Method for designing rolling bearings

Abstract

To provide a method for designing a rolling bearing capable of suppressing ridge marks caused by electric corrosion.SOLUTION: A first mathematical expression capable of determining a rolling bearing 10 that includes an inner ring 11, an outer ring 12, a plurality of rolling elements 13 and a lubricant LQ is prepared. According to the operating conditions of the rolling bearing 10, it is determined whether the first mathematical expression F=f(α,β,γ,δ) (1) satisfies the second mathematical expression F≤10 (2). In calculating parameters of the lubricant LQ, the lubricant LQ is divided into a first region and a second region. In a virtual electrical circuit corresponding to the rolling bearing 10, characteristic values of virtual elements respectively corresponding to the first and second regions are obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for designing a rolling bearing. [Background technology]

[0002] In recent years, most of the fan motors, three-phase motors, servo motors, etc. used in industrial machinery are controlled by inverters. This is hereafter referred to as inverter control. Inverter control is used to achieve high efficiency. The rotating shaft of an inverter-controlled motor is supported by rolling bearings.

[0003] Inverter control controls the AC voltage and frequency input to a motor to adjust the motor's rotational speed. As the switching frequency output by an inverter device increases, the frequency with which high shaft voltages occur in motors increases. Shaft voltage refers to the potential difference that occurs between the shaft of a rotating body such as a motor and other components. Shaft voltage can cause a potential difference between the outer and inner rings and the rolling elements of a rolling bearing installed in a motor. If this potential difference becomes large, it will exceed the breakdown voltage of the lubricant oil film between the outer and inner rings (races) and the rolling elements. This will cause discharges between the outer and inner rings (races) and the rolling elements, causing damage called electrolytic corrosion inside the bearing.

[0004] As electrolytic corrosion progresses, striped irregularities called ridge marks form on the rolling surfaces of the rolling elements or outer and inner rings. Ridge marks can cause noise and vibration in the bearing. For this reason, efforts are underway to develop bearings that are designed to suppress the formation of ridge marks on the rolling surfaces.

[0005] For example, Japanese Patent No. 4599769 (Patent Document 1) and Japanese Patent No. 4177057 (Patent Document 2) disclose inventions that use conductive grease and conductive seals to impart conductivity to bearings. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4599769 [Patent Document 2] Patent No. 4177057 Summary of the Invention [Problem to be solved by the invention]

[0007] The conductive grease and conductive seal disclosed in Patent Document 1 and Patent Document 2 generally have a volume resistivity of 10 4 Ωcm or more 10 8 This is high, at less than Ωcm. This makes it difficult to suppress the motor shaft voltage caused by the inverter. This can cause dielectric breakdown of the oil film caused by the lubricant in the rolling bearings built into the motor.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for designing a rolling bearing that can suppress ridge marks caused by electrolytic corrosion. [Means for solving the problem]

[0009] A method for designing a rolling bearing according to the present disclosure prepares a first mathematical formula capable of determining whether electrolytic corrosion can be suppressed in a rolling bearing including an inner ring, an outer ring arranged on the outer periphery of the inner ring, multiple rolling elements arranged freely to roll between the inner ring and the outer ring, and a lubricant. The configuration of the inner ring, outer ring, and multiple rolling elements is determined based on the usage conditions of the rolling bearing. The first mathematical formula is given by: where α is a mechanical parameter of the inner ring, outer ring, and multiple rolling elements, β is a parameter of the lubricant, γ is a constant for the other parameters, and δ is a parameter obtained from the usage conditions. F = f(α, β, γ, δ)…(1) The determining step is carried out by using the following second formula according to the conditions of use: F≦10…(2) The determining step includes a first parameter calculation step of determining a lubricant parameter β. In the first parameter calculation step, the lubricant is divided into a first region of the lubricant located between the first rolling surface, which is the rolling surface of at least one of the inner ring and the outer ring, and the second rolling surface, which is the rolling surface of the rolling element, in a region where the first rolling surface and the second rolling surface approach each other to form an ellipse, and a second region of the lubricant located outside the first region. Characteristic values ​​of virtual elements that correspond to the first and second regions in a virtual electric circuit corresponding to the rolling bearing are determined. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a rolling bearing and an electric motor that can suppress ridge marks caused by electrolytic corrosion. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of a rolling bearing according to an embodiment of the present invention. [Figure 2] 2 is a schematic cross-sectional view showing the configuration of an electric motor including the rolling bearing of FIG. 1 according to the present embodiment. [Figure 3] This is an equivalent circuit in which each component of a rolling bearing is likened to an electrical element. [Figure 4] 4 is a graph showing an example of a simulation result using the electric circuit of FIG. 3. [Figure 5] 1 is a flowchart showing an outline of a method for designing a rolling bearing according to an embodiment of the present invention. [Figure 6] 5 is a flowchart showing an outline of a rolling bearing mode determination step (S20) in the rolling bearing design method according to the present embodiment. [Figure 7] FIG. 2 is a schematic diagram showing a model for calculating lubricant parameters. [Figure 8] 3 is a flowchart showing an outline of a method for manufacturing a rolling bearing according to the present embodiment. [Figure 9] FIG. 10 is a schematic diagram of a model corresponding to the rolling bearing of FIG. 1, used in a first parameter calculation step in Example 4. [Figure 10] This is an equivalent circuit in which each component of the rolling bearing in Figure 9 is likened to an electrical element. [Figure 11] FIG. 10 is a schematic diagram of a model corresponding to the rolling bearing of FIG. 1, used in a first parameter calculation step in Example 5. [Figure 12] This is an equivalent circuit in which each component of the rolling bearing in Figure 11 is likened to an electrical element. [Figure 13] FIG. 20 is a schematic diagram of a model corresponding to the rolling bearing of FIG. 1, used in the first parameter calculation step in Example 6. [Figure 14] This is an equivalent circuit in which each component of the rolling bearing in Figure 13 is likened to an electrical element. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Configuration of rolling bearing 10 and electric motor 100) FIG. 1 is a schematic cross-sectional view showing the configuration of a rolling bearing according to this embodiment. Referring to FIG. 1, rolling bearing 10 according to this embodiment is, for example, a deep groove ball bearing. However, the present invention is not limited to this, and rolling bearing 10 may be a bearing having rolling elements other than a deep groove ball bearing. Rolling bearing 10 mainly comprises an inner ring 11, an outer ring 12, a plurality of rolling elements 13, a cage 14, and a seal member 15. Rolling bearing 10 is used, for example, in industrial motors.

[0013] An annular inner ring raceway surface 11A (first raceway surface) is formed on the inner ring 11. The outer ring 12 is arranged on the outer peripheral side of the inner ring 11 at a distance (in the radial direction RA) from the outer ring 12. An annular outer ring raceway surface 12A (first raceway surface) is formed on the outer ring 12. The plurality of rolling elements 13 are spherical members arranged so as to be able to roll between the inner ring 11 and the outer ring 12. A raceway surface 13A (second raceway surface) is formed on the surface of the plurality of rolling elements 13. The rolling elements 13 may be made of commonly known stainless steel, but are preferably made of ceramic.

[0014] The inner ring 11, outer ring 12, and rolling elements 13 are bearing components, and the inner ring raceway surface 11A, outer ring raceway surface 12A, and raceway surface 13A are contact surfaces of these bearing components. The rolling elements 13 have raceway surfaces 13A, which contact the outer ring raceway surface 11A and the inner ring raceway surface 12A, respectively. The multiple rolling elements 13 are spaced apart in the circumferential direction by an annular cage 14, and are thus held so that they can roll freely on an annular track. The cage 14 is formed with multiple openings called pockets 18, and each of the multiple pockets 18 houses one rolling element 13. This allows the multiple rolling elements 13 to be held at intervals in the circumferential direction of the annular shape of the inner ring 11, etc.

[0015] With the above configuration, the inner ring 11 and outer ring 12 of the rolling bearing 10 are rotatable relative to each other. That is, the inner ring 11 and outer ring 12 rotate about a central axis indicated by a dashed line extending in the left-right direction in FIG. 1. The direction in which this central axis extends is referred to as the axial direction AX. The direction in which the diameter of the annular inner ring 11 and outer ring 12 extends is indicated by a dashed line extending in the up-down direction in FIG. 1, and this direction is referred to as the radial direction RA. The position of a bearing component such as the inner ring 11 in the radial direction RA is the distance from the central axis indicating the axial direction AX.

[0016] A first seal groove 16 is formed in the inner ring 11. The first seal groove 16 is formed at both ends (left and right ends) in the axial direction AX of the outer peripheral surface (outer diameter surface) of the inner ring 11. A second seal groove 17 is formed in the outer ring 12. The second seal groove 17 is formed at both ends (left and right ends) in the axial direction AX of the inner peripheral surface (inner diameter surface) of the outer ring 12.

[0017] Sealing member 15 is arranged between inner ring 11 and outer ring 12 so as to close the gap between inner ring 11 and outer ring 12. In other words, inner ring 11 is arranged at a distance from outer ring 12 in the radial direction RA, and therefore a gap exists in the space between inner ring 11 and outer ring 12. Sealing members 15 are arranged at both ends of the gap in the axial direction AX to prevent the components housed in this gap from being exposed to the outside of rolling bearing 10. Sealing member 15 is fitted to the inner diameter surface of outer ring 12 and is arranged so as to come into contact with inner ring 11. Sealing member 15 is preferably made of a conductive rubber material.

[0018] In the rolling bearing 10 of this embodiment, a lubricant LQ is sealed in a gap formed between the inner ring 11 and the outer ring 12, in which a plurality of rolling elements 13 are arranged. The value of the oil film parameter Λ of the lubricant LQ is preferably 3 or less. The lubricant LQ is preferably grease.

[0019] In the rolling bearing 10 of this embodiment, F = f(α, β, γ, δ)…(1) The value of F calculated from (hereinafter referred to as the first formula) is F≦10…(2) (hereinafter, the second mathematical formula) is satisfied. Here, the first mathematical formula indicates that F is a function of the parameters α, β, γ, and δ. The second mathematical formula indicates that for rolling bearing 10 of this embodiment, the value of F, obtained by inputting the numerical values ​​of the parameters α, β, γ, and δ into the first mathematical formula, is preferably 10 or less.

[0020] In the first equation above, α is a mechanical parameter. The mechanical parameter α is a value calculated from the rotational speed of the inner ring 11 and outer ring 12, the load applied to the rolling bearing 10, the surface roughness of the inner ring 11 and outer ring 12 included in the rolling bearing 10, and the internal specifications of the bearing. The internal specifications of the bearing refer to 1) the material and dimensions of the inner ring 11 and outer ring 12 of the rolling bearing 10, and 2) the type (excluding material) of the rolling elements 13, based on their number, shape, and dimensions. Note that the parameters obtained from the rotational speed of the inner ring 11 and outer ring 12 and the load applied to the rolling bearing 10 are not considered mechanical parameters here, but are included in the "parameter δ obtained from the operating conditions," described below. This is because the rotational speed and load are values ​​entered by the user of the rolling bearing 10 on-site.

[0021] For example, when the rotation speed of the inner ring 11 and outer ring 12 of the rolling bearing 10 is high, the oil film of lubricant LQ becomes thicker, increasing the voltage at which the oil film breaks down. This increases the breakdown voltage of the oil film, making it less likely to break down. However, once breakdown occurs in the oil film between the inner ring 11 or the outer ring and the rolling element 13, the discharge craters formed on the inner ring rolling surface 11A and other areas become larger. Damage caused by discharge is hereinafter referred to as discharge craters. This increases the likelihood of ridge marks forming. In other words, the value of α in the first equation increases, exceeding 10, for example. When the load on the rolling bearing 10 is heavy, for example, the oil film of lubricant LQ between the inner ring 11 and the outer ring 12 and the rolling element 13 becomes thinner, reducing the voltage at which breakdown occurs. This reduces the discharge craters formed on the inner ring rolling surface 11A and other areas when a discharge occurs in the oil film. This makes the oil film more susceptible to breakdown, but even if breakdown does occur, the likelihood of ridge marks forming is low. That is, the value of α is calculated so that the value of F in the first formula becomes small, for example, to be 10 or less as in the second formula. As described above, α is calculated from the rotation speed of the inner ring 11, the load applied to the inner ring 11, and the surface roughness of the inner ring 11, and when this is substituted into the first formula, the value of F can be found.

