Optimal control for shift mechanism of a planetary two-speed transmission for electric vehicles|

For increasing mileage of electric vehicles (EVs), it is necessary to improve energy density of battery and the transmission efficiency of powertrain system. We designed a planetary two-speed transmission for using the high efficiency of motor effectively, which is beneficial to improve powerful and economic performances. It has an electronic mechanism replacing hydraulic system for shifting, which consists of worm gear systems driven by a brushless direct current (BLDC) motor. To improve shifting quality, the speed control of BLDC motor was developed utilising variation principle that is fitted by high order polynomials. The dynamic model of electronic actuator for shifting was built for evaluating the shifting control of the BLDC motor. The simulation results revealed that the speed of BLDC motor fitted by 5-order polynomial could make a smooth shift and low friction work of brakes compared with 3-order and 7-order polynomials.