An Investigation into the sources of vehicle tire noise

Rochester Institute of Technology

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4-1-2002

An Investigation into the sources of vehicle tire

noise

John Paoff

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Recommended Citation

An Investigation into the Sources of Vehicle

Tire Noise

By

John M. Paoff

A Thesis Submitted in

Partial Fulfillment of the

Requirements for the

Master of Science

In

Mechanical Engineering

Approved

by:

Dr. Josef S. Torok

Department of Mechanical Engineering

Dr. Ag Crassidis

Department of Mechanical Engineering

Dr. Alan Nye

Department of Mechanical Engineering

Dr. Ed Hensel

Department Head, Mechanical Engineering

(Thesis Advisor)

Department of Mechanical Engineering

Rochester Institute of Technology

Permission Granted

Investigation of Tire Noise

I, John Paoff, hereby grant permission to the Wallace Library of the Rochester Institute of

Technology to reproduce my thesis whole or in part. Any reproduction will not be for

commercial use or profit.

Date:

5

p/o

d-

Signature of Author:

_

Acknowledgments

Writing

this thesishas been a_{very challenging life}experienceforme,andthough

I almost gave_up and walked_{away from}

it,

Ifelt Icould notlet downthose whohelped

me out_alongtheway.

First,

Iwouldliketothank_myparentsfor supportingme

throughout_my academic career. Inthemechanical_{engineering department I}wantto

thank_mythesis advisor,Dr.

Torok,

for stickingwithme onthis thesis andfor making

learning

more

interesting

thanIeverimagined itcouldbe. Iwould alsoliketo thankDr.

Kempsifor

letting

meinfesttheGraduate Lab foraquarterorso.Iwouldliketo thankall

the teachers who put_upwithcountlessvisitsto theirofficeand me _askingamillion

questions (youknowwho youare!).I wouldalsoliketo thank thosewhoI hadthe

privilegetobecolleagues andfriends with eventhough_{I probably}annoyed a-lot of you

(Big

Mike,

Bret,

andothers).Iwouldliketo give aspecialthanksto thosewho cameto

RIT from Alfred State withme,itwasa

long

strange_trip, andthoughwehad our

disagreements,

Iwill neverforgetthefuntimes.

Thanks,

Abstract

Noiseproduced

by

a_rollingtireon pavementhasplagued automakersforyears

duetoits complexity.Tirenoiseis dependenton_manythingssuch astirematerial, tire

construction,road surface_texture,etc. Inthis

investigation,

an acousticalapproachto

modelingtirenoiseispresented.Basedonthemechanicsof a_{rotating tire,} acoustical

modelscanbe developed.

This,

alongwith some acoustical _analysis, leadsto

mathematicalmodels thatonecanutilizein ordertopredictthenoisethat the tirewill

produce.These models willprovide a goodbasisand_startingpointforreduction oftire

Table

of

contents

Chapter

Page

Chapter I Introduction

5

Chapter II General DiscussionofSound 7

Chapter III Sound Measure 1 1

Chapter IV Tire Construction 14

Chapter V Tiresand

Elasticity

17

Chapter VI InfluenceofMaterial Properties onTire Noise 22

Chapter VII TireConstructionandNoise 35

Chapter VIII Section 1: Road Texture andTire/Road Noise 42

Chapter VIII Section 2: Air

Pumping

as aNoise Source 43

Chapter IX Methodsof

Measuring

Tire Noise 44

Chapter X Patch

Frequency

53

Chapter XI TireBulge 56

Chapter XII The

Rubbing Theory

59

ChapterXIII Conclusions andFuture Recommendations 69

Resources 74

Chapter 1

-Introduction

Inthelast

twenty

years or_so,tire noise,has been modeledthroughmethods such

as: vibrationanalysis, acoustical

holography,

andothertechniques _usingvarious

laboratory

set-ups.Ofallthemethods outthere_{isn't any}one

theory

that_completely

captures

everything

that_{is producing}noisedueto the_complexityoftheautomobiletire.

Basicacoustical principles and_measuringtechniquesallowonetodeterminea

soundlevelof a source andtodistinguish it from backgroundorother_{simultaneously}

occurringnoises.This is done

by

anaddition and/or subtraction of sound pressure levels.

Thegoal ofthisworkistoprovide a_{basic understanding}ofacoustics and_apply

theprinciplesto an_everydayproblem, tirenoise.Thisobjectivewaschosenbecause

thereis nocompletemathematical or acoustical modelfortirenoise.This isnotan

attempttocreatetheperfect_model,butthrough observations andbasic acoustical

principles,morepieces ofthetire noisepuzzlecanbeadded.

Chapter 2 begins

by

_goingoverthebasicsof_sound;whatit

is,

how it ismeasured,

and some acoustical terminology.Chapter 3 goesinto detail onhowtomanipulate, add,

and subtractsoundlevels. Chapter 4givesbasic information ontireconstruction.Chapter

5 isabouttiresand elasticity. Itcovershowtires react under aloadandits resulting

deformations. Chapter

6

looks at workdone in thepast

by

M. Muthukrishnan

[12]

for

SAE in 1990titled_{"Effects ofMaterial Properties}on TireNoise." Theauthor shows

how noiselevels go_upwith

increasing

speedand

increasing

weight.He also

describes

in

detail howtirenoise is affected

by

tireproperties suchas modulus of_elasticityandTan

noise

levels.

Chapter 7 isonthepaper"Investigation intothe_{Influence of Tire}

Construction

on

Coast-by

Noise"

by

Don

Brackin, Nishuhata,

andSauerZapf [18]. The

main points madeintheirinvestigation arethat tire treadvibrationis greatestnearthe

contact patch ofthetire. It isalso concludedthatshouldertreadvibrationis thenoise

sourcethatbestcorrelatestomeasuredtirenoise.

They

also statehow

lowering

thecenter

contact pressure and or

increasing

theshouldertread

bending

stiffness will decreasethe

tiretreadvibration and reducetirenoise generated. Chapter 8coversthe_relationship

betweenroadtextureandtirenoise. Written ina conferencepaperfrom Noise-Con96

by

Yasuo OshinoandHideki Tachibana

[7], they

concludethat tire/roadnoiseincreaseswith

anincreaseof roadtexturedepth. Chapter 9 ison

Plotkin,

Montroll,

andFuller's

[4]

_study

onnoise sourcesthatare consistentwith airpumping.

They

describe how sound pressure

dueto air_{pumping is}

directly

relatedto thesecondderivative ofthevolumeof air

displaced fromtreadvoids.Chapter 10goesintothemethods of_measuringtirenoise that

are_commonlyused.Thesemethodsinclude "The

Coast

By

Method," "The Trailer

Method,"

and"The

Laboratory

Drum

Method."

Chapters 11-14arewherethe

mathematical_modelingthrough observationand experimentationis presented.Chapter

1 1 discussestirepatch

frequency

and astire patch

frequency

increasessodoesthe sound

level. Chapter 12 isabouttirebulge anditseffect on tirenoise. Chapter 13 takesyou

through thedevelopmentofthe_{rubbing theory,}whichis then_{backed up}through

experimentation. Chapter 14concludesthisinvestigation and givesfuture

Chapter

II

-

General

Discussion

of

Sound

Sound

canbe

described

as a_{disturbance spreading}through aphysicalmedium,

such as air. Theear perceivesitas a pressure wave superimposed upontheambientair

pressuretothe

listener.

Thesound pressureistherefore theincrementalvariation about

theambient atmospheric pressure. Todescribethesepressurewaveswe call_sound,

mathematically,it is besttolookattheattributesof a puretone. Apuretoneisa

sinusoidal pressurewave of aspecific

frequency

andamplitude,propagating at a_velocity

determined

by

thetemperatureand pressure of air.

A hypothetical sound_generator, asdescribed

by

Irwinand

Graf,

in Industrial

NoiseandVibration

Control,

is shownbelow:

o

Figure 1

-[17]

Thesource_{may be}thoughtofas anelastic _sphere,like a

balloon,

thatexpands

andcontracts sinusoi

dally

at a

frequency

f.astheballoon _{expands, thesurrounding}air

molecules arecompressed.Whentheballooncontracts, theair molecules spreadapart;

thegas israrefied.The sound wave generated willhave a

frequency

equalto thenumber

oftimesper secondinwhichtheballoon expandsand contracts. The

Amplitude

ofthe

The

frequency,

f,

of an_{oscillating disturbance is}equal to thenumberoftimesper

secondthat the

disturbance

passesthroughboth its positiveandnegativeexcursions.The

number of cyclespersecondis termed

Hertz

(cycles/sec). The

frequency

of a simple

puretone sound waveis recognized asthepitch ofthe tone.

