拖拉机的分类课程毕业设计外文文献翻译、中英文翻译、外文翻译

1 Classification of Tractors The tractor is a wheeled or tracked self-propelled vehicle used as a power means for moving agricult ural, road building, and other machines equipped with special tools, and also for towing trailers. The tractor engine can be used  as a prime mover for active moving tools or starting farm machinery through the intermediary of the power takeoff shaft or belt pulley. The uses of the tractor in agriculture are many, and so different types of tractors are needed to do different types of farm work. Farm tractors are classified as follows. AS TO PUR POS E, modern farm tractors are classed in three groups: general-purpose tractors (land utility), universal-row-crop (row-crop utility) tractors, and special-purpose tractors. Land utility tracto rs are used for major farm operations common to the cultivation of most crops, such as tillage, digging, general cultivations, harrowing, sowing, and harvesting. The tractors are characterized by a low ground clearance, increased engine power, and good tra ction. Thanking to their wide tires or tracks enabling them to develop a high pull. Universal-row-crop tractors are intended for row-crop work, as well as for many other field tasks. For this purpose, some row-crop utility tractors are provided with replac eable driving wheels of different tread widths-wide for general far m work and narrow for row-drop work, in order not to damage plants, the tractors have a high ground clearance and a wide wheel track that can be adjusted to suit the particular inter-tow distance. Special-purpose tractors are modifications of standard land or row-crop utilit y tractor models and are used for definite jobs, and under  2 certain condit ions. Thus, special tractors used to mechanize the cultivation of cotton have a single front whee l, swamp tractors are equipped with w ide tracks enabling them to operate on marshy soils, and hills ide tractors are designed to work on hills ides sloping at up to 16. AS  TO THE D ES IGN OF THE R UNNIN G GEAR， tractors are divided into crawler (track- laying) and wheeled types. Crawler tractors are distinguished by a large ground contact area and therefore have a good track adhesion; they crush and compact the soil ins ignificantly. S uch tractors show a high cross -country power and are capable of developing a high pull. Wheeled tractors are more versatile and can be used for both field and transport work, but their traction is lower than that of crawler tractors. Main Compone nt Parts of tractor The tractor is complex self-propelled machine consisting of separate interacting mechanisms and units that can be combined into certain groups. Irrespective of particular design features, all tractors consist of engine, drive line, running fear, steering mechanis m, working attachments, and auxiliary equipments. THE ENGINE converts thermal energy into mechanical energy. THE DR IVE LIN E comprises a set of mechanis ms which transmit the torque developed by the engine to the driving wheels or tracks and change the driving torque both in magnitude and direction. The drive line inc lud es the clutch, flexible coupling, transmission (gearbox) and rear axle. The clutch serves to disconnect the engine shaft from the transmission for a short period of time while the driver is shift ing gears  3 and also to connect smoothly the flow of power from the engine to the driving wheels or tracks when starting the tractor from rest.  The flexib le coupling incorporates elastic elements allow ing to connect the clutch shaft and the transmission drive shaft with a slight misalignment. The transmission makes it  possible to change the driving torque and the running speed of the tractor by engaging different pairs of gears. With the direction of rotation of the engine shaft remaining the same, the transmission enables the tractor to be put in reveres.  The rear- axle mechanisms increase the driving torque and transmit it to the driving wheels or tracks at right angles to the drive shaft. In most tractors, the rear axle also comprises brakes.  