Method for detecting damage in at least one engine roller bearing

1. A detection method for a damage of at least one roller bearing rotationally supporting at least one rotary shaft of an engine, comprising:

a) defining a measuring period during which a shaft speed varies between a low speed and a high speed that is higher than the low speed, said low speed and said high speed belonging to a wide range of speeds up to a maximum speed;

b) acquiring over the whole measuring period a current vibration signal of a mechanical vibration in engine components;

c) sampling the current vibration signal during the measuring period;

d) synchronizing the sampled vibration signal with respect to variations of the shaft speed over the measuring period;

e) converting the sampled and synchronized vibration signal into a frequency signal so as to obtain frequency spectral lines arranged according to the shaft speed that is a rotation speed of the shaft;

f) calculating a mean amplitude of the spectral lines so as to obtain a current vibration signature for the engine;

g) calculating a deviation ratio between the current vibration signature of the engine and a healthy reference vibration signature; and

h) comparing the deviation ratio to defect indicators of a predefined database, listing theoretical damages of the at least one roller bearing of the engine so as to determine potential damages of the at least one roller bearing.

2. The method according to claim 1 , wherein the healthy reference vibration signature is a healthy reference vibration signature of the engine.

3. The method according to claim 2 , wherein the healthy reference vibration signature of the engine is formed by calculating a mean of current vibration signatures of the engine being measured over a determined period of a lifetime of the engine, including at start.

4. The method according to claim 3 , wherein the healthy reference vibration signature of the engine has been previously validated by comparison to a standard family signature defined for a family of the engine.

5. The method according to claim 4 , wherein the standard family signature is formed from healthy reference signatures of engines of a same family.

6. The method according to claim 5 , wherein:

a set of healthy reference signatures is formed for a plurality of engines of the same family;

a family discordance ratio is calculated for each healthy reference signature by measuring a statistical deviation between the healthy reference signature and the other healthy reference signatures of the set;

from the set of healthy reference signatures, those of the healthy reference signatures having a discordance ratio higher than a determined discordance ratio are removed; and

the standard family signature is formed from remaining reference vibration signatures.

7. The method according to claim 6 , wherein:

a family discordance ratio is calculated for each healthy reference signature by measuring a statistical deviation between the healthy reference signature and a temporary family signature formed from the other healthy reference signatures of the set.

8. The method according to claim 1 , wherein the method further comprises eliminating spectrogram noise as a function of structural modes of the engine, the noise elimination being performed before calculating the mean amplitude of the spectral lines.

9. The method according to claim 1 , wherein the vibration signal being sampled with respect to the variations of the shaft speed over the measuring period by sampling again the signal being sampled at constant frequency is synchronized into a signal being sampled at a frequency proportional to the shaft speed.

10. The method according to claim 1 , wherein the vibration signal being sampled with respect to the variations of the shaft speed over the measuring period by calculating an angular path curve of the shaft in an order field and by projecting the current vibration signal on the angular path curve so as to obtain a synchronized current vibration signal.

11. The method according to claim 1 , wherein the healthy reference vibration signature is a standard family signature defined for a family of the engine.

12. The method according to claim 11 , wherein the standard family signature is formed from healthy reference signatures of engines of a same family.

13. The method according to claim 1 , wherein the high speed of the shaft speed includes a full speed.

14. The method according to claim 1 , wherein the low speed of the shaft speed includes an idling speed.