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1、 PLEASE SCROLL DOWN FOR ARTICLEThis article was downloaded by:Luo,MengOn:22 July 2010Access details:Access Details:subscription number 924718324Publisher Taylor&FrancisInforma Ltd Registered in England and Wales Registered Number:1072954 Registered office:Mortimer House,37-41 Mortimer Street,London
2、W1T 3JH,UKInternational Journal of CrashworthinessInternational Journal of CrashworthinessPublication details,including instructions for authors and subscription information:http:/ vehicle seat design concept for reducing whiplash injury risk in low-A vehicle seat design concept for reducing whiplas
3、h injury risk in low-speed rear impactspeed rear impactMeng Luoa;Qing Zhouaa State Key Laboratory of Automotive Safety and Energy,Department of Automotive Engineering,Tsinghua University,Beijing,ChinaOnline publication date:22 July 2010To cite this ArticleTo cite this Article Luo,Meng and Zhou,Qing(
4、2010)A vehicle seat design concept for reducing whiplash injury risk inlow-speed rear impact,International Journal of Crashworthiness,15:3,293 311To link to this Article:DOI:To link to this Article:DOI:10.1080/13588260903335282URL:URL:http:/dx.doi.org/10.1080/13588260903335282Full terms and conditio
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7、s or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.International Journal of CrashworthinessVol.15,No.3,June 2010,293311A vehicle seat design concept for reducing whiplash injury risk in low-speed rear impactMeng Luo
8、and Qing ZhouState Key Laboratory of Automotive Safety and Energy,Department of Automotive Engineering,Tsinghua University,Beijing,China(Received 12 April 2009;final version received 6 September 2009)To reduce whiplash injury risk in low-speed rear-impact accidents,a sliding mechanism of vehicle sea
9、t with crash energy-absorption(EA)functionisproposedandanalysedinthisstudy.Itcanreducerelativemotionbetweenoccupantheadandtorsounder rear impact and lower values of neck injury related parameters such as neck injury criterion(NIC),neck displacementcriterion(NDC)and neck forces and moment.A number of
10、 parameters of seat structure and countermeasures have greatinfluence on occupant headneck responses in rear impacts.They include head restraint position,seat recliner characteristicand seatback cushion stiffness,as well as the newly proposed seat sliding characteristic.A numerical model that includ
11、es aseat and a BIORID II dummy is used in a parametric study to evaluate effects of whiplash injury risk reduction.The analysisresults show that proper combinations of the values of these parameters can mitigate the whiplash injuries and they form thebasis of the existing countermeasures such as act
12、ive head restraint and yielding seat as well as the newly proposed slidingseat.The simulations demonstrate the effectiveness of the sliding seat in whiplash injury reduction.Potential merits of thesliding seat,compared to the existing countermeasures,are also discussed.Furthermore,appropriate struct
13、ural mechanismsfor EA sliding of seat are designed through quasi-static tests and finite element simulations and an implementation is alsopreliminarily sketched.Keywords:rear impact;seat;whiplash;neck injury;energy absorption1.IntroductionFatalities due to vehicle rear impact represent a lowpercenta
14、ge of all deaths relating to automobile accidents.According to accident data,the fatality rate of rear-endcollisions is approximately 5%11,14,16.Injuriesresulted from rear-end collisions,however,represent alarge portion of all automotive injuries.Roughly 30%of all injuries in road vehicle accidents
15、are caused byrear-end collisions,and typically occur as whiplash neckinjuries or whiplash associated disorders(WAD)3,4,10.Although usually classified as Abbreviated Injury Score(AIS)1 9,whiplash injuries are increasingly problematicregarding their long-term consequences and huge societalcosts.Over f
16、ive billion dollars 12 is spent annually inthe treatment and insurance claims of whiplash injuries inthe US.Therefore,reduction of neck injury risk throughbetter vehicle safety design would bring enormous socialbenefits.The underlying injury mechanism of whiplash has notbeen established.Various neck
17、 injury predictors were pro-posedtoevaluatethewhiplashrisksinroadtrafficaccidents.Bostrom et al.1 proposed the neck injury criterion(NIC),whichisbasedontheassumptionthatthepressuregradientscaused by the fluid flow within the spinal canal could resultin neck injuries.Kleinberger et al.5 established t
18、he Nijneck injury criterion,which combines the effects of forcesand moments acting at occipital condyle.Viano et al.18Corresponding author.Email:mengluomit.educonducted a series of rear-impact tests,analysed the testdata together with insurance claims data and then proposeda neck displacement criter
