Pulley structure

Abstract

To provide a pulley structure capable of having manufacturing quality and productivity in an assembly process while suppressing an outer or inner rotary body from vibrating to generate noise.SOLUTION: An outer rotary body has: an inner peripheral surface which radially faces a slide bearing and extends axially, the inner peripheral surface having its other end-side end part located on the other end side with respect to the slide bearing; and a side face which extends radially outward from the other end-side end part of the inner peripheral surface, and a corner part of the outer rotary body where the inner peripheral surface and the outer peripheral surface cross each other over the perimeter consists of a tapered surface which is a flat surface increasing inner diameter from the inner peripheral surface toward the side face and a convex curved surface which is an arcuate surface connecting the tapered surface and the side face together and swells outward to a certain curvature.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a pulley structure equipped with a sliding bearing. [Background technology]

[0002] The pulley structure described in Patent Document 1 includes an outer rotating body, an inner rotating body, and a pair of bearings. The outer rotating body is a cylindrical member around which a belt is wound and which rotates about a predetermined rotation axis due to torque applied from the belt. The inner rotating body is provided radially inside the outer rotating body and is rotatable relative to the outer rotating body around the rotation axis. A pair of bearings is disposed between the outer rotating body and the inner rotating body at one end and the other end in the axial direction along the rotation axis, respectively, and connects the outer rotating body and the inner rotating body so that they can rotate relative to each other. One of the pair of bearings is a sliding bearing, and the other is a rolling bearing. The sliding bearing is made of thermoplastic resin, formed into an annular shape with ends, and attached to the inner rotating body. The inner diameter of the outer rotating body is gradually reduced from the other end, where the sliding bearing is provided, to the one end, where the rolling bearing is provided.

[0003] Patent Document 1 discloses a pulley structure in which the sliding bearing is formed so that the thickness at both circumferential ends of the sliding bearing produced by injection molding is slightly greater than the thickness of the remaining portions of the sliding bearing. As a result, when force is applied from a belt on the outer rotating body, force is applied cyclically from the sliding bearing (at both circumferential ends) to the outer rotating body or the inner rotating body so as to widen the gap between the outer rotating body and the inner rotating body, causing vibrations in the outer rotating body or the inner rotating body and resulting in abnormal noise. In order to solve this problem, the structure of the sliding bearing is focused on, and the sliding bearing is formed so that the thickness at both circumferential ends is smaller than the thickness of the remaining portions of the sliding bearing.

[0004] The above problem (the problem of the outer rotating body or inner rotating body vibrating and generating abnormal noise) is caused by the sliding bearing applying a force radially outward to the outer rotating body so as to widen the gap between the outer rotating body and the inner rotating body, which occurs when, as the outer rotating body and the inner rotating body rotate relative to each other, the part of the sliding bearing where the thickness is greater than the reference dimension (the thicker parts at both circumferential ends) reaches a position opposite the part of the outer rotating body where force is applied from the belt. In other words, the above problem is caused by the convex portion of the sliding bearing itself, where the thickness of the sliding bearing is greater than the reference dimension. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-003064 Summary of the Invention [Problem to be solved by the invention]

[0006] Recently, in order to meet the demands for even higher quality (improvements in manufacturing quality, etc.) and lower costs due to the diversification of user needs and vehicle models, the manufacture of pulley structures is required to achieve both manufacturing quality and productivity.Therefore, it was necessary to achieve both manufacturing quality and productivity in the assembly process, which is relatively difficult to achieve labor savings in the pulley structure manufacturing process, especially in the process of setting the outer rotating body onto the inner rotating body which has a sliding bearing attached in advance.

[0007] In the pulley structure described in Patent Document 1, the largest outer diameter of the inner rotating body (the portion consisting of the sliding bearing and the inner rotating body) on which the sliding bearing is mounted is the outer peripheral surface of the sliding bearing. The inner diameter of the outer rotating body is gradually reduced from the other end of the axial direction where the sliding bearing is provided to the other end of the inner rotating body where the rolling bearing is provided. Therefore, when the outer rotating body is set on the inner rotating body, the other end of the outer rotating body is inserted into the inner rotating body first. When setting the outer rotating body on the inner rotating body, if the two rotating bodies are slightly misaligned in the initial state before setting, i.e., if the central axes of the inner rotating body and the outer rotating body are slightly misaligned in the radial direction (for example, by about 0.5 mm) before setting, interference will occur between the sliding bearing and the corner of the outer rotating body. The "corner" refers to the portion of the outer rotating body where the inner peripheral surface facing the sliding bearing intersects with the side surface extending radially outward from the other end of the inner peripheral surface (the end downstream in the insertion direction) around the entire circumference.

[0008] After extensive research, the inventors of the present application found that, depending on the shape of the corners of the outer rotating body, there is a risk that the sliding bearing may be damaged when it interferes with the corners of the outer rotating body, resulting in a decline in manufacturing quality, and that there is a risk that the centering of the outer rotating body and the inner rotating body cannot be ensured, resulting in a decline in productivity.The inventors also found that if the sliding bearing is damaged, vibrations may be generated in the outer rotating body or the inner rotating body when force is applied from the belt on the outer rotating body, which may cause abnormal noise, even if the sliding bearing is formed so that the thickness at both circumferential ends is smaller than the thickness of the part other than the both circumferential ends, as in the pulley structure described in Patent Document 1.

[0009] Therefore, an object of the present invention is to provide a pulley structure that can suppress the generation of abnormal noise due to vibration of the outer rotating body or the inner rotating body when force is applied from the belt of the outer rotating body, and that can achieve both manufacturing quality and productivity in the assembly process. [Means for solving the problem]

[0010] In order to solve the above problems, the pulley structure of the present invention comprises: a cylindrical outer rotating body around which a belt is wound and which rotates about a rotation axis by torque applied from the belt; an inner rotating body provided radially inside the outer rotating body and rotatable relative to the outer rotating body around the rotation axis; a pair of bearings interposed between the outer rotor and the inner rotor at one end and the other end in the axial direction along the rotation axis, connecting the outer rotor and the inner rotor so as to be rotatable relative to each other; One of the pair of bearings is a sliding bearing and the other is a rolling bearing, the sliding bearing is made of a thermoplastic resin, is formed into an annular shape with ends, and is in contact with the internal rotating body, the thickness of the sliding bearing at both circumferential ends is smaller than the reference dimension of the thickness of the sliding bearing, The outer rotating body is formed so that the inner diameter thereof gradually decreases from the other end side toward the one end side, and further The outer rotating body is an inner circumferential surface that faces the plain bearing in the radial direction and extends in the axial direction, and whose end portion on the other end side is located closer to the other end than the plain bearing; a side surface extending radially outward from an end portion of the inner circumferential surface on the other end side, The corner where the inner circumferential surface and the side surface intersect over the entire circumference is a tapered surface that is a flat surface whose inner diameter increases from the inner circumferential surface toward the side surface; and a convex curved surface that is an arcuate surface that bulges outward at a constant curvature and connects the tapered surface and the side surface.

[0011] According to this configuration, at the corner of the outer rotating body, the portion connected to the side of the outer rotating body is formed by a convex curved surface, which is an arcuate surface that bulges outward at a constant curvature. As a result, if the corner of the outer rotating body interferes with the sliding bearing during assembly, the sliding bearing will interfere with the convex curved surface of the corner, thereby preventing damage to the sliding bearing. As a result, it is possible to ensure manufacturing quality in the assembly process and prevent abnormal noise caused by vibration of the outer rotating body or inner rotating body when force is applied from the belt of the outer rotating body due to damage to the sliding bearing. Furthermore, in the assembly process, the sliding bearing abuts against the tapered surfaces of the corners of the outer rotating body, ensuring centering of the outer rotating body and the inner rotating body using the tapered surfaces as a guide, thereby ensuring productivity in the assembly process.As described above, with this configuration, it is possible to prevent the outer rotating body or the inner rotating body from vibrating and generating abnormal noise, and it is possible to achieve both manufacturing quality and productivity in the assembly process.

[0012] In addition, in the pulley structure of the present invention, The tapered surface is The taper angle is between 15° and 40°. The taper width is 0.4 mm or more and 0.9 mm or less. the taper length is 0.7 mm or more and is equal to or less than the length in the axial direction between the end face on the other end side of the sliding bearing and the side surface, The convex curved surface is The radius of curvature may be 0.3 mm or more and 1 mm or less.

