1、Unit Four Drive Train Passage ATransmissions Transmission is the most important component in the drive train Often the term“transmission”refers simply to gearbox Its jobs are to vary the gear ratio,controlling the car speed;to provide directional control,forward and reverse;and to interrupt the engi
2、ne power to the transmission to make the engine idle In accordance with the operational control mode,car transmissions can be divided into manual transmission(MT)and automatic transmission(AT).There are three main kinds of automatic transmissions,respectively is automatic transmission(AT),continuous
3、ly variable transmission(CVT)and direct shift gearbox(DSG).Manual Transmission(MT)A manual transmission mainly contains some shift forks,collars,different sizes of gears along the shafts such as input and output shafts,and lay shaft as shown in Fig.4-1 If you drive a car with a MT,you have to shift
4、the gears by yourself,usually with the gearshift on the console and the clutch pedal on the floor on the left side MT usually has five speeds The first gear is the lowest gear which is used to make your car start going The second gear is used to make your car move faster The third and fourth gears m
5、ean that both input and output shafts turn at the relatively the same rate of speed The wheels can go very fast The fifth gear is often regarded as“overdrive”which means the output shaft can turn faster than the input shaft for good fuel economy Some cars now have as many as six and seven gears Alth
6、ough the gear ratio may be the same as in six-or seven-speed transmission as in five-speed transmission,the more forward speeds,the smoother shifting is and more fuel-efficient the car becomes Automatic Transmission(AT)An automatic transmission is the most complicated mechanical component in todays
7、car It consists of mechanical system,hydraulic system,electrical system and electronic control system,all working together in perfect harmony If you have a car with an AT,the gears are changed automatically without any help from you This is accomplished through the torque converter,a planetary gear
8、set including a sun gear,planet gears and a carrier,and other shift operating devices(see Fig.4-2).All automatic transmissions have a gearshift that has at least 4 positions:park(P),reverse(R),neutral(N)and drive(D)as shown in Fig.4-3 Continuously Variable Transmission(CVT)A continuously variable tr
9、ansmission is not a complicated system CVT moves seamlessly from one gear ratio to the next through a pulley system which not only offers smoother shifting but also improves better fuel economy(see Fig.4-4).The major components of a CVT include an input drive pulley,an output driven pulley and a met
10、al belt as shown in Fig.4-5 Each pulley has two cones,forming a groove,and the belt rides in the two grooves As the distance between the cones changes,the belt rides higher or lower in the grooves,which determines the gear the car is in Direct Shift Gearbox(DSG)If you drive a car with DSG,the gears
11、shift automatically,or you can manually select them by yourself without operating a clutch pedal It is known as direct shift gearbox(DSG)(see Fig.4-6a)The greatest structural difference is that a DSG has two clutches One clutch operates the odd-numbered gears,and the other clutch controls the even-n
12、umbered gears The result is that the flow of power to the transmission from the engine isnt interrupted as the transmission shifts from one gear to another The DSG also has two transmission input shafts,one inside the other The hollow outer shaft contacts the even-numbered gears,and the shaft inside
13、 it contacts the odd-numbered gears(see Fig.4-6b)DSG operates more smoothly than ordinary AT or MT,and it can deliver better fuel economy,as wellNew Words and Expressions interrupt intrpt vt 中断;打断 idle aidl vi 空转,怠速 mode mud n 模式;方式 continuously kntinjusli adv 连续不断地 console knsul n 操纵台 relatively re
14、ltivli adv 相当地;相对地 overdrive uvdraiv n 超速档 fuel-efficient fjulifint adj 燃油效率高的 mechanical mknikl adj 机械的 hydraulic haidrlik adj 液压的 harmony hmni n 协调New Words and Expressions automatically tmtikli adv 自动地 accomplish kmpli vt 完成;实现 reverse rivs n 倒档 neutral njutrl n 空档 seamlessly si:mlisli adv 无缝地 pu
15、lley puli n 带轮 cone kun n 锥形盘 odd-numbered dnmbd adj 奇数的,单数的 even-numbered ivnnmbd adj 偶数的 in accordance with根据,按照 beregarded as被认为是Common Automobile Terms chassis si n 底盘,底架 gearbox gibks n 变速器(箱)gearshift iift n 变速杆 collar kl n 结合套 carrier kri n 行星齿轮架 drive train传动系统,驱动机构 manual transmission(MT)手动
16、变速器 automatic transmission(AT)自动变速器 continuously variable transmission(CVT)无级变速器 direct shift gearbox(DSG)直接换档变速器 双离合变速器Common Automobile Terms shift fork换档拨叉 clutch pedal离合器踏板 input shaft输入轴 output shaft输出轴 lay shaft中间轴 planetary gear set行星齿轮组 sun gear太阳轮 planet gear行星轮 pulley system带轮系统 drive pulley驱动带轮 driven pulley从动带轮
