汽車專業(yè)英語讀譯教程 第3版 教案 UNIT 8 CLUTCHES,MANUAL TRANSMISSIONS AND DRIVE LINE

授課題目UNIT11

SUSPENSION

ANDSTEERINGSYSTEMS

TEXTA

BasicPartsandTypesoftheSuspensionandSteeringSystems授課類型理論課首次授課時間學時2學時教學目標1、機械式（人力）轉(zhuǎn)向系統(tǒng)和傳統(tǒng)獨立懸架、麥弗遜獨立前懸架和非獨立懸架組成和結構特點；2、動力轉(zhuǎn)向系統(tǒng)組成和原理。重點與難點重點：機械式（人力）轉(zhuǎn)向系統(tǒng)和傳統(tǒng)獨立懸架、麥弗遜獨立前懸架和非獨立懸架組成和結構特點的英文難點：動力轉(zhuǎn)向系統(tǒng)組成和原理。教學手段與方法多媒體教學教學過程：（包括授課思路、過程設計、講解要點及各部分具體內(nèi)容、時間分配等）1.授課思路在學習了前置課程之后，通過專業(yè)英語的學習，進行與汽車相關技術結構原理的中文英文對接，培養(yǎng)和提高英文專業(yè)資料（信息）的閱讀能力，從而為與專業(yè)英語密切相關的后續(xù)課程奠定了必要的基礎。2.過程設計：（1）課程內(nèi)容簡介（5分鐘）（2）導入新課（15分鐘）。（3）新課內(nèi)容（75分鐘）教師根據(jù)學生學習的情況，對課程內(nèi)容的重點和難點進行講解。（4）課程小結（5分鐘）3.授課內(nèi)容：SuspensionSystemIfavehicle'saxleswerebolteddirectlytoitsframeorbody,everyroughspotintheroadwouldtransmitajarringforcethroughoutthevehicle.Ridingwouldbeuncomfortable,andhandlingatfreewayspeedswouldbeimpossible.Thefactthatthemodernvehicleridesandhandleswellisadirectresultofasuspensionsystem.Eventhoughthetiresandwheelsmustfollowtheroadcontour,thebodyshouldbeinfluencedaslittleaspossible[1].Thepurposeofanysuspensionsystemistoallowthebodyofthevehicletotravelforwardwithaminimumamountofup-and-downmovement.Thesuspensionshouldalsopermitthevehicletomaketurnswithoutexcessivebodyrollortireskidding.SuspensionSystemComponentsVehicleFrameAvehicle'sframeorbodymustformarigidstructuralfoundationandprovidesolidanchoragepointsforthesuspensionsystem.Therearetwotypesofvehicleconstructionincommonusetoday:body-over-frameconstruction,whichusesaseparatesteelframetowhichthebodyisboltedatvariouspointsandunibodyconstruction,inwhichthebodysectionsserveasstructuralmembers.Unibodyconstructionisthemostcommon,butbody-over-frameconstructionisstillusedonpickuptrucksandlargecars.SpringsThespringsarethemostobviouspartofthesuspensionsystem.Everyvehiclehasaspringofsomekindbetweentheframeorbodyandtheaxles.Therearethreetypesofspringsingeneralusetoday:leafspring,coilspring,andtorsionbar.Twodifferenttypesofspringscanbeusedononevehicle.Airspringswereonceusedinplaceoftheothertypesofsprings,butarenowobsolete.Manymodernvehicleshaveair-operatedsuspensions,buttheyareusedtosupplementthesprings.ShockAbsorbersWhenthevehicleistravelingforwardonalevelsurfaceandthewheelsstrikeabump,thespringisrapidlycompressed(coilsprings)ortwisted(leafspringsandtorsionbars).Thespringwillattempttoreturntoitsnormalloadedlength.Insodoing,itwillrebound,causingthebodyofthevehicletobelifted.Sincethespringhasstoredenergy,itwillreboundpastitsnormallength.Theupwardmovementofthevehiclealsoassistsinreboundingpastthespring'snormallength.Theweightofthevehiclethenpushesthespringdownafterthespringrebounds.Theweightofthevehiclewillpushthespringdown,butsincethevehicleistravelingdownward,theenergybuiltupbythedescendingbodywillpushthespringbelowitsnormalloadedheight.Thiscausesthespringtoreboundagain.Thisprocess,calledspringoscillation,graduallydiminishesuntilthevehicleisfinallystill.Springoscillationcanaffecthandlingandridequalityandmustbecontrolled.AirShockAbsorbersSomesuspensionsystemsincorporatetwoadjustableairshockabsorbersthatareattachedtotherearsuspensionandconnectedtoanairvalvewithflexibletubing.Airoperatedshockabsorbershavehydraulicdampeningsystemswhichoperateinthesamemannerasthoseonconventionalshocks.Inaddition,theycontainasealedairchamber,whichisactedonbypressurefromaheightcontrolsensor.Varyingthepressuretotheairchambercausestheairshocktoincreaseordecreaseitslengthoroperatingrange.Airpressureisdeliveredtotheairshocksthroughplastictubing.Thetubingconnectstheshockstoanairvalve.Airpressureforraisingtheshocksisgenerallyobtainedfromanoutsidesource,suchasaservicestationcompressor,andisadmittedthroughtheairvalve.Todepletetheshocksofunwantedair(lowervehiclecurbheight),theairvalvecoreisdepressed,allowingairtoescape.ControlArmsAllvehicleshaveeithercontrolarmsorstrutstokeepthewheelassemblyintheproperposition.Thecontrolarmsandstrutsallowthewheeltomoveupanddownwhilepreventingitfrommovinginanyotherdirection.Thewheelwilltendtomoveinundesirabledirectionswheneverthevehicleisaccelerated,braked,orturned.Vehiclesuspensionsmayhavecontrolarmsonlyoracombinationofcontrolarmsandstruts.TypesoftheSuspensionFrontSuspensionSystemsAlmostallmodernfrontsuspensionsystemsareindependent.Withanindependentsuspension,eachfrontwheelisfreetomoveupanddownwithaminimumeffectontheotherwheel.Inanindependentsuspensionsystem,thereisalsofarlesstwistingmotionimposedontheframethaninasystemwithasolidaxle.Nevertheless,afewoff-road,fourwheeldrivevehiclesandlargetruckscontinuetouseasolidaxlefrontsuspension.ThetwomajortypesofindependentfrontsuspensionaretheconventionalfrontsuspensionandtheMacPhersonstrutfrontsuspension.ConventionalFrontSuspensionIntheconventionalfrontsuspensionsystem,oneortwocontrolarmsareusedateachwheel.Inmostsystems,thecoilspringsaremountedbetweenthevehicle'sframeandthelowercontrolarm.Inoldersystems,coilspringsaremountedbetweentheuppercontrolarmandvehiclebody.Inatorsionbarfrontsuspensionsystem,thelowerarmmovesupward,ittwiststhetorsionbar.CoilSpringFrontSuspensionFig.11-1showsatypicalindependentfrontsuspensionthatusesrubberbushingcontrolarmpivots.Thetopofthecoilspringrestsinacup-likespotagainsttheframe(unshown).Thebottomofthecoilspringissupportedbyapadonthelowercontrolarm.Thetopofeachshockabsorberisfastenedtotheframe;thebottomisattachedtothelowercontrolarm.Whenthewheelstrikesabump,itisdrivenupward.Thiscausesarmstopivotupward,compressingthespringandshock.Rubberbumperslimitcontrolarmtravelandsoftentheblowwhenthelimitisreached.Forsteering,thefrontwheelsteeringknucklepivotsonballjoints.TorsionBarFrontSuspensionAtorsionbarislocatedoneachsideoftheframeinthefrontofthevehicle.Thelowercontrolarmisattachedtothefreeendofthetorsionbar.Whenthewheelisdrivenupward,thelowercontrolarmmovesupward,twistingthelongspringsteelbar.MacphersonStrutFrontSuspensionMostmodernvehicles,especiallythosewithfront-wheeldrive,usetheMacPhersonstrutfrontsuspensionsystems,Fig.11-2.NotethattheMacPhersonstrutcontainsacoilspring,whichismountedontopoftheheavystrut-and-pedestalassembly.TheentireMacPhersonstrutassemblyisattachedtothesteeringknuckleatthelowerpartofthepedestal.ThebottomoftheMacPhersonstrutassemblyisattachedtothesinglecontrolarmthroughaballjoint.SolidAxleFrontSuspensionTheuseofthesolidaxlefrontsuspension(ordependentsuspension)isgenerallyconfinedtotrucksandoff-roadvehicles.Thissystemusesasolidsteeldeadaxle(doesnotturnwithwheels)withaleafspringateachside.Pivotarrangementsbetweentheaxleandthewheelspindlesallowthewheelstoswiveloneachend.Anyupordownmovementofeitherfrontwheelcausesaverticaltippingeffectofbothwheelsbecausetheyshareacommonaxle.RearSuspensionSystemsRearsuspensionsonvehicleswithasolidrearaxlehousinggenerallyutilizecoilspringsorleafsprings.Whenthevehiclehasanindependentrearsuspensionsystem,coilsprings,MacPhersonstruts,asingletransverseleafspring,oreventorsionbarscanbeused.SteeringSystemThesteeringsystemisdesignedtoallowthedrivertomovethefrontwheelstotherightorleftwithaminimumofeffortandwithoutexcessivemovementofthesteeringwheel.Althoughthedrivercanmovethewheelseasily,roadshocksarenottransmittedtothedriver.Thisabsenceofroadshocktransferisreferredtoasthenonreversiblefeatureofsteeringsystems.PowerSteeringPowersteeringisdesignedtoreducetheeffortneededtoturnthesteeringwheelbyutilizinghydraulicpressuretobolster(strengthen)thenormaltorquedevelopedbythesteeringgear.Powersteeringsystemsshouldeasesteeringwheelmanipulationand,atthesametime,offerenoughresistancesothatthedrivercanretains