Rolling bearing

Abstract

A rolling bearing 1 in which there is a circumferential clearance between balls 4 and pocket formation surfaces 7 of a retainer 5 in a neutral state is configured such that, when one pocket 6 is defined as a reference pocket Sp, pockets 6 that have a circumferential center in areas AR1 offset 20°–70° and 200°–250° to one side in the circumferential direction with respect to a straight line SL that connects the circumferential center of the reference pocket Sp and the center of the retainer are defined as pockets that belong to a first group, and pockets that have a circumferential center in areas AR2 offset 110°–160° and 290°–340° to the one side in the circumferential direction with respect to the straight line SL are defined as pockets that belong to a second group, the minimum value δmin of the circumferential clearance Gb1 between the balls 4 and the pocket formation surfaces 7 that form the pockets 6 that belong to the first group is at least 0.1 mm greater than the maximum value δmax of the circumferential clearance Gb2 between the balls 4 and the pocket formation surfaces 7 that form the pockets 6 that belong to the second group.

Description

Rolling bearings

[0001] The present invention relates to a rolling bearing.

[0002] 11A and 11B show schematic cross-sectional views of a rolling bearing 100. The rolling bearing 100 shown in the figures comprises a pair of raceways (inner ring 101 and outer ring 102) that are arranged radially opposite each other and rotate relative to each other about a central axis via a plurality of rolling elements (here, balls) 103, and an annular cage 104 that holds the plurality of rolling elements 103 at intervals in the circumferential direction. The cage 104 is assembled between the inner ring 101 and the outer ring 102 so that, in an unloaded state in which gravity, rotational force, etc. are not acting on the rolling bearing 100, radial gaps 111 and 112 are formed between the cage 104 and the outer peripheral surface 101 a of the inner ring 101 and the inner peripheral surface 102 a of the outer ring 102, respectively, and a circumferential gap 113 is formed between the cage 104 and the rolling elements 103 that are accommodated in pockets 105 each consisting of a circular hole with a constant opening dimension along the radial direction. The radial clearances 111 and 112 are also called "guide clearances," and the circumferential clearance 113 is also called "pocket clearance." Due to the presence of the various clearances described above, the cage 104 incorporated between the inner and outer rings is able to move in the radial and circumferential directions when the rolling bearing 100 is in operation.

[0003] During operation of the rolling bearing 100, the cage 104 may experience an abnormally high-speed whirl (whirling at several times the cage rotation frequency or more), also known as the high-speed whirl phenomenon. The occurrence of the high-speed whirl phenomenon may cause problems such as abnormal noise, vibration, increased torque, torque fluctuation, and heat generation. The high-speed whirl phenomenon is said to be caused by, for example, frictional forces generated by radial contact between the raceway rings and the cage 104, or frictional forces generated by circumferential contact between the cage 104 (pocket forming surfaces 105 a) and the rolling elements 103. The mechanism by which the high-speed whirl phenomenon occurs due to contact between the cage 104 and the rolling elements 103 will be briefly described below with reference to FIGS. 11A and 11B .

[0004] First, as the rolling bearing 100 operates, as shown in Fig. 11A, the cage 104 is displaced in the 0 o'clock (12 o'clock) direction relative to the axis O, and the rolling elements 103 located at the 3 o'clock and 9 o'clock positions come into contact with the pocket forming surface 105a of the cage 104 at the 6 o'clock position. If the inner ring 101 is rotating clockwise at this time, a frictional force F is generated between the rolling elements 103 and the cage 104, displacing the cage 104 in the 3 o'clock direction. When the cage 104 is displaced by this frictional force F, the rolling elements 103 located at the 0 o'clock and 6 o'clock positions come into contact with the pocket forming surface 105a of the cage 104 at the 9 o'clock position, as shown in Fig. 11B. Accordingly, a frictional force F is generated, displacing the cage 105 in the 6 o'clock direction. Thereafter, the above-described contact and friction between the cage 104 and the rolling elements 103 is repeated, causing the cage 104 to whirl at high speed in the same direction as the rotation direction of the inner ring 101 .

