Bush and bolt fastening structure

Abstract

To prevent a phenomenon in which a bolt and a bush corotate when the bolt is fastened, in regard to a bolt fastening structure for making first and second members connected to each other by passing through a first member through-hole and a second member through-hole.SOLUTION: A bush 32 comprises: a cylindrical part 33 which has a central hole 37 subjected to insertion of a bolt and which is inserted into a first member through-hole 26; a flange part 34 which is integrally provided at one end of the cylindrical part 33 and which is locked to a first member; and a plurality of protrusions 36 which are provided on a contact surface 35 of the flange part 34 and which bite into the first member.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a component of a bolted structure. [Background technology]

[0002] For example, a conventional structure in which a number of battery units are stored in a metal tray, the tray is covered with a synthetic resin cover to seal the battery units inside, and the tray and cover are fastened together with bolts is known, for example, as described in Japanese Patent Laid-Open No. 2014-022154 (Patent Document 1). Patent Document 1 describes an in-vehicle battery pack in which through holes are formed in the outer edge of the tray on the bottom side of the battery pack and in the outer edge of the cover on the top side of the battery pack, and bolts are passed through these through holes and fastened together with bolts and nuts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-022154 Summary of the Invention [Problem to be solved by the invention]

[0004] When fastening the outer edge of the tray and the outer edge of the cover with multiple bolts as in the above-mentioned conventional technology, the bolts must be fastened to a predetermined torque. However, in order to reduce weight, the cover is often made of a thin synthetic resin. As a result, in this type of configuration, the rigidity of the bolt fastening points can be insufficient.

[0005] One solution to this problem, aimed at improving the durability of the bolted joints, is to press a cylindrical flanged bushing into the through-hole of the synthetic resin cover and then fasten the bolt through the center hole of the bushing. The flanged bushing bears the fastening force in the bolt axial direction, improving the durability of the bolted joints. Since many bolts are to be fastened in this way, multiple torque wrenches or similar tools are used simultaneously.

[0006] One concern in this case is that due to insufficient press-fitting of the bushings, some of the bushings may rotate together with the bolts (in other words, the bushings may rotate relative to the through holes in the synthetic resin cover), which may prevent the bolts from being tightened with the specified tightening torque, resulting in improper tightening and, in the future, the risk of a gap forming between the outer edge of the cover and the outer edge of the tray.

[0007] In view of the above-mentioned circumstances, the present invention aims to provide a bushing that does not rotate together with the bolt when the bolt is tightened to a predetermined torque in a case where a first member such as a cover and a second member such as a tray are fastened together by pressing the bushing into the first member and fastening them with a bolt. [Means for solving the problem]

[0008] For this purpose, the bushing of the present invention is a bolt fastening structure in which a bolt passing through a first member through hole and a second member through hole is threaded into a nut to join the first and second members together, the first member being made of synthetic resin and the second member being made of synthetic resin or metal, the metal bushing being provided in the first member through hole, the bushing comprising: a cylindrical portion having a central hole through which the bolt is passed and fitted into the first member through hole; a flange portion which is integrally provided at one end of the cylindrical portion and has an outer diameter larger than the first member through hole and which has a contact surface that abuts against the first member; and a plurality of protrusions which are provided on the contact surface and bite into the first member, the axial dimension from the contact surface of the flange portion to the other end of the cylindrical portion being the same as the axial dimension of the first member through hole, and the inclination gradient formed from the tip side of the protrusions toward the contact surface is steeper in the bolt tightening direction and gentler in the opposite direction. The plurality of protrusions are provided in large numbers and scattered from the inner diameter side to the outer diameter side of the contact surface. do.

[0009] According to the present invention, the bushing is fitted to the first member by the multiple protrusions on the contact surface biting into the first member, so that when the bolt is tightened, the bushing does not rotate with the bolt even if it comes into contact with the bolt. Therefore, when tightening a large number of bolts, all of the bolts are tightened with the specified tightening torque. Furthermore, according to the present invention, when the bushing is pressed into the first member, it bites into the first member at a gentle gradient, allowing it to bite in smoothly and effectively preventing the bushing from rotating in the direction of tightening the bolt when the first member is bolted.