Theperiod,

T,

ofthesinusoidal waveisthe timerequiredforone complete_cycle,

andis relatedtothe

frequency,/,

by:

r=J_ [I7]pg.3

/

Thewavelength,

A,

is thedistance between likepoints ontwosuccessive waves.The

wavelengthisrelatedto the

frequency

and_velocityof propagationby:

A

=- =_cT [l7]Pg.3

/

inwhich the_{velocity ofpropagation, c,}is inturn afunctionofthecharacteristics ofthe

propagation-supportingmedium._{The velocity}ofpropagation or speed ofsoundinairis

given

by

theequationbelow:

y*P

c=\- 2. [17]pg.3

Here y isspecificheatatconstant pressure over specific heatat constant volume.

specificheat

(c.p.)

Y

=

[17]pg.3 specificheat

(c.v.)

Pa

=Ambient_{or equilibrium pressure}

p

=_Ambientorequilibrium

density

\Al/2.

c=

49.03*(R)

_{whereR is the}

temperatureindegrees Rankin

or c =

20.05*(K)

whereK isthe temperaturein degrees Kelvin

Thesound power

level

describestheacoustical power radiated

by

a givensource

with respecttothe

international

referenceof 10A-12W. Thesound pressurelevel is

proportional to the

logarithm

oftheratio ofpressures squared.This is important inthat

thepressure squaredisproportionaltosomesoundpower;thus, boththesoundpower

level and sound pressurelevelare associatedwithpower. Soundpowersandsound

pressures are _commonlyexpressedina

logarithmic,

ratherthanalinearscale called

decibels. The decibel isthe

logarithm,

to thebase

10,

oftheratioofthe_{quantity in}

question,toan _arbitrarilychosenreference quantity.Theargument ofthelogarithm is

dimensionless.

Level=₁₀

log

<

Xs-KZ,

Z =

quantity inquestion

Z0

=_{chosenreference}

quantity

Thesound power

level, Lw,

is definedas:

[17]pg.6

'W\

*w=101og

W =_powerin_question

Wre

=10-12watt

Thesound pressure

level, Lp,

expressedin decibels is:

[17]pg.6

LP

=10

log

' p^

LP

=20

log

P v re

J

f P\

[17]

pg.8

P - Root

-mean

-square

(RMS)

sound pressure

in

question (Pa.or

N/m

2

)

Pre

=InternationalReference Pressure of

The

human

ear cannot respondtoall

frequencies

in anunbiased manner.Audible

range of a

human

being

ranges

from

20 Hzto20,000

Hz,

whichinfactwill _vary with

age,

health,

past exposure_{to noises,} and so

forth.

Theear also actslikeafilterand will

favor

certain

frequencies

overtheothers. Theearis most sensitivetosounds attherange

of1,000to

5,000

Hz,

and

particularly

at about4,000 Hz. Theperceived sound pressure

level or

loudness

is

frequency

dependent.

Figure2

-[19]

[image:12.557.32.534.223.697.2]

Chapter

III

-

Sound Measure

The

understanding

of noise problems_{commonly demands}thatpressuresand

powersbemanipulated

by

means ofdecibel additions andsubtractions.Sound Pressure

levels

(in

decibels)

are averagedinthecalculation ofsource_{directivity. For adding} and

subtractingand_averaging

decibels,

quantitative analysis areusedas well ascharts and

approximations.Inthis

investigation,

theappropriate quantitative analysis willbe

concentrated on.

Soundpowerlevels are_commonly addedwhen

determining

the total sound power

levelofasource. Becausenoise canberandom withrespecttophasemeasurements, it is

added on an _{energy basis. Assume}thesound pressurelevels

Lpl, Lp2, Lp3,

through Lpi

aretobe added.The sound pressurelevel

by

definition,

is:

'P*

yPreJ

[17]pg. 10

LPi=10Log

Where P istheroot meansquare

(rms)

sound pressureinquestion (Paor

N/mA2)

andPre

istheInternationalreference pressure of20*10A6 Paor.0002uBar

Thenext_{step is} todeterminethesquareofthepressure_ratio;

Thetotalsoundpressure

Lpt,

_{is simply}

(

V

P_

yPre J

fl \

=

antilog

v10,

Ln

=

10

log

n

1

[

"

)

2

"

i'=l

[p

Or intermsof sound pressure

levels,

Lpt

=

10

log

X

anti

log

1=₁

Simplifying

further,

v10

;

LPt

=

10

log

S10

10

1=₁

[17]pg. 10

Theexpressionforsound power_{levels may be}expressedas

n Lwj

Lwt

= ₁₀

log

5>

10 i=i

[17]pg. 10

Where

Lwt

=_{totalsound power}

th

Lwi

=i _{sound power}level

In manycases,it isdesiredtosubtractbackgroundor ambient sound pressure

level from atotalmeasuredleveltoobtainthe sound pressurelevelproducedfroma

single source. Theprocedure _{for subtracting decibels is}similarto thatofaddition.

Thetotalsound pressureindecibels is

Lft=101og

Intermsofthemean-squarepressureratio,

f \2

__

yPre

j

[17]

pg. 13

(

V

I _p_

KPreJ

=

antilog

(L

_pt

10

=

10

10

The

background

or ambient noise_{may be}represented

by

(

V

v

Pre

J

-antilog

(\^.\

pB

V

10

=

10

upB

LpB

=_{sound pressureleveloftheambient orbackground} noise.

The sought-after sound pressureleveloftheambient orbackgroundnoisein decibels is:

Lr

= ps

LPS

=

10

log

j

P

"2 ( p >

2

{Pre)

t KPre _Jb

10

log

10 10 - 10 10

^

J

or

[17]pg. 13

When averaging decibels it follows

directly

fromthesummation_that,

LPt

=

10

log

10

10

1=1

[17]pg. 16

theaveragedecibel

level, Lp,

isdetermined

by dividing

thesum

by

thenumber of

levels,

that

is,

LD

=10

log

(

i n

tlL\

-y

io

io

n _/=1

[17]pg. 16

Chapter IV

-Tire

Construction

Pneumatic

tires servethreemain purposes.

They

supporttheweight ofa_vehicle,

absorb road surface

irregularities,

and providetraction ontheroad. Tires haveatoroidal

shape and are _usually

filled

with compressed air.Thecarcass ofthe tireprovidesthe

structural supportforthetire.Thecarcassismade _upof_{many flexible filaments}ofhigh

modulus_cord,embeddedinandbondedtoa matrix oflowmodulus material,usually

[image:16.556.168.365.534.664.2]

rubber.Thechordsofthetire are made ofnatural_textile,synthetic_polymer,glass

fiber,

Figure 3 Filamentarrangementsthatareusedinpneumatic_{tires, a)}wovencord

b)

weftless cord _c) Cordwith lightwefts

[1]

pg.360

orfine hard drawn steel.

Thechords areanchoredon thebeads ofthetire,whicharehightensile steelwiresthat

seatontherimofthe tire.Thebeadsserve as afoundation forthecarcass and provideit

(a)

(h)

(c)

Figure 4

Essentialsofbead construction

(a)

Low

turn-up

construction

(b)

high

turn-up

construction

(c)

Overlap

construction

(d)

Detailoftypicalbead

[1]

pg.

361

with adequate

seating

ontherim. Thematerialin whichthebeads areincased in is

pressed againstthe

flange

oftherim

by

inflationpressure.

Mostofthe tire'svibrations anddeformationoccurinthesidewalkThetreadof

thetireis made of various typesof rubber

depending

onthe tireapplication. Whenthe

tireis inflatedwith_air, thepressure causestensioninthe chordswithinthecarcass.Load

fromtheweight oftheautomobile placedon therimto the wheel,hangs primarilyonthe

chordsinthesidewallsthrough thebeads. Thechords or plies runat an anglefromthe

centerline(circumfrentialcenterof

treads)

ofthe tire.Thenumber oflayers is determined

by

the tire

type,

the tire_size, andtheinflationpressuretobeused. Atypical tirewillhave

from 2-20plies with each layer running inoppositedirections. This angleiscalledthe

crown angle.This angle playsaroleintherideand

handling

ofthe tire.

