Cage and needle roller with cage

Abstract

To provide: a cage which is optimum to a planetary gear; and needle rollers with the cage.SOLUTION: In a state that each of needle rollers (2), which are accommodated respectively in pockets (40) of a cage, has a pair of flat faces (21) constituting both end faces in an axial direction, and angular parts (22) intersecting respectively with the flat faces, and each chamfered into a circular-arc shape with a radius as r1, the cage comprises: circular-arc shaped relief parts (61) each arranged at four corner parts (35) of the pocket within a range of the pocket in the axial direction with a radius r2 set larger than the radius r1; and protrusions (62) each formed at an inside face (34b) of an annular part facing the pocket, and contacting with the flat faces of the needle roller. A protrusion dimension of the protrusion is defined according to a difference between the radius r1 and the radius r2.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a cage and a needle roller and cage assembly, and more particularly to a cage and a needle roller and cage assembly used in a planetary gear of a planetary reduction mechanism. [Background technology]

[0002] In order to improve the lubricity of the sliding surfaces between the cage and the rollers, techniques for improving the oil permeability within the cage pockets have been proposed. For example, Japanese Patent Laid-Open Publication No. 2004-144244 (Patent Document 1) discloses a cage in which grooves extending from the inner periphery to the outer periphery are formed at predetermined intervals along the axial direction on the circumferential inner wall surface of the pocket, and protrusions are formed on the axial inner wall surface of the pocket that come into contact with the centers of the end faces of the rollers.

[0003] Furthermore, Japanese Patent Laid-Open Publication No. 2011-214702 (Patent Document 2) discloses a cage in which the axial position of a roller guide surface portion on one circumferential side surface of a pocket is different from the axial position of a roller guide surface portion on the other side surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-144244 A [Patent Document 2] JP 2011-214702 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, in order to reduce torque loss, the viscosity of lubricating oil has been reduced and the amount of oil used has been reduced, making the operating environment for bearings increasingly harsh, and so bearings with good lubrication are required. Also, in the case of planetary bearings for planetary gears used in planetary reduction mechanisms, centrifugal force is applied to the cage because the bearings revolve while rotating on their own axis. For this reason, the cage must be particularly strong.

[0006] Analysis has revealed that if the pocket shape of the cage of a needle roller bearing used in a planetary gear is, for example, a shape as disclosed in Patent Document 2 (a shape with no recessed portions at the corners), the maximum stress occurs at the corners of the pocket. Therefore, in order to apply this to planetary gears, it is necessary to alleviate the stress at the corners of the pocket.

[0007] In Patent Document 1, grooves are formed in the corners of the pocket to improve lubrication, but the grooves are formed beyond the axial range of the pocket. In this case, the width of the annular part of the cage is narrowed in the groove portion, which raises concerns about insufficient strength of the annular part.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a cage and needle roller and cage assembly that are optimal for planetary gears. [Means for solving the problem]

[0009] A cage according to one aspect of the present invention comprises a pair of annular portions, a plurality of column portions extending in the axial direction to connect the pair of annular portions, and a pocket formed between adjacent column portions in the circumferential direction and accommodating a needle roller. The needle roller has a pair of flat surfaces constituting both axial end faces, and a corner portion that intersects with the flat surfaces and is chamfered in an arc shape with a radius of r1. The cage comprises an arc-shaped recessed portion with a radius r2 larger than r1, which is provided within the axial range of the pocket at four corners of the pocket, and a protruding portion provided on an inner surface of the annular portion facing the pocket and in contact with the flat surface of the needle roller, and the protruding dimension of the protruding portion is determined according to the difference between the radius r1 and the radius r2.

[0010] Preferably, the protrusions are formed in a spherical shape, which reduces the contact area with the flat surface of the needle roller (point contact), thereby facilitating the rotation of the needle roller.

[0011] It is also preferable that the protrusions are provided so as to contact the centres of the flat surfaces of the needle rollers, thereby making it possible to suppress heat generation due to friction between the flat surfaces of the needle rollers and the protrusions.

[0012] Each of the first pocket surface and the second pocket surface of the column portion facing the pocket is provided with an inner diameter side roller stopper and an outer diameter side roller stopper. It is desirable that the axial position of the outer diameter side roller stopper on the first pocket surface and the axial position of the outer diameter side roller stopper on the second pocket surface are different from each other. This makes it possible to suppress oil film breakdown due to the outer diameter side roller stopper.

