Method for evaluating electrical corrosion resistance of rolling bearing

Abstract

To provide a method for evaluating the electrical corrosion resistance of a rolling bearing, the method making it possible to easily and appropriately evaluate the degree of electrical corrosion resistance possessed by the rolling bearing.SOLUTION: Whether the value of F1 obtained by the following equation exceeds a reference value is determined. When the value exceeds the reference value, the bearing is determined to be the one in which ridge marks due to electrical corrosion can occur on an inner ring raceway surface or an outer ring raceway surface. When the value does not exceed the reference value, the bearing is determined to be the one in which ridge marks do not occur. Herein, k represents a coefficient indicating the ratio of energy among electric energy of a single discharge that is applied to surfaces of an inner ring raceway surface, an outer ring raceway surface, and rolling elements; ts denotes the start point of a single discharge time; te denotes the end point of the single discharge time; Vb denotes a voltage measured by a voltage measurement unit when the single discharge occurs; and ib denotes a current measured by a current measurement unit when the single discharge occurs.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the electrolytic corrosion resistance of a rolling bearing. [Background technology]

[0002] In the field of industrial machinery, electric motors such as fan motors, three-phase motors, and servo motors are widely used. These electric motors are often controlled by inverters to achieve high efficiency. In addition, electric motors used to drive electric vehicles such as EVs (battery electric vehicles) and HEVs (hybrid electric vehicles) are also controlled by inverters.

[0003] An inverter converts DC voltage into AC voltage and controls the rotation speed of an electric motor by changing the frequency of that AC voltage. This inverter is generally controlled by pulse width modulation (PWM) control, which changes the duty ratio at a constant switching frequency, and in recent years the switching frequency of this inverter has tended to become higher.

[0004] When the inverter's switching frequency increases, leakage current from the stator windings of the electric motor generates high-frequency magnetic flux surrounding the rotor of the electric motor, creating a potential difference between both ends of the rotor, which can result in a potential difference between the inner and outer rings of the rolling bearing that supports the rotor.

[0005] Furthermore, in recent years, there has been a trend toward higher voltage power supplies in the field of electric vehicles. Higher voltage power supplies have the advantage of being able to reduce current even with the same output, thereby reducing copper loss in power cables and inverters. However, this also tends to increase the potential difference between the rotor potential and ground potential of the electric motor, which in turn increases the potential difference between the inner and outer rings of the rolling bearings that support the rotor.

[0006] When the potential difference between the inner and outer rings of the rolling bearing that supports the electric motor rotor becomes large, dielectric breakdown occurs in the oil film between the inner ring and rolling elements and in the oil film between the outer ring and rolling elements, causing current to flow between the inner and outer rings. When this happens, a discharge (spark) occurs at the point of dielectric breakdown, which can cause localized melting and damage (electrolytic corrosion) on the inner and outer ring rolling surfaces where the rolling elements roll and contact. As this electrolytic corrosion progresses, striped irregularities called ridge marks form on the inner and outer ring rolling surfaces, which can lead to noise and vibration.

[0007] Therefore, Patent Documents 1 to 3 disclose techniques for preventing the occurrence of ridge marks.

[0008] Patent Document 1 proposes a technology for imparting conductivity between the inner ring and the rolling elements and between the outer ring and the rolling elements by using conductive grease as a lubricant for lubricating the inside of the bearing.

[0009] Patent Document 2 proposes a technology for preventing current from flowing through the rolling elements by using a conductive seal made of conductive rubber as a seal to close the end opening of the annular bearing space formed between the inner and outer rings of a rolling bearing.

[0010] Patent Document 3 proposes a technology to prevent current from flowing through a rolling bearing by providing an electrically conductive brush near the rolling bearing that supports the rotor of the electric motor, which provides electrical conduction between the rotor of the electric motor and the housing.

[0011] However, when using conductive grease or conductive seals as in Patent Documents 1 and 2, if conductive grease or conductive seals with low volume resistivity are used, electrolytic corrosion of rolling bearings can be prevented, but on the other hand, there are problems such as a decrease in the original performance of the grease or seal and an increase in cost. On the other hand, when conductive grease or conductive seals with a relatively high volume resistivity (for example, 10 4 ~10 8If a high-strength grease (approximately Ωcm) is used, the performance of the grease and seals can be ensured, but the effectiveness of preventing electrolytic corrosion of the rolling bearings will be reduced, and there is a risk of ridge marks occurring.

[0012] Furthermore, as in Patent Document 3, providing an electrically conductive brush can prevent electrolytic corrosion of the rolling bearing, but requires space for the electrically conductive brush in addition to the space for the rolling bearing, which increases costs.

[0013] The inventors of the present application came up with the idea that if it were possible to easily and appropriately evaluate the level of electrolytic corrosion resistance of rolling bearings of various specifications that have been fitted with measures to prevent electrolytic corrosion, it would be possible to provide rolling bearings with optimal electrolytic corrosion resistance at low cost.

[0014] In other words, there has traditionally been no simple and appropriate method for evaluating the level of electrolytic corrosion resistance of rolling bearings that have been treated to prevent electrolytic corrosion. As a result, electrolytic corrosion prevention measures to date have relied heavily on empirical intuition and have tended to result in designs that are over-specified, making it difficult to reduce the cost of rolling bearings that have been treated to prevent electrolytic corrosion. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Patent No. 4599769 [Patent Document 2] Patent No. 4177057 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-320129 Summary of the Invention [Problem to be solved by the invention]

[0016] The problem to be solved by the present invention is to provide a method for evaluating the galvanic corrosion resistance of a rolling bearing, which is capable of easily and appropriately evaluating the level of galvanic corrosion resistance of a rolling bearing. [Means for solving the problem]

[0017] The inventors of the present application conducted tests in which a voltage was applied to each of a number of rolling bearing samples to check for the presence or absence of electrolytic corrosion. They found that when a discharge occurs between the inner or outer ring and the rolling element, in some cases a discharge mark (a tiny crater-like depression) is formed on the inner or outer ring rolling surface, and in other cases no discharge mark is formed on either the inner or outer ring rolling surface, and only discoloration occurs at the discharged point on the inner or outer ring rolling surface; in the former rolling bearings, when discharge continues, ridge marks (striped irregularities) due to electrolytic corrosion appear on the inner or outer ring rolling surface, while in the latter rolling bearings, no ridge marks due to electrolytic corrosion appear on the inner or outer ring rolling surface, even when discharge continues.

[0018] The inventors of the present application then came up with the idea that if they conducted tests on various rolling bearings with different specifications in which a single discharge was generated between the inner ring rolling surface or outer ring rolling surface of those rolling bearings and the rolling element, it would be possible to easily determine whether or not a discharge mark (a tiny crater-like depression) would be formed on the inner ring rolling surface or outer ring rolling surface based on the magnitude of the electrical energy measured from the voltage and current waveforms when the single discharge occurred, and that based on the determination results it would be possible to appropriately evaluate whether or not the rolling bearing is a bearing that is likely to develop ridge marks (striped irregularities) due to electrolytic corrosion on the inner ring rolling surface or outer ring rolling surface.

[0019] Based on this idea, in order to solve the above-mentioned problems, the present invention provides a method for evaluating the electrolytic corrosion resistance of a rolling bearing having the following configuration. [Configuration 1] A method for evaluating electrolytic corrosion resistance of a rolling bearing having an inner ring with an inner ring rolling surface formed on its outer periphery, an outer ring with an outer ring rolling surface formed on its inner periphery, a plurality of rolling elements in rolling contact with the inner ring rolling surface and the outer ring rolling surface, and a lubricant that lubricates the inside of the bearing, comprising: a power supply unit that applies a voltage to the rolling bearing and is capable of changing the magnitude of the voltage, a voltage measuring unit that measures the voltage between the inner ring and the outer ring, and a current measuring unit that measures the current flowing between the inner ring and the outer ring, a test is conducted in which a voltage is applied to the rolling bearing by the power supply unit while the inner ring and the outer ring are rotating relative to each other, and the voltage is gradually increased to generate a single discharge between the inner ring rolling surface or the outer ring rolling surface and the rolling element; Based on the test results, a determination is made as to whether the value of F1 obtained by the following formula exceeds a predetermined reference value, and if it exceeds the reference value, the bearing is determined to be one in which ridge marks due to electrolytic corrosion may occur on the inner ring rolling surface or the outer ring rolling surface, and if it does not exceed the reference value, the bearing is determined to be one in which such ridge marks will not occur.

number

[0020] By adopting this configuration, it becomes possible to easily and appropriately evaluate whether or not a variety of rolling bearings with different specifications are likely to develop ridge marks due to electrolytic corrosion on the inner ring rolling surface or outer ring rolling surface when used as a bearing supporting the rotor of an electric motor.