[0010] As an aspect of the present invention The bolt fastening structure of the present invention comprises the above-mentioned bushing of the present invention, a first member, a second member, a bolt, and a nut, The second member is a tray having a flat, band-shaped abutment on its upper edge, and the first member is a cover that fits over the tray and has a flat, band-shaped abutment on its lower edge that abuts against the abutment of the second member, a through-hole in the first member is provided in the abutment of the tray, and a through-hole in the abutment of the cover is provided in the abutment of the second member, and a sealing groove that extends around the entire periphery of the abutment is located between the abutment of the cover and the abutment of the tray, at a position inside the through-hole, and a sealing material is disposed in the sealing groove, so that the two abutment parts are tightly attached by the sealing material. The bolt fastening structure of the present invention includes the above-mentioned bushing of the present invention, a first member, a second member, a bolt, and a nut, and the second member Compared to through holes First member The through hole is larger than the thickness of the cylindrical part of the bushing, and the inner diameter of the center hole in the cylindrical part of the bushing is Material The diameter is the same as the inner diameter of the through hole and is larger than the outer diameter of the bolt shaft. Book In one aspect of the invention, the first member has a stepped portion at the rear end of the first-member through hole into which the flange of the bushing is fitted, and the axial dimension from the contact surface to the other end of the cylindrical portion is the same as the axial dimension of the first-member through hole. When the butt portions of the first member and the second member are mated and fastened with a bolt, the flange is fitted into the stepped portion and the cylindrical portion is fitted into the first-member through hole, and the other end of the cylindrical portion abuts against the second member. According to this aspect, the axial force of the bolt and nut is borne by the bushing, not the first member. As a result, even when the bolt is tightened with a predetermined torque, the first member made of synthetic resin is not crushed by the axial force of the bolt.

[0011] In another aspect of the present invention, a protrusion that bites into the step is integrally formed on the outer peripheral surface of the flange of the bushing. According to this aspect, not only the convex portion bites into the first member, but also the protrusion bites into the first member, so that when the bolt is tightened, co-rotation with the bolt as it turns can be reliably prevented, and the bolt can be tightened with a predetermined torque.

[0012] As a reference example The first member is made of synthetic resin, the second member is made of synthetic resin or metal, the axial dimension from the contact surface of the flange to the other end of the cylindrical portion is the same as the axial dimension of the through hole of the first member, and when the abutting portion of the first member and the abutting portion of the second member are aligned and fastened with a bolt, the other end of the cylindrical portion abuts against the second member. Reference example According to the specification, the axial force of the bolt and nut is borne by the bushing, not the first member. As a result, even when the bolt is tightened with a predetermined torque, the synthetic resin first member is not crushed by the axial force of the bolt.

[0013] Reference example The inclination gradient formed from the tip end of the convex portion of the bushing toward the contact surface is steeper in the bolt tightening direction and gentler in the opposite direction. Reference example According to this, when the bushing is press-fitted into the first member, it bites into the first member at a gentle gradient, allowing for smooth insertion, and effectively preventing the bushing from rotating in the direction of tightening the bolt when the first member is fastened with the bolt.

[0014] Reference example The convex portion of the bushing may be conical. If the convex portion is conical, the shape of the convex portion can be stably provided. Reference example According to this method, it is easy to form the convex portions using a press mold. Reference example The convex portion of the bushing may be pyramidal. Because the convex portion is pyramidal, the gradient can be easily changed, and the bushing can be smoothly press-fitted into the first member, and the shape of the pyramid and the gradient of the inclined surface can be easily set so as to prevent the bushing from rotating together with the bolt in the rotation direction. Reference exampleThe convex portion of the bushing is composed of a flat surface and a groove with a V-shaped cross section provided on the flat surface. This aspect allows a large number of fine protrusions to be provided. [Effects of the Invention]

[0015] According to the present invention, when fastening the first and second members together with multiple bolts, the bushings are held securely in place in the first member due to the protrusions that bite into them, preventing them from rotating together with the bolts and ensuring that all bolts are fastened with the specified tightening torque. This eliminates problems such as some bolts being insufficiently tightened. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is an exploded perspective view showing first and second members that are fastened together with a bolt. [Figure 2] 1 is an enlarged longitudinal cross-sectional view showing an embodiment of a bolt fastening structure. FIG. [Figure 3] 1 is a perspective view showing a bush according to a first embodiment of the present invention. [Figure 4] FIG. 2 is a bottom view showing the bush according to the first embodiment of the present invention. [Figure 5] FIG. 10 is a vertical cross-sectional view showing another embodiment of the bolt fastening structure. [Figure 6] FIG. 10 is a bottom view showing a bush according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a bottom view showing a bush according to a third embodiment of the present invention. [Figure 8] FIG. 10 is a bottom view showing a bush according to a fourth embodiment of the present invention. [Figure 9] FIG. 10 is a perspective view similar to FIG. 3, showing a bush according to a fifth embodiment of the present invention. [Figure 10] FIG. 10 is a perspective view similar to FIG. 3, showing a bush according to a sixth embodiment of the present invention. [Figure 11] FIG. 10 is a partially enlarged view of a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described in detail below with reference to the drawings. FIGS. 1 to 4 relate to one embodiment, showing an example in which the present invention is applied to bolting a tray and a cover that house a battery unit. FIG. 1 is an exploded perspective view showing first and second members to be bolted together, and only one portion of the bolted structure is shown to avoid cluttering the drawing. FIG. 2 is an enlarged longitudinal cross-sectional view of the bolted structure shown in FIG. 1. Referring to FIG. 1, the bolted structure connects a lower tray 11 (second member) and an upper cover 21 (first member) using a bushing 32, a bolt 41, and a nut 44. The tray 11 has a bottom wall 12, a wall-like edge portion 13 extending along the entire periphery of the bottom wall 12, a partition wall 14 extending inside the bottom wall 12 and connecting to the edge portion 13, and a flat, strip-shaped abutment portion 15 formed on the upper edge of the edge portion 13 and projecting outward. A predetermined number of battery units 31 are housed in an aligned state in a rectangular compartment on the bottom wall 12 surrounded by the edge 13 and the partition wall 14 .

