Rolling bearing

Abstract

Provided is a rolling bearing that can prevent wear of a pocket wall portion even at medium and high rotational speeds at a low cost and realize a reduction in wear of a retainer, by an improvement of the pocket shape of the retainer. This deep groove ball bearing (1) as a rolling bearing, comprises: an inner ring (2); an outer ring (3); a plurality of ball-shaped rolling elements (4) interposed between the inner and outer rings; and a retainer (5) retaining the rolling elements. The retainer has two annular bodies (5a, 5a) stacked on each other in an axial direction. Each annular body (5a) has a plurality of pocket wall portions (10) arranged in a circumferential direction, and each of which forms a pocket (8) for retaining the rolling element. Each pocket wall portion (10) is formed of a first spherical portion (11), a second spherical portion (12) having a smaller radius of curvature than the first spherical portion, and a third spherical portion (13) smoothly connecting between the first spherical portion and the second spherical portion.

Description

Rolling bearings Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-127858, filed August 2, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a rolling bearing, and to a technique applied to, for example, servo motors, generators, etc.

[0003] 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.

[0004] Furthermore, the steel cage of a deep groove ball bearing is guided by the rolling elements (balls) during rotation, and the rolling elements constantly come into contact with the pocket surface of the cage during high-speed rotation, causing sliding wear. Grease inside the pocket plays an important role in reducing this wear.

[0005] 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.

[0006] JP 2017-172749 A JP 2018-162875 A

[0007] 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 to suppress temperature rise during bearing rotation by limiting the cage band width, this prevents grease from accumulating inside the pocket, and therefore is not effective in reducing pocket wear.

[0008] Furthermore, under conditions requiring higher speeds, the wear caused by the pockets coming into contact with the rolling elements becomes more severe, and the grease does not easily accumulate inside the pockets due to centrifugal force, causing the cage pockets (especially the pocket bottoms) to wear more quickly, resulting in a shorter bearing lifespan.

[0009] 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.

[0010] The 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, wherein the cage has two annular bodies that overlap 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, and the pocket wall portions have 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 that connects 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.

[0011] According to this configuration, the cage pocket shape is improved so that 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). This prevents contact with the rolling elements at the pocket bottom, thereby reducing wear of the entire pocket. Here, the axial direction of the central axes of the inner and outer rings of the rolling bearing is defined as the "axial direction." A direction perpendicular to the "axial direction" is defined as the "radial direction." The "circumferential direction" refers to the direction along the circumference around the central axis of the inner and outer rings. The same definitions of these directions apply throughout the following description.

[0012] Furthermore, 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.

[0013] Preferably, the third spherical portion is circumscribing the first spherical portion and the second spherical portion, thereby making the pocket shape of the cage smooth and preventing wear on the pocket surface.

[0014] 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.

[0015] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims is included in the present invention.

[0016] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation, and should not be used to define the scope of the present invention, which is defined by the appended claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts.

[0017] Fig. 3 is a schematic longitudinal sectional view of a rolling bearing according to a first embodiment of the present invention; Fig. 4 is a perspective view of a waveform cage of the rolling bearing; Fig. 5 is a sectional view of the waveform cage of Fig. 2 taken along plane III; Fig. 6 is a sectional view of the waveform cage of Fig. 2 taken along plane IV; Fig. 7 is a perspective view of a pocket bottom formed in the cage; Fig. 8 is a characteristic diagram showing a load generated at the pocket bottom; Fig. 9 is a schematic sectional view showing an increased space at the pocket bottom; Fig. 10 is a diagram showing the movement locus of the cage centre

[0018] First Embodiment An embodiment of the present invention will now 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.

[0019] <Rolling bearing> 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 be made of resin.

[0020] 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 rolling elements 4 are made of, for example, high-carbon chromium bearing steel such as SUJ2 specified in JIS G 4805, which conforms to ISO 100Cr6, or martensitic stainless steel. However, the material is 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.

[0021] 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 that 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 one half of a pocket 8 that retains rolling elements 4.

[0022] Each annular retaining plate 5a has a flat connecting portion 7 connecting circumferentially adjacent pocket walls 10, 10, and 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.

[0023] The pocket wall portion 10 satisfies the following formulas (1) to (4): The first spherical portion (Ra spherical surface) 11 satisfies all of the following formulas.