[0021] [Configuration 2] 2. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to configuration 1, wherein the value of k is changed and set according to the viscosity of the lubricant so that the higher the viscosity of the lubricant, the larger the value of k.

[0022] By adopting this configuration, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion. In other words, the higher the viscosity of the lubricant inside the bearing, the more limited the diffusion of energy due to the vaporization and expansion of the lubricant when a discharge occurs due to insulation breakdown in the lubricant, and therefore the proportion of energy imparted to the inner ring rolling surface, outer ring rolling surface, and rolling element surfaces increases, making it more likely that discharge marks will occur on the inner ring rolling surface and outer ring rolling surface. Therefore, by setting the value of k so that the higher the viscosity of the lubricant, the larger the value of k, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion.

[0023] [Configuration 3] 3. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to configuration 1 or 2, wherein the value of k is changed and set in accordance with the volume resistivity of the lubricant so that the higher the volume resistivity of the lubricant, the larger the value of k.

[0024] By adopting this configuration, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion. In other words, the higher the volume resistivity of the lubricant, the higher the proportion of energy imparted to the inner ring rolling surface, outer ring rolling surface, and rolling element surfaces when a discharge occurs due to insulation breakdown of the lubricant, making it more likely that discharge marks will occur on the inner ring rolling surface and outer ring rolling surface. Therefore, by setting the value of k so that the higher the volume resistivity of the lubricant, the larger the value of k, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion.

[0025] [Configuration 4] 4. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of configurations 1 to 3, wherein the value of k is set in the range of 0.2 or more and 0.4 or less.

[0026] By adopting this configuration, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion. Specifically, the inventors' tests have shown that when dielectric breakdown of the lubricant occurs between the inner ring rolling surface or outer ring rolling surface and the rolling elements, causing a discharge, the proportion of energy imparted to the inner ring rolling surface, outer ring rolling surface, and rolling element surfaces of the electrical energy passing through the bearing due to the discharge is 20 to 40%. Therefore, by setting the value of k in the range of 0.2 to 0.4, it becomes possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion.

[0027] [Configuration 5] 5. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of configurations 1 to 4, wherein the time ts is the time when the voltage Vb starts to decrease when the single discharge occurs, or the time immediately before that.

[0028] [Configuration 6] A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to configuration 5, wherein it is determined that the single discharge has occurred when the voltage Vb has decreased by an amount equal to or greater than a predetermined decrease amount and the current ib has increased to a magnitude equal to or greater than a predetermined threshold value.

[0029] By adopting this configuration, it is possible to prevent false detection of single discharges due to noise in the voltage Vb or current ib, and to perform stable testing.

[0030] [Configuration 7] The predetermined decrease is set to a value of 0.1 V or more, 7. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to configuration 6, wherein the predetermined threshold value is set to a magnitude of 20 mA or more.

[0031] [Configuration 8] A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of configurations 1 to 7, wherein the point in time when the current ib increases due to the occurrence of the single discharge and then decreases and converges to 0, or the point in time immediately before that, is used as the point in time te.

[0032] [Configuration 9] A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of configurations 1 to 8, wherein, when it is determined that the value of F1 exceeds the predetermined upper limit, the method further determines whether the value of F2 obtained by multiplying the value of F1 by the number of discharges per unit time n expected when the rolling bearing is in use and the usage durability time T required of the rolling bearing exceeds a predetermined second reference value, and if the value of F2 exceeds the second reference value, it is determined that the bearing is likely to develop the ridge mark within the usage durability time T, and if the value of F2 does not exceed the second reference value, it is determined that the bearing will not develop the ridge mark within the usage durability time T.

[0033] By adopting this configuration, when it is determined based on the value of F1 described above that a bearing is susceptible to ridge marks due to electrolytic corrosion, it is possible to determine based on the value of F2 whether the rolling bearing is a bearing that will not develop ridge marks within the required usage durability time T, or a bearing that is likely to develop ridge marks within the required usage durability time T.

[0034] [Configuration 10] the rolling bearing is a rolling bearing that rotatably supports a rotor of an electric motor controlled by an inverter that operates at a constant switching frequency, 10. The method for evaluating electrolytic corrosion resistance of a rolling bearing according to configuration 9, wherein n is a value obtained by multiplying the switching frequency of the inverter by three.

[0035] By adopting this configuration, it is possible to easily determine the number of discharges per unit time (n) expected when the rolling bearing is in use, without testing. In other words, when an inverter drives an electric motor using pulse width modulation control, which changes the duty ratio at a constant switching frequency, discharges generally occur in the rolling bearing that supports the rotor of the electric motor three times the inverter's switching frequency. Therefore, the number of discharges per unit time (n) expected when the rolling bearing is in use can be calculated by multiplying the inverter's switching frequency by three.

[0036] [Configuration 11] a second test is conducted in which the inner ring and the outer ring are rotated relative to each other for a certain period of time while a voltage expected when the rolling bearing is used is applied to the rolling bearing; Observing the inner ring rolling surface or the outer ring rolling surface after the second test to determine the number of discharge marks formed on the inner ring rolling surface or the outer ring rolling surface; A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to configuration 9, wherein the number of discharge craters per unit time obtained by dividing the number of discharge craters by the fixed time is used as n.

[0037] By adopting this configuration, an actual test is conducted and the number of discharge marks is determined based on the test results, making it possible to determine with high reliability the number of discharges n per unit time that is expected when the rolling bearing is in use.

[0038] [Configuration 12] the rolling elements are balls, the inner ring rolling surface is an inner surface of an inner ring raceway groove having an arc-shaped cross section formed on the outer periphery of the inner ring, the outer ring rolling surface is an inner surface of an outer ring raceway groove having an arc-shaped cross section formed on an inner circumference of the outer ring, observing a portion of the inner ring rolling surface or the outer ring rolling surface after the second test, and calculating the number of discharge craters per unit area by dividing the number of discharge craters found in the observed area by the area of ​​the observed area; Then, the number of discharge marks formed on the inner ring rolling surface or the outer ring rolling surface is determined by calculating (the number of discharge marks per unit area) x (the major axis of the contact ellipse where the rolling element contacts the inner ring rolling surface or the outer ring rolling surface x correction coefficient) x π x (groove bottom diameter of the inner ring raceway groove or the outer ring rolling surface).

[0039] By adopting this configuration, it is not necessary to count the number of discharge marks over the entire circumference of the inner ring rolling surface or outer ring rolling surface to determine the number of discharge marks per unit area, but it is sufficient to count the number of discharge marks on a portion of the inner ring rolling surface or outer ring rolling surface, making it possible to determine the number of discharge marks in a relatively short time.

[0040] [Configuration 13] 13. The method for evaluating electrolytic corrosion resistance of a rolling bearing according to claim 12, wherein the correction coefficient is set to a value of 1.2 or more and 1.6 or less.

[0041] By adopting this configuration, it is possible to accurately determine the number of discharge craters formed on the inner ring rolling surface or the outer ring rolling surface. In other words, the inventors' tests have shown that when a large number of discharge craters actually formed on the inner ring rolling surface or the outer ring rolling surface are observed, the discharge craters do not occur only within the axial width corresponding to the contact ellipse between the rolling element and the inner ring rolling surface or the outer ring rolling surface, but occur uniformly over an axial range wider than the axial width corresponding to the contact ellipse between the rolling element and the inner ring rolling surface or the outer ring rolling surface. Here, since the axial width of the range in which actual discharge craters occur is 1.2 to 1.6 times the major axis of the contact ellipse, setting the correction coefficient to a value between 1.2 and 1.6 makes it possible to accurately determine the number of discharge craters formed on the inner ring rolling surface or the outer ring rolling surface. [Effects of the Invention]

