DYNAMICSOFRAILWAYFREIGHTVEHICLES

IwnickiS.D.1,StichelS.2,OrlovaA.3,HechtM.4

1. InstituteofRailwayResearch,UniversityofHuddersfield,Huddersfield,UK2. DivisionofRailwayVehicles,KTHRoyalInstituteofTechnology,Stockholm,

Sweden3. PetersburgStateTransportUniversity,St.Petersburg,Russia4. FachgebietSchienenfahrzeugeamInstitutfürLand‐undSeeverkehr,Technische

UniversitätBerlin,Belin,Germany

Keywords:Freightwagon;Vehicledynamics;Computersimulation;RailFreight;RunningGearDesign;FreightBogies

Abstract

Thispapersummarisesthehistoricaldevelopmentofrailwayfreightvehiclesandhowvehicledesignershavetackledthedifficultchallengesofproducingrunninggearwhichcanaccommodatetheveryhightaretoladenmassoftypicalfreightwagonswhilstmaintainingstablerunningatthemaximumrequiredspeedandgoodcurvingperformance.Themostcommoncurrentfreightbogiesaredescribedindetailandrecentimprovementsintechniquesusedtosimulatethedynamicbehaviourofrailwayvehiclesaresummarisedandexamplesofhowthesehavebeenusedtoimprovefreightvehicledynamicbehaviourareincluded.Anumberofrecentdevelopmentsandinnovativecomponentsandsubsystemsareoutlinedandfinallytwonewdevelopmentsarepresentedinmoredetail:theLEILAbogieandtheSUSTRAILbogie.

1 IntroductionFromtheirinceptionrailwayshavebeenpredominantinthecarriageofbulkgoodsandrailwaywagonshavebeendesignedtoallowthistobeeffectedefficientlyondifferenttypesofrailwayinfrastructure.Inmorerecenttimeswithchangesinindustrialneedsandcompetitionfromroadandairtransportrailwayshavecarriedaneverdecliningshareoffreight.Althoughthereissomeevidenceinsomecountriesthatthistrendhasstartedtochangerecentlyduetoroadcongestionthereisstillnotyetawidespreadevidenceofamajormodalshiftfromroadtorailwhichpoliticianshaveindicatedisdesirable.ForexampletheEuropeanTransportWhitepaper2011[1]setsatargetformodalshiftof30%by2030and50%by2050fromroadfreighttoothermodessuchasrailorwaterbornetransportfordistancesover300km.

Thebarrierstothisincreasedmodalshiftfromroadtorailseemtobelargelyduetotherequirementsfrommodernshippersforshorterend‐to‐endtimesbutevenmorethedemandisforhighreliabilityofserviceandforadditionalfeaturessuchastrackingandtracingofshipments,securityandtemperaturecontrol.AsHecht[2]pointsoutthelowerspeedsforrailfreightcomparedwithpassengerservicesarenotmainlyrelatedto

lowervehiclespeedcapabilitybutaremoreduetothefactthatfreighttrainsoftentravelonlowerspeedlinesorareheldforpassengertraffictopassandduetocomplexandlengthyshuntingandhandlingoperationsandmotivepowerandcrewchanges.

Neverthelessiffreightvehiclespeedsandaccelerationandbrakingcapabilitiescouldallowthemtobefullyintegratedwithpassengertrafficthiswouldbringastepchangeinendtoendfreighttrainspeedsaswellasoverallsystemcapacity.Akeyfactorinobtainingthisincreasedspeedistoensurethatthedynamicperformanceoffreightvehiclescanallowsafeandreliableoperationontrackwithdifferentlevelsofirregularitiesandsupportconditions.Runninggearhasevolvedwiththeexperienceofoperationondifferentrailwaysandmorerecentlytheuseofcomputersimulationtoolsandseveralstandardiseddesignsarenowubiquitous.Severalresearchprojectsandteamshaverecentlybeentryingtoadvancefromthispositionusinginnovativedesignsadaptedfrompassengervehiclesorusingothernoveltechniques.Theuseofcomputersimulationsisnowestablishedfordesignofrunninggearandisalsobecomingacceptedaspartofthevehicleacceptanceprocessesinmanycountries.

2 Earlydevelopmentsoffreightwagons

2.1 BackgroundDesignersoffreightvehiclerunninggearfacemanychallengesbutnotleastoftheseisthefactthattheratiooftheladentotaremassofafreightvehiclecanbeasmuchas5:1comparedwithamoremanageable1.5:1fortypicalpassengervehicles.Thiseffectivelymeansthatthesuspensionsystemhastobedesignedfortwodifferentvehicles(andeverystageinbetween).Anumberofcleverdesignshaveevolvedovertheyearsandthemostsuccessfulofthesearenowsummarised.

2.2 UICdoublelinkFreightwagonswithlinktypesuspensionshaveexistedformorethan100years,ascanbeseeninfigure1,andthelinksuspensionisprobablystillthemostcommonsuspensiontypefortwoaxlefreightwagonsinEuropetoday.Asearlyas1890theprincipleofthelinksuspensionwasdefinedasastandard.Areviewoffreightwagonswithlinksuspensioncanbefoundin[3].

Figure1:FreightwagonfromKockumsSweden,builtin1882[4].

AfterWorldWarIItheUICdoublelinksuspensionwasdefinedasastandard[5].Inthebeginningofthe1980sanumberofimprovementsweremade.Theaxleloadwasincreasedto22.5tonnesandtheparabolicleafspringwasintroducedasstandardcomponent[6],[7].TheUICdoublelinksuspensioninfigure2mainlyconsistsofthreeparts:Leafsprings,linksandaxleguards.Thevehicleisconnectedtotheparabolicorleafspringbydoublelinks.Theleafspringrestsontheaxlebox.Thisarrangementallowstheaxleboxtomoveinboththelongitudinalandlateraldirectionrelativetothewagonbody.Theaxleguardrestrictsthehorizontalmotionoftheaxlebox.Theprincipleofthesuspensionisthatofapendulum.Inthelongitudinaldirectionthesuspensionlinksareinclined,whereasinthelateraldirectiontheyareinaverticalplanewhenthevehiclebodyisinnominalposition[1],[8],[9],[10].Thecharacteristicsofthedouble‐linksuspensionarequitecomplex.ThemaincomponentsareshowninFigure3.

Figure2:UICdoublelinksuspension.

Figure3:Doublelinksuspension[8].Partsofdoublelink(a),assembleddoublelink(b)andmounteddoublelink(c).

Oneofthemainadvantagesofthelinkrunninggearisthatitissimple,robustandcheapandalsotakesuplittlespaceinbothlateralandverticaldirections.Bothstiffnessanddampingareprovidedbyonesystemandareloaddependent.Thequasistaticcurvingperformanceofthesingleaxlerunninggearwithlinksuspensionisgood.Foratypicaltwo‐axlefreightwagonwithawheelbaseof9mondryrailsgoodsteeringperformancedownto300mcurveradiuscanbeachieved[10].

Therunningbehaviouroftwo‐axlefreightwagonswithlinksuspensioncanberatherpoormainlyduetovehiclehunting.Theamountofdampingprovidedinthehorizontalplaneisoftennotsufficient.Additionallythecharacteristicsofthesuspensionchangeduringthelifeofthevehicle,duetosuspensionwear,andwiththerunningconditions[10].Thelinksuspensiontakesquitealotoflongitudinalspaceandisapoorisolatorforsoundandvibration.

2.3 LinksuspensionbogiesTheleafspringandlinksuspensionofthesingle‐axlerunninggearhasalsobeenusedonbogiessinceabout1925[1].Morerecentlyithasbeenstandardisedwithforexamplebogietype931(figure4),developedinthe1950sbyDeutscheBahnwithawheelbaseof2000mmandawheeldiameterof1000mm.Thisbogiewasdevelopedtorunat100km/hwithanaxleloadof20tandwasthefirstbogiestandardisedbyUIC[6],[7].

Figure4:.DBbogieType931[7].

Inthebeginningofthe1980sDBbogietype665wasintroducedwithnewfeatureslikeparabolicleafsprings,22.5tpermissibleaxleloadandshorterlinksasshowninfigure5[7].

Figure5:DBbogieType665[7].