[0005] In order to prevent the occurrence of abnormal noise, vibration, etc. resulting from the above-mentioned high-speed whirling phenomenon of the cage, for example, in the rolling bearing described in Patent Document 1 below, a predetermined amount of imbalance is intentionally imparted to the cage so that the cage is constantly eccentric with respect to the raceway, i.e., the cage is rotated with part of it constantly in contact with the raceway.

[0006] JP 2011-196513 A

[0007] However, if the technical means described in Patent Document 1 is adopted, the rolling elements held by the cage (housed in the pockets of the cage) will also rotate (revolve) in an eccentric state, which raises concerns about increased vibrations at the cage's revolution frequency (NRRO).

[0008] Furthermore, since the cage needs to be formed into a point-asymmetric shape, it takes time and effort to machine the cage with high precision. Furthermore, to ensure the durable life required for a rolling bearing, it is necessary to suppress wear at the constant contact area between the cage and the raceway. Therefore, it is necessary to take measures such as applying precision polishing or other finishing processes to the two opposing surfaces of the raceway and the cage that come into contact with each other, thereby finishing these two surfaces with extremely high precision. Therefore, adopting the technical means of Patent Document 1 poses the problem of high costs.

[0009] In view of the above circumstances, an object of the present invention is to provide a low-cost rolling bearing that can prevent, as much as possible, the occurrence of the high-speed whirl phenomenon caused by frictional forces generated by contact between the cage and the rolling elements, and further the occurrence of abnormal noise and vibrations that can result from this.

[0010] As described above, the cage is typically incorporated between the inner and outer rings in a state in which it is movable in the radial and circumferential directions, and the range of circumferential movement of the cage is limited by the circumferential clearance between the rolling elements and the pocket-forming surface of the cage, also known as the "pocket clearance." Note that a "pocket" refers to a space that accommodates the rolling elements, and a "pocket-forming surface" refers to a surface that constitutes the space (pocket) provided to accommodate the rolling elements and that comes into contact with and slides against the rolling elements. The inventors believed that by devising the arrangement of the pockets that form the circumferential clearance and the size of the circumferential clearance, it would be possible to control the movement (movement trajectory) of the cage during bearing operation and the contact between the cage and the rolling elements, thereby minimizing the occurrence of the high-speed whirl phenomenon caused by contact between the cage and the rolling elements.

[0011] Furthermore, the behavior of the cage during bearing operation can be estimated by dynamic analysis, and the region in which the cage can move without contacting the rolling elements (and further the inner and outer rings) (hereinafter, this region will also be referred to as the "cage movable region") can be determined by numerical calculation or the like from geometric relationships based on the arrangement of the cage pockets, etc. It has been found that under analytical conditions in which the high-speed whirl phenomenon is determined to occur through dynamic analysis, the shape of the cage movable region becomes circular or a polygonal shape close to a circle (for example, a regular polygon with obtuse interior angles at each vertex), whereas under analytical conditions in which the high-speed whirl phenomenon is determined not to occur, the shape of the cage movable region becomes an "irregular shape" that significantly deviates from a circular shape or the like. Therefore, the present inventors conducted extensive research and discovered a pocket arrangement, etc., that can make the shape of the cage movable region an "irregular shape." The present invention is based on this finding.

[0012] That is, the present invention, which has been devised to achieve the above object, is a rolling bearing comprising a pair of raceways which are arranged radially opposite to each other and rotate relative to each other via a plurality of rolling elements, and an annular cage which has a plurality of pockets formed at intervals in the circumferential direction and each pocket accommodating the rolling elements individually, and in which a circumferential clearance is formed between the pocket forming surface of the cage in a neutral state and the rolling elements, wherein one of the plurality of pockets is taken as a reference pocket, and pockets whose circumferential centers are in ranges shifted 20° to 70° and 200° to 250° to one side in the circumferential direction from a straight line connecting the circumferential center of this reference pocket to the center of the cage are defined as pockets belonging to a first group, and pockets whose circumferential centers are in ranges shifted 110° to 160° and 290° to 340° to one side in the circumferential direction from the straight line are defined as pockets belonging to a second group, The minimum value of the circumferential clearance formed between the rolling elements and the pocket forming surfaces that form the pockets belonging to the first group is 0.1 mm or more larger than the maximum value of the circumferential clearance formed between the rolling elements and the pocket forming surfaces that form the pockets belonging to the second group. Note that the "neutral state" in this invention refers to a state in which the centers of the pockets and the rolling elements are aligned and the cage and the rolling elements are not in contact with each other.