[0042] The method for evaluating the electrolytic corrosion resistance of a rolling bearing of this invention makes it possible to easily and appropriately evaluate, for a variety of rolling bearings with different specifications, whether or not ridge marks due to electrolytic corrosion are likely to occur on the inner ring rolling surface or outer ring rolling surface when the rolling bearing is used as a bearing supporting the rotor of an electric motor. This eliminates the need for over-specified designs for preventing electrolytic corrosion that have traditionally relied on empirical intuition, and makes it possible to provide rolling bearings with necessary and sufficient electrolytic corrosion resistance at low cost. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a rolling bearing for which electrolytic corrosion resistance is evaluated by an electrolytic corrosion resistance evaluation method according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a schematic diagram of an example of a test device for evaluating the electrolytic corrosion resistance of the rolling bearing of FIG. 1. [Figure 3]3(a) is a diagram showing an example of the change in voltage over time (voltage waveform) measured by the voltage measurement unit when a single discharge is generated inside a rolling bearing using the test device shown in FIG. 2, and FIG. 3(b) is a diagram showing an example of the change in current over time (current waveform) measured by the current measurement unit when a single discharge is generated inside a rolling bearing using the test device shown in FIG. 2. [Figure 4] Schematic diagram of a standard bearing [Figure 5] An example of the equivalent circuit of the standard bearing in Figure 4. [Figure 6] A schematic diagram of a bearing with an insulating coating to prevent electrolytic corrosion [Figure 7] FIG. 7 is a diagram showing an example of an equivalent circuit of the bearing of FIG. [Figure 8] A schematic diagram showing a bearing equipped with an earthing member as a measure to prevent electrolytic corrosion. [Figure 9] FIG. 9 is a diagram showing an example of an equivalent circuit of the bearing of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0044] [Structure of rolling bearings] An example of a rolling bearing 1 whose galvanic corrosion resistance performance is evaluated using the galvanic corrosion resistance evaluation method according to an embodiment of the present invention is shown in Figure 1. This rolling bearing 1 is a rolling bearing that rotatably supports a rotor 2 of an electric motor that is driven by an inverter (not shown) that operates at a constant switching frequency, and more specifically, it is a bearing that rotatably supports a rotor 2 of an electric motor for industrial machinery (not shown), or a bearing that rotatably supports a rotor 2 of an electric motor for driving an electric vehicle (EV, HEV, etc.) (not shown).

[0045] The rolling bearing 1 has an inner ring 3, an outer ring 4 arranged coaxially radially outward of the inner ring 3, a plurality of rolling elements 6 spaced circumferentially in an annular bearing space 5 formed between the inner ring 3 and the outer ring 4, a retainer 7 that maintains the circumferential spacing of the plurality of rolling elements 6, and a pair of seals 8 that close the end openings on both axial sides of the bearing space 5.

[0046] Here, the axial direction is the direction parallel to the central axis of the inner ring 3 (the central axis of the bearing), the radial direction is the direction perpendicular to the central axis of the inner ring 3, and the circumferential direction is the direction along the circumference centered on the central axis of the inner ring 3.

[0047] The rolling elements 6 are in rolling contact with an inner ring rolling surface 9 formed on the outer periphery of the inner ring 3 and an outer ring rolling surface 10 formed on the inner periphery of the outer ring 4. In this embodiment, the rolling elements 6 are balls, the inner ring rolling surface 9 is the inner surface of an inner ring raceway groove 11 that has an arc-shaped cross section and extends circumferentially around the outer periphery of the inner ring 3, and the outer ring rolling surface 10 is the inner surface of an outer ring raceway groove 12 that has an arc-shaped cross section and extends circumferentially around the inner periphery of the outer ring 4. The inner ring raceway groove 11 is formed so as to have a concave arc shape that is symmetrical about the axial center of the inner ring 3, and the outer ring raceway groove 12 is also formed so as to have a concave arc shape that is symmetrical about the axial center of the outer ring 4. This rolling bearing 1 is a deep groove ball bearing.

[0048] A lubricant (not shown) is sealed in the bearing space 5 between the inner ring 3 and the outer ring 4. In this example, the lubricant is grease. Grease is a lubricant containing a base oil such as synthetic oil (synthetic hydrocarbon) or mineral oil (refined from petroleum) and a thickener that disperses in the base oil to make it semi-solid. The lubricant lubricates the gap between the inner ring rolling surface 9 and the rolling elements 6, and the gap between the outer ring rolling surface 10 and the rolling elements 6. The seal 8 is formed by vulcanization bonding rubber 14 to a circular disk-shaped core metal 13.

[0049] The inner ring 3, outer ring 4, and rolling elements 6 are all made of metal (for example, steel material such as bearing steel). An insulating coating 15 is provided on the outer periphery of the outer ring 4 as a measure to prevent electrolytic corrosion. The insulating coating 15 is made of an insulating resin (a resin with a withstand voltage of 0.01 kV / μm or more, such as a resin based on epoxy resin or polyamideimide resin). The thickness of the insulating coating 15 is set to, for example, about 20 to 100 μm. The thickness of this insulating coating 15 is thinner than the thickness of the molded resin layer formed by insert molding on the outer ring 4 of a typical electrolytic corrosion prevention bearing.

[0050] [Test equipment configuration] 2 shows an example of a test device for evaluating the electrolytic corrosion resistance of the above-mentioned rolling bearing 1. This test device has a rotating shaft 20, a motor 21 that rotates and drives the rotating shaft 20, a rolling bearing 1 and a second rolling bearing 22 that rotatably support the rotating shaft 20, an inner ring-side terminal 23 electrically connected to the inner ring 3 of the rolling bearing 1 via the rotating shaft 20, an outer ring-side terminal 24 electrically connected to the outer ring 4 of the rolling bearing 1, a power supply unit 25 that applies a voltage between the inner ring-side terminal 23 and the outer ring-side terminal 24, a voltage measurement unit 26 that measures the voltage between the inner ring-side terminal 23 and the outer ring-side terminal 24, and a current measurement unit 27 that measures the current flowing between the inner ring-side terminal 23 and the outer ring-side terminal 24.

[0051] The outer periphery of the end portion on one axial side (the right side in the drawing) of the rotating shaft 20 is supported by a rolling bearing 1, and the outer periphery of the end portion on the other axial side (the left side in the drawing) of the rotating shaft 20 is supported by a second rolling bearing 22. A weight 28 that applies a radial load to the rolling bearing 1 is provided in the central portion of the rotating shaft 20 (the portion between the rolling bearing 1 and the second rolling bearing 22). The rotating shaft 20 is made of metal (for example, steel).

[0052] The motor 21 is connected to the rotating shaft 20 via an insulating coupling 29. The insulating coupling 29 is a shaft joint that connects the rotor shaft 30 of the motor 21 and the rotating shaft 20 so that they rotate together while being electrically insulated from each other.

[0053] The second rolling bearing 22 is an insulated bearing that rotatably supports the rotating shaft 20 while electrically insulated from the outside. The second rolling bearing 22 has a second inner ring 31 that fits onto the outer periphery of the end of the rotating shaft 20, a second outer ring 32 that is arranged radially outward of the second inner ring 31, and a plurality of second rolling elements 33 that are incorporated between the second inner ring 31 and the second outer ring 32. The second rolling elements 33 are made of ceramic. The second rolling elements 33 are, for example, ceramic balls.

[0054] The rolling bearing 1 is accommodated in a housing 34. The housing 34 incorporates an elastic member 35 that applies an axial load to the rolling bearing 1, and an insulating sleeve 36 that provides electrical insulation between the rolling bearing 1 and the housing 34.

[0055] The insulating sleeve 36 is fitted onto the inner periphery of the housing 34 so as to be movable in the axial direction. The insulating sleeve 36 is, for example, a cylindrical body made of an insulating resin material. The elastic member 35 is incorporated in an axially compressed state between the axially opposing surfaces of the insulating sleeve 36 and the housing 34, and presses the outer ring 4 of the rolling bearing 1 in the axial direction via the insulating sleeve 36. A metal spring (for example, a leaf spring) can be used as the elastic member 35.

[0056] The outer ring 4 of the rolling bearing 1 is fitted onto the inner periphery of an insulating sleeve 36. An outer ring side terminal 24 is attached to the insulating sleeve 36 so that the outer ring side terminal 24 comes into contact with the outer periphery of the outer ring 4 of the rolling bearing 1. The inner ring 3 of the rolling bearing 1 is fitted onto the outer periphery of the end of the rotating shaft 20. An inner ring side terminal 23 is attached to the shaft end of the rotating shaft 20.

[0057] The power supply unit 25 is provided midway along the conductive path 37 that electrically connects the outer ring side terminal 24 and the inner ring side terminal 23, and is capable of applying a voltage between the inner periphery of the inner ring 3 and the outer periphery of the outer ring 4 of the rolling bearing 1 via this conductive path 37. The power supply unit 25 uses a power supply device that can selectively output DC voltage or AC voltage and can arbitrarily change the magnitude of that voltage.

[0058] A rotary connector 38 is provided at the end of the conductive path 37 on the inner ring side terminal 23 side, which maintains electrical continuity between the inner ring side terminal 23 and the power supply unit 25 while allowing rotation of the inner ring side terminal 23. A slip ring incorporating a metal ring (not shown) that rotates at a fixed position and an electrically conductive brush (not shown) that slides against the metal ring can be used as the rotary connector 38. The rotary connector 38 is held by an insulating holder 39 so that it is electrically insulated from the outside.

