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Service Training
Noise Vibration and Harshness
Self Study Programme NVH
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4ABLEOF#ONTENTS
I
#OURSE'OALS
)NTRODUCTION
4HEORY#HARACTERISTICSOF.OISE6IBRATIONAND(ARSHNESS.6('ENERATIONOF
.OISEAND6IBRATION3OUNDAND3OUND7AVES!UDIBLE2ANGEOF3OUND
.6(4ERMINOLOGY4YPESOF.OISE#OMPELLING&ORCEAND6IBRATING"ODY
6IBRATION6IBRATION4RANSFER0ATH6IBRATION/RDER4YPESOF6IBRATION
2IDE#OMFORT
$IAGNOSIS
'ETTING'OOD)NFORMATIONFROM3ERVICE!DVISORS4HE&OUR3TEPS$IAGNOSINGAND3OLVING#USTOMER#ONCERNS/THER)NFORMATION
3OURCES0RE2OAD4EST)NSPECTION2OAD4EST4IPS2OAD4ESTING
%NGINE6IBRATIONS%NGINE3PEED2ELATED6IBRATIONS4YPESOF%NGINE6IBRATIONS%NGINE
6IBRATION&ORMULA%NGINE!CCESSORY&ORMULA4YPESOF%NGINE.OISE
%XHAUST.OISE%NGINE&IRING&REQUENCY&ORMULA
6EHICLE3PEED6IBRATIONS
4IRESAND7HEELS4IRE6IBRATION&ORMULAS$RIVE3HAFT&REQUENCY&ORMULA$RIVEAND!XLE3HAFTS$RIVELINE6IBRATION4RANSMISSION.OISE
AND6IBRATIONS$IFFERENTIAL/PERATION$RIVELINE3NAP3USPENSION
#OMPONENTS3TEERING#OMPONENTS
4OOLS3IROMETER%6!))#HASSIS%!2/THER4OOLS
'LOSSARY.6(4ERMINOLOGY
$IAGNOSTIC&LOW#HART
+NOWLEDGE!SSESSMENT
4HE3ELF3TUDY0ROGRAMPROVIDESYOUWITHINFORMATION
REGARDINGDESIGNSANDFUNCTIONS
4HE3ELF3TUDY0ROGRAMISNOTAREPAIRMANUAL
&ORMAINTENANCEANDREPAIRWORKALWAYSREFERTOTHE
CURRENTTECHNICALLITERATURE
)MPORTANT.OTE
.EW
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#OURSE'OALS
#OURSE'OALS
4HISCOURSEWILLENABLEYOUTO
s )DENTIFYTHETERMINOLOGYUSEDINDIAGNOSING
.OISE6IBRATIONAND(ARSHNESS.6(
CONCERNS
s )DENTIFYTHEDIFFERENTTYPESOF.6(
s )DENTIFYTHESTEPSOFTHE.6(SYSTEMATIC
DIAGNOSTICAPPROACH
s )DENTIFYTHEROADTESTPROCEDURES
NECESSARYTOISOLATEANOISEORVIBRATION
s #ALCULATE.6(FREQUENCIESNECESSARYFOR
COMPONENTCLASSIlCATION
s )DENTIFYTESTEQUIPMENTANDTOOLSUSEDINDIAGNOSINGANDCORRECTING.6(CONCERNS
s )DENTIFYDIAGNOSEANDSPECIFYTHE
COMPONENTCAUSINGTHE.6(CONCERN
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)NTRODUCTION
)NTRODUCTION
4HIS3ELF3TUDY0ROGRAMFOCUSESONVEHICLE
.OISE6IBRATIONAND(ARSHNESS.6(THEIRCAUSESANDDIAGNOSTICANDSERVICEPROCEDURES
TOLOCATEANDCORRECT.6(CONCERNS
-ODERNCARSANDTRUCKSUSEACOMBINATION
OFSYSTEMSTOPROVIDETHEDRIVERWITHTHE
SAFESTMOSTRESPONSIVEANDCOMFORTABLE
VEHICLEEVERBUILT4ODAYSDRIVERHASCOMETO
EXPECTASMOOTHANDQUIETRIDEINALLOPERATING
ENVIRONMENTS7HENVEHICLENOISEVIBRATION
ORRIDEHARSHNESSEXCEEDSTHEDRIVERS
EXPECTATIONSITISUPTOTHETECHNICIANTOCORRECTTHECAUSEOFTHECUSTOMERSCONCERN
6EHICLECOMPONENTSAREBEINGMANUFACTURED
USINGLIGHTERWEIGHTMETALS,IGHTERWEIGHT
METALSREDUCETHEOVERALLVEHICLEWEIGHTTHAT
REDUCEEMISSIONSANDIMPROVEFUELECONOMY
!STECHNOLOGIESDEVELOPSTRONGERANDMORE
LIGHTWEIGHTMETALSTHISTRENDWILLCONTINUE
,IGHTERVEHICLECOMPONENTSDONOTABSORB
NOISESANDVIBRATIONSASWELLASHEAVIER
COMPONENTS4HISLEADSTOANINCREASEIN.6(CONCERNS
$IAGNOSING.6(CONCERNSHASBEENDEVELOPED
INTOALOGICALANDALMOSTSCIENTIlCPROCEDURE
4HISCOURSEWILLPROVIDETHE!UDITECHNICIANWITH
CONCEPTSTOHELPUNDERSTANDANDDIAGNOSE.6(
CONCERNS
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4HEORY
'ENERATIONOF.OISEAND6IBRATION
!VIBRATINGOBJECTNORMALLYPRODUCESSOUNDAND
THATSOUNDMAYBEANANNOYINGNOISE)NTHECASEWHEREAVIBRATINGBODYISTHEDIRECTSOURCE
OFNOISESUCHASCOMBUSTIONCAUSINGTHE
ENGINETOVIBRATETHEVIBRATINGBODYORSOURCE
ISEASYTOlND)NOTHERCASESTHEVIBRATING
BODYMAYGENERATEASMALLVIBRATIONONLY
4HISSMALLVIBRATIONMAYCAUSEALARGERVIBRATION
ORNOISEDUETOTHEVIBRATINGBODYSCONTACT
WITHOTHERPARTS7HENTHISHAPPENSATTENTION
FOCUSESONWHERETHELARGEVIBRATIONORNOISE
OCCURSWHILETHEREALSOURCEOFTENESCAPESNOTICE
!NUNDERSTANDINGOFNOISEANDVIBRATION
GENERATIONASSISTSWITHTHETROUBLESHOOTING
PROCESS4HEDEVELOPMENTOFASMALLNOISE
INTOALARGERNOISEBEGINSWHENAVIBRATION
SOURCECOMPELLINGFORCEGENERATESAVIBRATION
2ESONANCEAMPLIlESTHEVIBRATIONWITHOTHER
VEHICLEPARTS4HEVIBRATINGBODYSOUND
GENERATINGBODYTHENRECEIVESTRANSMISSIONOF
THEAMPLIlEDVIBRATION
#HARACTERISTICSOF.OISE6IBRATION(ARSHNESS
.OISEISDElNEDASANYUNPLEASANTORUNEXPECTEDSOUNDCREATEDBYAVIBRATINGOBJECT
6IBRATIONISDElNEDASANYOBJECTIONABLE
REPETITIVEMOTIONOFANOBJECTBACKANDFORTHOR
UPANDDOWN
(ARSHNESSISDElNEDASANAGGRESSIVE
SUSPENSIONFEELORLACKOFhGIVEvINRESPONSETO
ASINGLEINPUT
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4HEORY
3OUNDSAND3OUND7AVES
!SOUNDWAVESCYCLEPERIODFREQUENCYAND
AMPLITUDEDETERMINETHEPHYSICALQUALITIESOFTHESOUNDWAVE4HEPHYSICALQUALITIESOFSOUNDARE
s !UDIBLERANGEOFSOUND
s 0ITCH
s )NTENSITY
!LLPEOPLEHAVEDIFFERENTCAPABILITIESFORHEARING
SOUND3OMEPEOPLEMAYNOTHEARSOUNDS
THATOTHERPEOPLECANHEAR+EEPTHESEFACTSINMINDWHILEDIAGNOSINGNOISECONCERNS-OST
CUSTOMERSBECOMETUNEDINTOANOISEAFTER
HEARINGITREPETITIVELY
7HENDIAGNOSINGAVEHICLEITMAY
BEBENElCIALTOHAVETHECUSTOMER
REPRODUCETHENOISEDURINGAROADTEST
!UDIBLE2ANGEOF3OUND
&ORSOUNDTOBEHEARDTHERESULTINGACOUSTIC
WAVEMUSTHAVEARANGEOFTO(Z
WHICHISTHEAUDIBLERANGEOFSOUNDFORHUMANS
7HILEMANYVEHICLENOISESARECAPABLEOFBEING
HEARDSOME.6(NOISESARENOTINTHEAUDIBLE
RANGE
,OWSPEEDDRONINGISANEXAMPLEOFALOW
FREQUENCY.6(CONCERNTHATMAYHAVE
COMPONENTSNOTINTHEAUDIBLERANGE4HIS
CONDITIONEXERTSPRESSUREONTHEDRIVERS
