This paper presents a detailed study of semi-active approach for railway wheelsets. A number of control strategies for active primary suspensions for both solid axle wheelset and independently rotating wheelsets are examined in detail and the key requirements of energy flows on both curved and straight tracks are investigated. A semi-active control scheme is then proposed for the independently rotating wheels and a comprehensive performance evaluation is provided to demonstrate that the proposed semi active control system can be used to continuously and reliably provide the necessary steering control without the need for the energy injection of full active control

CP Ward

G Shen

H Ren

JT Pearson

S Bruni

TX Mei

For motorcycles, various suspension concepts for the front steerable wheel have been developed over decades. Even if the telescopic front fork has been eventually established as a common design, other alternative designs are still being evolved. A design of such an alternative - a multi-link suspension, particularly utilised for motorcycles with a sidecar, is discussed in the present paper. Beside some modelling aspects, optimisation of suspension’s kinematics and benefits of an asymmetric layout for left and right cornering are elaborated

Tobolar, Jakub

Institute of Transport Research:Publications

Publications of the DLR elib This is the author’s copy of the publication as archived with the DLR’s electronic library at http://elib.dlr.de. Please consult the original publication for citation, see e.g. https://link.springer.com/chapter/10.1007/978-3-030-38077-9_192 Design of a Multi-link Suspension for Motorcycles with a Sidecar Jakub Tobolar For motorcycles, various suspension concepts for the front steerable wheel have been developed over decades. Even if the telescopic front fork has been eventually established as a common design, other alternative designs are still being evolved. A design of such an alternative - a multi-link suspension, particularly utilised for motorcycles with a sidecar, is discussed in the present paper. Beside some modelling aspects, optimisation of suspension’s kinematics and benefits of an asymmetric layout for left and right cornering are elaborated. Copyright Notice ©2020 Springer Nature. Personal use of this material is permitted. Permission from Springer Nature must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.  Tobolar J. (2020) Design of a Multi-link Suspension for Motorcycles with a Sidecar. In: Klomp M., Bruzelius F., Nielsen J., Hillemyr A. (eds) Advances in Dynamics of Vehicles on Roads and Tracks. IAVSD 2019. Lecture Notes in Mechanical Engineering. Springer, Cham. https://link.springer.com/chapter/10.1007/978-3-030-38077-9_192  Design of a multi-link suspension formotorcycles with a sidecarJakub TobolářGerman Aerospace Center (DLR), Institute of System Dynamics and Control,Wessling, Germany,Jakub.Tobolar@DLR.deAbstract. For motorcycles, various suspension concepts for the frontsteerable wheel have been developed over decades. Even if the telescopicfront fork has been eventually established as a common design, other al-ternative designs are still being evolved. A design of such an alternative -a multi-link suspension, particularly utilised for motorcycles with a side-car, is discussed in the present paper. Beside some modelling aspects,optimisation of suspension’s kinematics and benefits of an asymmetriclayout for left and right cornering are elaborated.Keywords: Motorcycle, multi-link suspension, modelling1 IntroductionIn the history of single track motor vehicles, various suspension concepts for thefront steerable wheel have been developed. Even if the telescopic front fork hasestablished itself as the preferable design, other solutions are possible and mayappear advisable.An invention from the early 1980s used two wishbones oriented in motorcy-cle’s driving direction and connecting the front fork to the motorcycle’s frame –a system used by BMW and named duolever, see e.g. [1]. Yet another innovationis used under the name telelever by BMW as well. It connects the lower forkbodies right above the front wheel to the motorcycle’s frame by means of onewishbone. The upper fork tubes are connected via a ball joint directly to theframe. A survey of alternative front suspension designs can be found in [2].The benefits of such suspensions are especially the improvement of motor-cycle’s handling due to higher twisting stiffness of the front suspension, see [3],and/or the improvement of handling qualities during braking manoeuvres byreducing brake dive.In the particular case of a motorcycle with a sidecar, the increased massof the whole motorcycle combination and, hence, higher acting forces motivateadditionally for alternatives. One of the preferable suspensions to fulfil the mo-torcycle combination requirements is a leading link fork [1].The front forks discussed in the previous feature symmetric steering be-haviour. Disadvantages of such property for motorcycles with sidecar and pos-sible improvement utilizing an asymmetric multi-link suspension together withcorresponding simulation results are presented in the following sections.2 Jakub Tobolář2 Multi-link front suspensionThe suspension designs described in the introduction have some parallels withindependent suspensions of common passenger cars. For example, the abovemen-tioned telelever compares to vehicle’s McPherson suspension and the duolever iscomparable to a double wishbone.These affinities of the motorcycles’ and automotive suspensions inspired theauthor to invent yet another automotive-like suspension – a multi-link – forfront suspension of motorcycles with sidecar, see [4]. In the following, modellingaspects of such a multi-link suspension (hereinafter called multi-link fork) andoptimisation of its kinematics for this particular scope of application are dis-cussed.2.1 Multi-link fork designAn actual automotive multi-link suspension – used especially for rear axles ofluxury vehicles – consists of five links connecting the wheel upright with thevehicle’s body [5]. The five links restrict the degrees of freedom to the upright’svertical compression and rebound only. If used for steerable automotive suspen-sion, one of the links is considered a steering rod, thus enforcing the steeringmovement. For the motorcycle’s multi-link fork, the four of five links are ar-ranged in driving direction, see Fig. 1. The fifth link can induce the steeringmovement, as discussed below in Sec. 2.3.Considering the motorcycle’s longitudinal dynamics, the links are orientedpairwise in a way to optimize braking support angle εBf , see Fig. 2. Togetherwith the rear suspension’s brake support angle εBr and the height hCG of thecentre of gravity of the vehicle it is crucially responsible for the amount of themotorcycle’s pitch movement during braking.According to [1], the angle εB can be calculated by means of the translationalvelocity v∗W at the “virtual” tire/road contact point W astan εB = ±v∗Wxv∗Wz. (1)Such virtual contact point is considered on the wheel with blocking brake duringwheel deflection and rebound. In the case of a conventional motorcycle withbrakes mounted on the wheel carrier this means that the wheel can be virtuallyfixed on the fork during computer aided investigation of εB . For practical reasonsthe point can simply be considered to be on the fork, too. This is also the casefor the described multi-link fork.The telescopic front fork is well known for its negative impact on the anti-diveeffect. In contrast, both the duolever and the telelever mitigate such behaviour.Utilizing the multi-link fork, a motorcycle’s front diving during braking can betuned as well.The lateral arrangement of the links can be done symmetrically to the longi-tudinal motorcycle’s plane. Liu, see [6], elaborated such a design of the motor-cycle’s multi-link fork and demonstrated simulation results of various comparingMulti-link suspension for motorcycles 312345C1C3A1, A2A3Fig. 1. Visualisation of the motorcycle’s multi-link fork: fork (1), handlebar (2), steer-ing assembly (3), motorcycle’s frame (4) and linkage (5). The links’ mounts on themotorcycle’s body are marked Ci with i = 1, . . . , 4 and those on the fork accord-ingly Ai whereby the even numbers are on the left and odd numbers on the rightside.analyses. Utilizing an asymmetric design of the multi-link could be a doable wayto deal with the particular steering handling of the (asymmetric) motorcyclewith side car.2.2 Cornering behaviourDespite of descending from the single track motorcycle, the motorcycle with side-car combination’s handling is quite different. Due to its particular arrangementit even differ significantly from that of double track vehicles. This is especiallydue to the laterally asymmetric location of steered wheel and of driven wheelrelative to the centre of mass of the whole motorcycle combination.Considering the cornering at stability limits with the motorcycle having thesidecar on the right, the particular motorcycle combination arrangement typi-cally yields a sidecar’s wheel lifting (“flying the chair”) in right turns. Duringleft turning there is, on the contrary, a risk of the sidecar’s nose diving. In bothcases, a wheel contact loss accompanied with sudden handling change occurswhich can lead to the lost of control over the vehicle.The present work concentrates on performing at driving conditions far belowsuch limits. Nonetheless, the asymmetric arrangement of the motorcycle com-bination still induces different behaviour during left and right cornering. Thisforces the driver to different handlebar actions for opposite turning. With the4 Jakub TobolářεBfv∗W εBrWPdriving directionCGhCGFig. 