Capacity measurement in a warehouse

Abstract

Storage arrangement (500), which includes: a bearing (100, 200, 300, 400) comprising an inner race (102), an outer race (104) and a plurality of rolling elements (106) arranged between the inner and outer race (102, 104) such that the inner race (102) is rotatable relative to the outer race (104); a bearing lubricant arranged inside the bearing (100, 200, 300, 400) to lubricate the rolling elements (106); wherein the bearing arrangement (500) comprises a first electrically conductive part and a second electrically conductive part, wherein the first and the second electrically conductive part are electrically insulated and arranged such that at least a portion of the bearing lubricant is located between the first and the second electrically conductive part; and a capacitance measuring device (502) comprising a first electrode connected to the first electrically conductive part and a second electrode connected to the second electrically conductive part, configured to measure a capacitance between the first and second parts in order to determine a water content in the lubricant based on the measured capacitance, characterized in that the first electrically conductive part and the second electrically conductive part are a first and a second sealing ring (108a, 108b) arranged on respective sides of the bearing (100, 200, 300, 400), each sealing ring (108a, 108b) being electrically insulated from the bearing (100, 200, 300, 400).

Description

Field of invention

[0001] The present invention relates to a bearing arrangement. In particular, the present invention relates to a bearing that has a capacitance sensor for determining a property of a lubricant in the bearing. Technical background

[0002] Bearings, and rolling bearings in particular, are used in a wide range of applications involving rotating shafts. Rolling bearings provide low-friction rotation by means of the rolling elements located between the outer and inner races of the bearing. To further reduce friction between the rolling elements and the races, thereby extending the bearing's service life, a bearing lubricant such as grease or oil is often used to lubricate the rolling elements.

[0003] To improve the availability / operating time and lifespan of, for example, a wind turbine, various bearing-related parameters such as vibrations, lubricant pressure, lubricant quality, lubricant temperature and bearing load can be monitored.

[0004] It has been found that bearing failures are frequently caused by water in the bearing lubricant. Water in the lubricant can cause surface erosion and cavitation within the bearing. It can also cause hydrogen embrittlement due to the extreme pressures in rolling bearings, which can reach 1 to 3 GPa. In this process, water can be split into its individual atoms, allowing hydrogen to penetrate the surface of the bearing elements and making them more brittle. Water can also cause additives to precipitate and lead to the formation of abrasive particles or sludge. Furthermore, water can cause the base oil to oxidize much more rapidly. Even without the addition of external water, the water content in the lubricant can easily increase due to the oxidation of hydrocarbons within the lubricant.

[0005] For example, a bearing exposed to the elements (such as a wheel bearing on a train or wagon) is more susceptible to contamination by both water and other contaminating particles.

[0006] Accordingly, it is important to be able to monitor the condition of the bearing so that a bearing can be replaced before it breaks.

[0007] Although the monitoring currently described in engineering helps in planning maintenance and predicting failures before they occur, and can thus improve the availability of rotating systems, many such systems are both complicated and impractical to be used in many applications.

[0008] Publication JP 2007 - 198 576 A discloses a bearing arrangement according to the preamble of claim 1 and a method according to the preamble of claim 5. Further prior art is disclosed in publications EP 2 682 732 A1 and US 2003 / 0 222 656 A1. Summary of the invention

[0009] In view of the desired properties of a bearing mentioned above and the disadvantages of the prior art mentioned above and others, it is an object of the present invention to provide an improved bearing and a method for monitoring the properties of the bearing so that unexpected bearing failure can be avoided.

[0010] According to a first aspect of the present invention, a bearing arrangement is therefore provided comprising: a bearing having an inner race, an outer race and a plurality of rolling elements arranged between the inner and the outer race such that the first race is rotatable relative to the second race; a bearing lubricant arranged within the bearing to lubricate the rolling elements; wherein the bearing arrangement comprises a first electrically conductive part and a second electrically conductive part, the first and the second electrically conductive part being electrically insulated and arranged such that at least a portion of the bearing lubricant is located between the first and the second electrically conductive part;and a capacitance measuring device comprising a first electrode connected to the first electrically conductive part and a second electrode connected to the second electrically conductive part, configured to measure a capacitance between the first part and the second part in order to determine a water content in the lubricant based on the measured capacitance.