[0022] In the first equation above, β is a parameter of the lubricant LQ. The parameter β of the lubricant LQ is a value calculated from the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant LQ. For example, if the lubricant LQ has a high volume resistivity, the oil film between the inner ring 11 and the rolling elements 13 is less likely to undergo dielectric breakdown. In this case, the voltage at which the oil film undergoes dielectric breakdown increases. Therefore, if dielectric breakdown occurs in the oil film between the inner ring 11 and the rolling elements 13, the discharge crater formed on the inner ring rolling surface 11A, etc., becomes large. This increases the likelihood of ridge marks. In other words, the value of β is calculated so that the value of F in the first equation becomes large, for example, exceeding 10. If the lubricant LQ has a high viscosity, the oil film between the inner ring 11 and the rolling elements 13 becomes thicker, increasing the voltage at which the breakdown voltage occurs. Therefore, as above, the discharge crater becomes large, and the value of β is determined so that the value of F in the first equation becomes large.

[0023] In the first formula above, γ is a constant for the rolling bearing 10 (any other parameter) other than α and β. γ is a parameter related to the effect of suppressing electrolytic corrosion of the rolling bearing 10, which is a particular function and effect of this embodiment. The value of γ for a standard bearing (hereinafter referred to as a standard bearing) that does not have the features of this embodiment is 1. In contrast, the more electrolytic corrosion reduction effects are provided, such as by providing insulating coatings 19 on the inner ring rolling surface 11A and outer ring rolling surface 12A, by having conductive brushes in the electric motor 100 (described below), and by making the sealing member 15 conductive, the smaller the value of γ becomes, reaching a minimum of 0. Therefore, the range of values ​​is 0≦γ≦1. The value of γ is 0 when electrolytic corrosion can be completely eliminated. For example, in a so-called hybrid bearing in which the rolling elements 13 are made of ceramic, the possibility of electrolytic corrosion is completely eliminated, and the value of γ is 0.

[0024] The insulating coating 19 is an electrically insulating thin film formed on the inner ring rolling surface 11A and the outer ring rolling surface 12A by surface treatment such as plating, coating, or paint application. The insulating coating 19 may be, for example, a synthetic resin layer or a paint film layer. Alternatively, the insulating coating 19 does not have to fall into either of the above categories. In any case, it is preferable to select an appropriate material for the insulating coating 19 so that the second equation holds when the parameter γ for the rolling bearing 10 is substituted into the first equation. Note that the insulating coating 19 behaves as a capacitor, and if the capacitance of this capacitor is small and the frequency of the AC voltage applied to the rolling bearing 10 is low, the value of F in the first equation will be small.

[0025] In the above first formula, δ is a parameter obtained from the usage conditions entered by the user when using the rolling bearing 10. The usage conditions include electrical parameters, etc. The electrical parameters are values ​​calculated from the AC voltage applied to the rolling bearing 10 when the user uses it, and the frequency of that AC voltage. The AC voltage is the value of the voltage that is expected to be applied when the user uses the rolling bearing 10. The frequency can be thought of as at least the value of the "frequency" that is expected to be applied when the user uses the rolling bearing 10. As will be described below, these electrical parameters and the user's usage conditions, such as the user's rotation speed, are converted into the parameter δ obtained from the usage conditions by calculation on a computer using a virtual electrical circuit 50 (see Figure 3) created on the computer.

[0026] From the above, of the above parameters α, β, γ, and δ, only δ is a parameter that can be controlled by the user of the rolling bearing 10, and the other parameters α, β, and γ are parameters that can be determined as design values ​​by the manufacturer of the rolling bearing 10 at the time of manufacture.

[0027] For example, if the voltage applied to the rolling bearing 10 is high, breakdown easily occurs even under conditions that normally prevent breakdown due to high breakdown voltages, such as a thick oil film between the inner ring 11 and the rolling element 13, or a high volume resistivity of the lubricant LQ. Furthermore, both a thick oil film and a high volume resistivity of the lubricant LQ are conditions that increase discharge marker size. Therefore, when a high voltage is applied to the rolling bearing 10, discharge marker size may increase depending on the mechanical parameter α and the lubricant parameter β. On the other hand, when the voltage applied to the rolling bearing 10 is low, the breakdown voltage of the lubricant LQ may not be reached, and no discharge marker may occur. Therefore, the voltage applied to the rolling bearing 10 has a greater impact on the likelihood of ridge mark formation due to the size of the discharge marker than the influence of conditions such as the oil film thickness, which is related to the mechanical parameter α, and the volume resistivity of the lubricant LQ, which is related to the lubricant parameter β. The likelihood of ridge marks occurring due to the size of the discharge mark is reflected in the value of F in the first formula, which is caused by electrical parameters.

[0028] Other usage conditions of the user include the rotation speed of the inner ring 11 and the outer ring 12, and the load applied to the rolling bearing 10. The rotation speed is the number of times that the inner ring 11 and the outer ring 12 are expected to rotate when the user uses the rolling bearing 10. The load is the force that is expected to be applied to the rolling bearing 10 when the user uses the rolling bearing 10.

[0029] For example, when a user uses rolling bearing 10 for an industrial motor, the rotation speed of rolling bearing 10 is 100 rpm or more and 20,000 rpm or less. When a user uses rolling bearing 10 for an industrial motor, the voltage applied to rolling bearing 10 is 2 V or more and 100 V or less. These rotation speed and voltage values ​​are the basis for parameter δ in the first formula above, and are values ​​determined by the user.

[0030] Fig. 2 is a schematic cross-sectional view showing the configuration of an electric motor according to this embodiment, including the rolling bearing of Fig. 1. Referring to Fig. 2, electric motor 100 according to this embodiment mainly includes stator 21, rotor 22, and conductive brush 30 in addition to the above-mentioned rolling bearing 10.

[0031] The stator 21 includes a stator yoke 21A, a stator core 21B, and a stator coil 21C. The stator yoke 21A is a component arranged in a circumferential shape on the outermost side of the radial direction RA of the entire electric motor 100. The stator core 21B is a portion extending from the inner peripheral surface of the stator yoke 21A in the radial direction RA toward the inside in the radial direction RA. The stator core 21B is formed integrally with the stator yoke 21A. The stator core 21B is a portion serving as the core of the entire stator 21. A plurality of stator cores 21B are arranged at intervals in the circumferential direction extending in the depth direction of the paper in FIG. 1 . The number of stator cores 21B arranged is arbitrary and may be, for example, 2, 4, 6, 8, or 12. A stator coil 21C is wound on the surface of the stator core 21B. A stator coil 21C is wound around the stator core 21B, and an alternating current flows through the stator coil 21C, causing the stator 21 (particularly the stator core 21B and the stator coil 21C) to function as an electromagnet.

[0032] The rotor 22 is disposed inside the stator 21 in the radial direction RA. The rotor 22 includes permanent magnets 22A and a shaft 22B. The shaft 22B is the rotation axis of the electric motor 100, extending along the axial direction AX through the center of the entire electric motor 100 in the radial direction RA. A plurality of the permanent magnets 22A are disposed at intervals in the circumferential direction. The number of the permanent magnets 22A is arbitrary, and may be any of 2, 4, 6, 8, or 12, for example. The permanent magnets 22A interact with an electromagnet formed by the stator core 21B and the stator coil 21C, causing the entire rotor 22 to rotate around the shaft 22B.

[0033] In the electric motor 100, the rolling bearing 10 is installed between the stator 21 and the rotor 22. More specifically, the shaft 22B of the rotor 22 is fitted into the inner ring 11 of the rolling bearing 10. This fixes the inner ring 11 to the shaft 22B. This allows the inner ring 11 to rotate together with the rotor 22. Furthermore, the outer ring 12 of the rolling bearing 10 is fitted into the inner wall surface of the stator yoke 21A of the stator 21. This fixes the outer ring 12 to the stator 21. This prevents the outer ring 12 from rotating and keeps it stationary at all times.

[0034] The conductive brush 30 is a member that supplies power to the stator 21. The conductive brush 30 includes a brush 31 and a fixing portion 32. The brush 31 has a positive side brush 31a and a negative side brush 31b. The positive side brush 31a and the negative side brush 31b contact the shaft 22B. The fixing portion 32 fixes the brush 31 to the stator yoke 21A.

[0035] In addition to the above, the electric motor 100 preferably includes an inverter device 40. The inverter device 40 controls, for example, the rotation speed of the rotor 22 included in the electric motor 100. By controlling the rotation speed of the rotor 22, the power consumption of the entire electric motor 100 including the rotor 22 can be reduced.

[0036] Figure 3 is an equivalent circuit in which each component of a rolling bearing is likened to an electrical element. Referring to Figure 3, by likening each member constituting the rolling bearing 10, such as the inner ring 11, to an element, a virtual electrical circuit 50 can be created, for example, on a computer. The electrical circuit 50 is constructed on a computer in accordance with the design values ​​(internal specifications of the bearing) of each member of the rolling bearing 10 of this embodiment. To make this easier to visualize, the rolling bearing 10 is shown in Figure 3 by a dotted line, overlapping with the elements constituting the electrical circuit 50.

[0037] In the virtual electric circuit 50, the resistance component R1 of the inner ring 11, the resistance component R2 of the outer ring 12, and the inductive component L2 of the housing of the electric motor 100, which are the above-mentioned "elements," are connected in series. Between these, a first parallel connection part of the resistance component Ra1 and the capacitance component Ca1, a resistance component R3 of the rolling element 13, and a second parallel connection part of the resistance component Ra2 and the capacitance component Ca2 are connected in series.

[0038] In the first parallel connection section described above, the resistance component Ra1 is the electrical resistance due to the lubricant LQ between the inner ring 11 and the rolling elements 13. The capacitance component Ca1 is the electrical capacitance due to the lubricant LQ between the inner ring 11 and the rolling elements 13. A switch S1 is connected in parallel to the first parallel connection section. The switch S1 turns on when the voltage applied to the lubricant LQ between the inner ring 11 and the rolling elements 13 exceeds a certain value (dielectric breakdown voltage). The switch S1 contains a resistance component Ra11 of the lubricant LQ at the time of dielectric breakdown.

[0039] In the second parallel connection section described above, the resistance component Ra2 is the electrical resistance due to the lubricant LQ between the outer ring 12 and the rolling elements 13. The capacitance component Ca2 is the electrical capacitance due to the lubricant LQ between the outer ring 12 and the rolling elements 13. A switch S2 is connected in parallel to the second parallel connection section. The switch S2 turns on when the voltage applied to the lubricant LQ between the outer ring 12 and the rolling elements 13 exceeds a certain value (dielectric breakdown voltage). The switch S2 contains a resistance component Ra12 of the lubricant LQ at the time of dielectric breakdown.

[0040] The AC voltage V applied to the rolling bearing 10 is applied to the resistance component R1. In other words, a potential V relative to the ground potential is applied to the rolling bearing 10. However, between the ground potential and the resistance component R1, as shown in Figure 3, an inductive component L5 and a resistance component R5 of the shaft 22B etc., and an inductive component L6 and a resistance component R6 outside the rolling bearing 10 all exist in series.

[0041] FIG. 4 is a graph showing an example of the results of a simulation using the electric circuit of FIG. 3. Referring to FIG. 4, a voltage is applied to a virtual electric circuit 50 shown in FIG. 3, which is created on a computer based on the internal specifications of the rolling bearing 10, to cause a current to flow. For example, the voltage applied to the electric circuit 50 by the user is shown in the graph as "power supply voltage." This value corresponds to the applied voltage "V" in FIG. 3. The value of the current flowing through each element (resistance component Ra12 or resistance component Ra11) in the electric circuit 50 at this time is shown in the graph as "bearing current." The value of the voltage applied to the electric circuit 50 at this time is also shown in the graph as "bearing voltage." This allows the current and voltage values ​​flowing through each element in FIG. 3 to be calculated. These values ​​are shown in FIG. 4 as "bearing voltage" and "bearing current." The "bearing voltage" and "bearing current" are output values ​​obtained by calculation based on the user's usage conditions input into the electric circuit 50.

[0042] 2, the inverter device 40 is merely shown as being connected to the electric motor 100 from the perspective of schematically showing that it is electrically connected to the electric motor 100 and can control the electric motor 100. In other words, the manner in which the inverter device 40 is connected to the electric motor 100 in FIG. 1 does not necessarily represent the actual appearance. The same applies to the electric circuit 50 in FIG. 3. In FIG. 2, the electric circuit 50 is simply given a symbol with an arrow pointing to the rolling bearing 10 in order to schematically show that this is an equivalent circuit of the rolling bearing 10 in the electric motor 100.

