JP7628241B2 - Anti-theft fastening structure - Google Patents

Description

The present invention relates to an anti-theft fastening structure that combines an anti-theft bolt and a female thread member .

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 fastening method that uses an anti-theft bolt that can be fastened with a normal tool but requires a special tool to be removed.

When such anti-theft bolts are used to secure license plates, car dealerships and other locations that may need to 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 financial burden on users. Furthermore, having the special tools available to dealers around the world also means a greater risk of plates being removed using the special tools.

Patent No. 4730721

SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to solve the above-mentioned problems of the conventional art and to provide an anti -theft fastening structure which does not require special tools for fastening and removing and which has an anti-theft effect.

The anti-theft fastening structure of the present invention, which has been made to solve the above-mentioned problems, is an anti-theft fastening structure that combines an anti-theft bolt and an internal thread member, wherein the anti-theft bolt has a plurality of external thread portions formed in sequence on a shaft portion, the external thread portions having threads in opposite directions from each other , and the thread diameter of the external thread portion on the head side of the bolt is larger than the thread diameter of the external thread portion adjacent to the shank tip side of the bolt, and the root diameter of the external thread portion on the head side of the bolt is larger than the outer diameter of the shaft portion directly below the bolt head, and the internal thread member has a plurality of internal thread portions inside a body having a bolt insertion port, which are threadedly engaged with the plurality of external thread portions in sequence, and the distance X between the end of the internal thread portion on the bolt insertion port side and the start of the internal thread portion adjacent to it is longer than the distance Y between the end of the external thread portion on the bolt head side and the start of the internal thread portion adjacent to it . In addition, it is preferable that 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, and the number of the threaded portions is preferably two or three.

In the anti-theft fastening structure of the present invention, a bolt is first turned in one direction using a normal tool to separate the male thread at the tip of the shaft from the corresponding female thread, resulting in zero rotational torque. However, at this stage, the male thread at the head of the bolt comes into contact with the corresponding female thread, making it impossible to pull out. Since this second male thread has a thread in the opposite direction to the first male thread, continuing to rotate in this state will simply result in free rotation. By rotating in the opposite direction from this state, the second male thread passes through while meshing with the second female thread, allowing the bolt to be pulled out.

Reversing the direction of rotation of the bolt midway through this process is not easy for someone who is unfamiliar with the structure of this anti-theft bolt, and requires time-consuming trial and error. This takes more time than expected, so there is a high chance of the user giving up, but the anti-theft effect is still achieved. Moreover, since no special tools are required, this has the advantage of reducing the financial burden on the user.

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, 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 damaged during fastening or 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, from right to left to right, further enhancing the anti-theft effect.

FIG. 2 is a perspective view of the anti-theft bolt of the first embodiment. FIG. 2 is a cross-sectional view of the female thread member of the first embodiment. FIG. 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. 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. FIG. 11 is a cross-sectional view showing a state in which the fastening is released. FIG. FIG. 4 is a cross-sectional view showing a second embodiment. FIG. 4 is a cross-sectional view showing a second embodiment. FIG. 4 is a cross-sectional view showing a second embodiment. FIG. 11 is a cross-sectional view showing a third embodiment. FIG. 11 is a cross-sectional view showing a third embodiment. FIG. 11 is a cross-sectional view showing a third embodiment. FIG. 11 is a cross-sectional view showing a modified example of a screw thread.

An embodiment of the present invention will be described below.
1 is a perspective view of an anti-theft bolt 10 used in the first embodiment, with 11 being a head portion and 12 being a shaft portion continuing on the head 11. In this embodiment, the shape of the head 11 is a hexagonal prism, but it may 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.

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.

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.

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 shaft portion 12 is determined in relation to the female threaded member 20, which will be described later.

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.

Figure 2 is a cross-sectional view of the female thread member 20 that constitutes the 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 its external shape can be changed as desired.