[0013] In one embodiment, the outer diameter side roller stop portion of the first pocket surface is constituted by one protrusion provided at the axial center, and the outer diameter side roller stop portion of the second pocket surface is constituted by two protrusions provided at both axial ends, respectively.

[0014] A needle roller and cage assembly according to another aspect of the present invention includes the above-mentioned cage and needle rollers housed in pockets of the cage. Effect of the Invention

[0015] According to the present invention, it is possible to suppress stress concentration at the corners of the pocket while ensuring the strength of the annular portion, and therefore it is possible to provide a cage and a needle roller with cage that are optimal for planetary gears. [Brief description of the drawings]

[0016] [Figure 1] 1A and 1B are diagrams showing a schematic diagram of a planetary reduction mechanism in which a needle roller and cage assembly according to an embodiment of the present invention is used, in which (A) is a schematic diagram of the planetary reduction mechanism, and (B) is a cross-sectional view of a planetary gear. [Diagram 2] FIG. 2 is a perspective view showing a cage according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a side view showing a cage according to an embodiment of the present invention. [Figure 4]4 is a partial cross-sectional view of the cage as viewed from the IV-IV direction in FIG. 3. [Diagram 5] 4 is a partial cross-sectional view of the retainer as viewed from the VV direction in FIG. 3. [Figure 6] 4 is an enlarged view showing an axial end portion of a pocket in a cage according to an embodiment of the present invention. FIG. [Figure 7] 13(A) and 13(B) are diagrams illustrating a schematic diagram of the relationship between the recessed portion and the protruding portion. [Figure 8] 13 is an enlarged view showing an axial end portion of a pocket in a cage when there is no protrusion. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0018] (Outline of planetary reduction mechanism) First, an overview of a planetary reduction mechanism 100 in which a needle roller with cage 1 according to this embodiment is used will be described with reference to Figures 1(A) and (B). With reference to Figure 1(A), the planetary reduction mechanism 100 includes an internal gear (ring gear) 101 that has internal teeth and surrounds the outer periphery, a sun gear (sun gear) 102 that has external teeth and is disposed at the center of the internal gear 101, and a plurality of planetary gears (pinion gears) 103 that have external teeth and are disposed between the internal gear 101 and the sun gear 102.

[0019] Each planetary gear 103 meshes with one internal gear 101 and one sun gear 102. A shaft-shaped pinion shaft 105 passes through a central hole of each planetary gear 103. The hole wall surface of the central hole forms the inner circumferential surface of the planetary gear 103. A needle roller with cage 1 is disposed in an annular space defined by the inner circumferential surface of the planetary gear 103 and the outer circumferential surface of the pinion shaft 105.

[0020] 1(B), an end of each pinion shaft 105 is fixed to a common carrier 104 via a washer 106. In this way, the plurality of planetary gears 103 are supported by one carrier 104. In addition, each planetary gear 103 is supported rotatably by a needle roller 1 with a cage.

[0021] For example, when the sun gear 102 rotates clockwise as indicated by the arrow in FIG. 1A while the internal gear 101 is stopped rotating, each planetary gear 103 rotates counterclockwise and revolves clockwise around the outer periphery of the sun gear 102, causing the carrier to rotate clockwise.

[0022] The planetary reduction mechanism 100 is used, for example, in automatic transmissions for automobiles, which are becoming increasingly multi-stage. A needle roller and cage assembly 1 is used to support the planetary gear 103 in the planetary reduction mechanism 100 so that it can revolve and rotate about its axis.

[0023] The needle roller and cage assembly 1 has an inner raceway surface that is the outer peripheral surface of the pinion shaft 105, and an outer raceway surface that is the inner peripheral surface of the planetary gear 103. The needle roller and cage assembly 1 is lubricated by lubricating oil that is supplied from the radially inner side to the radially outer side through a lubricating oil passage provided in the pinion shaft 105, for example.

[0024] (Configuration of needle roller and cage assembly) As shown in Fig. 1(B), needle roller and cage assembly 1 comprises multiple needle rollers 2 and a cage 3 that rotatably holds the multiple needle rollers 2. The material of the needle rollers 2 is typically high carbon chromium bearing steel. The cage 3 is made of resin, and from the standpoint of improving strength, it is particularly desirable for the cage 3 to be formed from a material containing polyamide 9T resin and fibrous filler.

