580 輕型載貨汽車設計（底盤設計）（有cad圖）
580 輕型載貨汽車設計（底盤設計）（有cad圖）,580,輕型載貨汽車設計（底盤設計）（有cad圖）,輕型,載貨,汽車,設計,底盤,cad
Classification of Tractors
The tractor is a wheeled or tracked self-propelled vehicle used as a power means for moving agricultural, 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 PURPOSE, 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 tractors 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 traction. 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 replaceable driving wheels of different tread widths-wide for general farm 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 utility tractor models and are used for definite jobs, and under certain conditions. Thus, special tractors used to mechanize the cultivation of cotton have a single front wheel, swamp tractors are equipped with wide tracks enabling them to operate on marshy soils, and hillside tractors are designed to work on hillsides sloping at up to 16o.
AS TO THE DESIGN OF THE RUNNING 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 insignificantly. Such 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 Component 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 mechanism, working attachments, and auxiliary equipments.
THE ENGINE converts thermal energy into mechanical energy.
THE DRIVE LINE comprises a set of mechanisms 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 includes 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 shifting gears 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 flexible coupling incorporates elastic elements allowing 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 distinct from its crawler counterpart the drive line includes 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 RUNNING 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 STEERING MECHANISM 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 WORKING ATTACHMENTS 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 TRACTOR AUXILIARIES include the driver’s cab with a spring-mounted seat and heating and ventilation equipment, hood, lighting equipment, tell tales (indicators), horns, etc.
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 transmission while he is shifting gears or starting the tractor moving from rest.
Modern tractors use friction clutches, ones employing friction forces to transmit power. The friction surfaces in such clutches are provided by discs, whose number depends on the magnitude of torque to single- and double-disc clutches.
Clutch 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 tightly clamped 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. Owing to the friction forces arising between the friction surfaces of the flywheel, 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 ends 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, and 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 force the pressure plate to the left. The driven disc is again clamped tightly between the flywheel and the pressure plate. The driven disc must again rotate with the flywheel. In this position, the clutch is engaged. The initial slipping of the driven disc, which occurs until the disc is fully clamped 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.
