Development of Continuously Variable Power Transmission for Electric Vehicle with Solar Assisted Battery

电动汽车在无废气排放、短距离续航的城市物流领域具有广阔的应用前景。电动汽车动力总成的技术问题是如何在有限的电能中平稳、快速地加速，并在减速或下坡时将机械能回收为电能。本项目旨在通过制作一台功率容量为2.2kW、速比范围为0.4~2.5的牵引传动样机，研究无级变速器作为电动汽车机械传动的可能性。这项创新技术是开发一种速比控制伺服机构，由一组螺母和螺丝以及小型滚动元件组成，最大赫兹压力为2.5 Gpa。试验结果表明，它以3000转/分的速度传递40 N.m扭矩，效率为85%，螺母和螺杆伺服机构的速比变化快，一阶时间常数为0.2s。无级变速器适用于废重250公斤的电动汽车，其中包括60公斤的铅酸蓄电池。该传动系由一台额定功率为36V-80A的串联绕组电机组成，其输出轴与CVT输入轴直接相连。无级变速器的输出扭矩通过减速比为12.5的差速器传递到轮轴。采用无级变速器的电动汽车的加速度比常速变速箱提高了10%。

Electric vehicles have a potential to be used in the urban-city logistics where no-emission of exhaust-gas is favorable and short range of cruising-range can be accepted. Technological issues for the power-train of the electric vehicle are how to provide smooth and quick acceleration within a limited electric energy-source and to recover the mechanical energy to electric energy at deceleration or down-hill. This project is to examine the possibility of the continuously variable power transmission, CVT, as an mechanical transmission for the electric vehicle by making a traction-drive prototype of 2.2kW power-capacity with speed-ratio range of 0.4 to 2.5. The innovative technology is to develop a speed-ratio control servomechanism consisting of a set of nut and screw and small-size rolling-elements working at a maximum Hertzian pressure of 2.5GPa. The test result is that it transmits 40N.m torques at 3000rpm with an efficiency of 85%, and the nut and screw servomechanism changes the speed-ratio quickly with a first-order time-constant of 0.2s. The CVT is applied to the electric vehicle with a dead mass of 250kg including 60kg lead-acid battery. The power train is consisted of a serially-wounded motor with 36V-80A rated-power of which output shaft is connected directly with the CVT input-shaft. The output torque of the CVT is transmitted to the wheel axle through the differential gear box with reduction-ratio of 12.5. The acceleration of the electric vehicle with CVT is improved by 10% compared to the constant-gear box.