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1、Gears are vital factors in machinery. One of the first mechanism invented using gears was the clocks. In fact, a clock is little more than a train of gears.Considerable study and research have been made on gears in recent years because of their wide use under exacting conditions. They have to transm
2、it heavier loads and run at higher speeds than ever before. The engineers and the machinists all consider gearing the prime elementin nearly all classes of machinery.齿轮在机械中占有极其重要的作用。第一个利用齿轮做成的机械装置就是钟表，事实上，它只不过是用了一系列的齿轮。对于它可以在严格的条件下的广泛使用，在齿轮上做了大量的学习和研究。相比过去，它们现在必须在更高的速度下传递更重的负荷。工程师和机器操纵工人都认为齿轮在几乎所有的机
3、器的零件中占有首要的因素。1. Spur gearsSpur gears are used to transmit power and rotary motion between parallel shafts. Theteeth are cut parallel to the axis of the shaft on which the gears are mounted. The smaller of two gears in mesh is called the pinion and the larger is customarily Designated as the gear. In
4、 most applications, the pinion is the driving element whereas the gear is the driven element.1.直齿圆柱齿轮直齿圆柱齿轮用于平行轴之间传递力和回转运动，轮齿被切制成与安装齿轮的轴之轴线相平行。两啮合齿轮中较小的叫小齿轮，大的习惯上叫齿轮，在大多数情况下，小齿轮是主动轮，大齿轮叫从动轮。2. Helical gearsHelical gears have certain advantages, for example, when connecting parallel shafts they have
5、a higher load-carrying capacity than spur gear with the same tooth numbers and cut with the same cutter.2斜齿圆柱齿轮斜齿圆柱齿轮具有特定的优点，比如，当连接平行轴的用相同刀具切削出来的并齿数相同的斜齿轮比直齿轮具有较高的承载能力。斜齿轮也能用于连接相互成任意角度的非平行轴。Helical gears can also be used to connect nonparallel , non-intersecting shaftsat any angle to one another.斜齿轮
6、也能用于连接相互成任意角度的非平行轴。The maximum gear ratio obtainable with a single pair of gears varies with the type of gear and the application. The following are approximate maxim a for the various type for average load conditions: spur, 8; parallel-shaft helical, 10; straight bevel , 6; spiral bevel, 8;hypoid ,
7、 12; and worm , 80. For lightly loaded, instrument, and positioning gears, these rations can be exceeded. Rations as high as 400 or higher can be obtained with gears that resemble tapered worms meshing with hypoid gear. For heavily loaded gear, the given rations may be so high that a reasonable gear
8、 size precludes a satisfactory pinion.一对齿轮能获得的最大传动比随齿轮类型和应用的变化而变化，以下是各种类型的齿轮的平均载荷条件的近似最大化，直齿是8，平行轴斜齿轮是10，直齿锥齿是6，曲线齿锥齿轮8，准双曲面12，蜗轮蜗杆8，对于轻载荷和定位齿轮这些传动比被超出，类似于成锥形的蜗轮蜗杆，和准双曲面齿轮能够获得的传动比高达400 或更高，如此高以至于00 的齿轮尺寸不可能令人满意。Since the ratio in a single pair of gears is the quotient of the tooth number, and since
9、there usually are limitations on both the minimum and maximum numbers of teeth on the available gears,it follows that the number of ratios obtainable in a single pair is limited. To enlarge the coverage it is necessary to use multiple pairs, or trains. The overall speed ratio in a train is the produ
10、ct of the ratios in each pair. In certain cases an exact ratio cannot be obtained with gears, but by using two or more parts, the desired ratio can be approximated to any degree of precision.一对齿轮的传动比齿数的商，它们通常是限制在有效齿轮的最大和最小齿数之间，因此，一对齿轮获得的传动比是受限制的，为了扩大范围，用多级齿轮副或系列是必要的，在一个系列中，总速比是每对齿轮产生的传动比。As a conven
11、ience for machine builders and users, packaged speed reducers, following an industry-accepted pattern , are manufactured in a wide variety of types,configurations , speed ratios, and capacities; these consist of a box or housing containing bearings, shafts, lubricant and shaft oil seals. Speed incre
