Method for evaluating electrolytic corrosion resistance of rolling bearing

Abstract

The method of the present invention employs: a testing step S1 in which a prescribed voltage is applied to a rolling bearing in a state in which the inner ring and the outer ring are rotating relative to one another; an investigation step S2 in which a search is conducted, within a first rolling surface and a second rolling surface that have completed the testing step, for an abnormal surface portion generated when a single electric discharge occurs between the first rolling surface or the second rolling surface and the rolling body; and an evaluation step S4 in which, if an abnormal surface portion comprising an electric discharge mark generated with an uneven shape is found in the investigation step, it is determined that the rolling bearing may generate ridge marks due to electrolytic corrosion on the first rolling surface or the second rolling surface, and if no electric discharge mark is found in the investigation step, it is determined that the rolling bearing does not generate ridge marks.

Description

Method for evaluating the electrolytic corrosion resistance of rolling bearings

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

[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. Furthermore, electric motors for vehicle traction used in 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 the 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 supporting the rotor of an electric motor becomes large, dielectric breakdown occurs in the oil film between the inner ring and the rolling elements and in the oil film between the outer ring and the 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 to the first and second rolling surfaces with which the rolling elements roll (electrolytic corrosion). As this electrolytic corrosion progresses, striped irregularities called ridge marks form on the first and second rolling surfaces, potentially resulting in noise and vibration.

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

[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 that closes 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 for preventing 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 ８ If a high-strength grease (approximately Ωcm) is used, the performance of the grease and seal can be ensured, but the effect of preventing electrolytic corrosion of the rolling bearing is 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 this requires space for the electrically conductive brush in addition to the space for the rolling bearing, which increases costs.

[0013] Japanese Patent No. 4599769 Japanese Patent No. 4177057 Japanese Patent Laid-Open No. 2006-320129

[0014] 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.

[0015] In other words, until now, there has 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 up to now 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.

[0016] The problem to be solved by this invention is to provide a method for evaluating the electrolytic corrosion resistance of a rolling bearing, which is capable of easily and appropriately evaluating whether the rolling bearing has the electrolytic corrosion resistance required to prevent the occurrence of ridge marks under certain usage conditions.

[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, and found that when a discharge occurs between the inner ring or the outer ring and the rolling element, an abnormal surface portion occurs on the rolling surface of the inner ring or the rolling surface of the outer ring, and that the form of this abnormal surface portion comes in two forms: one in which a discharge mark (a minute, crater- or pit-shaped irregularity) is formed, and one in which no discharge mark is formed on either the rolling surface of the inner ring or the rolling surface of the outer ring, and only a discolored portion without irregularity occurs at the point of discharge on the rolling surface of the inner ring or the rolling surface of the outer ring; in the former case, discharges occur continuously during use of the rolling bearing, and discharge marks are formed one after another, resulting in the aforementioned ridge marks on the rolling surface of the inner ring or the rolling surface of the outer ring; whereas in the latter case, no ridge marks occur even if discharges occur continuously.

[0018] Based on this finding, in order to solve the above-mentioned problems, the present invention provides a method for evaluating the galvanic corrosion resistance of a rolling bearing having an inner ring including a first rolling surface, an outer ring including a second rolling surface, a plurality of rolling elements that roll between the first rolling surface and the second rolling surface, and a lubricant that lubricates the inside of the bearing, the method comprising the steps of: applying a predetermined voltage to the rolling bearing while the inner ring and the outer ring rotate relative to each other; and selecting, from the first rolling surface and the second rolling surface that have completed the testing step, a lubricant that lubricates the first rolling surface or the second rolling surface. The method for evaluating the electrolytic corrosion resistance of a rolling bearing employs Configuration 1, which includes an investigation step of searching for an abnormal surface portion that occurs when a single discharge occurs between the rolling element and the rolling bearing, and an evaluation step of determining, if the investigation step finds an abnormal surface portion consisting of an uneven discharge mark, that the rolling bearing is capable of producing a ridge mark due to electrolytic corrosion on the first rolling surface or the second rolling surface, and determining, if the discharge mark is not found in the investigation step, that the rolling bearing is not susceptible to ridge marks.

[0019] According to the above configuration 1, a short-term test is conducted under test conditions corresponding to desired usage conditions (structure of the rolling bearing, shaft, housing, etc., bearing load conditions, electrical conditions, lubricant composition, etc.), and based on the presence or absence of discharge marks due to a single discharge on the first and second rolling surfaces after the test, it is possible to determine whether or not the rolling bearing has electrolytic corrosion resistance sufficient to prevent the occurrence of ridge marks. Therefore, it is possible to easily and appropriately evaluate whether a rolling bearing has electrolytic corrosion resistance sufficient to prevent the occurrence of ridge marks under certain usage conditions.

[0020] A configuration 2 of the method for evaluating the electrolytic corrosion resistance of a rolling bearing according to the above configuration 1 can be adopted, in which the testing step applies a voltage to the rolling bearing for a period of 10 minutes or less.

[0021] If the aforementioned electrolytic corrosion resistance is insufficient under the test conditions, the longer the time for which voltage is applied to the rolling bearing in a single test process (hereinafter simply referred to as the "voltage application time"), the greater the number of single discharges that occur, making it easier for multiple discharge craters to accumulate and thus making it difficult to accurately observe the shape of the discharge craters in the investigation process. Since the aforementioned insufficiency in electrolytic corrosion resistance can be determined in the evaluation process if a single discharge crater is formed, applying voltage to the rolling bearing for more than 10 minutes in a single test process is excessive. Limiting the voltage application time to 10 minutes or less, as in configuration 2 above, makes it easier to observe the shape of the discharge crater and shortens the time required for a single test process. This makes it easier to evaluate electrolytic corrosion resistance for a variety of rolling bearings with different specifications and test conditions.

[0022] It is possible to adopt a configuration 3 of the method for evaluating the electrolytic corrosion resistance of a rolling bearing as described in the above configuration 1 or 2, which further includes a quantification step of determining an evaluation value based on the results of the investigation in the investigation step, and if the discharge mark is found in the investigation step, the quantification step determines a larger evaluation value as the diameter of the discharge mark increases.