[0013] With this configuration, the tapered surface (taper angle, taper width, taper length) is formed in an appropriate manner, which more reliably ensures centering of the outer rotating body and the inner rotating body during assembly. Also, because the convex curved surface (radius of curvature) is formed in an appropriate manner, it is possible to further reduce damage to the sliding bearing when it interferes with the corners of the outer rotating body during assembly. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a pulley structure that can suppress the generation of abnormal noise due to vibration of the outer rotating body or the inner rotating body when force is applied from the belt of the outer rotating body, and that can achieve both manufacturing quality and productivity in the assembly process. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a pulley structure according to an embodiment of the present invention, taken along a direction passing through and parallel to a rotation axis of the pulley structure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is an enlarged view of part III in FIG. 2. [Figure 4] FIG. 2 is an enlarged view of part IV in FIG. 1, with the end cap omitted. [Figure 5] FIG. 5 is a view corresponding to FIG. 4 according to Comparative Example 1. [Figure 6] FIG. 1(a) is a cross-sectional view showing a state in which, during assembly, the sliding bearing according to Comparative Example 1 interferes with a portion radially inward relative to the side surface edge on the other end side of the corner of the outer rotating body, and FIG. 1(b) is a cross-sectional view showing a state in which the sliding bearing according to Comparative Example 1 interferes with the side surface edge on the other end side of the corner of the outer rotating body. [Figure 7] FIG. 5 is a view corresponding to FIG. 4 according to Comparative Example 2. [Figure 8] 1(a) is a cross-sectional view showing a state in which, during assembly, the sliding bearing according to Comparative Example 2 interferes with a portion radially inward relative to the side surface on the other end side of the corner of the outer rotating body; FIG. 1(b) is a cross-sectional view showing a state in which the sliding bearing according to Comparative Example 2 interferes with the side surface on the other end side of the corner of the outer rotating body; and FIG. 1(c) is a cross-sectional view showing the state of a damaged portion of the sliding bearing according to Comparative Example 2. [Figure 9] FIG. 1(a) is a cross-sectional view showing a state in which, during assembly, the sliding bearing interferes with a portion radially inward relative to the side surface on the other end side of the corner of the outer rotating body, according to an embodiment of the present invention; and FIG. 1(b) is a cross-sectional view showing a state in which the sliding bearing interferes with the side surface on the other end side of the corner of the outer rotating body, according to an embodiment of the present invention. [Figure 10] FIG. 2 is a schematic diagram of an idle testing machine. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Pulley structure> A pulley structure 1 according to an embodiment of the present invention shown in FIG. 1 is attached to a drive shaft S of an alternator in, for example, an accessory drive system for an automobile. The accessory drive system includes a drive pulley attached to an engine crankshaft, a driven pulley and pulley structure 1 that drive an accessory such as an alternator, and a belt B wound around these pulleys and pulley structure 1. The rotation of the crankshaft is transmitted to the driven pulley and pulley structure 1 via the belt B, thereby driving the accessory such as the alternator. As the rotation speed of the crankshaft fluctuates in response to combustion in the engine, the running speed of the belt B also fluctuates.

[0017] As shown in Figures 1 and 2, the pulley structure 1 includes an outer rotating body 2, an inner rotating body 3, a torsion coil spring 4 (hereinafter simply referred to as "spring 4"), an end cap 5, and a pair of bearings 6 and 7 consisting of a sliding bearing 6 and a rolling bearing 7.

[0018] The outer rotating body 2 and the inner rotating body 3 are both substantially cylindrical and have the same rotation axis A (the rotation axis of the pulley structure 1, hereinafter simply referred to as "rotation axis A"). The rotation axis A extends along the left-right direction (axial direction) in FIG. 1. In the following, the right side of FIG. 1 will be referred to as one end side in the axial direction, and the left side of FIG. 1 will be referred to as the other end side in the axial direction.

[0019] A belt B is wound around the outer circumferential surface of the outer rotating body 2.

[0020] The inner rotor 3 is provided inside the outer rotor 2 and is rotatable relative to the outer rotor 2. The inner rotor 3 has a cylindrical main body 3a into which the drive shaft S of the alternator is fitted, an outer cylindrical portion 3b disposed outside the other end of the cylindrical main body 3a, and an annular plate portion 3c connecting the other end of the cylindrical main body 3a and the other end of the outer cylindrical portion 3b. The drive shaft S is threaded into a thread groove on the inner peripheral surface of the cylindrical main body 3a.

[0021] The spring 4 is disposed between the outer rotating body 2 and the inner rotating body 3. Specifically, the spring 4 is housed in a space U defined by the inner circumferential surface of the outer rotating body 2, the inner circumferential surface of the outer cylindrical portion 3b of the inner rotating body 3, the outer circumferential surface of the cylindrical main body 3a of the inner rotating body 3, and the annular plate portion 3c of the inner rotating body 3, and is located on the other end side of the rolling bearing 7. The spring 4 is made of wire having a square cross section (for example, oil-tempered wire for springs (compliant with JIS G3560:1994)), and is left-handed (counterclockwise from the other end of the spring 4 toward one end).

[0022] A lubricant such as grease is sealed in the space U. The lubricant is poured into the space U in the form of a paste mass when the pulley structure 1 is assembled. The amount poured is, for example, about 0.2 g. When the pulley structure 1 is operated, the viscosity of the lubricant decreases due to a temperature rise and shear heat (frictional heat) in the space U, and the lubricant diffuses throughout the space U.

[0023] The end cap 5 is disposed at the other end of the outer rotating body 2 and the inner rotating body 3 .

[0024] A pair of bearings 6, 7 are interposed between the outer rotating body 2 and the inner rotating body 3 at one end and the other end, respectively. Specifically, the sliding bearing 6 is interposed in a gap (hereinafter referred to as the "cylindrical gap") between the inner circumferential surface at the other end of the outer rotating body 2 and the outer circumferential surface of the outer cylindrical portion 3b of the inner rotating body 3. A rolling bearing 7 is interposed between the inner circumferential surface at one end of the outer rotating body 2 and the outer circumferential surface at one end of the cylindrical main body 3a of the inner rotating body 3. The pair of bearings 6, 7 connect the outer rotating body 2 and the inner rotating body 3 so that they can rotate relative to each other. The outer rotating body 2 and the inner rotating body 3 rotate clockwise (the direction of the arrow in Figure 2; hereinafter referred to as the "forward direction") when viewed from the other end toward the one end.

[0025] The sliding bearing 6 is an annular member with ends, and a gap 6d exists between both circumferential ends of the sliding bearing 6. The sliding bearing 6 is made of a hard thermoplastic resin with a Rockwell R scale (compliant with JIS K7202-2:2001) of 80 to 130. Specifically, the sliding bearing 6 is made of polyacetal resin, polyamide resin, polycarbonate, modified polyphenylene ether, polyester (polybutylene terephthalate, polyethylene terephthalate, etc.), fluororesin, polyphenylene sulfide, polysulfone, amorphous polyarylate, polyetherimide, polyethersulfone, polyetherketones, liquid crystal polymer, polyamideimide, thermoplastic polyimides, syndiotype polystyrene, olefin-based resin (polyethylene, polypropylene, etc.), styrene-based resin (ABS resin, polystyrene, etc.), polyvinyl chloride, vinylidene chloride-based resin, methacrylic resin, polyvinyl alcohol, styrene-based block copolymer resin, or the like. However, from the viewpoint of low-friction sliding properties and wear resistance, it is more preferable that the sliding bearing 6 be made of polyacetal resin or polyamide resin among these materials.Moreover, it is more preferable that the hardness of the sliding bearing 6 be approximately 85 to 125 on the Rockwell R scale.

[0026] Furthermore, the sliding bearing 6 may be a single layer formed from one type of resin composition, or may be two or more layers formed from two or more types of resin compositions. However, from the perspective of manufacturing costs, it is more preferable that the sliding bearing 6 be a single layer formed from one type of resin composition. Furthermore, the sliding bearing 6 is manufactured by injection molding using an injection molding machine and mold (injection molding mold).

[0027] As shown in Figure 3, the sliding bearing 6 is mounted on the outer peripheral surface of the outer cylindrical portion 3b of the inner rotating body 3 in a slightly expanded diameter state, and the inner peripheral surface 6a of the sliding bearing 6 is in close contact with the outer peripheral surface of the outer cylindrical portion 3b due to its self-elastic restoring force. The inner peripheral surface 6a of the sliding bearing 6 has a substantially constant diameter over its entire circumference, and the entire circumference of the inner peripheral surface 6a is in close contact with the outer peripheral surface of the outer cylindrical portion 3b. As shown in Figure 4, protrusions 3b1 are provided on both sides of the sliding bearing 6 on the outer peripheral surface of the outer cylindrical portion 3b to prevent the sliding bearing 6 from coming off. The sliding bearing 6 is able to move slightly in the axial direction between these protrusions 3b1.

[0028] A gap R (sliding gap) of, for example, 0.1 mm exists between the outer peripheral surface 6b of the sliding bearing 6 and the inner peripheral surface (inner peripheral surface 2c, described below) of the outer rotating body 2. The lubricant sealed in the space U enters the gap R, suppressing wear on the friction surface of the sliding bearing 6 (the surface of the sliding bearing 6 that comes into contact with the outer rotating body 2). The lubricant almost never leaks out of this gap to the other end.

[0029] As shown in FIG. 3 , the outer peripheral surface 6b of the sliding bearing 6 has chamfered portions 6b1 at both circumferential ends of the sliding bearing 6, with the diameter gradually decreasing toward each end. As a result, the diameter of both circumferential ends of the outer peripheral surface 6b of the sliding bearing 6 is smaller than the diameter of the outer peripheral surface 6b of the sliding bearing 6 other than both circumferential ends. Because of this and because the diameter of the inner peripheral surface 6a of the sliding bearing 6 is approximately constant over the entire circumference, the thickness (radial width) of the sliding bearing 6 at both circumferential ends is smaller than the thickness (radial width) of the sliding bearing 6 other than both circumferential ends. In other words, the thickness of the sliding bearing 6 at both circumferential ends is smaller than the reference dimension of the thickness of the sliding bearing 6. In other words, the sliding bearing 6 has a main portion with a substantially constant thickness and both end portions with a thinner thickness. Furthermore, the sliding bearing 6 does not have locally thick portions. The reference dimension of the thickness of the sliding bearing 6 refers to the design reference dimension of the thickness of the sliding bearing 6, which is 1.4 mm in this embodiment, for example.

