1、 1 中文 3860 字 How Automatic Transmissions Work by Karim Nice Introduction to 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
2、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
3、 thing, but they do it in totally different ways. It turns out that the way an automatic transmission does it is absolutely amazing! Automatic Transmission Image Gallery 2 In this article, well work our way through an automatic transmission. Well start with the key to the whole system: planetary gea
4、rsets. 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. Just like that of a manual transmission, the automatic transmissions primary job is to allow the engine to operate in its narrow range of
5、 speeds while providing a wide range of output speeds. Photo courtesy DaimlerChrysler Mercedes-Benz CLK, automatic transmission, cut-away model 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 spee
6、d. 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, an
7、d 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 undriveable. So the transmission uses gears to make more effective use of the engines torque, and to keep the engine operating at an appropriate speed. 3 The key d
8、ifference 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 planetar
9、y gearset is the device that makes this possible in an automatic transmission. Lets take a look at how the planetary gearset works. Planetary Gearsets & Gear Ratios When you take apart and look inside an automatic transmission, you find a huge An ingenious planetary gearset A set of bands to lock pa
10、rts of a gearset A set of three wet-plate clutches to lock other parts of the gearset An incredibly odd hydraulic system that controls the clutches and bands A large gear pump to move transmission fluid around The center of attention is the planetary gearset. About the size of a cantaloupe, this one
11、 part creates all of the different gear ratios that the transmission can produce. Everything else in the transmission is there to help the planetary gearset do its thing. This amazing piece of gearing has appeared on HowStuffWorks before. You may recognize it from the electric screwdriver article. An automatic transmission contains two complete planetary gearsets folded together into one component. See How Gear Ratios Work for an introduction to planetary gearsets. From left to right: the ring gear, planet carrier, and two sun gears