There aretwobasic typesof_{tires, Bias ply}andRadialply. Ina_{Bias ply tire,} the

chords extend

diagonally

acrossthecarcassfrom beadto beadwithacrown angleof

about40 degrees. Whenthe tireisrolling, the diagonalpliesflex andrub,thiselongates

thediamondshapedelementsformed

by

thechords andtherubberfiller. This

flexing

action producesa_wipingmotionbetweenthe tread andtheroad.

Figure

5 Conventionalcross-biastire.

[1]

pg.369

Ina radial_{ply tire,} thereisone ormore layersofchords_{extending radially}from

beadto

bead,

_{resulting in} a crown angle of90 degrees. Underthe_tread,atalowcrown

angle of about 20

degrees,

arefittedseverallayeredbeltsmadeofhigh_elasticitymaterial,

usuallysteel. All together,there aretworadialpliesof rayonorpolyester, twoplies of

steel_cords, andtwoplies of synthetic materiallikenylon. Aradial _plytirehasa_relatively

uniformground pressuredistributionunderthecontact patch (no wipingmotion).The

ground pressureforabias plytirevaries_{greatly from}pointtopoint astreadelements

passingthrough thecontact regiongothrough acomplex_wipingmotion.

Chapter V Tires

and

Elasticity

In

Mechanics

_of

Pneumatic

Tires,

by

S K. Clark

[1]

(section

3.8),

themechanismof

load

carrying

of atoroidalortire-likestructure ofan

infinitely

flexiblemembranewith a

rigidtubularrim forthecentral zone orboreofthe toroidis

discussed,

seefigure below.

CZ)

[image:19.556.228.370.219.330.2]

Co) bl

Figure 7 Toroidalmembrane on cylindrical rim

[1]

pg. 396

It isassumedthat thejunction betweenthe thinflexiblemembrane andtherigid

tubularrimorbase haszero

bending

rigidity. Inflationofthestructure putstensionsinthe

membrane andittakesa shape asdetermined

by

equilibrium and_{compatibility}

conditions.Themembranetensionsare resisted

by

reactions atthe edge ofthetubular

rim. Forthepresentpurpose, thesecan be discussed interms oftwocomponents;

radiallyoutwardtension andtensionin an axialdirection (that isparalleledtotheaxis of

rotational _symmetryorrotationofsurface_generators) at each point aroundtheedge of

therim.Ifaflatplateis pressed againstthemembrane whilethestructureis supported

by

therim areactionwill

develop

betweenmembrane and plate wheretheloadwillbeequal

As seeninthe

figure

below,

thecurvature ofthewallofthemembraneincreasesin

theregion

between

the

loading

plate andtheadjacentrim.

i.J/'

Figure

8

Perspectivesketch oftoroidalshell contact

[1]

pg.397

Hence,

becauseofthe increasedcurvature, themembranestressesin thisregionare

lowerthanelsewhereinthemembrane walls. The deflectionalso causes themembrane

todistort

locally,

increasing

theanglebetweenthedirection ofthewall and alinenormal

to theplatefromthe

rim;

thisistruewhateverthecross sectional_shape, seefigure below.

Figure

9

Crosssections ofFigure 7 showing

deflections

of sidewallswhich reducethe tension component_radially

outwardattheinnercylinder edge

[1]

pg.397

This increaseof anglereduces_{algebraically}thecosine ofthe angle

between

thewall

andthelineof action oftheappliedloadontheplate.

Thenet effect ofthereducedtensionand reduced component atthedeflectedregion

isto

develop

therequired reaction. Ineffect, therimhangs inthe tensionsofthe

undeflected walls as _shown,see

figure below.

[image:21.556.195.351.148.297.2]

TTTTT

Figure 10 Polarplot of_radiallyoutward component of

walltensionofmembranetoroidon innercylinder

[1]

pg.397

The radiallyoutward components ofthewalltensionsare greaterintheundeflected

regionsthaninthedeflectedregion.

Theusefulinformation wegetfromthis isthat thereducedtension inthe

deflectedregion causesthestiffnessintheshoulder regiontodrop.

Decreasing

pressure

on atirewill increasetheamountthe tire

deflects,

this deflectionwill increasethebulge

of atire.Asa_result,tirebulge increaseswithtire

deflection,

which meanstherewillbe

lesstire stiffnessinthedeflectedregion (thetire _shoulder)whichmeans therewillbe

morevibrationoftheshouldertreads_producingmore noise. Theelastic effects ofthe tire

causethistohappen. The deflectedsidewallwill _{snap back into}shape upon

leaving

the

From Samuel K.

Clark's,

Mechanics

_{of Pneumatic}

Tires,

November 1971

[1],

Figure

10,

showstherotation of a wheel

transmitting

_{torque, Mt. As}aresult ofthe torque

transmittedthrough the_wheel,two sets offorcesact uponit. One isthereactionofthe

wheel axis

Pk,

and equaltoitandintheopposite

direction,

thereaction oftheroad_acting

in theplaneofcontact. Asafirst_{approximation,it may be}assumedthatthereactionof

theroad

Pk

is evenly distributed overthe areaof contact.The componentoftangential

stressfrom

Pk

isdenotedasxp.

t-T

Figure

11

Rotationofa

Driving

Wheel (theDistributionofLongitudinal Tangential

Stress

in the

Contact

Region

of

Driven,

Driving

andBraked Wheels).

[1]

pg.490 [image:22.556.138.410.262.645.2]

There isa certain amount of adhesion overthecontact region.Thetirepossesses

longitudinal

tangential elasticity, _allowingthe torqueofthe tirewill compressthe tread

elementsinthezone

immediately

_beforethecontact region

(-)

andatthesametimewill

stretchtheelementsin theareajust afterthecontactregion (+). Again

looking

atFigure

1

1,

an

initially

compressed element

Ax,

ofthe treadisreleasedfrom longitudinal

compression asitpassesthrough thecontact_{area, reverting}toits normalstate

Axi,

thenit

undergoes

stretching

and emergesfromthecontact regionin astretchedstateAx2. Since

the elements,as

they

passintothecontact _area,are in directcontact withtheroad,any

change intheirdimensions isprevented

by

theforcewith whichelement gripstheroad

surface, andlongitudinal tangentialstress_xkariseintheplane of contact. Thesestresses

causethere tobean area of slippage attherearofthecontactpatchdue to the tension

pullingthe treadsout ofthecontact patch.

Lenqtnsv^of contact X

Figure

12 Displacementoftreadelements_alongcontactlengthoftire:

(a)

free

_rolling,

(b)

driving,

(c)

braked.

[1]

pg.465

ZoneI Longitudinaltangentialstressactingfromtiretoroadway in directionof motion.

[image:23.556.126.388.388.644.2]

Chapter

VI

-

Influence

of

Material

Properties

on

Tire Noise

In thearticle

"Effects

_{of Material Properties}on Tire

Noise"

by

M. Muthukrishnan

[12],

SAE, 1990,

theresults of an experimental_studytodeterminetheeffectofmaterial

properties ontirenoise are

discussed.

Theproperties

they

usecoverawide rangeof

moduli andtandelta fortreadand sidewalkAn explanation oftan delta is locatedon page

25. Thetiresweretestedatdifferentspeeds,loads andinflationpressures.From this,

they

obtained overall noiselevels and

frequency

content.Thetestsindicatealarger

influenceoftreadmodulusontirenoise, anditwas observedthat theinteractionbetween

treadand sidewallproperties affecttirenoise levelssignificantly.

Theresultsofthisreportare presentedin twoparts:

(1)

the effects of

load,

pressure,and speed on _{tire noise,}and

(2)

_{Material property}effects ontirenoise.The

resultsof_varyingtheloadshowthatloadchangesdonotaffectnoiselevel in any

significant way.The

testing

wasdone atfive differentspeeds,andfive different

microphone locations.

ROADWHEEL.NOISETEST

TJE

f

si

I

I I \

^_

2,1m

4

V

\ s

V

MlcrophuntLocation

"~" }

Figure 13 microphonelocationsaroundthetire

[12]

pg.

3

Load EffectsonTire Noise

(dBA)

Roadwheel

Testing

_{Inflation Pressure: 35}psi.

