Rolling bearing

Abstract

To provide a rolling bearing capable of preventing abrasion of a pocket wall part at low cost even at middle and high rotation speed and reducing abrasion of a cage by improving a pocket shape of the cage.SOLUTION: This rolling bearing has an inner ring 2, an outer ring 3, a plurality of ball-shaped rolling elements 4 interposed between these inner and outer rings, and a cage 5 for holding these rolling elements. The cage has two annular body side walls and a side 5a overlapping each other in the axial direction, and each annular body side 5a has a plurality of pocket 5a parts 10 arranged in the circumferential direction and constituting pockets 8 for holding the rolling elements. The pocket wall part 10 is formed of a first spherical part 11, a second spherical part 12 having a radius of curvature smaller than that of the first spherical part, and a third spherical part 13 smoothly connecting the first spherical part and the second spherical part.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing, and to a technique applied to, for example, servo motors, generators, etc. [Background technology]

[0002] Low-speed servo motors, generators, and other applications use deep groove ball bearings with steel cages, which are relatively inexpensive to manufacture. However, steel is more susceptible to wear than plastic, and is heavier. This causes the steel cage to wear out quickly and heat up easily, so steel cages are not used in bearings for medium- to high-speed servo motors and generators, and plastic cages are used instead.

[0003] In addition, the steel plate cage of a deep groove bearing is guided by the rolling elements (balls) during rotation, and the rolling elements, rotating at high speed, constantly come into contact with the pocket surface of the cage, causing sliding wear. Grease inside the pocket plays an important role in reducing this wear.

[0004] In the prior art of Patent Documents 1 and 2, a coating film of a resin composition such as a fluororesin, or a solid lubricant layer, is formed on the pocket surface of the cage that slides against the rolling elements, thereby reducing wear on the pocket surface of the cage, increasing torque, and suppressing temperature rise. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-172749 [Patent Document 2] Japanese Patent Application Publication No. 2018-162875 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Documents 1 and 2, an additional process of forming a resin coating on the pocket surface of a pressed steel plate cage was added, which posed a problem of higher manufacturing costs. Also, while it is conceivable that limiting the cage band width would suppress temperature rise during bearing rotation, this would prevent grease from accumulating inside the pocket, and therefore would not be effective in reducing pocket wear.

[0007] Furthermore, under conditions requiring higher speeds, the wear caused by the pockets coming into contact with the rolling elements becomes more severe, and grease cannot easily accumulate inside the pockets due to centrifugal force, causing premature wear in the cage pockets (especially at the bottom of the pockets), resulting in a shorter bearing lifespan.

[0008] In light of the problems with the conventional technology described above, the present invention aims to provide a rolling bearing that prevents pocket wear at low cost even at medium to high rotational speeds, thereby reducing wear on the entire cage, by improving the pocket shape of the cage. [Means for solving the problem]

[0009] A rolling bearing according to the present invention is a rolling bearing having an inner ring, an outer ring, a plurality of ball-shaped rolling elements interposed between the inner ring and the outer ring, and a cage that holds the rolling elements, the cage has two annular bodies overlapping each other in the axial direction, each annular body having a plurality of spherical pocket wall portions that form pockets that hold the rolling elements, and a connecting portion between adjacent pocket wall portions, and the annular bodies are connected to each other at the connecting portion; The pocket wall portion has a first spherical portion provided at a circumferential end of the pocket wall portion, a second spherical portion provided at an axial end of the pocket wall portion, and a third spherical portion connecting the first spherical portion and the second spherical portion, and the second spherical portion is configured with a smaller radius of curvature than the first spherical portion.

[0010] According to this configuration, the pocket shape of the retainer is improved, and the pocket wall is formed of a first spherical portion, a second spherical portion with a smaller radius of curvature, and a third spherical portion connecting these.Therefore, the first spherical portion and the second spherical portion with the smaller radius of curvature form a convex portion on the pocket surface (hereinafter referred to as the pocket bottom), which prevents contact with the rolling elements at the pocket bottom and reduces wear on the entire pocket. Here, the axial direction of the central axes of the inner and outer rings of the rolling bearing is referred to as the "axial direction." The direction perpendicular to the "axial direction" is referred to as the "radial direction." The "circumferential direction" refers to the direction along the circumference that goes around the central axis of the central axes of the inner and outer rings. The definitions of these directions are the same in the following explanation.

[0011] In addition, the space inside the pocket through which grease can pass is larger, making it possible to suppress temperature rise even at medium to high rotational speeds. In addition, the convex shape of the pocket makes it easier for grease to accumulate at the bottom, improving the lubrication environment inside the pocket and reducing wear on the entire pocket. This makes it possible to prevent wear on the pocket surface at low cost and reduce wear on the entire cage. Furthermore, because the first and second spherical portions are spherical, it is easy to create a molding die.