12、asers are usually custom build.在某种情况下，一个确切的传动比不能由齿轮副获得，但是用两对或更多对时，要求的传动比能达到精确等级，为了对机器制造者和使用者方便起见，各种整装式减速器，根据工业通用的试样被大量的多样化的类型的组合的速度比的生产制造，这些由箱子组成或给含有轴承轴润滑剂和轴油封装外罩增速器通常被定别。All speed reducers when operating continuously become hot because of friction in the teeth, in the lubricant, in the bearings, an
13、d in the oil seals. If the heat is generated at a faster rate than it can be dissipated to the atmosphere, the lubricant may deteriorate and the gear or bearing fail.所有的减速器当被连续使用时，由于轮齿在润滑剂轴承和油封件的摩擦会变热，如果热量的产生在空气中散逸的速度还快的话，润滑剂不能损坏，并且轴承和齿轮失效。Worm gear sets are widely used because of the many advantage
14、s obtained by their tooth action and load carrying capacity. A large speed reduction or a high increase oftorque can be attained with the worm gear set. Compactness of design is easy to obtain with such a combination, Worm gear drives are quiet and vibration free.蜗轮装置由于啮合作用和传递载荷能力获得的许多优点而被广泛应用，大量转矩的
15、减速或增速装置由蜗轮装置完成，设计的紧凑，用这样一个结合体是容易得到的，蜗轮是平稳且无振动的。A worm gear set consists of the worm, which is very similar to a screw, and the wormgear, which is a helical gear. The shafts upon which the worm and the gear are mounted are usually at right angels but not in the same plane. The usual practice is to ha
16、ve the worm drive the worm gear. With same ratios, it is possible to have a gear driver the worm. However, with large ratios, it is impossible for the gear to drive the worm.一个蜗轮装置由蜗杆非常类似于螺丝和蜗轮一个斜齿轮组成的，安装蜗杆和蜗轮的轴通常相互垂直而不在同一平面中，通常习惯上使蜗杆驱动蜗轮。小的传动比，使一个齿轮驱动蜗杆是有可能的，但是，大的传动比，使一个齿轮驱动蜗杆是不可能的。The worm can be
17、made with either right-hand or left-hand thread. Also, like a screw, it can be made with single, double, triple, or quadruple thread. A single-thread worm advances the worm gear a distance equal to pitch for each complete worm rotation. The distance advanced is called the lead. Thus, the pitch equal
18、s the lead for a single thread. A double-threaded worm has a lead which is twice the pitch.蜗杆可以被制成右螺纹或左螺纹，同样像螺丝一样，蜗杆可以被制成单、双螺纹，三重或四重螺纹，单螺纹的蜗杆推进蜗轮等节距前进来完成每个完整的蜗杆转动，间距的推进称为节距。因而节距等于单螺纹的螺距，双螺纹的蜗杆螺距是两倍的节距。The geometry of a worm is similar to that of a power screw. Rotation of the wormsimulates a linearl
19、y advancing involute rack The geometry of worm gear(sometimes called a worm wheel) is similar to that of a helical gear, except that the teeth are curved to envelop the worm. Sometimes the worm is modified to envelop the gear. This gives a greater area of contact, but requires extremely precise moun
20、ting.蜗杆的几何形状类似于机械螺纹，蜗杆的转动与一个渐开线导轨直线移动是相仿的。蜗轮几何形状（有时被称为蜗轮）类似于斜齿轮，除了包围在蜗轮上的齿是弯曲的以外。有时把蜗杆齿制成包裹在蜗轮，这就提供了更大的接触面积，但安装精度要求更高了。A rotary cam is part on a machine which mechanically changes cylindrical motion to straight-line motion. The cam, which is mounted on a shaft, is usually driven by a motor either ap
21、plied directly to the cam shaft or connected by pulleys orgears. The purpose of a cam is to transmit various kinds of motions to other parts of amachine.一个转动的凸轮是机械的一部分，也就是用机械的方式使回转运动变为直线运动。凸轮被安装在轴上通常由直接用到凸轮轴或是由皮带轮或齿轮联结成的任一原动力驱动。凸轮的目的是传递各种各样的运动到机械的其他部分。Practically every cam must be designed and manuf
22、actured to fit special requirements. Though each cam appears to be quite different from the other, all the cams work in a similar ways. In each case, as the cam is rotated or turned, another part in contact with the cam, called a follower, is moved either left and right, up and down, or in and out.