MicrophoneLocation 1 MicrophoneLocation 2 Microphone Location 3 Microphone Location 4 MicrophoneLocation 5 Speed

(MPH)

30

636 Lbs. 1190 Lbs. 636 Lbs. 1190 Lbs. 636 Lbs. 1190 Lbs. 636 Lbs. 11 90 Lbs. 636 Lbs. 1190 Lbs.

76.6 77.2 74.5 75.2 74.5 76.2 74.6 76.2 74.2 74.5

40 80.9 81.4 79.4 79.3 79.2 79.5 78.2 78.4 76.5 75.6

45 83 83 81.4 80.5 81.3 79.6 80 79.2 78.5 76.6

50 84.4 83.9 82.4 81.4 81.7 80 80.5 79.5 79 77.5

60 83.6 85.3 82.4 83.4 82 82.4 81.3 82.1 78.8 80.5

Figure

14

Load Effects

onTire

Noise

(dBA) [12]

pg.3

Thechanges innoiselevelswere atmost+- 2 dBA.

Next,

pressureeffectsontire

noise,were shown

by

_comparingnoise levelsattwodifferentpressuresfor differentloads

and speeds. Atthelighter

load,

anincrease in 15 psiledtoan increase innoiselevelsof

aboutoneto three dBA. Atthelarger

load,

thereis areversal andtheincrease in inflation

pressureis accompanied

by

adecrease inthenoiselevel

by

as much astwodBA.

!1SfiLJ*OJSE

P^Ss.jEE CPF""? m M₁

& _Oll LoC-d; S-Ift *.. .i Si **,:

^s*kHi^

20**.

5

K-UJ *t- ^^n * ^^^^^^ Ul flCM fa- _*~*m. ^---****

^^*^*^

E JO'

?

*-.

? TT' _**

jr*J

**

U>flJ: 1ISC Dl.

a s 4

UlCA&PMOH'E lOCatiom

Figure 15 Pressure Effectson Tire Noise

[12]

pg.

4

[image:25.576.147.395.380.651.2]

Theeffect of speed on noise level isshownin thefigure below. With

increasing

speed, thenoiselevel

generally

increases. There isalarge increase from 30to40mphs

atbothloads. After 40_{mph, the}increase isnot uniform andis even reducedatcertain

speed ranges.

S

IP -r"

-P

1J

T

UJ

5

8

GO

T1RE

NOISE

epeiici

Effects

4

ED [image:26.556.76.487.156.569.2]

&PEEU

(MPHJ

Figure 16 Speed EffectonTire Noise

[12]

pg.5

Forthematerial_propertyparametersontire/roadnoise, a widerangeof moduli

andtandeltaare used.Ninegroupsoftireswere

built,

thesegroups canbe seeninthe

Table below.

Experimental Design

(Fractional

Factorial)

4

Variables:

Tread Modulus

Tread Tan Delta

Sidewall Package Modulus

Sidewall Package

Tan Delta

The

Group

ID

Mod

ulus

Tan Delta

Tread

Sidewall

Package

Tread

Sidewall

Package

A

Control

Control

Control

Control

B

Low

Low

Control

Control

C

High

Low

Control

Control

D

Low

High

Control

Control

E

High

High

Control

Control

F

Control

Control

Low

Low

G

Control

Control

High

Low

H

Control

Control

Low

High

1

Control

Control

High

High

Figure 17 Tire

Groups

[12]

pg.2

There isone control _group,

A,

fourgroups

(B, C, D,

and

E)

with _{varyingmoduli,}

andfourmore groups

(F, G, H,

and

J)

with_varyingtan deltaandconstant moduli for both

the treadandsidewall.

Looking

attan

delta,

theelasticmodulusis

E',

andtheE" isthelossmodulus. Thetwo

casescanbeseen in Figure 18.

[image:27.556.126.410.57.376.2]

Varying

ElasticModulus/ConstantTan Delta

Varying

Tan

Delta/ Constant

Elastic

Modulus

Figure 18 Tan DeltaandElastic

Modulus

[12]

pg.2

25

i

H,

In Figure

18,

E' istheElastic

Modulus

or

Storage

Modulus,

E"is the

loss

modulus,E*

isthecomplex_modulus,

5

is the

loss

angle, and 1,2arethetwoconditions. Allmaterials

have a_{viscoelasticity,}whichis a combination of_viscosityand_{elasticity in varying}

amounts. When viscoelasticity ismeasured

dynamically,

thereis a phaseshiftbetween

the

force

applied as stimulus

(stress)

andthestrain

(skew)

whichoccursinresponse.

Generally,

themeasurement results are represented asa complex_elasticitymodulus to

insure accurate expression._{This relationship is} shownbelow.

Ifthe_{relationship between}E* andTan5 isplotted, the result,isagraph liketheone

shown below.

E* = E'

+iE"

E"

tan

8

= E'

[12]

pg.6

E"

Figure 19

Fromtheresults ofthemodulus

testing

itcanbe seenthat treadmodulushasalarger

influence

on overall noise

levels

than thesidewallmodulus. Anincrease in treadmodulus

when averaged over allthe_varyingconditions causednoise level increasesfrom 2to7

dBA,

and an

increase

insidewall modulus caused anoise level increasefrom 1 to3 dBA.

Tread Modulus S.W. Modulus Interactions

Speed Mic. No. Low High Low High Extreme Gross

1 82.7 89.5 86.1 87.4 87.7 85.7

2 82 87.5 84.7 85.6 86.3 83.9

60MPH 3 82.3 87.2 84.2 86 86.1 84.1

4 80.7 84.5 81.3 84.1 83.8 81.7

5 80.1 82.6 80.7 82.1 82.2 80.5

1 80.1 85.9 82.4 84.4 84.6 82.2

2 78 84 80.8 82.7 82.9 80.4

45MPH 3 79.2 84.4 80.9 83.3 83.2 81

4 76.9 81.9 78.5 80.8 80.6 78.7

5 76 80.2 77.2 79.4 79.4 77.2

1 75.6 79.4 76.7 78.6 78.3 77.1

2 74.6 78.1 75.7 77.3 77.2 75.8

30MPH 3 74.8 79 75.7 78.4 78 76.2

4 73.9 77.3 74.4 76.9 76.6 74.8

5 73 76.4 74.1 75.5 75.7 73.8

avg.ofB&D avg.ofC&E avg. ofB&C avg. ofD&E avg. ofB&E avg. ofC&D

[image:29.556.52.509.204.427.2]

Thisexperiment also shows that thereis a cross_{coupling between}treadandsidewall

effects. For_example,

going from

_low tohightreadmoduluswithlow sidewall modulus

increases noise

level

by

five

dBA. Whereas

doing

thesame with ahigh sidewall modulus

produces an increaseof

8.6

dBA. The influenceoftreadmodulus on sidewall modulus

effects are shownin thelasttwocolumns ofFigure 17:

Low to High Tread Modulus Lowto HighSidewall Modulus

Speed Mic. No. LowS.W. High S.W. Low TR. High TR.

1 5.0 8.6 -1.1 2.5

2 3.2 7.9 -2.2 2.5

60MPH 3 3.1 6.2 -0.1 3.0

4 2.0 5.2 0.9 4.1

5 0.8 3.9 -0.4 2.7

1 3.8 7.6 -0.5 3.3

2 2.9 7.1 -0.8 3.4

45MPH 3 3.3 6.7 0.2 3.6

4 3.5 6.3 0.5 3.3

5 2.3 5.8 0.0 3.5

1 2.9 4.6 0.9 2.6

2 2.2 4.6 0.2 2.6

30MPH 3 2.8 5.4 1.1 3.7

4 1.8 4.7 0.7 3.6

[image:30.556.66.498.207.434.2]

5 1.6 5.0 -0.7 2.7

Figure 21 Interaction Effects

Change

in Noise Level

(dBA) [12]

pg.7

Thenoiselevel spectrum wasthenintegratedand plottedit as afunctionof

frequency.

[image:31.556.134.415.192.401.2]

qooo 1CHXS

Figure 22 IntegratedSpectrum

[12]

pg.8

The integratedspectrum at agiven

frequency

givesthe totalnoisecontribution_uptothat

frequency

starting fromthe

frequency

ofinterest. This is donefor differentmoduli

MV

Tire Noise

(moduluseffects)

Speed=60_mph

J

Tread Modulus Sidewall Modulus

B Low Low

c High Low

D Low High

E High High

itto 2000

Frequency

(Hz)

Figure

23 Integrated Noise

Spectra

[12]

pg.

8

icfe*

Itcanbeseenfromthis thatinthe

frequency

rangefrom 750to 1500

Hz,

the

contributions _{vary significantly}

depending

ontheparticulartread/sidewallmodulus

combination.In this

frequency

range, many noise-generatingmechanisms areinvolved.

