Active Front Steering Control Method Research Of Four Wheel Drive Electric Vehicle

Steering system is an important part of automobile, the system controls the vehicleroute and direction, and its performance is directly related to the vehicle handling andstability. The traditional steering system of vehicle, mostly used hydraulic steering systemand electric hydraulic power, the system has a complex structure, high energy consumption,and it is diffcult to maintain the defects and not suitable for four wheel drive chassisstructure and energy saving requirements of new electric car. In order to solve the aboveproblems, it needs to build a new type of steering system. In this paper, four wheel driveelectric vehicle as the research object, in Shenyang science projects of electric vehicledoubly fed drive differential speed and handling stability research on the key technology ofcontrol (F12-277-1-11) funding, research on electric vehicle steering system power controland high speed large angle steering process stability control problem.For the research of vehicle steering system, first of all, it needs to reduce thedimensions of the seven degree of freedom nonlinear dynamic model and get the electricvehicle model of two degrees of freedom. According to the mathematical model of thetraditional passive steering, steering system simulation model is built. Simulation analysisof steering can be obtained, the traditional passive steering system steering is laborious, theoperating force is not up to the large angle steering wheel angle limit value, so it isnecessary to take power control, reducing the driver’s workload.According to the structure and characteristics of electric vehicles, the EPS (ElectricPower Steering) system for power control, the ECU (Electronic Control Unit) which basedon the steering wheel input torque and the real-time speed, controls EPS motor output thepower torque, compensate the driver’s control force. In the original steering system basis,to build a EPS system model. Through simulation analysis, EPS system can effectivelyprovides assistance, and improves the agility of low speed and the security of high speed.EPS system can effectively solve the power problem, but the vehicle which equippedEPS system at the high speed and large angle steering condition exists instability problem, so it needs to take control of vehicle stability, with active steering control. The foundationdesigns a new active front steering that based on EPS system. Adding the double planetarygear mechanism and the angle assist motor to the original EPS system, and change thetransmission ratio, active steering and stability control. Because the vehicle is nonlinear, sousing the robust control and the fuzzy control algorithm, and tracking the desired yaw ratecontrol the vehicle stability. Through simulation, the AFS system is an effective solution tothe control problem of fixed transmission ratio and vehicle stability.