《汽车专业英语》-Chapter Three Chassis Control Technology

3.1AutomaticTransmissions3.1.1Semi-AutomaticTransmissionsAsemi-automatictransmission，oraclutchlessmanualtransmission，isdefinedbytheSocietyofAutomotiveEngineersinAmericaas“atransmissioninwhichsomeofthefunctionsofnormalratiochangesareeffectedautomatically”Actually，semi-automatictransmissions(seeFig3-2)aremanualgearboxesonwhichalloperationsnormallyperformedbythedriverwhenchanginggeararecarriedoutbyelectronicallycontrolledactuatorsystems.Ituseselectronicsensors，processorsandactuatorstodogearshiftsonthecommandofthedriverThisremovestheneedforaclutchpedalwhichthedriverneedstodepressbeforemakingagearchange，sincetheclutchitselfisactuatedbyelectronicequipmentwhichcansynchronizethetimingandtorquerequiredtomakegearshiftsquickandsmooth.

下一页返回3.1AutomaticTransmissionsTherehavebeenmanyversionsofsemi-automatictransmissions，whichhavebasicallysuperimposedadegreeofautomaticcontrolovercountershaftandplanetarygearboxesusedinconjunctionwithfrictionclutches，magneticclutches，fluidcouplingsandtorqueconverters.Withtheaidofmodernelectronicsithasbecomepossibletoconferasophisticatedautomaticcontroloveraconventionalfrictionclutch，whichusedinconjunctionwithanexistingcountershaftgearboxprovidesacost-effectivesemi-automatictransmissionthateliminatestheneedforaclutchpedalAttheheartofthissystemisanelectromechanicalactuator，whichconvertssignalsreceivedfromanelectroniccontrolunitintoangulardisplacementoftheclutchwithdrawalfork.上一页下一页返回3.1AutomaticTransmissions3.1.2AutomaticTransmissionsAnautomatictransmission（seeFig3-3），usuallyreferredtoasafullyautomatictransmission，hasthereforebeendefinedbytheSocietyofAutomotiveEngineersinAmericaas“atransmissioninwhichratiochangesareeffectedautomaticallywithoutmanualassist”Automatictransmissionschangegearunderload，i.e.thepowercontinuestobetransmittedtothedrivingwheelsduringagear-shiftoperation.Unlikeasemi-automatictransmissionsystem，anautomaticonecompletelyrelievesthedriverofthedutyofchanginggear，whilestillallowingthedrivertooverdriveitsnormaloperationifthought上一页下一页返回3.1AutomaticTransmissionsdesirable.Thepower-transmissionefficiencyofsuchautomatictransmissionsisinherentlyslightlylowerthanthatofmanualandsemi-automatictransmissionsHowever，inmanyapplicationsthisiscompensatedforbyshiftprogramsdesignedtokeepengineoperationinsidethemaximumeconomyrange上一页下一页返回3.1AutomaticTransmissionsAutomatictransmissionswerefirstintroducedbackintheearlypartlastcenturyinAmericaandstilltodaytheautomatictransmissionispredominanttherewithveryfewAmericansactuallyknowinghowtodrive“Stickshift”Automatictransmissionsareveryeasyandpleasurabletodrive，especiallyinbuilt-upareasandtowns，wherethetrafficisconstantlystoppingandstartingTheonlythingyouhavetodoafterengagingagearistopresstheacceleratortogoandtopressthebraketostopNothingcouldbeeasier!Theautomatictransmissionreliesonhydraulicfluidpressuretoshiftthegearsupanddown上一页下一页返回3.1AutomaticTransmissionsTheautomatictransmissionanticipatestheengine’sneedsandselectsgearsinresponsetovariousinputs(enginevacuum，roadspeed，throttleposition，etc)tomaintainthebestapplicationofpowerTheoperationsusuallyperformedbytheclutchandmanualtransmissionareaccomplishedautomatically，throughtheuseofthefluidcoupling，whichallowsaveryslight，controlledslippagebetweentheengineandtransmission.Tinyhydraulicvalvescontroltheapplicationofdifferentgearratiosondemandbythedriver(positionsoftheacceleratorpedal)，orinapresetresponsetoengineconditionsandroadspeed上一页下一页返回3.1AutomaticTransmissions3.1.3ElectronicControlofAutomaticTransmissionsTheautomatictransmissionisoneimportantpartofthedrivetrainthatmustbecontrolled.Traditionally，theautomatictransmissioncontrolsystemhasbeenhydraulicandpneumaticToday，sophisticatedmicroprocessorcontrolisastandardfeatureofalmostallpassengercarautomatictransmissionsTherearesomepotentialbenefitstotheelectroniccontroloftheautomatictransmission.Themainaimofelectronicallycontrolledautomatictransmission（ECAT）istoimproveonconventionalautomatictransmissioninthefollowingways：上一页下一页返回3.1AutomaticTransmissions①Gearchangesshouldbesmootherandquieter②Performanceshouldbeimproved③Fuelconsumptionshouldbereduced④Characteristicchangesoversystemlifeshouldbereduced⑤Reliabilityshouldbeincreased上一页下一页返回3.1AutomaticTransmissionsKeyWordsandExpressionsAutomatictransmission—anautomobilegearboxthatcanchangegearratiosautomaticallyasthecarortruckmoves，thusfreeingthedriverfromhavingtoshiftgearsmanually自动变速器Semi-automatictransmission—alsocalledclutchlessmanualtransmission,asystemwhichuseselectronicsensors，processorsandactuatorstodogearshiftsonthecommandofthedriver半自动变速器Continuouslyvariabletransmission（CVT）—atypeofautomatictransmissionsthatcanchangethe“gearratio”（gearsarenotgenerallyinvolved）toanyarbitrarysettingwithinthelimits无级变速器上一页下一页返回3.1AutomaticTransmissionsPlanetarygear—agearsysteminwhichsmallpinionwheelsrunbetweenaninternallytoothedannularwheelandacentralexternallytoothedwheel，oftencalledasunwheel行星轮系Multiplateclutch—aclutchwithmorethanonedrivenplate多盘离合器Bandbrake—anexternalbandwithfrictionlining，sometimesusedasanadditionalparkingbrake，andasachange-speedbrakeincertaintypesofsemi-automaticgearboxes带式制动器Manualgearbox—characterizedbygearratiosthatareselectablebyengagingpairsofgearsinsidethegearbox手动变速器上一页下一页返回3.1AutomaticTransmissionsCountershaft（layshaftinUK）—theshaftinagearboxrunningparalleltothemainshaftandcarryingthepairedgearwheelsorpinionsthateffectthechangesingearratio中间轴Frictionclutch—aclutchinwhichengagementisachievedbyfrictionbetweenrotatingsurfacesincontactunderpressure，asintheconventionalsingleplateclutch，multi-plateclutchandconeclutch摩擦离合器上一页下一页返回3.1AutomaticTransmissionsMagneticclutch—themagneticattractionbetweenacurrent-carryingcoilandaferromagneticclutchplateservestoactuateadisk-typeclutch电磁离合器Fluidcoupling—ahydraulicdeviceusedfortransmittingmechanicalshaftpowerfromarotatingdrivertoarotatingdrivenload液力偶合器Torqueconverter—amechanicalorhydraulicdeviceforchangingtheratiooftorquetospeedbetweentheinputandoutputshaftsofamechanism变矩器Stickshift—anautomotivetransmissionwithashiftleveroperatedbyhand手动换挡Diaphragmspring—adisc-shapedmetalspring，usedparticularlyinclutchesThespringforceisexertedbybendingoffingersformedbyradialslotting膜片弹簧上一页下一页返回3.1AutomaticTransmissionsPowerstage—usingpowertransistorsinthedrivetoapplyvoltagetothemotorwindings功率级Potentiometer—aninstrumentformeasuringdifferencesinelectricpotential电位计Overdrive—ahighgearusedathighspeedstomaintainthedrivingspeedwithlessoutputpower超速挡Displacement—volumedisplacedbyeachpistonmovingfrombottomdeadcentertotopdeadcenter排量上一页返回3.2ContinuouslyVariableTransmissions3.2.1TheDevelopmentofCVTsThenotionofprovidingacontinuouslyvariabletransmissionsystemformotorvehiclesisfarfrombeinganewone.RobertPhilips，whowasanearlyauthorityonvehicletransmissions，wrotein1916that“nothingismorefascinatingthanthepossibilityofeffectingasmoothandgradualchangeofspeedoverthewholedesiredrange，wherebytheprimemovercanalwaysbekeptrunningatitsmosteffectivespeed”.Itisalsointerestingthat，ofthedifferentvariable-speedmechanismshelistedatthetime，theexpandingpulleysandbeltsystemwasmentionedfirst，becauseitisthemodernapplicationofthisprinciplewithwhichwearenowconcerned.

