Anti-theft fastening structure

Abstract

To provide a theft prevention bolt that does not need a special tool upon fastening and removal and further has a theft prevention effect, and a theft prevention fastening structure using the theft prevention bolt.SOLUTION: A theft prevention bolt is configured such that a plurality of male screw parts 13, 14 are sequentially formed on a shaft part 12 of the bolt. The plurality of male screw parts have threads in opposite directions, and a thread diameter of the male screw part 13 on the head side of the bolt is made larger than a thread diameter of the male screw part 14 adjacent to the shaft tip side of the bolt. The male screw parts 13, 14 are combined with female screw member 20 having female screw parts 25, 25 to be screwed sequentially to form a theft prevention fastening structure.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an anti-theft bolt. And the female threaded part The present invention relates to a combined anti-theft fastening structure. [Background technology]

[0002] For example, in order to secure the number plate of an automobile, various anti-theft bolts are used that are structured so that they cannot be easily removed after fastening. Many of the anti-theft bolts are structured so that they cannot be removed without using special tools. For example, Patent Document 1 describes an anti-theft bolt that can be fastened with a normal tool but requires a special tool to be removed. Anti-theft fastening is stated.

[0003] If such anti-theft bolts are used to secure license plates, car dealers and other places that sometimes remove license plates will have to provide special tools to everyone who needs them. However, unlike mass-produced general tools, special tools tend to be expensive, which places a heavy economic burden on users. Furthermore, having the special tools available to dealers around the world also means that the risk of plates being removed using the special tools increases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4730721 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to solve the above-mentioned problems of the conventional technology, to provide a device that does not require special tools for fastening and unfastening, and has an anti-theft effect. Prepared Theft The object of the present invention is to provide a fastening structure that prevents the fastening from being broken. [Means for solving the problem]

[0006] The present invention has been made to solve the above problems. The anti-theft fastening structure is a theft-prevention fastening structure combining an anti-theft bolt and a female screw member, the anti-theft bolt having a shaft portion on which a plurality of male screw portions having threads in opposite directions are sequentially formed, The thread diameter of the male thread portion on the head side of the bolt is made larger than the thread diameter of the male thread portion adjacent to the shank tip side of the bolt, and the root diameter of the male thread portion on the head side of the bolt is made larger than the outer diameter of the shank directly below the bolt head. The female thread member is provided with a body having a bolt insertion opening and a plurality of female thread portions which are sequentially screwed into the plurality of male thread portions, and the distance X between the end of the female thread portion on the bolt insertion opening side and the start of the adjacent female thread portion is longer than the distance Y between the end of the male thread portion on the bolt head side and the start of the adjacent male thread portion. In addition, it is preferable that the root diameter of the male thread portion on the head side of the bolt is larger than the thread diameter of the male thread portion adjacent to the shank tip side of the bolt, and the number of the male thread portions is preferably two or three.

[0007] Effect of the Invention

[0008] The anti-theft fastening structure of the present invention comprises: When a bolt is first turned in one direction using a standard tool to separate the male thread at the tip of the shaft from the corresponding female thread, the rotational torque becomes zero. However, at this stage, the male thread at the head of the bolt comes into contact with the corresponding female thread, so it cannot be pulled out as is. This second male thread has threads in the opposite direction to the first male thread, so if it continues to rotate as is, it will just spin freely. By rotating it in the opposite direction from this state, the second male thread will pass through while engaging with the second female thread, and the bolt can be pulled out.

[0009] For those who are unfamiliar with the structure of this anti-theft bolt, reversing the direction of rotation of the bolt midway through the process is not easy, and requires time and trial and error. This means that there is a high chance of the user giving up due to the extra time it takes, and the anti-theft effect can be achieved. Moreover, since no special tools are required, there is an advantage in that the economic burden on the user can be reduced.

