Unit 2-活塞連桿、曲軸

PROFESSIONALENGLISHUnit2ConnectingRodsandCrankshaft

Unit2

ConnectingRodsandCrankshaft

Readingmaterial

EngineConditionTests本次課學習內容本次課學習目標掌握活塞連桿、曲軸主要部件的英文名稱掌握常用術語（phrasesandexpressions）了解相關術語（relatedterms）

NEWWORDSmechanism[‘mek?niz?m]n機械assembly[?‘sembli]n裝配crankcase[‘kr??kkeis]n曲軸箱function[‘f??k??n]n功能mechanical[mi‘k?nikl]adj.機械的vehicle[‘vi:ikl]n車輛cylindrical[si‘lindrikl]n圓柱體;汽缸block[bl?k]n塊;滑輪serial[‘si?ri?l]adj連續(xù)的；一系列的cast[kɑ:st]n,v鑄件；澆鑄suck[s?k]vt.吸intricate[‘intrikit]adj復雜的rigid[‘rid?id]adj堅硬的;剛性的distortion

[dis‘t?:??n]n變形;扭曲inertia[in‘?:?i?]n.慣性;慣量periodic[.pi?ri‘?dik]adj.周期的taper[‘teip?]adj.錐形的diameter[dai‘?mit?]n.直徑groove[ɡru:v]n.溝,槽reciprocating[ri‘sipr?keiti?]adj.往復的;來回的rotary[‘r?ut?ri]adj.旋轉的;轉動的transmit[tr?nz‘mit]vt.傳送shank[???k]n.軸;柄crank[kr??k]n.曲柄;曲軸bearing[‘b??ri?]n.支承;承受camshaft[‘k?m?ɑ:ft]n.凸輪軸actuate[‘?ktjueit]vt.開動(機械等);驅使journal[‘d??:nl]n.軸頸excessive[ik‘sesiv]adj.過度的distortion[dis‘t?:??n]n.扭曲;歪曲absorb[?b's?:b]vt.吸收NEWWORDSclutch[kl?t?]n.離合器;聯(lián)軸器turbulence[‘t?:bj?l?ns]n.紊亂circumference[s?‘k?mf?r?ns]n.圓周shallow[‘??l?u]adj.淺的indentation[,inden‘tei??n]n.凹槽indicate[‘indikeit]vt.指示;指出mechanism[‘mek?niz?m]n.機械;機械裝置compose[k?m'p?uz]vt.組成;構成pistonrings活塞環(huán)connectingrod

連桿pistonpin

活塞銷NEWWORDSAND

PHRASESConnectingRodsandCrankshaft

Inanengine,thepowermechanismiscalledthecrankshaftandconnectingrodassembly.Pistonrodgroupconsistsofpistons,pistonrings,pistonpin,connectingrodetc(seeFig2-1Apistonandaconnecting-rods).Inthisassembly,allofthemajorunitssuchastheenginecrankcaseandcylinderblock,thepistonandconnectingrod,thecrankshaftandflywheelworktogethertoconvertthermalenergyintomechanicalenergyusedtodrivethevehicle.PistonsThepistonconvertsthepotentialenginesofthefuelintothekineticenergythatturnsthecrankshaft.Thepistonisacylindricalshapedhollowpartthatmovesupanddowninsidetheenginescylinder.Duringintakestroke,thepistonsucksthefreshchargeofair-fuelmixturethroughinletvalveandcompressesduringthecompressionstrokeinsidethecylinder.Bythiswaypistonreceivespowerfromtheexpandinggasesafterignitionincylinder,alsoforcestheburntexhaustgasesoutofthecylinderthroughexhaustvalve.

Designerstrytokeeppistonweightlow,particularlyinhighspeedengines.Inordertolightenthepistonistomakeitoflightmetal.Theidealpistonmaterialwouldbelightandstrong,conductheatwell,expandonlyslightwhenheated,resistwear,andbelowincost.Thus,mostenginepistonstodayaremadeofaluminum,whichislessthanhalfasheavyasiron.Ironpistonswerecommonintheearlierengines.Aluminumexpandsmorerapidlythanironwithincreasingtemperature.Pistonscanbedividedintothreeparts,pistoncrown,pistonheadandpistonskirt.Thetoppartofthepistonisthehead,orcrown.Thecrownismachinedonslighttaper,thediameterbeinggreatestwherethecrownmeetstheskirtandbecominglesstowardthetop.Thepistoncrownmaybeflat,concave,domeorrecessed.PistonRings