EARDRUMANDCANBEEXTREMELYUNCOMFORTABLE
/NTHEOTHERENDOFTHEAUDIBLERANGEOFVEHICLE
NOISESAREWINDNOISEANDBRAKESQUEAKING
4HEHIGHFREQUENCIESOFTHESE.6(CONCERNS
PRODUCEAHIGHPITCHEDNOISETHATCANBE
EXTREMELYANNOYING4HElGUREBELOWILLUSTRATES
THEAUDIBLERANGEOFAUTOMOTIVENOISES
-AXIMUM!UDIBLE,EVEL
!VERAGE!UDIBLE,EVEL
-INIMUM!UDIBLE,EVEL
3/5.$,%6%L).4%.3)49D"
&2%15%.#9(Z
K K K
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4HEORY
#YCLE
#YCLEISTHEPATHAWAVETRAVELSBEFORETHEWAVE
BEGINSTOREPEATTHEPATHAGAIN)FAN!LTERNATING
#URRENT!#SINEWAVEBEGINSAPATHATZERO
VOLTSTHEWAVECOMPLETESONECYCLEWHENIT
RETURNSTOZEROVOLTSFROMAPOSITIVEVOLTAGE
&REQUENCY
&REQUENCYISTHENUMBEROFCOMPLETECYCLES
THATOCCURINONESECOND3OUNDANDVIBRATION
WAVESAREMEASUREDIN(ZOR#YCLES0ER
3ECOND#03/NE(ZISEQUALTOONE#03
" " " " " " "
!"!"#
.6(4ERMINOLOGY
)NOTHERWORDSTHEWAVECOMPLETESONECYCLE
BYTRAVELINGTHEPATHFROMANEGATIVEVOLTAGETO
ZEROVOLTSTHENTOAPOSITIVEVOLTAGEANDTHEN
BACKTOZEROVOLTS
4HESOUNDWAVEINTHElGUREBELOWHASA
FREQUENCYOF(ZBECAUSEITCOMPLETESSEVEN
#034HEFREQUENCYOFASOUNDORVIBRATIONCAN
AIDINTROUBLESHOOTINGAN.6(CONCERN
4HEREARECOMMONTERMSUSEDWHENDISCUSSING
AN.6(CONCERN4HEFOLLOWINGTERMSANDGRAPHICSWILLHELPWHENDISCUSSING.6(WITH
OTHERPEOPLEWITHATECHNICALBACKGROUND
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4HEORY
0ITCH
0ITCHISTHEPHYSICALQUALITYOFSOUNDTHATRELATES
TOTHEFREQUENCYOFTHEWAVE)NCREASINGTHE
FREQUENCYOFASOUNDINCREASESTHEPITCHOFTHESOUND)FFREQUENCYDECREASESPITCHALSO
DECREASES
,ISTENINGTOANACCESSORYDRIVEBELTSQUEAKING
ISANEXAMPLEOFAHIGHPITCHEDHIGHFREQUENCY
TYPEOFNOISE!HIGHPITCHEDHIGHFREQUENCY
NOISEISIRRITATINGTOMOSTPEOPLE
!ROLLERBEARINGTHATMAKESNOISEISANEXAMPLE
OFALOWPITCHEDLOWFREQUENCYTYPEOFNOISE
(IGH&REQUENCY(IGH0ITCH
,OW&REQUENCY,OW0ITCH4)-%
!-0,)45$%
!MPLITUDE
!MPLITUDEREFERSTOTHEVERTICALMEASUREMENT
BETWEENTHETOPANDTHEBOTTOMOFAWAVE
4WOWAVESCANHAVETHESAMEFREQUENCYBUT
DIFFERINAMPLITUDE!MPLITUDEISTHEQUANTITY
ORAMOUNTOFENERGYPRODUCEDBYAVIBRATING
COMPONENT
-AXIMUM
-INIMUM
0ITCH
!MPLITUDE
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4HEORY
(IGH!MPLITUDE(IGH)NTENSITY
,OW!MPLITUDE,OW)NTENSITY
4)-%
!-0,)45$%
3OUND)NTENSITY
3OUNDINTENSITYISTHEPHYSICALQUALITYOFSOUND
THATRELATESTOTHEAMOUNTANDDIRECTIONOFTHE
mOWOFACOUSTICENERGYATAGIVENPOSITION4HElGUREILLUSTRATESTWOSOUNDWAVESWITH
THESAMEFREQUENCYBUTDIFFERENTAMPLITUDES
DIFFERENTINTENSITYLEVELS
3OUNDINTENSITYISMEASUREDINDECIBELS
!DECIBELISAUNITFOREXPRESSINGRELATIVE
DIFFERENCEINPOWERBETWEENACOUSTICSIGNALS
3OUNDSGREATERTHANDECIBELSAREDANGEROUS
TOHUMANHEARING
$IFFERENCESINPITCHTHESOURCEOFEACHSOUND
ORTHEPERSONWHOHEARSTHESOUNDCANCREATE
THEPERCEPTIONTHATTWOSOUNDSOFTHESAME
INTENSITYHAVEDIFFERENTLEVELSOFLOUDNESS
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4HEORY
2ESONANCE
2ESONANCEISTHETENDENCYOFASYSTEMTO
RESPONDTOACOMPELLINGFORCEOSCILLATINGATOR
NEARTHENATURALFREQUENCYOFTHESYSTEM!LLOBJECTSHAVENATURALFREQUENCIESANDEXPERIENCE
MAXIMUMRESPONSEATTHEPOINTOFRESONANCE
4HENATURALFREQUENCYOFATYPICALAUTOMOTIVE
FRONTSUSPENSIONISINTHETO(ZRANGE4HIS
ISDESIGNEDFORRIDEANDHANDLINGCONSIDERATIONS
!SSEENINTHElGURETHESUSPENSIONSNATURAL
FREQUENCYISTHESAMENOMATTERWHATTHE
VEHICLESPEED!STHETIRESPEEDINCREASES
ALONGWITHTHEVEHICLESPEEDTHEDISTURBANCE
CREATEDBYTHEUNBALANCEDTIREINCREASESIN
FREQUENCY%VENTUALLYTHEFREQUENCYOFTHE
UNBALANCEDTIREINTERSECTSWITHTHENATURAL
FREQUENCYOFTHESUSPENSIONCAUSINGTHE
SUSPENSIONTOVIBRATE4HISINTERSECTIONPOINTIS
CALLEDTHERESONANCE
-0(
(Z
0OINTOF2ESONANCE
#OMPE
LLING&
ORCE
6IBRATION3PEED
3USPENSION&REQUENCY
4HEAMPLITUDEOFAVIBRATIONISGREATESTATTHE
POINTOFRESONANCE!LTHOUGHTHEVIBRATIONCAN
BEFELTABOVEANDBELOWTHEPROBLEMSPEEDITISMOSTPROMINENTATTHEPOINTOFRESONANCE
2ESONANCEEXPLAINSWHYATIREVIBRATIONOCCURS
ATCERTAINVEHICLESPEEDS)FTHEVEHICLEgS
SUSPENSIONHASANATURALFREQUENCYOF(Z
THESUSPENSIONWILLTRANSMITORRESONATETHE
VIBRATIONATSPEEDSINTHE(ZRANGE4HE
VEHICLEWILLVIBRATEATMPHMPHAND
MPHBECAUSETHESESPEEDSCAUSEATIRE
VIBRATIONTORESONATETHROUGHTHESUSPENSION
INTOTHEVEHICLE
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4HEORY
4YPESOF.OISE
4HERECANBEMANYTYPESOFNOISECONCERNSON
AVEHICLE4HECLASSIlCATIONOFNOISESASSISTSTHETECHNICIANINTROUBLESHOOTINGANDREPAIRINGTHE
CUSTOMERSVEHICLE
.OISEISANUNPLEASANTORUNEXPECTEDSOUND
CREATEDBYAVIBRATINGOBJECT)NTERPRETATIONPLAYS
ALARGEROLEINDElNINGNOISECHARACTERISTICS
4ERMSUSEDTODESCRIBENOISEINCLUDE
s $RONING
s "EAT
s 2OADNOISE
s "RAKESQUEAL
4HEFREQUENCYOFNOISEVIBRATIONSISMUCHHIGHER
THANTHATWHICHCANONLYBEFELTOFTENRANGING
BETWEENAND(Z#ERTAINNOISESCAN
BEASSOCIATEDWITHTHECOMPONENTSYSTEMS
OFAVEHICLESUCHASTHEENGINEDRIVELINEAXLE
BRAKESORBODYCOMPONENTS
)NOTHERSITUATIONSANOISECANTELEGRAPH
THROUGHTHEBODYOFAVEHICLE&OREXAMPLE
ACHIRPINGNOISEMAYBEHEARDINTHEAREAOF
THEINSTRUMENTPANELWHENINFACTITISBEING
PRODUCEDBYTHEREARBRAKES4HESOUNDHAS
TRAVELEDORTELEGRAPHEDTHROUGHTHEPARKING
BRAKECABLES&OLLOWINGASYSTEMATICAPPROACH
WHENTROUBLESHOOTINGAN.6(CONCERNHELPSTO
LOCATETHECAUSEANDCORRECTTHECONDITION
.OISECANBEANNOYINGTOSOMEPEOPLEWHILE
OTHERSlNDITACCEPTABLE!UTOMOTIVENOISESCANBEAUDIBLEATCERTAINSPEEDSORUNDER
