Bearing monitoring by pressure sensors

Abstract

A wind turbine has a bearing housing, a rolling element bearing located within the bearing housing, and a space within the bearing housing for receiving a grease for lubricating the rolling element bearing. A shaft is rotatably supported by the rolling element bearing. A pressure sensor in fluid communication with the space measures the pressure of the grease in the space within the bearing housing.

Description

Technical Field

[0001] The present invention belongs to the field of monitoring rolling element bearings of wind turbines. Background Art

[0002] The main shaft of a wind turbine is rotatably supported by a rolling element bearing within a main bearing housing located in the nacelle of the wind turbine. A gearbox may support the main shaft at the rear end of the main shaft. The rolling element bearing is typically monitored by temperature and / or vibration sensors. These two sensors can only detect potential failures of the rolling element bearing after the rolling element bearing has been damaged.

[0003] Therefore, it is desirable to be able to monitor the rolling element bearing and / or the grease level within the main bearing housing so that actions can be taken to prevent damage to the rolling element bearing. Summary of the Invention

[0004] A first aspect of the present invention provides a wind turbine comprising: a bearing housing; a rolling element bearing located within the bearing housing and a space within the bearing housing for accommodating grease for lubricating the rolling element bearing; a shaft rotatably supported by the rolling element bearing; and a pressure sensor, wherein the pressure sensor is in fluid communication with the space and is configured to measure the pressure of the grease within the space within the bearing housing.

[0005] At least an advantage of the first aspect is that the use of a pressure sensor can avoid time-consuming inspections of the rolling element bearing, which need to be carried out by removing the main bearing housing cover and / or by disassembling a part of the rolling element bearing to periodically monitor the rolling element bearing. The pressure sensor can be used to generate important information for a service plan to save resources. The pressure sensor can be used to generate an early warning of grease loss that may be caused by seal damage or wear. The pressure sensor can be used to monitor the fluid pressure within the bearing housing to ensure proper ventilation and sealing functions. The wind turbine can be used to support the lubrication system function, for example, to convey grease from a grease reservoir into the space within the bearing housing to achieve a grease level. The wind turbine can be used to cold-trigger the lubrication system as an emergency mediation, for example, to convey all the grease from the grease reservoir into the space within the bearing housing until service can be organized.

[0006] The bearing housing may further include a grease outlet for adding grease to and / or removing grease from the space within the bearing housing. The pressure sensor may be coupled to the grease outlet and may be adapted to hold the grease within the bearing housing during operation of the wind turbine.

[0007] The rolling element bearing may include a plurality of rolling elements separated by a cage.

[0008] The pressure sensor may be a first pressure sensor. The wind turbine may further include a second pressure sensor in fluid communication with the space, and the second pressure sensor may be configured to measure the pressure of the grease in the space within the bearing housing. The first pressure sensor may be in fluid communication with the space at a first measurement point, and the second pressure sensor may be in fluid communication with the space at a second measurement point.

[0009] The rolling element bearing may further include a second plurality of rolling elements separated by a second cage. The first measurement point may be positioned to measure the pressure of the grease in the space adjacent to the first plurality of rolling elements, and the second measurement point may be further positioned to measure the pressure of the grease in the space adjacent to the second plurality of rolling elements.

[0010] The bearing housing may be the main bearing housing of the wind turbine. The shaft may be the main shaft of the wind turbine.

[0011] A second aspect of the present invention provides a method for monitoring a wind turbine of the first aspect, the method comprising:

[0012] Rotating the shaft;

[0013] As the shaft rotates, measuring the pressure of the grease in the space within the bearing housing using the pressure sensor to generate a pressure signal; and

[0014] Determining a cage slip ratio of the rolling element bearing and / or an amount of grease in the space within the bearing housing based on the pressure signal.

[0015] The step of determining the cage slip ratio of the rolling element bearing may include: determining a cage frequency based on the pressure signal, wherein the cage frequency may correspond to an angular rotational speed of the plurality of rolling elements of the rolling element bearing; measuring a shaft angular rotational speed; and calculating the cage slip ratio of the rolling element bearing based on the determined cage frequency and an ideal cage frequency at the measured shaft angular rotational speed.

[0016] The step of determining the cage frequency based on the pressure signal may include: decomposing the pressure signal into its component frequencies and identifying the frequency corresponding to the angular rotational speed of the plurality of rolling elements of the rolling element bearing.

[0017] The step of determining the amount of grease in the space within the bearing housing may include: decomposing the pressure signal into its constituent frequencies and identifying the frequencies corresponding to the angular rotational speeds of the plurality of rolling elements of the rolling element bearing; measuring the amplitude of the decomposed pressure signal at the frequencies corresponding to the angular rotational speeds of the plurality of rolling elements of the rolling element bearing; and estimating the amount of grease in the space within the bearing housing based on the measured amplitude.