Thebogieframeisaweldedsteeldesignbutinsomeplacesforgedcomponentsareused.Theframeisconnectedtoparabolicortrapezoidalleafsprings,thatrestontheaxlebox,beingconnectedbyswinglinks.Nominallythesuspensionlinksarepositionedinalongitudinalverticalplaneandinclinedinthisplane.Duringvehicleoperationthelinksswinginthatplaneandalsolaterally[1],[6],[7],[11].Asphericalcentre‐pivotandtwosidebearersconnectthebogieframeandthewagonbody.Thesidebearerscanbeeitherrigidorverticallysuspendedandhavethreefunctions:

toactasstaticsupportforthecarbody. toactasrollstiffness. toprovidefrictiondampingbetweencarbodyandbogie

Thequasistaticcurvingperformanceofabogiewithlinksuspensionisgenerallyverygooddueto:

theshortwheelsetdistanceinthebogieof1.8m. thesoftlongitudinalprimarysuspension.

Evenifshortlinks(higherstiffness)areusedinsteadofthelonglinksthecurvingperformanceisstillgood[11].Thesoftsuspensioneffectivelyisolatesthebogieframefromthemotionofthewheelsets.Adisadvantagethatcanbementionedisthattheweightofabogiewithlinksuspensionisabout100kghigherthantheweightofaY25bogie.Furthertherunningbehaviourontangenttrackcannotberegardedasgoodeventhoughexistinglimitsfortrackforcesandrideindexareingeneralnotexceeded.Thedynamiccurvingperformancecanbecritical.Thesuperpositionofquasistaticanddynamiclateralaccelerationscancauserepeatedbumpstopimpactswhenthevehicleishuntingincurveswithcantdeficiency,becauseofthesoftlateralprimarysuspension[11],[12].

2.4 TheY25StandardBogieMostrailwayvehicleshavebogiesortruckswhichallowlongervehiclessupportedontwobogieswhilestillkeepingattackanglesbetweenwheelsandrailincurvestoreasonablelevels.Thisarrangementalsoallowstwostagesofsuspensionwiththe‘primary’suspensionbetweenwheelsetandbogieandsecondarysuspensionbetweenbogieandcoachorwagonbody.Theprimarysuspensioncanisolatethebogiefromshortwavelengthirregularitieswhilethesecondarysuspensiondealswiththelongerwavelength,lowerfrequencyexcitations.

Aspreviouslymentioned,aspecificchallengefordesignersoffreightvehiclerunninggearisthelargedifferencebetweentareandladenvehiclemass.IntheY25bogieprogressivedampingwithverticalloadiseffectedbytheuseof‘Lenoirlinks’whichtakepartoftheverticalloadthroughanangledlinkandapusherontoaverticalfrictionsurface.Thisgivesalevelofdampingwhichisbroadlyproportionaltothevehiclemass.TheY25bogiedesignoriginatedinFrancein1948andwasstandardisedbytheOREsteeringcommitteein1967.Itisshowninfigure6.

Figure6:AY25typebogie

ThedesignhasbeenhugelysuccessfulandY25typebogiesarethemostpredominantfreightbogieinEurope.

2.5 ‘three‐piece’FreightBogiesThethree‐piecebogieswerefirstdevelopedin1930sandseemedtooriginatesimultaneouslyintheUSA(Barberbogie)andtheSovietUnion(Haninbogie).Nowthethree‐piecebogieanditsmoresophisticateddescendentsarethemostcommonsuspensionforfreightwagonsacrossNorthandSouthAmericas,CIScountries,China,Africa,IndiaandAustralia.Maximumaxleloadsrangebetween7and36t.Themostcommonstandardsforthree‐piecebogiesareAAR[13]for1435mmgaugeandGOST[14]for1520mmgauge.Areviewofthree‐piecebogiescanbefoundin[15].

TheRussianmodel18‐100bogieshowninfigure7isagoodexampleofanearlytypeofthree‐piecebogie.Theterm‘three‐piece’referstothedesignofthebogieframewhichconsistsofthreeinterconnectedparts:twosideframesandonebolster.Theframepartsareusuallycast.

Thebogieisequippedwithcentralsuspensionbetweenthesideframesandthebolsterthatconsistsofasetofspringsandwedgefrictiondampersworkinginverticalandlateraldirectionandkeepingtheframesquare.Thesideframeswiththeirflatsurfacesrestontheaxle‐boxes(orbearingadapters).Thesizeoftheopeninginthesideframeprovidesclearancesinlongitudinalandlateraldirectionwithinwhichtheaxle‐boxmovesresistedbydryfrictionforces.Thecarbodyrestsontheflatcenterbowl,itsrollmotionrelativetothebolsterislimitedbysidebearerswhichareusuallystiffverticalstopsincludingclearancewhenthewagonbodyisinthecentralposition.

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Figure7:Model18‐100bogie:a–generalview,b–centralsuspensionscheme,c‐primary‘suspension’scheme(1–wheelset;2–sideframe;3–bolster;4–brakingleverage;5–centralpivot;6–rigidsidebearings;7–suspensionsprings;8–frictionwedge;9–axle‐box)

Thethree‐piecebogieisaveryrobustdesignwiththeadvantageofbeinglowcostinproduction,operationandrepair.Thefollowingitemsareconsideredasdisadvantagesoftraditionalthree‐piecebogieandattemptshavebeenmadetoaddresstheseinitsfurtherdevelopments[15],[16],[17]:

Limitedcriticalspeedoftheemptywagon)withswayoscillationofcarbodybeingthemajorlossofstabilitymode);

Wheelflangecontactincurvesproducedbywarpingbetweensideframesandbolster;

Sideframesaddingtotheunsprungmassandthusincreasingtrackimpactonshortwavelengthirregularities;

Deteriorationofrideperformancewithwearoffrictionwedgesandotherfrictionsurfaces.

3 ComputersimulationComputersimulationoffreightvehiclesisnotatallascommonasforpassengervehicles.SincemanyoftheEuropeanfreightvehiclesarestandardizedverylittlenewdevelopmenthasbeencarriedoutandthemanufacturersdoingeneralnotperformasimulationanalysisoftherunningbehaviouroffreightwagon.However,inseveralresearchgroupsatuniversitiesandresearchinstitutesandatsomeconsultingcompaniescomputersimulationoffreightvehiclesisnowperformed.

Sincemanufacturersdonotusuallybuildsimulationmodelsoffreightvehiclesthemselvesoneofthemainchallengesinmodellingafreightwagonistoobtainallthe

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inputparametersrequired.Anotheraspectisthatmostsuspensionelementsarestronglynon‐linearandinmanycasesevenmathematicallynon‐smooth.Thismakesitverydifficulttobuildupsimulationmodelsthatprovidegoodresultscomparedtomeasurementresults.Someofthephenomenaobservedduringsimulationoffreightvehicleswillbediscussedbelow.

Further,asdescribedinSection3.1,thecharacteristicsofthesuspensionelementscanvaryduringoperationduetowearorenvironmentaleffectssuchasforexamplesurfacecontaminationchangingthefrictioncoefficientinslidingsurfaces.

Themainpurposeofsimulationstudiesoffreightvehiclesisveryoftenastabilityanalysis(seeSection3.2)oraninvestigationofthecurvingbehaviourofthefreightwagon(seeSection3.3).Sincetheaxleloadsoffreightwagonsareusuallyhigh,theinvestigationofwheelorrailwearandrollingcontactfatigueisoftentheprimaryreasonforasimulationstudyincurves.

3.1 SuspensioncomponentsThesuspensioninmostfreightvehiclesreliesonfrictiondamping.Frictionelementsarelowcost,requirelittlemaintenanceandareusuallyloaddependent.Thismeansthattheleveloffrictiondampingchangeswithaxleload,animportantfeatureinfreightwagonsduetothehightaretoladenratioalreadymentioned.Surveysofmodellingoffrictioncomponentsinfreightwagoncanbefoundforexamplein[18]‐[22].Papers[18]and[19]aregeneralreviewsofrailvehiclesuspensioncomponents,while[20]isfocusedonfreightvehiclesandalsodiscussesissuessuchasstabilityandcurvingoffreightvehicles.Papers[21]and[22]arefocussedonmodellingfrictionwedgesofthree‐piecebogies.AlsointheproceedingsfromtheEuromech500colloquium[23]manyvaluablecontributionsonthetopicofnon‐smoothsuspensionelementscanbefound.Variousarrangementsofsuspensionelementstosimulatevehiclesuspensionsaredocumentedin[24],[25].

