汽车构造英文Chapter 4 Cylinder blockcrankshaft and bearings.docx

汽车构造英文Chapter 4 Cylinder blockcrankshaft and bearings.docx

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汽车构造英文Chapter4Cylinderblockcrankshaftandbearings

Chapter4

Cylinderblocks

Cylinder-blockconstruction

Cylindersleeves

Cylindersurface-finish

Crankshafts

Crankshaftbearings

Cylinderblockandcrankcasedesign

Enginevibrationandbalance

Balanceofreciprocatingparts

Balanceshafts

Technicalterms

Reviewquestion

Thecy1inderblockisthelargestpartoftheengineandisthebasetowhichmanyotherpartsareassembledorattached.Theupperpartoftheblockcarriesthecylindersandpistons,andthelowerpartformsthecrankcasewhichsupportsthecrankshaft.Thecylinderblockhastoberigidtowithstandthestressesandvibrationtowhichitissubjected,andmustbeunaffectedbytemperaturesreachedwhentheengineisinoperation.

Balanceisanimportantpartofenginedesignandsothishasalsobeenincludedinthischapter.

Cylinderblocks

Cylinderblockaremadeofcastironorofaluminiumalloy.Aluminiumcylinderblocksarecastfromalumimiumalloyedwithothermaterials.Castironcylinderblocksareusuallycastfromgreyironalloyedwithothermetalssuchasnickelorchromium.

Duringmanufacture,patternsthataretheshapeofthecylinderblockareusedtoformasandmould.Moltencastironisthenpouredintothemouldwhereitcoolstobecomearoughcastingofacylinderblock.

Beforecasting,theshapesofwater-jackets,cylindersandsomeotherpartsaremadeupassandcores.Thecoresarefittedintothemouldssothatthesepartsoftheblockdonotbecomesolidcastironduringthecastingprocess.

Aftercasting,thecoresandisremovedthroughholesinthesidesandendsoftheblockprovidedforthispurpose.Thisleasesinternalspacesforthewater-jacketsandotherparts.Theholesarelaterfittedwithsteelplugswhicharereferredtoasexpansionplugs,coreplugs,orwelshplugs.TheycanbeseeninthecylinderblockinFigure4.1.Wheninstalled,theyareheldinplacebysealerandexpansionoftheplug

againstthehole.

Figure4.1BarecylinderblockwithitspartsidentifiedMAZDA

■Theplugsinthesideoftheblockarecupshapedandtheoneintherearendoftheblockisconvex.

Duringmanufacture,thecastingundergoesanumberofmachiningoperationswhichincludeboringandfinishingthecylinders,machiningsurfaces,drillingholesandcuttingthreadstoproducethefinishedcylinderblock.

Cylinder-blockassembly

Thecomponentsofabasiccylinder-blockassemblyareshowninFigure4.2.Thesearesomeofthemainpartsoftheengine.Anassembledcylinderblock（withthecrankshaft,connectingrodsandpistons）issometimesreferredtoasashortmotor.Ashortmotordoesnotincludethecylinderbead,theoilpan,thetimingpulleys,timingbeltortheflywheel.

Thelowersectionoftheengineblockformsthecrankcase,andthepartofthecrankcasethatextendsbelowthemainbearingsiscalledtheskirt.Insomeengines,theskirtisextendedwellbelowthecenterlineofthecrankshaftandiscalledafullskirt.Thisisdonetogivetheenginerigidity.Otherengineshaveaveryshortskirtornoneatallandrigidityisobtainedinotherways.

Figure4.2Basiccylinder-blockassemblyforafour-cylinderengineTOYOTA

Cylinder-blockconstruction

Inmostengines,thecylinders,cylinderblockandcrankcaseareallcasttogether.Thisisknownasmonoblockconstruction,asdistinctfromenginesthathavetheircy1indersasseparateparts.Thisisthecasewithair-cooledengine,wherethecylindersaremadeseparatelytothecrankcase.

Monoblockengineswithcast-ironblockshavethecylinderboreddirectlyinthecastironcasting.Castironisasuitablematerialforcy1indersbecauseitwearswellandresisttheeffectsofheat.Cylinderwallscanbeplatedwithchromium,whichisveryresistanttowear,althoughthisisnotcommonforpassengercarengines.

Aluminiumcylinderblocks

Somecylinderblocksarccastinaluminiumalloy.Thishastheadvantageofbeinglighterthancastiron.Aluminiumalloyonitsownisnotsuitableforcylinders.Itisasoftmaterialthatwearsrapidlyundertheactionofthepistonsandpistonrings.Forthisreason,linersofahardermaterialareoftenusedinthecylinders.

Thelinersarecastironsleevesthatareeithercastorpressedintotheblock.Linersthatarecastintotheblockhavegroovesontheoutsidethatformakeybetweenthelinerandtheblock.Thispreventsanypossiblemovementandthesleevebecomesapermanentpartoftheblock.（Thecy1inderblocksinFigure4.5areofcastaluminiumalloywithcastironliner.）

■Thetermscylinderlinerandcylindersleevearegenerallyinterchangeable.

