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28马力轮式拖拉机变速箱设计【优秀含4张CAD图纸+Word全套车辆类毕业设计】

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关键词：: 28 马力轮式拖拉机变速箱设计优秀优良 cad 图纸 word 全套车辆毕业设计

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28马力轮式拖拉机变速箱设计

摘要

为了获得适合各种农业工作的不同速度和牵引力，我们就必须通过变速箱来降低从发动机传出的较快的转速并将动力传递给驱动装置来行走或作业。在田间或公路运输时要求有较快的行驶速度，但是在田间作业和工程施工时则需要较慢的速度和较大的牵引力。

为了实现这种目的，大部分必要的减速通常通过变速箱总成中的滑移齿轮来实现，进一步的减速则是通过中央传动和最终传动的大、小齿轮的啮合来实现的。在现代的拖拉机中，拖拉机不仅被用来田间作业，还用来搞运输、粉碎饲料等。为了满足不同工况的需要和提高经济性，一般都是多挡位的，本设计采用8个前进挡的设计方案。

对于拖拉机来说，一般变速箱总成都采用直齿圆柱齿轮以降低成本，则用滑移齿轮前后移动与中间轴上齿轮啮合以获得需要的速度。为了满足拖拉机的中耕和其它作业需要，例如耕地、耙地、工程施工等。都需要在设计中设计动力输出装置，通过动力输出轴将从发动机传来的扭矩传到拖拉机后部，以带动各种机具工作。

关键词：拖拉机，变速箱，滑移齿轮，动力输出轴

TRANSMISSION DESIGN OF 28 HP TRACTOR

ABSTRACT

We must reduce the relatively fast speed of the engine and transmit its power to the driving menbers to obtain suitable speeds and pulling power for the different farm jops. You may want a fst forward speed for hauling form the field or on the highway but a much slower fortions.Aslo,you msut have some means of reversing the direction of rotation of the driving members.

Much of the necessry speed reduction is accomplished by the sliding(speed-changing)gears of the assembly which is ususlly called the “transmission.”Further reduction is secured at the differential and by the final drive pinions and bull gears.In today’s tractors there are still more gear combingations giving more forward speeds; these are needed for the many operations now performed with farm tractors.

You select the speed you want by shifting one of the sliding gears,which are splined to be transmission shaft.With the gear shift lever,you can move then forward or backward;you can mesh any certain sliding gear with it’s mating gear on the counter-shaft.Live power take-off is an asset with many p.t.o.driven machine .

