Method and device for monitoring a bearing clearance of roller bearings

Abstract

In the methods for monitoring a bearing clearance of a roller bearing (4), in particular the bearing clearance of a main bearing of a wind turbine, within the scope of a first measuring series using at least one distance sensor (18), a distance (a, a.sub.1, a.sub.2) between a rotating part (12) and a stationary part (14) is respectively sensed in at least two different recurring load states (L1, L2), and a difference (Δa) between the measured distances (a.sub.1, a.sub.2) is determined. At a later time the distance measurements are repeated in the same at least two recurring load states (L1, L2) within the scope of a second measuring series. A change in the bearing clearance is inferred on the basis of the changes in the distance difference (Δa) within the scope of condition monitoring.

Claims

1. A method for monitoring a bearing clearance of a roller bearing that has a rotating part and a stationary part comprising: within the scope of a first measuring series, sensing via a distance measurement via at least one distance sensor, a distance between a rotating part and a stationary part in at least two different recurring load states, wherein the there is a difference between the measured distances, after sensing the first measuring series, the distance measurement for sensing the respective distance is repeated in the at least two recurring load states within the scope of a second measuring series, changes in a bearing clearance of the roller bearing are inferred on the basis of the changes in the difference between the measured distances in the two measuring series.

2. The method as claimed in claim 1, in which a change between the load states is sensed.

3. The method as claimed in claim 1, in which the different load states are adjusted.

4. The method as claimed in claim 1, in which during a respective measuring series over a specified measuring time period a multiplicity of distance measurements are carried out, and, a recurring load time behavior of the distances is sensed and evaluated with respect to the differences between the distances.

5. The method as claimed in claim 4, in which a statistical evaluation of the load time behavior of the distances is carried out and a statistical characteristic value is used as a measure for the difference between the measured distances, and this statistical characteristic value is monitored for changes.

6. The method as claimed in claim 1, in which a reference measurement is carried out in order to measure the distance between the rotating part and the stationary part over at least one revolution of the roller bearing in order to sense deviations in the roller bearing and to take the deviations into account in the measuring series, wherein the reference measurement is determined in a constant load state.

7. The method as claimed in claim 6, in which, in the reference measurement, the measured distances are sensed depending on an angle of rotation between the rotating part and the stationary part and the distances measured in the reference measurement are compared with distances sensed after the reference measurement at the same angles of rotation.

8. The method as claimed in claim 7, wherein at least one mark is provided, and the mark is used to correlate the reference measurement and the distance measurements with one another.

9. The method as claimed in claim 8, in which the distance sensor measures against a measurement surface and the mark is designed as an indentation or elevation on the measurement surface.

10. The method as claimed in claim 1, wherein a plurality of distance sensors are arranged around a circumference, and a respective distance is measured to each distance sensor and the change in their distances is sensed.

11. The method as claimed in claim 10, in which a simultaneous mean value is sensed by sensing the distances from the plurality of distance sensors at the same time and forming a mean value therefrom.

12. The method as claimed in claim 11, wherein a phase shift of the individual sensor signals of the plurality of arranged distance sensors is carried out in order to determine fabrication deviation by bringing the signals into congruence.

13. The method as claimed in claim 10, in which the distances determined by the distance sensors are evaluated and averaged over a plurality of revolutions.

14. The method as claimed in claim 1, wherein a concentricity behavior and axial run-out behavior are monitored over time.

15. The method as claimed in claim 10, in which a distance profile is repeatedly modeled over one revolution from the measured distances from the distance sensors and is monitored for changes.

16. The method as claimed in claim 15, wherein a floating mean value of the distance profile is determined.

17. The method as claimed in claim 1, wherein at least one additional operating parameter selected from at least one of the operating parameters including power, rotational speed, load or temperature is used for identifying comparable operating states, in order to compare distance measured values of the same operating states.

18. The method as claimed in claim 1, in which the bearing clearance of the main bearing of a wind turbine is monitored.

19. A device having at least one distance sensor for measuring a distance between a rotating component and a stationary component of a roller bearing and having an evaluation apparatus which is designed to carry out a method having the following steps: within the scope of a first measuring series using a distance measurement using at least one distance sensor, a distance between a rotating part and a stationary part is respectively sensed in at least two different recurring load states, wherein there is a difference between the measured distances, after the first measuring series is sensed, the distance measurement for sensing the respective distance is repeated in the at least two recurring load states within the scope of a second measuring series, changes in a bearing clearance of the roller bearing are inferred on the basis of the changes in the difference between the measured distances in the two measuring series.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0061] FIG. 1 shows a sectional illustration of a bearing unit in which different bearing states are shown for illustrative purposes,

[0062] FIG. 2A shows a temporal profile of a load state and, in correlation therewith, the temporal profile of a distance between a rotating and a stationary part in a starting state of the bearing and

[0063] FIG. 2B shows the profiles according to FIG. 2A, but after a certain operating time and in the case of wear,

[0064] FIG. 3A shows the temporal profile of a stochastically varying load state and a profile, in correlation therewith, of the distance between a rotating and a stationary part in a starting state of the bearing and

[0065] FIG. 3B shows the profiles according to FIG. 3A, but after a certain operating time and in the case of wear,

[0066] FIG. 4A shows the temporal profile of the distance between a rotating and a stationary part that has fabrication deviations,

[0067] FIG. 4B shows the temporal profile of the distance of a reference measurement for determining the fabrication deviations and

[0068] FIG. 4C shows the profile, illustrated in FIG. 4A, of the distance after correction by the fabrication deviations according to FIG. 4B.

