Research On Damage Dynamic Modeling And Fault Diagnosis Of Planetary Gear Train

Planetary gears are widely used in power transmission systems of various kinds of equipment such as helicopters,construction machinery,wind turbines,etc.since they can provide a large transmission ratio in a narrow space,withstand large external load,and have the advantages of energy diversion,power diversion and strong shock and vibration resistance.As an important transmission component,gear transmission is prone to crack and other damage when operating under high speed,heavy load and bad working conditions.If one does not intervene in time,those damages will inevitably lead to the deterioration of the overall performance of the equipment,resulting in shutdown and even major accidents such as casualties.Therefore,it is of great significance to carry out researches on fault monitoring and diagnosis of planetary gear train.However,related researches are facing the challenges of unknown fault mechanism and complex components of monitoring signals.This project is supported by the National key research and development plan project "Intelligent Operation and Maintenance Closed-loop Feedback Major Equipment Manufacturing Service Fusion Technology and Platform"(project No.2018YFB1702401).The dynamics of planetary gear train of helicopter main gear reducer is studied intensively.The main research contents include the following:(1)The modified potential energy method is proposed and a formula for calculating the time-varying meshing stiffness of planetary gear train is derivedTime-varying meshing stiffness is an vital parameter in the dynamic equation of gear.The equation solving correctness is directly related to the dynamic response characteristics.First,the strict derivation of the potential energy method is given.Then,in view of the lack of consideration of factors such as the non-coincidence of the base circle and the root circle,and the deformation of the gear body,the time-varying meshing stiffness expression is derived under two situations based on the base circle is smaller than the root circle or larger to establish improved potential energy method.After that,the meshing rigidity of outer and inner meshing gear teeth under the condition of health and crack damage is simulated based on the improved potential energy method.Finally,the process of solving the meshing stiffness of the planetary gear train is given by considering the phase relation among the components of the planetary gear train.The comparison study shows that the calculated results of the improved potential energy method are more consistent with the actual situation.The calculated time-varying mesh stiffness curve can provide a powerful parameter support for the subsequent dynamic modeling and simulation.(2)Based on different assumptions and lumped-parameter theory,the translational torsion model with 21 degrees of freedom is constructed.To verify the effectiveness of the improved potential energy method while providing simulation data support for the subsequent research on fault diagnosis algorithm.Firstly,the torsional mechanics model of planetary gear train is established by using energy conservation and Newton’s second law.Then,on the basis of establishing the pure torsion mechanics model of planetary gear train,considering the translational vibration,engagement phase,support stiffness/damping of each member,integrating the time-varying meshing stiffness/damping and transmission error,the translational-torsional dynamic model with 21 degrees of freedom(There are 7members in total,and each member contains two translational movements and one rotation)of planetary gear train is established.Finally,based on the above model,the dynamic response simulation calculation and crack fault implantation experiment were carried out.By analyzing the vibration signals of the simulation and experiment,the frequency characteristics under the condition of health and crack damage are obtained to reveal the typical damage vibration mechanism of the gear.The simulation and experimental results show that the modified potential energy method can effectively evaluate the time-varying meshing stiffness under health and crack.By substituting the time-varying meshing stiffness calculated by the modified potential energy method into the established dynamic model,the vibration response of the planetary gear train under different states can be simulated correctly.It provides theoretical support and data support for fault diagnosis of planetary gear train.(3)Based on the optimized variational mode decomposition method,planetary gear train fault diagnosis research is carried out.In order to solve the problem of planetary gear train fault diagnosis with diverse excitation and complex frequency components,a planetary gear train fault diagnosis method based on optimal variational mode decomposition(VMD)was proposed,combined with genetic optimization algorithm and sample entropy optimization criterion.Firstly,the effectiveness of the proposed method is verified by using complex harmonics as simulation signals.Then,based on the sample entropy optimal criterion,the genetic algorithm was used to obtain the optimal parameter combination of variational modal decomposition.Further,the modal decomposition capability of the method is verified by using the vibration response simulation signal of the dynamic model of planetary gear train.Finally,the variational mode decomposition method is used to process the planetary gear train experimental signals to verify its ability on fault diagnosis of planetary gear,the results are also compared with the empirical mode decomposition method and the set empirical mode method.The research in this dissertation lay a foundation for dynamic modeling and fault diagnosis of planetary gear train.It has a strong practical significance for monitoring and diagnosis of important equipment such as wind turbine gearbox and helicopter main transmission.