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1、Chapter7DesignofGearMechanisms1.ParallelShaftGears(1)SpurgearsTheteetharestraightandparalleltothegearaxis.Thisgearisspurgear.Ifthegearshaveexternalteethontheoutersurfaceofthecylinders,theyrotateintheoppositedirection,asshowninFig7-1a.Aninternalgearcanmeshwithaexternalpiniononlyandtheyrotateinthesam
2、edirection,asshowninFig7-1b.Thepinionandrackcombinationconvertsrotarymotionintotranslationalmotionorviceversa,asshowninFig7-1c.7.1ClassificationofGearMechanismsFig.7-1 Spurgears(直齿圆柱齿轮)Fig.7-2 Helicalgears(斜齿圆柱齿轮)(2)HelicalgearsLikespurgears,helicalgearscanalsobeusedtoconnectparallelshafts,butthei
3、rteetharenotparalleltotheirshaftsaxes,eachbeinghelicalinshape.Twomeshinggearshavethesamehelixangle,buthaveteethofoppositehands,asshowninFig7-2.Helicalgearcanalsobeclassifiedasexternalcontact,internalcontact,helicalpinionandrack.Fig.7-3 Herringbonegears(人字齿轮)(3)HerringbonegearsHerringbonegearsareeq
4、uivalenttoapairofhelicalgearswithoppositehelixanglesmountedsidebyside,asshowninFig7-3.Theaxialthrustforcesofthetworowsofteethcanceleachother.Sotheycanbeusedathighspeedswithlessnoiseandvibrations.2.SpatialGears(1)IntersectingshaftgearsIftheteethareformedontheconesurface,thisgeariscalledabevelgear.I
5、ftheteetharestraightandcoincidentwiththeirconeelements,thisgeariscalledstraightteethbevelgearshowninFig7-4a.Whentheteethofbevelgearareinclinedatanangletothefaceofbevel,thisgearisknownashelicalbevelgearorspiralbevelgear,asshowninFig7-4b.Thecurvedteethbevelgearhasteeththatarecurved,butwithazerodegree
6、spiralangle,asshowninFig7-4c.Fig.7-4 Bevelgears(锥齿轮)Fig.7-6 Wormgears(蜗轮蜗杆)(2)SkewshaftgearsTotransmitmotionbetweentheskewshafts,thespiralgearsorcrossedhelicalgears,wormgearsandHypoidgearsareoftenusedinmachines.Thespiralgearsorcrossedhelicalgearsarelimitedtohighload,andtheirshaftscanbesetatanyangle
7、,asshowninFig7-5.(3)WormgearsFig7-6showswormgearsinwhichafewteethofthesmallergeararewrappedarounditscircumferenceanumberoftimesandformscrewthreads,andthelargerwheelhasconcaveshapeinitsdiameterdirectionsotha