DETAILED DESCRIPTION

[0069] FIG. 1 illustrates a bearing unit 2 by way of example and in highly schematic form. The illustrated bearing unit 2 is not necessarily a real situation, but rather FIG. 1 serves to explain different states. In the illustrated FIG. 1, the bearing unit 2 has two roller bearings 4 that are spaced from one another. The roller bearing 4 illustrated in the right-hand half of the image is in this case designed as a double-row, mounted and preloaded roller bearing. The roller bearing 4 illustrated in the left-hand half of the image is by contrast designed as a single-row roller bearing in the form of a floating bearing with positive bearing clearance (in contrast to the negative bearing clearance in the case of a preloaded bearing).

[0070] A respective roller bearing 4 in each case has at least an inner ring 6, an outer ring 8 and rolling bodies 10 arranged between them. In the case of the roller bearing 4 illustrated in the left-hand half of the image with the positive bearing clearance, what is known as bearing play is therefore formed and illustrated between the rolling bodies 10 and one of the rings 6, 8.

[0071] The roller bearings 4 generally serve to mount a rotor 12 opposite a stator 14. In the exemplary embodiment, the inner part is designed as a rotor 12 that rotates about an axis of rotation 16 during operation. The rotor 12 is in this case often also referred to as a shaft. The stator 14 is for example a (bearing) housing of the overall bearing unit.

[0072] The method described here is used in particular in the case of large bearings, and specifically in a main bearing of a wind turbine. Large bearings are generally understood to mean bearings that are designed for high payloads of for example several tonnes and typically have a diameter of greater than 0.5 meters, and in particular greater than two meters. The main bearing of a wind turbine is such a large bearing. By way of the main bearing, a rotor, not illustrated in more detail here, of the wind turbine is mounted, which rotor bears a rotor hub on the end thereof. The individual rotor blades are arranged on said rotor hub, by way of which rotor blades the wind power is received and converted into a rotational movement of the rotor.

[0073] The method described here is however not necessarily restricted to such large bearings. Correctly setting and maintaining a bearing clearance is however of critical importance for the functionality of the bearing unit 2 precisely in the case of such large bearings.

[0074] In this case, both radial bearing forces F.sub.R, axial bearing forces F.sub.A and torques M may occur during operation. These bearing forces in this case vary in a load-dependent manner, that is to say depending on the loads currently acting on the individual bearing components. Specifically due to the size of the bearing unit 2, such load changes are reflected in particular in distance changes between a rotating part, for example the rotor 12, and a stationary part, for example the stator 14.

[0075] FIG. 1 illustrates two distance sensors 18 by way of example, these being designed to measure a radial distance a.sub.R or an axial distance a.sub.A. The distance sensors 18 here in each case perform measurements onto a measurement surface that is not illustrated in more detail here. This is arranged for example on the rotor 18 or on an auxiliary component. When monitoring the bearing clearance, at least one of the distances, preferably both of them, are monitored and evaluated within the scope of condition monitoring. For the sake of simplicity, only a distance a is mentioned below.

[0076] Load states are generally understood to mean torques, forces, pressures, temperatures or else rotational speeds acting on the roller bearing 4. These load states are in some cases derived load states from external loads applied to the bearing, specifically for example wind loads, as the main cause of varying load states. Different load states furthermore also result for example from load-free operation, operation at partial load and operation at full load. Different load states also result for example during startup, when the turbine and the roller bearing 4 are still at ambient temperature and all of the components of the bearing are virtually at the same temperature level and a following operating situation with an increased operating temperature. This is also characterized by temperature gradients between the individual components, which may lead to stresses etc. and therefore to different torques and forces.

[0077] FIGS. 2A, 2B each show a temporal profile of a load state L in the lower half of the image. This is illustrated in simplified form by a step function between two load states L1, L2. The load states change within a measurement time period ΔT. The measured distance a also changes in correlation with the varying load states L. This measured distance decreases in the exemplary embodiment by a distance difference Δa. This is also referred to as distance delta.

[0078] In order to sense the two distances a1, a2 in the load states L1, L2, two individual measurements at the time t.sub.1 and t.sub.2 are carried out in the starting state according to FIG. 2a. The measurement time period ΔT, that is to say the temporal distance between the two individual measurements, is for example in the region of minutes or else in the region of hours, depending on which time period is required for the two load states to change between the load states L1 and L2. The two individual measurements in this case define a first measuring series.

