speed transforming gear

例句：

1. 1. The car'sspeed transforming gear is designed to adjustthe engine's RPMs quicklyand smoothly.
   汽车的变速齿轮设计用来快速而平滑地调整发动机的转速。
2. 2.The engineer used a special tool to changethe gears on the transmission.
   工程师使用一种特殊的工具来更换变速器上的齿轮。
3. 3. The oldcar had worn out its gears,so it needed to be replaced.
   这辆旧车齿轮磨损了，所以需要更换。