[0025] In this embodiment, the end face shape of needle roller 2 is flat. In other words, needle roller 2 has a pair of flat surfaces 21 located at both axial ends. Such needle roller 2 can have a longer straight portion (shaft portion) (longer effective length) than needle rollers with rounded (spherical) end faces, so the contact surface pressure is lower and it is suitable for planetary gear 103.

[0026] A configuration example of the retainer 3 will be described with further reference to Fig. 2 and Fig. 3. Fig. 2 and Fig. 3 are a perspective view and a side view, respectively, of the retainer 3 according to this embodiment. In the following description, the direction along the central axis C1 of the retainer 3 will be referred to as the "axial direction", the direction perpendicular to the central axis C1 as the "radial direction", and the circumferential direction around the central axis C1 as the "circumferential direction".

[0027] The cage 3 has a plurality of pockets 40 that hold the needle rollers 2. The cage 3 is of a cage type and has a pair of annular portions 30 located at both axial ends of the pockets 40, and a plurality of pillar portions 31 that connect the pair of annular portions 30 to each other. The pillar portions 31 extend along the axial direction of the cage 3 and are joined to the pair of annular portions 30 at their both ends 32, 32. The pillar portions 31 extend linearly along the axial direction with a constant thickness. When the pillar portions 31 are cut along the radial direction, the cross-sectional shape of the pillar portions 31 is a trapezoid that is larger on the outer diameter side than on the inner diameter side.

[0028] The pocket 40 is defined between the column portions 31, 31 adjacent to each other in the circumferential direction. Specifically, the pocket 40 is surrounded by pocket surfaces 33a, 33b formed on the adjacent column portions 31, 31 and facing each other in the circumferential direction, inner end faces 34a, 34b formed on the pair of annular portions 30 and facing each other in the axial direction, and four corner portions 35 located at the intersections between the pocket surfaces 33a, 33b and the inner end faces 34a, 34b. The shape of the pocket 40 is substantially rectangular when viewed from the outer diameter side of the cage 3, but the four corner portions 35 are provided with recessed portions 61, as described later.

[0029] Each pocket surface 33a, 33b extends from one end 32 of the column portion 31 to the other end 32, and faces the rolling surface of the needle roller 2 (the outer peripheral surface of the straight portion). Each inner end surface 34a, 34b faces the flat surfaces 21 (FIG. 1(B)), which are both end surfaces of the needle roller 2. The distance L1 between the opposing inner end surfaces 34a, 34b is larger than the overall length of the needle roller 2, and the distance L2 between the opposing pocket surfaces 33a, 33b is larger than the diameter of the needle roller 2. Note that the distance L1 corresponds to the axial length of the pocket 40 (the distance in the longitudinal direction), and the distance L2 corresponds to the distance in the lateral direction of the pocket 40 (the circumferential direction of the cage 3).

[0030] (Example of roller stopper configuration and layout) Pocket surfaces 33a, 33b of cage 3 are provided with roller stopper portions 51-54 that restrict radial movement of needle rollers 2. A specific configuration and arrangement example of roller stopper portions 51-54 will be described with further reference to Figs. 4 and 5. Fig. 4 is a partial cross-sectional view of cage 3 seen from direction IV-IV in Fig. 3, showing one pocket surface 33a. Fig. 5 is a partial cross-sectional view of cage 3 seen from direction VV in Fig. 3, showing the other pocket surface 33b.

[0031] As shown in Fig. 4, roller stop portions 51, 52 are provided on the inner diameter side and the outer diameter side of one pocket surface (hereinafter referred to as the "first pocket surface") 33a, respectively. The roller stop portion 51 on the inner diameter side is composed of two protrusions 51a, 51b arranged symmetrically on the left and right sides with respect to the axial center line C2 of the cage 3. The protrusions 51a, 51b are respectively arranged at both axial ends of the first pocket surface 33a. The roller stop portion 52 on the outer diameter side is composed of one protrusion 52a arranged on the axial center line C2.