2. On the calculation of front and rear braking support angles εBf and εBr, re-spectively.multi-link fork, both the steering assembly design and the asymmetric linkagecould reduce such a behaviour.2.3 Steering assemblyVarious mechanical assemblies can be employed to transform the handlebar inputto the front wheel. As mentioned in Sec 2.1, utilizing the fifth link would be anexpected option which even enables to realise a variable steering angle transfor-mation to diminish the differences between left and right turning. Nonetheless,this solution would also induce an unwanted variation of wheel’s steering angleduring suspension’s compression and rebound even for constant handlebar input.This could be especially crucial for the motorcycle combination where payload– and consequently the suspensions’ compression – can change significantly. An-other drawback is the need for additional space to in any way connect the fifthlink to the handlebar.Therefore, a steering assembly with constant handlebar input transformationis preferred here. In [6], a drive shaft with two Hooke’s joints and length changecompensation is utilized for steering. Yet another mechanism are considerable.An option shown in Fig. 1 uses two rods connected by one laterally oriented rev-olute joint and a double Hooke’s joint. Thus, the steering movement is restrictedwhile the vertical movement is still available.2.4 Other elementsSuspending elements can be arranged in various manners. In the variant shownin Fig. 1, there is one spring/damper unit placed above the wheel and connectingthe motorcycle’s fork with the motorcycle’s frame beneath the handlebar. Evenif other configurations are possible, they are not object of the study and will notbe further elaborated here.Multi-link suspension for motorcycles 53 Simulation resultsTo verify the theory discussed previously, a multi-body motorcycle model wasestablished using Modelica [7] and analysed by means of simulations.3.1 Model of motorcycle with sidecarThe investigated multi-body model comprises front and rear suspensions, wheels,frame with sidecar, rider and one sidecar’s passenger. The steering assembly isbeing considered a part of the front suspension. The parameters of the motor-cycle without sidecar are largely based on those given by [3]. In contrast to [3],neither frame elasticities nor the rider’s upper body movement are considered.The parameters of the sidecar are estimated and summarised in Table 1. Stiffnessand damping properties were adapted to fulfil vertical dynamics requirementsfor motorcycle combination with mass and its distribution different to [3].Table 1. Sidecar’s parameters.Parameter ValueMass 85 kgPassenger mass 75 kgTrack 1.1 mWheel longit. offset to rear wheel 0.3 mThe tyre geometry considers tyre width and its circular cross-section accord-ing to [8]. While considering such a geometry is significant for proper modellingof motorcycle’s behaviour at large tilting angles [9], it can generally be neglectedfor the motorcycles with sidecar as just minimum tilting angles occur. The multi-link fork can, in contrast, induce significant wheel camber and, therefore, suchtyre geometry is considered as well. Tire forces were modelled using the Pacejka’sMagic Formula [10] to assess the vehicle dynamics behaviour.In the analysed multi-link fork, the upper pair of links is located above thewheel whereby the lower pair is mounted under the wheel centre. Thus, a widebasis to support the braking torque is reached. Moreover, to place the upperlinkage above the wheel allows for more space to optimize its lateral position.3.2 Cornering AssessmentThe vertical and longitudinal positions of the links’ mounts were determined ina way to comply with braking requirements discussed in Sec. 2.1. The lateralpositions of the mounts were found by means of an optimisation process in orderto minimize the discrepancy between left and right turning.6 Jakub TobolářThe simulated manoeuvre is quasi-stationary left and right cornering at con-stant velocity of 20 km/h with monotonous increase of handlebar angle δH . Thediscrepancy is given as difference between self-steering gradients (SSG) of cor-responding turns,SSG =∆δH∆ay, (2)with ∆δH being an increment of the handlebar angle and ∆ay the correspondingincrement of lateral acceleration.The improvement of the self-steering behaviour of the motorcycle combina-tion with optimized multi-link fork can be concluded from Fig. 3. In the upperdiagram, the black lined SSG of the motorcycle combination with multi-linkfork reflects improvements over the full range of lateral acceleration comparedto those of conventional motorcycle combination (indicated by red dashdottedlines). A particular improvement is achieved for ay between ±2 m/s2 where goodsymmetry of SSG can be observed. This facilitates the driver riding straight onwith small left and right handlebar corrections as such corrections evoke sim-ilar motorcycle’s cornering reaction. A secondary effect is a slight increase ofmaximum lateral acceleration to be reached during right turn.The lower diagram in Fig. 3 shows resulting SSG for motorcycle combinationcornering at higher constant velocity of 40 km/h. This was additionally investi-gated to prove the optimized multi-link fork at different conditions. The positiveeffects of the multi-link fork appear less distinctive but are still present.4 ConclusionsA multi-link fork design was proposed to compensate for unfavorable effectsduring left and right cornering of motorcycles with sidecar. The suggested me-chanical design complies with requirements on longitudinal and lateral dynamics.Particular attention was paid to achieve similar reactions during left and rightcornering in order to relax driver’s turning effort.Presented simulation results confirmed improvements in cornering handling.Nonetheless, as the multi-link fork features far more tuning possibilities thanconsidered in the present work, manoeuvres such as braking, braking in a turnor cornering at various velocities should be comprised in future optimisation.References1. Matschinsky W.: Radführungen der Straßenfahrzeuge. Springer-Verlag Berlin Hei-delberg, 3rd edition, in German, doi: 10.1007/978-3-540-71197-1 (2007)2. Mavroudakis B. and Eberhard P.: Analysis of alternative front suspension sys-tems for motorcycles. Vehicle System Dynamics, 44:sup1 pp. 679–689, doi:10.1080/00423110600883447 (2006)3. Sharp R., Evangelou S. and Limebeer D.: Advances in the Modelling of MotorcycleDynamics. Multibody System Dynamics, issue 3(12), pp. 251-283 (2004)Multi-link suspension for motorcycles 70123SSG/◦s2m−1multi-link left turnmulti-link right turntelescopic left turntelescopic right turn−6 −4 −2 0 2 4 6 800.51ay/m s−2SSG/◦s2m−1Fig. 3. Self-steering gradient SSG over lateral acceleration ay for motorcycle withsidecar driving in a turn at 20 km/h (above) and at 40 km/h (below). Positive ayindicates left turn while negative values are for right turn.4. Tobolar J.: Radaufhängung für ein lenkbares Rad. German patentDE 10 2012 204 031 B4 (2011)5. Enke K.: Improvement of the ride/handling compromise by progress in the elasto-kinematic system of wheel suspension. In Road Vehicle Handling, I Mech E Confer-ence Publications 1983–5, Torino (1983)6. Liu Ch.: A multibody dynamics model of a motorcycle with a multi-link front suspension. Electronic Theses and Dissertations. 7376.https://scholar.uwindsor.ca/etd/7376 (2017)7. Otter M., Elmqvist H. and Mattsson S.E.: Multi-domain Modeling with Modelica.In CRC Handbook of Dynamic System Modeling, Chapman & Hall, pp. 36.1–36.27,(2007)8. Zimmer D. and Otter M.: Real-time models for wheels and tyres in an object-oriented modelling framework. Vehicle System Dynamics, 48:2, pp. 189–216, doi:10.1080/00423110802687596 (2010)9. Cossalter V.: Motorcycle Dynamics. 2nd edition, https://www.academia.edu/23761702/ Vittore Cossalter Motorcycle Dynamics BookZZ (2006)10. Pacejka H. B.: Tire and Vehicle Dynamics. Elsevier Ltd, Oxford, 3rd edition, (2012)