Propeller 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 main, 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. First, the engine and transmission are more or less rigidly attached to the car frame. Second, the rear-axle housing (with wheels and differential) is attached to the frame by springs. As the rear wheels encounter irregularities in the road, the springs are compressed or expanded. These change the angle of drive and the distance between the transmission and the differential, and the propeller shaft should take care of these two changes. That is to say, as the rear axle housing, with differential 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 than 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.
The propeller shaft may be solid or hollow, protected by an outer tube or exposed. Some applications include 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 member called the spider. 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 bearings in the yokes permit the yokes to swing around on the trunnions with each revolution. 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 effective change of length of the propeller shaft as the rear axles move toward or away from the car frame.
6
大學畢業(yè)設計（論文）開題報告
（學生填表）
院系：車輛與動力工程學院 2013年4月12日
課題名稱
輕型載貨汽車設計（底盤設計）
學生姓名
專業(yè)班級
課題類型
畢業(yè)設計
指導教師
職稱
課題來源
組合生產(chǎn)
1. 設計（或研究）的依據(jù)與意義
隨著現(xiàn)在科學技術的發(fā)展，人們出行的日益繁忙，汽車作為一種快速便捷的交通工具，在外出，旅行，載貨中起著越來越重要的作用，給人們生活帶來了許多的方便。被稱為“改變世界的工具”。汽車品種的多樣性可滿足各種生產(chǎn)、生活活動的需求，而且有良好的社會效益。
汽車的進步如同社會進步一樣，與我們息息相關。從早期的蒸汽機到后來的內(nèi)燃機車再到現(xiàn)在的電動汽車、燃料汽車等，反映出了一條汽車發(fā)展的軌跡。汽車誕生100多年來，涌現(xiàn)了各種有關汽車技術發(fā)明，汽車面貌日新月異，隨著汽車工業(yè)的不斷發(fā)展，人們對汽車各方面的性能也提出更高的要求。不僅要求汽車有良好的動力性，經(jīng)濟性，更要求有最好的安全性，更低的污染以及舒適的乘坐性能和輕便的駕駛性能等。
底盤是汽車上由傳動系、行駛系、轉向系和制動系四部分組成的組合，支承、安裝汽車發(fā)動機及其各部件、總成，形成汽車的整體造型，承受發(fā)動機動力，保證正常行駛。 底盤由傳動系、行駛系、轉向系和制動系四部分組成。
2. 國內(nèi)外同類設計（或同類研究）的概況綜述
國內(nèi)輕型卡車產(chǎn)品與國外產(chǎn)品相對，對國內(nèi)環(huán)境適應能力更強。我國輕型車使用范圍廣闊，從田間到工地，從廣大農(nóng)村到大城市，各種環(huán)境對輕型卡車的環(huán)境適應能力提出了較高的要求。我國輕型卡車制造商，對產(chǎn)品多年持續(xù)不斷的適應性設計，使我國輕卡產(chǎn)品能夠應對國內(nèi)復雜的使用環(huán)境，而國外進口同類產(chǎn)品，對國內(nèi)的環(huán)境適應能力則相對薄弱很多。
隨著世界汽車對汽車發(fā)動機動力性、經(jīng)濟性和排放提出了更高要求和計算機技術的迅速發(fā)展，柴油機被公認為節(jié)能的代表和減少汽車尾氣排放污染的有力工具，汽車柴油化也是汽車發(fā)動機發(fā)展的一大趨勢。柴油機的開發(fā)焦點已由傳統(tǒng)的優(yōu)先考慮經(jīng)濟性、可靠性和耐久性逐步轉為目前的優(yōu)先考慮環(huán)保的要求，即以優(yōu)先保護好人類賴以生存的地球環(huán)境為出發(fā)點去考慮采用何種技術，去評價其先進性。