CERTAINDRIVINGCONDITIONS!GEARDRIVENUNIT
SUCHASANAUTOMOTIVEDRIVEAXLEPRODUCESA
CERTAINAMOUNTOFNOISE)NDEALINGWITHTHESE
CONCERNSITISIMPORTANTTOKNOWWHATANORMAL
CONDITIONISANDEXPLAINITTOTHECUSTOMERIN
TERMSTHEYCANUNDERSTAND
4RYINGTOREPAIRANORMALVEHICLECONDITIONCAN
BEFRUSTRATING$ESPITEGOODINTENTIONSAN
ATTEMPTEDREPAIRCANALSOBECOMEALIABILITYIF
LEGALACTIONISINITIATED
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4HEORY
$RONING
4HESENSATIONPEOPLEEXPERIENCEWHENDRIVING
INTOATUNNELATHIGHSPEEDORCLIMBINGTOA
HIGHALTITUDEISAFEELINGOFEARDISCOMFORT4HEEARDRUMSFEELASIFTHEYAREBEINGFORCEDIN
OROUTDUETOSUDDENCHANGESINATMOSPHERIC
PRESSURE!NUNPLEASANTDRONINGCAUSESA
SIMILARSENSATIONDUETOLARGEmUCTUATIONSOFAIR
PRESSUREINTHECAR
!CUSTOMERMAYREFERTOUNPLEASANTDRONING
NOISESASHUMMINGNOISES4HEREARETHREE
TYPESOFUNPLEASANTDRONING
s ,OWSPEED
s -IDDLESPEED
s (IGHSPEED
5NPLEASANTDRONINGATLOWANDMIDDLESPEED
DRIVINGISALONGDURATIONLOWPITCHEDNOISETHAT
ISNONDIRECTIONAL)TISHARDTOHEARANDFEELSLIKEPRESSUREINTHEEARS
&EELINGASMALLAMPLITUDEVIBRATIONISCOMMON
WITHLOWANDMIDDLESPEEDDRONING,OWSPEED
DRONINGHASARANGEOFUPTOMPHKPH
ANDHASAFREQUENCYOFTO(Z-IDDLE
SPEEDDRONINGHASARANGEOFTOMPH
TOKPHWITHAFREQUENCYOFTO(Z
5NPLEASANTDRONINGATHIGHSPEEDDRIVINGISA
LONGDURATIONNONDIRECTIONALHUMMINGNOISE
THATISUNCOMFORTABLETOTHEEARS(IGHSPEED
DRONINGHASARANGEOFMPHKPHANDUP
WITHAFREQUENCYOFTO(Z
4HETHREECLASSIlCATIONSOFDRONINGARESPEED
ANDFREQUENCYRELATED!LOWSPEEDDRONING
SOUNDHASALOWERPITCHTHANAHIGHSPEED
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4HETABLESUMMARIZESTHESPEEDANDFREQUENCY
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MPH
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4HEORY
$RONINGCANOCCURWHENACCELERATING
DECELERATINGORDRIVINGATACONSTANTSPEEDBUT
MOSTOFTENOCCURSWHENACCELERATING$RONINGUSUALLYISAPPARENTATASPECIlCENGINERPMOR
VEHICLESPEED&OREXAMPLETHElGUREILLUSTRATES
HOWTHENOISELEVELOFAVEHICLEINCREASES
WITHVEHICLESPEED!SVEHICLESPEEDREACHES
ACERTAINRANGETHESOLIDCOLOREDAREASOFTHE
lGUREALARGEINCREASEINTHENOISELEVELOCCURS
4HESPEEDORRPMRANGEATWHICHUNPLEASANT
DRONINGOCCURSISRELATIVELYNARROW7HEN
DRONINGOCCURSATASPECIlCVEHICLESPEEDTHERANGEISGENERALLYWITHINMPHKPHOFTHAT
SPEED7HENDRONINGOCCURSATASPECIlCENGINE
RPMTHETECHNICIANSHOULDCHANGEVEHICLESPEED
VERYSLOWLY#HANGINGVEHICLESPEEDQUICKLYWILL
MAKEITDIFlCULTTOCHECKTHEDRONINGBECAUSE
RPMWILLPASSTHROUGHTHESPECIlCRANGETOO
QUICKLY
$RONINGISUSUALLYGENERATEDBYMORETHANONE
COMPONENT)NMOSTCASESITISNECESSARYTO
ELIMINATEALLTHECAUSESINORDERTOREMOVETHEDRONINGNOISE&OREXAMPLEUNPLEASANTDRONING
CANOCCURWHENENGINEANDDRIVELINEVIBRATIONS
ARETRANSMITTEDTOTHEBODYPANELSCAUSINGTHEM
TORESONATE!IRCLEANERAIRINTAKEANDEXHAUST
NOISESCANCOMBINEANDCAUSEDRONINGINTHE
PASSENGERCOMPARTMENT
/THERITEMSTHATARESOMETIMESRESPONSIBLEFOR
UNPLEASANTDRONINGINCLUDE
s "ENDINGRESONANCEOFEXHAUSTPIPESs 2ESONANCEOFAUXILIARYEQUIPMENT
s "ENDINGRESONANCEOFPROPELLERSHAFT
s 2ESONANCEOFSUSPENSIONLINKS
s 4RANSMISSIONOFENGINEVIBRATION
s 4RANSMISSIONOFEXHAUSTNOISE
s 4RANSMISSIONOFINTAKEAIRNOISE
4HEBENDINGRESONANCEISANORMALOCCURRENCE
FORSTRAIGHTTUBESANDPIPESANDEXHAUST
ANDDRIVESHAFTS4HESECOMPONENTSDEFORM
RESONATEATKNOWNFREQUENCIES%NGINEERS
DESIGNCOMPONENTSSOTHATTHEBENDING
RESONANCEWILLNOTOCCURDURINGTHENORMAL
OPERATIONOFTHEVEHICLE
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4HEORY
"EAT
&ORBEATSOUNDSTODEVELOPTHEREMUSTBE
TWOSOUNDSOURCES&OREXAMPLESTRIKINGA
TUNINGFORKPRODUCESAPURETONEOFACERTAINFREQUENCYPITCH)FASECONDTUNINGFORKWITH
AVERYDIFFERENTPITCHISSTRUCKEACHTONEIS
DISTINGUISHABLEFROMONEANOTHER(OWEVERIF
THEPITCHESOFTHETUNINGFORKSARESIMILARTHE
TWOTONESPRODUCEABEATSOUNDWITHAPITCH
THATOCCURSINCYCLESATTHEDIFFERENCEOFTHETWO
FREQUENCIES)FTHEPITCHESOFTHETWOSOUNDS
ARETHESAMEORONLYSLIGHTLYDIFFERENTTHEY
AREINDISTINGUISHABLEANDAREPERCEIVEDASONE
SOUND4HElGUREILLUSTRATESTWOTUNINGFORKSPRODUCING
SOUNDWAVESWITHTROUGHSANDPEAKS4HETWO
WAVESHAVESLIGHTLYDIFFERENTFREQUENCIES4HE
SOUNDLEVELBECOMESHIGHERWHENTHEIRPEAKS
OCCURATTHESAMETIME4HESOUNDLEVELDROPS
WHENAPEAKOFONEWAVEOCCURSATTHESAME
TIMEASTHETROUGHOFTHEOTHERWAVE7HENTHE
TWOWAVESCOMBINETHEYPRODUCEABEATSOUND
INWHICHLOUDNESSCHANGESPERIODICALLY
!
"
#
(Z
(Z
3OUND7AVES#ARETHESUMOF3OUND7AVES!AND"
4HEmUCTUATIONIN-AGNITUDEIS0HASINGOR"EATING
4HESENSATIONOFABEATSOUNDISMOST
NOTICEABLEWHENTHEFREQUENCYDIFFERENCEIS
TO(Z)FTHETWOFREQUENCIESARECLOSERTHEIRTONESAREINDISTINGUISHABLEANDARESENSED
ASTHESAMESOUND)FTHETWOFREQUENCIES
AREGREATERTHAN(ZAPARTEACHTONEIS
DISTINGUISHABLEFROMONEANOTHER
"EATSOUNDSCANRESULTFROMACOMBINATION
OFMANYTYPESOFVIBRATIONS#OMMON
COMBINATIONSTHATRESULTINBEATSOUNDSINCLUDE
s %NGINEANDAIRCONDITIONINGCOMPRESSOR
s %NGINEANDPOWERSTEERINGHYDRAULIC
PUMPOROTHERACCESSORIES
s %NGINEANDVIBRATIONSOFTHEDRIVESHAFT
s 4IRENONUNIFORMITY
s 4IREANDDRIVESHAFTVIBRATIONS
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4HEORY
2OAD.OISE
4HESOUNDSTHATOCCURWHILEDRIVINGONGRAVEL
ORROUGHLYPAVEDROADSISANEXAMPLEOFROAD
NOISE4HISTYPEOFNOISEISCONTINUOUSANDHASACONSTANTCHARACTER2OADNOISECANOCCURATALL
VEHICLESPEEDSORWHENTHEVEHICLEISCOASTING
ANDHASAFREQUENCYRANGEOFTO(Z!