19、ion(NDC),which is based onthe relative displacement and rotation between the occipitalcondyle and the T1 vertebrate.Besides bending momentand forces at lower neck,head rotation relative to the up-per torso were also suggested as potential injury criteria ofwhiplash injuries 13.Although the exact mec
20、hanisms of whiplash injuriescontinue to be a debate,most researchers agree thatwhiplash injuries are related to the relative motion be-tween head and torso 7.The seat(and head restraint)is the only safety device to counteract large accelerationsof head and torso during a rear impact.Furthermore,it h
21、asbeen shown that the occupant responses to rear impact aregreatly affected by seat structural design parameters,suchas head restraint position 2,7 and seatback properties13.Therefore,good seat designs could lead to a decreasein the incidence of whiplash injuries.For example,VolvosWHIPSseat4,SaabsAc
22、tiveHeadRestraint(SAHR)19and General Motors(GMs)High Retention seat 17 haveshown great advantage in reducing the headtorso relativemotion,and thus mitigating whiplash injuries.To reduce the relative motion between head and torsoduring rear impact,Saabs Active Head Restraint movesforward to catch the
23、 head and reduces its backward motion,Volvos WHIPS seat and GMs High Retention seat allowISSN:1358-8265 print/ISSN:1754-2111 onlineC?2010 Taylor&FrancisDOI:10.1080/13588260903335282http:/Downloaded By:Luo,Meng At:16:25 22 July 2010294M.Luo and Q.Zhouoccupant torso moving backward.Likewise,an energy-
24、absorption(EA)sliding seat mechanism is proposed in thisstudy,aiming to reduce the relative motion between headand torso by allowing vehicle frontal seat to slide back-ward for a certain distance under rear impact.Some kineticenergy can also be absorbed in the sliding.As the first step of this study
25、,a numerical model in-cluding a seat and a BIORID II dummy was establishedin the environment of MADYMO;a series of parametricstudies were then performed with the model to investigatethe effect of seatback properties and head restraint positionon the occupant responses to rear impact.Several injurycr
26、iteria described above are used to evaluate the whiplashinjuryrisk.Thenintheparametricanalysis,theeffectoftheEA sliding seat in terms of lessening neck injury risk wasassessed and demonstrated by the numerical simulations.Finally,two mechanisms of sliding and EA,which may beimplemented into an ordin
27、ary vehicle seat,were designedthrough quasi-static tests and finite element analyses.2.Seat design parametric study for whiplash injuryreductionThe seatback properties and head restraint position are themost significant seat design parameters that can influencethe incidence of whiplash injury in low
28、-speed rear impact.Svensson et al.15 and Kleinberger et al.6 respectivelyinvestigatedtherelationshipbetweenheadrestraintpositionand occurrence of neck injuries through experiments andsimulations.Their results showed that most neck injurycriteria decreased as the head restraint was moved higherand cl
29、oser to the back of occupants head.Prasad et al.13conducted a series of rear-impact sled tests with differentseat designs and showed that neck injury numbers increasewhen the seatback recliner stiffness is high.In this study,theeffectsofheadrestraintpositionandseatbackpropertieson whiplash injury ri
30、sk in rear impact are analysed usingMADYMO numerical simulations.2.1.Model for parametric studyA rear-impact numerical model was established in the en-vironment of MADYMO.MADYMO is a major softwarepackage widely used in automotive safety analysis.As isshown in Figure 1,the model consists of BIORID I
31、I rear-impact dummy,seat and vehicle floor.Only the seat and thefloor will interact with the occupant in a low-speed rear im-pact,and therefore other elements of the occupant restraintsystem and the vehicle interior are not present in the model.The BIORID II dummy is one of the few rear-impactdummie
32、swhichcanprovidegoodbio-fidelityforhead/neckand vertebrate responses in low-speed rear impact.Thedummy model employed in this study is a BIORID II facetQdummyintheMADYMOpackage.Afacetmodelisbasi-cally a multi-body system,while the bodies are representedby membrane elements that enable better geometr
33、ic mod-elling.Null material properties are assigned to all parts,and the stiffness of the facet surface is defined by forcedisplacement functions.Q dummy,developed by TNO,is aseries of facet dummy models with high quality,and all thenumericaldummyresponseshavebeenvalidatedbyvariouscrash tests or com
34、ponent experiments.A facet seat model was built based on the geometry ofthe driver side front seat of a midsize sedan manufacturedFigure 1.Rear impact MADYMO model.Downloaded By:Luo,Meng At:16:25 22 July 2010International Journal of Crashworthiness295Figure 2.Seat recliner torquerotation curve.in Ch
