Study Of Shift Strategy Of 2 Speed Automatic Mechanical Transmission (2AMT) For Electric Vehicles

Electric vehicle industrialization has become an important solution to sustainable development of the world economy and society.At present,most researches are focused on battery and energy management and propulsion control strategy of electric vehicles with only one speed main reducer for improving mileage range per charge.In recent years,however,a number of investigators pay much attention to multi-shift transmissions for electric vehicles.Though the single speed reducer is satisfactory in general to demands of the vehicle power performance and fuel economy,it can't meet simultaneously power performance demands,maximum speed and acceleration time,or otherwise one more powerful drive motor is required to match the acceleration requirements.In general speaking,the high efficiency zone of drive motors in one-speed reducer may not match its routine operation area to a certain extent.For alleviation of the contradiction,2-speed AMT application is an economical and effective choice for the electric vehicles,which makes the powertrain cover a larger torque region for standstill acceleration and a higher speed region for a required maxium speed.Improvement of the motor work point spectrum and efficiency means a considerable energy saving in electricity economy under the same specified conditions of power performance.In this thesis,mechanical structure of the 2-speed AMT is demonstrated first showing its distinguishing features including non-clutch,lightweight differential and electrical gear shifting actuator.Then an efficient procedure of gear ratio optimization for the 2-speed AMT is proposed,based upon Particle Swarm Optimization algorithm.The two dimension search space of the gear ratios is set according to requirements in power performance and the objective function in terms of the gear ratios is established for averaged efficiency optimization of the drive motor of the electric vehicle operated under New Europe Drive Cycle.After finishing optimization of gear ratios,shifting schedule of the 2-speed AMT is analyzed based on power and economy respectively.And an optimized shifting schedule based on requirements of power is established in order to maximum drive motor efficiency when satisfying power performance at same time.In this shifting schedule,accelerating pedal is mapping to output torque on wheel instead of output torque of drive motor.Transmission controller(TCU)chooses a gear which makes the drive motor operate in higher efficiency zone by comparing the efficiency under first gear and second gear.And then TCU controls motor to produce the required torque.Finally,the shifting control strategy is proposed which requires TCU and motor controller(MCU)work in coordination.Because of elimination of clutch in the 2-speed AMT,which means motor connects gear box in perpetuity,drive motor must be able to change its rotate speed to a certain one asked by TCU during shifting.Three work patterns of drive motor are designed and a dynamic model of synchronizer is built.The whole shifting process is simulated in Simulink with a PID control of shifting motor.The study in the thesis is mostly focused on some crucial fields in theory when designing the transmission for pure electric vehicle and it definitely has a significant influence on following development of the 2-speed AMT which will be produced and tested in electric vehicles.