Study On Dynamic Characteristics Of Two-Stage Gear Transmission System With Typical Faults

Gear transmission,as an important part of mechanical transmission system,is widely used in shipbuilding,mining machinery,automobile and other industries because of its compact structure,high transmission efficiency and stable transmission ratio.Gear is the key component of gear transmission system,which is prone to various faults during operation due to the influence of machining accuracy,meshing error and internal and external excitation,which seriously affects the service life of gears.Moreover,gear transmission system often works under heavy load and high speed environment,and the worsening of friction and wear can easily lead to gear failure,even cause equipment damage and economic losses.Therefore,in-depth study of the dynamic characteristics of the secondary gear transmission system with typical faults(inclined crack,through crack,tooth surface fracture,tooth surface pitting corrosion,etc.)and analysis of the influence of gear fault factors on the dynamic load of the system can provide a certain judgment basis for fault diagnosis,which has a certain practical value.In this paper,the two-stage gear transmission system composed of involute spur gears is taken as the research object,considering the influence of time-varying meshing stiffness on the system,the time-varying meshing stiffness of gears is calculated by combining the finite element method,the calculated time-varying meshing stiffness is taken as internal excitation,and the fault factor is introduced.The dynamic model of the two-stage gear transmission system is constructed,and the two-stage gear with typical faults are Dynamic load variation and vibration characteristics of drive gear system.The main conclusions of this paper are as follows:1.The time-varying meshing stiffness of gears is the main cause of vibration and impact of gear transmission system.Accurate calculation of meshing stiffness is the key to study the meshing characteristics of gears.In this paper,considering the influence of fault factors on meshing characteristics,the time-varying meshing stiffness of gears with root cracks,tooth surface fracture and pitting corrosion faults is obtained by combining the finite element method.It is found that the meshing stiffness change caused by crack depth is more obvious than that caused by crack angle;the meshing stiffness change of penetrating crack is more prominent than that caused by crack depth;the meshing stiffness of gears is seriously affected by the size of gear surface fracture surface,and the meshing number of gears is affected by pitting erosion;the meshing stiffness is less affected by tooth surface pitting.2.In order to analyze the influence of fault factors on root stress,the load distribution coefficient of tooth direction is introduced,and the stress distribution characteristics of typical fault forms are obtained.By adjusting the equivalent stress of the contact tooth surface,the stress distribution between the contact tooth surfaces is analyzed.The results show that the load distribution varies nonlinearly,and the load distribution caused by the change of crack depth varies more dramatically than that caused by the change of crack angle.The stress distribution of the fault-free tooth surface is uniform along the contact line,which is similar to that of the through-crack gear surface,while the stress concentration occurs in the fault location due to the inclined crack,the fracture of the tooth surface and the pitting corrosion of the tooth surface.3.When the gear teeth fail,the change of meshing stiffness will impact the meshing process of the gear teeth,which will increase the dynamic load amplitude of the system,and the instantaneous product will increase sharply in the time domain of the dynamic load,accompanied by the quenching and tempering phenomenon in the frequency domain.Among the typical faults,the dynamic load fluctuation caused by crack and tooth surface fracture is the most obvious,and the influence of pitting corrosion on the system is relatively weak;the spectrum with fault teeth appears obvious side frequency band,and the fault teeth appear in the first stage(high-speed stage),which has a significant impact on the high-speed stage,while the fault teeth appear in the second stage(low-speed stage),which has a greater impact on the two levels of gear system.