[0030] 1, the rolling bearing 7 is a contact-sealed ball bearing that includes an outer ring 7a fixed to the inner peripheral surface of the outer rotating body 2, an inner ring 7b fixed to the outer peripheral surface of the cylindrical main body 3a of the inner rotating body 3, a plurality of balls (rolling elements) 7c arranged to roll freely between the outer ring 7a and the inner ring 7b, and annular contact seal members 7d arranged on both axial sides of the plurality of balls 7c. By filling the interior of the rolling bearing 7 with a lubricant such as grease (for example, the same lubricant as that filled in the space U), wear on the friction surfaces of the rolling bearing 7 (contact surfaces of the balls 7c with the outer ring 7a and / or inner ring 7b) is suppressed.

[0031] The inner diameter of the outer rotating body 2 decreases in three stages from the other end to the one end. The inner circumferential surface of the outer rotating body 2 at the smallest inner diameter portion is called the pressure contact surface 2a, and the inner circumferential surface of the outer rotating body 2 at the second smallest inner diameter portion is called the annular surface 2b. The inner circumferential surface of the outer rotating body 2 at the largest inner diameter portion is called the inner circumferential surface 2c, which faces the sliding bearing 6 in the radial direction and extends in the axial direction. The inner diameter of the outer rotating body 2 at the pressure contact surface 2a is smaller than the inner diameter of the outer cylindrical portion 3b of the inner rotating body 3. The inner diameter of the outer rotating body 2 at the annular surface 2b is the same as or larger than the inner diameter of the outer cylindrical portion 3b of the inner rotating body 3.

[0032] The axial length of the inner circumferential surface 2c is longer than the axial length of the outer circumferential surface 6b of the sliding bearing 6. The other end of the inner circumferential surface 2c is located closer to the other end than the sliding bearing 6.

[0033] 4, a side surface 2s on the other end side of the outer rotating body 2 extends radially outward from the other end side edge of the inner circumferential surface 2c. The side surface 2s faces the end cap 5 in the axial direction. A corner C where the side surface 2s and the inner circumferential surface 2c intersect over the entire circumference will be described in detail later.

[0034] 1, the outer diameter of the cylindrical main body 3a of the inner rotating body 3 is larger on the other end side. The outer peripheral surface of the cylindrical main body 3a of the inner rotating body 3 in this portion is called a contact surface 3ax.

[0035] The spring 4 has a one-end region 4a that contacts the outer rotor 2 at one end, an other-end region 4b that contacts the inner rotor 3 at the other end, and a middle region 4c that is located between the one-end region 4a and the other-end region 4b and does not contact either the outer rotor 2 or the inner rotor 3. The one-end region 4a and the other-end region 4b refer to regions that extend over half a circumference (180° or more around the rotation axis) from one end and the other end of the spring 4, respectively. Within the other-end region 4b, a portion near a position 90° away from the other end of the spring 4 around the rotation axis is referred to as a second region 4b2, a portion closer to the other end than the second region 4b2 is referred to as a first region 4b1, and the remaining portion is referred to as a third region 4b3 (see FIG. 2).

[0036] The spring 4 has a constant diameter over its entire length when not subjected to external force, and the outer diameter of the spring 4 at this time is smaller than the inner diameter of the outer rotating body 2 at the annular surface 2b and larger than the inner diameter of the outer rotating body 2 at the pressure contact surface 2a. The spring 4 is housed in the space U with the one end region 4a in a reduced diameter state.

[0037] The spring 4 is compressed in the axial direction when no external force is applied to the pulley structure 1 (i.e., when the pulley structure 1 is stationary). At this time, the outer peripheral surface of the one end region 4a of the spring 4 is pressed against the pressure contact surface 2a by the self-elastic restoring force of the spring 4 in the diameter expansion direction, and the other end region 4b of the spring 4 is in contact with the contact surface 3ax in a slightly expanded diameter state. In other words, the inner peripheral surface of the other end region 4b of the spring 4 is pressed against the contact surface 3ax by the self-elastic restoring force of the spring 4 in the diameter contraction direction.

[0038] 2, the other end portion of the inner rotating body 3 is formed with a contact surface 3d that faces the other end surface 4bx of the spring 4. In addition, a protrusion 3e that protrudes radially inward of the outer cylindrical portion 3b and faces the outer peripheral surface of the other end region 4b is provided on the inner peripheral surface of the outer cylindrical portion 3b. The protrusion 3e faces the second region 4b2.

[0039] When the inner peripheral surface of the other end region 4b of the spring 4 is in contact with the contact surface 3ax, a gap is formed between the outer peripheral surface of the other end region 4b of the spring 4 and the inner peripheral surface of the outer cylindrical portion 3b of the inner rotating body 3. Also, a gap is formed between the annular surface 2b of the outer rotating body 2 and the outer peripheral surface of the spring 4. In this embodiment, when no external force is applied to the pulley structure 1, as shown in FIG. 2, the outer peripheral surface of the torsion coil spring 4 and the protrusion 3e are separated from each other, and a gap is formed between them, but they may also be in contact with each other.

[0040] In the pulley structure 1 described above, the thickness of the sliding bearing 6 at both circumferential ends is smaller than the thickness of the portions other than the both circumferential ends, so that when force is applied from the belt B of the outer rotating body 2, it is possible to suppress the generation of vibrations in the outer rotating body 2 or the inner rotating body 3 and the generation of abnormal noise. This will be explained in detail below.

[0041] When belt B is looped around outer rotating body 2 of pulley structure 1, the portion of outer rotating body 2 to which force is applied from belt B is pressed toward sliding bearing 6. As a result, the sliding gap R narrows to almost zero in the portion of outer rotating body 2 to which force is applied from belt B. At this time, the sliding gap R widens (to about 0.2 mm, for example) in the portion of outer rotating body 2 to which force is applied from belt B and the portion to which force is not applied from belt B on the opposite side relative to rotation axis A.

[0042] In this case, unlike the present embodiment, if the thickness of both circumferential ends of the sliding bearing is greater than the thickness of the remaining parts, then each time both circumferential ends of the sliding bearing (thicker parts) reach a position facing the part of the outer rotating body to which force is applied from the belt (periodically), the sliding bearing will apply a radially outward force to the outer rotating body so as to widen the gap between the outer rotating body and the inner rotating body. This may cause the outer rotating body or inner rotating body to vibrate, resulting in the generation of abnormal noise.

[0043] In contrast, in this embodiment, the thickness of the sliding bearing 6 at both circumferential ends is smaller than the thickness of the remaining portions. Therefore, even when both circumferential ends of the sliding bearing 6 reach positions facing the portions of the outer rotating body 2 to which force is applied from the belt B, the sliding bearing 6 does not apply force to the outer rotating body 2 radially outward so as to widen the gap R between the outer rotating body 2 and the inner rotating body 3. This makes it possible to prevent the outer rotating body 2 or the inner rotating body 3 from vibrating and generating abnormal noise.

[0044] <Configuration of the corner of the outer rotating body> Next, before describing the configuration of the corner portion C of the outer rotating body 2 according to this embodiment, first, prerequisite matters will be described.

[0045] As described above, the largest outer diameter of the inner rotating body 3 (the portion consisting of the sliding bearing 6 and the inner rotating body 3) on which the sliding bearing 6 is mounted is the outer peripheral surface 6b of the sliding bearing 6. The inner diameter of the outer rotating body 2 is formed to gradually decrease from the other end in the axial direction where the sliding bearing 6 is provided to one side where the rolling bearing 7 is provided. For this reason, in the process of setting the outer rotating body 2 on the inner rotating body 3, the other end of the outer rotating body 2 is inserted into the inner rotating body 3 first. When setting the outer rotating body 2 on the inner rotating body 3, if the two rotating bodies 2, 3 are slightly misaligned in the initial state before setting, the sliding bearing 6 will interfere with the corners of the outer rotating body 2.

[0046] The inventors of the present application have found that, depending on the shape of the corners of the outer rotating body 2, there is a risk that the sliding bearing 6 may be damaged when it interferes with the corners of the outer rotating body 2, and that it may not be possible to ensure centering between the outer rotating body 2 and the inner rotating body 3, resulting in reduced productivity. They have also found that if the sliding bearing 6 is damaged, vibrations may be generated in the outer rotating body 2 or the inner rotating body 3 when force is applied from the belt B of the outer rotating body 2, and abnormal noise may be generated, even if the sliding bearing 6 is formed so that the thickness at both circumferential ends is smaller than the thickness of the portion other than both circumferential ends. This is explained in detail below.

[0047] First, consider the case where the corner of the outer rotating body 2 is corner D as shown in Fig. 5 (hereinafter referred to as "Comparative Example 1"). Corner D is composed of a convex curved surface DP, which is an arc surface that bulges outward with a certain curvature (the radius of curvature is, for example, 0.5 mm to 1 mm).

[0048] In the case of Comparative Example 1, as shown in FIG. 6(b), even if the sliding bearing 6 interferes with the corner D (convex curved surface DP) of the outer rotating body 2 during assembly, there is almost no risk of damage to the sliding bearing 6 made of thermoplastic resin, and it is thought that manufacturing quality can be ensured. On the other hand, as shown in FIG. 6(a), Comparative Example 1 has a configuration that makes it difficult to ensure centering between the outer rotating body 2 and the inner rotating body 3 using the convex curved surface DP as a guide. In other words, with Comparative Example 1, the radial misalignment between the outer rotating body 2 and the inner rotating body 3 must be corrected and the setting operation must be repeated frequently. As a result, Comparative Example 1 has a configuration that is insufficient to ensure productivity.