近幾年來國內(nèi)輕卡在設計上已經(jīng)趨于成熟，但由于大眾思維觀念制約，在安全性和耐久性方面與國外產(chǎn)品還有一定差距。日前我國輕卡市場競爭日趨激烈，主要是在功能和舒適性上比拼，在發(fā)動機功率、駕駛室寬度、外觀造型、舒適化程度等方面進展迅速，而可靠性方面，受車輛制造成本限制，提高速度并不快。此外，國內(nèi)輕型卡車在環(huán)保性方面落后于總體水平。由于國內(nèi)輕型卡車以中低端產(chǎn)品為主，提升環(huán)保標準增加的成本，會降影響用戶接受能力，因此在環(huán)保方面，輕型卡車產(chǎn)品一直處于被動接受狀態(tài)，在環(huán)?？刂屏悴考x擇上，使用不達標準產(chǎn)品，降低環(huán)保功能件成本，結果導致輕型貨車的發(fā)展與國外產(chǎn)品存在一定的差距，因此，柴油貨車的環(huán)保性能設計具有很大的市場前景。燃料性能的改進，對減少排放起到很大作用，日本繼美歐之后，從1997年開始把輕油中的硫含量降到0.05%以下，以此大幅度減少排放顆粒中的硫酸鹽，同時減少EGR造成的發(fā)動機內(nèi)部的腐蝕磨耗及催化劑中毒；進一步減少硫含量，提高十六烷值，可進一步降低NOx。減少芳香烴，尤其是減少3環(huán)以上的芳香族成分，可減少排放顆粒中的硫化物、降低90%的蒸餾溫度、改進點火性能；通過使用含氧燃料或添加劑，可降低黑煙顆粒。為了適應低硫化及噴射壓力的大大增加，確保燃油噴射裝置的潤滑性，人們對燃料的改進開發(fā)寄予了很大期望。
3. 課題設計（或研究）的內(nèi)容
完成輕型汽車的底盤設計，進行發(fā)動機與傳動系的合理匹配優(yōu)化計算，確定最佳的變速器與驅(qū)動橋的主要參數(shù)?？偣ぷ髁坎簧儆?張零號圖紙，編寫設計說明書，內(nèi)容不少于12000字，說明書要求計算機打印。至少完成1張1號圖紙的機繪圖，保證30學時的計算機上機工作量。閱讀不少于15篇的參考文獻；編寫不少于400字符的中文摘要，并翻譯成外文；要有1萬字符的外文翻譯資料。
4. 設計（或研究）方法
根據(jù)所給技術條件和要求，并參照其他類似的成熟車型對比設計。由經(jīng)驗公式確定一系列的參數(shù)，包括總體的外型尺寸，軸間距，載荷分布等。還有制動器的所需的制動力，力矩等。并根據(jù)要求進行校核。
5. 進度計劃
調(diào)研，收集資料 一周
確定方案，畫草圖 四周
完成總裝圖 四周
撰寫說明書，整理圖紙 二周
互評、答辯 一周
指導教師意見
指導教師簽字： 年 月 日
研究所（教研室）意見
研究所所長（教研室主任）簽字： 年 月 日
拖拉機的分類
拖拉機是一種輪式或履帶式的自走式車輛工具，它能被用來做移植農(nóng)作物，鋪路和其他裝備特殊工具的機械的動力裝置。也能用做牽引掛車的動力，拖拉機的發(fā)動機也能被用來做自動工具，固定式農(nóng)業(yè)機械的有原動力，通過用力輸出軸和皮帶輪做中間媒介。
拖拉機在農(nóng)業(yè)中的應用是非常的廣泛的，并且不同類型的拖拉機做不同的農(nóng)業(yè)作業(yè)。
農(nóng)業(yè)拖拉機被分為以下幾類。
就功能來說，現(xiàn)代的農(nóng)用拖拉機可以分為三類，普通功能的拖拉機，中耕拖拉機和專用拖拉機。
普通用途的拖拉機主要的農(nóng)業(yè)作業(yè)是大部分農(nóng)作物的栽培，比如耕地，犁地，耕種，耙地，播種和收割。這種拖拉機的典型特征就是有一個比較小的離地間隙，增加了發(fā)動機的扭矩和有比較好的牽引力，由于它們有較寬的輪胎或履帶，使他們能夠產(chǎn)生比較大的牽引力。
中耕拖拉機主要用來中耕作業(yè)，也可以進行許多其它的田間作業(yè)，為了達到這個目的，一些中耕拖拉機被裝備了不同胎面寬度的可替換的驅(qū)動輪。用來進行一般的田間作業(yè)和耙地，為了不損壞農(nóng)作物，這種拖拉機有一個比較大的離地間隙和比較寬的輪胎，能適應特殊的農(nóng)作物間距。
專用拖拉機不同于普通的拖拉機和中耕式拖拉機，它被用于特定的作業(yè)，或者在特定的條件下用于不同的作業(yè)。因此被用來棉花中耕機械化的專用拖拉機常常有一個前輪，在沼澤地里工作的拖拉機一般裝備有很寬的履帶，這樣能夠使它們在潮濕的土壤上工作。山地拖拉機一般被設計能在16度的斜坡上工作。
按驅(qū)動裝置的設計，拖拉機有可分為輪式和履帶式。
履帶式拖拉機因它較大的接地面積而著稱，所以它有一個很好的牽引附著性，它們能碾壓土壤并能緊緊的抓住土壤。因此這種拖拉機有很好的越野性并且能夠提供很好的牽引力。
輪式拖拉機的應用也很廣泛，能被用來在田間作業(yè)并且能夠用來進行交通運輸，但是它們的牽引能力比履帶式拖拉機要小。
拖拉機的主要組成部分
拖拉機是復雜的自走式機械，它由相互獨立相互作用的機構和單元組合而成。
如果不考慮特殊的設計，所有的拖拉機都有發(fā)動機，傳動系，行駛系，轉向系，作業(yè)機構和輔助裝置組成。
發(fā)動機把燃料的化學能轉化成機械能。
傳動系包括一系列的機械裝置，它們能傳遞發(fā)動機產(chǎn)生的扭矩給驅(qū)動輪或履帶。并且能把驅(qū)動扭矩變成有大小和方向的力，傳動系包括，離合器，連軸器，變速器和后橋。
離合器的主要用途就是當駕駛員正在掛擋時，暫時的把發(fā)動機輸出軸與變速器分離一段時間。當發(fā)動機從停機啟動時，它也能使發(fā)動機傳遞到驅(qū)動輪上的較低的動力連接平衡。
連軸器包括很多的彈性元件，這些彈性元件能夠把不在同一條直線上的離合器軸和變速器軸連接在一起。
變速器通過不同的嚙合齒輪，使改變驅(qū)動扭矩和發(fā)動機轉速成為可能。在發(fā)動機曲軸旋轉方向不變的情況下，變速器能夠是拖拉機倒駛。
后橋機構增加了驅(qū)動扭矩，且把它傳遞到驅(qū)動輪上或履帶上在適當?shù)慕嵌葌鹘o驅(qū)動軸。在大部分的拖拉機上，后橋上也包含剎車。
在輪式拖拉機上，不同于履帶式的地方。就是傳動系還包括差速器，當拖拉機在轉彎時或行駛在不平整的路面上時，它能是驅(qū)動輪以不同的速度旋轉，它的左右輪在相同的時間內(nèi)行駛過不同的距離。
行駛系能夠使拖拉機移動，驅(qū)動輪或者履帶和地面接觸的旋轉運動被轉化成拖拉機的直線運動。
轉向系主要用來改變拖拉機的行駛方向，在輪式拖拉機上是靠旋轉它的前輪，在履帶式拖拉機上，是靠改變一個履帶的速度。
作業(yè)機構被用來耕作。充分應用拖拉機發(fā)動機的動力去實現(xiàn)各種農(nóng)作業(yè)。它包括動力輸出軸，懸掛機構，農(nóng)具掛接機構，皮帶輪。
輔助裝置包括裝有彈簧坐椅及加熱、通風裝置的駕駛室，發(fā)動機罩，照明設備，指示器，喇叭等。
離合器
在傳動系中離合器位于發(fā)動機與變速器之間，作用就是使駕駛員可以把發(fā)動機與變速器結合和脫離。
現(xiàn)代拖拉機上廣泛應用摩擦片式離合器。這種離合器利用摩擦力來傳遞動力，這種離合器的摩擦面由壓盤提供，它的數(shù)量取決于傳遞扭矩的大小。大部分拖拉機上廣泛應用的是單片和雙片式離合器。