Themajorsourcesof noise are saidtobe

(a)

_{tread patterns,} and

(b)

radial andtangential

vibrationsofthe treadelements atthe _entryand exit ofthe contact patch.It is also

described inthisreportthatvibrations generated atthecontactpatch dependon stiffness

(modulus)

andthe

damping

ofthe treadelements. It isthenreasonedthathighmodulus

treadblocksproducelarger levels ofvibration, resulting inmore noisefrom 750to 1500

Hz. Italsois observedthatahighmodulus sidewall amplifies thevibrations ofthehigh

modulustreadelements more effectively. Thisexplainsthecross_coupling effect

observedin Figure 15 & 16.

Figure

29,

showstheoveralleffects oftreadand sidewalltandeltaontire noise

forall

testing

conditions. Itcan be seenthatthe tandeltaof eitherthe treads or sidewall

has negligible effectonoveralltirenoise levels.

Muthukrishnan

concludesthe

following

from hisexperiments:

1. Treadmodulushas a much larger influenceonexteriortirenoiselevelthan

sidewall modulus.

2. Tan deltaof eithertreador sidewall hastheleasteffect ontirenoiselevel.

3. Significant interactions existbetweentreadand sidewall properties. Noise

levels dependonthetreadand sidewallconditionstogether.

Thenextfewpagesincludeother

interesting

graphsfrom "Effects_ofMaterial

TERg

NQI5E

Traca

To-nifc

tf'eCtS

as -i

?e

Tira-E NQ1

aio#wgll T"on&- E^^eCi?

e-s _-n

Figure

24,

25

Tread Tan Delta Effectson

Tire

Noise,

Sidewall

Tan

Delta

EffectsonTire Noise

[12]

pg.

9

[image:34.556.77.482.44.663.2]

Pressure EffectsonTire Noise

(dBA)

Roadwheel

Testing

Load: 636 Lbs.

Microphone Location 1 MicrophoneLocation 2 Microphone Location 3 Microphone Location 4 Microphone Location 5 Speed

(MPH)

30 40 45 50 60

20psi 35psi 20psi 35 psi 20psi 35psi 20psi 35psi 20psi 35psi

75.4 79.6 80 80.1 81.9 76.6 80.9 83 84.4 83.6 73.5 78.2 78.6 79 80.5 74.5 79.4 81.4 82.4 82.4 73.8 78.8 79.2 78.9 79.9 74.5 79.2 81.3 81.7 82 73.8 78 78.2 78 79.6 74.6 78.2 80 80.5 81.3 72.9 76.4 76.4 75.8 77.8 74.2 76.5 78.5 79 78.8

Roadwheel

Testing

Load:1190 Lbs.

Microphone Location 1 Microphone Location 2 Microphone Location 3 Microphone Location 4 MicrophoneLocation 5 Speed

(MPH)

30 40 45 50 60

20psi 35 psi 20psi 35psi 20 psi 35 psi 20psi 35psi 20psi 35psi

78.4 83.1 83.6 84.4 86.2 77.2 81.4 83 83.9 85.3 76.3 80.3 81.6 83.9 85.4 75.2 79.3 80.8 81.4 83.4 76 79.2 80 80.8 83.2 76.2 79.5 79.6 80 82.4 75.5 78.1 78.9 80.4 83.9 76.2 78.4 79.2 79.5 82.1 73.8 76.5 77.5 78.9 82.7 74.5 75.6 76.6 77.5 80.5

Figure 26 Pressure EffectsonTire Noise

(dBA)

[12]

Testing

at

12

Hz.

Item

M

Control

odulus

(p

Low

si)

High

Control

Tan

Delta

Low

High

Tread

2250

938

5048

0.22

0.11

0.265

Sidewall

100

530

2504

0.144

0.123

0.218

Rimstrip

2790

1444

8250

0.292

0.189

0.327

[image:35.576.16.565.56.310.2]

Bead

Filler

5350

3901

23555

0.197

0.037

1.14

Figure 27 Material

Property

Values

[12]

Tire Noise

(dBA)

Levels forallModulusandTan DeltaCombinations:Roadwheel

Testing

Inflation Pressure: 35psi Load: 11 90 Lbs.

Low Tread LowSidewall

(B)

ModulusCombinations High Tread Low Tread Low Sidewall HighSidewall

(C)

(D)

High Tread High Sidewall

(E)

Low Tread LowSidewall

(F)

Modulus Combinations

High Tread LowTread

Low Sidewall High Sidewall

(G)

(H)

High Tread High Sidewall

(J)

Speed

(MPH)

Mic. No. Control

(A)

60

1 85.3 83.2 88.2 82.1 90.7 86.0 87.1 86.2 85.8

2 83.7 83.0 86.2 80.8 88.7 84.4 85.7 85.1 84.1

3 82.9 82.5 85.6 82.4 88.6 84.3 84.2 84.9 84.1

4 82.3 80.2 82.2 81.1 86.3 83.4 83.0 83.0 82.7

5 81.1 80.3 81.1 79.9 83.8 82.5 82.2 81.7 82.0

45

1 82.9 80.3 84.1 79.8 87.4 82.2 83.4 83.2 82.7

2 81.0 79.2 82.1 78.4 85.5 81.0 81.8 82.4 81.4

3 79.9 79.1 82.4 79.3 86.0 81.9 81.0 81.7 80.1

4 79.0 76.6 80.1 77.1 83.4 80.6 79.1 79.5 77.6

5 76.7 76.0 78.3 76.0 81.8 77.9 77.0 77.2 76.4

30

1 77.0 75.1 78.0 76.0 80.6 77.2 79.1 77.7 79.1

2 75.3 74.5 76.7 74.7 79.3 75.8 77.5 76.3 77.9

|

3 75.9 74.2 77.0 75.3 80.7 76.6 77.2 75.9 77.6

4 75.6 73.5 75.3 74.2 78.9 76.1 76.7 75.8 76.8

5 74.4 73.3 74.9 72.6 77.6 74.6 74.2 75.4 74.1

Figure28 Tire

Noise,

All

Combinations

[12]

Speed

(MPH)

Mic. No.

Tread T Low an delta High Sidewall Low Tan delta High Interactions Extreme Cross 60

1 86.1 86.5 86.6 86.0 85.9 86.7

2 84.8 84.9 85.1 84.6 84.3 85.4

3 84.6 84.2 84.3 84.5 84.2 84.6

4 83.2 82.9 83.2 82.9 83.1 83.0

5 82.1 82.1 82.4 81.9 82.3 82.0

45

1 82.3 83.1 82.8 83.0 82.5 83.3

2 81.7 81.6 81.4 81.9 81.2 82.1

3 81.8 80.6 81.5 80.9 81.0 81.4

4 80.1 78.4 79.9 78.6 79.2 79.3

5 77.6 76.7 77.5 76.8 77.2 77.1

30

1 77.5 79.1 78.2 78.4 78.2 78.4

2 76.1 77.7 76.7 77.1 76.9 76.9

3 76.3 77.4 76.9 76.8 77.1 76.6

4 76.0 76.8 76.4 76.3 76.5 76.3

5 75.0 74.2 74.4 74.8 74.4 74.8

tJ

Avg.of F&B

tJ

Avg.of G&J

tr

Avg.of F&G

tr

Avg. of H&J

tJ

Avg.of F&J

tr

Avg.of G&H

Figure 29 Tan Delta Effectsontire

Noise

(dBA) [12]

[image:36.581.86.486.353.629.2]

Chapter

VII

-

Tire

Construction

and

Noise

In thearticle"Investigation intothe_{Influence of Tire Construction} on

Coast-by

Noise"

by

Doan,

Brackin, Nishihata,

andSauer Zapf

[18],

the dominantsource oftire

noiseis identifiedas shouldertiretreadvibration._{It is generally known}thatahighpeak

value exists at around onekHz. Inthe_coast-bynoisespectrum andthis

frequency

dominatesthe_coast-bynoiselevel. Thisphenomenon occursin tires

having

treaded

patterns and alsofor blanktires. Rib-styletreadpatternedtires are_usuallyquieterand

showthe smallestdifference innoiselevelsas comparedtoblanktires. Tireconstruction

and materials will havetobetakenintoaccounttoreduce noiselevels. Noise is not_only

generated

by

tread patterns,butalso

by

thevibration ofthe tirecomponents.

