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Fors, V., Olofsson, B. & Nielsen, L. (2019). Attainable force volumes of optimal autonomous at-the-limit vehicle manoeuvres. Vehicle System Dynamics, 1-22
Open this publication in new window or tab >>Attainable force volumes of optimal autonomous at-the-limit vehicle manoeuvres
2019 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, p. 1-22Article in journal (Refereed) Epub ahead of print
Abstract [en]

With new developments in sensor technology, a new generation of vehicle dynamics controllers is developing, where the braking and steering strategies use more information, e.g. knowledge of road borders. The basis for vehicle-safety systems is how the forces from tyre–road interaction is vectored to achieve optimal total force and moment on the vehicle. To study this, the concept of attainable forces previously proposed in literature is adopted, and here a new visualisation technique is devised. It combines the novel concept of attainable force volumes with an interpretation of how the optimal solution develops within this volume. A specific finding is that for lane-keeping it is important to maximise the force in a certain direction, rather than to control the direction of the force vector, even though these two strategies are equivalent for the friction-limited particle model previously used in some literature for lane-keeping control design. More specifically, it is shown that the optimal behaviour develops on the boundary surface of the attainable force volume. Applied to lane-keeping control, this observation indicates a set of control principles similar to those analytically obtained for friction-limited particle models in earlier research, but result in vehicle behaviour close to the globally optimal solution also for more complex models and scenarios.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Active safety, force vectoring, vehicle dynamics control, tyre–road interaction, vehicle manoeuvre strategy
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:liu:diva-156638 (URN)10.1080/00423114.2019.1608363 (DOI)000470461700001 ()2-s2.0-85064738528 (Scopus ID)
Note

Funding agencies: Swedish Government; Wallenberg AI, Autonomous Systems and Software Program (WASP) - Knut and Alice Wallenberg Foundation

Available from: 2019-05-02 Created: 2019-05-02 Last updated: 2019-07-03Bibliographically approved
Fors, V., Olofsson, B. & Nielsen, L. (2019). Yaw-Moment Control At-the-Limit of Friction Using Individual Front-Wheel Steering and Four-Wheel Braking. In: : . Paper presented at 9th IFAC Symposium on Advances in Automotive Control (AAC) (pp. 458-464). , 52(5)
Open this publication in new window or tab >>Yaw-Moment Control At-the-Limit of Friction Using Individual Front-Wheel Steering and Four-Wheel Braking
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A simplified combined-slip model that only considers the extreme case at the friction limit is suggested and used in a closed-loop controller for autonomous vehicle handling in at-the-limit maneuvers. In the development of the controller it is assumed that the front wheels are individually steered, but it is demonstrated in a left-hand turn scenario that with a simple adaptation, the method is still applicable for a vehicle with equal front-wheel angles.

Series
IFAC-PapersOnLine, ISSN 2405-8963 ; 5
Keywords
tire modeling, chassis control, yaw control, departure prevention, optimal control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-160480 (URN)10.1016/j.ifacol.2019.09.073 (DOI)
Conference
9th IFAC Symposium on Advances in Automotive Control (AAC)
Funder
ELLIIT - The Linköping‐Lund Initiative on IT and Mobile CommunicationsWallenberg AI, Autonomous Systems and Software Program (WASP)
Available from: 2019-10-08 Created: 2019-10-08 Last updated: 2019-10-08
Fors, V., Olofsson, B. & Nielsen, L. (2018). Formulation and interpretation of optimal braking and steering patterns towards autonomous safety-critical manoeuvres. Vehicle System Dynamics, 57(8), 1206-1223
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, Vol. 57, no 8, p. 1206-1223Article in journal (Refereed) Published
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)000470891200008 ()
Funder
Knut and Alice Wallenberg Foundation
Note

Funding agencies: Swedish Government (Sveriges Regering); Wallenberg AI, Autonomous Systems and Software Program (WASP) (Knut och Alice Wallenbergs Stiftelse) - Knut and Alice Wallenberg Foundation

Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2019-07-15Bibliographically approved
Fors, V. (2018). Optimal Braking Patterns and Forces in Autonomous Safety-Critical Maneuvers. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Optimal Braking Patterns and Forces in Autonomous Safety-Critical Maneuvers
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:nbn:se:liu:diva-147719 (URN)10.3384/lic.diva-147719 (DOI)9789176853016 (ISBN)
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: 2019-10-12Bibliographically approved
Fors, V., Olofsson, B. & Nielsen, L. (2018). Slip-Angle Feedback Control for Autonomous Safety-Critical Maneuvers At-the-Limit of Friction. In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC’ 18): . Paper presented at International Symposium on Advanced Vehicle Control (AVEC).
Open this publication in new window or tab >>Slip-Angle Feedback Control for Autonomous Safety-Critical Maneuvers At-the-Limit of Friction
2018 (English)In: Proceedings of the 14th International Symposium on Advanced Vehicle Control (AVEC’ 18), 2018Conference paper, Published paper (Refereed)
Abstract [en]

From the basis of optimal control, a closed-loop controller for autonomous vehicle maneuvers at-the-limit of friction is developed.The controller exploits that the optimal solution tends to be close to the friction limit of the tires.This observation allows for simplifications that enable the use of a proportional feedback control in the control loop,which provides a smooth trajectory promising for realization in an actual control system.The controller is in comparison with an open-loop numerical optimal control solution shown to exhibit promising performance at low computational cost in a challenging turn scenario.

National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-149899 (URN)
Conference
International Symposium on Advanced Vehicle Control (AVEC)
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-11-27Bibliographically approved
Fors, V., Olofsson, B. & Nielsen, L. (2017). Formulation and Interpretation of Optimal Braking Patterns in Autonomous Lane-Keeping Maneuvers. In: : . Paper presented at 2nd IAVSD Workshop on Dynamics of Road Vehicles. Berlin, Germany
Open this publication in new window or tab >>Formulation and Interpretation of Optimal Braking Patterns in Autonomous Lane-Keeping Maneuvers
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The two perspectives of autonomous driving and new active safety in vehicles are complementary, and both hold promise to reduce the number of accidents and associated severe or fatal injuries. They both coincide in the recent interest in finding alternatives to traditional yaw-control systems that can utilize the full potential of the vehicle. By considering the control problem as that of lane-keeping, also at high speed and at-the-limit of tire friction, rather than that of yaw control, leads to the possibility of optimization-based active-braking systems with better performance than those existing today. Here, we investigate the optimal braking patterns in completely autonomous lane-keeping maneuvers resulting from a formulation where the optimization criterion used is an interpolation between the initial and final velocities of the maneuver. Varying the interpolation parameter, i.e., the relative weight between the initial and final velocity, results in different vehicle behavior. The analysis of these behaviors provides several new insights into stabilizing braking patterns for vehicles in at-the-limit maneuvers. Specifically, it is to be noted that the benefits of a lane-keeping strategy are immediate, both in terms of the maximum possible initial velocity and the velocity reduction. The formulation embeds the traditional yaw control and optimal lane-keeping as the end-point values of the interpolation parameter, and adds a continuous family of behaviors in between. This gives a new perspective for investigating the relation between traditional yaw control and optimal lane-keeping for autonomous vehicles.

Place, publisher, year, edition, pages
Berlin, Germany: , 2017
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-152756 (URN)
Conference
2nd IAVSD Workshop on Dynamics of Road Vehicles
Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2018-11-27
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-4034-2868

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