汽车专业英语读译教程 作者 宋进桂_ 16-U9TB-C.ppt

UNIT 9 AUTOMATIC TRANSMISSIONS TEXT B/CContinuously Variable Transmissions (CVT)  UNIT 9 AUTOMATIC TRANSMISSIONS TEXT B-C Continuously Variable Transmissions (CVT) ? History of the CVT ? Driving a car with a CVT ? How CVT Works ? Advantages of the CVT ? Disadvantages of the CVT 本次课学习目标 掌握无级变速器的有关英文专业词汇 掌握无级变速器的结构与工作原理 训练快速阅读能力，较高的阅读速度 NEW WORDS Though there are several types of CVTs, most cars use a pair of variable-diameter pulleys, each shaped like a pair of opposing cones, with a metal belt or chain running between them(Fig.9-6) [1]. One pulley is connected to the engine (input shaft), the other to the drive wheels (output shaft). The halves of each pulley are moveable; as the pulley halves come closer together the belt is forced to ride higher on the pulley, effectively making the pulleys diameter larger. Changing the diameter of the pulleys varies the transmissions ratio (the number of times the output shaft revolves for revolution of the engine), in the same way that a 10-speed bike routes the chain over larger or smaller gears to change the ratio. Making the input pulley smaller and the output pulley larger gives a low ratio (a large number of engine revolutions producing a small number of output revolutions) for better low-speed acceleration. As the car accelerates, the pulleys vary their diameter to lower the engine speed as car speed rises. This is the same thing a conventional automatic or manual transmission does, but while a conventional transmission changes the ratio in stages by shifting gears, the CVT continuously varies the ratio - hence the name continuously variable transmission. Advantages of the CVT Engines do not develop constant power at all speeds; they have specific speeds where torque, horsepower and fuel efficiency are at their highest levels. Because there are no gears to tie a given road speed directly to a given engine speed, the CVT can vary the engine speed as needed to access maximum power