专业英语9-10.ppt

1、机械工程专业英语,Unit9GearTransmission,Ageardrivesystemisonewhereamotorturnsaseriesofgearstodowork.Itplaysaveryimportantroleoftransmittingpower,achievingconveyingandadjustingtorqueinnumerousindustrialequipmentlikemachinetool,automobile,engineeringmachinery,agriculturemachineryandconstructionmachinery.,intro

2、duction,Typically,shaftorientation,efficiency,andspeeddeterminewhichofthesetypesshouldbeusedforaparticularapplication.Thissectionongearingandgeardrivesdescribesthemajorgeartypes;itevaluates(评估，评价)howthevariousgeartypesarecombinedintogeardrivesandconsiderstheprincipalfactorsthateffectgeardrive.轴的方位、效

3、率和速度决定了在实际应用中应该采用上述哪一类齿轮。这一节主要介绍齿轮传动中的主要齿轮类型。它评定了不同类型的齿轮是如何组合起来构成齿轮驱动以及影响齿轮驱动的主要因素。,introduction,GearTypes,introduction,Neartherootofthetooth,however,thetooltracesatrochoidal(摆线)path,Fig.9.2,providingaheavier,andstronger,rootsection.Becauseofthisgeometry,contactbetweentheteethoccursmostlyasrollingra

4、therthansliding.在接近齿根处，刀具轨迹呈摆线，这使吃根除更厚实。由于采用这种几何曲线，齿轮接触处主要是滚动摩擦而不是滑动摩擦。Andbecausecontactissimultaneouslyacrosstheentirewidthofthemeshing（啮合）teeth,acontinuousseriesofshocksisproducedbythegear.由于接触是沿着整个啮合齿宽同时发生，因此齿轮就会产生连续冲击。,SpurGears,External-toothgears.Themostcommontypeofspurgearhasteethcutontheouts

5、ideperimeter(周边的)ofmatingcylindricalwheels,withthelargerwheelcalledgearandthesmallerwheelthepinion(小齿轮).Thesimplestarrangementofspurgearsissinglepairofgearscalledasinglereductionstage(一级减速装置),whereoutputrotationisinadirectionoppositethatoftheinput.图9.3所示的是最普通的直齿轮类型，其轮齿是切削加工在配对齿轮的外圆周上。大齿轮称为gear，小齿轮称为

6、pinion。直齿轮最简单的布置就是一级减速装置，其输入转向于输出转向相反。,SpurGears,Highernetreductionisproducedwithmultiplestagesinwhichthedrivengearisrigidlyconnectedtoathirdgear.Thisthirdgearthendrivesamatingfourthgearthatservesas(充当，担任)outputforthesecondstage.Inthismanner,severaloutputspeedsondifferentshaftscanbeproducedfromasing

7、leinputrotation.更大的减速比可以采用多级减速来实现，齿轮的第四个齿轮以实现二级减速。采用这种方式，输入一个旋转运动就可以在不同的轴上获得不同的输出转速。,SpurGears,Internal(ring)gears.Asthenameimplies(顾名思义),teetharecutontheinsidesurfaceofacylindricalring,insideofwhicharemountedasingleexternal-toothspurgearorsetofexternal-toothspurgears,typicallyconsistingofthreeorfou

8、rlargergears(planets)usuallysurroundingasmallercentralpinion(sun).顾名思义，在内啮合传动方式中，轮齿是在圆柱环的内表面加工出来的。在它的里面还安装有一个或一套外啮合齿轮，最典型的是由三个到四个大齿轮（行星轮）围绕一个较小的中心小齿轮（太阳轮）。,SpurGears,Normally,theringgearisstationary,causingtheplanetstoorbit(在轨道上运行)thesuninthesamerotationaldirectionasthatofthesun.forthisreason,thiscl

9、assofgearifoftenreferredtoasaplanetarysystem.一般情况下，环形齿轮是静止的，它使行星轮绕中心齿轮转动，其选装方向与中心轮一致。由于这个原因，这一类齿轮经常被称为行星齿轮系。,SpurGears,Rack-and-piniongears.Astraightbarwithteethcutstraightacrossit,Fig.9.5,iscalledarack.Basically,thisrackisconsideredtobespurgearunrolled(展开)andlaidoutflat.Thus,therack-and-pinionisasp