[0059] Voltage measurement unit 26 is provided midway along voltage detection conductive path 40, which connects the portion of conductive path 37 between rotary connector 38 and power supply unit 25 and the portion of conductive path 37 between outer ring side terminal 24 and power supply unit 25. Voltage measurement unit 26 measures the potential difference between inner ring side terminal 23 and outer ring side terminal 24 (i.e., the voltage between inner ring 3 and outer ring 4 of rolling bearing 1) via voltage detection conductive path 40, and records waveform data that shows the change in the measured value over time. Voltage measurement unit 26 is, for example, an oscilloscope.

[0060] The current measuring unit 27 is provided in a portion of the conductive path 37 between the outer ring side terminal 24 and the power supply unit 25, and measures the magnitude of the current flowing in the conductive path 37 (i.e., the magnitude of the current flowing between the inner ring 3 and the outer ring 4 of the rolling bearing 1), and records waveform data that shows the change in the measured value over time. The current measuring unit 27 is, for example, an oscilloscope.

[0061] [Test method] Next, an example of a test method for evaluating the electrolytic corrosion resistance of the rolling bearing 1 using the test device shown in FIG. 2 will be described.

[0062] First, motor 21 is operated to rotate rotating shaft 20, causing inner ring 3 and outer ring 4 of rolling bearing 1 to rotate relative to each other at a constant rotational speed. Next, power supply unit 25 applies a DC voltage between inner ring 3 and outer ring 4, and the magnitude of this voltage is gradually increased over time. When the magnitude of the voltage applied from power supply unit 25 exceeds the breakdown voltage of the lubricant inside rolling bearing 1, a single discharge occurs between inner ring rolling surface 9 or outer ring rolling surface 10 of rolling bearing 1 and rolling element 6, as shown in FIG. 1. When this single discharge occurs, voltage waveform data (see FIG. 3(a)) and current waveform data (see FIG. 3(b)) are recorded in voltage measurement unit 26 and current measurement unit 27, as shown in FIG. 2.

[0063] Here, whether or not a single discharge has occurred is determined as follows: That is, when the voltage Vb in the voltage waveform data shown in Fig. 3(a) decreases by an amount equal to or greater than a predetermined decrease (this decrease is preset to 0.1 V or greater), and when the current ib in the current waveform data shown in Fig. 3(b) increases to an amount equal to or greater than a predetermined threshold (this threshold is preset to 20 mA or greater), it is determined that a single discharge has occurred.

[0064] [Evaluation method for electrolytic corrosion resistance based on F1 value] Thereafter, the value of F1 in the following equation is calculated based on the waveform data of the voltage when a single discharge occurs (see FIG. 3(a)) and the waveform data of the current when a single discharge occurs (see FIG. 3(b)).

number

[0065] In the above formula, the value of k is set by varying it depending on the viscosity of the lubricant, so that the higher the viscosity of the lubricant, the larger the value of k. It is also set by varying it depending on the volume resistivity of the lubricant, so that the higher the volume resistivity of the lubricant, the larger the value of k. In this case, the value of k is set by varying it within a range of 0.2 to 0.4 depending on the viscosity and volume resistivity of the lubricant. That is, when a dielectric breakdown of the lubricant occurs between the inner ring rolling surface 9 or the outer ring rolling surface 10 and the rolling elements 6 shown in FIG. 1 and a discharge occurs, the proportion of the energy imparted to the inner ring rolling surface 9, the outer ring rolling surface 10, and the surfaces of the rolling elements 6 due to the discharge (energy equivalent to the thermal energy used to form the discharge craters, if any) of the electrical energy passing through the bearing is 20 to 40%. Therefore, the value of k is set by varying it within a range of 0.2 to 0.4.

[0066] In the above equation, the start point ts of the single discharge time is the point at which the voltage Vb in the waveform data of the voltage when a single discharge occurs (see FIG. 3(a)) starts to decrease or the point immediately before (for example, the point at which the voltage Vb starts to decrease). The end point te of the single discharge time is the point at which the current ib increases due to the occurrence of a single discharge, then decreases and converges to zero or the point immediately before.

[0067] It is then determined whether the value of F1 calculated using the above formula exceeds a predetermined reference value. This reference value is the boundary between a case where the single discharge test described above results in the formation of a discharge mark (a tiny crater-like depression) on the inner ring raceway surface 9 or the outer ring raceway surface 10, and a case where no discharge mark is formed on either the inner ring raceway surface 9 or the outer ring raceway surface 10, and only discoloration occurs at the location of the discharge on the inner ring raceway surface 9 or the outer ring raceway surface 10.

[0068] If the value of F1 exceeds a predetermined reference value, the rolling bearing 1 is determined to be a bearing in which, when used as a bearing supporting the rotor 2 of an electric motor, ridge marks (striped irregularities) due to electrolytic corrosion may occur on the inner ring rolling surface 9 or the outer ring rolling surface 10 shown in Figure 1; on the other hand, if the value of F1 does not exceed the predetermined reference value, the bearing is determined to be a bearing in which, when used as a bearing supporting the rotor 2 of an electric motor, ridge marks will not occur on the inner ring rolling surface 9 or the outer ring rolling surface 10 shown in Figure 1.

[0069] [Evaluation method for electrolytic corrosion resistance based on F2 value] When the value of F1 exceeds the reference value, i.e., when it is determined that the bearing is susceptible to ridge marks, the value of F2, which will be described later, is used to determine whether the rolling bearing 1 is a bearing that will not produce ridge marks within the required usage durability time T, or a bearing that is likely to produce ridge marks within the required usage durability time T.

[0070] Specifically, the value of F2 obtained by multiplying the value of F1 calculated by the above formula by the number of discharges n per unit time expected when the rolling bearing 1 is in use and the required usage durability time T of the rolling bearing 1 is determined to be greater than a predetermined second reference value.

[0071] That is, first, the value of F2 in the following equation is calculated, and it is determined whether or not the value of F2 exceeds the second reference value. F2 = (value of F1) x (number of discharges per unit time n) x (required usage endurance time T)

[0072] In the above formula, the value of the number of discharges per unit time, n, can be three times the inverter switching frequency. In other words, when an inverter drives an electric motor using pulse width modulation control, which changes the duty ratio at a constant switching frequency, discharges generally occur in the rolling bearing 1 that supports the rotor 2 of the electric motor three times the inverter switching frequency. Therefore, the value of three times the inverter switching frequency can be used as the number of discharges per unit time, n, that is expected when the rolling bearing 1 is in use.

[0073] In the above formula, the value of the number of discharges per unit time n can also be set based on the results of a second test, which will be described later.

[0074] That is, a second test is conducted in which the inner ring 3 and outer ring 4 are rotated relative to each other for a fixed period of time while a voltage equivalent to that expected when the rolling bearing 1 is in use is applied to the rolling bearing 1. This second test is conducted, for example, using the testing equipment shown in Figure 2, in which a specified AC voltage (a voltage equivalent to that expected to be applied to the rolling bearing 1 when it is used as a bearing supporting the rotor 2 of an electric motor) is applied between the inner ring 3 and outer ring 4 of the rolling bearing 1 from power supply unit 25 while the inner ring 3 and outer ring 4 of the rolling bearing 1 are rotated relative to each other at a fixed rotational speed, and this state is maintained for a fixed period of time.

[0075] Thereafter, rolling bearing 1 is disassembled to enable observation of inner ring rolling surface 9 on the outer circumference of inner ring 3 and outer ring rolling surface 10 on the inner circumference of outer ring 4, as shown in Figure 1. Then, inner ring rolling surface 9 or outer ring rolling surface 10 is observed using an optical microscope or the like to determine the number of discharge marks formed on inner ring rolling surface 9 or outer ring rolling surface 10.

[0076] The number of discharge marks formed on the inner ring rolling surface 9 can be found by counting the number of discharge marks over the entire circumference of the inner ring rolling surface 9, but it is also possible to calculate the number of discharge marks per unit area by observing a portion of the inner ring rolling surface 9 and dividing the number of discharge marks found in that observation area by the area of ​​the observation area, and then find the number of discharge marks formed on the inner ring rolling surface 9 by calculating (number of discharge marks per unit area) × (major axis of the contact ellipse where the rolling element 6 contacts the inner ring rolling surface 9 × correction coefficient) × π × (groove bottom diameter of the inner ring raceway groove 11). In this way, it is not necessary to count the number of discharge marks over the entire circumference of the inner ring rolling surface 9, but it is only necessary to count the number of discharge marks over a portion of the inner ring rolling surface 9, making it possible to find the number of discharge marks in a relatively short time.

