外文翻译--齿轮机构（整理）.doc

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1、翻译部分英文原文GearmechanismsGearmechanismsareusedfortransmittingmotionandpowerfromoneshafttoanotherbymeansofthepositivecontactofsuccessivelyengagingteeth・Inabout2,600B.C・，ChineseareknowntohaveusedachariotincorporatingacomplexseriesofgearslikethoseillustratedinFig.2.7.Aristotle,inthefourthcenturyB.C.wroteo

2、fgearsasiftheywerecommonplace.InthefifteenthcenturyA.D.,LeonardodaVincidesignedamultitudeofdevicesincorporatingmanykindsofgears.Incomparisonwithbeltandchaindrives,gcardrivesarcmorecompact.canoperateathighspeeds,andcanbeusedwhereprecisetimingisdesired・Thetransmissionefficiencyofgearsisashighas98perce

3、nt.Ontheotherhand,gearsareusuallymorecostlyandrequiremoreattentiontolubrication,cleanliness,shaftalignment,etc.,andusuallyoperateinaclosedcasewithprovisionforproperlubrication.Gearmechanismscanbedividedintoplanargearmechanismsandspatialgearmechanisms.Planargearmechanismsareusedtotransmitmotionandspa

4、tialgearmechanisms.Planargearmechanismsarcusedtotransmitmotionandpowerbetweenparallelshafts,andspatialgearmechanismsbetweennonparallelshafts.Typesofgears(1)Spurgears.ThespurgearhasacylindricalpitchsurfaceandhasstraightteethparalleltoitsaxisasshowninFig.28Theyareusedtotransmitmotionandpowerbetweenpar

5、allelshafts.Thetoothsurfacesofspurgearscontactonastraightlineparalleltotheaxesofgears・Thisimpliesthattoothprofilesgointoandoutofcontactalongthewholefacewidthatthesametime.Thiswillthereforeresultinthesuddenloadingandsuddenunloadingonteethasprofilesgointoandoutofcontact.Asarcsuit,vibrationandnoisearcp

6、roduced・(2)Helicalgears.Thesegearshavetheirtoothelementsatanangleorhelixtotheaxisofthegear(Fig.2.9).Thetoothsurfacesoftwoengaginghelicalgearsinnplanargearmechanismscontactonastraightlineinclinedtotheaxesofthegears.Thelengthofthecontactlinechangesgraduallyfromzerotomaximumandthenfrommaximumtozero・The

7、loadingandunloadingoftheteethbecomegradualandsmooth.Helicalgearsmaybeusedtotransmitmotionandpowerbetweenparallelshafts[Fig.2.9(a)]orshaftsatanangletoeachothcr[Fig.2.9(d)].Aherringbonegear[Fig.2.9(c)]i