Research On Integrated Control Method Of Power Performance And Stability For Variable-speed Pure Electric Vehicle

In order to ensure energy security and alleviate the contradiction among economic development,resources and environment,clear energy vehicles have become a strategic emerging industry in China.Electrification,intelligentization and networked are inevitable development trends for the automobile industry.Pure electric vehicles are the main development direction of new energy vehicles in China.Due to short development time and limited technology accumulation,there are still some bottleneck in the existing products and researches in terms of vehicle dynamics,economy,stability and safety:(1)Improving the efficiency of the transmission system by equipping a multi-speed AMT(Automated Mechanical Transmission)is an effective method to further reduce energy consumption and extend the cruising range for pure electric vehicles,but the traditional AMT has the drawback of long power interruption time and poor shift smoothness and so on.(2)The chassis structure of the pure electric vehicle is obviously different from the traditional fuel vehicles,such as the motor instead of the engine,the large mass battery pack,etc.,resulting in a large change in the vehicle dynamics characteristics and new stability control problems.(3)The intelligent control algorithms are the critical and research focus for fully electric vehicles.However,integrated control methods that combine longitudinal dynamics,yaw and roll stability lack systematic and in-depth research.Based on the above background and the support of Chinese high-level automobile independent research and capacity development projects,the National Natural Science Foundation projects,Chongqing's major science and technology projects and Enterprise technology development projects,in this study,the integrated control method of the power performance and stability are investigated for variable-speed AMT pure electric vehicle and the relevant experimental verification are carried out at the support of vehicle system dynamic,intelligent control theory.The main contents and novelty of the study are as follows:(1)A motor torque and speed combination shift control strategy are design for the pure electric vehicles equipped with two-speed clutchless AMT.According to the vehicle performance index,the required power,torque and speed of driving-motor are calculated,the transmission system parameters such as the transmission ratio and the final drive ratio are determined.The multi-body dynamics model of the transmission system is establish,and then the optimal power performance and economic performance shift schedules are developed.On this basis,the motor torque and speed combination shift control strategies are designed to develop a complete shift control process.The shift simulations are carried out under different throttle opening,and the shift quality is analyzed according to the evaluation indexes such as shift time and shift smoothness.The test results verify the effectiveness and robustness of the proposed combined shift control strategy.(2)A novel state observer based on T-S(Takagi-Sugeno)fuzzy model and robust H? control is proposed to obtain the vehicle state variables during the real-time driving,and to provide accurate input information for the yaw plane and roll stability control.The T-S fuzzy rules are introduced to linearize the Dugoff nonlinear tire model,and then the linearization dynamic model consists of yaw and roll motion is obtained.The robust H? control method is used to solve the observer gain matrix.The state estimation results are analyzed and evaluated in fishhook,serpentine and double line change simulation tests and different noise intensity.The results show that the designed state observer has better robustness and it can accurately obtain the state estimation value.(3)A control approach of vehicle yaw plane controller integrated with shift control is proposed.The seven-degree-of-freedom dynamics model is built,and the state observer estimates the vehicle state information based on the output signal of the dynamic model;The longitudinal velocity,the sideslip angle and the yaw rate are used as control objective,the yaw plane controller applicate model prediction method to distribute the braking torque of four wheels and the driving torque of front wheels in real time based on the vehicle state estimation information;The power output characteristic of motor is considered to insure the desired driving torque of front wheel can be obtained from motor;The brake torque of four wheel and the motor output drive torque are used as control inputs to achieve the optimal control of brake and driving torque under the premise of ensuring vehicle stability.The numerical simulation results show that the designed yaw plane controller can significantly improve the lateral stability of the vehicle.(4)A hierarchical controller for the anti-roll oil-gas coupling suspension with the objective of optimizing yaw and roll plane coupling motion is designed,which consists of state observer,output torque controller and actuator pressure tracking controller.The state observer is used to obtain high-precision vehicle motion state information;Based on the vehicle state information and the motor power output characteristics,the desired braking torque of four wheels and the active anti-roll moment for body are allocated by the output torque controller with model predictive control method;In order to deal with the uncertainty of the hydraulic system parameters,the actuator pressure tracking controller applicate adaptive Backstepping control algorithm to dominate the hydraulic actuator accurately tracking the desired active anti-roll moments.The various simulation results verify the effectiveness and robustness of the proposed hierarchical control algorithm.(5)A variable-speed AMT pure electric vehicle power transmission test bench is constructed,and the vehicle control frame and shift strategy are designed.The electric vehicle static shift,dynamic upshift and downshift test are carried out in the test rig.The experiment results indicate that the shift time and shift smoothness satisfy the requirements and standard,and it verify the effectiveness of shift control strategy due to it nearly consistent with the simulation results.Meanwhile,the vehicle coupling dynamics model is established,and the validity and accuracy of the model are verified by the prototype vehicle test data.On this basis,the vehicle coupling dynamics model is used to verify the effectiveness of the designed yaw and roll stability controllers.The results show that the designed controller can significantly improve the vehicle dynamic stability of the yaw and roll planes under the premise of ensuring the vehicle power performance.In summary,the shift quality of the variable-speed pure electric is significantly improved by applying the proposed shift control strategy,and the integrated control approach with considering longitudinal power dynamics,yaw and roll motion is able to improve lateral and roll stability under the premise of ensuring the power performance of the whole vehicle.The effectiveness and robustness of shift control strategies and integrated controller are verified through implementing bench test.As a consequence,this study deepen the study of pure electric vehicle system dynamic and control method,and it is able to provide theoretical guidance and engineering experience for improving the research and development capabilities of clear energy vehicles.