação de sistemas multicorpos integrado a um controle de estabilidade direcional virtual. O modelo do veículo simplificado utilizado, de três graus de liberdade, proporciona o cálculo em tempo real das grandezas utilizadas para o controle de atitude de veículos, como velocidade em guinada e ângulo de deriva. Por isso, sua utilização como modelo de referência. O controle desenvolvido se mostrou bastante confiável e suficientemente simples. Os resultados mostraram boa aproximação através de uma avaliação subjetiva do comportamento do veículo. Finalmente, pode ser observado que o uso de ferramentas com uma interface amigável com o usuário proporcionam tempos de desenvolvimento mais curtos e estudos paramétricos mais fáceis, possibilitando ao projetista alcançar as características desejadas do veículo com custos muito menores
Handling characteristics of an automotive vehicle were studied with the aid of a computational tool for mutibody system simulation integrated to a virtual directional stability control. The simplified vehicle model used, a three degrees of freedom model, makes possible the real time calculus of the parameters used in the yaw active control systems, like yaw rate and vehicle sideslip angle. Due to that, the use of it as a reference model. The developed control strategy is enough credible and sufficiently simple. Results showed good agreement through the subjective vehicle evaluation. Finally, it can be observed that the use of a tool with a user friendly interface makes development times shorter and parametric studies easier, enabling the designer to achieve the desired vehicle characteristics control much less costly

Hunting is a very common instability exhibited by rail vehicles operating at high speeds. The hunting phenomenon is a self excited lateral oscillation that is produced by the forward speed of the vehicle and the wheel-rail interactive forces that result from the conicity of the wheel-rail contours and the friction-creep characteristics of the wheel-rail contact geometry. Hunting can lead to severe ride discomfort and eventual physical damage to wheels and rails. A comprehensive study of the lateral stability of a single wheelset, a single truck, and the complete rail vehicle has been performed. This study investigates bifurcation phenomenon and limit cycles in rail vehicle dynamics. Sensitivity of the critical hunting velocity to various primary and secondary stiffness and damping parameters has been examined. This research assumes the rail vehicle to be moving on a smooth, level, and tangential track, and all parts of the rail vehicle to be rigid. Sources of nonlinearities in the rail vehicle model are the nonlinear wheel-rail profile, the friction-creep characteristics of the wheel-rail contact geometry, and the nonlinear vehicle suspension characteristics. This work takes both single-point and two-point wheel-rail contact conditions into account. The results of the lateral stability study indicate that the critical velocity of the rail vehicle is most sensitive to the primary longitudinal stiffness. A method has been developed to eliminate hunting behavior in rail vehicles by increasing the critical velocity of hunting beyond the operational speed range. This method involves the semi-active control of the primary longitudinal stiffness using the wheelset yaw displacement. This approach is seen to considerably increase the critical hunting velocity.
Master of Science

Apresenta um modelo completo em sistemas multicorpos de uma combinação veicular formada por um cavalo mecânico e um semi-reboque para um estudo de dirigibilidade. O modelo multicorpos foi desenvolvido no MSC.Adams/Car e inclui a suspensão primária, sistema de direção, trem de força, modelo de pneu e um quadro flexível para o cavalo mecânico, e a suspensão primária, modelo de pneu e quadro rígido para o semi-reboque. A resposta dinâmica lateral de uma composição veicular depende das características combinadas de estabilidade direcional, dirigibilidade e interação pneu/pavimento da unidade motora e da unidade rebocada. Os parâmetros mais importantes em relação à dinâmica lateral dos veículos longos combinados são: a velocidade longitudinal, o concerning stiffness dos pneus da combinação veicular, as elasticidades dos sistemas de suspensão e esterçamento do cavalo mecânico, a localização, distribuição do carregamento e momento de inércia em guinada da unidade movida e transferência lateral de carga do veículo como um todo. O modelo foi validado no âmbito dos modos de vibração. As análises de dirigibilidade foram realizadas mediante execução de manobras de mudança simples de pista e de esterçamento com entrada rampa, no MSC.Adams/Car, para calcular métricas comumente utilizadas para avaliação da dinâmica lateral de veículos longos combinados como aceleração lateral, velocidade de guinada, offtracking dinâmico e o gradiente de esterçamento. Análises dos resultados mostraram a influência no tempo de resposta, em regime transitório, do cavalo quando atrelado ao semi-reboque e um comportamento sub-esterçante nas velocidades longitudinais simuladas. A combinação veicular utilizada para este estudo apresenta um comportamento direcional estável.
This work presents a complete multibody model of a heavy articulated vehicle with a tractor and a semitrailer for handling study purposes. The model had been developed on MSC.Adams/Car and includes primary suspension system, steering system, powertrain, tire model and a flexible frame for tractor, suspension system, tire model and a rigid frame for semitrailer. The lateral dynamics response of a heavy articulated vehicle depends on tractor/semitrailer combined characteristics of the directional stability, the manouverability and the tire/road interaction. The most important parameters concerning of the lateral dynamics of heavy articulated vehicles are: longitudinal velocity, combined tire cornering stiffness of vehicular composition, suspensions systems compliance and steering system compliance of tractor, location, load distribution and yaw moment of towing unit and vehicle overall lateral load transfer. The model was validated about modal shapes and frequencies vibrations. Handling analyses had performed with single lane change and ramp steer maneuvers simulation on MSC.Adams/Car to calculate common measures for heavy articulated vehicles lateral dynamics evaluation as lateral acceleration, yaw velocity, dynamic offtracking and understeer gradient. The results analyses showed that the towing unit influences on response of the tractor and an understeer behavior of all vehicular composition over longitudinal velocity range simulated. The heavy articulated vehicle used on this study shows a stable directional behavior.

