Research On Torque Distribution Control Of Four-wheel Drive Electric Vehicles With Improved Steering Characteristics

As two difficult problems the global world facing today,the energy crisis and environmental pollution seriously restrict the sustainable and rapid development of human society.From the view point of transportation,in "The twelfth five-year plan for national economic and social development" and "The energy conservation and new energy vehicles development plan",Chinese government pointed out that the electric vehicles will be the best choice for energy conservation and emissions reduction in the future,and the electric vehicle field is the strategic emerging industry for China.From the view point of control,the decentralized drive structure for electric vehicles belongs to over-actuated system.The over-actuated system can not only realize the driving auxiliary function,such as lane keeping,reversing auxiliary,and automatic parking,but also can effectuate many active safety control,including Anti-lock Brake System(ABS),Traction Control System(TCS),and Electronic Stability Control(ESC).In summary,the over-actuated system can improve vehicle stability and handling performance significantly.In order to improve the vehicle dynamic steering characteristic,this paper proposed a novel torque distribution control strategy for decentralized drive electric vehicles.First of all,this paper builds up the 14 degrees of freedom vehicle model in MATLAB/Simulink.Under typical test conditions,the accuracy of the 14-DOF vehicle model is validated by comparing with the high precision vehicle model in CarSim.The 14-DOF model is an important foundation for the development and validation of the subsequent control strategy.Secondly,in order to support the proposed control system,this paper develops some estimators of the vehicle driving states,containing the side slip angle,the vehicle velocity,the real-time tire forces,and road friction coefficient.The effectiveness of all these estimators are verified in the CarSim-Simulink joint simulation platform.Thirdly,use is made of the hierarchical control structure to design the core torque distribution control strategy.The upper yaw moment controller utilizes both the vehicle yaw rate and side slip angle as the control variables,and obtains the desired yaw moment through the Sliding Mode Control method.Then the lower torque distribution controller outputs optimal torque commands to meet up with the desired yaw moment command from upper controller.The results of CarSim-Simulink joint simulation and real vehicle tests demonstrate the effectiveness and merits of the proposed control.Furthermore,this paper proposed a new wheel slip prevention approach to ensure good traction performance in slippery condition.The reference wheel accelerations are calculated based on the proposed data fusion algorithm.Then the wheel slip is constrained by reducing the redundant wheel acceleration deviation.The simulation results demonstrate the accuracy of the reference acceleration and the effectiveness of the proposed slip prevention approach.Finally,the semi-physical simulation tests are carried out to evaluate the proposed control system.According to the simulation results with the same test configurations,the test results are analyzed and discussed thoroughly.Last but not least,this paper concludes the potential factors that affect the test results from four aspects,laying a good foundation for the development of the experimental platform in the future.