[0023] When a single discharge occurs between the first or second rolling surface and the rolling element, the high-current density arc column reaches a temperature of several thousand degrees Kelvin, melting and evaporating the materials of the rolling surface and the rolling element. At this time, the lubricant between the rolling surface and the rolling element vaporizes and explodes, generating a large explosion pressure between the rolling surface and the rolling element. The explosion pressure causes the molten material to scatter, forming a discharge crater on the rolling surface. From the mechanism by which this discharge crater occurs, there is a correlation between the magnitude of the electrical energy of the single discharge that generates the arc column and the diameter of the discharge crater formed by the single discharge. The larger the diameter of the discharge crater that occurs, the more insufficient the electrolytic corrosion resistance of the rolling bearing under those test conditions is, and the more likely it is that a ridge mark will form on the rolling element. Therefore, by quantifying the results of the investigation process as in configuration 3 above, and obtaining an evaluation value that reflects the diameter of the discharge marks, in particular when discharge marks are present, it is possible to obtain an indication of the extent to which the electrolytic corrosion resistance is deficient, and by comparing this with evaluation values ​​obtained for rolling bearings of different specifications or evaluation values ​​obtained under different test conditions, it is possible to easily determine the relative extent to which the electrolytic corrosion resistance performance differs between the compared objects.

[0024] A fourth configuration can be adopted, which is the method for evaluating the electrolytic corrosion resistance of a rolling bearing according to the third configuration, in which the evaluation step determines the evaluation value to be a value F1 obtained by the following formula 1, where X (μm) is the diameter of the discharge crater and a is an arbitrarily determined constant: F1=X+a...Formula 1

[0025] According to the above configuration 4, it is possible to evaluate the electrolytic corrosion resistance of a rolling bearing by reflecting the diameter of the discharge crater and also reflecting any factor of consideration as the constant a.

[0026] In the evaluation step, a comparison can be made to see whether the evaluation value exceeds a predetermined reference value, and if it exceeds the reference value, the rolling bearing is judged to be one in which the ridge mark may occur, and if it does not exceed the reference value, the rolling bearing is judged to be one in which the ridge mark will not occur, as in Configuration 5, which is a method for evaluating the electrolytic corrosion resistance of a rolling bearing as described in Configuration 3 or 4 above.

[0027] According to the fifth aspect, it is possible to more appropriately evaluate whether or not the material has electrolytic corrosion resistance capable of preventing the occurrence of the ridge marks, taking into consideration the desired factors described above.

[0028] A configuration 6 can be adopted as the method for evaluating the electrolytic corrosion resistance of a rolling bearing as described in configuration 5 above, in which if neither the abnormal surface portion consisting of a discolored portion that is not uneven nor the discharge mark is found in the inspection process, the evaluation value in the quantification process is determined to be a first value that is smaller than the reference value, and if no discharge mark is found in the inspection process and an abnormal surface portion consisting of the discolored portion is found in the inspection process, the evaluation value in the quantification process is determined to be a second value that is smaller than the reference value and larger than the first value.

[0029] According to the sixth aspect, for a rolling bearing having electrolytic corrosion resistance capable of preventing the occurrence of ridge marks, the evaluation of electrolytic corrosion resistance can be simplified by limiting it to two categories.

[0030] It is possible to adopt a configuration 7, which is a method for evaluating the electrolytic corrosion resistance of a rolling bearing as set forth in any one of configurations 1 to 6 above, in which specification details to be changed from the specifications of a rolling bearing that was determined in the evaluation process to be susceptible to ridge marks are determined, a specification change process is carried out to prepare a rolling bearing configured to the determined specification details, the testing process, the investigation process and the evaluation process are carried out again on the rolling bearing prepared in the specification change process, and the specification change process, the testing process, the investigation process and the evaluation process are repeated until it is determined that the rolling bearing prepared in the specification change process is one that will not produce ridge marks.

[0031] According to the above configuration 7, it is possible to avoid constructing a rolling bearing with over-specified electrolytic corrosion resistance, and therefore it is possible to provide a rolling bearing with optimal electrolytic corrosion resistance at low cost.

[0032] Configuration 8 can be adopted, which is a method for evaluating the electrolytic corrosion resistance of a rolling bearing as set forth in any one of configurations 1 to 7 above, in which a durability evaluation step is carried out in which, if it is determined in the evaluation step that the rolling bearing is one in which the ridge mark may occur, a single discharge energy based on the diameter of the discharge mark, the number of discharges per unit time expected when the rolling bearing is in use, and the usage durability time required of the rolling bearing are multiplied to determine whether the calculated value exceeds a predetermined threshold, and if the threshold is exceeded, the rolling bearing is determined to be one in which the ridge mark may occur within the usage durability time, and if the threshold is not exceeded, the rolling bearing is determined to be one in which the ridge mark will not occur within the usage durability time.

[0033] According to the above configuration 8, it is possible to determine whether or not a rolling bearing that has been determined to be susceptible to ridge marks will develop ridge marks within a required service life.

[0034] It is possible to adopt configuration 9, which is the method for evaluating the electrolytic corrosion resistance of a rolling bearing as described in configuration 8 above, in which the rolling bearing rotatably supports the rotor of an electric motor controlled by an inverter that operates at a constant switching frequency, and the number of discharges per unit time is three times the switching frequency of the inverter.

[0035] According to configuration 9, it is possible to easily determine, without testing, the number n of discharges per unit time expected when a rolling bearing is in use. That is, when an inverter drives an electric motor using pulse width modulation control that 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 value obtained by multiplying the inverter's switching frequency by three can be used as the number of discharges per unit time expected when a rolling bearing is in use.

[0036] It is possible to employ configuration 10, which is the method for evaluating the electrolytic corrosion resistance of a rolling bearing as described in configuration 8 above, in which a 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 applied to the rolling bearing, and the number of discharge marks formed on the first rolling surface or the second rolling surface after the test is determined, and the value obtained by dividing the number of discharge marks by the certain period of time is used as the number of discharges per unit time.

[0037] According to the above configuration 10, an actual test is conducted and the number of discharge marks is determined based on the test results, so that the number of discharges per unit time expected when the rolling bearing is in use can be determined with high reliability.