[0011] Since the capacitance of a lubricant depends on its composition, any change in composition resulting in different dielectric properties would lead to a change in capacitance. In particular, the dielectric constant of water is significantly higher than that of conventionally used bearing lubricants such as grease and oil. Thus, adding water to the bearing lubricant would lead to an increase in the observed capacitance. Early detection of water in the bearing lubricant can significantly reduce the occurrence of bearing failures. It is also possible to detect the presence of other contaminants in the lubricant, such as metal particles, which also lead to a change in capacitance.Capacity measurements are well known and the invention described above can be easily installed in new bearings, and capacity measurement equipment can also be retrofitted in existing bearings.

[0012] Capacitance is measured between two conductive elements separated by a dielectric material. The conductive elements are electrically insulated, meaning they are not electrically connected to each other or to any other part of the bearing; they are only connected to the respective electrode of the capacitance meter. In this application, the dielectric material is the bearing lubricant, and the conductive elements can be parts of the bearing itself or separate conductive components. Non-conductive greases and oils commonly used in bearings have a dielectric constant of approximately 2–5, whereas water has a dielectric constant of approximately 80 at room temperature. Therefore, due to the large difference in dielectric constant, even a small amount of water in the lubricant would cause a change in capacitance, making it possible to detect even a small amount of water.

[0013] During normal operation of a bearing, no significant change in capacity is expected. Therefore, any change in capacity during operation can be considered a sign that something is wrong. A sudden increase in capacity may indicate the addition of water or contaminants. A sudden decrease could indicate physical damage to the bearing, such as a damaged seal causing grease to leak out. Furthermore, capacity can be measured both during operation, i.e., when the bearing is rotating, and when the bearing is stationary.

[0014] The first and second electrically conductive parts are a first and second sealing ring, respectively, located on opposite sides of the bearing, with each sealing ring electrically insulated from the bearing. Sealing rings are commonly present in bearings to retain lubricant within the bearing. By using electrically conductive sealing rings, the sealing rings can be used to measure the capacitance of the bearing lubricant. The sealing rings then act as the plates in a parallel-plate capacitor. The sealing rings are electrically insulated from the bearing to prevent short circuits.

[0015] According to one embodiment of the invention, the bearing arrangement can further comprise an electrically insulating frame positioned between the sealing ring and the bearing to electrically isolate the sealing ring from the bearing. A typically ring-shaped frame can be used to electrically isolate the sealing ring from the bearing. The frame can, for example, be made of a plastic or rubber material.

[0016] In one embodiment of the invention, the bearing arrangement can further include a temperature sensor configured to determine the temperature of the lubricant. The lubricant temperature can vary significantly during bearing operation, and there can be a particular difference in temperature when comparing a static bearing with one rotating at high speed. Generally, the dielectric constant of lubricants and oils does not vary significantly with temperature. On the other hand, the dielectric constant of water varies considerably with temperature. Therefore, by measuring the temperature, a small change in capacitance, which might be interpreted as a small change in the water content of the lubricant, can instead be correctly attributed to a temperature variation.Furthermore, by observing the temperature-dependent capacitance, the current water content in the lubricant can be determined more accurately. The temperature sensor can be any type of temperature sensor known to a person skilled in the art.

[0017] In one embodiment of the invention, the capacitance meter is configured to measure the capacitance at different frequencies or via a sine sweep. Frequency here refers to the frequency of an alternating current used by the capacitance meter to measure the capacitance. Grease has a different frequency dependence of its dielectric constant than water, and water has a well-known dielectric constant (relative permittivity) that varies with frequency. Therefore, the frequency dependence can be used to estimate the water content. Measuring the capacitance at different frequencies or via a sine sweep allows for the estimation of the water content even if the grease content changes or the location of the grease within the bearing changes.

[0018] According to a second aspect of the invention, a method according to claim 5 is also provided.

[0019] The measured value, which is indicative of the capacitance between the first and the second electrically conductive part, can be, for example, the capacitance measured directly at a predetermined frequency, or a ratio of capacitances measured at two different frequencies, or the temperature derivative of the capacitance, dC / dT.

[0020] In one embodiment of the invention, the predetermined value against which the measured value is compared can be a previously measured value for the same bearing in the same application. Alternatively, or in combination, the measured value can also be compared with a reference value based on measurements on a similar bearing. The reference value can also be based on analytical models and simulations.

[0021] If a detected difference is smaller than a predetermined threshold, it can be determined that the difference is merely the result of noise or within the range of known measurement uncertainties. Furthermore, the threshold can also be used to prevent the temperature dependence of the lubricant's dielectric constant from being mistakenly identified as a change in the lubricant's water content. In particular, if it is known that the change in capacitance due to a change in the lubricant's temperature is within a certain range, only detected capacitances outside this known range are considered to represent a change in the lubricant's composition.

