Insert nut and fastening structure

Abstract

In particular, the present invention makes it possible to maintain the holding force of an insert nut (in other words, the holding force against being pulled out) at a high level after movement of a bolt by rotation.　An insert nut 2 is fastened to a bolt 1 for fixing mating members 4, 5 to a base member 3 in a state in which the insert nut 2 is embedded in the base member 3 except for a part of said insert nut 2. A main section is configured from: a flange section 20 forming an insertion port 21 for inserting the bolt 1; and a cylindrical section 22 integrated with the flange section and having formed on the inner circumference thereof a female thread 24 that screws together with the male thread of the bolt. In addition, the main section has a knurl 26 composed of an inclined groove 27 formed on the outer circumference of the cylindrical section 22, and the main section is formed so that the groove directions of the female thread 24 and the inclined groove 27 are different directions from each other in the bolt insertion direction.

Description

Insert Nut and Fastening Structure

[0001] The present invention relates to an insert nut inserted into a base member and a fastening structure for fixing a mating member to the base member with the insert nut and a bolt.

[0002] FIGS. 9A and 9B show the fastening structure disclosed in Patent Document 1 below. FIG. 9A is a state diagram before fastening, and FIG. 9B is a state diagram after fastening. In this fastening structure, the first relay bus bar 31 and the first high-voltage bus bar 71 of the relay bus bar constituting the mating member are fixed to the resin base member (first fixing portion) with a nut (first nut) 41 and a bolt 42. Among these, the nut 41 is an insert nut press-fitted into the fitting portion 11 provided in the base member. The first relay bus bar 31 is provided with an insertion hole 311 for inserting a bolt, and the first high-voltage bus bar 71 is provided with an insertion hole 711 for inserting a bolt. Then, the first high-voltage bus bar 71 and the first relay bus bar 31, which are mating members, are provided such that the insertion holes 311 and 711 are coaxial with the female thread of the nut 41, and the bolt 42 is screwed into the female thread of the nut 41 to be fastened to the base member via the nut 41.

[0003] That is, in this fastening structure, as shown in FIG. 9A, with a gap between the base member and the first relay bus bar 31 (without deforming or moving the base member and the mating member), the nut is forcibly moved in the removal direction by rotating the bolt to absorb the gap. In this structure, if the first high-voltage bus bar and the first relay bus bar, which are mating members, are forcibly pulled into the base member, there is a risk of forced deformation or damage to the mating members and the base member, and further, there is a risk that the bolt may loosen due to the force trying to return to the initial position. However, such problems can be solved.

[0004] Japanese Unexamined Patent Application Publication No. 2023 - 184302

[0005] However, in the fastening structure described above, the mating members (the first high-voltage busbar and the first relay busbar) are positioned by the movement of the insert nut relative to the base member, or by the fastening of the bolt and insert nut relative to the base member. If the insert nut is subjected to an impact or vibration in the direction of dislodgement, it may overcome the holding force in the direction of dislodgement (the gripping force of the resin) and loosen, or it may even move further in the direction of dislodgement.

[0006] Therefore, the objective of the present invention is to provide a configuration in which an insert nut is moved to absorb the gap between a base member and a mating member without deforming the base member or the mating member, and in particular, to maintain a high holding force of the insert nut after it has moved due to the rotation of the bolt, that is, a holding force in the direction of removal. Other objectives will be clarified in the following description.

[0007] To achieve the above objective, the present invention provides an insert nut that is embedded in a base member except for a portion and fastened with a bolt for fixing a mating member to the base member, comprising a flange portion forming an insertion opening for inserting the bolt, and a cylindrical portion integrated with the flange portion and having a female thread on its inner circumference that engages with the male thread of the bolt, and further comprising knurling formed by inclined grooves on the outer circumference of the cylindrical portion, and characterized in that the groove directions of the female thread and the inclined grooves are formed to be opposite to each other in the bolt insertion direction.

[0008] In the insert nut according to the present invention, the knurling preferably has numerous inclined grooves formed at equal intervals in the same direction, and is formed continuously from one end to the other of the cylindrical portion. In this embodiment, for example, the insert nut can easily rotate with movement in the direction of removal relative to the base member.

