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Exploiting individual wheel actuators to enhance vehicle dynamics and safety in electric vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. (KTH Vehicle Dynamics)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on individual wheel actuators in road vehicles intended for vehicle motion control. Particular attention is paid to electro-mechanical actuators and how they can contribute to improving vehicle dynamics and safety. The employment of individual wheel actuators at the vehicle's four corner results in a large degree of over-actuation. Over-actuation has a potential of exploiting the vehicle's force constraints at a high level and of controlling the vehicle more freely. One important reason for using over-actuated vehicles is their capability to assist the driver to experience the vehicle as desired. This thesis demonstrates that critical situations close to the limits can be handled more efficiently by over-actuation.

To maximise the vehicle performance, all the available actuators are systematically exploited within their force constraints.  Therefore, force constraints for the individually controlled wheel are formulated, along with important restrictions that follow as soon as a reduction in the degrees of freedom of the wheel occurs. Particular focus is directed at non-convex force constraints arising from combined tyre slip characteristics.

To evaluate the differently actuated vehicles, constrained control allocation is employed to control the vehicle. The allocation problem is formulated as an optimisation problem, which is solved by non-linear programming.

To emulate realistic safety critical scenarios, highly over-actuated vehicles are controlled and evaluated by the use of a driver model and a validated complex strongly non-linear vehicle model.

it is shown that, owing to the actuator redundancy, over-actuated vehicles possess an inherent capacity to handle actuator faults, with less need for extra hardware or case-specific fault-handling strategies.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , x, 84 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2009:33
Keyword [en]
autonomous wheel corner, actuators, vehicle dynamics, control allocation, electric vehicles, vehicle modelling
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-11005ISBN: 978-91-7415-387-3 (print)OAI: oai:DiVA.org:kth-11005DiVA: diva2:233961
Public defence
2009-09-25, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100722Available from: 2009-09-08 Created: 2009-09-03 Last updated: 2010-07-22Bibliographically approved
List of papers
1. Autonomous corner modules as an enabler for new vehicle chassis solutions
Open this publication in new window or tab >>Autonomous corner modules as an enabler for new vehicle chassis solutions
2006 (English)In: FISTA TransactionArticle in journal (Refereed) Published
Abstract [en]

Demands for new functions and refined attributes in vehicle dynamics are leading to more complex and more expensive chassis design. To overcome this, there has been increasing interest in a novel chassis design that could be reused in the development process for new vehicle platforms and mainly allow functions to be regulated by software. The Autonomous Corner Module (ACM) was invented at Volvo Car Corporation (VCC) in 1998. The invention is based upon actively controlled functions and distributed actuation. The main idea is that the ACM should enable individual control of the functions of each wheel; propulsion/braking, alignment/steering and vertical wheel load. This is done by using hubmotors and by replacing the lower control arm of a suspension with two linear actuators, allowing them to control steering and camber simultaneously. Along with active spring/damper and wheel motors, these modules are able to individually control each wheel's steering, camber, suspension and spin velocity. This provides the opportunity to replace mechanical drive, braking, steering and suspension with distributed wheel functions which, in turn, enable new vehicle architecture and design.

The aim of this paper is to present the vehicle dynamic potential of the ACM solution, by describing its possible uses and relating them to previous research findings. Associated work suggests chassis solutions where different fractions of the functions of the ACM capability have been used to achieve benefits in vehicle dynamics. For instance, ideas on how to use active camber control have been presented. Other studies have reported well-known advantages, such as, good transient yaw control from in-wheel motor propulsion and stable chassis behaviour from four-wheel steering, when affected by side wind. However, this technology also presents challenges. One example is how to control the relatively large unsprung mass that occurs due to the extra weight from the in-wheel motor. The negative influence from this source can be reduced by using active control of vertical forces. The implementation of ACM, or similar technologies, requires a well-structured hierarchy and control strategy. Associated work suggests methods for chassis control, where tyre forces can be individually distributed from a vehicle path description. The associated work predominately indicates that the ACM introduces new opportunities and shows itself to be a promising enabler for vehicle dynamic functions.