[0043] (Method of designing rolling bearing 10) Fig. 5 is a flowchart showing an outline of a design method for a rolling bearing according to this embodiment. Referring to Fig. 5, first a formula preparation step (S10) is performed. That is, a formula is prepared that can determine whether or not electrolytic corrosion can be suppressed in a rolling bearing 10 that includes an inner ring 11, an outer ring 12, a plurality of rolling elements 13 between the inner ring 11 and the outer ring 12, and a lubricant LQ. If this formula is, for example, F = f(α, β, γ, δ)…(1) is.

[0044] Next, the configurations of the inner ring 11, outer ring 12, and multiple rolling elements 13 are determined (S20) based on the conditions (rotation speed, load, AC voltage, etc.) that are previously obtained and input by the user when using the rolling bearing 10. This will be described in detail below.

[0045] Fig. 6 is a flowchart showing an outline of the rolling bearing mode determination step (S20) in the rolling bearing design method according to this embodiment. Referring to Fig. 6, the determination step (S20), which is one step in the design method of Fig. 5, for example, further includes a first parameter calculation step (S21) for determining a parameter β of the lubricant LQ. That is, the determination step (S20) also determines the type of lubricant LQ to be used, among other things. At this time, the lubricant is divided (S21A) and the operating temperature of the electric motor is taken into consideration (S21B). Specific details of these steps will now be described.

[0046] FIG. 7 is a schematic diagram showing a model for calculating lubricant parameters. For ease of explanation, FIG. 7 exaggerates the distance between inner ring raceway surface 11A and raceway surface 13A. Furthermore, to show that rolling element 13 and inner ring 11 form a contact ellipse, the lower end of rolling element 13 and inner ring raceway surface 11A are shown as straight lines extending in the left-right direction. Referring to FIG. 7, in the first parameter calculation step (S21), lubricant LQ is divided (S21A) into two regions: a first region LQ1 and a second region LQ2. First region LQ1 is a portion of lubricant LQ located between inner ring raceway surface 11A and raceway surface 13A in the region where either inner ring raceway surface 11A or outer ring raceway surface 12A (inner ring raceway surface 11A in FIG. 7) contacts raceway surface 13A. The first region LQ1 corresponds to the region of the rolling element 13 closest to the inner ring raceway surface 11A. The first region LQ1 is the region of lubricant LQ between the rolling surface 13A of the rolling element 13 and the inner ring raceway surface 11A, where the two come close to each other and are about to come into elliptical contact due to, for example, their mutual elastic forces. The second region LQ2 is the region of lubricant LQ on the inner ring 11 side other than the first region LQ1. The second region LQ2 is, for example, the region around the first region LQ1 in the axial direction AX (see FIGS. 1 and 2). In the first region LQ1, the lubricant LQ is closer to both the inner ring raceway surface 11A and the raceway surface 13A than in the second region LQ2. Compared to the second region LQ2, the first region LQ1 is subjected to more pressure by being sandwiched between the rolling element 13 and the inner ring raceway surface 11A, which are approaching each other. Taking into consideration that this pressure causes the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant to change between the first region LQ1 and the second region LQ2, each parameter β of the lubricant LQ (volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength) is calculated.

[0047] Furthermore, in consideration of the operating temperature of the motor (S21B), the parameter β of the lubricant LQ is calculated taking into account that each parameter β (volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength) of the lubricant LQ changes depending on the operating temperature of the rolling bearing 10 containing the lubricant LQ. Specifically, it has been found that when the temperature of the lubricant LQ drops from 30°C to 40°C, the dielectric breakdown voltage of the lubricant LQ increases by approximately three to five times, and the discharge crater formed around it becomes larger. Therefore, by taking into account that the value of the parameter β, such as the volume resistivity of the lubricant LQ, changes depending on the temperature of the lubricant LQ, the F value can be accurately calculated using the first formula.

[0048] The mode determination step (S20) further includes a second parameter calculation step (S22) for determining the mechanical parameter α and other parameter constants γ (parameters related to the effect of suppressing electrolytic corrosion of the rolling bearing 10). The mode determination step (S20) further includes a third parameter calculation step (S23) for determining a parameter δ obtained from the usage conditions. The mode determination step (S20) further includes an F-value calculation step (S24).

[0049] In the third parameter calculation step (S23), an output value is obtained by inputting the usage conditions into the electric circuit 50 and performing calculations. This output value is found as the parameter δ obtained from the usage conditions. The electric circuit 50 is a virtual circuit created on a computer or the like, with the components comprising the inner ring 11, outer ring 12, rolling elements 13, and lubricant LQ that make up the rolling bearing 10 treated as elements. The electric circuit 50 may also include components contained in the rolling bearing 10 other than those mentioned above (such as the insulating coating 19 related to the parameter γ). This further improves the accuracy of the calculations.

[0050] The mechanical parameter α, lubricant parameter β, and other parameter constant γ determined in the first parameter calculation step and the second parameter calculation step, as well as the user's usage conditions for the rolling bearing 10, are input to an electric circuit 50 (see FIG. 3). The user's usage conditions for the rolling bearing 10 are, for example, the "power supply voltage" in FIG. 4. As a result, the "bearing voltage" and "bearing current" shown in FIG. 4 are obtained as "output values" from the electric circuit 50. The parameter δ obtained from the usage conditions is determined based on these "bearing voltage" and "bearing current". In other words, the parameter δ obtained from the usage conditions may be the output value itself from the electric circuit 50, or may be a value obtained by further processing this output value.

[0051] Here, the "rotation speed," "load," "AC voltage," and "frequency" of the rolling bearing 10, which are the basis for δ of the above-mentioned parameters α, β, γ, and δ, do not represent the characteristics of the rolling bearing 10 as a physical object, but are in many cases the user's usage conditions. In other words, it is difficult for the manufacturer to change the values ​​of the "rotation speed," "load," and "AC voltage." For this reason, in the mode determination step (S20), a determination is made (S25) based on the arbitrary rotation speed of the inner ring 11 and the outer ring 12, the load applied to the inner ring 11 and the outer ring 12, and the voltage value applied to the rolling bearing 10 (usage conditions) when the user is using the rolling bearing 10, whether the mechanical parameter α, such as the physical shape and dimensions of the rolling bearing 10, the parameter β of the lubricant, and the constant γ of other parameters (such as the conductive brush 30) used for suppressing electrolytic corrosion satisfy the second mathematical formula. That is, the value of F is calculated by substituting the mechanical parameter α, the lubricant parameter β, the constant γ of other parameters, and the parameter δ obtained from the usage conditions into the first formula (S24). It is then determined whether the value of F is 10 or less (S25).

[0052] If the second formula is not satisfied as a result of performing step (S25), step (S20), i.e., steps (S21) to (S25), are repeated while changing the parameters α, β, and γ until the second formula is satisfied. The values ​​of the parameters α, β, and γ are determined based on the values ​​of the parameters α, β, and γ when the second formula is satisfied in step (S25). As a result, the internal specifications of the bearing, such as the inner ring 11, outer ring 12, rolling elements 13, and type and dimensions of the lubricant LQ of the rolling bearing 10, are selected. The presence or absence of an insulating coating 19, which is related to the parameter γ of the rolling bearing 10, is also determined. By the above procedure, F = f(α, β, γ, δ)…(1) The value of F derived from F≦10…(2) The rolling bearing 10 is designed so that:

[0053] As described above, the internal specifications of the bearing that can be controlled during manufacturing are determined by first understanding the intended user's usage conditions and taking them into consideration. The size, surface roughness, shape, and material of the inner ring 11, outer ring 12, and rolling elements 13 are selected based on input conditions determined by the user, such as the rotation speed, load, and applied voltage of the rolling bearing 10. The volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant LQ are also determined. The presence or absence of insulating coating 19 (see Figure 1) on the inner ring rolling surface 11A and outer ring rolling surface 12A, as well as the materials of the conductive brush 30 and sealing member 15, all of which affect the value of δ, are also determined. This allows the value of F in the first formula to be controlled to satisfy the second formula. As a result, electrolytic corrosion and the resulting ridge marks in the rolling bearing 10 can be suppressed.

[0054] However, if the rolling elements 13 were made of ceramic, for example, in order to change the parameter γ related to the effect of suppressing electrolytic corrosion, the occurrence of ridge marks could be suppressed, but costs would increase. Therefore, it is preferable to make the second formula valid by changing the internal bearing specifications: 1) the dimensions and materials of the inner ring 11 and outer ring 12; and 2) the type of rolling elements 13 (excluding the material), or the type of lubricant LQ. In this way, the same effect of suppressing ridge marks as when the rolling elements 13 are made of ceramic can be obtained at a lower cost than by changing the rolling elements 13. This will be explained again in the examples below. Therefore, the procedure is to first consider whether the second formula is valid by changing the internal bearing specifications and lubricant. If the second formula still does not hold, it is preferable to consider changing the constant γ of other parameters that suppress electrolytic corrosion. From the above, the method for manufacturing the rolling bearing 10 in the above embodiment is determined.

[0055] Once the values ​​of parameters α, β, and γ are determined according to parameter δ based on the above design method, the components that make up rolling bearing 10, such as inner ring 11, outer ring 12, rolling elements 13, and lubricant LQ, are actually formed. Then, rolling bearing 10 is manufactured. FIG. 8 is a flowchart outlining a method for manufacturing a rolling bearing according to this embodiment. Referring to FIG. 8, inner ring 11 of rolling bearing 10, such as the deep groove ball bearing shown in FIG. 1, outer ring 12 disposed on its outer periphery, and multiple rolling elements 13 disposed between them so as to roll freely, are prepared (S100). More specifically, this process includes a forming process for each component, a heat treatment process, a finish machining process, and other processes, but detailed descriptions are omitted here. Additionally, components necessary to complete rolling bearing 10 shown in FIG. 1, such as cage 14 and seal member 15, are prepared, along with lubricant LQ.

[0056] In order to form insulating coating 19 on inner ring rolling surface 11A and outer ring rolling surface 12A, a process such as resin coating or injection molding is performed. In addition, to form sealing member 15, a process such as mold molding is performed.

[0057] Next, an assembling step (S200) is performed. Specifically, the inner ring 11, outer ring 12, and plurality of rolling elements 13 formed in step (S100) are respectively combined with a separately prepared cage 14, seal member 15, etc. Furthermore, lubricant LQ is sealed in the gap formed between the inner ring 11 and outer ring 12 and in which the plurality of rolling elements 13 are arranged (S300). The lubricant LQ is supplied into the gap by a commonly known injection method.

[0058] As described above, in the preparation step (S100) in the manufacturing method of rolling bearing 10, the inner ring 11, outer ring 12, multiple rolling elements 13, and lubricant LQ are prepared in the configuration determination step (S20), which is a design step carried out in advance, so that the value of F derived from the first formula satisfies the second formula.

[0059] That is, in the preparation step (S100), the F value is calculated (S24). This is a step in which the values ​​of the above parameters α, β, γ, and δ are substituted into the first mathematical formula, and the value of F is derived from the values. At this time, particularly for the parameter β of the lubricant LQ, the value found by taking steps (S21A) and (S21B) into consideration is substituted into the first mathematical formula.

[0060] (Action and effect) A rolling bearing 10 according to the present disclosure is used in an inverter-controlled motor. The rolling bearing 10 comprises an inner ring 11, an outer ring 12, a plurality of rolling elements 13, and a lubricant LQ. The outer ring 12 is arranged on the outer peripheral side of the inner ring 11. The plurality of rolling elements 13 are arranged to be able to roll freely between the inner ring 11 and the outer ring 12. The lubricant LQ is sealed in a gap formed between the inner ring 11 and the outer ring 12 and in which the plurality of rolling elements 13 are arranged. For example, when used in an industrial motor, the rotation speed of the rolling bearing 10 during use is 100 rpm or more and 20,000 rpm or less. The voltage applied to the rolling bearing 10 during use is 2 V or more and 100 V or less. If the mechanical parameter is α, the lubricant parameter is β, the constant of the other parameters is γ, and the parameter obtained from the use conditions is δ, then the following first mathematical formula can be obtained: F = f(α, β, γ, δ)…(1) The value of F calculated from the second formula below F≦10…(2) Meet the following.