3.1.1 FrictiondampingInmostfreightvehiclesimulationmodelsfrictionismodelledasdryCoulombfriction,wherethefrictionforceisproportionaltothenormalload.Thefrictioncoefficientisassumedtobeconstant,seeforce‐deflectioncurveinfigure8,left.ThedisadvantageoftheCoulombmodelisthatitisnon‐smooth,i.e.multi‐valuedandnon‐differentiable.Anotherwaytomodelfrictioniswithalinearspringinserieswithafrictionsliderasinfigure9withtheresultingforce‐displacementcharacteristicinfigure8,right.Sincemostfrictiondamperarrangementshaveafiniteflexibility,suchmodelscouldalsoberegardedasmorerealistic.Note,howeverthatthemodelwithaspringinseriesisstillnon‐smooth.Toavoidthedifficultiesmentionedaboveregularizationmethodsareoftenapplied,seeforexample[26],[27]and[28].

Figure8:Force‐displacementcurveofCoulombfrictionmodel(left)andCoulombmodelwithspringinseriesasin[29](right).

Figure9:Frictionelementwithspringinseries.

Piotrowskidevelopedanon‐smoothrheologicalmodel[29],[30],whichemploysthenotionofthedifferentialsuccessioninvolvingacontingentderivativeofthenon‐smooth,multi‐valuedcharacteristicsofCoulombfriction.TanandRogers[31]proposedequivalentviscousdampingmodelstoavoidthenumericalproblemsofCoulombfriction.Theyclaimthatthissubstitutionworksverywellforcaseswhereslidingmotionspredominate.

Inmanyrunninggeararrangementstwo‐dimensionalfrictionelementsareneeded,e.g.intheY25andinthethree‐piecebogie.Inthesedesignsmotionsintwodirectionstangentialtothefrictionsurfacesarepossible.Two‐dimensionalCoulombfrictionmodelscanbefounde.g.in[32],[33].

Anotherphenomenonthatisimportanttotakeintoaccountisstochasticexcitationsthatsmooththedryfrictiondamping.Alsomidfrequencyexcitationgeneratedinthewheelrailcontact–oftencalleddither–cansmoothendryfrictionandthereforehaveasignificantinfluenceonthesimulationresults,seeforexample[30],[33].

TrueandAsmund[33]investigatedtheeffectsofdryfrictioninthesuspensionofasimplefreightvehicle.Theyusedarelativelysimplemodelofdryfrictionandfoundthatthestablebehaviourforthesystemwithfrictionexhibitedalaterallyoscillatingmotionwhichmakesthesystemsensitivetoexternalperiodicforcing.

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3.1.2 Wagonswithlinksuspension

3.1.2.1 Basicmodelofleafspringandlinksuspension

Leafspringsareoftenusedasverticalsuspension.Inmultibodysimulationmodelstheyareusuallyregardedasrigidinboththelongitudinalandlateraldirections.Fordynamicdisplacementsaroundastaticequilibriumpositionleafspringsarecharacterizedbyarelativelyhighstiffnessforsmalldisplacementsandasignificantlylowerstiffnessforlargerdisplacement,(figure10).LeafspringsaredescribedintheOREreports[34],[35].

Figure10:Typicalforce‐displacementdiagramofleafspring/linksuspension.Exampleofcurveforsmalldisplacementsaroundstaticequilibrium.

Sincelinksuspensionsshowverysimilarcharacteristicstheyareoftenmodelledinasimilarwaytoleafsprings,atleastforthelaterallinkbehaviour.Theinitialhigherstiffnessk1inleafspringsiscausedbyfriction,i.e.theleavesofaleafspringsticktogetherforsmalldisplacementsandstarttoslideoneachotherforlargerdisplacements.Inthesamewaythelinkrollsintheendbearingaslongasthereisnoslidinginthecontactarea.Thelowerstiffnessk2isthevalueforslidingintheleafspringorthesocalledpendulumstiffnessofalink.TheforceFddeterminestheamountofdampinginthehysteresis.Acommonlyusedmodeltorepresentthetwodifferentstiffnessvalueswiththehysteresisistousealinearspringandafrictionelementinseries,inparallelwithanotherlinearspring,asshowninfigure11.Itshouldbetakenintoaccountthatthecharacteristicsofleafspringsvaryduetowearinrunningordeteriorationorlubricationstate.

Thethreeparametersinthemodeldescribedabovecanbederivedfrommeasurements.Thismodel,however,issimplifiedsincetheshapeofthehysteresiscurveisusuallyroundedasshowninfigure10.Measurementresultsandmoredetaileddescriptionsoflinksuspensionscanbefoundin[34]‐[48].

Figure11:ModelforleafspringorlinksuspensionasusedforexamplebyKTH[40].Seefigure10fordefinitionofk1andk2.

3.1.2.2 AdvancedsimulationmodelsForlateraldisplacementsofadouble‐linkallfourjointsareassumedtostarttoslideatthesametime;thereforethemodelinfigure11issufficient.Inthelongitudinaldirection,however,itismorelikelythatthejointsstarttoslideatdifferentdisplacementsasshowne.g.byPiotrowski[29].Heusesasetoffourslidersandspringelementswithdifferentbreakoutforcesinparalleltodescribethesecharacteristics.AlsoinamodelusedbyStiepelseveralelementsinparallelareused[44].

Togiveabetterrepresentationoftheroundedshapeofthehysteresiscurves,Fancherdevelopedamodelfortruckleafsprings[45],[46]usingexponentialexpressions.Jönsson[42]usedasimilarapproach,wherethetotalforceoverthesuspensioncomponentisseparatedintopiece‐wiseelasticandfrictionforces.Themodelisusedforbothleafspringsanddouble‐links.

Anotherpossibilitytodescribehysteresiswithroundedshapeforlinksuspensionsistouserollingcontacttheory,whichhasbeenproposedbyPiotrowski[33].Basedontheslipvelocitythecreepageinthecontactiscalculated.

3.1.3 Modellingthethree‐piecebogie

3.1.3.1 ModelsofthecentralsuspensionMostoftheresearchinmodellingthree‐piecebogies,suchas[21],[22],isfocussedonthecentralsuspensionelementofthethree‐piecetruckthatprovidesdampingwithfrictionwedges.Earlymodelsoffrictionwedgesuspensionsrecognizedonlyverticalload‐dependentfrictionforce,latermodelsincludedtwo‐dimensionalfrictionintheverticalandlateraldirections[46],[50].

Thefirstapproachtoaccountforpossibleangularandlongitudinaldisplacementsofbolsterrelativetothesideframesistointroducewarpingandlongitudinalnonlinear

resistancecharacteristicsintothemodel,asitisdonein[15],[17].Insuchcasethewedgesarenotmodelledasseparatebodies,buttheequivalentforceagainstdisplacementcharacteristicsareintroducedaccountingforwedgeparameters,suchasinclinationangle,widthoftheverticalsurface,widthoftheinclinedsurface,frictioncoefficientsoninclinedandverticalsurfaces,etc.

Thesecondapproachtoaccountforallpossibledegreesoffreedombetweensideframeandbolsteristointroducemultiplecontactpointsmappedalongtheedgesofthewedgewithtwo‐dimensionalfrictionforceelementsineachofthem.SuchanapproachwasusedbyBallewetal[46],itisimplementedinsimulationtoolssuchasVAMPIRE[52],andtheUniversalMechanismsoftware[52].Numerouscontactelementsrequireanefficientnumericalsimulationalgorithmtobeimplementedintothesoftwarethatprovidesfastsolutiontoresultingstiffsystemofequations,suchastheonedevelopedbyPogorelov[57].Thewedgesaretreatedasmassless.Contacttypemodelsallowthestudyofsuchcomplicatedphenomenonasunevendistributionofcontactforcesoverthewedgesurfaces,implementationofresilientpadsonwedgesurfaces,jammingandwedging[54].Inpaper[56]theauthorsincludedthemassofthewedgeintoconsiderationtostudyitsdynamicproperties.

3.1.3.2 ModelsoftheaxletosideframeinteractionInthefirstapproachsimilartofrictionwedgestheaxletosideframeinteractioncanbedescribedbynonlinearequivalentcharacteristicsasin[15],[17].Thedryfrictioninteractionbetweentheaxleboxcrownandthesideframepedestalismodelledbytwodimensionaldryfrictionelementinparallelwithanothernonlinearelementthatdescribesbumpstopsinlongitudinalandlateraldimension.Atypicalcharacteristicofthebumpstopelementispresentedinfigure12.Toimprovenumericalintegrationthetransitionfromclearancetobumpstopisoftensmoothed.

Iftheinteractionbetweenthecrownandpedestalisaflatsurface,thenitswidthcanresultinrollstiffnessthatisproducedbygravity.Suchstiffnesscanbeintroducedintothemodeldependingontheaxleload.

