Research On Skid Steering And Driving Control For The Multi-wheel-drive Vehicle

The skid steering vehicle,as its low-speed maneuverability and good handling performance,is widely used in military vehicles,construction machinery,unmanned ground vehicles and other fields.In recent years,the electric vehicle with in-wheel motors is considered one of the most promising vehicle structure,and with the development of electronic control technology,the skid steering vehicle may be easily controlled and achieve multifunction.Compared with the traditional way of deflecting the steering wheel,“skid steering” make vehicle eliminate the mechanical steering linkage mechanism,be more easily arranged,have a flexible steering mode and achieve zero-turning radius.In this paper,the multi-wheel skid steering vehicle with independent in-wheel motors has been studied,and the basic theory and dynamic characteristics of skid steering vehicle have been studied through its dynamic model.The static rules and dynamic allocation method of wheel torques have been discussed for multi-wheel drive vehicle,and all wheel torques are coordinated by introduing control allocation method.The driving control system was developed of the multi-wheel skid steering vehicle,and simulation and experimental study of the control strategy have been carried out,which provides theoretical and practical basis for the multi-wheel skid steering vehicle.Based on linear tire model,a dynamic model of multi-wheel skid steering vehicle is developed and the lateral resistance torque and tire slip angle characteristics were simulated and researched which can be a theoretical reference for steering control strategies.The 5 degrees of freedom(DOF)dynamics model of the multi-wheel skid steering vehicle is established considering the roll and pitch motion of vehicle and tire cornering and longitudinal slip joint properties.The sensitivity of the vehicle speed and structure parameters to steering performance and effect of steering time-varying input on vehicle mobility have been studied and 18 DOF vehicle dynamic model as a basic platform for simulation of subsequent control strategy was created based on the physical topology of the vehicle including motors,articulated arms,tires,and body models.With respect to the degrees of freedom of vehicle control,multi-wheel driving vehicle is one type of over-actuated systems.In the course of vehicle traveling,it is required that the kinematics and dynamics of all wheels have to be coordinated and controlled.Therefore the coordinated wheel torque control is the key factor in achieving skid steering and vehicle driving control.The static and dynamic rule based wheel torque distribution method has been studied in this paper,as well as optimal torque allocation method based on control allocation.The control allocation error and control energy are weighted as the optimization target,and wheel torque control allocation problem can be solved mathematically using quadratic programming method for which the optimization algorithm is correspondingly designed.The wheel slip control and actuator fault redundancy control schemes are integrated with optimization allocation algorithm,which improved the dynamic performance and safety of skid steering vehicle.The effectiveness of wheel torque distribution strategy was validated using Matlab/Simulink software and the simulation platform of the multi-wheel drive vehicle,and the simulation results show that the wheel torque,when a wheel motor fails,can be redistributed among the effective motors.Based on the proposed torque control allocation algorithm,one hierarchical driving control strategy is developed for the multi-wheel drive vehicle.Upper controllers including the vehicle speed controller and yaw rate controller receive from the driver the throttle and steering input commands which are interpreted respectively as the reference value of straight running total traction force and that of yaw moment when steering.The lower controllers mainly complete wheel torque dynamic allocation and generation of motor torque commands,and the tire forces were estimated in real time using articulated arm dynamics model.Simulation results from the multi-wheel drive vehicle also validated the effectiveness of the effectiveness of the driving control strategy under the condition of straight running,skid steering and J-turn maneuvers.A pure electric skid steering ground vehicle with six independent in-wheel motors is used as real vehicle test platform,and the vehicle driving control system was constructed to study dynamics and distributed control method of this type vehicle.The CAN bus communication protocol of more control nodes was designed including the master ECU,battery manager,motor controller,and so on,and vehicle ECU controller model was developed appling the rapid prototype platform,which realized the vehicle control function such as traveling straight,steering,emergency braking,parking,etc.In the hard road conditions,the vehicle is verified to be well-working under the operation modes such as traveling straight,open-loop steering and closed-loop steering,and experimental results from real vehicle test also validated the effectiveness and reliability of the vehicle driving control strategy and algorithm program.