Reseacrh On Safety Control Method Of Automotive Brake System Based On X-by-wirc

The research of automotive safety technology has attracted considerable attentionduring recent years，and the brake system plays an important role in maintainingvehicle driving safety. Using X-by-wire technology to establish the electronic controlsystem can greatly improve the automotive safety performance, reliability andstability. Brake-by-wire has brought fundamental changes to automotive structure andbraking system performance, which has significant advantages compared withconventional hydraulic or electro-hydraulic brake system. Although the use ofBrake-by-wire will promote vehicle maneuverability, comfort, fuel economy andenvironmental protection, there are many technical and design challenges haveimpeded its commercialization, such as the lack of design method for system structurewhich will ensure a more safety and reliability Brake-by-wire system, the modeling ofglobal X-by-wire non-linear dynamic system, the strategies of brake force distributionbased on the independent four-wheel brake control, and reliable real-time constrainednonlinear optimal control algorithm. This dissertation is intended to tackle the mainareas of interest in the Brake-by-wire system, namely the safety control method, andthe research will be conducted as following:(1) The development, application, major impediments and key technologies ofvehicle break-by-wire system are discussed in this dissertation, and the X-by-wiresafety control technologies are mainly considered, including the structure design ofwire-control system, the optimal braking force distribution strategy based on thefour-wheel independent braking control, the optimal slip-ratio estimator, and thesliding mode controller (SMC) for ABS in BBW systems.(2) Five kinds of failure modes of brake system are summarized, and then a methodwhich combed failure modes&effects analysis (FMEA) and fault tree analysis (FTA)is used to investigate the reliability of brake-by-wire (BBW) system. Finally astructure design method based on reliability analysis and fault tolerance technology isused to design double redundant structure for BBW system and duo-duplexarchitecture for the pedal module.(3) Based on the slip ratio, an ideal brake force distribution strategy for four-wheelindependent brake control system is proposed. Moreover, the optimal braking forcedistribution curve is obtained through the improved particle swarm optimizationalgorithm. This new braking force distribution strategy not only can maintain thesame braking intensity and brake speed as traditional method, but also always ensures greater slip ratio for front wheels and then guarantee the vehicle direction stabilityduring braking, and preventing rear axle shaft from locking prior to front axle, furtherprevented dangerous side slide, and making front and rear wheel braking forcedistribution more close to ideal braking force distribution curve, so as to provide theoptimal braking parameters for breaking force control.(4) Considering the nonlinear property of vehicle braking process, an improvedBurckhardt model based on RBF Neural Network (RBFNN) is proposed. At the sametime, a new hybrid parameter optimization algorithm PSO-SNPOM is designed tooptimize the parameters for RBF neural networks. This algorithm combined structurednonlinear parameter optimization method (SNPOM) with Particle SwarmOptimization (PSO).(5) A new method based on Improved Burckhardt model is proposed to estimate theoptimal slip ratio on-line in any setting road condition, and the effectiveness andfeasibility of this identification method is verified by simulation results.(6) A fuzzy sliding mode controller (SMC) based on the switching gain adaption isdesigned; SMC method combined variable structure control and fuzzy control.According to the non-linear feature of the braking process, a fuzzy sliding modecontroller based on slip ratio is designed for ABS in BBW systems. The co-simulationof MATLAB/Simulink and CarSim as well as the hard-in-loop test platform are set upseparately to simulate the brake-by-wire ABS control strategy under single pavementand variable pavement conditions. The simulation results indicate that, compared withPID and the conventional sliding mode control algorithm, the sliding mode controlalgorithm based on gain fuzzy control has higher accuracy and robustness, whichcould make the automobile obtain a better braking performance and a betteradaptability in varied roads. Meanwhile, the braking performance of the ABS controlsystem based on optimal slip rate is superior to that of ABS system based on constantslip rate.The research of vehicle X-by-wire safety control technology will improve thevehicle safety and stability. This research not only built up the theory foundation forthe practical application of X-by-wire system, but also formed the basis for itsapplication in other vehicle electronic control system or other types of vehicles.