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8/13/2019 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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