[0038] Configuration 11 can be adopted, which is a method for evaluating the electrolytic corrosion resistance of a rolling bearing as set forth in Configuration 10, in which the rolling elements are balls, and the first or second rolling surface is composed of raceway grooves that are arc-shaped in cross section, and a portion of the first or second rolling surface is observed after the relative rotation for the certain period of time, and the number of discharge craters found in the observed area is divided by the area of ​​the observed area to calculate the number of discharge craters per unit area, and then the number of discharge craters formed on each of the first and second rolling surfaces is determined by calculating (the number of discharge craters per unit area) × (the major axis of the contact ellipse where the rolling elements contact the first rolling surface × correction coefficient) × π × (the groove bottom diameter of the first rolling surface) or (the number of discharge craters per unit area) × (the major axis of the contact ellipse where the rolling elements contact the second rolling surface × correction coefficient) × π × (the groove bottom diameter of the second rolling surface).

[0039] According to the above configuration 11, in order to determine the number of discharge marks per unit area, it is not necessary to count the number of discharge marks over the entire circumference of the first rolling surface of the inner ring or the second rolling surface of the outer ring, but it is sufficient to count the number of discharge marks on a portion of the first rolling surface or a portion of the second transfer surface, so that the number of discharge marks can be determined in a relatively short time.

[0040] Aspect 12 of the method for evaluating electrolytic corrosion resistance of a rolling bearing according to aspect 11 above can be adopted, in which the correction coefficient is set to a value of 1.2 to 1.6.

[0041] According to the above-described configuration 12, the number of discharge craters formed on the first rolling surface of the inner ring or the second transfer surface of the outer ring can be determined with high accuracy. That is, the inventors' tests have revealed that when a large number of discharge craters actually formed on the first rolling surface or the second transfer 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 first rolling surface or the second transfer surface, but occur uniformly over an area in the axial direction wider than the axial width corresponding to the contact ellipse between the rolling element and the first rolling surface or the second transfer surface. Here, since the axial width of the area 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 determine with high accuracy the number of discharge craters formed on the first rolling surface or the second transfer surface.

[0042] The method for evaluating the galvanic corrosion resistance of a rolling bearing according to the present invention, by employing the above-mentioned configuration 1, makes it possible to easily and appropriately evaluate whether a rolling bearing has the galvanic corrosion resistance required to prevent the occurrence of ridge marks under certain usage conditions, thereby making it easy to provide a rolling bearing with necessary and sufficient galvanic corrosion resistance at low cost.

[0043] FIG. 1 is a flowchart showing a method for evaluating the galvanic corrosion resistance of a rolling bearing according to an embodiment of the present invention; FIG. 2 is a cross-sectional view showing an example of a rolling bearing whose galvanic corrosion resistance is evaluated by a method for evaluating the galvanic corrosion resistance of a rolling bearing according to an embodiment of the present invention; and FIG. 3 is a schematic diagram showing an example of a test device for evaluating the galvanic corrosion resistance of the rolling bearing of FIG. 1.

[0044] [Configuration of rolling bearing] Figure 2 shows a rolling bearing whose galvanic corrosion resistance performance is evaluated by a method for evaluating galvanic corrosion resistance performance of a rolling bearing according to an embodiment as one example of the present invention. The rolling bearing 1 shown in Figure 2 is a rolling bearing that rotatably supports the 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 the rotor 2 of an electric motor for industrial machinery (not shown), or a bearing that rotatably supports the 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 a first rolling surface 9 formed on the outer periphery of the inner ring 3 and a second rolling surface 10 formed on the inner periphery of the outer ring 4. In this embodiment, the rolling elements 6 are balls, the first rolling surface 9 is made up of raceway grooves 11 with an arc-shaped cross section that extend circumferentially around the outer periphery of the inner ring 3, and the second rolling surface 10 is made up of raceway grooves 12 with an arc-shaped cross section that extend circumferentially around the inner periphery of the outer ring 4. The first rolling surface 9 is formed so as to have a concave arc shape that is symmetrical about the axial center of the inner ring 3, and the second rolling surface 10 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 the base oil semi-solid. The lubricant lubricates the gap between the first rolling surface 9 and the rolling element 6, and the gap between the second rolling surface 10 and the rolling element 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 polyamide-imide resin). The thickness of the insulating coating 15 is set to, for example, approximately 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-preventive bearing.

[0050] 3 shows an example of a test apparatus for evaluating the electrolytic corrosion resistance of the above-mentioned rolling bearing 1. This test apparatus has a rotating shaft 20, a motor 21 that rotationally 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 figure) 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 figure) 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 fitted between the axially opposing surfaces of the insulating sleeve 36 and the housing 34 in an axially compressed state, 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 a 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 as to be electrically insulated from the outside.

[0059] The voltage measurement unit 26 is provided midway along a voltage detection conductive path 40 that connects the portion of the conductive path 37 between the rotary connector 38 and the power supply unit 25 and the portion of the conductive path 37 between the outer ring side terminal 24 and the power supply unit 25. The voltage measurement unit 26 measures the potential difference between the inner ring side terminal 23 and the outer ring side terminal 24 (i.e., the voltage between the inner ring 3 and the outer ring 4 of the rolling bearing 1) via the voltage detection conductive path 40, and records waveform data that shows the change in the measured value over time. The 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] [Method for Evaluating Electrolytic Corrosion Resistance of Rolling Bearing 1] Next, a flowchart of a method for evaluating the electrolytic corrosion resistance of rolling bearing 1 using the test device shown in FIG. 3 is shown in FIG. 1 (hereinafter, refer to FIGS. 1 to 3 as appropriate).

[0062] [Testing Step] First, desired test conditions are set, and a testing step is performed in which a voltage is applied to the rolling bearing 1 for a fixed period of time (S1).

[0063] The test conditions here include the operating conditions of the rolling bearing 1 (load to be applied, rotation speed, rotation time, lubrication environment, etc.) and the electrical conditions when voltage is applied (voltage value, current value, voltage application time, etc.). The set test conditions are constructed using the test device shown in Figure 3.

