Gearbox

in gearboxes, rolling bearings are also the main cause of gearbox failures. Common failures of bearings are pitting and fatigue spalling of the inner and outer rings.

After the fatigue spalling and pitting of the inner and outer rings and rolling elements of the rolling bearing, there is an obvious modulation peak group near the fixed frequency of the outer ring in the medium and high frequency region of the spectrum, resulting in the natural frequency modulation phenomenon with the fixed frequency of the outer ring as the carrier frequency and the frequency of the bearing as the modulation frequency. Because the vibration generated by the rolling bearing in the transmission box is smaller than the vibration of the gear, the modulation frequency amplitude in the demodulation spectrum is smaller, and generally only the first order appears.

gearbox intermediate shaft has 1/2 turns of severe fatigue spalling, and the other half ring has a large spalling pit when the vibration acceleration spectrum and filtered demodulation spectrum. Modulation peak groups containing 34.79Hz and 23.80Hz components appeared near the frequency of 2258.3Hz in the range of 2000-3000Hz, while the first-order natural frequency of the outer ring was 2246.09Hz in the measured free state, and the calculated passing frequencies of the outer ring and rolling elements were 34.47Hz and 23.6Hz respectively. Because the vibration generated by the rolling bearing in the transmission box is smaller than the vibration of the gear, the modulation frequency amplitude in the demodulation spectrum is smaller, and generally only the first order appears.

from the failure mechanism analysis, in the gearbox shaft system, the general rolling bearing inner ring and the shaft are mostly close interference fit, that is, the shaft and the inner ring are firmly connected as a whole, and the natural frequency of the rolling bearing inner ring needs a large amount of energy to excite, And the natural frequency of the rolling bearing inner ring is completely different from the frequency measured or calculated in the free state. Although the fit between the outer ring and the box bearing seat is also an interference fit, it is much looser than the fit between the inner ring and the shaft, and the outer ring has been under greater pressure from the rolling body during work. When the bearing is faulty or after running with a fault for a period of time, the outer ring and the bearing seat are basically completely loose, and the natural frequency of the outer ring is basically equal to the frequency measured in the free state. Because the outer ring is loose and the mass is small, not only the outer ring or rolling body will arouse its natural frequency when pitting or fatigue spalling, but also when the inner ring or rolling body is faulty, the vibration energy will also be transmitted through the rolling body The outer ring excites its natural frequency, so the carrier frequency of the rolling bearing in the gearbox is generally the natural frequency of each order of the outer ring, the modulation frequency is the passing frequency of the fatigue spalling element (inner ring, outer ring or rolling element).

the energy of vibration signal generated by rolling bearing fault is much smaller than that generated by gear or shafting fault, the fault signal is submerged in other vibration signals, and the fault characteristics are not obvious, which brings great difficulties to diagnosis.