Rolling bearings and electric motors

Abstract

The present invention provides a rolling bearing that can reduce bearing torque and contribute to compliance with high-efficiency motor standards, as well as an electric motor incorporating the rolling bearing. [Solution] The rolling bearing 1 comprises an inner ring 2 and an outer ring 3, a plurality of rolling elements 4 interposed between the inner and outer rings, and grease 7 sealed in the bearing space. The grease has a kinematic viscosity of 40 mm at 40°C. 2 [ln(v)] / n is obtained from the apparent viscosity gradient n in the following formula (1), which is calculated from the apparent viscosity of the grease 7 at at least two arbitrary shear rates measured using a rheometer, and the kinematic viscosity v of the base oil at 40°C. TIFF2026067898000008.tif12147 However, the symbols in the formula represent: η: apparent viscosity [Pa·s], n: apparent viscosity gradient, γ: shear rate [s] -1 ], a: a constant specific to each type of grease.

Description

[Technical Field]

[0001] The present invention relates to a grease-filled rolling bearing and an electric motor incorporating the rolling bearing. [Background technology]

[0002] In recent years, due to environmental issues such as global warming, automobiles and industrial machinery are required to be even more energy-efficient. In particular, industrial motors are said to account for about 40% of the world's total electricity consumption, and therefore require high efficiency.

[0003] Against this backdrop, motor efficiency regulations are being implemented in countries around the world. In Japan, a new premium efficiency standard has been applied to induction motors with a power output of 0.75kW or more but less than 7.5kW sold since January 2017. Furthermore, there is a movement toward next-generation efficiency regulations, and the development of even higher-efficiency motors is progressing (see, for example, Non-Patent Document 1). In order to achieve these standards, efficiency improvements are essential for each component of the motor, and rolling bearings, one of these components, are required to have even lower torque.

[0004] Furthermore, it has been reported that 0.6% of the power consumption of motors, which account for a significant portion of the total power consumption in industry, is attributable to bearings. For example, in 2015, the number of motors produced in Japan was estimated at approximately 5 million units, with a production capacity of approximately 20 million kW. If bearings with a 50% reduction in bearing torque were used, power consumption could be reduced by approximately 60,000 kW. Generally, rolling bearings are filled with lubricating grease to reduce rolling friction and sliding friction. The grease sealed in the rolling bearing adheres to the rolling elements and cage as the bearing rotates, and is agitated, generating bearing torque. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Dorrell D.G., "A Review of the Methods for Improving the Efficiency of Drive Motors to Meet IE4 Efficiency Standards", Journal of Power Electronics, 2014, Vol.14, No.5, p.842-851

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a rolling bearing capable of reducing bearing torque and contributing to compliance with the standards of high-efficiency motors, and an electric motor incorporating the rolling bearing.

Means for Solving the Problems

[0007] The rolling bearing of the present invention is a rolling bearing having an inner ring, an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease enclosed in the bearing inner space, wherein the grease has a kinematic viscosity at 40°C of 40 mm 2 / s or less, contains a base oil and a thickener, and the apparent viscosity gradient n in the following formula (1) calculated from the apparent viscosity of the grease at at least two or more arbitrary shear rates measured using a rheometer, and [ln(v)] / n (where ln(v) represents the natural logarithm of the kinematic viscosity v) obtained from the kinematic viscosity v of the base oil at 40°C is 5 or less.

Equation

[0008] The apparent viscosity gradient n in the formula (1) is 0.80 or more.

[0009] The kinematic viscosity v of the base oil at 40°C is 20 mm 2 / s to 35 mm 2 / s, and the value of [ln(v)] / n is 3 to 4.

[0010] The apparent viscosity gradient n is the gradient between the apparent viscosity at a shear rate of 10 s -1 ~300 s -1 measured by a rheometer and the apparent viscosity at a shear rate of 1000 s -1 ~5000 s -1 measured by a rheometer.

[0011] The motor of the present invention is a motor comprising a stator, a rotor, and a rolling bearing that rotatably supports a rotating shaft, wherein the motor satisfies the IE3 standard of the international standard IEC60034-30, and the rolling bearing is the rolling bearing of the present invention.