Figure12Modelforbumpstopelement(∆‐clearance, –stiffnessofthebumpstop)

Thesecondapproachistointroducemultiplecontactpointsontheedgesofthecrownwithtwo‐dimensionalfrictionelementsinthem.Thebumpstopsarethenalsothecontactelementsbetweentheaxleboxoradapterandthestopsinthesideframejaws.Suchapproachisusedin[57]aswellasinUniversalMechanismsoftware[52].

3.1.3.3 ModelsofthecentrebowlandsidebearersThesameapproachescanbeappliedtomodelsofthecentrebowltocentreplateinteractionandatthesidebearers.

Inthefirstapproach,see[15],[17],centreplatetocentrebowlinteractionworkssimultaneouslyasonedimensionalyawfrictionandnonlinearrollandpitchtorquewithsoftcharacteristicsasshowninfigure13.Knowingtheclearanceinthesidebearersthenonlinearrollcharacteristiccanbelinearized.

Figure13Modelforcenterplateelement(∆‐distancebetweencenterplateedgeandcarbodycenterofgravity, –rollangle, –weightofthecarbodyperonecenterplate, –rolltorque, –equivalentrollstiffness)

Thesecondapproachistointroducemultiplecontactpointsontheedgesofthecentreplatewithtwo‐dimensionalfrictionelementsinthem.Theinteractionwiththecentrebowlrimisthenalsothecontactelements.Suchanapproachisusedin[57]aswellasinUniversalMechanismsoftware[52].

3.2 StabilityFreightvehiclesinmostcasesoperateatmuchlowerspeedsthanpassengervehicles.Typicalrunningspeedsareataround100km/h.Thissuggeststhatstabilityinvestigationsarenotasimportantasforfasterpassengervehicles.Ontheotherhandfreightvehiclesoftenaremuchlessdampedthanpassengervehiclesandstabilityinvestigationsarethereforenecessary.Severalofthewagontypesintroducedabovecan–inunfavourablerunningconditions‐showsignificanthuntingbehaviouratspeedsaslowas70km/h.

Inabogievehiclebasicallythreetypesofhuntingmotioncanarise:

Wheelsethuntingwhereonewheelsetperformsthehuntingmotion.

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Bogiehuntingwhereawholebogieistakingoverthehuntingmotion. Carbodyhuntingwherethecarbodyperformsayawmotionandthetwobogies

mainlyfollowthecarbodywithlateralmotions,i.e.thewholevehicletakesoverthehuntingmotion.

Carbodyhuntingisoftenatypeofresonancephenomenon,wheretheKlingelhuntingfrequencygivenmainlybyvehiclespeedandconicityinthecontactcoincideswiththeyaweigenfrequencyofthecarbody.

Huntingmotionwithanon‐zerolimitcycledependsonthewheel‐railgeometry,thesuspensionandthemassesandinertiasofthevehicle.Sincethemassandinertia,andinmostcasesthesuspensionstiffnessanddampingofthefreightwagonwillsignificantlychangewithload,thetypeofhuntingmotionobservedusuallydiffersbetweenanemptyandaloadedwagon.Sincethestiffnessvaluesbetweenaxleboxandbogieframe(inabogievehicle)arelowerinanunloadedvehicle,theriskforwheelsetorbogiehuntingishigher.Inloadedvehicles,vehiclehuntingcanoftenbeobserved.Sincethefrequencyofwheelsethuntingisusuallylow(typicallybetween1and2Hz)thewheelrailforcesinducedarerelativelylowandinmostcasesbelowthelimitvaluesstipulatedinstandards.Therefore,thevehicledesigninrealityallowsforthecarbodyinstabilitytohappeninsomeconditions.Otherwisethesuspensionneedstobesostiffthatthecurvingperformancewouldsuffer,andtheamountofwearandRCFwouldincreasesignificantly.Theriskofcarbodyhuntingcanvarywiththetypeofloadsincethiscaninfluencetheyaweigenfrequencyofthecarbody.

Duetothesignificantinherentnon‐linearityandnon‐smoothnessofthesuspensionelementslinearizationofthemodelsisusuallynotrealistic.Itisthereforenecessarytoperformtimesteppigintegrationwiththefullnon‐linearmodel.Thetaskisingeneraltofindthenon‐linearcriticalspeedvBofthewagonascanbeseeninthegenericbifurcationdiagraminfigure14.

Figure14:Genericbifurcationdiagram

Incomplexmodelsitisverydifficulttofindtheexactcriticalspeed,forexamplewithapathfollowingmethod[58].Thereforeotherengineeringmethodsareused.Onepossibilitythathasbeensuggestede.g.byPolach[59]istoexcitethevehiclewithaninitialdisturbancethatcaneitherbedeterministicorstochastic.Aftertheinitialdisturbancethevehicleisrunonidealsmoothtrack.Iftheoscillationvanishesthevehicleisregardedasstable.Thesimulationshavetoberepeatedwithincreasingspeeduntiltheoscillationsdonotdisappear.Inthatcasethenon‐linearcriticalspeedvb(figure15)isreached.Ariskwiththismethodisthattheinitialdisturbanceisnothighenoughtoinitiatealimitcycleoscillationandthatthecriticalspeeddetectedishigherthantherealnon‐linearcriticalspeed.

Anothermethodtodetectthenon‐linearcriticalspeedisstartthesimulationsataveryhighspeedtobesurethatthevehiclehasreachedthenon‐zeroattractor(limitcycle).Thenthespeediscontinuouslyreduceduntilthelimitcyclebehaviourdisappears.Polachalsodescribesthismethod.IthasbeenusedforexamplebyBoronenkoetal[15]totunethesuspensionofthree‐piecebogies.

Asimilarmethod,showninfigure15,issuggestedin[60]todeterminetheso‐callednon‐linearcriticalspeed.ThedifferencetothemethodintroducedaboveisthatthespeedisnotreducedcontinuouslybutindiscretestepsassuggestedbyTrue[98].

Figure15:Proceduretofindthenon‐linearcriticalspeed[60].

Figure16showsthebifurcationdiagramforaloadedtwo‐axlevehiclecalculatedwiththismethod.Itcanbeobservedthatonlythestablebranchesofthebifurcationdiagramcanbedetermined,nottheunstablepart.Thezerosolutionisalsopossibleatleastuptoaspeedof120km/h(boldsolidline).Thiswassimulatedusingtheprocedureabove,startingfromlowspeedandincreasingthespeedstepwise.

Figure16:Bifurcationdiagramforaloadedtwo‐axlevehiclewithlinksuspension(21taxleload)Wheel:somewhatwornS1002.Rail:NominalUIC60[42].

Hoffmanalsoinvestigatedthestabilityofatwo‐axlewagonwithlinksuspension[43],[61].HeusesthelinkmodeldevelopedbyPiotrowski[29].TheleafspringsmodelisbasedonFancheretal[46].Figure17.showsattractorsfortwodifferenttypesoffreightwagons.Theresultsareinprinciplequitesimilartothoseinfigure16.

Figure17:AttractorsfortheHbbills311andtheG69freightwagons.ThemodelwiththemeasuredcharacteristicsoftheUIClinksisdampinglessthanthemodelwiththecylindricalcharacteristics.Thehuntingattractorexistsevenforlowspeeds[61].

Gialleonardoetal[62]extendedthistypeofstabilityanalysisforatwo‐axlewagonwithlinksuspensiononcurvedtrack.Ascanbeseeninfigure18.theleadingwheelset(ylw)

showsmuchsmalleroscillationamplitudesthanthetrailingwheelset(ytw)andthecarbody.Thisisbecausetheouterwheeloftheleadingwheelsetexperiencesflangecontact.Ingeneraltheresultsshowthepresenceoflargeperiodicoscillationsinnarrowcurvesatcommercialoperatingspeeds.Itisalsoshowninthepaperthatthecouplingforcesbetweenwagonassembliessignificantlyreducetheoscillationamplitudes.

Figure18Mapoflateraloscillationamplitudeinsinglewagonasfunctionofcurveradius[62].

Zhaietal[63]extendedthestabilityanalysisforafreightwagonwiththree‐piecebogiestoalsoincludeavisoelastictrackstructure.ThestabilityanalysisisperformedaccordingtothemethodologysuggestedbyPolach,whichisexplainedabove.Theauthorsfoundthatalowercriticalhuntingspeedisobtainedonelastictrackcomparedwiththerigidtrackcase.Thedifferenceinthecriticalhuntingspeedsbetweentheelastictrackbaseandtherigidtrackbaseis4.4%fortheloadedfreightcar.

3.3 CurvingAsindicatedabovesimulationsoftherunningbehaviouroffreightwagonsincurvesareoftenperformedtoinvestigatetheriskofwheelwearandRollingContactFatigue(RCF).