Design of a Multi-link Suspension for Motorcycles with a Sidecar

Crossref

Application of State Estimators in Active Control of Railway Wheelsets

B Mavroudakis

R Sharp

D Zimmer

HB Pacejka

Advances in Dynamics of Vehicles on Roads and Tracks

This volume contains the official proceedings of the 26th IAVSD Symposium on Dynamics of Vehicles on Roads and Tracks, which took place on 12–16 August 2019, at the Lindholmen Conference Centre in Gothenburg, Sweden. The main objective of the International Association for Vehicle System Dynamics (IAVSD, see www.iavsd.org) is to promote the development of, and applications in, the field of ground vehicle system dynamics. The IAVSD Symposium on Dynamics of Vehicles on Roads and Tracks is a leading international symposium bringing together researchers, scientists and engineers from academia and industry to present and exchange their latest ideas and results. These biennial symposia, held at various locations around the world, have contributed greatly to a better understanding of ground vehicle system dynamics-related problems. The organisers of the 26th Symposium were the Department of Mechanics and Maritime Sciences, Chalmers Railway Mechanics (CHARMEC), which is theCentre of Excellence in Railway Mechanics at Chalmers University of Technology, and the Vehicle and Traffic Safety Centre at Chalmers (SAFER). Both centres are part of the Transport Area of Advance hosted at Chalmers University of Technology.The symposium was attended by 380 delegates from 28 countries and five continents (Africa, Asia, Australia, Europe and North America). Most participants arrived from China (88), Sweden (73), UK (36), Germany (32), Japan (25), Austria (18), Italy (12) and Korea (11).Each day of the symposium started with a plenary session and an invited state-of-the-art presentation (60 minutes). These state-of-the-art papers have been published in the journal Vehicle System Dynamics (Taylor &amp; Francis), volume 57, issue number 7 (July 2019). After the morning coffee break, the presentations were divided into five parallel sessions with various themes on road and railway vehicle dynamics.The number of extended abstracts submitted to the symposium was 338 with 131 related to road vehicle dynamics and 207 to railway vehicle dynamics. After peer review by the International Scientific Committee, 63 road abstracts and 83 railway abstracts were selected for 30-minute oral presentations, while 38 road and 47 railway abstracts were selected for poster presentations (3-minute oral introduction followed by individual discussions in front of each poster). Out of those, 218 presentations were selected for publication as full papers in this book, which represents the official conference proceedings.Part of the chapters gathered in this book covers different topics in railway vehicle system dynamics such as adhesion and friction, vehicle modelling, condition monitoring, wheel and rail profiles, active suspension, switches and crossings, and wheel out-of-roundness. Further topics include vibration and control, track modelling, traction and braking, vehicle design and components, safety and derailment analysis, wheel‒rail contact, wheel and rail damage, pantograph‒catenary dynamics, and wheel and rail wear. The remaining chapters cover themes in road vehicle system dynamics such as\ua0advanced driver-assistance systems (ADAS), handling dynamics, driving automation, integrated chassis control and powertrain/driveline control. Further topics include state estimation, standards, assessment and validation, tyre modelling, suspension and ride, and specialised vehicles. We expect that this volume of the Lecture Notes in Mechanical Engineering, published by Springer Nature, will serve as a timely reference guide and a source of inspiration for scientists and engineers in the field of ground vehicle system dynamics