[0018] Cover 21 has a shape that corresponds to tray 11 and has a top wall 22, a vertical edge 23 that stands upright around the entire periphery of top wall 22 and protrudes downward, and a flat, strip-shaped abutment 25 that is formed at the lower edge of edge 23 and protrudes outward. Cover 21 covers tray 11 from above and seals all of the battery units 31, 31.... The abutment 15, 25 abut against each other.

[0019] The butting portions 15, 25 are formed with cover through-holes 26 (first member through-holes) and tray through-holes 16 (second member through-holes) at predetermined intervals, respectively. Both the cover through-holes 26 (first member through-holes) and the tray through-holes 16 (second member through-holes) are hereinafter simply referred to as "through-holes." When the butting portions 15, 25 are butted against each other, the centers of the through-holes 16, 26 are aligned. The through-hole 26 is larger than the through-hole 16 by the thickness of the cylindrical portion 33 of the bushing 32. The inner diameter of a center hole 37 formed in the cylindrical portion 33 of the bushing 32 is approximately the same as the inner diameter of the through-hole 16, but is slightly larger than the outer diameter of the shank 42 of the bolt 41. A step 27 into which the flange 34 of the bushing 32 fits is provided at the rear end of the through-hole 26 (the upper end of the through-hole 26 in FIG. 2 ). In this embodiment, the bushing 32 is press-fitted into the through-hole 26 from the rear end side (the flange side) of the through-hole 26.

[0020] FIG. 3 is a perspective view showing the bushing 32 of this embodiment, viewed from below. Referring to FIGS. 2 and 3, the bushing 32 is made of a metal such as aluminum or stainless steel, and includes a cylindrical portion 33 and a flange portion 34. The flange portion 34 is integrally formed on the rear end (one end) of the cylindrical portion 33, with an outer diameter larger than the inner diameter of the through-hole 26. The flange portion 34 has a disk-like flange shape that extends outward from the outer peripheral surface of the cylindrical portion 33 and is adapted to fit into a step portion 27 provided in the through-hole 26. The step portion 27 is provided on the upper surface of the butting portion 25, and the inner diameter of the cylindrical surface 27a of the step portion 27 is approximately the same as the outer diameter of the flange portion 34, allowing for a tight fit, or is slightly larger, allowing for a loose fit. The height of the step portion 27 is approximately the same as the height of the flange portion 34, and the axial dimension (height) of the cylindrical portion 33 is the sum of the axial dimension of the through-hole 26 and the height of the step portion 27.

[0021] A central hole 37 of the cylindrical portion 33 extends through the bushing 32. The inner diameter of the cylindrical portion 33 (central hole 37) of the bushing 32 is slightly larger than the outer diameter of the shank 42 of the bolt 41 so that the shank 42 of the bolt 41 can be easily inserted. The shank 42 is formed with a male thread that screws into a nut 44 welded to the butt portion 15. The outer diameter of the cylindrical portion 33 of the bushing 32 is approximately the same as the inner diameter of the through-hole 26, allowing for a tight fit.

[0022] When the bushing 32 is fitted into the through-hole 26, the cylindrical portion 33 is press-fitted into the through-hole 26, the outer peripheral surface 34a of the flange 34 fits into the cylindrical surface 27a of the step portion 27, and the flat contact surface 35 is pressed against and abuts against the flat surface 27b of the step portion 27. In addition, the contact surface 35 is pressed against the flat surface 27b of the step portion 27, and the rear end surface of the flange 34 (the surface opposite the contact surface 35) and the surface of the abutting portion 25 (the surface opposite the surface that mates with the abutting portion 15 of the tray 11) are abutted together in a flush relationship.

[0023] As a result, the other end (tip) of cylindrical portion 33 of bushing 32 and the underside of butt portion 25 are flush with each other, and when cover 21 is placed on tray 11 and fastened with bolts, butt portions 15, 25 come into contact with each other, and at the same time, the tip of cylindrical portion 33 of bushing 32 comes into contact with the upper surface of butt portion 15 of tray 11 around through hole 16. This prevents butt portion 25 of synthetic resin cover 21 from being crushed by the tightening force of the bolts, even when the bolts are tightened to a predetermined torque.