35、ina.Figures 2 and 3 show the curves of the reclinertorquerotation,seat cushion stiffness,seatback cushionstiffness and head restraint padding stiffness.They weremeasured on a dynamic servo seat testing machine.Inthis way,all the facet surface stiffness and the charac-teristic of the revolution joint
36、 between seatback and seatpan of the baseline seat model were obtained from thetests.Thedummywasseatedinnormaloccupantposture,andgravity field was imposed on the system.The seat back wasinclinedto22fromtheverticalline.Thefrictioncoefficientbetween the dummy and the seat was set to be 0.45,whichwas m
37、easured through simple experiments.As shown in Figure 4,the imposed crash pulse is a half-sine FMVSS 202 real impact pulse,corresponding to arear-end collision of approximately 17 km/h delta-V.It is inthe range in which whiplash injury most frequently occurs.Initially,the whole system(dummy/seat/sle
38、d)is stationary,and then the acceleration pulse is applied onto the seat andsled,which accelerate the dummy thereafter.Several groups of simulations were performed to in-vestigate the effect of head restraint position,seat reclinerFigure 3.Seatback,seat pan and head restraint cushion stiffness curve
39、s.Downloaded By:Luo,Meng At:16:25 22 July 2010296M.Luo and Q.ZhouFigure 4.FMVSS 202 rear impact pulse.characteristic and seat back cushion stiffness on whiplashinjury risk.Since currently there is no consensus on anywhiplash injury criterion,some commonly used neck in-jury criteria were calculated t
40、o evaluate incidence of thewhiplash injury.The quadratic response surface method-ology was employed to investigate the trend of these in-jury criteria.All the response surfaces were generated byAutoDOE,a software package that can be coupled withMADYMO runs.2.2.Effect of head restraint positionTwo fa
41、ctors,the backset dX and height difference dZ be-tween the head gravitational centre(GC)and the head re-straint centre,were utilised to define the head restraint po-sition,as shown in Figure 5.dZ is defined as positive if thehead restraint centre is above the head GC.Each factor has5 levels,and a nu
42、merical factorial experiment with totally25 MADYMO runs was performed.Levels of the factorsare shown in Table 1.Quadratic response surfaces of themaximum NIC,NDC,shear force,axial force and bend-ing moment on neck were generated by AutoDOE,and areshown in Figures 6 to 11.All other seat parameters we
43、rekept the same as the baseline seat.From the response surfaces,one can see that all of thesix neck injury criteria decrease as the backset of head re-straint dX goes down.NIC,NDC horizontal displacementand axial force on upper neck decrease monotonically asTable 1.Levels of head restraint position
44、factors.Level 1 Level 2Level 3(Baseline)Level 4 Level 5Backset dX(mm)0306090120Height difference502502550dZ(mm)Figure 5.Definition of head restraint backset dX and heightdifference dZ.Figure 6.Response surface of NIC to head restraint position.Figure 7.Response surface of upper neck shear force to h
45、eadrestraint position.Downloaded By:Luo,Meng At:16:25 22 July 2010International Journal of Crashworthiness297Figure 8.Response surface of upper neck bending moment tohead restraint position.the head restraint height increases,while neck shear force,bending moment and NDC rotation angle achieve mini-
46、mum if the head restraint centre is with the same height ofoccupant head GC.Therefore,the whiplash injury risk canbe reduced if the head restraint is moved closer to the backof the occupants head,as well as at the same height as orslightly higher than the GC of the occupants head.2.3.Effect of seat
47、recliner characteristicAs shown in Figure 2,the recliner characteristic can bedescribed by the torquerotation angle curve.In order tofacilitate the parametric study,a linear fitting of the ex-Figure 9.Response surface of upper neck axial force to headrestraint position.Figure 10.Response surface of
48、NDC horizontal displacement tohead restraint position.perimental curve was performed and then two factors,ro-tational stiffness and yielding torque,were extracted todefine the recliner characteristic.A close analogy of ro-tational stiffness and yielding torque is the Youngs modu-lus and yielding str
49、ess of a perfectly elastoplastic material.Different combinations of rotational stiffness and yieldingtorque will give different recliner rotational characteristics.As shown in Table 2,each factor is given 4 levels,and thusthere are 16 combinations of recliner rotational stiffnessand yielding torque
50、in simulations in total.Quadratic re-sponse surfaces of the peak values of several neck injuryFigure 11.Response surface of NDC rotation angle to head re-straint position.Downloaded By:Luo,Meng At:16:25 22 July 2010298M.Luo and Q.ZhouFigure12.ResponsesurfaceofNICtoseatreclinercharacteristic.criteria