Keyword
Chassis control, vehicle dynamics, steering, propulsion, active suspension
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6769 (URN)
Note
QC 20100721Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2010-07-21Bibliographically approved
2. Stability of an electric vehicle with permanent magnet in-wheel motors during electrical faults
Open this publication in new window or tab >>Stability of an electric vehicle with permanent magnet in-wheel motors during electrical faults
2007 (English)In: World Electric Vehicle Journal, ISSN 2032-6653, E-ISSN 2032-6653, Vol. 1, 100-107 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an analysis of the stability of an electric vehicle equipped with in-wheel motors of permanent-magnet type during a class of electrical faults. Due to the constant excitation from the permanent magnets, the output torque from a faulted wheel cannot easily be removed if an inverter shuts down, which directly affects the vehicle stability. In this paper, the impact of an electrical fault during two driving scenarios is investigated by simulations; using parameters from a 30 kW in-wheel motor and experimentally obtained tire data. It is shown that the electrical fault risks to seriously degrading the vehicle stability if the correct counteraction is not taken quickly. However, it is also demonstrated that vehicle stability during an electrical fault can be maintained with only minor lateral displacements when a closed-loop path controller and a simple method to allocate the individual tire forces are used. This inherent capacity to handle an important class of electrical faults is attractive; especially since no additional fault-handling strategy or hardware is needed.

Keyword
control system, electrical failure, inverter, in-wheel motor
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6770 (URN)2-s2.0-70849121041 (Scopus ID)
Note

QC 20100721

Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2016-12-09Bibliographically approved
3. Control of electric vehicles with autonomous corner modules: implementation aspects and fault handling
Open this publication in new window or tab >>Control of electric vehicles with autonomous corner modules: implementation aspects and fault handling
2008 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 3, no 3, 213-228 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, vehicle dynamics for electric vehicles equipped with in-wheel motors and individual steering actuators are studied adopting the principles of optimal tyre-force allocation. A simple method for describing the constraints owing to tyre and actuator limitations is described. The control architecture is evaluated by investigating its response to realistic fault conditions. The evaluation demonstrates that the control architecture's ability to ensure vehicle stability generally is good. However, during major faults and extreme driving situations, vehicle stability is not maintained unless the constraints in the optimisation process used for tyre-force allocation are adapted to the specific fault.

Keyword
ACM; Adhesion potential; Autonomous corner module; Electric in-wheel motor; Electric vehicle; Fault handling; Force allocation; Tyre constraints; Vehicle control; Vehicle dynamics
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6771 (URN)10.1504/IJVSMT.2008.023839 (DOI)2-s2.0-63149174243 (Scopus ID)
Note

QC 20100721

Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2013-12-04Bibliographically approved
4. Exploiting autonomous corner modules to resolve force constraints in the tyre contact patch
Open this publication in new window or tab >>Exploiting autonomous corner modules to resolve force constraints in the tyre contact patch
2008 (English)In: Vehicle System Dynamics, ISSN 0042-3114, Vol. 46, no 7, 553-573 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a general force allocation strategy for over-actuated vehicles, utilising technologies where tyre forces can be more freely controlled than in conventional vehicles. For the purpose of illustration, this strategy has been applied and evaluated using a design proposal of an autonomous corner module (ACM) chassis during a transient open-loop response test. In this work, the vehicle has been forced to follow a trajectory, identical to the performance of a conventional front-steered vehicle during the manoeuvre studied. An optimisation process of tyre force allocation has been adopted along with tyre force constraints and cost functions to favour a desired solution. The vehicle response has been evaluated as open-loop, where tyre forces are shown to be allocated in a different manner than in conventional front-steered vehicles. A suggested approach for a control scheme of steering actuators is presented, where the actuator limitation is related to the lateral force possible. Finally, the force allocation strategy involves the ability to control vehicle slip independently from vehicle yaw rate. This opportunity has been adapted in the ACM vehicle in order to relax vehicle slip from the original trajectory description. In such circumstances, the ACMs demonstrate better utilisation of the adhesion potential.

Keyword
autonomous corner module; force allocation; steering actuator; tyre constraints; vehicle control; vehicle dynamics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6772 (URN)10.1080/00423110701504215 (DOI)000257029700001 ()2-s2.0-46349108582 (Scopus ID)
Note
QC 20100629Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2011-11-07Bibliographically approved
5. Design and evaluation of an active electromechanical wheel suspension system
Open this publication in new window or tab >>Design and evaluation of an active electromechanical wheel suspension system
2008 (English)In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 18, no 4, 218-230 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an electromechanical wheel suspension, where the upper arm of the suspension has been provided with an electric levelling and a damper actuator, both are allowed to work in a fully active mode. A control structure for the proposed suspension is described. The complex design task involving the control of the electric damper and its machine parameters is tackled by genetic optimisation. During this process, these parameters are optimised to keep the power dissipation of the electric damper as low as possible, while maintaining acceptable comfort and road-holding capabilities. The results of the evaluations carried out demonstrate that the proposed suspension can easily adopt its control parameters to obtain a better compromise of performance than that offered by passive suspensions. If the vehicle is to maintain acceptable performance during severe driving conditions, the damper has to be unrealistically large. However, if the electric damper is combined with a hydraulic damper, the size of the electric damper is significantly reduced. In addition, the design of the electric damper with the suggested control structure, including how it regenerates energy, is discussed.