In the wheeled tractor, as dist inct from its crawler counterpart the drive line inc ludes the differential which enables the driving wheels to revolve with different speeds when making turns of running over a ragged terrain, at which time the left -and right- hand wheels must travel different distances during one and the same time. THE RUNN IN G GEAR is needed for the tractor to move. The rotation of the driving wheels (or the movement of the tracks) in contact with the ground is converted into translatory motion of the tractor. THE S TEERIN G M ECHAN ISM  serves to change the direction of movement of the tractor by turning its front wheels (in wheeled tractors) or by varying the speed of one of the tracks (in crawler tractors).  THE WORKIN G ATTACHM EN TS of the tractor are used to utilize the useful power of the tractor engine for various farm tasks. They include the power takeoff shaft, drawbar (hitch device), implement-attaching (mounting) system, and belt pulley.   THE TR ACTOR AUXILIAR IES inc lude the driver s cab with a spring- mounted seat and heating and ventilation equipment, hood, lighting equipment, tell tales (indicators), horns, etc.   4 The Clutch The clutch is located in the power train between the engine and the transmission. The clutch allows the driver to couple the engine or to uncouple the engine from the transmiss ion while he is shi ft ing gears or starting the tractor moving from rest. Modern tractors use fr iction clutches, ones employing fr iction forces to transmit power. The friction sur faces in such clutches are provided by discs, whose number depends on the magnit ude of torque to single- and double- disc clutches. C lutch driving disc (pressure plate) is connected to the engine flywheel, while driven disc is mounted on transmission clutch ( input) shaft. The driven disc has splines in its hub that match splines on the input shaft. The disc is tight ly c lamped between the pressure plate and the flywheel by a series of coil springs, called the pressure springs held between the clutch cover and the pressure plate. O wing to the frict ion forces arising between the fr iction surfaces of the fl ywheel, driven disc, and pressure plate , torque transmission input shaft.  In this position, the clutch is engaged. The clutch is operated by the clutch linkage which passes on the movement of clutch pedal to clutch release (throw-out) bearing. When the driver steps on the pedal, the clutch linkage, which includes an operating rod and a release fork, forces the release bearing inward (to the left). As the release bearing moves left, it pushes against the inner ends of three release levers. When the inner e nds of three release levers are pushed in by the release bearing, the outer ends of the levers move the pressure plate to the right, compressing pressure springs. With the spring pressure off the driven disc, spaces appear between the disc, the flywheel, a nd the pressure plate. Now the clutch is disengaged (released), and the flywheel can rotate without sending power through the driven disc. When the clutch pedal is released, the pressure springs  5 force the pressure plate to the left. The driven disc is again clamped tight ly between the flyw heel and the pressure plate. The driven disc must again rotate with the flywheel. In this position, the clutch is engaged. The init ial s lipping of the driven disc, which occurs unt il the disc is fully cla mped between the flywheel and the pressure plate, tends to make the engagement smooth. The clutch described above is known as the spring- loaded dry friction type. Propelle r Shaft and Universal Joint The propeller shaft is a drive shaft to carry the power from the transmission to the rear- wheel axels. It connects the transmission ma in, or output shaft to the differential at the rear axels. Rotary motion of the transmission main shaft is carried by the propeller shaft to the differential, causing the rear wheels to rotate.  