Research On Differential Coordinated Control Of Hydraulic Hub-motor Drive System For Heavy Vehicle Front Axle

The heavy vehicle plays a pivotal role in social infrastructure construction and economic development.Due to its variable use occasions and complex working environment,the contradiction between the power performance on bad roads and the economics of good roads of heavy vehicle is increasingly prominent.The heavy vehicle equipped with a hub-motor hydraulic hybrid system uses the road surface adhesion of front wheels for hydraulic auxiliary driving when the road surface is bad,and mechanical rear wheels driving when the road surface is good,it can realize time-sharing full drive and has a good application prospect.However,because of the complexity of driving conditions of the heavy vehicle and the uncertainty of driver's operation,the condition of one side wheel fall into the quagmire or steering often occur during hydraulic auxiliary driving.At this time,the required speed and torque of the two hydraulic motors of front wheels are different,and the output of the same speed and torque are bound to cause parasitic power such as tire wear,even dangerous conditions such as sideslip running.Therefore,the research of differential coordinated control based on two hydraulic motors of the front axle is the key to improve the adaptability of hydraulic hub-motor drive system under full operating conditions and improve its driving safety.In this paper,aiming at the problem of differential coordinated control of hydraulic hub-motor heavy vehicle front axle,researchs on the working condition adaptation layer based on the road adhesion coefficient identification,the implementation subsystem based on the throttle valve design and control,and the logic threshold differential control strategy based on the optimal slip rate are carried out.The main content of this dissertation includes the following elements:Firstly,according to the research objective of this paper,a configuration scheme of a hub-motor hydraulic hybrid system capable of controlling two hydraulic motors independently on the front axle is proposed,and its differential working principle is analyzed.Modeling and analysis of mechanical system and hydraulic system were carried out respectively according to the system configuration scheme.Among them,the seven-degree-of-freedom vehicle model can accurately simulate the dynamic state of the vehicle under conditions such as steering and provide the required vehicle kinematic parameters.Longitudinal slip characteristics and sideslip characteristics of Dugoff tire model provides theoretical reference for the subsequent simulation analysis research.Secondly,the realization of vehicle differential control strategy is inseparable from the perception of working condition information.Aiming at the study of working condition adaptation layer of pavement adhesion coefficient identification,a pavement adhesion coefficient estimation algorithm based on extended Kalman filter is developed.A joint simulation platform is built based on TruckSim heavy vehicle model,working condition model and Simulink estimation algorithm model.Then simulation verification is conducted on high-adhesion road surface,low-adhesion road surface,split road surface and docking road surface respectively.The result shows that the developed estimation algorithm can accurately identify pavement conditions within a reasonable error range and has good timeliness.Thirdly,for the research on the execution subsystem of throttle valve design and control,the selection of the throttle and the determination of the basic structural parameters are based on the working pressure of the hydraulic system and the basic parameters of the hydraulic motor.Then a throttle valve control model is constructed based on the AMESim software,by analyzing the influence factors of its cross-sectional area,the control rules for the relationship between the input signal and the output flow are extracted.Finally based on the PID feedback control and feedforward + feedback control method to check the response effect of the throttle valve,the results show that the feedforward + feedback control method has a better control effect on the throttle valve outlet flow.Finally,in order to study the logic threshold differential speed control strategy of optimal slip rate,the target speed of each wheel under steering condition is firstly analyzed based on ackerman steering model,which is used as the control input of hydraulic motor,and the differential coordinated control algorithm is developed based on the different optimal sliding rate range under different road conditions as the logical threshold.Secondly a joint simulation platform based on the AMESim mechanical transmission system model,Simulink vehicle model and differential control strategy model is built.At last,the simulation experiment is set up based on the turning condition and the straight running condition including split road surface and docking road surface.Through the analysis of vehicle speed following effect,wheel speed control effect,slip rate control effect and vehicle trajectory effect,the accuracy and effectiveness of the differential coordinated control algorithm is proved.