变速器

例句：

1. 1. The car's engine has a manual gearbox that allows for easy shifting between speeds.
   这辆车的引擎有一个手动变速箱，可以轻松地在速度之间切换。
2. 2. The old truck had a simple gearbox that was prone to failure.
   那辆旧卡车有一个简单的变速箱，容易出故障。
3. 3. The engineer replaced the worn-out gearbox with a new one to improve performance.
   工程师用一个新的变速箱替换了磨损的齿轮箱，以改善性能。