[0024] When connecting the tray 11 and the cover 21, a bolt 41 is inserted from one side through the center hole 37 of the bushing 32 fitted in the cover 21, and the shaft 42 of the bolt 41 passes through the through-hole 16 of the tray 11. By twisting the bolt 41, the male thread of the shaft 42 is threaded into a nut 44. The tray 11 of this embodiment is made of a metal such as aluminum or stainless steel. The cover 21 of this embodiment is made of synthetic resin. Because the tray 11 is made of metal, the butting portion 15 is rigid even if it is thin. However, because the cover 21 is made of synthetic resin, the butting portion 25 must be slightly thicker. Therefore, the thickness of the butting portion 25, i.e., the dimension in the extension direction of the through-hole 26, is made larger than the thickness of the butting portion 15. A sealing groove is formed on the butting surface of the butting portion 25, and a sealing material 45 is provided in the sealing groove. The sealing material 45 is positioned inside the tray relative to the through-hole 26. The seal material 45 extends around the entire periphery of the cover 21. When each bolt 41 is tightened, the seal material 45 comes into close contact with the mating abutment 15. This seals the battery units 31, 31...

[0025] Referring to Fig. 3, the flange-shaped collar 34 has a circular contact surface 35 on the cylindrical portion 33 side, and protrusions 36, 36... protruding from the contact surface 35 are integrally formed thereon. In contrast, the end surface of the collar 34 opposite the contact surface 35 is smooth and has no protrusions. Fig. 4 is a bottom view showing the bushing 32 as viewed from below (the tip end side of the bushing). In this embodiment, a large number of protrusions 36 are provided, scattered at approximately equal intervals from the inner diameter side to the outer diameter side of the contact surface 35.

[0026] An example of a method for forming the bushing 32 having the protrusion 36 will be briefly described below.

[0027] The bushing 32 is formed, for example, by press working using upper and lower molds. A single wire is subjected to multiple press processes to integrally form the cylindrical portion 33 and flange portion 34, and in one of these press processes, the flange portion 34 is integrally molded with the protrusion 36. In particular, the protrusion 36 is tapered toward the tip of the bushing 32 and does not form an undercut in the direction in which the upper and lower molds are opened. This allows the molds to be opened smoothly.

[0028] Before the cover 21 is placed on the tray 11, the cylindrical portion 33 of the bushing 32 is press-fitted into the through-hole 26 provided in the butt portion 25 of the cover 21. When the bushing 32 is press-fitted into the through-hole 26, the cylindrical portion 33 fits into the through-hole 26. At the same time, the contact surface 35 of the flange 34 is pressed against and comes into contact with the flat surface 27b of the step portion 27 of the butt portion 25 of the cover 21, and the outer peripheral surface 34a of the flange 34 fits into the cylindrical surface 27a of the step portion 27. By further press-fitting the bushing 32 into the through-hole 26, the protrusions 36 of the flange 34 bite into the butt portion 25 of the cover 21. Note that the height, shape, size, position, number, etc. of the protrusions 36 are set so that when the protrusions 36 bite into the butt portion 25, the butt portion 25 does not significantly deform or crack. The protrusion 36 of the first embodiment is a cone that protrudes from the flat contact surface 35 by 0.01 mm to 2.0 mm.

[0029] The cover 21 with the bushing 32 fitted in it is placed over the tray 11, and the center of the central hole 37 of the bushing 32 is aligned with the center of the through-hole 16 of the tray 11. Then, the shank 42 of the bolt 41 is inserted into the central hole 37 and the through-hole 16, and the head 43 of the bolt 41 is screwed in to fasten the shank 42 with the nut 44. Towards the end of the bolt tightening operation, the head 43 of the bolt 41 will be in contact with the flange 34 of the bushing 32, but the head 43 of the bolt 41 slides relative to the bushing 32 as the bolt 41 rotates clockwise until it is screwed in to the specified torque.

[0030] During this fastening operation, multiple bolts 41 are screwed in to a predetermined torque using an automated machine or the like. When the bolts 41 are finally screwed in, the rotation of the bolts 41 can cause the bushing 32 to rotate relative to the through-hole 26 of the butt portion 25. If the bolts 41 and the bushing 32 rotate together, the predetermined tightening torque cannot be achieved, resulting in a tightening failure. In contrast, according to this embodiment, even if the bolt 41 rotates in the tightening direction during bolt tightening, the bushing 32 is not only fitted into the through-hole 26 but also has a protrusion that bites into the butt portion 25, preventing it from rotating together with the bolt 41. Therefore, the bolt 41 is tightened into the nut 44 with a predetermined tightening torque. In particular, the protrusion 36 on the contact surface 35 of the flange 34 is positioned farther from the outer periphery of the cylindrical portion 33 of the bushing 32, which significantly suppresses the rotation of the bushing 32 and effectively prevents it from rotating together with the bolt 41 during bolt tightening.