Les Véhicules Etroits et Inclinables (VEI) sont la convergence d'une voiture et d'un motocycle. Un mètre de largeur seulement suffit pour transporter une ou deux personnes en Tandem. Les VEI sont conçus dans le but de résoudre partiellement les problèmes de trafic routier, de minimiser la consommation énergétique et l'émission de polluants. De par leurs dimensions(ratio hauteur/largeur), ces véhicules doivent s'incliner en virage pour rester stable en compensant l'effet de l'accélération latérale. Cette inclinaison doit dans certains cas être automatique : elle peut être réalisée à l'aide d'un couple d'inclinaison généré par un actionneur dédié (système DTC), soit encore en modulant l'angle de braquage des roues (Système STC). Nous avons proposé dans ce mémoire une méthodologie de synthèse d'un régulateur structuré minimisant la norme H2 d'un problème bien posé au bénéfice d'une régulation optimisée de l'accélération latérale, considérant tour à tour les systèmes DTC et STC. Les régulateurs proposés sont paramétrés par la vitesse longitudinale et s'avèrent performants et robustes, et les moyens de réglages proposés permettent d'étudier l'intérêt relatif d'une solution DTC pure ou mixte DTC/STC, permettant de supporter les développements futurs sur le sujet. L'originalité des solutions proposées en regard des études rencontrées dans la littérature porte en particulier sur le fait de choisir de réguler directement l'accélération latérale perçue (plutôt que l'angle d'inclinaison), en anticipant la prise de virage par la prise en compte des angles et vitesse de braquage. L'optimisation de la régulation permet de réduire de manière importante le couple d'inclinaison requis, et l'accélération latérale subie par les passagers est faible. Tous les développements proposés s'appuient naturellement en amont sur un travail de modélisation (recherche du modèle juste nécessaire), et de bibliographie conséquent. Le modèle retenu comprend 5 degrés de libertés. Nous avons démontré qu'il possédait la propriété intéressante d'être plat, et avons utilisé cette propriété pour ouvrir des perspectives relatives à la conception d'un régulateur non-linéaire robuste, susceptible apriori d'accroître les performances dans le cas de " grands mouvements ". Au contraire de ce qui existe dans la littérature,le régulateur multivariable conçu pour le système SDTC permet le contrôle coordonné des actions sur les systèmes STC et DTC.

Le transport routier évolue considérablement vers l’électrification dans le monde entier. Un marché pour les solutions de mobilité légère électrifiée a émergé. Les dispositifs à transmission intégrale joue un rôle important dans cette nouvelle tendance. Cette technologie offre de nouvelles opportunités et pose de nouveaux défis dans le contrôle de châssis globale « Global Chassis Control (GCC) » qui a récemment atteint des niveaux remarquables. Cette étude présente une approche de supervision pour le contrôle vertical, longi-tudinal et latéral dans les véhicules électriques légers. Le système de contrôle développé repose sur la méthode CRONE qui peut assurer la robustesse du degré de stabilité contre les variations paramétriques du système. Pour la dynamique verticale, diverses solutions de contrôle sont développées pour les suspensions automobiles afin d’améliorer le confort des passagers et la tenue de route. Pour la dynamique longitudinale, une étude de la fonction ABS est réalisée pour l’amélioration du système de freinage, tenant en compte l’effet de la dynamique verticale. Ensuite, une combinaison de contrôle ABS et de contrôle de suspension est présentée dans le but de réduire l’effet de détérioration de la dynamique vertical. Enfin, les travaux portent sur le dé-veloppement du contrôle latéral de la stabilité du véhicule, où l’effet de la dynamique verticale du véhicule est analysé. Les résultats obtenus permet-tent de vérifier l’efficacité des stratégies de contrôle conçues pour améliorer le confort, la maniabilité et la sécurité du véhicule. En outre, la bonne com-préhension de l’influence de la dynamique verticale, ainsi que le rôle clé de la suspension contrôlée sur les autres dynamiques du véhicule, ouvrira de nouveaux horizons pour le développement de nouvelles stratégies pour le contrôle global du châssis des véhicules électriques légers
Road transportation is shifting significantly toward electrification around the globe. A market for light electric mobility solutions had emerged where all-in-wheel devices are expected to play an important role in this new trend. This technology offers new opportunities and raises new challenges in Global Chassis Control (GCC) that rises, recently, to remarkable levels. This study is based on a supervision control approach for vertical, longitudinal, and lateral control in light electric vehicles. The developed control system designs rely on the CRONE method which can ensure the robustness of the stability degree against the system parametric variations. For vertical dynamics, various control solu-tions are developed for automotive suspensions to improve passenger comfort and road holding. For longitudinal dynamics, a study for the ABS function is done for braking system enhancement while considering the effect of the vertical dynamics. Then, a combination of ABS control and suspension control is presented in the sense of reducing the deterioration effect of vertical dynamics. Finally, the work is concerned by the development of vehicle lateral stability control, where the effect of the vehicle vertical dynamics was analyzed. The obtained results verify the effectiveness of the designed control strategies in enhancing the vehicle comfort, handling, and safety. Moreover, the well understanding of the influence of the vertical dynamics, as well as the key role of the controlled suspension on other vehicle dynamics, will open up new prospects to the development of new strategies for global chassis control of light electric vehicle

