The automatic transmission of car are mostly used planetary gear transmission

and has the development trend of multi-shifts

the effective method of analysis and design multi-shifts transmission mechanism is the goal of the scientific researchers.The structure and transmission scheme of a four-row planetary gear train for a latests 9-speed ZF automatic transmission is analyzed

and the transmission ratio of each shift is calculated based on the lever method.Three back shifts is got through adding a brake without the original structure being changed

the speed range of transmission is expanded.A theoretical reference is provided for the design of transmission scheme and analysis of structure of multi-shifts automatic transmission.