570_履帶拖拉機變速器改進(jìn)設(shè)計,履帶,拖拉機,變速器,改進(jìn),改良,設(shè)計 履帶拖拉機變速器改進(jìn)設(shè)計 Ⅳ 摘 要 隨著農(nóng)業(yè)的不斷進(jìn)步發(fā)展，農(nóng)業(yè)生產(chǎn)機械化、規(guī)?；吧a(chǎn)資料和農(nóng)田建設(shè)材料等各種物資運輸量越來越大，農(nóng)民越來越需要拖拉機的幫助，因此，農(nóng)用拖拉機的發(fā)展前景很廣闊，會有較大的發(fā)展。 滿足拖拉機的動力性和經(jīng)濟性指標(biāo)，這與變速器的檔數(shù)、傳動比的范圍和各檔傳動有關(guān)。拖拉機工作的道路條件越復(fù)雜、比功率越小，變速器的傳動比范圍越大。變速器與主減速器及發(fā)動機參數(shù)作優(yōu)化配置，可得到良好的動力性和經(jīng)濟性。 變速器的結(jié)構(gòu)對動力性，經(jīng)濟性，操縱的可靠性與輕便性，工作噪聲等都有直接影響。變速器主要用來改變發(fā)動機傳到驅(qū)動輪上的轉(zhuǎn)矩和轉(zhuǎn)速，目的是在起步、爬坡、轉(zhuǎn)彎、加速等各種行駛工況下，獲得不同的牽引力和速度，同時使發(fā)動機在最有利的工況下范圍工作，設(shè)有空檔和倒檔。 本次設(shè)計按照傳統(tǒng)設(shè)計方法，本著半經(jīng)驗半理論的設(shè)計原則通過類比法確定方案，參照已有車型變速器結(jié)構(gòu)，最后以機械零件的強度和剛度理論對確定的形狀和尺寸進(jìn)行必要的計算和校核，以滿足約束條件，進(jìn)而縮短設(shè)計周期，降低設(shè)計成本。 關(guān)鍵詞：變速器，傳動比，設(shè)計，計算，校核 TRACKED TRACTOR TRANSMISSION IMPROVED DESIGN Ⅳ ABSTRACT With the continuous progress of agricultural development, agricultural production mechanization, the scale of the means of production and agricultural land and building materials and other goods traffic increasing, more and more farmers need the help of tractors, therefore, farm tractors development prospects are broad, there will be greater development. Tractors to meet the power and economic indicators, and transmission of the file, the transmission ratio of the scope and the transmission of the file. Tractor work of the road conditions more complex than the smaller power, the transmission of the transmission ratio greater. Reducer and the main transmission and engine parameters to optimize the allocation and availability of power and good economy. In order to make it come true that the transmission is adapted to the engine and its structure is sound, I pay close attention to the development of the clutch transmission shaft and collectivity arranging designers in my design, and have a repeating discussion with them . For shifting gear steadily , fourth and third gear have synchrotron ,and in consideration of the simplicity and reliability .According to the traditional mean of design ,part experience and theory and analogism ,the blue print come into being .by virtue of tradition transmission I verify the size of element which have been chosen, according to mechanical theory, in consideration of the qualification bringing down the cost and cycle time. KEY WORD： Transmission, transmission ratio, design, calculations, checking 符 號 說 明 A 中心距 D 直徑 E 彈性模量 傳動比 f 撓度 轉(zhuǎn)角 M 彎矩 汽車總質(zhì)量 kg 重力加速度 N/kg 道路最大阻力系數(shù) 驅(qū)動輪的滾動半徑 mm 發(fā)動機最大扭矩 N·m 主減速比 汽車傳動系的傳動效率 一檔傳動比 汽車滿載載荷 N 路面附著系數(shù) 中心距系數(shù) 直齒輪模數(shù) 齒輪壓力角 ° 斜齒輪螺旋角 ° 齒輪寬度 mm 齒輪齒數(shù) 齒輪彎曲應(yīng)力 MPa 齒輪接觸應(yīng)力 MPa 齒輪所受圓周力 N 軸向力 N 徑向力 N 計算載荷 N·m 應(yīng)力集中系數(shù) 摩擦力影響系數(shù) 齒輪材料的彈性模量 MPa 重合度影響系數(shù) 主動齒輪節(jié)圓半徑 mm 從動齒輪節(jié)圓半徑 mm 主動齒輪節(jié)圓處的曲率半徑 mm 從動齒輪節(jié)圓處的曲率半徑 mm 扭轉(zhuǎn)切應(yīng)力 MPa 軸的抗扭截面系數(shù) 軸的材料的剪切彈性模量 MPa 軸截面的極慣性矩 垂直面內(nèi)的撓度 mm 水平面內(nèi)的撓度 mm 目 錄 第一章 緒論 1 第二章 變速器傳動方案的研究與改進(jìn) 3 §2.1 變速器的功用與要求 3 §2.2 變速器的種類 4 §2.3 課題變速箱存在的問題與解決方案 5 §2.4 變速器改進(jìn)方案的確定 6 第三章 變速器傳動方案與參數(shù)的確定 8 §3.1 變速器檔位與傳動比的初定 8 §3.1.1 最高檔傳動比的選擇 8 §3.1.2 最低檔傳動比的選擇 8 §3.1.3 各檔位傳動比的分配 9 §3.2 變速箱外形尺寸的初定 9 §3.2.1 變速箱齒輪中心距的確定 9 §3.2.2 變速箱的軸參數(shù)確定 10 §3.3 變速器各項參數(shù)的最終確定 10 §3.3.1 齒輪齒數(shù)及其參數(shù)的確定 10 §3.3.2 齒輪模數(shù)確定 11 §3.3.3 齒輪其他參數(shù)的計算 12 §3.3.4 齒形、壓力角α、螺旋角β 15 §3.3.5 齒寬的確定 15 §3.3.6 中心距的最后確定 16 第四章 齒輪與軸的校核 17 §4.1 齒輪的校核 17 §4.1.1 齒輪的損壞形式 17 §4.1.2 齒輪的強度校核與計算 17 §4.2 軸的校核 19 §4.2.1 軸剛度的校核 19 §4.2.2 軸的強度校核 20 第五章 軸承的校核 22 第六章 嚙合套的設(shè)計 23 §6.1 換擋機構(gòu)形式 23 §6.2 防脫擋措施 23 第七章 變速器操縱機構(gòu)設(shè)計 26 第八章 結(jié)論 27 參考文獻(xiàn) 28 致 謝 30 VI 畢 業(yè) 設(shè) 計（論 文） 題目 履帶拖拉機變速器改進(jìn)設(shè)計 Ⅳ 畢業(yè)設(shè)計（論文）包含內(nèi)容及裝訂順序 1. 畢業(yè)設(shè)計（論文）任務(wù)書 2. 中英文摘要（含關(guān)鍵詞） 3. 目錄 4. 前言 5. 正文 6. 結(jié)論 7. 參考文獻(xiàn) 8. 致謝 9. 附錄 10. 