La problématique étudiée dans cette thèse concerne le guidage en formation d’une flotte de robots mobiles en environnement naturel. L’objectif poursuivi par les robots est de suivre une trajectoire connue (totalement ou partiellement) en se coordonnant avec les autres robots pour maintenir une formation décrite comme un ensemble de distances désirées entre les véhicules. Le contexte d’évolution en environnement naturel doit être pris en compte par les effets qu’il induit sur le déplacement des robots. En effet, les conditions d’adhérence sont variables et créent des glissements significatifs des roues sur le sol. Ces glissements n’étant pas directement mesurables, un observateur est mis en place, permettant d’obtenir une estimation de leur valeur. Les glissements sont alors intégrés au modèle d’évolution, décrivant ainsi un modèle cinématique étendu. En s’appuyant sur ce modèle, des lois de commande adaptatives sur l’angle de braquage et la vitesse d’avance d’un robot sont alors conçues indépendamment, asservissant respectivement son écart latéral à la trajectoire et l’interdistance curviligne de ce robot à une cible. Dans un second temps, ces lois de commande sont enrichies par un algorithme prédictif, permettant de prendre en compte le comportement de réponse des actionneurs et ainsi d’éviter les erreurs conséquentes aux retards de la réponse du système aux commandes. À partir de la loi de commande élémentaire en vitesse permettant d’assurer un asservissement précis d’un robot par rapport à une cible, une stratégie de commande globale au niveau de la flotte est établie. Celle-ci décline l’objectif de maintien de la formation en consigne d’asservissement désiré pour chaque robot. La stratégie de commande bidirectionnelle conçue stipule que chaque robot définit deux cibles que sont le robot immédiatement précédent et le robot immédiatement suivant dans la formation. La commande de vitesse de chaque robot de la formation est obtenue par une combinaison linéaire des vitesses calculées par la commande élémentaire par rapport à chacune des cibles. L’utilisation de coefficients de combinaison constants au sein de la flotte permet de prouver la stabilité de la commande en formation, puis la définition de coefficients variables est envisagée pour adapter en temps réel le comportement de la flotte. La formation peut en effet être amenée à évoluer, notamment en fonction des impératifs de sécurisation des véhicules. Pour répondre à ce besoin, chaque robot estime en temps réel une distance d’arrêt minimale en cas d’urgence et des trajectoires d’urgence pour l’évitement du robot précédent. D’après la configuration de la formation et les comportements d’urgence calculés, les distances désirées au sein de la flotte peuvent alors être modifiées en ligne afin de décrire une configuration sûre de la formation
This thesis focuses on the issue of the control of a formation of wheeled mobile robots travelling in off-road conditions. The goal of the application is to follow a reference trajectory (entirely or partially) known beforehand. Each robot of the fleet has to track this trajectory while coordinating its motion with the other robots in order to maintain a formation described as a set of desired distances between vehicles. The off-road context has to be considered thoroughly as it creates perturbations in the motion of the robots. The contact of the tire on an irregular and slippery ground induces significant slipping and skidding. These phenomena are hardly measurable with direct sensors, therefore an observer is set up in order to get an estimation of their value. The skidding effect is included in the evolution of each robot as a side-slip angle, thus creating an extended kinematic model of evolution. From this model, adaptive control laws on steering angle and velocity for each robot are designed independently. These permit to control respectively the lateral distance to the trajectory and the curvilinear interdistance of the robot to a target. Predictive control techniques lead then to extend these control laws in order to account for the actuators behavior so that positioning errors due to the delay of the robot response to the commands are cancelled. The elementary control law on the velocity control ensures an accurate longitudinal positioning of a robot with respect to a target. It serves as a base for a global fleet control strategy which declines the overall formation maintaining goal in local positioning objective for each robot. A bidirectionnal control strategy is designed, in which each robot defines 2 targets, the immediate preceding and following robot in the fleet. The velocity control of a robot is finally defined as a linear combination of the two velocity commands obtained by the elementary control law for each target. The linear combination parameters are investigated, first defining constant parameters for which the stability of the formation is proved through Lyapunov techniques, then considering the effect of variable coefficients in order to adapt in real time the overall behavior of the formation. The formation configuration can indeed be prone to evolve, for application purposes and to guarantee the security of the robots. To fulfill this latter requirement, each robot of the fleet estimates in real time a minimal stopping distance in case of emergency and two avoidance trajectories to get around the preceding vehicle if this one suddenly stops. Given the initial configuration of the formation and the emergency behaviors calculated, the desired distances between the robots can be adapted so that the new configuration thus described ensures the security of each and every robot of the formation against potential collisions