Klomp, Matthijs

Bruzelius, Fredrik

Nielsen, Jens

Hillemyr, Angela

Chalmers Research

Advances in Dynamics of Vehicles on Roads and Tracks : Proceedings of the 26th Symposium of the International Association of Vehicle System Dynamics, IAVSD 2019, August 12-16, 2019, Gothenburg, Sweden

Mei, TX

Zaeim, A

Li, H

E-space: Manchester Metropolitan University's Research Repository

Mei, TX and Zaeim, A and Li, H (2020) Control of Railway Wheelsets – ASemi-active Approach. In: Advances in Dynamics of Vehicles on Roads andTracks. IAVSD 2019, August 12-16, 2019, Gothenburg, Sweden. LectureNotes in Mechanical Engineering..Downloaded from: https://e-space.mmu.ac.uk/626979/Publisher: SpringerDOI: https://doi.org/10.1007/978-3-030-38077-9_2Please cite the published versionhttps://e-space.mmu.ac.ukControl of Railway Wheelsets – A Semi-Active Approach  T X Mei1, A Zaeim1 and Hong Li2 1 School of Science, Engineering and Environment, University of Salford, UK 2 School of Engineering Manchester Metropolitan University Manchester, UK t.x.mei@salford.ac.uk Abstract. This paper presents a detailed study of semi-active approach for rail-way wheelsets. A number of control strategies for active primary suspensions for both solid axle wheelset and independently rotating wheelsets are examined in detail and the key requirements of energy flows on both curved and straight tracks are investigated. A semi-active control scheme is then proposed for the inde-pendently rotating wheels and a comprehensive performance evaluation is pro-vided to demonstrate that the proposed semi active control system can be used to continuously and reliably provide the necessary steering control without the need for the energy injection of full active control. Keywords: Railway wheelset control, Semi-active control, Solid-axle wheelset, Independently rotating wheelset. 1 Introduction Active control for railway wheelsets can provide effective solutions to reduce substan-tially the contact forces and associated problems of wear/RCF and other track damages caused by passive primary suspensions [1]. Active control can be used to stabilise the inherent hunting of solid axle wheelset without interfering its natural curving ability or to supplement the passive suspensions with additional steering action on curves [2]. It can also provide the necessary guidance control that is missing in independently-rotat-ing wheels [3].  However, full active control necessitates the use of actuators that are capable of both injecting into and dissipate energy from the system and such actuators are not only expensive but also tend to be bulky in size – this can lead to considerable increase in the overall costs of railway vehicles and also difficulties in installations in space tight bogie frames. In addition, active wheelset control is safety critical and the use of hard-ware redundancies (e.g. duplication of actuators) would exacerbate the problems and potentially hinder or even prevent practical adoption of such technologies for commer-cial applications despite its clear advantages. There have been a few studies of semi-active approaches for solid axle wheelset, looking into the possible use of variable/controllable passive devices to replace the more costly actuators. Variable longitudinal stiffness in the primary suspensions has been proposed to improve the hunting instability of railway carriages [4]. It would clearly be beneficial to be able to increase the stiffness for high speed operations and 2 reduce it when a vehicle negotiate tight curves at low speeds, but mechanisms to achieve this could be problematic in practice. The use of variable dampers either in the primary suspensions to supplement the passive means [5] or in the secondary suspen-sions to replace the yaw dampers of fixed coefficient [6] can help to improve the vehicle performance, but they do not solve the fundamental trade-off between the stability and curving of the solid axle wheelsets. So far, no studies on the semi-active control of independently rotating wheelsets are found. The control of railway wheelset is concerned with the issues of stability and/or track following – both issues are safety critical and therefore the research challenge for any semi-active control approach is to provide the necessary control effort at all times within the obvious constraint of energy dissipation only (i.e. no energy injection into the system). This is significantly more demanding than the semi-active control for sec-ondary suspensions where the switching between active and passive modes is inherent and accepted. In this paper, detailed studies of control design for active primary suspensions with solid axle wheelset and independently rotating wheelsets are presented to examine power flows on different track conditions. A control scheme for the active steering of independently rotating wheelsets (IRW) that can be implemented with semi-active means (via the use of variable/controller dampers) is proposed. The semi-active control scheme, where the control is achieved with the use of magnetorheological (MR) damp-ers, is then applied to a two-axle vehicle with IRWs. Computer simulation results demonstrate that the proposed semi active control system can be used to continuously and reliably provide the necessary steering control without the need for any energy injection of full active control. 2 Semi-Active Devices There are broadly three categories of variable devices that can be used for semi-active controls – variable stiffness springs, variable dampers and variable inerters. The variable springs involve some form of moveable mechanisms or vary the load transfer ratio by moving the location of the point of attachment to control stiffnesses [7, 8]. The variable dampers control the damping forces by either adjusting flow rate of the fluid in the device by controlling orifice positions [9] or changing the characteristics of the fluid using magnetic/electro means [6]. The variable inerters produce the forces that are proportional to the acceleration between the two terminals of the device with a control-lable-inertia flywheel such that the effective inertia is adjustable [10].  The variable stiffness or inerters are capable of storing and returning energy from/back to a system, but the use of moveable mechanisms tends to slow the control responses and also potentially raises the reliability issues that are critical for the control of railway wheelsets. On the other hand, the variable dampers are by far the most commonly used for semi-active control applications – they are relatively straight forward to control with very fast responses, but they are not able to dissipate energy in the system so can only be used in applications where energy injection or storage is required.  3 3 Control Analysis This study examines the known active wheelset control schemes and explores the potentials for implementation using variable dampers rather than full active controls. The use of variable stiffness or inerter is not considered in this study, not only because of the reasons mentioned above but also it would likely require different control design approaches. Also, the analysis is limited to active controls as a replacement of passive suspensions rather than supplementary to passive stabilization such that the full ad-vantage of active control is obtained.  