| Planetary gear transmission has many unique advantages,such as greater transmission ratio,stronger carrying capacity,and more compact structure.It is these distinctive advantages that make it widely used in aircraft engines,wind power gearboxes,shield reducers and other important transmission occasions.In these devices,planetary gear transmission has the characteristics of complex mechanical structure,various forms of motion,poor load conditions,etc.,and any failure form of the transmission parts may affect the power transmission function of the whole system.Therefore,it is of great significance to analyze and predict the reliability for planetary gear transmission system.Reliability is determined by load and strength,so accurate information of the load and strength is a prerequisite for effective prediction of reliability.In this paper,the unavoidable unequal load sharing problem and the universal randomness of service load in planetary gear transmission system are analyzed respectively,and the load calculation results are used as load input variable for reliability prediction;meanwhile the statistical results of fatigue test data of specific gears are used as strength input variable for reliability prediction.Finally,the reliability prediction of the planetary gear transmission system respectively in a helicopter main rotor reducer and a wind turbine accelerator is completed.And the main research contents are as follows.(1)The NGW planetary transmission is taken as the research objective,and aiming at the problem of unequal load sharing,the expression method of partial load degree and the selection principle of eccentric load mechanism are discussed.The kinematics calculation of planetary gear transmission is carried out,which provides a theoretical basis for the detailed partial load analysis and the reliability prediction.(2)Detailed mechanism analysis and stress calculation are carried out for the two most common types of gear failure,tooth bending fatigue and tooth surface contact fatigue.The failure reason and damage evolution process are discussed from macro and micro levels,which provides the failure physics basis for corresponding reliability prediction methods.(3)The causes,states and consequences about unequal load sharing of the planetary transmission in a helicopter main rotor reducer are studied in detail.The reducer is simulated by using Rotation Master software,and the unequal load sharing mechanism of the planetary gear transmission system is analyzed,and the stress histories of each gear in the system under partial load state are obtained.At the same time,according to the Miner cumulative damage theory,the stress histories are transformed into equivalent constant amplitude cyclic stresses,which provide a load input variable for the reliability prediction model.In the process of stress spectrum acquisition,a series of discrete eigenvalues are used to describe the stress history,which greatly reduces the amount of calculation for the simulation model.In addition,the partial load coefficient is used to describe the partial load degree of planetary gear transmission system and the variation law of the partial load state of the system during running process,which provides contrast information for reliability prediction of the gear system under partial load condition.(4)The service load characteristic of wind turbine is analyzed,and the randomness of wind load is described by random process theory,and the nature and source of load randomness are explained from macro and micro levels.The simulation calculation of a 5 MW large wind turbine accelerator is completed by using the Rotation Master software,then the relationship between the input torque of gear system and gear stress is established,and then the torque history is effectively transformed into the stress history.At the same time,according to the rain flow counting method,the Goodman curve method and the Miner cumulative damage theory,the variable amplitude stress history of gear is converted into equivalent constant amplitude cyclic stress,whose statistical result is used as the load input variable for the reliability prediction model of wind turbine gear transmission system.(5)The fatigue test was carried out on two groups of gear samples by group method,the bending fatigue property of tooth root and the contact fatigue property of tooth surface were measured respectively.In the gear bending fatigue test,domestic JG-150 power flow closed gear test bench was upgraded,the oil return temperature and gear revolution were measured accurately by using advanced sensors,and the vibration monitoring instrument was used to effectively realize automatic stop of the test machine when tooth breaks,so as to ensure the accuracy of test data.In the tooth surface contact fatigue test,a high resolution linear camera was used to monitor the tooth surface topography,and the damage state on tooth surface was analyzed and reconstructed by software,so as to ensure the consistency of the failure state,and also ensure the accuracy of test data.In the test data processing,the Weibull distribution function with two parameters was used to fit the life data at each stress level,which provides strength information for the reliability prediction model.(6)The reliability prediction for planetary gear transmission system of a helicopter has been completed.According to the failure characteristics of gear,the probability life relationship between gear and tooth is established by using the concept of minimum order statistics.Thus,the life information of gear can be converted into the strength information of tooth which can be directly input into the reliability model.At the same time,the effectiveness of the conversion idea is verified by the statistical method of random censored data.Then,the reliability prediction model of planetary gear transmission system is established by using the Weibull distribution function and the reliability product law,and the reliability prediction results under the equal load sharing and unequal load sharing states can be obtained by model calculation.Finally,the quantitative relationship between the partial load degree and the reliability is constructed.(7)The fatigue reliability analysis and modeling for the gear transmission system of a large wind turbine are carried out.The traditional stress and intensity interference theory is extended,based on the total probability formula and the concept of conditional reliability,a weighted average algorithm of fatigue reliability is proposed,which can be used to calculate fatigue reliability directly according to the fatigue life distribution.At the same time,according to the random characteristics of wind load,a reliability prediction model which can reflect the failure correlation among parts is established.By comparing the results of new model and traditional model,it is proved that the new model can more effectively and truly reflect the reliability change rule of the wind turbine gear transmission system in service process. |
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