KEY WORDS： tractor, transmission，sliding gears，power take-off

第一章前言1

第二章结构分析与设计2

§2.1 概述2

§2.1.1变速箱的功用、要求2

§2.2 布置方案的分析与确定2

§2.2.1传动机构的方案分析与确定2

§2.2.2 变速箱零、部件结构分析与确定3

§2.2.3 发动机和轮胎选择6

第三章变速器主要参数的确定7

§3.1 概述7

§3.2 变速器主要参数的确定7

§3.3 常啮合齿轮参数的确定10

第四章变速器圆柱齿轮的结构和设计12

§4.1 齿轮的变位12

§4.2 齿轮的强度计算13

第五章中央传动主要参数的确定16

§5.1 概述16

§5.2 中央传动主要参数的确定16

§5.3 圆柱齿轮的结构与计算17

§5.4 齿轮强度计算18

第六章最终传动参数的确定20

§6.1 概述20

§6.2 最终传动主要参数的确定20

§6.3 圆柱齿轮的结构与计算21

§6.4 齿轮强度计算22

第七章轴的校核24

§7.1 概述24

§7.2 轴的强度计算24

§7.3 轴的刚度计算25

第八章轴承的校核28

§8.1 概述28

§8.2 轴承的校核28

结论30

参考文献31

致谢32

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操纵机构.jpg

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总成4GAI (2).jpg

内容简介：: 1 FARM TRACTOR The history of tractor development is to lang to relate here .Landmarks along the road include the fires use of an internall combustion engine in a tractor in the United States in 1890;the Ivel tractor of 1901; the American Ford of 1917 , and the International Farmall of 1923 . During the 1930s , the use of low-pressure pneumatic tyres soon became popular , and the first Ferguson system tracrors incorporating three-point linkage with hydraulic draught control were introduced . Classification of tractor types.Tractors as now manufactured can be classified as follows: A. According to method of securing traction and self-propulsion: 1. Wheel tractors a. Three tractors b. Four wheels 2. Track-type tractors B. According to utility : 1. General-purpose or utility 2. All-purpose or row-crop type Wheel tractors. The wheel-type tractor is the predomingating type,particularly for agricultural purposes.Wheel tractors are made either with three wheels or with four wheels .The usual arrangement consists of two rear-drive wheels and one or two front steering members. Track-type tractors. The traction mechanism in the nts 2 track-type tractor consists essentially of two heavy,endless,metal-linked devices known as tracks themselves by reducing the movement of one track below the speed of the other. General-purpose or utility tractor.A general-purpose tractor is one ofmore or less conventinal design such as an ordinary four-wheel machine or a track-type machine.This type is also referred to as autility troctor. It is made to perform only the usual tractor jops,including both field and belt work such as plowing ,harrowing,road grading ,combining,feed grinding,and the like. All-purpose tractors.An all-purpose or row-crop type is a tractor designed to handle practically all the field and belt jops on the average farm,including the planting and intertillage of row crops. The conventional tractor consists basically of two engine-driwen wheels,usually at the rear, and two support wheels st the front . The type of the engine used to power the heart of the tractor; it is here that the fuel,the chemical potential energy , is converted into the mechanical emergy which causes the wheels to turn. The difference between n internal and external combustion engine is simply that in an internal combustion engine ,the conversion of potential energy into mechanical energy takes place wholly in the cylinder,whereas with external combustion the fuel is burnt outside the cylinder .A steam engine or a gas turbine is a good example of the latter. How can liquid fuel be changed into rotational mechaanical energy? This is achieved by accurately mixing nts 3 the fuel with air and then burning it in controlled condition.When this mixture burns ,it expands and pressure builds up ,forcing the piston to move down the cylinder in a straight line. It is said to rotary motion .This linear motion is converted into rotary motion by a connecting rod and crank arrangement joined to the piston. To be able to use this energy effectively, the burning and combustion proce and the force of expansion have to be controlled. To do this , the enginemust have : 1. A tube or cylinder closed at one end ,in which the mixture of fuel and air can be compressed and burnt . 2. A piston , which slides freely and yet fits closely in the cylinder ,so that the expanding gas force it down the cylinder ,and do not escape past it . 3. Two passages or ports in the cylinder . One for the mixture of fuel and air to enter the cylinder , the inlet prot , and the other to allow the used gases to escape , the exhaust port. 4. Two valves , the inlet valve to control the the movement of the mixture to the cylinder , and the exhaust valve to control the escape of the used gases . By carefully timing the ignition of the mixture in relation of the opening and closing of the valves and the position of the piston , it is possible to make the piston move up and down the cylinder continuously . The working of an internal combusition engine , once it is started , involves a sequence or cycle of operations in nts 4 each cycle and the two-stroke cycle . In the four-stroke cycle , the crankshaft completes two revolutions and the piston four strokes , a stroke being the movement of the piston from one end of the cylinder to the other . In the two-stroke cycle , the crankshaft makes one revolution and the piston two strokes in each cycle . Your tractor probably has a complete electric system which