[0077] Here, the contact ellipse is the elliptical surface contact portion formed between the rolling element 6 and the inner ring rolling surface 9 when a load is applied between them, and its dimensions are determined from an equation based on Hertz's theory, based on the Young's modulus and Poisson's ratio of the inner ring 3, the Young's modulus and Poisson's ratio of the rolling element 6, the curvature of the inner ring rolling surface 9, the surface curvature of the rolling element 6, and the magnitude of the load acting between the rolling element 6 and the inner ring rolling surface 9.

[0078] Furthermore, the correction coefficient can be set to a value between 1.2 and 1.6 (for example, 1.5). In other words, when a large number of discharge craters formed on the inner ring rolling surface 9 are actually observed, the discharge craters do not occur only within the axial width corresponding to the contact ellipse between the rolling element 6 and the inner ring rolling surface 9, but occur uniformly over an axial range wider than the axial width corresponding to the contact ellipse between the rolling element 6 and the inner ring rolling surface 9. Here, since the axial width of the range in which actual discharge craters occur is 1.2 to 1.6 times the major axis of the contact ellipse, setting the correction coefficient to a value between 1.2 and 1.6 (for example, 1.5) makes it possible to accurately determine the number of discharge craters formed on the inner ring rolling surface 9.

[0079] Similarly, the number of discharge marks formed on the outer ring rolling surface 10 can be determined by observing a portion of the outer ring rolling surface 10, dividing the number of discharge marks found in that observation area by the area of ​​the observation area to calculate the number of discharge marks per unit area, and then calculating (number of discharge marks per unit area) × (major axis of contact ellipse where the rolling elements 6 contact the outer ring rolling surface 10 × correction coefficient) × π × (groove bottom diameter of outer ring raceway groove 12), to determine the number of discharge marks formed on the outer ring rolling surface 10. In this way, it is not necessary to count the number of discharge marks over the entire circumference of the outer ring rolling surface 10, but it is only necessary to count the number of discharge marks in a portion of the outer ring rolling surface 10, making it possible to determine the number of discharge marks in a relatively short time.

[0080] The correction coefficient can be set to a value between 1.2 and 1.6 (for example, 1.5). In other words, when observing the numerous discharge craters that are actually formed on the outer ring raceway surface 10, the discharge craters do not occur only within the axial width corresponding to the contact ellipse between the rolling element 6 and the outer ring raceway surface 10, but occur uniformly over an axial range that is wider than the axial width corresponding to the contact ellipse between the rolling element 6 and the outer ring raceway surface 10. Here, since the axial width of the range in which actual discharge craters occur is 1.2 to 1.6 times the major axis of the contact ellipse, setting the correction coefficient to a value between 1.2 and 1.6 (for example, 1.5) makes it possible to accurately determine the number of discharge craters formed on the outer ring raceway surface 10.

[0081] After determining the number of discharge marks formed on the inner ring rolling surface 9 or the outer ring rolling surface 10 as described above, the number of discharge marks can be divided by the time that voltage was applied to the rolling bearing 1 in the second test to obtain the number of discharge marks per unit time n.

[0082] The value of F2 obtained by the calculation described above corresponds to the total energy imparted to the inner ring rolling surface 9, the outer ring rolling surface 10, and the surfaces of the rolling elements 6 when the rolling bearing 1 is used for the usage durability time T.

[0083] If the value of F2 exceeds the second standard value, the rolling bearing 1 is determined to be a bearing that may develop ridge marks on the inner ring raceway surface 9 or the outer ring raceway surface 10 within the usage durability time T when used as a bearing supporting the rotor 2 of an electric motor, and on the other hand, if the value of F2 does not exceed the second standard value, the bearing is determined to be a bearing that will not develop ridge marks on the inner ring raceway surface 9 or the outer ring raceway surface 10 within the usage durability time T when used as a bearing supporting the rotor 2 of an electric motor.

[0084] By employing the method for evaluating the electrolytic corrosion resistance of a rolling bearing 1 according to this embodiment, it is possible to easily and appropriately evaluate various rolling bearings 1 with different specifications to determine whether or not ridge marks due to electrolytic corrosion are likely to occur on the inner ring rolling surface 9 or the outer ring rolling surface 10 when the rolling bearing 1 is used as a bearing supporting the rotor 2 of an electric motor. This eliminates the need to implement electrolytic corrosion prevention measures that rely on overly sophisticated designs that have hitherto been based on empirical intuition, and makes it possible to provide a rolling bearing 1 that has sufficient electrolytic corrosion resistance at low cost.

[0085] Furthermore, in the method for evaluating the electrolytic corrosion resistance of rolling bearing 1 of this embodiment, the value of k in the formula for calculating F1 is set so that the higher the viscosity of the lubricant, the larger the value of k, making it possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion. In other words, the higher the viscosity of the lubricant inside the bearing, the more limited the diffusion of energy due to the vaporization and expansion of the lubricant when a discharge occurs due to insulation breakdown of the lubricant. Therefore, when a discharge occurs, a higher proportion of energy is imparted to the surfaces of inner ring rolling surface 9, outer ring rolling surface 10, and rolling elements 6 shown in FIG. 1 , making it more likely that discharge marks will occur on inner ring rolling surface 9 and outer ring rolling surface 10. Therefore, by setting the value of k so that the higher the viscosity of the lubricant, it is possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion.

[0086] Furthermore, in the method for evaluating the electrolytic corrosion resistance of rolling bearing 1 of this embodiment, the value of k in the formula for calculating F1 is set so that the higher the volume resistivity of the lubricant that lubricates the inside of the bearing, the larger the value of k, making it possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion. In other words, the higher the volume resistivity of the lubricant, the higher the proportion of energy imparted to the surfaces of inner ring rolling surface 9, outer ring rolling surface 10, and rolling elements 6 shown in FIG. 1 when a discharge occurs due to dielectric breakdown of the lubricant, making it more likely that discharge marks will occur on inner ring rolling surface 9 and outer ring rolling surface 10. Therefore, by setting the value of k so that the higher the volume resistivity of the lubricant, it is possible to accurately determine whether or not a bearing is susceptible to ridge marks due to electrolytic corrosion.

[0087] Furthermore, when the method for evaluating the electrolytic corrosion resistance of rolling bearing 1 in this embodiment has determined that the bearing is one in which ridge marks due to electrolytic corrosion are likely to occur based on the value of F1 described above, it is possible to determine, based on the value of F2, whether the rolling bearing 1 is a bearing that will not produce ridge marks within the required usage durability time T, or a bearing that is likely to produce ridge marks within the required usage durability time T.

[0088] In the above embodiment, the test device shown in FIG. 2 was used to determine the value of F1, but the value of F1 may also be determined for an electric motor in operation by connecting a conductive path 37 having a power supply unit 25, a voltage measurement unit 26, and a current measurement unit 27 shown in FIG. 2 to the outer ring 4 and the inner ring 3 of the rolling bearing 1 that supports the rotor 2 of the electric motor and conducting a test similar to that described above.

[0089] [Evaluation method for electrolytic corrosion resistance based on F value] F1 in the above embodiment corresponds to a lower concept of the value of F calculated by the following formula. F=f(α,β,γ,δ)

[0090] In the above formula for calculating F, α is a mechanical parameter of the inner ring 3, outer ring 4, and rolling elements 6, β is a parameter of the lubricant that lubricates the inside of the bearing, γ is a parameter related to measures to prevent electrolytic corrosion, and δ is a parameter related to the conditions of use of the rolling bearing 1. Here, F is a function with α, β, γ, and δ as parameters.

[0091] The mechanical parameter α is a value calculated based on the material and dimensions of the inner ring 3 and outer ring 4, the surface roughness of the inner ring rolling surface 9 and outer ring rolling surface 10, and the shape, number, and dimensions of the rolling elements 6. The lubricant parameter β is a value calculated based on the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant inside the bearing. The parameter γ related to electrolytic corrosion prevention measures is set to γ ​​= 1 for standard bearings with no electrolytic corrosion prevention measures. For hybrid bearings with ceramic rolling elements 6, γ = 0 because there is no possibility of electrolytic corrosion. For electrolytic corrosion prevention bearings in which the outer ring 4 or inner ring 3 is coated with a resin insulating film, γ is set in the range 0 < γ < 1. The parameter δ related to the operating conditions is a value calculated based on the frequency of the AC voltage applied to the rolling bearing 1 during use, the rotational speed (rpm) of the rolling bearing 1 during use, and the magnitude of the load applied to the rolling bearing 1 during use.