Forpassengervehiclescurvingsimulationsareoftenperformedonidealtrack,i.e.thestochastictrackirregularitiesareneglected.Authorsareinthiscaseinterestedinthequasistaticbehaviourofthevehicle,i.e.themeanwheelsetattackanglesorthemeanenergydissipationinthecontactpoints.Forfreightvehicleswithnon‐linearandnon‐smoothsuspensionthiscanleadtosignificantmistakesasshownintheexamplefromJönsson[42].Onidealtrackthefrictionsurfacesmightsticktogetherandforcethewheelsetintoamoreunfavourableposition.Trackirregularitieshelptogetrelativemotioninthefrictionsurfaces,whichusuallyleadstobetter–andmorerealistic–steeringbehaviourofthevehicle.Asseeninfigure19,theenergydissipationasa

measurefortheamountofwearorRCF,ismuchlowerwhensimulatingrunningwithtrackirregularities.

Figure19:Energydissipation.Comparativesimulationwithandwithouttrackirregularities.Two‐axlevehiclewithlinksuspension.22.5taxleload[42].

Inoneoftheirnumerousstudiesonthree‐piecebogiesBoronenkoetal[15]investigatethereasonforexcessiveflangewearinsomeoftheRussianwagons.Oneconclusionisthatthemainreasonforflangewearistheunstablebehaviourofthebogiesincurves(ruttingmode)[16],whenthebogieisflangingwithatwo‐pointcontactsituationinsteadofnegotiatingthecurveusingthewheelconicity.Theflangingistheresultofbogiewarping,whichincreasestheangleofattackcomparedtoaradialposition.Inthearticleanumberofdifferentdesignsarediscussed.Amongothersitisconcludedthatabogiedesignwithradialarmssignificantlyreducestheangleofattackandthewearnumberincurves,seefigure20.

Figure20:Angleofattack(a)andwearnumber(b)forwagonsinacurveof200mradiusat60km/hwith18‐100bogiesrespectivelybogieswithradialarmupgrade[15].

Berghuvud[64]investigatedthecurvingbehaviourofdifferenttypesofthree‐piecebogiewithandwithoutbraking.Heconcludedthattheinfluenceofbrakingonthecurvingbehaviouriscomplex.Brakingcanhaveapositiveeffectontheangleofattackofthewheelsetsinacurvesinceithelpstoovercomethestaticfrictionintheprimarysuspension.Itcanalsoincreasetheangleofattackiflargelongitudinalforcespushthewheelsetlongitudinallytowardsthelimitoftheplayandthuslockthewheelsetinanunfavourableposition.

3.3.1 VehicleResistanceRadiallysteeringbogiesdonotonlyreduceflangewearincurvesbutalsoreducetherequiredtractionenergy.

Figure21:Y25bogierunningina300mcurve

Wheelsliplateralandlongitudinalatallwheelrailcontactpoints,90ttankcarwithaY25‐Bogieina300mcurve,speed80km/h,lateralaccelerationaq=0,67m/s²,s1002Wheelprofile,UIC60E1,1:40railinclination

Figure22:Radiallysteeredbogierunningina300mcurve

Wheelsliplateralandlongitudinalatallwheel‐railcontactpoints,90ttankcarwithaLeila‐Bogieina300mcurve,speed80km/h,lateralaccelerationaq=0,67m/s²,s1002Wheelprofile,UIC60E1,1:40railinclination

Figure21showsaconventionalY25bogie(runningtotheright).Theouterwheeloftheleadingaxlehastwopointcontactwithratherhighlateralandlongitudinalcreepages.Theinnerleadingwheelislessaffectedandthetrailingwheelsethasmuchsmallervalues.Withradialsteering,(figure22)theleadingaxlealsohasverysmallcreepages.Thisresultsinlowerwearandrunningresistance.Asaresultontrackwithtightcurvesmorethan20%oftheoverallrunningresistancecanbereducedwithsimilarlevelsofenergysaving[66].

Ofcourseradialsteeringmayaffectrunningstabilityonstraighttrack.ThereforebogiedesignswithcrossanchorssuchastheTVP2007ortheLeilabogiehaveanadvantageoverindividualradialsteeringaxlesasintheswinghangerbogie.

3.3.2 InfluenceofcurvingonwheelandraildamagephenomenaAsmentionedintheintroductiontothissectionthecurvingperformanceofafreightwagonisveryimportantforthelevelofwheelandraildamage.Thismeansinturnthatthevehicletrackinteractionincurvesdeterminestoalargeextentthemaintenancecostforthewholesystem.In[66]Fröhlingdiscussestheinfluenceof,amongothers,bogiedesign,bogiemaintenanceandthewheel/railinterfaceinheavyhauloperationondifferentdamagephenomenaonwheelsandrails.InalaterpublicationFergussonetal[67]presentananalysisofwheelwearasafunctionoftherelationshipbetweenthelateralandlongitudinalprimarysuspensionstiffnessandthecoefficientoffrictionatthecentreplatebetweenthewagonbodyandthebolstertominimisethewheelwearrate

ofaself‐steeringthree‐piecebogiewithoutcompromisingvehiclestability.Simulationresultsindicatethatwheelwearistheoreticallythelowestforlowlateralandlongitudinalprimarysuspensionstiffnessandnofrictionatthecentreplate.Casanuevaetal[68]extendthewearpredictionmethodologyforfreightwagonstoalsoincludeswitchesandcrossings.Itisconcludedthatwearonsomepartsofthewheelprofilecanonlybeexplainedwithrunningthroughswitches.

TunnaandUrban[69]carriedoutaparametricstudytoquantifytheeffectsofvariousfreightvehicleparametersonthegenerationofRCF.Threedifferentfreightsuspensionswerconsidered:anenhancedthree‐piecebogie,arigid‐framebogiewithprimarysuspension,andatwo‐axlevehiclewithleafsprings.Simulationswereperformedfortrackcurvaturerangingfrom400to10000m.TojudgethegenerationofRCFtheTgammamodelfromBurstow[70]wasused.Itisstatedthatparametersthatclearlyneedtobeconsideredwhenevaluatingrailsurfacedamagearecurvedistribution,trackquality,conicity,vehicletypeandloadingstateofthewagon.Sinceseveralparametersarelinedependentitisconcludedthataroutebasedanalysisisnecessary.

In[71]asimulationmodelofanironorewagonwiththree‐piecebogieisdevelopedtoinvestigatetheriskofRCFontheSwedishandNorwegianironoreline.43loadcaseswithvariousconditionswereusedasinputs.TheriskforRCFwasestimatedwiththeso‐calledshakedownmap.Thewearnumber,whichistheproductofcreepagesandcreepforces,wascalculatedtoestimatewhereinitiatedcracksdeveloporarewornaway.Infigure23areasonthewheelprofilewithhighriskofRCFcanbeseen.TheareaonthewheeltreadcoincidesverywellwithfieldobservationsofRCFbuttheareasintheflangerootandontheflangedidnotshowRCFdamage.Itcanbeconcludedthattheenergydissipationishighenoughtowearawayinitiatedcracks.Itseemsthatsimulationofthecurvingbehaviouroffreightwagonscanprovidevaluableinformationabouttheriskofwheeldamageforspecificoperatingconditions.

In[71]asimulationbyDukkipatiandDongexaminetheeffectsofafreightwagonrunningoveradippedjoint.InaveryrecentpaperWangandGaoinvestigatethewheelwearofafreightvehiclewiththree‐piecebogieincurves[99].Itisshownthatwearismostsevereontheouterleadingwheelinthebogie.

Figure23:CalculatedRCFpositionsofthewheelwithcorrespondingaveragewearnumber.Thefar‐leftlineisalsoreportedastheobservedapproximatelocationforRCFinitiation.

3.4 ParameteridentificationTheestablishmentofthecorrectparametersforuseincomputermodelsisclearlyofgreatimportance.Someparameterscaneasilybemeasuredorprovidedbythemanufacturersbutothersareverydifficulttoestablish.Renetel[74]demonstratetheuseofatestrigwithaslidingplateunderneathonewheelsettoestablishkeyparameters.Theslidingplateismovedwithactuatorsandforcesmeasuredtoallowthelateral,shearandwarpstiffnesstobeestablishedaswellasthefrictioncharacteristicsofthebogie.

