外文翻译--卡车和货车.doc
附录1:英文原文TrucksandWagons3.1GeneralTrucksarehaulingunitswhich,becauseoftheirhighspeedswhenoperatingonsuitableroads,havehighcapacitiesandproviderelativelylowhaulingcosts.Theyprovideahighdegreeofflexibility,asthenumberinservicemaybeincreasedordecreasedeasilytopermitmodificationsinthetotalhaulingcapacityofafleet.Mosttrucksmaybeoperatedoveranyhaulroadforwhichthesurfaceissufficientlyfirmandsmoothandonwhichthegradesarenotexcessivelysteep.Someunitsnowinusearedesignatedasoff-highwaytrucksbecausetheirsizesandtotalloadsarelargerthanthatarepermittedonhighways.Thesetrucksareusedforhaulingmaterialsonlargeprojects,wherethesizesandcostsarejustified.Trucksmaybeclassifiedaccordingtoagreatmanyfactors,includingthefollowing:1.Sizeandtypeofengine-gasoline,diesel,butane,propane.2.Numberofgears.3.Kindofdrivetwo-wheel,four-wheel,six-wheel,etc.4.Numberofwheelsandaxlesandarrangementofdrivingwheels.5.Methodofdumpingtheloadrear-dump,side-dump.6.classofmaterialhauledearth,rock,coal,ore,etc.7.Capacity,intonorcubicmeter(cubicyards).8.Methodofdumpingtheloadforreardumps,hydraulicorcableIftruckaretobepurchasedforgeneralmaterialhauling,thepurchasershouldselectunitsthatareadaptabletothepurposesforwhichtheywillbeusedHowever,iftruckaretobeusedonagivenprojectforagivenpurpose,thepurchasershouldselecttrucksthatmostnearlyfittherequirementoftheproject1RearDumpTrucks2Rear-dumptrucksaresuitableforuseinhaulingmanytypesofmaterialsTheshapeofthebody,suchastheextentofsharpangles,corners,andthecontouroftherear,throughwhichthematerialsmustflowduringdumping,willaffecttheeaseordifficultyofdumpingj41ThebodiesoftruckthatwillbeusedtohaulwetclayandsimilarmaterialsshouldbefreeofsharpanglesandcornersDrysandandgravelwillfloweasilyfromalmostanyshapeofbodyIfquarryrockistobehauled,bodiesshouldbeshallowwithslopingsideboards2BottomDumpWagonsIfunitsaretobeusedtohaulmaterials,suchassand,gravel,reasonabledryearth,coal,etcwhichfloweasily,theuseofbottomdumpwagonswillreducethetimerequiredtounloadtheunitsSuchunitsareparticularlysuitableforusewherethematerialsaredistributedinlayersonafilloraredischargedthroughgrizzliesintohoppersWhendischargingtheloadontofills,thewagonscandumptheirloadswhilemovingWhendischargingthroughgrizzlies,theywillneedtostopforonlyafewsecondsTherapidrateofdischargingtheloadgivesthesewagonsatimeadvantageoverreardumptrucksAsthedoorsthroughwhichtheseunitsdischargetheirloadhavelimitedopenings,difficultiesmaybeexperiencedindischargingsuchmaterialsaswet,stickyclay,especiallyiftheyareinlargelumpsThesewagonsaresatisfactoryhaulingunitsonprojectssuchasearthendams,levees,highwaysandairports,wherelargequantitiesofmaterialsaretobetransportedandhaulroadscanbekeptinreasonablygoodconditionTheymaybeloadedbypowershovels,draglines,orportablebeltloaders3CapacitiesofTrucksandWagonsThereareatleastthreemethodsofexpressingthecapacitiesoftrucksandwagons:bytheloadwhichitwillcarry,expressedintons;byitsstruckvolume;andbyitsheapedvolume。thelattertwoexpressedincubicmeter(orcubicyards)Thestruckcapacityofatruckisthevolumeofmaterialwhichitwillhaulwhenitisfilledtothetopofthesides,withnomaterialabovethesidesTheheapedcapacityisthevolumeofmaterialwhichitwillhaulwhentheloadisheapedabovethesidesThecapacityshouldbeexpressedincubicmetersWhilethetruckcapacityremainsfixedforanygivenunit,buttheheapedcapacitywillvarywiththeheighttowhichthematerialmayextendabovethesidesandwiththelengthandwidthofthebodyWetearthorsandyclaymaybehauledwithaslopeof1:1,whiledrysandorgravelmaynotpermitaslopegreaterthan3:1Inordertodeterminetheprobableheapedcapacityofaunit,itisnecessarytoknowthestruckcapacity,thelengthandwidthofthebody,andtheslopeatwhichthematerialwillremainstablewhiletheunitismoving.Smoothhaulroadswillpermitalargeheapedcapacitythanroughhaulroads.Becauseofvariationsintheheapingcapacitiesofunitsitmaybebettertocomparethemonthebasisoftheirstruckcapacities.Inaneeventthecapacitiesshouldbedeterminedorcomparedinarealisticmanner.Theweightcapacitymaylimitthevolumeoftheloadwhenaunitisusedtohaulheavymaterial,suchasironoreHowever,whenthespecificgravityofthematerialissuchthatthesafeloadisnotexceeded,aunitmaybefilledtoitsheapedcapacityInsomeinstancesitispossibletoaddsideboardstoincreasethedepthofthebodyofatruckorwagon,therebypermittingittohaulalargerloadThispracticeprobablywillincreasethehourlycostofoperatingaunit,becauseofhigherfuelconsumption,reducedtirelifemorefrequentfailuresofparts,suchasaxles,gears,brakes,andclutches,andhighermaintenancecostsHowever,ifthevalueoftheextramaterialhauledisgreaterthanthetotalincreaseinthecostofoperatingavehicle,theoverloadingisjustifiedInconsideringhaulinglargervolumesofmaterials,themaximumsafeloadsonthetiresshouldbecheckedtopreventexcessiveoverloading,whichmightresultinconsiderablelosttimeduetotirefailures.32DesignandPrincipalMechanismsofTracksTheprincipalmechanismsofmostmoderntruckshaveaverysimilardesignandlayoutEachtruckconsistsessentiallyofthreecomponentparts:engine,chassisandbodyTrucksarepoweredmainlybycarburetorordieselenginesThebodyisintendedtocarryloadorpeopleThedriverscabisusuallyseparatedfromthebody,anditsformanddesignconformtothepurposethetruckistoserveThechassiscarriestheengine,body,transmission.runninggearandcontrolsThepowertrainofatruckisacombinationofmechanismsfortransmittingthetorquedevelopedbytheenginecrankshafttothedrivingwheelsThepowertrainofamass-producedtruck(Fig3-1)incorporatesthefollowingmainmechanisms,thepurposeanddesignofmostofwhichdonotdifferinprinciplefromthecorrespondingmechanismsintractors:engine1,clutch2,transmissionbox3,universaljointshaft4,finaldrive8withdifferential5anddrivingwheels6withaxleshafts7Whentheresistancemetbythetruckincreases,forexampleinclimbinguphill,thetransmissionboxisusedtoincreasethetorqueattheexpenseofalowerspeed6jThetransmissionboxesoftrucksandtractorsaredesignedsimilarlyandthefunctionsperformedbytheengineclutcharethesameTheuniversaljointshafttransmitstorquefromthetransmissionboxtothefinaldrive.Thetransmissionboxisattachedrigidlytothetruckframe,whilethefinaldriveandtherearaxleareconnectedtotheframebymeansofspringAsthetyresofthetruckhitbumpsintheroadtherearaxleoscillatescontinuously,changingtheanglebetweenthetransmissionboxandfinaldriveshaftsForthisreason,themainpurposeoftheuniversaljointshaftisthetransmissionoftorquebetweenshaftincludedatdifferentanglesThefinaldriveamplifiesthetorqueandtransmitsitfromthelongitudinaluniversal-jointshafttothedrivingaxleshaftsandthewheelsThefinaldrivesintrucksandtractorsservethesamepurposeThedifferentialusedintruckfinaldrivesallowsthedrivingwheelstorotateatdifferentspeeds,whichisnecessarywhenthetruckturnsorgoesoverunevenroadandtherightandleftwheelstraveldifferentdistancesduringthesametimeInatruckmovingstraightonasmoothroadthismayOccurwhentheradiioftherightandleftwheelsareunequalPhenomenoniscausedbyanunequalpressureinthetyres,nonuniformwearofthetyresordifferentloadactingonthewheelsTherunninggearofatruckcomprisesaframesupportingthebodyandallothermechanisms,aswellasthefrontandrearaxlesspringsforanelasticsuspensionoftheaxlestotheframe,andair-tyredwheelsThespringsandtyrestransmitloadfromtheframetotheroad,andatthesametimedampjerksandshockswhenthetruckhitsbumpsintheroad.TheresultantoscillationsaredampedbyspecialshockabsorbersThesteeringcontrolincludessteeringgear,brakesystem,enginecontrolandpowertraincontro1Thesteeringgearisusedtochangethedirectionofmotionbyturningthewheels.WhicharelinkedwiththesteeringwheelbyasystemofleversandrodsThebrakesystemcontributestowardssafetyandslowsdownatruckgoingdownaslope.Thebrakesaremountedonthetruckwheelsandsometimesontheuniversal-jointshaft.Thebrakesareconnectedwiththebrakepedalorleverbymeansofmechanical,hydraulicorair-operateddevicesEnginecontrolallowsachangeinthenumberofrevolutionstobeeffectedinaccordancewiththedemands,whilethepowertraincontrolboilsdowntoengaginganddisengagingtheclutchandchangingspeeds.EffortstoimprovethepropertiesoftrucksoradaptthemforspecialpurposescontinuouslychangeandimproveboththeindividualelementsandthegenerallayoutForallthat,anddespitethegreatdiversityoftypes,alltrucksconsistessentiallyofthemainelementsdescribedabove33PowerTrainofTrucks1、ClutchInconformitywithitsfunction,theclutchshouldsmoothlyengageandjustassmoothlyandrapidlycomeoutofengagement.Drydiskclutchesaremostwidespread.Thedesignoftheclutchpressureassemblysubdividesallclutchesintospring-loadedandovercentreclutches.Intheformertypethepressuredisksareconstantlycompressedbyspringsandtheclutchcanbedisengagedbydepressingthepedalwhich,overcomingthespringtension,willdrawapartthefrictionsurfaces.Assoonasthepedalisreleasedthediskswillbeagainbroughtincontactbythesprings.Inthelattertypethedrivinganddrivendisksarepressedtogetherbyalevermechanismandtheclutchleverorpedalneednotbeconstantlydepresse.Effortisappliedtotheleveronlyduringengagementordisengagement.Theseclutchesareemployedmainlyingeneralpurposecrawleragriculturaltractorswhereshort-timestoppagesareaffectedbydisengagingtheclutch,becausethetransmissiongearcannotbechangedwhilerunningandaresomewhatdifficulttoengageanddisengageinviewoftheirlargesize.Spring-loadedclutchesareusedpredominantlyintrucks.Fig.3-2illustratesoneofthemostwide-spreadandsimpletypesofsingle-diskspring-loadedclutch.Clutchshaft13(transmissionboxdrivingshaft)ismountedintwoballbearings,itsfrontendrestingintheflywheelopeningandtherearendinthefrontwallofthetransmissionbox.Housing3isattachedtoengineflywheel1.Thepressureondrivendisk2fittedontothesplintedportionofshaft13isprovidedbysprings5installedbetweenthehousingandpressuredrivingdisk4.Threereleaselevers11aremountedonspindles12attachedtohousing3.Thepressuredisk,rotatingtogetherwiththehousingandflywheel,canbeshiftedtoeithersideofthedrivendisktoincreasetheforceoffrictionbetweenthedrivinganddrivendisks.Theclutchreleasemechanismoperatesasfollows.Whensleeve10movestowardstheflywheel,thrustbearing6pressesagainsttheendsofthereleaselevers11whichtherebyturnontheiraxlesandseparatethepressuredrivingdiskfromtheflywheel,releasingthedrivendiskfromtheactionofthespring.Thesleeveisshiftedbyfork9,connectedwithpedal7throughasystemofarmsandrods.Whenthepedalisreleased,sleeve10returnstoitsinitialpositionandthepressurediskisshiftedbythespringstowardstheflywheel.Althoughfrictionclutchesofthistypereduceimpactloadswhenthegearsarebeingchangedinthetransmissionbox,frequentengagementandcontinuousslippingtendtoheatthemexcessively.Insometrucksthepowertrainincorporatesaturboclutch,wherethehydrodynamiceffectofcirculatingfluidisutilizedtotransmittorque.Thispreventstheclutchfromheatingandwearingasaresultofcontinuousslippingandmakesitpossibletoreducethenumberofswitching-overoperationsinthetransmissionbox.