VERYlNEVIBRATIONALSOMAYBENOTICEABLE
2OADROUGHNESSANDTIRESAREMAJORSOURCESOF
NOISEANDVIBRATIONTHATOCCURDURINGDRIVING
3INCETHESOURCEOFROADNOISEISIRREGULARROAD
SURFACESDIFFERENTTYPESOFTIRESCANINmUENCE
THEAMOUNTOFROADNOISE4HEIMPACTFORCEFROM
ROADSURFACESTRANSMITSTOTHETIRESCAUSINGTHEMTOVIBRATE4HISVIBRATIONINTURNTRANSMITS
TOTHESUSPENSIONANDBODY4HERESONANCE
CHARACTERISTICOFTHEPASSENGERCOMPARTMENT
AMPLIlESTHEVIBRATIONANDGENERATESANNOYING
ROADNOISE
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4HEORY
"RAKE3QUEAL
4HEMOSTCOMMONBRAKESYSTEM.6(CONCERN
ISBRAKESQUEAL"RAKESQUEALISAHIGHPITCHED
NOISE)FBRAKESQUEALONLYAPPEARSWHENTHEVEHICLEISlRSTPUTINTOOPERATIONITMAYBEDUE
TOMOISTUREONTHEBRAKELININGS
"RAKESQUEALALSOCANOCCURWHENFRICTIONIS
CREATEDBETWEENBRAKECOMPONENTSDURING
BRAKING7ORNORDAMAGEDBRAKECOMPONENTS
CANPRODUCEAVIBRATIONRESULTINGINBRAKESQUEAL
4HISHIGHFREQUENCYNOISECANOCCURUNDER
DIFFERENTBRAKEPEDALPRESSURESVEHICLESPEEDS
ANDBRAKETEMPERATURES
$RUMBRAKESUSUALLYEMITALOWERPITCHNOISE
THATGETSLOUDERWITHINCREASEDBRAKEPEDAL
PRESSURE$ISCBRAKENOISEISGENERALLYAHIGH
PITCHEDSQUEALTHATOCCURSUNDERLIGHTPEDAL
PRESSURE
4HEMAJORVIBRATIONSOURCESOFBRAKESQUEALARE
s 7ORNBRAKESHOES
s .ONUNIFORMTHICKNESSOFBRAKEDISCOR
DRUMSs %XCESSIVERUNOUT
s $AMAGEORCONTAMINATIONOFFRICTION
SURFACES
"ECAUSEOFTHECOMPLEXNATUREOFBRAKESAND
THEMANYDIFFERENTPARTSFOUNDINTHEMTHE
BESTWAYTOCORRECTBRAKESQUEALISTOFOLLOW
SERVICEPROCEDURES$URINGBRAKESERVICE
ALWAYSTHOROUGHLYCLEANANYFRICTIONSURFACEBEFOREREASSEMBLINGTHEBRAKE!WIDEVARIETY
OFCOATINGMATERIALSUSEDONBRAKEBACKING
SURFACESANDTHEINSTALLATIONOFSHIMSANDCLIPS
CANHELPELIMINATEBRAKESQUEAL.6(CONCERNS
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4HEORY
#OMPELLING&ORCEAND6IBRATING"ODY
6IBRATIONSOCCURWHENTHEREISACOMPELLING
FORCEOREXCITINGFORCEACTINGUPONANOBJECTTHATCAUSESTHEBODYTOVIBRATE,OCATINGTHE
COMPELLINGFORCETHESOURCEOFTHEVIBRATION
CANASSISTINELIMINATINGAN.6(CONCERN
4HEMAJORCOMPONENTGROUPSTHATPRODUCE
COMPELLINGFORCESARE
s 4IREANDWHEEL
s $RIVELINE
s %NGINEANDTORQUECONVERTER
6IBRATION4RANSFER0ATH
6IBRATIONSTRAVELTHROUGHAVEHICLESSTRUCTURE
SIMILARTOTHEWAYRADIOWAVESTRAVELTHROUGH
AIR6IBRATIONSAREOFTENNOTICEDINACOMPONENT
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ISCALLEDhTELEGRAPHINGv&OREXAMPLEANOUTOFBALANCEFRONTTIREANDWHEELASSEMBLYMAY
RESULTINANOTICEABLESTEERINGWHEELSHAKE)N
THISCASETHEWHEELANDTIREASSEMBLYISTHE
ORIGINATOROFTHEVIBRATIONTHESUSPENSIONISTHE
CONDUCTORANDTHESTEERINGWHEELISTHEREACTOR
6IBRATION
6IBRATIONISTHEREPETITIVEMOTIONOFANOBJECT
BACKANDFORTHORUPANDDOWN4HISMOTION
ISAFUNCTIONOFTIMEANDISMEASURABLEIN(Z
6IBRATIONCANBEDESCRIBEDINMANYWAYSWHICH
INCLUDE
s 3HAKE
s 3HIMMY
s 3HUDDER
6IBRATIONSCANBECONSTANTORVARIABLEAND
OCCURDURINGAPORTIONOFTHETOTALOPERATING
SPEEDRANGE6IBRATIONSUSUALLYARECAUSEDBY
SOMEROTATINGCOMPONENTORCOMPONENTSOR
SOMETIMESBYTHECOMBUSTIONOFTHEAIRFUEL
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THEVIBRATIONCANBEUSEDTOMATCHITWITH
COMPONENTSTHATARETHELIKELYCAUSE
4HEREAREMANYTYPESOFVIBRATIONPROBLEMSON
AVEHICLE4HECLASSIlCATIONOFVIBRATIONSASSISTS
THETECHNICIANINTROUBLESHOOTINGANDREPAIRING
THECUSTOMERCONCERN
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4HEORY
6IBRATION/RDER
/RDERISTHENUMBEROFDISTURBANCESCREATED
INONEREVOLUTIONOFACOMPONENT!SINGLEHIGHSPOTONATIRECAUSESONEDISTURBANCEPER
REVOLUTIONANDISCALLEDAlRSTORDERDISTURBANCE
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AREDISTURBANCESPERSECOND4HISCREATESA
lRSTORDERDISTURBANCEOF(Z
)FTHETIREDEVELOPEDASECONDHIGHSPOTA
SECONDORDERDISTURBANCEWOULDRESULT4HE
WHEELROTATINGTIMESPERSECONDPRODUCES
DISTURBANCESPERSECOND4HISCREATESASECOND
ORDERDISTURBANCEOF(Z4HREEHIGHSPOTS
CREATEATHIRDORDERDISTURBANCEANDFOURHIGH
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ORDERDISTURBANCESCONTINUETOPROGRESSINTHIS
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TROUBLESHOOTING&OREXAMPLEAVEHICLEHASAN.6(CONCERNTHATISPRODUCINGAVIBRATIONAT
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REVOLUTIONOFTHEDRIVESHAFT!MISSINGDRIVE
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OFPOSSIBILITIESBECAUSETHISSITUATIONWOULD
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&IRSTORDER6IBRATION
3ECONDORDER6IBRATION
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4HEORY
6IBRATION/RDER%XAMPLES
(ALFORDERVIBRATION
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COMPONENTTHATROTATESATHALFTHECRANKSHAFT
SPEEDISOUTOFBALANCEORHASEXCESSIVERUNOUT
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"ALANCINGTHECOMPONENTORCORRECTINGTHE
RUNOUTMAYBRINGTHEVIBRATIONTOANACCEPTABLE
LEVEL
&IRSTORDERVIBRATION
&IRSTORDERVIBRATIONISCREATEDWHENANY
COMPONENTTHATROTATESATCRANKSHAFTSPEED
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IMBALANCEANDCYLINDERTOCYLINDERMASS
DIFFERENCES)NRARECASESTHECRANKSHAFTITSELF
MAYBEIMBALANCED"ALANCINGTHECOMPONENT
ORCORRECTINGTHERUNOUTMAYBRINGTHEVIBRATION
TOANACCEPTABLELEVEL
3ECONDORDERVIBRATION
3ECONDORDERVIBRATIONISCAUSEDBYTHEUPAND
DOWNMOTIONOFTHEPISTONS4HISREVERSALOF
MASSANDMOTIONCREATESANATURALVIBRATION
3YMPTOMSOFENGINEIMBALANCEINCLUDE
s !LOWSPEEDSHAKEFELTBETWEENAND
2EVOLUTIONS0ER-INUTERPMTHAT
HASAFREQUENCYOFTO(Z
s !ROUGHNESSSOMETIMESFELTANDHEARD
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COMPONENTTHATHASTHREEHEAVYSPOTS
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4HEORY
3HAKE
6IBRATIONSATTHESTEERINGWHEELORSEATORANANNOYINGVIBRATIONATTHEmOORAREINDICATORSOF
hSHAKEv3HAKEGENERALLYHASAFREQUENCYOF
TO(Z4HEREARETWOTYPESOFSHAKE
s 6ERTICALUPANDDOWN
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LATERALSHAKEARE
s 2OUGHNESSOFROADs 4IREIMBALANCE
s .ONUNIFORMTIRES
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s "RAKE6IBRATION3HUDDER
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4HEORY
3HIMMY
6IBRATIONTHATCAUSESTHESTEERINGWHEELTO
OSCILLATEISKNOWNAShSHIMMYv4HEBODYOF
THEVEHICLEALSOMAYVIBRATELATERALLY3HIMMYGENERALLYHASAFREQUENCYOFTO(Z4HERE
ARETWOTYPESOFSHIMMY
s (IGHSPEEDSHIMMY
