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TYREINFLATIONANDMONITORINGSYSTEMS(TIMS)

ContentNomenclature

1.0

Abstract

2.0Introduction

2.1ProjectMotivation

3.0DesignObjectives

3.1AbilitytoProvideProperTirePressure

3.2MinimizeNegativeVisualAesthetics

3.3AbilitytoProvideAutomaticSystem

3.4LowCostDevice3

4.0ProductDesign

4.1ProductOverview

5.0ProductComponentDescription

5.1Rotaryjointdesign

5.2Compressor

5.3Sensors

5.4SolenoidValve

5.5Tubing

6.0ElectronicallyAutomatedSystem

6.1OOPic

6.2ElectronicControlProgramDescription

6.3RequiredHardwareInterface

7.0ENGINEERINGANALYSIS

7.1PressurereductioninStraightGradient

7.2Shaftstresses

7.3StressConcentrationFactors

7.3EvaluatedDiameter

8.0BUDGET

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Conclusion

References

NOMENCLATURE

V Volume[in3] Densityoftherotaryjoint[lbf/in3]

T Temperature[F] G Gravity[ft/s2]

P Pressure[psi] Cv CoefficientofFlow

Avisible Visibleareaoftherotaryjoint [in2] Q Flowrate[ft3/hr]

Adisk Visibleareaofthebrakedisk[in2] N Moles

Cp Constantheatcapacity[kJ/kgk] Vdisk Initialvolumeofthedisk[in3]

T1 Inlettemperatureofcompressor[F] k Stiffnessoftheshaft[lbf/in]

T2 Outlettemperatureofcompressor[F] m Massofthedisk[lbfs2/ft]

h2 Outletenthalpiesofvalve[kJ/kJk] lshaft Lengthoftheshaft[in]

h1 Inletenthalpiesofvalve[kJ/kJk] P1 Inletpressureofvalve[psi]W Workdoneonthecompressor[kJ] P2 Outletpressureofvalve[psi]

V2 Outletvelocityofvalve[ft/s] Vtire Velocityofthetire[ft/s]

tire Angularvelocityoftherotaryjointshaft

system[rpm]

Cf Totalfixedcost[$]

P Pressuredropthroughthevalve[psi] Cv Variablecost[$]

Ashaft Crosssectionalareaoftheshaft[in2] Designchangevector

E Elasticmodulusoftheshaft[kpsi] d Designelasticityvector

Ve Volumeoftheeccentricity[in3] p Priceelasticity

me Massoftheeccentricity[lbfs2/ft] Maximumdemand

rtire Radiusofthetire[in] P Profit[$]

drim Diameteroftherim[in] Dampingcoefficient

crit Criticalspeedoftherotaryjoint

shaftsystem[rpm]

Xdisk Deflectionamplitudeoftherotary

jointshaftsystem[in]

G Specificgravityrelativetoairat

atmosphericcondition[ft/s2kg]

n Naturalfrequencyoftherotary

jointshaftsystem[rpm]

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1.0ABSTRACTDrivenbystudiesthatshowthatadropintirepressurebyjustafewPSIcanresultinthereduction

ofgasmileage,tirelife,safety,andvehicleperformance,wehavedevelopedanautomatic,self

inflatingtiresystemthatensuresthattiresareproperlyinflatedatalltimes.Ourdesignproposes

andsuccessfullyimplementstheuseofacentralizedcompressorthatwillsupplyairtoallfourtiresviahosesandarotaryjointfixedbetweenthewheelspindleandwheelhubateachwheel.The

rotaryjointseffectivelyallowairtobechannelledtothetireswithoutthetanglingofhoses.Withthe

recentoilpricehikesandgrowingconcernofenvironmentalissues,thissystemaddressesapotential

improvementingasmileage;tirewearreduction;andanincreaseinhandlingandtireperformance

indiverseconditions.

4 INTRODUCTION

2.1

PROJECT

MOTIVATION

Vehiclesbeingoperatedwithunderinflatedtiresposeasignificantsafetyproblem.Accordingtothe

RubberManufacturersAssociation,therewere647fatalitiesin1999thatinvolvedtirerelated

factors.Theyfurtherstatethattheleadingcauseoftirefailureisunderinflation.Accordingto

DonaldShea,RubberManufacturersAssociationpresidentandCEO,Thesinglemostimportant

factorintirecareisinflationpressure.

