Abstract: The core technology of the composite transmission system is matching. Based on the actual importance and adaptability of each evaluation index in different composite transmission systems, the optimal scheme is selected from all possible applicable power split schemes to complete a complete optimal selection design. In order to avoid the problem that the excellent scheme is missed, the speed ratio and torque of 12 composite transmissions are analyzed firstly, and then proposes 3 torque coefficients at different key places in drive line which are selected according to torque capacities of components. Secondly, with the range of speed ratio and 3 torque coefficients as objective functions, a nondominated genetic algorithmII (NSGAII) is applied to optimize two fixed gear ratios of gear pairs, the comprehensive optimal state of the 12 classic compound transmissions is obtained. Lastly, according to the importance and adaptability of evaluation indicators, a multistep preranked selection method for compound transmission with continuously variable characteristic parameter is proposed, and an integrated design process with optimization and type selection is conducted. Compared to the preoptimization systems,  the speed ratio range is increased by 24%, the maximum output torque is increased by 18.92%, and the efficiency is increased by 2.25%.

Key words: planetary gear train, compound transmission, torque coefficient, multiobjective optimization, preranked multistep selection

摘要： 复合传动系的核心技术在于匹配，基于不同复合传动系统中各项评价指标实际的重要性与适应性，从所有可能适用的功率分流方案中选出最优方案，完成一次完整的优化选型设计。为避免优秀方案被漏选的问题，对12种复合传动的速比和转矩进行分析，根据传动系统各部件的转矩能力，提出传动路线中3个关键位置的转矩系数。以速比变化范围和3个转矩系数为目标函数，使用非支配遗传算法NSGA-II优化两个固定齿轮副传动比，得出12种复合传动的综合最优状态。基于评价指标重要性与适应性，提出一套行星排特性参数连续可变复合传动系统的分级多步选型方法，完成一次完整的优化选型设计。相比优化前的系统:速比范围提高24%，最大输出转矩提高18.92%，效率提高2.25%。

关键词: 行星排, 复合传动, 转矩系数, 多目标优化, 分级多步选型