[0092] If the value of F obtained by the above calculation formula satisfies F≦10, then the rolling bearing 1 can be determined to be a bearing in which ridge marks due to electrolytic corrosion will not occur on the inner ring rolling surface 9 or the outer ring rolling surface 10 shown in Figure 1 when used as a bearing supporting the rotor 2 of an electric motor; on the other hand, if F>10, then the rolling bearing 1 can be determined to be a bearing in which ridge marks may occur on the inner ring rolling surface 9 or the outer ring rolling surface 10 shown in Figure 1 when used as a bearing supporting the rotor 2 of an electric motor.

[0093] It is also possible to add a parameter for the usage durability time T required of the rolling bearing 1 to the formula for calculating the value of F. In this case, the formula for calculating F becomes as follows: Note that F2 in the above-described embodiment corresponds to a subordinate concept of the value of F calculated by the following formula. F=f(α,β,γ,δ,T)

[0094] If the value of F obtained by this calculation formula satisfies F≦10, then the rolling bearing 1 is determined to be a bearing in which ridge marks will not occur on the inner ring raceway surface 9 or the outer ring raceway surface 10 within the usage durability time T when used as a bearing supporting the rotor 2 of an electric motor; on the other hand, if F>10, then the rolling bearing 1 can be determined to be a bearing in which ridge marks may occur on the inner ring raceway surface 9 or the outer ring raceway surface 10 within the usage durability time T when used as a bearing supporting the rotor 2 of an electric motor.

[0095] The magnitude of the voltage between the inner periphery of the inner ring 3 and the outer periphery of the outer ring 4 when dielectric breakdown of the lubricant occurs between the inner ring rolling surface 9 or the outer ring rolling surface 10 and the rolling element 6 shown in Figure 1, and the magnitude of the current flowing between the inner ring 3 and the outer ring 4 at that time, can be determined by creating an equivalent circuit in which each component of the rolling bearing 1 and each surrounding component is replaced with an electric circuit element, and simulating the operation of that equivalent circuit on a computer, as will be described below.

[0096] <Standard bearing simulation> A standard bearing (a rolling bearing with no measures to prevent electrolytic corrosion) is shown schematically in Figure 4. In this standard bearing, an oil film 16 made of lubricant that lubricates the inside of the bearing is formed between the inner ring rolling surface 9 and the rolling elements 6, and an oil film 17 made of lubricant that lubricates the inside of the bearing is also formed between the outer ring rolling surface 10 and the rolling elements 6.

[0097] The oil film 16 between the inner ring rolling surface 9 and the rolling elements 6 has an oil film region 16a inside the contact ellipse between the rolling elements 6 and the inner ring rolling surface 9, and an oil film region 16b inside an enlarged ellipse (excluding the inside of the contact ellipse) obtained by multiplying the major axis and minor axis of the contact ellipse between the rolling elements 6 and the inner ring rolling surface 9 by a predetermined coefficient (this coefficient is set to a value between 1.2 and 1.6, for example, 1.5 times). The size of the contact ellipse can be calculated using Hertz's theory. When a dielectric breakdown of the lubricant occurs between the inner ring rolling surface 9 and the rolling elements 6 and a discharge occurs, the discharge occurs in either the oil film region 16a or the oil film region 16b.

[0098] Similarly, the oil film 17 between the outer ring rolling surface 10 and the rolling elements 6 has an oil film region 17a inside the contact ellipse between the rolling elements 6 and the outer ring rolling surface 10, and an oil film region 17b inside an enlarged ellipse (excluding the inside of the contact ellipse) obtained by multiplying the major axis and minor axis of the contact ellipse between the rolling elements 6 and the outer ring rolling surface 10 by a predetermined coefficient (this coefficient is also set to a value between 1.2 and 1.6, for example 1.5). When a dielectric breakdown of the lubricant occurs between the outer ring rolling surface 10 and the rolling elements 6 and a discharge occurs, the discharge occurs in either the oil film region 17a or the oil film region 17b.

[0099] A rotor 2 of an electric motor is fitted onto the inner periphery of the inner ring 3, and a housing 18 of the electric motor is fitted onto the outer periphery of the outer ring 4.

[0100] FIG. 5 shows an example of an equivalent circuit in which the components of the standard bearing shown in FIG. 4 and the components around it are replaced with electrical circuit elements.

[0101] R1 and C1 shown in FIG. 5 correspond to the resistance component (component equivalent to electrical resistance) and capacitance component (component equivalent to capacitor) of the oil film region 16a shown in FIG. 4, respectively. As shown in FIG. 5, the resistance component R1 and capacitance component C1 are connected in parallel. Also, S1 and Ra1 shown in FIG. 5 correspond to a switch that becomes conductive when a voltage equal to or greater than the breakdown voltage is applied to the oil film region 16a shown in FIG. 4, and the resistance component at the time of breakdown of the oil film region 16a, respectively. As shown in FIG. 5, the switch S1 and resistance component Ra1 are connected in series. The series connection portion of the switch S1 and resistance component Ra1 is connected in parallel to the parallel connection portion of the resistance component R1 and capacitance component C1.

[0102] Similarly, R2 and C2 shown in FIG. 5 correspond to the resistance component and capacitance component of the oil film region 16b shown in FIG. 4, respectively. As shown in FIG. 5, the resistance component R2 and capacitance component C2 are connected in parallel. Furthermore, S2 and Ra2 shown in FIG. 5 correspond to a switch that becomes conductive when a voltage equal to or greater than the breakdown voltage is applied to the oil film region 16b shown in FIG. 4, and the resistance component at the time of breakdown of the oil film region 16b, respectively. As shown in FIG. 5, the switch S2 and resistance component Ra2 are connected in series. The series connection portion of the switch S2 and resistance component Ra2 is connected in parallel to the parallel connection portion of the resistance component R2 and capacitance component C2.

[0103] Furthermore, R3 and C3 shown in FIG. 5 correspond to the resistance component and capacitance component of the oil film region 17a shown in FIG. 4, respectively. As shown in FIG. 5, the resistance component R3 and capacitance component C3 are connected in parallel. Furthermore, S3 and Ra3 shown in FIG. 5 correspond to a switch that becomes conductive when a voltage equal to or greater than the breakdown voltage is applied to the oil film region 17a shown in FIG. 4, and the resistance component at the time of breakdown of the oil film region 17a, respectively. As shown in FIG. 5, the switch S3 and resistance component Ra3 are connected in series. The series connection portion of the switch S3 and resistance component Ra3 is connected in parallel to the parallel connection portion of the resistance component R3 and capacitance component C3.

[0104] Furthermore, R4 and C4 shown in FIG. 5 correspond to the resistance component and capacitance component of the oil film region 17b shown in FIG. 4, respectively. As shown in FIG. 5, the resistance component R4 and capacitance component C4 are connected in parallel. Furthermore, S4 and Ra4 shown in FIG. 5 correspond to a switch that becomes conductive when a voltage equal to or greater than the breakdown voltage is applied to the oil film region 17b shown in FIG. 4, and the resistance component at the time of breakdown of the oil film region 17b, respectively. As shown in FIG. 5, the switch S4 and resistance component Ra4 are connected in series. The series connection portion of the switch S4 and resistance component Ra4 is connected in parallel to the parallel connection portion of the resistance component R4 and capacitance component C4.

[0105] Furthermore, R5, R6, and R7 shown in Figure 5 correspond to the resistance components of the inner ring 3, outer ring 4, and rolling element 6 shown in Figure 4, respectively; R8 and L8 shown in Figure 5 correspond to the resistance components and inductive components (components corresponding to the induction coil) of the housing 18 and the like shown in Figure 4, respectively; R9 and L9 shown in Figure 5 correspond to the resistance components and inductive components of the rotor 2 and the like shown in Figure 4, respectively; and V shown in Figure 5 corresponds to the AC voltage that is expected to be applied to the rolling bearing that supports the rotor 2 of the electric motor when the electric motor is driven by an inverter.

[0106] 5, the equivalent circuit portion of the oil film region 16a (including the resistance component R1, the capacitance component C1, the switch S1, and the resistance component Ra1) is connected in parallel with the equivalent circuit portion of the oil film region 16b (including the resistance component R2, the capacitance component C2, the switch S2, and the resistance component Ra2). Similarly, the equivalent circuit portion of the oil film region 17a (including the resistance component R3, the capacitance component C3, the switch S3, and the resistance component Ra3) is connected in parallel with the equivalent circuit portion of the oil film region 17b (including the resistance component R4, the capacitance component C4, the switch S4, and the resistance component Ra4).