[0012] Preferably, the third spherical portion is circumscribing the first spherical portion and the second spherical portion, which makes the pocket shape of the cage smooth, thereby preventing wear on the pocket surface.

[0013] It is also preferable that the pocket wall portion has a shape that satisfies the formula described below in a radial cross section of the bearing. [Effects of the Invention]

[0014] By improving the pocket shape of the cage, the rolling bearing of the present invention prevents wear on the pocket surface at low cost, and also increases the space through which grease can pass, suppressing temperature rise even at medium to high speed rotation. Grease is more likely to accumulate at the bottom of the pocket, improving the lubrication environment inside the pocket and making it possible to reduce wear on the entire cage. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic vertical cross-sectional view of a rolling bearing according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of a wave cage of the rolling bearing. [Figure 3] 3 is a cross-sectional view of the waveform cage of FIG. 2 taken along plane III. [Figure 4] 4 is a cross-sectional view of the waveform holder of FIG. 2 taken along plane IV. [Figure 5] FIG. 4 is a perspective view showing a pocket bottom formed in the cage. [Figure 6] FIG. 10 is a characteristic diagram showing a load generated at the bottom of a pocket. [Figure 7] FIG. 10 is a schematic cross-sectional view showing the increased space at the bottom of the pocket. [Figure 8] FIG. 10 is a diagram showing the movement locus of the center of the cage. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A deep groove ball bearing, which is a rolling bearing of the present invention, is used in industrial machinery such as servo motors and generators. However, the deep groove ball bearing can also be used in applications other than servo motors.

[0017] <Rolling bearings> As shown in Fig. 1, a deep groove ball bearing 1 according to a first embodiment of the present invention is generally composed of inner and outer rings 2 and 3, a plurality of ball-shaped rolling elements 4 interposed between the inner ring 2 and the outer ring 3, and a steel cage 5 having a cage width W that holds the rolling elements 4. The plurality of rolling elements 4 interposed between the raceway surfaces 2a and 3a of the inner and outer rings 2 and 3 are held at regular intervals in the circumferential direction by the cage 5. The cage is not limited to being made of steel and may also be made of resin.

[0018] A lubricant such as grease is sealed in the bearing space between the inner and outer rings 2, 3. The inner and outer rings 2, 3 and the rolling elements 4 are made of, for example, high-carbon chromium bearing steel such as SUJ2 or martensitic stainless steel, but are not limited to these steels. A sealing member (not shown) that seals the bearing space may be disposed between the inner and outer rings 2, 3.

[0019] <Cage> As shown in Figure 2, the steel plate cage 5 is a corrugated cage formed by combining two annular retaining plates (annular bodies) 5a, 5a that have hemispherical bulges 6 arranged at predetermined intervals along the circumferential direction and are stacked together in the axial direction. Each annular body 5a has a plurality of hemispherical pocket walls 10 that are lined up in the circumferential direction and each form half of a pocket 8 that holds the rolling elements 4.

[0020] Each annular retaining plate 5a has a flat connecting portion 7 connecting circumferentially adjacent pocket walls 10, 10, and the two annular retaining plates 5a, 5a are overlapped with each other at the connecting portions 7, 7, and these connecting portions 7, 7 are joined via rivets Rb or engaging claws (not shown). Each hemispherical bulge 6 faces each other to form a ring-shaped pocket 8. A rolling element 4 is held in each pocket 8. The pocket surface 8a is formed with a curved surface such as a spherical surface. In this embodiment, the pocket shape of the cage 5 is improved as described below. Each annular retaining plate 5a is a pressed product of, for example, a cold-rolled steel strip.

[0021] The pocket wall 10 satisfies the following formulas (1) to (4). First spherical part (R a For the spherical surface 11, all of the following equations are satisfied.

number

[0022] In the above formula (1), R a is H a Larger than H a is greater than R and R a and H a The relationship involving and R is limited by a constant value.

[0023] The second spherical part (R b For spherical surface 12, all of the following equations are satisfied.

number

[0024] In the above formula (2), R b is R a is greater than and R a R b and H b The relational expression involving R a is limited between a constant value of and a constant value of W.

[0025] The third spherical part (R c For the spherical surface 13, all of the following equations are satisfied.

number

[0026] In the above formula (3), R c is greater than 10 mm and R c R a and R b The relations involving are restricted by their relation to a constant value of W.

