机械类外文文献及翻译机械类论文及翻译.docx

机械类外文文献及翻译机械类论文及翻译.docx

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机械类外文文献及翻译机械类论文及翻译

机械类外文文献及翻译

（文档含中英文对照即英文原文和中文翻译）

原文：

GEARANDSHAFTINTRODUCTION

Abstract:

Theimportantpositionofthewheelgearandshaftcan'tfalterintraditionalmachineandmodernmachines.Thewheelgearandshaftsmainlyinstallthedirectionthatdeliversthedintattheprincipalaxisbox.Thepassingtoprocesstomakethemcanisdividedintomanymodelnumbers,usingformanysituationsrespectively.Sowemustbethemultilayerstotheunderstandingofthewheelgearandshaftinmanyways.

Keywords:

Wheelgear;Shaft

Intheforceanalysisofspurgears,theforcesareassumedtoactinasingleplane.Weshallstudygearsinwhichtheforceshavethreedimensions.Thereasonforthis,inthecaseofhelicalgears,isthattheteetharenotparalleltotheaxisofrotation.Andinthecaseofbevelgears,therotationalaxesarenotparalleltoeachother.Therearealsootherreasons,asweshalllearn.

Helicalgearsareusedtotransmitmotionbetweenparallelshafts.Thehelixangleisthesameoneachgear,butonegearmusthavearight-handhelixandtheotheraleft-handhelix.Theshapeofthetoothisaninvolutehelicoid.Ifapieceofpapercutintheshapeofaparallelogramiswrappedaroundacylinder,theangularedgeofthepaperbecomesahelix.Ifweunwindthispaper,eachpointontheangularedgegeneratesaninvolutecurve.Thesurfaceobtainedwheneverypointontheedgegeneratesaninvoluteiscalledaninvolutehelicoid.

Theinitialcontactofspur-gearteethisalineextendingallthewayacrossthefaceofthetooth.Theinitialcontactofhelicalgearteethisapoint,whichchangesintoalineastheteethcomeintomoreengagement.Inspurgearsthelineofcontactisparalleltotheaxisoftherotation;inhelicalgears,thelineisdiagonalacrossthefaceofthetooth.Itisthisgradualoftheteethandthesmoothtransferofloadfromonetoothtoanother,whichgivehelicalgearstheabilitytotransmitheavyloadsathighspeeds.Helicalgearssubjecttheshaftbearingstobothradialandthrustloads.Whenthethrustloadsbecomehighorareobjectionableforotherreasons,itmaybedesirabletousedoublehelicalgears.Adoublehelicalgear（herringbone）isequivalenttotwohelicalgearsofoppositehand,mountedsidebysideonthesameshaft.Theydevelopoppositethrustreactionsandthuscanceloutthethrustload.Whentwoormoresinglehelicalgearsaremountedonthesameshaft,thehandofthegearsshouldbeselectedsoastoproducetheminimumthrustload.

Crossed-helical,orspiral,gearsarethoseinwhichtheshaftcenterlinesareneitherparallelnorintersecting.Theteethofcrossed-helicalfearshavepointcontactwitheachother,whichchangestolinecontactasthegearswearin.Forthisreasontheywillcarryoutverysmallloadsandaremainlyforinstrumentalapplications,andaredefinitelynotrecommendedforuseinthetransmissionofpower.Thereisondifferencebetweenacrossedheli:

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calgearandahelicalgearuntiltheyaremountedinmeshwitheachother.Theyaremanufacturedinthesameway.Apairofmeshedcrossedhelicalgearsusuallyhavethesamehand;thatis,aright-handdrivergoeswitharight-handdriven.Inthedesignofcrossed-helicalgears,theminimumslidingvelocityisobtainedwhenthehelixangleareequal.However,whenthehelixanglearenotequal,thegearwiththelargerhelixangleshouldbeusedasthedriverifbothgearshavethesamehand.

Wormgearsaresimilartocrossedhelicalgears.Thepinionorwormhasasmallnumberofteeth,usuallyonetofour,andsincetheycompletelywraparoundthepitchcylindertheyarecalledthreads.Itsmatinggeariscalledawormgear,whichisnotatruehelicalgear.Awormandwormgearareusedtoprovideahighangular-velocityreductionbetweennonintersectingshaftswhichareusuallyatrightangle.Thewormgearisnotahelicalgearbecauseitsfaceismadeconcavetofitthecurvatureoftheworminordertoprovidelinecontactinsteadofpointcontact.However,adisadvantageofwormgearingisthehighslidingvelocitiesacrosstheteeth,thesameaswithcrossedhelicalgears.

Wormgearingareeithersingleordoubleenveloping.Asingle-envelopinggearingisoneinwhichthegearwrapsaroundorpartiallyenclosestheworm..Agearinginwhicheachelementpartiallyenclosestheotheris,ofcourse,adouble-envelopingwormgearing.Theimportantdifferencebetweenthetwoisthatareacontactexistsbetweentheteethofdouble-envelopinggearswhileonlylinecontactbetweenthoseofsingle-envelopinggears.Thewormandwormgearofasethavethesamehandofhelixasforcrossedhelicalgears,butthehelixanglesareusuallyquitedifferent.Thehelixangleonthewormisgenerallyquitelarge,andthatonthegearverysmall.Becauseofthis,itisusualtospecifytheleadangleontheworm,whichisthecomplementofthewormhelixangle,andthehelixangleonthegear;thetwoanglesareequalfora0-deg.Shaftangle.