23、The follower is usually connected to other parts on the machine to accomplish the desired action. The direction the follower move depends upon the position of the framework which attaches the cam and follower to the machine. If thefollower loses contact with the cam, it will fail to work.几乎每个凸轮必须被设计
24、和制造以适合特殊的要求，虽然每个凸轮显现的十分不同于其他凸轮。但是所有的凸轮都以类似的方式工作。在任何情况下，与凸轮转动或旋转时，与凸轮接触的另一部分成为从动件，向左或向右，向上或向下，向里或向外移动。从动件通常联结机械的其他部分以完成要求的运动，从动件运动的方向取决于结构的位置也就是在机械中联结凸轮和从动轮。如果从动件与凸轮不接触，它将不能工作。The faster the cam turns, the more rapid is the motion of the follower. The motion of the follower caused by rotating the cam
25、 is exactly the same for each complete turn of the cam. 凸轮旋转越快，从动轮的运动越迅速，从动件的运动是由凸轮转动导致的并且这种运动与每个凸轮整个旋转运动是正好相反。Belt drives offer a maximum of versatility as power transmission elements. They allow the designer considerable flexibility in location of driver and driven machinery,and tolerances are not
26、 critical as is the case with gear drives. Another advantage of belt drives is that they reduce vibration and shock transmission. Furthermore, belt drives are relatively quiet.皮带传动装置作为传递动力的元件用途极广。这种装置使设计人员在确定主动机械与从动机械的位置时有相当大的灵活性，而且公差要求也不像齿轮传动装置那样严格。皮带传动另一个优点是可以减少振动及其传播。不仅如此，皮带传动噪声也比较小。Large flat le
27、ather belts were in general use many years ago, when the usual practice was to use one large engine to driver several different pieces of machinery. Some leather belts are in use at this time as well as flat steel, rubber, plastic, and fabric belts. Light, thin flat belts are practical on high speed
28、 machinery where vibration may be a problem用皮革制成的大的平皮带在许多年前曾用得很普遍，那时，通常是用一台大功率的发动机驱动好几台不同的机器。现在，除了平钢带、橡皮带、塑料带和布带外，一些皮革做的皮带还在使用。轻质薄型平皮带在高速机械上很实用，因为这里振动可能是一个问题。V belts are probably the most common means of transmitting power between electric motor and driven machinery. Conventional V belts are made of
29、 rubber. Most often, both driver and driven pulleys lie in the same vertical plane, and the speed ration is constant.三角皮带大概是在电动机与从动机械之间传递动力的最为普通的手段。普通的三角皮带用橡皮制造。通常，主动轮与从动轮位于同一个垂直面上，速比是恒定的。Smooth flat belt and V belts depend on friction on the pulleys and some slippage isInherent in their operation.
30、Therefore, speed ratios are not precise. Most heavy dutypulleys are made of cast iron or formed steel.平皮带和三角皮带依靠在皮带轮上的摩擦进行传动，所以在传动中总是有一些滑动，因此，速比就不精确。大多数大的皮带轮是用铸铁和型钢制造的。Note that the capacity of the belt drive is determined by the angle of wrap on the smaller pulley, and that this is particularly cri
31、tical for drives involving pullets of greatly differing size,special closely together. Screws have been used as fasteners for a long time . As indicated in the section on single machine, a screw acts with a wedging action and consists of a circular cylinder (or truncated cone) with a helical Groove
32、in it. When used for fastening, all screws are provided with means for applying a torque(twisting moment) to them; this may consist of a square of hexagonal head for a wrench, a head with a slot or a cross-shaped recess for a screwdriver, a cylindrical head with a recess fitting a special wrench, or
33、 a slot or recess on one end fitting a screwdriver or special wrench and no head.螺钉已经被用来作为一种长期有效的紧固件。如本章的机床剖视图，螺钉的功能类似于一种楔紧作用，由具有螺纹的圆柱体（或者圆锥体）组成。当用于固定作用时，所有的螺钉都提供了一种施加扭矩的方式，这些方式有用于扳手的等边六角形，用于改锥的一字槽或者十字槽，用于配合特殊扳手的圆头凹槽，或者甚至没有螺钉头但配合特殊改锥或特殊扳手的槽或凹坑。Screws with screwdriver slots have heads of several shap
34、es, such as flat, oval round, and fillister(cylindrical with a round top). Wood screws are tapered, and self-tappingscrews have tapered ends and a variety of special points. The latter are usually hardened and cut or form a mating internal thread when screwed into the proper size hole.Screws with he
35、xagonal heads are usually known as cap screws . Screws with other types of heads are also known as cap screws in the larger sizes and as machine screws in the small sizes. All of these screws are used to clamp machine parts together when one of the parts has an internal thread. If neither part is th
36、readed ，a bolt must be used: this consist of screw with a hexagonal head, a Nut (hexagonal ring with an internal thread), and usually a washer(flat 扁 ring).带有六角形顶端的螺钉通常称为有头螺钉。这类螺钉用于当零件之一有内螺纹时把机器的零件加紧在一起。如果零件上未切出螺纹，则必须使用螺栓。螺栓由带有六角形顶端的螺钉、螺母（是一个有内螺纹的六角环）、通常还有一个垫圈组成。In operation, shafts are subjected to