La thématique étudiée dans ce mémoire est axée sur la préservation de la stabilité dynamique de véhicules évoluant en environnement naturel. En effet, la mobilité en milieu tout-terrain est une activité particulièrement pénible et dangereuse en raison de la nature difficile de l'environnement de conduite et de la reconfigurabilité des machines. Le caractère changeant et incertain des interactions rencontrées entre des véhicules à dynamique complexe et variable et leur environnement entraîne régulièrement des risques accrus de renversement et/ou de perte de contrôle (dévalement, dérapage déclenché par une perte soudaine d'adhérence) pour le conducteur. Une forte accidentalité mortelle est, en effet, recensée dans ce secteur, en particulier, dans le milieu agricole ou le renversement de véhicule est classé comme étant la première cause de mortalité au travail. A l'heure actuelle, les approches existantes sur la stabilité d'engins agricoles sont qualifiées à juste titre de passives car elles ne permettent pas d'éviter que les accidents ne se produisent. Par ailleurs, la transposition directe des solutions de sécurité active du secteur de l'automobile (ABS, ESP) s'est révélée inadaptée aux véhicules tout-terrain a cause des hypothèses simplificatrices (routes plates et homogènes, conditions d'adhérence constantes, etc.) dont souffre la conception de ces dispositifs. Ainsi, le développement de systèmes actifs de sécurité prenant en compte les spécificités de la conduite en milieu tout-terrain se révèle être la meilleure voie d'amélioration à suivre. Eu égard à ces circonstances, ce projet se propose d'adresser cette problématique en étudiant des métriques de stabilité pertinentes permettant d'estimer et d'anticiper en temps réel les risques afin de permettre des actions correctives pour la préservation de l'intégrité des machines tout-terrain. Afin de faciliter l'industrialisation du dispositif actif de sécurité conçu, l'une des contraintes sociétales et commerciales de ce projet a été l'utilisation de capteurs compatibles avec le coût des machines visées. L'objectif ambitieux de cette étude a été atteint par différentes voies. En premier lieu, une approche de modélisation multi-échelle a permis de caractériser l'évolution dynamique de véhicules en milieu tout-terrain. Cette approche à dynamique partielle a offert l'avantage de développer des modèles suffisamment précis pour être représentatifs du comportement réel de l'engin mais tout en présentant une structure relativement simple permettant la synthèse d'asservissements performants. Puis, une étude comparative des avantages et des inconvénients des trois grandes familles de métriques répertoriées dans la littérature a permis de mettre en exergue l'intérêt des métriques analytiques à modèle dynamique par rapport aux catégories de critères de stabilité dits statiques et empiriques. Enfin, l'analyse approfondie des métriques dynamiques a facilité le choix de trois indicateurs (Lateral and Longitudinal Load Transfer (LLT), Force Angle Stability Measurement (FASM) et Dynamic Energy Stability Measurement (DESM)) qui sont représentatifs d'un risque imminent de renversement du véhicule. La suite du mémoire s'appuie sur la théorie d'observation pour l'estimation en ligne des variables non directement mesurables en milieu tout-terrain telles que les rigidités de glissement et dérive du pneumatique. Jumelée aux différents modèles dynamiques du véhicule, la synthèse d'observateurs a permis donc d'estimer en temps réel les efforts d'interaction pneumatiques-sol nécessaires à l'évaluation des indicateurs d'instabilité. Le couplage de ces modèles multi-échelles à la théorie d'observation a ainsi constitué un positionnement original à même de briser la complexité de la caractérisation de la stabilité de véhicules à dynamiques complexes et incertaines. (...)
This work is focused on the thematic of the maintenance of the dynamic stability of off-road vehicles. Indeed, driving vehicles in off-road environment remains a dangerous and harsh activity because of the variable and bad grip conditions associated to a large diversity of terrains. Driving difficulties may be also encountered when considering huge machines with possible reconfiguration of their mechanical properties (changes in mass and centre of gravity height for instance). As a consequence, for the sole agriculture sector, several fatal injuries are reported per year in particular due to rollover situations. Passive protections (ROllover Protective Structure - ROPS) are installed on tractors to reduce accident consequences. However, protection capabilities of these structures are very limited and the latter cannot be embedded on bigger machines due to mechanical design limitations. Furthermore, driving assistance systems (such as ESP or ABS) have been deeply studied for on-road vehicles and successfully improve safety. These systems usually assume that the vehicle Center of Gravity (CG) height is low and that the vehicles are operating on smooth and level terrain. Since these assumptions are not satisfied when considering off-road vehicles with a high CG, such devices cannot be applied directly. Consequently, this work proposes to address this research problem by studying relevant stability metrics able to evaluate in real time the rollover risk in order to develop active safety devices dedicated to off-road vehicles. In order to keep a feasible industrialization of the conceived active safety device, the use of compatible sensors with the cost of the machines was one of the major commercial and societal requirements of the project. The ambitious goal of this study was achieved by different routes. First, a multi-scale modeling approach allowed to characterize the dynamic evolution of off-road vehicles. This partial dynamic approach has offered the advantage of developing sufficiently accurate models to be representative of the actual behavior of the machine but having a relatively simple structure for high-performance control systems. Then, a comparative study of the advantages and drawbacks of the three main families of metrics found in the literature has helped to highlight the interest of dynamic stability metrics at the expense to categories of so-called static and empirical stability criteria. Finally, a thorough analysis of dynamic metrics has facilitated the choice of three indicators (Longitudinal and Lateral Load Transfer (LLT), Force Angle Stability Measurement (FASM) and Dynamic Energy Stability Measurement (DESM)) that are representative of an imminent rollover risk. The following of the document is based on the observation theory for estimating online of variables which are not directly measurable in off-road environment such as slip and cornering stiffnesses. Coupled to the dynamic models of the vehicle, the theory of observers has helped therefore to estimate in real time the tire-soil interaction forces which are necessaries for evaluating indicators of instability. The coupling of these multiscale models to the observation theory has formed an original positioning capable to break the complexity of the characterization of the stability of vehicles having complex and uncertain dynamics. (...)

