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The tail gear reducer is an important component of the helicopter transmission system, and bearing preloading is a key link in the assembly of the tail gear reducer, which directly affects the stability, service life, and noise of the helicopter tail rotor. According to the bearing support configuration, a force model of the preloaded bolt is established to obtain the tightening torque of the bolt and the axial force applied to the support surface; based on the stress relationship, a finite element analysis model for the preloading of the tail reducer bearing is established, and the installation error of the bevel gear pair is extracted according to the analysis results. The processing results show that the tooth surface clearance of the spiral bevel gear pair decreases with the increase of the torque, and the imprint position gradually moves towards the large end with the increase of the torque; the experimental results are in good agreement with the finite element calculation results, and the method can be further extended to other types of reducers.

Taking the rotor system supported by angular contact ball bearing as the research object, the dynamic model of rotor bearing system is established by using Lagrange equation. Based on the Archard wear model, the calculation model of wear depth of bearing raceways considering lubrication effects is presented. The wear depth is introduced into the system dynamics model as the bearing clearance. The dynamic characteristics of rotor-bearing system and the evolution of bearing wear are carefully analyzed taking into account the rotor speed, bearing preload and disc position. The results show that the influence of bearing wear on dynamic characteristics of rotor-bearing system is closely related to rotor speed and bearing preload. Changing disc position does not lead to the significant variation of dynamic characteristics of rotor-bearing system with wear depth of bearing raceways. The rotor speed significantly affects the bearing wear, the bearing preload has very limited effect on bearing wear, and the variation of the disc position results in the weak difference of wear depth of bearings.

Considering the influence of the nonlinear factor of bearing preload on the dynamic stiffness of bearing support,a dynamic model of grinding motorized spindle system is established. Considering the unbalanced force caused by the eccentricity of the rotor mass in the rotor system,the numerical integration method is used to study the nonlinear dynamic behavior of the motorized spindle rotor system under different preload and rotating speeds. The results show that the bearing preload is an important factor affecting the nonlinear dynamic characteristics of the motorized spindle rotor system. Rational selection of the operating parameters of the rotor system can improve the stability of the system.

In order to analyze the influence of bearing preload on the dynamic characteristics of high-speed and heavy-load planetary gear transmission system， a dynamics model of high-speed heavy-load planetary gear transmission is established. Considered bearing preload factors， the preload of planetary pin bearing influence is analyzed for system support stiffness， natural frequency， internal and external Engagement vice dynamic meshing force. The results show that the planetary pin bearing preload can effectively increase the support stiffness of the planetary pin； the natural frequency of the system decreases with the preload and then increases， and increases with the increase of the clearance；the peak value of the dynamic meshing force of the internal and external meshing pairs of the planetary gear increases with the preload and then decreases， and increases with the increase of the clearance. The research results can provide support for optimizing the bearing preload of high-speed and heavy-load planetary gear transmission.

Aiming at the problem that die cutter frame was repeatedly disassembled due to unreasonable axial preload of bearing, the axial preload force of cutter roller bearing on die cutter holder was studied. Optimization methods and shortcomings of die cutting tool roll structure and bearing preload were summarized. Mathematical models were respectively established for limiting axial preload under minimum interference condition and maximum interference state by using relation between fit interference volume and axial preload . Based on finite element technique, optimization method of axial preload of die cutter bearing was proposed, and reliability verification was carried out using six Sigma method in ANSYS Workbench. The research results show that when the bearing meets the limit axial load condition, the actual assembly axial preload is maintained between 9 231.89 N -11 552.05 N. After the optimization, the maximum equivalent stress of the cutter roll in the minimum and maximum interference state is reduced by 7.2% and 5.1%, the maximum deformation in the minimum and maximum interference state is reduced by 6. 9% and 5. 1 %, and the reliability of the axial preload is improved by 49%. The problem of repeated disassembly during assembly of the die-cutting tool holder is improved. [ABSTRACT FROM AUTHOR]