自動變速器如何工作外文文獻翻譯@中英文翻譯@外文翻譯

1 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, well work our way through an automatic transmission. Well start with the key to the whole system: planetary gear sets. Then well 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 transmissions 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. Youve probably never tried driving a manual transmission car using only third gear. If you did, youd 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 engines 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 2 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. Lets 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. Youll 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 3 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. Its 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. Lets 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. Lets 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 4 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. Youve 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, well discuss the key components of the hydraulic system; then well 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. 5 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. 6 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. Lets 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. 7 自動變速器如何工作 如果你曾經(jīng)駕駛過一輛帶著自動變速器的車 , 那么你就知道自動變速器和手動變速器之間有很大的不同 : 在一個帶著自動變速器的汽車中沒有離合器踏板。 在一個帶著自動變速器的汽車中沒有變動的傳輸器。 一旦你把變速器放入駕駛車之內(nèi)，其他每個部件都是自動的。 雖然自動變速器 (加上它的扭矩變換器 ) 和一個手動變速器 (借由它的離合器 ) 完成同 樣的工作 , 但是他們操作方法完全不同。 自動變速器的操作方法另人覺得非常了不起！ 在這里，我們將通過自動變速器來研究我們的方法。 我們將會從整個系統(tǒng)的關(guān)鍵開始著手 :行星齒輪。然后我們將會看到變速器如何被集合 ,學(xué)習(xí)控制器如何工作而且討論一些關(guān)于控制變速器方面的文章。 基礎(chǔ)部分： 正如手動變速器一樣 , 自動變速器最初的工作是允許機器在很小的速度范圍內(nèi)操作，同時提供各種不同范圍的速度。 沒有傳輸器 , 汽車對一個齒輪比率會被限制 ,并且那個比率必須被選擇允許汽車渴望旅行的最高速度。如果您想要 80里 /時 的最高速度 ,那么齒輪比率會與大多數(shù)帶有手動變速器的汽車的第三個齒輪相似。 你或許從未嘗試過駕駛只使用第三個齒輪的帶有手動傳輸器的汽車。如果你嘗試過，你很快就會發(fā)現(xiàn)當(dāng)汽車發(fā)動時，你幾乎沒法加速。當(dāng)你高速行駛時，引擎就會在紅線附近發(fā)出尖叫聲。如果這樣的話，汽車很快就會被磨損而且很快就會無法操作。 因此變速器使用齒輪可以使引擎的扭矩更加有效的使用，并且使引擎在一個適當(dāng)?shù)乃俣炔僮鳌?手動變速器和自動變速器最關(guān)鍵的區(qū)別在于：手動變速器的鎖和開不同的套齒輪對輸出軸達到各種各樣的齒輪比率，同時自動變速器中相同的套齒輪會導(dǎo)致所有不同的齒輪比率。