[0018] A maintenance request for the wind turbine may be sent based on the determined cage slip ratio and / or the amount of grease.

[0019] The method may include controlling the speed of the shaft or stopping the operation of the wind turbine based on the determined cage slip ratio and / or the amount of grease.

[0020] The method may include performing maintenance on the wind turbine based on the determined cage slip ratio and / or the amount of grease.

[0021] A third aspect of the present invention provides a method of assembling or retrofitting a wind turbine, the wind turbine comprising: a bearing housing; a rolling element bearing located within the bearing housing and a space within the bearing housing for accommodating grease for lubricating the rolling element bearing; and a shaft rotatably supported by the rolling element bearing, the method comprising:

[0022] Assembling a pressure sensor such that the pressure sensor is in fluid communication with the space and the pressure sensor is configured to measure the pressure of the grease in the space within the bearing housing.

[0023] The method may include removing a plug from the grease outlet. The plug may be adapted to contain grease within the bearing housing. The method may include: assembling the pressure sensor to the grease outlet in a state where the shaft of the wind turbine is idle. The pressure sensor may be assembled to be adapted to contain grease within the bearing housing during operation of the wind turbine.

[0024] In any of the above aspects, the rolling element bearing may be a bearing that carries a load by placing rolling elements (such as balls or rollers) between two bearing rings called raceways. Relative movement of the raceways may cause the rolling elements to roll with very little rolling resistance and little sliding.

[0025] In any of the above aspects, the cage slip ratio directly reflects the sliding state between the rolling elements and the raceways of the rolling element bearing. The cage slip ratio may be the ratio of the angular rotational speed of the cage to the ideal angular rotational speed of the cage with respect to a specific angular velocity of the inner raceway.

[0026] In any of the above aspects, a maintenance request can be any sent signal that may result in maintenance being performed on the wind turbine. This can be a specific value (e.g., the amount of grease or the cage slip ratio), which can be analyzed at a control center different from the wind turbine, and which can indicate that the wind turbine requires maintenance. Alternatively, this can be a direct request for maintenance of the wind turbine, which may include details or reasons for the request. For example, this can be formatted as: request for maintenance; wind turbine address; and / or further details (e.g., low amount of grease). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments of the present invention will now be described with reference to the drawings, in which:

[0028] Figure 1 A wind turbine is shown.

[0029] Figure 2 A cross-section of the nacelle of the wind turbine is schematically shown, showing the main shaft, the bearing housing, the gearbox, and the generator.

[0030] Figure 3 A cross-section of the rolling element bearing and the main shaft of the wind turbine is schematically shown.

[0031] Figure 4 A schematic example of the rolling element bearing and its components is shown.

[0032] Figure 5a Is schematically shown Figure 3 An enlarged cross-section of, showing a single pressure sensor located in the grease outlet and a rolling element bearing.

[0033] Figure 5b Is schematically shown Figure 3 An enlarged cross-section of, showing two pressure sensors located in the corresponding grease outlet and a rolling element bearing.

[0034] Figure 5c Is schematically shown Figure 3 An enlarged cross-section of, showing two rolling element bearings each having a corresponding grease outlet and a pressure sensor.

[0035] Figure 6 A flowchart of a method for monitoring a rolling element bearing in a wind turbine is shown.

[0036] Figure 7a A graph of bearing grease pressure versus time is shown, which is received experimentally from a pressure sensor in fluid communication with the grease in the rolling element bearing.

[0037] Figure 7b Shows the frequency map found by performing Figure 7a the fast Fourier transform (FFT).

[0038] Figure 8 Shows a schematic diagram of a rolling element bearing and shows characteristic variables associated with the rolling element bearing. Detailed Description

[0039] Figure 1 An example of a wind turbine 1 is shown in a schematic perspective view. The wind turbine 1 includes a tower 2, a nacelle 3 disposed at the apex of the tower, and a rotor 4 that is operatively coupled to a generator housed within the nacelle 3. In addition to the generator, the nacelle houses various components required to convert wind energy into electrical energy and various components required to operate, control, and optimize the performance of the wind turbine 1.

[0040] The rotor 4 of the wind turbine 1 includes a central hub 5 and a plurality of blades 6 projecting outwardly from the central hub 5. In the illustrated wind turbine 1, the rotor 4 includes three blades 6, but the number may vary. Additionally, the wind turbine includes a control system. The control system may be placed within the nacelle or at multiple locations distributed inside (or outside) the turbine and communicatively connected.

[0041] When the wind blows against the wind turbine 1, the blades 6 generate lift, which causes the rotor 4 to rotate, which in turn causes the generator within the nacelle 3 to generate electrical energy.