[0013] In the rolling bearing according to the present invention having the above configuration, assuming that the plurality of pockets (all pockets) are arranged in four quadrants on a two-dimensional plane (XY plane), quadrants mainly composed of "pockets belonging to the first group" and quadrants mainly composed of "pockets belonging to the second group" will alternate. In other words, if the center of the reference pocket is located on the positive portion of the X-axis, the first and third quadrants will be mainly composed of "pockets belonging to the first group," and the second and fourth quadrants will be mainly composed of "pockets belonging to the second group." If such a pocket arrangement is adopted and the minimum value of the circumferential clearance formed between the pocket forming surfaces of the "pockets belonging to the first group" and the rolling elements is 0.1 mm or more larger than the maximum value of the circumferential clearance formed between the pocket forming surfaces of the "pockets belonging to the second group" and the rolling elements, the shape of the cage movable region described above can be made into an "irregular shape" that can prevent the occurrence of the high-speed whirl phenomenon. This makes it possible to prevent as much as possible the occurrence of the high-speed whirl phenomenon caused by frictional forces generated by contact between the cage (the pocket forming surface of the cage) and the rolling elements.

[0014] Furthermore, the present invention merely involves ingenuity in the arrangement and opening dimensions of the pockets provided in the cage, and does not involve any particular complication in the formation and processing of the pockets. Furthermore, unlike the conventional rolling bearing disclosed in Patent Document 1, the rolling bearing of the present invention does not intentionally make the cage eccentric (in contact) with the raceway rings, so there is no need to perform time-consuming and costly processing such as precision polishing on the cage or raceway rings, and there is no need to consider vibration issues at the orbital frequency of the cage. Therefore, the rolling bearing of the present invention can be produced at significantly lower cost than the rolling bearing of Patent Document 1.

[0015] The rolling bearing according to the present invention can be easily realized by configuring (all of) the pockets belonging to the first group among the multiple pockets as large pockets, and configuring (all of) the pockets belonging to the second group as small pockets with opening dimensions smaller than those of the large pockets.

[0016] As described above, according to the present invention, it is possible to realize at low cost a rolling bearing that can prevent as much as possible the occurrence of the high-speed whirl phenomenon caused by frictional forces generated by contact between the cage and the rolling elements, as well as the abnormal noise and vibrations that can result from this.

[0017] 1 is a partial schematic plan view of a rolling bearing according to an embodiment of the present invention. FIG. 1 is a cross-sectional view taken along the arrows A1-A1 in FIG. 1. FIG. 1 is a cross-sectional view taken along the arrows A2-A2 in FIG. 1. FIG. 2 is a schematic plan view of a cage incorporated in the rolling bearing shown in FIG. 1. FIG. 3 is a diagram showing the cage movable area, etc., of a rolling bearing employing the cage shown in FIG. 4. FIG. 4 is a schematic view for explaining how to determine the cage movable area. FIG. 5 is a diagram showing the cage movable area of ​​a rolling bearing not having the configuration of the present invention. FIG. 6 is a diagram showing the cage movable area of ​​a rolling bearing not having the configuration of the present invention. FIG. 7 is a diagram showing the displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing according to this embodiment employing the cage shown in FIG. 4, where the friction coefficient of the pocket forming surfaces of the cage is set to 0.10. FIG. 8 is a diagram showing the displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing according to this embodiment employing the cage shown in FIG. 4, where the friction coefficient of the pocket forming surfaces of the cage is set to 0.15. 7A is a diagram showing a displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing according to the present embodiment employing the cage shown in FIG. 4 , where the friction coefficient of the pocket forming surfaces of the cage is set to 0.20. FIG. 7B is a diagram showing a displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing that provides the cage movable region shown in FIG. 7A , where the friction coefficient of the pocket forming surfaces of the cage is set to 0.10. FIG. 7C is a diagram showing a displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing that provides the cage movable region shown in FIG. 7A , where the friction coefficient of the pocket forming surfaces of the cage is set to 0.15. FIG. 7D is a diagram showing a displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing that provides the cage movable region shown in FIG. 7A , where the friction coefficient of the pocket forming surfaces of the cage is set to 0.20. FIG. 7B is a diagram showing a displacement mode of the cage during 10 rotations of the inner ring of a rolling bearing that provides the cage movable region shown in FIG. 7B , where the friction coefficient of the pocket forming surfaces of the cage is set to 0.10. 7B is a diagram showing the displacement mode of the cage during 10 rotations of the inner ring of the rolling bearing in which the cage movable range shown in Figure 7B is obtained, where the friction coefficient of the pocket forming surface of the cage is 0.15. Fig. 7C is a diagram showing the displacement mode of the cage during 10 rotations of the inner ring of the rolling bearing in which the cage movable range shown in Figure 7B is obtained, where the friction coefficient of the pocket forming surface of the cage is 0.20. Fig. 7D is a schematic cross-sectional view of a general rolling bearing.11B is a cross-sectional view showing a state in which the cage of the rolling bearing shown in FIG. 11A is displaced in the radial direction. FIG.