[0049] Next, consider a case where the corner of the outer rotating body 2 is corner E as shown in Fig. 7 (hereinafter referred to as "Comparative Example 2"). Corner E is composed of a tapered surface ET, which is a flat surface whose inner diameter increases from the inner circumferential surface 2c toward the side surface 2s.

[0050] In the case of Comparative Example 2, as shown in Figure 8(a), during assembly, the sliding bearing 6 abuts against the tapered surface ET, and the tapered surface ET acts as a guide to ensure centering between the outer rotating body 2 and the inner rotating body 3. In other words, compared to Comparative Example 1, Comparative Example 2 can reduce the frequency with which the setting operation needs to be redone to correct radial misalignment between the outer rotating body 2 and the inner rotating body 3, and as a result, productivity can be ensured.

[0051] However, in the case of Comparative Example 2, if the outer rotating body 2 and the inner rotating body 3 are slightly misaligned in the initial state before setting, as shown in Figure 8(b), the sliding bearing 6 may become caught in the edge portion EE of the outer rotating body 2 during the setting operation, potentially damaging the sliding bearing 6. The edge portion EE refers to the edge (ridge line) portion with a sharp cross section where the tapered surface ET and the side surface 2s intersect all around the circumference.

[0052] Specifically, when the outer rotating body 2 is set on the inner rotating body 3 with the sliding bearing 6 engaged with the edge portion EE of the outer rotating body 2, part of the damaged portion of the sliding bearing 6 is formed in a convex shape, as shown in Figure 8(c). Through detailed observations by the present inventors, it was inferred that due to the damaged portion formed in this convex shape, there is a risk that the outer rotating body 2 or the inner rotating body 3 will vibrate and generate abnormal noise, even if a sliding bearing 6 formed so that the thickness at both circumferential ends is smaller than the reference dimension of the thickness of the sliding bearing 6 is used.

[0053] (Observation results) In the assembled state, the sliding bearing 6 cannot be visually inspected, and therefore it is not possible to observe whether the sliding bearing 6 is damaged or not. Therefore, assembly and disassembly inspections were repeated to observe the misalignment state of the two rotating bodies 2, 3 during assembly, as well as the state of the sliding bearing 6 after assembly.

[0054] As a result, when the outer rotating body 2 is inserted into the inner rotating body 3, which has the plain bearing 6 already attached, and set, the outer rotating body 2 has a margin of radial misalignment (for example, a runout of about 1 mm) of up to the minimum gap dimension VM (see FIG. 7 ) between the inner circumferential surface 2c of the outer rotating body 2 and the outer circumferential surface of the inner rotating body 3, on the one end side of the plain bearing 6 (the side where the rolling bearing 7 is provided). In this embodiment, the minimum gap dimension VM is the radial length between the inner circumferential surface 2c of the outer rotating body 2 and the protrusion 3b1 of the inner rotating body 3, which is located on the one end side of the plain bearing 6. Note that the degree of misalignment can naturally be reduced if the outer rotating body 2 is set using a device rather than by hand.

[0055] However, even when using this device, radial alignment errors accumulate, and misalignment of the two rotating bodies 2, 3 can occur within a range of approximately 0.5 mm in the initial state before installation. If the installation operation is performed with misalignment, the plain bearing 6 may become trapped in the edge portion EE near the side surface on the other end of the corner E, damaging the plain bearing 6. This damaged area (one location on the circumference) will have the appearance shown in Figure 8(c). That is, the trapped area (one location on the circumference) will plastically deform into an uneven shape, creating a recessed portion and a bulged portion. This bulged portion will be configured in a convex shape. Therefore, the area consisting of the plain bearing 6 and the damaged portion of the plain bearing 6 that occurred during assembly may become a portion (convex portion) whose overall thickness is greater than the standard dimension of the plain bearing 6's thickness.

[0056] (Inferences) In the case of Comparative Example 2, in which corner E of the outer rotating body 2 is composed of a tapered surface ET, productivity in the assembly process can be ensured, but manufacturing quality cannot. Furthermore, it was inferred that not only the convex portion of the sliding bearing 6 itself (the portion where the thickness of the sliding bearing is greater than the standard dimension) but also the convex portion composed of the sliding bearing 6 and parts of the sliding bearing 6 that were damaged during assembly (the portion where the total thickness of the part composed of the sliding bearing 6 and parts of the sliding bearing 6 that were damaged during assembly is greater than the standard dimension of the sliding bearing thickness), when force is applied from belt B of the outer rotating body 2 while the outer rotating body 2 and inner rotating body 3 rotate relative to each other, each time the convex portion composed of the sliding bearing 6 and parts of the sliding bearing 6 that were damaged during assembly reaches a position opposite the part to which force is applied from belt B of the outer rotating body 2, the convex portion may apply a force radially outward to the outer rotating body 2 so as to widen the gap R between the outer rotating body 2 and inner rotating body 3.

[0057] As described above, in the case of Comparative Example 2, even if a sliding bearing 6 is used that is formed so that the thickness at both circumferential ends is smaller than the reference dimension for the thickness of the sliding bearing, this does not sufficiently solve the problem of the outer rotating body 2 or the inner rotating body 3 vibrating and generating abnormal noise when force is applied from belt B of the outer rotating body 2.

[0058] In order to solve the above problem, the corner C according to this embodiment is configured with a tapered surface CT and a convex curved surface CP, as shown in FIG.

[0059] The tapered surface CT is a flat surface whose inner diameter increases from the inner peripheral surface 2c toward the side surface 2s. The convex curved surface CP is an arcuate surface that bulges outward at a constant curvature and connects the tapered surface CT and the side surface 2s.

[0060] According to the above configuration, at the corner C of the outer rotating body 2, the portion connected to the side surface 2s of the outer rotating body 2 is configured with a convex curved surface CP, which is an arcuate surface that bulges outward with a constant curvature. As a result, as shown in FIG. 9(b), when the corner C of the outer rotating body 2 interferes with the sliding bearing 6 during assembly, the sliding bearing 6 interferes with the convex curved surface CP of the corner C, thereby preventing damage to the sliding bearing 6. As a result, it is possible to ensure manufacturing quality in the assembly process and to prevent abnormal noise caused by vibration of the outer rotating body 2 or the inner rotating body 3 when force is applied from the belt B of the outer rotating body 2 due to damage to the sliding bearing 6.

[0061] 9(a), in the assembly process, the sliding bearing 6 abuts against the tapered surface CT of the corner C of the outer rotor 2, ensuring centering of the outer rotor 2 and the inner rotor 3 using the tapered surface CT as a guide, thereby ensuring productivity in the assembly process. As described above, according to this embodiment, it is possible to prevent the outer rotor 2 or the inner rotor 3 from vibrating and generating abnormal noise, and it is possible to achieve both manufacturing quality and productivity in the assembly process.

[0062] In this embodiment, the taper angle (θ), taper width (TW), and taper length (TL) of the tapered surface CT are set to fall within the following numerical ranges.

[0063] · The taper angle (θ) is between 15° and 40°. ·Taper width (TW) is 0.4 mm or more and 0.9 mm or less. The taper length (TL) is 0.7 mm or more and is equal to or less than the axial length SD between the end face on the other end side of the sliding bearing 6 and the side surface 2s.

[0064] Here, the "taper angle (θ)" is the angle formed between the inner peripheral surface 2c of the outer rotor 2, where the taper start point TS is located, and the tapered surface CT, as shown in FIG.

[0065] The "taper width (TW)" is the radial length of the tapered surface CT, and more specifically, the radial length between the taper start point TS on the inner peripheral surface 2c of the outer rotating body 2 and the taper end point TE on the side surface 2s of the outer rotating body 2. When the corner C has a convex curved surface CP as in this embodiment, the taper end point TE exists as an imaginary point where an imaginary extension line of the tapered surface CT intersects with an imaginary extension line of the side surface 2s.

[0066] The "taper length (TL)" is the axial length of the tapered surface CT portion, specifically, the axial length between the taper start point TS on the inner surface 2c of the outer rotating body 2 and the taper end point TE on the side surface 2s of the outer rotating body 2.

[0067] In this embodiment, the radius of curvature of the convex curved surface CP is set to be within the following numerical range.

[0068] ·The radius of curvature is 0.3 mm or more and 1 mm or less.

[0069] In this embodiment, the taper angle (θ), taper width (TW), and taper length (TL) of the tapered surface CT, and the curvature radius of the convex curved surface CP are set to the following values.

[0070] ·Taper angle of tapered surface CT (θ): 30° Tapered surface CT taper width (TW): 0.4 mm Tapered surface CT taper length (TL): 0.7 mm Convex curved surface CP curvature radius: 0.5 mm

[0071] As described above, by setting the values ​​of the taper angle (θ), taper width (TW), and taper length (TL) of the tapered surface CT, as well as the radius of curvature of the convex curved surface CP, within the above numerical ranges, it is possible to more reliably ensure the centering of the outer rotating body 2 and the inner rotating body 3 during assembly, as will be described below, and it is also possible to further prevent damage to the sliding bearing 6 when it interferes with the corner C of the outer rotating body 2.

[0072] In other words, if the taper angle (θ) is set to 40° or less, the radial force component (action) will not be dominant, making it easier to ensure centering between the outer rotating body 2 and the inner rotating body 3. Furthermore, if the taper angle (θ) is set to 15° or greater, it becomes easier to ensure the dynamic performance of the sliding bearing (particularly the suppression of abnormalities in the sliding bearing).