[0010] If the root diameter of the male thread on the head side of the bolt is made larger than the thread diameter of the male thread adjacent to the bolt's shank tip side, after the male thread on the head side passes through the corresponding female thread, the male thread adjacent to the shank tip side can pass freely through the inside of this female thread, and the threads will not be stripped during fastening and removal. Also, if the number of male threads is set to three, the rotation direction needs to be reversed twice, further enhancing the anti-theft effect. Also, by making the thread on the head side larger than the middle thread, the rotation direction can be changed twice, for example, right rotation, left rotation, right rotation, etc., further enhancing the anti-theft effect. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a perspective view of the anti-theft bolt of the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of a female screw member according to the first embodiment. [Diagram 3] FIG. [Figure 4] 4 is a cross-sectional view showing a state in which the male thread portion at the tip end of the shaft has been removed from the female thread portion. FIG. [Diagram 5] 13 is a cross-sectional view showing a state in which the male thread portion on the head side passes through while meshing with the female thread portion. FIG. [Figure 6] FIG. 11 is a cross-sectional view showing a state in which the fastening is released. [Figure 7] FIG. [Figure 8] FIG. 4 is a cross-sectional view showing a second embodiment. [Figure 9] FIG. 4 is a cross-sectional view showing a second embodiment. [Figure 10] FIG. 4 is a cross-sectional view showing a second embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing a third embodiment. [Figure 12] FIG. 11 is a cross-sectional view showing a third embodiment. [Figure 13] FIG. 11 is a cross-sectional view showing a third embodiment. [Figure 14] FIG. 11 is a cross-sectional view showing a modified example of a screw thread. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment of the present invention will be described below. FIG. 1 shows the first embodiment. Used for This is a perspective view of an anti-theft bolt 10, with 11 being a head and 12 being a shaft portion continuing on from the head 11. In this embodiment, the shape of the head 11 is a hexagonal prism, but it can be any shape as long as the anti-theft bolt 10 can be rotated without requiring a special tool. In this first embodiment, two male threads 13, 14 are formed in sequence on the shaft portion 12. 13 is the male thread portion on the head side of the bolt, and 14 is the male thread portion on the shaft tip side of the bolt.

[0013] These male threads 13, 14 have threads in opposite directions, and in this embodiment, the male thread 14 on the shaft tip side is a typical right-hand thread, and the male thread 13 on the head side is a left-hand thread. However, conversely, the small diameter male thread 14 may be a left-hand thread, and the large diameter male thread 13 may be a right-hand thread.

[0014] In addition, the thread diameter of the male thread portion 13 on the head side is made larger than the thread diameter of the male thread portion 14 adjacent to the shaft tip side. In this embodiment, the large diameter male thread portion 13 is M8 size, and the small diameter male thread portion 14 is M5 size. Furthermore, it is preferable to make the root diameter of the male thread portion 13 on the head side larger than the thread diameter of the male thread portion 14 adjacent to the shaft tip side. According to the JIS for metric coarse threads, the root diameter of an M8 thread is 6.647 mm, and the outer diameter of an M5 thread is 5.000 mm, which satisfies this condition. The reason for setting this condition will be described later. It goes without saying that the specific thread size can be changed in various ways within the range of this condition.

[0015] In this embodiment, the male threaded portion 13 and the male threaded portion 14 are adjacent to each other, but an appropriate gap may be provided between them. The length of the unthreaded shank 12 is determined in relation to the female threaded member 20 described below, and will be described later.

[0016] The threads of the male thread portion 13 on the head side may not be complete threads, but may be trapezoidal with the top cut out as shown in Fig. 14. This is because the male thread portion 13 on the head side does not receive axial force when fastened. On the other hand, the male thread portion 14 on the shaft tip side receives axial force when fastened, so it is desirable for it to be a complete thread.

[0017] 2 is a cross-sectional view of a female thread member 20 that constitutes an anti-theft fastening structure in combination with the above-mentioned anti-theft bolt 10. In this embodiment, the female thread member 20 is box-shaped, but the external shape thereof can be changed as desired.