下一页返回3.2ContinuouslyVariableTransmissions3.2.2ThePrinciplesofCVTsThemajorelementsinthecontinuouslyvariablemechanicaltransmissions（seeFig3-10）forpassengercarsare：①Engagementmechanismforstartingoff（wetmultiplateclutch，magnetic-particlecouplingorhydrodynamictorqueconverter）②Theprimaryandthesecondarydiskswithaxiallyadjustabletaper-disksectionsandpowertransferviasteelbands;③Electronic/hydraulictransmissioncontrol;④Reversingmode，and;⑤Finaldriveunitwithdifferential上一页下一页返回3.2ContinuouslyVariableTransmissionsInsteadofusinggears，rotarymotioncanbetransmittedfromoneshaftpulleytoanotherbyanendlessflexiblemetalbelt（asshowninFig3-11）.ItistheforceoffrictionthatcompelsthedrivingpulleytodrivethebeltandlikewisethebelttorotatethedrivenpulleyThisforceoffrictionisderivedfromthecontactpressureofthebeltagainsttherimsofthepulleys，whichinturnisimposedbyinitialbelttensionThevelocityratioofapulleydriveisequaltothediameterofthedrivingpulleydividedbythediameterofthedrivenpulley；inotherwords，thespeedsoftheshaftsexpressedinrev/minareinverselyproportionaltothediametersoftheirpulleys上一页下一页返回3.2ContinuouslyVariableTransmissions3.2.3ElectronicallyControlledCVTs（ECVTs）

Throughout1990s，SubaruintroducedanelectroniccontinuouslyvariabletransmissionandHondaintroducedtheirversionCVT.InSubaruECVTshowninFig3-12，themicrocomputer-basedtransmissioncontrollercontrolsboththeelectromagneticpowerclutchandthehydraulicsystem，usinginputsfromvarioussensorstoindicatethevehicleoperatingmode

上一页下一页返回3.2ContinuouslyVariableTransmissionsAshiftleverpositionswitchisusedtopreventengagementoftheclutchwhenthetransmissionisinthe“P”or“N”positionSimilarly，abrakepedalswitchisusedtosignaltothecontrollerthatthevehicleisslowingdownWhenthecontrollerreceivesthissignal,itdisengagestheelectromagneticclutch，preventingastallAnacceleratorpedalpositionswitchinformsthecontrolunitthatthedriverhaspressedthepedalandsowishestodriveawayAnenergizingcurrentisthensuppliedtotheclutchelectromagnet，causinggradualengagementofdrive.Thecontrollerjudgesvehiclespeed，maximizingthiscurrentasnormalroadspeedsarereached上一页下一页返回3.2ContinuouslyVariableTransmissionsKeyWordsandExpressionsDirectdrive—whenthegearingissuchthatthecrankshaftanddriveshaftrevolveatthesamespeed，thevehicleisindirectdrive直接挡Electromagneticclutch—anyclutchinwhichamagneticforceisusedtoholdthedriveinengagement，suchasthatinthecompressordriveofanair-conditioningsystem电磁离