Advantages of the Invention

[0012] The rolling bearing of the present invention is a bearing filled with grease, and the grease contains a base oil having a kinematic viscosity at 40°C of 40 mm 2 / s or less and a thickener, and the value of [ln(v)] / n obtained from the apparent viscosity gradient n in the above formula (1) calculated from the apparent viscosity of the grease measured using a rheometer and the kinematic viscosity v of the base oil at 40°C is 5 or less, so that the bearing torque can be reduced.

[0013] Furthermore, since the apparent viscosity gradient n in the above formula (1) is 0.80 or more, the rolling bearing can be further reduced in torque.

[0014] The motor of the present invention satisfies the IE3 standard (premium efficiency) of the international standard IEC60034-30, and where high efficiency is required for the motor, the rolling bearing of the present invention is incorporated as a rolling bearing that rotatably supports the rotating shaft, thus contributing to compliance with the IE3 standard.

Brief Description of the Drawings

[0015] [Figure 1] This figure shows a rolling bearing filled with grease according to the present invention. [Figure 2] This is a schematic diagram showing an example of a rotary rheometer. [Figure 3] This is a diagram showing the apparent viscosity gradient of the grease. [Figure 4] This is a schematic diagram showing an example of a capillary rheometer. [Figure 5] This figure shows the relationship between bearing torque and [ln(v)] / n. [Figure 6] This figure shows the relationship between bearing torque and apparent viscosity gradient. [Modes for carrying out the invention]

[0016] The inventors, through diligent research aimed at reducing bearing torque, discovered that bearing torque correlates with the gradient of the apparent viscosity of grease with respect to shear rate. More specifically, they found that bearing torque exhibits a linear relationship with [ln(v)] / n. This invention is based on these findings.

[0017] An example of a rolling bearing of the present invention will be described with reference to Figure 1. Figure 1 is a cross-sectional view of a deep groove ball bearing. The rolling bearing 1 has an inner ring 2 having an inner ring raceway surface 2a on its outer circumference and an outer ring 3 having an outer ring raceway surface 3a on its inner circumference, arranged concentrically, with a plurality of balls 4 arranged between the inner ring raceway surface 2a and the outer ring raceway surface 3a. These balls 4 are held by a cage 5. In addition, the axial openings 8a and 8b at both ends of the inner and outer rings are sealed by a sealing member 6, and grease 7 is sealed around at least the balls 4. The inner ring 2, outer ring 3 and balls 4 are made of an iron-based metal material, and the grease 7 is interposed on the raceway surface with the balls 4 to lubricate them.

[0018] The grease sealed in the rolling bearing of this invention has a kinematic viscosity of 40 mm at 40°C. 2It contains a base oil with a viscosity of / s or less and a thickener, and is characterized in that the value of [ln(v)] / n, as described later, is 5 or less. As a result, bearing torque can be reduced as shown in the examples.

[0019] In the grease used in the present invention, the base oil, thickener, and additives added as needed can be any known combination within the range where the kinematic viscosity of the base oil and the value of [ln(v)] / n satisfy the above numerical range.

[0020] The base oil can be a common type typically used in the grease field. For example, highly refined oils, mineral oils, ester oils, ether oils, synthetic hydrocarbon oils (PAO oils), silicone oils, fluorinated oils, and mixtures thereof can be used. The kinematic viscosity of the base oil at 40°C should be 35 mmHg. 2 It is preferable that the kinematic viscosity is less than or equal to / s. The lower limit of the kinematic viscosity is, for example, 10 mm. 2 The kinematic viscosity is / s. A more preferred range for this kinematic viscosity is 20 mm 2 / s~35mm 2 It is / s.

[0021] The thickener can be one of the common types used in the field of grease. For example, soap-based thickeners such as metal soaps and complex metal soaps, and non-soap-based thickeners such as bentone, silica gel, urea compounds, and urea-urethane compounds can be used. Examples of metal soaps include sodium soap, calcium soap, aluminum soap, and lithium soap, while examples of urea compounds and urea-urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds. The amount of thickener added is not particularly limited, but it is preferable that it be included in an amount of 5% to 30% by mass relative to the total amount of grease.

