Method and assembly for state monitoring of a bearing that supports a planetary gear of a planetary transmission on a planet carrier

1. A method for state monitoring of a bearing that supports a planetary gear of a planetary transmission on a planet carrier, the method comprising:

measuring a structure-borne noise of the planetary transmission at a stationary position on the planetary transmission in order to generate a digital measurement signal, wherein the digital measurement signal has a sample value at a sample time point;

determining a relative speed of the planetary gear with respect to the stationary position for the sample time point;

determining a corrected measurement signal, wherein the corrected measurement signal includes the sample value with a corrected sample time point, the corrected sample time point being shifted to compensate for a Doppler effect frequency shift with respect to the sample time point based on the relative speed;

forming an envelope-curve signal based on the corrected measurement signal;

determining a frequency spectrum for the envelope-curve signal; and

comparing the frequency spectrum with at least one reference spectrum in a given frequency range, wherein the given frequency range is based on a frequency of rotation of the planetary gear about the planet carrier, and on a geometry of the bearing,

wherein the corrected sample time point falling temporally before the sample time point for a first relative speed indicates a movement of the planetary gear away from the stationary position, and the corrected sample time point falling temporally after the sample time point for a second relative speed indicates a movement of the planetary gear towards the stationary position.

2. The method according to claim 1 , wherein forming the envelope-curve signal for the corrected measurement signal comprises:

band-pass filtering the corrected measurement signal in a first frequency range that depends on at least one material of the bearing;

rectifying the band-pass-filtered corrected measurement signal; and

low-pass filtering the rectified signal in a second frequency range that exclusively includes lower frequencies than the first frequency range.

3. The method according to claim 1 , wherein the given frequency range comprises frequencies of three times to ten times the frequency of rotation of the planetary gear about the planet carrier.

4. The method according to claim 1 , wherein the stationary position is located on a ring gear of the planetary transmission and wherein the determining the relative speed of the planetary gear is effected based on an angle of the planetary gear to the stationary position on the ring gear relative to an axis of rotation of the planet carrier, a geometry of the planetary transmission, and a revolution frequency of the planet carrier.

5. The method according to claim 1 , wherein the number of peaks in the frequency spectrum in the given frequency range is determined and for at least one peak an amplitude and a frequency characterizing the peak is determined.

6. The method according to claim 5 , wherein a characterizing frequency spectrum is determined for at least two successive points in time and wherein a change of an amplitude of the characterizing frequency is determined for at least one peak of the characterizing frequency spectrum between the successive time points.

7. The method according to claim 1 ,

wherein forming the envelope-curve signal for the corrected measurement signal comprises:

band-pass filtering the corrected measurement signal in a first frequency range that depends on at least one material of the bearing;

rectifying the band-pass-filtered corrected measurement signal; and

low-pass filtering the rectified signal in a second frequency range that exclusively includes lower frequencies than the first frequency range,

wherein the corrected sample time point falls temporally before the sample time point for a first relative speed that indicates a movement of the planetary gear away from the stationary position, and the corrected sample time point falls temporally after the sample time point for a second relative speed that indicates a movement of the planetary gear towards the stationary position,

wherein the given frequency range comprises frequencies of three times to ten times the frequency of rotation of the planetary gear about the planet carrier,

wherein the stationary position is located on a ring gear of the planetary transmission and wherein the determining the relative speed of the planetary gear is effected based on an angle of the planetary gear to the stationary position on the ring gear relative to an axis of rotation of the planet carrier, a geometry of the planetary transmission, and a revolution frequency of the planet carrier,

wherein the number of peaks in the frequency spectrum in the given frequency range is determined and for at least one peak an amplitude and a frequency characterizing the peak is determined, and

wherein a characterizing frequency spectrum is determined for at least two successive points in time and wherein a change of an amplitude of the characterizing frequency is determined for at least one peak of the characterizing frequency spectrum between the successive time points.

8. An assembly for state monitoring a bearing that supports a planetary gear of a planetary transmission on a planet carrier, comprising:

a sensor at a fixed position on the planetary transmission, the sensor being configured to measure structure-borne noise of the planetary transmission in order to generate a digital measurement signal, wherein the measurement signal has a sample value at a sample point; and

a signal-processing device that is coupled with the sensor, wherein the signal-processing device is configured:

to determine a relative speed of the planetary gear with respect to the sensor for the sample time point;

to determine a corrected measurement signal, wherein the corrected measurement signal includes the sample value with a corrected sample time point, which is shifted to compensate for a Doppler effect frequency shift with respect to the sample time point depending on the relative speed;

to form an envelope-curve signal based on the corrected measurement signal;

to form a frequency spectrum for the envelope-curve signal; and

to compare the frequency spectrum with at least one reference spectrum in a given frequency range, wherein the given frequency range is determined by a frequency of rotation of the planetary gear about the planet carrier, and a geometry of the bearing,

wherein the corrected sample time point falling temporally before the sample time point for a first relative speed indicates a movement of the planetary gear away from the stationary position, and the corrected sample time point falling temporally after the sample time point for a second relative speed indicates a movement of the planetary gear towards the stationary position.

9. The assembly according to claim 8 ,

wherein the sensor is disposed on a ring gear of the planetary transmission,

wherein the assembly comprises a further sensor, which is configured to determine an angle of the first planetary gear to the stationary position of the sensor on the ring gear based on an axis of rotation of the planet carrier, and

wherein the signal-processing device is configured to determine the relative speed of the planetary gear with respect to the sensor depending on the angle determined by the further sensor, a geometry of the planetary transmission, and a revolution frequency of the planet carrier.

10. The assembly according to claim 9 , wherein the given frequency range comprises frequencies from three times to ten times the frequency of rotation of the planetary gear about the planet carrier.

11. The assembly according to claim 8 , wherein the given frequency range comprises frequencies from three times to ten times the frequency of rotation of the planetary gear about the planet carrier.