Unit 2-活塞连杆、曲轴

PROFESSIONALENGLISHUnit2ConnectingRodsandCrankshaft

Unit2

ConnectingRodsandCrankshaft

Readingmaterial

EngineConditionTests本次课学习内容本次课学习目标掌握活塞连杆、曲轴主要部件的英文名称掌握常用术语（phrasesandexpressions）了解相关术语（relatedterms）

NEWWORDSmechanism[‘mekənizəm]n机械assembly[ə‘sembli]n装配crankcase[‘kræŋkkeis]n曲轴箱function[‘fʌŋkʃən]n功能mechanical[mi‘kænikl]adj.机械的vehicle[‘vi:ikl]n车辆cylindrical[si‘lindrikl]n圆柱体;汽缸block[blɔk]n块;滑轮serial[‘siəriəl]adj连续的；一系列的cast[kɑ:st]n,v铸件；浇铸suck[sʌk]vt.吸intricate[‘intrikit]adj复杂的rigid[‘ridʒid]adj坚硬的;刚性的distortion

[dis‘tɔ:ʃən]n变形;扭曲inertia[in‘ə:ʃiə]n.惯性;惯量periodic[.piəri‘ɔdik]adj.周期的taper[‘teipə]adj.锥形的diameter[dai‘æmitə]n.直径groove[ɡru:v]n.沟,槽reciprocating[ri‘siprəkeitiŋ]adj.往复的;来回的rotary[‘rəutəri]adj.旋转的;转动的transmit[trænz‘mit]vt.传送shank[ʃæŋk]n.轴;柄crank[kræŋk]n.曲柄;曲轴bearing[‘bɛəriŋ]n.支承;承受camshaft[‘kæmʃɑ:ft]n.凸轮轴actuate[‘æktjueit]vt.开动(机械等);驱使journal[‘dʒə:nl]n.轴颈excessive[ik‘sesiv]adj.过度的distortion[dis‘tɔ:ʃən]n.扭曲;歪曲absorb[əb'sɔ:b]vt.吸收NEWWORDSclutch[klʌtʃ]n.离合器;联轴器turbulence[‘tɜ:bjʊləns]n.紊乱circumference[sə‘kʌmfərəns]n.圆周shallow[‘ʃæləu]adj.浅的indentation[,inden‘teiʃən]n.凹槽indicate[‘indikeit]vt.指示;指出mechanism[‘mekənizəm]n.机械;机械装置compose[kəm'pəuz]vt.组成;构成pistonrings活塞环connectingrod

连杆pistonpin

活塞销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