In recent years car manufacturers and tech companies have been investing huge resources to develop autonomous driving vehicles, with the aim of enhancing the efficiency of transports and the safety of passengers on the roads. Nowadays, several vehicles on the market are equipped with driving assistant devices, ranging from self parking and automatic braking systems up to an effective and real autonomous driving. A Multi-Actuated Ground Vehicles (MAGV) can be considered as a complex engineering system having a set of parallel subsystems requiring both individual and integrated control to secure simultaneously criteria of efficient dynamics, safety, and user (and environment) friendly operation. Within this context, the topics of passenger safety, driving quality and energetic efficiency have become of interest in particular for computer and control engineers, with this trend increasing its momentum exponentially. To shed light on the scientific aspects of these devices, a survey of some of the most successful vehicle stability control system is provided in the first part of this dissertation, with particular focus on those which utilize the well established Sliding Mode Control technique (SMC). Advanced Driver Assistance Systems (ADAS), such as the already mentioned ESC and ABS, as well as Automated Driving (AD) technologies, can be enhanced by the knowledge of vehicle planar motion states (longitudinal and lateral velocities of the center-of-gravity and side-slip angles). In particular, the estimation of tire-ground contact forces has become an important subject of investigation. In fact, the knowledge of the forces exerted can help to prevent over-steering or under-steering phenomena, which often generate accidents. This can be caused by a tire undergoing excessive slip/skid, so that the driver does not reach the intended trajectory. Currently, sensors exist able to measure tire-ground forces. Nevertheless, their cost amounts to several tens thousand euros per piece, which makes them incompatible with commercial automobiles mass production. The introduction of observers to estimate these forces is an effective solution for this problem. However, to provide estimates of the forces with sufficient accuracy is still considered an arduous task, since the variation of vehicle mass, Center of Gravity (COG) position, road slope or bank angle, along with road irregularities and load transfer effects, increase the problem complexity considerably. In the second part of this work this problem is faced, with the proposal of a novel method for model-based tire forces estimation, which relies on a development of SMC, namely the Second Order Sliding Mode (SOSM). One of the most challenging tasks for engineers in the implementation of vehicle stability control systems, which concerns both fields of AD and sport racing, is the handling of the vehicle on different kinds of road surface. In fact, the vehicle should autonomously interact with the environment, without endangering the safety of people on board and their surroundings. However, safety aspects are not the only ones to be considered, in fact by means of proper control techniques, it is also possible to improve the car performances. In the last part of this dissertation, the problem of minimizing the travel time of an AV running on a low friction terrain (such as gravel or dirt road) is considered. Such setting can be seen as an emulation of the behavior of a rally driver which, on slippery surfaces, might require to exploit a drifting maneuver while cornering. Two solutions to this problem are proposed, which exploit the information regarding the physical limits of the vehicle and the tire-road interaction forces, in order to obtain high speed solutions which guarantee the stability of the vehicle.
|Titolo:||Vehicle Dynamics Control in MAGV: Forces Estimation and Motion Planning Methods|
|Data di pubblicazione:||26-feb-2020|
|Appare nelle tipologie:||8.01 Tesi di dottorato|