Research On Vehicle Reconfigurable Steering Feel Strategy For Steer-by-wire System

Steer-by-wire(SBW)system eliminates the mechanical connection between steering wheel and the front wheel.It can realize the free design of steering angle transfer and force transfer characteristics,and plays an important role in optimizing vehicle performance,improving driving feel,integrating chassis control and realizing automatic driving active steering.In this paper,SBW system hardware-in-loop(HIL)simulation test bench based on d SPACE HIL real-time simulation platform was built.From the perspectives of steering angle transmission and steering feel feedback,the characteristics of steering angle ratio characteristic and steering torque ratio characteristic reconfiguration strategy and algorithm were studied and designed.In order to optimize the variable steering angle ratio of SBW system,an SBW angular transmission ratio controller based on fuzzy neural network was designed.The controller takes vehicle longitudinal speed and steering wheel angle as input,and outputs desired steering angle ratio.The input and output sample set used for the learning and training of controller network parameters comes from simulation experiment and calculation analysis.The SBW variable steering ratio characteristic dependent on longitudinal speed was mainly obtained through the double lane-change simulation experiments based on objective evaluation index for vehicle handling performance,which were conducted on a "driver-vehicle-road" closed-loop system.On the other hand,the SBW variable steering ratio characteristic dependent on steering wheel angle was obtained aiming to enlarge the steering wheel angle range with constant vehicle yaw rate gain.The simulation results of multiple maneuvers show that,compared with a steering system with fixed steering ratio,the proposed vriable steering ratio system can not only improve steering agility at low speed and path following performance at medium and high speed,but also reduce driver’s driver’s steering workload in controlling the vehicle.As an important driver-vehicle interaction component,steering system is responsible for providing drivers with steering feel feedback.The special structure of SBW system determines that it can only rely on steering feel imitation approach.In this paper,from two aspects of SBW steering feel feedback control strategy,the algorithm design of feedback torque reconfiguration strategy and steering torque ratio characteristics varying with longitudinal speed was carried out respectively.The purpose is to realize the basic functionalities and requirements of traditional steering system,and also to exploit the flexibility advantages of SBW system to the full.At the meantime,after sorting out ISO vehicle dynamics standard and GB vehicle maneuvering stability test standard,objective evaluation indexes of steering wheel force characteristics and corresponding experimental conditions for SBW steering feel feedback evaluation were screened and extracted.Finally,results of SBW HIL experiments show that the design of the steering feel feedback control strategy can provide drivers with a good sense of the road,to meet the requirements of steering easiness at low speed,clear and accurate feedback at high speed.