[0073] If the taper width (TW) is 0.4 mm or more, when the device is used to set them, there is a risk that the two rotating bodies will be misaligned within a range of about 0.5 mm in the initial state before setting. However, since the radial position of the outer peripheral surface 6b of the sliding bearing 6 will only be shifted radially outward relative to the radial position of the inner peripheral surface 2c of the outer rotating body 2, up to an upper limit of about 0.4 mm minus the size of the gap R (sliding gap) (about 0.1 mm), centering ability can be ensured more reliably. Furthermore, if the taper width (TW) is set to 0.9 mm or less, it becomes easier to ensure the dynamic performance of the sliding bearing.

[0074] Furthermore, if the taper length (TL) exceeds the axial length SD between the end face on the other end side of the sliding bearing 6 and the side surface 2s, the axial length of the sliding surface that faces the sliding bearing 6 in the radial direction across the gap R will be shorter than the axial length of the sliding bearing 6, and there is a risk that the function and durability of the sliding bearing 6 will be reduced by that amount (the pressure-receiving area of ​​the sliding bearing 6 will be reduced). Therefore, by making the taper length (TL) equal to or less than the axial length SD between the end face on the other end side of the sliding bearing 6 and the side surface 2s, it is possible to prevent the function and durability of the sliding bearing 6 from being reduced. Furthermore, by making the taper length (TL) 0.7 mm or more, centering performance (productivity) can be ensured more reliably.

[0075] If the radius of curvature of the convex curved surface CP is 0.3 mm or greater, it is possible to further prevent damage to the sliding bearing 6 when the outer rotating body 2 is set on the inner rotating body 3. Furthermore, if the radius of curvature of the convex curved surface CP exceeds 1 mm, it becomes impossible to form the tapered surface CT when the taper width is 0.4 mm and the taper angle is formed to be 40° (the corners of the outer rotating body will be formed only by the convex curved surface), making it difficult to ensure centering performance.

[0076] In addition, in the specifications for "taper angle (θ)," "taper width (TW)," and "taper length (TL)," the lower limit or upper limit value for which no numerical specification is given is a value that is automatically determined in relation to the other specified ranges (for example, in the case of the lower limit value for "taper angle (θ)" for which no numerical specification is given, it is in relation to "taper width (TW) being 0.4 mm or more" and "taper length (TL) being equal to or less than the axial length SD between the end face on the other end side of the sliding bearing 6 and the side surface 2s").

[0077] <Operation of the pulley structure> Next, the operation of the pulley structure 1 will be described.

[0078] First, a case where the rotation speed of the outer rotor 2 becomes higher than the rotation speed of the inner rotor 3 (that is, a case where the outer rotor 2 accelerates) will be described.

[0079] In this case, the outer rotor 2 rotates relative to the inner rotor 3 in the forward direction (the direction of the arrow in Figure 2). As the outer rotor 2 rotates relative to the inner rotor 3, the one-end region 4a of the spring 4 moves together with the pressure contact surface 2a and rotates relative to the inner rotor 3. This causes the spring 4 to twist in the radial expansion direction. The pressure force of the one-end region 4a of the spring 4 against the pressure contact surface 2a increases as the twist angle of the spring 4 in the radial expansion direction increases. The second region 4b2 is most susceptible to torsional stress, and as the twist angle of the spring 4 in the radial expansion direction increases, it moves away from the contact surface 3ax. At this time, the first region 4b1 and the third region 4b3 are in pressure contact with the contact surface 3ax. At approximately the same time that the second region 4b2 moves away from the contact surface 3ax, or when the twist angle of the spring 4 in the radial expansion direction further increases, the outer peripheral surface of the second region 4b2 abuts against the protrusion 3e. The outer peripheral surface of the second region 4b2 abuts against the protrusion 3e, restricting deformation of the other-end region 4b in the radial direction, dispersing the torsional stress to portions of the spring 4 other than the other-end region 4b, and particularly increasing the torsional stress acting on the one-end region 4a of the spring 4. This reduces the difference in torsional stress acting on each portion of the spring 4, allowing the entire spring 4 to absorb strain energy, preventing local fatigue failure of the spring 4.

[0080] Furthermore, the pressure contact force of the third region 4b3 against the contact surface 3ax decreases as the torsion angle of the spring 4 in the radial expansion direction increases. When the second region 4b2 abuts against the protrusion 3e, or when the torsion angle of the spring 4 in the radial expansion direction further increases, the pressure contact force of the third region 4b3 against the contact surface 3ax becomes substantially zero. The torsion angle of the spring 4 in the radial expansion direction at this time is θ1 (e.g., θ1 = 3°). When the torsion angle of the spring 4 in the radial expansion direction exceeds θ1, the third region 4b3 deforms in the radial expansion direction and moves away from the contact surface 3ax. However, the spring 4 does not curve (bend) near the boundary between the third region 4b3 and the second region 4b2, and the other-end-side region 4b maintains an arc shape. In other words, the other-end-side region 4b maintains a shape that allows it to easily slide against the protrusion 3e. Therefore, when the torsional angle of the spring 4 in the radial expansion direction increases and the torsional stress acting on the other-end region 4b increases, the other-end region 4b slides against the protrusion 3e and the contact surface 3ax in the circumferential direction of the outer rotor 2, against the pressing force of the second region 4b2 against the protrusion 3e and the pressing force of the first region 4b1 against the contact surface 3ax. Then, the other-end surface 4bx presses against the contact surface 3d, thereby ensuring reliable transmission of torque between the outer rotor 2 and the inner rotor 3.

[0081] When the twist angle of the spring 4 in the radial expansion direction is equal to or greater than θ1 and less than θ2 (e.g., θ2 = 45°), the third region 4b3 is separated from the contact surface 3ax and does not contact the inner circumferential surface of the outer cylindrical portion 3b of the inner rotor 3, and the second region 4b2 is pressed against the protrusion 3e. Therefore, in this case, the effective number of turns of the spring 4 is greater and the spring constant is smaller than when the twist angle of the spring 4 in the radial expansion direction is less than θ1. Furthermore, when the twist angle of the spring 4 in the radial expansion direction reaches θ2, the outer circumferential surface of the middle region 4c of the spring 4 abuts against the annular surface 2b, or the twist angle of the spring 4 in the radial expansion direction reaches its limit. This restricts further deformation of the spring 4 in the radial expansion direction, and the outer rotor 2 and the inner rotor 3 rotate integrally. This prevents damage to the spring due to deformation in the radial expansion direction.

[0082] Next, a case where the rotation speed of the outer rotor 2 becomes lower than the rotation speed of the inner rotor 3 (that is, a case where the outer rotor 2 decelerates) will be described.

[0083] In this case, the outer rotating body 2 rotates relative to the inner rotating body 3 in the opposite direction (the opposite direction to the arrow in FIG. 2). As the outer rotating body 2 rotates relative to the inner rotating body 3, the one-end region 4a of the spring 4 moves together with the pressure contact surface 2a and rotates relative to the inner rotating body 3. This causes the spring 4 to twist in the diameter-reducing direction. When the twist angle of the spring 4 in the diameter-reducing direction is less than θ3 (for example, θ3 = 10°), the pressure contact force of the one-end region 4a against the pressure contact surface 2a is slightly lower than when the twist angle is zero, but the one-end region 4a is still in pressure contact with the pressure contact surface 2a. In addition, the pressure contact force of the other-end region 4b against the contact surface 3ax is slightly higher than when the twist angle is zero. When the twist angle of the spring 4 in the diameter-reducing direction is θ3 or more, the pressure force of the one-end region 4a against the pressure contact surface 2a becomes substantially zero, and the one-end region 4a slides against the pressure contact surface 2a in the circumferential direction of the outer rotating body 2. Therefore, torque is not transmitted between the outer rotating body 2 and the inner rotating body 3.

[0084] In this way, when the inner rotor 3 rotates relative to the outer rotor 2 in the forward direction, the spring 4 engages with each of the outer rotor 2 and the inner rotor 3 to transmit torque between the outer rotor 2 and the inner rotor 3, whereas when the inner rotor 3 rotates relative to the outer rotor 2 in the reverse direction, the spring 4 slides (in this embodiment, slides in the circumferential direction of the outer rotor 2) against at least one of the outer rotor 2 and the inner rotor 3 (in this embodiment, the spring 4 slides against the pressure contact surface 2a) and does not transmit torque between the outer rotor 2 and the inner rotor 3. The pulley structure 1 is also configured to transmit or block torque between the outer rotor 2 and the inner rotor 3 by expanding or contracting the diameter of the spring 4.

[0085] <Manufacturing method of pulley structure> Next, a method for manufacturing the pulley structure 1 will be described.

[0086] First, the spring 4 is press-fitted into the inner rotor 3 from one axial end, thereby attaching the spring 4 to the inner rotor 3. Next, the plain bearing 6 is press-fitted into the outer cylindrical portion 3b of the inner rotor 3 from the other end, thereby attaching the plain bearing 6 to the inner rotor 3. At this time, the annular plain bearing 6, in its expanded diameter state, moves over the other of the two protrusions 3b1 on the outer cylindrical portion 3b and moves to the portion axially sandwiched between the two protrusions 3b1. Next, the outer rotor 2 is attached from one axial end to the inner rotor 3 on which the spring 4 and plain bearing 6 are attached. Next, a rolling bearing 7 is press-fitted between one axial end of the outer rotor 2 and one axial end of the inner rotor 3. After that, an end cap 5 is attached to the other axial end of the outer rotor 2. This completes the pulley structure 1.