4 ModernDevelopments

4.1 TheBritishRailHSFBogiesWickensandcolleaguesatBritishRailResearchcarriedouttheoreticalandpracticalworkaimedatunderstandingthedynamicperformanceoftwoaxlefreightvehicles[75],[76].Theaimwastoincreasetheoperatingspeedoffreightvehiclesandreducetherateofderailments.Aseriesofexperimentaltwoaxlevehicleswereconstructedtoconfirmtheresultsoftheanalysis.Theyincludedcoilspringsandviscousdampersandlongitudinalrodstocontrolyawmotionandwereinitiallytestedonafullsizerollerrig.Computersimulationsofcurvingandstabilitywerecarriedoutwithvariousdamperconfigurationsandon‐tracktestsofseveralprototypeswereundertaken

Theresultofthisworkwastheprototype‘HSFV.4’highspeedfreightvehiclewithviscousdamping(figure24)whichwastestedatspeedsofupto120km/handprovedtorunwithouthuntingforawiderangeofeffectiveconicityvalues.

Figure24:TheHSFV.1experimentalfreightwagon

4.2 TheUnitruckrunninggearTheUnitrucksingle‐axlerunninggearwithlateral“swinghangers”wasfirstdevelopedfortheAmericanmarketandinthe1990’sadjustedtosuitEuropeanconditions.VehicleswithUnitruckrunninggear[76]aretodayusedbothinNorthAmericaandEurope.Theyhaveonlyonestagesuspension,whichalsoincludesfrictiondamping.AsintheY25bogie,theverticalforceintheprimarysuspensionisusedtopreloadthedifferentfrictioncomponentsviaaninclinedsurface.Figure25leftshowsthewedgeelement,whichisinserieswithoneofthecoilspringsandincontactwiththecarbodyviaaninclinedfrictionsurface;theverticalsurfaceincontactwiththesaddleisalsoafrictionsurface.Newerdesignshavesubstitutedtheinclinedfrictionsurfacebyaroller(figure25left)[77],thusenablingthedisplacementinthelongitudinaldirection,butreducinglongitudinaldamping.Also,addingacouplingplateinthecentreofthecoilspringsincreaseslongitudinalstiffness(Figure25right),whichimprovescriticalspeedcomparedtotherunninggearwithrollersandclassiccoilsprings.

Figure25:Unitruckrunninggear(left)andmodificationsforimprovingcurvingbehaviour(right).

4.3 The‘SwingMotion’Bogie

Figure26:The‘Swingmotion’bogie

The‘SwingMotion’bogie(figure26)isavariantofthethree‐piecefreightbogieandwasoriginallydevelopedforheavyhauloperationsinNorthAmerica.IntheSwingMotiondesignanadditionalcrossmemberortransomisincludedwhichconnectsthetwosideframestogetherviapivotsatthebaseofthesecondaryspringpack.Thebolsterstillsitsonthetopofthespringpacksandisdampedthroughfrictionwedges.Apivotbetweentheaxleboxesandthesideframesisalsoincludedsothatthesideframescanpivotorswingtoaccommodatelateralmotionofthebolster.Theswingmotiongivesincreasedlateralstabilityatspeedsupto176km/handisclaimedtoreducewheelandrailwear,reducerollingresistanceandforcesontrackandvehiclebodycomparedwithstandardthree‐piecebogies.

4.4 The‘LTF’bogieInthe1980sBritishRailResearchintheUKdevelopedanovel,trackfriendlybogieusingpassengervehicletechnology.TheLTF25bogieisshowninfigure27andisdescribedin[79].

Figure27:The‘LTF25’bogie

TheLTF25bogiewasspecificallydesignedtoreducedynamictrackforcesandaspartofthiseffortwasmadetoreducetheunsprungmass.Smallwheels(813mmdiameter)wereusedandinsideaxleboxesgivinga30%reductioninwheelsetmassalthoughthisnecessitatedtheuseofon‐boardhotboxdetectors.

Primarysuspensionisthroughsteelcoilspringsandsecondarysuspensionisthroughrubberspringelementsandhydraulicdampers.

ThehighcostoftheLTF25bogieandconcernsaboutaxlefatiguewithinboardaxleboxesmilitatedagainstitsadoptionbutPowellDuffrynproducedamodifiedversionofthebogiesknownastheTF25bogie(showninfigure28)whichhasachieved

considerableproductionsuccess.

Figure28:TheTF25bogie

4.5 The‘Gigabox’bogieThe‘Gigabox’bogieusespedestalunitscontainingprogressiverubberspringswithintegralhydraulicdampingasshowninfigures29and30).ThesystemwasdevelopedbyContiTecandSKFandisclaimednottorequiremaintenanceforupto1millionkmandtoprovidegoodnoiseandvibrationisolation.Areductionofupto20%inlateralforcesisclaimedaswellasa2dBreductioninnoise.

Figure29:TheGigaboxbogie

Figure30:Pedestalunitandcrosssection

4.6 TheDoubleRubberRingSpring(DRRS)bogieOriginallydesignedbyTalbottheDRRSbogieusesdoublerubbertorroidalringspringswithloadproportionalfrictiondampingasshowninfigure31.Containerwagons with DRRS bogies entered service with the DB ‘Inter Cargo Express‐System’.Maximumaxle‐loadrangesfrom22.5tat100km/hto18.375tat160km/h.

Figure31:TheDRRSbogieandcrosssection

4.7 Advancesinthree‐piecebogiesThemajordriversforadvancesofAARthree‐piecebogiesweretighteningrideperformanceandtrackimpactstandards,suchasM‐1001[79]andM‐976[80],since2000.

Anoverviewofimprovementsinthesuspensionsisgivenin[81].Suspensionspringstendtoincreasethedeflection.Usinghighercontrolspringsunderthewedgesincreasesfrictionundertheemptywagonthusprovidingitsbetterstability,andmakesdampinglessdependentonthewearofwedgesthemselves.Differentheightoftheinnerandouterspringsallowshavinglowerlateralstiffnessofthesuspensionundertheemptywagon,thusimprovingitsrunningperformance.Usingthesetof9doublespringspereachsideofthebogieincreaseswarpingresistance.

Theinnovativedesignsofthewedgesareshowninfigure32.Bothdesignsaimtoincreasingthewarpingresistanceofthebogie.Thesplitwedgeconsistsoftwosymmetricpartsinclinedtowardseachotherandinteractswiththespatialinsertinthebolsterpocket.Inthespatialwedgethesurfacesareinclinedintheotherdirectionandtheyarewiderthantheverticalsurface,whichgivesthesameeffect.

Figure32:Splitwedge(left)andspatialwedge(right).

Intheinteractionbetweenthesideframeandthewheelsetaxlevariouselasticcomponentsareintroducedtoreduceunsprungmassaswellastoreduceresistancetowheelsetdisplacementinplane,thusreducingthelateraltrackforces.Someofthedesignsofelasticshearpadsareshowninfigure33.

Split wedge 

Insert 

Inclined surfaces 

Visual wear indicators 

Figure33:AdapterPlus®byAmsted(left)andlayeredshearpadinRussian18‐9800bogie(right).

Therigidsidebearingswithclearanceshavetransformedinmodernthree‐piecebogiesintoconstantcontactsidebearings,incorporatingtheelasticelementcompressedbytheweightofthecarbody,[82].Examplesofthedesignareshowninfigure34.Constantcontactsidebearingsprovideyawdampingforthebogiesonstraighttrack,aswellasadditionalcarbodyrollresistanceforbettercurvingperformance.Therollerspositionedwithaclearanceproviderigidbumpstopthatlimitstheelasticelementdeflectionwithoutincreasingtheyawresistance.

Figure34:Constantcontactsidebearingwithsprings(left)andwithnon‐metalelementandroller(right).

Thereareseveraldevicesusedtoincreasewarpingstiffnessofthree‐piecebogies,themostcommonofwhichisusingcross‐bracesbetweenthesideframesshowninfigure35.

    Cap 

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1–topbrace;2–bottombrace;3‐bolt;4–washer;5‐nut;6–fasteningunit;7–rings;8–lockingplate;9–washer;10‐bolt;11–elasticpad;12–safetywire;13,14‐bracket;15,16,17‐plate;18–key

Figure35Cross‐bracesbetweensideframes.

UsingtheconceptofshearandbendingstiffnessofthebogieScheffel[83],developedseveralnoveldesignsofthree‐piecebogies(figure36).Atfirstthehorizontalmotionoftheframeisdecoupledfromthewheelsetsbyhorizontallysoftprimarysuspension.Thentheaxleboxesareinterconnectedthroughsub‐framesorarmsbyelasticelementsthatsupporttheirradialpositionincurves,butresistin‐phaseyaw[84].Scheffelbogieshavingtheaxleloadof32tprovidemileagebetweenwheelturningofupto1.5millionkilometresthusprovingthehighefficiencyofthedesigntoreducetrackforces.