[0064] Thereafter, the motor 21 is operated to rotate the rotating shaft 20, causing the inner ring 3 and outer ring 4 of the rolling bearing 1 to rotate relative to each other at a constant rotational speed. Next, a DC voltage is applied between the inner ring 3 and the outer ring 4 by the power supply unit 25. This application is carried out for a predetermined time of 10 minutes or less, for example, 5 minutes. The magnitude of the applied voltage and current may be constant, for example, or may be changed as a predetermined amount of time elapses.

[0065] [Investigation step] Once the test has been completed such that the test conditions are satisfied, the rolling bearing 1 is disassembled, and the inner ring 3 and outer ring 4 are cleaned as appropriate (only the lubricant adhering to the inner ring 3 and outer ring 4 is removed), leaving the first raceway surface 9 of the inner ring 3 and the second raceway surface 10 of the outer ring 4 in a state where they can be observed. The first raceway surface 9 or the second raceway surface 10 is then observed with an optical microscope or the like to search for abnormal surface portions within the first raceway surface 9 or the second raceway surface 10 that would be produced when a single discharge occurs between the first raceway surface 9 or the second raceway surface 10 and the rolling element 6 (S2).

[0066] The areas to be searched for here are uneven discharge craters and discolored areas that do not have an uneven shape. The greater the electrical energy of the arc column during a single discharge, the larger the diameter of the hole-like discharge crater that is formed. When the electrical energy of the single discharge is relatively high, the discharge crater is formed in a roughly round crater shape. When the electrical energy of the single discharge is relatively low, the discharge crater is formed in a shallow pit shape. Discolored areas are formed when the first raceway surface 9 or the second raceway surface 10 does not locally melt, but the metal structure is locally hardened. Discharge craters and discolored areas are clearly different from the surface roughness and surface color that are achieved by polishing the first raceway surface 9 and the second raceway surface 10 during their manufacture.

[0067] In the observation, the entire surface of both raceways 9, 10 is the search area. If a discharge crater is found, the diameter (μm) of the discharge crater is recorded. Here, the diameter of the discharge crater is the value of the largest diameter (the width across the largest hole) in a single discharge crater. Once the entire surface of both raceways 9, 10 has been searched, the investigation process ends.

[0068] If the only objective is to evaluate whether the rolling bearing under test has electrolytic corrosion resistance that can prevent the occurrence of ridge marks, the inspection process may be terminated when one discharge mark is found during the search, thereby shortening the time required for the inspection process.

[0069] [Quantification Step] A quantification step is then carried out (S3), in which an evaluation value is determined based on the results of the investigation step. The quantification step is a step for accumulating evaluation results for rolling bearings of various specifications and desired test conditions, and for making it possible to numerically compare the galvanic corrosion resistance performance of comparison targets between rolling bearings of any specifications and test conditions. For example, regardless of differences in specifications or test conditions, the evaluation value of a test rolling bearing serves as a numerical guide for determining the level of galvanic corrosion resistance compared to the evaluation values ​​of other tested rolling bearings. If one simply wants to evaluate whether a test rolling bearing has galvanic corrosion resistance sufficient to prevent the occurrence of ridge marks under desired test conditions, the quantification step may be omitted.

[0070] Here, we show an example of a quantification in which the evaluation value is set to F1 and F1 is determined to classify the investigation results according to whether discharge marks were found during the investigation process, whether discolored areas were found, or whether neither discharge marks nor discolored areas were found.

[0071] That is, if neither discharge marks nor discolored areas are found in the inspection process, the evaluation value F1 is set to a first value N. N is a constant that can be arbitrarily determined as a value smaller than a predetermined reference value r. The reference value r is a value that serves as a boundary for separating an insufficient performance category in which ridge marks may occur from other performance categories in which ridge marks can be prevented from occurring, when determining the electrolytic corrosion resistance performance of a rolling bearing based on an evaluation value that quantifies the test results.

[0072] Furthermore, if no discharge traces are found but discolored areas are found during the inspection process, the evaluation value F1 is set to a second value M. M is a constant that can be arbitrarily determined as a value smaller than the reference value r and larger than the first value N. If only discolored areas occur due to a single discharge, then long-term use of the rolling bearing may result in matte frosting on the raceway surfaces 9, 10, but this does not result in ridge marks, so the occurrence of discolored areas is acceptable. Therefore, the second value M can be set to a value smaller than the reference value r. Since the occurrence of discolored areas indicates that the insulation inside the bearing is incomplete, the second value M can be set to a value larger than the first value N, which would be used if the insulation were considered to be complete.

[0073] Furthermore, if a discharge crater is found in the investigation process, the larger the diameter of the discharge crater, the larger the evaluation value F1 is set to. If multiple discharge craters are found when performing a full search of both raceways 9, 10, the evaluation value F1 can be determined based on the largest value of the diameters of those discharge craters.

[0074] The evaluation value F1 based on the diameter of the discharge mark can be determined as a value obtained by the following formula 1, where X (μm) is the diameter of the discharge mark and a is an arbitrarily determined constant: F1=X+a...formula 1

[0075] Here, the constant a can be set to the same value as the reference value r. For example, if the first value N is set to 0, the second value M is set to 5, and the constant a is set to the reference value r to 10, a range width of 5 can be provided for classification. If the constant a is simply set to the reference value r, it is possible to distinguish between cases where the electrolytic corrosion resistance is insufficient and discharge marks have occurred and cases where this is not the case, based on the magnitude relationship between the evaluation value F1 and the reference value r. As long as this distinction is possible, the reference value r and the constant a may be determined appropriately, and may be set to a magnitude relationship other than the same value.

[0076] For example, the reference value r may be a known value of F1 obtained from test results of rolling bearings with other specifications, or a theoretically calculated simulation value. Furthermore, the constant a may be determined by performing calculations that take into consideration desired factors such as the specifications of the rolling bearing to be tested, test conditions, measurement errors, disturbances, etc.

[0077] [Evaluation Step] Thereafter, it is determined whether the value of F1 determined in the quantification step exceeds a reference value r (S4). If the value of F1 exceeds the reference value r, it is determined that ridge marks (striped irregularities) due to electrolytic corrosion may occur on the first raceway surface 9 or the second raceway surface 10 when the rolling bearing 1 is used as a bearing supporting the rotor 2 of an electric motor. On the other hand, if the value of F1 does not exceed the reference value r, it is determined that ridge marks will not occur on the first raceway surface 9 or the second raceway surface 10 when the rolling bearing 1 is used as a bearing supporting the rotor 2 of an electric motor.

