Stability Control Of Four-Wheel Independent Drive Electric Vehicle Considering Economy

The stability control of the traditional automobile is mostly in the form of braking,which will inevitably affect the speed of the vehicle.However,the four-wheel independent drive electric vehicle(FWIDEV)is driven by four motors separately,which can realize the decoupling control of the wheel torque,therefore a combination of driving and braking can be used to avoid this deficiency.At the same time,the torque control of FWIDEV possesses the characteristics of fast response and accurate control,and has an incomparable advantage over the traditional automobile in the stability control of the vehicle.Based on the above advantages,domestic and foreign scholars have carried out a lot of researches on the stability control of FWIDEV,and have achieved good results.However,the current researches mostly focus on the design of vehicle stability controller,but there are still some deficiencies in the coordination between driving force and braking force in wheel torque distribution.Besides,the economic improvement of FWIDEV under the comprehensive conditions are deficient.In this paper,a hierarchical control structure is employed to achieve the stability and economy improvement of FWIDEV.Firstly,the stability controller of the upper control is designed,and based on which,the wheel torque allocation scheme of the lower control is studied in order to ensure the stability of the vehicle and improve its economy.The specific research contents are as follows:(1)The degree of freedom of the model is determined by analyzing the kinematic characteristics affecting vehicle stability.Simulink is used to establish eight-degree-of-freedom(8DOF)vehicle model including body kinematics,steering system,wheel dynamics and tire model.The parameters of the hub motor are matched and the motor efficiency model is established.The accuracy of the 8DOF model is verified using Carsim.(2)The factors affecting vehicle stability and their influencing mechanism are analyzed.On this basis,the sliding mode controller(SMC)is utilized to accomplish the stability controller.Then,the stability controller is optimized and different conditions are simulated to test the two stability controller.(3)The influence of different working wheels on vehicle under different conditions,including steering and straight running,is researched.And the effect of different distribution forms for the required additional yaw moments on the vehicle economy and stability is studied.In order to reduce the workload,a method of selecting different torque distribution forms of left and right wheels is proposed,and finally three kinds of distribution forms satisfying the requirements are obtained.The torque distribution aiming at economy and stability is constructed respectively to improve the economy of vehicle going straight and ensure the vehicle stability.(4)A comprehensive strategy is proposed,which is to control the stability for unstable vehicle and improve the economy for the stabilized vehicle.The phase plane method is employed to obtain the stability conditions and other vehicle states are also added the conditions vehicle for vehicle state switching.In doing so,a comprehensive control under different operating conditions can be realized.The simulation analysis of different control strategies is conducted under single lane change condition,and the results show that the comprehensive control strategy proposed by this paper can further improve vehicle economy under the premise of ensuring vehicle stability.