行星齒輪很有可能在自動變速器中成為一個設(shè)備。 齒輪 這一個自動變速器使用一組齒輪 , 稱作復(fù)式的行星齒輪 , 像行星齒輪一樣的外貌但是實際上像被聯(lián)合的二行星齒輪的作用。這里有一個作為變速器輸出的環(huán)齒輪，但是它有二個太陽輪和二組行星。 讓我們看一些零件 : 一檔齒輪 在一檔齒輪中，較小的太陽輪被扭力變換器的輪機駕駛順時針運轉(zhuǎn)。 行星臺車試著向反時針方向快速旋轉(zhuǎn) ,但是被單向離合器 (只允許順時針方向旋轉(zhuǎn)的裝置 ) 保持靜止，而且環(huán)齒輪輸出。 小的齒輪有 30顆牙齒而環(huán)齒輪有72顆牙齒 ,因此 齒輪比是 : 比 =-半徑 /S=- 72/30=-2.4:1 因此旋轉(zhuǎn)裝置是負(fù) 2.4:1, 意味著輸出方向與輸入方向相反。 但是輸出 8 方向真的相同于輸入方向 -這和二組行星的進入有關(guān)。 第一組行星答應(yīng)第二個組 ,第二組昨星轉(zhuǎn)動環(huán)齒輪 ; 這個結(jié)合顛倒了方向。 你能意識到這也會導(dǎo)致較大的太陽輪快速旋轉(zhuǎn) ; 但是就因為那一個離合器被釋放 , 較大的太陽輪自由的往輪機的反方向快速旋轉(zhuǎn)。 二檔齒輪 這個變速器做真正的整潔是為了使比率與二檔齒輪相符合。 它運轉(zhuǎn)起來就像兩個行星齒輪與一個普通的行星載體互相連接。 行星載體的第一 階段實際上使用更大的太陽齒輪作為環(huán)齒輪。 因此第一階段包括太陽 (更小的太陽齒輪 ), 行星載體 , 并且環(huán)齒輪 (更大的太陽齒輪 ) 。 輸入的是小的太陽齒輪 ; 環(huán)齒輪 (大的太陽齒輪 ) 被傳輸帶所固定，而輸出的是行星載體，所以公式是 : 1 + R/S=1 + 36/30 =2.2:1 小太陽齒輪每轉(zhuǎn)動一次，行星載體轉(zhuǎn)動 2.2次。在第二階段 , 行星載體作為第二個星球齒輪集合的輸入 ,較大的太陽齒輪 (被穩(wěn)固的 ) 作為太陽，而環(huán)齒輪作為輸出 , 因此齒輪比率是 : 1/(1+ S/半徑 )=1/(1+36/72)=0.67:1 為了使整體減少為二檔齒輪，我們通過第一階段和第二階段相乘（ 2.2 x 0.67），使它以 1.47： 1的速率減少，我們在第二 , , 之前乘第一個級得到一個 1.47:1 還原。 這可能聽起來有點奇怪 , 但它可以運轉(zhuǎn)。 三檔齒輪 大多數(shù)的自動變速器在三檔齒輪中有 1:1的 比率。從早先部分可以看出我們必須使行星齒輪的三個部件中的任何兩個結(jié)合在一起，都以 1： 1的比率輸出。在齒輪組的安排下，它變得更加容易，我們必須做的就是使所有的都參與離合器，把每個太陽齒輪結(jié)合成渦輪。 如果兩個太陽齒輪在相同的方向運轉(zhuǎn) ,那么 行星齒輪就要被鎖定起來，因為他們僅僅只能在相反的方向快速旋轉(zhuǎn)，把環(huán)齒輪與行星齒輪鎖定在一起，就會使每個部位快速旋轉(zhuǎn)，就如一個單位 ,產(chǎn)生 1:1 的比率。 加速擋 由定義，一個加速擋輸出速度比輸入速度更快，它是速度的增加。在這傳輸中 , 參與加速檔可立即完成二件事。 如果你讀扭力變換器如何工作 , 你就學(xué)習(xí)扭力變換器的鎖定。 為了提高效率 , 有些汽車就有一個機制可以鎖定扭力變換器，以便引擎的輸出直接達到變速器。 在這一個變速器中，當(dāng)加速擋參與其中，附有扭矩交換器 (被閂上引擎飛輪 ) 的軸由離合器連接到行星載體。小的 太陽齒輪輕松快活地運轉(zhuǎn)，而較大的太陽齒輪被加速擋傳輸帶所固定。沒有東西與渦輪相連接， 唯一的輸入來自變換器殼。讓我們再一次回去我們上面的圖 ,這次行星載體作為輸入，太陽齒輪被固定，環(huán)齒輪作為輸出。 比 率 =1/(1+ S/半徑 )=1/(1+36/72)=0.67:1 所以引擎自轉(zhuǎn)每轉(zhuǎn)每三分之二，輸出裝置快速旋轉(zhuǎn)一次。 如果引擎以每分鐘(RPM) 2000次的速度旋轉(zhuǎn)，那么裝置輸出速度就是 3000 RPM 。 這樣汽車在引擎速度保持好很慢的狀態(tài)下以高速公路的速度行駛。 倒擋 倒擋和一擋齒輪非常相似 , 除了代 替小太陽齒輪被扭矩交換器渦輪被駕駛 ,較大的太陽齒輪被駕駛，而且一個小的在相反的方向輕松快活地運轉(zhuǎn)。行星 9 載體由反向帶拿著對住房。 因此 , 根據(jù)我們的方程序從最后頁 , 我們有 : 比率 =-R/S=72/36 =2.0:1 因此，倒擋的比率稍微比變速器的一檔齒輪更少。 齒輪比 這一個變速器有四個前進齒輪和一個倒車齒輪。 讓我們概述齒輪比，輸入和輸出 : 齒輪 輸入 輸出 固定的 齒輪比率 一檔 30 齒輪的太陽 72-齒圈 行星載體 2.4:1 二檔 30 齒輪的太陽 行星載體 36-齒圈 2.2:1 行星載體 72-齒圈 36 齒輪的太陽 0.67:1 總計之第二 1.47:1 三檔 30和 36齒輪的太陽 72-齒圈 1.0