[0022] Examples of additives include amine-based and phenol-based antioxidants, chlorine-based, sulfur-based, and phosphorus-based compounds, extreme pressure agents such as organic molybdenum, and rust inhibitors such as petroleum sulfonates, dinonyl naphthalene sulfonates, and sorbitan esters.

[0023] Here, [ln(v)] / n can be calculated using the following method.

[0024] First, the apparent viscosity of the grease at at least two arbitrary shear rates is measured by rheological measurement using a rheometer. Preferably, a rotary rheometer having a cone-plate type cell is used as the rheometer. An overview of such a rheometer is shown in Figure 2. As shown in Figure 2, the rotary rheometer 11 consists of a cone-plate type cell 12 and a horizontal disc plate 13. The cell 12 and the plate 13 are arranged to be in contact at one point (with a slight gap), and the sample grease 14 is placed between them. In this rheometer, the shear rate applied to the grease 14 is the same at any position, regardless of the distance from the center of the cell. Conditions for rheological measurement include (1) dependence on rotational speed at constant temperature and constant rotation direction, (2) dependence on vibration frequency at constant temperature and constant shear strain, and (3) dependence of dynamic viscoelasticity on shear stress at a constant frequency, but in this invention, measurements are mainly performed under condition (1).

[0025] The specific rheological measurement conditions involve using a rotary rheometer (Thermo Fisher Scientific HAAKE RheoWin MARS1) with a cone-plate type cell having a diameter of 20 mm and a tip angle of 178°, at a constant temperature and direction of rotation, such as at 20°C. In this case, the apparent viscosity is defined as the viscosity at which steady states are reached at at least two arbitrary shear rates. There are no particular restrictions on the apparent viscosity measured by the rheometer, but 10s -1 ~300s -1 The apparent viscosity at the shear rate and 1000 s -1 ~10000s -1 Preferably, it contains apparent viscosity at the shear rate, 10s -1 ~100s -1 The apparent viscosity at the shear rate and 1000 s -1 ~5000s -1It is more preferable to include the apparent viscosity at the shear rate.

[0026] Figure 3 shows an example with a shear rate of 100 s. -1 and shear rate 3000s -1 The results of measuring the apparent viscosity at 100 s are shown. Figure 3 is a log-log graph plotted with the common logarithm of the shear rate γ on the horizontal axis and the common logarithm of the apparent viscosity η of the grease on the vertical axis. The straight line connecting each plot is represented by the following equation (1), and the apparent viscosity gradient n can be calculated from this equation (1). In Figure 3, the apparent viscosity gradient n is given by the shear rate 100 s -1 ~3000s -1 This is calculated as a viscosity gradient relative to [the given value].

number

[0027] In the above, the apparent viscosity gradient n is calculated from the measurement results of two apparent viscosity points, but the apparent viscosity gradient n may also be calculated based on the measurement results of three or more apparent viscosity points. For example, the shear rate between the two shear rates mentioned above (in the case of Figure 3, for example, a shear rate of 1000 s) -1 The apparent viscosity may be measured at ) and the apparent viscosity gradient n may be calculated using three points including that point. Alternatively, the apparent viscosity at shear rates lower or higher than the range of the two points may be used. When using measurement results from three or more points, the apparent viscosity gradient n is calculated from the regression line obtained by the least squares method.

[0028] Furthermore, the apparent viscosity of grease can be measured not only using a rotary rheometer, but also, for example, using a capillary rheometer. An overview of viscosity measurement using a capillary rheometer is shown in Figure 4. As shown in Figure 4, the capillary rheometer 21 has a cylinder 23 with a capillary 24 at the bottom, a piston 22 that can move up and down inside the cylinder 23, and a load cell 26 provided at one end of the piston 22. With grease 25 filled inside the cylinder 23, the piston 22 is lowered at a constant speed, and the load p when the grease 25 is pushed out is detected by the load cell 26. Using the dimensions of each part of the capillary rheometer 21, the apparent viscosity η at at least two arbitrary shear rates (unit: 1 / s) can be determined according to equations (2) to (4) below. Then, the apparent viscosity gradient n is calculated from the obtained equation (1) above.