[0087] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims.

[0088] The values ​​of the taper angle (θ), taper width (TW), and taper length (TL) of the tapered surface at the corner are not limited to the above-mentioned numerical ranges (taper angle (θ) of 15° or more and 40° or less; taper width (TW) of 0.4 mm or more and 0.9 mm or less; taper length (TL) of 0.7 mm or more and not more than the axial length SD between the end face on the other end side of the sliding bearing 6 and the side surface 2s). Similarly, the radius of curvature of the convex curved surface at the corner is not limited to the above-mentioned numerical range (curvature radius of 0.3 mm or more and 1 mm or less).

[0089] There is no limitation to the presence of a gap between both circumferential ends of the sliding bearing. Both axial ends of the sliding bearing may be in contact with each other, with almost no gap between the circumferential ends of the sliding bearing.

[0090] The pulley structure may be configured to transmit or interrupt torque between the outer rotating body and the inner rotating body by a clutch configured differently from a coil spring clutch including a torsion coil spring. Furthermore, the pulley structure may not be provided with a clutch that transmits or interrupts torque between the outer rotating body and the inner rotating body. That is, the pulley structure may be configured so that torque is always transmitted between the outer rotating body and the inner rotating body, or so that torque is always interrupted between the outer rotating body and the inner rotating body. [Example]

[0091] In the present invention, in the pulley structure, when force is applied from the belt of the outer rotating body, it is possible to suppress the outer rotating body or the inner rotating body from vibrating and generating abnormal noise, and it is also necessary to achieve both manufacturing quality and productivity in the assembly process. Therefore, in this example, pulley structures according to Examples 1 to 9 and Comparative Examples 1 to 7 (hereinafter referred to as "test specimens") were fabricated, and assembly tests and idle tests were carried out for comparative verification. The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0092] (Common to all specimens) (slide bearing) It is a circular component with two ends, and the outer surface of the plain bearing has chamfered sections at both circumferential ends of the plain bearing (portions located within 2 mm from both circumferential end faces) that extend so that the diameter decreases toward each end. - Thickness reference dimension (thickness other than both ends in the circumferential direction): 1.4 mm Thickness at 0 mm from the circumferential end face (thickness at the circumferential end face): 1.2 mm Thickness at 2mm from the circumferential end: 1.4mm Axial length: 6mm Inner diameter at circumferential ends: 55 mm

[0093] (Manufacturing of sliding bearings) The sliding bearing was made of polyacetal resin (trade name "Vestal G" (manufactured by Mitsuboshi Belting Co., Ltd.)) with a Rockwell R scale of 114. The above resin material was used in the same mold (injection molding mold) (not shown) having a cavity corresponding to the above shape and dimensions to fabricate a sliding bearing. Furthermore, for each test specimen, it was confirmed that sliding bearings in which the thicknesses of each part were the above-mentioned thicknesses could be produced with good reproducibility using the injection molding method described above, and then a pulley structure was formed using a sliding bearing having the above-mentioned thickness. Regarding the injection molding conditions, the temperature of the resin during injection molding was approximately 170°C at the rear of the plasticizing cylinder (the part opposite the nozzle), approximately 200°C at the front of the plasticizing cylinder (the part on the nozzle side), and approximately 210°C at the nozzle. The mold temperature was approximately 70°C. The resin injection pressure was approximately 80 MPa, and the resin injection speed was approximately 30 mm / sec. The molding shrinkage was approximately 2%.

[0094] (Between the inner peripheral surface of one end of the outer rotating body and the outer peripheral surface of one end of the cylindrical body of the inner rotating body) -Before the belt is attached, the cylindrical gap is 1.5 mm Sliding gap before the belt is attached: 0.1 mm Minimum gap dimension (VM) before the belt is attached: 1.0 mm Axial length (SD) between the other end face of the sliding bearing and the other end side face of the outer rotating body (side face 2s): 1.5 mm

[0095] (Different for each test specimen) (Configuration of the corner of the outer rotating body) For each test piece, the configuration of the corners of the outer rotor shown below was set in accordance with the shapes and dimensions shown in Tables 1 to 4, and the outer rotor was fabricated by cutting. -Whether or not there is a corner shape formed by a tapered surface CT, and whether or not there is a corner shape formed by a convex curved surface CP When both the tapered surface CT and the convex curved surface CP are present at the corner of the outer rotation body, the values ​​of the taper angle (θ), taper width (TW), and taper length (TL) of the tapered surface CT, as well as the curvature radius of the convex curved surface CP, are

[0096] [Manufacturing of pulley structures] Pulley structures (each specimen) were fabricated according to the method described in the above embodiment. However, the assembly test described below is conducted at a stage when the outer rotating body (single body) has not yet been attached to the inner rotating body to which the spring and sliding bearing are attached. For each specimen, a combination of the inner and outer rotors that would not result in radial fitting errors was selected and used for the test, so that the outer rotor could be attached from one axial end to the inner rotor, which was equipped with a spring and sliding bearing, according to the misalignment amount (0.4 mm or 0.5 mm) set in the assembly test described below.

[0097] [Evaluation of Pulley Structures: Items, Methods, and Criteria] For each test specimen (Examples 1 to 9 and Comparative Examples 1 to 7 listed in Tables 1 to 4), in order to determine whether a pulley structure capable of resolving the problems of the present application was obtained, the manufacturing quality in the assembly process (presence or absence of damage to the sliding bearing), productivity in the assembly process (centering ability), and dynamic performance of the sliding bearing (presence or absence of abnormal noise, presence or absence of abnormalities in the sliding bearing) were verified.

[0098] [Assembly test] (Assembly equipment) The assembly device (not shown) has an upper load cell connector that can move up and down, and an upper gripping section for gripping the outer rotor with one end facing upward. The lower fixed section has a lower gripping section for gripping the inner rotor, with one end facing upward. The upper load cell connector is connected to a load cell (load detector). After inputting the load (pressing load) to be applied during assembly and the movement speed (e.g., 50 mm / min) into the control panel in advance, the device is started. The upper load cell connector moves downward along the central axis of the outer rotor, allowing the outer rotor to be set from one axial end onto the inner rotor, which is equipped with the spring and plain bearing. This assembly device is normally set up so that the central axis of the inner rotating body and the central axis of the outer rotating body are aligned radially (i.e., there is no misalignment) in the initial state before they are set up. However, this assembly device has an adjustment mechanism that can fine-tune the relative positions of the upper and lower gripping parts (the radial positional relationship of each rotating body) so that the central axes of the inner rotating body and the outer rotating body can be intentionally slightly misaligned radially (with a misalignment of 0.4 mm or 0.5 mm) in the initial state before they are set up for testing. Furthermore, when interference occurs between the sliding bearing and the corner of the outer rotating body during assembly, the reaction force (load) in the direction of the central axis received from the corner of the outer rotating body is detected by the load cell, and a chart (stroke-load diagram) of this is recorded sequentially on a PC (personal computer).

[0099] (Test Method) (1) Using the above assembly device, with the misalignment set to 0.4 mm, the outer rotating body was attached to one end of the axial direction of the inner rotating body, to which the spring and sliding bearing were attached, and the centering performance was checked using the above chart. (2) The inner and outer rotating bodies were disassembled, and the sliding bearing attached to the inner rotating body was replaced with a new one. (3) Using the above assembly device, with the misalignment set to 0.5 mm, the outer rotating body was attached to one end of the axial direction of the inner rotating body, on which the spring and sliding bearing were attached, and the centering ability was checked using the above chart. (4) The inner and outer rotating bodies were disassembled, and the misalignment was set to 0.5 mm. Then, the sliding bearings were visually inspected for damage after they were reassembled.

[0100] (Judgment criteria) (manufacturing quality) When the sliding bearing was assembled with a misalignment of 0.5 mm and showed no damage (convex, bulging plastic deformation) or signs of damage (no convex, bulging plastic deformation, but slight indentations), it was deemed that the manufacturing quality of the pulley structure assembly process could be ensured, and was given an A rating. When the sliding bearing was assembled with a misalignment of 0.5 mm, no damage (convex, bulging plastically deformed areas) was found, but signs of damage (no convex, bulging plastically deformed areas, but slight indentations) were found, the manufacturing quality of the pulley structure assembly process was assessed as slightly inferior, and a grade of B was given. If damage (protruding plastic deformation areas) was found in the sliding bearing when assembled with a misalignment of 0.5 mm, it was determined that the manufacturing quality of the pulley structure assembly process could not be ensured, and the product was rated C. From the viewpoint of suitability for practical use in this application (manufacturing quality in the assembly process of the pulley structure), pulley structures rated a and b were deemed to be at the pass level.