[0027] The above c value is calculated using the following formula.

number

[0028] As shown in FIG. 3, which is a cross section taken along plane III of FIG. 2, the pocket wall 10 of the cage 5 has a circumferential cross section in which the base (circumferential end) BP near the joint between the two annular retaining plates 5a, 5a is formed into a first spherical portion 11 (R a The second spherical portion 12 (R b The base BP and the apex TP are connected smoothly by a curved third spherical portion 13 (R c Furthermore, the distal end portion BPe of the base portion BP is curved so as to smoothly connect to the connecting portion 7.

[0029] As shown in Fig. 4, which is a cross section taken along plane IV in Fig. 2, the cage 5 has a cage width W in a direction perpendicular to the circumferential direction. In other words, the entire cage 5, including the pocket wall portions 10 and the connecting portions 7 in Fig. 3, has the same width W.

[0030] The pocket surface 8a of the pocket 8 in FIG. 3 is a spherical surface R centered at a position Rac that is shifted in the axial direction AD from the spherical center CC of the rolling element 4. a、 R centered on another position Rbc shifted to the other side of the axial direction AD b Spherical, R a Sphere and R b R circumscribing both spheres c It is formed by a three-stage spherical surface called a spherical surface. Here, the distance CC-Rac between the center position Rac of the Ra sphere and the spherical center CC is approximately CC-Rac = (0.01 to 0.1)R, where R is the radius of the rolling element, and the distance CC-Rbc between the center position Rbc of the Rb sphere and the spherical center CC is approximately CC-Rbc = (0.1 to 0.7)R, where R is the radius of the rolling element. Also, the radius of the Rc sphere exceeds 10 mm. Ha is the height from CC to the zenith of the Ra sphere. Hb is the height from CC to the zenith of the Rb sphere.

[0031] FIG. 5 is a perspective view showing a pocket bottom 15 of the present invention formed on the pocket surface 8a of the steel plate cage 5. Due to the geometric relationship between the first spherical portion of the base portion BP in FIG. 3 and the second spherical portion of the apex portion TP with a smaller radius of curvature, the first spherical portion has a convex shape, thereby forming a convex space portion (pocket bottom 15) inside the pocket. The third spherical portion 13 smoothly connects the first spherical portion 11 and the second spherical portion 12 and ensures that the pocket bottom 15 has a constant size (FIGS. 3 and 4). The pocket bottoms 15 are provided on each of the two annular bodies 5a, 5a, and are formed in pairs facing each other in one pocket 8.

[0032] Calculation data for the steel plate cages of the conventional product and the product of the present invention are shown. <Dynamic analysis: pocket bottom data and others> Figure 6 shows the results of calculations for the conventional product and the product of the present invention, with one pocket 8 being the target during the process of the cage 5 making approximately 10 rotations under the operating conditions in Table 1.

[0033] [Table 1]

[0034] As shown in Figure 6, the pocket bottom 15 of the product of the present invention does not come into contact with the rolling elements 4, and the load acting on the pocket bottom 15 within 10 rotations of the cage (black line in Figure 6) is 0N. In contrast, the bottom of the conventional product comes into contact with the rolling elements 4, generating a load (gray line in Figure 6) with a maximum value of 38N. The number of times the rolling elements 4 came into contact with the pocket surface 8a was 8,225 times for the conventional product and 4,989 times for the product of the present invention, a 39% reduction for the product of the present invention. The result of integrating the load acting on the pocket surface 8a was 0.39N for the conventional product and 0.34N for the product of the present invention, a 13% reduction for the product of the present invention. * Wear is positively correlated with the product of surface pressure and relative velocity, but to compare the wear of conventional products and the product of this invention, it is sufficient to look at the ratio of the integrals of the loads.

[0035] <Geometric calculation: Grease passage space> As shown in Figure 7, the product of the present invention has an increased space for grease to pass between the rolling elements 4 and the pocket 8 by approximately 23% (the black part in Figure 7) compared to the conventional product. The pocket surface 8a formed into a three-step spherical surface prevents the rolling elements 4 from hitting the pocket bottom 15, increasing the space for grease to pass through, and bringing about the following effects.

[0036] <Effect of rolling elements not hitting the bottom of the pocket> At the pocket bottom 15, there is no contact with the rolling elements 4, so sliding wear does not occur. For the entire pocket 8, the number of contacts between the rolling elements 4 and the pocket surface 8a has been reduced by 39% compared to the conventional product, and the integral of the load acting on the pocket surface 8a over a certain period of time has also been reduced by 13% compared to the conventional product, which has also made it possible to reduce wear on the entire pocket surface 8a.