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Unless otherwise specified, the terms "axial direction," "radial direction," and "circumferential direction" used below to indicate directionality refer to a direction parallel to the axis O of the rolling bearing 1 shown in Figure 1, a radial direction of a circle centered on the axis O, and a circumferential direction of a circle centered on the axis O, respectively.

[0019] Fig. 1 is a partial schematic plan view of a rolling bearing 1 according to an embodiment of the present invention, and more specifically, a partial schematic plan view of the rolling bearing 1 in an unloaded state in which gravity, rotational force, and the like are not acting. Fig. 2 is a cross-sectional view taken along line A1-A1 in Fig. 1, and Fig. 3 is a cross-sectional view taken along line A2-A2 in Fig. 1. The rolling bearing 1 shown in Fig. 1 and other figures is a ball bearing comprising a pair of raceways (inner ring 2 and outer ring 3) made of a highly rigid metallic material such as bearing steel (high carbon chromium bearing steel), a plurality of balls 4 rollably interposed between the inner ring 2 and the outer ring 3, and an annular cage 5 that holds the plurality of balls 4 at intervals in the circumferential direction. More specifically, it is an angular contact ball bearing in which the balls 4 contact an arc-shaped inner raceway surface 2b formed on the outer peripheral surface 2a of the inner ring 2 and an arc-shaped outer raceway surface 3b formed on the inner peripheral surface 3a of the outer ring 3 at a contact angle α.

[0020] The cage 5 has a plurality of pockets 6 formed therein, each accommodating one ball 4, and the cage 5 shown in the figure has a total of 24 pockets 6 formed at intervals of 15°. As shown in Figures 2 and 3, each pocket 6 is a circular hole with a constant opening dimension (pocket diameter) W along the radial direction, and the pocket forming surface 7 of the cage 5, which forms the pockets 6, is formed as a cylindrical surface with a constant diameter.

[0021] A resin cage made of a resin material such as PA66 resin or phenolic resin is used as the cage 5. However, as long as each pocket 6 is formed with a circular hole as described above, it is also possible to use a known cage other than a resin cage, such as a machined cage obtained by cutting a metal material into a predetermined shape, or a pressed cage obtained by joining a pair of cage blanks that have been press-molded (punched) into a predetermined annular shape.

[0022] 2 and 3 , in an unloaded state in which gravity, rotational force, and the like are not acting on the rolling bearing 1, the cage 5 is in a neutral state (a state in which it is not in contact with the balls 4, or the inner ring 2 or the outer ring 3) in which it forms radial clearances between itself and the inner ring 2 and the outer ring 3, and forms circumferential clearances between itself and the balls 4 accommodated in the pockets 6. Therefore, when the cage 5 is in the neutral state, a first radial clearance Ga1 is formed between the outer peripheral surface 2 a of the inner ring 2 and the inner peripheral surface 5 a of the cage 5, a second radial clearance Ga2 is formed between the inner peripheral surface 3 a of the outer ring 3 and the outer peripheral surface 5 b of the cage 5, and a circumferential clearance Gb, also referred to as a "pocket clearance," is formed between the balls 4 and the pocket-forming surface 7 of the cage 5. By setting these various clearances, the cage 5 is able to move radially and circumferentially when the rolling bearing 1 is in operation, ensuring good operability of the rolling bearing 1. In the illustrated example of the rolling bearing 1, the size of the first radial gap Ga1 is larger than the size of the second radial gap Ga2, and further, the size of the second radial gap Ga2 is larger than the size of the circumferential gap Gb (both the circumferential gaps Gb1 and Gb2 described later).