[0031] In the case of fastening the cover 21 to the tray 11 with a large number of bolts 41, as in this embodiment, an automatic machine or the like is used to fasten the large number of bolts 41 at once, so if the tightening torque is insufficient in even one location, the tightening work will be interrupted and productivity will drop significantly. For this reason, the bushing 32, which can prevent the bushing 32 from rotating together with the bolt when tightening the bolt, as in this embodiment, is quite effective when tightening a large number of bolts to a specified torque using an automatic machine.

[0032] As a modified example, the convex portion 36 may be a convex spherical surface. Furthermore, the rotational resistance may increase in the tightening direction of the bolt 41. In the present invention, the tightening direction of the bolt is the direction of arrow A when viewed from the bolt shank to the head as shown in Figures 3 and 4, and is the clockwise direction when the tightening rotation direction when tightening the bolt 41 is viewed in the bolt advancement direction from the head to the bolt shank.

[0033] In this embodiment, the conical projection 36 has the same gradient from all directions around it, but the gradient may be changed so that the rotational resistance increases in the tightening direction. For example, the conical projection 36 may have a sloped surface where the cone portion on the front side in the clockwise direction is carved to have a flat slope. Alternatively, the apex of the cone may be shifted toward the bolt tightening direction, so that the slope gradient on the bolt tightening direction side is steeper than in other directions. The positions and number of projections 36 are not limited to those shown in the drawings and may be changed.

[0034] Next, a bolt fastening structure according to another embodiment of the present invention will be described. Figure 5 is a longitudinal cross-sectional view showing another embodiment of the present invention. In this embodiment, components common to the above-described embodiment are given the same reference numerals and will not be described again, and only the different components will be described below. In this embodiment, the tray 11 is made of a synthetic resin such as fiber-reinforced plastic (FRP) because it requires strength to support the battery unit 31. Furthermore, the thickness of the butt portion 15 of the tray 11 is approximately the same as the thickness of the butt portion 25 of the cover 21, but may be thinner if there are no problems in terms of strength.

[0035] Furthermore, in the above-described embodiment, the cover 21 was provided with a step 27 into which the flange 34 of the bushing 32 is inserted, but in the embodiment shown in Fig. 5, the cover 21 does not have the step 27. In the embodiment shown in Fig. 5, the manufacturing of the through hole 26 and the fitting of the bushing are easier than in the embodiment of Fig. 2. In contrast, in the embodiment of Fig. 1, the contact area of ​​the bushing 32 with the cover 21 is larger and contact occurs in multiple directions than in the embodiment of Fig. 5, so the bushing 32 is less likely to slip when the bolt 41 is twisted and fastened.

[0036] In the embodiment shown in Figure 5, when the bolt 41 is tightened, the bushing 32 is not only fitted into the through hole 26, but also has the protrusion 36 biting into the abutment portion 25, so that the bushing 32 is prevented from rotating together with the rotation of the bolt 41 in the tightening direction, and the bolt 41 is tightened into the nut 44 with a predetermined tightening torque.

[0037] The nuts 44 may be embedded in advance in the tray 11 made of synthetic resin.

[0038] 2, the step portion 27 may be provided in the embodiment of FIG. 5, and conversely, the step portion 27 may be omitted in the embodiment of FIG. 2, as in the embodiment of FIG. 5.

[0039] Next, a bushing according to a second embodiment of the present invention will be described. Figure 6 is a bottom view of a bushing 51 of the second embodiment. In the second embodiment, components common to the previous embodiments are given the same reference numerals and will not be described again, and only the different components will be described below. In the second embodiment, a number of intersecting grooves 52 are provided on the end surface of the flange 34. The grooves 52 are, for example, V-shaped grooves carved into the end surface of the flange 34. The grooves 52 are formed, for example, by knurling.

[0040] Because groove 52 is a recess, the portion of the end face of flange 34 other than groove 52 relatively becomes a protrusion 53. When bushing 51 is press-fitted into through hole 26 of cover 21, the outer circumferential surface of cylindrical portion 33 is tightly fitted into through hole 26 of cover 21, protrusion 53 of flange 34 bites into butt portion 25, and the groove side surface of groove 52 comes into contact with butt portion 25. In the second embodiment, as in the first embodiment, bushing 32 is not only fitted into through hole 26 but also has protrusion 53 biting into butt portion 25, so bushing 32 is prevented from rotating together with the rotation of bolt 41 in the tightening direction, and bolt 41 is tightened into nut 44 with a predetermined tightening torque.

[0041] The V-shaped cross section of the groove 52 may have one side and the other side with the same gradient, like an isosceles triangle, or may have one side and the other side with different gradients, like a scalene triangle.