1‐sideframe;2‐bolster;3‐wheelset;4–primarysuspension;5–elasticconnectionbetweensub‐frames

Figure36:ScheffelHSbogie(left)andbogieretrofittedwithRadialArmdesign(right).

4.8 TheLenoirpusherspringVariousalternativestothedoubleLenoirlinkagehavebeenexploredwiththeaimofprovidingreducedlongitudinalstiffnessatlowcost.Oneexampleisthe‘Lenoirpusherspring’whichconsistsofaplungerandwasherspringsmountedoppositetheLenoirpusher(figure37).Thisallowsmorelongitudinalmotionthantheconventional

Figure37:TheLenoirpusherspring

Piotrowski[86]reportshowthisarrangementhasbeenshowntogivegoodperformanceinaprototypevehiclewithsignificantreductionsinwheelwear.

4.9 TheRC25NTBogie

EisenbahnLaufwerkeHalle(Germany)hasdevelopedtheRC25NTself‐steeringthree‐piecebogiewithdirectinter‐axlelinkageswhichwaspresentedattheInnotransexhibitionin2010)[87](figure38).Thebogiehashorizontallysoftrubberbushesintheprimarysuspensionandflexicoildualratespringswithfrictiondampinginthesecondarysuspension.Thebogieisequippedwithdiskbrakes.Theaimofthedevelopmentwastobuildabogiecapableofstablerunningupto120km/h,keepinglownoisecriteriaandnegotiatingcurveswithminimumofwear.ThebogieisdesignedtoreplacetheY25typebogiewithoutchangestothewagonbody.

SimulationshaveshownthattheRC25NTprovidesbetterstabilityonstraighttrackthantheY25(figure39)andlesswheelandrailwearincurves(figure40).ThebogiewastestedaccordingtotheUIC518standardinSwedenin2010forspeedsupto160km/h.TheRC25NTdemonstratesthatdirectinter‐axlelinkagescanallowfreightcarbogiestorunat120km/hwithpropersteeringandlowwearincurves.

Figure38:RC25NTbogiewithdirectinter‐axlelinkages

Figure39:SimulationstabilityresultsforRC25NTbogievs.Y25bogie(upperfigure=highconicity,lowerfigure=lowconicity)

Figure40:SimulatedwearnumberforRC25NTbogievs.Y25bogie

4.10 The‘LEILA’BogieTheLEILAbogie(‘LEIchtesundLärmArmesGüterwagenDrehGestell’withthemeaningoflightandlownoisefreightbogie)isapassiveradialsteeringbogiewithamaximumaxleloadof22.5tandwasdevelopedbetween2000and2005duringaGermanandSwissresearchproject[88].TheInstituteofRailVehiclesoftheTechnischeUniversitätBerlinwasoneoftheinvolvedpartner.Theaimtodevelopthisbogiewas:

toreducethenoiseemissionsoffreightwagons; toreducethemassofabogietobeunder4tand toreducesignificantlywearandrunningresistance.

Inaddition:

thereliabilityandavailabilityoffreightwagons; transparencyinthetransportchain; theactiveandpassivesafetyofthefreighttrafficand; thetransportvelocityshouldbesimilarlyincreased[89].

Figure41and42showthemaincomponentsofthisbogie.ComparedtothestandardbogiessuchasY25,theLEILAbogiehasinnerbearings.Theresultingbetterforceflowleadtoaweightreductionofthebogieframeandwheelsetresultinginanoverallweightreductionof750kgperbogiecomparedtoY25bogie.Atthewebofthewheels(diameter:920mm),discbrakesaremounted.Theprimarylayerconsistsofrubberspringsandtheloaddependentstiffnesscharacteristicsareseparatedinverticalandhorizontalworkingcomponents.Thebogiehaspassiveradialsteeringtechnologyofthewheelsets.Wheelsetsareabletorotateabouttheverticalaxiswithoutanyexternalenergybutonlybytherollradiusdifferencebetweentheinnerandouterwheel.Bothwheelsetsareconnectedwithcrossanchors;mountedonoppositeaxleboxes.ThesecondarylayerisdefinedUICcentreofpivotandsidebearer(latterguaranteestheexchangeabilitytoY25bogies).Inaddition,thecentreofpivothasanelasticallybearingusingasecondaryrubberspring.TheLEILAbogieprototypewasexaminedduringvariousfieldtestswhereitdemonstrateditsadvantagescomparedtoaY25bogie.Thenoiseemissionswerereducedupto18dB(A)comparedtoaY25bogiewithcastironbrakeblocksandupto8dB(A)comparedtoaY25bogiewithcompositeblocks(k‐blocks).Butthebogiefailedatthattimetoenterthemarket.Duringtheverygoodongoinghomologationprocesstheproducerofthebogiedecidedtostoptheproductionofnewfreightwagonsandbogies.Thereforethehomologationwasstoppedandnotfinishedjustforcommercialreasons.RightnowasmoreandmoreEMUsareproducedwithinnerbearingsitisexpectedthattheacceptabilityofinnerbearingbogieswiththeadvantageslessweightandlowerforcesattheaxlesincurveswillbemoreacceptable.

Figure41:MaincomponentsofLEILAbogie[88]

Figure42:LeilaBogiefrombeneathwiththeinnerbearings,crossanchorandwheeldiscbrakesclearlyvisible

4.11 TheTVP2007BogieTheTVP2007isavariantoftheY25bogiedevelopedbyTatravagónkaa.s..Itsmaindifferenceisamodifiedprimarysuspensioncharacteristic:TwodoubleLenoirlinksandenablesalongitudinalplayof±4mm.Theoppositeaxleboxesareconnectedbycrossanchorstoimprovetherunningcharacteristic.TheTVP2007isshowninfigure43.

Figure43:TVP2007bogiebyTatravagónkaa.s.

Morethan3000bogiesareinoperationsince2009ontheEuropeancontinentunderdifferentwagonstructures.ThebigadvantagesarethatmainlystandardY25componentscanbeusedexceptforslightlymodifiedaxlebearingsandthecrossanchorsthemselves.AswiththeLeilabogiethecrossanchorcouplesthetwoaxlessothattheyturnwithaphaseshiftof180°.Thisstabilizestheradialsteeringeffectevenwhenthewheel‐railcontactisnotperfectandthesecondveryimportanteffectisdynamicstabilisationwithoutyawdampersforhighspeedstraighttrackrunning.Oncurvytracksignificantflangeandrunningsurfacewearreductionandalsosignificantreductionoftherunningresistanceoccur.

4.12 TheSUSTRAILBogieTheaimoftheSUSTRAILprojectistopromotemodalshiftoffreightinEuropefromroadtorail.TheSUSTRAILprojectintendstoprovidetheapproach,structure,andtechnicalcontenttosupportthismodalshiftthroughimprovementsintherailwayfreightsystemincludinginnovationsinrollingstockintrackcomponents.Theprojectincludesworkpackagesfocusedonmarketresearch,vehicles,infrastructureandassessmentofcostbenefits.Theworkdescribedhereispartofworkpackage3:‘Thefreightvehicleofthefuture’.

ThemainscientificandtechnologicalinnovationsbeingconsideredfortheSUSTRAILfreightvehicleare:

The development of advanced vehicle dynamics concepts based on new wheelprofilesandimprovementsinsuspensiondesignrespondingtotheneedsofamixedtrafficrailway;

Developmentsinthetractionandbrakingsystemsforhighspeedlowimpactfreightoperation;

Noveldesignsandmaterials for lightweighthighperformance freightwagonbodyvehiclesandbogiestructures;

Advancedconditionbasedpredictivemaintenance tools for critical componentsofbothrailwayvehiclesandthetrack;

Identification of performance based design principles to move towards the zeromaintenanceidealforthevehicle/tracksystem.

Partnersintheprojecthavecarriedoutatechnologyreviewtoidentifythepotentialinnovativetechnologiestomeettheaboverequirementsandtheresultshavebeenrankedandtwoconceptvehiclesarebeingdesigned.The‘Conventional’vehiclewilluseoptimisedexistingtechnologyandademonstratorforthisisbeingbuiltaspartoftheproject.The‘Futuristic’vehiclewillutilisetechnologywhichhasnotyetbeenprovenintherailwayfieldbuthaspotentialtomakegreaterimprovements.

