中文譯文 車身結(jié)構(gòu)和自動變速器 1 車身結(jié)構(gòu) 車是一個人可以擁有的最迷人的設(shè)備，汽車也是一最普遍的設(shè)備，一輛車包含了許多不同的技術(shù)。每一個零部件都有自己專門的設(shè)計和工程技術(shù)領(lǐng)域。但是，任何汽車是由四個基本部分：發(fā)動機，底盤，車身和電氣系統(tǒng)。 作為動力源，發(fā)動機要求一個燃油系統(tǒng)提供燃料或混合空氣。它在動力生產(chǎn)過程中起著非常重要的作用。假設(shè)該發(fā)動機是一個汽油發(fā)動機，燃油泵系統(tǒng)的液體汽油從油箱到化油器位置使汽油與空氣可以混合?；旌衔锉粋鬟f到發(fā)動機燃燒。如果發(fā)動機電噴發(fā)動機，燃料從油箱被傳遞給噴油器通過一個電動燃油泵。燃料噴油器，直接控制進氣歧管中的燃油計量，由電控燃油噴射系統(tǒng)發(fā)出脈沖。電控燃油噴射系統(tǒng)根據(jù)發(fā)動機狀態(tài)確定的空氣燃料比。 一個是作為一個支持車身框架的底盤用來組裝所有的汽車零部件上。事實上，當從發(fā)動機的動力傳送到底盤，動力系統(tǒng)開始，接著轉(zhuǎn)向，車輪懸架，制動系統(tǒng)和輪胎。這些組件彼此聯(lián)系密切。實際上，驅(qū)動系統(tǒng)將發(fā)動機的動力傳輸?shù)津?qū)動輪。該驅(qū)動系統(tǒng)由離合器，變速箱，萬向節(jié)，驅(qū)動橋等組成。 汽車車身框架在底盤上，其功能是為用戶提供舒適，保護和空間。車身一般分為四個部分：前，上部或頂部，后部和底部。這些部分是進一步分成小單位，如發(fā)動機罩，擋泥板，頂板，車門，儀表盤，保險杠和行李艙。電氣系統(tǒng)被認為是汽車的電源為汽車供應照明用電。電氣系統(tǒng)包含電池的電氣系統(tǒng)，燈光，發(fā)電機，發(fā)動機點火，照明電路，以及控制其使用的各種開關(guān)。 隨著汽車工業(yè)的迅猛發(fā)展，新式的車正在設(shè)計和性能方面變得更好。當汽車非常受人們歡迎時，許多關(guān)于相應事實的負面問題應當由科學家考慮，如能源危機，空氣污染和交通堵塞。因此，科學家和汽車制造商致力于改善燃油經(jīng)濟性，控制廢氣排放；同時政府正積極采取措施來解決交通問題。 2自動變速器 什么是變速器？ 變速器是一個連接到發(fā)動機的背后和發(fā)送來自發(fā)動機的功率以驅(qū)動車輪的裝置。汽車發(fā)動機在一定轉(zhuǎn)速（旋轉(zhuǎn)/分鐘）處于最佳運行的范圍時，它的職責是傳輸以確保動力被傳遞到車輪使保持在該范圍內(nèi)的發(fā)動機通過不同的齒輪聯(lián)合工作。在低速檔，發(fā)動機會使驅(qū)動輪轉(zhuǎn)得更快而在高速運轉(zhuǎn)時的發(fā)動機則是在偷懶----即汽車可能會在70邁的速度持續(xù)。除了各前進檔，傳輸也有個空擋即車輪斷開驅(qū)動和倒檔----驅(qū)動輪向相反的方向運動。最后，還有抱死的位置，在這個位置上，一種閉鎖裝置（不同于那些房門上呆板的自動鎖）是在輸出軸槽中插入鎖定驅(qū)動器以防止車輪轉(zhuǎn)動從而防止車輛滑動。 現(xiàn)代的自動變速箱是迄今為止，在今天的汽車中最復雜的機械部件。自動變速器包含機械系統(tǒng)，液壓系統(tǒng)，電氣系統(tǒng)和計算機控制，所有的工作中去幾乎沒有注意的完美和諧在一起，直到有一個問題。對于現(xiàn)代的汽車，自動變速器是一個復雜的組件，這種傳遞動力的方式，是液力變矩期充當離合器來連接發(fā)動機和變速器。 兩個基本類型的自動變速器基于該車輛是否是前驅(qū)動或后驅(qū)動。對發(fā)動機前置后驅(qū)動的汽車，變速器通常安裝在發(fā)動機后底盤中心與油門配合。變速器輸出軸連接到后橋，把發(fā)動機的動力傳遞到后輪，動力傳輸系統(tǒng)是直線的，從發(fā)動機通過液力變矩器、變速器、傳動軸、最后直接到到達車輪。 對于發(fā)動機前置前輪驅(qū)動的汽車，變速器通常和差速器裝在一起。對于前驅(qū)動的汽車，變速器安裝在發(fā)動機一側(cè)，前車軸直接連接到差速器上，把動力傳遞給前輪。在這個布置中，動力來自于發(fā)動機，通過液力變矩器、變速器輸出的動力通過了一個180度大轉(zhuǎn)彎，經(jīng)過變速器沿發(fā)動機側(cè)邊通過傳動軸輸出到前輪。 還有其它的一些布置，發(fā)動機前置前驅(qū)動，發(fā)動機橫向布置，裝設(shè)一個分動器可以實現(xiàn)四輪驅(qū)動。但這種形式目前是最常用的：發(fā)動機中置后驅(qū)動，可以使重量均勻的分布在前、后輪之間，改善了操作性能；發(fā)動機后置后驅(qū)動，發(fā)動機、變速器、驅(qū)動輪都在后方，這種后置式的發(fā)動機的安排，是最滿意的。 現(xiàn)代的自動變速器包括了許多組件和系統(tǒng)的協(xié)同工作，有行星齒輪組、液壓系統(tǒng)、密封件和墊圈、變矩器、調(diào)節(jié)器、節(jié)氣門拉線、計算機控制這些都是多年來由機械式演變過來的。這用簡單、通用的解釋，描述一下這些系統(tǒng)。 2.1行星齒輪組 ? ? 自動變速器箱體內(nèi)有很多齒輪，有各種不同的組合，在一個變速箱內(nèi)，齒輪的滑動沿軸線從一個位置到另一個位置，對各種大小齒輪的要求，有正確的傳動比。在一個自動變速箱，至始至終，不是齒輪的機械移動來達到這一點的，通過行星齒輪組來完成。 基本的行星齒輪組成由一個太陽輪、一個齒圈、并且有兩個或兩個以上的行星齒輪，全部齒輪都是常嚙合。行星齒輪的相互聯(lián)系通過一個共同的載體，使齒輪相互嚙合在一起。一個傳遞方式，這個系統(tǒng)可以從發(fā)動機的輸出連接到齒圈作為主動件，連接行星輪作為從動件，并鎖定太陽輪，使起不能轉(zhuǎn)動。在這情況下，當我們把齒圈、行星齒輪，沿太陽輪轉(zhuǎn)動，主動件與從動件就同向轉(zhuǎn)動，從動件的轉(zhuǎn)速慢，齒輪減速就類似汽車的一擋。 如果解開太陽輪和鎖定其它兩個元素，這就會使這三個要素以同樣的速度轉(zhuǎn)動，齒輪的傳動就類似于汽車是第三或高擋位。另一個方式是，把行星架鎖定，使太陽輪作為主動輪，齒圈作為從動件，這時它們的轉(zhuǎn)動方向就相反，就類似以汽車的到擋。 上面所說的，在實際的傳動過程是如何控制。齒圈為輸入軸，行星架為輸出軸，都是通過盤式離合器控制。太陽輪一個單向離合器，一個制動器，當制動器作用時，太陽輪只能從一個方向轉(zhuǎn)動。 在這情況下，離合器的使用，鎖定行星架與太陽輪迫使它們以相同的轉(zhuǎn)速轉(zhuǎn)動。如果它們的離合器和制動器都被釋放，該系統(tǒng)在自由狀態(tài)。變速器的行星齒輪組太陽輪是自由的，比輸出動力。在一擋位，制動器制動太陽輪跟隨轉(zhuǎn)動，從第一擋到高擋制動器釋放和離合器使用到輸入軸，它們以同一個速度轉(zhuǎn)動。 使用兩個或兩個以上的行星齒輪組以各種方式連接，可提供不同的前進速度和扭矩，普遍的使用以現(xiàn)代的自動變速器。 2.2 片式離合器 片式離合器主要由若干交替排列的離合器盤和離合器片組成。每片離合器盤上有伸出的突線，勾住離合器鼓，以輸入軸連接。離合器片內(nèi)的鍵槽與離合器殼互相嚙合，離合器殼與中間軸鍵槽連接，中間軸又與后行星排內(nèi)齒圈用鍵槽連接。