Pistonringsmustbeusedtoprovidethenecessaryseal.Theringsareinstalledingroovesinthepiston.Actually,therearetwotypesofrings,compressedringsandoil-controlrings.Pistonringspreventsthecompressedchargeoffuel-airmixturefromleakingtotheothersideofthepiston.Oilringsisusedforremovinglubricatingoilfromthecylinderafterlubrication.Thisringpreventstheexcessoiltomixwithcharge.Thenumberpistonringswasreducedtothree,twocompressedringsandoneoil-controlring.Theringshavesplit,sothattheycanbeexpandedandslippedoverthepistonheadandintotherecessedgroovescutinthepiston.Theringsaresomewhatlargerindiameterthantheywillbewheninthecylinder.Then,whentheyareinstalled,theyarecompressedsothatthejointsarenearlyclosed.Compressingtheringsgivethemaninitialtension;theypresstightlyagainstthecylinderwall.1-2-compressionrings3-oilrings4-piston5-pistonpin6-piston-pinring7-connectingrodbushing8-connectingrod9-connectingrodbolt10-connectingrodnut11.12-crankbearinghalfshells13-connectingrodcapCoolingsystemThecombustionoftheair-fuelmixtureintheenginecreatesveryhightemperature.Thecoolingsystemtakesheatawayfromtheenginebycirculatingaliquidcoolant(watermixedwithantifreeze)betweentheengineandaradiator.Thecoolantgetshotasitgoesthroughtheengine.Itcoolsoffasitgoesthroughtheradiator.Thus,thecoolantcontinuallytakesheatawayfromtheengine,whereitcould

do

damage,

and

delivers

theheattotheradiator.Airpassingthroughtheradiatortakesheatawayfromtheradiator.Theroleofcoolingsystemistoabsorbpartoftheheatingparttimelydisseminationoftheheatouttoensurethattheengineattheoptimumtemperatureconditionsatwork.Water-cooledengine'scoolingsystemisusuallysetbythecoolingwater,pump,fans,watertanks,thermostatsoon.Ignitionsystem

Theenginerequiresafourthsystem,theignitionsystem.Theignitionsystemprovideshigh-voltageelectricsparksthatignite,orsetfiretothechargesofair-fuelmixtureintheenginecombustionchambers.Ignitionsystemincludesbattery,generator,distributor,ignitioncoilsandsparkplugssoon.ConnectingRod

Connectingrodchangesthereciprocatingmotionofpistonintorotarymotionatcrankshaft.Bythiswayconnectingrodtransmitsthepowerproducedatpistontocrankshaft.TheconnectingrodshowninFig.3.1isinformofabarwithringshapedheadsatitsend.Theyarecomposedofconnectingrodsmallend,connectingrodshank,connectingrodbigend,connectingrodcap,andconnectingrodbearinghalfshells.

Theconnectingrodisattachedatoneendtoacrankpinonthecrankshaftandattheotherendtoapiston,throughapistonpinorwristpin.Theconnectingrodmustbeverystrongandrigidandalsoaslightaspossible.Theconnectingrodcarriesthepowerthrustsfromthepistontothecrankpin.Atthesametime,therodisineccentricmotion.Tominimizevibrationandbearingloads,therodmustbelightinweight.Tomaintaingoodenginebalance,connectingrodsandcapsarecarefullymatchedinsetsforengines.PistonPin

Thepistonpinholdstogetherthepistonandtheconnectingrod.Thispinfitsintothepistonpinholesandintoaholeinthetopendoftheconnectingrod.Thetopendoftheconnectingrodismuchsmallerthantheendthatfitsonthecrankshaft.Thissmallendfitsinsidethebottomofthepiston.Thepistonpinfitsthroughonesideofthepiston,throughthesmallendoftherod,andthenthroughtheothersideofthepiston.Itholdstherodfirmlyinplaceinthecenterofthepiston.Pinsaremadeofhigh-strenghsteelandhaveahollowcenter.Manypinsarechrome-platedtohelpthemwearbetter.Crankshaft(seeFig2-2crankshaft)Crankshaftreceivesoscillatingmotionfromconnectingrodandgivesarotarymotiontothemainshaft.Italsodrivesthecamshaftwhichactuatethevalvesoftheengine.Thecrankshaftiseitherforgedfromahighqualitysteelorcastinahigh-strongiron.ThecrankshaftshowninFig.3.2isactuallymadeupofvariouspartssuchasmainbearingjournals,rodjournal,crankarmbearing,counter-balancedweightandflywheelend.Thecrankshaftisaone-piececastingorforgingofheattreatedalloysteelofconsiderablemechanicalstrength.Itisusuallymadefromcarbonsteel.Thecrankshaftmustbestrongenoughtotakethedownwardthrustsofthepistonsduringthepowerstrokeswithoutexcessivedistortion.Themainbearingjournalsfitintothecylinderblockandthebigendjournalsalignwiththeconnectingrods.Attherearendofthecrankshaftisattachedtheflywheel.FlywheelTheflywheelisarelativelyheavymetalwheel,whichisfirmlyattachedtothecrankshaft.Theheaviertheflywheelorthelargeritsdiameter,thesmallerwillbethespeedchanges.Itsfunctionistohelptheenginetorunsmoothlybyabsorbingsomeoftheenergyduringthepowerstrokeandreleasingitduringtheotherstrokes.Itfitsontotherearofthecrankshaft.Aswellaskeepingtheenginerotatingbetweenpowerstrokesitalsocarriestheclutch,whichtransmitsthedrivetothetransmission,andhasthestarterringgeararounditscircumference.Thereisonlyoneworkingstrokeinfoursoaflywheelisneededtodrivethecrankshaftduringthetimethattheengineisperformingthenon-powerstroke