Simulationshavebeencarriedoutofthedynamicbehaviouroftheconceptdesignvehiclesrunningontypicaltrackintare,partladenandfullyladencases.Inlinewiththetargetofa50%reductioninlateralforcesonthetrackandstablerunningat140km/hasuspensionusingdoubleLenoirlinkages,longitudinallinkagesbetweenaxleboxesandcentrepivotsuspensionhasbeenselected.Computersimulationhasbeenusedtooptimisethesuspensionandtoselectsuitableparametersforthevariouscomponents.Assessmentoftheresultsisbasedon:

Stability:stablerunningontypicalEuropeantrackatthedesignspeedof140km/hmust be ensured and ride quality (vertical lateral and longitudinal accelerationsexperiencedbythegoodstransported)willbeassessed.

Reduced track forces: track geometrical deterioration (ballast settlement andhorizontallevel,alignmentandbuckling),railsurfacedamage(wear,rollingcontactfatigue – RCF) and track components damage (sleeper cracking, rail paddeterioration,railfatigue,fasteningdeterioration)willallbeassessed.

AbenchmarkvehiclehasbeenselectedbasedonaY25bogieandflatbedwagonandhasbeenusedtoallowquantificationofthebenefitsofthenewdesign.

AnumberofradicalinnovationswereconsideredduringthetechnologyreviewstageoftheprojectbutitwasdecidedthattheuseofdoubleLenoirlinkprimarysuspensionasin theY37 series of bogies (figure44),would be investigated.ThedoubleLenoir linksuspension provides much lower longitudinal primary stiffness while still utilisingstandard components and methods which are well established within the railwayindustry.

Figure44:AsuspensionwithdoubleLenoirlinks

Aspart of the optimisation of theprimary suspension the followingparameterswerevaried:

Theverticalcoilspringstiffness(Kc) ThelengthoftheLenoirlink(L) TheangleoftheLenoirlink(Aistheoffset) The friction coefficient at the sliding surfaces (μyz) (controlled through

changingmaterial) Theverticalclearancetothebumpstop(dz0)

Theseparametersareillustratedinfigure45.

Figure45:TheLenoirlinkshowingtheparametersvariednthiswork

A model of the SUSTRAIL vehicle was set up with double Lenoir links using thecomputer simulation tool Gensys and the influence of variations in the suspensionparametersonthecriticalspeedofthewagonwassimulated.Straighttrackwasusedforthissimulationandaninitiallateraldisturbancewasintroducedfollowedbyidealtrackwithnoirregularities.Axle loadis22.5t,wheelprofile isS1002andrailprofileUIC60inclinedat1:40.Thewheelrailcoefficientoffrictionissetat0.35.Thewagonspeedwasreducedfromaninitial170km/handcriticalspeedassumedtohavebeenreachedwhenthetrackshiftingforce(∑ )dropsbelow2.5kN.Anexampleisshowninfigure46.

Figure46:AsamplesimulationresultsshowingtheestablishmentofthecriticalspeedfortheSUSTRAILvehiclewithdoubleLenoirlinks

Theeffectsofthevarioussuspensionparametersonthecriticalspeedaresummarisedinfigure47.

Figure47:TheeffectofLenoirlinkangle,lengthandfrictioncoefficientonthecriticalspeedoftheSUSTRAILvehicle

The simulations were repeated with a speed of 120 km/h on straight track withmeasuredirregularitiesandthemaximumverticaltrackforcewasestablishedforeachtracksectionasshowninfigure48.

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Figure48:MaximumverticalforceontherailfortheSUSTRAILvehiclerunningat120km/h

Furthervariationswerecarriedoutandtheeffectofthefrictioncoefficientandstiffnesswithinthesuspensiononthemaximumcontactforceisshowninfigure49.

Figure49:Theeffectoffrictioncoefficientandspringstiffnessonthecontactforce

It can be seen that the maximum vertical contact forces tends to increase with thedampingandwiththespringstiffness.In order to improve the running behavior of the SUSTRAIL vehicle it was decided toassess thebenefitof linkagesprovividing longitudinal stiffnessbetween theaxleboxesusingaradialarm.AradialarmdesignedbyScheffel[90]wasstudiedpreviouslyintheInfra‐Radialproject [91]whichaimedtodevelopabogie forheavyhaulvehicles(axleloadsover25T)withreducedlifecyclecosts.Testsusing theradialarmwith fourdifferentprimarysuspension types showedgoodresultswithstablerunningandradiallyalignedwheelsetsincurves.Wearofthewheelswasseentoreducesignificantly[91].Intheworkreportedheresimulationwascarriedout using MEDYNA for the SUSTRAIL vehicle with double Lenoir links and modifiedradialarms.Simulationshaveconfirmedthattheradialarmshouldprovidelateralstiffnessbetweenthe wheelsets and optimised parameters have been defined. A prototype of theSUSTRAILfreightvehicleisbeingconstructedbyREMARULengineering.Inadditionto

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155

160

165

0.20.250.30.350.40.450.50.550.6

Max vertical contact force [kN]

Damping in primary suspension [-]

135

140

145

150

155

160

165

50 60 70 80 90 100

Max vertical contact force [kN]

Vertical coils spring stiffness [%]

theinnovativesuspensiondescribedinthispapertheSUSTRAILvehiclewillhavediskbrakeswithanelectroniccontrolsystem.Thebogiedesignisshowninfigure50.

Figure50:TheprototypeSUSTRAILfreightbogie

5 LongitudinaldynamicsThelongitudinaldynamicbehaviourofrailwayvehiclesisoftenneglectedasthelinktothevehicletrackinteractionisgenerallynotsignificantandithasbeencommontoassumethatallvehiclesofthesametypeinatrainwillbehaveidentically.Inheavyhaulfreightapplicationshoweverwherelongtrainsarecommontheeffectoflongitudinaldynamicscanbecomesignificant.In[71]forexampleQietalmodelthelongitudinalbehaviourofalongtrainincludingtractionandbrakingandthecouplingbetweenvehicles.Belforteetal[93]alsoanalysetheeffectsofseveretractionandbrakingforcesonlongitudinaldynamics.

Thereareseveralareaswherelongitudinaldynamicscaninteractwiththegeneralvehicledynamics.Theseinclude:

Wheelunloadingoncurvesduetolateralcomponentsofcouplerforces; Wagonbodypitchduetocouplerimpactforcesand Bogiepitchduetocouplerimpactforces

Cole[94]describeshowtheseeffectscanbeassessedindifferentcasesandMcClanachan[95]andElSibaie[96]presentresultsofcomputersimulationsincludingcouplermodels.

6 Conclusions

Freightvehicleshavetoprovidesatisfactoryperformanceatlowcostintareandladenconditiononvaryingtrackquality.ThishasresultedinseveralstandarddesignsincludingtheY25andthethree‐piecebogie.Thesedesignsusefrictiondampingproportionaltothevehiclemasstoprovidegooddynamicperformanceatallloadingconditions.Inrecentyearsvehicledesignershavetriedtoimproveonthedynamicperformanceoffreightwagonsandtheuseofcomputertoolshavehelpedtoovercomethecompromisebetweengoodcurvingperformanceandstabilityathigherspeeds.Thishasresultedinanumberofinnovativedesignswithdemonstrableperformanceimprovementsbutitisnotablethatfewofthesehaveyettomakesignificantimpactintheworldwidefreighttrainfleets.

Akeyreasonforthislackofadoptionisprobablytheinnatelyconservativenatureoftherailwayindustry.Ofcoursethisoftenhasasoundbasisin,forexample,thebenefitofusingstandardcomponentswhichalloweffectivemaintenanceofwidelydispersedfleetsofvehiclesbutinordertoallowthebenefitsoftheinnovativetechniquesanddesignssummarisedinthispaperitistimetoreconsiderthedesignoffreightvehicles.Thiscouldallowincreasesinspeedwithlowerimpactontrackandenvironmentandaresultingstepchangeinperformanceoftherailwaysystem.Oneencouragingsignistheestablishmentinsomecountriesoftrackaccesschargingwhichbenefitstheuseofvehicleswith‘trackfriendly’suspension.Togetherwithemerginglegislationandgrowingpressuresonsystemcapacityitislikelythatthedemandforfreightvehicleswithhigherdynamicperformancewillclimbrapidly.

Railfreightonlycancontributeinmitigatingtheenvironmentalimpactsoftransportationiftheknowledgeandtodaysexperienceforinnovativeproductsisused.Somebasicthoughtscanbefoundhereandin[97].Optimisingperformancethroughthedevelopmentofinnovativeproductsistobeplannedandprocuredcarefully.Thispaperhasdemonstratedthatfreightvehicledesignershaveinnovativedesignsofrunninggearandcomputersimulationtoolsreadyforthischallenge.

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