[0107] Furthermore, resistance component R9 and inductance component L9 of rotor 2, etc., resistance component R5 of inner ring 3, equivalent circuit portion of oil film region 16a and oil film region 16b (portion including resistance components R1, R2, capacitance components C1, C2, switches S1, S2, resistance components Ra1, Ra2), resistance component R7 of rolling element 6, equivalent circuit portion of oil film region 17a and oil film region 17b (portion including resistance components R3, R4, capacitance components C3, C4, switches S3, S4, resistance components Ra3, Ra4), resistance component R6 of outer ring 4, and resistance component R8 and inductance component L8 of housing 18, etc. are connected in series.

[0108] In the above-described equivalent circuit, the resistance values ​​of the resistance components R3 and R4, the capacitance values ​​of the capacitance components C3 and C4, the voltages Vsh3 and Vsh4 at which the switches S3 and S4 are conductive, and the resistance values ​​of the resistance components Ra3 and Ra4 at the time of dielectric breakdown can be calculated, for example, by the following method.

[0109] [Method 1 for finding the resistance values ​​of resistor components R3 and R4] The electrical resistance is measured under each condition using a tester or the like, and the resistance values ​​of the resistance components R3 and R4 are calculated based on the measured values.

[0110] [Method 2 for finding the resistance values ​​of resistor components R3 and R4] The value of R calculated by the following formula is the resistance value of the resistance components R3 and R4. R=Rv(T,P)×(oil film thickness) / (oil film area) where: Rv(T,P): Volume resistivity of the oil that forms the oil film T: Rolling bearing operating temperature P: Pressure applied to the oil film is.

[0111] In the above formula, the volume resistivity Rv(T, P) is a function with parameters of temperature T and pressure P. This function relates the temperature T and pressure P to the volume resistivity Rv so that the higher the operating temperature T of the rolling bearing, the higher the volume resistivity Rv of the oil, and the higher the pressure P applied to the oil film 17, the lower the volume resistivity Rv of the oil.

[0112] When calculating the resistance value of resistance component R3 using the above formula, the oil film thickness and area used are those of oil film region 17a shown in Figure 4 (i.e., the area of ​​the contact ellipse).When calculating the resistance value of resistance component R4 using the above formula, the oil film thickness and area used are those of oil film region 17b shown in Figure 4 (i.e., the area of ​​the expanded ellipse minus the area of ​​the contact ellipse).

[0113] Furthermore, when calculating the resistance value of the resistance component R3 using the above formula, the pressure P used is the surface pressure between the rolling element 6 and the outer ring rolling surface 10, which is calculated based on the load applied to the rolling bearing, and when calculating the resistance value of the resistance component R4 using the above formula, normal pressure (1 atmosphere) is used as the pressure P.

[0114] Whether the resistance values ​​of the resistance components R3 and R4 are obtained by the above-mentioned method 1 or method 2, the resistance values ​​of the resistance components R3 and R4 are usually several MΩ or more.

[0115] [Method 1 for finding the capacitance values ​​of capacitance components C3 and C4] The capacitance is measured under each condition using an impedance analyzer or the like, and the capacitance values ​​of the capacitance components C3 and C4 are calculated based on the measured values.

[0116] [Method 2 for finding the capacitance values ​​of capacitance components C3 and C4] The value of C calculated by the following formula is set as the capacitance value of the capacitance components C3 and C4. C=ε0×ε(T,P)×(oil film area) / (oil film thickness) where: ε0: Dielectric constant of vacuum (specifically, ε0 ​​= 8.854187816 × 10 -12 ) ε(T,P): relative permittivity of the oil that forms the oil film T: Rolling bearing operating temperature P: Pressure applied to the oil film is.

[0117] In the above equation, the relative permittivity ε(T,P) of the oil that forms the oil film 17 is a function with temperature T and pressure P as parameters. This function relates the temperature T and pressure P to the relative permittivity ε so that the higher the operating temperature T of the rolling bearing, the larger the relative permittivity ε becomes, and the higher the pressure P applied to the oil film 17, the lower the relative permittivity ε becomes. The relative permittivity ε(T,P) of the oil that forms the oil film 17 is a value between approximately 3.0 and 5.0.

[0118] When calculating the capacitance value of capacitance component C3 using the above formula, the oil film area and oil film thickness are respectively the area of ​​oil film region 17a (i.e., the area of ​​the contact ellipse) and oil film thickness shown in Figure 4. When calculating the capacitance value of capacitance component C4 using the above formula, the oil film area and oil film thickness are respectively the area of ​​oil film region 17b (i.e., the area of ​​the enlarged ellipse minus the area of ​​the contact ellipse) and oil film thickness shown in Figure 4.

[0119] Furthermore, when calculating the capacitance value of capacitance component C3 using the above formula, the pressure P used is the surface pressure between the rolling element 6 and the outer ring rolling surface 10, which is calculated based on the load applied to the rolling bearing, and when calculating the capacitance value of capacitance component C4 using the above formula, normal pressure (1 atmosphere) is used as the pressure P.

[0120] Whether the capacitance values ​​of the capacitance components C3 and C4 are obtained by the above method 1 or method 2, the capacitance values ​​of the capacitance components C3 and C4 are usually between several tens of pF and several hundred pF.

[0121] [Method 1 for finding the voltages Vsh3 and Vsh4] The breakdown voltage of the oil film 17 is measured under each condition using a tester or the like, and the values ​​of the voltages Vsh3 and Vsh4 at which the switches S3 and S4 are conductive are determined based on the measured values.

[0122] [Method 2 for finding the voltages Vsh3 and Vsh4] The value of Vsh obtained by the following formula is set to the values ​​of voltages Vsh3 and Vsh4 at which the switches S3 and S4 are turned on (that is, the breakdown voltages of the oil film regions 17a and 17b, respectively). Vsh = V(P,T,ε,R) × (oil film thickness) where: V(P,T,ε,R): Dielectric breakdown strength of the oil that forms the oil film P: Pressure applied to the oil film T: Rolling bearing operating temperature ε: relative permittivity of the oil that forms the oil film R: Resistance value is.

[0123] In the above formula, the dielectric breakdown strength V(P, T, ε, R) of the oil that forms the oil film 17 is a function with parameters of pressure P, temperature T, relative dielectric constant ε, and resistance R. This function relates pressure P, temperature T, relative dielectric constant ε, and resistance R so that the higher the pressure P applied to the oil film 17, the higher the dielectric breakdown strength V; the higher the operating temperature T of the rolling bearing, the lower the dielectric breakdown strength V; the higher the relative dielectric constant ε of the oil, the lower the dielectric breakdown strength V; and the higher the resistance R of the oil film 17, the higher the dielectric breakdown strength V.

[0124] When using the above formula to find the value of voltage Vsh3 at which switch S3 is turned on (i.e., the breakdown voltage of oil film region 17a), the pressure P used is the surface pressure between the rolling element 6 and the outer ring rolling surface 10, calculated based on the load applied to the rolling bearing, and when using the above formula to find the value of voltage Vsh4 at which switch S4 is turned on (i.e., the breakdown voltage of oil film region 17b), normal pressure (1 atmosphere) is used as the pressure P.

[0125] In addition, the relative dielectric constant ε in the above formula uses the value of the above-mentioned relative dielectric constant ε(T, P).

[0126] Furthermore, when using the above formula to find the value of voltage Vsh3 at which switch S3 is conductive (i.e., the breakdown voltage of oil film region 17a), the resistance R uses the resistance value of the aforementioned resistance component R3, and when using the above formula to find the value of voltage Vsh4 at which switch S4 is conductive (i.e., the breakdown voltage of oil film region 17b), the resistance R uses the resistance value of the aforementioned resistance component R4.

[0127] Whether the values ​​of voltages Vsh3 and Vsh4 are determined by the above-mentioned method 1 or method 2, voltages Vsh3 and Vsh4 usually have values ​​of several volts or more and ten and several volts or less.

[0128] [Method 1 for finding the resistance values ​​of resistance components Ra3 and Ra4] The breakdown voltage and the current value at that time are measured using an oscilloscope under each condition, and the resistance values ​​of the resistance components Ra3 and Ra4 at the time of breakdown are calculated by dividing the breakdown voltage obtained by the measurement by the current value.

[0129] [Method 2 for determining the resistance value at dielectric breakdown of resistance components Ra3 and Ra4] There is also a method of using a fixed value (a value between 0.1 Ω and 5.0 Ω, for example, 1 Ω) as the resistance value at the time of dielectric breakdown of the resistance components Ra3 and Ra4.

[0130] Using a method similar to that described above, it is also possible to determine the resistance values ​​of the resistance components R1 and R2, the capacitance values ​​of the capacitance components C1 and C2, the voltages Vsh1 and Vsh2 at which the switches S1 and S2 are conductive, and the resistance values ​​of the resistance components Ra1 and Ra2 at the time of dielectric breakdown.

