The coupling of mild wear fault data produces a 1.5-dimensional envelope spectrum, as shown in Figure 1.

It can be seen from Fig. 1 and Fig. 1 that when the gear surface of the gearbox is slightly worn, the meshing frequency and its multiple frequency will be coupled with the planetary carrier rotation frequency FPC and its multiple frequency, and the planetary gear fault frequency FP will also occur. The reason is that the fault frequency FP of planetary gear appears in the vibration signal after the gearbox wear fault, but the amplitude of the fault frequency FP of the planetary gear is small in the initial stage of wear, so it is difficult to directly observe its amplitude in the frequency spectrum.

However, through the 1.5-dimensional envelope spectrum generated by coupling, the characteristic frequency can be detected after coupling with each meshing frequency, which is of great help to the early fault diagnosis of gearbox.

The 1.5-dimensional envelope spectrum generated by data coupling of severe wear fault is shown in Fig. 2.

It can be seen from Figure 2 that with the deepening of wear degree, most of the meshing frequencies of each order are coupled with the fault characteristic frequency FP of planetary gear. This is because with the increase of wear degree, the amplitude of fault characteristic frequency of planetary gear increases, and the amplitude of frequency component generated by coupling with meshing frequency and its multiple frequency will also increase. Therefore, it can be clearly seen in Fig. 2 that the frequency components generated by the coupling of meshing frequency and its multiple frequency with the characteristic frequency of planetary gear fault are distributed in the side band of meshing frequency and its multiple frequency.

By studying the 1.5-dimensional envelope spectrum generated by the vibration signal coupling of planetary gearbox wear fault, it can be found that with the deepening of planetary gear wear, the secondary frequency coupling occurs between the meshing frequency of each order and other characteristic frequencies (planetary carrier rotation frequency, planetary gear fault frequency)

(1) under the normal working condition of planetary gear, the meshing frequency of each order is mainly coupled with the rotation frequency and its multiple frequency of planet carrier;

(2) with the deepening of tooth surface wear, the coupling between the meshing frequency of each step and the fault frequency of planetary gear appears gradually at the initial stage of wear;

(3) in the severe wear stage, it can be found that the frequency components of the meshing frequency and its multiple frequency coupling with the planetary fault frequency are basically in the side band of each meshing frequency.