Coupling dynamics of helical gear modification and friction excitation

Gear transmission is the most important and widely used mechanical transmission device, which is widely used in machinery, transportation, chemical industry, aviation, aerospace, shipbuilding and other industries. With the rapid development of science and technology, gear transmission is developing towards large-scale, high-speed, lightweight and high-precision. Designing new, efficient, low-noise and high-performance gears is not only an important goal of gear research, but also a hot topic of gear research. In the process of gear meshing, the dynamic meshing excitation caused by gear meshing contact tooth pair, tooth deformation, manufacturing and assembly error leads to gear vibration and noise. Its size is an important index to evaluate its dynamic characteristics. Helical gear transmission has the advantages of large transmission torque, stable start, high transmission efficiency and stable transmission. It is widely used in high-speed and heavy-duty mechanical transmission. For the helical gear system, the contact line of the contact tooth pair in the meshing process starts from the tooth top of the driving wheel on the front end face, then the contact line changes from short to long, and then from long to short. Finally, it separates at a certain point at the root of the driven tooth on the rear end face, and the coincidence degree increases, which reduces the vibration and impact in the transmission process of the helical gear system.

As an important part of the transmission system, the excessive vibration and noise of the gear is the main source of abnormal noise, but the problem is not caused by the unreasonable design of the gear parameters, but by the unreasonable contact condition of the tooth surface. In practical work, due to the deformation of the gear transmission system box, shaft and bearing and the dislocation caused by processing and manufacturing errors, the gear tooth surface contact is no longer ideal, there may be serious eccentric load and excessive transmission error of the gear, the gear growth capacity decreases, the transmission is unstable, and finally the vibration and noise of the gear system increases. Improving the transmission performance of the gear system only by improving the gear processing and installation accuracy will inevitably increase unnecessary cost and investment. Through gear modification, the impact of the above problems can be reduced to a certain extent, ensure the stability of the gear system and reduce the gear vibration and noise. With the research of gear transmission and the improvement of gear manufacturing technology, through gear profile modification, tooth direction modification and diagonal modification, or using different methods, we can get a reasonable modification curve, improve the contact condition of tooth surface and the stability of gear transmission, and reduce the vibration and noise of gear.

The working state of helical gear transmission system is extremely complex. There are not only external dynamic excitation caused by prime mover or load, but also internal dynamic excitation caused by time-varying stiffness, various errors and tooth deformation. Traditionally, it is considered that gear transmission error is the main excitation source of vibration and noise in gear system. By improving gear manufacturing accuracy and modification, the transmission error can be reduced to a certain extent. Under the condition of high torque and low speed, the static transmission error of gear is very small, and the vibration and noise level of gear system is still very high. The gear experimental research data of NASA and Ohio State University show that it is necessary to consider other additional excitation sources. The research shows that friction excitation is also one of the main causes of gear vibration and noise. Its dynamic response has a close impact on gear system vibration, tooth surface wear and gear life. Therefore, gear friction excitation is also the focus of gear dynamics research in recent years. In the process of gear meshing, the fluctuation of friction amplitude and the change of direction of gear pair form a periodic internal excitation. For helical gear system, the time-varying of contact line is one of the important characteristics of helical gear transmission. The change of the number of contact lines will cause the change of stiffness and tooth surface friction, which is the main source of vibration and noise. With the deepening of gear dynamics research, it is found that tooth surface friction is also one of the important excitation sources for gear vibration and noise. It is particularly important to study the influence of tooth surface friction on gear vibration and noise, especially for helical gear system.

At present, most of the studies on the dynamic response characteristics of helical gear system ignore the influence of friction on the dynamic characteristics of gear system. The dynamic characteristics of gear meshing have been studied by static transmission error and time-varying meshing stiffness. After the modification of helical gear, the stiffness excitation and friction excitation change, which has no in-depth study on the dynamic response of helical gear system. Therefore, through the research on helical gear modification and friction excitation, the coupling dynamic model of helical gear modification and friction excitation is established, and the influence of helical gear modification and friction on the dynamic response characteristics of helical gear is analyzed; Through the noise simulation analysis, the influence of helical gear modification and friction on the vibration and noise of helical gear system is obtained, which has important theoretical and engineering practical value for the development of gear transmission products with low vibration and low noise.

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