[0018] A bolt insertion hole 22 is formed on a surface 21 of the female thread member 20 into which the anti-theft bolt 10 is inserted. The inner diameter of the bolt insertion hole 22 is set to allow the large-diameter male thread portion 13 of the anti-theft bolt 10 to pass freely.

[0019] The inside of the female thread member 20 is a cavity 23, and a plurality of female thread portions 24, 25 are formed to be screwed with the above-mentioned plurality of male thread portions 13, 14 in sequence. Specifically, a large-diameter female thread portion 24 that is screwed with the large-diameter male thread portion 13 of the anti-theft bolt 10 is formed on the inlet side of the female thread member 20, and a small-diameter female thread portion 25 that is screwed with the small-diameter male thread portion 14 is formed on the inner side. In this embodiment, the female thread portion 24 is a left-handed M8 nut that engages with the male thread portion 13, and the female thread portion 25 is a right-handed M5 nut that engages with the male thread portion 14. The M8 nut and the M5 nut are inserted from the side into nut insertion portions formed above and below the cavity 23, and cannot move in the axial direction of the bolt. However, instead of a structure in which a nut is inserted into the female thread member 20 as in this embodiment, a female thread may be cut directly on the inner surface of the female thread member 20.

[0020] 3 shows the state in which the anti-theft bolt 10 is fastened to the female thread member 20. Reference numeral 30 denotes a fastened member, such as a license plate, fixed between the bearing surface of the head 11 of the anti-theft bolt 10 and the surface 21 of the female thread member 20. In this state, the male thread portion 14 at the axial tip of the anti-theft bolt 10 is screwed into the female thread portion 25 of the female thread member 20. The male thread portion 13 on the head side is inside the cavity 23.

[0021] When the anti-theft bolt 10 is rotated in the direction to loosen the right-hand thread (left) from the fastened state in Fig. 3, the male thread portion 14 of the anti-theft bolt 10 disengages from the female thread portion 25 of the female thread member 20 as shown in Fig. 4, and the rotational torque becomes zero at that point. A normal bolt should be able to be pulled out as is, but the anti-theft bolt 10 of the present invention cannot be pulled out as is because the end of the large-diameter male thread portion 13 hits the end face of the large-diameter female thread portion 24.

[0022] To pull out the anti-theft bolt 10, the male thread 13 must be rotated while being screwed into the female thread 24 as shown in Fig. 5. However, since the male thread 13 is a thread in the opposite direction to the male thread 14, in order to change the state of Fig. 4 to the state of Fig. 5, the anti-theft bolt 10 must be rotated in the opposite direction (rightward) while being pulled up. This operation cannot be performed by a person who does not know the structure of the anti-theft bolt 10 without repeated trial and error, and since it will take an unexpected amount of time to rob, the person will give up on removing the bolt and the anti-theft effect will be exerted. Moreover, this operation can be easily performed by a worker who knows the structure of the anti-theft bolt 10.

[0023] If the anti-theft bolt 10 is further rotated in the reverse direction from the state shown in FIG. 5, the male thread portion 13 will be disengaged from the female thread portion 24, and the fastening can be released as shown in FIG. 6, allowing the fastened member 30 to be removed. In this way, the anti-theft bolt of the present invention The anti-theft fastening structure using No special tools are required and the anti-theft effect can be achieved. To fasten the device, simply follow the steps above in reverse.

[0024] As described above, in order to pull out the anti-theft bolt 10 from the state in Fig. 5 to the state in Fig. 6, it is necessary to pass the small-diameter male thread portion 14 through the inside of the large-diameter female thread portion 24. For this reason, as described above, the root diameter of the male thread portion 13 on the head side of the bolt is made larger than the thread diameter of the male thread portion 14 adjacent to the shank tip side of the bolt. Since the root diameter of the male thread portion 13 is almost equal to the inside diameter of the female thread portion 24, this design makes it possible to pass the male thread portion 14 without damaging the threads of the female thread portion 24.