[0023] The characteristic configuration of the rolling bearing 1 of this embodiment having the above-described structure will be described below by taking as a representative example a case in which balls 4 having a design diameter of 8.73 mm are used.

[0024] In this rolling bearing 1, first, as shown in FIG. 4, any one of the 24 pockets 6 is set as a reference pocket Sp, and a range AR is set by shifting the reference pocket Sp to one side in the circumferential direction (counterclockwise in the illustrated example) by 20° to 70° and 200° to 250° with respect to a straight line SL connecting the circumferential center of the reference pocket Sp and the center of the cage. １The pockets 6 having their circumferential centers in the ranges AR110° to 160° and 290° to 340° shifted to one side in the circumferential direction with respect to the straight line SL are defined as "pockets belonging to the first group." ２ The pockets 6 having their circumferential centers at are defined as "pockets belonging to the second group." Under this definition, the minimum value δmin of the circumferential clearance Gb1 (see FIG. 3) formed between the pocket forming surfaces 7 that form the "pockets belonging to the first group" and the balls 4 is set to be 0.1 mm or more larger than the maximum value δmax of the circumferential clearance Gb2 (see FIG. 3) formed between the pocket forming surfaces 7 that form the "pockets belonging to the second group" and the balls 4 (satisfying the relational expression δmin - δmax ≥ 0.1 mm). Therefore, in the rolling bearing 1 of this embodiment, the sizes of the circumferential clearances Gb1, Gb2 and the radial clearances Ga1, Ga2 increase in the order of Gb2, Gb1, Ga2, and Ga1.

[0025] To achieve the above configuration, the cage 5 of the rolling bearing 1 of this embodiment forms two types of pockets, large and small, which have different opening dimensions (pocket diameters) W. That is, the pockets 6 include large pockets 6A and small pockets 6B whose pocket diameter W is smaller than that of the large pockets 6A. In this embodiment, in which a total of 24 pockets 6 are provided at intervals of 15°, as shown in Fig. 4 , large pocket groups each consisting of six large pockets 6A in the circumferential direction and small pocket groups each consisting of six small pockets 6B in the circumferential direction are arranged alternately in pairs in the circumferential direction, and one large pocket 6A constituting one of the two large pocket groups is set as a reference pocket Sp, thereby achieving the above configuration.

[0026] When the large pocket group and the small pocket group are arranged in the above manner, all of the pockets belonging to the first group are large pockets 6A, and all of the pockets belonging to the second group are small pockets 6B, as shown in Figure 4. Therefore, for example, if the pocket diameter W of the large pocket 6A is 9.13 mm and the pocket diameter W of the small pocket 6B is 8.93 mm, the minimum value δmin of the circumferential gap Gb1 formed between the pocket forming surface 7 forming the "pocket belonging to the first group" and the ball 4 is 9.13 mm - 8.73 mm = 0.4 mm in diameter, and the maximum value δmax of the circumferential gap Gb2 formed between the pocket forming surface 7 forming the "pocket belonging to the second group" and the ball 4 is 8.93 mm - 8.73 mm = 0.2 mm in diameter. Therefore, the condition δmin - δmax ≥ 0.1 mm is satisfied.

[0027] For the rolling bearing 1 of this embodiment having the above configuration, the cage movable area 10 was determined, that is, the area surrounded by lines connecting the outer edges of a scatter diagram obtained by plotting an infinite number of positions on a two-dimensional coordinate system where the cage 5 can exist without contacting the inner ring 2, the outer ring 3, and the balls 4. As shown in Figure 5, the determined cage movable area 10 has a non-circular shape with two alternating smooth arc portions 11 and two pointed acute-angle portions 12 provided along the longitudinal direction of its outer edge, and has an "irregular shape" that deviates significantly from a circle or a regular polygon close to a circle.