[0078] In the evaluation step, if it is determined that the rolling bearing 1 is one that does not produce ridge marks on the first rolling surface 9 or the second rolling surface 10, the evaluation of the electrolytic corrosion resistance performance of the rolling bearing 1 is terminated. The test conditions, evaluation value F1, etc. of the rolling bearing 1 may be recorded in a database.

[0079] [Durability evaluation step] If the evaluation step determines that the rolling bearing 1 is one in which ridge marks may occur on the first rolling surface 9 or the second rolling surface 10, a durability evaluation step (S5) is carried out to determine whether ridge marks may occur on the first rolling surface 9 or the second rolling surface 10 within the usage durability time required of the rolling bearing 1. If ridge marks do not occur within the usage durability time T, there is no need to add any further electrolytic corrosion prevention measures to the rolling bearing 1, and this determination makes it possible to prevent the adoption of excessive electrolytic corrosion prevention measures.

[0080] Here, let W be the energy of a single discharge based on the diameter of the discharge mark, n be the number of discharges per unit time expected when the rolling bearing 1 is in use, and T be the service life required of the rolling bearing 1. Let F2 be the value calculated using the following formula 2: F2 = W × n × T Formula 2

[0081] When a discharge occurs due to dielectric breakdown of the lubricant between the first rolling surface 9 or the second rolling surface 10 and the rolling element 6, the proportion of the energy imparted to the first rolling surface 9, the second rolling surface 10 and the surface of the rolling element 6 (energy equivalent to the thermal energy used to form discharge craters when they occur) of the electrical energy passing through the bearing due to the discharge is 20 to 40%. It is believed that the larger this proportion, the larger the diameter of the discharge crater that is formed, and therefore the single discharge energy W can be calculated based on the voltage and current set in the test conditions, the aforementioned proportion, and the diameter of the discharge crater.

[0082] The number of discharges per unit time, n, can be three times the switching frequency of the inverter. 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 supporting the rotor 2 of the electric motor three times the switching frequency of the inverter. Therefore, the number of discharges per unit time, n, expected when the rolling bearing 1 is in use can be taken as three times the switching frequency of the inverter.

[0083] The value of the number of discharges per unit time n can also be set based on test results described later.

[0084] That is, the test is carried out by rotating the inner ring 3 and the outer ring 4 relative to each other for a fixed period of time while a voltage that is expected when the rolling bearing 1 is in use is applied to the rolling bearing 1. This test is carried out, for example, using the testing equipment shown in Figure 3, by applying a specified AC voltage between the inner ring 3 and the outer ring 4 of the rolling bearing 1 from the power supply unit 25 (a voltage that is expected to be applied to the rolling bearing 1 when it is used as a bearing that supports the rotor 2 of an electric motor) while rotating the inner ring 3 and the outer ring 4 of the rolling bearing 1 relative to each other at a fixed rotational speed, and maintaining this state for a fixed period of time.

[0085] Thereafter, the rolling bearing 1 is disassembled to enable observation of the first raceway surface 9 on the outer circumference of the inner ring 3 and the second raceway surface 10 on the inner circumference of the outer ring 4, as shown in Figure 2. The first raceway surface 9 or the second raceway surface 10 is then observed with an optical microscope or the like to determine the number of discharge marks formed on the first raceway surface 9 or the second raceway surface 10.

[0086] The number of discharge craters formed on the first rolling surface 9 can be found by counting the number of discharge craters over the entire circumference of the first rolling surface 9, but it is also possible to observe a portion of the first rolling surface 9 and calculate the number of discharge craters per unit area by dividing the number of discharge craters found in that observation area by the area of ​​the observation area, and then find the number of discharge craters formed on the first rolling surface 9 by calculating (number of discharge craters per unit area) × (major axis of contact ellipse where the rolling element 6 contacts the first rolling surface 9 × correction coefficient) × π × (groove bottom diameter of raceway groove 11). In this way, it is not necessary to count the number of discharge craters over the entire circumference of the first rolling surface 9, and it is only necessary to count the number of discharge craters over a portion of the first rolling surface 9, making it possible to find the number of discharge craters in a relatively short time.

[0087] Here, the contact ellipse is an elliptical surface contact portion formed between the rolling element 6 and the first rolling surface 9 when a load is applied between them, and its dimensions are determined from an equation according to 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 first 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 first rolling surface 9.

[0088] 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 first raceway 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 first raceway 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 first raceway 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 first raceway surface 9.

[0089] Similarly, the number of discharge craters formed on the second rollover surface 10 can be determined by observing a portion of the second rollover surface 10, dividing the number of discharge craters found in that observation area by the area of ​​the observation area to calculate the number of discharge craters per unit area, and then calculating (number of discharge craters per unit area) × (major axis of contact ellipse where rolling element 6 contacts second rollover surface 10 × correction coefficient) × π × (groove bottom diameter of raceway groove 12), to determine the number of discharge craters formed on the second rollover surface 10. In this way, it is not necessary to count the number of discharge craters over the entire circumference of the second rollover surface 10, but it is sufficient to count the number of discharge craters in just a portion of the second rollover surface 10, making it possible to determine the number of discharge craters in a relatively short time.

[0090] 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 second raceway surface 10 are actually observed, the discharge craters do not occur only in the axial width corresponding to the contact ellipse between the rolling element 6 and the second raceway surface 10, but occur uniformly over an axial range wider than the axial width corresponding to the contact ellipse between the rolling element 6 and the second 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 second raceway surface 10.

[0091] After determining the number of discharge marks formed on the first rolling surface 9 or the second 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 during the test to obtain the number of discharges n per unit time.

[0092] The calculated value F2 obtained by the above formula 2 corresponds to the total energy imparted to the first rolling surface 9, the second rolling surface 10, and the surface of the rolling element 6 when the rolling bearing 1 is used for the usage durability time T.

