汽车座椅外文文献

ComparisonofSeatSystemResonantFrequencyTestingMethods

Aseatsystemdevelopedwithoutanaccuratestructuraldynamicsmodelhasahigher

probability

of

squeaks,

rattles,

excessiveseat

backmotion,

andpoorride

characteristics.

Iftheseissuesarenotaddressedduringdevelopmenttestingandareallowedtogointo

production,engineeringchangesaremorecostlyanddifficulttoimplement.Because

today’sseatsystemsaremorecomplex,engineersmustusethelatesttechnologyto

determinetheseatsystemresponsecharacteristics.

Modalanalysisistheprocessofdevelopingadynamicmodelofastructureora

mechanical

systemwhichwill

beusedfor

problemsolving

andtrouble

shooting,

simulation,

prediction

，andoptimization.The

dynamicmodelis

asetof

modalparameters

consisting

ofnatural

frequencies,

dampingfactors,

andmodeshapes.These

parameters

are

basedon

thestructureorsystem.Experimentalmodalanalysiscanuseeithertimebased,or

frequencydomainbasedmeasurementstocalculatethemodalparameters.Thismethod

providesthemostthoroughdefinitionofthedynamicresponsecharacteristicsofthe

isolatedseatingsystem.

ResonantImpactAnalysisisusedtodeterminetheapproximatedynamicresponseofa

seatingsystem.Thismethodprovidesfrequencyresponsefunctionswhichdescribethe

natural

frequencies

ofthe

system.Resonant

impact

analysis

provides

information

quickly,

but

doesnotdefine

the

dynamicresponsecharacteristics

ascompletely

asmodalanalysis.

Multi-axis

shakertable

testing

isanothertool

usedtodetermine

resonant

frequencies

intheseatsystem.Theshakertableisabletoinputsinesweepandrandominputsinto

theseatingsystem.Theamplitudeofthesinesweeporrandominputcanbecontrolled

inacceleration

or

displacement

control.The

shaker

table

is

alsocapable

of

simulating

roadconditions

of

acustomer’sproving

groundsin

the

laboratory.These

roads

generate

loadsin

vehiclecomponentssuchasseats.Controlled

laboratory

tests

allow

duplication

ofcomplexmulti-channel

timehistories

ofatest

specimen.The

shakertable

canreproduce

roadinputs

insix

degreesof

freedom:vertical,lateral,longitudinal,pitch,roll,

and

yawmotions.

EXPERIMENTAL

Acorrelationstudyofseatresonantfrequenciesinvolvedthecomparisonofseat

resonant

frequency

data

acquired

by:ResonantImpact

Analysis,

ModalAnalysis,

andShaker

TableTesting

using

asix-axis

simulation

reproducing

bothsinusoidal

sweepsandsimulated

roaddata.

All

seat

wereinstalled

in

theOEMdesign

position

andrigidly

attached

toeither

theshakertableormodalbedplatefortesting.

MODALANALYSIS

Modalanalysis

wasonemethodusedtocharacterize

thedynamicproperties

oftheseats.

This

involved

collecting

frequency

domain

measurements,

more

specifically

frequency

responsefunctions,todescribethedynamiccharacteristics.AnH1estimatorwasused

tocalculatethefrequencyresponsefunctionsoftheseat

systems.The

seatstructures

wereexcited

withtwoelectrodynamic

shakers,

onemountedlaterally

at

thetopofthe

seat

backandonemounted

fore/aft

at

the

bottomof

the

seat

back.The

response

wasmeasuredover

afrequency

rangeof0to

50Hzwith

200spectral

lines.Twenty

averages

weretakenforeachFRFmeasurement.

Theexcitation

signal

wasan80%burst

randomfunction.Burst

random

excitationwaschosentoexcitetheentirefrequencyrangeofinterest

uniformlyandallowthesystemresponsetodieoutpriortotheendof

themeasurement.A

burst

randomsignalis

for

FFTanalysis,

whichassumes

aperiodicsignal,because

itensuresthat

thesignallevels

arezeroat

thebeginningandattheendofthemeasurement.

Inaddition

to

theexcitation

technique,

it

wasimportant

to

test

the

seatsystems

inarepresentativeenvironment.Modalanalysiscanbe

performedinafree-free

environmentwherethe

seat

systemis

completely

suspended,

or

in

avariety

ofclampedpositions.The

samplestested

for

thispaperwereattachedtoarigid

bedplatein

designposition

tosimulate

theboundaryconditionspresentwhentheseatsystemsareinstalledin

avehicle.Therigidbedplateisexceptionallystiffrepresentingthe

optimalvehiclefloorpan.

Oncethemeasurementsweretakenandthefrequencyresponsefunctions

calculated,themodalparameterswere

estimated.Theleastsquares

complexexponentialmethodwasusedforestimatingthefrequencyand

dampingcharacteristics,

while

the

least

squaresfrequency

domainmethod

wasusedtoestimate

themodeshapes.This

methodis

accurate

for

systems

withtypicaldampingvaluesbelow5%,asseenintheseatsystemsthat

havebeentested.