[0029] γ = 32Q / πD 3 ...(2) τ = pD / 4L···(3) η = τ / γ···(4) However, the symbols in equations (2) to (4) above represent: Q: Volumetric flow rate [mm 3 [s], D: capillary inner diameter [mm], p: detected load [Pa], L: capillary length [mm], γ: shear rate [s] -1 Q is the cross-sectional area of ​​the piston [mm²]. τ is the shear stress [Pa]. 2 This value is obtained by multiplying [ ] by the piston speed [mm / s].

[0030] In the rolling bearing of the present invention, the apparent viscosity gradient n calculated as described above is preferably 0.80 or higher, and more preferably 0.85 or higher. The upper limit of the apparent viscosity gradient n of the grease is, for example, 1.0.

[0031] [ln(v)] / n can be determined using the apparent viscosity gradient n and the kinematic viscosity v of the base oil at 40°C. This value is obtained by dividing the natural logarithm of the kinematic viscosity v of the base oil at 40°C by the apparent viscosity gradient n. In the rolling bearing of the present invention, the value of [ln(v)] / n is 5 or less, and preferably 4 or less. The preferred range for the value of [ln(v)] / n is 3 to 4.

[0032] In Figure 1, a deep groove ball bearing is shown as an example of a rolling bearing according to the present invention, but it can also be applied to cylindrical roller bearings, tapered roller bearings, self-aligning roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings, thrust self-aligning roller bearings, and the like.

[0033] The rolling bearing of the present invention operates under relatively low rotational speed conditions, for example, 2000 min⁻¹. -1 This applies to bearings used in the following rotational speed range. Here, 2000 min -1 The term "used in the following rotational speed range" means that the main rotational speed (steady-state rotational speed) of the bearing under its operating conditions is 2000 min⁻¹. -1 The following applies: The rotational speed is 1500 min⁻¹. -1 The following is also acceptable. Specifically, a rotational speed of 1800 min⁻¹ -1 Motor bearings for general-purpose motors, and rotational speed 1500 min⁻¹ -1 This applies to axle bearings, etc.

[0034] In the rolling bearing of the present invention, the amount of grease to be sealed is not particularly limited as long as the desired lubrication characteristics can be ensured, but it is preferably 60% to 100% (volume ratio) of the static space volume in the bearing space, and more preferably 80% to 100%. Here, the static space volume is the volume of space in the space between the inner ring, outer ring, and seal member that the rolling elements and cage do not pass through when the bearing rotates. In the rolling bearing of the present invention, by using grease in which [ln(v)] / n is less than or equal to a predetermined threshold, the bearing torque can be reduced even when the amount of grease sealed is in a larger range.

[0035] The electric motor of the present invention comprises a stator, a rotor, and rolling bearings that rotatably support the rotating shaft. More specifically, the electric motor has a casing, a stator fixed to the casing, a rotor positioned opposite the stator, a rotating shaft that rotates integrally with the rotor, and rolling bearings that rotatably support the rotating shaft relative to the casing. Generally, two rolling bearings are provided spaced apart from the rotating shaft. The rolling bearings incorporated into this electric motor correspond to the rolling bearings of the present invention. One embodiment of the electric motor of the present invention is a sinusoidal three-phase AC motor.

[0036] In recent years, the international standard IEC60034-30 has been published, which defines the efficiency classes of motors driven at a constant speed. Efficiency classes are classifications of efficiency standards, with IE1 (standard efficiency), IE2 (high efficiency), and IE3 (premium efficiency) defined. Due to the trend towards energy conservation, motors that conform to IE2 and IE3 standards are in demand.

[0037] The rolling bearing of the present invention exhibits excellent motor efficiency due to its low torque, making it suitable for electric motors that meet the IE3 standard. The IE3 standard, for example, requires an efficiency of 80.7% for a three-phase AC motor with 2 poles and a rated output of 0.75 kW.

[0038] Furthermore, the present invention can also be a method for evaluating the bearing torque of a rolling bearing. Here, "evaluating bearing torque" means determining the superiority or inferiority of the bearing torque of a rolling bearing, and includes evaluating the magnitude of the bearing torque of the rolling bearing, as well as evaluating the magnitude of the bearing torque between multiple rolling bearings.

