中文摘要：

文章将一款单挡传动方案的纯电动汽车改为两挡变速传动的方案，分析了满足整车性能指标要求的动力系统电机及电池的参数匹配方法。为了提高整车能量利用率，以整车动力性要求为约束、NEDC工况下电机能量消耗最小为目标，采用遗传算法对传动系统的参数进行优化设计，分别制定了动力性和经济性换挡规律，以验证两挡传动方案的优势。仿真结果表明，相比于单挡传动方案，两挡传动方案时整车动力性和经济性都有一定的提升，并且降低了对电机功率和转矩的需求。其中，动力性换挡策略下整车百公里加速时间缩短了7．75％，经济性换挡策略下，整车能耗降低了4．7％。

英文摘要：

A scheme of two-speed transmission was proposed for an electric vehicle（EV） with a fixed gear rati- o, and the parameter matching design of motor and battery was analyzed based on the specifications of vehicle performance. Under the condition of ensuring the EV power performance, speed ratios of two-speed transmis- sion were optimized by using genetic algorithm aiming at the least energy consumption of the motor over the New European Driving Cycle（NEDC）. The dynamic and economic shift schedules were developed to test the advantage of two-speed transmission scheme. The simulation results show that the two-speed transmission scheme achieves better results in both power performance and economy compared with the fixed gear ratio scheme, and the requirements for motor power and torque are also reduced. The acceleration time in 100 km is reduced by 7.75% under dynamic shift schedule and the energy consumption is also reduced by 4. 7% under economic shift schedule.