Tables

1through4detail

the

modalanalysis

results

for

the

samples

tested.TheModeShapeisadescriptionofseatbackresponse,unless

thebaseisspecificallymentioned.TheFrequencyandDampingofeach

modeshapearealso

provided.Finally,

aModeParticipation

isassigned.

Thisnumber

is

thepercentage

ofthetotalresponseofthemodaldue

totheparticularmode.

Table1:BucketSeat1ModalAnalysistestResults

Modeshape

Frequency(Hz)

Damping

Mode

Participation

Backrollingabout/Axis

9.78

4.45%

2.4%

Lateral

11.76

3.85%

19.4%

Lateral

12.34

4.51%

40.4%

Fore/Aft

12.47

6.66%

22.5%

Lateraltorsionwith

14.69

2.10%

1.3%

Fore/aft

LateralBending

24.50

1.49%

3.6%

LateralBending

25.80

2.05%

6.6%

Torsion

35.59

4.54%

3.8%

Table2:BucketSeat2ModalAnalysistestResults

Modeshape

Frequency(Hz)

Damping

Mode

Participation

Fore/aft

14.22

2.16%

10.0%

Fore/aft

16.94

5.11%

26.4%

Lateral

19.38

2.21%

54.9%

VerticalTorsion

40.72

5.25%

8.7%

Table3:BucketSeat3ModalAnalysistestResults

Modeshape

Frequency(Hz)

Damping

Mode

Participation

Fore/aft

10.13

4.27%

33.1%

Fore/aft

10.80

3.14%

11.2%

Fore/aftwithSomeLateral

11.76

3.36%

32.7%

Lateral

12.49

2.68%

11.2%

Torsion

29.22

5.33%

11.8%

Table4:BucketSeat4ModalAnalysistestResults

Modeshape

Frequency(Hz)

Damping

Mode

Participation

Fore/aft

6.33

5.13%

2.5%

Fore/aft

12.15

4.19%

17.1%

LateralwithSomeFore/aft

14.22

1.47%

2.6%

Lateral

17.60

2.94%

50.9%

Torsion

31.64

3.66%

11.6%

BaseVertBackLatBending

36.57

4.05%

15.4%

RESONANTIMPACTTESTING–Whenacomplete

modalmodeisnotrequired,

resonanceimpact

analysis

is

usedto

determine

thelocation

of

seat

system

resonances.

This

method

involved

recording

the

frequencyresponse

functionoftheseatbackwhenexcitedbyanimpactfromamodalhammer.

Thehammerhadaforcetransduceratthetiptorecordtheinputforce,

while

accelerometerswere

attached

to

the

seat

back

to

measure

the

response.Theseatsystemswereimpactedatthetopleftcornerofthe

seat

backandthe

responses,

lateral

andfore/aft,

werecollected

at

top

centeroftheseat

back.The

responsewasmeasuredfrom0to

200Hzwith

800spectrallines.Thisresultedina25Hzresolution.Therewasa

10%exponential

windowplacedontheoutputandtwenty

averageswereused

togeneratethefrequency

responsefunction.The

impact

testing

results

are

detailed

in

Table

5.

Whenmorn

than

one

value

is

given

for

a

particularresonance,

thereareresonancesatmorethanonefrequency.

Table5:ResonantImpactResults

SampleLateralFore/Aft

Freq(Hz)

Coherence

Freq(Hz)

Coherence

11.75,14.00,

0.985,

BuckerSeat1

11.75,14.25

0.990,0.954

0.989,

15.00

0.994

BuckerSeat2

16.2519.75

0.992,0.996

16.25,20.00

0.997,

0.997

BuckerSeat3

12.50

0.994

11.75

0.992

BuckerSeat4

11.50,

0.982,0.989,

11.50,14.25

0.985,

14.25,17.25

0.981

0.992

TESTRESULTANALYSIS

The

frequency

responsefunctions

generated

by

resonance

impact

testingprovidethefore/aftandlateralresonantfrequenciesofthe

seating

system.Duetothelowlevel

ofexcitation

provided

bythe

impact

hammer,thismethodoftestingdoesnotalwaysexciteeveryresonance

effectively.Whenlooking

at

BucketSeat3there

wasasignificant

fore/aft

resonanceobserved

inthe10-11Hzrangefrombothmodalandshakertableanalysisthat

resonanceimpact

testing

could

not

differentiate

from

the

11.75

Hz

resonance.

Theextent

to

whichaparticular

seat

is

non-linear

cancauseimpact

testing

resonant

frequencies

to

be

slightly

different

than

resonant

frequenciescalculatedfromtestingthatprovidesexcitationlevels.

ThischaracteristicwasobservedinBuckerSeat2.Themodalanalysis

indicated

themainfore/aft

resonancetobe16.94Hzandthemainlateral

resonancetobeat19.38Hzwhileresonantimpactanalysisplacedthese

modesat16.25Hzand19.75Hzrespectively.