[0042] Figure 2 The interior of the nacelle 3 of the wind turbine 1 is schematically shown. The nacelle 3 includes a nacelle frame 13 that structurally supports the nacelle 3 and the components within the nacelle 3. The wind turbine 1 includes rotor blades 6 that are mechanically connected to a generator 10 via a gearbox 9. In direct drive systems and other systems, the gearbox 9 may be absent. The electrical power generated by the generator 10 is injected into the power grid via an electrical converter (not shown). The main shaft 11 is mechanically attached to the hub 5 at the front end. The bearing housing 12 is mechanically attached to the nacelle frame 13 and is configured to rotatably support the main shaft 11 such that the bearing housing 12 supports the hub 5 and the plurality of blades 6 to allow them to rotate relative to the nacelle 3. The main shaft 11 extends through the bearing housing 12 and enters the gearbox 9 (or the generator 10 in a direct drive system) at the rear end.

[0043] Figure 3 A cross-section of the main shaft 11 and the main bearing housing 12 of the wind turbine 1 is shown. The main bearing housing 12 houses a rolling element bearing 15. The main bearing housing 12 rotatably supports the main shaft 11 using the rolling element bearing 15. The rolling element bearing includes a cage ( Figure 3A plurality of rolling elements 17 separated (not shown in the figure) and a cage configured to guide the plurality of rolling elements 17.

[0044] The bearing housing 12 further houses a grease 18 or other lubricant for lubricating the rolling element bearing 15 (especially the plurality of rolling elements 17) in the space within the bearing housing. The grease 18 preferably partially fills (e.g., about half) the space, and the remaining part is air. The space can be ventilated. The space can be fluidly connected to a grease reservoir, which can supply grease to the space, for example, by a fluid pump. The space may include an oil sump or other low points within the bearing housing 12, where excess grease is collected under the action of gravity and delivered to the rolling element bearing 15 during bearing rotation.

[0045] These greases 18 can be monitored with a pressure sensor 20 to gain insights into the grease level and / or current condition of the rolling element bearing 15, and / or can be used as an early warning system that can notify the wind turbine 1 (via the control system) and / or the operator of potential adverse events that can be further avoided (e.g., through maintenance and / or by controlling the wind turbine 1).

[0046] The main shaft 11 is fixed to the inner race 22 of the rolling element bearing 15. The outer race 23 can be fixed such that it does not rotate relative to the main bearing housing 12 during the operation of the wind turbine 1. The outer race 23 can be fixed to the structure of the main bearing housing 12, the nacelle 3, or the nacelle frame 13. This allows the inner race to rotate relative to the fixed outer race 23 together with the main shaft 11 during the operation of the wind turbine 1.

[0047] There are many types of rolling element bearings 15. For example, the rolling element bearing 15 can be a cylindrical roller bearing as Figure 4 shown. Alternatively, many other types of rolling element bearings 15 can be used, such as: single-row deep groove ball bearings; single-row angular contact bearings; double-row angular contact ball bearings; self-aligning ball bearings; needle bearings; tapered roller bearings; and / or spherical roller bearings, etc.

[0048] Figure 4 An example of the rolling element bearing 15 is shown. The rolling element bearing 15 is shown as including an inner race 22, an outer race 23, and a plurality of rolling elements 17 separated by a cage 24. The cage 24 rotates within the inner race 22 and the outer race 23 around the center of the rolling element bearing at the rotational speed of the plurality of rolling elements. The rotational speed of the cage 24 can be less than the rotational speed of the inner race 22.

[0049] Figure 5a Shown is Figure 3An enlarged view of the rolling element bearing is shown. It can be seen that the wind turbine 1 also includes a pressure sensor 20. Pressure sensors (including the pressure sensor 20) are generally sensors that are easy to operate and low-cost to implement in order to monitor the grease 18 of the rolling element bearing 15. The pressure sensor 20 can reliably monitor the grease 18 without on-site intervention. Additional information regarding the operating state of the rolling element bearing 15 and / or the grease 18 can be extracted from the raw pressure sensor 20 data via a control system (not shown) upon request or by reading the pressure sensor 20.

[0050] The pressure sensor 20 is in fluid communication with the grease 18 and is configured to measure the pressure of the grease within the bearing housing 12. The pressure sensor 20 is preferably located in the oil sump or other low points of the bearing housing 12 where the grease 18 is collected under the action of gravity.

[0051] The bearing housing 12 includes a grease outlet 26 for adding and / or removing the grease 18 from the bearing housing 12, for example, during a grease replacement process. The grease outlet 26 can be located in the oil sump or other low points of the bearing housing 12. The grease outlet (such as the grease outlet 26) typically also includes a plug (not shown) that is suitable for containing the grease 18 within the bearing housing 12. The plug prevents the grease 18 from escaping from the bearing housing 12 during the normal operation of the wind turbine 1.