合器Solenoid—acoilofwirearoundanironcorebecomesamagnetwhenacurrentpassesthroughthecoil电磁线圈上一页返回3.3AntilockBrakeSystems3.3.1TheDevelopmentoftheABSItisperhapsofinteresttorecallthatthebasicideaofwhatwasthencalledananti-skidcontrolwasfirstemployedforrailwaybrakingsystemsbytheWestinghouseAirBrakeCompanyinAmerica，butitwasinthefurtherdevelopmentofthisideaanditsapplicationtothediscbrakesofaircraftthatthissamecompanyfoundthewidestdemandsinthelate1940s.Bytheearly1950ssimilaranti-skidcontrols，suchastheDunlopMaxaret，werealsobeingdevelopedfortheaircraftindustry.SoitwasasaresultoftheexperiencegainedinthisfieldthatthepossibilityofadaptingtheMaxaretsystemforuseonmotorvehicleswasinvestigatedbytheDunlopCompanyandaninstallationwastestedbytheRoadResearchLaboratory.下一页返回3.3AntilockBrakeSystemsAtthisjunctureitmustbeappreciatedthattheobjectivessoughtinapplyingthewheelanti-lockprincipletoaircraftandmotorvehiclebrakingsystemsweresomewhatdifferent.Withanaircrafttheobjectivesaretopreventatleastexpensivetiredamageandatworstapotentiallydangeroustireburst，byavoidingwheellockinghoweverbrieflyitmayoccurduringmaximumbrakingthroughthelandingrunIncomparisonwithanaircrafttire，thetireofamotorvehicleisrelativelylightlyloadedandanydamagecausedtoitbywheellockingisfarlesssignificant，butwhatisreallyimportantisanylossofdirectionalcontrolorstability上一页下一页返回3.3AntilockBrakeSystems3.3.2TireDynamicsToappreciatetheoperationofananti-lockbrakingsystemitisessentialtounderstandtiredynamics.Tiresareinvolvedwiththetransferenceofacceleratinganddeceleratingforcesbetweentheroadsurfaceandthevehicle.Thegripexertedbythetireontheroadsurfaceismeasuredintermsofthecoefficientoffriction，μ（pronounced“mew”）.Thevalueofμdependsonthenatureofthetwosurfaces；forexample，itreachesamaximumofabout1.0onadrytarmacroad，fallstoabout0.7onwettarmac，butisonlyabout0.2onasnow-coveredroad.Thusagreatervalueofμmeansmorebrakinggripandashorterstoppingdistance.Tiregripalsodependsontheslipratio.Theslipratio，asapercentageofvehiclespeedU，isgivenby上一页下一页返回3.3AntilockBrakeSystems3.3.3BasicComponentsoftheABSThereareafewvariationsbetweenmanufacturersinhowABSactuallyoperates.Thisinvolvestheuseofanumberofdifferentcomponents，showninFig3-14.Forthemajorityofsystemsjustthreemaincomponentsareaffected：thewheelspeedsensor，theelectroniccontrolunitandthehydraulicmodulatorThesewillnowbeexaminedinturn，togetherwithabrieflookatatypicalcircuitdiagram.