[0037] <Effect of increasing the space for grease to pass through> During high-speed rotation (for example, a rolling element rotation speed of 33,000 rpm), the rolling element 4 generates agitation heat due to the grease that has flowed into the small gap (0.2 mm) between the pocket surfaces 8a. It is generally recognized in the bearing industry that if this small gap is increased, the temperature rise during bearing rotation can be suppressed. However, in order to increase this gap space, the conventional single spherical R a The method of increasing the radius is not adopted. The reason is that the R of a single sphere a Increasing the radius can suppress temperature rise, but there are concerns that the increased cage movement will also increase bearing vibration and noise. The product of this invention increases the space through which grease can pass, and as shown in Figure 8, the movement of the steel cage 5 is kept to the same level as that of a conventional resin cage. The functions provided by this invention as described above have led to improved durability compared to conventional bearings.

[0038] <Action and effect> According to the deep groove ball bearing 1 described above, the pocket shape of the cage 5 is improved, and the pocket wall portion 10 is formed so that the first spherical portion 11 (R a spherical surface) and a second spherical portion 12 (R b spherical surface) and a third spherical portion 13 (R cSince the pocket is formed of a first spherical portion at the base BP and a second spherical portion at the apex TP with a smaller radius of curvature, a convex space (pocket bottom 15) is formed inside the pocket, and contact with the rolling elements 4 is avoided at this pocket bottom 15, thereby reducing wear of the entire pocket.

[0039] At the same time, pocket bottom 15 increases the space through which grease passes in pocket 8, making it possible to suppress temperature rise even at medium to high speed rotation. In addition, grease is more likely to accumulate at convex pocket bottom 15, improving the lubrication environment of pocket 8 and reducing wear on the entire pocket 8. This makes it possible to prevent wear on pocket surface 8a at low cost and reduce wear on the entire cage 5.

[0040] In this embodiment, the pocket shape of the cage 5 formed by a conventional single spherical surface is changed to three spherical surfaces (R a , R b , R c ) has been improved to reduce wear on the entire pocket 8, suppress temperature rise at medium to high rotation speeds, and improve bearing durability, making it possible to achieve high-speed rotation equivalent to that of conventional cages.

[0041] <Other embodiments> In the following description, parts corresponding to matters previously described in the above embodiment are given the same reference numerals, and duplicated description will be omitted. When only a part of the configuration is described, the other parts of the configuration are the same as those in the previously described embodiment unless otherwise specified. The same configuration produces the same effects. In addition to combining the parts specifically described in each embodiment, it is also possible to partially combine embodiments together, provided that there is no particular problem with the combination.

[0042] <Second embodiment> The rolling bearing according to the second embodiment satisfies only the above formulas (1) and (2). In the rolling bearing according to this embodiment, the pocket shape of the cage formed by a conventional single spherical surface is changed to two spherical surfaces (R a , R b ), and the small third spherical portion 13 does not need to follow a specific formula, as long as it has a smooth shape. This reduces wear on the entire pocket, suppresses temperature rise at medium to high rotational speeds, and improves bearing durability, making high-speed rotation equivalent to that of conventional cages possible.

[0043] In the deep groove ball bearing, a sealing member (not shown) that closes the bearing space may be provided on only one side. A lubricating oil other than grease may be used as a lubricant for deep groove ball bearings.

[0044] Although the embodiments for carrying out the present invention have been described above based on the examples, the embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0045] 1... deep groove ball bearing (rolling bearing), 2... inner ring, 3... outer ring, 4... rolling element, 5... wave cage, 5a... annular retaining plate (annular body), 7... joint portion, 8... pocket, 8a... pocket surface, 10... pocket wall portion, 11... first spherical portion, 12... second spherical portion, 13... third spherical portion, pocket bottom portion... 15, top portion... TP, base portion... BP, axial direction... AD

Claims

1. A rolling bearing having an inner ring, an outer ring, a plurality of ball-shaped rolling elements interposed between the inner ring and the outer ring, and a cage that holds the rolling elements, the cage has two annular bodies overlapping each other in the axial direction, each annular body having a plurality of spherical pocket wall portions that form pockets that hold the rolling elements, and a connecting portion between adjacent pocket wall portions, and the annular bodies are connected to each other at the connecting portion; the pocket wall portion has a first spherical portion provided at a circumferential end of the pocket wall portion, a second spherical portion provided at an axial end of the pocket wall portion, and a third spherical portion connecting the first spherical portion and the second spherical portion, the second spherical portion having a smaller radius of curvature than the first spherical portion.

2. The rolling bearing of claim 1, The third spherical portion is circumscribing the first spherical portion and the second spherical portion.

3. 2. The rolling bearing of claim 1, wherein the pocket wall portion satisfies at least formulas (1) and (2) of the following formulas (1) to (4): [Equation 1] [Equation 2] [Equation 3] [Equation 4]

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