[0039] The first embodiment of the above evaluation method is an evaluation method for evaluating the bearing torque generated when a rolling bearing has an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease sealed in the bearing space, wherein the grease comprises a base oil and a thickener, and the evaluation method is characterized by measuring the apparent viscosity of the grease at at least two arbitrary shear rates using a rheometer, and evaluating the bearing torque of the rolling bearing based on the apparent viscosity gradient n in the following formula (1) calculated from the measurement results and the kinematic viscosity v of the base oil at 40°C.

number

[0040] Generally, bearing torque is measured by actually rotating the bearing and using the load applied to it. On the other hand, a method is known to estimate bearing torque based on the viscosity of the base oil, depending on the type of grease (Reference: Palmgren, A., "Ball and Roller Bearing Engineering", 3rd ed. Burbank, 1959, pp. 34-41). However, the viscosity characteristics of grease are very complex, and even when using the same base oil, the torque value changes significantly if the type of thickener or additive is different, making it difficult to judge the superiority or inferiority of bearing torque.

[0041] In contrast, the above evaluation method evaluates bearing torque based on the apparent viscosity gradient n of the grease and the kinematic viscosity v of the base oil at 40°C. Specifically, the bearing torque is evaluated based on the magnitude of the [ln(v)] / n value obtained from the apparent viscosity gradient n and the kinematic viscosity v, so the superiority or inferiority of the bearing torque can be determined without actually performing an evaluation test in which the bearing is rotated.

[0042] Here, [ln(v)] / n has a linear relationship with bearing torque, as shown in Figure 5 below. Therefore, in the first form of evaluation method, the superiority or inferiority of bearing torque can be determined by the magnitude of the function between the apparent viscosity gradient n and the kinematic viscosity v of the base oil at 40°C. For example, by comparing [ln(v)] / n with a predetermined threshold, it can be determined that the bearing torque is small if [ln(v)] / n is less than or equal to the predetermined threshold, and that the bearing torque is large if [ln(v)] / n is greater than the predetermined threshold. The predetermined threshold can be set in advance by experiments conducted beforehand. For example, the threshold can be set to 5.

[0043] Furthermore, by comparing the magnitude of [ln(v)] / n among multiple greases, it is possible to select a grease with a low bearing torque. For example, the bearing torque of a rolling bearing with a relatively small [ln(v)] / n can be evaluated as lower than that of a rolling bearing with a relatively large [ln(v)] / n.

[0044] Furthermore, a second embodiment of the above evaluation method is an evaluation method for evaluating the bearing torque generated when a rolling bearing having an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease sealed in the bearing space is rotated, characterized in that the above evaluation method measures the apparent viscosity of the grease at at least two arbitrary shear rates using a rheometer, and evaluates the bearing torque of the rolling bearing based on the apparent viscosity gradient n in the following formula (1) calculated from the measurement results.

number

[0045] Here, the apparent viscosity gradient n shows a linear relationship with the bearing torque, as shown in Figure 6 below. Specifically, the bearing torque tends to decrease as the apparent viscosity gradient n increases. Therefore, in the second form of evaluation method, the superiority or inferiority of the bearing torque can be determined by the magnitude of the calculated apparent viscosity gradient n. For example, by comparing the apparent viscosity gradient n with a predetermined threshold, it can be determined that the bearing torque is small if the apparent viscosity gradient n is greater than or equal to the predetermined threshold, and that the bearing torque is large if the apparent viscosity gradient n is less than the predetermined threshold. The predetermined threshold can be set in advance by experiments conducted beforehand. For example, the threshold can be set to 0.80.

[0046] Furthermore, by comparing the magnitude of the apparent viscosity gradient n among multiple greases, it is possible to select a grease that produces a low bearing torque. For example, the bearing torque of a rolling bearing with a relatively large apparent viscosity gradient n can be evaluated as lower than that of a rolling bearing with a relatively small apparent viscosity gradient n.

