专业英语9-10.ppt

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1、机机 械械 工工 程程 专专 业业 英英 语语Unit 9 Gear Transmission123Introduction Spur GearsHelical Gears45Bevel GearsWorm Gearing6Gear GeometryA gear drive system is one where a motor turns a series of gears to do work.It plays a very important role of transmitting power,achieving conveying and adjusting torque in nu

2、merous industrial equipment like machine tool,automobile,engineering machinery,agriculture machinery and construction machinery.1introduction Typically,shaft orientation,efficiency,and speed determine which of these types should be used for a particular application.This section on gearing and gear d

3、rives describes the major gear types;it evaluates(评评估估，评评价价)how the various gear types are combined into gear drives and considers the principal factors that effect gear drive.轴轴的的方方位位、效效率率和和速速度度决决定定了了在在实实际际应应用用中中应应该该采采用用上上述述哪哪一一类类齿齿轮轮。这这一一节节主主要要介介绍绍齿齿轮轮传传动动中中的的主主要要齿齿轮轮类类型型。它它评评定定了了不不同同类类型型的的齿齿轮轮是是如

4、如何何组组合合起起来来构构成成齿齿轮轮驱驱动动以以及及影影响响齿齿轮轮驱驱动动的的主要因素。主要因素。1introduction Helical Gears（斜齿轮）（斜齿轮）Worm Gears（蜗轮蜗杆）（蜗轮蜗杆）Spur Gears（直齿轮）（直齿轮）Gear TypesHypoid Gears（双曲面齿轮）（双曲面齿轮）1introduction Near the root of the tooth,however,the tool traces a trochoidal(摆摆线线)path,Fig.9.2,providing a heavier,and stronger,root

5、section.Because of this geometry,contact between the teeth occurs mostly as rolling rather than sliding.在在接接近近齿齿根根处处，刀刀具具轨轨迹迹呈呈摆摆线线，这这使使吃吃根根除除更更厚厚实实。由由于于采采用用这种几何曲线，齿轮接触处主要是滚动摩擦而不是滑动摩擦。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。And because contact is simultaneously across the entire width of the meshing（啮啮合合）teeth,a

6、 continuous series of shocks is produced by the gear.由由于于接接触触是是沿沿着着整整个个啮啮合合齿齿宽宽同同时时发发生生，因因此此齿齿轮轮就就会会产产生生连连续续冲击。冲击。Spur Gears2External-tooth gears.The most common type of spur gear has teeth cut on the outside perimeter(周周边边的的)of mating cylindrical wheels,with the larger wheel called gear and the sma

7、ller wheel the pinion(小小齿齿轮轮).The simplest arrangement of spur gears is single pair of gears called a single reduction stage(一一级级减减速速装装置置),where output rotation is in a direction opposite that of the input.图图9.3所所示示的的是是最最普普通通的的直直齿齿轮轮类类型型，其其轮轮齿齿是是切切削削加加工工在在配配对对齿齿轮轮的的外外圆圆周周上上。大大齿齿轮轮称称为为gear，小小齿齿轮轮称称为为

8、pinion。直直齿齿轮轮最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。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。Spur Gears2Higher net reduction is produced with multiple stages in which the driven gear is rigidly connected to a third gear.This third gear then drives a mating fourth gear that serves as(充充当当，担担任任)output for the second stage.In

9、 this manner,several output speeds on different shafts can be produced from a single input rotation.更更大大的的减减速速比比可可以以采采用用多多级级减减速速来来实实现现，齿齿轮轮的的第第四四个个齿齿轮轮以以实实现现二二级级减减速速。采采用用这这种种方方式式，输输入入一一个个旋旋转转运运动动就就可可以以在在不不同同的的轴上获得不同的输出转速。轴上获得不同的输出转速。Spur Gears2Internal(ring)gears.As the name implies(顾顾名名思思义义),teeth

10、are cut on the inside surface of a cylindrical ring,inside of which are mounted a single external-tooth spur gear or set of external-tooth spur gears,typically consisting of three or four larger gears(planets)usually surrounding a smaller central pinion(sun).顾顾名名思思义义，在在内内啮啮合合传传动动方方式式中中，轮轮齿齿是是在在圆圆柱柱环

11、环的的内内表表面面加加工工出出来来的的。在在它它的的里里面面还还安安装装有有一一个个或或一一套套外外啮啮合合齿齿轮轮，最最典典型型的的是是由由三三个个到到四四个个大大齿齿轮轮（行行星星轮轮）围围绕绕一一个个较较小小的的中中心心小小齿齿轮轮（太阳轮）。（太阳轮）。Spur Gears2Normally,the ring gear is stationary,causing the planets to orbit(在在轨轨道道上上运运行行)the sun in the same rotational direction as that of the sun.for this reason,thi