s ,OWSPEEDSHIMMY
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SMOOTHROADSATHIGHSPEEDS(IGHSPEED
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WHEELBEGINSTOVIBRATEASTHEVEHICLEISDRIVEN
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4HEMAJORVIBRATIONSOURCESOFHIGHSPEEDAND
LOWSPEEDSHIMMYARE
s 2OUGHNESSOFROAD
s 4IREIMBALANCE
s .ONUNIFORMTIRES
s "ENTOROUTOFROUNDWHEELS
&OREXAMPLEATIREWITHEXCESSIVERUNOUTOUT
OFBALANCEOROUTOFROUNDMAYCAUSEHIGHOR
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GENERATESAVIBRATIONATAPARTICULARFREQUENCY
7HENTHEVIBRATIONOFTHETIREREACHESTHE
NATURALFREQUENCYOFTHEVEHICLESFRONTUNSPRUNG
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4HEORY
"RAKE6IBRATION3HUDDER
"RAKEVIBRATIONSHUDDERISTRANSMITTEDTHROUGH
THEBRAKEHYDRAULICLINESTOTHESUSPENSION
SYSTEMSTEERINGSYSTEMANDTHEBRAKEPEDAL"RAKEPEDALPULSATIONISGENERATEDWHEN
APPLYINGABRAKEWITHANONUNIFORMDIAMETER
DRUMORADISCBRAKEWITHNONUNIFORMBRAKE
DISCTHICKNESS
"RAKESHUDDERCAUSESTHEINSTRUMENTPANEL
STEERINGWHEELANDSOMETIMESTHEENTIRE
BODYTOVIBRATEVERTICALLYANDBACKANDFORTH
DURINGBRAKING)TALSOMAYRESULTINBRAKEPEDAL
PULSATIONRELATEDTOWHEELROTATIONANDCAN
OCCURDURINGANYBRAKINGCONDITIONORVEHICLESPEED.ORMALLYBRAKESHUDDERHASAPEAKAT
TOMPHTOKPHANDHASAFREQUENCYOF
TO(Z
#ERTAINOPERATINGCONDITIONSCANAFFECTTHE
CAUSEOFTHESEVIBRATIONS4HESEINCLUDE
s %XTENDEDPERIODSWHERETHEVEHICLEIS
NOTINOPERATION
s "RAKEDISCSURFACEIRREGULARITIESDUETO
FOREIGNAGENTSOILORGREASEANTIFREEZEETC
s $EFORMATIONOFBRAKEDRUMDUETOPOOR
INSTALLATION
)FTHEDISCROTORHASEXCESSIVETHICKNESS
VARIATIONFRICTIONFORCEONTHEBRAKINGSURFACE
VARIESDURINGBRAKEAPPLICATION4HECHANGEINTHEBRAKINGFORCEGENERATESAVIBRATIONATA
CERTAINFREQUENCY4HISVIBRATIONISTRANSMITTEDTO
THESUSPENSIONSTEERINGANDBRAKEPEDAL4HE
VIBRATIONCANALSOTRANSMITTOTHEBODYCAUSING
ITTORESONATE
4HEROOTCAUSEOFDISCBRAKEVIBRATIONSHUDDER
CONCERNSISTHICKNESSVARIATION4HICKNESS
VARIATIONCANBECAUSEDBYAROTORTHATHAS
LATERALRUNOUT,ATERALRUNOUTCANBECAUSED
BYIMPROPERWHEELTIGHTENINGPROCEDURESANDTORQUEVALUESASWELLASHUBRUNOUT!STHEROTOR
WOBBLESLATERALRUNOUTCONTACTISMADEWITH
THEBRAKEPADS!SSECTIONSOFTHEROTORMAKE
CONTACTWITHTHEPADSSMALLAMOUNTSOFMETAL
WEARFROMTHEROTORSURFACE4HISCONTINUES
UNTILENOUGHMETALISWORNINSECTIONSTOCAUSE
THICKNESSVARIATION4HISISWHYIMPROPERWHEEL
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MONTHSTOPRODUCEBRAKEVIBRATIONS
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ISUSUALLYASHORTTERMREPAIR!LWAYSFOLLOW
SERVICEINFORMATIONFORPROPERWHEELTIGHTENING
PROCEDURESANDTORQUEVALUES#HECKTHEHUB
FORLATERALRUNOUTWHENRESURFACINGORREPLACING
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SYSTEMREFERTOSERVICEMANUALINFORMATION
FORTHEVEHICLE0ROCEDURESTOCHECKDRUMS
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4HEORY
2IDE#OMFORT
2IDECOMFORTPLAYSALARGEPARTINACUSTOMERS
SATISFACTIONWITHTHEIRVEHICLE!VOIDINGABNORMALVIBRATIONSENSURESAQUALITYRIDECOMFORTLEVEL
.ORMALVEHICLEVIBRATIONSAREARESULTOFROAD
ROUGHNESS$URINGNORMALOPERATIONTHE
VEHICLEEXPERIENCESVIBRATIONBETWEENTHE
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THEUNSPRUNGCOMPONENTSAXLESTIRESAND
WHEELS4HISISANACCEPTABLECONDITIONUNLESS
THESPRUNGORUNSPRUNGCOMPONENTSBECOME
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7HENUNSPRUNGCOMPONENTSRESONATEWITHTHESPRUNGCOMPONENTSTHERESULTISPOORRIDE
COMFORT2IDECOMFORTVIBRATIONSMAYCAUSETHE
VEHICLETOROLLPITCHANDBOUNCEWHICHMAY
CAUSEACUSTOMERCONCERN0OORRIDECOMFORT
CANBEMINIMIZEDBYENSURINGSUSPENSIONAND
STEERINGCOMPONENTSARENOTDAMAGEDORWORN
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4HEORY
(ARSHNESS
(ARSHNESSRESULTSWHENTHEVEHICLEISUNABLETO
ABSORBVIBRATIONSPRODUCEDBYROADCONDITIONS
4HECAUSESMAYBEDUETODETERIORATIONOFVEHICLECOMPONENTSDAMAGEORMODIlCATION
OFTHEORIGINALEQUIPMENT)NMOSTCASES
HARSHNESSISRELATEDTOCHASSISCOMPONENTS
7HENDIAGNOSINGAHARSHNESSCONCERNPAY
CLOSEATTENTIONTOINTERIORNOISELEVELSINTHE
VEHICLE-ANYHARSHNESSCONDITIONSAREDUE
TOACOMPONENTTHATISNOTALLOWEDTOMOVE
WITHINITSNORMALTRAVELORONETHATHASLOSTITS
ISOLATINGGROMMETSORBUSHINGS4HISMAKES
ENGINEMOUNTSSUBFRAMEMOUNTSBUSHINGSANDSUSPENSIONCOMPONENTSPRIMESUSPECTSINTHE
DIAGNOSTICPROCEDURE
/VERSIZEDTIRESHEAVYDUTYSPRINGSANDSHOCKS
OROTHERVEHICLEMODIlCATIONSALSOMUSTBE
CONSIDERED3OMEAFTERMARKETTIRESEVENWHEN
THEYARETHECORRECTSIZEMAYPRODUCECHANGES
INTHEVEHICLETHATWILLGENERATEOWNERCONCERNS
-ANYCUSTOMERSUSETHEWORDhHARSHNESSvTO
DESCRIBERIDECOMFORTCONCERNS(ARSHNESSHAS
BECOMEAUNIVERSALTERMWHENDEALINGWITH.6(CONCERNSONAVEHICLE&ORTHEPURPOSE
OFTHISCOURSEHARSHNESSISANAGGRESSIVE
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TOASINGLEINPUT)TCANBEASSOCIATEDWITHAN
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MOVINGACROSSROADJOINTSPROJECTIONSSTEPPED
DIFFERENCESORDEPRESSIONSONPAVEDROADS
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OFTHETHUMPINGSOUND4HEIMPACTFORCEFROMTHEROADSURFACECAUSESTHETIRESTOVIBRATE
4HETIRESTRANSMITTHEVIBRATIONTHROUGHTHE
SUSPENSIONSYSTEMTOTHECARBODY(ARSHNESS
HASAFREQUENCYOFTO(Z
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4HEORY
6IBRATIONS
6IBRATIONSARENOTICEABLEATTHESTEERINGWHEEL
SEATSANDmOOR4HELEVELANDINTENSITYOFTHE
VIBRATIONCHANGESWITHTHESUSPENSIONTYPEANDTHEBUSHINGSUSED
,ONGITUDINALIMPACTFORCESARETRANSMITTEDTOTHE
LOWERARMSWHERESUSPENSIONBUSHINGSDAMPEN
THEVIBRATION4HEDAMPENEDVIBRATIONTHEN
TRANSMITSTHROUGHTHESUSPENSIONCROSSMEMBER
ANDSTRUTINSULATORSTOTHEBODY
4HERIGIDITYOFTHEBUSHINGSANDINSULATORSIN
THEVIBRATIONTRANSMISSIONPATHHASALARGE
INmUENCEONHARSHNESS4HEUSEOFLOWRIGIDITY
BUSHINGSANDINSULATORSTOPROVIDEGREATERFORE
AFTSUSPENSIONCOMPLIANCESOFTENSTHEIMPACT
FORCEEFFECTIVELYBUTRESULTSINLESSRESPONSIVE
STEERING
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TIRECHARACTERISTICSINmUENCETHEAMOUNTOF
HARSHNESS7HENTIRESEXPERIENCEANIMPACT
FORCEFROMAPAVEMENTJOINTTHEYDEFORMTO
CUSHIONTHERESTOFTHEVEHICLE4HETIRESABSORB
THEFORCETOSOMEEXTENTANDAREANIMPORTANT
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TOOTHERPORTIONSOFTHETIRES4HISCAUSESTHE
