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本帖最后由 白马啸西枫 于 2009-12-31 21:24 编辑 4 e0 y5 q& v' ^; `
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22# 小黄 8 G9 V) Z, m" W# S7 q: V( ?
4 O( C% d1 {6 n8 k- s- z, ]小黄,你说得对,但不全面。6 Z. p. ^' ?/ [, j
overdrive 档是汽车的最高档,也叫超速挡,超比档,正如shark 27所说: 此时的引擎曲轴转一圈时,齿轮箱的输出轴却可转超过一圈。对引擎而言,就是输出轴端的扭力变小了:
6 h5 ^5 H! }6 X8 N以下摘自维基百科:4 c* n. z3 t, l3 V0 G
超比(省油)档开关(O/D):自动变速器的最高档通常是超比档,该档位齿轮比(减速比)低于一,也就是该档位将引擎扭力放大倍数变成低于一倍,有助于省油,但不利于加速。超比开关关闭后,D档行驶时,自动变速器将无法换入超比档。通常在上坡及路面状况不良时应考虑将此开关关闭。" ]* Y; F8 u. I' h
A unit with a planetary gearset which turns the driveshaft faster than the transmission output shaft.
# Y0 \ k) u, c: L$ d5 _/ N$ |5 e% \An additional gearbox which is mounted in the driveline. Normally the final drive ratio is 1:1; but the overdrive makes it less (e.g., 0.87:1). The overdrive can reduce gas consumption at sustained high-speed driving, engine noise, and engine wear. Also called "overdrive transmission." Also see aftermarket overdrive" u+ |4 o3 x, A( l
Gearing in which less than one revolution of a transmission's input shaft causes one turn of the output shaft. The purpose of overdrive is to reduce engine rpm in high gear for better fuel economy. Example: A transmission with an overdrive top gear has a ratio of 0.70 to one. Turning the input shaft 0.7 revolutions causes 1.0 revolution of the output shaft.
7 f% D" [2 F Q# t因为输出轴端的扭距变小,所以变速箱的设计师有意将其设计成超车时踩油会降档,以提高变速箱输出端的扭距离和加速度,从而使汽车更快地加速。 |
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