The propeller-shaft design must take two facts into consideration. F irst, the engine and transmission are more or less rigidly attached to the car frame. S econd, the rear-axle housing (with wheels and differentia l) is attached to the frame by springs. As the rear wheels encounter irregularit ies in the road, the springs are compressed or expanded. These change the angle of drive and the distance between the transmission and the differentia l, and the propeller shaft should take care of these two changes. That is to say, as the rear axle housing, with differentia l and wheels, moves up and down, the angle between the transmission output shaft and propeller shaft changes. The reason why the angle increases is that the rear axle and differential move in a shorter tha n the propeller shaft. The center pointer of the axle- housing is rear-spring or control-arm attachment to the frame. In order that the propeller shaft may take care of these two changes, it must incorporate two universal joints to permit variations in the angle of drive. There must be a set of slip joint to make the propeller shaft change.   6 The propeller shaft may be solid or hollow, protected by an outer tube or exposed. Some applications inc lude bearings at or near the center of the propellers which are supported by a center bearing and coupled together by universal joints. A universal joint is essentially a double- hinged joint consisting of two y-shaped yokes, one on the driving shaft and the other on the driven shaft, and across-shaped me mber called the s pider. The four arms of the spider, known as trunnions, are assembled into bearings in the ends of the two shaft yokes. The driving shaft causes the spider to rotate, and the other two trunnions of the spider cause the driven shaft to rotate. When the two shafts are at an angle to each other, the b earings in the yokes permit the yokes to swing around on the trunnions with each revolut ion. A variety of universal joints have been used on automobiles, but the types now in most common use are the ball-and-trunnion joints.  A slip joint consists of outside splines on one shaft and matching internal splines in the mating hollow shaft. The splines cause the two shafts to rotate together but permit the two to move endwise with each other. This accommodates any effec tive change of length of the propeller shaft as the rear axles move toward or away from the car frame.     7 拖拉机的分类  拖拉机是一种轮式或履带式的自走式车辆工具，它能被用来做移植农作物，铺路和其他装备特殊工具的机械的动力装置。也能用做牵引挂车的动力，拖拉机的发动机也能被用来做自动工具，固定式农业机械的有原动力，通过用力输出轴和皮带轮做中间媒介。  拖拉机在农业中的应用是非常的广泛的，并且不同类型的拖拉机 做不同的农业作业。  农业拖拉机被分为以下几类。  就功能来说，现代的农用拖拉机可以分为三类，普通功能的拖拉机，中耕拖拉机和专用拖拉机。  普通用途的拖拉机主要的农业作业是大部分农作物的栽培，比如耕地，犁地，耕种，耙地，播种和收割。这种拖拉机的典型特征就是有一个比较小的离地间隙，增加了发动机的扭矩和有比较好的牵引力，由于它们有较宽的轮胎或履带，使他们能够产生比较大的牵引力。  中耕拖拉机主要用来中耕作业，也可以进行许多其它的田间作业，为了达到这个目的，一些中耕拖拉机被装备了不同胎面宽度的可替换的驱动轮。用来进行一般 的田间作业 和耙地，为了不损 坏农作物，这种拖拉机有一个比较大的离地间隙和比较宽的轮胎，能适应特殊的农作物间距。  专用拖拉机不同于普通的拖拉机和中耕式拖拉机，它被用于特定的作业，或者在特定的条件下用于不同的作业。因此被用来棉花中耕机械化的专用拖拉机常常有一个前轮，在沼泽地里工作的拖拉机一般装备有很宽的履带，这样能够使它们在潮湿的土壤上工作。山地拖拉机一般被设计能在 16 度的斜坡上工作。  按驱动装置的设计，拖拉机有可分为轮式和履带式。  履带式拖拉机因它较大的接地面积而著称，所以它有一个很好的牵引附着性，它们能碾压土 壤并能紧紧的 抓住土壤。因此这 种拖 8 拉机有很好的越野性并且能够提供很好的牵引力。  轮式拖拉机的应用也很广泛，能被用来在田间作业并且能够用来进行交通运输，但是它们的牵引能力比履带式拖拉机要小。  拖拉机的主要组成部分  拖拉机是复杂的自走式机械，它由相互独立相互作用的机构和单元组合而成。  如果不考虑特殊的设计，所有的拖拉机都有发动机，传动系，行驶系，转向系，作业机构和辅助装置组成。  发动机把燃料的化学能转化成机械能。  传动系包括一系列的机械装置，它们能传递发动机产生的扭矩给驱动轮或履带。并且能把驱动扭矩变成有大小和方 向的力， 传动系包括，离合器，连轴器，变速器和后桥。  离合器的主要用途就是当驾驶员正在挂挡时，暂时的把发动机输出轴与变速器分离一段时间。当发动机从停机启动时，它也能使发动机传递到驱动轮上的较低的动力连接平衡。  连轴器包括很多的弹性元件，这些弹性元件能够把不在同一条直线上的离合器轴和变速器轴连接在一起。  变速器通过不同的啮合齿轮，使改变驱动扭矩和发动机转速成为可能。在发动机曲轴旋转方向不变的情况下，变速器能够是拖拉机倒驶。  后桥机构增加了驱动扭矩，且把它传递到驱动轮上或履带上在适当的角度传给驱动轴。在大部分的拖 拉机上，后桥上也包含刹车。  在轮式拖拉机上，不同于履带式的地方。就是传动系还包括差速器，当拖拉机在转弯时或行驶在不平整的路面上时，它能是驱动轮以不同的速度旋转，它的左右轮在相同的时间内行驶过不同的距离。  行驶系能够使拖拉机移动，驱动轮或者履带和地面接触的旋转运动被转化成拖拉机的直线运动。  转向系主要用来改变拖拉机的行驶方向，在轮式拖拉机上是靠 9 旋转它的前轮，在履带式拖拉机上，是靠改变一个履带的速度。  作业机构被用来耕作。充分应用拖拉机发动机的动力去实现各种农作业。它包括动力输出轴，悬挂机构，农具挂接机构，皮带 轮。  辅助装置包括装有弹簧坐椅及加热、通风装置的驾驶室，发动机罩，照明设备，指示器，喇叭等。  离合器  在传动系中离合器位于发动机与变速器之间，作用就是使驾驶员可以把发动机与变速器结合和脱离。  现代拖拉机上广泛应用摩擦片式离合器。这种离合器利用摩擦力来传递动力，这种离合器的摩擦面由压盘提供，它