[0079] A second measuring series in the same load states L is thus carried out with the same load change at a temporal distance of for example several minutes, hours, days, weeks, months or else years. The load change illustrated here between two discrete load states L1, L2 is for example a load change upon startup of the turbine from the cold state to an operating temperature state (and with otherwise identical load conditions, such as for example wind loads).

[0080] FIG. 2B shows a situation after wear of the bearing has already occurred. This leads in principle to a situation whereby the difference Δa′ between the distance values a.sub.1′, a.sub.2′ that are now measured has increased in comparison with the earlier state shown in FIG. 2A, in particular starting state.

[0081] The change in the difference Δa (change in the distance delta) is correlated with a change in the bearing clearance. The bearing clearance is therefore monitored and evaluated on the basis of this distance delta Δa. Depending on the change in the distance delta, appropriate measures are then taken and the bearing clearance is generally inferred.

[0082] If consideration is given to the load changes caused by wind loads in the case of a wind turbine, then this involves varying load changes—even in the case of average constant wind loads over for example a time period of several minutes—that are typically subject to a stochastic variation. This situation is illustrated in FIGS. 3A, 3B. FIG. 3A again shows the conditions in a starting state, and FIG. 3B shows the conditions after a certain operating time and wear.

[0083] The lower half of the image in each case shows the profile of the load state. A multiplicity of individual measurements are then carried out in the measurement time period ΔT, such that a profile of the distances a over time is determined. A virtually continuous profile of the distance values that vary with respect to the profile of the variation of the load states L is therefore determined by way of the multiplicity of measurements. Both the change in the load state L and that of the distances a are therefore time-dependent functions. The sensed values of the distance a are subjected to a statistical evaluation that leads to a statistical characteristic value that is a measure at least of the differences Δa between the distances a in the multiplicity of individual measurements. This statistical characteristic value is for example a mean value in the simplest case. A deviation, for example a standard deviation or a variance of the mean value, is however preferably used as characteristic value for the evaluation.

[0084] As is able to be seen with reference to the illustration in FIG. 3B that shows the situation after wear, wear in addition to a change in the mean value also leads to a considerable increase in the deviation or variance of the mean value. This (statistical) characteristic value is used, from starting parameters, to assess changes in the bearing clearance.

[0085] When carrying out the distance measurements, load-dependent influences caused by fabrication tolerances and fabrication deviations, such as axial run-out defects and concentricity defects, are overlaid onto the distance delta Δa. These fabrication deviations are in some cases greater than the load-induced distance changes.

[0086] One key aspect in the method is therefore considered to be that of correcting and revising the measured distance values a by such fabrication-induced distance variations.

[0087] For explanation purposes, FIG. 4A illustrates, by way of example, a profile of the distances a over time, specifically between the times t1, t2, which define precisely one period, that is to say one full revolution of the rotor 12 about the axis of rotation 16. At the times t1, t2, in each case clear upward deflections are able to be seen. These are brought about intentionally by corresponding markers in the form of elevations or indentations within the measurement surface.

[0088] FIG. 4A illustrates a profile in the case of sensing of a multiplicity of distances for at least one period, wherein the fabrication-induced distance changes are also overlaid in addition to load-dependent distance changes.

[0089] FIG. 4B illustrates the profile of the distances a as a result of just fabrication deviations in the form of a reference curve. This reference measurement is in particular carried out in a load-free state.

[0090] For the evaluation of the measured distance profile according to FIG. 4A in order to extract a distance profile that is purely load-induced, the measured distance profile (FIG. 4A) is corrected by the distance profile according to the reference curve (FIG. 4B). Specifically, the reference curve according to FIG. 4B is subtracted from the measured curve according to FIG. 4A. A purely load-induced distance profile is then obtained (corrected profile), as is illustrated by way of example in FIG. 4C. This is then used for the further evaluation. That is to say, at a later time, a corrected load-dependent profile is again determined within the scope of a second measuring series and, as described above, the two distance profiles are evaluated in terms of the changes in the differences between the distance values.

[0091] There is in principle the possibility and risk that the initially installation-induced or fabrication-induced deviations, such as axial run-out defects and concentricity defects, will change during operation. This may be caused for example by wear or releasing of preloading elements. Setting in mounting joints (for example bearing seat) also leads to a change in the concentricity and axial run-out. The profile and the development of the fabrication-induced deviations and distance changes are therefore expediently monitored or sensed. For this purpose, a new reference measurement is carried out, for example at recurring times after a certain operating time—for example in advance of a second measuring series. The reference profile determined in this new reference measurement is then subtracted from the distance profile measured in the second measuring series in order to obtain the pure load-induced profile of the distance values a. The corrected distance profiles according to the second measuring series are then evaluated—in a manner comparable to the method illustrated in FIG. 3A, 3B.

[0092] With regard to FIG. 2 and FIG. 3, it should also be noted that the average level of the distance a in the described exemplary embodiments increases (FIG. 2) or decreases (FIG. 3) with wear. The distance delta Δa however increases in both cases. Wear always leads to a larger distance delta Δa.

[0093] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.