Research On Time-Frequency Characteristics Of Gearbox Faults With Rotational Frequency Fluctuation

As a rotating mechanical transmission part,the gearbox has a wide r ange of applications.It is widely used in aerospace,rail transit,wind power generation,ships,coal mining and transportation.The internal structure of the gearbox is complex,the operating environment is harsh,and its internal structure is easily dam aged.In particular,the passing effect of the planetary gear in the planetary gearbox and the complex modulation mechanism of the gearbox transmission chain further bring difficulties to the gearbox signal processing,so it is of great significance to stu dy the fault diagnosis of the gearbox.The frequency ambiguity of the vibration characteristic frequency of the gearbox is caused by the fluctuation of the rotation frequency.By studying the relationship between the vibration signal of the gearbox and the fluctuation law of the rotation frequency,the instantaneous frequency estimation method based on time-frequency analysis is used to estimate the fluctuation trend of the rotation frequency,and the order tracking is further used.The technology converts the non-stationary signal in the time domain into a stationary signal in the angular domain,and realizes the accurate extraction of the fault characteristics of the gearbox.The specific research contents of this paper are as follows:1)Based on the frequency ambiguity of the frequency spectrum structure of the gearbox vibration characteristic frequency spectrum caused by the rotational frequency fluctuation,the characteristic frequency distribution characteristics of the gearbox vibration under different rotational frequency fluctuation laws are explored.The distribution law of vibration spectrum characteristics of different fault types of gears of variable speed gearbox is analyzed;the vibration signal modulation model of variable speed gearbox is constructed;the numerical simulation model of vibration signal of local faults of each gear of variable speed planetary gearbox is established.Taking the partial failure of the sun gear as an example,the simulation analysis is carried out for different rotation frequency curves,and the influence of the periodic frequency characteristics of the rotation frequency on the modulation of the gearbox vibration signal is explored.2)In view of the noise interference and frequency ambiguity of the wind turbine gearbox vibration signal under time-varying conditions,the causes of the periodic fluctuation of the rotor blade rotational frequency are studied.In this paper,a tacho-less order tracking method for wind turbine gearboxes based on VMD-SET time-varying conditions is proposed.The method uses variational mode decomposition(VMD)filtering,uses synchronous extraction transformation(SET)to analyze the time-frequency signal of the gearbox vibration signal,and preliminarily extracts the characteristic frequency fluctuation trend of the bearing fault from the time-domain vibration signal of the bearing fault.The meshing frequency time-frequency ridge line is extracted from the meshing modulation time-domain vibration signal,and the cross-decoupling of the refined time-frequency ridge line is further used to optimize the instantaneous frequency extraction effect.A single spectral line of the characteristic order of the gearbox bearing fault is obtained from the angular domain order spectrum.Simulations and experiments verify the superiority and effectiveness of the method proposed.3)In view of the noise interference and frequency ambiguity of the gearbox vibration signal under variable speed,the traditional instantaneous frequency estimation method is prone to frequency mutation and low ridge fusion accuracy.By studying the gearbox vibration signal and the frequency fluctuation for tacho-less,based on the relationship between the laws,an improved multi-source time-frequency ridge extraction method based on SET is proposed.This method uses VMD filtering,uses SET to analyze the time-frequency of the vibration signal of the gearbox,uses the local peak search algorithm to obtain multiple time-frequency ridges from the low-frequency and high-frequency resonance frequency bands,and synchronizes with the highest energy spectrum in the time spectrum.Based on the traditional ridge line fusion method,the multi-source ridge line extraction algorithm is improved,the frequency mutation situation is improved,and the ridge line fusion accuracy is optimized.Finally,the optimized speed curve is used to track the vibration signal order of the gearbox,and the fault characteristic order of the gearbox bearing is obtained from the angular domain order spectrum.The effectiveness of the proposed method is verified by simulation and experiments.