[0032] The inner diameter side protrusions 51a, 51b and the outer diameter side protrusion 52a are arranged so that their axial positions do not overlap. The axial length of the inner diameter side roller stopper 51, i.e., the combined length of the axial dimensions L11 of the two protrusions 51a, 51b (dimension L11×2), is preferably 25% to 40% of the axial length L1 of the pocket 40. In addition, the axial length of the outer diameter side roller stopper 52, i.e., the axial dimension L12 of the protrusion 52a, is preferably 20% to 30% of the axial length L1 of the pocket 40.

[0033] As shown in FIG. 5, roller stoppers 53, 54 are provided on the inner diameter side and the outer diameter side of the other pocket surface (hereinafter referred to as the "second pocket surface") 33b, respectively. The roller stopper 53 on the inner diameter side is composed of two protrusions 53a, 53b arranged symmetrically about the axial center line C2. The protrusions 53a, 53b are respectively arranged at both axial ends of the second pocket surface 33b. The roller stopper 54 on the outer diameter side is also composed of two protrusions 54a, 54b arranged symmetrically about the axial center line C2. The protrusions 54a, 54b are similarly respectively arranged at both axial ends of the second pocket surface 33b.

[0034] With respect to the axial position, the inner diameter side protrusions 53a, 53b and the outer diameter side protrusions 54a, 54b are arranged so as to overlap each other. The axial dimension L21 of each of the inner diameter side protrusions 53a, 53b may be smaller than the axial dimension L22 of each of the outer diameter side protrusions 54a, 54b, but the axial length of the roller stopper parts 53, 54 is preferably the same as above. In other words, the axial length of the inner diameter side roller stopper part 53, i.e., the total length of the axial dimensions L21 of the two protrusions 53a, 53b (dimension L21×2) is preferably 25% to 40% of the axial length L1 of the pocket 40, and the axial length of the outer diameter side roller stopper part 54, i.e., the total length of the axial dimensions L22 of the two protrusions 54a, 54b (dimension L22×2) is preferably 20% to 30% of the axial length L1 of the pocket 40.

[0035] As can be seen from the above numerical ranges, in the roller and cage assembly 1, the axial length of the roller stopper portions 51, 53 on the inner diameter side may be longer than the axial length of the roller stopper portions 52, 54 on the outer diameter side. This makes it possible to more reliably prevent the needle rollers 2 from falling off to the inner diameter side.

[0036] 4 and 5, the protrusions 51a, 51b on the inner diameter side of the first pocket surface 33a and the protrusions 53a, 53b on the inner diameter side of the second pocket surface 33b are arranged to face each other. In other words, the axial positions of the protrusions 51a, 51b and the axial positions of the protrusions 53a, 53b completely overlap.

[0037] In contrast, the protrusion 52a on the outer diameter side of the first pocket surface 33a and the protrusions 54a, 54b on the outer diameter side of the second pocket surface 33b do not face each other. In other words, the axial position of the roller stopper portion 52 (protrusion 52a) on the outer diameter side of the first pocket surface 33a and the axial position of the roller stopper portion 54 (protrusions 54a, 54b) on the outer diameter side of the second pocket surface 33b do not overlap and are different from each other.

[0038] In this embodiment, the roller stop portions 51, 53 on the inner diameter side have the same configuration, but this is not limited to this example, and the number of protrusions on the roller stop portions 51, 53 on the inner diameter side, as on the outer diameter side, may be different, or the axial positions of the protrusions may be different from each other.

[0039] In addition, although the number of protrusions on the outer diameter side roller stop portions 52, 54 is different (one has one and the other has two), the numbers may be the same as long as their axial positions are different, and the number is not limited.

[0040] (Pocket end shape) 2, the cage 3 according to this embodiment has relatively large recessed portions 61 at the four corners 35 of the pocket 40. In addition, protrusions 62 are provided on the inner end faces 34a and 34b of the pocket 40.

[0041] Fig. 6 is an enlarged view of the axial end of the pocket 40 of the cage 3. In Fig. 6, the axial end of the needle roller 2 housed in the pocket 40 is illustrated.

[0042] Needle roller 2 in this embodiment has a pair of flat surfaces 21 constituting both axial end faces, and corner portion 22 that intersects with flat surfaces 21 and is chamfered into an arc. The chamfer R of corner portion 22 is, for example, 0.1 to 0.3 mm, and is 0.2 mm as one example. The chamfer R (radius of the arc) of corner portion 22 is hereinafter referred to as "radius r1". The center of the arc of corner portion 22 is at an equal distance from flat surfaces 21 and the outer peripheral surface 20 of the straight portion.