[0101] (Productivity) The reaction force (load) when the sliding bearing interfered with the corner of an outer rotating body that was configured only with a tapered surface with a known, pre-measured taper angle of 45° was used as a reference load, and the magnitude relationship of the measured load relative to this reference load was used as an index of manufacturability (centering ability). Specifically, for each test specimen, if the measured load when the sliding bearing interfered with the corner of the outer rotating body was less than the reference load, it was deemed to be a configuration that ensured manufacturability (centering ability). Even when the misalignment amount was set to 0.5 mm, if the centering ability was good (if the measured load when the sliding bearing and the corner of the outer rotating body interfered was less than the standard load), it was evaluated as being possible to ensure productivity in the pulley structure assembly process, and was given an A rating. When the misalignment amount was set to 0.4 mm, centering was good (the measured load when the sliding bearing and the corner of the outer rotating body interfered was less than the standard load), but when the misalignment amount was set to 0.5 mm, if centering was difficult (the measured load when the sliding bearing and the corner of the outer rotating body interfered was equal to or greater than the standard load), it was evaluated as being slightly inferior in terms of productivity in the pulley structure assembly process and given a rating of b. If centering was difficult even with the misalignment set to 0.4 mm (if the measured load when the sliding bearing and the corner of the outer rotating body interfered was equal to or greater than the standard load), it was determined that productivity in the pulley structure assembly process could not be ensured, and a rating of C was given. From the viewpoint of suitability for practical use in this application (productivity in the assembly process of the pulley structure), pulley structures rated a and b were deemed to be at the pass level.

[0102] [Idol Test] (Idle test machine) Using the test specimens of Examples 1 to 9 and Comparative Examples 1 to 7, an idle test machine 80 as shown in FIG. 10 was constructed, and the idle test machine 80 was operated to evaluate whether or not abnormal noise was generated. The idle test machine 80 includes an alternator 81, a test piece (pulley structure) 1x attached to the drive shaft S of the alternator 81, a crank pulley 83, a V-ribbed belt 84 wound around the crank pulley 83 and the test piece 1x, a timing pulley 85 fixed coaxially with the crank pulley 83, a motor 86, a timing pulley 87 connected to the drive shaft of the motor 86, and a timing belt 88 wound around the timing pulleys 85 and 87. The space containing the alternator 81, the test piece 1x, the crank pulley 83, and the V-ribbed belt 84 was used as a thermostatic chamber 82, and the ambient temperature was kept constant.

[0103] (Test Method) After the final disassembly inspection (checking for damage to the sliding bearing) of each test specimen in the above assembly test, the amount of misalignment was set to 0 mm (no misalignment), and the outer rotating body, on which the spring and sliding bearing were attached, was attached from one end in the axial direction to the inner rotating body. Next, the rolling bearing was pressed in and the end cap was attached, completing each test specimen 1x (pulley structure).

[0104] The idling test was carried out under the following conditions to evaluate whether or not abnormal noise was generated, by running the engine for about 20 minutes and then driving the engine for about 3 minutes. Crank pulley 83 rotation speed: Approximately 700 rpm (rotation speed fluctuation rate is approximately 10%) · Alternator 81 (auxiliary) and test piece 1x rotation speed: Approximately 1500 rpm Surface temperature of alternator 81 (auxiliary equipment) and test piece 1x: Approximately 130°C (the thermostatic chamber 82 was kept at 130°C, the same as the maximum temperature expected when an actual vehicle is idling).

[0105] In the evaluation of whether or not abnormal noises were generated, five evaluators without hearing impairments judged whether or not they could hear any abnormal noises other than the sounds generated in Comparative Example 1. Specifically, when the idle test machine 80 was operated as described above, the evaluators were positioned 2 m behind the alternator 81 (on the opposite side from the pulley structure) to judge whether or not any abnormal noises could be heard by their hearing.

[0106] In the idle test, the evaluation of the presence or absence of any abnormalities in the sliding bearings (equivalent to an evaluation of the functionality and durability of the sliding bearings) was carried out after running the vehicle for 100 hours under the same conditions as above. After the operation was completed, the pulley structure (each test specimen) was disassembled and the presence or absence of damage to the sliding bearings was visually inspected.

[0107] (Judgment criteria) (Dynamic performance of sliding bearings) If no abnormal noise was observed during the idle test, nor were any abnormalities in the sliding bearing (such as abnormal linear wear), or any signs of abnormality in the sliding bearing (such as slight linear scratches), the dynamic performance of the sliding bearing was deemed to be ensured, and the vehicle was given an A rating. During the idle test, neither abnormal noise nor abnormal sliding bearings (abnormal linear wear, etc.) were found, but if signs of abnormality were found in the sliding bearings (minor linear scratches, etc.), the dynamic performance of the sliding bearings was evaluated as being slightly inferior, and a grade of B was given. If abnormal noise was generated and / or abnormalities in the sliding bearing (such as abnormal linear wear) were found during the idle test, the dynamic performance of the sliding bearing was deemed to be insufficient, and a rating of C was given. From the perspective of suitability for practical use in this application (dynamic performance related to sliding bearings), pulley structures rated a and b were deemed to be at the pass level.

[0108] (Overall judgment) The criteria for the overall assessment (ranking) of a pulley structure that can solve this problem were determined as follows, based on the results of the assessments for the three test items above (productivity, manufacturing quality, and dynamic performance related to the sliding bearing). Rank A: If all of the above test items were rated as A, it was deemed to be completely satisfactory for practical use and was given the highest rank. Rank B: If there were no C ratings in the above test items, but even one B rating, the product was deemed to be somewhat inferior, although there was no practical problem. Rank C: If any of the above test items were rated C, the solution to this issue was deemed insufficient (failed).

[0109] (Verification results and considerations) The verification results are shown in Tables 1 to 4.

[0110] (Comparison of changing the shape of the corner of the outer rotating body) [Table 1]

[0111] (Example 1, Comparative Examples 1 and 2) The corners of the outer rotating body were changed to have or not have tapered surfaces (taper angle 30°, taper width 0.4 mm, taper length 0.7 mm), and the corners of the outer rotating body were changed to have or not have convex curved surfaces (curvature radius 0.5 mm), and these were compared. When both the tapered surface of the above configuration and the convex curved surface of the above configuration were provided at the corners of the outer rotating body (Example 1), the specified (acceptable level) manufacturing quality, productivity (centering ability), and dynamic performance of the sliding bearing were able to be ensured (rank A in the overall evaluation). In the case of a bearing having a convex curved surface of the above configuration but no tapered surface (Comparative Example 1), the manufacturing quality and the dynamic performance of the sliding bearing were both rated a, but the productivity (centering ability) was rated c (and the overall rating was also rank C). Conversely, in the case of a bearing having a tapered surface of the above configuration but no convex curved surface (Comparative Example 2), productivity (centering ability) was rated as a, but manufacturing quality and the dynamic performance of the sliding bearing were both rated as c (and the overall rating was also Rank C). From the above results, it can be said that a pulley structure having both a tapered surface and a convex curved surface at the corner of the outer rotating body is preferable in that it can ensure a specified (acceptable level) manufacturing quality in the assembly process, productivity (centering ability) in the assembly process, and dynamic performance related to the sliding bearing.

[0112] (Comparison with varying taper angle of tapered surface) [Table 2]

[0113] (Examples 1 to 3, Comparative Examples 3 and 4) In a pulley structure having both a tapered surface and a convexly curved surface at the corner of the outer rotating body, the taper angle of the tapered surface was varied by 30° based on the pulley structure of Example 1 (taper width of the tapered surface: 0.4 mm, radius of curvature of the convexly curved surface: 0.5 mm), and a comparison was made. As the taper angle of the tapered surface increases, the taper length of the tapered surface decreases and productivity (centering ability) tends to deteriorate; conversely, as the taper angle of the tapered surface decreases, the taper length of the tapered surface increases, ensuring productivity (centering ability), but tending to deteriorate the dynamic performance of the sliding bearing.

[0114] (Examples 1 to 3, Comparative Example 4) Specifically, in Example 3, in which the taper angle of the tapered surface was increased to 40° compared to Example 1 in order to confirm the upper limit level of the taper angle of the tapered surface, centering performance was good at a misalignment of 0.4 mm, but centering performance was difficult at a misalignment of 0.5 mm, and productivity (centering performance) was rated B (rank B in the overall evaluation). Furthermore, in Comparative Example 4, in which the taper angle of the tapered surface was increased to 45° compared to Example 1, centering became difficult even with a misalignment of 0.4 mm, and productivity (centering ability) was rated C (rank C in the overall evaluation). From these results, it can be said that the upper limit of the taper angle of the tapered surface is preferably about 40°, and more preferably about 30°.

[0115] (Examples 1 and 2, Comparative Example 3) In order to confirm the lower limit of the taper angle of the tapered surface, in Example 2, the taper angle of the tapered surface was reduced to 15° compared to Example 1, and Example 2 was awarded Rank A, equivalent to Example 1; however, in Comparative Example 3, in which the taper angle of the tapered surface was further reduced to 10°, the taper length of the tapered surface was 2.3 mm, which exceeded the SD dimension (axial length between the end face on the other end of the sliding bearing and the side surface 2s: 1.5 mm). Perhaps because this reduced the pressure-receiving area of ​​the sliding bearing, an abnormality (abnormal linear wear) occurred in the sliding bearing, and the dynamic performance of the sliding bearing was rated C (rank C in the overall evaluation as well). From this result, it can be said that the lower limit of the taper angle of the tapered surface is about 15°.

[0116] From the above results, it can be said that the preferred range for the taper angle of the tapered surface is 15° or more and 40° or less, and a more preferred range is 15° or more and 30° or less, in terms of being able to ensure the specified (acceptable level) productivity (centering ability) and the dynamic performance of the sliding bearing (in particular, suppressing abnormalities in the sliding bearing).