[0093] If the calculated value F2 exceeds the threshold value t, the rolling bearing 1 is determined to be a bearing that may develop ridge marks on the first rolling surface 9 or the second rolling 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 calculated value F2 does not exceed the threshold value t, the rolling bearing is determined to be a bearing that will not develop ridge marks on the first rolling surface 9 or the second rolling surface 10 within the usage durability time T when used as a bearing supporting the rotor 2 of an electric motor.

[0094] In the durability evaluation step, if it is determined that the rolling bearing 1 is one that does not produce ridge marks on the first rolling surface 9 or the second rolling surface 10, the evaluation of the electrolytic corrosion resistance performance of the rolling bearing 1 is terminated. The test conditions during the durability evaluation, the calculated value F2, etc. may be recorded in a database.

[0095] [Specification modification process] If it is determined in the durability evaluation process that the rolling bearing 1 is likely to develop ridge marks on the first rolling surface 9 or the second rolling surface 10 within the usage durability time T, a specification modification process is carried out in which specification changes to be made to the specifications of the rolling bearing 1 are determined and a rolling bearing configured to the determined specification changes is prepared (S6). In this specification modification, electrolytic corrosion prevention measures that are thought to improve electrolytic corrosion prevention performance compared to the rolling bearing 1 may be appropriately adopted.

[0096] Then, for the prepared rolling bearing, each step is repeated in order, starting with the above-mentioned testing step (S1), and finally, when a rolling bearing is obtained that satisfies evaluation value F1 < reference value r in the evaluation step (S4) or a rolling bearing that satisfies calculated value F2 < threshold value t in the durability evaluation step (S5), the evaluation of galvanic corrosion resistance performance is terminated. This makes it possible to complete the design of a rolling bearing that has galvanic corrosion resistance performance that can prevent the occurrence of ridge marks under the desired conditions.

[0097] For example, suppose a standard bearing, which is a rolling bearing that does not incorporate any special anti-electrolytic corrosion measures such as an insulating coating, undergoes the above-described test process (S1) through evaluation process (S4), resulting in an evaluation value F1 of 15, with F1 > reference value r and F2 > threshold value t, and is determined to lack the anti-electrolytic corrosion performance sufficient to prevent ridge marks under the desired conditions. In this case, modifying the standard bearing to incorporate ceramic rolling elements would provide the safest anti-electrolytic corrosion measure, but would be costly. In contrast, if an insulated-coated bearing, such as rolling bearing 1, that has been modified to incorporate an insulating coating undergoes the above-described test process (S1) through evaluation process (S4), resulting in an evaluation value F1 of 5, with F1 < reference value r, it is determined to have the anti-electrolytic corrosion performance sufficient to prevent ridge marks under the same conditions. Therefore, an insulated-coated bearing that is less expensive than a hybrid bearing can be provided as a rolling bearing that meets the requirements.

[0098] As another example, suppose a standard bearing undergoes the above-described testing process (S1) through evaluation process (S4) to obtain an evaluation value F1 of 13, with F1 > reference value r and F2 > threshold value t, and is determined to lack the electrolytic corrosion resistance required to prevent ridge marks under desired conditions. In this case, if a modified bearing, in which the lubricant used is changed from the standard bearing as an electrolytic corrosion prevention measure, undergoes the above-described testing process (S1) through evaluation process (S4) to obtain an evaluation value F1 of 5, with F1 < reference value r, it can be seen that this modification is less expensive than an insulating coating solution, yet still has the same level of electrolytic corrosion resistance as an insulating-coated bearing. Therefore, modified-specification bearings that are less expensive than insulating-coated bearings can be provided as rolling bearings that meet customer demands.

[0099] As another example, consider a case where a standard bearing undergoes the above-described testing process (S1) through evaluation process (S4) and is evaluated as having an F1 score of 13, with F1 > reference value r and F2 > threshold value t, indicating that the bearing does not have the galvanic corrosion resistance required to prevent ridge marks under the desired conditions. In this case, if a modified bearing, with bearing specifications and lubricant types altered from the standard bearing, undergoes the above-described testing process (S1) through evaluation process (S4), and the evaluation score is F1 = 5, with F1 < reference value r, it can be determined that the modified bearing has the same level of galvanic corrosion resistance as an insulated-coated bearing, despite being less expensive than an insulated-coated bearing. Therefore, modified bearings that are less expensive than insulated-coated bearings can be provided as rolling bearings that meet customer requirements. In this way, the above-described testing process (S1) through evaluation process (S4) narrow down the number of galvanic corrosion prevention measures available, eliminating the need for numerous verification experiments. Furthermore, because the galvanic corrosion prevention measures can be selected theoretically, explanations to users can be more accurate. Furthermore, when the oil film parameter Λ is 3 (boundary lubrication state) at the rolling contact portion between the rolling elements and the raceways, it is possible to provide a rolling bearing with a sufficient life against both electrolytic corrosion and peeling by adopting a lubricant that prevents surface-originated flaking (so-called peeling) and by modifying the specifications to apply a surface treatment to the rolling surfaces of the inner and outer raceways.

[0100] The method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment involves carrying out a short-term test (S1) under test conditions corresponding to the desired conditions of use (structure of the rolling bearing, shaft, housing, etc., bearing load conditions, electrical conditions, lubricant composition, etc.), and then judging whether the rolling bearing has electrolytic corrosion resistance sufficient to prevent the occurrence of ridge marks based on the presence or absence of discharge marks caused by a single discharge on the first and second rolling surfaces after the test (S2, S4), thereby making it possible to easily and appropriately evaluate whether the rolling bearing has electrolytic corrosion resistance sufficient to prevent the occurrence of ridge marks under those test conditions. This eliminates the need for overly-engineered electrolytic corrosion prevention measures that have relied on empirical intuition as in the past, and makes it easy to provide rolling bearings with the necessary and sufficient electrolytic corrosion resistance at low cost.

[0101] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, the time for which voltage is applied to the rolling bearing in the testing step (S1) is 10 minutes or less, which makes it easy to observe the shape of the discharge marks in the investigation step (S2) and shortens the time required for one testing step (S1), thereby making it easier to evaluate the electrolytic corrosion resistance performance of a variety of rolling bearings with different specifications and under various test conditions.

