Research On Sliding Rate Control Method Of Brake-by-Wire System Based On Direct-Drive Valve

As an essential component of advanced technology required for autonomous driving,the braking system plays a crucial role in road safety driving and vehicle handling stability.The deep integration of low-carbon,information and intelligent development has put forward new requirements for the braking system.Direct drive technology,with its advantages of high efficiency,energy saving,and compact structure,is gradually taking over the non-direct drive system market,providing new ideas for the development of the braking system.As an active safety control system,anti-lock braking system mainly controlled the slip rate of vehicles.In order to improve the longitudinal stability of the vehicle during emergency braking,the research on the slip rate control method has become a hot topic in the field of vehicle active safety.In this paper,the linear control system based on direct drive valve is taken as the research object.Firstly,through theoretical analysis,mathematical modeling,simulation analysis and experimental verification,the structure and hydraulic pressure tracking of the linear control system of direct drive valve are deeply studied.Secondly,on the basis of pavement optimal slip rate estimation,the slip rate control based on the drive-by-wire electro-hydraulic braking system is studied.The main work of this paper are as follows:(1)Design a configuration scheme of a new linear control dynamic system based on direct drive valve.According to the demand analysis of automobile drive-by-wire electro-hydraulic braking system,through the configuration selection of pressure supply unit and pressure regulating unit,an electronic hydraulic braking system with direct drive technology was proposed.The structure and working principle of the system are described in detail,the force analysis and calculation of the vehicle and the determination of the performance index are carried out,and the selection and parameter matching of the key components of the line control dynamic system are completed combined with the target model.(2)Establish the mathematical model of linear control dynamic system based on direct drive valve and build the test platform.On the basis of the design of linear control system based on direct drive valve,the mathematical model of linear control system including electromagnetic linear actuator,electromagnetic direct drive valve,high pressure accumulator and brake wheel cylinder is established.The simulation and test platform of brake system was built,the upper computer software was designed,and the characteristic curve of P-V relationship of brake wheel cylinder was measured.By tracking the actuator displacement of direct drive valve and the hydraulic pressure of brake system,the feasibility of the linear control system based on direct drive valve and the validity of the mathematical model are verified.(3)An optimal slip rate estimation method based on improved peak adhesion coefficient identification is proposed.Considering that the optimal slip rate of different pavement is different and the optimal control performance can be obtained only when the slip rate is near the optimal slip rate,an optimal slip rate estimation method based on the identification of peak adhesion coefficient is designed.First,a quarter vehicle dynamics model and a tire model were established.Secondly,on the basis of the existing identification of the road peak adhesion coefficient based on the analogy idea,the curve similarity principle is used to improve the identification method of the peak adhesion coefficient and divide the identification interval of the road peak adhesion coefficient.Finally,a simulation model was built to identify the peak adhesion coefficient of the target pavement under the typical pavement and the atypical pavement.(4)Design a slip rate cascade controller for the brake-by-wire system based on the direct drive valve.Aiming at the problems that the slip rate control performance of electromagnetic direct drive valve needs to be improved due to strong coupling and nonlinear factors,a cascade controller with the outer slip rate loop and the inner loop of the electromagnetic direct drive valve is designed.The fuzzy PID control is used for the outer loop,and the model-free adaptive sliding mode control is used for the inner loop,reducing the influence of the unmodeled dynamics of the actuator on the control performance.The simulation platform is built,and the slip-rate tracking and comparison analysis is carried out based on the given optimal slip-rate and the real-time identification of the optimal slip-rate.The results show that the braking distance and braking time under cascade control are 21.63 m and 2.172 s,respectively,when the initial speed is 70km/h on dry asphalt pavement.The braking distance and braking time under cascade control are reduced by7.9% and 4.2% compared with the inner loop PID control,which verifies that the proposed cascade control algorithm has good dynamic response performance.