La problématique de cette thèse réside dans la caractérisation et le maintien de la stabilité des Véhicules Légers Tout Terrain (VLTT). Elle se concentre plus particulièrement sur le développement de systèmes de sécurité actifs capables à la fois de prévenir le conducteur des risques encourus mais aussi de les limiter afin d'assurer l'évolution du véhicule dans une zone de stabilité prédéfinie. Comme le cadre expérimental privilégié est l'application à la stabilité des quadricycles légers à moteurs, plus connus sous le terme anglophone "quad", une des contraintes du projet a été de se limiter à un système sensoriel bas-coût afin d'être en mesure d'industrialiser un tel système. En premier lieu, les métriques de stabilité (Transfert de Charge Latéral et Longitudinal : TCLa et TCLo) ont été choisies grâce à une étude préliminaire sur la stabilité des VLTT. Par la suite, une modélisation 2D en roulis et en tangage avec la prise en compte des déplacements du pilote sur le véhicule sont présentées, ce qui permet d'estimer respectivement le TCLa et le TCLo uniquement à partir de la mesure de l'accélération latérale et longitudinale. Étant donné que pour la suite des travaux, l'anticipation du risque de renversement latéral est nécessaire, un modèle 2D en lacet du véhicule est proposé afin d'obtenir un modèle analytique décrivant la dynamique latérale du véhicule. La suite du mémoire présente les différentes techniques d'observation proposées pour l'estimation des variables et paramètres non-directement mesurables du modèle en lacet du véhicule et qui influencent sa stabilité latérale : les glissements, les conditions d'adhérence et les inclinaisons du véhicule. Plusieurs observateurs ont été proposés, dont le dernier permet de considérer des conditions d'adhérence différentes entre les essieux avant et arrière en utilisant plus largement les accélérations mesurées. Cela permet d'intégrer les passages de sous- à sur-vireur qu'il est essentiel de considérer quand on étudie la stabilité de ce type de véhicule. Ainsi, l'estimation des glissements est toujours pertinente, ce qui permet d'obtenir par la suite une meilleure prédiction de la métrique de stabilité latérale (TCLa) quel que soit le comportement du véhicule. Puis en s'appuyant sur les estimations des observateurs couplées aux modèles dynamiques du véhicule et sur l'extrapolation des commandes du conducteur sur un horizon de prédiction, il est possible de prédire les évolutions du TCLa. Cette valeur prédite ainsi que les estimations en ligne des métriques de stabilité constituent alors le point d'entrée pour la synthétisation d'un système de sécurité actif dédié aux VLTT. Celui-ci est basé sur la génération d'un retour d'effort au niveau de la gâchette des gaz permettant soit d'informer le pilote du risque encouru par la création d'une sensation de dureté, soit d'imposer le retour complet de la gâchette des gaz, ce qui implique une diminution de la vitesse et donc la réduction du risque. Finalement, dans le cas où il est possible de maîtriser la vitesse du véhicule par l'installation d'un système de rétroaction sur les freins (Quad haut de gamme ou robot mobile), les derniers travaux présentés s'intéressent aux techniques de commande prédictive à modèle afin de calculer en temps-réel la vitesse maximale admissible, qui assure l'évolution du critère de stabilité choisi dans un domaine de stabilité. Les modèles, les observateurs, la prédiction du TCLa et les 2 systèmes de prévention présentés dans ce mémoire ont été validés et testés au travers de simulations avancées et d'essais expérimentaux réalisés sur un quad agricole et un robot autonome. Il apparaît alors qu'en plus d'être efficace pour la prévention des risques de renversement à hautes dynamiques, le système de sécurité est industriellement viable. Cela a été rendu possible grâce à une conception reposant uniquement sur des actionneurs et un système sensoriel, dont les coûts sont en adéquation avec le prix d'un VLTT.