Theresonantimpacttestingmethodisofvaluewhenanapproximate

seatsystemfrequencyresponseneedstobedeterminedquickly.When

multiple

design

iterations

are

being

compared,impact

analysis

proves

to

beanexcellenttoolforrankingthefrequencyresponsecharacteristics

ofthe

designs.

Themethod’slimitations

in

providing

adequate

excitation

for

all

modesandadetailed

modelareoffset

bythe

speedwith

whichthemeasurementscanbetaken.

Whenafull

modal

analysis

is

performedon

aseating

system

significant

information

about

the

overall

structural

dynamicproperties

canbeascertainedinadditiontothefrequenciesatwhichtheseat

resonates.Theanalysiscanbeusedtomodelthestructureandprovide

datato

indicate

whatstructural

modifications

maybemadetoimprove

the

frequency

responsecharacteristics

of

theseatsystem.Modalanalysis

is

muchmorecomplicated

thanresonant

impact

testing

andis

usedonlywhen

structural

modifications

areneeded,orFEAmodelsneedto

becorrelated.

Modalanalysis

details

the

relative

importance

of

various

seat

modes

inthedynamicmodelmosteffectively.ImpactanalysisonBucketSeat

4revealedresonancesat11.5Hz,14.25Hz,and17.25Hz,butprovidedlimitedinformationtotheimportanceofeachresonance.ThemodalanalysisofBucketSeat4illustratedtheimportanceofeachmode.Alateralmodeat17.60Hzwas50.9%oftheresponse,afore/aftmodeat

12.15Hzwas17.1%fortheresponse,andlateralmode14.22Hzwas2.6%oftheresponse.

Whilemodalanalysisprovidesdetailedinformationaboutaseat’sfrequencyresponsecharacteristics,itgeneratesthisinformationby

uniformlyexcitingtheseat

system

with

abroadbandburst

randomsignal.This

isanexcellent

methodforexcitingall

themodesinthe

seat,butis

notrepresentative

oftheinputspectrumthatavehicleprovides.Itisimportanttohave

themainseatresonancesatfrequencies

whichthe

vehicle

doesnotexcite,

sotheirimpactcan

beminimized.Bucket

Seat4hada

mainlateralmode

at17.60Hzandaminorlateral

modeat

14.22

Hz,butthe

simulation

road

loadtestingonlyexcitedtheminorlateralresonance.

ShakertabletestingistoolusedbytheOEM

’sandsuppliersto

subjectspecimenstosqueak,rattleanddurabilitytesting.Aseatmay

besubjectedtothousands

ofsimulatedmiles

orusedto

inputsinesweep

inputs

toassist

indetermining

thesourceof

eachsqueakandrattle

issue.

Unoccupiedseat

shakeoften

causessqueakandrattle

issues

in

theseating

system.

Whenthe

resonant

frequency

of

a

seat

is

below

16

Hz

the

probabilityofin-vehiclesqueaksandrattlesincreases.

Thefirstmethodoftestingwassubjectingtheseatstosinusoidal

vertical,

andlongitudinal

inputs.The

inputs

weresimilar

tothose

used

forcurrent

testing

specifications.Acceleration

input

levels

are

very

importantwhenperformingsinesweeptests.Iftheaccelerationlevels

aretoo

high

it

will

not

accurately

represent

acceleration

levels

similar

tothoseseenontheroad.Tables6through8detailthesinesweep

testing.

Thevertical

input

to

the

shaker

table

wasfrom2to

20Hz.The

dataforeachinputwasanalyzed

todetermine

correlation

betweenvertical

inputandlateraloutput,verticalinputandfore/aftoutput,lateral

inputandlateraloutput,fore/aftinputandfore/aftoutput.Bucket

seat1,3and4hadsimilarresonantfrequencycharacteristicsinthe

fore/aft

direction

whichwasnotrevealed

during

thesine

sweeptesting.

Theresonantfrequencywastypicallylowerwhenanalyzingthedatafrom

lateralinputlateraloutputandfore/aftinputandfore/aftoutput.

During

the

sine

sweep

evaluation

the

start

and

stop

frequency

and

accelerationamplitudesarerecorded.ThesevaluesarecomparedtothevehicleASDplots.

Table6:VerticalSineSweepResults

Sample

Lateral(Hz)

Fore/Aft(Hz)

Bucketseat1

13.00

13.50

Bucketseat2

18.50

18.00

Bucketseat3

11.50

10.00

Bucketseat4

13.50

9.00

Table7:LateralSineSweepResults

Sample

Lateral(Hz)

Fore/Aft(Hz)

Bucketseat1

13.50

13.00

Bucketseat2

18.50

16.50

Bucketseat3

10.00

11.00

Bucketseat411.5011.50

Table8:LongitudinalSineSweepResults

Sample

Lateral(Hz)

Fore/Aft(Hz)

Bucketseat1

13.50

13.50

Bucketseat2

16.50

11.50

Bucketseat3

11.00

9.50

Bucketsea