provides electicuty for the self-starter , for igniting the fuel , and for lights . Insome designs electricity is also used for certain other accessory circuits. Such complete systems comprise several circuits : (1)generator circuit, (2) starting motor circuit , (3) lighing circuit , (4) ignition circuit . The storage battery may well be considered the basis of the complete system bacause it is connected to and works with all four of these principal circuits . We must reduce the relatively fast speed of the engine and transmit its power to the driving menbers to obtain suitable speeds and pulling power for the different farm jops. You may want a fst forward speed for hauling form the field or on the highway but a much slower fortions.Aslo,you msut have some means of reversing the direction of rotation of the driving members. Much of the necessry speed reduction is accomplished by the sliding(speed-changing)gears of the assembly which is ususlly called the “ transmission.” Further reduction is secured at the differential and by the final drive pinions and bull gears(Fig.9). nts 5 Fig.9 You select the speed you want by shifting one of the sliding gears,which are splined to be transmission shaft.With the gear shift lever,you can move then forward or backward;you can mesh any certain sliding gear with it s mating gear on the counter-shaft. In the schematic diagram(Fig.9),gears C,E,G,ang K are sliding gears.Gear A ,at the end of the drive shaft,and gear B,on the ciuntershaft,are in constant mesh.Hence,the countershaft and all it s rigidly connected gears are in motion whenever the drive shaft revolves. When you disengage the clutch, all gears are at rest and no power is transmittedto the drive wheels. However, when you move one of the sliding gears, such as C,into mesh with D,then by engaging the clutch,you complete the connection nts 6 bnetween the engine and the drive wheels. Contact between gears C and D(as shown ) would give low,or first, speed; engaging gears E and F would give sceond speed; gear G and H would give third speed. When none of the sliding gers is in mesh with it s countershaft gear, the gears are said to be in “ neutral.” Reverse speed is obtained by the use of a small/pinion R between the countershaft gear I and the sliding gear K ,which causes the transmission drive shaft ti be driven in the opposite direction. In today s tractors there are still more gear combingations giving more forward speeds; these are needed for the many operations now performed with farm tractors. In some tractor models,an additional speed-reducing and toedue-increasing unit is installed between the engine cluth and the transmision driving gear.This unit is controlled with a separate lever near the tractor seat. When the unit incereases the “ torque” or pulling force obtained from that speed. When you use this unit,you get a ratio of about three to two between the engine crankshaft and the transmission drive gear (when you are not using it you have the usual direct ratio between these two parts). Because this “ torque amplifier” is ahead of the regular speed-changing gears, it reduces each speed you obtain from the various gear combinations. So it doubles the number of available speeds,Each speed is reduced about one-third and the torque, or pulling force, from such slower speed is increased by 45 per cent . This is very helpful when plowing nts 7 through tough spots or diskding through wet spots . You can engage the torque amplifier-reduce speed and increase pull-without stopping.And, when through the heavy pull,you can disengage it and return to normal speed without stopping. 农用拖拉机拖拉机的发展历史很长，在这里不再赘述。拖拉机发展史上的几个里程碑是： 1890 年内燃机在美国拖拉机上的首次使用；1901 年 Ivel 拖拉机的问世； 1917 年美国福特拖拉机以及 1923年万国公司 Farmall 拖拉机的相距出现。 30 年代，低压充气轮胎的应用迅速普及，并且推广了第一批 Forguson 系统的拖拉机，这种拖拉机配有力调节的三点液压悬挂装置。拖拉机的分类。目前制造的拖拉机可分类如下： A. 按照获得牵引力及自身推进的方法分： 1.轮式拖拉机 1）三轮拖拉机。 2）四轮拖拉机。 2履带式拖拉机 B. 按照用途分： 1通用型，即多用型拖拉机。 2万能型，即中耕型拖拉机。轮式拖拉机：轮式拖拉机是主要的拖拉机类型，特别是在农用方面。现在制造的轮式拖拉机有三轮的或四轮的。通常的配置是在两个后驱动轮及一个或两个前导向轮。履带式拖拉机：履带式拖拉机的牵引机构实质上由两条成为履带的重型封闭金属链条装置构成。每以条履带在两个铁轮上运转，其中一个铁轮具有链齿，用作驱动轮，另一个用作惰轮。转向是通过履带本身来完成的，即通过减慢其中一条履带的运动速nts 8 度使之低于另一条的速度的办法来完成的。通用型即多用型拖拉机：通用型拖拉机基本上是一种传统设计的拖拉机，例如普通的四轮拖拉机或履带式拖拉机。这种类型也被成为多用型拖拉机，它仅用来完成一般的拖拉机作业，包括田间作业和皮带作业，例如耕地、耙地、平路、联合收获、饲料粉碎等等。万能型拖拉机：万能型拖拉机即中耕型拖拉机，用来完成一般的农场的几乎所有的田间作业和皮带作业，包括中耕作物的播种和中耕在内。传统的拖拉机通常有两个用发动机驱动的后轮和两个支重的前轮。用来为拖拉机提供动力的发动机类型是内燃机。发动机是拖拉机的心脏。正是在这里燃料的化学年能被转化为使轮子转动的机械能。内燃机和外燃机的区别仅仅是在：在内燃机力，势能转化为机械能完全与空气精确的混合，然后在控制的条件下燃烧。这种混合燃烧时就会膨胀，压力增大，推动活塞沿着气缸直线地向下运动。我们就说活塞作直线运动。该直线运动通过与活塞连接的连杆和曲柄机构转变为旋转运动。为了能有效地利用这种能量，对燃烧过程和膨胀压力必须加以控制。为此发动机必须具有： 1.一端密闭的管子即气缸，在这里燃油和空气的混合气被压缩和燃烧 2.活塞，它可以在气缸里只有滑动，但又与气缸配合严密，这样，膨胀的气体就能推动活塞沿着气缸向下运动而不从周围漏掉。 3.气缸的两个同期道：一个是燃料和空气的混合气进入气缸的进气口，另一个是排泄废气的排气口。 4.两个阀门：控制混合气进入气缸的进气门和控制废气排放的排气门。根据阀门的开笔和活塞的位置，使混合气正时点火，nts 9 就可以使活塞连续地在气缸里上下运动。内燃机一旦运动，其工作过程就是指每个气缸里所发生的一系列的动作。一般有两种不同的循环：四行程循环和二行程循环。在四冲程循环中，曲柄转两圈，活塞完成四个行程，一个行程就是指活塞自气缸的一端运动到另一端。在二行程循环中，每一个循环曲柄转一圈，活塞完成两个行程。拖拉机大概都有一套完整的电系来为电动机、燃料点火和照明设备供电。在有些拖拉机的设计上还要为其它一些辅助线路供电。一套完整的电系包括下面几条线路：（ 1）发电线路；（ 2）电起动机线路；（ 3）照明线路；（ 4）点火线路。因为蓄电池与所有这四条主要线路连接并为其供电，所以完全可以把它看作是整个电系的基础。为了获得适合各种农业工作的速度和牵引力，我们就必须降低发动机较快的转速并将其动力传递给驱动装置。在田间或公路运输时需要较快的前进速度，但在重负荷田间作业时需要较慢的前进速度和较大的牵

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