La voiture autonome pourrait réduire le nombre de morts et de blessés sur les routes tout en améliorant l'efficacité du trafic. Cependant, afin d'assurer leur déploiement en masse sur les routes ouvertes au public, leur sécurité doit être garantie en toutes circonstances. Cette thèse traite de l'architecture de planification et de contrôle pour la conduite automatisée et défend l'idée que l'intention du véhicule doit correspondre aux actions réalisées afin de garantir la sécurité à tout moment. Pour cela, la faisabilité cinématique et dynamique de la trajectoire de référence doit être assurée. Sinon, le contrôleur, aveugle aux obstacles, n'est pas capable de la suivre, entraînant un danger pour la voiture elle-même et les autres usagers de la route. L'architecture proposée repose sur la commande à modèle prédictif fondée sur un modèle bicyclette cinématique afin de planifier des trajectoires de référence sûres. La faisabilité de la trajectoire de référence est assurée en ajoutant une contrainte dynamique sur l'angle au volant, contrainte issue de ces travaux, afin d'assurer que le modèle bicyclette cinématique reste valide. Plusieurs contrôleurs à haute-fréquence sont ensuite comparés afin de souligner leurs avantages et inconvénients. Enfin, quelques résultats préliminaires sur les contrôleurs à base de commande sans modèle et leur application au contrôle automobile sont présentés. En particulier, une méthode efficace pour ajuster les paramètres est proposée et implémentée avec succès sur la voiture expérimentale de l'ENSIAME en partenariat avec le laboratoire LAMIH de Valenciennes
Autonomous vehicles are believed to reduce the number of deaths and casualties on the roads while improving the traffic efficiency. However, before their mass deployment on open public roads, their safety must be guaranteed at all time.Therefore, this thesis deals with the motion planning and control architecture for autonomous vehicles and claims that the intention of the vehicle must match with its actual actions. For that purpose, the kinematic and dynamic feasibility of the reference trajectory should be ensured. Otherwise, the controller which is blind to obstacles is unable to track it, setting the ego-vehicle and other traffic participants in jeopardy. The proposed architecture uses Model Predictive Control based on a kinematic bicycle model for planning safe reference trajectories. Its feasibility is ensured by adding a dynamic constraint on the steering angle which has been derived in this work in order to ensure the validity of the kinematic bicycle model. Several high-frequency controllers are then compared and their assets and drawbacks are highlighted. Finally, some preliminary work on model-free controllers and their application to automotive control are presented. In particular, an efficient tuning method is proposed and implemented successfully on the experimental vehicle of ENSIAME in collaboration with the laboratory LAMIH of Valenciennes

Bone’s capacity to repair following trauma is both unique and astounding. However, fractures sometimes fail to heal. Hence, the goal of fracture treatment is the restoration of bone’s structure, composition and function. Fracture fixation devices should provide a favourable mechanical and biological environment for healing to occur. The use of internal fixation is increasing as these devices may be applied with less invasive techniques. Recent studies suggest however that, internal fixation devices may be overly stiff and suppresses callus formation. The degree of mechanical stability influences the healing outcome. This is determined by the stiffness of the fixation device and the degree of limb loading. This project aims to characterise the fixation stability of an internal plate fixation device and the influence of modifications to its configuration on implant stability. As there are no standardised methods for the determination of fixation stiffness, the first part of this project aims to compares different methodologies and determines the most appropriate method to characterise the stiffness of internal plate fixators. The stiffness of a fixation device also influences the physiological loads experienced by the healing bone. Since bone adapts to this applied load by undergoing changes through a remodelling process, undesirable changes could occur during the period of treatment with an implant. The second part of this project aims to develop a methodology to quantify remodelling changes. This quantification is expected to aid our understanding of the changes in pattern due to implant related remodelling and on the factors driving the remodelling process. Knowledge gained in this project is useful to understand how the configuration of internal fixation devices can promote timely healing and prevent undesirable bone loss.