[0025] In addition, in the present invention, the rotation direction of the anti-theft bolt 10 is reversed midway, so it is necessary that the male threaded portion 14 of the anti-theft bolt 10 is disengaged from the female threaded portion 25 of the female threaded member 20, and the male threaded portion 13 of the anti-theft bolt 10 is not screwed into the female threaded portion 24, as shown in Figure 4. To achieve this, it is necessary to make the distance X between the end A of the female threaded portion 24 of the female threaded member 20 and the start B of the female threaded portion 25 longer than the distance Y between the end C of the male threaded portion 13 of the anti-theft bolt 10 and the start D of the male threaded portion 14, as shown in Figure 7. This creates a state where the rotational torque is zero midway, making it possible to rotate the anti-theft bolt in the opposite direction next.

[0026] A second embodiment of the present invention will be described with reference to Figs. 8 to 10. In this embodiment, three male threads 41, 42, and 43 are formed on the shaft 12 of the anti-theft bolt 10. The thread diameter of the male thread on the head side of the bolt is larger than the thread diameter of the male thread adjacent to the shaft tip side of the bolt, and the threads are in the opposite directions. For example, the thread directions of the male threads 41, 42, and 43 are set to right, left, and right. However, they may be left, right, and left. The female thread member 20 also has three female threads 51, 52, and 53 into which the male threads 41, 42, and 43 are screwed.

[0027] When the anti-theft bolt 10 is rotated in one direction from the fastened state shown in Fig. 8 to disengage the male thread portion 43 from the female thread portion 53, it reaches the state shown in Fig. 9. When the anti-theft bolt 10 is now rotated in the reverse direction, the male thread portion 42 passes the female thread portion 52, resulting in the state shown in Fig. 10. When the anti-theft bolt 10 is further rotated in the initial direction, the male thread portion 41 passes the female thread portion 51, and the fastening can be released. Since it is necessary to reverse the rotation direction twice in this way, the anti-theft effect can be further improved.

[0028] A third embodiment of the present invention will be described with reference to Figures 11 to 13. This embodiment is similar to the second embodiment in that three male threads 41, 42, and 43 are formed on the shaft 12 of the anti-theft bolt 10, but the sizes of the female threads 51, 52, and 53 are changed. As described above, the present invention can be modified in various ways.

[0029] As described above, the present invention does not require special tools for fastening and removal, and has an excellent anti-theft effect. Excellent theft It provides a fastening structure to prevent accidental breakage. [Explanation of symbols]

[0030] 10 Anti-theft bolt 11 Head 12 Shaft 13 Male thread 14 Male thread 20 Female thread member 21 Surface 22 Bolt insertion port 23 Cavity 24 Female thread 25 Female thread 26 Step section 30 Parts to be fastened 41 Male thread 42 Male thread 43 Male thread 51 Female thread 52 Female thread 53 Female thread

Claims

1. An anti-theft fastening structure that combines an anti-theft bolt and a female thread member, The anti-theft bolt has a shaft portion on which a plurality of male threads having threads in opposite directions are successively formed, Furthermore, the thread diameter of the male thread portion on the head side of the bolt is larger than the thread diameter of the male thread portion adjacent to the shank tip side of the bolt, and the root diameter of the male thread portion on the head side of the bolt is larger than the outer diameter of the shank directly below the bolt head, The female screw member has a body with a bolt insertion port and includes a plurality of female screw portions that are screwed into the plurality of male screw portions in sequence, A theft-preventive fastening structure characterized in that a distance X between an end of the female thread portion on the bolt insertion port side and a start of the adjacent female thread portion is longer than a distance Y between an end of the male thread portion on the bolt head side and a start of the adjacent male thread portion.

2. 2. The anti-theft fastening structure according to claim 1, wherein the root diameter of the threaded portion on the head side of the bolt is larger than the thread diameter of the threaded portion adjacent to the shank tip side of the bolt.

3. 3. The anti-theft fastening structure according to claim 1, wherein the number of said plurality of male threads is two or three.

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