Abstract:

Due to the cancellation of the mechanical connection between the steering wheel and the steering gear， the interaction torque between the road surface and the tires， the unevenness of the road surface and other information cannot be directly transmitted to the steering wheel， and the driver cannot obtain the real "road feeling" when controlling the steering wheel， so the road sense simulation is one of the key technologies of the steer-by-wire system. At present， the road sense simulation method of steer-by-wire system in flat road conditions has been relatively mature， but it is still difficult and challenging to simulate road sense in bumpy road conditions. In this paper， an extended state observer is designed based on the steer-by-wire actuator model to estimate the steering rack force， and the main torque of the SBW system is determined with reference to the power assist characteristics of the electric power steering system （EPS）， and the system friction torque， damping torque， active return torque and limit torque that need to be estimated in the SBW road sensing simulation under conventional road conditions are analyzed. Considering the particularity of the bumpy road sense simulation， it is necessary to determine the corresponding compensation torque according to the influence of the steering wheel vibration frequency on the driver， grasp the driver's acceptance of different frequencies of the bumpy road surface based on the wavelet decomposition of the vibration signal， and reconstruct the bumpy road vibration through screening， attenuation or amplification of the rack force signal， so as to reasonably calculate and compensate the road sense simulation torque of the bumpy road. The simulation and bench experiment results show that the bumpy road sense simulation method based on wavelet decomposition and reconstruction not only does not affect the steering comfort of the driver， but also makes the driver clearly feel the unevenness of the road surface and obtain a good road feeling.

Key words: steer-by-wire （sbw） system, road feel simulation, bumpy road torque, wavelet decomposition and reconstruction