求翻译：梭式变速箱是在一般变速箱的基础上改进得到的。梭式变速箱速器使拖拉机的倒档由原来的四个增加到八个，可以使拖拉机在工作时快进，也可以快退，满足了更多工作的需要。拖拉机的前进、后退，增速、减速都要靠变速器传动来实现。而且变速器在拖拉机的动力性和燃油经济性上也有很重要的影响。是什么意思？

The shuttle transmission is obtained on the basis of the general transmission improvements. Shuttle transmission speed allows the tractor reverse from four to eight, you can make tractors at work, fast forward, rewind, and to meet the need for more work. Tractor forward, backward, growth rate, decel