back coil

例句：

1. 1. The car has a back coil that makes it easier to start.
   这辆车有一个回旋弹簧，使启动更容易。
2. 2.The back coil is responsible for the car's suspension system.
   回旋弹簧负责汽车的悬挂系统。
3. 3. The engineer used a back coil to make the machine more efficient.
   工程师使用回旋弹簧使机器更加高效。