Research On Driving Torque Distribution Characteirstics And Sliding Mode Control Strategy For Four Wheel Drive Vehicle

In recent years, with the continuous development of technology related to thedriving torque distribution for four-wheel drive vehicle, people are no longersatisfied with the four-wheel drive vehicle which merely improves the tractionperformance,and begin to pursue an overall improvement in the tractionperformance, handling performance and stability performance by driving torquedistribution.This paper deals with the problem of how to achieve an overall improvement invehicle performance by the control technology of driving torque distribution. Avehicle dynamic method and a simulation method are firstly used to clarify thevehicle dynamics effected by driving torque distribution, not only between the frontand rear wheels but also between the left and right wheels. Then control algorithmsof driving torque distribution are proposed and an off-line simulation platform isbuilt to explore the torque distribution control for the four-wheel drive vehicle. Themain content of the thesis are as follows:1.Two method was used to explore the effect characteristics on vehicle powerperformance, steering performance and driving stability of driving torquedistribution, not only between the front and rear wheels but also between the left andright wheels。One is theoretical analysis on the basis of the principle of vehiclesystem dynamics， the other one is simulation based on the CarSim andMATLAB/Simulink joint simulation platform under different fixed driving torquedistribution.2. Given that the research involve in driving torque distribution, not onlybetween the front and rear wheels but also between the left and right wheels, thetorque distribution devices，including the central coupling and the electronically controlled rear limited slip differential，are dynamics modeled and implemented inMATLAB/Simulink in details，while the vehicle model was modeled directly inCarSim software based on on the target vehicle parameters on the basis that theassembly configuration is determined. The Simulink model should be associatedwith the CarSim vehicle model during the co-simulation.3. on the basis of study on the vehicle performance impact by driving torquedistribution, the vehicle driving conditions are divided into straight line drivingconditions and steering driving conditions according to the vehicle control objectivesin different conditions. The corresponding driving torque distribution controlstrategy and controller are also made. On the straight driving conditions, thecontroller initial front and rear torque distribution ratio through longitudinalacceleration signal and the road slope signal, then use the sliding mode variablestructure control method to determine the correction ratio to minimize the the frontand rear wheel speed difference; on the turn driving conditions, the controller get thedesired yaw rate from the two degrees of freedom linear vehicle model to determinethe vehicle steering state: if the vehicle oversteers, the controller use the slidingmode variable structure control method to determine the driving torque distributionratio between the left and right rear wheel; if the vehicle understeers, the controlleruse PID control algorithm to determine the driving torque distribution ratio betweenthe front and rear wheels.4. on the basis of the dynamic model for four-wheel drive vehicle and torquedistribution control algorithms, the simulation is performed on MATLAB/Simulinkand CarSim simultaneously according to the modular thinking. During thesimulation Several blocks, e.g. torque distribution devices and torque distributioncontrol algorithms in the Simulink exchange the simulation signal with the vehiclemodel in the CarSim. The offline simulation is proceeded by means of straightcondition, climbing accelerated conditions and steering accelerated conditions. Theresult of the simulation shows the effectiveness of driving torque distribution controlalgorithms.