| High reliability of Electric Multiple Units (EMU) has become an important feature of high-speed railways. How to evaluate the reliability of EMU and how to improve the reliability of it by the proper maintenance means have become the key factors to ensure the safety and reliability of the high-speed railways. Now the performance of EMU made in China is approaching the international advanced level, but the EMU reliability assessment in China still remains to be improved. The reliability problem of EMU has attracted great attention of the researchers and engineers in this area. Reliability modeling is an important part of the EMU reliability research. Correct modeling is the precondition and guarantee of the reliability assessment and improvement. Nowadays, the EMU reliability modeling and assessment are based on limited failure data of its subsystem. And entirety reliability assessment study is under the postulated condition of "as-good-as-new" perfect repair. However, for the complex system such as EMU, the repair effect is "as-bad-as-old" if only repairing the fault system. Therefore, the EMU entirety reliability modeling should be improved according to the repair effect. The maintenance strategy of EMU should be studied with considering the harm extent, risk and cost of all kinds of failures.In this paper, EMU and its subsystems were the main objects of study. The EMU reliability assessment and maintenance strategy optimization were the problems to be solved. Statistics, reliability theory, maintenance engineering, life cycle assessment theory and computer simulation are involved in. The following aspects were studied:(1) According to EMU reliability modeling features, basic properties of components of EMU, such as function, structure, material, life and so on, were considered, relevant relations among components are definite and a comprehensive relation matrix was acquired through analytic hierarchy process, and a clustering model of EMU system partition based on modularization theory was proposed. The feasibility and effectiveness of this model and algorithm was verified through sensitivity analysis. The EMU system partition results were presented by adopting population genetic algorithm and MATLAB simulating calculation. The research results lay theoretical foundations for reliability model and analysis of EMU system. This system partition method is conducive to EMU modular design, and helps reduce maintenance load, shorten repair time, cut life cycle costs.(2) Each subsystem’s reliability of EMU is a key part of the evaluation of entirety reliability. Based on EMU application failure data, fault law and reliability of each subsystem were studied by using statistical theory and reliability theory. The fault tree model of each subsystem was set up with the analysis of its structure and function. The reliability rule of each subsystem was derived and proven according to each subsystem’s failure mode, frequency, causes and effects. The reliability evaluation index and calculation method of each subsystem were given.(3) According to the assumption of two states and independent subsystems, the reliability model of the whole EMU was set up with the analysis of its functional and structure. The model is applicable to assessing the EMU entirety reliability under the precondition that all subsystems’ fault laws are known. The Monte Carlo simulation results verified that this reliability model is rational and valid.(4) This paper firstly presented the EMU reliability model based on "as-bad-as-old" minimal maintenance. The model is the mathematical model of the non-homogeneous Poisson process with theoretical analysis of EMU repairable system. It avoids the interference of each subsystem disadvantage, and implements effective evaluation of EMU entirety reliability. Compared with that of the EMU reliability model based on structure and function, the simulation results proved that the model can reveal the EMU reliability principle more rationally and validly, and fit the fault data of EMU practical application better.(5) Based on the reliability model of the whole EMU and each subsystem, repair strategies including repair mode and maintenance cycle were optimized. According to the harm degree of the part’s failure, its repair mode was optimized. This paper firstly proposed the optimization model of prevention repair cycle with the analysis of availability and risk. A feasible and effective maintenance decision method was provided to improve the EMU availability and reduce maintenance costs,.(6) To ensure that the newly purchased EMU meet application needs, the reliability and maintainability parameters and indicators were analysed and demonstrated. Based on the principles of reliability and maintainability, how to determine the parameters and indexes was presented. According to the characteristics of EMU, the relevant parameters, indicators and contract parameters were given. Through the technical and economic analysis, the optimized procurement scheme and the reliability test solution provide effective reference for EMU procurement and acceptance. |
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