The dynamic excitation study of the gear system shows that the dynamic excitation during the gear meshing process is the basic reason for the vibration of the gear transmission system. Dynamic excitation of the gear system includes internal and external excitation. Generally, the dynamic excitation of the gear mesh is mainly internal excitation, and the internal excitation of the gear includes three forms: stiffness excitation, error excitation and meshing impact excitation. Stiffness excitation refers to the dynamic excitation caused by the time-varying of the meshing comprehensive stiffness during the gear meshing process; the error excitation is that the gear meshing tooth profile deviates from the ideal meshing position, causing the gear instantaneous transmission ratio to change, causing collision and impact between the teeth and the teeth; Impact excitation means that due to the error of the gear and the elastic deformation of the load, when the gear teeth enter and exit the engagement, the meshing point deviates from the theoretical meshing point on the meshing line, causing an impact. This study will analyze the vibration response of the helical gear system under the action of gear stiffness excitation, error excitation and meshing impact excitation.
The parameters of the meshing gear pair are numerically simulated by the three-dimensional contact finite element method of gear teeth. The gear deviation is determined according to the accuracy grade of the gear design, and the error simulation is performed by the simple harmonic function method. The excitation force-time history curve generated by gear stiffness excitation and error excitation is numerically simulated by the finite element method. 3 Interference with the visiting scholars of the State Key Laboratory of Mechanical Transmission of Chongqing University caused a sharp rise in impact force. Its instantaneous amplitude can reach nearly twice the mean value, and the impact time is nearly 5.
3 Helical Gear System The finite element model gear system is divided into a transmission system (gear, drive shaft) and a structural system (box), which are coupled by bearings. The finite element model of the whole system is established by taking powder metallurgy and 38CrMoAl helical gear system as the research object.
Use UG software to build a precise 3D model of the helical gear system and export data files in Parasolid format. Import the CAD model with MSC1Patran. Use the Bolean command to integrate the zeros and components of the helical gear system into a finite element model of the entire system. Accurate models are used for each part and component, and the model can truly reflect the actual working conditions.
The four-node tetrahedral element is used to adaptively mesh the helical gear system to obtain 30,533 nodes and 126,560 units. Define the material and unit properties of the model.
In order to accurately reflect the actual state of the helical gear system, the bottom plane of the box is taken as a fixed constraint boundary condition in the modal analysis and vibration response solution.
Vibration Frequency Response Analysis of 412 Helical Gear System The vibration frequency response of the helical gear system is solved by the modal frequency response analysis module (SOL111) of MSC1Nastran. When applying a load, the stiffness, error, and meshing shock time domain excitation are first transformed into a frequency domain excitation by fast Fourier transform. Then load the load on the meshing line of the main and driven gears respectively, along the direction of the common normal of the contact point.
The damping of the system is an important parameter in the dynamic response analysis. Damping in actual systems can be divided into viscous damping and structural damping. Structural damping is mainly due to the internal friction of the elastic structural material and the friction between the contact surfaces at the fixed joints of the structure. The structural damping of the rigid gear is 1-3, the internal friction of the powder metallurgy gear material is large, the structural damping is 8-12, the smaller damping ratio is taken in the high frequency band, and the larger damping ratio is taken in the lower frequency band.
According to the above model, MSC1Nastran is submitted for frequency response analysis, and the frequency response of displacement, velocity and acceleration can be obtained. The comparison curve of the displacement response of the powder metallurgy helical gear system and the rigid helical gear system, PM represents the response curve of the powder metallurgy helical gear system, and ST represents the response curve of the 38CrMoAl rigid gear system.
The vibration response amplitude of the powder metallurgy helical gear system is significantly lower than that of the 38CrMoAl helical gear system, and the response peak frequency is lower than that of the 38CrMoAl helical gear system.
The peak response frequency of the gear is 695Hz, and the peak response frequency of the 38CrMoAl helical gear system is 76215Hz.
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