| With the vehicular X-by-wire technologies and the in-wheel motor drive technologies become increasingly mature,the four-wheel independently actuated electric vehicle which can drive,steer or brake its four wheels independently,will be a new development trend of future electric vehicles.This type of vehicle uses the distributed electric chassis structure,comparing with the conventional chassis,it has more controllable degrees and better control precision.With the design of chassis control strategy,the vehicle integrated performance such as maneuverability,energy saving and stability can be improved significantly.This thesis is funded by National Natural Science Foundation of China(NSFC)project ‘Research on Reconfigurable Integrated Chassis Control Strategy for Four-Wheel Independently Actuated Electric Vehicle'(No:51505178),and ‘Research on The Control Mechanism and Evaluation Method of The Novel Steering-by-wire System Based on The Driver's Characteristics'(Number: 51575223).According to the characteristics of the four-wheel independently actuated electric vehicle,this thesis has proposed an integrated chassis control strategy based on multi-objective optimization algorithm.The ideal longitudinal speed and yaw angle velocity are served as the tracking goal,and the optimal allocation algorithm is used to improve the energy saving performance under normal conditions.The specific research are divided into several parts as follows:1)The joint simulation platform based on the unique chassis structure of four-wheel independently actuated electric vehicle is established,which can fully reflect the physical characteristics and response characteristics of the vehicle.Based on the electromagnetic properties of the permanent magnet synchronous motor(PMSM),the in-wheel-motor driving/braking system model and the control strategies are built in MATLAB/Simulink.Electro-hydraulic braking(EHB)system model was established by MATLAB/Sim Hydraulics software,based on the structure and working principles of EHB system.Four wheel independent steering system is also built in MATLAB/Simulink software,and the three closed-loop control structure is used to make the steering motors respond more quickly and accurately.The joint simulation platform is constituted by the subsystem model and the vehicle model modified in Car Sim software.2)Based on the established joint simulation platform,this article proposed a multi-objective optimization chassis integrated control strategy,a hierarchical integrated control structure is used to divide the whole strategy into motion control layer and control distribution layer.The motion controller uses 2Dof model as ideal reference model to calculate the ideal state of vehicle,and then the target control instruction is calculated by sliding mode controller,for making sure that the vehicle tracks the ideal longitudinal speed and yaw angular velocity,and has good linear handling characteristics.Under normal conditions,the minimum energy consumption severs as the optimization goal,and the control allocation layer distributes the driving/braking torque.At the same time,based on the ideal Ackerman law and the influence of tire side slip characteristics,the four wheel turning angles are allocated,to improve the handling performance of the electric vehicle and reduce tire wear.3)From the point of energy optimization,an optimal allocation strategy is proposed for in-wheel-motor drive\brake system.In order to improve the performance of energy saving,the optimal allocation strategy is combined with the regeneration braking control strategy.The traction efficiency MAP figure is obtained by analysis of the power of in-wheel-motor,the analysis is form a virtual test platform of motor characteristics.And based on the MAP figure,the total energy consumption of motor can be chose as the optimization objective function,the sequential quadratic programming(SQP)is used to solve the optimal in-wheel-motor driving/braking torque. |
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