[0022] Furthermore, by observing the temperature dependence of the capacity, it may be possible to accurately determine the current water content of the lubricant by correlating the observed temperature dependence with the known temperature dependence of water for different percentages of water in the lubricant.

[0023] Furthermore, if the water content in the lubricant has been accurately determined, for example by direct capacitance measurement or by observing the temperature dissipation, the total amount of lubricant present in the bearing can be approximated. Since the dielectric constants of water and grease are generally known, and the rest of the system should be constant, this can be accomplished. This eliminates the scenario in which a loss of grease plus a small addition of water would result in a similar capacitance to that of a properly lubricated bearing with the correct amount of grease and no water, because water introduces a temperature dependence to the dielectric constant.

[0024] Further effects and features of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the invention.

[0025] Furthermore, additional features and advantages of the present invention will become apparent upon studying the attached claims and the following description. The person skilled in the art will realize that different features of the present invention can be combined to produce embodiments other than those described below, without deviating from the scope of protection of the present invention. Brief description of the drawings

[0026] These and other aspects of the present invention will now be described in more detail with reference to the attached drawings, which show an exemplary embodiment of the invention, wherein: Fig. 1 schematically represents an exploded view of a bearing arrangement according to an embodiment of the invention; Fig. 2 schematically shows an exploded view of a bearing arrangement according to an embodiment that is not according to the invention; Fig. 3 schematically shows an exploded view of a bearing arrangement according to an embodiment of the invention; Fig. Figure 4 schematically depicts a bearing arrangement and a bearing housing according to an embodiment that is not according to the invention; and Fig. 5 schematically represents a bearing arrangement according to an embodiment of the invention; and Fig. 6 is a flowchart that represents the general steps of a method according to an embodiment of the invention. Detailed description of preferred embodiments of the invention

[0027] In this detailed description, various embodiments of a bearing arrangement according to the present invention are discussed, primarily with reference to a ball bearing. It should be noted that this in no way limits the scope of the present invention, which is equally applicable to any type of bearing incorporating a lubricant.

[0028] Fig. Figure 1 is an exploded view of a bearing 100, which has an inner race 102, an outer race 104, and a plurality of rolling elements 106 in the form of balls arranged between the inner and outer races. The bearing also has sealing rings 108a-b arranged on the respective sides of the bearing to seal it. Here, both the sealing rings 108a-b and the races 102, 104 are made of a conductive material. Furthermore, electrically insulating frames 110a-b are arranged to electrically insulate the sealing rings 108a-b from the races 102, 104. A lubricant (not shown) is arranged inside the bearing to provide lubrication for the rolling elements 106. Bearings are also frequently provided with a cage to hold the rolling elements in place.Such cages can be arranged and designed in many different ways known to the skilled person, and bearing cages are therefore not shown here to avoid complicating the drawings.

[0029] In Fig. The first conductive part is the first sealing ring 108a, and the second conductive part is the second sealing ring 108b, thus forming a plate capacitor in which the lubricant acts as the dielectric. Therefore, the capacitance of the lubricant can be measured by connecting a capacitance meter to the two sealing rings 108a-b.

[0030] In Fig. 2 is a 200-capacity bearing, similar to the one in Fig. 1 shown, depicted. The camp in Fig. The bearing assembly 2 has two sets of rolling elements 202, 204, and a perforated plate 206 is arranged between the rows of rolling elements 202, 204. The perforated plate 206 is conductive and can be connected to an electrode of a capacitance meter. The connection can be made, for example, through an opening 208 in the outer race 104. Such an opening is preferably sealed with a sealing material to ensure that no lubricant escapes from the bearing and that no contaminants can enter the bearing. It is, of course, also possible to form the connection through the inner race 102 or through any sealing ring 108a-b, depending on the design of a particular bearing and its arrangement during use. The perforation of the ring 206 allows the lubricant to circulate within the bearing through the openings in the ring.By connecting one electrode of a capacitance meter to the perforated ring 206 and the other electrode to one of the sealing rings 108a-b, the capacitance can be measured on each side of the perforated ring 206. This makes it possible not only to determine the properties of the lubricant but also to detect if the lubricant properties differ between the respective sides of the bearing. This can be advantageous, for example, to identify if contamination or water is entering the bearing from either side.