[0024] In the above formula (1), Ra is greater than Ha, Ha is greater than R, and the relational expression including Ra, Ha, and R is limited by a constant value.

[0025] The second spherical portion (Rb spherical surface) 12 satisfies all of the following formulas.

[0026] In the above formula (2), Rb is greater than Ra, and the relationship involving Rb and Hb to Ra is limited between a fixed value of Ra and a fixed value of W.

[0027] The third spherical portion (Rc spherical surface) 13 satisfies all of the following formulas.

[0028] In the above equation (3), Rc is greater than 10 mm, and the relationship of Rc to Ra and Rb is limited by its relationship to a fixed value of W.

[0029] The above c value is calculated using the following formula.

[0030] 3, which is a cross section taken along plane III in FIG. 2, the pocket wall 10 of the cage 5 has a circumferential cross section in which a base portion (circumferential end portion) BP near the joint of the two annular retaining plates 5a, 5a is formed by a first spherical portion 11 (Ra spherical surface), a top portion (axial end portion) TP is formed by a second spherical portion 12 (Rb spherical surface) having a smaller radius of curvature than the base portion BP, and a curved third spherical portion 13 (Rc spherical surface) that smoothly connects the base portion BP and the top portion TP. Furthermore, an end portion BPe of the base portion BP is curved so as to smoothly connect to the joint portion 7.

[0031] As shown in Fig. 4, which is a cross section taken along plane IV of 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 of Fig. 3, has the same width W.

[0032] The pocket surface 8a of the pocket 8 in Figure 3 is formed by three spherical surfaces: a spherical surface Ra centered at a position Rac offset in the axial direction AD from the spherical center CC of the rolling element 4; an Rb spherical surface centered at another position Rbc offset to the other side of the axial direction AD; and an Rc spherical surface circumscribing both the Ra spherical surface and the Rb spherical surface. Here, the distance CC-Rac between the center position Rac of the Ra spherical surface and the spherical center CC is approximately CC-Rac = (0.01 to 0.1)R, where R is the radius of the rolling element. The distance CC-Rbc between the center position Rbc of the Rb spherical surface and the spherical center CC is approximately CC-Rbc = (0.1 to 0.7)R, where R is the radius of the rolling element. The radius of the Rc spherical surface exceeds 10 mm. Ha is the height of the zenith of the Ra spherical surface from CC. Hb is the height of the zenith of the Rb spherical surface from CC.

[0033] Figure 5 is a perspective view showing the pocket bottom 15 of the present invention formed on the pocket surface 8a of the steel plate cage 5. The geometric relationship between the first spherical portion of the base portion BP in Figure 3 and the second spherical portion of the apex portion TP, which has a smaller radius of curvature, causes the first spherical portion to have a convex shape, thereby forming a convex space (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 (Figures 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 each pocket 8.

[0034] The calculation data for the steel plate cages of the conventional product and the product of this invention are shown below. <Dynamic analysis: pocket bottom data and others> Figure 6 shows the results of calculations for the conventional product and the product of this invention, targeting one pocket 8 during the process of the cage 5 making approximately 10 rotations under the operating conditions in Table 1.

[0035]

[0036] As shown in Figure 6, the pocket bottom 15 of the present invention does not come into contact with the rolling elements 4, so the load acting on the pocket bottom 15 within 10 cage revolutions (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 contacts between the rolling elements 4 and the pocket surface 8a was 8,225 for the conventional product and 4,989 for the present invention, a 39% reduction for the present invention. The integrated load generated on the pocket surface 8a was 0.39N for the conventional product and 0.34N for the present invention, a 13% reduction for the present invention. * While wear is positively correlated with the product of surface pressure and relative velocity, the wear of the conventional product and the present invention can be compared by looking at the ratio of the integrals of the loads.

[0037] <Geometric calculation: grease passage space> As shown in Figure 7, the space through which grease passes between the rolling elements 4 and the pocket 8 in the product of the present invention is increased by approximately 23% (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 through which grease can pass, and bringing about the following effects.

[0038] <Effect of rolling elements not hitting pocket bottom> At pocket bottom 15, the rolling elements 4 do not hit each other, so sliding wear does not occur. For the entire pocket 8, the number of contacts between the rolling elements 4 and 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, making it possible to reduce wear on the entire pocket surface 8a.