[0117] (Comparison with varying taper width and taper length of the tapered surface) [Table 3]

[0118] (Examples 1 and 4, Comparative Examples 5 to 6) In a pulley structure having both a tapered surface and a convexly curved surface at the corner of the external rotation, the pulley structure of Example 1 (taper angle of the tapered surface: 30°, radius of curvature of the convexly curved surface: 0.5 mm) was used as a base, and the taper width of the tapered surface was varied by 0.4 mm and the taper length of the tapered surface was varied by 0.7 mm, and comparisons were made. Under the above conditions, an increase in the taper width of the tapered surface means that the taper length of the tapered surface also increases. As the taper width of the tapered surface increases, the taper length of the tapered surface also increases, and there is a tendency for the dynamic performance of the sliding bearing to deteriorate. Conversely, as the taper width of the tapered surface decreases, the taper length of the tapered surface also decreases, and while the dynamic performance of the sliding bearing is ensured, there is a tendency for productivity (centering ability) to deteriorate.

[0119] (Examples 1 and 4, Comparative Example 6) Specifically, in order to confirm the upper limit levels for the taper width and taper length of the tapered surface, Example 4, in which the taper width of the tapered surface was increased to 0.9 mm and the taper length of the tapered surface to 1.5 mm (equivalent to the SD dimension) compared to Example 1, was awarded Rank A, equivalent to Example 1. However, in Comparative Example 6, in which the taper width of the tapered surface was further increased to 1.0 mm and the taper length of the tapered surface to 1.7 mm, the taper length of the tapered surface exceeded the SD dimension (1.5 mm). This probably reduced the pressure-receiving area of ​​the sliding bearing, and resulted in the occurrence of an abnormality (abnormal linear wear) in the sliding bearing, and the dynamic performance of the sliding bearing was rated C, resulting in a Rank C. From this result, it can be said that the upper limit of the taper width of the tapered surface is about 0.9 mm, and the upper limit of the taper length of the tapered surface is about the SD dimension (1.5 mm).

[0120] (Example 1, Comparative Example 5) In order to confirm the lower limit of the taper width and the lower limit of the taper length of the tapered surface, the taper width of the tapered surface was reduced to 0.3 mm and the taper length of the tapered surface was reduced to 0.5 mm compared to Example 1. In Comparative Example 5, the specified (acceptable level) productivity (centering ability) could not be ensured (evaluation: c), and the result was ranked C. From this result, it can be said that the lower limit of the taper width of the tapered surface is about 0.4 mm, and the lower limit of the taper length of the tapered surface is about 0.7 mm. From the above results, it can be said that the preferred range for the taper width of the tapered surface is 0.4 mm or more and 0.9 mm or less, and the preferred range for the taper length of the tapered surface is 0.7 mm or more and the SD dimension (1.5 mm in this embodiment) or less, in order to ensure the specified (acceptable level) productivity (centering ability) in the assembly process and the dynamic performance of the sliding bearing (in particular, suppressing abnormalities in the sliding bearing).

[0121] (Comparison of varying the radius of curvature of a convex curved surface) [Table 4]

[0122] (Examples 1, 5 to 9, Comparative Examples 2 and 7) In a pulley structure having both a tapered surface and a convexly curved surface at the corner of the outer rotating body, the pulley structure of Example 1 (taper angle of the tapered surface: 30°, taper width of the tapered surface: 0.4 mm, taper length of the tapered surface: 0.7 mm) was used as a base, and the radius of curvature of the convexly curved surface was varied by 0.5 mm, and a comparison was made with a case having a tapered surface of the above configuration but not a convexly curved surface (Comparative Example 2). The larger the radius of curvature of the convex curved surface, the worse the productivity (centering ability) tends to be. Conversely, the smaller the radius of curvature of the convex curved surface, the better the productivity (centering ability) is ensured, but the manufacturing quality and the dynamic performance of the sliding bearing tend to be worse.

[0123] (Examples 1, 8-9, Comparative Example 7) Specifically, in order to confirm the upper limit level of the radius of curvature of the convex curved surface, Example 8, in which the radius of curvature of the convex curved surface was increased to 1.0 mm compared to Example 1, was ranked A, equivalent to Example 1. However, in Example 9, in which the radius of curvature of the convex curved surface was further increased to 1.1 mm, although centering performance was good at a misalignment of 0.4 mm, centering performance was difficult at a misalignment of 0.5 mm, and productivity (centering performance) was ranked B (and the overall evaluation was also ranked B). Furthermore, in Comparative Example 7, in which the radius of curvature of the convex curved surface was increased to 1.2 mm compared to Example 1, centering became difficult even with a misalignment of 0.4 mm, and productivity (centering ability) was rated C (rank C in the overall evaluation). From these results, it can be said that the upper limit of the radius of curvature of the convex curved surface is preferably about 1.1 mm, and more preferably about 1.0 mm.

[0124] (Examples 1, 5 to 7, Comparative Example 2) In order to confirm the lower limit level of the radius of curvature of the convexly curved surface, the radius of curvature of the convexly curved surface was reduced to 0.3 mm compared to Example 1 in Example 7, and this resulted in an A rank, equivalent to Example 1. However, in Examples 6 (0.2 mm) and 5 (0.1 mm), in which the radius of curvature of the convexly curved surface was further reduced, signs of damage were found in the sliding bearings in an assembled state with a misalignment of 0.5 mm (no convex plastically deformed portions, but minor indentations), and the manufacturing quality was assigned a B rating (and the overall rating was also Rank B). In Comparative Example 2, in which the radius of curvature of the convex curved surface was set to 0 mm (i.e., the convex curved surface was eliminated), the sliding bearing in the assembled state described above was damaged (convex plastically deformed portion), the manufacturing quality was rated C, abnormal noise occurred during the idle test, and the dynamic performance of the sliding bearing was also rated C (the overall rating was also Rank C). From this result, it can be said that the lower limit of the radius of curvature of the convex curved surface is preferably about 0.1 mm, and more preferably about 0.3 mm. From the above results, it can be said that the preferred range for the radius of curvature of the convex curved surface is 0.1 mm or more and 1.1 mm or less, and a more preferred range is 0.3 mm or more and 1.0 mm or less, in terms of being able to ensure the specified (acceptable level) manufacturing quality in the assembly process, productivity (centering ability) in the assembly process, and dynamic performance of the sliding bearing (in particular, suppression of the generation of abnormal noise).

[0125] (Effects obtained) From the results in Tables 1 to 4, it can be seen that the pulley structures of Examples 1 to 9 address the issues, and by configuring the corner C of the outer rotating body with a tapered surface CT and a convex curved surface CP, the centering of the outer rotating body and the inner rotating body during assembly is ensured, making it easier to ensure productivity in the assembly process and to prevent damage to the sliding bearing when the sliding bearing interferes with the corner C of the outer rotating body, making it easier to ensure manufacturing quality in the assembly process and to prevent abnormal noise caused by vibration of the outer rotating body or inner rotating body when force is applied from the belt of the outer rotating body due to damage to the sliding bearing. Furthermore, by designing the taper angle (θ), taper width (TW), and taper length (TL) of tapered surface CT, as well as the radius of curvature of convex curved surface CP, to fall within appropriate numerical ranges, it is possible to prevent a decrease in the functionality and durability of the sliding bearing (the occurrence of abnormalities in the sliding bearing), and more reliably ensure the centering of the outer rotating body and inner rotating body during assembly. As a result, it is possible to more reliably ensure productivity in the assembly process, and more reliably prevent damage to the sliding bearing when it interferes with corner C of the outer rotating body. As a result, it is possible to more reliably ensure manufacturing quality in the assembly process, and more reliably prevent abnormal noise caused by vibration of the outer rotating body or inner rotating body when force is applied from the belt of the outer rotating body due to damage to the sliding bearing. [Explanation of symbols]

[0126] 1 Pulley structure 2. External Rotating Body 2c Inner surface 2s side 3 Internal Rotating Body 6. Plain bearings 7. Rolling bearings B Belt C Corner CT tapered surface CP convex curved surface

Claims

[Claim 1] a cylindrical outer rotating body around which a belt is wound and which rotates about a rotation axis by torque applied from the belt; an inner rotating body provided radially inside the outer rotating body and rotatable relative to the outer rotating body around the rotation axis; a pair of bearings interposed between the outer rotor and the inner rotor at one end and the other end in the axial direction along the rotation axis, connecting the outer rotor and the inner rotor so as to be rotatable relative to each other; One of the pair of bearings is a sliding bearing and the other is a rolling bearing, the sliding bearing is made of a thermoplastic resin, is formed into an annular shape with ends, and is in contact with the internal rotating body, the thickness of the sliding bearing at both circumferential ends is smaller than the reference dimension of the thickness of the sliding bearing, The outer rotating body is formed so that the inner diameter thereof gradually decreases from the other end side toward the one end side, and further The outer rotating body is an inner circumferential surface that faces the plain bearing in the radial direction and extends in the axial direction, and whose end portion on the other end side is located closer to the other end than the plain bearing; a side surface extending radially outward from an end portion of the inner circumferential surface on the other end side, The corner where the inner circumferential surface and the side surface intersect over the entire circumference is a tapered surface that is a flat surface whose inner diameter increases from the inner circumferential surface toward the side surface; a convex curved surface that is an arcuate surface that bulges outward at a constant curvature and connects the tapered surface and the side surface, The tapered surface is The taper angle is 15° or more and 40° or less. The taper width is 0.4 mm or more and 0.9 mm or less, a taper length of 0.7 mm or more and less than the length in the axial direction between the end face on the other end side of the sliding bearing and the side surface, The convex curved surface is A pulley structure, characterized in that the radius of curvature is 0.3 mm or more and 1 mm or less.

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