37、 a shearing stress , whose magnitude depends on the torque and the dimensions of the cross section. This stress is a measure of the resistance that the shaft material offers to the applied torque. All shafts that transmit a torque are subjected to torsional shearing stress .轴在转动时承受剪应力，其大小取决于扭转和断面的尺寸
38、。这个剪应力是轴的材料对作用扭矩所产生的抗力的一种量度。所有传递扭矩的轴都承受扭转剪应力。In addition to the shearing stresses, twisted 扭曲shafts are also subjected to shearingdistortions. The distorted state is usually defined by the angle of twist per unitlength, i.e., the rotation of one cross section of a shaft relative to another cross sec
39、tion at a unit distance from it.轴的某一截面相对于间隔一个单位长度的另一截面的旋转角度。除剪应力之外，传递扭转的轴还会产生剪切变形。扭转的状态通常用每单位长度的扭转角来表示，即用轴的某一截面所转过的角度来表示。A coupling is a device for connecting the ends of adjacent shafts. In machine construction, couplings are used to effect a semipermanent connection between adjacent rotating shaft
40、s. The connection is permanent in the sense that it is not meant to be broken during the useful life of the machine, but it can be broken and restored in an emergency or when worn parts are replaced.联轴器是一种联接两根相邻轴末端的装置。机械构件中，联轴器可以用来实现相邻两根旋转轴的半永久性联接。在机器的正常使用周期内，联轴器通常不必拆开，在这个意义上可以说联轴器的联接是永久性的，而在紧急情况下或者
41、需要更换已磨损的零件时，可先把联轴器拆开并重新联接上。There are several types of shaft couplings; their characteristics depend on the purposefor which they are used. If an exceptionally long shaft is required for a line shaft in amanufacturing plant or a propellershaft on a ship, it is made in sections that are coupled togeth
42、er with rigid couplings. A common type of rigid coupling consists of two mating radial flanges(disks) that are attached by key-driven hubs to the ends of adjacent shaft sections and bolted together through the flanges to form a rigid connection. Alignment of the connected shafts is usually effected
43、by means of a rabbet joint on the face of the flanges, i.e., a short cylindrical projection on the face of one flange fits snugly in a circular recess on the face of the other flange。联轴器有几种类型，其特性随其用途而定。如果制造厂中或者船舶的螺旋桨需要一根特别长的轴时，可以分段制造，然后采用刚性联轴器将这些轴联接起来。常用的刚性联轴器包括两个匹配的径向法兰（盘），他们是通过靠键传动的轮毂来连接到相邻两轴的两端，然
44、后用螺栓穿过法兰联接起来形成了刚性联接。相互联接的两轴是靠法兰面上的槽口来对准的，也就是说，在其中一个法兰面上的短圆柱上的凸起部分与另一个法兰面上的圆形凹进部分相互紧贴。In connecting shafts belonging to separate devices (such as an electric motor and a gear-box), precise aligning of the shafts is difficult and a flexible coupling is used. This coupling connects the shafts in such a
45、 way as to minimize the harmful effects of shaft misalignment.Flexible couplings also permit the shafts to deflect under their separate systems of loads and to move freely (float) in the axial direction without interfering with one another. Flexible couplings can also serve to reduce the intensity o
46、f shock loads and vibrations transmitted from one shaft to another.在把两个属于不同设备（如电机和变速箱）的轴联接起来时，要把这些轴精确对准是很困难的，因此可以采用弹性联轴器。采用这种联轴器联接两轴时，可以把由于轴联接中轴线不重合所造成的损害降到最小。弹性联轴器还可允许被联接的轴在各自载荷系统中偏斜和在轴向上自由移动（浮动），而不相互干扰。弹性联轴器还能用来减小从一根轴传到另一根轴的冲击载荷和振动强度。A clutch is a device for quickly and easily connecting or discon
47、necting a rotatable shaft and a rotating coaxialkEu5AksEl shaft. Clutches are usually placed between the input shaft to a machine and the output shaft from the driving motor, and provide a convenient means for starting and stopping the machine and permitting the driver motor or engine to be started
48、in an Unloaded state.离合器是一个用来使从动轴与位于同一轴线上的主动轴进行快速和顺利的联接或脱开的装置。离合器通常位于机器的输入轴和驱动电机的输出轴之间，以提供一个方便地启动和停止机器的手段，并使得驱动电机或发动机在无荷载的状态下启动。The rotor (rotating member) in an electric motor has rotational inertia, and a torque is required to bring it up to speed when the motor is started. If the motor shaft is r
49、igidly connected to a load with a large rotational inertia, and the motor is started suddenly by closing a switch, the motor may not have sufficient torque capacity to bring the motor shaft up to speed before the windings in motor are burned out by the excessive current demands. A clutch between the motor and the load shafts will restrict the starting torque on the motor to that required to accelerate the rotor an