TIRESTOUNDERGOCOMPLICATEDRESILIENTVIBRATIONS
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EFlCIENTINCONTROLLINGTHEPROBLEMOFHARSHNESS
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$IAGNOSIS
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s ,ISTKNOWNSYMPTOMS
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s 4RYTODUPLICATETHECONCERN
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$IAGNOSIS
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POSSIBLEROADTESTWITHTHECUSTOMER
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s 2EMEMBERTHATTHEVIBRATINGBODYMAY
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$IAGNOSIS
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#LASSIFYTHENOISEORVIBRATION
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$IAGNOSIS
.EUTRAL#OAST$OWN3PEED4EST
4HENEXTVEHICLECHECKWHENPERFORMINGTHE
ROADTESTISTHENEUTRALCOASTDOWNSPEEDTEST
4HISTESTDIVIDESTHEPOSSIBLECAUSESOFTHENOISEORVIBRATIONINTOTWOCATEGORIES
s 6EHICLESPEEDRELATED
s %NGINESPEEDRELATED
s 7HEELSPEEDRELATED
4HESTEPSOFTHENEUTRALCOASTDOWNSPEEDTEST
ARE
$RIVETHEVEHICLEATASPEEDHIGHERTHANTHE
SPEEDINWHICHTHENOISEORVIBRATIONWAS
OBVIOUSINTHESLOWACCELERATIONTEST
0LACETHEVEHICLEIN.EUTRALANDCOASTDOWN
THROUGHTHESPEEDWHERETHECONCERN
OCCURS
#LASSIFYTHE.6(CONCERNASEITHERVEHICLE
SPEEDRELATEDORENGINESPEEDRELATED
s )FTHENOISEORVIBRATIONEXISTSTHENTHECONCERNISVEHICLEORWHEELSPEED
RELATED4HISELIMINATESTHEENGINEAND
TORQUECONVERTERASPOSSIBLECAUSES
s )FTHE.6(CONCERNDIDNOTOCCURDURING
THENEUTRALCOASTDOWNSPEEDTEST
PERFORMADOWNSHIFTSPEEDTESTTO
CONlRMTHECONCERNASENGINESPEED
RELATED
$OWNSHIFT3PEED4EST
4HISVEHICLECHECKHELPSTOCONlRMTHE.6(
CONCERNASENGINESPEEDRELATED4HESTEPSOF
THEDOWNSHIFTSPEEDTESTARE
3TOPTHEVEHICLEANDPLACETHETRANSMISSION
INALOWERGEAR
$RIVETHEVEHICLEATTHEENGINERPMINWHICH
THENOISEORVIBRATIONOCCURS
s )FTHENOISEORVIBRATIONEXISTSTHENTHE
CONCERNISENGINESPEEDRELATED4HIS
ELIMINATESTIRESWHEELSBRAKESAND
SUSPENSIONCOMPONENTS
s )FNECESSARYREPEATTHETESTUSINGOTHER
GEARSAND.EUTRALTOCONlRMTHERESULTS
4ORQUE#ONVERTER4EST
4HISVEHICLECHECKDETERMINESHOWTHETORQUE
CONVERTERCONTRIBUTESTOANENGINESPEEDRELATED
CONDITION4HESTEPSOFTHETORQUECONVERTERTEST
ARE
$RIVETHEVEHICLEATTHESPEEDINWHICHTHE
.6(CONCERNEXISTS
/PERATETHETORQUECONVERTERBYTAKINGIT
INANDOUTOFLOCKUPBYLIGHTLYDEPRESSING
THEBRAKEPEDALWHILEMAINTAININGVEHICLE
SPEED
#HECKFORNOISEWHENTHETORQUECONVERTERIS
NOTLOCKEDUP
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$IAGNOSIS
3TEERING)NPUT4EST
4HENEXTROADTESTSTEPSARETHETWOSTEERING
INPUTTESTS4HESETESTSDETERMINEIFTHEWHEEL
BEARINGSANDOTHERSUSPENSIONCOMPONENTSARECONTRIBUTINGTOASPEEDRELATEDCONDITION
4HESTEPSOFTHE3TEERING)NPUT4ESTARE
$RIVETHEVEHICLEATTHESPEEDINWHICHTHE
.6(CONCERNEXISTS
-AKEWIDESWEEPINGTURNSINBOTH
DIRECTIONS
s )FTHECONCERNGOESAWAYORGETSWORSE
WHEELBEARINGSHUBS5NIVERSAL*OINTS5JOINTSDRIVEAXLESCONSTANTVELOCITY
JOINTSANDTIRETREADWEARMAYBETHE
COMPONENTSCAUSINGTHECONCERN
3TEERING)NPUT4EST
0ERFORMTHE3TEERING)NPUT4ESTIFTHE.6(
CONDITIONOCCURSWHENTURNINGONLY4HESTEPSOF
3TEERING)NPUT4ESTARE
$RIVETHEVEHICLEATASPEEDHIGHERTHANTHE
SPEEDATWHICHTHENOISEORVIBRATIONOCCURS
0LACETHEVEHICLEIN.EUTRALANDCOASTDOWN
THROUGHTHESPEEDWHERETHE.6(CONCERN
ISOBVIOUSWHILEMAKINGWIDESWEEPING
TURNSINBOTHDIRECTIONS
s )FTHECONCERNEXISTSCHECKFORWORN
WHEELBEARINGSSUSPENSIONBUSHINGS
CONSTANTVELOCITYJOINTSAND5JOINTSCONTAINEDINTHEAXLESOFQUATTRO
APPLICATIONS
s )FTHEVIBRATIONDOESNOTOCCURSTOPTHE
VEHICLEANDENGAGETHETRANSMISSION
TRANSAXLE!LTERNATELYACCELERATEAND
DECELERATETHROUGHTHESPEEDATWHICH
THE.6(CONCERNAPPEARSWHILEMAKING
WIDESWEEPINGTURNSINBOTHDIRECTIONS
s )FTHECONCERNRETURNSTHENTHECAUSEISDEPENDENTUPONENGINELOAD4HE
PROBABLECAUSESARECONSTANTVELOCITY
JOINTSOR5JOINTSCONTAINEDINTHEAXLES
OFQUATTROAPPLICATIONSANDLOOSEOR
MISSINGLUGNUTS
s )FTHENOISEISAhCLUNKINGSOUNDvENGINE
ANDTRANSAXLEMOUNTSSUSPENSION
BUSHINGSAND5JOINTSAREPROBABLE
CAUSES
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$IAGNOSIS
4HESTEPSOFTHE%NGINE,OADED4ESTARE
"LOCKTHEFRONTANDBACKWHEELS !PPLYTHEPARKINGANDSERVICEBRAKES
0UTTHETRANSMISSIONIN$RIVEWHILEKEEPING
THEBRAKESAPPLIED
)NCREASETHEENGINERPMTOTHERPMATWHICH
THE.6(CONCERNOCCURRED)FNECESSARY
MAKENOTEOFTHERPMANDFREQUENCYOFTHE
.6(CONCERN
2ETURNENGINETOIDLE
0UTTHETRANSMISSIONIN2EVERSEWHILE
KEEPINGTHEBRAKESAPPLIED
)NCREASETHEENGINERPMTOTHERPMATWHICH
THE.6(CONCERNOCCURRED)FNECESSARY
MAKENOTEOFTHERPMANDFREQUENCYOFTHE
.6(CONCERN
)MMEDIATELYAFTERENGINELOADEDTEST
RUNINNEUTRALFORMINUTESATASLIGHTLY
ELEVATEDRPMTOCOOLTHETRANSMISSION
.EUTRAL2UN5P4EST
0ERFORMTHE.EUTRAL2UN5P4ESTIFTHE.6(
CONCERNISENGINESPEEDRELATED5SETHETEST
ASAFOLLOWUPTOTHEDOWNSHIFTTESTORWHENTHE.6(CONCERNOCCURSATIDLE4HESTEPSARE
)NCREASETHEENGINERPMWHILEIN0ARKOR
.EUTRAL
)FNECESSARYMAKENOTEOFTHERPMAND
FREQUENCYOFTHE.6(CONCERN
%NGINE,OADED4EST
0ERFORMTHE%NGINE,OADED4ESTIFTHE.6(CONCERNISENGINESPEEDRELATED4HISTESTMAY
HELPREPRODUCEENGINESPEEDRELATEDCONCERNS
NOTEVIDENTWITHTHENEUTRALRUNUPORNEUTRAL
COASTDOWNSPEEDTESTS4HEENGINELOADED
TESTALSOIDENTIlESNOISEANDVIBRATIONSENSITIVE
TOENGINELOADORTORQUE4HESE.6(CONCERNS
OFTENAPPEARDURINGHEAVYACCELERATIONORWHEN
CLIMBINGAHILL
7ARNING"LOCKTHEFRONTANDBACKWHEELSORINJURYTOPERSONNELMAY
RESULT$ONOTEXCEEDlVESECONDS
WHENPERFORMINGTHEENGINELOADED
TESTORDAMAGETOTHETRANSMISSION
TRANSAXLEMAYRESULT
)FTHECONCERNISDElNITELYENGINESPEEDRELATED
PERFORMTHE%NGINE!CCESSORY4ESTTONARROW
DOWNTHEPOSSIBLESOURCEOFTHECONCERN
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$IAGNOSIS
%NGINE!CCESSORY4EST
0ERFORMTHE%NGINE!CCESSORY4ESTIFTHE.6(
CONCERNISENGINESPEEDRELATED4HISTESTHELPS
LOCATEFAULTYBELTSANDACCESSORIESTHATARECAUSINGENGINESPEEDRELATED.6(CONCERNS
4HESTEPSARE
"LOCKTHEFRONTANDBACKWHEELS
!PPLYTHEPARKINGANDSERVICEBRAKES
2EMOVETHEACCESSORYDRIVEBELTS
)NCREASEENGINERPMTOTHERPMATWHICHTHE
.6(CONCERNOCCURRED
s )FTHEVIBRATIONOCCURSTHEBELTSAND
ACCESSORIESARENOTTHESOURCEOFTHE
CONCERN
s )FTHEBELTSANDACCESSORIESARETHE
SOURCEOFTHE.6(CONCERNCONTINUETO
ADDORREMOVESPECIlCACCESSORYBELTS
