When there is pitting on the gear surface, the pitting will reduce the time-varying meshing stiffness and the sliding friction of the gear. Therefore, there are some problems to be solved: in the early stage of small pitting failure, is the impact on the dynamic response of gear system from stiffness excitation or friction excitation? Therefore, in order to study the influence of meshing stiffness and sliding friction on the dynamic response of gear system in the early stage of small pitting failure, three cases of gear system dynamic response modeling are given in this paper, which are respectively defined as case I, case II and case III.
In case I of dynamic response model simulation, only the influence of gear meshing stiffness reduction due to tooth surface pitting fault on the dynamic response of gear system is considered, so the meshing stiffness is brought into the dynamic model of gear system as internal excitation. The friction coefficient of tooth surface is set as a constant, that is, the friction coefficient of healthy gear is 0.05.
In case II of dynamic response model simulation, only the influence of the increase of sliding friction coefficient on the dynamic response of gear system due to the pitting fault is considered. The sliding friction of tooth meshing is changed by changing the friction coefficient. The specific friction coefficient setting is given in. The stiffness excitation of gear is the meshing stiffness of healthy gear.
In case III of dynamic response model simulation, the influence of the decrease of time-varying meshing stiffness and the increase of friction coefficient on the dynamic response of gear system is considered. The meshing stiffness and friction coefficient of different gear states are one-to-one corresponding.
In the dynamic model simulation of gear system, the speed of driving gear on the input side is set at 500rpm, and the braking torque of driven gear on the output side is set at 200nm, which is consistent with the operating conditions of the gear in the experiment. Through calculation, the theoretical rotation frequency of driven gear is 4.63hz and the meshing frequency of gear is 333.3hz. The Runge Kutta method is used to solve the differential equation of gear system dynamics, and MATLAB ode45 function can be used to solve the numerical solution, in which the sampling frequency is 40000 Hz.