The solid-axle wheelset can provide the self-centering/steering on a track, and per-fect curving is maintained if this natural curving is not interfered by the stabilization that is necessary to manage the unstable kinematic mode [11]. The stability control (whether classical control strategies or model based approaches) require feedback sig-nals that are out-phase with the control effort (e.g. yaw control) such as the yaw angle or lateral velocity of the wheelset [12-15]. Consequently, the control will require both injecting and dissipating power at different times, which makes it impossible to use the semi-active devices such as variable dampers. Figures 1 and 2 show the power require-ment of an actively stabilized solid-axle wheelset on straight and curved tracks respec-tively. It is clear that the control will need to provide energy (negative power) at most times and consume energy (positive power) at other times.  On the other hand, independently rotating wheelsets require both stabilization and guidance control as the natural curving is not available because the two wheels on an axle are allowed to rotate freely. However, provision of the stabilization and guidance control for independently rotating wheelsets is much more straight forward than that for the solid-axle counterparts. Not only the required control effort is much lower, but also it is possible to only use the feedback signals that are in phase with the control effort [3]. Figures 3 and 4 show that the power requirement of an actively controlled independently rotating wheelset can be made to consume power only – paving the way for the implementation with semi-active means.     Figure 1 Power of active control on straight track with irregularities – solid axle   4   Figure 2 Power of active control on curved track – solid axle   Figure 3 Power of active control on straight track with irregularities – IRW   Figure 4 Power of active control on curved track – IRW  5 4 Semi-Active Control Figure 5 shows the proposed semi-active control scheme for a 2-axle vehicle with in-dependently rotating wheelsets. This is very similar to a full active control system, but the actuators are now replaced with variable dampers – in this case, magnetorheological dampers are used for their ease of control and fast response.                  Figure 5. Semi-active control scheme of a 2-axle vehicle with IRWs  Figures 6-8 compare the control effort, the velocity and power of the control device of the proposed semi-active control approach with those of a full active control on a high speed straight track. It can be seen that the semi-active performs as well as the full active. No power injection is needed and no extra benefits may be expected from the full active control  Figure 6. Control effort on a straight track – Full active vs Semi-active IRW 1 IRW 2 Control (IRW 1) Control (IRW 2) Semi-active (MR damper) Semi-active (MR damper) sensors sensors 2-Axle Vehicle 6  Figure 7. Velocity of MR damper on a straight track – Full active vs Semi-active   Figure 8. Power on a straight track – Full active vs Semi-active  The semi-active control is also capable of providing the necessary guidance on curved track. Figures 9-11 compare the control effort, the velocity and power of the control device of the proposed semi-active control approach with those of a full active control on a curved track. Again, there are not much differences between the two as the control system in either case only dissipate the energy from the wheelset and there is no re-quirement to provide any additional energy.           7  Figure 9. Control effort on a curved track – Full active vs Semi-active  Figure 10. Velocity of MR damper on a curved track – Full active vs Semi-active     Figure 11. Power on a curved track – Full active vs Semi-active 8 5 Conclusions This paper has presented the development of a semi-active control scheme for the in-dependently rotating wheelsets in railway vehicles. Detailed analysis of the control re-quirements and power flows are provided. Computer simulation has demonstrated that the proposed semi-active control can be used to deliver the stability and guidance con-trol for independently-rotating wheelsets that matches the performance of a full active control, providing a much more cost effective way for active wheelset control In the future.  References 1. Bruni, S, Goodall, R.M. Mei, T.X. and Tsunashima H “Control and Monitoring of railway vehicle dynamics” Vehicle System Dynamics, Vol 45, Issue 7/8, 2007, pp743-779. 2. Mei, T.X.; and Goodall, R.M. “Stability control of railway bogies using absolute stiffness – Skyhook spring approach”, Vehicle System Dynamics, Vol. 44 Supplement, 2006, 83-92 3. Mei, T.X. and Goodall, R.M. "Practical Strategies for Controlling Railway Wheelsets With Independently Rotating Wheels", ASME, Journal of Dynamic Systems, Measurement and Control, Vol. 125/3, 2003, pp 354-360 4. Abood K H and Khan R A, “Investigation to improve hunting stability of railway carriages using semi-active longitudinal primary stiffness suspension”, Mechanical Engineering Re-search, Vol 2(5), Oct 2010, pp 97-105 5. Gajdar T and Rudas I, “Active and semi-active control of uncertain railway wheelset”, 21st IEEE IECON, Orlando, Nov 1995 6. Baiasu D, Ghita G and Sebesan I, “Control system with magnetorheological fluid device for migigation of the railway vehicle oscillations, 13th ERME2012, Ankara, July 2012 7. Aardama J A, “Variable Stiffness Spring Suspension”, US patent – US4832321A, 1998 8. Anubi O M, Patel D R and Crane C D, “A new variable stiffness suspension system: passive case”, Mechanical Sciences, 2013, Vol. 4, pp 139–151 9. Oh S K, Yoon Y H and Krishna A, “A Study on the Performance Characteristics of Variable Valve for Reverse Continuous Damper”, Intl Journal of Mechanical Systems Science and Engineering, Vol. 1, No 3, 2007, pp 129-134 10. Hu Y and Chen M et al, "Semiactive inerter and its application in adaptive tuned vibration absorbers". IEEE Transactions on Control Systems Technology. 25 (1), 2017 pp 294-300 11. Shen S, Mei, T. X., Goodall, R.M., Pearson, J.T. and Himmelstein G “A Study of Active Steering Strategies for A Railway Bogie”, Vehicle System Dynamics, Vol. 41 Supplement, 2004, pp 282-291 12. Bideleh S M M, Mei T X and Berbyuk V, “Robust Control and Actuator Dynamics Com-pensation for Railway Vehicles”, Vehicle System Dynamics, Vol 54, No 12, 2016, pp. 1762-1784 13. Mei, T.X. and Goodall, R.M. "Robust Control for Independently-Rotating Wheelsets on a Railway Vehicle using Practical Sensors ", IEEE Transactions on Control Systems Technol-ogy, Vol. 9, No. 4, July, 2001, pp. 599-607. 14. R.M. Goodall and H. Li, “Solid Axle and Independently-rotating Railway Wheelsets - A Control Engineering Assessment of Stability”, Journal of Vehicle System Dynamics, Vol 33, 2000, pp. 57-67 9 15. Mei, T.X.; and Goodall, R.M. “Stability control of railway bogies using absolute stiffness – Skyhook spring approach”, Vehicle System Dynamics, Vol. 44 Supplement, 2006, 83-92  