&-<-1

a

-63

J

^

f

fi

0 0

1.1

u

I- ! ', v

II

i'

iflftSnjIO0* Cixi*a 7aotftQE"-ii*

Tinic _(Soc] O fiK

Figure

30

Excitation LevelofTreadsas

They

Pass

Through the

Contact

Region,

[image:37.556.83.445.406.661.2]

Thevibrations were measured with accelerometersmounted atthecenter ofthe

belt,

nearthebeltedge,andthe sidewall ofthe tire.Thevibrations atthecenterandbelt

edges are referredtoas 'tread

part'

vibrations.

Looking

atFigure 31

below,

at 1 kHz it

canbeseen thatthe

leading

and

trailing

edges arenoise sources. Resultsshowthat tire

noise around 1 kHz is generated

by

treadpartvibration atthe

leading

edge,

trailing

edge,

and shoulder_treads, andthattheacceleration ofthe treadpartis greaterthanthatofthe

sidewall _especiallyaround 1 kHz. The

following

graphs showthattire treadband

vibrationdoes in factgenerate noisesources relatedto thesound produced

by

_coast-by

tests.

Size: 2IS/70R16

,. Putcra: Maingroovesoc.ly

9

0

Srral 57 bet

I

MJf

v.

[5

Lcodng&3D

Trading E<J*

5 t SsMh _"-'"v-.

(at MeanendOmi-<S<isLevsis.

.IL

V

'

I JX 2.5K

i,V,MrctrtiiTicd VB&rKdeeAzcc:rc~<:.r.Leuela.

HG.il.

-Gr^lhmwf^tofottb^tenCMW-hyxoB*l^si^t^y(br*t<>iiIm>s

Figure

31 Graphs

Showing

Correlation Between

Coast-By

Noise

andtread Vibration Levels

[18]

[image:38.556.84.499.325.570.2]

Thecorrelation coefficientsthat

they

reportedfortheshouldertreadvibration andthe

generatedtirenoiseis

relatively

high,

as comparedto thecentertreadvibrationandthe

generatedtirenoise.

I,J>HUE 1 t"'^TvfeiY.-uj/nit,r<il v.AiYnv.-.n d!Ikeshotftdkr

irriii"

SMJc.>.-W->'imliS5awAwr<*-Mrirxfiitose,

C;.m I'V-aii Noise ImlivJ.

L"'I'J_JVoivc

40 5fl "HI 70 " 5D >*0

km.ti km^ km.-. K-nirt. km." _{klt^, ki/b} ^'^

Figure 32

Correlation

betweenvibrationattheshouldertreadand _coast-by

noise/indoordrumtirenoise

[18]

They

found highaccelerationlevelsatthe

leading

and

trailing

edges and_{relatively low}

levels in thecontactregion.

They

also _say,"Thecontactpressure andtirestiffness_may

beusedtodescribe thissystem ofvibration,becausethecontactpressure canbe thought

ofas aforcewhich acts onthe_tire, andtheamplitudeoftirevibration canthoughtofas

being

dependentontirestiffness.Thismeansthat treadvibrationisequaltotheinput

forcesmultiplied

by

some vibration transfer

properties."

Thetreadvibration mechanism

model couldbeexplainedin detail asfollows: The inputforcecanbeseenin Figure 33

foj TJw VitratumMedianhm

t

(b)Context Prrrsvr*

Itf

yJ

iii

Simian tfTiodPuI

CWirfTjMdftn

Figure 33 Tire Forcesatthe

Leading

and

Trailing

Edgescaused

by

Contact

Pressure Variation andRoad Surface Roughness

[18]

The dynamicpressureincreasesatthe

leading

edge

(AB),

stays_nearlyconstant

during

contact

(BC),

andthendecreases atthe

trailing

edge(CD). Thiscontactdistribution can

be assumedtoberepresentative oftheforcesthatexcitethe tirestructure. The amplitude

ofthemaximumdynamic contact pressure aroundB andC canbeconsidered asthe

maximum amplitude oftheexcitationforcespresent. In _addition,theroad surface

roughnesstends to _amplifytheexcitation forcesand mustbe considered.Thetirein

Figure33 isapproximated

by

the _springmassdamperand_{step input}systemofFigure 34

9

fr

if

r~

JPt^SfiSwfwBWlOS

c _;>

I

.tC

'***iWt

i'.v.i,J^-.,iimtft f^-v

Ur<4fFrequency <Hi)

Figure

34

A

typicaltire transferfunctionand systemused torepresenttireproperties_{a) the}

Wherethemaximum

dynamic

contactpressure, atthe

leading

and

trailing

edges,

representsthe

input forces.

Ifthis

hypothesis

isused, thedisplacementresponse_step

function

_{x(t) in}the time

domain

can beexpressed as:

x(t)=F*

(

_1-e-a>t _{cosXn4l-C2t)+}

y=L=sin

[18]

Where:

x(t) =

displacement

_response

F=_{input force}

K=_stiffness

t\

=

damping

_ratio

C0n=_{natural radial}

frequency

Dueto the

difficulty

of_calculatingthe

damping

ratio andthemass _effects,

they

further

simplifythemodel

by

_assumingthedisplacementresponseis onlyproportionalto the

inputforcemultiplied

by

thereciprocal ofthestiffness,as shownintheequationbelow:

x{t) - F*

[18]

K

Inthis equation,Frepresentstheinputforceand1/K isthe transfer

function. Further

the

input

force,

F,

canbeapproximated

by

_usingthemaximum

dynamic

contact pressure and

theroad surfaceroughness,and canbe representedin therelation

below:

*(0=ar*P*

[18]

lv

Inwhich:

a=_{road roughness coefficient}

P=

dynamic

_{contact pressure}

K=_{tire stiffness}

Theauthors also _saythat thecenter contact pressure andthetread

bending

stiffnessatthe

shoulderhave themostinfluenceon theshouldertreadvibration.

Therefore,

having

atire

with alowercontactpressurearoundthecenter andanincreasedtread

bending

stiffness

atthe shouldershould reducetheshoulder_{tread vibration, thusreducing}thenoiseit

produces.Thetiretreadvibration onthe shoulder was obtained_{using linear}regression

analysis.

14

.--i

MtrsA

I

r-CJ?rtJ!

;-r

71 3 Zi

ft

,s

> _s

s

" V

-1-1

3 "

3

.

C t

s^ K*fr

!_*;<:>* W.iJ.1.

C

I

small

[

i^rea

MEASUREDVALUE

i*

J

Figure35 Calculatedcorrelationvaluestableand graph_showingactual versus

estimatedtreadvibration

for

aspeed of

60 km/hr.

[image:42.556.77.470.442.667.2]

and resultsinthe

following

equation:

x{t) =

a0

+ ai*Pa*--

[18]

Ksh

inwhich:

ao,ai = _{single regression constants}

Pce

=_{static pressure around center}

Ksh

=_tread

bending

stiffness aroundtheshoulder

Basedon_{their research,}

they

madethe

following

conclusions:

1. Theregionofthe tire inthevicinityofthe contactpatchdominatestire treadvibration

2. The A-weightedspectra oftreadpartacceleration,coast-bynoise, andindoordrum

testnoise

display

thesame

tendency

(ahighpeak around1 kHz.).

3. Shouldertreadvibrationisthenoise source thathasthemost relation to tirenoise

produced.

4.

Lowering

thecenter contact pressure and/or

increasing

theshouldertread

bending

Chapter VIII

-

Section 1: Road Texture

and

Tire/Road Noise

Intheconference paper

"Relationships

between Road TextureandTire/Road

Noise"

from Noise-Con

96,

Yasuo OshinoandHideki Tachibana

[7],

performeda_study

of noise radiatedfroma passenger car andamedium sizedtruckanddifferentroad

surfaces

(paving

_{materials,chipping} sized grain andsurfacetexture).Fromthis

investigation,

relationshipsbetweentire/roadnoiseandroadsurfacecharacteristics were

developed. Inthis_study, twokinds ofmeasurements were made.Thefirstonewas

performed on atest trackpaved withfive kindsof constructions

by

_usingapassenger car

and a medium sizedtruck.

Therefore,

it has been confirmedthat thesoundpower

spectrum oftire/roadnoise variesquite abit duetodifferences intheroad surface

materials.

They

also statedthat theopen graded asphaltsurfaceisthe _{best among}all

tested toreducethe tire/roadnoise.

Tire/roadnoise was alsomeasuredatsixteen sites of publicroads paved with

denseasphalt concrete

by

_usingthesame passenger carequipped withfourtypesoftire

andthesame medium sizedtruckequippedwithtwo types oftire.

