Research On Straight-driving Stability Of Small Unmanned Four-wheel Drive Ground Vehicle

Electric,intelligent and networked are the important development direction of China’s new energy vehicles.Distributed drive is a key technology of new energy vehicles,which provides an important prerequisite for the development of drive-by-wire chassis.Although the distributed drive mode has the characteristics of independent control of driving wheel torque,easy measurement of torque speed and high transmission efficiency,the coordinated distribution of driving force and motion control have always been the core problems to be solved urgently for distributed drive electric vehicles.This study takes a small unmanned ground vehicle with four wheels independent drive as the research object,aiming to solve the stability problem of the vehicle in the process of straight driving.The main research contents are as follows:1)Complete vehicle model establishment.The multi-body simulation model of the vehicle was established by ADAMS/ VIEW software.Based on vehicle dynamics and motor external characteristics,the motor model and 7-DOF dynamics model were established respectively in MATLAB/Simulink.Coupling the two,the same driving torque is input to the driving motors on both sides of the vehicle respectively to evaluate the driving capability of the vehicle model.The results show that the motor output torque is in accordance with the instruction,and the vehicle offset and yaw velocity are very small.The established vehicle model has high reliability,which provides a reliable basis for the subsequent control system analysis.2)Stability analysis of four-wheel independent drive vehicle in straight driving.Based on the longitudinal and lateral force characteristics of the vehicle,the causes of vehicle deviation in straight line driving were analyzed.According to relevant standards,the objectives of straight running and driving stability of small unmanned ground vehicles were proposed,and the driving stability was analyzed from the Angle of driving wheel slip rate.The influencing factors of vehicle driving stability were analyzed from two aspects of wheel motor output torque difference and different road surface interference.3)A coordinated control strategy for the stability of direct driving is proposed.In order to ensure the stability of the vehicle in straight line,a coordinated control system for the stability of small unmanned ground vehicle in straight line was designed by using the layered control system.The control system includes the upper controller based on PID algorithm and fuzzy PID algorithm and the lower controller based on logic judgment.The upper controller includes a speed tracking controller,an additional yaw moment controller,a road identification module and a driving anti-skid controller.The lower controller puts forward the corresponding coordinated control strategy according to the driving wheel sliding condition.4)Integrate the vehicle model with the steering stability coordination control system,and build a four-wheel independent drive small electric vehicle co-simulation platform based on ADAMS-Simulink.The simulation analysis was carried out under the conditions of different motor torque characteristics and road surfaces with different adhesion coefficients,and the test results of the sample vehicle were compared with the simulation results.Simulation results show that: in the above different motor output torque and under different road adhesion coefficient and vehicle scooters turn rate can be effectively controlled,vehicle yawing angular velocity control in a small range,the vehicle lateral offset control in small range,vehicle has a good ability to straight and straight line driving stability;The actual vehicle test results verify the effectiveness of the steering stability control strategy.