Control of Railway Wheelsets – A Semi-active Approach

This paper presents the development of a state observer for the estimation of output torque of an electromechanical actuator in the application of active wheelset control for railway vehicles. The output from the state estimator is essential to ensure that actuator responds appropriately and deliver accurate and fast control effort as demanded to maintain the stability of wheelsets. The formulation and design of the observer is based on the use of the actuator model only, so that it reduces substantially the complexity and difficult uncertainties related to the model of a full rail vehicle. The performance and robustness assessments of the state estimator integrated active control system are carried out with the use of a full bogie vehicle model

Weerasooriya, L

Luo, Y

Weerasooriya, L and Mei, TX and Li, H and Luo, Y (2020) Application ofState Estimators in Active Control of Railway Wheelsets. In: Advances inDynamics of Vehicles on Roads and Tracks Proceedings of the 26th Sym-posium of the International Association of Vehicle System Dynamics, IAVSD2019, August 12-16, 2019, Gothenburg, Sweden.Downloaded from: https://e-space.mmu.ac.uk/626980/Publisher: SpringerDOI: https://doi.org/10.1007/978-3-030-38077-9_6Please cite the published versionhttps://e-space.mmu.ac.ukApplication of State Estimators in Active Control of Railway Wheelsets Lushan Weerasooriya1, T. X Mei1, Hong Li2 and Y Luo3 1 University of Salford, Salford M5 4WT, United Kingdom 2 Manchester Metropolitan University, Manchester M15 6BH, United Kingdom 3 Tongji University, Shanghai, P R China L.Weerasooriya@edu.salford.ac.uk Abstract. This paper presents the development of a state observer for the estima-tion of output torque of an electromechanical actuator in the application of active wheelset control for railway vehicles. The output from the state estimator is es-sential to ensure that actuator responds appropriately and deliver accurate and fast control effort as demanded to maintain the stability of wheelsets. The formu-lation and design of the observer is based on the use of the actuator model only, so that it reduces substantially the complexity and difficult uncertainties related to the model of a full rail vehicle. The performance and robustness assessments of the state estimator integrated active control system are carried out with the use of a full bogie vehicle model. Keywords: Active Wheelset Control, Actuator Dynamics, State Estimators, Torque Sensing 1 Introduction Active control for railway wheelset can help to substantially reduce wear and tear of wheels and track surfaces by lowering creep forces [1]. In the design of such active control systems, in addition to the main wheelset controller, local controllers for the actuators are also used to ensure a fast and accurate delivery of the control effort de-manded by the wheelset control system. However, the feedback of the output torque of the actuators applied at the wheelset can be very difficult to measure reliably in practice due to the harsh working conditions. This study presents the development of a model based approach to provide the estimation of the output torque. The proposed solution does not involve the vehicle dynamics which can be very complex - the design is based on the local actuator dynamics only and the simple measurements of the actuator cur-rent and velocity are used.  There are many previous studies conducted on the use of model based estimation techniques on railway vehicles with actively controlled suspension systems in order to estimate measurements which are difficult/impractical to obtain with readily available sensors. A research has focused on the use of a kalman filter to estimate the cant angle 2 of a track using measurements from accelerometers and gyros mounted on the railway vehicle and wheelset accordingly [2] in both random and deterministic tracks. Another similar study has shown the application of using estimation techniques to obtain lateral displacement and yaw angle of wheelsets along with track condition such as curvature and cant angle [3]. In addition, a research has been done on use of multiple kalman filters to estimate creep coefficients and a kalman-bucy filter for the estimation of creep forces and interpretation of estimates through post-processing  has enabled the detec-tion of lateral and yaw creep forces [4]. Similarly, estimation techniques have been used in a semi-active control system to estimate torque and damping values of a vehicle suspensions [5] where an unscented kalman filter is used in the study to estimate vehicle suspension states such as vertical velocity of stiffness components while its vertical acceleration and stroke velocity are provided as measurable states which assist in de-veloping a sliding mode controller.  In this study, a full active wheelset control scheme involving a wheelset controller and an actuator controller for each wheelset is developed for a full bogie vehicle model with the addition of having a state observer to provide the torque feedback to the actu-ator controller. The observer is developed based on the simple actuator model only, and it does not involve the dynamics of the vehicle which would result in a much more complex solution. The observer is formulated in such a way to consist of two states (the motor speed and toque applied to the wheelset). The measurements of the motor current and speed measurement used for correcting estimation errors in the observer are much easier to obtain accurately and reliably compared to the measurement of the torque out-put at the wheelset. Performance of the state observer is assessed using a full bogie vehicle model with a number of different track inputs including the curves and straight track with irregu-larities. The robustness of the observer is also evaluated to account for the uncertainties and inaccuracies of the actuator parameters used in the observer.  