因此，離合器盤和離合器片分別與輸入軸和湖行星排內(nèi)齒圈連接。操作離合器的活塞安裝以離合器鼓上，離合器鼓亦稱做為活塞缸。 2.3 單向離合器 單向離合器是一種只可以使元件在一個方向轉(zhuǎn)動，如把齒圈自由在一貫方向，而不能反向轉(zhuǎn)動，這種作用就象是，自行車踏板轉(zhuǎn)動時，可以帶動車輪轉(zhuǎn)動，當車輪轉(zhuǎn)動或向另一個方向轉(zhuǎn)動是自由的 一個單向離合器用于一擋時，在驅(qū)動方向是，當從停止開始加速，在第一個齒輪輸出動力，如果繼續(xù)加速，不在一擋位？汽車繼續(xù)加速，他就是一個方向自由的。此時，單向離合器不在輸出動力，當車速慢下來時，轉(zhuǎn)速慢，它就可以起作用。這一個現(xiàn)象由于，在提供力的時候它才起作用，在高速時，是自由的。 2.4 液力變矩器 對于自動變速器，液力變矩器取代離合器裝于車上。它的作用是：當車停下來，發(fā)動機還可以繼續(xù)運轉(zhuǎn)。傳遞扭矩的原理，比如，把一個風扇吹向另一個，另一個不用插電也能跟它一起轉(zhuǎn)動，如果你壓住扇片，它就不會轉(zhuǎn)動，但你一放手，它就開始加速，直到速度接近動力風扇。它們兩者的差異就是：變矩器不是利用空氣，而是利用油液，以使他的傳遞更加準確。 液力變矩器是一個較大的盆壯裝置，安裝在發(fā)動機與變速器之間。它包含三個部件，協(xié)同工作，為變速器提供動力，液力變矩器的三要素是：泵論、渦輪、導輪，泵論是通過螺栓直接安裝在發(fā)動機的曲軸上，轉(zhuǎn)速與發(fā)動機的相同，渦輪連接到變速器的輸入軸上，為汽車提供動力，導輪上裝有一個單向離合器，使他只可以在一個方向轉(zhuǎn)動，而在另一方被固定，每一個要素之間通過液流傳遞扭矩。 發(fā)動機啟動后，輸入軸開始旋轉(zhuǎn)，帶動泵輪旋轉(zhuǎn)，因旋轉(zhuǎn)產(chǎn)生的離心力使泵輪葉片間的液流沿葉片從外緣向外甩出；接著又由于泵輪和渦輪轉(zhuǎn)速差引起泵輪葉片外緣與渦輪葉片外緣產(chǎn)生了壓力差，液流從液壓高的泵輪葉片外緣流進渦輪葉片外緣，同時，泵輪的旋轉(zhuǎn)也使得其葉片帶動液流隨工作輪旋轉(zhuǎn)，這一旋轉(zhuǎn)就使液流流進渦輪時方向改變，從而沖擊渦輪葉片推動渦輪繞泵輪同一方向旋轉(zhuǎn)。從渦輪流出的液流進入固定不動的導輪，經(jīng)導輪葉片改變方向后回流至泵輪。如果渦輪的速度大大低于泵輪轉(zhuǎn)素時，導輪仍鎖住不動。導輪停止，液流通過導輪時重新進入泵輪，促使泵輪旋轉(zhuǎn)起到扭矩增大的作用。由于泵輪和導輪的轉(zhuǎn)速增加，液流開始改變方向流向泵輪葉片背面，也可以產(chǎn)生增矩的作用。由于車速的提高，這三要素句以相同的轉(zhuǎn)速旋轉(zhuǎn)，為了提高燃油經(jīng)濟性，在液力變矩器上裝了一個鎖止離合器，車速達到40—50英里的時候，鎖止離合器就把三要素連為一體，這種控制是計算機控制。 2.5 液壓系統(tǒng) 液壓系統(tǒng)是一個復雜的迷宮壯通道，液流壓力控制變速器扭矩的輸出。液流有若干用途，包括：換擋控制、潤滑、冷卻。不象發(fā)動機，它只用來潤滑，每一個流動，是依賴于不斷提供的液體壓力。為了使油液在一個正常的溫度工作，部分液流從散熱器中流過以便散熱。液體通過此通道被冷卻，然后返回到傳輸通道。液里變矩器和散熱器，是用來給液流散熱的。事實上大部分的摩擦表面都淹沒在油液中，比如：離合器盤、離合器片，也能正常的工作。 2.6 油泵 油泵主要是負責提供油液傳輸過程中的壓力，油泵安裝在前面的泵輪上，并且以發(fā)動機的曲軸相連，當發(fā)動機轉(zhuǎn)動時，帶動油泵運轉(zhuǎn)，產(chǎn)生壓力，提供足夠的油。油進入油泵時通過一個空氣濾清器，安裝在油底殼的底部。壓力調(diào)節(jié)器、調(diào)壓閥、壓力修正閥調(diào)節(jié)后送到各個管路。 2.7 閥體 閥體是自動變速器的控制中心。它包含一個迷宮壯的通道輸送液壓油，在每一個工況下控制離合器和其它伺服機構(gòu)，順利的控制齒輪傳動情況。 最重要的閥門一個直接控制的手動閥。手動閥是直接連接到齒輪變速箱里面的，根據(jù)它所在位置打開或關(guān)閉各種通道，控制換擋節(jié)奏。用齒輪變速傳動來舉例說明，監(jiān)控車輛的速度和油門的位置，以便它能確定最佳的換擋時間，。計算機的控制，通過電磁閥控制油壓壓力，控制離合器或制動器，以更精確的控制換擋點。 2.8 密封墊和墊圈 一個自動變速器有許多的密封件和墊圈，以控制流動的液壓油，使它不外泄。主要有兩個外部密封墊：前油封和后油封。前油封安裝到變速器的變矩器，這使得油底殼到變矩器的油液能自由流動，而不外泄。后密封墊使游液不泄漏到輸出軸。 密封墊通常用橡膠（類似汽車擋風玻璃雨刮器葉片），它是用來保持不泄漏到其它部分，如旋轉(zhuǎn)軸。在有的情況下，用一個彈簧和橡膠在一起，如用在花鍵軸。 墊圈是一種用來密封兩個固定部分，使其連接在一起。一些常見的襯墊材料是：硬紙、軟木、橡膠、有機硅和軟金屬。 除了主要的密封墊，也有一些其它的密封墊和墊片，因使用條件而定，有的從軸到軸的連接。一個常見的例子是橡膠O型密封圈用來密封換的擋軸。就是說，你所操作的邊速杠在轉(zhuǎn)動時，另一個例子是大部分常見的油底殼墊片，事實上，密封墊是隨時進行更換，防止油不泄漏。 2.9計算機控制 計算機控制是利用傳感器對發(fā)動機和變速器提取數(shù)據(jù)，因為節(jié)氣門位置、汽車行駛速度、發(fā)動機轉(zhuǎn)速、發(fā)動機負荷等是變數(shù)。利用這些數(shù)據(jù)可以精確控制換擋點，以便換擋平順。一些電腦數(shù)據(jù)，能了解行駛條件，并不斷的適應行駛條件的變化，使汽車穩(wěn)定的行駛。 由于計算機的控制，通過一個特殊的元素代替了手動控制，在每一個工況都是安全的。計算機的控制，確保發(fā)動機轉(zhuǎn)速不至于過高而使發(fā)動機損壞。 另一個好處是，這些精確的數(shù)據(jù)輸入系統(tǒng)，有一個自診斷系統(tǒng)，以便能使我們及時的發(fā)現(xiàn)問題，當有問題時，故障指示燈就閃爍。維修人員就可以根據(jù)檢測設(shè)備檢測出的故障碼，很快的找到問題所在部位。 參考文獻 [1]岡村和柏原，傳輸?shù)陌l(fā)展3KType無級變速（第一次報告，傳動設(shè)計）。 JSME，C系列57-538，（1991），288-293。 [2]弗蘭克·NAJLEPSZY，機械設(shè)計，57-25（1985），68-75 本科畢業(yè)設(shè)計英文參考資料 題 目Structure of Automobile and Automatic Transmission 院 系 機 械 學 院 專 業(yè) 機械設(shè)計制造及其自動化 姓 名_ 學 號 學習年限 指導教師 申請學位 2012年 5 月 10 日 英文原文 Structure of Automobile and Automatic Transmission 1 Structure of Automobile The car is one of the most fascinating devices that a person can own. Cars are also one of the most pervasive devices, A car contains dozens of different technologies. Everything from the engine to the tires is its own special universe of design and engineering. But any automobiles are made up of four basic sections: engine, chassis, body and electrical system. As the source of power, the engine requires a fuel system to supply with fuel or the mixture of air and fuel. It plays a vital role in the power-producing process. Suppose the engine is a gasoline engine, the fuel system pumps liquid gasoline from a tank into the carburetor where the gasoline can be mixed with air. The mixture is delivered to the engine where it is burned. If the engine is EFI engine, fuel is delivered from the tank to the injector by means of an electric fuel pump. The fuel injectors, which directly controls fuel metering to the intake manifold, is pulsed by the ECU. The ECU determines air/fuel ratio of the engine according to engine condition. A chassis which is considered as a support frame for an auto body is used to assemble all auto spare parts on it. In fact, when power from engine continues to be transmitted to chassis, it begins with power train, goes on to steering, wheel suspension, brakes and tires. These individual components interact with each other closely. In effect, the driving system works by transmitting engine power to the driving wheels. The driving system consists of the clutch, transmission, universal joint, driving axle, etc. With the rapid development of automobile industry, the new models of automobiles are becoming better and better in design and performance. When automobiles are very popular with people, many negative problems corresponding to the facts have to be considered by scientists, such as energy crisis, air pollution and traffic jam. So scientists and auto manufacturers are doing their best to improve fuel economy, control exhaust emissions; the governments are taking active measures to resolve traffic problems at the same time. The automobile body which is regarded as the framework is seated on the chassis. Its function is obvious for occupants to provide comfort, protection and shelter. The automobile body is generally divided into four sections: the front, the upper or top, rear and the underbody. These sections are further divided into small units, such as the hood, the fenders, the roof panels, the door, the instrument panel, the bumpers and the luggage compartment. The electrical system is considered an auto electric power source supplies lighting power for the automobile. The electrical system contains battery, lights, generator, engine ignition, lighting circuit, and various switches that control their use. 2 Automatic Transmission What is a transmission? The transmission is a device that is connected to the back of the engine and sends the power from the engine to the drive wheels.? An automobile engine runs at its best at a certain RPM (Revolutions Per Minute) range and it is the transmission's job to make sure that the power is delivered to the wheels while keeping the engine within that range.? It does this through various gear combinations. In first gear, the engine turns much faster in relation to the drive wheels, while