Infact,80%ofpassengervehiclesontheroadhaveatleastoneunderinflatedtireand36%of

passengercarshaveatleastonetirethatis20%ormoreunderinflated.Oftenpressurelossintires

isaresultofnaturalpermeationofthegasthroughtheelasticrubber,roadconditions(suchas

potholes),andseasonalchangesintemperature(AccordingtoWeisslerofPopularMechanics,for

everydropof10F,tirepressuredropsby1psi).Mostvehicleownersareunawareofthefactthat

theirtiresarenotatthecorrectpressuresbecauseitisdifficulttodeterminethetirepressure

visually;atirethatisproperlyinflatedtothecorrectpressurelooksverysimilartoonethatiseither

overinflatedorunderinflated(Fig1).AccordingtotheRubberManufacturingAssociation(RMA)survey,80%ofpeopleareunsureofhowtochecktheirtirepressures.Thus,fromtheviewpointof

passengervehicleowners,theyarelosingmoneyduetoincreasedtirewearanddecreasedfuel

efficiency,andasolutionneedstobefoundtocorrectthisissue.Fromtheviewpointofthe

designers,however,therootcauseofimproperlyinflatedtiresisduetovehicleownersnotknowing

propertirepressuresforcertainconditions,difficultyfindinganairpump,lackofpressure

measuringdevice,andagenerallackofconcern.Thus,thecombinationoftheuserandexpert

viewpointswillbeusedtomakedecisionsinourdesignprocessofthisproduct.

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Tire

Wear,

Fuel

Economy,

Performance,

and

Safety

Anunderinflatedtirecanhavedramaticeffectsontirewear.Sincethecontactpatchofthetirehas

alargerwavepattern,frictionandheatincreasecausethecontactpatchtowearoutmorequickly

thanifthetirewasinflatedproperly.

Goodyearestimatedthatatiresaveragetreadlifewoulddropto68percentoftheexpectedtread

lifeiftirepressuredroppedfrom35psito17psiandremainedthere.Accordingtoanunpublished

studybyGoodyear,theaveragecostforatire#10,000,andtheaveragetreadlifeis45,000miles.

Thus,atanaveragecostof#10,000/tire,andgivenasacircumstancethattheownerkeepsavehicle

for100,000miles,theownerwillhavetochangethetiresthreetimesinsteadoftwice.Theowner

wouldthenbepaying#40,260morefortires,andinbothsituations,themostrecentlyinstalledtires

willonlyhaveapproximately10,000milesofuse.DoranManufacturingoffersmorestatistics

regardingtheeffectsofunderinflatedtires:

20%underinflationcanreducetirelifeby30%

20%underinflationcanincreasetireswearby25%

Fueleconomyisalsogreatlyaffectedbyunderinflatedtires.Accordingtofueleconomy.gov,an

underinflationof1psiinallfourtiresonapassengervehiclereducesefficiencyby0.4%.Basedon

averagegasprices,thereisapotentialof3.3%insavings,whichtranslatesto#14.85pergallon.As

vehiclespeedsincrease,thetirepressuresshouldalsoincreaseaccordinglytoreducerolling

resistance(whichimprovesfueleconomy)andtolimitdamageduetotheincreasedfrequencyof

tireprofiledeflections.Sincehighwaysaretypicallysmootherthanlocalroads,increasingthetire

pressurewillnotnegativelyimpactridequalityintermsofnoiseandvibrations.

Properlyinflatedtiresalsohaveasignificanteffectonsafety;thereductionintirewearandincrease

invehiclesafetyarestronglycorrelated.660deathsandapproximately33,000injuriesperyearare

associatedwithunderinflatedtiresaccordingtoNationalHighwayTrafficSafetyAdministration

(NHTSA).Wornouttireshaveasignificantnegativeimpactontractioninallweatherconditions.

Underinflatedtiresalsoincreasesthestoppingdistanceofvehiclesonbothdryandwetroads.At

thesametime,driverswouldalsofindanoteworthylossofsteeringprecisionandcornering

stability.Additionally,heatbuildupandthewearofthetirestructurecancauseasudden

unexpectedblowoutonthehighways,whichisacommoncauseofmanyaccidents.

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3.0DESIGNOBJECTIVESTheoverallgoalofourdesignprojectistodevelopaproductthatwilldecreasetirewearwhile

improvingfueleconomy,performanceandsafetyofapassengervehiclethroughdynamically

adjustable

tire

pressures.