2 Active Control As illustrated in Figure 1, a conventional railway bogie vehicle model with solid-axle wheelsets and with an active wheelset control scheme is used in the study. Only the yaw and lateral dynamic motions [6] of the wheelsets and those of the bogie/body frames are taken into account in this model since the other dynamics such as vertical, pitch and roll movements are largely dynamically decoupled from the plan view motions and therefore not expected to have any substantial effect in this case. In order to assess the performance and evaluate the performances of the observer estimations and its impact on actuator dynamics/controller, a number of different track conditions are used in the study, including a curved track with a curve radius of 300m and a cant angle of 6 degrees at a relatively low speed of 25 m/s and a straight track with generically generated irregularities at the high speed 83m/s.   3                          Fig. 1. Active Primary Suspension – Full Bogie Model   The actuation for each wheelset is provided by an electro-mechanical actuator. As de-picted in Figure 2 below, a DC electrical motor and a gearbox is used as the actuator model in the investigation. Parameters of the actuator such as gear ratio (n), stiffness (Kg) and the damping (Cg) at the gear wheel-load connection is selected after a thorough comparison of the performance to obtain optimum results. Equations 1-4 represent the dynamics of the electrical motor and the mechanical coupling with the wheelset.          Fig. 2. The electro-mechanical actuator   𝐶𝑝2 Front Wheel Set 𝐾𝐿𝑠2 𝐾𝐿𝑠2 𝐾𝑝2 𝐾𝑠2 𝐶𝑠2 Rear Wheel Set Front Bogie Front Half of the Train Body Torque Actuator Torque Actuator 𝐾𝑔     𝑉 𝑖    𝐶𝑚 (Motor Damping)    𝐶𝑔   𝑇𝐿 (Applied Torque)     𝐼𝑚𝑜𝑡𝑜𝑟 + 𝑛2𝐼𝑔𝑒𝑎𝑟      Motor 𝑳𝒐𝒂𝒅  (𝑾𝒉𝒆𝒆𝒍𝒔𝒆𝒕)    4  𝑖?̇? = −𝑟𝑎𝑟𝑚𝑙𝑎𝑟𝑚𝑖𝑎 −𝑘𝑒𝑙𝑎𝑟𝑚𝜃?̇? +1𝑙𝑎𝑟𝑚𝑣𝑎                (1)  (𝐼𝑚 + 𝐼𝑔𝑛2)𝜃?̈? = 𝑘𝑡𝑖𝑎 − 𝑐𝑚𝜃?̇? − 𝑛𝑇𝐿               (2)  (𝐼𝑚 + 𝐼𝑔𝑛2)𝜃?̈? = 𝑘𝑡𝑖𝑎 − 𝑐𝑚𝜃?̇? − 𝐶𝑔𝑛2𝜃?̇? − 𝐾𝑔𝑛2 𝜃𝑚 + 𝑛𝐾𝑔  𝜓𝑚 + 𝑛𝐶𝑔𝜓?̇?     (3)  𝑇𝑜𝑟𝑞𝑢𝑒 (𝑇𝐿) = 𝐾𝑔𝑛 𝜃𝑚 + 𝐶𝑔𝑛 𝜃?̇? − 𝐾𝑔  𝜓𝑚 − 𝐶𝑔𝜓?̇?          (4)   A number of different control strategies such as classical feedback controllers or model based optimal controllers have been previously proposed to provide stability control without interfering the natural curving of the solid axle wheelset [6-9], although there are also control schemes that are proposed to provide steering actions on curves to over-come the constraint on curving caused by passive suspensions [10]. In this study, the concept of absolute yaw stiffness method is applied to generate the torque required to stabilise the wheelsets as shown in Figure 3 while allowing the natural curving move-ments of the wheelsets [9].                Fig. 3. Wheelset Controller and Actuator Controller  Two feedback control loops for each wheelset are used - the wheelset controller gen-erates a torque demand for stabilising the wheelset whereas the local actuator controller ensures the motor to apply the required toque to the wheelset. Because the wheelset stability control is of high bandwidth in nature, the actuator controller is considered essential for the delivering of control efforts with fast and accurate responses.  Yaw Angle (ψ)  Torque  Demand High-Pass Filter Wheelset Controller Actuator Controller Actuator  Wheelset Torque Supplied + - 5 3 State Observers The actuator controller requires the feedback of the actuator output torque applied at the wheelset which is very difficult to measure reliably due to the harsh operating environ-ments of wheelsets. This study develops a model-based approach to estimate the required feedback from sensors that are much more reliable and easier to install. The proposed approach for the design is based on the dynamic relationship between the actuator and the torque applied to the wheelsets using the readily available measurements such motor current, and motor speed. This is a much simplified approach compared with the full state estimation that would also need to include the vehicle dynamics that can be poten-tial very complex.    The simplified observer is formulated to have only two states - the rotor speed of the electric motor (?̇?𝑚) and the torque applied at the wheelset (𝑇𝐿). The output measurement is the rotor speed and there is an additional input of the motor current that is also easily obtainable. The formulation and design process are shown in equations 5-9, where 𝑥 is defined to be the two states and 𝑦 is defined to be the system output while matrices A, B, C, D, G and H represent the dynamics of the system. Furthermore, 𝑤 is considered as the process noise associated with the system, where 𝑤 is represented as 𝑇?̇? , while 𝑣 is representing the noise associated with measurements. 𝐿 is represents the observer gains which are designed using the pole placement technique and β is a parameter which is added to state space to maintain the full rank of the A matrix such that the system is observable. (𝐼𝑚 − 𝑚𝑜𝑡𝑜𝑟 𝑟𝑜𝑡𝑜𝑟 𝑖𝑛𝑒𝑟𝑡𝑖𝑎, 𝐼𝑚 − 𝑔𝑒𝑎𝑟 𝑤ℎ𝑒𝑒𝑙 𝑖𝑛𝑒𝑟𝑡𝑖𝑎, 𝑛 − 𝑔𝑒𝑎𝑟 𝑟𝑎𝑡𝑖𝑜, 𝑘𝑡 −𝑚𝑜𝑡𝑜𝑟 𝑡𝑜𝑟𝑞𝑢𝑒 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡)  ?̇? = [−𝑐𝑚𝐼𝑚+𝐼𝑔𝑛2−𝑛𝐼𝑚+𝐼𝑔𝑛20 𝛽] [?̇?𝑚𝑇𝐴] + [𝑘𝑡𝐼𝑚+𝐼𝑔𝑛20] [𝑖𝑎] + [01] [ 𝑇?̇? ]    (5)   ?̇? = 𝐴x̂ + 𝐵𝑢 + 𝐺𝑤 + 𝐿(𝑦𝑡 − ?̂?𝑡)               (6) ?̂?𝑡 = 𝐶x̂                        (7) 𝐶 = [1  0]                        (8)  𝐿 = [207.34−8.92]                      (9)      6 4 Performance Analysis  4.1 Estimation Assessment  An analysis is performed to compare the actual output torque and the estimated output toque of the actuator to assess the accuracy of the estimations using full bogie vehicles when simulated using both deterministic, random tracks and measured tracks. How-ever, only the behaviour of the first wheelset of the vehicle model is shown since other wheelsets show very similar behaviour. Fig. 4. Estimation Analysis for Deterministic Track – Full Bogie Vehicle  Fig. 4 shows that there are minor errors between the actual and estimated torques when full bogie vehicle is assessed. This can be clearly seen during the areas where the torque is zero and slight difference can be expected due to the process noise and noise associated with the measurement signals.  