Body & Chassis Design

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    G.N.Kotwal

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    Contents

    Considerations

    BodyStyles sedan,hatchback,stationwagon,SUV,etc.

    BodyComponents:Bumpers,grills,glasses,headlights,

    etc.

    Bodyinteriors passengercompartment restraintsystems,airbags,Dashboard,trimmings,seats,

    ma er a s, . ChassisDesign:

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    Tomaintaintheshapeofthevehicleandtosupportthevariousloadsappliedtoit.

    Accountsforalargepartofthedevelopmentandmanufacturingcostinanewvehicle.

    Imp.Criteria:strengthandstiffness.

    Adesignaimstoachievethesewithaslittlemassas

    StructuralDesigninvolves Selectionoftype.

    edgeforcesbetweensimplestructuralsurfaces) SizingofPanels,Sections&Joints.

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    Strength&Stiffness

    SufficientStrengthforallloadcases.(Resistance

    againstfailure)

    Stiffness Deflectionswithinelasticlimit. ,

    Geometry.Majoronesnecessary:

    Torsional Stiffness

    freq.

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    , , ,

    plastic,orcompositematerials

    Serves

    as

    an

    attractive

    covering

    for

    the

    c ass s

    IntegralwithChassisforLightVehicles(Wt.

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    everythingattachedtoitexceptthebody , , ,

    transmission,driveaxleassembly,and

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    Frame

    otherpartsofthevehicle

    BoxorChannelsectionsused.

    Hasadeepersectioninthecentrearea thebendingstressisgreatest.

    ,membersattachment),specialstrengtheningsupportsarefitted.

    o yover rame o yonc ass scons ruc on a er chassispartsandbodybolttotheframe

    Unibod unitized construction

    sheetmetalbodypanelsareweldedtogethertoformthebodyandframe

    .

    Forprotectionagainstrustandcorrosion,theymaybe

    galvanized,ortreated

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    Unibody Construction

    Theframe

    is

    an

    integral

    part

    of

    the

    body

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    .

    Externalloads:thewheelgroundinterface,

    elements,andfromtheaerodynamics.

    Interna oa s:masso t eve c ean

    payloads(suchaspassengersandbaggage).

    AlsoDuetothereactionforcesofthepowertrainsuspension.

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    Chassisstructures:

    Canbeseparatedfromthebody,(asinindustrialvehiclesandsomecommercialandoffroad

    ,

    ortheycanbeintegrated,asfoundinunitized.

    Inthiscase,auxiliarystructuresareapplied,to

    ,suspensionmechanisms,engineorpowertrain,

    transmissionandfinaldrive.

    Chassisstructuresinthesethreecasesarealso

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    UNDERBODY

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    UNDERBODY

    .Alsocalledplatform.

    Modularunderbodiesaredesignedsothat

    interchangeablesidebeamsandcrossbeamsof

    differentlengthcanbeassembledtogethertogeneratelatforms for the different wheelbases and tracks

    producedbycommonfacilities.

    Theintegratedbeamsperformingthefunctionofthe

    thelongitudinalelementsarestillcalledsidebeams,andthecrossbeamscrossthebodyshell.

    Theshapeofthesebeamsalsoplaysamajorroleindeterminingthebehaviorofthebody(deformation,energyabsorptionandoccupantprotection)intheeventofacrash.

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    structurefortheunderbody,andatopframe,,

    elements,thepillars.

    ,

    calledApillars,whilethosebehindthefront

    .

    behindthereardoors.

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    SUBFRAME

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    SUBFRAME Subframes orauxiliar frames erformthefollowin functions:

    tothefrontofthecar,offermountingpointsforsuspensionlowerarms,antirollbar,steeringboxandpartofthepowertrain.

    tothebodyareamostsuitablefromastructuralstandpoint.

    Buildasecondarysuspension,whenmountedonthebodywithelasticelements abletofiltervibrationsfromthepowertrain andwheels,atfrequenciescriticaltoacousticcomfort.

    contributetomanagebodydeformationsintheeventofacrash.

    Offeranassemblysupporttomanyelementsofthechassis,

    Their reduced dimensions as com ared with the dimensions

    ofthebody,allowbettercontroloftoleranceofthesuspensionmounts,withbenefitsfortheirelastokinematicbehavior.

    connectedtothebod throu htwolar emounts flexiblerubberbushing,designedtofilter powertrainandwheelvibrations.

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    Body Shell / Space Frame

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    BodyShell/SpaceFrame

    Imaginedasaspaceframe(allbeamsmakinguptheframedonotlieonasingleplane,asinconven ona rames w many npane s,suc

    aswall,roof,sidesandfloor contributingtothe.

    SideBeams:thelongitudinalintegratedbeams

    erformin thefunctionofthechassisstructure. Offer stiffmountstosuspensions,powertrain,

    bumpersandotherchassis components.

    Beamc/sshape playsamajorroleindeterminingthebehavior(deformation,energyabsorptionandoccupantprotection)intheeventofacrash.

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    ByStylists&Engineers FirstDesignStu io setupin1927atGM.