However,

there

are

several

key

objectives

that

the

team

has

targeted

our

designtomeet,andtheseobjectivesincludebothdesigncharacteristicsandbusinessobjectives.

3.1AbilitytoProvideProperTirePressure

Theidealfunctionalobjectiveofourdesignisitscapabilitytoadjustthepressuresinallfourtiresof

apassengervehicletoobtaintheproperpressureforvaryingroad/drivingconditions.Specifically,it

isdesiredthat:

Coldtirepressureismaintainedduringvehicleusetoaccountforslowleaksandfluctuating

tiretemperatures

Asvehiclespeedincreases,tirepressuresincreases

Asvehiclespeeddecreases,tirepressuresdecreases

As

vehicle

load

increases,

tire

pressures

increases

Asvehicleloaddecreases,tirepressuresdecreases.

Basedonmoredetailedresearchonthecomponentsnecessaryforthesystem,itwasdiscovered

thataspecializedrotaryjointmustbedesignedtosupportthisprocess.Thisdesignconsideration

requiredadditionalproductdevelopmenttimethatwasnotoriginallyanticipated.Therefore,the

idealfunctionalobjectiveshavebeenmodifiedtoaccountforthisdesignrequirement.Specifically,

thenewobjectivesrequirethat:

Coldtirepressure(35psi)ismaintainedbyensuringthattherotaryjointshaftsystemdoes

notfailstructurally

Coldtirepressure(35psi)ismaintainedbyensuringthattherotaryjointshaftsystemdoes

notleakexcessively

Coldtirepressure(35psi)ismaintainedbyensuringthattheentiresystem(compressor,airtubes,rotaryjoint,etc.)canprovidedsufficientflowrate

Becauseofthedetailedlevelofexplanationrequiredfortheseitems,theseobjectivesaredescribed

numericallyintheEngineeringAnalysisandOptimizationsectionofthisdocument.

3.2MinimizeNegativeVisualAesthetics

Anotherdesignobjectiveistoensurethattheproductwillnothaveanegativeeffectoncurrent

vehicleaesthetics.Allcomponentsshouldbelocatedasinconspicuouslyaspossibleandshouldonly

beseenwhenservicingtheunit.However,inthecaseoftherotaryjoints,whichmaystillbevisible

throughthewheelrims,anattemptmustbemadetominimizeitsvisibilityaroundthebrakedisks

3.3AbilitytoProvideAutomaticSystem

A

third

objective

is

to

provide

all

of

the

said

benefits

to

the

user

through

an

automatic

system,

thus

minimizinguserintervention.Specifically,itisdesiredthatthesystemautomaticallyincreaseor

decreasethetirepressuresforthegivenroadconditions.

3.4LowCostDevice

Forboththecustomer(OEM)andenduser(vehicleowner),itisimperativetokeepthepriceofthe

deviceaslowaspossible.Consideringthepotentialbenefitsandcostsavingsthatthisdesignhasto

offerandthepricesofoptionalequipmentforpassengervehicleswithsimilarcomplexity,thetarget

pricerangeforthisdevicehasbeenidentifiedas2500030000.ThisisthepriceforboththeOEM

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andvehicleowner,assumingthattheOEMdoesnotmarkuptheprice.Inaddition,thispricerange

shouldbeabletosupportthecostsofcomponentsofthesystem,manufacturing,andanynecessary

installation.

4.0PRODUCTDESIGN4.1

PRODUCT

OVERVIEW

Wehave

developed

asystem

that

iscapable

of

automatically

maintaining

tire

pressure

ina

passengervehicle.Thishasbeenachievedthroughuseofacentralizedaircompressorthatisplaced

intheenginecompartmentofavehicle.Thiscompressorisattachedtoadistributionblockwhich

houses(4)solenoidvalvesusedtocontrolwhichtiresreceiveinflationpressure.Fromthis

distributionblock,theairtravelsviadia.hosestoarotaryjointlocatedateachwheel.Thisrotary

jointallowsoursystemtopassairfromthevehiclechassistotherotatingtire.Thesystemthatwe

havedevelopedistobeintegratedwiththetirepressuremonitoringsystemscurrentlyfoundon

vehiclestoprovideourmicroprocessorwithtirepressuredata.Toreducetirepressures,oursystem