Aluminiumcylinderblockwithoutliners

Alumniumcylinderblockscanbedesignedwithoutliners,butspecialalloysareneeded.Figure4.3showsaV-8cy1inderblockthathasnocylinderliners.Thealuminiumalloyofthecy1indcrshasbeenspeciallytreatedtoexposehardsiliconcrystals.Thisprovidesalow-wearingsurfaceforthepistonsandpistonrings.

Figure4.3AnaluminiumalloycylinderblockforaV-8engine–ithasspeciallytreatedaluminiumboresVOLKSWAGEN

Aluminiumalloyisusedinthecylinderblocktoreducetheweightoftheengine,butthereisalsoanadvantagethatitisbetterattransferringheatthancastiron.Thealuminiumoftheblockhasasimilarexpansionratetothepistons.

Cylinderblockforhorizontallyopposedengine

ThearrangementofthecylindersforahorizontallyopposedengineisshowninFigure4.4.Thishasasplitcrankcase.Thereareactuallytwocylinderblocksjoinedtogetherbytheflangesofthecrankcase.Thecylinderblocksareofaluminiumalloy,withcylinderlinersofcastironcastintothealuminiumblockduringmanufacture.

Aswithallcylinderblocks,thealuminiumalloycastingsaremadewithribs,websandfilletstoproviderigidity.

Figure4.4Cylinder-blockarrangementforahorizontallyopposedengine-thecylinderblocksareofaluminiumalloywithcast-ironcylinderlinersSUBARU

Two-partcylinderblock

Tilecylinderblockforthefourcylinderin-lineengineshowninFigure4.5ismadeintwoparts-thecylinderblockandthebaseplate.Bothpartsaremadefromaluminium.Thecylindershavedrylinersthatarepressedintotheblockandthesearenotreplaceable.

Themainbearingcapsarecombinedwiththebaseplatewhichhaswebsthatcarrythelowerhalvesofthecrankshaftmainbearings.Thecylinderblockandthebaseplatearematchedduringmanufactureandcannotbereplacedseparately.

■Withthisdesign,therearenoindividualcapsforthemainbearings.

Themethodsusedtomakealuminiumcastingsenabledetailedcomponentstobeproduced.Forexample,inthecylinderblockshown,theoilfilterhousingiscastaspartofthecylinderblockandthebaseplatehasthemountingforthestarter.

Inadditiontothetwopartsofthecy1inderblock,thereisacastaluminuimoilpanboltedtotheundersideofthebaseplate.Thisfurtherincreasestherigidityoftheassembly.

Figure4.5Two-partaluminiumcylinderblockwithpressed-incylinderlinersHOLDENLTD

Cylindersleeves

Cylinderblockscanbedesignedwithcylindersleeves（orliners）.Thesearefittedtocastironblocksandaredifferenttothelinerthatarecastintoaluminiumalloycy1inderblocks.

Withcastironblocks,thesleevesarecastseparatelyandthenfittedintoplaceintheblockwhentheengineisbeingassembled.Separatesleevesallowmorecontroloverthemanufacturingprocessandagradeofironthatisdifferentfromtheblockcanbeused.Thecastironfortheblockcanbeofagradewhichiseasytocast,whilethesleeveismademoreresistanttowear.

Therearethreetypesofcylindersleeves:

drysleeves,flangesdrysleeves,andwetsleeves（Figure4.6）

Drysleeves

Athindrysleeveisofuniformdiameterthroughoutitslengthandisapressfitinitsboreinthecylinderblock.Thewallofthesleeveisabout2mmthick,anditsoutersurfaceisincontactwiththeblockforitsfulllength.Thetopofthesleeveisfinishedflushwiththetopofthecylinderblockandishardlyvisible.

Thistypeofsleeveissometimefittedtonewengines,butisusedtoreconditionbadlywornordamagedcylindersthatcannotbereboredwithoutremovingexcessmetal.

■Thesedryesleevesformapermanentpartofthecylinderblockandnormallycannotberemoved.

Flangeddrysleeves

Flangeddrysleevearesometimesusedonlargerengines.Thesearesimilartoanormaldrysleeve,exceptthattheyhaveaflangeatthetopwhichfitsintoarecessinthesurfaceofthecylinderblock.Thesleeveisnotatightfit,anditcanberemovedwhenwornandanewsleevefittedinitsplace.Thecylinderheadholdstheflangedownandpreventsthesleevefrommoving.

Theboreintheblockmustbetruebecausetheaccuracyoftilesleevedependsonitscontactwiththeblock.Thisalsohasabearingonheattransferfromthecylinder.

Thistypeofsleeveisnotgenerallyusedforpassengerorlightcommercialvehicles.

Wetsleeves

Theoutersurfaceofawetsleeveformspartofthewaterjacketaroundthecylinder.Itiscalledawetsleevebecauseithascoolantagainstitsoutersurface.Thiseliminatesproblemsofheattransferbetweenthesleeveandthecoolantinthewaterjackets.However,thesleevemustbesealedtopreventcoolantleaks.Sealsareusedatthetoptopreventcoolantfromenteringthecombustionchamberandatthebottomtopreventcoolantfromenteringthecrankcase.

Figure4.7showsacylinderblockandwetsleeve.Theblockdoesnothavefull-lengthbores,buthasmountingholesatthetopandbottom.Wetsleeveshavethickerwallsthandrysleeves.Theydonothavethesamesupportintheblockandtheydependontheirwallthicknesstopreventdisto