in high gear the engine is loafing even though the car may be going in excess of 70 MPH.? In addition to the various forward gears, a transmission also has a neutral position which disconnects the engine from the drive wheels, and reverse, which causes the drive wheels to turn in the opposite direction allowing you to back up.? Finally, there is the Park position.? In this position, a latch mechanism (not unlike a deadbolt lock on a door) is inserted into a slot in the output shaft to lock the drive wheels and keep them from turning, thereby preventing the vehicle from rolling. The modern automatic transmission is by far, the most complicated mechanical component in today's automobile.? Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony which goes virtually unnoticed until there is a problem.The modern automatic transmission is by far , the most complicated mechanical component in today’s automobile . It is a type of transmission that sifts itself . A fluid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine . There are two basic types of automatic transmission based on whether the vehicle is rear wheel drive or front wheel drive . On a rear wheel drive car , the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position . A drive shaft connects the transmission to the final drive which is located in the rear axle and is used to send power to the rear wheels . Power flow on this system is simple and straight forward going from the engine , through the torque converter , then trough the transmission and drive shaft until it reaches the final drive where it is split and sent to the two rear transmission . On a front wheel drive car , the transmission is usually combined with the final drive to form what is called a transaxle . The engine on a front wheel drive car is usually mounted sideways in the car with the transaxle tucked under it on the side of the engine facing the rear of the car . Front axles are connected directly to the transaxle and provide power to front wheels . In this example , power floes from the engine , through the torque converter to a larger chain that sends the power through a 180 degree turn to the transmission that is along side the engine . From there , the power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles . There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of sideways and there are other systems that drive all four wheels but the two systems described here are by far the most popular . A much less popular rear and is connected by a drive shaft to the torque converter which is still mounted on the engine . This system is found on the new Corvette and is used in order to balance the weight evenly between the front and rear wheels for improved performance and handling . Another rear drive system mounts everything , the engine , transmission and final drive in the rear . This rear engine arrangement is popular on the Porsche. The modern automatic transmission consists of many components and systems that designed to work together in a symphony of planetary gear sets , the hydraulic system, seals and gaskets , the torque converter , the governor and the modulator or throttle cable and computer controls that has evolved over the years into what many mechanical inclined individuals consider to be an art from . Here try to used simple , generic explanation where possible to describe these systems . 