上一页下一页返回3.3AntilockBrakeSystems3.3.4ABSSystemVariantsAnABShydrauliccontrolunitisdescribedbythenumberofbrakingcircuits（or“channels”）thatregulatestwo，three-andfour-channelsystems.Avarietyofversionsareavailabledependinguponthebraking-force-distributionconcept，thetypeofvehicledriveconcerned，functionalstipulations，andcostsfactor.Theoverviewbelowshowssixsystemvariants，whicharedescribedinthefollowingaccordingtothenumberofchannelsandsensors（seeFig3-15）.上一页下一页返回3.3AntilockBrakeSystemsKeyWordsandExpressionsGrip—thefrictionbetweenabodyandthesurfaceonwhichitmoves（asbetweenanautomobiletireandtheroad）.摩擦力Brakingefficiency—theratioofactualdecelerationachievedonagivensurfacecomparedwiththetheoreticalmaximum制动效Brakingdistance—thedistancebetweentwopointswherebrakingstartsandends制动距离Camber—averticalangleofthetireseenwhenviewingthetirefromthefrontortherear；usedprimarilytoreducetirewear车轮外倾角上一页下一页返回3.3AntilockBrakeSystemsCadencebraking—atechniqueusedtostopacarorothervehiclemorequicklyonaslipperysurfaceCadencebrakinginvolvespumpingthebrakepedalrapidlybutdeliberately，tomakethewheelslockandunlock有规律地重复快速踩下—放松制动踏Discbrake—properlycalledcaliperdiscbrake,atypeofbrakethatconsistsofadiscthatrotatesatwheelspeed，straddledbyacaliperthatcansqueezethesurfacesofthediscnearitsperipheryDiscbrakesprovideamorelinearresponseandoperatemoreefficientlyathightemperaturesandwetconditionsthandrumbrakes盘式制动器上一页下一页返回3.3AntilockBrakeSystemsJack-knife—theactionofavehicle（tractor）withatrailerinwhichthetrailerandthevehicleforma“V”insteadofnormallybeingpulledinastraightlineUsuallythisistheresultofaskidinwhichthetrailerswingsarounddangerouslyandtriestoovertakethecab折叠Allwheeldrive—allfourwheels，orAWD，canbedriven.AWDaretermsusedtodescribeafour-wheeledvehiclewithadrivetrainthatallowsallfourwheelstoreceivepowerfromtheenginesimultaneously全轮驱动Coefficientoffriction—thecoefficientoffriction（alsocalledCOF，orfriction）isameasurementoftheforceittakestoslideanobjectacrossanothersurfacedividedbytheobject’sweight摩擦系数上一页下一页返回3.3AntilockBrakeSystemsWheelspeedsensor—adevicetodeliverelectricpulsesfromwhichtheECU（ElectronicControlUnit）computesthespeedofthewheels轮速传感器Permanentmagnet—amagnetthathasahighcoercivity，meaningthatitretainsmagnetismforalongtime永磁铁Fail-safe—anequipmentthatisdesignedtomaintainsafetyevenwhenafailureoccursinanycomponent失效安全模式

μ-split—thesurfacewithdifferentfrictioncoefficients对开路面Kerb—anedgebetweenasidewalkandaroadwayconsistingofalineofcurbstones（usuallyformingpartofagutter）路缘石上一页下一页返回3.3AntilockBrakeSystemsWheelbase—thedistancefromthecenterlineofthefrontwheelstothecenterlineoftherearwheels轴距Momentofmassinertia—thesumoftheproductsofeachmasselementofabodymultipliedbythesquareofitsdistancefromanaxis惯性矩Yawmoment—themomentorappliedtorquetendingtodisplaceavehicleintheyawsense横摆力矩上一页返回3.4TheElectronicBrake-ForceDistribution3.4.1TheBasicsoftheEBDWhenarotatingwheelissubjectedtoexcessiveheavybraking，itispronetolock-up.Inmotorvehicles，theanti-lockbrakingsystemworkstopreventthisbymonitoringwheelspeedsandtakingactionintheformofreleasingpressureonthebrakingcircuit，whenarapiddecelerationoccursinanyofthewheelstoensuresteeringandvehicularcontrolismaintainedduringheavyoremergencybraking.Thishasitsdisadvantagesthough，asdifferentamountsofbrakingpressurearerequiredtolockarotatingwheelondifferentsurfacesForexample，lessbrakingpressurewouldbeneededtolockawheelwhichwasincontactwithicethanawheelwhichwasincontactwithanasphaltroad.