[0009] Furthermore, the present invention provides a fastening structure for fixing a mating member to a base member with a nut and a bolt, wherein the nut has a flange portion forming an insertion opening for inserting the bolt, a cylindrical portion integrated with the flange portion and having a female thread on its inner circumference that engages with the male thread of the bolt, and a knurled groove formed on the outer circumference of the cylindrical portion and consisting of an inclined groove, and is an insert nut embedded in the base member with part or all of the flange portion exposed, and the bolt passes through a through hole provided in the mating member and is screwed into the female thread of the insert nut embedded in the base member, thereby causing the insert nut to rotate relative to the base member in the same direction as the rotation of the bolt and move towards the mating member.

[0010] In the present invention described above, the base member is a resin-made mounting member for fixing a mating member, which is a mounting member. The mating member is a mounting member fixed to the base member, and is not limited to a single member but may consist of multiple members. Depending on when the insert nut is inserted into the base member, there are methods such as inserting it during the molding of the base member, or inserting it after molding using a press-fit or hot press-fit method, and any of these methods may be used.

[0011] In the fastening structure according to the present invention, it is preferable that the inclined grooves constituting the knurling are formed in large numbers at equal intervals and in the same direction, or that the groove directions of the female thread and the inclined grooves are in different directions from each other in the bolt insertion direction. In this embodiment, the insert nut is easily moved in a direction that protrudes from the base member with rotation as the bolt is rotated.

[0012] In the fastening structure according to the present invention, it is preferable that the inclined grooves constituting the knurling are inclined at a gradient of 15 degrees or more compared to flat knurling or straight knurling. In this embodiment, the resistance of the insert nut embedded in the base member to coming loose is maintained at a predetermined level, and unintentional coming loose due to impact or vibration in the direction of coming loose is also prevented. In this regard, the inventors created insert nuts with the same groove width and depth as the inclined grooves, and varied the gradient of the inclined grooves relative to the straight grooves, as schematically shown in Figure 7A, and compared the resistance to coming loose in the same usage manner as the embodiments described later. As a result, it was found that it is preferable that the gradient is greater than 15 degrees and less than 75 degrees. This is because the smaller the gradient and the closer it is to the straight groove, the easier it is to loosen or shift in the direction of coming loose, and if the gradient is greater than 75 degrees, the load when moving the insert nut by bolt rotation operation tends to become excessive.

[0013] In the fastening structure according to the present invention, the knurling is preferably divided into circumferential grooves with numerous inclined grooves arranged in the circumferential direction. In this embodiment, the insert nut has increased resistance to coming loose at the circumferential grooves, and at the same time, it becomes easier to prevent unintentional loosening or movement in the direction of coming loose due to impact or vibration.

[0014] In the insert nut according to claim 1 of the present invention, the insert nut has knurling, particularly consisting of inclined grooves provided on the outer circumference of the cylindrical portion, and is embedded in the base member with part or all of the flange portion exposed. Therefore, when the insert nut according to the present invention is used in the fastening structure according to the present invention, as shown in the embodiment example described later, the insert nut moves easily so as to be pulled toward the mating member while rotating in the same direction as the rotation direction when the bolt is rotated, and it is also easier to prevent it from loosening or moving in the direction of coming out due to vibrations such as shocks after the movement.

[0015] In the fastening structure according to the present invention, a mating member is fastened to a base member with a nut and bolt. In particular, the insert nut moves so as to be pulled towards the mating member while rotating in the same direction as the bolt's rotation relative to the base member, due to the inclined grooves that constitute the knurling. Therefore, if there is a gap between the base member and the mating member, the movement of the nut can be adjusted to absorb the gap. At the same time, after the movement, the inclined grooves that constitute the knurling maintain a high holding force against pulling the insert nut towards the mating member, making it easier to prevent the insert nut from unintentionally loosening or coming off even when vibrations such as shocks are applied.

