built-up gear

例句：

1. 1. The new car has a built-up gear that makes it more efficient.
   这辆新车有一个组合齿轮，使它更高效。
2. 2. The machine uses a built-up gear to reduce the amount of power needed.
   这台机器使用一个组合齿轮来减少所需的功率。
3. 3. The engineer designed a built-up gear to improve the performance of the machine.
   工程师设计了一个组合齿轮来提高机器的性能。