1、附件：外文翻译 外文原文： PASSAGE A Power Train The power train serves two functions： it transmits power from the engine to the drive wheels, and it varies the amount of torque. The power train includes： 1.engine： that produces power； 2.transmission： either manual or automatic；3.clutch： used only on manual tran
2、smission, or torque converter.： used only on automatic transmission； 4.drive shaft： that transmits the power from transmission to differential； 5.that carries the power to the two wheel axles.See Fig.5-1. Manual transmission The function of a manual transmission,shown in Fig.5-2, is to transfer engi
3、ne power to the drive shaft and rear wheels. Gears inside the transmission change the car s drive-wheel speed and torque in relation to engine speed and torque.This keeps the engine s output matched as close as possible to varying road speeds and loads. A manual transaxle， shown in the Fig.5-3.,is a
4、 single unit composed of a manual transmission, differential, and drive axles. Most front-wheel-drive（ FWD） cars are equipped with a transaxle. Such transaxle are also found on some front-engined or rear-wheel-drive （ RWD ） ,four-wheel-drive （ 4WD ） cars and on rear-engined and rear-wheel-drive cars
5、. A manual transmission requires use of a clutch to apply and remove engine torque to the transmission input shaft.The clutch allows this to happpen gradually so that the car can be started from a complete stop. Manual transmission usually have four or five speeds, and often have “ overdrive” , whic
6、h means that the output shaft can turn faster than the input Shaft for fuel economy on the highway. When you use it, it will reduce the engine speed by one-third,while maintaining the same road speed. Clutch Driving a car with a manual transmission, you depress the clutch, select a gear, and release
7、 the clutch while applying power to get the car to move. The clutch allows engine power to be applied gradually when a vehicle is starting out, and interrupts power to avoid gear crunching when shifting. Engaging the clutch allows power to transfer from the engine to transmission and drive wheel. Di
8、sengaging the clutch stops the power transfer and allows the engine to continue turning without force to the drive wheels. The clutch basic components are： the flywheel, clutch disk, pressure plate, release bearing and linkage. See Fig.5-4. The flywheel is bolted to the crankshaft of the engine. Its
9、 main function is to transfer engine torque from the engine to the transmission. The clutch disk is basically a steel plate, covered with a frictional material that goes between the flywheel and the pressure plate. A pressure plate is bolted to the flywheel. It includes a sheet metal cover, heavy re
10、lease springs, a metal pressure ring that provides a friction surface for the clutch disk. The release bearing is the heart of clutch operation. When the clutch pedal is depressed, the throw-out bearing moves toward the flywheel, pushing in the pressure plate s release fingers and moving the pressur
11、e plate fingers or levers against pressure plate spring force. The linkage transmits and multiplies the driver s leg force to the fork of the clutch pressure plate. A mechanical clutch linkage usually consists of the clutch pedal, a series of linkage rods and arms, or a cable. A hydraulic clutch lin
12、kage typically includes a clutch master cylinder and reservoir, a hydraulic line and a slave cylinder. Automatic transmission Both an automatic transmission and a manual transmission accomplish exactly the same thing, but they do it in totally different ways. The key difference between a manual and
13、an automatic transmissions is that the manual transmission locks and unlocks and 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 different gear ratios. The planetary gear-set is the device that
14、makes this possible in an automatic. Automatic transmissions are used in many rear-wheel-drive and four-wheel-drive vehicles. Automatic transaxles are used in most front-wheel-drive vehicles. The major components of a transaxle are the same as those in a transmission, except the transaxle assembly i
15、ncludes the final drive and differential gears, in addition to the transmission. An automatic transmission receives engine power through a torque converter, which is driven by the engine s crankshaft. Hydraulic pressure in the converter allows power to flow from the torque converter to the transmiss
16、ion s input shaft. The input shaft drives a planetary gear set that provides the different forward gears, a neutral position, and one reverse gear. Power flow through the gears is controlled by multiple-disk clutches, one-way clutches, and friction bands. Passage B Power Train Torque Converter The k
17、ey to the modern automatic transmission is the torque converter. It takes the place of a clutch in a manual transmission to send the power from the engine to the transmission input shaft. The torque converter offers the advantage of multiplying the turning power provided by the engine. It has three
18、parts that help multiply the power： an impeller（ or pump）connected to the engine s crankshaft, a turbine to turn the turbine shaft which is connected to the gears, and a stator（ or guide wheel） between the two. See Fig. 5-6. The torque converter is filled with transmission fluid that is moved by imp
19、eller blades. When the impeller spins above a certain speed, the turbine spins, driven by the impeller. Planetary Gearing Planetary gears provide for the different gear ratios needed to move a vehicle in the desired direction at the correct speed. A planetary gear set consists of a sun gear, planet
20、gears, and a internal ring. See Fig. 5-7. In the center of the planetary gear set is the sun gear.Planet gears surround the sun gear, just like the earth and other planets in our solar system. These gears are mounted and supported by the planet carrier and each gear spins on its own separate shaft.
21、The planet gears are in constant mesh with the sun and ring gears. The ring gear is the outer gear of the gear set. Its has internal teeth and surrounds the rest of the gear set. Its gear teeth are in constant mesh with the planet gears. The number of planet gears used in a planetary gear set varies
22、 according to the loads the transmission is designed to face. For heavy loads, the number of planet gears is increased to spread the work load over more gear teeth. The planetary gear set can provide a gear reduction or overdrive, direct drive or reverse, or a neutral position. Because the gears in
23、constant mesh, gear changes are made without engaging or disengaging gears, as is required in a manual transmission. Rather, clutches and bands are used to either hold or release different members of the gear set to get the proper direction of rotation and/or gear ratio. Different On FWD cars, the d
24、ifferential unit is normally part of the transaxle assembly. On RWD cars, it is part of the rear axle assembly. Located inside the differential case are the differential pinion shafts and gears and the differential side gears. See Fig.5-8 The differential assembly revolves with the ring gear. Axle s
25、ide gears are splined to the rear axle or front axle drive shafts. When an automobile is moving straight ahead, both wheels are free to rotate. Engine power is applied to the pinion gear, which rotates the ring gear. Beveled pinion gears are carried around by the ring gear and rotate as one unit. Ea
26、ch axle receives the same power, so each wheel turns at the same speed. See Fig. 5-9. When the car turns a sharp corner, only one wheel rotates freely. Torque still comes in on the pinion gear and rotates the ring gear, carrying the beveled pinions around with it. However, one axle is held stationary and the beveled pinions are forced to rotate on their own axis and “ walk around”
