Research On Cooperative Steering Strategy Of Distributed Drive Electric Vehicles

The distributed drive electric vehicle(DDEV)has the characteristics of compact structure,high-efficiency transmission,independent control of four wheels’ drive and braking torque and so on.In-wheel-motor or hub motor are commonly used in driving wheel.DDEV can be steered by the differential speed and torque between wheels.Steer-By-Wire(SBW),as a new type of steering system composed by active steering modules and road-sensing modules,breaks the constraints of the mechanical connection of the transmission steering system.In this thesis,a steering coordination control strategy is proposed to improve the under-steer situation when the in-wheel-motor DDEV differential steers under partial working conditions.Not only vehicle’s steering ability is improved,the trajectory tracking ability and steering response speed are also promoted.In addition,the designed steering coordination scheme can also realize safety redundancy in hardware,to ensure the steering safety.Firstly,a DDEV dynamics simulation model including the differential steering model is built based on the software MATLAB/Simulink platform,and the built model is verified by simulation comparison.Secondly,the property of differential steering is studied on a all-wheel independent drive electric vehicle by controlling vehicle steering through the differential steering independently,and a controller based on the Active disturbance rejection control(ARDC)differential steering is designed.The displacement of the rack is selected as the controller output,and the torque difference between the left and right steering drive wheels of the front axle is the controller input.The nonlinear characteristics of the system and the requirements of the actual situation are considered to design the controller logic.The active disturbance rejection control theory is chosen as the control algorithm because of the greatly improved stability and robustness compared with PID.The effectiveness of the controller is verified by simulation tests.Furthermore,it can be found by the simulation analysis that the designed differentia l steering controller has a tendency of understeer and large trajectory tracking deviatio n when the vehicle at a the low adhesion coefficient road.To solve the problem,a coo rdination steering strategy to the DAS equipped with SBW is proposed to make full us e of the steering advantages.Variable weight coefficient method is taken to adjust the vehicle vehicle’s differential steering weight coefficient dynamically,which ma kes the coordinated steering vehicle have a faster steering response speed and higher t rajectory tracking accuracy.Finally,a Hardware-in-loop simulation experiment was carried out based on Carsim and Lab VIEW RT.It was verified that the steer-by-wire control system and the differential steering control system can realize steering independently.At last,an all-wheel independent drive electric vehicle equipped with steer-by-wire system is refit and built from existing vehicles in the laboratory.The cooperative control experiment of steer-by-wire and differential steering are carried out,which verifies the effectiveness of the cooperative control scheme.