[0039] <Effects of Increasing Grease Passage Space> During high-speed rotation (e.g., 33,000 rpm), rolling elements 4 generate agitation heat due to grease flowing into the small gaps (0.2 mm) between the pocket surfaces 8a. It is generally recognized in the bearing industry that increasing this small gap can reduce temperature rise during bearing rotation. However, the conventional method of increasing the Ra radius of the single spherical surface to increase the clearance space has not been adopted. This is because, while increasing the Ra radius of the single spherical surface can reduce temperature rise, it is feared that the increased cage movement will increase bearing vibration and noise. The product of the present invention not only increases the grease passage space, but also suppresses the movement of the steel cage 5 to a level similar to that of a conventional resin cage, as shown in Figure 8. The above-mentioned functions of the present invention lead to improved durability compared to conventional bearings.

[0040] <Effects> According to the deep groove ball bearing 1 described above, the pocket shape of the retainer 5 has been improved so that the pocket wall 10 is formed of a first spherical portion 11 (Ra spherical surface) of the base BP, a second spherical portion 12 (Rb spherical surface) of the apex TP having a smaller radius of curvature than that of the first spherical portion 11 (Ra spherical surface), and a third spherical portion 13 (Rc spherical surface) that smoothly connects these together.Therefore, a convex space (pocket bottom 15) is formed inside the pocket by the first spherical portion of the base BP and the second spherical portion of the apex TP having a smaller radius of curvature, and contact between this pocket bottom 15 and the rolling elements 4 is avoided, thereby reducing wear of the entire pocket.

[0041] At the same time, the pocket bottom 15 increases the space through which grease passes in the pocket 8, making it possible to suppress temperature rise even at medium to high speed rotation. In addition, the convex shape of the pocket bottom 15 makes it easier for grease to accumulate, improving the lubrication environment of the pocket 8 and reducing wear on the entire pocket 8. This makes it possible to prevent wear on the pocket surface 8a at low cost and reduce wear on the entire cage 5.

[0042] In this embodiment, the pocket shape of the retainer 5, which was formed by a conventional single spherical surface, has been improved to three spherical surfaces (Ra, Rb, Rc) with different radii of curvature, thereby reducing wear on the entire pocket 8, suppressing temperature rise at medium to high rotational speeds, and improving bearing durability, making it possible to achieve high-speed rotation equivalent to that of conventional retainers.

[0043] <Regarding Other Embodiments> In the following description, parts corresponding to matters previously described in the above embodiment are assigned the same reference numerals, and duplicated description will be omitted. When only 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.

[0044] Second Embodiment A rolling bearing according to a second embodiment satisfies only the above formulas (1) and (2). In this rolling bearing, the pocket shape of the cage, which was formed by a conventional single spherical surface, has been improved to have two spherical surfaces (Ra, Rb) with different radii of curvature that satisfy formulas (1) and (2), and the third spherical portion 13, which is a small portion, does not need to conform to a specific formula as long as it has a smooth shape. This makes it possible to reduce wear of the entire pocket, suppress temperature rise at medium to high rotational speeds, and improve bearing durability, enabling high-speed rotation equivalent to that of a conventional cage.

[0045] In the deep groove ball bearing, a seal member (not shown) that closes the bearing space may be provided on only one side.Lubricating oil other than grease may be used as a lubricant in the deep groove ball bearing.

[0046] As described above, the preferred embodiment has been described with reference to the drawings, but various additions, modifications, and deletions can be made without departing from the spirit of the present invention. Therefore, such additions, modifications, and deletions are also included in the scope of the present invention.

[0047] DESCRIPTION OF SYMBOLS 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 15... pocket bottom portion TP... top portion BP... base portion AD... axial direction

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, wherein the cage has two annular bodies that overlap 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, the annular bodies being connected to each other at the connecting portion, and the pocket wall portions having a first spherical portion provided at the circumferential end of the pocket wall portion, a second spherical portion provided at the axial end of the pocket wall portion, and a third spherical portion that connects 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.

2. A rolling bearing according to claim 1, wherein the third spherical portion is circumscribing the first spherical portion and the second spherical portion.

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

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