[0052] As Figure 5a shown, the pressure sensor 20 additionally serves the same function as the plug 26. The pressure sensor 20 is connected to the grease outlet 26 such that it is suitable for containing the grease 18 within the rolling element bearing 15 at least during the operation of the wind turbine 1. Therefore, there is no longer a need to use a plug. Alternatively, a plug adapter (not shown) can be used to connect the pressure sensor 20 to the grease outlet 26 such that it can be suitable for containing the grease 18 within the bearing housing 12 at least during the operation of the wind turbine 1.

[0053] Figure 5b is shown in connection with Figure 5aThe same features, except that it shows two pressure sensors 20a, 20b instead of one pressure sensor 20. The first pressure sensor 20a is associated with the first plurality of rolling elements 17a. The first pressure sensor 20a is in fluid communication with the grease 18 in the space within the bearing housing 12 and is positioned such that it can measure the pressure of the grease 18 associated with the first plurality of rolling elements 17a of the rolling element bearing 15. The position of the first pressure sensor 20a relative to the first plurality of roller bearings 17a is thus proximal. The benefit of a proximal pressure sensor (such as 20, 20a, and / or 20b) is a larger received pressure signal. This is because the pressure signal attenuates as it passes through the grease 18 and / or any air in the grease. In practice, this may mean that the first pressure sensor 20a is positioned closer to the first plurality of roller bearings 17a than to the second plurality of roller bearings 17b. The position of the first pressure sensor 20a can be defined as the first measurement point. The first measurement point is positioned to measure the pressure of the grease 18 corresponding to the first plurality of rolling elements 17a such that the pressure signal caused by the first plurality of rolling elements 17a can be identified through the first pressure sensor 20a and subsequent analysis of the output signal of the first pressure sensor 20a.

[0054] Similarly, the second pressure sensor 20b corresponds to the second plurality of rolling elements 17b in substantially the same manner as described above. It should be noted that the rolling element bearing 15 includes a first plurality of rolling elements 17a and a second plurality of rolling elements 17b, each separated by a respective cage ( Figure 5b not shown in the figure). Since each of the plurality of rolling elements 17a and 17b is part of the same rolling element bearing, the plurality of rolling elements 17a and 17b both share the same grease 18 in the same space within the bearing housing 12.

[0055] Figure 5c It is shown that the main shaft 11 can be supported by a main bearing housing 12, which rotatably supports the main shaft 11 with a first rolling element bearing 15a and a second rolling element bearing 15b. Each rolling element bearing 15a, 15b includes: a plurality of rolling elements 17a, 17b; and a corresponding cage ( Figure 5c not shown in the figure); and grease 18a, 18b for lubrication (from the corresponding space within the bearing housing 12). Each rolling element bearing 15a, 15b further includes a pressure sensor 20a, 20b, which is in fluid communication with the corresponding grease 18a, 18b in the corresponding space. Each pressure sensor 20a, 20b is configured to measure the pressure of the corresponding grease 18a, 18b in the corresponding space associated with the corresponding rolling element bearing 15a, 15b in the common bearing housing 12.

[0056] By using a pressure sensor 20 in fluid communication with a grease 18 associated with a rolling element bearing 15, the grease level within the rolling element bearing 15 and / or within the bearing housing of the wind turbine 1 can be monitored. The output of the pressure sensor 20 can be analyzed to determine whether maintenance or other action is required, and / or whether maintenance or other action will be required in the future. Such monitoring can allow the control system (not shown) of the wind turbine 1 to stop the operation of the wind turbine 1 in the event of a major failure of the rolling element bearing 15. For example, if there is a sudden loss of the grease 18, the rolling element bearing 15 will heat up by friction and may be damaged if the wind turbine 1 continues to operate.

[0057] Typically, a temperature sensor (not shown) in the wind turbine 1 can be used to indirectly sense that the bearing housing 12 has exceeded normal heat limits and then stop the operation of the wind turbine 1. However, once the temperature has risen high enough to trigger an alarm, it may be too late for the rolling element bearing 15 to be saved and it may need to be replaced. This can result in additional costs for replacing the bearing 15, and losses associated with the downtime of the wind turbine.

[0058] Accordingly, by using a pressure sensor 20 in fluid communication with the grease 18 within the space in the bearing housing 12, such events can be avoided and further maintenance benefits can be provided, which can increase the operating life of the rolling element bearing 15. The pressure sensor 20 can also be used to indicate a low grease level and prompt the addition of additional grease 18 from the lubrication system to the bearing. Such preemptive 'bridging' actions between normal scheduled maintenance can significantly reduce the number of additional maintenance services required between normal scheduled maintenance intervals.