12、s class of gear if often referred to as a planetary system.一一般般情情况况下下，环环形形齿齿轮轮是是静静止止的的，它它使使行行星星轮轮绕绕中中心心齿齿轮轮转转动动，其其选选装装方方向向与与中中心心轮轮一一致致。由由于于这这个个原原因因，这这一一类类齿齿轮轮经经常常被被称称为行星齿轮系。为行星齿轮系。Spur Gears2Rack-and-pinion gears.A straight bar with teeth cut straight across it,Fig.9.5,is called a rack.Basically,thi

13、s rack is considered to be spur gear unrolled(展展开开)and laid out flat.Thus,the rack-and-pinion is a special case of spur gearing.The rack-and-pinion is useful in converting rotary motion to linear and vice versa(反之亦然反之亦然).Conversely,in machine tools,lift trucks升升降降机机,power shovels挖挖土土机机,and other hea

14、vy machinery where rotary motion of the pinion drives the straight-line action of a reciprocating(往复的往复的)part.4Spur Gears2Helical gearing differs from spur gearing in that helical teeth are cut across the gear face at an angle rather than straight.Thus,the contact line of the meshing teeth progresse

15、s across the face from the tip(尖尖端端、末末端端)at one end to the root of the other,reducing the noise and vibration characteristic of spur gears.斜斜齿齿轮轮传传动动与与直直齿齿轮轮传传动动的的区区别别在在于于斜斜齿齿轮轮的的轮轮齿齿是是沿沿齿齿面面呈呈某某一一角角度度而而不不是是垂垂直直于于端端面面切切削削加加工工出出来来的的。如如此此，啮啮合合齿齿的的接接触触线线是是由由端端面面一一端端的的齿齿顶顶到到达达另另一一端端的的齿齿根根处处，相相比比直直齿齿轮轮传传

16、动动而而言，降低了噪声和振动。言，降低了噪声和振动。Helical Gears 3Also,several teeth are in contact at any one time,producing a more gradual loading of the teeth that reduces wear substantially.The increased amount of sliding action between helical gear teeth,however,places greater demands on the lubricant to prevent metal-

17、to-metal contact and resulting premature gear failure.另另外外，在在啮啮合合过过程程中中，几几个个齿齿同同时时接接触触，而而且且是是逐逐级级加加载载，这这样样有有利利于于大大幅幅度度减减少少磨磨损损。斜斜齿齿轮轮的的滑滑动动摩摩擦擦增增加加，对对润润滑滑提提出出了了更高的要求以避免金属间接触而导致过早的齿轮失效。更高的要求以避免金属间接触而导致过早的齿轮失效。Helical Gears 3Also,since the teeth mesh at an angle,a side thrust(推推力力)load is produced alo

18、ng each gear shaft.Thus,thrust bearings must be used to absorb this load so that the gears are held in proper alignment(对齐，排成直线对齐，排成直线).另另外外，由由于于轮轮齿齿是是沿沿一一定定角角度度进进入入啮啮合合的的，沿沿每每个个齿齿轮轮的的轴轴线线方方向向都都会会产产生生一一个个侧侧向向推推力力载载荷荷，因因此此，要要采采用用推推力力球球轴轴承承来来吸吸收收这个载荷以保证齿轮的正常啮合。这个载荷以保证齿轮的正常啮合。Helical Gears 3A special c

19、lass of bevels called miter gears have gears of the same size with their shafts at right angles.Often there is no room to support bevel gears at both ends because the shafts intersect（相交）（相交）.还还有有一一类类特特殊殊的的锥锥齿齿轮轮称称之之为为等等径径锥锥齿齿轮轮，它它们们的的尺尺寸寸相相同同而而且且轴轴相相交交成成直直角角。由由于于齿齿轮轮轴轴相相交交，轴轴的的两两端端常常常常没没有有空空间间来来支支撑

20、撑锥齿轮。锥齿轮。4Bevel Gears This overhang load(OHL)may deflect the shaft and misalign the gears,which causes poor tooth contact and accelerates wear.Shaft deflection may be overcome with straddle(跨跨越越的的两两边边)mounting in which a bearing is placed on each side of the gear provided space permits.这这个个悬悬臂臂载载荷荷就

21、就可可能能使使齿齿轮轮轴轴挠挠曲曲，使使它它们们不不能能对对准准（错错位位），会会导导致致轮轮齿齿接接触触不不好好，从从而而加加速速磨磨损损。如如果果空空间间允允许许的的话话，可可以以采采用用跨跨越越式式结结构构，在在齿齿轮轮两两端端各各装装一一个个轴轴承承，就就可可以以解解决决齿齿轮轮轴轴的挠曲变形问题。的挠曲变形问题。4Bevel Gears 4Bevel Gears Straight-tooth bevels直齿锥齿直齿锥齿轮轮Also known as plain(简简单单的的)bevels,have teeth cut straight across the face of the