[0016] Figure 1A shows a perspective view of the insert nut, and Figure 1B shows a partially broken perspective view of the insert nut. This is a schematic enlarged view illustrating the inclined grooves that make up the knurling of the insert nut. Figure 3A is a schematic perspective view showing a modified example 1 of the insert nut, and Figure 3B is a partially broken perspective view showing a modified example 2 of the insert nut. This shows the relationship between the base member having the insert nut, the mating members, the first and second mounting members and the bolt. Figure 4A is a top view thereof, and Figure 4B is an enlarged cross-sectional view of Figure 4A along the line IVB-IVB. This shows the state in which the bolt is rotated and started to screw into the insert nut. Figure 5A is a top view thereof, and Figure 5B is an enlarged cross-sectional view of Figure 5A along the line VB-VB. This shows the state in which the bolt is rotated and the insert nut is moved toward the mating member. Figure 6A is a top view thereof, and Figure 6B is an enlarged cross-sectional view of Figure 6A along the line VIB-VIB. Figure 8A is a schematic perspective view showing the relationship between members in an embedded state with a portion of the flange portion exposed, partially broken. Figure 8B is a schematic perspective view showing the relationship between members in a partially broken state with the insert nut maintaining its embedded state from the time of molding, and Figure 8B is a schematic perspective view showing the relationship between members in a completed state with the insert nut having moved upward until it absorbs the gap due to the rotation of the bolt, partially broken. The fastening structure of Patent Document 1 is shown, and Figures 9A and 9B show Figures 6(a) and 6(b) disclosed in Patent Document 1.

[0017] The optimal embodiment of the present invention will be described below with reference to the drawings. In this description, the insert nut and its modified forms will be described in detail with reference to Figures 1A to 3B, and then the fastening structure shown in Figures 4A to 8B will be clarified.

[0018] (Example of form) Figures 1A and 1B show a single insert nut to which the present invention is applied. This insert nut 2 is of the type that is inserted or fitted during resin molding of the base member 3, and as shown in Figure 4B, it is embedded in the resin base member 3 except for a part of it, and is fastened with bolts 1 for fixing the mating members, the first and second mounting members 4 and 5, to the base member 3. The material is stainless steel (SUS), which has high rigidity and excellent corrosion resistance, but other metals such as brass may also be used.

[0019] Structurally, it consists of a flange portion 20 that forms an insertion opening 21 for inserting the bolt 1, and a cylindrical portion 22 that is integrated with the flange portion 20 and has a female thread 24 on its inner circumference that engages with the male thread 13 of the bolt 1. Of these, the flange portion 20 is formed in a donut shape, and the upper and lower edges 20a and 20b are chamfered. The flange portion 20 is inserted or fitted when the insert nut 2 is resin molded into the base member 3, and in this inserted state, a part of the upper part protrudes from the base member 3, and the protruding upper surface becomes a receiving surface that receives the mounting members 4 and 5.

[0020] The cylindrical portion 22 protrudes integrally from the lower surface of the flange portion 20, and its lower end 23 is formed in a substantially L-shape in cross-section. The lower end 23 has a larger diameter on the inside, and a disc-shaped bottom plate 25 that closes the lower end of the cylindrical portion is engaged and held in this larger diameter portion. In addition to the engagement and holding configuration, the bottom plate 25 may also be configured to close the tip (lower end) side of the cylindrical portion 22 with a lid-like or cap-like wall portion, similar to an existing cap nut.

[0021] Furthermore, female threads 24 that engage with the male threads 13 of the bolt 1 are continuously formed on the inner circumference of the flange portion 20 and the cylindrical portion 22. In this example, the thread direction is right-hand thread (configured to be screwed in when the nut is fixed and the bolt is turned clockwise). The outer circumference of the cylindrical portion 22 is provided with knurling 26, which is made up of numerous inclined grooves 27. In this example, the groove directions of the female threads 24 and the inclined grooves 27 that make up the knurling 26 are formed to be opposite to each other in the bolt insertion direction. That is, if the female threads 24 are right-hand threads (threads from the left to the upper right), the groove shape of the inclined grooves 27 is in the opposite direction, i.e., grooves from the right to the upper left. If the female threads 24 are left-hand threads (threads from the right to the upper left), the groove shape of the inclined grooves 27 is in the opposite direction, i.e., grooves from the left to the upper right.