下一页返回3.4TheElectronicBrake-ForceDistributionInasituationwherethewheelsofavehicleareonthedifferentsurfaces（forexample,thetwoleftwheelsareonaconcreteroadandthetworightwheelsareonsnow），duringanemergencystoptheABSdetectsthetworightwheelsabouttolockandactivates，eventhoughthetwoleftwheelsdon’tlockwhentherightwheelsdo.TheEBDdetectssuchconditionsandelectronicallycontrolsthebrakingforceappliedtoeachindividualwheel，andthereforemaximizesthebrakingforcetoensureamaximumbrakingeffectivenessThefinalresultismorepreciseandeffectivebrakingunderallconditions，andalsomakesthecarmuchmorestableunderheavybraking，reducingfrontenddive上一页下一页返回3.4TheElectronicBrake-ForceDistributionTheEBDisanadditionalfeatureofmoresophisticatedABSbrakingsystems，whereanelectroniccontrolsystemmeasuressuchparametersasroadspeedtodistributebrakingforcemoreeffectivelyInotherwords,thesystemautomaticallyvariestheamountofforcewhichisappliedtoeachindividualbrake.Itworksthisoutbytakingintoaccounttheroadconditions，speed，loadandotherfactors.TractioncontrolworksattheoppositeendofthescalefromtheABS—dealingwithaccelerationratherthandecelerationStill，sincemanyofthesameprinciplesareappliedtobothofthesystems，itmightbebesttovisualizeitassortofABSinreverse.TheABSworksbysensingslippageatthewheelsduringbraking，andcontinuallyadjustingbrakingpressuretoensuremaximumcontactbetweenthetiresandtheroad.Youcanactuallyhearthesystemworking（agrindingsound）andfeelit（thepedalpulsing）.上一页下一页返回3.4TheElectronicBrake-ForceDistribution3.4.2TheEBDControlIntheABS，theelectroniccontrolisusedsotherearwheelbrakehydraulicpressureduringbrakingisregulatedbytherearwheelcontrolsolenoidvalvesinaccordancewiththevehicle’srateofdeceleration，andthefrontandtherearwheelslippagewhichiscalculatedfromthesignalsreceivedfromthevariousABSsensorsTheEBDcontrolisacontrolsystemwhichprovidesahighlevelofcontrolforbothvehiclebrakingforceandvehiclestability.Thesystemhasthefollowingfeatures.

上一页下一页返回3.4TheElectronicBrake-ForceDistribution①Becausethesystemprovidestheoptimumrearwheelbrakingforceregardlessofvehicleloadconditionsandtheconditionoftheroadsurface，itreducestherequiredpedaldepressionforce，particularlywhenthevehicleisheavilyloadedordrivenonroadsurfaceswithhighfrictionalcoefficients.②Becausethedutyplacedonthefrontbrakesisreduced，theincreasesinpadtemperaturecanbecontrolledduringbrakesapplicationtoimprovethewearresistancecharacteristicsofthepad.③Controlvalvessuchastheproportioningvalvesarenotrequired上一页下一页返回3.4TheElectronicBrake-ForceDistribution(1)BrakingForceDistributionBetweentheFrontandtheRearWheels(2)TheBrakingForceDistributionBetweentheLeftandtheRightWheels上一页下一页返回3.4TheElectronicBrake-ForceDistribution3.4.3TheBrakeAssistSystemTheBrakeAssist，knownasBA，isanotherelectronicbrakingsystemandisoftenpartneredwiththeEBDTheBAmonitorsadriver’sbrakingandifitdetectsthatadriverisinanemergencybrakingmaneuver，itautomaticallysupplementsthedriver’sattempttostopquicklybyboostingbrakepowertothemaximum.TheBAstopsworkingimmediatelyafterthedriverliftsuponthebrakepedal.UnliketheABS，theBAcanhelptoimprovevehiclestoppingdistancesResearchhasshownthesystemevenhelpsprodriversstopmoreeffectively.