alsoincorporatessolenoidvalvesateachtirevalvewhichplantobeoperatedeitherthrough

wirelesstechnologyorelectricalcontactsineachrotaryjoint

5.0PRODUCTCOMPONENTDESCRIPTION

5.1

ROTARY

JOINT

DESIGN

Wearedesigningthisdeviceforcommonpassengervehicles,andthemainchallengeisthe

presenceoftheaxleshaftthatrunsstraightintothecenterofthewheelforcingustofindan

alternativemethodofroutingtheair. Ourproposedsolutiontothischallengeistoplacearotary

jointthathasonehalfspinningwiththedriveaxlehubandtheotherhalfstationarywiththe

spindle. Withinthisrotaryjointwillbeanairchamberthatwillallowairtopassfromthe

stationaryhalfofthejointintothehalfthatisrotating.

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Therearenumeroustypesofairtightrotaryjointsavailableonthemarket;however,wewere

unabletofindonethathadalargeboreinthecentertorunacaraxlethroughoronethathadair

inlets/outletslocatedonthefaroutsideradius. Mostofthejointsthatwewereabletofindwerefor

airenteringandexitingdirectlyintheaxisofrotationanddidnotallowforanyobjecttobeplacedin

thecenterofthem. Sincewecouldnotfindarotaryjointthatmetourcriteria,wechosetodesign

ourown

Themaincriteriaforourrotaryjointdesignwerethefollowing:

Musthavea40mmholeinthecentertoallowfortheaxletoeitherpassthroughor

supportthejoint.

Airinletsandoutletsmustbelocatedattheouterradiustoallowthehosesontheoutside

ofthejointtoclearthevehiclespindleandhub.

Overallthicknessofthejointmustbenogreaterthan25mmtosoasnottointerferewith

thevehicledrivelineorsuspensioncomponents.

Ballbearingsystemmustbeusedtoreducecontactfrictionbetweenthetworotating

halvesbothaxialandplanar.

TIMS

Adapter

Plate

Assembly

Arubberhosethreadedintotheholeinthetopoftheadapterplateconnectedtheplatetothetires

valvestem.Threeextralongstainlesssteellugnutsreplacedthenormalnutsandconnectedthe

platetothewheel.Theplateandthehoseconnectingittothevalvestemrotatewiththewheel.On

theothersideoftherotatingaircoupling(rotaryunion),aplastichoseconnectedtheuniontothe

pressuremanifoldinsidethevehicle.Theplastichosewastapedtothecartopreventitandthe

outsidepieceoftherotaryunionfromrotating

Material

Consideration

UsingHeattransferrelativecastironvsmassrelativetocastirongraph

Rotaryjointadapter

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BerylliumanditsalloypreferablyBeAl40%.OtherwiseAlloysCopperwin

RelativePenaltyFunctionareconsidered.

NotePSBisusedinourmethodofanalysisratherthanWSB.

5.2COMPRESSOR

Wehaveselectedareciprocatingaircompressorforourdesignpurpose.Herewehavebreakdown

drawingsanddiagramsofPistonaircompressorsaswellasforRotaryScrewaircompressors.There

areothertypes,butthevastmajorityofaircompressorsinusetodayareoneofthese.Ingeneral

theyconsistofanairpump,amotororengineandatanktoholdthecompressedair.Thereare

manydifferentpartsandpiecesthatmakeupanaircompressor.Althoughsomemaybefairly

generic,mostpartswillvarydependingonthemakeandmodelofthecompressor.

Apistoncompressor(alsoknownasareciprocatingcompressor)usespistonsdrivenbyacrankshaft

todeliverairathighpressure.Theimageswiththebreakdownsbelowdisplaythemostprominent

componentsofthecompressor.Theimagebelowisastandardstationarycompressor(Ingersoll

RandSS5L5).

1.PressureSwitch2.CheckValve3.CompressorPump4.Belt5.Pulley6.Motor7.Tank

AnexampleofthisisaPORTABLE300psICOMPRESSORThisportableaircompressorhasasmall

electricmotorthatcompressestheairinasmallattachedcylindertank;Itcanbepluggedintoa12V

carsystemforonthegorepairsorinflation.It'sidealforcarandbicycletires,sportsballs,and

inflatablematerials;Itcanbepoweredthroughacigarettelighterinyourvehicle,itisincredibly

versatile.

The300psIcompressorhasarelativelylowcostat3050.

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Itrequireslessinputpowerof12vtopower.

Itissmallinsizeandcanbefittedatanydesiredplace.

