Research On Tooth Surface Spalling Fault Mechanism And Feature Extraction Method Of High-contact-ratio Gear

Gears and their transmission devices are the core basic components of high-end intelligent equipment,which are widely used in new energy vehicles,aerospace and other major fields.Spur gear transmission is one of the most common forms of transmission.Compared to the normal-contact-ratio spur gear,the high-contact-ratio gear has the advantages of high load capacity,smooth transmission and good sound vibration quality.However,due to the influence of many factors such as complex working environment and the growth of service time,the key components such as high-contact-ratio gear often fail,which seriously affects the normal operation and safety of mechanical equipment.Therefore,it is of great significance to study the condition monitoring and fault diagnosis of high-contact-ratio gear.Tooth spalling is one of the main fault forms of high-contact-ratio gear.By focusing on tooth surface spalling and investigating the research status at home and abroad,it is found that there are some problems such as unclear mechanism of tooth surface spalling fault and difficulty in extracting features of spalling fault in the research of condition monitoring and fault diagnosis of high-contact-ratio gear.Therefore,from the perspective of dynamics,this article discussed the failure mechanism of tooth surface spalling of highcontact-ratio gear and analyzed the extraction of tooth surface spalling fault information under the background of strong noise,focusing on the calculation of time-varying mesh stiffness,the dynamic characteristics of spalled gears,the mapping relationship between the degree of failure and vibration response,and the combination of failure dynamics model and signal processing,in order to play an active role in the service safety and reliability of high-contact-ratio gear as well as the extension of service life.The main research contents of this thesis include:(1)A modified analytical model for time-varying mesh stiffness calculation of highcontact-ratio gear was established based on the principle of the minimum potential energy method,considering the effects of the exact tooth shape including tooth root transition curve and displacement,inter-tooth load distribution,structural coupling effect of adjacent teeth,structural coupling effect of spaced teeth and nonlinear contact stiffness.(2)Aiming at the fact that the shape of the tooth surface spalling contour and the characteristics of the bottom of the spalling hole are not fully considered in the classical rectangular spalling geometric model,the traditional geometric model of regular spalling of the curved bottom(ellipsoid spalling)and the fractal geometric model of irregular spalling of the curved bottom(irregular spalling)were established.On this basis,an analytical model for calculating the time-varying mesh stiffness of high-contact-ratio gear under spalling fault mode was derived.(3)The torsional dynamical model of high-contact-ratio gear pair was established,including gear mesh stiffness,tooth surface friction and gear backlash.The influence of different spalling types on the mesh stiffness under the same spalling profile size of tooth surface was analyzed.The bifurcation characteristics of the high-contact-ratio gear system under different spalling types,as well as the difference of dynamic response of different spalling types were analyzed and discussed.(4)Considering the effects of gear mesh stiffness under different spalling degrees,fractal backlash,and time-varying friction coefficient under elastic flow lubrication,a coupled dynamical model of a high-contact-ratio gear-rotor-bearing-box system was established to analyze the vibration characteristics of the system under different tooth spalling faults and explore the mapping relationship between the degree of tooth spalling fault and vibration response.Finally,a verification test of the vibration response characteristics of a high-contact-ratio gearbox with spalling fault was carried out.(5)To address the problem that the low-frequency tooth surface spalling fault signals are easily disturbed by noise,which makes it difficult to extract fault pulses,and the parameters of variational modal decomposition(VMD)and maximum correlated kurtosis deconvolution(MCKD)have to be selected by manual experience,a parameter-adaptive tooth surface spalling fault feature extraction method based on the sparrow search algorithm(SSA)was proposed.The vibration signals obtained by gear dynamical model in spalling failure mode were used as samples to carry out the study of extracting fault feature information from multi-source signals by SSA-VMD-MCKD method.A gear spalling fault simulation test bench was built and the collected test vibration signals were analyzed to verify the correctness of the proposed algorithm.