2.1 Planetary gear sets Automatic transmission contain many gears in various combinations . In a manual transmission , gears slide along shafts as you move the shift lever from one position to another , engaging various sizes gears as required in order to provide the correct gear ratio . In an automatic transmission , how ever , the gears are never physically moved and are always engaged to the same gears . This is accomplished through the use of planetary gear sets . The basic planetary gear set consists of a sun gear , a ring and two or more planet gears , all remaining in constant mesh . The planet gears are connected to each other through a common carrier which allows the gears to spin on shafts called “pinions” which are attached to the carrier . One example of a way that this system can be used is by connecting the ring gear to the input shaft coming from the engine , connecting the planet carrier to the output shaft , and locking the sun gear so that it can’t move . In this scenario , when we turn the ring gear , the planets will “walk” along the sun gear ( which is held stationary ) causing the planet carrier to turn the output shaft in the same direction as the input shaft but at a slower speed causing gear reduction ( similar to a car in first gear ) . If we unlock the sun gear and lock any two elements together , this will cause all three elements to turn at the same speed so that to output shaft will turn at the same rate of speed as the input shaft . This is like a car that is third or high gear . Another way we can use a planetary gear set is by locking the planet carrier from moving , then applying power to the ring gear which will cause the sun gear to turn in opposite direction giving us reverse gear . The illustration in Figure shows how the simple system described above would look in an actual transmission . The input shaft is connected to the ring gear , the output shaft is connected to the planet carrier which is also connected to a “Multi-disk” clutch pack . The sun gear is connected to drum which is also connected to the other half of the clutch pack . Surrounding the outside of the drum is a band that can be tightened around the drum when required to prevent the drum with the attached sun gear from turning . The clutch pack is used , in this instance , to lock the planet carrier with the sun gear forcing both to turn at the same speed . If both the clutch pack and the band were released , the system would be in neutral . Turning the input shaft would turn the planet gears against the sun gear , but since noting is holding the sun gear , it will just spin free and have no effect on the output shaft . To place the unit in first gear , the band is applied to hold the sun gear from moving . To shift from first to high gear , the band is released and the clutch is applied causing the output shaft to turn at the same speed as the input shaft . Many more combinations are possible using two or more planetary sets connected in various way to provide the different forward speeds and reverse that are found in modern automatic transmission . 