外文資料譯文 How Automatic Transmissions Work If you have ever driven a car with an automatic transmission, then you know that there are two big differences between an automatic transmission and a manual transmission: There is no clutch pedal in an automatic transmission car. There is no gear shift in an automatic transmission car. Once you put the transmission into drive, everything else is automatic. Both the automatic transmission (plus its torque converter) and a manual transmission (with its clutch) accomplish exactly the same thing, but they do it in totally different ways. It turns out that the way an automatic transmission does it is absolutely amazing! In this article, we'll work our way through an automatic transmission. We'll start with the key to the whole system: planetary gear sets. Then we'll see how the transmission is put together, learn how the controls work and discuss some of the intricacies involved in controlling a transmission. Some Basics Just like that of a manual transmission, the automatic transmission's primary job is to allow the engine to operate in its narrow range of speeds while providing a wide range of output speeds. Without a transmission, cars would be limited to one gear ratio, and that ratio would have to be selected to allow the car to travel at the desired top speed. If you wanted a top speed of 80 mph, then the gear ratio would be similar to third gear in most manual transmission cars. You've probably never tried driving a manual transmission car using only third gear. If you did, you'd quickly find out that you had almost no acceleration when starting out, and at high speeds, the engine would be screaming along near the red-line. A car like this would wear out very quickly and would be nearly undrive able. So the transmission uses gears to make more effective use of the engine's torque, and to keep the engine operating at an appropriate speed. The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission, the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission. Gears This automatic transmission uses a set of gears, called a compound planetary gear set, that looks like a single planetary gear set but actually behaves like two planetary gear sets combined. It has one ring gear that is always the output of the transmission, but it has two sun gears and two sets of planets. Let's look at some of the parts: First Gear In first gear, the smaller sun gear is driven clockwise by the turbine in the torque converter. The planet carrier tries to spin counterclockwise, but is held still by the one-way clutch (which only allows rotation in the clockwise direction) and the ring gear turns the output. The small gear has 30 teeth and the ring gear has 72, so the gear ratio is: Ratio = -R/S = - 72/30 = -2.4:1 So the rotation is negative 2.4:1, which means that the output direction would be opposite the input direction. But the output direction is really the same as the input direction -- this is where the trick with the two sets of planets comes in. The first set of planets engages the second set, and the second set turns the ring gear; this combination reverses the direction. You can see that this would also cause the bigger sun gear to spin; but because that clutch is released, the bigger sun gear is free to spin in the opposite direction of the turbine Second Gear This transmission does something really neat in order to get the ratio needed for second gear. It acts like two planetary gear sets connected to each other with a common planet carrier. The first stage of the planet carrier actually uses the larger sun gear as the ring gear. So the first stage consists of the sun (the smaller sun gear), the planet carrier, and the ring (the larger sun gear). The input is the small sun gear; the ring gear (large sun gear) is held stationary by the band, and the output is the planet carrier. so the formula is: 1 + R/S = 1 + 36/30 = 2.2:1 The planet carrier turns 2.2 times for each rotation of the small sun gear. At the second stage, the planet carrier acts as the input for the second planetary gear set, the larger sun gear (which is held stationary) acts as the sun, and the ring gear acts as the output, so the gear ratio is: 1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1 To get the overall reduction for second gear, we multiply the first stage by