Gear box is the most commonly used power and motion transmission device in mechanical equipment. Gear transmission has many advantages such as fixed transmission ratio, large torque transmission, compact structure, high transmission efficiency, long service life and so on. Therefore, gear box is widely used in industrial and military fields.
However, due to the high working load of gear pair, the bad working environment and the frequent occurrence of gear surface fatigue damage, the probability of gear failure will be greatly increased. 80% of the faults in traditional machinery are caused by gears, about 10% of the faults in rotating machinery and 60% of the faults in gear boxes are caused by gears 90% of the gear faults are local faults on the tooth surface, such as cracks and broken teeth. The occurrence of gear failure will directly affect the safe and reliable operation of mechanical equipment, reduce the production efficiency and machining accuracy. In today’s era of rapid development of science and technology, with the gradual large-scale, automation, continuous, high-speed and complexity of mechanical equipment, the loss caused by gear failure to the whole production and society is more and more large. Therefore, in order to ensure the safe, reliable and normal operation of gear box, the early fault diagnosis of gear is particularly prominent. If the gear fault can not be detected in the early stage of the fault, the health status of the gear will continue to deteriorate, which will cause serious economic losses and even mechanical accidents, so the early fault diagnosis of gears is of great significance.
Gear fatigue pitting is caused by insufficient contact fatigue strength of tooth surface. This kind of fault is a common failure form of closed gear transmission with soft tooth surface, and it is a distributed fault on each tooth surface of a gear.
The formation process of tooth surface pitting is as follows: in the process of gear meshing, pulsating cyclic tooth surface contact stress and tooth surface tangential friction force will be produced. When the fluctuating cycle change contact stress exceeds the contact fatigue limit of tooth surface in long-term operation, Small fatigue cracks will appear on the surface of the gear teeth; when the fatigue cracks appear on the surface of the gears, the lubricating oil of the gears will enter into the cracks through the crack openings. Due to the meshing of the gears, the crack openings are blocked by the gear tooth surfaces, which will cause the pressure of the lubricating oil in the cracks to increase, which will lead to the further propagation of the fatigue cracks and finally the tooth surface pitting.