Theory Research On Reliability-based Robust Design Of Gear Transmission With Multiple Failure Modes

An essential index of product’s quality, reliability attracts more and more attention in engineering with its rapid development and widely application. One of the objectives of mechanical structure design is that the reliability of the structure meets the requirements with its stability. However, the reliability of mechanical structure is influenced by some uncertain factors which affect the structure in different extent and cannot be ignored. For the sake of determining the degrees that each factor affects the structure, grasping key points in mechanical structure design and manufacturing, reducing costs and improving efficiency, reliability sensitivity design is very necessary for mechanical structures. Gear is an important part of mechnical transmission. As a result, it is necessary to analyze and design the structural parameters of gear system. Reliability-based robust design, a reliability optimization design based on reliability sensitivity analysis, provides a realistic approach for a gear transmission and mechanical structure in which reliability is needed.The contents of this thesis are as follows:1. Reliability analysis theories, domestic and foreign development of reliability sensitivity design and reliability optimization design are elaborated. It also discusses the background, objectives and meaning of the subject selected, and the importance of research on reliability and robust design for a stochastic dynamic structure system.2. Reliability optimization design of gear transmission system with multi-failure modes is investigated. This part presents the stochastic perturbation method, the Edgeworth series method and its related empirical revised formulas, and the reliability theories and optimization design of multi-failure modes. Combining reliability analysis theories with optimization design methods, a reliability optimization design approach for gear transmission with arbitrary distribution parameters is proposed in this part, which is a development of gear transmission reliability design theories with arbitrary distribution parameters. Taking into account of correlation of failure models, the reliability evaluation method of mechanical system with multi-failure modes is investigated. Moreover, it suggests that the reliability optimization design of gear transmission with arbitrary distribution parameters and with multi-failure mode can be processed through computer software provided that the first four moments of basic random parameters are given. Finally, the approach proposed is verified with examples.3. Reliability-based sensitivity design of gear transmission is researched. Combining reliability design theories and sensitivity analysis method, with the foundation of reliability mathematics, a calculating method for reliability-based sensitivity design for gear transmission is proposed, which gives the changing rule of reliability sensitivities, researches on the influential degrees of design parameters’variety to components’reliability, and more over provides a theoretical basis for gear transmission’reliability design. Given the first four moments of random parameters, the unknown state functions’probability distribution can be expressed by standard normal distribution using stochastic perturbation method and the Edgeworh series method and its empirical modified formulas. The reliability calculating formulas for gear transmission with arbitrary parameter distribution is then determined, and the related reliability-based sensitivity’s calculating formulas is deduced using sensitivity solving method. There is no limitation of random parameters’probability distribution types on the method proposed, thus it is more accessible to solve the realistic mechanical components’ reliability problems in engineering. Similarly, this approach is verified by examples in the following.4. Reliability-based robust design of gear transmission system is studied. Combining reliability-based sensitivity theories with robust design methods, gear transmission’s reliability-based robust design is investigated based on the reliability optimization model, a numerical calculating method for reliability-based robust design is proposed. Adding the reliability based sensitivity to aims of the optimization designing model, the reliability-based robust design is then come down to multi-objective optimization problems which also satisfy the reliability requirements. Therefore, reliability-based robust design of gear transmission with multi failure modes is achieved provided that the reliability requirements are satisfied. Examples are checked out to verify the effectiveness of the method proposed.5. The gradual varying reliability and reliability based-sensitivity problems of the gear transmission system with multi failure modes are investigated. In consideration of the strength degradation, combining the gradual varying reliability theory and the reliability based sensitivity analysis method, with the foundation of reliability mathematics, the evaluating method of the gradual varying reliability and reliability-based sensitivity analysis of the gear transmission system with multi failure modes is build. The changing rule of the reliability-based sensitivity taking the strength degradation into accordance is given, and the influence level of the designing parameters’ varying to the gear transmission systems’ reliability is studied. It provides the theory support for the gear transmission systems’ reliability design.