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foreword
As a key component for connecting and transmitting power in mechanical equipment, gearboxes are widely used in large and complex mechanical equipment such as wind turbines, helicopters, automobiles, agricultural machinery, and metallurgical machinery. However, affected by working conditions such as harsh working environment, strong load, high speed, and long-term continuous operation, some typical components in the gearbox, such as gears and rolling bearings, are prone to various types of failures, which in turn affect the overall mechanical system The safety and reliability of operation will lead to the decline of product or service quality, and cause huge economic losses and casualties. Therefore, it is of great significance to carry out research on fault diagnosis technology of gearboxes, identify fault modes in a timely and accurate manner and provide guidance for subsequent maintenance, which is of great significance to ensure the safe and reliable operation of mechanical systems and avoid major accidents.
1. Vibration characteristics of typical gear faults
Due to the harsh working environment and untimely maintenance, the gearbox is prone to various local and distributed faults, which will directly affect the safe and reliable operation of the equipment. Among them, gear pitting, shedding, cracks, etc. are some of the more common local failure modes of gearboxes. If these partial faults are not found in time, the faulty gear will easily form defects with a certain width and depth during the long-term operation. At the same time, as the defects deepen, it is very likely to cause missing or broken teeth, and eventually cause the gearbox to fail. . In the actual operation process, when a gear with a partial fault meshes with other gears, an impact phenomenon will occur, and this impact phenomenon will repeat at a certain time interval under the action of the rotational motion of the gear. Therefore, due to the existence of continuous impact, the vibration signal under the gear partial fault state has serious amplitude modulation and frequency modulation. In addition to the above-mentioned local faults, some typical distributed faults (such as uniform wear of gears, eccentricity of gear or shafting mass) will cause low-frequency periodic changes in mesh stiffness, and this low-frequency periodic change in mesh stiffness will modulate the vibration signal amplitude and instantaneous frequency. Moreover, even in a healthy gearbox, manufacturing or installation errors (such as tooth profile errors) are unavoidable, and these conditions have very similar modulation characteristics to typical distributed faults of gears. In addition, the complexity of the signal transmission path and the instability of the operating conditions will also produce additional modulation on the vibration signal. Therefore, this section combines the actual operating conditions of the gearbox, and considers the typical gear failure mode and the amplitude modulation and frequency modulation effect of the operating condition changes on the vibration signal, and studies the frequency spectrum characteristics of the vibration signal under typical fault conditions.
2. Research status
Helical gears have the advantages of stable transmission, low noise and large load capacity, and are widely used in mechanical transmission equipment. However, early fault diagnosis of helical gears under low-speed conditions is difficult. When the helical gear operates at a low speed, the vibration impact energy generated by the local fault on the tooth surface is small. It is disturbed by the vibration of rotating parts such as shafts and bearings by the king: its fault characteristics are difficult to be extracted. In addition, the early failure of gears usually occurs on a single tooth surface or a few tooth surfaces. Only when the faulty tooth is in the meshing position can a small vibration shock be generated, so the early failure characteristics of the gear are easily affected by the vibration of the normal tooth and Overwhelmed by ambient noise. At present, the methods for early fault diagnosis of gears mainly achieve the purpose of extracting weak features by suppressing noise and improving signal-to-noise ratio. Commonly used methods include wavelet noise reduction, stochastic resonance, cyclostationary demodulation, and Kalman filter. Although these methods have achieved good results in suppressing noise interference and improving the signal-to-noise ratio, it is difficult to effectively filter out the irrelevant periodic components in the signal, and in the gear transmission system formed by bearings, shafts and other rotating components Periodic noise interference cannot be ignored.
references
[1] SONG Baoyu, XIE Zhijie, ZHANG Feng, et al. Fault diagnosis of low-speed helical gears based on simultaneous average and order analysis in angle domain [J]. Journal of Jilin University: Engineering Edition, 2015, 45(2):454-459 .