[0059] Figure 6 A method of monitoring a rolling element bearing 15 of a wind turbine 1 is shown for at least Figure 3 , Figure 5a , Figure 5b or Figure 5c . First, in step S1, the main shaft typically rotates due to the operation of the wind turbine 1. The rotation of the main shaft causes the inner race 22 to move relative to the cage 24. The rotation of the main shaft causes the cage 24 to move relative to the outer race 23. This causes pressure fluctuations in the grease 18 that correspond to: (i) the amount of grease 18; and (ii) the rotation of the plurality of rolling element bearings 17, as will be described below. These pressure fluctuations can be sensed by the pressure sensor 20.

[0060] In step S2, the pressure fluctuations of the grease 18 can be measured by the pressure sensor 20 to generate a pressure signal. Figure 7a The pressure signal is shown relative to time. Figure 7a The pressure along the y-axis and the time across the x-axis are shown.

[0061] In step S3, the amount of grease 18 in the rolling element bearing 15 can be determined by, for example, isolating a pressure signal component, e.g., by decomposing the pressure signal into its constituent frequencies and identifying the frequencies corresponding to the angular rotational speeds of the plurality of rotating elements 17. Return reference Figure 7a , the pressure signal component 29 is shown to correspond to the rotational speeds of the plurality of rolling elements. Component 29 can be a relatively high frequency signal compared to other signal components from the pressure sensor 20. Component 29 can also have a relatively stable amplitude 30 over many cycles. As Figure 7a shown, component 29 can be a consistent signal and can exist relatively isolated for the majority of the time.

[0062] The presence of a large number of pressure signal values different from component 29 can be seen from Figure 7a . These can be artifacts of the particular test equipment used to collect the measurement results and may not be present during the operation of the wind turbine.

[0063] In step S4, as Figure 7a shown, the amplitude of the pressure signal component 29 is measured, resulting in the measured amplitude 30. Alternatively, the measured amplitude 30 can be an average of the amplitudes over a period of time.

[0064] In step S5, the amount of grease 18 in the rolling element bearing 15 can be estimated based on the measured amplitude 30. If the grease level is normal, the amplitude 30 will be large. If the grease level is low, the amplitude 30 will be small. If no pressure signal component due to the angular rotational speeds of the plurality of rotating elements 17 is observed in the pressure signal, it can be determined that the grease level is very low or too low because there is no grease to transmit the shock between the pressure sensor 20 and the roller bearing elements. Thus, the measured pressure signal component 29 and the amplitude 30 of the pressure signal component 29 can be good proxies for the amount of grease 18 in the rolling element bearing 15. If there is a sub - optimal amount of grease 18 in the rolling element bearing 15, then the pressure fluctuations of the grease 18 will be more attenuated. This is because the pressure fluctuations of the grease 18 require the grease 18 to propagate to the pressure sensor 20.

[0065] As a supplement or alternative to estimating the amount of grease 18 in the rolling element bearing 15, a pressure signal can be used to estimate the cage slip ratio of the rolling element bearing 15. The cage slip ratio can be defined as the ratio of the angular rotational speed of the cage relative to the ideal speed of the cage for a particular angular rotational speed of the inner race 21 (i.e., the shaft rotational speed). The ideal cage slip ratio for a range of angular rotational speeds of the inner race can be calculated from the bearing dimensions or can be provided by the bearing manufacturer. The cage slip ratio is a proxy (or tracer) for bearing wear. Specifically, the cage slip ratio can be used to determine the wear of one or more of the plurality of rolling elements 17. The more the measured cage slip deviates from the idealized cage slip (calculated from the bearing dimensions or received from the manufacturer's data sheet), the more wear will occur. This wear can be well indicated by the pressure signal before any significant performance loss or failure of the bearing. Accordingly, maintenance for repairing or replacing the bearing can be scheduled in advance. The operation of the wind turbine can be adjusted, for example, by restricting the rotor speed, to extend the operation of the turbine to bridge until the next scheduled maintenance. This can avoid unscheduled ad-hoc maintenance that might otherwise become necessary.

[0066] The method begins at step S6, where the cage frequency can be determined, which corresponds to the angular rotational speed of the plurality of rolling elements 17. Refer to Figure 7b , Figure 7b shows Figure 7a the fast Fourier transform (FFT) of the signal shown. Figure 7b shows that there is a frequency component 32 of approximately 2.6 Hz (although this value depends on a number of factors). The frequency component 32 corresponds to the FFT of the time domain component 29. The frequency component 32 can be a relatively high frequency signal compared to other signal components from the pressure sensor 20. Due to the coherence of the component 29 (i.e., the pressure signal), the frequency component 32 can be characterized by a relatively large amplitude. The frequency component 32 can be one of the highest frequency signals with the largest amplitude. The frequency component 32 can have a peak amplitude that is greater than 400% of the peak amplitude of any other frequency component within a 1 Hz or 2 Hz range of the frequency component 32. The frequency component 32 represents the rotational frequency of the cage 24 multiplied by the number of rolling elements in the plurality of rolling elements 17. For example, if there are ten rolling elements in the rolling element bearing 15, during one rotation of one cage 24, ten rolling elements will pass a fixed position of the outer race 23. The fixed position can be the position of the pressure sensor 20.

