The comprehensive use of characteristic parameters can make a simple diagnosis of tractor, that is, to judge whether there is a fault in tractor gearbox. After the fault is found, the frequency analysis of vibration signal shall be further carried out to determine the type and cause of the fault.
Spectrum analysis has many advantages, which makes it the most widely used method in fault diagnosis. Amplitude spectrum and power spectral density function are commonly used in spectrum analysis. Assuming that x (f) = f [x (T)], there are:
The amplitude spectrum is:
The power spectrum is:
In addition, the decibel spectrum is commonly used in engineering, that is, the logarithm of the power spectrum is taken.
Generally speaking, the vibration spectrum of tractor gearbox can be divided into three frequency bands: low frequency, medium frequency and high frequency. The low frequency is the frequency range below the shaft frequency. The dynamic balance of the tractor gear itself and the alignment of the shaft are often reflected in this frequency range. The intermediate frequency band is in the range from shaft frequency to meshing frequency. It is generally considered that the medium frequency band has a great relationship with the resonance frequency of the low-order structure of the tractor gearbox. In fact, there are many influencing factors of the medium frequency band, which vary with the structure and speed of the tractor gearbox. In addition, the characteristic frequencies of tractor gears and bearings may also appear in this frequency band. The frequency band above the meshing frequency is the high frequency band, which is generally considered to contain more information.