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RESEARCHARTICLEZhibinLIU,HaiboXIE,HuayongYANGSimulationanalysisofpressureregulationofhydraulicthrustsystemonashieldtunnelingmachineHigherEducationPressandSpringer-VerlagBerlinHeidelberg2011AbstractHydraulicthrustsystemisanimportantsysteminashieldtunnelingmachine.Pressureregulationofthrustcylindersisthemostimportantfunctionforthrustsystemduringtunnelexcavation.Inthispaper,ahydraulicthrustsystemisexplained,andacorrespondingsimulationmodeliscarriedoutinordertostudythesystemcharacteristics.Pressureregulationofacertaingroupscylindershaslittleinuenceonregulationoftheothergroupscylinders.Theinuencewillnotaffecttheprocessmuchduringtunnelexcavation.Pumpdisplacementmayhaveagreatereffectonpressureregulationandoilsupplyowrateshouldbeadaptivetothesystemsdemand.Aexactingsituationissimulatedtoexplainhowpressureregulationworksduringtunnelexcavation.Keywordstunnel,hydraulicthrustsystem,pressureregulation,simulation1IntroductionAshieldtunnelmachineisalargeandcomplexmachineusedinundergroundtunnelexcavation.Itisusedinconstructionprojectssuchasundergroundraillines,urbanpipelines,submarinetunnels,andsoon.Hydraulictechniqueiswidelyappliedinashieldtunnelingmachine.Forinstance,itisusedinthethrustsystem,thecutterheaddrivesystem,thescrewconveyor,andthesegmenterector.Researchworksabouttunnelexcavationhavebeencarriedout.SugimotoandSramoonbuiltatheoreticalmodelfortunnelexcavationbasedonmechanicsanalysis1；theirsimulationresultsareingoodagreementwithobserveddata2.MaynarandRodriguezusedadiscretenumericalmodeltoanalyzetheexcavationprocess.Somestudiesaboutthrustforceandtorquewerealsocarriedout3.Xuetal.havediscoveredsomerelationshipbetweenworkingparametersduringtunnelexcavation4.Onlyafewstudiesaboutthehydraulicsystemonthemachinehavebeendone.Huetal.havedonesomeworkonathrustsystemofamachine.Pressureandowcompoundcontrolhavealsobeenresearched5.AdifferentsysteminRef.5isstudiedinthisresearch.Pressureregulationofthrustsystemisstudiedbyusingasimpliedsimulationmodelandcasesofsuchregulationarediscussed.2ThrustsystemAthrustsystemisanimportantpartofashieldtunnelingmachine.Thesystemconsistsofpowerunits(electricmotorandhydraulicpump),hydraulicvalves,andhydrauliccylindersasactuators.Thenumberofthrusthydrauliccylindersisusually16or32.Ifindividualcontrolofhydrauliccylindersisapplied,ahighnumberofproportionalcontrolvalvesandpressuresensorsarerequired.Moreover,themachineoperatorhastocontrol16or32pressureparametersduringexcavation.Individualcontrolisrathercomplicatedandexpensive.Nowadays,thrustcylindersareusuallydividedintofourorvegroups,withthefour-grouparrangementmorecommon.Four-groupcylindersaredividedintoGroupA,GroupB,GroupC,andGroupD,correspondingtorightzone,lowerzone,leftzoneandupperzone.TheproportionofABCDisusually4543,asshowninFig.1.MorecylindersarerequiredinGroupBsoastocountertheweightofcutterheadandthehigherearthpressureinthelowerzone.Oilpressuresindifferentcylindersarethesameiftheyareinthesamegroup.Inthiscase,onlyfourproportionalcontrolvalvesarerequired,andthemachineoperatoronlyhastocontrolfourpressureparameters.Duringtunnelexcavation,hydrauliccylindersaresuppliedwithhigh-pressurehydraulicoil,whichexertsonthesegmentstogenerateathrustforcetopushthemachineReceivedJanuary28,2011；acceptedJune10,2011ZhibinLIU,HaiboXIE(),HuayongYANGStateKeyLaboratoryofFluidPowerTransmissionandControl,ZhejiangUniversity,Hangzhou310027,ChinaE-mail:Front.Mech.Eng.2011,6(3):377382DOI10.1007/s11465-011-0226-yforward.Themachineoperatormayadjusthydraulicpressuresofthrustcylinderstoachievesteeringcontrolandmachinepostureadjustment.Afterathrustprocessisover,segmentswillbeinstalledtocomposeanewringoftunnel.Meanwhile,thrustcylindersareretractedinordertomakeroomforthosesegments.Whenasegmentislocated,correspondingcylindersareextendedout.Thesecylindersexertonthesegment,supportingthesegmentwithasmallforcetocompletetheinstallationprocess.3HydrauliccircuitandmodelingThehydrauliccircuitdiagramforthethrustsystemisshowninFig.2.Thesystemmainlyconsistsofavariabledisplacementpump1,apressurereliefvalve2,adirectionalcontrolvalve3,fourpressurereducingvalves4andsixteenhydrauliccylinders7.Pumpdisplacementisproportionaltotheinputsignal.Apressurereliefvalvekicksintoactionwhenthesystemisoverloaded,andadirectionalcontrolvalveisusedtocontroltheextensionmotionorretractionmotionofcylinders.Thepressurereducingvalveisthemostimportantcomponentandisusedtoadjustthehydraulicpressureofthecylinders.Whenthecylinderisextending,high-pressureoilcomesfromhydraulicpump1,andthenowsthroughdirectionalcontrolvalve3,pressurereducingvalve4,checkvalve5,on/offvalve6,nallyenteringtherearchamberofhydrauliccylinder7.Thebackpressureoilowsoutoftherodchamberofcylinder7,thenthroughdirectionalcontrolvalve3andbackintotheoiltank.Whenthecylinderisretracting,oilowsthroughdirectionalcontrolvalve3,thenintotherodchamberofhydrauliccylinder7.Thebackpressureoilowoutoftherearchamber,thenthroughon/offvalve6,checkvalve8,directionalcontrolvalve3,andnallyintotheoiltank.CommercialsoftwareAMESimisusedastheanalysistoolforthesimulation.Tosimplifythemodel,twogroupsofhydrauliccylinders(typicallyleftzoneandrightzone)areconsideredforanalysis.Byusingthesetwozones,itispossibletosimulatethesteeringmotionoftheshieldmachine.ThesimulationmodelisshownasFig.3.Allthehydraulicmodelsarethenormalmodelsprovidedbythesoftwareexceptforthepressurereducingvalves.Thevalveisbuiltasa“super-component”bycompositingseveralnormalmodels.Thevalvegivesmoredetailsaboutnotonlytheworkingparametersbutalsotheinternalstructures.Avariabledisplacementpumpisappliedasproportionaldisplacementcontrolpumpasithasthesamefunctionasthatonaworkingshieldmachine.Thepumpdisplacementisproportionaltotheinputsignal.Threekindsofforcesareconsideredinthecylinderloadmodel:earthpressureforce,friction,andtheforcecausedbythethrustmotion.Earthpressureexertsonthecutterheadandliningsofthemachine.Thepressureforceexertedonthecutterheadaffectsthethrustmotion,andthepressureforceontheliningcanbeignored.Thefrictionforceonliningsofthemachinecausedbytheearthpressureisconsiderable,accountingforabouthalformoreofthethrustforce.Duringexcavation,however,thepressureforceandfrictionforcealmostmaintaincon-stantly.Thus,thesetwoforcesaresetasconstantinthemodel.Earthpressureissetbytheinputsignaloftheloadmodel,andfrictionissetinthemassmodelofcylinder.Thereisalinearrelationshipbetweenadvancingspeedandthrustforce,asshowninFig.44.Theblackstardotsrepresenttheexperimentalresultsfora68%openratiocutterhead,andthewhitesquaredotsrepresenttheresultsfor36%openratio.Eachsolidlineshowsthelinearrelationshipbetweenadvancingspeedandthrustforce.ThelinearrelationshiphasagoodagreementwiththeobserveddatainconstructionofLineNo.3intheGuangzhouMetro6.Fig.1Arrangementof4-grouphydrauliccylindersFig.2Hydrauliccircuitofthrustsystem378Front.Mech.Eng.2011,6(3):377382Agreaterthrustforcecausesahigheradvancingspeed.Thatisbecausegreaterforceinducesagreaterfeedrateofcutters,andmoresoilwillbecutoffinaxedtimeinterval.Thethrustforceshouldbegreaterthanearthpressureexertedonthecutterheadtogetherwithfrictionforceonthelining,inordertopushthemachinetoadvance.Ifthrustforceisnotgreatenough,themachinewillnotadvance.InFig.3,thereisadeadbandintheloadmodel.Thedeadbandrepresentsthesituationinwhichthrustforceisnotgreatenoughtopushthemachineforward；suchasituationisreferredtoinRef.6.Whilethemachineisadvancing,anincreaseofthethrustforcewillcauseanincreaseofadvancingspeed.Thisexperimentresultisappliedtotheloadmodel.Theorientationofmachineadvanceisinuencedbythepressuredistributionofthrustcylinderssopressureregulationdeterminestheprocessionofexcavation.Themachineoperatormaycontrolthepostureofthemachinebyadjustingthepressuresofcylindergroups.Themachinemaysteerleftorright,oradvancealongasmallangleofslopeifcorrespondingsettingsofpressureregulationaregiven.Normally,attheendofatunnelexcavation,thedifferencebetweenactualtunnelaxisanddesignedtunnelaxisshouldbenomorethan20mm.Themachineoperatorwilladjustthemachineadvancingaxistoagreewiththedesignedaxis.Asaresult,pressureregulationisaveryimportantfunctionduringtunnelexcavation.4SimulationThesimulationparametersshowninTable1areobtainedfromashieldtunnelingmachineusedintheconstructionoftheNanjingMetro.Theleftandrightthrustgroupsareusedforsimulation,andsixteenhydrauliccylindersarereducedtoeight.A63cc/revmaximumdisplacementpumpshouldbereducedto31.5cc/rev.Pistondiameterofarealcylinderis300mm,androddiameteris240mm.Eithertheleftorrightthrustgroup,eachofwhichcontainsfourhydrauliccylinders,issimpliedtoonehydrauliccylinder,whichhasthesameworkareaastheoriginalcylindergroup.Asaresult,thepistondiameterandroddiameterofsimulationcylinderare600and480mm,respectively.Whenoilpressureisabout8MPa,whichsuppliesabout9200kNofthrustforce,themachinebeginstomove.Reference7refersthatfrictionforceaccountsforabout53.5%73%ofthrustforce.Accordingly,frictionforceissetat6000kN,about65%ofthrustforce.Theremaining3200kNisexertedonthecutterheadfortunnelexcavation.4.1PressureregulationSteeringcontrolissimulatedinthiscase.Bothhydrauliccylindersareinitiallysettoabout14MPa.Themachineadvancesstraightandisexpectedtosteerleft.Thepressureofrightcylinder(Pright)shouldbehigherthanthatoftheleft(Pleft).Pleftmaymaintainat14MPa.Prightissetto20MPa.SimulationresultisshowninFigs.5and6.Prightisadjustedto20MPaasthestepsignalisgiven.ThereisasmallovershootofthepressureinFig.5asthereisamass-springsysteminthepilotstage.OvershootoftheFig.3SimulationmodelofthethrustsystemFig.4Thrustforceversusadvancingspeedinsoftground4Table1MainsimulationparametersItemSettingvaluePumpmaximumdisplacement30cc/revReliefpressure35.3MPaNominalpumpspeed1500revPistondiameterofcylinder600mmRoddiameterofcylinder480mmForceexertedoncutterhead3200kNFrictionforce6000kNZhibinLIUetal.Simulationanalysisofpressureregulationofhydraulicthrustsystem379mass-springsystemcausesovershootoftheoutletpressureinthemainstage.PlefthasapulsewhenPrightisadjustedandincreasesslightlyafteradjustment.Thesuddenchangeininletpressurewillcausethesamepulseinoutletpressureatrst.Becausethepilotstagefrequencyresponseisnothighenough,whenthepilotstagemechanismstartsadjustingthevalvesopeningarea,outletpressurewilldecreasetothesetvalue.ThesmallincreaseofPleftmightbecausedbytheincreaseofpumpoutletowrate.Thepumpoutletowratewillbediscussednext.Thissmalldifferenceinpressurewillnotaffectthetunnelexcavation.Higheradvancingspeedisachievedontherightside,asshowninFig.6.Aleftsteeringmotioniscarriedout.4.2PumpdisplacementadjustmentPumpdisplacementshouldbeadjustedwhenpressureregulationiscarriedout.Threecasesareilluminatedtoexplaintheproblem.Pressureregulationisoperatedasinthepreviouscase.Case1:Displacementmaintainsatabout75%ofmaximum.TheresultisshowninFig.7.Prightisadjustedto20MPa.Pressureregulationisachieved.However,pumpoutletpressureisat35.3MPa,whichmeansthesystemisoverloadedandthepressurereliefvalveopens.Powerlosscausedbyreliefowisconsiderable.Case2:Displacementmaintainsatabout50%ofmaximum.TheresultisshowninFig.8.