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    PassengerProtection

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    g

    Inadditiontothestrengthrequiredfornormalconditions,vehiclesaredesignedtoprotect

    theoccupantsintheeventofacollision.

    Twomajorareasofareprovidedforthis:

    1.Crumplezones, 2.Sideimpactprotection.

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    Inacollisionthekineticenergyisabsorbedin

    stort ngt eve c estructure.

    Ifthisdistortioncantakeplaceoutsidethe

    passengercompartment,adegreeofprotectionfor

    thevehicleoccupantscanbeprovided.

    Thefrontandrearendsaredesignedtocollapsein

    theeventofacollision knownascrum lezones

    Prototypevehiclesaresubjectedtorigorousteststo

    setbygovernmentalbodies.

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    arefi

    tted insidethe

    doors

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    Aerodynamics studyoftheforcesgenerated

    Maingoals

    ,minimizingnoiseemission,

    reventin undesired lift forces and other causes

    ofaerodynamicinstabilityathighspeeds. Racin vehicles To roducedownforce to

    improvetractionand corneringabilities.

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    Atruckwithaddedbodyworkontopofthecabto

    reducedrag.

    History:

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    reducingaerodynamicdragathigherspeeds. 1950s:Systematicallyanalyzetheeffectsof

    automot ve rag ort e g erper ormanceve c es.

    Late1960s :Scientistsalsobecameawareofthe

    automobilesathighspeed.

    Aerodynamics

    AffectsVehicle

    design

    &

    performance

    infollowingways:FuelConsumption(pollution)

    Noise&VibrationControlandHandling

    Shape&Styling

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    Alotofenginepowerisconsumedindrivingavehicleagainsttheairresistance.

    Theairresistanceisaffectedbydragcoefficient

    dependentontheshapeofthevehicle

    Airresistance

    =

    C *

    A

    *

    V

    2

    whereCdisthedragcoefficient, Aisthefrontalareaofthe

    vehicle,and

    Visthevelocityofthevehiclerelativetothewindspee .

    FeaturesofStreamlined/AerodynamicVehicles

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    . Integratethewheelarcsandlightsintotheoverallshape

    Recessingdoorhandlesandshapingofexteriormirrors,Roofrails,etc.

    AtailcalledafastbackorKammback orliftback.

    Reducetheareaoftheirback.

    , ,passengers,thenreacceleratedbyanozzleandthenejectedunderthefloor.

    Flatandsmoothfloortosupportthe

    Venturi effectandproducedesirable

    downwardsaerodynamicforces.

    .

    reducesunderbodyturbulence. Suspensioniseitherstreamlinedor

    .

    Airflowthroughthewheelbaysissaidto

    increasedrag

    ComparisonwithAircraftAerodynamics

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    Roadvehicle muchlessstreamlinedcomparedtoanaircraft. Vehicleoperatesveryclosetotheground,ratherthaninfreeair.

    squareofspeed).

    Vehiclehasfewerdegreesoffreedomthananaircraft, its.

    Vehicleshavespecificdesignconstraints intendedpurpose,

    g sa etystan ar s requ r ng, orexamp e,more ea structuraspacetoactascrumplezones),and

    certainregulations.

    oa s muc worse smoo ness, e r s an eaverage

    airstrip. Cardrivers vastlyundertrainedcomparedtopilots,anddonot

    r ve omax m zee c ency.

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    Dragcoefficient(Cd) '

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    smoothness,relatedtotheshapeofthecar.

    MultiplyingCd bythecar'sfrontalareagivesanindexofo a rag. eresu sca e ragarea.

    Thewidthandheightofcurvycarsleadtogrossoverestimationoffrontalarea.

    Downforce

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    allowsittotravelfasterthroughacornerbyholdingthecartothetrackorroadsurface.

    Increaseinvehicledownforce mayalsoincreasedrag.

    Veryimportanttoproduceagooddownwardaerodynamicforce affectsthecarsspeedandtraction.

    Principleofcreatingliftinaeroplanesusedinreversetoapplyforcethatpresses ecaraga ns eroa re erre oas aero ynam cgr p an differentfrom"mechanicalgrip,"whichisafunctionofthecarmassrepartition,tiresandsuspension.

    'minimumspeedinordertoproduceasignificanteffect.

    Twoprimarycomponentsusedtocreatedownforce : shapeofthebody,and

    useofairfoils(wingsorspoilers).

    Bodyworkontopofthecarcanbeaddedtoallowasmoothflowofairtoreachthedownforcecreatingelements(i.e.,wingsorspoilers,andu n e r o y unne s .

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    OtherAerodynamicConsiderations Cd &Cd xA(TotalDrag)

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    Makingvehiclesmallerinfrontview. Slipperiness

    MoreAirPressureonto thanunderneath.

    AirBreathingneeded BreathingApertures

    EngineCooling Opening 2/3oftheradiatorsize.

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    Steel:Cheapest,versatile,cheapesttoform,

    Strong,Ductile(Formable),Weldable,Durable,

    Recyclable,Corrodable.

    Aluminium :Notsoformable,weldable,

    , ,

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