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Exploring force allocation control of over actuated vehicles
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics. (Vehicle Dynamics)
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

As the concern for environmental changes and diminishing oil resources grows more and more, the trend of new vehicle concepts now includes full electric or partly electric propulsion systems. The introduction of electric power sources enables more advanced motion control systems due to electrification of the vehicle's actuators, such as individual wheel steering and in wheel hub motors. This can enable a control methodology that uses different chassis control strategies into a system that will be able to fully utilise the vehicle. Due to this, future vehicles can be more optimised with respect to energy consumption, performance and active safety.

Force allocation control is a method that distributes the wheel forces to produce the desired response of the vehicle. In order to evaluate if this methodology can be implemented in future series production vehicles, the aim of this work is to explore how force allocation control can be utilised in a real vehicle to improve vehicle dynamics and safety.

In order to evaluate different approaches for generic vehicle motion control by optimization, modelling and simulation in combination with real vehicle experiments will be needed to fully understand the more complex system, especially when actuator dynamics and limitations are considered. The use of a scale prototype vehicle represents a compromise between development cost, efficiency and accuracy, as it allows realistic experiments without the cost and complexity of full vehicle test. Moreover since the vehicle is unmanned it allows studies of at-the-limit situations, without the safety risks in full vehicle experiments.

A small scale prototype vehicle (Hjulia) has been built and equipped with autonomous corner module functionality that enables individual control of all wheels. A cost effective force allocation control approach has been implemented and evaluated on the prototype vehicle, as well as in vehicle simulation. Results show improvement of stopping distance and vehicle stability of a vehicle during split-m braking. The aspects of vehicle dynamic scaling are also discussed and evaluated, as it is important to know how the control implementation of small scale prototype vehicles compares with full size vehicles. It is shown that there is good comparison between vehicles of different scales, if the vertical gravitational acceleration is adjusted for. In Hjulia, gravity compensation is solved by adding a specific lifting rig.

Studies of vehicles considering optimal path tracking and available actuators are also made to evaluate control solutions of evasive manoeuvres at low and high friction surfaces. Results show differences in how the forces are distributed among the wheels, even though the resulting global forces on the vehicle are approximated to be scaled by friction. Also it is shown that actuator limitations are critical in at-the-limit situations, such as an obstacle avoidance manoeuvre. As a consequence these results will provide good insights to what type of control approach to choose to handle a safety critical situation, depending on available actuators.

The built prototype vehicle with implemented force allocation control has shown to be a useful tool to investigate the potential of control approaches, and it will be used for future research in exploring the benefits of force allocation control.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , viii, 42 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2011:80
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-48969OAI: oai:DiVA.org:kth-48969DiVA: diva2:459003
Presentation
2011-12-02, Sal V1, KTH, Teknikringen /2, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note
QC 20111202Available from: 2011-12-02 Created: 2011-11-24 Last updated: 2011-12-02Bibliographically approved
List of papers
1. The developement of a down-scaled over-actuated vehicle equipped with autonomous corner module functionality
Open this publication in new window or tab >>The developement of a down-scaled over-actuated vehicle equipped with autonomous corner module functionality
Show others...
2010 (English)In: FISITA Proceedings 2010, paper F2010B056, 2010Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the development of a functional down-scaled prototype of a passenger car with capability to control steering, wheel torques, wheel loads and camber individually. The adopted chassis technology is based on a modularised platform, referred to as Autonomous corner modules (ACM), which simplifies the re-use of components at the four corners of the vehicle and between different vehicles.

This work gives an insight in the design of the vehicle and the selection of electrical actuators and sensors to provide all ACM functions. Since a part of the implemented chassis components do not admit to be scaled down at the same level, necessary design modifications are suggested. The problems of scaling, meaning that a down-scaled prototype cannot fully emulate a full-scaled vehicle’s all functions simultaneously, are a great disadvantage of down scaling. For example is gravity one desired parameter that is hard to physically scale down.

In order to evaluate the behaviour of the down-scaled prototype, it is of high importance to establish the characteristics of the developed vehicle and its subsystems. In particular, tyre design is considered as complex. For this reason, different ideas of methods to confirm tyre characteristics are proposed.

Also the paper presents the initial process of developing the prototype vehicle that is later to be used in vehicle dynamics research.

Keyword
autonomous corner modules, active chassis, down-scaled prototype, over-actuation
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-48917 (URN)
Conference
FISITA 2010
Note

QC 20111124

Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2014-11-14Bibliographically approved
2. Implementation and evaluation of force allocation control of a down-scaled prototype vehicle with wheel corner modules
Open this publication in new window or tab >>Implementation and evaluation of force allocation control of a down-scaled prototype vehicle with wheel corner modules
2013 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, Vol. 8, no 4, 335-363 p.Article in journal (Refereed) Published
Abstract [en]

The implementation of wheel corner modules on vehicles creates new possibilities of controlling wheel forces through the utilisation of multiple actuators and wheel motors. Thereby new solutions for improved handling and safety can be developed. In this paper, the control architecture and the implementation of wheel slip and chassis controllers on a down-scaled prototype vehicle are presented and analysed. A simple, cost-effective force allocation algorithm is described, implemented and evaluated in simulations and experiments. Straight line braking tests were performed for the three different controller settings individual anti-lock brakes (ABS), yaw-torque-compensated ABS and force allocation using both wheel torque and steering angle control at each wheel. The results show that force allocation is possible to use in a real vehicle, and will enhance the performance and stability even at a very basic level, utilising very few sensors with only the actual braking forces as feedback to the chassis controller.

Keyword
Active chassis, Force allocation, Over-actuation, Scaling, Slip control, Stability, Wheel corner modules
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-48964 (URN)10.1504/IJVSMT.2013.057528 (DOI)2-s2.0-84887911818 (Scopus ID)
Note

QC 20140116. Updated from submitted to published.

Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2014-11-14Bibliographically approved
3. Road friction effect on the optimal vehicle control strategy in two critical manoeuvres
Open this publication in new window or tab >>Road friction effect on the optimal vehicle control strategy in two critical manoeuvres
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2014 (English)In: International Journal of Vehicle Safety, ISSN 1479-3105, Vol. 7, no 2, 107-130 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents results on how to optimally negotiate two safety-critical vehicle manoeuvres depending on available actuators and road friction level. The motive for this research has been to provide viable knowledge of limitations of vehicle capability under the presence of environmental preview sensors, such as radar, camera and navigation. An optimal path is in this paper found by optimising the sequence of actuator requests during the two manoeuvres. Particular interest is paid on how the vehicle control strategy depends on friction. This work shows that actuation of forces and torques on and around the vehicle centre of gravity are all approximately scaled with the friction coefficient. However, this pattern is not valid at a wheel individual level, i.e. the optimal force allocation among the wheels differs under different friction conditions. One key is that lower friction level yields lower load transfer which substantially influences the wheel individual tyre force constraints.

Keyword
Vehicle Control; Actuator; Integrated Motion Control; Road Friction; Optimisation
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-48965 (URN)10.1504/IJVS.2014.060145 (DOI)2-s2.0-84897470574 (Scopus ID)
Note

Updated from "Submitted" to "Published" QC 20141114

Available from: 2011-11-24 Created: 2011-11-24 Last updated: 2014-11-14Bibliographically approved

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