When the central bevel gear transmission system works, the fatigue fracture fault of the central bevel gear often occurs due to the vibration of the central bevel gear within the working speed range. This kind of fault seriously endangers the flight safety of the aircraft and may cause significant economic losses. When the bevel gear vibrates in the axial direction, it is very easy to have pitch diameter traveling wave resonance, which causes the vibration damage of the central bevel gear. The characteristic of resonance failure is that the crack starts at the rim at the bottom of the tooth groove and then propagates on the central bevel gear along the vibration mode. When the vibration stress is relatively large, the crack can continue to develop along the radial direction, causing damage to the rim of the central bevel gear.
The vibration of central bevel gear is divided into bending vibration and torsional vibration. The bending vibration of the central bevel gear is also called traveling wave vibration. It is excited by the dynamic load of the central bevel gear teeth in the meshing process. Its excitation source is the torsional vibration of the gear transmission system when the central bevel gear is running. The torsional vibration of the central bevel gear transmission system increases the dynamic load during meshing, which is extremely dangerous to the central bevel gear.
Firstly, two kinds of torsional vibration of central bevel gear transmission system are introduced: low-frequency torsional vibration and high-frequency torsional vibration. The low-frequency torsional vibration is determined by the vibration of the system. For the central bevel gear of aeroengine, because the natural frequency of low-frequency torsional vibration is usually outside the working speed of the central bevel gear, it is not dangerous to the rim of the central bevel gear. The most dangerous is the high-frequency torsional vibration whose frequency is the meshing frequency of the central bevel gear and its frequency multiplication, and its vibration source is the change of tooth stiffness in the meshing process. Because the coincidence degree of transmission gears of most aviation accessories is between 1 and 2, a pair of teeth and two pairs of teeth mesh alternately in the working process of gear teeth.
Then, the natural characteristics of bevel gear under different constraint boundary conditions are calculated and analyzed by finite element method. It is found that the higher the number of pitch diameters, the less sensitive the natural frequency calculation results to the constrained boundary conditions. At the same time, the higher the vibration order, the natural frequency calculation results are also insensitive to the constrained boundary conditions. The first three natural frequencies, vibration modes and vibration stress distributions of the driving bevel gear and the driven bevel gear with 0 ~ 4 pitch diameters are calculated by using an appropriate constraint boundary. According to the basic principle of traveling wave resonance, the traveling wave resonance of central bevel gear pair is analyzed. Both the driving bevel gear and the driven bevel gear have forward traveling wave and backward shaped wave resonance of the second order with two pitch diameters, and forward traveling wave and backward shaped wave resonance of the first order with four pitch diameters.