[0042] In this way, when the protrusions 53 are formed by providing a large number of grooves 52, a large number of protrusions 53 can be formed, and therefore the size of each protrusion 53 can be made minute.

[0043] In the bolt fastening structure shown in Figures 2 and 5 described above, even when bushing 51 shown in Figure 6 is used to fasten a bolt, not only is cylindrical portion 33 of bushing 51 fitted into through hole 26 of butt portion 25, but convex portion 53 formed by groove 52 is also biting into butt portion 25, so when bolt 41 is tightened, bushing 51 does not rotate together with bolt 41 in the tightening direction, and bolt 41 is tightened into nut 44 with a predetermined tightening torque.

[0044] Next, a bushing according to a third embodiment of the present invention will be described. Figure 7 is a bottom view of a bushing 61 according to the third embodiment. In the third embodiment, components common to the previous embodiments are given the same reference numerals and will not be described again, and only the different components will be described below. In the third embodiment, a protrusion 62 is provided on the contact surface 35 of the flange 34. The protrusion 62 is a pyramid, for example a triangular pyramid.

[0045] As shown in FIG. 7 , when looking from the cylindrical portion 33 to the flange portion 34 in the axial direction of the bushing 61, the protrusions 62 are arranged circumferentially. By arranging the protrusions 62 along the outer diameter edge of the contact surface 35, a strong centrifugal force acts to prevent the bushing 32 from rotating in the same direction as the bolt 41 rotates in the tightening direction. Therefore, it is preferable to position the protrusions 62 as close to the outer diameter edge as possible. By arranging the protrusions 62 along the outer diameter edge of the contact surface 35, more of them are provided than when they are arranged on the inner diameter side. Furthermore, the protrusions 62 are provided in large numbers by being continuously arranged without gaps. The protrusions 62 have an asymmetrical sawtooth shape. The side 64 of the protrusions 62 in the direction of arrow A (clockwise side) is steeply sloped to prevent co-rotation with the bolt when tightening, while the counterclockwise side 63 of the protrusions 62 is gently sloped to gently bite into the butt portion 25 of the mating member.

[0046] 2 and 5 described above, when a bushing 61 shown in Fig. 7 is used to fasten a bolt instead of the bushing 32, not only is the cylindrical portion 33 of the bushing 61 fitted into the through hole 26 of the butt portion 25, but the convex portion 62 also bites into the butt portion 25, so that when the bolt 41 is tightened, the bushing 51 does not rotate together with the bolt 41 in the tightening direction, and the bolt 41 is tightened into the nut 44 with a predetermined tightening torque. In particular, because the gradient of the convex portion 62 is different in the clockwise and counterclockwise directions, the convex portion 62 gently bites into the butt portion 25 and can be more strongly prevented from rotating together with the bolt 41 when tightened.

[0047] Next, a fourth embodiment of the present invention will be described. Figure 8 is a bottom view of a bushing 71 of the fourth embodiment. In the fourth embodiment, components common to the previous embodiments are given the same reference numerals and will not be described again, and only the different components will be described below. In the fourth embodiment, a protrusion 72 is provided on the contact surface 35 of the flange 34. The protrusion 72 is a polygonal pyramid, for example, a triangular pyramid.

[0048] As shown in FIG. 8 , when viewing the bushing 71 in the axial direction from the cylindrical portion 33 to the flange portion 34, the protrusions 72 are irregularly arranged. The protrusions 72 are formed with a steep slope on some side surfaces 73, a gentle slope on other side surfaces 74, and an even gentler slope on still other side surfaces 75. In the embodiment shown in FIG. 8 , the side surfaces 73 are oriented approximately perpendicular to the contact surface 35. The multiple protrusions 72 are oriented in a common manner so that the common side surfaces 73, 73... face the same direction in the circumferential direction of the bushing 71 (the same applies to the other side surfaces 74, 75). In the fourth embodiment, the side surfaces 73, 73... face in the direction of arrow A. The other side surfaces 74, 75 (the same applies to the other side surfaces 74, 75) face in the opposite direction to arrow A, with the side surface 74 facing toward the inner diameter and the side surface 75 facing toward the outer diameter. The direction of arrow A is the rotation direction when fastening bolt 41, and side surface 73 on the front side in the rotation direction has a steep slope, which effectively prevents bushing 71 from rotating together with bolt 41 as it rotates in the tightening direction.

[0049] 2 and 5 described above, when a bushing 71 of the fourth embodiment shown in Fig. 8 is used to fasten a bolt instead of the bushing 32, not only is the cylindrical portion 33 of the bushing 71 fitted into the through hole 26 of the butting portion 25, but the convex portion 72 is also wedged into the butting portion 25, so that when the bolt 41 is tightened, the bushing 51 does not rotate together with the bolt 41 in the tightening direction, and the bolt 41 is tightened into the nut 44 with a predetermined tightening torque. Furthermore, since the multiple side surfaces 73 of the multiple convex portions 72 are steeply inclined and the multiple convex portions 72 are positioned in the same position in the circumferential direction of the bushing 71, the steepest-inclined side surface 73 of the convex portion 72 increases the frictional force in the co-rotation direction, effectively preventing the bushing 71 from rotating together with the nut 44.