[0061] An oil film of lubricant LQ is formed between the inner ring 11 and outer ring 12 (race rings) and the rolling elements 13 of a rolling bearing 10 used in an inverter-controlled motor. This oil film can function as a capacitor component. When a voltage applied to this oil film exceeds the breakdown voltage of the oil film, a discharge occurs between the races and the rolling elements. This discharge can cause electrolytic corrosion inside the rolling bearing 10. The size of the discharge vestige caused by electrolytic corrosion is an indicator of whether damage will lead to ridge marks. In this embodiment, it has been newly discovered that the size of the discharge vestige varies depending on the above-mentioned parameters α, β, γ, and δ. It has been discovered that if the rotation speed of a user's rolling bearing 10 during use is 100 rpm or more and 20,000 rpm or less, the voltage applied during use (effective value of AC voltage) is 2 V or more and 100 V or less, and the value of F in the first formula, which is a function of the parameters α, β, γ, and δ, is 10 or less, the size of the discharge vestige will be below a certain value, and the occurrence of ridge marks can be suppressed. By satisfying F≦10, the size of the discharge marks that occur in the rolling bearing 10 can be kept below the maximum allowable value. Therefore, even if the bearing is used under conditions that would cause electrolytic corrosion in a normal bearing, the occurrence of ridge marks can be suppressed.

[0062] In the rolling bearing 10, the oil film parameter Λ of the lubricant LQ may be 3 or less. This reduces the oil film thickness and the voltage at which the oil film breaks down. Therefore, even if the oil film does break down, the discharge traces are smaller. Therefore, the possibility of ridge marks developing is reduced. Furthermore, setting the Λ value to 3 or less reduces the torque of the shaft 25 and rotor 22 on which the rolling bearing 10 is mounted. However, an oil film parameter Λ of 3 or less is a so-called boundary lubrication state, which raises concerns about surface-originated peeling on the rolling surfaces of the raceways and rolling elements. For this reason, it is preferable to set the oil film parameter Λ to 3 or less and use a lubricant LQ that can prevent surface-originated peeling in advance, or to provide a bearing with a surface treatment. In this way, even if a rolling bearing 10 uses a lubricant LQ with a Λ value of 3 or less, which is inherently prone to peeling, it is possible to prevent both ridge marks due to electrolytic corrosion and surface peeling. Therefore, the life of the rolling bearing 10 can be sufficiently extended.

[0063] In the rolling bearing 10, the lubricant LQ may be grease. In this case, the relationship F≦10 derived from the above formula can be satisfied, and the occurrence of ridge marks can be suppressed.

[0064] The above-described rolling bearing 10 further comprises a seal member 15 fitted onto the inner diameter surface of the outer ring and arranged so as to come into contact with the inner ring, and the seal member 15 may be formed from a conductive rubber material. This enhances the effect of reducing electrolytic corrosion and suppresses the occurrence of ridge marks.

[0065] An electric motor 100 according to the present disclosure includes a stator 21 and a rotor 22. The rotor 22 is disposed radially inside the stator 21 and is rotatable. The above-described rolling bearing 10 is installed between the stator 21 and the rotor 22. An inverter device 40 capable of controlling the rotation of the rotor 22 is connected to the electric motor 100. This makes it possible to provide an electric motor 100 that uses a rolling bearing 10 that is less likely to fail due to ridge marks, even when used under conditions that would cause electrolytic corrosion in a normal bearing.

[0066] In a method for designing a rolling bearing according to the present disclosure, a first mathematical formula is prepared (S10) that can determine whether electrolytic corrosion can be suppressed in a rolling bearing 10 that includes an inner ring 11, an outer ring 12 arranged on the outer periphery of the inner ring 11, a plurality of rolling elements 13 arranged freely to roll between the inner ring 11 and the outer ring 12, and a lubricant LQ. Based on the usage conditions of the rolling bearing 10, the configuration of the inner ring 11, the outer ring 12, and the plurality of rolling elements 13 is determined (S20). The first mathematical formula is expressed as follows, where α is a mechanical parameter of the inner ring 11, the outer ring 12, and the plurality of rolling elements 13, β is a parameter of the lubricant, γ is a constant for the other parameters, and δ is a parameter obtained from the usage conditions (by the user): F = f(α, β, γ, δ)…(1) The determining step (S20) is carried out by using the following second formula according to the use conditions: F≦10…(2) The method includes a step of determining whether the following is satisfied.

[0067] The parameter δ obtained from the usage conditions is a simulated value of the bearing current, etc., calculated based on the user's usage conditions (applied voltage, etc.). In this way, it is possible to design the rolling bearing 10 so that electrolytic corrosion and ridge marks are less likely to occur. In addition, by doing so, it is possible to evaluate whether the designed rolling bearing 10 is prone to electrolytic corrosion and ridge marks, depending on the value of F. This makes it possible to avoid providing over-specified rolling bearings 10 (rolling bearings 10 that are prone to ridge marks due to electrolytic corrosion) that have traditionally relied on empirical intuition.

[0068] In the above-described rolling bearing design method, the determining step (S20) includes a first parameter calculation step (S21) of determining a lubricant parameter β. In the first parameter calculation step (S21), the lubricant LQ is divided into a first region LQ1 of the lubricant LQ located between first raceway surfaces 11A, 12A, which are the raceway surfaces of at least one of inner ring 11 and outer ring 12, and second raceway surface 13A, which is the raceway surface of rolling element 13, in a region where these surfaces approach each other to form an ellipse, and a second region LQ2 of the lubricant LQ located outside the first region, and the lubricant parameter β is calculated taking into account that the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of first region LQ1 change with pressure compared to those of second region LQ2. This method obtains more accurate results, enabling the provision of a more suitable, lower-cost bearing.

[0069] In other words, the method for designing a rolling bearing according to this embodiment may have the following features, as will be specifically explained in Example 4 onwards, which will be described later. In the method for designing a rolling bearing according to the present disclosure, a first mathematical formula is prepared (S10) that can determine whether electrolytic corrosion can be suppressed in a rolling bearing 10 that includes an inner ring 11, an outer ring 12 arranged on the outer periphery of the inner ring 11, a plurality of rolling elements 13 arranged freely to roll between the inner ring 11 and the outer ring 12, and a lubricant LQ. The configurations of the inner ring 11, the outer ring 12, and the plurality of rolling elements 13 are determined based on the usage conditions of the rolling bearing 10 (S20). The first mathematical formula is expressed as follows, where α is a mechanical parameter of the inner ring 11, the outer ring 12, and the plurality of rolling elements 13, β is a parameter of the lubricant, γ is a constant for the other parameters, and δ is a parameter obtained from the usage conditions (by the user): F = f(α, β, γ, δ)…(1) The determining step (S20) is carried out by using the following second formula according to the use conditions: F≦10…(2) The determining step (S20) includes a step of determining whether the following expression is satisfied. The determining step (S20) includes a first parameter calculation step (S21) of determining a lubricant parameter β. In the first parameter calculation step (S21), in the region where first rolling surfaces 11A, 12A, which are the rolling surfaces of at least one of inner ring 11 and outer ring 12, and second rolling surface 13A, which is the rolling surface of rolling element 13, come close to form an ellipse, lubricant LQ is divided into a first region LQ1 of lubricant LQ located between first rolling surfaces 11A, 12A and second rolling surface 13A, and a second region LQ2 of lubricant LQ outside the first region. In a virtual electrical circuit 50 corresponding to rolling bearing 10, characteristic values ​​of virtual elements corresponding to first region LQ1 and second region LQ2 are determined. In this way, more accurate results can be obtained, and a more suitable and less expensive bearing can be provided. In other words, since the parameter β of the lubricant LQ can be obtained with higher accuracy, it is possible to provide a rolling bearing 10 that can more reliably suppress ridge marks caused by electrolytic corrosion.

[0070] In the above-described rolling bearing design method, in the first parameter calculation step (S21), the lubricant parameter β is calculated taking into consideration that the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant LQ change depending on the operating temperature of the rolling bearing 10 (electric motor 100) containing the lubricant LQ. In this way, more accurate results can be obtained, and a more appropriate and lower-cost bearing can be provided.

[0071] In the above-mentioned rolling bearing design method, the determining step (S20) includes a second parameter calculation step (S22) of determining the mechanical parameter α and a constant γ of other parameters. The determining step (S20) includes a third parameter calculation step (S23) of determining a parameter δ obtained from the above-mentioned (user-defined) usage conditions. The determining step (S20) calculates a first mathematical formula from the mechanical parameter α, the lubricant parameter β, and the constant γ of other parameters obtained in the first parameter calculation step (S21) and the second parameter calculation step (S22), and the parameter δ obtained from the usage conditions. F = f(α, β, γ, δ)…(1) The method further includes a step (S24) of calculating the value of F obtained by the above formula. In the third parameter calculation step (S23), the parameter δ obtained from the usage conditions is found based on the output value obtained by inputting the above usage conditions (by the user) into a virtual electric circuit 50, which is assembled by treating the components consisting of inner ring 11, outer ring 12, rolling elements 13, and lubricant LQ that make up rolling bearing 10 as elements. In the step (S24) of calculating the value of F, the mechanical parameter α, the lubricant parameter β, the constant γ of the other parameters, and the parameter δ obtained from the usage conditions are substituted into the first mathematical formula.

[0072] This allows for easy computer-based design changes to the rolling bearing 10. It also allows for easy calculation of the F value for the redesigned rolling bearing 10. Furthermore, this design method also allows for calculation of the F value when the values ​​of each element in the electrical circuit are changed. Therefore, for example, it is possible to propose to the user the optimal rolling bearing 10 for the user's operating conditions, taking into account factors such as the rate of reduction in the F value when switching from a standard bearing (without the insulating coating 19) to an insulating-coated bearing (with the insulating coating 19). In other words, it is possible to propose low-cost, optimal design specifications for the rolling bearing 10 for each user that suppress electrolytic corrosion and the resulting ridge marks. This enables smaller design changes to be made without changing the entire rolling bearing 10. Specifically, for example, it is possible to optimize the bearing model number or the type of lubricant LQ contained in the rolling bearing 10. Small design changes are low-cost. When making small changes, the parameter to be changed may be β, but is not limited to this and may be the internal bearing specifications α, the insulating coating δ, or the like.

[0073] In the above-mentioned method for designing a rolling bearing, the determining step (S20) includes a judging step (S25) for calculating a second mathematical formula F≦10…(2) This makes it possible to design a rolling bearing 10 that can reliably suppress electrolytic corrosion.

[0074] In a manufacturing method of a rolling bearing according to the present disclosure, an inner ring 11, an outer ring 12 arranged on the outer periphery of the inner ring 11, a plurality of rolling elements 13 arranged freely to roll between the inner ring 11 and the outer ring 12, and a lubricant LQ are prepared (S100). The inner ring 11, outer ring 12, and a plurality of rolling elements 13 are combined (S200). The lubricant LQ is sealed in a gap formed between the inner ring 11 and the outer ring 12 and in which the plurality of rolling elements 13 are arranged (S300). The inner ring 11, outer ring 12, a plurality of rolling elements 13, and lubricant LQ are calculated using the following first mathematical formula, where α is a mechanical parameter, β is a lubricant parameter, γ is a constant for other parameters, and δ is a parameter obtained from the usage conditions of the rolling bearing 10: F = f(α, β, γ, δ)…(1) The value of F derived from the second formula below F≦10…(2) is prepared to satisfy.

[0075] By satisfying F≦10, which is derived from the above formula, it is possible to keep the size of the discharge marks that occur in the rolling bearing 10 below the maximum allowable value. As a result, it is possible to provide a rolling bearing 10 that can suppress the occurrence of ridge marks even when used under conditions that would cause electrolytic corrosion in a normal bearing.

[0076] In the above-mentioned method for manufacturing a rolling bearing, in the preparation step (S100), the mechanical parameter α, lubricant parameter β, constant γ of other parameters, and the types of inner ring 11, outer ring 12, and rolling elements 13 are selected according to the desired rotation speed of inner ring 11 and outer ring 12 during use, the load on inner ring 11 and outer ring 12, and the voltage value applied to rolling bearing 10. In this way, it is possible to manufacture and provide a rolling bearing 10 that has the above parameters and optimal internal bearing specifications at low cost for each user, in consideration of the user's conditions such as rotation speed, load, and applied voltage, in order to suppress the occurrence of electrolytic corrosion and the resulting ridge marks. [Example]

[0077] A study was conducted to compare the values ​​of F obtained using the first formula and the presence or absence of ridge marks for rolling bearings 10 included in the testing machine for the electric motor 100 in Figure 2: a "standard bearing," a "hybrid bearing," and an "insulated-coated bearing with an altered γ value according to this embodiment (hereinafter, "insulated-coated bearing"). The evaluation item was the presence or absence of ridge marks as determined by observing the rolling surface. The definitions of these bearings have been described above. The "standard bearing" is a comparative bearing that does not have an insulating coating 19 and has metallic rolling elements 13, and does not have the features of this embodiment. The "hybrid bearing" differs from the standard bearing only in that the rolling elements 13 are made of ceramic. The "insulated-coated bearing" differs from the standard bearing only in that the value of γ is altered by providing an insulating coating 19 on the rolling surface, as shown in Figure 1. The evaluation conditions for this embodiment are shown in Table 1 below.

