Research And Simulation Analysis On Vehicle EPS Torque Assistance Characteristic Curve

With the continuous improvement of science and technology,the vehicle steering system has been developed from the traditional mechanical steering system to the power assisted steering system which represented by the hydraulic assist type,the electro-hydraulic assist type and the electric power steering system.Nowadays,known as its comfortable driving,compact structure,energy saving and environmental-friendly,the research on EPS has become more and more popular among all research institutes.In this paper,taking a miniature vehicle equipped with EPS as the research subject,and the influence of the EPS system matching the different torque assistance characteristics curves on the vehicle maneuverability is mainly studied.First of all,on the basis of consulting a large number of related literatures,combined with the structure and working principle of automobile EPS,the math model of each component of EPS system is established,and built the mathematical model for the parts including steering column,torque sensor and EPS motor.Afterwards,through the detailed analysis of the torque assistance characteristics of EPS,according to the contact characteristics of wheel and road,the tire,king pin and other structural models are established,and also confirm the main relations between parameters of the steering system,the tire ground parameters and the steering wheel resistance torque.According to the formation principle of EPS boost torque,the difference between the steering wheel resistance torque and the driver’s ideal steering wheel torque of the non-power steering system is determined under the conditions of still working conditions,medium-low speed conditions and mid-high speed condition,then the steering torque under static condition,medium-low speed condition and mid-high speed condition was analyzed in simulink.According to the difference of steering torque,the design of new EPS torque assistance characteristic curve was completed.Through the analysis of the control strategy of EPS,the control strategy and control mode required in this paper are confirmed.Then the simulation models of the mechanical steering system,the control system and the EPS motor system in EPS are established in MATLAB/Simulink.Finally,a complete vehicle simulation model is built by the vehicle datasets in CarSim.According to the provisions of GB/T-6323-2014,with the method of co-simulation,the influence of the EPS matching with different torque assistance characteristic curves on the driveability of the vehicle is compared.The simulation results show that EPS matching with the new type torque assistance characteristic curve can increase the handling stability and have a better effect on the steering stability of the vehicle.