Reliability Analysis Of EMUs Braking System Based On Fuzzy Dynamic Fault Tree

With the development of high-speed railway in China,China high-speed railway has gradually stepped into the forefront of the world.In order to ensure the high speed,safety and economic operation of EMUs,the reliability of EMUs has been attached great importance.As one of the most important systems of EMU,the braking system determines whether the EMU can run at high speed steadily.Therefore,it is significant to analyze the reliability of the braking system.Firstly,this paper summarizes the common reliability analysis methods and the related research of EMU reliability.According to the constitution and principle of CRH2 braking system,the fault mechanism of the system is analyzed.and the analysis model of the basic braking system is constructed by the fault tree analysis method.Aiming at the uncertainty of the fault rate of the basic events of the system,the expert confidence index survey method is used to obtain the data,and the triangular fuzzy number is used to modify the data.The theory of fuzzy mathematics is introduced to solve the problem of calculating fuzzy numbers,which makes the results of the target parameters more reasonable,the importance degree of different parts of the system is finally obtained,and the weak links of the target system are found by reliability analysis.Secondly,aiming at the dynamic characteristics of fault in braking system,the Markov model analysis method is introduced.The transformation process of dynamic logic gate and dynamic fault tree to markov model is described.Through the establishment of dynamic fault tree analysis model of brake control system and using triangular fuzzy number to describe the system transfer rate in different states,dynamic fault tree model is converted into markov state transition diagram according to the corresponding rules,and the state transition matrix is deduced.The system fault tree top event membership function of fuzzy failure rate is obtained by deduction and calculation,which is used to forecast the system reliability.Finally,on account of the combination explosion problem in solving complex dynamic fault systems by applying Markov model,which can only be used for global modeling analysis but cannot analyze the influence of individual components on the system,the Bayesian network model is introduced,and the transformation between logic gates and conditional probability tables is described.In consideration of the conditional independence of the model,the correlation between variables is described by conditional probability table,which reduces the complex reasoning process and the computational workload.The model of the system is constructed by combining the dynamic fault tree analysis method and transformed into the Bayesian network model.Taking advantage of its bidirectional reasoning ability,the change trend of system reliability can be obtained by forward reasoning,and the posterior failure probability of each basic event can be obtained by reverse reasoning,and then the weakness of the system appears.The results of system reliability analysis provides theoretical foundation for the formulation of system maintenance strategy.