[0067] At step S7, the spindle frequency can be measured from the spindle angular rotational speed. The spindle rotational frequency can be measured by a built-in or otherwise spindle dynamometer (not shown) of the wind turbine 1 or any other sensor.

[0068] In step S8, the cage slip ratio of the rolling element bearing 15 is calculated based on the determined cage frequency and the idealized cage frequency at the measured shaft angular rotation speed. The idealized cage frequency at the measured main shaft rotation frequency can be known based on the design of the rolling element bearing 15, and / or can be received from the bearing manufacturer's data sheet (or easily calculated from the bearing manufacturer's data sheet). Refer to Figure 8 , the idealized cage frequency is denoted as ω cr , where:

[0069]

[0070] where, R r is the radius of the rolling elements among the plurality of rolling elements 17, R m is the bearing pitch circle radius, and, ω t is the angular velocity of the inner race 22 = the angular velocity of the main shaft.

[0071] The cage slip ratio can be defined as:

[0072]

[0073] where, ω c is the angular velocity of the cage 24.

[0074] Figure 8 shows a schematic diagram of the rolling element bearing 15 and can help define the parameters used in the above equations (1), (2).

[0075] Based on a predetermined recommended amount of the grease 18, or alternatively, based on the limitation of the amount of the grease 18 for the acceptable functionality of the rolling element bearing 15, the wind turbine 1 can send a maintenance request. Additionally or alternatively, the wind turbine 1 can send a maintenance request based on the cage slip ratio. The microcontroller (not shown) of the control system (not shown) of the wind turbine 1 can process the incoming data and send a maintenance request based on the determined cage slip ratio and / or the amount of the grease 18. Alternatively, the control system (not shown) of the wind turbine 1 can also further process the results of step S8 and step S5 to determine when to send a maintenance request in case a maintenance request is really to be sent.

[0076] In step S10, the control system (not shown) of the wind turbine 1 can switch the operating state of the wind turbine 1. The calculated slip ratio and / or the estimated value of the amount of the grease can be compared with a predetermined or variable threshold, and if exceeded, the wind turbine 1 can be controlled to reduce the speed of the main shaft 11. The speed of the main shaft 11 can be reduced via a braking system (not shown) that pitches the blades 6 or other mechanisms.

[0077] Alternatively, the calculated slip ratio and / or the estimated amount of grease may be compared with a predetermined or variable threshold, and if exceeded, the wind turbine 1 may be controlled to completely stop the operation of the wind turbine 1 or switch the wind turbine 1 to an idle operating state.

[0078] A cage slip ratio of less than 0.5% may be considered within normal operating limits. The predetermined or variable threshold associated with the cage slip ratio may be 0.5%, 1%, 2%, 5% or any value that may be considered to require maintenance (which may be determined from the manufacturer's data sheet). The threshold may further depend on: the type of rolling element bearing 15; and / or the operating conditions. The predetermined or variable threshold associated with the amount of grease 18 may be a percentage of the maximum amount of grease 18 for a particular rolling element bearing 15, such as 0.5%, 1%, 2%, 5%, 10%, 20% or any value that may be considered to require maintenance (which may be determined from the manufacturer's data sheet). The threshold may further depend on the type of rolling element bearing 15 and / or the operating conditions.

[0079] For example, if the amount of grease estimated in step S5 is significantly lost, then step S10 may be required. This may indicate a sudden loss of grease 18 pressure that could cause damage to the rolling element bearing 15. Alternatively, a large change in the value of the cage slip ratio may indicate a damaged rolling element bearing 15.

[0080] Although not shown in the figures, a breather / pressure relief valve may be used with the grease chamber or space of the bearing housing 12 to accommodate pressure changes with temperature. Such pressure changes with temperature may be taken into account in any calculations of the amount of grease 18 and / or the cage slip ratio. A temperature sensor may be used for this purpose.

[0081] In step S11, maintenance is performed on the rolling element bearing 15 based on the determined cage slip ratio and / or the amount of grease 18. The maintenance may include adding grease to the rolling element bearing 15. The maintenance may include replacing the grease 18 in the rolling element bearing 15. The maintenance may include disassembling the rolling element bearing 15 and replacing some or all of the components or parts. For example, at least some of the plurality of rolling elements 17 or any other component of the rolling element bearing 15 may be replaced.

