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1、<p>  AUTOMATIC TRANSMISSION</p><p>  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 f

2、luid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine .</p><p>  There are two basic types of automatic transmission based on whether the v

3、ehicle 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

4、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 </p>&l

5、t;p>  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 t

6、ransaxle 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 , thro

7、ugh the torque converter to a larger chain that sends the power throu</p><p>  There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of sid

8、eways 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 st

9、ill 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</p><p>  The modern automatic transmission consists of

10、 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 com

11、puter 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 .</p>

12、;<p>  1)Planetary gear sets </p><p>  Automatic transmission contain many gears in various combinations . In a manual transmission , gears slide along shafts as you move the shift lever from one po

13、sition 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

14、gears . This is accomplished through the use of planetary gear sets . </p><p>  The basic planetary gear set consists of a sun gear , a ring and two or more planet gears , all remaining in constant mesh . Th

15、e 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 . </p><p>  One example of a way that this syst

16、em 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 tu

17、rn 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 r

18、eduction ( similar to a c</p><p>  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 ra

19、te 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

20、cause the sun gear to turn in opposite direction giving us reverse gear . </p><p>  The illustration in Figure shows how the simple system described above would look in an actual transmission . The input sha

21、ft 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 o

22、f 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 s</p><p>  The clutch pack is used , in this instan

23、ce , 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 plan

24、et 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 m

25、oving . To shift fro</p><p>  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 automa

26、tic transmission . </p><p>  2)Clutch pac

27、k</p><p>  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 fric

28、tion 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

29、 time to squeeze the clutch pack together so that the two components become locked a</p><p>  3)One-way Clutch </p><p>  A one-way clutch ( also known as a “sprag” clutch ) is a device that will

30、 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 ped

31、aling backward . </p><p>  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

32、 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 y

33、ou let go of the gas in this case , you will feel the engine slow you down just like a standard shif</p><p>  4)Torque Converter </p><p>  On automatic transmission , the torque converter take

34、s 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 plu

35、gged 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 co

36、mes clo</p><p>  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

37、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 a

38、nd turns at engine speed . The turbine is inside the housing and is connected directly to </p><p>  With the engine running , transmission fluid is pulled into the pump section and is pushed outward by centr

39、ifugal 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 considerabl

40、y 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 s</p><p>  5)Hydraulic System <

41、/p><p>  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 s

42、erves 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

43、constant supply of fluid is send pressure . In order to keep the transmission a</p><p>  6)Oil Pump </p><p>  The transmission oil pump ( not to confused with the pump element inside the torq

44、ue 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 crank

45、shaft , 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 bot</p><p>

46、  7)Valve Body </p><p>  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 activ

47、ate 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 e

48、xample the 2-3 shift valve activates the 2nd gear up-shift or the 3-2 shift timing valve which deter</p><p>  The most important valve and the one that you have direct control over is the manual valve. The m

49、anual 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 manu

50、al 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 </p><p>  8)Seals and Ga

51、skets </p><p>  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 rea

52、r 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

53、 rear seal keeps fluid from leaking past the output shaft . </p><p>  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

54、 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 .</p><p>  A gasket is a type of seal used to seal two statio

55、nary parts that are fasted together . Some common gasket materials are : paper , cork , rubber , silicone and soft metal . </p><p>  Aside from the main seals , there are also a number of other seals and gas

56、ket 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 ex

57、ample 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 l</p>&l

58、t;p>  9)Computer Controls </p><p>  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

59、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 precis

60、ely when you would need it .</p><p>  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

61、special gate , then tapping it in one direction or the other in order to up-shift at will . The computer monitors this activity to make sure that the driver dose not select a gear that could over speed the engine and dam

62、age it .</p><p>  Another advantage to these “ smart” transmission is that they have a self diagnostic mode which can detect a problem early on and warn you with an indicator light on the dash . A technician

63、 can then plug test equipment in and retrieve a list of trouble codes that will help pinpoint where the problem is .</p><p><b>  自動變速器</b></p><p>  對于現(xiàn)代的汽車,自動變速器是一個復(fù)雜的組件,這種傳遞動力的方式,是液

64、力變矩期充當(dāng)離合器來連接發(fā)動機(jī)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(jī)前置后驅(qū)動的汽車,變速器通常安裝在發(fā)動機(jī)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(jī)的動力傳遞到后輪,動力傳輸系統(tǒng)是直線的,從發(fā)動機(jī),通過液力變矩器、變速器、傳動軸、最后直接到到達(dá)車輪。 對于發(fā)動機(jī)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(jī)一側(cè),前車軸直接連接到差速

