自动变速器的工作原理外文翻译中英文翻译外文文献翻译.docx

1、自动变速器的工作原理外文翻译中英文翻译外文文献翻译How Automatic Transmissions Workby Karim NiceIntroduction to How Automatic Transmissions WorkIf 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 n

2、o clutch 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

3、 the same 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 GalleryIn this article, well work our way through an automatic transmission. Well start with the key to the whole system: planetar

4、y gearsets. 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 ran

5、ge of speeds while providing a wide range of output speeds.Photo courtesy DaimlerChryslerMercedes-Benz CLK, automatic transmission, cut-away modelWithout 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 sp

6、eed. 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,

7、and 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. The key di

8、fference 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 planetary

9、 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 RatiosWhen you take apart and look inside an automatic transmission, you find a huge An ingenious planetary gearset A set of bands to lock part

10、s 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 p

11、art 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

12、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 gearsAny planetary gearset has three main components: The sun gear Th

13、e planet gears and the planet gears carrier The ring gear Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset. Lets take a look at a single planetary gearset. One of the planetary gears

14、ets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset.InputOutputStationaryCalculationGear RatioASun (S)Planet Carrier (C)Ring (R)1 + R/S3.4:1BPlanet Carrier (C)Ring (R)Sun (S)1 / (1 + S/R)0.71:1CSun (S)Ring

15、 (R)Planet Carrier (C)-R/S-2.4:1Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a reduction - the output speed is slower than the input speed. The second is an overdrive - the output speed

16、is faster than the input speed. The last is a reduction again, but the output direction is reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the ones that are relevant to our automatic transmission. You can try these out in the animation below:

17、So this one set of gears can produce all of these different gear ratios without having to engage or disengage any other gears. With two of these gearsets in a row, we can get the four forward gears and one reverse gear our transmission needs. Well put the two sets of gears together in the next secti

18、on. Compound Planetary GearsetThis automatic transmission uses a set of gears, called a compound planetary gearset, that looks like a single planetary gearset but actually behaves like two planetary gearsets combined. It has one ring gear that is always the output of the transmission, but it has two

19、 sun gears and two sets of planets. Lets look at some of the parts: How the gears in the transmission are put togetherLeft to right: the ring gear, planet carrier, and two sun gearsThe figure below shows the planets in the planet carrier. Notice how the planet on the right sits lower than the planet

20、 on the left. The planet on the right does not engage the ring gear - it engages the other planet. Only the planet on the left engages the ring gear. Planet carrier: Note the two sets of planets.Next you can see the inside of the planet carrier. The shorter gears are engaged only by the smaller sun

21、gear. The longer planets are engaged by the bigger sun gear and by the smaller planets. Inside the planet carrier: Note the two sets of planets.Automatic Transmission GearsFirst GearIn first gear, the smaller sun gear is driven clockwise by the turbine in the torque converter. The planet carrier tri

22、es to spin counterclockwise, but is held still by the one-way clutch (which only allows rotation in the clockwise direction) and the ring gear turns the output. The small gear has 30 teeth and the ring gear has 72, so the gear ratio is: Ratio = -R/S = - 72/30 = -2.4:1So the rotation is negative 2.4:

23、1, which means that the output direction would be opposite the input direction. But the output direction is really the same as the input direction - this is where the trick with the two sets of planets comes in. The first set of planets engages the second set, and the second set turns the ring gear;

24、 this combination reverses the direction. You can see that this would also cause the bigger sun gear to spin; but because that clutch is released, the bigger sun gear is free to spin in the opposite direction of the turbine (counterclockwise). Second Gear This transmission does something really neat

25、 in order to get the ratio needed for second gear. It acts like two planetary gearsets connected to each other with a common planet carrier. The first stage of the planet carrier actually uses the larger sun gear as the ring gear. So the first stage consists of the sun (the smaller sun gear), the pl

26、anet carrier, and the ring (the larger sun gear). The input is the small sun gear; the ring gear (large sun gear) is held stationary by the band, and the output is the planet carrier. For this stage, with the sun as input, planet carrier as output, and the ring gear fixed, the formula is: 1 + R/S =

27、1 + 36/30 = 2.2:1The planet carrier turns 2.2 times for each rotation of the small sun gear. At the second stage, the planet carrier acts as the input for the second planetary gear set, the larger sun gear (which is held stationary) acts as the sun, and the ring gear acts as the output, so the gear

28、ratio is: 1 / (1 + S/R) = 1 / (1 + 36/72) = 0.67:1To get the overall reduction for second gear, we multiply the first stage by the second, 2.2 x 0.67, to get a 1.47:1 reduction. This may sound wacky, but it works. Third GearMost automatic transmissions have a 1:1 ratio in third gear. Youll remember

29、from the previous section that all we have to do to get a 1:1 output is lock together any two of the three parts of the planetary gear. With the arrangement in this gearset it is even easier - all we have to do is engage the clutches that lock each of the sun gears to the turbine.If both sun gears t

30、urn in the same direction, the planet gears lockup because they can only spin in opposite directions. This locks the ring gear to the planets and causes everything to spin as a unit, producing a 1:1 ratio. OverdriveBy definition, an overdrive has a faster output speed than input speed. Its a speed i

31、ncrease - the opposite of a reduction. In this transmission, engaging the overdrive accomplishes two things at once. If you read How Torque Converters Work, you learned about lockup torque converters. In order to improve efficiency, some cars have a mechanism that locks up the torque converter so th

32、at the output of the engine goes straight to the transmission. In this transmission, when overdrive is engaged, a shaft that is attached to the housing of the torque converter (which is bolted to the flywheel of the engine) is connected by clutch to the planet carrier. The small sun gear freewheels, and the larger sun gear is held by the overdrive band. Nothing is connected to the turbine; the only input comes from the converter housing.