[0050] Next, a fifth embodiment of the present invention will be described. FIG. 9 is a perspective view of a bushing of the fifth embodiment. In the fifth embodiment, components common to the previous embodiments are designated by the same reference numerals and will not be described again; only the differences will be described below. In the fifth embodiment, although not shown, the through-hole 26 is provided with a step 27 into which the flange 34 fits, as in the embodiment of FIG. 1. The fifth embodiment is a modification of the bushing 32 shown in FIG. 3. The flange 34 has a plurality of integrally formed minute protrusions 81 that protrude radially outward on the outer peripheral surface 34a and engage with the cylindrical surface 27a of the step 27. The protrusions 81 are, for example, conical or polygonal pyramidal. The protrusions 81 are either integrally formed near the final step in the molding process for the bushing 32, or are formed in a separate process.

[0051] In the fifth embodiment, when the bushing 32 is press-fitted, the outer peripheral surface 34a of the flange 34 fits into the cylindrical surface 27a of the stepped portion 27, and the flat contact surface 35 is pressed into contact with the flat surface 27b of the stepped portion 27. At the same time, the convex portion 36 bites into the flat surface 27b of the stepped portion 27, and the protrusion 81 bites into the cylindrical surface 27a of the stepped portion 27. According to the fifth embodiment, even if the bolt 41 rotates in the tightening direction when the bolt is tightened, not only is the bushing 32 fitted into the through hole 26, but the convex portion bites into the abutting portion 25 and the protrusion 81 bites into the cylindrical surface 27a of the stepped portion 27, so that rotation of the bushing 32 in accordance with the rotation of the bolt in the tightening direction when the bolt is tightened can be further suppressed.

[0052] Next, a sixth embodiment of the present invention will be described. FIG. 10 is a perspective view of a bushing 32 of the sixth embodiment. FIG. 11 is a partially enlarged view of the bushing of the sixth embodiment. In the sixth embodiment, components common to the previous embodiments are designated by the same reference numerals and will not be described again. The following describes the differences. In the sixth embodiment, a step 27 is provided in the through hole 26, similar to the embodiment of FIG. 1, although not shown. The sixth embodiment is a modification of the bushing 32 shown in FIG. 3. The outer peripheral surface 34a of the flange 34 is provided with a plurality of minute protrusions 91 that protrude radially outward and engage with the cylindrical surface 27a of the step 27. The protrusions 91 extend from the rear end surface of the flange 34 to the front end surface (contact surface 35). The protrusions 91 are triangular pyramids formed by inclined surfaces 93 and 94, whose protruding height, as viewed radially from the rear end side of the flange 34 to the front end side, gradually decreases. The other triangular pyramid 94 is flush with the rear end surface of the flange 34. This shape prevents undercuts when the bushing is press-molded, allowing the protrusion 91 to be molded integrally with the press die used to mold the bushing. The inclined surface 92 has a steeper slope than the inclined surface 93. In the sixth embodiment, as shown in Figure 11, the inner diameter of the step 27 is slightly larger than the outer diameter of the flange 34, allowing the bushing 32 to be fitted loosely.

[0053] In the sixth embodiment, when the bushing 32 is press-fitted, the outer peripheral surface 34a of the flange 34 is loosely fitted into the cylindrical surface 27a of the stepped portion 27, and the flat contact surface 35 is pressed into contact with the flat surface 27b of the stepped portion 27. At the same time, the convex portion 36 bites into the flat surface 27b of the stepped portion 27, and the protrusion 91 bites into the cylindrical surface 27a of the stepped portion 27, which further effectively prevents the bushing 32 from rotating in the tightening direction when the bolt is tightened.

[0054] 11, in the sixth embodiment, the inner diameter of the cylindrical surface 27a of the step portion 27 is larger than the outer diameter of the outer peripheral surface 34a of the flange portion 34. Then, when the outer peripheral surface 34a is loosely fitted into the cylindrical surface 27a, the protrusions 91 bite into it, but the resin in the bitten area can escape into the gap between the outer peripheral surface 34a of the flange portion 34 and the cylindrical surface 27a of the step portion 27, so that the butting portion 25 can be prevented from being significantly cracked or deformed, and the protrusions can be reliably bitten into it.