2.2 Clutch pack A clutch pack consists of alternating disks that fit inside a clutch drum . Half of the disks are steel and have splines that fit into groves on the inside of the drum . The other half have a friction material bonded to their surface and have splines on the inside edge that fit groves on the outer surface of the adjoining hub . There is a piston inside the drum that is activated by oil pressure at the appropriate time to squeeze the clutch pack together so that the two components become locked and turn as one . 2.3 One-way Clutch A one-way clutch ( also known as a “sprag” clutch ) is a device that will allow a component such as ring gear to turn freely in one direction but not in the other . This effect is just like that bicycle , where the pedals will turn the wheel when pedaling forward , but will spin free when pedaling backward . A common place where a one-way clutch is used is in first gear when the shifter is in the drive position . When you begin to accelerate from a stop , the transmission starts out in first gear . But have you ever noticed what happens if you release the gas while it is still in first gear ? The vehicle continues to coast as if you were in neutral . Now , shift into Low gear instead of Drive . When you let go of the gas in this case , you will feel the engine slow you down just like a standard shift car . The reason for this is that in Drive , one-way clutch is used whereas in Low , a clutch pack or a band is used . 2.4 Torque Converter On automatic transmission , the torque converter takes the place of the clutch found on standard shift vehicles . It is there to allow the engine to continue running when the vehicle comes to a stop . The principle behind a torque converter is like taking a fan that is plugged into the wall and blowing air into another fan which is unplugged . If you grab the blade on the unplugged fan , you are able to hold it from turning but as soon as you let go , it will begin to speed up until it comes close to speed of the powered fan . The difference with a torque converter is that instead of using air it used oil or transmission fluid , to be more precise . A torque converter is a lager doughnut shaped device that is mounted between the engine and the transmission . It consists of three internal elements that work together to transmit power to the transmission . The three elements of the torque converter are the pump , the Turbine , and the Stator . The pump is mounted directly to the torque housing which in turn is bolted directly to the engine’s crankshaft and turns at engine speed . The turbine is inside the housing and is connected directly to the input shaft of the transmission providing power to move the vehicle . The stator is mounted to a one-way clutch so that it can spin freely in one direction but not in the other . Each of the three elements has fins mounted in them to precisely direct the flow of oil through the converter . With the engine running , transmission fluid is pulled into the pump section and is pushed outward by centrifugal force until