| Intelligent vehicle is a key automobile technology which will play an important role in the future transportation system.Deceleration tracking control can realize precise longitudinal motion control of vehicles and ensure safety,while wheel slip tracking control is conducive to wheel torque distribution and improve vehicle handling,which is of great significance.Brake by wire system is an important technology to realize the active braking and torque distribution of intelligent vehicles.This paper studies the control methods of deceleration tracking and wheel slip tracking for a kind of Brake by wire system composed of electric servo master pump and hydraulic control unit.Firstly,the control problems caused by nonlinear characteristics and uncertainties of electric servo master pump are discussed.Based on the sliding mode control method,the controller is designed to realize the deceleration tracking control.Secondly,this paper analyzes the control problems caused by the discontinuity of the on/off valve in the hydraulic control unit,and proposes a switching control method based on the backstepping method,which can realize the dynamic tracking control of the wheel slip.The specific contents of the paper are as follows.Firstly,the structure and working principle of the Brake by wire system are analyzed.The hardware-in-loop(HIL)system is built to test the characteristics of hydraulic control unit,and the data model of flow valve hydraulic characteristics is established,which is ths basis for the design of the wheel slip tracking controller.Finally,the system model is built based on Simulink for simulation validation,and veDYNA hydraulic module is modified to match the simulation platform and experimental bench.Secondly,the deceleration tracking control problem is transferred to master cylinder pressure tracking control problem because of the relationship between deceleration and master cylinder pressure.Considering the modeling of motor,transmission device and main cylinder,a control-oriented model is obtained.Considering the uncertainty of the model,a sliding mode controller is designed to track the pressure of the msater cylinder and the system stability is ensured by Lyapunov theory.In order to overcome the influence of slope,vehicle quality and other external factors on the acceleration-pressure relationship,a feedforward and feedback control method is adopted for pressure reference value planning,and the control effect is verified by simulation.Finally,the tire-road friction characteristics,wheel dynamics and hydraulic actuator characteristics are analyzed,and the slip control model with the rate of braking torque change as input is established,and the backstepping method is used to design the continuous control law.Considering the existence of on/off valve in the actual hydraulic control unit,the application of continuous control law is limited,so the switch control law is introduced,and the stability of the control system is proved by combining Fillipov and Lyapunov theory.Finally,the effect of the controller is verified based on simulation and HIL simulation system. |
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