vAccording to the number of sub-files of the transmission ratio, the final drive can be divided into single speed and two-speed type.
疑问：
what is sub-files of transmission ration?
出处：宋红英，汽车专业英语 3.5
推测来自中文：
按主减速器传动比档数分，有单速式和双速式；
谷歌搜索“sub-files of the transmission ratio”，仅此一条结果，表明英文根本没这种说法。