机械制造 毕业设计 外文英文 文献 翻译 齿轮和齿轮传动.doc

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1、GearsandgeardriveGearsarethemostdurableandruggedofallmechanicaldrives.Theycantransmithighpoweratefficienciesupto98%andwithlongservicelives.Forthisreason,gearsratherthanbeltsorchainsarefoundinautomotivetransmissionsandmostheavy-dutymachinedrives.Ontheotherhand,gearsaremoreexpensiveth

2、anotherdrives,especiallyiftheyaremachinedandnotmadefrompowermetalorplastic.Gearcostincreasessharplywithdemandsforhighprecisionandaccuracy.Soitisimportanttoestablishtolerancerequirementsappropriatefortheapplication.Gearsthattransmitheavyloadsorthanoperateathighspeedsarenotparticularl

3、yexpensive,butgearsthatmustdobotharecostly.Silentgearsalsoareexpensive.Instrumentandcomputergearstendtobecostlybecausespeedordisplacementratiosmustbeexact.Attheotherextreme,gearsoperatingatlowspeedinexposedlocationsarenormallytermednocriticalandaremadetominimumqualitystandards.Forto

4、othforms,size,andquality,industrialpracticeistofollowstandardssetupbytheAmericanGearManufacturesAssociation(AGMA).ToothformStandardspublishedbyAGMAestablishgearproportionsandtoothprofiles.Toothgeometryisdeterminedprimarilybypitch,depth,andpressureangle.Pitch：Standardspitchesareusual

5、lywholenumberswhenmeasuredasdiametralpitchP.Coarse-pitchgearinghasteethlargerthan20diametralpitch-usually0.5to19.99.Fine-pitchgearingusuallyhasteethofdiametralpitch20to200.Depth:Standardizedintermsofpitch.Standardfull-depthhaveworkingdepthof2/p.Iftheteethhaveequaladdenda(asinstandar

6、dinterchangeablegears)theaddendumisl/p.Stubteethhaveaworkingdepthusually20%lessthanfull-depthteeth.Full-depthteethhavealargercontractratiothanstubteeth.Gearswithsmallnumbersofteethmayhaveundercutsothantheydonotinterferewithoneanotherduringengagement.Undercuttingreduceactiveprofilean

7、dweakensthetooth.Matinggearswithlongandshortaddendumhavelargerload-carryingcapacitythanstandardgears.Theaddendumofthesmallergear(pinion)isincreasedwhilethatoflargergearisdecreased,leavingthewholedepththesame.Thisformisknowasrecess-actiongearing.PressureAngle:Standardanglesare20°and2

8、5"•Earlierstandards