碩士
國立成功大學
航空太空工程學系碩博士班
101
This thesis focuses on the lateral stability control design for an unsteady tailless aircraft. The aircraft configuration reference design is based on Northrop YB-49 which was developed by Northrop Corporation. The aerodynamic coefficients were determined by DATCOM software and the results show that the stability of the tailless aircraft is unsteady. Instead of traditional root locus method, the eigenvalues assignment method suitable for multi-input multi-output (MIMO) systems is adopted for the analysis of two forms of control designs, P and PID. The equations of motion are linearized and Laplace transform is used to transform the linear differential equations into a set of algebraic equations. For P control, the differential equations are of the fourth order and therefore have four eigenvalues to be assigned. For PID control, the differential equations are of the eighth order and therefore have eight eigenvalues. However, since two of the eigenvalues are always zero, there are only six eigenvalues which can be assigned. This thesis primarily analyzes the gains for P and PID control designs by the eigenvalue assignment method. After the gains are determined, simulations are conducted for the flight control system to check if the response characteristics and tracking performances are satisfied.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.
Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1285. Adviser: Andrew Alleyne. Includes bibliographical references (leaves 166-170) Available on microfilm from Pro Quest Information and Learning.

碩士
大葉大學
車輛工程學系碩士班
96
The purpose of this study is to develop an appropriate vehicle yaw stability control system by using vehicle longitudinaland lateral dynamic simulation model. The system input of this study includes the steering wheel angle, vehicle speed change, and vehicle yaw rate to calculate the distribution of vehicle traction and braking force distribution so that the vehicle lateral stability control can be assured. This study established vehicle longitudinal and lateral dynamic simulation model from vehicle dynamics of longitudinal and lateral force, and vehicle design parameters. The object oriented simulation program Matlab/Simulink® was used to analyze vehicle motion dynamic response. Simulation program can be used to predict the yaw rate response of vehicle when one side wheel slip happened. When the vehicle yaw rate is calculated, the proper locked and controlled Limited Slip Differential (LSD) mechanism and brake force applied to reduce the yaw motion of the vehicle. This study propose a compound traction force control method by using fuzzy logic controller to determine the proportion of longitudinal traction distribution out of LSD from vehicle wheel speed and yaw rate. Vehicle yaw stability control hardware-in-the loop simulation used CAN Bus as the By-Wire platform communication network. Vehicle longitudinal and lateral dynamic simulation program established in this study integrated the CAN control interface card with xPC Target with vehicle sensors and actuators to analyze the vehicle yaw controlled response. This study developed vehicle stability control simulation and hardwires integration methodology which can be used to optimize vehicle controlled lateral stability states with shorter tuning period. This method can improve vehicle active safety, reliability and prevent vehicle instability accident, reduce research and development time of vehicle stability control system.

碩士
國立臺北科技大學
車輛工程系所
103
In this work, a three-level design control strategy is proposed for lateral dynamics stability control of electric vehicles with four in-wheel motors. In order to avoid the design of complex control laws which require the knowledge of vehicle parameters, a yaw rate following controller based on model-based proportional control is designed in the first level. The sideslip angle limitation is not considered in the first level to reduce the need of sideslip angle estimation and simplify the control law design. The second level is control allocation which distributes the wheel torques to generate the required yaw moment command according to the constraint of work load ratio at each wheel. The associated weighting matrix is designed using the work load ratio at each wheel and combined with torque ratio feedback to prevent saturating at tire. Active Fault Tolerant Control is integrated to enhance the vehicle’s safety. The bearing damping coefficient is estimated by using Kalman filter approach for system identification. This implementation significantly improves the convergence time of bearing damping identification. The maximum transmissible torque estimation method is used as the third level for traction control and anti-lock braking. The proposed control is evaluated using double lane change maneuver in CarSim. Electric differential can be achieved for the normal driving condition. Under critical driving situation on road surface with low

