Research On Modeling Simulation And Evaluation Method Of Road Feel For Electric Power Steering System

Electric power steering system(EPS)has a poor road feel and is difficult to develop.It mainly relies on field vehicle tests.It has become an international research hotspot to explore the use of virtual tests instead of field tests.The electric power steering system is one of the main directions in the current electrification of the automobile industry.However,compared with the hydraulic power assistance,the introduction of the power assist motor causes the feedback of aligning torque felt by the driver through the steering wheel to be insufficient,resulting in unclear road feel.At present,there is no theoretical basis for the development of road feel,and relies mainly on field tests and subjective evaluation for adjustment and matching.Most international scholars and engineers are committed to exploring how to replace field tests with virtual tests,which can greatly shorten the development cycle,save development costs,and reduce the difficulty of matching.In order to realize the virtual test development of the steering system road feel,the steering system transient modeling and road feel evaluation issues are currently faced.Existing vehicle dynamics models can not support the research of road feel well.Most of the models lack key segments such as steering dry friction and carrier elasticity that affect the road feel,and cannot describe the steering transient process.Especially for the power steering system,the existing commercial software only has the nonlinear look-up table of the assistance characteristics,lacks the return and damping control,and cannot accurately describe the road feel of returning and high-speed running conditions.The research results of the research group for many years are summarized in this paper.Akemann steering mechanism modeling is completed,and the static and dynamic friction,the carrier elasticity and the aligning torque around the main pin and other factors are considered to establish the model of the key segments that affects road feel.For the steering assist control model,based on the assistance characteristics,the return control and the damping control are added.The road feel simulation capability of the model under the return conditions and high-speed straight-line driving conditions is improved effectively.Existing international automotive steering performance evaluation standards do not adequately describe the road feel.After investigation,it has been found that road sensation is not only concerned with the magnitude of steering wheel torque feedback,the magnitude of vehicle response,and the speed of return,but also concerned with the correspondence between steering wheel input and vehicle response and vehicle speed,that is the predictability and accuracy and other performance of road feel.In the existing evaluation system,the research on this correspondence is mainly concentrated in the high-speed center area.For the conditions such as situ steering,low-speed driving and turning,there are no evaluation indicators for the road feel such as predictability and accuracy.Starting from the relationship between the steering wheel torque,the angle of rotation and the vehicle response(yaw rate,lateral acceleration),the characteristic indexes that can evaluate the predictability and accuracy of road feel are attempted to be explored.And using the neural network model to establish a subjective scoring prediction model based on the calculation of the characteristic indexes.Comparing the model simulation results with the field test results,it shows that the model can be used for dynamic simulation of road feel under all conditions;It has been verified that the characteristic indexes associated with the input amount of steering wheel and the vehicle response amount that are initially explored in this paper can describe the subjective evaluation phenomenon such as road feel predictability and accuracy;and through the comparison of the subjective rating prediction results with the actual subjective rating results of the auto assessors,it is verified that the subjective rating prediction model of this article can accurately predict the road feeling performance.Based on the successful establishment of the road feel simulation model,the EPS assisted control model,and the establishment of a road feel evaluation method,through the simulation of the model,analyzing the influence of different EPS booster characteristic and control parameters on the road feel performance has been realized.It has certain guiding significance for the matching and optimization of the road feel of the electric power steering system.