22、gear.They are subject to much of the same operating conditions as spur gears in that straight-tooth bevels are efficient but somewhat(稍稍微微,有有点点)noisy.They produce thrust(推推力力)loads in a direction that tends to separate the gears.Spiral-bevels螺旋锥齿螺旋锥齿轮轮Curved teeth provide an action somewhat like tha

23、t of a helical gear.This produces smoother,quieter operation than straight-tooth bevels.Thrust loading depends on the direction of rotation and whether the spiral angle at which the teeth are cut is positive or negative.Straight and Spiral Bevel GearsWorm gearing5WORM AND WORM GEARWorm gear sets con

24、sist of a screw-like worm(comparable to a pinion)that meshes with a larger gear,usually called a wheel5In this way,a wide range of speed ratios up to 60:1 and higher can be obtained from a single reduction.Most worms are cylindrical in shape with a uniform pitch diameter.However,a double-enveloping

25、worm has a variable pitch diameter that is narrowest in the middle and greatest at the end.Worm gearing5However,a reversible worm-gear has the worm and wheel pitches so proportioned(均均衡衡的的)that movement of the wheel rotates the worm.In most worm gears,the wheel has teeth similar to those of a helica

26、l gear,but the tops of the teeth curve inward(向内向内)to envelop(包络包络)the worm.在在可可逆逆式式涡涡轮轮蜗蜗杆杆传传动动过过程程中中，二二者者的的节节距距比比例例要要合合适适，蜗蜗杆杆才才能能驱驱动动蜗蜗杆杆。在在大大多多数数蜗蜗轮轮中中，其其轮轮齿齿与与斜斜齿齿轮轮轮轮齿齿相相似似，但但是是轮齿曲线顶部是向内包络蜗杆的。轮齿曲线顶部是向内包络蜗杆的。Worm gearing5Because of this high level of rubbing(摩摩擦擦)between the worm and wheel teet

27、h,the efficiency of worm gearing is lower than other major gear types.One of the worm gear is low wear,due mostly to the full-fluid lubricant film that tends to be formed between tooth surfaces by the worm sliding action.Worm gearing5Gear Geometry6Nomenclature of Spur GearsGear Geometry6Module(m)Pre

28、ssure angle()Base circle(db)Pitch circle(d)Addendum circle(da)Root circle(df)Addendum(ha)Dedendum(hf)Whole depth(h)Face width(B)PitchPitch point模数模数压力角压力角基圆基圆节圆节圆齿顶圆齿顶圆齿根圆齿根圆齿顶高齿顶高齿根高齿根高齿全高齿全高齿宽齿宽节距节距节点节点rbO齿顶圆齿顶圆(addendum circle)齿根圆齿根圆(dedendum circle)齿厚齿厚(tooth thickness)齿槽宽齿槽宽(tooth space)齿距齿距(周节

29、周节)(space width)raskekrfpkNomenclature of Spur GearsrbOpn齿顶高齿顶高(Addendum)齿根高齿根高(Dedendum)齿全高齿全高(Tooth depth)齿宽齿宽(Face width)hahfhBpra分度圆分度圆(Reference circle)seskekpbrfrpkNomenclature of Spur GearsGear Geometry6Module(m)模数Pressure angle()压力角Base circle(db)基圆Pitch circle(d)节圆Addendum circle(da)齿顶圆Root

30、 circle(df)齿根圆Addendum(ha)齿顶高Dedendum(hf)齿根高Whole depth(h)齿全高Face width(B)齿宽Pitch节距Pitch point节点Gear Geometry6Circular pitch(p)周节周节Gear center 齿轮中心齿轮中心Diametral pitch 径节径节Line of center 中心线中心线Axial pitch轴向节距轴向节距Line of action 啮合线啮合线Base pitch基节基节Line of contact 接触线接触线Axial base pitch 轴向基轴向基节节Point o

31、f contact 接触点接触点Tooth surface轮齿表面轮齿表面Center distance 中心距中心距Tooth profile 齿廓齿廓Lead 导程导程Flank 齿侧齿侧 Backlash 侧隙侧隙rb2r2O2 2rb1r1O11pb2pb1=pb2pb1能正确啮合能正确啮合!PN1N2B2B1重要结论：重要结论：一一对对渐渐开开线线齿齿轮轮的的正正确确啮啮合合条条件件是是：它们模数和压力角应分别相等。它们模数和压力角应分别相等。Gears being an important part of a machine have immense usage within various industries.These industries include automotive industry,coal power plants(热热 电电 厂厂),steel plants,paper mills（造纸厂）（造纸厂）,mines and many more.They are used as conveyors(传传送送带带),elevators(升升降降机机),separators(分离器分离器),cranes(起重机起重机)and lubrication system.6Gear Geometry