TOLOCATETHECONCERN#AUTION7ITHTHEACCESSORYBELT
REMOVED
s $ONOTDRIVETHEVEHICLE
s $ONOTOPERATETHEENGINEFOREXTENDEDPERIODS
n 7ATERCOOLEDALTERNATORSCANFAIL
n %NGINESCANOVERHEAT
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.OTES
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%NGINE6IBRATIONS
%NGINE3PEED2ELATED6IBRATIONS
$URINGTHEINITIALVEHICLEROADTESTUSINGTHE
ROADTESTPROCEDURETHEVIBRATIONCAUSINGTHECONCERNWILLBECLASSIlEDINTOEITHERENGINE
SPEEDRELATEDORVEHICLESPEEDRELATED4HIS
SECTIONWILLBEUSEDWHENTHEVIBRATIONISFOUND
TOBEENGINESPEEDRELATED
%NGINESPEEDRELATEDVIBRATIONSARECAUSED
BYACOMPONENTTHATISDRIVENBYTHEENGINE
4HESECOMPONENTSMAYBEPARTOFTHEENGINE
ASSEMBLYORANENGINEACCESSORY
5SINGTHEFREQUENCYOFTHEVIBRATIONAND
MATHEMATICALFORMULASTHEENGINESPEEDRELATEDVIBRATIONCANBECLASSIlEDINTOTHESE
CATEGORIES
s %NGINE#OMPONENTS
s %NGINE!CCESSORIES
s %NGINE#YLINDERS&IRING&REQUENCY
4YPESOF%NGINE6IBRATIONS
-ANY.6(CONCERNSARERELATEDTOTHEENGINE
SYSTEMS4HEOPERATIONOFTHEENGINECREATESANATURALVIBRATION)FANYONECOMPONENTIS
SLIGHTLYOUTOFBALANCETHENATURALVIBRATIONOF
THEENGINEISCOMPOUNDED%NGINEVIBRATIONIS
GENERALLYCAUSEDBYANYOFTHEFOLLOWING
s &IRSTANDSECONDORDERENGINEIMBALANCE
s %NGINElRINGFREQUENCY
s %NGINEMOUNTS
s %NGINEACCESSORIES
&IRSTAND3ECOND/RDER%NGINE)MBALANCE
!lRSTORDERENGINEIMBALANCEISCREATEDWHEN
ANYCOMPONENTTHATROTATESATCRANKSHAFTSPEED
ISOUTOFBALANCEORHASEXCESSIVERUNOUT
%XAMPLESAREHARMONICBALANCERmYWHEELOR
TORQUECONVERTERIMBALANCEANDCYLINDERTO
CYLINDERMASSDIFFERENCES)NRARECASESTHE
CRANKSHAFTITSELFMAYBEIMBALANCED"ALANCING
THECOMPONENTORCORRECTINGTHERUNOUTMAYBRINGTHEVIBRATIONTOANACCEPTABLELEVEL&IRST
ORDERENGINEVIBRATIONSCANBEOFFSETBYPROPER
ARRANGEMENTOFCRANKSHAFTCOUNTERWEIGHTS
3ECONDORDERENGINEIMBALANCEISCAUSEDBYTHE
UPANDDOWNMOTIONOFTHEPISTONS4HISREVERSAL
OFMASSANDMOTIONCREATESANATURALVIBRATION
3YMPTOMSOFENGINEIMBALANCEINCLUDE
s !LOWSPEEDSHAKEFELTBETWEENAND
RPMTHATHASAFREQUENCYOFTO(Z
s !ROUGHNESSSOMETIMESFELTANDHEARD
BETWEENTORPMATA
FREQUENCYOFTO(Z
&IRSTANDSECONDORDERENGINEIMBALANCESARE
USUALLYDETECTEDDURINGTHE.EUTRAL2UN5P4EST
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%NGINE6IBRATIONS
4ORQUE#ONVERTER
(ALF/RDER%NGINE6IBRATION
!HALFORDERVIBRATIONISCREATEDWHENANY
COMPONENTTHATROTATESATHALFTHECRANKSHAFT
SPEEDISOUTOFBALANCEORHASEXCESSIVERUNOUT!NEXAMPLEOFTHISISCAMSHAFTIMBALANCE
"ALANCINGTHECOMPONENTORCORRECTINGTHE
RUNOUTMAYBRINGTHEVIBRATIONTOANACCEPTABLE
LEVEL
4ORQUE#ONVERTER
!LTHOUGHNOTACTUALLYANENGINECOMPONENTTHE
TORQUECONVERTERROTATESATENGINESPEEDANDITS
VIBRATIONFREQUENCIESAREOFTENTHESAMEASTHEENGINE4HETORQUECONVERTERISAmUIDCOUPLING
THATUSESTRANSMISSIONmUIDTOTRANSFERAND
MULTIPLYENGINETORQUETOTHEINPUTSHAFTOFAN
AUTOMATICTRANSMISSION
4HEMOVEMENTOFTHEmUIDBETWEENTHE
IMPELLERWHICHISCONNECTEDTOTHEENGINEAND
THETURBINEWHICHCONNECTSTOTHETRANSMISSION
CANSOMETIMESGENERATEABEATSOUND)FTHIS
ISTHECASEHOWEVERTHESOUNDDISAPPEARS
WHENTHETORQUECONVERTERCLUTCHENGAGESMECHANICALLYLOCKINGTHEIMPELLERANDTURBINE
TOGETHER
!NOTHER.6(CONCERNTHATMAYBECAUSEDBY
THETORQUECONVERTERISVIBRATIONDURINGCLUTCH
ENGAGEMENT)FTHECONVERTERCLUTCHDOESNOT
APPLYSMOOTHLYITMIGHTRESULTINAJERKINGOR
SHAKINGVIBRATIONTHATCANBEFELTTHROUGHOUT
THEVEHICLE4HISVIBRATIONDISAPPEARSWHENTHE
CLUTCHlNALLYENGAGESCOMPLETELY
#ONVERTERCLUTCHVIBRATIONSALSOCANOCCURDURINGDOWNSHIFTSANDCOASTINGIFTHECLUTCH
FAILSTORELEASECORRECTLY)FACONVERTERCLUTCH
MALFUNCTIONISTHESUSPECTEDCAUSEOFAN
.6(CONCERNREFERTOTHEAPPROPRIATESERVICE
PUBLICATIONSFORTRANSMISSIONDIAGNOSTIC
PROCEDURES
4ORQUECONVERTERIMBALANCEISALSOAPOSSIBILITY
WHENDEALINGWITHANENGINEDEPENDENT.6(
CONCERN!LTHOUGHRAREONNEWVEHICLESTHISTYPEOFVIBRATIONMAYAPPEARIFTHETORQUE
CONVERTERHADBEENREPLACEDORINSTALLED
INCORRECTLYDURINGTRANSMISSIONSERVICE!LSO
INSPECTTHEmEXPLATEFORDAMAGEASTHISCOULD
CAUSENOISEORVIBRATION
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%NGINE6IBRATIONS
%NGINE-OUNTS
4HElRSTCOMPONENTSTHATISOLATEVIBRATIONFROM
THEENGINETOTHEPASSENGERCOMPARTMENT
AREENGINEMOUNTS%NGINEANDTRANSMISSIONMOUNTINGCONSISTSOFANUMBEROFRELATIVELY
SMALLPARTSANDARESOMETIMESIGNOREDWHEN
TROUBLESHOOTING(OWEVERTHESEPARTSARE
EXTREMELYIMPORTANTINPREVENTINGNOISEAND
VIBRATIONPRODUCEDBYTHEENGINE
4ORQUEREACTIONFORCEOFTHEENGINEACTSDIRECTLY
ONTHETRANSMISSIONCAUSINGENGINEMOUNTSTO
BESUBJECTEDTOALARGEFORCE4HEREFOREENGINE
MOUNTSMUSTBERIGIDTOSTABILIZETHEENGINE
/NTHEOTHERHANDTOMINIMIZEINHERENTENGINEVIBRATIONSANDNOISEDURINGALLENGINESPEEDS
THEENGINEMOUNTSALSOMUSTBESOFT!NYFAULT
INTHEENGINEMOUNTINGSYSTEMCANLEADDIRECTLY
TONOISEANDVIBRATION
)NSPECTENGINEMOUNTSFORCRACKSORDAMAGE
TOTHEINSULATORANDTHEBRACKET'ROUNDEDTHE
ENGINEMOUNTEDBRACKETCONTACTINGTHEFRAME
MOUNTEDBRACKETORSTRAINEDENGINEMOUNTS
MAYNOTISOLATEENGINEVIBRATIONS
%NGINEMOUNTSMUSTBEINSTALLEDCORRECTLY)FTHEMOUNTSAREINSTALLEDINCORRECTLYOR
INCORRECTPARTSAREUSEDTHEYCANNOTABSORB
ENGINEVIBRATION4HE23ENGINEMOUNTSUSE
SEVERALMOUNTINGHOLESDEPENDINGONWHICH
ENGINEOPTIONISINSTALLEDINTHEVEHICLE3ERVICE
INFORMATIONDETAILSTHEPROCEDURETOREMOVEAND
INSTALLTHEENGINEMOUNTINGBOLTSANDLOCATOR
PINS
3EVERAL!UDIMODELSUSE%LECTRO(YDRAULIC
%NGINE-OUNT3OLENOID6ALVES4HESEVALVESSOFTENORSTIFFENTHEENGINEMOUNTSDEPENDING
UPONENGINEOPERATINGCHARACTERISTICS4HE
SYSTEMMAYBETHESOURCEOFANENGINE
VIBRATIONATIDLEIFNOTOPERATINGPROPERLY
#ONSULT!UDISERVICEINFORMATIONFORDIAGNOSTIC
PROCEDURESFORTHISSYSTEM
%LECTRO(YDRAULIC
%NGINE-OUNT
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%NGINE6IBRATIONS
!CCESSORY6IBRATION
%NGINEACCESSORIESCANBEASOURCEOFENGINE
VIBRATION&OREXAMPLEAIRCONDITIONING
COMPRESSORSARESUSCEPTIBLETOOVERCHARGINGWHICHCANRESULTINAN.6(CONDITION!CCESSORY
PULLEYMISALIGNMENTORFAULTYCOMPONENTSALSO
CANCAUSEVIBRATIONS
7ITHTHEADVENTOFSERPENTINEBELTSITISNO
LONGERPOSSIBLETOREMOVEBELTSONEATATIME
TOISOLATETHESOURCECOMPONENT"ECAUSE
THESERPENTINEBELTDRIVESALLCOMPONENTS
ONECOMPONENTMAYAFFECTANOTHERTHROUGH
RESONANCE)FREMOVINGTHESERPENTINEBELT
ELIMINATESTHEVIBRATIONREINSTALLTHEBELTANDOPERATEEACHCOMPONENTSEPARATELY"YTURNING
THEAIRCONDITIONING/.AND/&&ORBYTURNING
THESTEERINGWHEELSOMECOMPONENTSCANBE