[0102] Furthermore, the method for evaluating the electrolytic corrosion performance of rolling bearings according to this embodiment further includes a quantification step (S3) for determining an evaluation value F1 based on the results of the investigation in the investigation step (S2). If a discharge mark is found in the investigation step (S2), the larger the diameter of the discharge mark, the larger the evaluation value determined in the quantification step (S3), thereby providing an indication of the extent to which the electrolytic corrosion resistance is deficient. Furthermore, by comparing this evaluation value with evaluation values ​​obtained for rolling bearings of different specifications or evaluation values ​​obtained under different test conditions, it is possible to easily determine the relative extent of the difference in electrolytic corrosion resistance between the compared objects.

[0103] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, when the diameter of the discharge mark is X (μm) and an arbitrarily determined constant is a, by determining the evaluation value to be the value F1 obtained by the following formula 1 in the evaluation step (S4), it is possible to evaluate the electrolytic corrosion resistance performance of the rolling bearing while reflecting the diameter of the discharge mark and an arbitrary consideration factor as the constant a: F1=X+a...formula 1

[0104] Furthermore, in the evaluation step (S4) of the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, a comparison is made to see whether the evaluation value F1 exceeds a predetermined reference value r, and if it exceeds the reference value r, the rolling bearing is judged to be one in which ridge marks may occur, and if it does not exceed the reference value r, the rolling bearing is judged to be one in which ridge marks will not occur, thereby making it possible to more appropriately evaluate whether the rolling bearing has the electrolytic corrosion resistance performance sufficient to prevent the occurrence of the aforementioned ridge marks, taking into account the desired factors described above.

[0105] Furthermore, in the method for evaluating the electrolytic corrosion performance of rolling bearings according to this embodiment, if neither an abnormal surface portion consisting of a discolored portion that is not uneven nor a discharge mark is found in the investigation step (S2), the evaluation value F1 is set to a first value N that is smaller than the reference value r in the quantification step (S3); and if no discharge mark is found in the investigation step (S2) and an abnormal surface portion consisting of a discolored portion is found, the evaluation value F1 is set to a second value M that is smaller than the reference value r and larger than the first value N in the quantification step (S3).This makes it possible to simply limit the evaluation of electrolytic corrosion resistance performance to two categories for rolling bearings that have electrolytic corrosion resistance that is capable of preventing the occurrence of ridge marks.

[0106] Furthermore, the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment determines the specification changes to be made to the specifications of a rolling bearing that has been determined in the evaluation step (S4) to be susceptible to ridge marks, carries out a specification change step (S6) to prepare a rolling bearing configured to the determined specification changes, and then performs the testing step (S1), investigation step (S2) and evaluation step (S4) again on the rolling bearing prepared in the specification change step (S6). The specification change step (S6), testing step (S4), investigation step (S2) and evaluation step (S4) are repeated until the rolling bearing prepared in the specification change step (S6) is determined to be one that will not produce ridge marks (S4, S5). This makes it possible to avoid constructing a rolling bearing with over-specified electrolytic corrosion resistance, and therefore makes it possible to provide a rolling bearing with optimal electrolytic corrosion resistance at low cost.

[0107] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, if the rolling bearing is determined in the evaluation step (S4) to be one in which ridge marks may occur, a calculation value F2 obtained by multiplying a single discharge energy W based on the diameter of the discharge mark, the number of discharges per unit time n expected when the rolling bearing is in use, and the endurance usage time T required of the rolling bearing is determined to exceed a predetermined threshold value t, and if the threshold value t is exceeded, the rolling bearing is determined to be one in which ridge marks may occur within the endurance usage time T, and if the threshold value t is not exceeded, the rolling bearing is determined to be one in which ridge marks will not occur within the endurance usage time T. By performing this durability evaluation step (S5), it is possible to determine whether a rolling bearing determined to be one in which ridge marks may occur will develop ridge marks within the required endurance usage time T.

[0108] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, the rolling bearing 1 rotatably supports the rotor 2 of an electric motor controlled by an inverter that operates at a constant switching frequency, and by using a value obtained by multiplying the inverter's switching frequency by three as the number of discharges per unit time n, the number of discharges per unit time n expected when the rolling bearing is in use can be easily determined without testing.

[0109] Furthermore, the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment involves conducting a test in which the inner and outer rings are rotated relative to one another for a fixed period of time while a voltage that is expected to be applied to the rolling bearing when it is in use, determining the number of discharge marks formed on the first rolling surface or the second rolling surface after the test has been completed, and using the value obtained by dividing the number of discharge marks by the fixed period of time as the number of discharges per unit time n, thereby making it possible to determine with a high degree of reliability the number of discharges per unit time that is expected to be generated when the rolling bearing is in use, based on the results of actual testing.

[0110] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, the rolling elements are balls, the first rolling surface is made up of raceway grooves with an arc-shaped cross section, and a portion of the first rolling surface is observed after the relative rotation for the specified period of time, and the number of discharge craters found in the observed area is divided by the area of ​​the observed area to calculate the number of discharge craters per unit area.The number of discharge craters formed on the first rolling surface is then found by calculating (the number of discharge craters per unit area) × (the major axis of the contact ellipse where the rolling elements contact the first rolling surface × correction coefficient) × π × (the groove bottom diameter of the first rolling surface).This means that to find the number of discharge craters per unit area, it is not necessary to count the number of discharge craters over the entire circumference of the first rolling surface of the inner ring, but it is sufficient to count the discharge craters on only a portion of the first rolling surface, and the number of discharge craters can be found in a relatively short time.

[0111] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, by setting the correction coefficient to a value between 1.2 and 1.6, the number of discharge marks formed on the first rolling surface of the inner ring can be determined with high accuracy.

[0112] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, the rolling elements are balls, the second rolling surface is made up of raceway grooves with an arc-shaped cross section, and a portion of the second rolling surface is observed after the specified period of relative rotation, and the number of discharge craters found in the observed area is divided by the area of ​​the observed area to calculate the number of discharge craters per unit area. Thereafter, the number of discharge craters formed on the second rolling surface is found by calculating (number of discharge craters per unit area) × (major axis of contact ellipse where the rolling elements contact the second rolling surface × correction coefficient) × π × (groove bottom diameter of the second rolling surface). This means that to find the number of discharge craters per unit area, it is not necessary to count the number of discharge craters over the entire circumference of the second rolling surface of the outer ring, but it is sufficient to count the discharge craters in a portion of the second rolling surface, and the number of discharge craters can be found in a relatively short time.