[0031] Fig. Figure 3 is a schematic representation of a bearing 300 in which perforated plates 302a-b are arranged between the respective sealing rings 108a-b and the bearing. Each of the perforated plates 302a-b has a respective edge 304a-b, 306a-b, which is arranged around both the inner and outer circumference of the plates 302a-b. The edges 304a-b, 306a-b are preferably electrically insulating, so that the plate is electrically isolated from the sealing rings and from the bearing races. Furthermore, the edges 304a-b, 306a-b can act as a spacer, so that a gap is formed between the perforated plates 302a-b and the corresponding sealing rings, allowing a lubricant to flow freely through the perforations.

[0032] Fig. Figure 4 is a schematic representation of a bearing arrangement located in a bearing housing 402a-b. When the bearing is located in a housing, the housing acts to seal the bearing from the environment, and no sealing rings are required. The perforated plates 302a-b can thus be arranged on the sides of the bearing without an additional sealing ring, and the bearing lubricant can then flow through the perforated rings 302a-b between the bearing housing and the interior of the bearing, thus lubricating the rolling elements 106.

[0033] Fig. Figure 5 is a schematic representation of a bearing arrangement 500 in which a capacitance meter 502 is connected to each of the sealing rings 108a-b so that the capacitance between the plates can be measured. In some embodiments, the bearing arrangement also includes a temperature sensor (not shown) to determine the temperature of the grease. The temperature sensor can be located inside the bearing, for example, attached to a sealing ring, mounted on a cage, or integrated into it. The temperature sensor can also be located on the outside of the bearing, provided that the relative influence of the measured temperature on the capacitance measurement is known.

[0034] Fig.Figure 6 is a flowchart illustrating the general steps of a method according to one embodiment of the invention. First, 602, a capacity measurement is performed to determine a capacity value. Next, 604, the measurement is compared to a predetermined value. The predetermined value may be based on previous measurements on a similar device, or it may be based on theoretical calculations. However, most preferably, the predetermined value is a previously measured capacity of the same bearing under similar conditions. For example, it may be the last measured value before the current measurement. By continuously monitoring the capacity to determine whether there is a change in capacity, changing characteristics of the bearing can be identified without knowing the specific capacity of a bearing in a particular application.

[0035] The detected difference is also compared to a threshold value, 606, and the difference should also be greater than the threshold value to exclude variations caused, for example, by measurement inaccuracies. The threshold value can be set by performing calibration measurements. If the detected difference is greater than the threshold value, it is determined, 608, that the properties of the lubricant have changed.

[0036] Typically, an increase in capacity is a sign that the properties of the lubricant have changed in a way that is detrimental to the lubricant's performance.

[0037] Furthermore, the temperature derivative of the capacitance can be determined. The temperature derivative of the capacitance can be determined, for example, during a phase in which the lubricant temperature is known to change, such as during the starting or stopping of a rotating machine. The capacitance (or dielectric constant) can be measured twice at different bearing temperatures (for example, when the machine is first started and when it is at its operating temperature). The temperature derivative can then be compared with a known derivative to determine whether the lubricant properties are changing. Moreover, the temperature derivative of commonly used lubricants is typically close to zero, at least within the operating temperatures of a bearing.Accordingly, any non-zero temperature dissipation can be taken as an indication that the lubricant's properties have changed. Water, in particular, has a temperature-dependent dielectric constant, which makes it possible to detect the addition of water as a change in the lubricant's temperature dissipation.

[0038] Furthermore, the capacitance (or dielectric constant) can be measured across different frequencies or via a sine sweep. Grease exhibits a different frequency dependence of the dielectric constant than water, and water has a well-known dielectric constant (relative permittivity) that varies with frequency. Therefore, the frequency dependence can be used to estimate the water content. For example, a capacitance ratio at two frequencies can be useful for representing the water content. 90 Hz and 100 kHz can be used, with 90 Hz being advantageous because it is not a multiple of 50 or 60 Hz. The ratio can then be compared to a known or predetermined ratio to determine whether the lubricant's properties have changed.

[0039] In one scenario, the high-frequency capacitance (e.g., 100 kHz) decreases significantly over time (or between two or more measurements). However, at the same time, the low-frequency capacitance (e.g., 90 Hz) is much higher than the high-frequency measurement. This could indicate that some grease has been lost (e.g., through a damaged seal) and water has entered the housing. In another scenario, the high-frequency capacitance increases only slightly, but the low-frequency capacitance increases significantly. This could mean that the grease content has remained roughly the same, but that there has been water contamination. In yet another scenario, the high-frequency capacitance measurement decreases by approximately the same percentage as the low-frequency measurement. This could mean that there has been no water contamination, but that there has been some grease loss (or that the grease has shifted significantly).