Keyword
Automotive; Active suspensions; Electric vehicles; Electric dampers
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-11012 (URN)10.1016/j.mechatronics.2007.11.003 (DOI)000256114800005 ()2-s2.0-41149090113 (Scopus ID)
Note
QC 20100722Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
6. Modelling and parameterisation of a vehicle for validity under limit handling
Open this publication in new window or tab >>Modelling and parameterisation of a vehicle for validity under limit handling
2008 (English)In: Proceedings of 6th Modelica Conference, 2008Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes how a vehicle model from the VehicleDynamics Library is configured, parameterized and validated for predicting limit handling maneuvers. Especially, attention is given to the selection of subsystem models with suitable levels-of-detail as well the selection of performed measurements and measurement equipment. A strong principle throughout the presented work is component-based design where parameterizations are done on sub-system levels, no tuning on the final vehicle models is made. As a final test, the vehicle model is exposed to a sinusoidal steering input. It turns out that the correspondence between the model used and the real vehicle is acceptable for the driving scenario selected up to the limit of adhesion.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-11014 (URN)
Conference
6th Modelica Conference
Note

QCR 20160608

Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2016-06-08Bibliographically approved
7. Using future path information for improving stability of an overactuated vehicle
Open this publication in new window or tab >>Using future path information for improving stability of an overactuated vehicle
2009 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 4, no 3, 218-231 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, model predictive control (MPC) is applied for controlling an over-actuated vehicle. The control problem is associated with the distribution of the tyre forces to ensure vehicle stability. The use of MPC is shown to be a suitable method if the vehicle's future desired trajectory is known. Simulation studies conducted show that access to information in advance, even if such information is restricted to only a few seconds, significantly contributes to maintaining vehicle stability. Furthermore, a longer prediction horizon results in earlier actions and stabilises the vehicle even better.

Keyword
MPC; model predictive control; vehicle systems modelling; vehicle control; vehicle dynamics; over-actuated vehicles; tyre forces; vehicle stability; simulation.
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-11015 (URN)10.1504/IJVSMT.2009.029390 (DOI)2-s2.0-70849095042 (Scopus ID)
Note
QC 20100722Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2010-07-22Bibliographically approved
8. Global force potential of over-actuated electric vehicles
Open this publication in new window or tab >>Global force potential of over-actuated electric vehicles
2010 (English)In: International Journal of Vehicle System Dynamics, ISSN 0042-3114, Vol. 48, no 9, 983-998 p.Article in journal (Refereed) Published
Abstract [en]

This paper formulates force constraints of over-actuated road vehicles. In particular, focus is put on different vehicle configurations provided with electrical drivelines. It is demonstrated that a number of vehicles possesses non-convex tyre and actuator constraints, which have an impact on the way in which the actuators are to be used. By mapping the actuator forces to a space on a global level, the potential of the vehicle motion is investigated for the vehicles studied. It is concluded that vehicles with individual drive, compared with individual brakes only, have a great potential to yaw motion even under strong lateral acceleration.

Keyword
brute force; combined slip; electric vehicles; force allocation; tyre forces; over-actuated vehicles
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-11016 (URN)10.1080/00423110903243232 (DOI)000280153200001 ()2-s2.0-77954897616 (Scopus ID)
Note

QC 20100722

Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2016-06-08Bibliographically approved
9. Investigation of the non-convex force constraints imposed by individual wheel torque allocation
Open this publication in new window or tab >>Investigation of the non-convex force constraints imposed by individual wheel torque allocation
2009 (English)Article in journal (Refereed) Submitted
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-11018 (URN)
Note
QS 20120315Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2012-03-15Bibliographically approved
10. Utilisation of actuators to improve vehicle stability at the limit: from hydraulic brakes towards electric propulsion
Open this publication in new window or tab >>Utilisation of actuators to improve vehicle stability at the limit: from hydraulic brakes towards electric propulsion
2009 (English)In: 21st InternationalSymposium on Dynamics of Vehicles on Roads and Tracks, 2009Conference paper, Published paper (Refereed)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-11019 (URN)
Note
QC 20100722Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2010-07-22Bibliographically approved

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