ItcanbeintegratedwiththeECUorcontrolpanelforoptimization.

Itsuppliesahighpressureof300psIwherealossinpressurewillnotadverselyaffectit.

Tomaintainasteadyflowthroughthetubes,thecrosssectionalareaofthetubemustbesmall,

havingauniformdiameter.Whencompressedairpassesthroughthepressuretubesfromthe

compressortothesolenoidvalve,thesizingofthevalvewillincludeadditionalfactorsthatenhance

theperformanceandreducepressuredrop.

Pressuredropwhichresultsfromthefrictionproducedbytheflow

ofcompressedairinpipelinesandfromthesystemcomponentsthemselves,verticalpipedifference

orelevation,changesofkineticenergyiscalculatedandcheckedateachcomponenttoimprove

efficiency

5.3SENSORS

Apressuresensorusuallyactsatransducer,itgeneratesasignalasafunctionofthepressure

imposed.Thesensorsphysicallymeasurethepressureofthetiresandbroadcastthepressuredata

viaawirelessradiofrequencytransmittertocentralreceiver.Thedataisanalyzedandtheresultis

senttotheLCDdisplayinthevehicle.Thesesensorsfacetheproblemofexposuretotough

environmentswhichlimitstheirusefullifebecausemajorityofthemarepoweredbybatteries.We

wouldbemakinguseofthesensorsthatutilizeawirelesspowersystem,thissolvestheproblemof

limitedbatterylifebyelectromagneticinduction.

Apressuresensorusuallyactsatransducer,itgeneratesasignalasafunctionofthepressure

imposed.Thesensorsphysicallymeasurethepressureofthetiresandbroadcastthepressuredata

viaawirelessradiofrequencytransmittertocentralreceiver.Thedataisanalyzedandtheresultis

senttotheLCDdisplayinthevehicle.Thesesensorsfacetheproblemofexposuretotough

environmentswhichlimitstheirusefullifebecausemajorityofthemarepoweredbybatteries.We

wouldbemakinguseofthesensorsthatutilizeawirelesspowersystem,thissolvestheproblemof

limitedbatterylifebyelectromagneticinduction.

5.4SOLENOIDVALVE

Asolenoidvalveisanelectromechanicallyoperatedvalve.Thevalveiscontrolledbyanelectric

currentthroughasolenoid:inthecaseofatwoportvalvetheflowisswitchedonoroff.Solenoid

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Therearevarioustypesofairhosesincluding;rubberairhose,PVCairhose,polyurethane(PU)air

hose,andnylonairhose.Forourdesignpurposetherubberhoseispreferredovertheabove

mentioned.

Rubberhoseispreferredbecause;Itisflexibleinallweatherconditions,Itcanwithstandmore

physicalabusethantheothertypes,Itisalsoeasilyfoundinthemarket,Itischeapaddurable,It

uncoilseasilyunliketheothertypesthathappentobestiffer,Theyalsocanbeeasilyrepairedoreasilyreplaced

SpecificallywechoseVitonrubberbecause;itresistscorrosiveenvironments.Italsohasexceptional

resistancetoheat,aging,weather,ozone,oxygen,sunlight,solventschemicals,airdiffusionetc.

Goodflameresistance,hasatensilestrengthof8N/mm,withamaximumtemperaturerangeof

25/+200C

Insummary,thematerialisparticularlyheatresistantandresistanttooil,solventsandstrongacids

andcanalsowithstandmostweatherconditions.

6.0ELECTRONICALLYAUTOMATEDSYSTEM

Ourfinalproductpossessestheabilitytoautomaticallymaintainthecoldtirepressureinallfour

individualtiresofthevehiclethatitisinstalledon. Themainfunctionsoftheseelectronicsisto

takethepressuresensorreadingfromeachofthetires,andthendecidewhetherornottoinflate

themordeflatethemtoensurepropercoldtirepressure.

6.1OOPic

TheOOPicisthemaincomponentofourelectronicssystem. Essentially,anOOPicisanObject

OrientedPeripheralInterfaceMicroController. Thisallowsustomakevirtualcircuitsinasmall

chipsowecanlinklogicbetweenourdifferentobjects(compressor,pressuresensors,and

solenoidvalves). Figure19showsthedifferentcomponentsofanOOPicboard

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ComponentsofanOOPicBoard

6.2ElectronicControlProgramDescription

ThelogicthatourOOPicneedstocontrolisquitebasic.Wehave13componentswhichweare

interfacingwith:aircompressor,(4)intirepressuresensors,(4)distributionblocksolenoidvalves,

(4)pressurereleasesolenoidvalves.