10、ecialcaseofspurgearing.Therack-and-pinionisusefulinconvertingrotarymotiontolinearandviceversa(反之亦然).Conversely,inmachinetools,lifttrucks升降机,powershovels挖土机,andotherheavymachinerywhererotarymotionofthepiniondrivesthestraight-lineactionofareciprocating(往复的)part.4,SpurGears,Helicalgearingdiffersfromspu

11、rgearinginthathelicalteetharecutacrossthegearfaceatanangleratherthanstraight.Thus,thecontactlineofthemeshingteethprogressesacrossthefacefromthetip(尖端、末端)atoneendtotherootoftheother,reducingthenoiseandvibrationcharacteristicofspurgears.斜齿轮传动与直齿轮传动的区别在于斜齿轮的轮齿是沿齿面呈某一角度而不是垂直于端面切削加工出来的。如此，啮合齿的接触线是由端面一端的齿

12、顶到达另一端的齿根处，相比直齿轮传动而言，降低了噪声和振动。,HelicalGears,Also,severalteethareincontactatanyonetime,producingamoregradualloadingoftheteeththatreduceswearsubstantially.Theincreasedamountofslidingactionbetweenhelicalgearteeth,however,placesgreaterdemandsonthelubricanttopreventmetal-to-metalcontactandresultingpremat

13、uregearfailure.另外，在啮合过程中，几个齿同时接触，而且是逐级加载，这样有利于大幅度减少磨损。斜齿轮的滑动摩擦增加，对润滑提出了更高的要求以避免金属间接触而导致过早的齿轮失效。,HelicalGears,Also,sincetheteethmeshatanangle,asidethrust(推力)loadisproducedalongeachgearshaft.Thus,thrustbearingsmustbeusedtoabsorbthisloadsothatthegearsareheldinproperalignment(对齐，排成直线).另外，由于轮齿是沿一定角度进入啮合的

14、，沿每个齿轮的轴线方向都会产生一个侧向推力载荷，因此，要采用推力球轴承来吸收这个载荷以保证齿轮的正常啮合。,HelicalGears,Aspecialclassofbevelscalledmitergearshavegearsofthesamesizewiththeirshaftsatrightangles.Oftenthereisnoroomtosupportbevelgearsatbothendsbecausetheshaftsintersect（相交）.还有一类特殊的锥齿轮称之为等径锥齿轮，它们的尺寸相同而且轴相交成直角。由于齿轮轴相交，轴的两端常常没有空间来支撑锥齿轮。,BevelGe

15、ars,Thisoverhangload(OHL)maydeflecttheshaftandmisalignthegears,whichcausespoortoothcontactandaccelerateswear.Shaftdeflectionmaybeovercomewithstraddle(跨越的两边)mountinginwhichabearingisplacedoneachsideofthegearprovidedspacepermits.这个悬臂载荷就可能使齿轮轴挠曲，使它们不能对准（错位），会导致轮齿接触不好，从而加速磨损。如果空间允许的话，可以采用跨越式结构，在齿轮两端各装一个

16、轴承，就可以解决齿轮轴的挠曲变形问题。,BevelGears,BevelGears,StraightandSpiralBevelGears,Wormgearing,WORMANDWORMGEAR,Wormgearsetsconsistofascrew-likeworm(comparabletoapinion)thatmesheswithalargergear,usuallycalledawheel5Inthisway,awiderangeofspeedratiosupto60:1andhighercanbeobtainedfromasinglereduction.Mostwormsarecyl

17、indricalinshapewithauniformpitchdiameter.However,adouble-envelopingwormhasavariablepitchdiameterthatisnarrowestinthemiddleandgreatestattheend.,Wormgearing,However,areversibleworm-gearhasthewormandwheelpitchessoproportioned(均衡的)thatmovementofthewheelrotatestheworm.Inmostwormgears,thewheelhasteethsimi

18、lartothoseofahelicalgear,butthetopsoftheteethcurveinward(向内)toenvelop(包络)theworm.在可逆式涡轮蜗杆传动过程中，二者的节距比例要合适，蜗杆才能驱动蜗杆。在大多数蜗轮中，其轮齿与斜齿轮轮齿相似，但是轮齿曲线顶部是向内包络蜗杆的。,Wormgearing,Becauseofthishighlevelofrubbing(摩擦)betweenthewormandwheelteeth,theefficiencyofwormgearingislowerthanothermajorgeartypes.Oneofthewormgearislowwear,duemostlytothefull-fluidlubricantfilmthattendstobeformedbetweentoothsurfacesbythewormslidingaction.,Wormgearing,GearGeometry,Nomencl