[0078] [Table 1]

[0079] The F value and the presence or absence of ridge marks for each bearing are shown in Table 2. Note that the lubricant for the standard bearings in Table 2 was oil, more specifically, the lubricant "oil" was DURASYN (registered trademark) 166 POLYALPHAOLEFINS.

[0080] [Table 2]

[0081] As can be seen from Table 2, for standard bearings, the value of F exceeds 10 and does not satisfy the second formula. As a result, ridge marks occur. With conventional standard bearings that do not have the features of this embodiment, the threshold for determining whether or not ridge marks occur is unknown, and it is often unclear how to improve the situation. As shown in Table 2, if a large-scale measure such as using a hybrid bearing is taken, the value of F can be reduced to 0, and ridge marks can be suppressed. Although using a hybrid bearing is expensive, it is the safest, and therefore the most reliable, way to suppress ridge marks. In the past, when it was unclear how to improve the situation, ridge marks were suppressed using this method, but it is desirable to suppress ridge marks using a smaller-scale, lower-cost measure.

[0082] Therefore, by using this embodiment, an insulated-coated bearing is used, which has an insulating coating 19, and the γ value is changed from 0.7 for a standard bearing to 0.3 for the insulated-coated bearing. This reduces the value of F from 15 to 6 as shown in Table 2, making it possible to satisfy the second formula at a lower price than a hybrid bearing. As a result, no ridge marks occurred in the insulated-coated bearing. In this way, by using an insulated-coated bearing, it is possible to suppress ridge marks to the same extent as a hybrid bearing, at a lower price than a hybrid bearing.

[0083] The values ​​of F in Table 2 were found by calculating the capacitance component due to the oil film between the inner ring 11 and the rolling elements 13 of various bearings in a virtual electric circuit 50 in the electric motor 100, which includes this capacitance component as a capacitance component in Figure 3. In particular, electric motors 100 that include rolling bearings 10 with insulating coatings 19, such as insulating-coated bearings, have a capacitance component due to the insulating coating 19 in addition to the capacitance component due to the oil film. In the case of insulating-coated bearings, the calculation was performed using a series-connected circuit of the oil film capacitance component and the insulating coating 19 capacitance component. [Example]

[0084] In Example 1, the value of parameter γ was controlled (changed), whereas in Example 2, the lubricant parameter β was controlled (changed). That is, an investigation was conducted to compare the value of F in the first formula and the presence or absence of ridge marks when the type of lubricant LQ of the rolling bearing 10 was changed.

[0085] The "standard bearings" are exactly the same as the "standard bearings" in Example 1. The "standard bearings" in Example 2 used oil (DURASYN (registered trademark) 166 POLYALPHAOLEFINS) as the lubricant LQ. The "insulating coated bearings" are exactly the same as the "insulating coated bearings" in Example 1. The lubricant LQ for the "insulating coated bearings" was the same oil as for the "standard bearings." In contrast, the lubricant LQ for the "β value-changed bearings" was changed to grease (Multemp SRL, manufactured by Kyodo Yushi). Table 3 shows the F values ​​and the presence or absence of ridge marks for each bearing.

[0086] [Table 3]

[0087] Table 3 shows that compared to standard bearings where the lubricant LQ is oil, β-value-modified bearings, in which the lubricant LQ has been changed to grease, were able to achieve ridge mark suppression effects while keeping the value of F in the first formula at 10 or less. In this way, by using β-value-modified bearings, ridge marks can be suppressed to the same extent as with insulated-coated bearings, at an even lower price than insulated-coated bearings.

[0088] In this embodiment, in the β value variable bearing, if the type of lubricant LQ changes and the lubricant parameter β changes, the dielectric constant of the oil film (lubricant) between the inner ring 11 etc. and the rolling element 13, the thickness of the oil film, and the breakdown voltage of the oil film will change.

[0089] In this embodiment, the dielectric constant and thickness of the oil film change the value of the oil film's capacitance component on the electric circuit 50. The breakdown voltage of the oil film changes the threshold value of switches S1 and S2 (see FIG. 3), which switch whether the oil film acts as capacitance components Ca1 and Ca2 (see FIG. 3) or as resistance components Ra11 and Ra12 at the time of breakdown of the oil film. A virtual circuit (e.g., electric circuit 50: see FIG. 3) in which the lubricant LQ is changed in this way is assumed. The F value is calculated using this electric circuit 50. As a result, in this embodiment, ridge marks were suppressed when the F value was 10 or less, as shown in Table 3.

[0090] Conventional countermeasures have involved confirming the suppression of ridge marks on insulated coated bearings and other bearings through empirical information or experiments, and then proposing the conditions for doing so. However, the conditions of this embodiment (this example) make it possible to narrow down the countermeasure methods, eliminating the need for many of the verification experiments that were previously conducted empirically. Furthermore, because countermeasures for ridge mark occurrence can be selected theoretically, they can be explained accurately to users. [Example]

[0091] In Example 1, the value of parameter γ was controlled (changed), and in Example 2, the lubricant parameter β was controlled (changed). In contrast to these, in Example 3, the value of the oil film parameter Λ was changed to 3. Specifically, both the rotation speed of the testing machine (inner ring 11, etc.), which is determined by the user among the mechanical parameters α, and the lubricant parameter β were controlled (changed). In other words, an investigation was conducted in which the rotation speed of the inner ring 11, etc. of the rolling bearing 10, and the type of lubricant LQ were changed to a type different from that in Example 2, and the value of F in the first formula and the presence or absence of ridge marks were compared.

[0092] The "standard bearing" is exactly the same as the "standard bearing" in Example 1. In the standard bearing, the rotation speed of the inner ring 11 and the like is 1600 rpm, and the lubricant LQ has a viscosity of 30 mm 2 / s oil was used. The surface roughness of the inner ring 11 and outer ring 12 was 0.02 μm. As a result, the value of the oil film parameter Λ of the standard bearing was approximately 6.5. The "insulating coated bearing" is exactly the same as the "insulating coated bearing" in Example 1. The rotation speed of the insulating coated bearing was also 1600 rpm, and the lubricant LQ was the same oil as the standard bearing. The surface roughness of the inner ring 11 and outer ring 12 was 0.02 μm. As a result, the value of the oil film parameter Λ of the insulating coated bearing was approximately 6.5. In contrast, a low-viscosity oil was used as the lubricant LQ for the "oil film parameter Λ-changed bearing." The viscosity of the low-viscosity oil was 25 mm 2 / s. The rotation speed of the inner ring 11 and other components of the bearing with modified oil film parameter Λ was set to 400 rpm, and the surface roughness of the inner ring 11 and outer ring 12 was 0.02 μm. This is because the rolling surfaces of the inner ring 11 and outer ring 12 were surface treated. Based on the above, the value of the oil film parameter Λ for the standard bearing was set to 3. Table 4 shows the values ​​of F and the presence or absence of ridge marks for each bearing.

[0093] [Table 4]

[0094] Table 4 shows that in comparison with a standard bearing where the lubricant LQ is oil, the lubricant LQ was changed to a low-viscosity oil, the rotational speed was reduced to 400 rpm, and the oil film parameter Λ value was reduced to 3. This resulted in a bearing with an oil film parameter Λ modification that was able to suppress ridge marks while keeping the value of F in the first equation at 10 or less. In this way, by using a bearing with an oil film parameter Λ modification, it is possible to suppress ridge marks to the same extent as an insulation-coated bearing, at an even lower price than an insulation-coated bearing.

[0095] In this example, the oil film parameter Λ of the lubricant LQ was changed to 3, resulting in a mixed lubrication state. Mixed lubrication is a state in which fluid lubrication and boundary lubrication coexist. Fluid lubrication occurs when a large amount of liquid or gas is present between two solid surfaces, and the fluid pressure within the film supports the load. Boundary lubrication is a state in which an adsorption film, rather than an oil film, physically and chemically supports the load. In other words, boundary lubrication occurs when the oil film is not stable and there are areas where the rolling surface and the rolling element are in contact. Therefore, the lubricant LQ between the inner ring 11 and the rolling element 13 does not form a stable oil film. In other words, because the rolling element 13 and the inner ring rolling surface 11A are in contact, dielectric breakdown may be less likely to occur in the oil film between them. Even if dielectric breakdown does occur, the oil film is thin, resulting in small discharge marks and less likely to form ridge marks.

[0096] In this embodiment, a virtual circuit (for example, electric circuit 50: see FIG. 3) is assumed in which the rolling bearing 10 acts as a resistor (resistance component R1, etc.: see FIG. 3) on the electric circuit 50. The F value is calculated using this electric circuit 50. As a result, in this embodiment, ridge marks were suppressed when the F value was 10 or less, as shown in Table 3.

[0097] Conventional countermeasures have been to confirm, through empirical information or experiments, that the occurrence of ridge marks in insulating coated bearings and the like can be suppressed, and then to propose the conditions for doing so. However, according to the conditions of this embodiment (the present example), by achieving a so-called boundary lubrication state in which the oil film parameter Λ is 3, it is possible to obtain both the effect of preventing ridge marks caused by electrolytic corrosion and the effect of preventing surface peeling, and it is possible to provide a rolling bearing 10 with a sufficiently long life. [Example]

[0098] This example describes the results of an investigation into a method for determining values ​​such as the electrical resistance of the lubricant LQ in FIG. 3 in more detail than in the embodiment for the electrical circuit 50 in FIG. 3 corresponding to the rolling bearing 10 in FIG. 1. FIG. 9 is a schematic diagram of a model corresponding to the rolling bearing in FIG. 1 that was used in the first parameter calculation step in Example 4. Referring to FIG. 9, Example 4 uses the standard rolling bearing 10 in FIG. 1 as a model. The first parameter calculation step (S21) in FIG. 6 is performed based on this model. At this time, characteristic values ​​of virtual elements that correspond to the first region LQ1 and second region LQ2 of the lubricant LQ are calculated. The characteristic values ​​of each virtual element are the value of electrical resistance and the value of capacitance component. The characteristic values ​​are calculated by measurement or calculation (estimation).

[0099] For ease of explanation, in FIG. 9, as in FIG. 7, the spacing between some components is exaggerated to make it appear slightly different from the actual product. The same applies to the schematic diagrams of each model described below. The first region LQ1 and second region LQ2 in FIG. 9 are the same as in FIG. 7. The first region LQ3 in FIG. 9 is basically the same as the first region LQ1. The first region LQ3 corresponds to the region of the rolling element 13 closest to the outer ring rolling surface 12A. The first region LQ3 is a region of lubricant LQ located between the rolling surface 13A of the rolling element 13 and the outer ring rolling surface 12A, where the two come close to each other and are about to come into elliptical contact due to, for example, their mutual elastic forces. The second region LQ4 is a region of lubricant LQ on the outer ring 12 side other than the first region LQ3. The second region LQ4 is, for example, a region around the first region LQ3 in the axial direction AX (see FIGS. 1 and 2).

[0100] FIG. 10 is an equivalent circuit in which the components of the rolling bearing in FIG. 9 are likened to electrical elements. Referring to FIG. 10, a virtual electrical circuit 50, which is an equivalent circuit similar to that in FIG. 3, is shown. The first region LQ1 of the lubricant LQ is the region surrounded by the dotted line (the region forming the contact ellipse). The first region LQ1 includes, as likened elements, a resistance component Ra1A, a capacitance component Ca1A, a switch S1A, and a resistance component Ra11A. The resistance component Ra1A is the electrical resistance due to the first region LQ1 between the inner ring 11 and the rolling element 13. The capacitance component Ca1A is the electrical capacitance due to the first region LQ1 between the inner ring 11 and the rolling element 13. The resistance component Ra1A and the capacitance component Ca1A are connected in parallel, and the switch S1A is connected in parallel to them. The switch S1A corresponds to the switch S1 in FIG. 1. The switch S1A includes the resistance component Ra11A of the first region LQ1 at the time of dielectric breakdown.