[0113] Furthermore, in the method for evaluating the electrolytic corrosion performance of a rolling bearing according to this embodiment, by setting the correction coefficient to a value between 1.2 and 1.6, the number of discharge marks formed on the second rolling surface of the outer ring can be determined with high accuracy.

[0114] In this embodiment, the test device shown in Fig. 3 is used to determine the value of F1, but the test process may also be performed using an actual machine. For example, for an electric motor in operation, the value of F1 may be determined 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. 3 to the outer and inner rings of a rolling bearing that supports the rotor of the electric motor and performing a test similar to that described above.

[0115] 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.

[0116] REFERENCE SIGNS LIST 1 Rolling bearing 2 Rotor 3 Inner ring 4 Outer ring 6 Rolling element 9 First rolling surface 10 Second rolling surface 11 Raceway groove 12 Raceway groove F1 Evaluation value a Constant N First value M Second value F2 Calculated value T Durability time W Single discharge energy n Number of discharges per unit time t Threshold value

Claims

1. A method for evaluating the electrolytic corrosion resistance of a rolling bearing having an inner ring including a first rolling surface, an outer ring including a second rolling surface, a plurality of rolling elements that roll between the first rolling surface and the second rolling surface, and a lubricant that lubricates the inside of the bearing, comprising: a testing step of applying a predetermined voltage to the rolling bearing while the inner ring and the outer ring rotate relative to each other; an investigation step of searching for an abnormal surface portion that would occur when a single discharge occurs between the first rolling surface or the second rolling surface and the rolling elements in the first rolling surface and the second rolling surface after the testing step has been completed; and an evaluation step of determining, if an abnormal surface portion consisting of a discharge mark formed in an uneven shape is found in the investigation step, that the rolling bearing is capable of producing ridge marks due to electrolytic corrosion on the first rolling surface or the second rolling surface, and if no discharge mark is found in the investigation step, determining that the rolling bearing is not susceptible to ridge marks.

2. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1, wherein in the testing step, the voltage is applied to the rolling bearing for a period of 10 minutes or less.

3. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 1 or 2, further comprising a quantification step of determining an evaluation value based on the results of the investigation in the investigation step, wherein if the discharge crater is found in the investigation step, the larger the diameter of the discharge crater is, the larger the evaluation value determined in the quantification step.

4. The method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 3, wherein, in the digitizing step, the evaluation value is determined to be a value F1 obtained by the following formula 1, where X (μm) is the diameter of the discharge crater and a is an arbitrarily determined constant: F1=X+a...Formula 1 5. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 3 or 4, wherein in the evaluation step, a comparison is made to determine whether the evaluation value exceeds a predetermined reference value, and if the reference value is exceeded, the rolling bearing is judged to be one in which the ridge mark may occur, and if the reference value is not exceeded, the rolling bearing is judged to be one in which the ridge mark will not occur.

6. A method for evaluating the electrolytic corrosion resistance of a rolling bearing as set forth in claim 5, wherein, if neither the abnormal surface portion consisting of a discolored portion that is not uneven nor the discharge mark is found in the inspection step, the evaluation value is determined to be a first value that is smaller than the reference value in the quantification step, and if the discharge mark is not found in the inspection step and the abnormal surface portion consisting of the discolored portion is found in the inspection step, the evaluation value is determined to be a second value that is smaller than the reference value and larger than the first value in the quantification step.

7. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of claims 1 to 6, comprising the steps of: determining specifications to be changed from the specifications of a rolling bearing that has been determined in the evaluation step to be one in which ridge marks may occur; carrying out a specification change step to prepare a rolling bearing configured to the determined specifications; repeating the testing step, the investigation step and the evaluation step on the rolling bearing prepared in the specification change step; and repeating the specification change step, the testing step, the investigation step and the evaluation step until it is determined that the rolling bearing prepared in the specification change step is one in which ridge marks will not occur.

8. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to any one of claims 1 to 7, comprising a durability evaluation step of determining whether a calculated value obtained by multiplying a single discharge energy based on the diameter of the discharge mark, the number of discharges per unit time expected when the rolling bearing is in use, and the endurance usage time required of the rolling bearing exceeds a predetermined threshold value if the calculated value exceeds the threshold value, and determining that the rolling bearing is one in which the ridge mark may occur within the endurance usage time if the calculated value does not exceed the threshold value.

9. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 8, wherein the rolling bearing rotatably supports the rotor of an electric motor controlled by an inverter that operates at a constant switching frequency, and the number of discharges per unit time is three times the switching frequency of the inverter.

10. A method for evaluating the electrolytic corrosion resistance of a rolling bearing as set forth in claim 8, wherein a test is conducted in which the inner ring and the outer ring are rotated relative to each other for a fixed period of time while a voltage expected when the rolling bearing is applied to the rolling bearing, the number of discharge marks formed on the first rolling surface or the second rolling surface after the test is determined, and the value obtained by dividing the number of discharge marks by the fixed period of time is used as the number of discharges per unit time.

11. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 10, wherein the rolling elements are balls, and the first or second rolling surface is composed of raceway grooves with an arc-shaped cross section, and a portion of the first or second rolling surface is observed after the fixed period of relative rotation, and the number of discharge craters found in the observed area is divided by the area of ​​the observed area to calculate the number of discharge craters per unit area, and then the number of discharge craters formed on each of the first and second rolling surfaces is determined by calculating (the number of discharge craters per unit area) × (the major axis of the contact ellipse where the rolling elements contact the first rolling surface × correction coefficient) × π × (the groove bottom diameter of the first rolling surface) or (the number of discharge craters per unit area) × (the major axis of the contact ellipse where the rolling elements contact the second rolling surface × correction coefficient) × π × (the groove bottom diameter of the second rolling surface).

12. A method for evaluating the electrolytic corrosion resistance of a rolling bearing according to claim 11, wherein the correction coefficient is set to a value of 1.2 to 1.6.

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