[0028] The range of the cage movable area 10 indicates that the cage 5 can move freely without coming into contact with the inner ring 2, the outer ring 3, and the balls 4, and therefore, if the center of the cage 5 is located within the range of the cage movable area 10 during bearing operation, the center of the cage 5 will be subjected to centrifugal force and will move to the outer edge of the cage movable area 10. When the center of the cage 5 reaches the outer edge of the cage movable area 10, the cage 5 will come into contact with the balls 4 and will be subjected to a frictional force in the tangential direction, causing it to move along the outer edge of the cage movable area 10.

[0029] At this time, a pointed acute angle portion 12 is provided on the outer edge of the cage movable region 10, and the direction of the frictional force changes significantly at this acute angle portion 12, so it is possible to prevent a linear increase in the whirling speed of the cage 5 even if contact and friction between the cage 5 and the balls 4 is repeated during operation of the rolling bearing 1. This makes it possible to prevent the occurrence of a high-speed whirling phenomenon of the cage 5, which is driven by the frictional force generated by contact between the cage 5 and the balls 4.

[0030] The rolling bearing 1 of this embodiment essentially provides the pockets 6 in the cage 5 with two types of pockets, large and small, 6A and 6B, each with a predetermined difference in opening dimension (pocket diameter) W, and by devising an ingenious arrangement of the large and small pockets 6A and 6B, it is possible to prevent the occurrence of the high-speed whirl phenomenon, without any particular complication in the formation and processing of the pockets 6. Furthermore, unlike conventional rolling bearings, the rolling bearing 1 of this embodiment does not intentionally cause the cage 5 to be eccentric (in contact) with the inner ring 2 and the outer ring 3, so there is no need to subject the cage 5 and the like to time-consuming and costly processing such as precision polishing, and there is no need to consider vibration problems at the orbital frequency of the cage 5. Therefore, the rolling bearing 1 of this embodiment has high support performance, yet can be realized at significantly lower cost than conventional rolling bearings.

[0031] Here, a method for determining the position where the cage 5 can exist without contacting the balls 4, which is necessary for determining the cage movable area 10, will be briefly described with reference to FIG.

[0032] 6 is a conceptual diagram showing a portion of the cage 5 and two balls 4 housed in pockets 6 of the cage 5. In the figure, the symbol O indicates the axis, the symbol C indicates the center of the cage 5, the symbol B indicates the center of the ball 4, and the symbol P indicates an arbitrary point on the pocket forming surface 7 of the cage 5. Note that the subscript (index) of the symbol B and the left-hand character of the subscript of the symbol P indicate the numbers of the ball 4 and the pocket 6 that houses it, and the right-hand character of the subscript of the symbol P indicates the j-th point when the pocket forming surface 7 is discretized (mesh divided).

[0033] First, the center B of ball 4 ｉ From an arbitrary point P on the pocket forming surface 7 of the pocket 6 containing the ball 4 ｉ,j The magnitude (absolute value d) of the vector pointing to the point P on the pocket forming surface 7 is compared with the radius (r) of the ball 4. If the absolute value d is greater than the radius r of the ball 4, ｉ,j If the absolute value d is equal to or smaller than the radius r of the ball 4, it is determined that the point P on the pocket forming surface 7 does not interfere with the ball 4. ｉ,j is determined to interfere with the ball 4. Thereafter, the same determination process is carried out for other points P.

[0034] In the example shown in FIG. 6, the point P on the pocket forming surface 7 of the pocket 6 containing the ball 4 having the center indicated by the symbol B1 1,j and point P 1,j+1 does not interfere with the ball 4, and the pocket 6 accommodating the ball 4 has a center indicated by the symbol B2. 2,j and point P 2,j+1 will interfere with the balls 4. If the relational expression f(i, j)>0 holds for all i and j when f(i, j)=d-r, then the position of the cage center C at that time can be said to be a point at which the cage 5 can exist without coming into contact with the balls 4. Therefore, a point that satisfies the above is determined to be a point at which the cage 5 can exist without coming into contact with the balls 4.

[0035] Next, the position of the cage center C and the phase of the cage are changed, and a determination operation similar to the determination operation performed in the first step is performed. Then, if there is even one phase at the selected position of the cage center C that is determined to be the above-mentioned "point on the cage movable area," the selected position of the cage center C is determined to be a "point on the cage movable area."