[0101] The second region LQ2 of the lubricant LQ is the region surrounded by the dotted line (the region other than the contact ellipse forming region). The second region LQ2 is connected in parallel to the first region LQ1. The second region LQ2 includes, as analogous elements, a resistance component Ra1B, a capacitance component Ca1B, a switch S1B, and a resistance component Ra11B. The resistance component Ra1B is the electrical resistance due to the second region LQ2 between the inner ring 11 and the rolling element 13. The capacitance component Ca1B is the electrical capacitance due to the second region LQ2 between the inner ring 11 and the rolling element 13. The resistance component Ra1B and the capacitance component Ca1B are connected in parallel, and the switch S1B is connected in parallel to them. The switch S1B corresponds to the switch S1 in Figure 1. The switch S1B includes the resistance component Ra11B of the second region LQ2 at the time of dielectric breakdown.

[0102] The first region LQ3 of the lubricant LQ is the region surrounded by the dotted line (the region forming the contact ellipse). The first region LQ3 includes, as analogous elements, a resistance component Ra2A, a capacitance component Ca2A, a switch S2A, and a resistance component Ra12A. The resistance component Ra2A is the electrical resistance due to the first region LQ3 between the outer ring 12 and the rolling element 13. The capacitance component Ca2A is the electrical capacitance due to the first region LQ3 between the outer ring 12 and the rolling element 13. The resistance component Ra2A and the capacitance component Ca2A are connected in parallel, and the switch S2A is connected in parallel to them. The switch S2A corresponds to the switch S1 in Figure 1. The switch S2A includes the resistance component Ra12A of the first region LQ3 at the time of dielectric breakdown.

[0103] The second region LQ4 of the lubricant LQ is the region surrounded by the dotted line (the region other than the contact ellipse forming region). The second region LQ4 is connected in parallel to the first region LQ3. The second region LQ4 includes, as analogous elements, a resistance component Ra2B, a capacitance component Ca2B, a switch S2B, and a resistance component Ra12B. The resistance component Ra2B is the electrical resistance due to the second region LQ4 between the outer ring 12 and the rolling element 13. The capacitance component Ca2B is the electrical capacitance due to the second region LQ4 between the outer ring 12 and the rolling element 13. The resistance component Ra2B and the capacitance component Ca2B are connected in parallel, and the switch S2B is connected in parallel to them. The switch S2B corresponds to the switch S1 in Figure 1. The switch S2B includes the resistance component Ra12B of the second region LQ4 at the time of dielectric breakdown.

[0104] 10 also shows, as in Fig. 3, a resistance component R2 of the outer ring 12, a resistance component R3 of the rolling element 13, an inductive component L2 of the housing of the electric motor 100, an inductive component L5 of the shaft 22B, and a resistance component R5 of the shaft 22B. Each of these components is connected in series with the parallel connection portion of the first region LQ1 and the second region LQ2 and the parallel connection portion of the first region LQ3 and the second region LQ4.

[0105] 10 mainly shows the equivalent circuit of the lubricant LQ, and therefore omits the resistance component R1 of the inner ring 11, the inductive component L6 outside the rolling bearing 10, and the resistance component R6.

[0106] The following describes, as an example, how to determine the values ​​of each element in the portion of the lubricant LQ between the outer ring 12 and the rolling elements 13 (first region LQ3 and second region LQ4). However, the method for determining the values ​​of each element in the portion of the lubricant LQ between the inner ring 11 and the rolling elements 13 (first region LQ1 and second region LQ2) is similar to the method described below.

[0107] 9 and 10, the values ​​of the resistance components Ra2A and Ra2B are determined by either the following first or second method. The determined values ​​are approximately several MΩ (for example, 1 MΩ) or more.

[0108] In the first method, values ​​measured by a tester or the like under each condition are determined as the characteristic values ​​of the resistance components Ra2A and Ra2B.

[0109] As a second method, the value of R obtained using the following equation (3) is estimated as the characteristic value of the resistance components Ra2A and Ra2B.

[0110]

number

[0111] Rv(T, P) in equation (3) is the volume resistivity Rv of the lubricant, which is determined by a function of temperature T and pressure P. Roughly speaking, the higher the temperature T, the higher the volume resistivity Rv. Roughly speaking, the higher the pressure P, the lower the volume resistivity Rv.

[0112] In equation (3), S is the area of ​​the lubricant oil film. If the resistance component is Ra2A, the area S is the area of ​​the contact ellipse. If the resistance component is Ra2B, the area S is the value obtained by subtracting the area of ​​the actual contact ellipse from the area of ​​the virtual ellipse when the major and minor axes of the contact ellipse are 1.5 times those of the actual contact ellipse. d in equation (3) is the thickness of the lubricant oil film.

[0113] The temperature T in equation (3) is the operating temperature of the rolling bearing 10. The pressure P in equation (3) is the pressure applied to each region of the lubricant. In the case of the resistance component Ra2A, the pressure P is the surface pressure of the lubricant calculated from the load of the rolling bearing 10. In the case of the resistance component Ra2B, the pressure P is normal pressure that is not dependent on the load.

[0114] Next, the values ​​of the capacitance components Ca2A and Ca2B are determined by either the following first or second method. The determined values ​​are approximately several tens of pF to several hundreds of pF (for example, 10 pF to 500 pF).

[0115] In the first method, values ​​measured under each condition by an impedance analyzer or the like are determined as the characteristic values ​​of the capacitance components Ca2A and Ca2B.

[0116] As a second method, the value of C obtained using the following equation (4) is estimated as the characteristic value of the capacitance components Ca2A and Ca2B.

[0117]

number

[0118] In equation (4), ε0 is the dielectric constant of a vacuum, and ε0 = 8.854187816E-12. ε(T, P) in equation (4) is the relative dielectric constant ε of the lubricant, which is determined by a function of temperature T and pressure P. The value of the relative dielectric constant ε is approximately between 3 and 5. However, as the temperature T increases, the value of the relative dielectric constant ε increases. Also, as the pressure P increases, the value of the relative dielectric constant ε decreases.

[0119] In equation (4), S is the area of ​​the opposing pair of electrodes that constitute the capacitance, which is assumed to correspond to each region of the lubricant. For capacitance component Ca2A, area S is the area of ​​the contact ellipse. For capacitance component Ca2B, area S is the value obtained by subtracting the area of ​​the actual contact ellipse from the area of ​​the imaginary ellipse when the major and minor axes of the contact ellipse are 1.5 times those of the actual contact ellipse. In other words, area S in equation (4) is equal to area S (the area of ​​the oil film) in equation (3).

[0120] In equation (4), d is the thickness of the lubricant oil film. The oil film thickness d in equation (4) is equal to the oil film thickness d in equation (3). The temperature T in equation (4) is the operating temperature of the rolling bearing 10. The pressure P in equation (4) is the pressure applied to each region of the lubricant. In the case of the volume component Ca2A, the pressure P is the surface pressure of the lubricant calculated from the load of the rolling bearing 10. In the case of the volume component Ca2B, the pressure P is the normal pressure that is not dependent on the load.

[0121] Next, the value of the breakdown voltage Vsh at which the switches S2A and S2B for the first zone LQ3 and the second zone LQ4 on the outer ring side are turned on is determined by either the first or second method below. The value for the switches S1A and S1B for the first zone LQ3 and the second zone LQ4 on the inner ring side is determined in the same way. The determined value is between several volts and a dozen volts (for example, between 1 volt and 15 volts).

[0122] In the first method, a value measured by a tester or the like under each condition is determined as the value of the breakdown voltage Vsh.

[0123] As a second method, the value of Vsh obtained using the following equation (5) is estimated as the value of the breakdown voltage Vsh of the switches S2A and S2B.

[0124]

number

[0125] From equation (5), the value of the breakdown voltage Vsh is determined by the voltage V(P, T, ε, R), which is determined by the pressure P, temperature T, relative dielectric constant ε of the lubricant, and the values ​​of the resistance components Ra2A and Ra2B, and the thickness d of the lubricant oil film. The higher the pressure P, the higher the breakdown voltage Vsh. The higher the temperature T, the lower the breakdown voltage Vsh. The higher the relative dielectric constant ε of the lubricant, the lower the breakdown voltage Vsh. The higher the resistance components Ra2A and Ra2B, the higher the breakdown voltage Vsh. Equation (5) is valid for the lubricant on both the outer and inner ring sides.

[0126] When considering the breakdown voltage Vsh of switch S2A, the pressure P in equation (5) is the surface pressure of the lubricant calculated from the load of rolling bearing 10. When considering the breakdown voltage Vsh of switch S2B, the pressure P is normal pressure that is not dependent on the load.

[0127] The temperature T in equation (5) is the operating temperature of the rolling bearing 10. The value of the relative permittivity ε of the lubricant in equation (5) is the same as ε(T,P) in equation (4). The value of R in equation (5) is the same as the resistance components Ra2A and Ra2B calculated from equation (3). That is, the resistance component Ra2A is used when calculating the breakdown voltage Vsh of the switch S2A in the first region LQ3. Furthermore, the resistance component Ra2B is used when calculating the breakdown voltage Vsh of the switch S2B in the second region LQ4.

[0128] Finally, the values ​​of the resistance components Ra12A and Ra12B at the time of dielectric breakdown are determined by either the following first or second method. The determined values ​​are approximately several Ω (for example, 0.1Ω or more and 5Ω or less).

[0129] In the first method, the breakdown voltage Vsh of the switches S2A and S2B is measured under each condition using an oscilloscope, and the current value I in the switches S2A and S2B when that voltage is applied is used to calculate Vsh / I.

[0130] As a second method, there is also a method in which the resistance components Ra12A and Ra12B are set to 1 Ω as a provisional value.

[0131] (Summary of this Example: Actions and Effects) The design method for a rolling bearing according to the disclosure of this example has basically the same features as the design method for a rolling bearing of embodiment 1. Specifically, it includes some overlapping parts as described above, but has the following features: In the first parameter calculation step (S21), characteristic values ​​(electrical resistance values, electrical capacitance values, and switch breakdown voltage values) of virtual elements that are assumed to correspond to the first regions LQ1, LQ3 and the second regions LQ2, LQ4 in a virtual electric circuit 50 corresponding to the rolling bearing 10 are found.

[0132] The above-described rolling bearing design method has the following features. In a virtual electric circuit 50, the first regions LQ1, LQ3 and the second regions LQ2, LQ4 are connected in parallel. In each of the first regions LQ1, LQ3 and the second regions LQ2, LQ4, resistance components (Ra1A, Ra1B, Ra2A, Ra2B) and capacitance components (Ca1A, Ca1B, Ca2A, Ca2B) are connected in parallel as the above-described virtual elements. The characteristic values ​​of the resistance components (Ra1A, Ra1B, Ra2A, Ra2B) are estimated as shown in equation (3) above from the volume resistivity Rv of the lubricant LQ, which is determined by a function of temperature T and pressure P, the thickness d of the oil film of the lubricant LQ in either the first regions LQ1, LQ3 or the second regions LQ2, LQ4, and the area S of the oil film of the lubricant LQ.

[0133] The design method for the above rolling bearing has the following features: The characteristic values ​​of the capacitance components (Ca1A, Ca1B, Ca2A, Ca2B) are estimated as the above formula (4) from the dielectric constant ε0 of a vacuum, the relative dielectric constant ε of the lubricant which is determined by a function of temperature T and pressure P, the area S of the oil film which is the area where a pair of electrodes which constitute a capacitance regarded as corresponding to either the first region LQ1, LQ3 or the second region LQ2, LQ4 face each other, and the thickness d of the oil film as the lubricant LQ in either the first region LQ1, LQ3 or the second region LQ2, LQ4.

[0134] The design method for the above rolling bearing has the following features. The first regions LQ1, LQ3 and the second regions LQ2, LQ4 each include switches S1A, S1B, S2A, and S2B connected in parallel to a resistance component and a capacitance component. The switches S1A, S1B, S2A, and S2B turn on when the voltage applied to the lubricant LQ exceeds the breakdown voltage Vsh. The breakdown voltage Vsh of the switches S1A, S1B, S2A, and S2B is estimated as shown in equation (5) above from the voltage V, which is determined by the pressure P, temperature T, relative dielectric constant ε of the lubricant, and the values ​​of the resistance components, as well as the thickness d of the lubricant oil film.

[0135] The parameter β of the lubricant LQ is determined based on the resistance components Ra1A, Ra1B, Ra2A, and Ra2B, the capacitance components Ca1A, Ca1B, Ca2A, and Ca2B, the breakdown voltage Vsh, and the like determined as described above. [Example]

[0136] FIG. 11 is a schematic diagram of a model corresponding to the rolling bearing of FIG. 1, used in the first parameter calculation step in Example 5. Referring to FIG. 11, the model corresponding to the rolling bearing 10 of this example is basically the same as that of Example 4 in FIG. 9. For this reason, in FIG. 11, the same components as in FIG. 9 are given the same reference numerals, and their description will not be repeated. However, in the model of the rolling bearing 10 in FIG. 11, an insulating coating 19 is formed on the outer ring 12. In Example 5, a characteristic value of a virtual coating capacitance component that can be compared to the insulating coating 19 in FIG. 11 is found.