單片離合器的壓盤和發(fā)動機飛輪連接在一起，但是從動盤安裝在變速器離合器輸入軸上。從動盤上有花鍵轂與輸入軸上的花鍵相配合。從動盤被一組螺旋彈簧緊緊地壓在壓盤與飛輪之間，這一組壓力彈簧被支撐在離合器和壓盤之間，由于在飛輪，從動盤與壓盤之間產(chǎn)生了摩擦力，所以扭矩能夠被從發(fā)動機傳遞到變速器輸入軸，在這個位置時離合器開始工作。
離合器通過離合器轉向傳動機構來操作，離合器轉向傳動機構包括一個操作桿和一個分離撥叉。它能夠傳遞離合器踏板的運動給離合器分離軸承。當駕駛員踏離合器踏板時，離合器轉向傳動機構迫使分離軸承向內(nèi)（向左）移動。隨著分離軸承向左移動，它就向左推三個分離桿的內(nèi)端。當三個分離桿的內(nèi)端被分離軸承向左推時，分離桿的外端就使壓盤向右移動，壓縮螺旋彈簧。隨著彈簧壓力從從動盤上消失，在從動盤，飛輪和壓盤之間出現(xiàn)空隙，這時離合器被分離。但飛輪繼續(xù)轉動，但不通過從動盤傳遞動力。當離合器踏板被松開，螺旋彈簧通過使壓盤向左移動，從動盤再次被緊緊的壓在飛輪與壓盤之間，從動盤再次隨著飛輪一起旋轉。在這個位置，離合器開始工作，剛開始從動盤進行滑動，直到它被完全壓緊在飛輪與從動盤之間，使工作趨于平滑。上邊所描述的是干式摩擦彈簧離合器。
傳動軸和萬向節(jié)
傳動軸將動力從變速器傳送到后橋的驅(qū)動軸上。傳動軸將變速器的主軸或是輸出軸，連接到后橋上的差速器。變速器主軸的旋轉運動通過傳動軸傳遞到差速器上，使后車輪轉動。
設計傳動軸時必須考慮兩個因素。第一，發(fā)動機和變速器是剛性地安裝在車架上。第二，后橋殼（連同車輪和差速器）是通過彈性元件與車架相連。當后車輪在高低不平的路面上滾動時，彈簧上下伸縮，使變速器和差速器之間的傳動角度和距離發(fā)生變化。傳動軸要能適應這些變化，也就是說，當后橋殼隨差速器車輪一起上下運動時，與變速器輸出軸之間的角度變大的原因是后橋和差速器運動的弧度小于傳動軸運動的弧度。后橋殼弧線擺動的中心點是固定在車架的后彈簧或控制臂上。為了使傳動軸適應這兩種變化，就筆削裝有兩套獨立的裝置。一個或幾個萬向節(jié)來適應傳動角度的變化，一套伸縮花鍵，能夠改變傳動軸的現(xiàn)有長度。
傳動軸可以是實心的也可以是空心的，有套管加以保護或裸露在外。有些傳動軸在中心或在中心附近裝有支撐軸承。兩段傳動軸之間各有中間支撐軸承，并由萬向節(jié)傳動連接。
萬向節(jié)基本是個雙鉸鏈節(jié)，有兩個Y型萬向叉，一個在主動軸上，另一個在從動軸上，還有一個叫萬向節(jié)十字軸的十字形零件。萬向節(jié)十字軸的四個軸頸叫做萬向節(jié)十字頭，分別裝在兩個萬向節(jié)叉頂端的軸承中。主動軸使萬向節(jié)十字軸轉動，另外兩個萬向節(jié)十字頭使從動軸轉動。當兩軸相互處在同一角度上，主動軸轉動時萬向叉上的軸承使萬向節(jié)叉繞萬向節(jié)十字軸擺動。汽車上使用的萬向節(jié)有多種形式，但是使用最普遍的是雙十字軸萬向節(jié)、等速萬向節(jié)和球叉萬向節(jié)。
伸縮花鍵由在傳動軸上的外花鍵和與之相連的空心軸中對應的內(nèi)花鍵組成。伸縮花鍵使兩軸一起轉動，也能使兩軸相對移動。當后橋在車架上向前或向上運動時，這種結構足以調(diào)整轉動軸長度的任何變化。
Classification of Tractors
The tractor is a wheeled or tracked self-propelled vehicle used as a power means for moving agricultural, 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 PURPOSE, 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 tractors 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 traction. 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 replaceable driving wheels of different tread widths-wide for general farm 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 utility tractor models and are used for definite jobs, and under certain conditions. Thus, special tractors used to mechanize the cultivation of cotton have a single front wheel, swamp tractors are equipped with wide tracks enabling them to operate on marshy soils, and hillside tractors are designed to work on hillsides sloping at up to 16o.
AS TO THE DESIGN OF THE RUNNING 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 insignificantly. Such 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 Component 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 mechanism, working attachments, and auxiliary equipments.
THE ENGINE converts thermal energy into mechanical energy.