[0047] In the evaluation methods of the first and second embodiments described above, the kinematic viscosity of the base oil at 40°C is not particularly limited, but is 10 mm 2 / s~180mm 2 / s is preferred, 20mm 2 / s~130mm 2 / s is more preferable. By keeping the kinematic viscosity within this range, it is possible to accurately determine the superiority or inferiority of the bearing torque. [Examples]

[0048] The apparent viscosity gradient n was calculated for 12 types of grease (Examples 1-6 and Comparative Examples 1-6). First, the apparent viscosity of each grease was measured using a rheometer (HAAKE RheoWin MARS1, Thermo Fisher Scientific) with a cone-plate type cell having a diameter of 20 mm and a tip angle of 178°. Shear rate: 100 s -1 and shear rate 3000s -1The apparent viscosity of each grease was measured when it reached a steady state. Using the above equation (1) derived from the obtained measurement results, the apparent viscosity gradient n and the intrinsic constant a for each type of grease were calculated. The apparent viscosity gradient n for each grease is shown in Table 1.

[0049] Table 1 also lists the kinematic viscosity v of the base oils of the 12 types of grease at 40°C. Note that the kinematic viscosity of the base oils is the same for each combination of Examples 3-5, Example 6, Comparative Example 1, and Comparative Examples 3-4.

[0050] Using the obtained apparent viscosity gradient n and the kinematic viscosity v of the base oil at 40°C, [ln(v)] / n was calculated. This value is also shown in Table 1.

[0051] Furthermore, bearing torque was measured for each grease. The testing machine is designed to apply load in the axial direction of the bearing. The test bearing rotates at the inner ring, and a load cell is connected to the housing of the outer ring to measure bearing torque. A deep groove ball bearing 6204 (bearing dimensions: inner diameter 20 mm, outer diameter 47 mm, width 14 mm) was filled with each grease so that the amount of grease filled equals 100% of the static space to obtain the test bearing. The test bearing was subjected to an axial load of 20 N and a rotation speed of 1200 min⁻¹. -1 The inner wheel was rotated under the following conditions.

[0052] In the test, the tangential force acting on the housing during bearing rotation was measured using a load cell, and the bearing torque was calculated from the outer diameter of the housing. The bearing torque was measured 5 minutes after the start of the test. The bearing torque for each grease is listed in Table 1.

[0053] [Table 1]

[0054] As shown in Table 1, the kinematic viscosity of the base oil at 40°C is 40 mm². 2Examples 1-6, which used grease with an apparent viscosity gradient n of 0.8 or less and a value of [ln(v)] / n of 5 or less, showed lower torque than Comparative Examples 1-6, which used grease with a value of [ln(v)] / n greater than 5. Furthermore, Examples 1-2 and 5-6, which had an apparent viscosity gradient n of 0.8 or higher, showed even lower torque than Examples 3-4 (apparent viscosity gradient n less than 0.8).

[0055] Figure 5 shows a plot of bearing torque and [ln(v)] / n for each grease. As shown in Figure 5, there was a tendency for bearing torque to increase as [ln(v)] / n increased. As a result, for example, the bearing torque of a rolling bearing filled with grease with [ln(v)] / n of 5 or less can be evaluated as lower (lower torque) than the bearing torque of a rolling bearing filled with grease with [ln(v)] / n greater than 5. Furthermore, from the results in Table 1 and Figure 5, it was found that even among greases with the same kinematic viscosity of the base oil (for example, Example 6 and Comparative Example 1, Comparative Example 3 and Comparative Example 4), the superiority or inferiority of bearing torque can be determined by using [ln(v)] / n.

[0056] Figure 6 shows a plot of bearing torque and apparent viscosity gradient n for each grease. As shown in Figure 6, there is a tendency for bearing torque to decrease as the apparent viscosity gradient n of the grease increases. As a result, for example, the bearing torque of a rolling bearing filled with grease with an apparent viscosity gradient n of 0.85 or higher can be evaluated as lower (lower torque) than the bearing torque of a rolling bearing filled with grease with an apparent viscosity gradient n of less than 0.80. Furthermore, from the results in Table 1 and Figure 6, it was found that even among greases with the same kinematic viscosity of the base oil (for example, Examples 4 and 5, Comparative Example 3 and Comparative Example 4), the superiority or inferiority of bearing torque can be determined by using the apparent viscosity gradient n of the grease.