[0022] Furthermore, the knurled surface 26 has numerous inclined grooves 27 formed at equal intervals in the same direction. Here, the depth of each inclined groove 27 is a fairly shallow groove of about 0.2 to 0.6 mm. The groove width is about 0.3 to 0.8 mm. It is preferable that the depth and width of the grooves be set to be at least less than 1 mm. Each inclined groove 27 is formed continuously from one end to the other end of the cylindrical portion 22. These configurations allow the insert nut 2 to move in the direction of removal without requiring excessive stress and to move with rotation while embedded in the base member 3. This movement is intended to absorb the gap as the insert nut 2 moves from Figure 5B to Figure 6B. At the same time, after the movement as shown in Figure 6B, a predetermined holding force is maintained by the gripping force of the resin, preventing it from loosening or moving unintentionally in the direction of removal due to impact or vibration. In other words, as shown in Figures 5B to 6B, the initial movement can be performed without excessive rotational resistance, and in the moved state shown in Figure 6B, a predetermined holding force is maintained so that it does not easily move, loosen, or move in the direction of coming off. The present invention was completed after repeated studies to satisfy these conflicting operational requirements.

[0023] In addition, although the numerous inclined grooves 27 described above are formed on the entire outer circumference of the cylindrical portion 22, they may also be formed on only a part of the outer circumference of the cylindrical portion. In that case, however, it is preferable that they be inclined at a gradient of 15 degrees or more compared to flat knurling or straight knurling. These are to maintain a predetermined frictional resistance so that the insert nut 2 embedded in the base member 3 does not loosen or move in the direction of coming out when in use as shown in Figure 6B, as described above.

[0024] Regarding the gradient of the inclined groove 27, the inventors created insert nuts 2 with the same groove width and depth as schematically shown in Figure 2, and varied the gradient of the inclined groove 27 relative to the straight groove to 10 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 75 degrees, as schematically shown in the same figure. They then compared the resistance to coming out after gap absorption, as shown in Figure 6B, under the same usage conditions as the example. The results showed that the gradient was less than 15 degrees and approached the straight groove, making it relatively easy to move or loosen, which posed a design problem. It was also found that when the gradient was greater than 60 degrees, an increasingly larger load was required when moving from Figure 5B to Figure 6B. From these findings, it is preferable to set the gradient of the inclined groove 27 to be between 15 degrees and 60 degrees.

[0025] (Modification 1) Figure 3A shows an example of a modified insert nut 2. In this insert nut 2, the knurling 26 is divided vertically or horizontally by a circumferential groove 28 that divides a number of inclined grooves 27 into upper and lower or front and back sections. In this circumferential groove 28, the depth of the groove is relatively shallow, about 0.2 to 0.6 mm, similar to the inclined grooves 27. The groove width is set to about 0.5 to 1.5 mm. If the groove width is larger than 1.5 mm, it tends to require excessive stress when moving to absorb the gap G in Figure 5B, so it is preferable to form it relatively narrow, at 1.5 mm or less, to avoid this.

[0026] (Modification 2) Figure 3B shows a modified example in which the bottom plate 25 is omitted from the insert nut 2. This insert nut 2 lacks the lower end 23 of the approximately L shape in Figure 1B, and the inner diameter of the flange portion 20 and the cylindrical portion 22 is penetrated vertically. Such a structure is suitable for cases where the insert nut 2 is a hot-press type inserted into the base member 3 after the base member is formed, or an expansion type in which the tip portion is expanded after being driven into the base member.

[0027] (Fastening Structure) Figures 4A to 8B show fastening structures in which a mounting member (mating member) is fixed to a base member (the member to be mounted) as an example of the use of the insert nuts described above. Next, the fastening structures of the example forms will be described in detail with reference to these. Figures 7 and 8A and 8B are schematic external views to facilitate understanding of the main parts of Figures 4A to 6B.

