Performance Research And Parameter Optimization Of Commerical Vehicle Electroniccally Controlled Hybrid Power Steering System

Development of electronic control technology is relatively slow in commercial vehicle steering system due to the limitation of the conventional on-board electric supply system.Nowadays,Hydraulic Power Steering System(HPS)is still widely used in commercial vehicles,which has drawbacks of large energy consumption,immutable assistance characteristic and poor steering feeling at high speed.With the surging concern on electrification and intelligence,an Electro-hydraulic Coupling Steering System(EHCS)is proposed,which has combined the technology of both hydraulic and electric steering.Based on the structure of HPS,an electric motor and a control unit are added to realize the active torque and angle control of steering system.EHCS is featured with high energy density and high-level intelligence.However,EHCS overcomes steering resistance moment mainly through the hydraulic system,and the electric system only improves the steering feeling of drivers with small electric torque output failing to significantly reduce the energy consumption of the steering system.Because of defects of EHCS,a novel Electronically Controlled Hybrid Power Steering System(ECHBPS)is proposed based on the structure of HPS in this paper.In ECHBPS,electric assistance torque is coupled to the recirculating ball gear through both valve torque bar and new-designed assist torque coupling device.According to working principle of ECHBPS and characteristics of the assist torque coupling device,the parameters of the hydraulic subsystem were reset;Handling stability and energy consumption were studied through co-simulation of Simulink and Trucksim;The comprehensive evaluation index of ECHBPS was established and parameters of ECHBPS system were optimized by the improved particle swarm optimization algorithm.The research contents of this paper are as follows:(1)The structure and working principle of ECHBPS were introduced.Models of ECHBPS and the vehicle were established by Simulink and Trucksim.Accuracy of models was verified by comparing bench test results of the electric and hydraulic systems with the simulation test ones.(2)Parameters of hydraulic subsystem were reset to avoid the impact of assist torque coupling device on steering feeling,according to the maximum steering resistance moment of the commercial vehicle at the lowest normal driving speed which was calculated through vehicle tests and theoretical analysis of steering resistance moment.The matching results show that,compared with HPS,the cylinder diameter of ECHBPS decreases by 17.48% and hydraulic flow by 28.57%.(3)According to driver preferred manoeuvring torque under steering condition,assistant characteristic curves of electric and hydraulic subsystems were designed.The open-loop handling stability performance of ECHBPS was studied through the simulation test.The results show that,compared to HPS,maximum steering torque is decreased by 21.01% and 22.91% respectively under the parking manoeuvring condition and portability steering test condition,and steering feeling under the on-center steering condition is improved by 109.06%.The energy consumption of ECHBPS was analyzed by simulation test.The results show that,compared to HPS,ECHBPS can save 65.99%,34.85% and 15.74% energy in direct,low-speed and high-speed steering conditions,respectively.(4)The single-point preview driver model was established and the comprehensive evaluation index of ECHBPS considering handling stability and energy consumption of steering system was proposed,under the Man-Vehicle-Road closed-loop objective evaluation system.Weight coefficients in the index were calculated by the entropy method and influence of simultaneous change of single and twin parameters on the index was studied.The results show that the system structure parameters have great influence on the comprehensive evaluation index of ECHBPS,and the non-linearity is strong.(5)To further improve comprehensive performance of ECHBPS,a ring topology particle swarm optimization algorithm with dynamic neighborhood and diversity enhancement mechanism and compression factor(D-DNLPSO)was proposed.Eight system parameters of ECHBPS were optimized by D-DNLPSO.After optimization,the comprehensive evaluation index of ECHBPS is improved by 11.11% and the handling stability index by 4.05% and the energy consumption index by 27.26%,respectively.Meanwhile,the optimization results show that the improved D-DNLPSO can find solutions with higher quality and search efficiency.