65、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(jī),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(jī)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(jī)前置前驅(qū)動,發(fā)動機(jī)橫向布置,裝設(shè)一個分動器可以實(shí)現(xiàn)四輪驅(qū)動。但這種形式目前是最常用的:發(fā)動機(jī)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(jī)后置后驅(qū)動,發(fā)動機(jī)、變速器、驅(qū)動輪都在后方,這種后置式的發(fā)動機(jī)的安排,是最滿意的。

66、 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</p><p>  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(shí)它們的轉(zhuǎn)動方向就相反,就類似以汽車的到擋。</p><p>  上面所說的,在實(shí)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

67、盤式離合器控制。太陽輪一個單向離合器,一個制動器,當(dāng)制動器作用時(shí),太陽輪只能從一個方向轉(zhuǎn)動。</p><p>  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。</p><

68、;p>  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(jìn)速度和扭矩,普遍的使用以現(xiàn)代的自動變速器。</p><p><b>  2)片式離合器</b></p><p>  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

69、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。</p><p>  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(shí),可以帶動車輪轉(zhuǎn)動,當(dāng)車輪轉(zhuǎn)動或向另一個方向轉(zhuǎn)動是自由的</p><p>  一個單向離合

70、器用于一擋時(shí),在驅(qū)動方向是,當(dāng)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?yán)^續(xù)加速,他就是一個方向自由的。此時(shí),單向離合器不在輸出動力,當(dāng)車速慢下來時(shí),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(shí)候它才起作用,在高速時(shí),是自由的。</p><p><b>  4)液力變矩器</b></p><p>  對于自動變速器,液力變矩器取代離合

71、器裝于車上。它的作用是:當(dāng)車停下來,發(fā)動機(jī)還可以繼續(xù)運(yùn)轉(zhuǎn)。傳遞扭矩的原理,比如,把一個風(fēng)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(fēng)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(zhǔn)確。</p><p>  液力變矩器是一個較大的盆壯裝置,安裝在發(fā)動機(jī)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

72、變矩器的三要素是:泵論、渦輪、導(dǎo)輪,泵論是通過螺栓直接安裝在發(fā)動機(jī)的曲軸上,轉(zhuǎn)速與發(fā)動機(jī)的相同,渦輪連接到變速器的輸入軸上,為汽車提供動力,導(dǎo)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。</p><p>  發(fā)動機(jī)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

73、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(jìn)渦輪葉片外緣,同時(shí),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(jìn)渦輪時(shí)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(jìn)入固定不動的導(dǎo)輪,經(jīng)導(dǎo)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(shí),導(dǎo)輪仍鎖住不動。導(dǎo)輪停止,液流通過導(dǎo)輪時(shí)重新進(jìn)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(dǎo)輪的轉(zhuǎn)速增加,液流開始改變方向流向泵輪葉片背面

74、,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(jì)性,在液力變矩器上裝了一個鎖止離合器,車速達(dá)到40—50英里的時(shí)候,鎖止離合器就把三要素連為一體,這種控制是計(jì)算機(jī)控制。</p><p><b>  5)液壓系統(tǒng)</b></p><p>  液壓系統(tǒng)是一個復(fù)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

75、、潤滑、冷卻。不象發(fā)動機(jī),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(shí)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。</p><p><b>  6)油泵</b></p><p>

76、  油泵主要是負(fù)責(zé)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(jī)的曲軸相連,當(dāng)發(fā)動機(jī)轉(zhuǎn)動時(shí),帶動油泵運(yùn)轉(zhuǎn),產(chǎn)生壓力,提供足夠的油。油進(jìn)入油泵時(shí)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。</p><p><b>  7)閥體</b></p><p>  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

77、液壓油,在每一個工況下控制離合器和其它伺服機(jī)構(gòu),順利的控制齒輪傳動情況。</p><p>  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(shí)間,。計(jì)算機(jī)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(diǎn)。</p><p>

78、;<b>  8)密封墊和墊圈</b></p><p>  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。</p><p>  密封墊通常用橡膠(類似汽車擋風(fēng)玻璃雨刮器葉片),它是用來保持不泄漏到其它部分

79、,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。</p><p>  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(jī)硅和軟金屬。</p><p>  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(shí),另一個例子是大部

80、分常見的油底殼墊片,事實(shí)上,密封墊是隨時(shí)進(jìn)行更換,防止油不泄漏。</p><p><b>  9)計(jì)算機(jī)控制</b></p><p>  計(jì)算機(jī)控制是利用傳感器對發(fā)動機(jī)和變速器提取數(shù)據(jù),因?yàn)楣?jié)氣門位置、汽車行駛速度、發(fā)動機(jī)轉(zhuǎn)速、發(fā)動機(jī)負(fù)荷等是變數(shù)。利用這些數(shù)據(jù)可以精確控制換擋點(diǎn),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(yīng)行駛條件的變化,使汽車穩(wěn)定的行駛。

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