[0082] Any one of steps S9, S10, and S11 can be carried out in any order. For some operations, or even at all, at least some of steps S9, S10, and S11 may not occur. For example, steps S1 to S8 can be carried out during a maintenance test, so steps S9 and S10 do not need to be carried out during that test. Additionally, step S11 is only required if there is a result from step S8 and / or S5 that requires maintenance of the rolling element bearing 15. Furthermore, it will be clear to those skilled in the art that steps S3 to S5 or steps S6 to S8 do not need to be carried out at all, such that only one of the cage slip ratio and / or the amount of grease 18 in the rolling element bearing 15 can be determined.

[0083] Figure 3 The main bearing housing 12 and / or the rolling element bearing 15 can be assembled or retrofitted by adding a pressure sensor 20 to any of the following: the rolling element bearing 15; the main bearing housing 12; or, any part of the wind turbine 1. The addition of the pressure sensor 20 places the pressure sensor 20 in fluid contact with the grease 18 of the rolling element bearing 15. Since the only requirement is for the pressure sensor 20 to be in fluid contact with the grease 18 of the rolling element bearing 15, there may be few physical restrictions on the location of the pressure sensor 20. The pressure sensor 20 can have a small overall size, and / or can be a wireless sensor (in some applications, the pressure sensor can be wired). These features enable the pressure sensor 20 to have few physical location restrictions during assembly or retrofit. For example, the pressure sensor 20 can be positioned in the grease outlet 26 during assembly.

[0084] Retrofit can place the pressure sensor 20 in a sub-optimal location for pressure sensing but that only results in a minimal change to the existing rolling element bearing 15 to accommodate the pressure sensor 20. Thus, depending on the application and purpose, this system may generally be optimal. Positioning the pressure sensor 20 in the grease outlet 26 is particularly useful for retrofit, as the grease outlet 26 is already an access point for the grease 18. In another example, the pressure sensor 20 can be manufactured such that it is inside the rolling element bearing 15, or outside the rolling element bearing 15 but at another location inside the main bearing housing 12. If the pressure sensor 20 is inside the rolling element bearing 15, the pressure sensor can be positioned on the outer race 23 in fluid contact with the grease 18, or on the inner race 22, or at a side of the rolling element bearing 15 that is positioned such that the multiple rolling elements 17 are not obstructed in their path. In summary, the pressure sensor 20 can be manufactured to be positioned anywhere around the rolling element bearing 15, as long as the pressure sensor can measure the presence of grease 18 in the bearing housing in contact with the rolling element bearing 15.

[0085] As described above, the grease outlet 26 is particularly convenient for retrofitting a pressure sensor into an existing rolling element bearing housing 12. The process of retrofitting the pressure sensor 20 may require removing the plug from the grease outlet 26 and inserting the pressure sensor 20 into the grease outlet 26. Ideally, this process occurs when the main shaft of the wind turbine 1 is stationary to avoid unnecessary pressure loss of the grease 18 and to allow access for maintenance personnel. The end result of the retrofit is that the pressure sensor 20 is fastened in the grease outlet 26 such that it is adapted to contain the grease 18 within the rolling element bearing 15 during operation of the wind turbine 1. Accordingly, the pressure sensor 20 can serve as a fixed installation item for a condition monitoring system (CMS) or as a diagnostic tool for maintenance technicians.

[0086] If there are two pressure sensors 20a, 20b to be retrofitted or assembled onto the same rolling element bearing 15 in the above-described manner, the method of manufacturing a wind turbine (specifically, the main bearing housing 12 and / or the rolling element bearing 15) by assembling or retrofitting the pressure sensors 20 is equally applicable.

[0087] The benefits of the wind turbine and the corresponding method are:

[0088] 1. Avoid time-consuming inspections of the rolling element bearing 15, which otherwise would need to be carried out by removing the main bearing housing 12 cover and / or by disassembling a portion of the rolling element bearing 15 to periodically monitor the rolling element bearing 15.

[0089] 2. Generate important information for service planning to save resources.

[0090] 3. Generate early warnings of losses of the grease 18 that may be caused by seal damage or wear.

[0091] 4. Monitor the internal pressure of the rolling element bearing 15 to ensure proper ventilation and sealing functions.

[0092] 5. Support the lubrication system function.

[0093] 6. Cold triggering of the lubrication system as an emergency mediation until service can be organized.

[0094] Although the invention has been described above with reference to one or more preferred embodiments, it should be understood that various changes or modifications can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A wind turbine, the wind turbine comprising: Bearing housing; A rolling element bearing located within the bearing housing and a space within the bearing housing for containing grease for lubricating the rolling element bearing; A shaft rotatably supported by the rolling element bearing; And a pressure sensor, wherein the pressure sensor is in fluid communication with the space, and the pressure sensor is configured to measure the pressure of the grease in the space within the bearing housing; wherein the rolling element bearing includes a plurality of rolling elements separated by a cage, and a control system of the wind turbine is capable of determining a cage slip ratio of the rolling element bearing based on a pressure signal of the pressure sensor.