The autonomous driving is one of the automotive research challenges of the last years, and even if a lot of technologies steps forward have been taken, it remains an open research issue. So, the aim of this PhD thesis was to improve the current level of dynamic control of an autonomous car using commercial hardware and sensor technologies and respecting their functioning constraints. The research focused on the development and implementation of different logic layers inside the autonomous car framework. The first step was to develop an algorithm to localize the vehicle and estimate the car speeds. In this way, the signals required for the correct operation of the control architecture are added to the input signals provided by the sensors. Two of the most adopted technologies were tested. However, the estimation errors made were too high to guarantee the desired level of operation of the control systems. Therefore, based on the characteristics and issues given by the design of these systems, we developed a vehicle speeds estimator consisting of a combination of both. In this way, even in high non-linear dynamic conditions, the errors on the estimation were reduced, improving the car localization and functioning of the control algorithms. Then, an on-line Path Planning was developed able to define the performances that maximize the car speed in a known track. The focuses were: to ensure a real-time trajectory calculation (updating it with the current vehicle dynamics and environmental conditions); and allow computational cost compatible with the correct functioning of the other systems involved. For this reason, it was chosen an optimization algorithm that allows to maintain a linear cost function simplifying the car model and limiting the computational times. However, in order to ensure the most correct representation of vehicle dynamics a more accurate modelling of the car GG-V has been implemented as constraint equations. Once defined the trajectory, a high-level controller was developed to track the dynamic performances provided by the Path Planning. So, was implemented an algorithm that ensures a feed-back control of the Steering Wheel Angle (SWA), accelerator and brake pedal by dividing the later dynamic model from the longitudinal one. In addition, was added a feed-forward control that tracks the lateral and longitudinal acceleration calculated by the planner. Thus, the performances tracking delay and the feed-back control modelling errors were reduced. Finally, to enhance the lateral and longitudinal stability, an Electronic Stability System (ESC) and Anti-lock Brake System (ABS) controls are developed with the aim of improve the current commercial systems performances. About the lateral stability control, a tracking controller was implemented to define the brake input corrections that must be added to the ones established by the Trajectory Tracking to follow reference yaw rate and side slip angle. Instead, to ensure that the wheels don’t lock, a discrete control allows the wheels to follow a target longitudinal speed. In this way, it was found that comparing with the standard ABS the tuning process takes less time and the brake performances are increased, in terms of reduction of the brake distance; and increased stability during full braking manoeuvres. The different layers ware developed independently achieving their own performance improvement and then are integrated together with specific interfaces. Furthermore, two mathematical modelling types were made starting from available experimental data: a sensor characterization to ensure the input signals have their delays, noise and sample time; and a transfer function model of the Brake-By-Wire system developed by Meccanica 42 srl, to ensure actuation outputs delay and constraints. Thus, the real exchange of signals between the architecture developed and the vehicle model is ensured, and the correct operation of the controls once implemented in the car is verified. A real-time static simulator placed at Meccanica 42 srl is used to develop and test the architecture and compare the performances obtained with the ones of a driver. The results showed that: it was possible to obtain an optimisation and tracking of the trajectory that update in real-time taking into account the current dynamic conditions; some good improvements were achieved both with regard to the estimation of the states and the stability of the vehicle; and it was possible to integrate the various layers together guaranteeing satisfactory dynamic performance even if worse than the individual one.

The main aim of this research project is to extend theories of four-wheel-steering as developed by J. Ackermann to include an individually steered four-wheel steering system for passenger vehicles. Ackermann’s theories, including theories available in this subject area, dwell much on vehicle system dynamics developed from what is called single track model and some call it a bicycle model. In the bicycle model, the front two wheels are bundled together. Similarly, the rear wheels are bundled together. The problem with this is that it assumes two front wheels or two rear wheels to be under the same road, vehicle and operating conditions. The reality on the ground and experiments that are conducted are to the contrary. Therefore this study discusses vehicle disturbance rejection through robust decoupling of yaw and lateral motions of the passenger vehicle. A mathematical model was developed and simulated using Matlab R2008b. The model was developed in such a way that conditions can be easily changed and simulated. The model responded well to variations in road and vehicle conditions. Focus was in the ability of the vehicle to reject external disturbances. To generate yaw moment during braking, the brake on the left front wheel was disconnected. This was done because lateral wind generators, as used by Ackermann, were not available. The results from both simulations and experiments show disturbance rejection in the steady state. Copyright
Dissertation (MSc)--University of Pretoria, 2010.
Mechanical and Aeronautical Engineering
unrestricted

The Texas Department of Transportation (TxDOT) has completed the design of a signature bridge in Fort Worth, TX. The proposed structure is comprised of precast, post-tensioned concrete network arches. The arches will be cast on their sides and then rotated into the vertical orientation. Concerns exist about the durability and stability of the arches during stressing, handling, and transportation. The rotation process in particular represents a critical period in the life of the arches. A monitoring system was proposed to track stresses in the arches throughout the construction operations. The primary goals of the project are to install vibrating wire gages (VWGs) in the arches prior to casting to monitor the performance of the arches until the bridge is completed. The instrumentation will be used to provide real-time feedback to TxDOT and the contractor during stressing, handling, and bridge construction. This thesis focuses on the results of a preliminary laboratory study conducted in support of the instrumentation initiative. The purpose of the study was two-fold: to establish the capabilities and limitations of the VWGs and to study the buckling behavior of slender concrete elements with unbonded post-tensioning. More than sixty axial load tests were performed on two slender concrete specimens instrumented with VWGs. Observations are made on the accuracy and reliability of the VWGs. In general, the VWGs were found to be both accurate and reliable in measuring structural parameters and reporting trends in behavior, even at low loads. Some apparent errors were identified, but these were attributed to testing inconsistencies and scale factors rather than to gage error. Observations were also made on the buckling behavior of the elements under a variety of axial loading configurations. The effects of the engagement of the tensioned strand with the duct had a significant impact on the behavior. Strand engagement was shown to increase the buckling capacity of the members through stiffening action, but did not necessarily eliminate the risk of instability. Both the gage resolution study and the stability tests are expected to significantly enhance the ability of the research team to support the arch construction operations.
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