With the increase of vehicle ownership year by year,the problems of environmental pollution,energy shortage and climate change are also increasing.New energy electric vehicles are an important way to solve the above problems.Four-wheel distributed-driving electric vehicles(4WDDEV)are one of the development directions of new energy vehicles,and the use of vehicle stability control system is the prerequisite for exerting the advantages of distributed-driving electric vehicles.Active steering and direct yaw moment control(DYC)are commonly used stability control systems at present.According to different controlled wheels,active steering can be divided into active front-wheel steer(AFS)and active rear-wheel steer(ARS).The two active steering modes have different effects in maintaining vehicle driving stability,maintaining vehicle driving trajectory and improving steering characteristics.Therefore,it is necessary to compare and analyze the control effects of AFS and ARS,so as to lay a foundation for selecting an active steering type suitable for stability control of 4WDDEV.Because torques for four wheels of4WDDEV can be controlled independently,the motor torque can be distributed by the combination of differential driving and braking,so as to realize DYC of 4WDDEV.Because the control effects and control limits of the two kinds of automobile stability control systems are different,it is necessary to coordinate the active steering and DYC.Therefore,this paper foucuses on the following four aspects:(1)The cosimulation platform was built by using Matlab/Simulink software and Car Sim software.The vehicle model of 4WDDEV was built and parameterized based on Car Sim.The driver model,driving motor model and steering system model were built based on Matlab/Simulink,which were connected through signal ports to build a cosimulation platform.The correctness of the cosimulation platform was verified under step response and erpentine maneuver,.(2)Based on the Linear Quadratic Regulator(LQR)theory,the LQR controller for AFS and the LQR controller for ARS were built respectively.L9(33)orthogonal test was designed to solve the problem of determining the proportional coefficient in LQR controller,and the optimal proportional coefficient of AFS and ARS LQR controller was determined respectively with the maximum sideslip angle and variance of road offset as the optimization objectives.Simulation analysis was carried out under the condition of double line maneuver,and the difference of stability control effect between AFS and ARS is obtained,so an active steering mode suitable for stability control of 4WDDEV was selected.(3)DYC was designed based on the idea of hierarchical control.DYC upper control used fuzzy PID to solve the required yaw moment of the whole vehicle.The lower control was a torque distribution module.Firstly,the instability state of the vehicle was judged according to the steering wheel direction and the relative value between the yaw rate reference value and the actual value,and then the torque distribution mode with differential drive,differential drive/brake combination or friction brake participation was selected according to the wheel stress.The proposed DYC can satisfy the stability control under step response and sinusoidal maneuver.(4)Coordinated control of AFS and DYC was completed based on phase plane theory.Firstly,the influences of vehicle velocity,road adhesion coefficient and front wheel angle on the sideslip angle-yaw rate phase plane(β-ωr phase plane)and sideslip angle phase plane(βphase plane)were analyzed,and theβphase plane,which changes little with the three factors,was selected as the basis for judging the stability of coordinated control in this paper.Secondly,according to the control characteristics of AFS and DYC,the control area ofβ-phase plane was divided,based on cosine function,the work weight coefficient of AFS and DYC was calculated.Finally,under the condition of double line maneuver,the simulation results showed that the proposed coordinated control strategy was correct. |