Research On System Design And Control Method Of W-ECHPS For Heavy Commercial Vehicles

To date,heavy commercial vehicles widely adopt hydraulic power steering(HPS)system,which has fixed assistance characteristic leading to insufficient high-speed steering feel as well as degraded handling performance,and has pump overflow loss leading to high system energy consumption.Therefore,it is of great significance to investigate steering systems with variable assistance characteristics and low energy consumption for heavy commercial vehicles.Since the motor power cannot fulfill the assistance requirement,the electrohydraulic power steering system and electric power steering system which are applied for passenger cars and light commercial vehicles are inapplicable to heavy commercial vehicles.The electronically controlled hydraulic power steering(ECHPS)system is the improvement solution to the heavy commercial vehicle HPS system now,which has variable assistance characteristics.Although the electromagnetic slip coupling-type ECHPS system can effectively reduce the system energy consumption,the electromagnetic slip coupling requires continuous electric current when operating,which is less efficient and not beneficial for application.Therefore,a novel winding type permanent magnet coupling(WTPMC)-based ECHPS(W-ECHPS)system is proposed in this thesis.The researches are conducted in terms of variable assistance characteristic curve design,design and steady-state performance analysis of WTPMC,adaptive dynamic surface control of WTPMC output speed,vehicle handling stability simulation and energy consumption analysis,field test for handling stability and energy consumption,response performance analysis under emergency steering condition,which are as follows:The mathematical and simulation models of W-ECHPS mechanical and hydraulic subsystems are established for simulation of assistance characteristic curve.To validate the model accuracy,simulated and experimental assistance characteristic curve of HPS system are compared.To ensure that the driver perceives good steering feel at different vehicle speeds,the design method of variable assistance characteristic curve of W-ECHPS system based on feature point is proposed.By adopting different methods for steering resistance,the assistance characteristic curves of W-ECHPS system under pivot steering condition and steering conditions at typical vehicle speeds are designed.By combining curves under these steering conditions,the variable assistance characteristic curve of W-ECHPS system is obtained.The simulation calculations for WTPMC operating parameters such as input speed,output speed and load torque under different driving conditions are carried out.The design of WTPMC is conducted based on the operating limit under pivot steering condition.Finite element simulations of WTPMC using Ansoft Maxwell software are conducted to study the steady-state(constant slip speed)performances,including electromagnetic,speed-regulating and slip power recovery performances.The simulation results show that the WTPMC has good electromagnetic performance and can meet the requirement of operating limit.By regulating the duty cycle of IGBT,the WTPMC can operate under different driving conditions.The WTPMC has good slip power recovery performance,and the slip power recovery efficiency is between 67.4% and72.5% under different driving conditions.The WTPMC prototype is manufactured and bench tests are carried out.To validate the effectiveness of finite element simulation results,simulated and experimental line back-EMF under no-load condition,duty cycle of IGBT and terminal voltage of ultracapacitor are compared.The mathematical model of WTPMC is established for deriving its state equation.For the control problem of WTPMC output speed with parameter uncertainties,an adaptive dynamic surface control scheme is proposed.The state equation of WTPMC is established,and the adaptive dynamic surface controller is designed.The adaptive estimation for uncertain parameters is conducted,and the stability analysis of WTPMC closed-loop control system is carried out by applying Lyapunov synthesis.The simulation model of WTPMC closed-loop control system is established,and simulations of step tracking,anti-load disturbance and comprehensive driving condition are conducted.The rapid control prototyping system of WTPMC based on dSPACE is established,and bench tests of step tracking,anti-load disturbance and comprehensive driving condition are carried out.Simulation and experimental results show that the proposed adaptive dynamic surface control scheme can realize the accurate control of WTPMC output speed and its control performance is better than that of PI control,thus the effectiveness of adaptive dynamic surface control scheme is validated.The models of vehicle dynamics and steering resistance are established,and the simulation model for vehicle handling stability is developed.To validate the model accuracy,simulation and experimental results of double lane change and slalom test conditions are compared.Simulations of steering portability and on-center handling test conditions are conducted.The simulation results show that the W-ECHPS system has good low-speed steering portability performance as the HPS system,and its high-speed steering feel is significantly better than the HPS system.Thus,the vehicle handling stability is improved.The energy-saving mechanism of W-ECHPS system is analyzed,and energy consumptions under straight driving and steering conditions are calculated.The results show that the energy consumption of W-ECHPS system is reduced by10.2-54.9% compared with that of HPS system under different driving conditions,and the energy consumption reduction rate increases with vehicle speed.Thus,the energy-saving performance of W-ECHPS system is validated.The WTPMC prototype is installed on the test vehicle,and field tests of steering portability and on-center handling are conducted.The field test results show that the W-ECHPS system has good low-speed steering portability performance as the HPS system,and its high-speed steering feel is significantly better than the HPS system.Thus,the vehicle handling stability is improved.Field tests of energy consumption under straight driving and steering conditions are carried out.The field test results show that the energy consumption of W-ECHPS system is reduced by9.2-48.9% compared with that of HPS system under different driving conditions,and the energy consumption reduction rate increases with vehicle speed.Thus,the energy-saving performance of W-ECHPS system is validated.For the assistance pressure response delay problem of W-ECHPS system under emergency steering condition,the steering wheel torque step input is adopted to simulate emergency steering condition,and the simulation of assistance pressure response is conducted based on the simulation model for vehicle handling stability.Parameters such as WTPMC slip rate,WTPMC electric current,moment of inertia of WTPMC inner rotor,torsion bar stiffness and pump displacement are selected as influence factors,and assistance pressure responses are analyzed.The movement relationship model under typical emergency steering condition is established,and the relationship between assistance pressure response and collision avoidance route is analyzed.Simulations of assistance pressure response time threshold for realizing collision avoidance at different vehicle speeds are carried out,which provide basis for investigating control strategies of realizing emergency steering collision avoidance by improving the response performance of W-ECHPS system.