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 .
對于現代的汽車，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動或后驅動。對發(fā)動機前置后驅動的汽車，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)動機前置前輪驅動的汽車，變速器通常和差速器裝在一起。對于前驅動的汽車，變速器安裝在發(fā)動機一側，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度大轉彎，經過變速器沿發(fā)動機側邊通過傳動軸輸出到前輪。
還有其它的一些布置，發(fā)動機前置前驅動，發(fā)動機橫向布置，裝設一個分動器可以實現四輪驅動。但這種形式目前是最常用的：發(fā)動機中置后驅動，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)動機后置后驅動，發(fā)動機、變速器、驅動輪都在后方，這