Thread structure

Abstract

According to the invention, the proportion of the distributed load of the fastening axial force attached to the first thread tooth can be reduced, and the anti-loosening effect caused by the leading torque can be generated. In a threaded structure provided with a bolt (1) and a nut (2), a female thread (20) of the nut (2) has a first threaded region (21) and a second threaded region (22) in which threaded surfaces (22a, 22b) have a convex arc shape, in a state in which the female thread (20) is screwed to the female thread (10) of the bolt (1), in the first threaded region (21), a pressure-receiving-side threaded surface (21a) is in contact with the male thread (10), but a gap is present between gap-side threaded surfaces (21b, 10b), and in the state in which the pressure-receiving-side threaded surface (21a) and the gap-side threaded surface (21b, 10b) are in contact with each other. In the second thread region (22), the pressure-receiving side and gap-side thread surfaces (22a, 22b) of the female thread (20) are in contact with the pressure-receiving side and gap-side thread surfaces (10a, 10b) of the male thread (10), respectively.

Description

Technical Field

[0001] The present invention relates to a thread structure. Background Art

[0002] The applicant of this case has been developing locknuts since before, and a locknut having a convex arc surface on the thread surface of the internal thread is disclosed in Patent Document 1 below.

[0003] By setting the thread surface as a convex arc surface, the clearance (play) between the internal thread of the nut and the external thread of the bolt is substantially eliminated, thereby suppressing the relative movement of the nut with respect to the bolt in a vibration environment, and thus the generation of loosening of the nut can be reduced. In addition, not only the load-bearing side thread surfaces of the internal thread and the external thread are brought into contact with each other, but also the clearance side thread surfaces of the internal thread and the external thread are brought into contact with each other, thereby enabling a prevailing torque to be generated in the nut during the nut tightening operation, and thus a lock prevention effect due to such a prevailing torque is also generated.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-105444 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] It is known that when a nut is tightened on a bolt, the tightening axial force is distributed and loaded on a plurality of thread teeth of the internal thread that appear in a longitudinal section, and the proportion of the distributed load of the tightening axial force loaded on the first thread tooth (the thread tooth closest to the seating surface of the nut) of the internal thread is the largest.

[0009] In the case where an excessive axial force is generated, the first thread tooth breaks first, and the breakage gradually progresses from there until the entire internal thread breaks. In addition, even when the axial force does not reach the breaking level, when the tightened nut is placed in, for example, a vibration environment, the first thread tooth that bears a large distributed load is also subjected to an impact force caused by vibration and is slightly deformed axially, and thus the tightening axial force may be significantly reduced.

[0010] An object of the present invention is to reduce the proportion of the distributed load of the tightening axial force applied to the first thread tooth and to generate a lock prevention effect due to a prevailing torque.

[0011] Means for Solving the Problems

[0012] The thread structure according to the present disclosure may include: a first thread member having a threaded shaft with external threads formed on its outer peripheral surface; and a second thread member having a threaded hole with internal threads formed on its inner peripheral surface and engaging with the external threads. The internal threads may have a first thread region and a second thread region. Preferably, in a state where the external threads are engaged with the internal threads, in the first thread region, the load-bearing side thread surface of the internal threads contacts the load-bearing side thread surface of the external threads, but there is a gap between the clearance side thread surface of the internal threads and the clearance side thread surface of the external threads. More preferably, the external threads and the internal threads are configured such that in the second thread region, the load-bearing side thread surface and the clearance side thread surface of the internal threads contact the load-bearing side thread surface and the clearance side thread surface of the external threads, respectively. Preferably, in the first thread region, the load-bearing side thread surface and the clearance side thread surface of the internal threads are flat in a longitudinal section. Preferably, in the second thread region, at least one of the load-bearing side thread surface and the clearance side thread surface of the internal threads has a convex arc shape in a longitudinal section.

[0013] In addition, a threaded member having threads according to the present disclosure has a first thread region and a second thread region. Preferably, in the first thread region, the load-bearing side thread surface and the clearance side thread surface of the threads are flat in a longitudinal section. Preferably, in the second thread region, at least one of the load-bearing side thread surface and the clearance side thread surface of the threads has a convex arc shape in a longitudinal section.

[0014] Advantages of the Invention

[0015] According to the present disclosure, it is possible to reduce the proportion of the distributed load of the fastening axial force applied to the first thread tooth and to generate a loosening prevention effect by the dominant torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a longitudinal sectional view of an embodiment of a thread structure based on the present disclosure.

[0017] Figure 2 is a perspective view showing an example of a convex portion.

[0018] Figure 3 is a perspective view showing another example of a convex portion.

[0019] Figure 4 is a longitudinal sectional view of an embodiment of a threaded member based on the present disclosure.

[0020] Figure 5 is a longitudinal sectional view for explaining a stamping process for reducing the diameter of a convex portion. DETAILED DESCRIPTION

[0021] 〔Embodiment of Thread Structure〕

[0022] The thread structure involved in the present disclosure may include: a first thread member having a thread shaft with external threads formed on its outer peripheral surface; and a second thread member having a thread hole with internal threads formed on its inner peripheral surface and engaging with the external threads. The internal threads may have a first thread region and a second thread region.

