Themissionofseatbeltistoensurethat,duringtheeventswhichcouldcreateinjuries,theoccupantsofthevehiclearekeptinthecorrectpositionavoidinganyimpactagainsttheinteriorparts.Wearingseatbeltsproperly,isfundamentaltoyoursafetyandthesafetyofyourpassenger.Duringacrashoremergencystop,seatbeltscanhelpkeepyoufrombeingthrownagainsttheinsideofthecar,againstyourpassenger,oroutofthecar.Ofcourse,seatbeltscannotcompletelyprotectyouineverycrash.But,inmostcases,theyreduceyourchanceofseriousinjury.Theycanevensaveyourlife.Thatiswhyregulatoryrequireyoutowearseatbelts.Seatbeltsarestrongnylonstrapsthatholdpeopleintheirseatsduringacollision.Lapbeltsextendacrossaperson'slap.Shoulderbeltsextendoveraperson'sshoulderandchest.Thesecomponentsareessentiallystandardized,becausethesamecomponentisusedondifferentcarsandbydifferentcar-manufacturers.Smalldifferencescanbeonlygeneratedbyspecificconditionsforbeltsinstallation.ThemaintraditionalcomponentsareshowninFig.10.1.WebbingThewebbingisthecomponentofthesafetyseatbeltsthathasthemissionofphysicallyrestrainingtheoccupantsontheseat.Itconsistsofafabricwithstructure,warpandweft,wovenwithtechniquesandmaterialsinsuchawayastoprovidehighresistancetobreakageandsevereagingcycles.Thewebbingisalsoresponsiblefortheso-calledcomfortofuse,whichisdeterminedbytheperceptionoftheuserwhentheseatbeltisworn.Awebbingwhichissoftandsmoothwithlowtransversestiffnessisusuallyperceivedbetterintermsofcomfortthanawebbingwithhardedges.PillarloopInpracticethepillarloopistheeffectiveupperanchorpointwhichcaneitherbefixed,ifanchoreddirectlytothecentralpillar,ormobileintermsofheightwiththeseatbeltsheightadjuster.Themostcommonimplementationusesametalringcoveredwithanin-mouldedplasticmaterial.Althoughthiscomponentappearstobequitesimple,itiscriticalintermsofthestressesthatmustbeenduredanddamagetothewebbingthatcouldresult.Forthisreason,thepillarloopisdesignedtoresistimpulsiveloads,andpreventthewebbingrunningthroughitveryquicklyduringtheimpactorbecomingtwistedoveritswidthwhichmaycausesignificantabrasionandresultinbreakageofthewebbing.BuckleassemblyThebuckleisthecomponentoftheseatbelttowhichthetongueisengaged,madewithplasticmaterialin-mouldedonametalinsertsimilartothepillarloop.Thebuckleassemblyiscomposedofacouplercontainedinaplasticcasingequippedwithareleasebuttonwhichmustensurereleaseoperation,particularlyfollowinganaccidentsandprovidealinktotherealanchorpoint.Today,asalreadymentioned,therealanchorpointisplacedontheseat,whereasinthepastitwaslocatedonthefloor;thelinkcanbemadewithametalcableorflatmetal.HeightadjusterThisdeviceisinstalledonthecentralpillar(Bpillar),accordingtotheproceduredescribedpreviouslyforthedefinitionofeffectiveanchorpoints,S1andS2,andisdesignedtoenabletheappropriatepositioningofthewebbingontheshoulderofoccupant,accordingtodifferentpopulationpercentiles(i.e.peopleofvariousheights).Itcomprisesaslide-shapeddevicewithamobilepartslidinginatrack,andafixedparttowhichthecursorcanbefixedinthechosenpositions.Thepillarloopisfixedonthecursor.RetractorTheretractorconstitutestheheartofthesafetybeltsystem,havingthetaskofwrappingthewebbingonaspool,enablingtheunwindingandensuringthattheseatbeltdoesnotcausetheunwantedsensationofexcessiveshootingorimpedimenttooccupantmovement,whichmaybecausedespeciallyifextractionofthewebbingisblockedwhennotrequiredtodoso.InsteadthelockingofthewebbingisstandardizedbytheregulationR16andisgovernedbytwoindependentsystems:thegeometricanddynamicsystem.Thegeometricsystemcausesthelockingofthebeltwhen,duetoexternalevents(deceleration,shock,etc.),thecarmovesbyasignificantnumberofdegreescomparedtothereferencehorizontalposition.LoadlimiterToretainvehicleoccupantswithsafetybeltswithoutpenalizingthecomfortorcreatesecondaryinjuriesisarelativelycomplextask;theloadlimiterrepresentsavaluableaidtoreachthegoal,thankstotheuseofthepretensioners,bynowalmoststandard,whichareanalyzedbelow.Theloadlimiter,nowadayspracticallyanintegralpartoftheretractor,hasthetaskoflimitingtheforcetransmittedbythebelttotheshoulderandthechestduringanimpact,soastomitigateanyeffectontheoccupants.Partoftheloadlimiteristhetorsionbar,locatedintheretractor.Duringimpact,ittwistsaround,enablingalimitedandcontrolledunwindingofthewebbingsoastolimittheforceexertedontheoccupantandtherebymitigatingdamagetotheshoulderandchest.Seatbeltsaredesignedforadultsandlargerchildren.Smallchildrenmustbeproperlyrestrainedinchildsafetyseats.Apregnantwomanneedstowearaseatbelttoprotectherselfandherunbornchild.