the second, 2.2 x 0.67, to get a 1.47:1 reduction. This may sound wacky, but it works. Third Gear Most automatic transmissions have a 1:1 ratio in third gear. You'll remember from the previous section that all we have to do to get a 1:1 output is lock together any two of the three parts of the planetary gear. With the arrangement in this gear set it is even easier -- all we have to do is engage the clutches that lock each of the sun gears to the turbine. If both sun gears turn in the same direction, the planet gears lockup because they can only spin in opposite directions. This locks the ring gear to the planets and causes everything to spin as a unit, producing a 1:1 ratio. Overdrive By definition, an overdrive has a faster output speed than input speed. It's a speed increase. In this transmission, engaging the overdrive accomplishes two things at once. If you read How Torque Converters Work, you learned about lockup torque converters. In order to improve efficiency, some cars have a mechanism that locks up the torque converter so that the output of the engine goes straight to the transmission. In this transmission, when overdrive is engaged, a shaft that is attached to the housing of the torque converter (which is bolted to the flywheel of the engine) is connected by clutch to the planet carrier. The small sun gear freewheels, and the larger sun gear is held by the overdrive band. Nothing is connected to the turbine; the only input comes from the converter housing. Let's go back to our chart again, this time with the planet carrier for input, the sun gear fixed and the ring gear for output. Ratio = 1 / (1 + S/R) = 1 / ( 1 + 36/72) = 0.67:1 So the output spins once for every two-thirds of a rotation of the engine. If the engine is turning at 2000 rotations per minute (RPM), the output speed is 3000 RPM. This allows cars to drive at freeway speed while the engine speed stays nice and slow. Reverse Reverse is very similar to first gear, except that instead of the small sun gear being driven by the torque converter turbine, the bigger sun gear is driven, and the small one freewheels in the opposite direction. The planet carrier is held by the reverse band to the housing. So, according to our equations from the last page, we have: Ratio = -R/S = 72/36 = 2.0:1 So the ratio in reverse is a little less than first gear in this transmission. Gear Ratios This transmission has four forward gears and one reverse gear. Let's summarize the gear ratios, inputs and outputs: Gear Input Output Fixed Gear Ratio 1st 30-tooth sun 72-tooth ring Planet carrier 2.4:1 2nd 30-tooth sun Planet carrier 36-tooth ring 2.2:1 Planet carrier 72-tooth ring 36-tooth sun 0.67:1 Total 2nd 1.47:1 3rd 30- and 36-tooth suns 72-tooth ring 1.0:1 OD Planet carrier 72-tooth ring 36-tooth sun 0.67:1 Reverse 36-tooth sun 72-tooth ring Planet carrier -2.0:1 Hydraulic System The automatic transmission in your car has to do numerous tasks. You may not realize how many different ways it operates. For instance, here are some of the features of an automatic transmission: · If the car is in overdrive (on a four-speed transmission), the transmission will automatically select the gear based on vehicle speed and throttle pedal position. · If you accelerate gently, shifts will occur at lower speeds than if you accelerate at full throttle. · If you floor the gas pedal, the transmission will downshift to the next lower gear. · If you move the shift selector to a lower gear, the transmission will downshift unless the car is going too fast for that gear. If the car is going too fast, it will wait until the car slows down and then downshift. · If you put the transmission in second gear, it will never downshift or up shift out of second, even from a complete stop, unless you move the shift lever. · You've probably seen something that looks like this before. It is really the brain of the automatic transmission, managing all of these functions and more. The passageways you can see route fluid to all the different components in the transmission. Passageways molded