Figure20isaflowchartofthelogicstepsthatwewillbetakinginourprogram.Whentheprogram

startsup,thefirstthingthatitdoesischeckallofthetirepressures. Ifatleastoneofthetire

pressuresislow,itwillturnonthecompressor. Forthegivenlowpressuretire,thecorresponding

distributionblocksolenoidvalvewillopenallowingthetiretoinflate. Thisinflationprocesswill

continueuntilthepressuresensordetectsthatthetirehasreachedtheoptimalpressure;the

solenoidvalvewillthenclose. However,ifatirepressureistoohigh,thepressure

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6.3

Required

Hardware

Interface

WecannotcontroltheaircompressordirectlythroughtheOOPic.Thecompressormotorrequires

atleast12VDCand3AtooperateandtheOOPicsuppliesamaximumof5VDCand0.25A. Wecan

dealwiththisissuebyusingatwochannelamplifierthatamplifiesthepowerfromtheOOPicin

ordertooperatethemotor. WecanthenuseapulsewidthmodulationoutputfromtheOOPicas

thepositivereferenceinputontheamplifier.Pulsewidthmodulationisamethodpredefined

withintheOOPicthatallowsustospecifythevoltage(between0Vand5VDC)weoutputfromthe

OOPic.Whenweoutputa5VsignalfromtheOOPictheamplifierwillamplifya+12Vsignaland

turnthecompressoron.

Similarly,allofoursolenoidvalveswillrequire12VDCtoopen,andduetothecurrentdraw,we

cannotcontrolthecompressordirectlythroughtheOOPic. Howeverhavinganamplifierforall(8)

solenoidvalvesinoursystemwouldbetoocomplexandcostly. Thebetterroutetotakewouldbe

touserelaysforeachvalve.Arelayworkslikeanelectronicallytriggeredswitch.Whenitis

powered,itcompletesthecircuitand12VDCfromthepowersupply(carbattery)issentstraightto

thesolenoidvalvetoopenit. Whenthe12voltsisremovedfromthesolenoidvalve,it

automaticallycloses

ThetirepressuresensorwillbeinterfaceddirectlywiththeOOPic. Thecomponentcanbe

poweredbythe5VDCprovidedbytheOOPic. ThereisaspecialInput/OutputareaoftheOOPicwherethepinsarearrangedsuchthatonerowofpinswillpoweradeviceandtakeaninputfrom

thedevice. However,wedonothavethespecificsontheparticularoutputreadingsofthetire

pressuremonitoringdevice. Optimally,wewouldhavealinearrelationshipbetweenthetire

pressurereadingandthedevicesoutputvoltage.

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7.0ENGINEERINGANALYSIS

7.1PRESSURE

REDUCTION

IN

STRAIGHT

LAYOUT

Forthepressuredropalongstraightlinesfromthecompressortoreliefvalveandsolenoidendto

axleterminal.Straightlayoutappearsabout18times,theequivalentpressuredropintheorificeis

givenas:

. .

~

....

.

(HazenWillams/Blausius1845)

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Where,

=pressuredrop(kg/m2)

Q=airvolumeflowatatmosphereconditions(m3/s)

L=lengthoftube(m)

d=insidediameteroftubing(.0635m)

Critical

Pressure

Drop

Sections

Thefollowingpartshassignificantpressuregradient;

Pressureelevationdifference(variable)

Frictionalflowresultingfromairflowinthetubing:itwascalculatedtobe1.354psiforan

effectiverunof6.4m)

Frictionaldropintherelayvalve

Totalorificepressuregradientincontrolvalue:0.56psi

Totalrotaryassemblyairleakage(variableowningtoreplacementandvibrations)

Thecompressorportlinkingtube(~.37psi)

Fromthestatedfactorsandotherpressureconcentratedareathewillalwaysbelessthan

3psipressurereductionunderastableenvironmentalcondition.

7.2

SHAFT

STRESSES

Thetheoryoftorsionalvibrationofcylindricalshaftisgivenas[KhurmiGupta,2006]:

Systemtorsionalfrequencies factorslikecouplingstiffness(331

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7.3STRESSCONCENTRATIONFACTORS

Theobjectiveofthisphaseisdoneviaforcevibrationanalysisateachmassandonthestresseson

eachshaft.ThevaluesderivedbyMichelin{MichelinMaterialindexHandbook,2007}.

