Reducing gear transmission noise during gear reducer operation has become an important research topic in the industry. Many scholars at home and abroad regard the change of gear meshing stiffness in gear transmission as the main factor of gear load, vibration and noise. With the modified method, the dynamic load and speed fluctuations to minimize, in order to achieve the purpose of reducing noise. This method proved to be a more effective method in practice. However, in this method, the process needs modification equipment, the majority of small factories often can not be implemented.
       After many years of research, it has been proposed that the meshing impact speed is minimized by optimizing the gear parameters such as displacement coefficient, tooth height coefficient, pressure angle and center distance, and the ratio of the meshing impact velocity to the meshing impact velocity is within a certain value Range, reduce or avoid the meshing of pitch circle gear design method, but also can significantly reduce gear reducer gear noise.