THE DRIVE LINE comprises a set of mechanisms 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 includes 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 shifting gears 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 flexible coupling incorporates elastic elements allowing 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 distinct from its crawler counterpart the drive line includes 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 RUNNING 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 STEERING MECHANISM 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 WORKING ATTACHMENTS 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 TRACTOR AUXILIARIES include the driver’s cab with a spring-mounted seat and heating and ventilation equipment, hood, lighting equipment, tell tales (indicators), horns, etc.
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 transmission while he is shifting gears or starting the tractor moving from rest.
Modern tractors use friction clutches, ones employing friction forces to transmit power. The friction surfaces in such clutches are provided by discs, whose number depends on the magnitude of torque to single- and double-disc clutches.
Clutch 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 tightly clamped 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. Owing to the friction forces arising between the friction surfaces of the flywheel, 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 ends 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, and 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 force the pressure plate to the left. The driven disc is again clamped tightly between the flywheel and the pressure plate. The driven disc must again rotate with the flywheel. In this position, the clutch is engaged. The initial slipping of the driven disc, which occurs until the disc is fully clamped 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.
Propeller 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 main, 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. First, the engine and transmission are more or less rigidly attached to the car frame. Second, the rear-axle housing (with wheels and differential) is attached to the frame by springs. As the rear wheels encounter irregularities in the road, the springs are compressed or expanded. These change the angle of drive and the distance between the transmission and the differential, and the propeller shaft should take care of these two changes. That is to say, as the rear axle housing, with differential 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 than 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.
The propeller shaft may be solid or hollow, protected by an outer tube or exposed. Some applications include 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 member called the spider. 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 bearings in the yokes permit the yokes to swing around on the trunnions with each revolution. 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 effective change of length of the propeller shaft as the rear axles move toward or away from the car frame.
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