De nos jours, la plupart des véhicules sont équipés de Directions Assistées Electriques (DAE). Ce type de systèmes d'aide à la conduite permet de réduire les efforts que le conducteur doit fournir pour tourner les roues. Ainsi, grâce à un moteur électrique, la DAE applique un couple additionnel en accord avec le comportement du conducteur et la dynamique du véhicule. Il est donc nécessaire de développer une commande en couple basée en particulier sur le signal provenant d'un capteur mesurant le couple agissant au niveau de la barre de torsion (correspondant à une image du couple conducteur). Ce composant est donc essentiel au fonctionnement de la DAE. Or, une défaillance de ce capteur entraine le plus souvent une coupure de l'assistance, pouvant mener à un risque d'accidents. Au regard de la sécurité fonctionnelle, un développement d'un mode de sécurité est recommandé, par de plus en plus de constructeurs automobiles. D'autre part, le marché des équipementiers automobiles reste un secteur très concurrentiel où une baisse des coûts de production est un challenge constamment recherché afin de gagner de nouvelles parts de marchés. Cet aspect de réduction du nombre de capteurs et d'analyse de la dynamique du véhicule s'inscrit donc dans le prolongement de la stratégie de sécurité. Cette thèse, menée au sein de JTEKT Europe, aborde ces divers enjeux. Après une présentation des différents systèmes de directions assistés électriques, des modèles sont présentés pour être utilisés lors de la conception de lois de commande et d'estimateurs. Ensuite deux méthodes d'estimation du couple conducteur sujet aux perturbations de la route et aux bruits de mesures sont proposées : la première est un observateur proportionnel intégral (PI) à synthèse mixte $H_infty/H_2$, et la seconde une approche par filtrage $H_infty$. Puis plusieurs stratégies de commande sont proposées suivant deux cas de figures distincts, soit en utilisant un observateur PI qui estime les états du système et le couple conducteur (LQR, commande LPV par retour d'état), soit en faisant abstraction d'estimateur de couple conducteur (commande $H_infty$ par retour de sortie dynamique). Ce dernier aspect présente l'avantage de nécessiter moins de mesures que le précédent. Ces approches ont été validées en simulation et mises en œuvre sur un véhicule prototype où des résultats prometteurs ont été obtenus. / Nowadays, modern vehicles are equipped with more and more driving assistance systems, among them Electric Power Steering (EPS) helps the driver to turn the wheels. Indeed, EPS provides through an electric motor, an additional torque according to the driver's behaviour and the vehicle's dynamics to reduce the amount of effort required to the driver. Therefore, a torque control is developed based on the torque sensor signal which measures in practice the torsion bar torque (corresponding to an image of the driver torque). Consequently, this component is essential to the functioning of EPS systems.Indeed, a torque sensor failure usually leads to shut-off the assistance which may increase the risk of accident. Regarding functional safety, a back-up mode is recommended and required by more and more car manufacturers. On the other hand, a major challenge for automotive suppliers is to reduce cost production in order to meet growing markets demands and manage in the competitive sector. This issue considering a reduction of sensors' numbers and analysis of vehicle's dynamics is therefore an extension of applying the safety strategy. This thesis, carried out within JTEKT Europe, addresses these various issues.After introducing an overview of the different EPS systems, some models used for the design of controllers and estimators are presented. Then, two methods to estimate the driver torque subject to road disturbances and noise measurements are proposed: the first is a proportional integral observer (PI) with mixed synthesis $H_infty / H_2 $, whereas the second is an $ H_infty $ filtering approach. Then, several control strategies are proposed according to two different cases, either by using a PI observer which estimates the system states and the driver torque (LQR, LPV feedback control) or by not taking into account the driver torque estimation ($ H_infty $dynamic output feedback control). This latter approach has the advantage to require less measurements than the previous one. These approaches have been validated in simulation and implemented on a prototype vehicle where promising results have been obtained.

Road feedback is an essential part of the driving experience, representing a connection betweenthe driver and the vehicle motion. Road feedback in a steer-by-wire system must berecreated and transferred to the driver through a feedback motor mounted on the steeringwheel. This project aimed to implement a function in the feedback motor control with thepurpose of giving the driver road feedback. The function should enhance the drivers trustand confidence in the steering system. Specifically, the function should provide the driverwith a feeling of being connected to the vehicle. A pre-study on the subject of steering feel was made as well as an interview study, whichresulted in a list of hypotheses. The hypotheses became a basis for generating conceptideas, together with measurement data of vehicle network signals for different drivingscenarios. Two different functions were then modelled and implemented in MathWorksSimulink. Function 1 models force components acting on the front road wheels in longitudinal,lateral and vertical direction. The forces result in a torque contribution fromeach dimension that acts around the steering axis and represents a reaction in the steeringsystem due to road disturbances. The torque is then translated to a steering wheel torque.Function 2 strives to capture road surface roughness through the high frequency informationin the steering rack motor torque. Three different road surfaces were studied; smoothasphalt, rough asphalt and gravel road. A test rig was used in order to verify the behaviour of the functions. The final step of theproject was to implement the functions in a test vehicle, where they could be further tunedand evaluated. The force component models of Function 1 captured different types of roadfeedback which were evaluated separately by timing, authenticity and desirability. Theresult of this evaluation was positive considering them separately. When the models werecombined it resulted in an unwanted behaviour. Function 2 gave torque feedback that feltauthentic and natural, especially for the gravel road case. However, it was more difficult todistinguish different asphalt types. The conclusion was that neither Function 1 nor 2 couldbe approved as finished functions, however both are considered as interesting concepts forfurther development. Fully steer-by-wire steering transmissions have now been approved for usage. This meansthat one of the remaining challenges for implementing steer-by-wire cars on today’s marketis the subjective views from the customers. Function 1 and 2 could be a way to providethe drivers with trust towards the steering, and at the same time, enhance the drivingexperience. / <p>The presentation was held at ACAS at Linköping University. The presentation included a summary and learnings from the project. A short demonstration was performed using a test-rig consisting of a steering wheel, a feedback motor and a control unit. </p>