They

foundthat the

general

tendency

impliedthat tire/roadnoiseincreaseswiththeincreaseoftexturedepth.

This has been found foralmost alltiresbutthe_relationshipvaries dueto the typeoftire.

Theseresults suggestthat thereis a greater_{exciting force}onthetread

bands

atthe

leading

and

trailing

edges. Sothedeeperthetexture

depth,

themorethe treadbandsget

excited, andhence thegreaterthenoise produced.

Chapter

VIII

-

Section 1: Air

Pumping

as a

Noise

Source

Anothersource oftirenoiseis air pumping. Air_pumping,occurswhen air

movementfromtreadvoids give risetomonopole sound radiation.Itis acousticallya

local source, with sound radiated

directly

asthe void compresses.This is validatedas a

sound sourcein thearticle_{"The Generation of Tire Noise}andCarcass

Vibration",

Plotkin,

Montroll,

Fuller,

Intemoise-1980 [4]. Intheir study,

they

foundthat there are

concentrated noise sources consistent with air pumping.These wereidentifiedatthe

entranceto thecontactpatch.Thesoundpressureduetoair_{pumping is}

directly

relatedto

thesecondderivativeofthevolume ofairdisplaced fromtreadvoids.The void profiles

were

directly

measuredforthe test tires. Thiswas accomplished

by

_measuringthe

volume of waterdisplacedfromabladder inthevoidasthe tirewas advancedthrough

thecontactpatch.Themeasured profiles werethendifferentiatednumerically.The

calculated results showed good agreement withthemeasured sound pressure. The

calculations_strongly suggestthattheconcentrated sources observed wereduetoair

pumping.

Chapter

IX

-

Methods

of

Measuring

Tire

Noise

Tire/pavement

interaction

produces a non-uniform noiseradiation. There are

threeareasin which noiseis radiated;

they

arethe

leading

edge,

trailing

edge, and sidewall_regions,nearthecontact region(see Figure 31).

w

Trailing

Edge

Leading

Edge

Contact

Region

Figure36

Therearethreeprominentmethodsfor measuringtire/roadnoise:The Coast

by

Method,

The

Laboratory

Drum

Method,

andThe Trailermethod.

The Coast

by

Method isthemost representativeof actualfield operatingconditions and soundpropagationto the road environment. Inthis_method, the testvehiclecoasts

by

a roadside _microphone,whichis placed1.2m abovetheroadlevel and7.5 mfromthe centerline ofthevehicle's path. Theengineis switchedoff.

Using

atimeconstant

nicknamedfast anda

frequency

_rating

"A,"

themaximum soundlevel

during

the

coast-by

is recorded.It isrecommendedthatthe

frequency

spectrum also berecorded atthe

maximum sound

level,

althoughthisisnotmandatory.

Usually,

fiveruns are made and

averaged. Asforall methods, therecommendedspeedis 70

km/hr.

If

lower

or

higher

[image:46.556.146.410.208.412.2]

speeds are_required,it isrecommendedthat

they

be chosenfrom

30,

50, 90,

or 110 km/hr.

Themain reasonsfor

choosing

70

km/hr

arethatthisspeed givesgoodsignaltonoise

ratio andlow

influence

of external variables(suchastestvehicle

design)

aswell as safe

and practical

driving

conditions. In_addition, 70km/hr isa speed atwhichtire/roadnoise

is

likely

tobea great nuisanceto theenvironmentinmosttypesoftraffic. Thismethod

canbeusedfortype

testing

oftiresand road_surfaces,andforall

testing

wherehigh

precision and representative operation are essential. TheCoast

by

Methoddoes have its

disadvantages,

such as:

a specialtest trackor aroadwith suitablesurfaceisrequired;

atestvehicle equippedwith4-6test tiresisrequired; the testvehicle mustbe

coasted _alongthe test area;

unlesscareis taken there_{may be}an influence fromvehicle_type,

brakes,

transmissionandsuspension.

There may bepracticaland_safetyproblemsforsomevehicles when

they

are

coasted.

In addition,itis necessarytominimize:

climatic andmeteorological

influences;

Sensitivity

todisturbance fromother_{traffic, if}any, and other

background

noises.

IntheTrailer

Method,

atest tireis mountedon a

trailer,

whichistowed

by

a car

ortruck. Thetrailer_{may be} ofasingle-wheeltypeorhaveextra

supporting

wheels. A

microphoneispositioned closeto the tire/roadinterfaceandthearticulated vehicleis

driven alongatesttrack or a road

having

asuitable surface. The microphone positionis

0.2moutsidetheundeflected_{tire sidewall,} .lmabovetheroadleveland0.2m behindthe

vertical axle plane. The 0.2m distances are changedto0.4m fortruck tires. In orderto

increasethesignal/noise ratio and reduce climatic

influence,

an enclosure aroundthe test

tireand microphoneissometimes used. Specialcare_concerning acoustical reflections

mustthenbeobserved. Thismethodis suitable where_{relatively high}precisionis

requiredbutsome lackofrealistic operationcanbe accepted. _{It is especially}

recommendedinenvironmentswith

disturbing

_{traffic, for instance}on

highly

trafficked

roads where no other methodis possiblewithout_closingtheroad.

Long

_measuringtimes

canbeusedtoreduceerrors. The disadvantages ofthismethodare:

Itrequiresaspecialtowedtrailer;

Backgroundnoisefromwindturbulenceinthemicrophone canbe a problem

atlow

frequencies;

Theclose measurement position gives somelackof realismduetoacoustical

reflections; and

Thenear-field microphonelocation is unsuitableforroadsurfaces

having

a

significant sound absorption.

In the

Laboratory

Drum

Method,

atest tireis mounted sothatitcan roll against a

drumsurface. Special care mustbetaken_concerningtheacoustical environment. The

microphoneispositionedas inthe trailermethod. A drumdiameterof atleast 1.5m is

requiredforan "outer drum"

facility,

whenthetireisrolledagainsttheouter part ofthe

drumshell. Thismethodis suitable wherehigh precisionis important

but

lack of realistic

operation canbeaccepted.

Surveys

of noise emissionfrom largenumbers oftiresunder

various_operatingconditions canbecarried outin a shorttime. Thismethod could also

beusefulforresearch and

development

work andfor

detecting

smalldifferences innoise

emission

from different

tires. It is

independent

of weather conditions andrequireslittle

space and_onlyonetiresample pertest.

Long

_measuringtimescanbeusedtoreduce

errors. The

disadvantages

ofthismethodare:

Aspecialdrum

facility

is _required;

The drum isnot a good representativeofroad surfacedue toitscurvature.

Inall_{three methods,many factors influence}themeasurednoise. Thesefactors

includetire_type,road surface_type,area ofcontact_patch,tireinflationpressure,and

vehicle speed. In general,with_anycombination oftheabovevariablesthesoundlevel

increases asthevehicle speedincreases.

InthereportTire/Pavement Interaction Noise Source Identification using

Multi-PlanarNearfield Acoustical

Holography

by

Richard J. Ruhalaand

Courtney

B.

Burroughs

(1999)

[16],

theauthors usedthe trailermethod andidentifiedthemajor areas

ofmaximum noise radiationtobethe

trailing

edge,

leading

edge, and sidewallregions

nearthecontactpatch.Twotiresweretestedin_{this experiment,} a monopitchtire and a

[image:49.557.191.384.576.643.2]

productiontire.

Figure 37. Photographofmonopitch

(left)

and productiontirethreads.

[14]

Themonopitchtire

has

_{64 equally} spacedtransversegroovescutin

it,

_alongwith

threecircumfrential grooves.Thetreadpassage

frequency

isequalto:

_

NV

Where N isthenumberoftransverse grooves,V isthevehicle_speed, andC isthe

circumference ofthetire.Theproductiontirehastreadblocksthat_{vary in}size and

spacing aroundthecircumference ofthe tire. Thetire alsohas fourcircumfrential

groovesthatseparatethreerowsof55treadblocksandtworowsof89 blocks. The

sidewallhasone_plypolyester_cord;the tread_{has three,} one polyester cordandtwosteel

cords. Thistestshowedthat thereis speeddependenceon sound pressure levels.

Overall,

bothtiresshowedincreasedsound pressurelevelswithincreasedspeed,butthesound

pressurelevel fromthemonopitch tiredidnot alwaysincreasewith speed.

This, they

_say

is probably dueto the treadpassage_{harmonics cycling}throughvarious resonances.