[0137] In Figure 11, the insulating coating 19 is shown on the underside of the outer ring 12 (opposite the rolling elements 13) to simplify the positional relationship with the equivalent circuit described below. However, in reality, the insulating coating 19 may be located on the rolling elements 13 side (upper side) of the outer ring 12, as shown in Figure 1. The presence of the insulating coating 19 on either the upper or lower side of the outer ring 12 does not affect the calculation results. Also, Figure 11 shows an example in which the insulating coating 19 is applied to the outer ring 12 as an example. However, even in an example in which the insulating coating 19 is applied to the inner ring 11, the characteristic value of the coating capacitance component can basically be found by the method described below, just as in the case in which the insulating coating 19 is applied to the outer ring 12.

[0138] FIG. 12 is an equivalent circuit in which each component of the rolling bearing in FIG. 11 is likened to an electrical element. Referring to FIG. 12, the configuration of the electrical circuit 50 here is generally similar to the electrical circuit 50 of Example 4 in FIG. 10. However, this example shows the electrical circuit 50 of the entire rolling bearing 10. For this reason, FIG. 12 additionally includes a resistance component R1a in the first region LQ1. Similarly, FIG. 12 includes a resistance component R1b in the second region LQ2. The first region LQ3 includes a resistance component R2a. The second region LQ4 includes a resistance component R2b. Each of these resistance components is connected in series with the parallel connection within each region. The resistance components R1a and R1b in FIG. 12 are the resistance components of the inner ring 11. The resistance components R2a and R2b in FIG. 12 are the resistance components of the outer ring 12.

[0139] 12, a film capacitance component Cc corresponding to the insulating film 19 is connected within the electrical circuit 50 of the rolling bearing 10. A resistance component R20 is further connected between the film capacitance component Cc and the inductive component L2. The resistance component R20 is a resistance component of the housing of the electric motor 100, etc.

[0140] The capacitance component Cc of the insulating coating 19 in this embodiment is determined by either the first or second method below. The determined value is approximately several pF to several hundred pF (for example, 1 pF to 100 pF).

[0141] In the first method, a value measured by an impedance analyzer or the like under each condition is determined as the characteristic value of the film capacitance component Cc.

[0142] As a second method, the value of Cc obtained using the following equation (6) is estimated as the characteristic value of the film capacitance component Cc.

[0143]

number

[0144] In equation (6), ε0 is the dielectric constant of a vacuum, and ε0 = 8.854187816E-12. In equation (6), ε is the relative dielectric constant of the insulating coating 19. In equation (6), a is the inner radius of the insulating coating 19. The inner radius refers to the diameter of the surface of the insulating coating 19 that is not exposed. In other words, if the insulating coating 19 is formed on the outside of the outer ring 12, a refers to the outer diameter of the outer ring 12. In equation (6), b is the outer radius of the insulating coating 19. The outer radius refers to the diameter of the surface of the insulating coating 19 that is exposed. In other words, if the insulating coating 19 is formed on the outside of the outer ring 12, b refers to the sum of the outer diameter of the outer ring 12 and the thickness of the insulating coating 19. In equation (6), L refers to the width of the rolling bearing 10, that is, the left-right dimension of the rolling bearing 10 in FIG. 11.

[0145] (Summary of this Example: Actions and Effects) The method for designing a rolling bearing according to the disclosure of this example has the following features in addition to the features of the methods for designing a rolling bearing of Embodiment 1 and Example 4. In the second parameter calculation step (S22), a characteristic value of a virtual coating capacitance component Cc is found, which is likened to the insulating coating 19 formed on at least one of the inner ring 11 and the outer ring 12 in the virtual electric circuit 50. The characteristic value of the virtual coating capacitance component Cc is estimated as equation (6) above from the permittivity ε0 of a vacuum, the relative permittivity ε of the insulating coating 19, the inner radius a of the insulating coating 19, the outer radius b of the insulating coating 19, and the width L of the rolling bearing 10.

[0146] In this embodiment, in addition to the calculation in the fourth embodiment, the constant γ of another parameter is calculated based on the value of the film capacitance component Cc of the insulating film 19 calculated as described above. [Example]

[0147] FIG. 13 is a schematic diagram of a model corresponding to the rolling bearing of FIG. 1, used in the first parameter calculation step in Example 6. Referring to FIG. 13, the model corresponding to the rolling bearing 10 of this example is basically the same as that of FIG. 9 in Example 4. For this reason, in FIG. 13, the same components as in FIG. 9 are given the same reference numerals, and their description will not be repeated. However, the model of the rolling bearing 10 in FIG. 13 is formed with an earthing mechanism ETH that connects the inner ring 11 and the outer ring 12. The earthing mechanism ETH is formed with a grounding member 60 that conducts electricity between the inner ring 11 and the outer ring 12. In Example 6, the value of the grounding member 60 in FIG. 13 is found.

[0148] Figure 14 is an equivalent circuit in which each component of the rolling bearing in Figure 13 is likened to an electrical element. Note that while Figure 13 shows an earthing mechanism ETH, the earthing mechanism ETH may be one in which the sealing member 15 in Figure 1 is made of conductive rubber. The sealing member 15 in Figure 1 made of conductive rubber becomes the equivalent circuit of the earthing mechanism ETH in Figure 14. Referring to Figure 14, the configuration of the electrical circuit 50 here is roughly the same as the electrical circuit 50 of Example 4 in Figure 10. As with Figure 12, Figure 14 shows the electrical circuit 50 of the entire rolling bearing 10.

[0149] 14, resistance component Re1, capacitance component Ce1, resistance component Re2, and capacitance component Ce2 corresponding to the grounding member 60 of the grounding mechanism ETH are connected in the electric circuit 50 of the rolling bearing 10. In FIG. 13, the grounding mechanism ETH (grounding member 60) is arranged in parallel with the rolling bearing 10. In FIG. 14, the grounding mechanism ETH is arranged in parallel with the electric circuit 50 of the rolling bearing 10.

[0150] In FIG. 14, the earth mechanism ETH includes a parallel connection of a resistance component Re2 and a capacitance component Ce2, and a series connection of a resistance component Re1 and a capacitance component Ce1. The earth mechanism ETH may have such a configuration, but is not limited to this. The earth mechanism ETH may include a capacitance component or an inductive component (not shown). The earth mechanism ETH may include only one of a capacitive component and an inductive component, or may include both. Furthermore, the resistance component and the reactance component (capacitive component or inductive component) may be connected in series or in parallel.

[0151] The value of the grounding member 60 in this embodiment is obtained by the following method. First, the impedance value (complex impedance) of the grounding member 60 is measured using an impedance analyzer. From the measured impedance value, it is determined whether the grounding member 60 has a capacitive component or an inductive component. Specifically, if the reactance value of the complex impedance of the grounding member 60 is positive, it has an inductive component, and if it is negative, it has a capacitive component. The grounding member 60 may have both a capacitive component and an inductive component. If it has both a capacitive component and an inductive component, the capacitive component and inductive component of the grounding member 60 can be resolved by the impedance angle when the complex impedance value of the grounding member 60 is illustrated on a complex plane.

[0152] Whether the grounding member 60 has a series circuit or a parallel circuit of a reactance component (capacitive or inductive component) and a resistive component is determined by the person measuring the impedance value of the grounding member 60. Specifically, assume a configuration in which a resistive component and a capacitive component are connected in series and in parallel, as in the grounding mechanism ETH shown in FIG. 14 . First, the impedance value of the grounding mechanism ETH is measured assuming that the two components are connected in series, such as a resistive component Re1 and a capacitive component Ce1. Second, the impedance value of the grounding mechanism ETH is measured assuming that the two components are connected in parallel, such as a resistive component Re2 and a capacitive component Ce2. These two measurement results are compared, and which value is more likely is determined. Based on the results of this determination, it is determined whether the grounding mechanism ETH includes a series circuit or a parallel circuit of a resistive component and a capacitive component. If the grounding mechanism ETH includes an inductive component, the same method as described above is used to determine whether the grounding mechanism ETH includes a series or parallel connection with the resistive component.

[0153] (Summary of this Example: Actions and Effects) The design method for a rolling bearing according to the disclosure of this example has the following features in addition to the features of the design methods for a rolling bearing of embodiment 1 and example 4. In the second parameter calculation step (S22), the impedance value of the earthing mechanism ETH (grounding member 60) connecting the inner ring 11 and the outer ring 12 is measured. From the impedance value of the earthing mechanism ETH, it is determined whether the earthing mechanism ETH has a capacitive component or an inductive component.

[0154] In the above-described rolling bearing design method, it is determined whether the earthing mechanism ETH has a series circuit or a parallel circuit of a reactance component, which is at least one of a capacitive component and an inductive component, and a resistance component. In the determination, a first impedance value of the earthing mechanism ETH is measured on the assumption that the reactance component and the resistance component are connected in series, and a second impedance value of the earthing mechanism ETH is measured on the assumption that the reactance component and the resistance component are connected in parallel. The first impedance value and the second impedance value are compared.

[0155] In this embodiment, in addition to the calculation in the fourth embodiment, the constant γ of the other parameters is calculated based on the value of the impedance of the earth mechanism ETH calculated as described above.

[0156] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. Unless there is a contradiction, at least two of the embodiments disclosed herein may be combined. The basic scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0157] Various aspects of the present disclosure are summarized below as appendices.

[0158] (Appendix 1) preparing a first formula capable of determining whether or not electrolytic corrosion can be suppressed in a rolling bearing including an inner ring, an outer ring arranged on the outer peripheral side of the inner ring, a plurality of rolling elements arranged to be free to roll between the inner ring and the outer ring, and a lubricant; determining the configuration of the inner ring, the outer ring, and the plurality of rolling elements based on usage conditions of the rolling bearing, The first formula is expressed as follows, where α represents the mechanical parameters of the inner ring, the outer ring, and the plurality of rolling elements, β represents the parameter of the lubricant, γ represents a constant for the other parameters, and δ represents a parameter obtained from the conditions of use: F = f(α, β, γ, δ)…(1) and The determining step is performed by using the following second formula in accordance with the use conditions: F≦10…(2) and determining whether the determining step includes a first parameter calculating step of calculating a parameter β of the lubricant; a first region of the lubricant located between a first rolling surface, which is the rolling surface of at least one of the inner ring and the outer ring, and a second rolling surface, which is the rolling surface of the rolling element, in a region where the first rolling surface and the second rolling surface approach each other to form an ellipse, and a second region of the lubricant located outside the first region, and a second region of the lubricant located outside the first region, and a characteristic value of a virtual element corresponding to the first region and the second region in a virtual electrical circuit corresponding to the rolling bearing is determined.

[0159] (Appendix 2) the first region and the second region are connected in parallel in the virtual electric circuit; In each of the first region and the second region, a resistance component and a capacitance component are connected in parallel as the virtual element, The characteristic value of the resistance component is calculated from the volume resistivity Rv of the lubricant, which is determined by a function of temperature T and pressure P, the thickness d of the oil film of the lubricant in either the first region or the second region, and the area S of the oil film of the lubricant, as follows:

[0160]

number

[0161] The method for designing a rolling bearing according to Supplementary Note 1, wherein the rolling bearing is estimated as follows:

[0162] (Appendix 3) The characteristic value of the capacitance component is calculated from the dielectric constant ε of a vacuum, the relative dielectric constant ε of the lubricant which is determined by a function of the temperature T and the pressure P, the area S of the oil film as the area where a pair of electrodes constituting a capacitance regarded as being in either the first region or the second region face each other, and the thickness d of the oil film as the lubricant in either the first region or the second region,

[0163]

number

[0164] The method for designing a rolling bearing according to Appendix 2, wherein the rolling bearing is estimated as follows:

[0165] (Appendix 4) each of the first region and the second region includes a switch connected in parallel to the resistance component and the capacitance component; the switch is turned on when the voltage applied to the lubricant exceeds a breakdown voltage; The breakdown voltage of the switch is calculated from the voltage V, which is determined by the pressure P, the temperature T, the relative dielectric constant ε of the lubricant, and the resistance component, and the thickness d of the oil film of the lubricant, as follows:

[0166]

number

[0167] 4. The method for designing a rolling bearing according to claim 2 or 3, wherein the rolling bearing is estimated as follows:

[0168] (Appendix 5) 5. A method for designing a rolling bearing according to any one of appendix 1 to 4, wherein in the first parameter calculation step, a parameter β of the lubricant is calculated taking into consideration that the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant change depending on the operating temperature of the rolling bearing containing the lubricant.