[0043] The recess 61 is formed in an arc shape with a radius of r2. The recess 61 cuts out the end 32 of the column portion 31 in the same shape along the thickness direction. The radius r2 of the recess 61 is larger than the chamfer R (radius r1) of the needle roller 2. The recess 61 is provided within the axial range of the pocket 40 (the range of the axial length L1 shown in FIG. 3). In other words, the recess 61 is provided without protruding toward the annular portion 30. Therefore, the width of the portion of the annular portion 30 adjacent to the pocket 40 is equal to or larger than the specified dimension W.

[0044] 8, if the convex portion 62 is not provided on the inner end surface 34b (and 34a) of the pocket 40, the corner portion 22 of the needle roller 2 will interfere with the cut-out portion 61, as shown diagrammatically by hatching. In contrast, in the present embodiment, the convex portion 62 is provided on the inner end surface 34b (and 34a) of the pocket 40, so that the corner portion 22 of the needle roller 2 does not interfere with the cut-out portion 61. In other words, the convex portion 62 is provided so that the corner portion 22 of the needle roller 2 does not interfere with the cut-out portion 61.

[0045] The protrusion 62 is provided at the center of the inner end face 34b. The protrusion 62 protrudes spherically from the inner end face 34b toward the axial center (center line C2 side) of the pocket 40. In this case, when viewed from the radial outside, the tip of the protrusion 62 (the apex of the sphere) is located on the circumferential center line C3 of the pocket 40. As a result, the tip of the protrusion 62 contacts the center of the flat surface 21 of the needle roller 2. Since the central part of the flat surface 21 of the needle roller 2 has a slower peripheral speed than the outer periphery, heat generation due to friction between the flat surface 21 of the needle roller 2 and the protrusion 62 can be suppressed.

[0046] The protruding height H of the convex portion 62 is determined according to the size of the recessed portion 61. In other words, it is determined according to the difference between the chamfer R (radius r1) of the corner portion 22 of the needle roller 2 and the arc radius r2 of the recessed portion 61 (hereinafter referred to as the "radius difference").

[0047] The relationship between the radius difference (r2-r1) and the protruding height H of the protruding portion 62 is shown in the following Table 1. Note that the protruding height H in this embodiment represents the axial dimension from the inner end surface 34b (34a) of the pocket 40 to the tip of the protruding portion 62 (the apex of the sphere).

[0048] [Table 1]

[0049] In Table 1, the case where the radius difference is 0 is shown as a comparative example. In this case, the radius r2 of the recessed portion 61 is equal to the chamfer R of the corner portion 22 of the needle roller 2, and the interference as shown in Fig. 8 does not occur. Therefore, although this is feasible from the design point of view, it is not desirable from the viewpoint of mitigating the stress concentration at the corner portion 35.

[0050] In this embodiment, as shown in Examples 1 to 4 in Table 1, the radius difference is set to be greater than 0, that is, r2>r1. The radius difference in Example 1 corresponds to 1 / 2 the chamfer R of needle roller 2, and the radius difference in Example 2 is equal to the chamfer R of needle roller 2. The radius difference in Example 3 corresponds to 3 / 2 the chamfer R of needle roller 2, and the radius difference in Example 4 is twice the chamfer R of needle roller 2.

[0051] The protruding height H of the convex portion 62 is designed to be higher as the radius difference is larger. Fig. 7(A) shows a schematic diagram of the relationship between the recessed portion 61a and the convex portion 62b in the case of the first embodiment, and Fig. 7(B) shows a schematic diagram of the relationship between the recessed portion 61a and the convex portion 62b in the case of the fourth embodiment.

[0052] As shown in Examples 1 to 4, it is expected that the radius difference will be used at 0.1 to 0.4 mm. When the radius difference is expressed in relation to the chamfer R of needle roller 2, the radius difference may be, for example, within a range of 1 / 2 to 2 times the chamfer R of needle roller 2. Note that the shape of convex portion 62 is spherical as shown in the figure, and although it is desirable that the tip portion of convex portion 62 has a rounded surface, the tip portion of convex portion 62 may also have a flat surface.