Thenoise

levels

ofthe

leading

_edge,

trailing

_edge,andsidewall change with

speed.Thenoise level forthemonopitchtireincreasedwith speed above40 km/hrat

(a)

120 -110 !

Loading

-D-Trailing

00 1oo -A-_Sidewall u c 90 BO 1 Q. 70

j-so _,

10 56 ioo

Spaed

(km/hr)

(b)

m a. 120 i HO +-t 10O 90 80 70 60

\

1

?-Leading

j

">

Trailing

k-Si

dwall

10

Speed

(km/hr)

100

Figure

38

Sound pressurelevels in dB. Ref. 20uPainthe

frequency

range

2600

Hz. for

(a)

monopitchand

(b)

productiontires.

[14]

[image:51.556.51.498.136.643.2]

40*log(speed).

Fortheproduction

tire,

the

leading

and

trailing

edgesdominatethe

sidewall noise above40

km/hr.

Theoverall noise level increasesat arateof

40*log(speed)

below 56

km/hr,

and

20*log(speed)

above56 km/hr.

For

further

_{analysis, the}monopitch andtheproductiontiresweretestedata speed

of58 km/hron smooth asphalt pavement. Forthemonopitch_tire,theareas of maximum

radiation were

localized

tothesidewall nearthe

leading

edge,centerline ofthe

leading

(a)

side 1 , > ,i \\ J~ rx^*** f^>>M7S '.* ''

>\l*\'~,*

[image:52.556.93.465.235.600.2]

* |V'"SJ<*.-,'

'

"

: _X

\ffl-fr'Y Jg

-'

W/^>^=r^f^ :A

-0> 0.1 8 4 0

J

fror

(

it

^4\

/ :

HI

(((

fror t " rear

"

Cn

^

\

Figure 39 Threeviews of active acoustic

intensity

frommonopitchtire

running

on smooth

asphalt at56 km/hr.

Frequency

ranges are

(a)

450 Hz. To

550

Hz.

(tread

passage

frequency),

(b)

900to 1100

Hz.,

and

(c)

1400 Hz.

To

1600 Hz.

Data

arereconstructed

[14]

edge,and centerline ofthe

trailing

edge. Thespectrumwasdominated

by

theharmonics

ofthetreadpassage events.Atthetreadpassage

frequency

of500

Hz,

radiationfromthe

sidewalldominatedthesoundpower.Thisnoise was_mainly generated

by

the vibrationof

thesidewall dueto theradial

(normal)

displacementofthe treadblocks passingthrough

thecontact region. AtonekHzthenoiseisgenerated

by

thesamemeans,but has nearly

equal radiation_alongthe

leading

edge

trailing

edge,andthe sideofthecontact patch.At

1.5

kHz,

noise radiationis localizedtothe

leading

and

trailing

edges.Theprobable cause

ofthisis vibrationenhanced

by

air_pumpingandthe second mode ofthecircumfrential

Fortheproduction

tire, less

radiationis observedfromthesidewall and more

fromthe

leading

and

trailing

edges.Between 500 Hz and onekHzthefrequencies

increasewith_speed,

showing

that

they

are relatedto thetreadpassage events.Thesound

poweris highest from

650

Hzto950

Hz,

whichis probablyamplified

by

thefirstmode of

circumfrential groove resonance and air pumping.

Again,

thenoiseis

likely

generated

'

rear

s * i t.

ft

(b)

(c)

front

1

m

!vl

Figure 40 Threeviews of activeacoustic

intensity

from

production tire

running

on

smooth asphaltat56 km/hr.

Frequency

rangesare

(a)

300

Hz.

To 600

Hz.

(tread

passage

frequency), (b)

650

Hz. to 950

Hz.,

and

(c)

1300

Hz.

To

1500 Hz. Data

are

reconstructedon planes

touching

surface oftire.

Contour lines

arein 2 dB.

increments

beginning

at

78

dB.

Solid

contourlines are positiveanddashed

lines

represent negative directionnormaltotheplane.

[14]

[image:54.556.102.484.196.582.2]

fromvibrations ofthe treadband duetoradial

(normal)

displacementofthe treadblocks

passingthrough thecontact region atthe

leading

and

trailing

edges.Thesecond modeof

thecircumfrentialgroove resonance canbeseeninthe

frequency

region from (1300 Hz

to 1500 Hz). Ateven higher

frequencies,

generationis localizedto thecontact patch near

the

leading

edge and_{may be}caused

by

treads

being

forced intothecontact region.

Chapter

X

-

Patch

Frequency

Inthissection, a

dynamic

model of atireis

developed.

Thetire hasa radius

('R')

in_meters, and angular speed

(to)

inradians/sec.Theouter circumferenceofthe tireis

W

Trailing

Edge

Leading

Edge

Contact

Region

Figure 41

made_upof,

NPi

numberof patches. Apatch consists of atreadpattern anda gap.

Thetotallengthofthepatch isthecircumfrential

length

_ofthe tread

(I)

plusthe

circumfrentiallength ofthe_{gap (y).}

[image:56.556.123.445.199.435.2]

I

Figure 42 Patch

Thenumber of patches on atire

(Np)

is thecircumference ofthe tiredivided

by

thepatch

length. (This is always a whole_number)

tire

circumference

2nR

Np

= =

patch

length

/

+

y

The

frequency

ofpatches _passingthrough thecontact regionistheangularspeedtimes

thenumber of patchesdivided

by

theperiod,27t:

fi)N

f

=

J n

In

Another formofthisequationis:

VN

f,

= p

2nR

In whichV is thevehicle speedandR isthe tireradius.

Frequencieswerethengraphedfor

increasing

speedsand agiven

Np.

Tofindan

appropriate rangeofangular_velocities,carspeeds, 0to 180

km/hr,

were chosenand

convertedtom/s.

Next,

aradius of.2159m

(17")

waschosen;anywheelradius could

have beenchosen.The speed wasthen convertedtoangular_{velocity using}theequation

(0=V/R, which has unitsofradians/second.

Next,

randomvaluesof

Np

werechosen

starting from Np=10toNp=100. Thesegraphs showthelinearrelation betweenpatch

f(hz)

vs. N &

W(rad/sec)

300000

250000

200000

r 150000

100000

50000

- _N=10 -N=20

N=30 N=40 *-N=50 --N=60

+-N=70

N=80 N=90 N=100

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

[image:58.585.22.536.26.408.2]

w(rad/sec)

Figure 43

Frequency

inHz. vs.Angular

Speed,

u)

Theamplitudeofnoise producedfrompatches wouldbeafunctionofthedepthorlength

ofthe treads onthe tire. Thegreaterthe treadlengththegreatertheexcitationwhen_going

through thecontact region.

Chapter

XI

-Tire Bulge

When atireis_rolling, thetirecarcass nearthecontact patchbulges out.

Figure 44

Theextentofthebulge dependsonthelateralstiffness,

KL,

ofthe tire. Itcanbeobserved

that themorebulgeatirehasthelouderthenoiseitradiates(flattire). Sincethe amount

ofbulge is

inversely

proportionalto thelateralstiffness ofthe_tire,theamplitude ofthe

noiseisproportionalto tirebulge and

inversely

proportionalto thelateral stiffness.

A

_noise ~

Tire

Bule

K

KL

oc

Itcan alsobesaidthat thelengthofthecontact_region,

Cp,

is

inversely

proportionalto

thelateralstiffness.

cp~

1

KL

Asimple analysis canbeusedtodeterminethe

frequency

ofthebulgewith _varying

angulartirespeeds.

Figure45

Where: to=_{theangular speed}ofthe tire.

R=_theradius to theoutside ofthe tire

Cp

= length_{of contact region}

Sp

=Arc lengthoftirewithincontact region

0

=AngleofArc

Sp

Nsp

=_numberofSp'spertire

Thearclength

Sp

equalsR*9 .

Next,

usingthelaw ofcosines:

2_td2 or.2

CP

=2R2

-2R2cos(6)

Solving

for

0,

9

=

cos"1

(-CP2+2R2^

2R2

Substituting

into

Sp,

Sp

f-Cp2+2R2^

2R2

V. J

Theamplitude of noiseis proportionalto the_velocityofthe_tire,whichisequalto the

tire'sangular_velocitytimes theradiusofthe_tire,

Ano,seoc^

=

*^

In which ct)istheangular_velocityofthetire, R istheouterradius ofthe_tire, andV isthe

Chapter

XII

-

The

Rubbing

Theory

Atire_rubbingor

sliding

on a surfaceisanother source oftirenoise.Thiscanbe

explained

by

whati