[0169] (Appendix 6) The determining step includes a second parameter calculating step of calculating a constant γ of the mechanical parameter α and the other parameters; a third parameter calculation step of calculating a parameter δ obtained from the use conditions; The first mathematical formula is calculated from the mechanical parameter α, the lubricant parameter β, and the constant γ of the other parameters calculated in the first parameter calculation step and the second parameter calculation step, and the parameter δ obtained from the use conditions. F = f(α, β, γ, δ)…(1) and calculating the value of F obtained by In the third parameter calculation step, a parameter δ obtained from the usage conditions is found based on an output value obtained by inputting the usage conditions into the virtual electric circuit assembled by regarding the components of the rolling bearing, which are the inner ring, the outer ring, the rolling elements, and the lubricant, as elements, and performing a calculation; 6. A method for designing a rolling bearing according to any one of Appendices 1 to 5, wherein in the step of calculating the value of F, the mechanical parameter α, the lubricant parameter β, a constant γ of the other parameters, and a parameter δ obtained from the usage conditions are substituted into the first mathematical formula.

[0170] (Appendix 7) In the second parameter calculation step, a characteristic value of a virtual coating capacitance component that is assumed to be an insulating coating formed on at least one of the inner ring and the outer ring in the virtual electric circuit is obtained, The characteristic value of the virtual coating capacitance component is calculated from the dielectric constant ε of a vacuum, the relative dielectric constant ε of the insulating coating, the inner radius a of the insulating coating, the outer radius b of the insulating coating, and the width L of the rolling bearing as follows:

[0171]

number

[0172] The method for designing a rolling bearing according to Supplementary Note 6, wherein the rolling bearing is estimated as follows:

[0173] (Appendix 8) In the second parameter calculation step, an impedance value of an earthing mechanism connecting the inner ring and the outer ring is measured, 8. The method for designing a rolling bearing according to claim 6 or 7, wherein it is determined from the impedance value of the earthing mechanism whether the earthing mechanism has a capacitive component or an inductive component.

[0174] (Appendix 9) It is determined whether the earth mechanism has a series circuit or a parallel circuit of a reactance component, which is at least one of the capacitive component and the inductive component, and a resistive component; Appendix 9. A method for designing a rolling bearing according to claim 8, wherein the determination involves measuring a first impedance value of the earthing mechanism on the assumption that the reactance component and the resistance component are connected in series, and measuring a second impedance value of the earthing mechanism on the assumption that the reactance component and the resistance component are connected in parallel, and comparing the first impedance value with the second impedance value.

[0175] (Appendix 10) The determining step is performed by determining the second equation F≦10…(2) 10. The method for designing a rolling bearing according to any one of appendices 1 to 9, wherein the above is repeated until the following is satisfied.

[0176] (Appendix 11) A rolling bearing for use in an inverter-controlled motor, With inner circle, an outer ring disposed on an outer peripheral side of the inner ring; a plurality of rolling elements arranged to roll freely between the inner ring and the outer ring; a lubricant sealed in a gap formed between the inner ring and the outer ring and in which the plurality of rolling elements are arranged, The rotation speed of the rolling bearing during use is 100 rpm or more and 20,000 rpm or less, The voltage applied when the rolling bearing is in use is 2 V or more and 100 V or less, If the mechanical parameter is α, the parameter of the lubricant is β, the constant of other parameters is γ, and the parameter obtained from the use conditions is δ, then the following first formula can be obtained: F = f(α, β, γ, δ)…(1) The value of F calculated from the second formula below F≦10…(2) Meet the rolling bearings.

[0177] (Appendix 12) 12. The rolling bearing according to claim 11, wherein the lubricant has an oil film parameter Λ of 3 or less.

[0178] (Appendix 13) 13. The rolling bearing according to claim 11 or 12, wherein the lubricant is grease.

[0179] (Appendix 14) a seal member fitted to an inner diameter surface of the outer ring and arranged to contact the inner ring, 14. The rolling bearing according to any one of claims 11 to 13, wherein the sealing member is made of a conductive rubber material.

[0180] (Appendix 15) An electric motor comprising a stator and a rotatable rotor disposed radially inside the stator, The rolling bearing according to any one of Supplementary Notes 11 to 14 is installed between the stator and the rotor, an electric motor connected to an inverter device capable of controlling the rotation of the rotor;

[0181] (Appendix 16) preparing an inner ring, an outer ring arranged on the outer peripheral side of the inner ring, a plurality of rolling elements arranged to roll freely between the inner ring and the outer ring, and a lubricant; combining the inner ring, the outer ring, and the plurality of rolling elements; and sealing the lubricant in a gap formed between the inner ring and the outer ring and in which the plurality of rolling elements are arranged, The inner ring, the outer ring, the plurality of rolling elements, and the lubricant are expressed by the following first formula, where α is a mechanical parameter, β is a parameter of the lubricant, γ is a constant of other parameters, and δ is a parameter obtained from the usage conditions of the rolling bearing. F = f(α, β, γ, δ)…(1) The value of F derived from the second formula below F≦10…(2) The method for manufacturing a rolling bearing is prepared so as to satisfy the above.

[0182] (Appendix 17) Appendix 17. A method for manufacturing a rolling bearing according to claim 16, wherein in the preparing step, the mechanical parameter α, the lubricant parameter β, the constant γ of the other parameter, and the types of the inner ring, the outer ring, and the rolling elements are selected according to an arbitrary rotation speed of the inner ring and the outer ring during use, the load applied to the inner ring and the outer ring, and a voltage value applied to the rolling bearing. [Explanation of symbols]

[0183] 10 rolling bearing, 11 inner ring, 11A inner ring rolling surface, 12 outer ring, 12A outer ring rolling surface, 13 rolling element, 13A rolling surface, 14 cage, 15 seal member, 16 first seal groove, 17 second seal groove, 18 pocket, 21 stator, 21A stator yoke, 21B stator core, 21C stator coil, 22 rotor, 22A permanent magnet, 22B shaft, 30 conductive brush, 31 brush, 31a positive side brush, 31b negative side brush, 32 fixed part, 40 inverter device, 50 electric circuit, 60 grounding member, 100 electric motor, ETH earthing mechanism, LQ lubricant, LQ1, LQ3 first region, LQ2, LQ4 second region, Ca1, Ca2, Ce1, Ce2 capacitance component, Cc Coating capacitance component, L2,L5,L6 Induction component, R1,R1a,R1b,R2,R2a,R2b,R3,R5,R6,Ra1,Ra1A,Ra1B,Ra2,Ra2A,Ra2B,Ra11,Ra11A,Ra11B,Ra12,Ra12A,Ra12B,Re1,Re2,R20 Resistance component, S1, S1A, S1B, S2, S2A, S2B switch.

Claims

1. preparing a first mathematical formula capable of determining whether or not electrolytic corrosion can be suppressed in a rolling bearing including an inner ring, an outer ring arranged on the outer peripheral side of the inner ring, a plurality of rolling elements arranged to be free to roll between the inner ring and the outer ring, and a lubricant; determining the configuration of the inner ring, the outer ring, and the plurality of rolling elements based on usage conditions of the rolling bearing, The first formula is expressed as follows, where α represents a mechanical parameter of the inner ring, the outer ring, and the plurality of rolling elements, β represents a parameter of the lubricant, γ represents a constant of the other parameters, and δ represents a parameter obtained from the conditions of use: F=f(α,β,γ,δ)…(1) and The determining step is performed by using the following second formula in accordance with the use conditions: F≦10…(2) and determining whether the determining step includes a first parameter calculating step of calculating a parameter β of the lubricant; a first region of the lubricant located between a first rolling surface, which is the rolling surface of at least one of the inner ring and the outer ring, and a second rolling surface, which is the rolling surface of the rolling element, in a region where the first rolling surface and the second rolling surface approach each other to form an ellipse, and a second region of the lubricant located outside the first region, and a second region of the lubricant located outside the first region, and a characteristic value of a virtual element corresponding to the first region and the second region in a virtual electrical circuit corresponding to the rolling bearing is determined.

2. the first region and the second region are connected in parallel in the virtual electric circuit; In each of the first region and the second region, a resistance component and a capacitance component are connected in parallel as the virtual element, The characteristic value of the resistance component is calculated from the volume resistivity Rv of the lubricant, which is determined by a function of temperature T and pressure P, the thickness d of the oil film of the lubricant in either the first region or the second region, and the area S of the oil film of the lubricant, as follows: [Equation 1] The method for designing a rolling bearing according to claim 1, wherein the rolling bearing is estimated as follows:

3. The characteristic value of the capacitance component is the dielectric constant ε of a vacuum. ０ and a relative dielectric constant ε of the lubricant determined by a function of temperature T and pressure P, an area S of the oil film as an area where a pair of electrodes constituting a capacitance regarded as being in either the first region or the second region face each other, and a thickness d of the oil film as the lubricant in either the first region or the second region, [Equation 2] The method for designing a rolling bearing according to claim 2, wherein the rolling bearing is estimated as follows:

4. each of the first region and the second region includes a switch connected in parallel to the resistance component and the capacitance component; the switch is turned on when the voltage applied to the lubricant exceeds a breakdown voltage; The breakdown voltage of the switch is calculated from the voltage V, which is determined by the pressure P, the temperature T, the relative dielectric constant ε of the lubricant, and the resistance component, and the thickness d of the oil film of the lubricant, as follows: [Equation 3] The method for designing a rolling bearing according to claim 2, wherein the rolling bearing is estimated as follows:

5. 2. The method for designing a rolling bearing according to claim 1, wherein in the first parameter calculation step, the parameter β of the lubricant is calculated taking into consideration that the volume resistivity, viscosity, dielectric constant, and dielectric breakdown strength of the lubricant change depending on the operating temperature of the rolling bearing containing the lubricant.

6. The determining step includes a second parameter calculating step of calculating a constant γ of the mechanical parameter α and the other parameters; a third parameter calculation step of calculating a parameter δ obtained from the use conditions; The first mathematical formula is calculated from the mechanical parameter α, the lubricant parameter β, and the constant γ of the other parameters calculated in the first parameter calculation step and the second parameter calculation step, and the parameter δ obtained from the use conditions. F=f(α,β,γ,δ)…(1) and calculating the value of F obtained by In the third parameter calculation step, a parameter δ obtained from the usage conditions is found based on an output value obtained by inputting the usage conditions into the virtual electric circuit, which is assembled by regarding components comprising the inner ring, the outer ring, the rolling elements, and the lubricant that constitute the rolling bearing as elements, and performing a calculation; 2. The method for designing a rolling bearing according to claim 1, wherein in the step of calculating the value of F, the mechanical parameter α, the lubricant parameter β, the constant γ of the other parameters, and a parameter δ obtained from the usage conditions are substituted into the first mathematical equation.

7. In the second parameter calculation step, a characteristic value of a virtual coating capacitance component that is assumed to be an insulating coating formed on at least one of the inner ring and the outer ring in the virtual electric circuit is obtained, The characteristic value of the virtual film capacitance component is the dielectric constant of vacuum, ε ０ From the relative dielectric constant ε of the insulating coating, the inner radius a of the insulating coating, the outer radius b of the insulating coating, and the width L of the rolling bearing, [Equation 4] The method for designing a rolling bearing according to claim 6, wherein the rolling bearing is estimated as follows:

8. In the second parameter calculation step, an impedance value of a grounding mechanism connecting the inner ring and the outer ring is measured, 8. The method for designing a rolling bearing according to claim 6, wherein it is determined whether the earthing mechanism has a capacitive component or an inductive component from the impedance value of the earthing mechanism.

9. It is determined whether the earth mechanism has a series circuit or a parallel circuit of a reactance component, which is at least one of the capacitive component and the inductive component, and a resistive component; 9. A method for designing a rolling bearing according to claim 8, wherein in the determination, a first impedance value of the earthing mechanism is measured on the assumption that the reactance component and the resistance component are connected in series, and a second impedance value of the earthing mechanism is measured on the assumption that the reactance component and the resistance component are connected in parallel, and the first impedance value and the second impedance value are compared.

10. The determining step is performed by determining the second equation F≦10…(2) 3. The method for designing a rolling bearing according to claim 1, wherein the above formula is repeated until the following formula is satisfied:

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