[0036] To confirm the usefulness of the present invention, a dynamic analysis was conducted to verify the displacement of the cage during bearing operation (here, when the inner ring was rotated 10 times) for both a rolling bearing 1 employing a cage 5 according to an embodiment of the present invention (a cage 5 that provides the cage movable region 10 shown in FIG. 5 ) shown in FIG. 4 , and a rolling bearing employing a cage according to a comparative example not incorporating the configuration of the present invention. The frictional force generated by contact between the cage and the balls increases as the coefficient of friction (more specifically, the "dynamic friction coefficient"; hereinafter, this also applies when referred to as the "friction coefficient") of the pocket-forming surface of the cage increases. The greater this frictional force, the more likely the cage's high-speed whirl phenomenon occurs. Therefore, the dynamic analysis was conducted under the following analytical conditions, with the coefficient of friction of the pocket-forming surface set to 0.10, 0.15, and 0.20. [Specifications of the rolling bearing used for analysis] Inner ring inner diameter: φ70 mm, outer ring outer diameter: φ110 mm, axial width of inner and outer rings: 20 mm Ball diameter: 8.73 mm Number of balls: 24 Ball pitch circle diameter (pcd): 90 mm [Operating conditions of the rolling bearing] Axial load: 650 N Rotational speed: 3000 rpm

[0037] Specific examples of the cage movable area 10 of a rolling bearing employing a cage according to a comparative example are shown in Figures 7A and 7B. The cage movable area 10 shown in Figures 7A and 7B is obtained when a cage is employed in which the arrangement of the large pockets 6A and the small pockets 6B is different from that of the cage 5 shown in Figure 4. While the arrangement of the pockets 6 (6A, 6B) is not shown, the cage movable area 10 shown in Figure 7A is obtained when a cage (hereinafter referred to as the "cage according to comparative example 1") is employed in which large pocket groups each consisting of four large pockets 6A in the circumferential direction and small pocket groups each consisting of four small pockets 6B in the circumferential direction are arranged alternately in groups of three in the circumferential direction. The cage movable area 10 shown in Figure 7B is obtained when a cage (hereinafter referred to as the "cage according to comparative example 2") is employed in which large pockets 6A and small pockets 6B are arranged alternately in groups of twelve in the circumferential direction.

[0038] When the cage according to Comparative Example 1 and the cage according to Comparative Example 2 are employed, large pockets 6A and small pockets 6B are mixed in both the "pockets belonging to the first group" and the "pockets belonging to the second group." Therefore, the minimum value δmin of the circumferential clearance Gb1 and the maximum value δmax of the circumferential clearance Gb2 are the same value (δmin - δmax = 0), and the relationship δmin - δmax ≥ 0.1 mm that the rolling bearing 1 according to the present invention should satisfy is not satisfied.

[0039] 8A, 8B, and 8C show the results of dynamic analysis of the rolling bearing 1 of this embodiment employing the cage 5 according to the example shown in Fig. 4, where the friction coefficients of the pocket forming surfaces of the cage are set to 0.10, 0.15, and 0.20. Similar analysis results for the rolling bearing employing the cage according to Comparative Example 1 and the rolling bearing employing the cage according to Comparative Example 2 are also shown in Figs. 9A to 9C and 10A to 10C, respectively.

[0040] 8A and 8B, it can be seen that the occurrence of the high-speed whirl phenomenon of the cage can be prevented when the friction coefficient of the pocket forming surface of the cage in the rolling bearing 1 according to this embodiment is set to 0.10 and 0.15. Based on the analysis result shown in Fig. 8C, when the friction coefficient of the pocket forming surface is set to 0.20, the displacement period of the cage is extremely short immediately after the start of bearing operation, and therefore it can be seen that the high-speed whirl phenomenon of the cage occurs immediately after the start of bearing operation. However, after a certain amount of time has passed, the displacement period of the cage becomes significantly longer, and it is thought that the high-speed whirl phenomenon disappears.

[0041] 8B with 9B, and 8C with 9C, it can be seen that the displacement period of the cage is shorter in the rolling bearing employing the cage according to Comparative Example 1 than in the rolling bearing according to this embodiment. Furthermore, comparing Figures 8A with 10A, 8B with 10B, and 8C with 10C, it can be seen that the displacement period of the cage is significantly shorter in the rolling bearing employing the cage according to Comparative Example 2 than in the rolling bearing according to this embodiment. Therefore, it can be said that the rolling bearing employing the cage according to Comparative Example 1 or Comparative Example 2 is more susceptible to the high-speed whirl phenomenon than the rolling bearing according to this embodiment.