Fig. 5. Estimation Analysis for Generic Random Track – Full Bogie Vehicle 7  Similar analysis is done with the random track to evaluate the observer performances and there is an approximately 10% of error between the actual and estimated torques, as it can be seen in Fig 5. 4.2  Robustness Assessment  In order to assess the robustness of the observer, key parameters which are difficult to measure and define in a practical environment are varied while observing the perfor-mance of the observer. Thus, internal damping of the motor (𝑐𝑚), motor constant (𝑘𝑡) and the various inertias, such as gear wheel inertia (𝐼𝑔) and motor rotor inertia (𝐼𝑚), is being varied within a reasonable margin (±20%) to evaluate the observer performances. For this analysis, generic random track is being used while the travel speed is 83 ms-1. It is evident from Fig. 6 that the internal damping of the motor does not affect the per-formance of the observer within a reasonable margin.   Fig. 6. Estimation Error vs. Robustness Assessment – Motor Damping    Similarly, the gear wheel inertia is varied by ±20% of the value, for which it is found that observer performance is not affected by this variation as it can be seen in Fig. 7. However, as it can be seen from Fig 8, the motor rotor inertia variation does have an effect though it does not result in any detrimental performance within the op-erational range.   8 Fig. 7. Estimation Error vs. Robustness Assessment – Gear Wheel Inertia  Fig. 8. Estimation Error vs. Robustness Assessment – Motor Rotor Inertia Fig. 9. Estimation Error vs. Robustness Assessment – Motor Constant - 1  9 It is evident from the Fig. 9 that changing of motor constant does pose some affect to the observer performance as the error is increasing significantly (error > 100%) as the effective value is 20% less than the original value. However, when the effective value is 20% higher, estimation error appears to rise approximately 70%. Thus, ob-server gains require to be tuned accordingly on the cases where observer performances are compromised due to motor constant variation.  Further analysis is done to assess the observer robustness while reducing the defined value of motor constant by 10% and it can be seen from Fig. 10 that the observer main-tains its robustness. It is evident form the results that the there is only a minor error increase as the effective value is being reduced by 10%. Thus, it is evident that observer is robust motor constant values where it deviates -10% to + 20% from original/defined value. Fig. 10. Estimation Error vs. Robustness Assessment – Motor Constant - 2  These robustness assessments provides valuable insight in to the state observer per-formances, since, in a realistic environment, it is highly plausible that actuator param-eters to be slightly different from the values used to design the sate observer. This could lead to inaccurate estimations and subsequent instability of the system. However, re-sults of the tests are conducted indicate that the observer is capable of producing accu-rate estimations within a reasonable range of parameter variations since parameter var-iation can be expected to some extent in a realistic situation. 5 Discussions  As it is evident from all the results presented above, it can be concluded that the state observers can serve a significant role in this application since its capability to generate accurate estimations enables the overall system to be more practical and realistic. Anal-ysis of the performance of the model also indicates that there is a high potential of using state estimators in active control of wheelsets with full bogie vehicle while it performed 10 well in both deterministic track and measured and generic (computer generated) and measured random tracks as well. Further reviewing elaborates that estimator has ade-quate frequency response for a similar type other applications which deal with DC mo-tors. Finally, the robustness analysis re-assures the functional capabilities of the estimator under different parameter conditions and provides insight into the effect of each indi-vidual parameter.  References 1. Mei, T.X. and Goodall, R.M., "Recent Development in Active Steering of Railway Vehi-cles", Vehicle System Dynamics Vol 39/6, (2003). 2. T.X. Mei, H. Li and R.M. Goodall, Kalman filters applied to actively controlled railway vehicle suspensions, Transactions of the Institute of Measurement and Control 23,3 pp. 163–181, (2001).  3. T.X. Mei, R.M. Goodall, H. Li, Kalman Filter for The State Estimation of A 2-Axle Railway Vehicle, European Control Conference (ECC) Germany, (1999) 4. C.P. Ward, R.M. Goodall, R. Dixon and G.A. Charles, Adhesion estimation at the wheel-rail interface using advanced model based filtering, (2012). 5. Hongbin Ren, Sizhong Chen, Yuzhuang Zhao, Gang Liu & Lin Yang State observer-based sliding mode control for semi-active hydro-pneumatic suspension, Vehicle System Dynam-ics, 54:2, 168-190, (2016).  6. Stefano Bruni, Roger Goodall, T. X. Mei and Hitoshi Tsunashima, Control and monitoring for railway vehicle dynamics - Vehicle System Dynamics International Journal of Vehicle Mechanics and Mobility, (2007). 7. Pearson, J.T., Goodall, R.M., Mei, T.X. and Himmelstein, G, Active stability control strat-egies for a high speed bogie. Control Engineering Practice, 12, 1381–1391 (2004). 8. T.X. Mei And R.M. Goodall, Modal Controllers for Active Steering of Railway Vehicles with Solid Axle Wheelsets, (2000). 9. T. X. Mei and R. M. Goodall, Stability control of railway bogies using absolute stiffness – skyhook spring approach, (2006). 10. Shen, G. and Goodall, R.M., Active yaw relaxation for improved bogie performance. Vehi-cle System Dynamics, 28, 273 – 289, (1997)   

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