it reaches the turbine section which stars it running . The fluid continues in a circular motion back towards the center of the turbine where it enters the stator . If the turbine is moving considerably slower than the pump , the fluid will make contact with the front of the stator fins which push the stator into the one way clutch and prevent it from turning . With the stator stopped , the fluid is directed by the stator fins to re-enter the pump at a “help” angle providing a torque increase . As the speed of the turbine catches up with the pump , the fluid starts hitting the stator blades on the back-side causing the stator to turn in the same direction as the pump and turbine . As the speed increase , all three elements begin to turn at approximately the same speed . Sine the ‘80s , in order to improve fuel economy , torque converters have been equipped with a lockup clutch which locks the turbine to the pump as the vehicle reaches approximately 40-50 mph . This lockup is controlled by computer and usually won’t engage unless the transmission is in 3rd or 4th gear . 2.5 Hydraulic System The hydraulic system is a complex maze of passage and tubes that sends that sends transmission fluid and under pressure to all parts of the transmission and torque converter and . Transmission fluid serves a number of purpose including : shift control ,general lubrication and transmission cooling . Unlike the engine ,which uses oil primary for lubrication ,every aspect of a transmission ‘s function is dependant on a constant supply of fluid is send pressure . In order to keep the transmission at normal operating temperature , a portion of the fluid is send to through one of two steel tubes to a special chamber that is submerged in anti-freeze in the radiator . Fluid passing through this chamber is cooled and then returned to the transmission through the other steel tube . A typical transmission has an avenge of ten quarts of fluid between the transmission , torque converter , and cooler tank , In fact , most of the components of a transmission are constantly submerged in fluid including the clutch packs and bands . The friction surfaces on these parts are designed to operate properly only when they are submerged in oil . 2.6 Oil Pump The transmission oil pump ( not to confused with the pump element inside the torque converter ) is responsible for producing all the oil pressure that is required in the transmission . The oil pump is mounted to front of the transmission case and is directly connected to a flange on the engine crankshaft , the pump will produce pressure whenever the engine is running as there is a sufficient amount of transmission fluid available . The oil enters the pump through a filter that is located at bottom of the transmission oil pan and travels up a pickup tube directly to the oil pump . The oil is then sent , under pressure to the pressure regulator , the valve body and the rest of the components , as required . 