Study On Reliability Of Planetary Transmission System In Shield Machine Based On Dynamic

As one of the four quality characteristics for the products, Reliability is becoming more and more important with the development of modern scientific technology and the high requirement for the products, especially for large machinery transmission devices, like shield machine cutter drive high-power reducer. Shield machine specializes in digging tunnels underground. Its cutter drive high-power reducer is the main working device, functioning as driving the cutter to cut soil. Shield method is a complex kind of construction activity undeground. The cutter drive reducer works under variable load conditions because of complex geological structure. Meanwhile, the complex structure of the reducer makes the probability increase greatly that the failure of each relevant part leads to the failure of the system, and it's very difficult to maintain it underground. All these require the reducer high reliability and good dynamic characteristic. Accurate reliability analysis and evaluation must be carried out considering dynamics of the system during product design. The study relys on a project of National High-tech R&D Program (863 Program)"The high transmission power reducer of Earth Pressure Balance Shield Machine". Considering the structural characteristic of 3-stage planetary transmission, the dynamic model of the system is developed, and dynamic stress of each gear pair is obtained by dynamic response analysis. Based on the above, the dynamic reliability model of the system is presented under conditions of multi-failure modes relevance and strength degradation, and Monte Carlo method is applied to simulate the reliability of the system. Then,the contact and bending fatigue reliability sensitivity of the planetary gears is studied. Finally, based on the dynamic model, the reliability model and reliability sensitivity analysis, reliability robust dynamic optimization for the system is carried out to provide a theoretical reference for the design and manufacturing of the shield machine high-power reducer. The main researches are as follows:①The study on dynamic characteristics for the shield machine high-power 3-stage planetary transmission system. The lumped parameter method is applied to develope the purely torsional dynamic model of 3-stage planetary transmission system used in shield machine cutter drive. Internal excitation such as time-varying meshing stiffness, meshing error and external excitation caused by the fluctuating external load are all considered. By vibration modes analysis, the natural modes of the planetary transmission system are investigated. By dynamic response analysis, the dynamic meshing force of each gear pairs is obtained to computer the dynamic stress, which should contribute to the following reliability design based on the stress-strength interference theory for the system.②The study on reliability model for the shield machine high-power 3-stage planetary transmission system. The important parts and main failure modes of the shield machine planetary gear reducer are obtained by using FMEA method, and the reliability block diagram of the system is built accordingly. The reliability computation models of both gear failure units and bearing failure units are developed by using approximate probability method to describe the distribution laws of random variables such as stress and strength. By completeing the reliability of the failure units, the failure modes that tend to occur are obtained. By applying the stress-strength interference theory at the system level, general reliability computation model for mechanical transmission system is presented under conditions of multi-failure modes and multifactor relevance, and applied to the reliability analysis and evaluation accurately for the 3-stage planetary transmission system used in shield machine cutter drive. The units that tend to fail are mainly considered as there are too many failure units; the relevance on load is mainly considered as there are multi-factor relevances. Finally, the dynamic reliability of the system is studied to obtain the reliability curve and failure rate curve of the system.③The study on reliability simulation for the shield machine high-power 3-stage planetary transmission system. Monte Carlo method andχ2-type goodness-of-fit test method are applied to simulate and test the distribution laws of the contact stress, the contact strength, the bending stress and the bending strength of planetary transmission gears used in shield machine cutter drive. Based on the distribution laws of stress and strength, the contact and bending reliability of gear failure units and 3-stage gear system is obtained by simulating to verify the accuracy of the reliability model for the shield machine failure units and system, compared with the results that the analytical method obtains, which provides an accurate numerical method and theoretical reference for the reliability design of the shield machine cutter drive planetary reducer.④The study on reliability sensitivity of the gear of shield machine high power planetary reducer. Based on the above reliability analysis, fourth-moment method is applied to analyze the contact and bending reliability sensitivity of the gear of shield machine planetary reducer. Meanwhile, importance sampling method is used to obtain the accurate solution for reliability sensitivity to verify the above results, which provides the basis and reference for the following reliability robust design and the manufacturing of the planetary gears.⑤The study on reliability robust dynamic optimization for the shield machine high-power 3-stage planetary transmission system. As the high-power reducer used in shield machine cutter driver requires high reliability and good dynamic characteristic,based on the above reliability model,the dynamic model and reliability sensitivity analysis, the multi-objective optimization model of 3-stage planetary transmission system used in shield machine cutter driver is developed to improve the reliability,the robust and the dynamic characteristic of the system, in which the reliability of the system, reliability sensitivity of the sun gear of the low-speed stage and the product of the application factor and dynamic factor of external gear for each stage are taken as the objective function, and the reliability of gear failure units,the volume/mass of the system and other requirements are taken as the design constraints.The optimization of a practical example using particle swarm algorithm and penalty function method is carried out. The result demonstrates that the optimization model and method can effectively increase the reliability and the robust and improve the dynamic characteristic of the 3-stage planetary transmission system used in shield machine cutter driver.