Aduplexbearingispreloadedbyeliminating the"stick-out"presentinthebearing3.Thestick-outis producedbygrindingthefacesofthebearingringsduringthemanufacture ofthebearing.Thesprings providearelativelysoftmembertoloadthebearingandeliminatethestick-out. Also,ifthespringshowninFigure6werenotpresent,theloadapplied,whentheinnerandouter retainerswereclampedwouldresultindeflectionofotherpartsofthesystemsuchasthebearingraces, anybearingspacersortheretainersthemselves. Iftheresultingstressfromthisappliedloadwere greaterintheouterracethantheinnerrace,theresultingstrainwouldcauseachangeintheeffective preloadofthebearing.Thus,springsareusedtoprovideadefinedpointofdeflectioninabearingmount. Thuswaveanddiskwashersarenoteffectiveforhighprecisionapplications, whicharerequiredto undergoseverevibrations. Giventheselimitationsandtherequirement forlargeloadcapacityandacompactdesign,adifferent approachwasdeveloped. Thebasicideabehindthenewdesignwastoapplyacontrolledload(axial deflection)tothebearingwhileatthesametimegivingthebearingtheabilitytosurvivehighvibration loads.Thenewdesigneliminatessensitivitytothetorqueappliedontheretainingboltsofthebearing. Thedesignchallengewastohaveaverycompactdesignrequiringlittleaxialdeflectionwhileatthesame timehavingastiffnessthatwaslowrelativetotherestofthesystem,andadequatestrengthwithrespecttoyield. ThediscussionofFigures7and8illustratethebearingmountdesignthathasbeenimplemented andis alsoshowninFigure4.Figure7showstherearbearingretainer.Thispartisdesignedasaspringelement. Initialattemptsweremadetosimplymaketheretainingwasherthinnerandtotaperit.Effectivelyacting asacantileverbeamofdecreasing thickness.Theseattemptscouldnotreducethespringratetoless than350,000N/mm.Subsequently, anideawasdevelopedforaslottedretainerconceptwhichenableda muchlowerspringrate.Adjustments werethenmadetothedesigntoreducestressconcentrations and totailorthethicknesstoproducethedesiredspringrate. Sincetheretainerpossessed thetypeofsymmetryknownascyclicsymmetry,onlyasegmentofthe retainerneededtobemodeled.Takingadvantageofsymmetryallowstheuseofamuchhigherlevelof detailformoreaccuratestressresultswhilekeepingoverallmodelsizesmall.Sincetherewereeight fastenersequallyspaced,thereareeight"cycles"ofsymmetry. However,eachoftheeightcycles possessed bilateralsymmetrywhichallowedfurthersubdivision. Theanalysismodelusedaonesixteenthsegmentofthewhole(ascanbeseenintheFigure7). Asappealingasapurelylinearanalysiswouldhavebeen,thelinearassumption breaksdownbadlyfor thispart.Theproblemliesinthegeometryofthepartandtheloadingconditions. Asinmany mechanically fastenedparts,thisretainerisheldagainstthesurfaceofthemotorhousing(preload)by eightscrews.Then,astheloadisappliedtotheinnerdiameteroftheretainerthroughthebearingspacer system,theretainerispushedawayfromthemotorhousing.Thiscreatesagapregioninwhichthereis nocontactbetweentheretainerandthemotorhousing.Thisgapisverysmallbutitisnonetheless real anditchangesthespringrateoftheretainer.Thischangeofspringrateiscausedbecausethegap essentiallymakesalongermomentarm,whichlowerstherate.Thespringrateactuallydecreasesfor increasingloadanddeflection. Toanalyzethisconditionitisnecessarytomodelthecontactsurface.Thiswasdonebyusingcontact surfaceanalysiscapabilityinPATRANcalledAdvancedFiniteElementAnalysis(AFEA).Thisprogramis anadaptationofthewellprovenABAQUSfiniteelementprogram.Becausenonlinearsolutionsarevery timeconsuming, thenonlinearsolutionwasusedtofindthecontactseparationareaandtolearnhowthe nonlinearbehavioraffectedtheperformance ofthedesign.Thenthecontacting surfacethatwas identifiedbythenonlinearanalysiswasconstrained foralinearsolutionusingthesameloads.This essentiallycombinedthebestofbothsolutiontechniques byfindingrealisticboundaryconstraints through thenonlinearsolutionandapplyingthoseconstraints inamuchfasterlinearsolution.Thisenabledmany moredesigniterationsthanwouldhavebeenpossiblewithanexclusively nonlinearanalysis. 42