2.7 Valve Body The valve body is the control center of the automatic transmission . It contains a maze of channels and passages that direct hydraulic fluid to the numerous valves which when activate the appropriate clutch pack of band servo to smoothly shift to the appropriate gear for each driving situation . Each of the many valves in the valve body has a specific purpose and is named for that function . For example the 2-3 shift valve activates the 2nd gear up-shift or the 3-2 shift timing valve which determines when a downshift should occur . The most important valve and the one that you have direct control over is the manual valve. The manual valve is directly connected to the gear shift handle and covers and uncovers various passages depending on what position the gear shift is paced in . When you place the gear shift in Drive , for instance , the manual valve directs fluid to the clutch pack ( s ) that activates 1st gear . It also sets up to monitor vehicle speed and throttle position so that it can determine the optimal time and the force for the 1-2 shift . On computer controlled transmission , you will also have electrical solenoids that are mounted in the valve body to direct fluid to the appropriate clutch packs or bands under computer control to more precisely control shift points . 2.8 Seals and Gaskets An automatic transmission has many seals and gaskets to control the flow of hydraulic fluid and to keep it from leaking out . There are two main external seals : the front seal and the rear seal . The front seal seals the point where the torque converter mounts to the transmission case . This seal allows fluid to freely move from the converter to the transmission but keeps the fluid from leaking out. The rear seal keeps fluid from leaking past the output shaft. A seal is usually made of rubber (similar to the rubber in a windshield wiper blade) and is used to keep oil from leaking past a moving part such as a spinning shaft. In some cases, the rubber is assisted by a spring that holds he rubber in close contact with the spinning shaft. A gasket is a type of seal used to seal two stationary parts that are fasted together. Some common gasket materials are: paper, cork, rubber , silicone and soft metal . Aside from the main seals, there are also a number of other seals and gasket that vary from transmission to transmission. A common example is the rubber O-ring that seals the shaft for the shift control lever. This is the shaft that you move when you manipulate the gear shifter. Another example that is common to most transmission is the oil pan gasket. In fact, seals are required anywhere that a device needs to pass through the transmission case with each one being a potential source for leaks. 2.9 Computer Controls The computer uses sensors on the engine and transmission to detect such things as throttle position, vehicle speed , engine speed , engine load , stop light switch position , etc .to control exact shift points as well as how soft or firm the shift should be . Some computerized transmission even learn your driving style and constantly adapt to it so that every shift is timed precisely when you would need it. Because of computer controls , sports models are coming out with the ability to take manual control of the transmission as through it were a stick shift lever through a special gate , then tapping it in one direction or the other in order to