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Optimal Braking Patterns and Forces in Autonomous Safety-Critical Maneuvers
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-4034-2868
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The trend of more advanced driver-assistance features and the development toward autonomous vehicles enable new possibilities in the area of active safety. With more information available in the vehicle about the surrounding traffic and the road ahead, there is the possibility of improved active-safety systems that make use of this information for stability control in safety-critical maneuvers. Such a system could adaptively make a trade-off between controlling the longitudinal, lateral, and rotational dynamics of the vehicle in such a way that the risk of collision is minimized. To support this development, the main aim of this licentiate thesis is to provide new insights into the optimal behavior for autonomous vehicles in safety-critical situations. The knowledge gained have the potential to be used in future vehicle control systems, which can perform maneuvers at-the-limit of vehicle capabilities.

Stability control of a vehicle in autonomous safety-critical at-the-limit maneuvers is analyzed by the use of optimal control. Since analytical solutions of the studied optimal control problems are intractable, they are discretized and solved numerically. A formulation of an optimization criterion depending on a single interpolation parameter is introduced, which results in a continuous family of optimal coordinated steering and braking patterns. This formulation provides several new insights into the relation between different braking patterns for vehicles in at-the-limit maneuvers. The braking patterns bridge the gap between optimal lane-keeping control and optimal yaw control, and have the potential to be used for future active-safety systems that can adapt the level of braking to the situation at hand. A new illustration named attainable force volumes is introduced, which effectively shows how the trajectory of a vehicle maneuver relates to the attainable forces over the duration of the maneuver. It is shown that the optimal behavior develops on the boundary surface of the attainable force volume. Applied to lane-keeping control, this indicates a set of control principles similar to those analytically obtained for friction-limited particle models in earlier research, but is shown to result in vehicle behavior close to the globally optimal solution also for more complex models and scenarios.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. , p. 19
Series
Linköping Studies in Science and Technology. Licentiate Thesis, ISSN 0280-7971 ; 1804
National Category
Transport Systems and Logistics
Identifiers
URN: urn:nbn:se:liu:diva-147719DOI: 10.3384/lic.diva-147719ISBN: 9789176853016 (print)OAI: oai:DiVA.org:liu-147719DiVA, id: diva2:1204256
Presentation
2018-05-18, Ada Lovelace, B-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-11-27Bibliographically approved
List of papers
1. Formulation and interpretation of optimal braking and steering patterns towards autonomous safety-critical manoeuvres
Open this publication in new window or tab >>Formulation and interpretation of optimal braking and steering patterns towards autonomous safety-critical manoeuvres
2018 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, p. 1-18Article in journal (Refereed) Epub ahead of print
Abstract [en]

Stability control of a vehicle in autonomous safety-critical at-the-limit manoeuvres is analysed from the perspective of lane keeping or lane changing, rather than that of yaw control as in traditional ESC systems. An optimal control formulation is developed, where the optimisation criterion is a linear combination of the initial and final velocity of the manoeuvre. Varying the interpolation parameter in this formulation turns out to result in an interesting family of optimal braking and steering patterns in stabilising manoeuvres. The two different strategies of optimal lane-keeping control and optimal yaw control are shown to be embedded in the formulation and result from the boundary values of the parameter. The results provide new insights and have the potential to be used for future safety systems that adapt the level of braking to the situation at hand, which is demonstrated through examples of how to exploit theresults.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Vehicle stability, yaw control, lane keeping, lane change, avoidance manoeuvre, at-the-limit
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-152896 (URN)10.1080/00423114.2018.1549331 (DOI)
Funder
Knut and Alice Wallenberg Foundation
Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2018-11-27

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