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英文原文ConnectingrodInareciprocatingpistonengine,theconnectingrodorconrodconnectsthepistontothecrankorcrankshaft.Theconnectingrodwasinventedsometimebetween1174and1200whenaMusliminventor,engineerandcraftsmannamedal-JazaribuiltfivemachinestopumpwaterforthekingsoftheTurkishArtuqiddynastyoneofwhichincorporatedtheconnectingrod.Transferringrotarymotiontoreciprocatingmotionwasmadepossiblebyconnectingthecrankshafttotheconnectingrod,whichwasdescribedintheBookofKnowledgeofIngeniousMechanicalDevices.Thedouble-actingreciprocatingpistonpumpwasthefirstmachinetoofferautomaticmotion,butitsmechanismsandotherssuchasthecam,wouldalsohelpinitiatetheIndustrialRevolution.InternalcombustionenginesInmodernautomotiveinternalcombustionengines,theconnectingrodsaremostusuallymadeofsteelforproductionengines,butcanbemadeofaluminium(forlightnessandtheabilitytoabsorbhighimpactattheexpenseofdurability)ortitanium(foracombinationofstrengthandlightnessattheexpenseofaffordability)forhighperformanceengines,orofcastironforapplicationssuchasmotorscooters.Theyarenotrigidlyfixedateitherend,sothattheanglebetweentheconnectingrodandthepistoncanchangeastherodmovesupanddownandrotatesaroundthecrankshaft.Thesmallendattachestothepistonpin,gudgeonpin(theusualBritishterm)orwristpin,whichiscurrentlymostoftenpressfitintotheconrodbutcanswivelinthepiston,afloatingwristpindesign.Thebigendconnectstothebearingjournalonthecrankthrow,runningonreplaceablebearingshellsaccessibleviatheconrodboltswhichholdthebearingcapontothebigend；typicallythereisapinholeboredthroughthebearingandthebigendoftheconrodsothatpressurizedlubricatingmotoroilsquirtsoutontothethrustsideofthecylinderwalltolubricatethetravelofthepistonsandpistonrings.Theconrodisundertremendousstressfromthereciprocatingloadrepresentedbythepiston,actuallystretchingandrelaxingwitheveryrotation,andtheloadincreasesrapidlywithincreasingenginespeed.Failureofaconnectingrod,usuallycalledthrowingarodisoneofthemostcommoncausesofcatastrophicenginefailureincars,frequentlyputtingthebrokenrodthroughthesideofthecrankcaseandtherebyrenderingtheengineirreparable；itcanresultfromfatiguenearaphysicaldefectintherod,lubricationfailureinabearingduetofaultymaintenance,orfromfailureoftherodboltsfromadefect,impropertightening,orre-useofalreadyused(stressed)boltswherenotrecommended.Despitetheirfrequentoccurrenceontelevisedcompetitiveautomobileevents,suchfailuresarequiterareonproductioncarsduringnormaldailydriving.Thisisbecauseproductionautopartshaveamuchlargerfactorofsafety,andoftenmoresystematicqualitycontrol.Whenbuildingahighperformanceengine,greatattentionispaidtotheconrods,eliminatingstressrisersbysuchtechniquesasgrindingtheedgesoftherodtoasmoothradius,shotpeeningtoinducecompressivesurfacestresses(topreventcrackinitiation),balancingallconrod/pistonassembliestothesameweightandMagnafluxingtorevealotherwiseinvisiblesmallcrackswhichwouldcausetherodtofailunderstress.Inaddition,greatcareistakentotorquetheconrodboltstotheexactvaluespecified；oftentheseboltsmustbereplacedratherthanreused.Thebigendoftherodisfabricatedasaunitandcutorcrackedintwotoestablishprecisionfitaroundthebigendbearingshell.Therefore,thebigendcapsarenotinterchangeablebetweenconrods,andwhenrebuildinganengine,caremustbetakentoensurethatthecapsofthedifferentconrodsarenotmixedup.Boththeconrodanditsbearingcapareusuallyembossedwiththecorrespondingpositionnumberintheengineblock.RecentenginessuchastheFord4.6literengineandtheChrysler2.0literengine,haveconnectingrodsmadeusingpowdermetallurgy,whichallowsmoreprecisecontrolofsizeandweightwithlessmachiningandlessexcessmasstobemachinedoffforbalancing.Thecapisthenseparatedfromtherodbyafracturingprocess,whichresultsinanunevenmatingsurfaceduetothegrainofthepowderedmetal.Thisensuresthatuponreassembly,thecapwillbeperfectlypositionedwithrespecttotherod,comparedtotheminormisalignmentswhichcanoccurifthematingsurfacesarebothflat.Amajorsourceofenginewearisthesidewaysforceexertedonthepistonthroughtheconrodbythecrankshaft,whichtypicallywearsthecylinderintoanovalcross-sectionratherthancircular,makingitimpossibleforpistonringstocorrectlysealagainstthecylinderwalls.Geometrically,itcanbeseenthatlongerconrodswillreducetheamountofthissidewaysforce,andthereforeleadtolongerenginelife.However,foragivenengineblock,thesumofthelengthoftheconrodplusthepistonstrokeisafixednumber,determinedbythefixeddistancebetweenthecrankshaftaxisandthetopofthecylinderblockwherethecylinderheadfastens；thus,foragivencylinderblocklongerstroke,givinggreaterenginedisplacementandpower,requiresashorterconnectingrod(orapistonwithsmallercompressionheight),resultinginacceleratedcylinderwear.CompoundrodsMany-cylindermulti-bankenginessuchasaV-12layouthavelittlespaceavailableforthatmanyconnectingrodjournalsonalimitedlengthofcrankshaft.Thisisadifficultcompromisetosolveanditsconsequencehasoftenledtoenginesbeingregardedasfailures.Thesimplestsolution,almostuniversalinroadcarengines,istousesimplerods.Thisrequirestherodbearingstobenarrower,increasingbearingloadandtheriskoffailureinahigh-performanceengine.Thisalsomeanstheopposingcylindersarenotexactlyinlinewitheachother.Incertaintypesofengine,themasterrodcarriesoneormoreringpinstowhichareboltedthemuchsmallerbigendsofslaverodsonothercylinders.Radialenginestypicallyhaveamasterrodforonecylinderandslaverodsforalltheothercylindersinthesamebank.CertaindesignsofVenginesuseamaster/slaverodforeachpairofoppositecylinders.Adrawbackofthisisthatthestrokeofthesubsidiaryrodisslightlyshorterthanthemaster,whichincreasesvibrationinaveeengine.Theusualsolutionforhigh-performanceaero-enginesisaforkedconnectingrod.Onerodissplitintwoatthebigendandtheotheristhinnedtofitintothisfork.Thejournalisstillsharedbetweencylinders.TheRolls-RoyceMerlinusedthisstyle.CranklinkageofthetypeandcharacteristicsTheuseoftheinternalcombustionenginecranklinkageofmanytypes,accordingtokinematicsperspectivecanbedividedintothreecategories,namely:Heartcranklinkage,theeccentriccranklinkageandthemainvice-linkcranklinkage.Centrecranklinkageischaracterizedbythecylinderthroughthecenterlineofthecrankshaftrotationcentreandperpendiculartotheaxisofrotationofthecrank.Thistypeoflinkageintheinternalcombustionenginecrankinthemostwidelyused.Thesingle-enginegeneral,tiedforlinkagewiththeuseoftheV-shapedchaxinglinktheinternalcombustionengine,andthehomeofthepistoninternalcombustionenginecranklinkagefallintothiscategory.Eccentriccranklinkageischaracterizedbyverticalcylindercenterlineofthecrankshaftrotatinginthecenter,butnotbycrankshaftrotarycentre,thecylindercenterlinedistancebetweenthecrankshaftwitharotaryaxisoffsete.Thiscranklinkageinstitutionscanreducetheswellingintheitineraryofthepistonandcylinderintramurallargestlateralpressuresothatthepistonsintheexpansionprogrammeandpressurereductionprogrammeinthecylinderwallattheroleoflateralpressureonbothsidesoftherelativelyuniformsize.Vice-linkthemaincranklinkageischaracterizedby:theinternalcombustionenginecylinderwithamainlink,theotheroutvice-linkcylinderused,thesearenotdirectlinktothebottomofthecrankpins,butonsalethroughthedeputylinkwithinthemainlinkofthebigheads,formedajointmovement,suchinstitutionsalsosometimesreferredtoasjointsongstalklinkage.Cranklinkageinthejoint,acrankcanputafewofconnectingrodandpiston,Thisstructurewillshortenthelengthoftheinternalcombustionengine,compactandwidelyusedinhigh-powerlocomotivesusedtanksandV-shapedinternalcombustionengine.BoringInmachining,boringistheprocessofenlargingaholethathasalreadybeendrilled(orcast),bymeansofasingle-pointcuttingtool(orofaboringheadcontainingseveralsuchtools),forexampleasinboringacannonbarrel.Boringisusedtoachievegreateraccuracyofthediameterofahole,andcanbeusedtocutataperedhole.Thetermboringisalsosometimesusedfordrillingahole.MachineBoringTheboringprocesscanbecarriedoutonalatheforsmalleroperations,butforlargerproductionpiecesaspecialboringmill(workpiecerotationaroundaverticalaxis)orahorizontalboringmachine(rotationaroundhorizontalaxis)areused.Ataperedholecanalsobemadebyswivelingthehead.Theboringmachines(similartothemillingmachinessuchastheclassicVanNorman)comeinalargevarietyofsizesandstyles.Workpiecediametersarecommonly1-4m(3-12ft)butcanbeaslargeas20m(60ft).Powerrequirementscanbeasmuchas200hp.Thecontrolsystemscanbecomputer-based,allowingforautomationandincreasedconsistency.Becauseboringismeanttodecreasetheproducttolerancesonpre-existingholes,severaldesignconsiderationsmustbemade.First,largelength-to-bore-diametersarenotpreferredduetocuttingtooldeflection.Next,throughholesarepreferredoverblindholes(holesthatdonottraversethethicknessoftheworkpiece).Interruptedinternalworkingsurfaceswherethecuttingtoolandsurfacehavediscontinuouscontactshouldbeavoided.Theboringbaristheprotrudingarmofthemachinethatholdscuttingtool(s),andmustbeveryrigid.ForgingForgingisthetermforshapingmetalbyusinglocalizedcompressiveforces.Coldforgingisdoneatroomtemperatureornearroomtemperature.Hotforgingisdoneatahightemperature,whichmakesmetaleasiertoshapeandlesslikelytofracture.Warmforgingisdoneatintermediatetemperaturebetweenroomtemperatureandhotforgingtemperatures.Forgedpartscanrangeinweightfromlessthanakilogramto170metrictons.Forgedpartsusuallyrequirefurtherprocessingtoachieveafinishedpart.TheselectionofbaseandpositioningThebasepositionisprotocolmachiningline,determinetheprocessingplanoftheimportantworktodofirstMake.Choosecorrectly,theyankeeswilldirectlyinfluencethereasonableornot,themachiningofqualityandproductivity.Whenselectingpositionintheplane,needtoconsiderthefollowingquestions:(1)inwhichasurfaceastheessenceandsurfaceorunifiedstandards,(2)toensuremachiningprecision,(3)Makethemachiningprocesssmoothly?(4)forprocessingthepureplaneorunity,(5)shouldbeadoptedasaroughsurfaceplane?(6)whetherindividualprocessesforspecialprocessingrequirements,(7)needtoemployunifiedstandardsofplaneoutside?Accordingtotheessenceandtheyankeeschoice:fine,fineandselectionprinciplesshouldbeconsideredwhenthefirst,thebenchmarkoverlapIn