[0055] The protrusion 91, when viewed in the radial direction of the flange 34, is formed as a triangular pyramid formed by inclined surfaces 92, 93 that gradually decrease in height from the rear end side to the front end side of the flange 34. Such inclined surfaces make it easier for the protrusion 91 to bite into the cylindrical surface 27a of the step portion 27. Furthermore, by making the inclined surfaces 92, 93 gently inclined, the protrusion 91 can smoothly bite into the butt portion 25 even when pressed against the butt portion 25. In the sixth embodiment, the inclination of the inclined surface 92 on the side of the arrow A is steeper than the inclination of the inclined surface 93 on the opposite side, making it difficult for the bushing to rotate when the bolt 41 is rotated in the tightening direction.

[0056] In the sixth embodiment, the inclinations of the inclined surfaces 92 and 93 are different, but the inclinations of the inclined surfaces 92 and 93 may be the same. In addition, the protrusion 91 is provided over a length from the rear end face of the outer circumferential surface 34a of the flange portion 34 to the front end face (contact surface 35), but it may be shorter than this. In the sixth embodiment, the protrusion 91 is a triangular pyramid, but the protrusion may have a smooth shape with smoothly curved surfaces connecting the boundaries of the inclined surfaces 92, 93 of the triangular pyramid. Also, instead of a triangular pyramid, the inclined surfaces may be formed like a cone.

[0057] Furthermore, the protruding height of the flange portion 34 when viewed in the radial direction does not have to be a triangular pyramid formed by an inclined surface that gradually decreases from the rear end side to the tip end side, but may be the same protruding height from the rear end side to the tip end side.

[0058] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiments within the same scope as the present invention or within an equivalent scope. For example, some components may be extracted from one embodiment described above, and other components may be extracted from another embodiment described above, and these extracted components may be combined. [Industrial Applicability]

[0059] The present invention is advantageously used in an assembly structure in which two parts are fastened together with bolts. [Explanation of symbols]

[0060] 11 tray (second member), 13 edge portion, 15, 25 abutment portion, 16 through hole (second member through hole), 21 cover (first member), 23 edge portion, 26 through hole (first member through hole), 27 step portion, 32, 51, 61, 71 bushing, 33 cylindrical portion, 34 flange portion, 34a outer peripheral surface 35 contact surface 36, 53, 62, 72 convex portion 37 center hole, 41 bolt, 44 nut, 51 bushing, 52 grooves, 81,91 projections.

Claims

1. In a bolt fastening structure in which a bolt passing through a first member through hole and a second member through hole is screwed into a nut to connect the first member and the second member to each other, The first member is made of synthetic resin, and the second member is made of synthetic resin or metal, A metal bushing provided in the first member through hole, a cylindrical portion having a center hole through which the bolt is passed and fitted into the first member through hole; a flange portion integrally formed at one end of the cylindrical portion and having an outer diameter larger than that of the first member through hole, the flange portion having a contact surface that abuts against the first member; a plurality of protrusions provided on the contact surface and configured to bite into the first member; an axial dimension from the contact surface of the flange portion to the other end of the cylindrical portion is the same as an axial dimension of the first member through hole, The inclination gradient formed from the tip side of the convex portion toward the contact surface side is steeper on the bolt tightening direction side and gentler on the opposite direction side, The plurality of protrusions are provided in large numbers and scattered from the inner diameter side to the outer diameter side of the contact surface.

2. A bolt fastening structure comprising the bushing of claim 1, the first member, the second member, the bolt, and the nut, the second member is a tray having a flat band-shaped abutment portion on an upper edge thereof, the first member is a cover that is placed on the tray and has a flat, band-shaped abutting portion at a lower edge thereof that abuts against the abutting portion of the second member; the second member through hole is provided in the abutting portion of the tray, and the first member through hole is provided in the abutting portion of the cover, A bolt fastening structure in which a sealing groove extends around the entire circumference of the butt portion between the butt portion of the cover and the butt portion of the tray, at a position inside the through hole, and a sealing material is placed in the sealing groove so that the two butt portions are tightly sealed together by the sealing material.

3. A bolt fastening structure comprising the bushing of claim 1, the first member, the second member, the bolt, and the nut, A bolt fastening structure in which the first member through hole is larger in dimension than the second member through hole by the thickness of the cylindrical portion of the bushing, and the inner diameter of a central hole provided in the cylindrical portion of the bushing matches the inner diameter of the second member through hole and is larger in dimension than the outer diameter of the shank of the bolt.

4. the first member has a stepped portion, into which the flange portion of the bushing is fitted, at a rear end side of the first member through hole, an axial dimension from the contact surface to the other end of the cylindrical portion is the same as an axial dimension of the first member through hole, 2. The bushing of claim 1, wherein when the butt portion of the first member and the butt portion of the second member are aligned and bolted together, the flange portion is fitted into the step portion and the cylindrical portion is fitted into the through hole of the first member, and the other end of the cylindrical portion abuts against the second member.

5. a projection that bites into the step portion is integrally provided on the outer peripheral surface of the flange portion of the bushing; 5. The bushing of claim 4.

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