上一页下一页返回3.4TheElectronicBrake-ForceDistributionKeyWordsandExpressionsAdhesion—gripbetweentheroadandthetire，proportionaltothestaticcoefficientoffriction附着（力）Fading—reductionofbrakingeffortresultingfromoverheatingorothertransienteffect衰退上一页返回3.5ElectronicControlofSuspensionSystems3.5.1TheBasicsofSuspensionSystemsTheautomotivesuspensionsystemcomprisessprings，dampers（ofteninappropriatelycalled“shockabsorbers”），andvariouslinkagestoconnectthewheelassemblytothecarframeThefunctionofthevehiclesuspensionsystemistoisolatethecarbodymotionasmuchaspossiblefromwheelmotionduetoroughroadinputAtthesametimethetiresmustbekeptincontactwiththeroadandmadetobehaveinacontrolledfashionThisimprovestheridecomfortandminimizesundesirablemotionsofthebody，resultinginincreasedstabilityandsafety

下一页返回3.5ElectronicControlofSuspensionSystems3.5.2TheElectronicSuspensionControlSystemThetypicalelectronicallycontrolledsuspensionsystemconsistsofseveralcomponentsinadditiontothenormalsuspensioncomponentsThecontrolsystemforatypicalelectronicsuspensionsystemisdepictedintheblockdiagramofFig3-19.ThecontrolsystemconfigurationinFig3-19isgenericandnotnecessarilyrepresentativeofthesystemforanyproductioncarThissystemincludessensorsformeasuringvehiclespeed；steeringinput（i.e)，angulardeflectionofsteeredwheels）；relativedisplacementofthewheelassemblyandcarbody/chassis；lateralacceleration；andyawrate.上一页下一页返回3.5ElectronicControlofSuspensionSystemsTheoutputsareelectricalsignalstotheshockabsorber/strutactuatorsandtothemotor/compressorsthatpressurizethepneumaticsprings（ifapplicable）.Perhapsthemostimportantcomponentisthecomputer，whichinterpretsinputfromvarioussensorsthatmonitorsuchinformationastheautomobile’sheight，pitch，androll；howfastthewheelsarespinning；andhowquicklytheautomobileisturning.

上一页下一页返回3.5ElectronicControlofSuspensionSystemsThesimplestelectronicallycontrolledsuspensionsystemsmerelymaintainalevelrideheight，counteractingthetendencyoftheweightofpassengersandluggagetolowertherearendSystemswithfour-wheelheightadjustmentlowertheautomobile’srideheighttoreduceaerodynamicdragandimprovefueleconomyathighwayspeeds.Inoff-roadvehicles，thesesystemscanraisethevehicletoincreasegroundclearanceoverroughterrain上一页下一页返回3.5ElectronicControlofSuspensionSystemsThecontrolsystemtypicallyisintheformofamicrocontrollerormicroprocessor-baseddigitalcontroller.Theinputsfromeachsensoraresampled，convertedtodigitalformat，andstoredinmemoryThebodyaccelerationmeasurementcanbeusedtoevaluateridequality.Thecontrollerdoesthisbycomputingaweightedaverageofthespectrumoftheacceleration.Therelativebody/wheelmotioncanbeusedtoestimatetirenormalforce，anddampingisthenadjustedtotrytooptimizethisnormalforce上一页下一页返回3.5ElectronicControlofSuspensionSystems3.5.3ElectronicallyControlledAirSuspensions（ECAS）

Airsuspensionsarecomplexandexpensive，buttheyhavetheabilitytostayataconstantheight，regardlessofloadInsomecases，airsuspensionsprovideavariableheightthatiscontrolledbythedriveroracomputer-controlledvariablerateandheightforimprovedhandlingorvehicleaerodynamics.Airsuspensionsusethecompressibilityofairforaspring.Thespringrateisdeterminedbythesizeoftheairchamberandtheamountofairpressure.Ifthecaristoolow，theairpressureinthespringchamberisincreased；ifthecaristoohigh，someoftheairpressureisreleased.上一页下一页返回3.5ElectronicControlofSuspensionSystemsTheno-loadspringratesareusuallylowerthanifsteelspringsareusedbecauseairsuspensionshavetheabilitytocompensateforheavierloadsAnaircontrolledsuspensionsystemprovidesavariablespringratewhichleadstoaconstantsuspensionfreq