[0042] The above results are summarized in Table 1 below. In Table 1, "◎" indicates a case where it is recognized that the high-speed whirl phenomenon does not occur, "◯" indicates a case where it is recognized that the high-speed whirl phenomenon occurs but that the phenomenon disappears with the passage of time, and "×" indicates a case where it is recognized that the high-speed whirl phenomenon occurs (a case where it is recognized that the phenomenon does not disappear even after a predetermined time has passed after the phenomenon occurs). Note that configurations rated "◎" or "◯" present no practical problems and are suitable for use in rolling bearings, while configurations rated "×" present practical problems and should be avoided from being used in rolling bearings.

[0043]

[0044] The rolling bearing 1 according to an embodiment of the present invention has been described above, but the embodiment of the present invention is not limited to this, and various modifications can be made within the scope that does not deviate from the gist of the present invention.

[0045] For example, rollers (cylindrical rollers, needle rollers, etc.) can be used instead of balls 4 as the rolling elements that make up rolling bearing 1. In other words, the present invention is applicable not only to ball bearings, but also to roller bearings such as cylindrical roller bearings and needle roller bearings.

[0046] As described above, the present invention can prevent the occurrence of high-speed whirl in the cage 5 constituting the rolling bearing 1, and is therefore particularly suitable for use in rolling bearings used in applications where the high-speed whirl is likely to occur. For example, when a ball bearing is used as a rolling bearing for supporting the main spindle of a machine tool or the reaction wheel of a spacecraft, the ball bearing is subjected to a relatively large axial preload during use. Specifically, the ratio of the radial load Fr to the axial load Fa (= Fr / Fa) applied during operation is often 3 or less, and in such cases, the high-speed whirl is particularly likely to occur. This is because the more uniform the spacing between the rolling elements (balls), the more likely the high-speed whirl is to occur. Conversely, when the radial load acting on the ball bearing is significantly greater than the axial load (for example, when the above ratio Fr / Fa exceeds 3), lead / lag occurs among the balls, resulting in uneven ball spacing, making the high-speed whirl less likely to occur. Therefore, the present invention can be particularly suitably applied to ball bearings used in applications where the relationship Fr / Fa≦3.0 holds, such as support bearings for the main spindles of machine tools and reaction wheels of space equipment.

[0047] The rolling bearing 1 according to the present invention has been described above, but the present invention is not limited to the embodiment described above, and can be embodied in various other forms without departing from the spirit of the present invention.

[0048] 1 Rolling bearing 2 Inner ring 3 Outer ring 4 Ball (rolling element) 5 Cage 6 Pocket 6A Large pocket 6B Small pocket 7 Pocket forming surface 10 Cage movable area Gb, Gb1, Gb2 Circumferential clearance SL Straight line W Opening dimension (pocket diameter)

Claims

1. A rolling bearing comprising a pair of raceways arranged radially opposite each other and rotating relative to each other via a plurality of rolling elements, and an annular cage having a plurality of pockets formed at intervals in the circumferential direction and each of which individually houses the rolling elements, wherein a circumferential clearance is formed between the rolling elements and the pocket forming surface of the cage in a neutral state, wherein one of the plurality of pockets is taken as a reference pocket, and pockets whose circumferential centers are in the ranges shifted 20° to 70° and 200° to 250° to one side in the circumferential direction from a straight line connecting the circumferential center of this reference pocket to the center of the cage are defined as belonging to a first group, and pockets whose circumferential centers are in the ranges shifted 110° to 160° and 290° to 340° to one side in the circumferential direction from the straight line are defined as belonging to a second group, A rolling bearing characterized in that the minimum value of the circumferential clearance formed between the pocket forming surfaces that form the pockets belonging to the first group and the rolling elements is 0.1 mm or more larger than the maximum value of the circumferential clearance formed between the pocket forming surfaces that form the pockets belonging to the second group and the rolling elements.

2. A rolling bearing according to claim 1, wherein the pockets belonging to said first group are large pockets, and the pockets belonging to said second group are small pockets having opening dimensions smaller than those of said large pockets.

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