ELIMINATEDORISOLATEDAS.6(SOURCES
7HENDIAGNOSINGACCESSORYVIBRATIONMAKE
SURETHESOURCEOFTHEVIBRATIONISNOTCAUSEDBY
THEENGINEORENGINElRINGFREQUENCIES%NGINE
lRINGFREQUENCIESCANCAUSECOMPONENTSTO
RESONATEANDVIBRATE4HEVIBRATIONAMPLITUDE
MAYINCREASEWITHTHEACCESSORIESLOADED4HEMOSTEFFECTIVEREPAIRMAYBEISOLATINGTHE
DISTURBANCEBYINTERRUPTINGITSTRANSFERPATH
RATHERTHANATTEMPTINGTOELIMINATETHESOURCE
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%NGINE6IBRATIONS
%NGINE6IBRATION&ORMULA
&ORPURPOSESOFVIBRATIONDIAGNOSISTHEENGINE
ALSOINCLUDESTHETORQUECONVERTERANDEXHAUSTSYSTEM7HENAN.6(PROBLEMISTORQUE
SENSITIVETHEVIBRATIONMAYAPPEARORDISAPPEAR
ATDIFFERENTVEHICLESPEEDSMPHKPHBUTIS
PRESENTATTHESAMEENGINERPM&OREXAMPLEIF
AVEHICLEHASSOMEVIBRATIONATMPHKPH
MPHKPHANDMPHKPHBUTIS
WORSEATAPARTICULARSPEEDTHE.6(CONCERN
ISPROBABLYTORQUESENSITIVESINCETHECONDITION
OCCURSATTHESAMEENGINERPMBUTATADIFFERENT
LOAD
5SETHEENGINERPMATWHICHTHE.6(SYMPTOM
OCCURSTODETERMINEENGINEFREQUENCY#ALCULATE
ENGINEFREQUENCYASFOLLOWS
$IVIDETHEENGINERPMBYTHENUMBEROF
SECONDSINAMINUTE
R P M ( Z E N G I N E F R E Q U E N C Y
&OREXAMPLEIFTHECORRESPONDINGENGINERPMOF
AN.6(PROBLEMONAVEHICLEISRPMTHE
RESULTINGENGINEFREQUENCYIS(Z
( Z
4OGETTHESECONDANDTHIRDORDERFREQUENCY
MULTIPLYTHElRSTORDERFREQUENCYBYFOR
SECONDORDERFORTHIRDORDERETC
& I R S T O R D E R X 3 E C O N D O R D E R
& I R S T O R D E R X 4 H I R D O R D E R
%NGINEVIBRATIONSALSOMAYHAVEHALFORDER
FREQUENCIESHALFORDERFREQUENCIESARE
CALCULATEDBYDIVIDINGTHElRSTORDERBY
& I R S T O R D E R ( A L F O R D E R
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%NGINE6IBRATIONS
%NGINE!CCESSORY&ORMULA
"ELTDRIVENENGINEACCESSORIESPRODUCE
VIBRATIONSATDIFFERENTFREQUENCIESTHANTHEENGINEITSELF4HISISBECAUSETHEDRIVERATIO
CREATEDBYTHEDIFFERENTSIZEPULLEYSCAUSES
THEMTOROTATEATDIFFERENTSPEEDS$ETERMINING
ENGINEACCESSORYFREQUENCYISCOMPARABLETO
CALCULATINGDRIVELINEFREQUENCY
#ALCULATEENGINEACCESSORYFREQUENCYBY
PERFORMINGTHEFOLLOWINGSTEPS
$ETERMINETHESIZERATIOBETWEENTHE
ACCESSORYPULLEYANDTHECRANKSHAFTPULLEY
BYDIVIDINGTHECRANKSHAFTPULLEYDIAMETERBYTHEACCESSORYPULLEYDIAMETER
# R A N K S H A F T P U L L E Y D I A M E T E R ! C C E S S O R Y P U L L E Y D I A M E T E R
0 U L L E Y R A T I O
&OREXAMPLEIFTHEDIAMETEROFTHECRANKSHAFT
PULLEYISMMINCHESANDTHEACCESSORY
PULLEYDIAMETERISMMINCHESDIVIDE
BY4HEACCESSORYPULLEYROTATESTHREETIMES
FOREVERYCRANKSHAFTROTATION
! C C E S S O R Y ( Z
-ULTIPLYTHEENGINERPMINWHICHTHE.6(
CONDITIONOCCURSBYTHEPULLEYRATIO
% N G I N E R P M X 0 U L L E Y R A T I O
! C C E S S O R Y R P M
&OREXAMPLEIFTHEENGINERPMISRPM
ENGINESPEEDMULTIPLYBY4HE
ACCESSORYISROTATINGATRPM
X R P M
$IVIDETHEACCESSORYRPMBYTHENUMBEROFSECONDSINAMINUTETOOBTAINTHE
ACCESSORY(Z
! C C E S S O R Y R P M ! C C E S S O R Y ( Z
&OREXAMPLETHEENGINEACCESSORYRPMIS
DIVIDEBY4HEENGINEACCESSORY
FREQUENCYIS(Z
( Z
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%NGINE6IBRATIONS
4YPESOF%NGINE.OISES
7HENENGINECOMPONENTSDEVIATEFROMTHE
PRECISESPECIlCATIONSINWHICHTHEYWEREENGINEEREDTHEENGINECREATESEXCESSIVEOR
INTOLERABLENOISES
2ECIPROCATINGMOTIONOFTHEPISTONSANDTHE
ROTATINGMOTIONOFOTHERENGINECOMPONENTS
CREATEINHERENTNOISES#AUSESOFENGINENOISES
INCLUDE
s #OMBUSTIONn.OISESAREPRODUCEDWHEN
THEAIRFUELMIXTUREISIGNITED
s &RICTION
s -OVINGPARTSANDTHEIMPACTBETWEEN
RECIPROCATINGPARTS
s 4OLERANCEhSLAPvn0ISTONSMOVEUPAND
DOWNANDTHETOLERANCEBETWEENPARTSIS
REPEATEDLYPULLEDINALTERNATINGDIRECTIONS
!BNORMAL#OMBUSTION
!NYABNORMALITIESINTHECOMBUSTIONPROCESS
CANLEADTOAUDIBLEENGINEVIBRATIONS!BNORMAL
COMBUSTIONCANINCLUDEANYOFTHEFOLLOWING
s 3PARKKNOCKPINGING
s "ACKlRING
$ETONATION0INGING
0INGINGISGENERALLYDISTINGUISHEDBYAHIGH
PITCHEDSTRIKINGNOISEGENERATEDWHENTHETHROTTLEISFULLYOPENORDURINGHARDACCELERATION
)FOPERATIONISCONTINUEDINTHISSTATETHE
PISTONSANDVALVESAREADVERSELYAFFECTED
RESULTINGINADAMAGEDENGINE
#AUSESOFENGINESPARKKNOCKPINGINGINCLUDE
THEFOLLOWING
s )NADEQUATEFUEL
s )NCORRECTTIMING
s #ARBONDEPOSITSINTHECOMBUSTION
CHAMBER
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%NGINE6IBRATIONS
%XHAUST.OISE
4HEEXHAUSTSYSTEMCANBEASOURCEOFNOISE
%XHAUSTNOISESINCLUDE
s %XHAUSTGASSOUNDS
s -UFmERANDPIPE
%XHAUSTGASSOUNDSAREFURTHERSUBDIVIDEDINTO
THREECATEGORIES
s 0ULSATING
s !IRCOLUMNRESONANCE
s !IRSTREAMSOUNDS
%XHAUSTGASESAREDISCHARGEDEACHTIMETHE
EXHAUSTVALVESOPENCREATINGAPULSATINGSOUND
4HESOUNDISCYCLICANDISASSOCIATEDWITH
ENGINESPEEDANDTHENUMBEROFCYLINDERS4HE
SOUNDISRELATIVELYLOWPITCHEDCONSISTINGMAINLY
OFTHISBASICFREQUENCY
!IRCOLUMNRESONANCECONSISTSOFSOUNDS
PRODUCEDINEXHAUSTPIPESANDMUFmERS0IPE
LENGTHANDTHECROSSSECTIONALAREAOFTHEPIPE
DETERMINETHEFREQUENCY!IRSTREAMSOUNDSCAN
BEPRODUCEDBYHIGHSPEEDEXHAUST!NEXAMPLE
OFTHISISTURBULENCECAUSEDBYAIRGOINGTHROUGH
THEMUFmERORJETNOISEWHENEXHAUSTIS
DISCHARGEDFROMTHETAILPIPE
-UFmERANDEXHAUSTNOISESCANBECAUSED
BYEXHAUSTSYSTEMMISALIGNMENTINCORRECTLY
INSTALLEDORDAMAGEDMOUNTINGBRACKETSOR
FAILEDHANGERS4HISCANCAUSEAVARIETYOFANNOYINGNOISESTHATCANBELOCATEDWITHA
THOROUGHVISUALINSPECTION
!NYOFTHESESOUNDSINTHEEXHAUSTSYSTEMCAN
BECARRIEDORTRANSMITTEDTHROUGHOUTMANYOF
THEEXHAUSTSYSTEMCOMPONENTSANDINTOTHE
PASSENGERCOMPARTMENT
"ACKlRING
/NETYPEOFBACKlREKNOWNASPOPBACKOCCURS
WHENTHECYLINDERISlREDBEFORETHEINTAKE
VALVECLOSES7HENTHEINTAKEVALVEOPENSTHEAIRFUELMIXTUREINTHEINTAKEMANIFOLDISIGNITED
ANDBURNS4HISSITUATIONISSOMETIMESVIOLENT
ENOUGHTOCAUSEANEXPLOSIVEREPORTWITHIN
THEMANIFOLD0OPBACKCANBECAUSEDBYTHE
FOLLOWING
s %XCESSIVELYLEANFUELMIXTURE
s )NCORRECTVALVETIMING
)FTHEMIXTUREISTOOLEANmAMESPEED
BECOMESSLOWERTAKINGLONGERTOCOMPLETE
THECOMBUSTIONPROCESS)FTIMINGHASBEEN
DISTURBEDAPOPBACKCANOCCURANDPOSSIBLYTHE
ENGINEWILLNOTSTART
!NOTHERTYPEOFBACKlREISAFTERlRE!FTERlREIS
COMBUSTIONINTHEEXHAUSTSYSTEMPRODUCINGA
LOUDREPORTORmAMESATTHETAILPIPE#ONDITIONS
THATCANPRODUCEAFTERlREARE
s $RIVINGFORPERIODSOFTIMEWITHTHEENGINEBRAKED
s 4HETHROTTLEVALVECLOSINGRAPIDLY
!FTERlREOCCURSWHENUNBURNEDFUELISRELEASED
FROMTHECOMBUSTIONCHAMBERANDISREHEATED
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