Whengearsaretobeusedtotransmitmotionbetweenintersectingshaft,someofbevelgearisrequired.Althoughbevelgearareusuallymadeforashaftangleof0deg.Theymaybeproducedforalmostanyshaftangle.Theteethmaybecast,milled,orgenerated.Onlythegeneratedteethmaybeclassedasaccurate.Inatypicalbevelgearmounting,oneofthegearisoftenmountedoutboardofthebearing.Thismeansthatshaftdeflectioncanbemorepronouncedandhaveagreatereffectonthecontactofteeth.Anotherdifficulty,whichoccursinpredictingthestressinbevel-gearteeth,isthefacttheteetharetapered.

Straightbevelgearsareeasytodesignandsimpletomanufactureandgiveverygoodresultsinserviceiftheyaremountedaccuratelyandpositively.Asinthecaseofsqurgears,however,theybecomenoisyathighervaluesofthepitch-linevelocity.Inthesecasesitisoftengo:

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oddesignpracticetogotothespiralbevelgear,whichisthebevelcounterpartofthehelicalgear.Asinthecaseofhelicalgears,spiralbevelgearsgiveamuchsmoothertoothactionthanstraightbevelgears,andhenceareusefulwherehighspeedareencountered.

Itisfrequentlydesirable,asinthecaseofautomotivedifferentialapplications,tohavegearingsimilartobevelgearsbutwiththeshaftoffset.Suchgearsarecalledhypoidgearsbecausetheirpitchsurfacesarehyperboloidsofrevolution.Thetoothactionbetweensuchgearsisacombinationofrollingandslidingalongastraightlineandhasmuchincommonwiththatofwormgears.

Ashaftisarotatingorstationarymember,usuallyofcircularcrosssection,havingmounteduponitsuchelementsasgears,pulleys,flywheels,cranks,sprockets,andotherpower-transmissionelements.Shaftmaybesubjectedtobending,tension,compression,ortorsionalloads,actingsinglyorincombinationwithoneanother.Whentheyarecombined,onemayexpecttofindbothstaticandfatiguestrengthtobeimportantdesignconsiderations,sinceasingleshaftmaybesubjectedtostaticstresses,completelyreversed,andrepeatedstresses,allactingatthesametime.

Theword“shaft”coversnumerousvariations,suchasaxlesandspindles.Anaxleisashaft,witherstationaryorrotating,norsubjectedtotorsionload.Ashirtrotatingshaftisoftencalledaspindle.

Wheneitherthelateralorthetorsionaldeflectionofashaftmustbeheldtocloselimits,theshaftmustbesizedonthebasisofdeflectionbeforeanalyzingthestresses.Thereasonforthisisthat,iftheshaftismadestiffenoughsothatthedeflectionisnottoolarge,itisprobablethattheresultingstresseswillbesafe.Butbynomeansshouldthedesignerassumethattheyaresafe;itisalmostalwaysnecessarytocalculatethemsothatheknowstheyarewithinacceptablelimits.Wheneverpossible,thepower-transmissionelements,suchasgearsorpullets,shouldbelocatedclosetothesupportingbearings,Thisreducesthebendingmoment,andhencethedeflectionandbendingstress.

AlthoughthevonMises-Hencky-Goodmanmethodisdifficulttouseindesignofshaft,itprobablycomesclosesttopredictingactualfailure.Thusitisagoodwayofcheckingashaftthathasalreadybeendesignedorofdiscoveringwhyaparticularshafthasfailedinservice.Furthermore,thereareaconsiderablenumberofshaft-designproblemsinwhichthedimensionareprettywelllimitedbyotherconsiderations,suchasrigidity,anditisonlynecessaryforthedesignertodiscoversomethingaboutthefilletsizes,heat-treatment,andsurfacefinishandwhetherornotshotpeeningisnecessaryinordertoachievetherequiredlifeandreliability.

Becauseofthesimilarityoftheirfunctions,clutchesandbrakesaretreatedtogether.Inasimplifieddynamicrepresentationofafrictionclutch,orbrake,twoin:

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ertiasIandItravelingattherespectiveangularvelocitiesWandW,oneofwhichmaybezerointhecaseofbrake,aretobebroughttothesamespeedbyengagingtheclutchorbrake.Slippageoccursbecausethetwoelementsarerunningatdifferentspeedsandenergyisdissipatedduringactuation,resultinginatemperaturerise.Inanalyzingtheperformanceofthesedevicesweshallbeinterestedintheactuatingforce,thetorquetransmitted,theenergylossandthetemperaturerise.Thetorquetransmittedisrelatedtotheactuatingforce,thecoefficientoffriction,andthegeometryoftheclutchorbrake.Thisisprobleminstatic,whichwillhavetobestudiedseparatelyforeathgeometricconfiguration.However,temperatureriseisrelatedtoene