internal gear

例句：

1. 1. The internalgears are responsible for the smooth operationof the machine.
   内部齿轮负责机器的平稳运行。
2. 2. The internal gears were designedto improve efficiency and reduce wear.
   内部齿轮被设计来提高效率和减少磨损。
3. 3. Theinternal gears were replaced with new onesafter a few months of use.
   使用几个月后，内部齿轮被更换了新的。