Research On Dynamic Control Of Multi-axle Vehicle Based On Hub Motor Response Difference And Fault

Hub motor driven vehicle adopts electric wheel configuration,which has many advantages such as high integration,high transmission efficiency,diverse driving forms,simplified vehicle structure and flexible spatial arrangement,etc.,and is widely regarded as the ultimate form of automobile development.With the characteristics of large mass,long size and strong power,the multi-axle heavy load vehicle plays a role in promoting the development of national defense industry and national economic construction.With the improvement of our national defense strength and economic level,it puts forward higher design requirements for multi-axle load vehicle,which are mainly reflected as strong motivation,high flexibility,low noise,high reliability and the energy supply and survivability under complex conditions.The upsurge of new energy vehicles and higher requirements for multi-axle heavy load vehicles promote the research and development of multi-axle hub motor driven heavy-duty vehicles.Relying on the national key R&D program project "Multi-system efficient integrated hub motor action module and vehicle torque vector distribution technology"(2021YFB2500703),aiming at the difference in wheel motor response and fault problems,starting from the perspective of vehicle dynamics,taking the eight-axis hub motor driving integral vehicle as the research object,and improving the driving stability of the vehicle as the main research goal,this paper analyzes the dynamic modeling of multi-axle vehicles,linear driving stability control,steering control stability control,and Key technologies such as in-wheel motor fault diagnosis and active fault-tolerant control have been thoroughly studied.The main research work of this paper is as follows:(1)Dynamic analysis and modeling of integrated vehicle driven by eight-axis hub motor.Based on the theory of vehicle system dynamics,the vehicle was divided into several subsystems,and the 39-degree-of-freedom vehicle dynamics models of body,steering,wheel rotation and runout were established respectively.In order to verify the accuracy of the vehicle dynamics model,Amesim is used to build the vehicle model with the same parameters and configuration,and the simulation and comparison of straight running and steering conditions are carried out.The simulation results show that the two main vehicle state parameters match very well under the above conditions,and the maximum error of simulation accuracy is less than 5%,which verifies the accuracy of the 39-degree-offreedom vehicle dynamics model.(2)Analysis of wheel motor response difference and its influence on vehicle driving stability.Firstly,the existence principle of hub motor response difference is analyzed.The inductance parameter is susceptible to cross-coupling effect,which is a common reason leading to the response difference of hub motor.Then,the hub motor response differences are further subdivided into steady-state and dynamic response differences.The influence mechanism of hub motor response difference on linear driving stability and steering stability was analyzed.Combined with simulation,it was shown that: The response difference of hub motor will cause the vehicle to run off when the vehicle runs in a straight line,and will affect the steering characteristics of the vehicle when the vehicle turns to run.The steady-state response difference has a greater impact on the vehicle running stability,while the dynamic response difference has an impact on the vehicle only when the expected torque changes.(3)Research on vehicle dynamics control strategy based on hub motor response difference.Aiming at the linear driving stability control of vehicles,firstly,the linear driving stability control index was summarized and analyzed.Combined with the characteristics of the maximum moment of inertia of eight-axle vehicles and the accuracy of commonly used IMUs in the market,the wheel speed was selected as the control index of linear driving stability.After filtering,a sliding mode variable controller based on the wheel rotation dynamic equation was designed to calculate the torque adjustment.Side hub motor with small compensating torque;For vehicle handling stability control,the idea of hierarchical control was adopted,and yaw velocity and side deflection Angle of the center of mass were selected as control indexes to deviate from the ideal output value of the twodegree-of-freedom model of the eight-axle vehicle.The upper controller calculated additional yaw torque based on LQR algorithm,and the lower controller took the sum of the square of tire load rate as the objective optimization function for optimal torque distribution.(4)Research on hub motor fault diagnosis method and active fault tolerant control.Firstly,a fault diagnosis method based on sliding rate of driving wheel was proposed,and fuzzy control was used to judge wheel failure.Then,an active fault-tolerant controller compatible with steering stability control was designed using the idea of active faulttolerant control.The upper control calculated the additional yaw moment and total longitudinal force,and the lower torque distribution controller optimally alocated the remaining driving wheels according to the failure of hub motor,road surface limit and motor output limit.(5)Vehicle coordination control simulation verification and real vehicle test.On the basis of the simulation and verification of linear driving stability control,steering stability control and hub motor fault tolerance control effect,the vehicle coordination control was simulated and verified under the condition of response difference of complex hub motor,fault and complex driving condition.The automatic wheel drive vehicle test platform was developed to verify the stability control of straight line driving.