1、Automatic TransmissionThe modern automatic transmission is by far , the most complicated mechanical component in todays 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
2、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 ga
3、s 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
4、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 t
5、he 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
6、 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 vehic
7、les 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 e
8、ngine . 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 arrangem
9、ent 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 compute
10、r 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 .1）Planetary gear sets Automatic transmission contain many gears in various combinations . In
11、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 t
12、he 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 s
13、pin 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 cant move . In this
14、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 ) . 2）Clutch pack
15、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 s
16、urface 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 . 3）One-way Clutch A one-way clutch ( also known as a “sprag” clutch ) is a device th
17、at 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 firs
18、t 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 , s
19、hift 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 . 4）Torque Converter On automatic tra
20、nsmission , 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 difference with a torque converter is that instead of using air it used oil or transmission fluid , to be more
21、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 S
22、tator . The pump is mounted directly to the torque housing which in turn is bolted directly to the engines 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 mou
23、nted 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 outwa
24、rd 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 o
25、f 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 start
26、s 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 wi
27、th 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 wont engage unless the transmission is in 3rd or 4th gear . 5）Hydraulic System The hydraulic system is a complex maze of passage and tubes that se
28、nds 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 as
29、pect of a transmission s function is depend 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 . Fl
30、uid 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 constantl
31、y 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 .6）Oil Pump The transmission oil pump ( not to confused with the pump element inside the torque converter ) is responsible for produci
32、ng 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 flui
33、d 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 . 7）Valve
34、 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
35、 . 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
36、 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 pac
37、k ( 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 flui
38、d to the appropriate clutch packs or bands under computer control to more precisely control shift points .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 se
39、al 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
40、 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
41、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 r
42、ubber 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 transmissio
43、n case with each one being a potential source for leaks .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
44、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 .自动变速器对于现代的汽车，自动变速器是一个复杂的组件，这种传递动力的方式，是液力变矩期充当离合器来连接发动机和变速器。两个基本类型的自动变速器基于该车辆是否是前驱动或后驱动。对发动机前置后驱动的汽车，变速器通常安装在发动
45、机后底盘中心与油门配合。变速器输出轴连接到后桥，把发动机的动力传递到后轮，动力传输系统是直线的，从发动机，通过液力变矩器、变速器、传动轴、最后直接到到达车轮。对于发动机前置前轮驱动的汽车，变速器通常和差速器装在一起。对于前驱动的汽车，变速器安装在发动机一侧，前车轴直接连接到差速器上，把动力传递给前轮。在这个布置中，动力来自于发动机，通过液力变矩器、变速器输出的动力通过了一个 180 度大转弯，经过变速器沿发动机侧边通过传动轴输出到前轮。还有其它的一些布置，发动机前置前驱动，发动机横向布置，装设一个分动器可以实现四轮驱动。但这种形式目前是最常用的：发动机中置后驱动，可以使重量均匀的分布在前、后轮
46、之间，改善了操作性能；发动机后置后驱动，发动机、变速器、驱动轮都在后方，这种后置式的发动机的安排，是最满意的。现代的自动变速器包括了许多组件和系统的协同工作，有行星齿轮组、液压系统、密封件和垫圈、变矩器、调节器、节气门拉线、计算机控制这些都是多年来由机械式演变过来的。这用简单、通用的解释，描述一下这些系统。1）行星齿轮组自动变速器箱体内有很多齿轮，有各种不同的组合，在一个变速箱内，齿轮的滑动沿轴线从一个位置到另一个位置，对各种大小齿轮的要求，有正确的传动比。在一个自动变速箱，至始至终，不是齿轮的机械移动来达到这一点的，通过行星齿轮组来完成。基本的行星齿轮组成由一个太阳轮、一个齿圈、并且有两个或
47、两个以上的行星齿轮，全部齿轮都是常啮合。行星齿轮的相互联系通过一个共同的载体，使齿轮相互啮合在一起。一个传递方式，这个系统可以从发动机的输出连接到齿圈作为主动件，连接行星轮作为从动件，并锁定太阳轮，使起不能转动。在这情况下，当我们把齿圈、行星齿轮，沿太阳轮转动，主动件与从动件就同向转动，从动件的转速慢，齿轮减速就类似汽车的一挡。2）片式离合器片式离合器主要由若干交替排列的离合器盘和离合器片组成。每片离合器盘上有伸出的突线，勾住离合器鼓，以输入轴连接。离合器片内的键槽与离合器壳互相啮合，离合器壳与中间轴键槽连接，中间轴又与后行星排内齿圈用键槽连接。因此，离合器盘和离合器片分别与输入轴和湖行星排内
48、齿圈连接。操作离合器的活塞安装以离合器鼓上，离合器鼓亦称做为活塞缸。3）单向离合器单向离合器是一种只可以使元件在一个方向转动，如把齿圈自由在一贯方向，而不能反向转动，这种作用就象是，自行车踏板转动时，可以带动车轮转动，当车轮转动或向另一个方向转动是自由的一个单向离合器用于一挡时，在驱动方向是，当从停止开始加速，在第一个齿轮输出动力，如果继续加速，不在一挡位？汽车继续加速，他就是一个方向自由的。此时，单向离合器不在输出动力，当车速慢下来时，转速慢，它就可以起作用。这一个现象由于，在提供力的时候它才起作用，在高速时，是自由的。4）液力变矩器对于自动变速器，液力变矩器取代离合器装于车上。它的作用是：
49、当车停下来，发动机还可以继续运转。它们两者的差异就是：变矩器不是利用空气，而是利用油液，以使他的传递更加准确。液力变矩器是一个较大的盆壮装置，安装在发动机与变速器之间。它包含三个部件，协同工作，为变速器提供动力，液力变矩器的三要素是：泵论、涡轮、导轮，泵论是通过螺栓直接安装在发动机的曲轴上，转速与发动机的相同，涡轮连接到变速器的输入轴上，为汽车提供动力，导轮上装有一个单向离合器，使他只可以在一个方向转动，而在另一方被固定，每一个要素之间通过液流传递扭矩。发动机启动后，输入轴开始旋转，带动泵轮旋转，因旋转产生的离心力使泵轮叶片间的液流沿叶片从外缘向外甩出；接着又由于泵轮和涡轮转速差引起泵轮叶片外缘与涡轮叶片外缘产生了压力差，液流从液压高的泵轮叶片外缘流进涡轮叶片外缘，同时，泵轮的旋转也使得其叶片带动液流随工作轮旋转，这一旋转就使液流流进涡轮时方向改变，从而冲击涡轮叶片推动涡轮绕泵轮同一方向旋转。从涡轮流出的液流进入固定不动的导轮，经导轮叶片改变方向后回流至泵轮。如果涡轮的速度大大低于泵轮转素时，导轮仍锁住不动。导轮停止，液流通过导轮时重新进入泵轮，促使泵轮旋转起到扭矩增大的作用。由于泵轮和导轮的转速增加，液流开始改变方向流向泵轮叶片背面，也可以产生增矩的作用。由于车速的提高，这三要素句以相同的转速旋转，为了提高燃油经济性，在液力变