[0131] <Simulation of bearings with insulating coating> Figure 6 shows a schematic diagram of a rolling bearing provided with an insulating coating as a measure to prevent electrolytic corrosion. This rolling bearing differs from the standard bearing shown in Figure 4 (a rolling bearing with no measures to prevent electrolytic corrosion) only in that an insulating coating 15 is provided on the outer ring 4, but otherwise the configuration is the same. Therefore, parts corresponding to those in the standard bearings in Figures 4 and 5 are given the same reference numerals and their explanations will be omitted.

[0132] Figure 7 shows an example of an equivalent circuit in which the components of the rolling bearing shown in Figure 6 and the components around them are replaced with electrical circuit elements. A capacitance component C10 of the insulating coating 15 is provided between a resistance component R6 of the outer ring 4 and a resistance component R8 of the housing 18, etc.

[0133] In the equivalent circuit of FIG. 7, the electrostatic capacitance value of the capacitance component C10 of the insulating coating 15 can be determined, for example, by the following method.

[0134] [Method 1 for finding the capacitance value of capacitance component C10] The capacitance is measured under each condition using an impedance analyzer or the like, and the capacitance value of the capacitance component C10 is calculated based on the measured values.

[0135] [Method 1 for finding the capacitance value of capacitance component C10] The value of C10 calculated by the following formula is set as the electrostatic capacitance value of the capacitance component C10.

number

[0136] Whether the capacitance value of the capacitance component C10 is found by the above-mentioned method 1 or method 2, the capacitance value of the capacitance component C10 is usually 1 pF or more and 10000 pF or less.

[0137] <Simulation of bearings equipped with earthing members> Figure 8 shows a schematic diagram of a rolling bearing provided with an earth member 19 as a measure to prevent electrolytic corrosion. This rolling bearing differs from the standard bearing shown in Figure 4 (a rolling bearing with no measures to prevent electrolytic corrosion) only in that it is provided with an earth member 19, but otherwise has the same configuration. Therefore, parts corresponding to those in the standard bearings in Figures 4 and 5 are given the same reference numerals and their explanations will be omitted.

[0138] The earthing member 19 is a member that provides electrical conduction between the inner ring 3 and the outer ring 4. Examples of the earthing member 19 include a conductive seal that uses conductive rubber as the rubber 14 that forms the seal 8 shown in Fig. 1, and an electrically conductive brush (a so-called earthing ring) that is attached near the rolling bearing so as to provide electrical conduction between the rotor of the electric motor and the housing 18.

[0139] Figure 9 shows an example of an equivalent circuit in which the constituent members of the rolling bearing shown in Figure 8 and the members surrounding them are replaced with electrical circuit elements. Resistance components R11, R12 and capacitance components C11, C12 of earth member 19 are connected between the inner ring 3 side and the outer ring 4 side to electrically connect them. Resistance component R12 and capacitance component C12 are connected in parallel, and resistance component R11 and capacitance component C11 are connected in series to this parallel connection.

[0140] In the equivalent circuit of FIG. 9, the resistance values ​​of the resistance components R11 and R12 of the earth member 19 and the electrostatic capacitance values ​​of the capacitance components C11 and C12 can be determined by measuring the impedance value of the earth member 19 using an impedance analyzer or the like.

[0141] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0142] 1. Rolling bearings 2 rotors 3. Inner circle 4 outer ring 6 rolling elements 9 Inner raceway 10 Outer ring raceway 11 Inner ring raceway groove 12 Outer ring raceway groove 25 Power supply section 26 Voltage measurement section 27 Current measurement section

Claims

1. A method for evaluating electrolytic corrosion resistance of a rolling bearing having an inner ring with an inner ring rolling surface formed on its outer periphery, an outer ring with an outer ring rolling surface formed on its inner periphery, a plurality of rolling elements in rolling contact with the inner ring rolling surface and the outer ring rolling surface, and a lubricant that lubricates the inside of the bearing, comprising: a power supply unit that applies a voltage to the rolling bearing and is capable of changing the magnitude of the voltage, a voltage measuring unit that measures the voltage between the inner ring and the outer ring, and a current measuring unit that measures the current flowing between the inner ring and the outer ring, a test is conducted in which a voltage is applied to the rolling bearing by the power supply unit while the inner ring and the outer ring are rotating relative to each other, and the voltage is gradually increased to generate a single discharge between the inner ring rolling surface or the outer ring rolling surface and the rolling element; Based on the test results, a determination is made as to whether or not the value of F1 obtained by the following formula exceeds a predetermined reference value, and if it exceeds the reference value, the bearing is determined to be one in which ridge marks due to electrolytic corrosion may occur on the inner ring rolling surface or the outer ring rolling surface, and if it does not exceed the reference value, the bearing is determined to be one in which such ridge marks will not occur. [Equation 1] where: k: Coefficient representing the proportion of the electrical energy of a single discharge that is imparted to the inner ring rolling surface, outer ring rolling surface, and rolling element surface ts: start point of single discharge time te: End point of single discharge time Vb: Voltage measured by the voltage measuring unit when a single discharge occurs ib: current measured by the current measuring unit when a single discharge occurs is.

2. 2. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein the value of k is set by varying it according to the viscosity of the lubricant so that the higher the viscosity of the lubricant, the larger the value of k.

3. 3. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein the value of k is changed and set in accordance with the volume resistivity of the lubricant such that the higher the volume resistivity of the lubricant, the larger the value of k.

4. 3. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein the value of k is set in the range of 0.2 to 0.

4.

5. 3. The method for evaluating electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein the time ts is the time when the voltage Vb starts to decrease when the single discharge occurs or the time immediately before that.

6. 6. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 5, wherein it is determined that the single discharge has occurred when the voltage Vb decreases by an amount equal to or greater than a predetermined decrease amount and the current ib increases to a magnitude equal to or greater than a predetermined threshold value.

7. The predetermined decrease is set to a value of 0.1 V or more, 7. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 6, wherein the predetermined threshold value is set to a value equal to or greater than 20 mA.

8. 3. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein the time te is the time when the current ib increases due to the occurrence of the single discharge and then decreases and converges to 0, or the time just before that.

9. 3. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein, when it is determined that the value of F1 exceeds the predetermined upper limit, it is further determined whether or not the value of F2 obtained by multiplying the value of F1 by the number of discharges per unit time n expected when the rolling bearing is in use and the usage durability time T required of the rolling bearing exceeds a predetermined second reference value; and if the value of F2 exceeds the second reference value, it is determined that the bearing is one in which the ridge mark may occur within the usage durability time T, and if the value of F2 does not exceed the second reference value, it is determined that the bearing is one in which the ridge mark will not occur within the usage durability time T.

10. the rolling bearing is a rolling bearing that rotatably supports a rotor of an electric motor controlled by an inverter that operates at a constant switching frequency, 10. The method for evaluating electrolytic corrosion resistance of a rolling bearing according to claim 9, wherein a value obtained by multiplying the switching frequency of the inverter by three is used as n.

11. a second test is conducted in which the inner ring and the outer ring are rotated relative to each other for a certain period of time while a voltage expected when the rolling bearing is used is applied to the rolling bearing; Observing the inner ring rolling surface or the outer ring rolling surface after the second test to determine the number of discharge marks formed on the inner ring rolling surface or the outer ring rolling surface; The method for evaluating electrolytic corrosion resistance of a rolling bearing according to claim 9, wherein the number of discharge craters per unit time obtained by dividing the number of discharge craters by the fixed time is used as n.

12. the rolling elements are balls, the inner ring rolling surface is an inner surface of an inner ring raceway groove having an arc-shaped cross section formed on the outer periphery of the inner ring, the outer ring rolling surface is an inner surface of an outer ring raceway groove having an arc-shaped cross section formed on an inner circumference of the outer ring, observing a portion of the inner ring rolling surface or the outer ring rolling surface after the second test, and calculating the number of discharge craters per unit area by dividing the number of discharge craters found in the observed area by the area of ​​the observed area; The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 11, further comprising the steps of: (the number of discharge marks per unit area) x (the major axis of the contact ellipse where the rolling element contacts the inner ring rolling surface or the outer ring rolling surface x correction coefficient) x π x (groove bottom diameter of the inner ring raceway groove or the outer ring rolling surface), thereby determining the number of discharge marks formed on the inner ring rolling surface or the outer ring rolling surface.

13. 13. The method for evaluating electrolytic corrosion resistance of a rolling bearing according to claim 12, wherein the correction coefficient is set to a value equal to or greater than 1.2 and equal to or less than 1.6.

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