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

The inside of the female thread member 20 is a cavity 23, and multiple female thread portions 24, 25 are formed to be screwed with the multiple male thread portions 13, 14 described above. Specifically, a large diameter female thread portion 24 that screws with the large diameter male thread portion 13 of the anti-theft bolt 10 is formed on the entrance side of the female thread member 20, and a small diameter female thread portion 25 that screws with the small diameter male thread portion 14 is formed on the back 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 axially on the bolt. However, instead of a structure in which a nut is inserted inside 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.

Figure 3 shows the state in which the anti-theft bolt 10 is fastened to the female threaded member 20. 30 is a fastened member, such as a license plate, fixed between the seat surface of the head 11 of the anti-theft bolt 10 and the surface 21 of the female threaded member 20. In this state, the male threaded portion 14 at the shaft tip of the anti-theft bolt 10 is screwed into the female threaded portion 25 of the female threaded member 20. The male threaded portion 13 on the head side is inside the cavity 23.

When the anti-theft bolt 10 is rotated in the direction to loosen the right screw (left direction) from the fastened state shown in Figure 3, the male thread portion 14 of the anti-theft bolt 10 comes off the female thread portion 25 of the female thread member 20 as shown in Figure 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.

To pull it out, the male thread 13 of the anti-theft bolt 10 must be moved by rotating it while screwing it into the female thread 24, as shown in Figure 5. However, since the male thread 13 is threaded in the opposite direction to the male thread 14, in order to change from the state shown in Figure 4 to the state shown in Figure 5, the anti-theft bolt 10 must be pulled up and rotated in the opposite direction (to the right) from the previous state. This operation cannot be performed by someone who does not know the structure of the anti-theft bolt 10 without repeated trial and error, and since it would take an unexpected amount of time to prevent theft, the person will give up on removing it and the anti-theft effect will be realized. Moreover, this operation can be easily performed by an operator who knows the structure of the anti-theft bolt 10.

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 disengage from the female thread portion 24, and the fastening can be released and the fastened member 30 can be removed as shown in Fig. 6. In this way, the anti-theft fastening structure using the anti-theft bolt of the present invention can obtain an anti-theft effect without requiring special tools. Note that when fastening, the above steps can be reversed.

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

In addition, in this invention, the direction of rotation 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 disengages from the female threaded portion 25 of the female threaded member 20 as shown in Figure 4, and that the male threaded portion 13 of the anti-theft bolt 10 is not screwed into the female threaded portion 24. To achieve this, as shown in Figure 7, 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 must be 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. 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.

Figures 8 to 10 illustrate a second embodiment of the present invention. 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 bolt shaft tip side, 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 also 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.

When the anti-theft bolt 10 is rotated in one direction from the fastened state shown in Figure 8 to disengage the male thread portion 43 from the female thread portion 53, it will reach the state shown in Figure 9. If the anti-theft bolt 10 is then rotated in the reverse direction, the male thread portion 42 will pass the female thread portion 52, resulting in the state shown in Figure 10. If the anti-theft bolt 10 is further rotated in the initial direction, the male thread portion 41 will pass the female thread portion 51, and the fastening can be released. As the rotation direction needs to be reversed twice along the way, the anti-theft effect can be further improved.

Figures 11 to 13 explain the third embodiment of the present invention. 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 such, the present invention can be modified in various ways.

As described above, the present invention provides an anti- theft fastening structure which does not require special tools for fastening and removal and which is excellent in the anti-theft effect.

10 Anti-theft bolt 11 Head 12 Shank 13 Male thread portion 14 Male thread portion 20 Female thread member 21 Surface 22 Bolt insertion opening 23 Cavity 24 Female thread portion 25 Female thread portion 26 Step portion 30 Fastened member 41 Male thread portion 42 Male thread portion 43 Male thread portion 51 Female thread portion 52 Female thread portion 53 Female thread portion

Claims (3)

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. 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. 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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