资料课件讲义Chapter 4

Chapter4SteeringandSuspensionSystems,4.1SteeringSystem4.1.1BasicPartsofSteeringSystem4.1.2TypesofSteeringSystem4.1.3PowerSteeringSystems4.2SuspensionSystems4.2.1BasicPartsofSuspensionSystem4.2.2Frontsuspension4.2.3RearSuspension,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,NewWords,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Thesteeringsystemisdesignedtoallowthedrivertomovethefrontwheelstotherightorleftwithaminimumofeffortandwithoutexcessivemovementofthesteeringwheel.Althoughthedrivercanmovethewheelseasily,roadshocksarenottransmittedtothedriver.4.1.1BasicPartsofSteeringSystemThebasicsteeringsystem(Figure4-1)canbedividedintothreemainassemblies:Thespindleandsteeringarmassemblies.Thelinkageassemblyconnectingthesteeringarmsandsteeringgear.Thesteeringwheel,steeringshaft,andsteeringgearassembly.,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-1Basicpartsofsteeringsystem,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,4.1.2TypesofSteeringSystemTherearetwotypesofsteeringsystems:manualsteeringandpowersteeringsystems.Inthemanualsteeringsystems,driverdoesalltheworkofturningthesteeringwheel,steeringgear,andtires.Inthepowersteeringsystems,hydraulicorelectricpower-assistedsteeringisusedtoreducetheeffortrequiredbyturningthesteeringwheel.Therearethreetypesofthesteeringgearsinuse:recirculatingballsteeringgear,worm-and-rollersteeringgearandrack-and-pinionsteeringgear.4.1.3PowerSteeringSystemsHydrauliclack-and-pinionpowersteeringsystem.Thissystemconsistsofmechanicalrack-and-pinionsteeringgear,hydraulicworkingcylinderswithworkingplungers,rotaryslidevalve,oilpump,pressure-limitingvalveandoilreservoir(Figure4-2).,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-2Ahydraulicrack-and-pinionpowersteeringsystemwithrotaryslidevalve,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Electro-hydraulicpowersteeringsystem-Servotronic.Servotronicisanelectronicallycontrolledrack-and-pinionsteeringsysteminwhichthehydraulicassistingforcesareinfluencedbythedrivingspeed.Atlowdrivingspeeds,thefullassistingforceofthehydraulicrack-andpinionsteeringtakeseffect.Thehydraulicassistingforceisreducedasdrivingspeedincreases.So,Servotronicisaspeed-sensitivepowersteering.Servotronicconsistsofelectronicspeedometer,ECU,hydraulicrack-and-pinionsteeringgear,oilreservoir,electro-hydraulicconverterandoilpump(Figure4-3).,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-3Servotronic-aelectro-hydraulicpowersteeringsystem,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Electricpowersteering-Servolectric.WithServolectric(Figure4-4),theassistingforceisgeneratedbyanelectronicallycontrolledelectricmotor.Theelectricmotorisonlyswitchedonwhenrequired.Thesteeringtorqueappliedbythedriverismeasuredviaatorsionrodwithatorquesensorandinadditionthespeedismeasuredviaaspeedsensor.ThetwosignalsarefedtotheECU.TheECUcalculatesthetorquerequiredanditsforce-transferdirectionusingstoredprogrammapsandsendstherelevantoutputsignalstotheelectricmotor.Thelattergeneratesanassistingtorquewhichistransformedbyaworm-gearpairandtransmittedtotherackand-pinionsteeringgear.,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-4Servolectric-aelectricpowersteeringsystem,Chapter4SteeringandSuspensionSystems4.2SuspensionSystems,NewWords,Chapter4SteeringandSuspensionSystems4.2SuspensionSystems,Ifavehiclesaxleswerebolteddirectlytoitsframeorbody,everyroughspotontheroadwouldtransmitaforcethroughoutthevehicle.Ridingwouldbeuncomfortable,andhandlingatfreewayspeedswouldbeimpossible.4.2.1BasicPartsofSuspensionSystemSprings.Everyvehiclehasspringsofsomekindbetweentheframeorbodyandtheaxles.Therearethreetypesofspringsingeneralusetoday:leafspring,coilspring,andtorsionbar.Twodifferenttypesofspringscanbeusedononevehicle.ShockAbsorbers.Whenthevehicleistravelingforwardonalevelsurfaceandthewheelsstrikeabump,thespringisrapidlycompressed(coilsprings)ortwisted(leafspringsandtorsionbars).Thespringwillattempttoreturntoitsnormalloadedlength.,Chapter4SteeringandSuspensionSystems4.2SuspensionSystems,Insodoing,itwillrebound,causingthebodyofthevehicletobelifted.Theweightofthevehiclethenpushesthespringdownafterthespringrebounds.Thiscausesthespringtoreboundagain.Thisprocess,calledspringoscillation,graduallydiminishesuntilthevehicleisfinallystill.Springoscillationcanaffecthandlingandridequalityandmustbecontrolled.Shockabsorbersareusedtoattenuatetheoscillation.ControlArms.Allvehicleshaveeithercontrolarmsorstrutstokeepthewheelassemblyintheproperposition.Thecontrolarmsandstrutsallowthewheeltomoveupanddownwhilepreventingitfrommovinginanyotherdirection.,Chapter4SteeringandSuspensionSystems4.2SuspensionSystems,4.2.2Frontsuspension前悬架Almostallmodernfrontsuspensionsystemsareindependent.Withanindependentsuspension,eachfrontwheelisfreetomoveupanddownwithaminimumeffectontheotherwheel.Inanindependentsuspensionsystem,thereisalsofarlesstwistingmotionimposedontheframethaninasystemwithasolidaxle.ThetwomajortypesofindependentfrontsuspensionaretheconventionalfrontsuspensionandtheMcPhersonstrutfrontsuspension.ConventionalFrontSuspension.Intheconventionalfrontsuspensionsystem,oneortwocontrolarmsareusedateachwheel(Figure4-5).Inmostsystems,thecoilspringsaremountedbetweenthevehiclesframeandthelowercontrolarm.Inatorsionbarfrontsuspensionsystem(Figure4-6),thelowerarmmovesupward,ittwiststhetorsionbar.,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-5Atypicalindependentfrontsuspension,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-6Atorsionbarfrontsuspensionsystem,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,McPhersonStrutFrontSuspension.Mostmodernvehicles,especiallythosewithfront-wheeldrive,usetheMcPhersonstrutfrontsuspensionsystems(Figure4-7).TheentireMcPhersonstrutassemblyisattachedtothesteeringknuckleatthelowerpartofthepedestal.ThebottomoftheMcPhersonstrutassemblyisattachedtothesinglecontrolarmthroughaballjoint.TheadvantageoftheMcPhersonstrutisitscompactdesign,whichallowsmoreroomforserviceonsmallcarbodies.SolidAxleFrontSuspension.Theuseofthesolidaxlefrontsuspension(ordependentsuspension)isgenerallyconfinedtotrucksandoff-roadvehicles.Thissystemusesasoliddeadaxle(doesnotturnwithwheels)withaleafspringateachside.,Chapter4SteeringandSuspensionSystems4.1SteeringSystem,Figure4-7AMcPhersonstrutfronts