Active Front Wheel Steering System (AFS)

Chapter 2

Conventional Steering System

• Rack and pinion system

• Constant steering ratio

• Fully mechanical system

AFS

• Wheel steer angle = superposition of steering wheel

angle and AFS actuator

• Variable steering ratio

• Combination of mechanical and electrical systems

Vehicle Handling Model (without side wind force)

Vehicle Handling Model (with side wind force)

Assumptions in modeling and control AFS

Fx = 0 (No braking or throttle inputs)

- Fyf = Cf f

- Fyr = Cr r

Where Cf = cornering stiffness of front tires

Cr = cornering stiffness of rear tires

wheel side slip angle

Controller Structure of AFS

Wind model

Performance Comparison of AFS and non-AFS vehicles

Yaw Rate

AFS

Non-AFS

Lateral acceleration

Simulation Data

• m=3950• Iz=6172• Lf=1.1• Lr=1.36• Cf=71600• Cr=77130• Vx=20• Lw=0.4