into the metal are an efficient way to route fluid; without them, many hoses would be needed to connect the various parts of the transmission. First, we'll discuss the key components of the hydraulic system; then we'll see how they work together. The Pump Automatic transmissions have a neat pump, called a gear pump. The pump is usually located in the cover of the transmission. It draws fluid from a sump in the bottom of the transmission and feeds it to the hydraulic system. It also feeds the transmission cooler and the torque converter. The inner gear of the pump hooks up to the housing of the torque converter, so it spins at the same speed as the engine. The outer gear is turned by the inner gear, and as the gears rotate, fluid is drawn up from the sump on one side of the crescent and forced out into the hydraulic system on the other side. The Governor The governor is a clever valve that tells the transmission how fast the car is going. It is connected to the output, so the faster the car moves, the faster the governor spins. Inside the governor is a spring-loaded valve that opens in proportion to how fast the governor is spinning -- the faster the governor spins, the more the valve opens. Fluid from the pump is fed to the governor through the output shaft. The faster the car goes, the more the governor valve opens and the higher the pressure of the fluid it lets through. Valves and Modulators Throttle Valve or Modulator To shift properly, the automatic transmission has to know how hard the engine is working. There are two different ways that this is done. Some cars have a simple cable linkage connected to a throttle valve in the transmission. The further the gas pedal is pressed, the more pressure is put on the throttle valve. Other cars use a vacuum modulator to apply pressure to the throttle valve. The modulator senses the manifold pressure, which drops when the engine is under a greater load. Manual Valve The manual valve is what the shift lever hooks up to. Depending on which gear is selected, the manual valve feeds hydraulic circuits that inhibit certain gears. For instance, if the shift lever is in third gear, it feeds a circuit that prevents overdrive from engaging. Shift Valves Shift valves supply hydraulic pressure to the clutches and bands to engage each gear. The valve body of the transmission contains several shift valves. The shift valve determines when to shift from one gear to the next. For instance, the 1 to 2 shift valve determines when to shift from first to second gear. The shift valve is pressurized with fluid from the governor on one side, and the throttle valve on the other. They are supplied with fluid by the pump, and they route that fluid to one of two circuits to control which gear the car runs in. The shift valve will delay a shift if the car is accelerating quickly. If the car accelerates gently, the shift will occur at a lower speed. Let's discuss what happens when the car accelerates gently. As car speed increases, the pressure from the governor builds. This forces the shift valve over until the first gear circuit is closed, and the second gear circuit opens. Since the car is accelerating at light throttle, the throttle valve does not apply much pressure against the shift valve. When the car accelerates quickly, the throttle valve applies more pressure against the shift valve. This means that the pressure from the governor has to be higher (and therefore the vehicle speed has to be faster) before the shift valve moves over far enough to engage second gear. Each shift valve responds to a particular pressure range; so when the car is going faster, the 2-to-3 shift valve will take over, because the pressure from the governor is high enough to trigger that valve. Electronic Controls Electronically controlled transmissions, which appear on some newer cars, still use hydraulics to actuate the clutches and bands, but each hydraulic circuit is controlled by an electric solenoid. This simplifies the plumbing on the transmission and allows for more advanced control schemes.