汽车专业英语读译教程 第3版 教案 UNIT 8 CLUTCHES,MANUAL TRANSMISSIONS AND DRIVE LINE

授课题目UNIT11

SUSPENSION

ANDSTEERINGSYSTEMS

TEXTA

BasicPartsandTypesoftheSuspensionandSteeringSystems授课类型理论课首次授课时间学时2学时教学目标1、机械式（人力）转向系统和传统独立悬架、麦弗逊独立前悬架和非独立悬架组成和结构特点；2、动力转向系统组成和原理。重点与难点重点：机械式（人力）转向系统和传统独立悬架、麦弗逊独立前悬架和非独立悬架组成和结构特点的英文难点：动力转向系统组成和原理。教学手段与方法多媒体教学教学过程：（包括授课思路、过程设计、讲解要点及各部分具体内容、时间分配等）1.授课思路在学习了前置课程之后，通过专业英语的学习，进行与汽车相关技术结构原理的中文英文对接，培养和提高英文专业资料（信息）的阅读能力，从而为与专业英语密切相关的后续课程奠定了必要的基础。2.过程设计：（1）课程内容简介（5分钟）（2）导入新课（15分钟）。（3）新课内容（75分钟）教师根据学生学习的情况，对课程内容的重点和难点进行讲解。（4）课程小结（5分钟）3.授课内容：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