[0028] This fastening structure is an example of fixing a first mounting member 4 and a second mounting member 5, which are mating members, to a base member 3, which is the member to be mounted, using an insert nut 2 and a bolt 1. Here, as described above, the insert nut 2 has a female thread 24 provided on the inner circumference of the flange portion 20 and the cylindrical portion 22 that screws into the male thread 13 of the bolt 1, and a knurled 26 provided on the outer circumference of the cylindrical portion 22 excluding the flange portion 20, which is composed of a number of inclined grooves 27, and is inserted into the base member 3 in an embedded state with a part of the flange portion 20 exposed. Reference numeral 33 denotes a vertical hole located directly below the insert nut 2 formed during the insert molding of the base member 3. On the other hand, the bolt 1 has a circular flange portion 12 integrally between the head 10 and the male thread 13, and as shown in Figure 5B, when the male thread 13 is screwed into the female thread 24 of the insert nut 2, the flange portion 12 abuts against the second mounting member 5. The head 10 is hexagonal and can be rotated with a wrench or spanner. The head 10 also has a hexagonal socket 11 and can be rotated using a hex wrench. The flange 12 distributes the pressure applied to the second mounting member 5, which is the point of fastening. As shown in Figure 6B, the male thread 13 is long enough so that it does not touch the bottom plate 25 of the insert nut when fully screwed into the female thread 24 of the insert nut. In this fastening structure, the first and second mounting members 4 and 5 are integrally fixed in an overlapping state between the flange 12 of the bolt 1 and the flange 20 of the insert nut 2.

[0029] More specifically, in this fastening operation, for example, as shown in Figures 4B and 7, the first mounting member 4 and the second mounting member 5 are superimposed with their through holes 4a and 5a aligned, and while maintaining this state, the through holes 4a and 5a are positioned on the female threads 24 of the insert nut 2 relative to the base member 3. Here, the base member 3 integrally comprises a mounting plate 30 positioned on the lower side, a base 31 protruding from the upper surface of the mounting plate 30, and a pair of restricting walls 32 protruding from opposing sides of the base 31. The mounting plate 30 extends front to back and has mounting holes 34 provided near the front and rear ends, and is attached to the target equipment side via the mounting holes 34 and bolts, etc. The base 31 is positioned between the restricting walls 32 with the first mounting member 4 and the second mounting member 5 superimposed. At that time, each through hole 4a and 5a is positioned on the female threads 24 of the insert nut 2. In this example, the first mounting member 4 and the second mounting member 5 are supported at the height shown in Figure 7 by a member (not shown), and their downward movement is restricted.

[0030] Next, as shown in Figures 5B and 8A, the bolt 1 is positioned so that the male thread 13 passes through the through holes 5a and 4a and fits into the female thread 24 of the insert nut 2 from the insertion opening 21, and the bolt 1 is rotated from this position. In this operation, the bolt 1 is rotated using, for example, a hex wrench (not shown) that fits onto the head 10, while screwing the male thread 13 into the female thread 24. In the state shown in Figure 8A, the insert nut 2 maintains its embedded state from the time of molding, and a predetermined gap G is created between the initial first mounting member 4 and the flange portion 20 of the insert nut.

[0031] Next, Figures 6B and 8B show the completed fastening state, where the insert nut 2 has moved upward until it has absorbed the gap G due to the rotation of the bolt 1. In this structure, the inclined groove 27, which constitutes the knurling 26 of the insert nut 2, prevents the rotation of the bolt 1 from becoming excessively large. At the same time, even if the insert nut 2 is subjected to a predetermined amount of impact or vibration in the state shown in Figure 8B, the inclined groove 27 prevents it from easily loosening or moving in the direction of coming out.

[0032] (Operation) Next, the main operation of the fastening structure described above will be explained. (1) In this structure, the first and second mounting members 4 and 5 are fastened to the base member 3 with nuts and bolts. In particular, the insert nut 2 moves towards the first and second mounting members 4 and 5 without requiring excessive load, rotating in the same direction as the rotation direction of the bolt 1 relative to the base member 3 by the inclined groove 27 which constitutes the knurling 26. This allows the insert nut 2 to adjust and absorb any unnecessary gap G between the base member 3 and the first mounting member 4 by moving. At the same time, the inclined groove 27 which constitutes the knurling 26 maintains a high holding force to prevent the insert nut 2 from unintentionally loosening or coming out after it has moved, and also prevents the insert nut 2 from unintentionally loosening or moving in the direction of coming out even when subjected to impact or vibration.