2. The wind turbine according to claim 1, wherein, The bearing housing further includes a grease outlet for adding grease to and / or removing grease from the space within the bearing housing, wherein the pressure sensor is coupled to the grease outlet and is adapted to retain the grease within the bearing housing during operation of the wind turbine.

3. The wind turbine according to claim 1 or 2, wherein, The pressure sensor is a first pressure sensor, and wherein the wind turbine further includes a second pressure sensor in fluid communication with the space, and the second pressure sensor is configured to measure the pressure of the grease in the space within the bearing housing; wherein the first pressure sensor is in fluid communication with the space at a first measurement point, and the second pressure sensor is in fluid communication with the space at a second measurement point.

4. The wind turbine according to claim 3, wherein, The rolling element bearing includes a first plurality of rolling elements separated by the cage, and the rolling element bearing further includes a second plurality of rolling elements separated by a second cage, wherein the first measurement point is positioned to measure the pressure of the grease in the space adjacent to the first plurality of rolling elements, and the second measurement point is further positioned to measure the pressure of the grease in the space adjacent to the second plurality of rolling elements.

5. The wind turbine according to claim 1 or 2, wherein, The bearing housing is a main bearing housing, and the shaft is a main shaft of the wind turbine.

6. A method of monitoring a wind turbine according to any one of claims 1 to 5, the method comprising: Rotating the shaft; While the shaft is rotating, measuring the pressure of the grease in the space within the bearing housing using the pressure sensor to generate a pressure signal; And Determining a cage slip ratio of the rolling element bearing based on the pressure signal.

7. The method according to claim 6, wherein, The step of determining the cage slip ratio of the rolling element bearing includes: Determining a cage frequency from the pressure signal, wherein the cage frequency corresponds to an angular rotational speed of the plurality of rolling elements of the rolling element bearing; Measuring an angular shaft rotational speed; and Calculating a cage slip ratio of the rolling element bearing based on the determined cage frequency and an ideal cage frequency at the measured angular shaft rotational speed.

8. The method according to claim 7, wherein The step of determining the cage frequency from the pressure signal includes: decomposing the pressure signal into its component frequencies and identifying the frequency corresponding to the angular rotational speed of the plurality of rolling elements of the rolling element bearing.

9. The method according to claim 6, the method further comprising determining an amount of grease in the space within the bearing housing based on the pressure signal, wherein, The steps for determining the amount of grease in the space within the bearing housing include: Decomposing the pressure signal into its component frequencies and identifying the frequencies corresponding to the angular rotational speeds of the plurality of rolling elements of the rolling element bearing; Measuring the amplitude of the decomposed pressure signal at the frequencies corresponding to the angular rotational speeds of the plurality of rolling elements of the rolling element bearing; and Estimating the amount of grease in the space within the bearing housing based on the measured amplitude.

10. The method according to claim 6, the method further comprising: Sending a maintenance request based on the determined cage slip ratio.

11. The method according to claim 9, the method further comprising: Sending a maintenance request based on the determined cage slip ratio and / or the amount of grease.

12. The method according to claim 6, the method further comprising: Controlling the speed of the shaft or stopping the operation of the wind turbine based on the determined cage slip ratio.

13. The method according to claim 9, the method further comprising: Controlling the speed of the shaft or stopping the operation of the wind turbine based on the determined cage slip ratio and / or the amount of grease.

14. The method according to claim 6, the method further comprising: Performing maintenance on the wind turbine based on the determined cage slip ratio.

15. The method according to claim 9, the method further comprising: Performing maintenance on the wind turbine based on the determined cage slip ratio and / or the amount of grease.

16. A method of assembling or modifying a wind turbine, the wind turbine comprising: Bearing housing; A rolling element bearing located within the bearing housing and a space within the bearing housing for accommodating grease for lubricating the rolling element bearing; And a shaft rotatably supported by the rolling element bearing, the method comprising: Installing a pressure sensor such that the pressure sensor is in fluid communication with the space and the pressure sensor is configured to measure the pressure of the grease in the space within the bearing housing, and the control system of the wind turbine can determine the cage slip ratio of the rolling element bearing based on the pressure signal of the pressure sensor.

17. The method according to claim 16, wherein The bearing housing further includes a grease outlet for adding grease to and / or removing grease from the space within the bearing housing, the method further comprising: Removing a plug from the grease outlet, the plug being adapted to contain grease within the bearing housing; and Installing the pressure sensor at the grease outlet in a state where the shaft of the wind turbine is idle, wherein the pressure sensor is installed to be adapted to contain grease within the bearing housing during operation of the wind turbine.

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