[0053] As described above, the cage 3 of this embodiment has recessed portions 61 provided at the four corners 35 of the pocket 40, and protruding portions 62 provided on the inner end faces 34a, 34b which are the inner surfaces of the annular portion 30. Therefore, a radially penetrating gap (a flow path for lubricating oil) can be secured between the needle rollers 2 and the annular portion 30, thereby improving the oil permeability within the pocket 40.

[0054] Furthermore, the roller stop portions 52, 54 on the outer diameter sides of the first and second pocket surfaces 33a, 33b of the pocket 40 are provided at offset axial positions so as not to face each other, and in this embodiment, the roller stop portion 52 on the outer diameter side of the first pocket surface 3a is provided in the axial center. Therefore, in the roller stop portion 52 on the outer diameter side, it is possible to suppress oil film breakdown around the joint between the straight portion of the needle roller 2 and the chamfer R (r1) of the corner portion 22, where peeling is likely to occur, and it is possible to improve the lubrication performance of the outer peripheral surface of the needle roller 2.

[0055] In addition, the arc radius r2 of the recessed portion 61 is made larger than the chamfer R of the corner portion 22 of the needle roller 2, and the protruding dimension of the convex portion 62 is determined according to the radius difference so that the corner portion 22 of the needle roller 2 does not interfere with the corner portion 35 of the pocket 40 (so that a gap is generated). Therefore, stress concentration on the corner portion 35 of the pocket 40 during use can be alleviated.

[0056] Furthermore, since the recessed portion 61 is provided (only) within the axial range of the pocket, it is possible to ensure the strength of the annular portion 30 of the cage 3. Therefore, the roller and cage assembly 1 of this embodiment is suitable for the planetary gear 103 that revolves while rotating on its axis.

[0057] The retainer-attached needle roller 1 of this embodiment can also be provided as a needle roller bearing for a planetary gear 103, together with a shaft (pinion shaft 105 in Figure 1) that is inserted into the central hole of the retainer 3 and forms the inner raceway surface of the needle roller 2.

[0058] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0059] 1 needle roller with cage, 2 needle roller, 3 cage, 21 flat surface, 22 corner portion, 30 annular portion, 31 column portion, 33a, 33b pocket surfaces, 34a, 34b inner end surfaces, 35 corner portion, 40 pocket, 51, 52, 53, 54 roller stopper portions, 51a, 51b, 52a, 53a, 53b, 54a, 54b protrusions, 61, 61a, 61b recessed portions, 62, 62a, 62b convex portions, 100 planetary reduction mechanism, 101 internal gear, 102 sun gear, 103 planetary gear, 105 pinion shaft, r1, r2 radii.

Claims

1. A cage comprising a pair of annular portions, a plurality of column portions extending in an axial direction and connecting the pair of annular portions, and pockets formed between adjacent column portions in a circumferential direction and receiving needle rollers, the needle roller has a pair of flat surfaces constituting both end faces in the axial direction, and a corner portion that intersects with the flat surfaces and is chamfered in an arc shape having a radius of r1, a recessed portion having a circular arc shape and a radius r2 larger than the radius r1, the recessed portion being provided at each of four corners of the pocket within an axial range of the pocket; a protrusion provided on an inner surface of the annular portion facing the pocket and in contact with the flat surface of the needle roller, A cage, wherein a protruding height of the convex portion based on an inner surface of the annular portion is designed to be higher as a radius difference obtained by subtracting the radius r1 from the radius r2 is larger.

2. The cage according to claim 1 , wherein the protrusion is formed in a spherical shape.

3. 3. The cage according to claim 1, wherein the protrusion is provided so as to contact a center portion of the flat surface of the needle roller.

4. a first pocket surface and a second pocket surface of the column portion facing the pocket are each provided with an inner diameter side roller stop portion and an outer diameter side roller stop portion, The cage according to any one of claims 1 to 3, wherein an axial position of the outer diameter side roller stop portion of the first pocket surface and an axial position of the outer diameter side roller stop portion of the second pocket surface are different from each other.

5. 5. The cage according to claim 4, wherein the outer diameter side roller stop portion of the first pocket surface is constituted by one protrusion provided at a center portion in the axial direction, and the outer diameter side roller stop portion of the second pocket surface is constituted by two protrusions provided at both ends in the axial direction.

6. A cage according to any one of claims 1 to 5, the needle rollers are housed in the pockets of the cage.

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