[0040] Although the invention has been described with reference to specific exemplary embodiments, many different variations, modifications, and the like will be obvious to those skilled in the art. For example, the described invention can be used in many different types of bearings. It should also be noted that parts of the system can be omitted, replaced, or arranged in different ways, and the bearing arrangement will still be able to perform the functionality of the present invention.

[0041] In addition, variations of the disclosed embodiments can be understood and implemented by a person skilled in the art by carrying out the claimed invention, based on a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the undefined article "a" or "an" does not exclude a plurality. The mere fact that certain measures are described in mutually dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

[1] Storage arrangement (500) which includes: a bearing (100, 200, 300, 400) comprising an inner race (102), an outer race (104) and a plurality of rolling elements (106) arranged between the inner and outer race (102, 104) such that the inner race (102) is rotatable relative to the outer race (104); a bearing lubricant arranged inside the bearing (100, 200, 300, 400) to lubricate the rolling elements (106); wherein the bearing arrangement (500) comprises a first electrically conductive part and a second electrically conductive part, wherein the first and the second electrically conductive part are electrically insulated and arranged such that at least a portion of the bearing lubricant is located between the first and the second electrically conductive part; and a capacitance measuring device (502) comprising a first electrode connected to the first electrically conductive part and a second electrode connected to the second electrically conductive part, configured to measure a capacitance between the first and second part in order to determine a water content in the lubricant based on the measured capacitance, characterized by , that the first electrically conductive part and the second electrically conductive part are a first and a second sealing ring (108a, 108b) arranged on respective sides of the bearing (100, 200, 300, 400), each sealing ring (108a, 108b) being electrically insulated from the bearing (100, 200, 300, 400). [2] Bearing arrangement (500) according to claim 1, further comprising an electrically insulating frame (110a, 110b) arranged between the sealing ring (108a, 108b) and the bearing (100, 200, 300, 400) to electrically insulate the sealing ring (108a, 108b) from the bearing (100, 200, 300, 400). [3] Bearing arrangement (500) according to one of the preceding claims, further comprising a temperature sensor configured to determine the temperature of the lubricant. [4] Bearing arrangement (500) according to one of the preceding claims, wherein the capacitance measuring device (502) is configured to measure the capacitance at different frequencies or via a sine sweep. [5] Method for determining the condition of a lubricant in a bearing (100, 200, 300, 400) which has: a housing (402a, 402b) comprising an inner running ring (102) and an outer running ring (104); a plurality of rolling elements (106) arranged between the inner and outer race (102, 104) such that the inner race (102) is rotatable relative to the outer race (104); a bearing lubricant arranged inside the housing (402a, 402b) to lubricate the rolling elements (106); and a first electrically conductive part and a second electrically conductive part, wherein the first and the second electrically conductive part are electrically insulated from each other and arranged such that at least part of the bearing lubricant is arranged between the first and the second electrically conductive part; the procedure exhibits: Measuring a value indicative of a capacitance between the first electrically conductive part and the second electrically conductive part (602); characterized by, that the first electrically conductive part and the second electrically conductive part are a first and a second sealing ring (108a, 108b) arranged on respective sides of the bearing (100, 200, 300, 400), each sealing ring (108a, 108b) being electrically insulated from the bearing (100, 200, 300, 400); wherein the method comprises: Determining a difference between the measured value and a predetermined value (604); and, If the difference is greater than a first predetermined threshold (606), determine that the properties of the lubricant have changed (608). [6] Method according to claim 5, wherein the measuring step comprises measuring the capacity (602). [7] Method according to claim 5 or 6, further comprising measuring the temperature of the lubricant. [8] Method according to claim 7, wherein the measuring step comprises measuring the temperature derivative of the capacitance, dC / dT. [9] Method according to any one of claims 5 to 8, wherein the predetermined value is a previously measured value for the same bearing. [10] Method according to any one of claims 5 to 9, wherein, if the measured value is greater than the predetermined value, it is determined that the water content of the lubricant is increased. [11] Method according to claim 8, further comprising continuous monitoring of the capacity during the operation of the bearing (100, 200, 300, 400) in a rotating machine. [12] Method according to claim 5, wherein the measuring step comprises measuring the capacitance at two or more different frequencies.

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