Modeling and control strategy of assist characteristic of recirculating-ball EPS system for bus

The mathematical model of primary modules of recirculating-ball electric power steering system for bus was built. The simulation model of the EPS system was constructed based on Matlab/Simulink. The control strategy of assist characteristic, which includes proportional and differential control of the torque transducer output signal and the assist motor angular velocity feedback, was purposed subsequently. The damp of EPS system can be changed with the demand, so the steering wheel shimmy is decreased, and the controllability and stability of steering system are both given attention during vehicle running. Adaptive fuzzy PID is adopted as the control strategy of motor current loop. The simulation results demonstrate that the assist characteristic algorithm proposed is effective in improving the dynamic performances of steering system.