Theshaftdimensionarebasedonthese,twist()betweeneachmass,materialproperties,andshaftdimensionsdefinestorsionalstress():

S=SCF

Where

S=stress,psi

D=minimumdiameter,inches

=twistbetweenadjacentmasses,radians

L=effectivelengthbetweenadjacentmasses,inches

G=shearmodulusofshaftmaterial,Ib/in2

SCF=stressconcentrationfactor(dimensionless)

WeusetheTorsiographtocarryoutthisexperimentwithseveraliterations.

7.3EVALUATEDDIAMETER

Formaximumtwistof30,stressof35psi,aneffectivelengthof15mand92.3GPamodulus

ofrigidity.Theminimumdiametermustbe

35 2 49.21

0.048 49 103 0.314

1.524

andusingforshaftsafetydesign(Beer&Johnston,2001)

3

32 2 0.752

Thevaluefactorofsafety,nisbetween3.54.0

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8.0

BUDGET

ELECTRICAL

COMPONENTS

PartName Part# Vendor Quantity UnitPrice

()

Total()

MSP430

DesignBoard

MSP

FET430U100

Texas

Instruments* 1 6100.00 6100.00

AirCompressor 15101.02 Tellico4x4.com 1 2750.00 2750.00

CheckValve 6D917 Grainger 1 1200.00 1200.00

PressureSwitch 5B419 Grainger 1 700.00 700.00

SafetyValve 5A708 Grainger 1 900.00 900.00

PressureGauge 5WZ11 Grainger 2 525.75 1051.50

SolenoidValve 6JJ52 Grainger 4 412.50 412.50

PressureSensor MLH050PGP06A DigiKey 2 3600.00 3600.00

total 18076.50

MECHANICAL

COMPONENTS

PartName Part# Vendor Quantity

Unit

Price() Total()

RotarySealAssembly NA IMSMachining 4 1108.25 4434.00

Rod

Squeeze

Seals

3"

9422K35

McMaster

Carr

4

375.00

1500.00

RodSqueezeSeals13/4" 9422K29 McMasterCarr 4 251.50 1006.00

ShoulderBolt 2713B53 McMasterCarr 16 132.50 2120.00

Tubing NA McMasterCarr 8m 235.00 1880.00

total 9059.00

Totalcostforthisprojectis26265.50

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CONCLUSIONSUMMARY

Thedynamicallyselfinflatingtiresystemwouldbecapableofsucceedingasanewproductinthe

automotivesupplierindustry.Itspecificallyaddressestheneedsoftheconsumersbymaintaining

appropriatetire

pressure

conditions

for:

Increasedfueleconomy

Increasedoverallvehiclesafety

Reducedtirewear

Becausesuchaproductdoesnotcurrentlyexistforthemajorityofpassengervehicles,themarket

conditionswouldbefavourablefortheintroductionofaselfinflatingtiresystem.Throughextensive

engineeringanalysis,ithasalsobeendeterminedthattheselfinflatingtiresystemwouldactually

functionasdesired.Inparticular,theproductwouldbecapableof:

Providingsufficientairflowtothetirewithminimalleakage

Withstandingthestaticanddynamicloadingexertedontherotaryjoints

Notethatlikewise,thissystemwouldnotproduceanynegativedynamiceffects(suchasCVjoint

failureduetoresonance)onsurroundingsystems.Mostsignificantly,theselfinflatingtiresystemwouldbeasuccessfulproductbecauseofits

economicbenefitstoinvestors.Specifically,thefinalproductwould:

Sellatabout$900/unit,withtotalfirstyearprofitandsalesofnearly$2.1millionand58,000

units,respectively

Experience12%annualmarketgrowtheachyearforthefirstfiveyearsoftheproduct,

bringingtotalsalesupto370,000units

Breakevenonthecapitalinvestmentinjustunderthreeyears

Forfurtherdevelopmentofthisproduct,werecommendincreasingthecapabilityofthesystemby

addingthefollowingfeatures:

Pressureadjustmentbasedonincreasingvehiclespeed

Pressureadjustmentbasedonincreasingvehicleload

Adaptability

for

recreational

use

(inflating

rafts,

sports

balls,

etc.)

Implementationofinteractivedisplay

Creationofuniversaldesignforaftermarketuse

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Documents

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