At present, this spectrum analysis method based on the envelope of the signal generated by high-frequency impact excitation has been proved to be a good method to solve the fault diagnosis of tractor gearbox. The advantages of resonance demodulation method include that it can distinguish the characteristic symptoms of several faults occurring in the same tractor gearbox at the same time, which can greatly improve the certainty of fault identification. The resonance demodulation method takes the signal associated with the fault out of the high-frequency modulation signal, so as to avoid confusion with other low-frequency interference, and has high diagnostic reliability and sensitivity.
When a part in the tractor gearbox fails, the impact impulse force will be generated during load operation. Because the frequency band of the impact impulse force is very wide, including the natural frequencies of gear, shaft, bearing, box and sensor, it is bound to arouse the resonance of the vibration measurement system. Therefore, the measured vibration acceleration signal contains multiple carrier resonance frequencies, fault characteristic frequency modulated on it and its harmonic components, so that the low-frequency envelope signal containing fault characteristic frequency and its frequency doubling components can be obtained. The fault of tractor gearbox can be easily diagnosed by spectrum analysis of the envelope signal.
It should be pointed out that the resonance demodulation method is usually only suitable for local damage faults, and the effect is not good for wear faults. Moreover, the resonance demodulation method needs manual judgment. Sometimes the envelope spectrum is very complex and difficult to identify, which requires high requirements for the operator. The center frequency of band-pass filter is required to be determined in advance in resonance demodulation analysis. Because the gearbox systems are very different, it is difficult to determine the natural frequency of these structural systems in advance. In most cases, the method of increasing the filter bandwidth can be used to make the resonance center frequency fall into the filter frequency band, but this will reduce the denoising effect. If the frequency band is too narrow, it may miss the center frequency of structural resonance and lose the ability of diagnosis.