[0033] (2) In this structure, the knurling 26 has many inclined grooves 27 formed at equal intervals in the same direction, and is formed continuously from one end to the other of the cylindrical portion 22, and the groove directions of the female thread 24 and the inclined grooves 27 are formed to be in different directions from each other in the bolt insertion direction, so for example the insert nut 2 can move in the removal direction without requiring an excessive load as a rotational operation on the base member 3.

[0034] (3) In this structure, if the inclined grooves 27 constituting the knurling 26 are inclined at a gradient of 15 degrees or more compared to flat knurling or straight knurling as shown in Figure 2, or if the gradient is set to be between 15 degrees and 60 degrees, the insert nut 2 can be moved to absorb the gap without requiring an excessive load to rotate the bolt, and after movement, it is possible to prevent unintentional loosening or movement in the direction of removal caused by shock or vibration. (4) Furthermore, if the knurling 26 is formed by dividing a large number of inclined grooves 27 with circumferential grooves 28 provided in the circumferential direction as in Modification 1 of Figure 3A, the insert nut 2 will have stronger resistance to coming loose at the location of the circumferential grooves 28, and at the same time, it will be easier to prevent unintentional loosening or movement in the direction of removal caused by shock or vibration.

[0035] As described above, the present invention only needs to have the configuration specified in the appended claims, and the details can be modified in various ways as needed, as shown in the modified examples. For example, the mating member is not limited to a configuration consisting of a first mounting member and a second mounting member as shown in the example form, but may also consist of a single mounting member or a configuration consisting of three or more mounting members.

[0036] 1. Bolt (10 is the head, 12 is the flange, 13 is the male thread) 2. Insert nut (20 is the flange, 21 is the insertion hole, 24 is the female thread) 3. Base member (30 is the fixing part, 31 is the base part, 31a is the top surface) 4. First mounting member (mating member) 5. Second mounting member (mating member) 25. Bottom wall 26. Knurling 27. Inclined groove 28. Circumferential groove G. Gap Note that the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2024-194263, filed on November 6, 2024, are incorporated herein by reference as the disclosure of the specification of the present invention.

Claims

1. An insert nut that is embedded in a base member except for a portion and fastened with a bolt for fixing a mating member to the base member, comprising a flange portion forming an insertion opening for inserting the bolt, and a cylindrical portion integrated with the flange portion and having a female thread on its inner circumference that engages with the male thread of the bolt, and further comprising knurling formed by inclined grooves formed on the outer circumference of the cylindrical portion, and characterized in that the groove directions of the female thread and the inclined grooves are formed to be opposite to each other in the bolt insertion direction.

2. The insert nut according to claim 1, characterized in that the knurling has a large number of inclined grooves formed at equal intervals in the same direction, and is formed continuously from one end to the other of the cylindrical portion.

3. A fastening structure for fixing a mating member to a base member with a nut and a bolt, wherein the nut has a flange portion forming an insertion opening for inserting the bolt, a cylindrical portion integrated with the flange portion and having a female thread on its inner circumference that engages with the male thread of the bolt, and a knurled groove formed on the outer circumference of the cylindrical portion and consisting of an inclined groove, and is an insert nut embedded in the base member with part or all of the flange portion exposed, and the bolt passes through a through hole provided in the mating member and is screwed into the female thread of the insert nut embedded in the base member, thereby causing the insert nut to move while rotating in the same direction as the rotation direction of the bolt relative to the base member and be pulled toward the mating member.

4. The fastening structure according to claim 3, characterized in that the inclined grooves constituting the knurling are formed in large numbers at equal intervals and in the same direction, and the groove directions of the female thread and the inclined grooves are formed to be in different directions from each other in the bolt insertion direction.

5. The fastening structure according to claim 3 or 4, characterized in that the inclined grooves constituting the knurling are inclined at a gradient of 15 degrees or more and 60 degrees or less compared to flat knurling or straight knurling.

6. The fastening structure according to claim 5, characterized in that the inclined grooves constituting the knurling are divided and formed by circumferential grooves provided on the outer circumference excluding the flange portion.

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