[0057] Here, bearing torque is a loss in the power transmission of mechanical equipment, so a smaller value is better. For example, it has been reported that in a certain three-phase AC motor, 12% of the power loss was due to mechanical losses, including bearings (URL: https: / / www.jraia.or.jp / member / seifu / pdf / meti20130128_4-2.pdf). Mechanical losses are mostly accounted for by losses due to bearings and cooling fans, and if we simply assume that the losses due to bearings and cooling fans are half, then 6% will be due to bearings. A three-phase AC motor with a rating of 0.75kW and 2 poles is subject to the IE3 standard, which requires an efficiency of 80.7% or higher. That is, the upper limit of the power loss due to transmission relative to the rated output is approximately 0.14kW. Applying the 6% estimate above, the loss due to bearings is 0.14kW × 0.06 = 0.084kW. Also, a motor usually incorporates two bearings, and the upper limit of power loss per bearing is 0.042kW. From a motor efficiency standpoint, bearings with a value lower than this are required. The power lost due to the bearings can be calculated using the following formula. Power lost due to bearing torque (kW) = 2π × bearing torque (Nm) × rotational speed (min) -1 ) / 60 / 1000

[0058] Using the above formula, the upper limit torque value of the bearing was calculated to be approximately 33 Nmm. Applying this to the greases evaluated above, the greases of Examples 1 to 6 are applicable. From these results, it can be concluded that rolling bearings incorporated into electric motors that meet the IE3 standard, more specifically, three-phase AC motors with a rating of 0.75 kW and 2 poles, should have a base oil with a kinematic viscosity of 40 mm at 40°C. 2 It is preferable to use a grease that is less than or equal to / s and has a value of [ln(v)] / n of 5 or less. [Industrial applicability]

[0059] The rolling bearing of the present invention can reduce bearing torque and contribute to compliance with high-efficiency motor standards, and is therefore particularly useful as a rolling bearing that rotatably supports the rotating shaft of a motor. [Explanation of symbols]

[0060] 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Balls (rolling elements) 5 Cage 6. Sealing member 7. Grease 8 openings 11. Rotary Rheometer 12 cone plate type cells 13 Horizontal disc plate 14 Grease 21 Capillary Rheometer 22 pistons 23 liters 24 capillaries 25 Grease 26 load cells

Claims

1. A rolling bearing having an inner ring and an outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and grease sealed in the bearing's internal space, The aforementioned grease has a kinematic viscosity of 40 mm at 40°C. ２ A rolling bearing comprising a base oil and a thickener with a viscosity of / s or less, characterized in that the value of [ln(v)] / n (where ln(v) is the natural logarithm of the kinematic viscosity v), which is obtained from the apparent viscosity gradient n in the following formula (1) calculated from the apparent viscosity of the grease at at least two arbitrary shear rates measured using a rheometer, and the kinematic viscosity v of the base oil at 40°C, is 5 or less. [Math 1] However, the symbols in the formula represent: η: apparent viscosity [Pa·s], n: apparent viscosity gradient, γ: shear rate [s] －１ ], a: a constant specific to each type of grease.

2. The rolling bearing according to claim 1, characterized in that the apparent viscosity gradient n in formula (1) is 0.80 or more.

3. The kinematic viscosity v of the base oil at 40°C is 20 mm². ２ / s ~ 35mm ２ The rolling bearing according to claim 2, characterized in that the value of [ln(v)] / n is 3 to 4, where / s.

4. The apparent viscosity gradient n is measured by a rheometer at 10s －１ ~300s －１ The apparent viscosity at the shear rate and 1000 s －１ ~5000s －１ A rolling bearing according to any one of claims 1 to 3, characterized in that it is a gradient between the apparent viscosity at the shear rate.

5. An electric motor comprising a stator, a rotor, and rolling bearings that rotatably support the rotating shaft, The electric motor is characterized in that it satisfies the IE3 standard of the international standard IEC 60034-30, and the rolling bearing is a rolling bearing according to any one of claims 1 to 4.

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