Research On The Fault Characteristics Of Planetary Gears Based On Theoretical And Experimental Signal Transmission Models

The measured signal components of the wind turbine gearbox are complex,which make it more difficult to extract the fault signal of the original weak planetary gear.However,due to the interaction between gear box multi-level transmission,planetary gear failure will cause more obvious joint faults during the fault signal transmission.Therefore,a signal transmission model is established based on theoretical and experimental signals to analyse and study the transmission characteristics of planetary gear faults and their associated faults.Taking WTDS wind turbine transmission system fault diagnosis integrated test bench as the research object,simulation experiments are conducted under four working state:normal state,planetary gear uniform wear fault state,planetary gear broken fault state,and planetary gear uniform wear fixed broken coupling fault state.The vibration signals are obtained from the surface of the box of parallel axle gear box and planetary gear box.By processing,analyzing and comparing,the unknown faults frequencies caused by planetary gear fault in the experimental signal are extracted.On the base of mechanism of planetary gear drive,the pure torsion dynamic model of the multistage gear drive system under normal condition is established by using the centralized parameter method,which considering the flexibility of the transmission shaft,time-varying meshing stiffness and comprehensive meshing error,but ignoring the box body,bearing,etc...On the basis of this model,the dynamic models under planetary gear uniform wear fault state,planetary gear broken fault state,and planetary gear uniform wear fixed broken coupling fault state are respectively obtained.The vibration differential equations are derived from Newton-Euler method.The theoretical vibration acceleration responses of gear meshing in different states are obtained by Runge-Kutta Method.According to the system identification theory,the multi-stage gear box is carried out as a four-input and single output system,the theoretical vibration acceleration responses of gear pair meshing are obtained as the input,and the measured signal on the surface of the gear box is used as the output.The ARX model of signal propagation under normal state,planetary gear uniform wear fault state,planetary gear broken fault state,and planetary gear uniform wear fixed broken coupling fault state are established,and the transfer functions are estimated.By analyzing the amplitude frequency characteristic curve of those transfer functions,the source of unknown fault frequency in the vibration signal power spectrum under planetary gear failure are found,which can assist in the fault diagnosis of planetary wheel with weak characteristics and difficult to extract.