[0023] Preferably, in a state where the external threads are engaged with the internal threads, in the first thread region, the load-bearing side thread surface of the internal threads contacts the load-bearing side thread surface of the external threads, but there is a gap between the clearance side thread surface of the internal threads and the clearance side thread surface of the external threads. More preferably, the external threads and the internal threads are configured such that in the second thread region, the load-bearing side thread surface and the clearance side thread surface of the internal threads respectively contact the load-bearing side thread surface and the clearance side thread surface of the external threads.

[0024] The "state where the external threads are engaged with the internal threads" includes not only the state where the first and second thread members are tightened, but also the state during the tightening operation when no tightening torque has been generated.

[0025] Typically, the first thread member is a bolt having a thread shaft. The thread shaft is typically a solid shaft, but it may also have a tubular structure. The first thread member can use an existing bolt manufactured according to the required specifications. The external threads have a specified thread profile defined by a specified thread pitch, a specified crest diameter, and a root diameter of the external threads. Both the load-bearing side and the clearance side thread surfaces of the external threads can be flat in a longitudinal section.

[0026] Typically, the second thread member is a nut having a thread hole. The first and second thread regions each have a specified axial length. Preferably, the first and second thread regions each have an axial length greater than one pitch of the internal threads. More preferably, the first and second thread regions have an axial length greater than two pitches of the external threads. The first and second thread regions are provided at different axial positions. The first and second thread regions may be continuously arranged axially, or another third thread region may be provided between the first and second thread regions. For the internal threads, preferably, the first thread region and the second thread region have different thread profiles to produce the contact state in the thread surfaces as described above.

[0027] Preferably, in the first thread region, the pressure-side thread surface and the clearance-side thread surface of the internal thread are flat in a longitudinal section. Preferably, in the second thread region, at least one of the pressure-side thread surface and the clearance-side thread surface of the internal thread has a convex arc shape in a longitudinal section. More preferably, in the second thread region, both the pressure-side thread surface and the clearance-side thread surface of the internal thread have a convex arc shape in a longitudinal section.

[0028] Preferably, the second threaded member has a main body and a convex portion that projects axially from an end face of the main body and has an outer diameter smaller than that of the main body, and the threaded hole is provided throughout the main body and the convex portion. The main body may be in the shape of a hexagon nut or a cylindrical nut. The convex portion may be in the shape of a cylinder or a frustum of a cone, or may have a structure similar to the lock nut disclosed in Japanese Patent Publication No. 3272265, which has a plurality of blocks arranged neatly in the circumferential direction and a thin-walled connecting portion connecting adjacent blocks. "Having an outer diameter smaller than that of the main body" means smaller than the average of the wall thickness in the radial direction from the outer periphery of the main body to the inner periphery of the thread, and also smaller than the average of the wall thickness in the radial direction from the outer periphery of the convex portion to the inner periphery of the thread. The convex portion with a thinner wall thickness than the main body is slightly deformed radially outward due to the reaction force acting on the two thread surfaces when the internal thread is screwed into the external thread, thereby suppressing the occurrence of galling.

[0029] Preferably, at least a part of the first thread region of the internal thread is provided on the main body. Preferably, at least a part of the second thread region of the internal thread is provided on the convex portion. Thus, when the second threaded member is screwed onto the first threaded member from the main body side, since only the first thread region, which has a clearance from the external thread at the beginning of the tightening operation, is engaged with the external thread, the second threaded member can be smoothly screwed in. When the screwing of the second thread region of the internal thread with the external thread starts, the pressure-side and clearance-side thread surfaces of the internal thread in the second thread region come into contact with the external thread, and a large leading torque is generated due to the frictional resistance. However, at this point, the entire first thread region is engaged with the external thread. Therefore, by rotating the second threaded member relative to the first threaded member with a tightening torque greater than the leading torque, the second threaded member can be screwed relative to the first threaded member.

[0030] Preferably, a part of the second thread region of the internal thread is provided on the main body. In a state where the internal thread is not screwed with the external thread, the diameter of a part of the second thread region provided on the convex portion is smaller than the diameter of a part of the second thread region provided on the main body. Such a structure can be obtained by causing the convex portion to contract and deform inward in the radial direction after the internal thread is formed. Since a part of the second thread region provided on the convex portion slightly deforms outward in the radial direction when the internal thread is screwed into the external thread, it has the same diameter as a part of the second thread region provided on the main body in a state where the internal thread is screwed to the external thread.

[0031] 〔Embodiments of Thread Members〕

[0032] The thread member according to the present disclosure includes a thread having a first thread region and a second thread region.

[0033] Preferably, in the first thread region, the load-bearing side thread surface and the clearance side thread surface of the thread are flat in a longitudinal section. Preferably, in the second thread region, at least one of the load-bearing side thread surface and the clearance side thread surface of the thread has a convex arc shape in a longitudinal section. The thread of the thread member can be either an external thread or an internal thread.

[0034] Preferably, in the second thread region, both the load-bearing side thread surface and the clearance side thread surface of the internal thread have a convex arc shape in a longitudinal section.

[0035] Preferably, the thread member is a nut having a nut body and a convex portion that protrudes axially from an end surface of the nut body and has an outer diameter smaller than that of the nut body. In this case, the thread is an internal thread provided on the inner circumference of a threaded hole provided throughout the nut body and the convex portion.

[0036] Preferably, at least a part of the first thread region of the internal thread is provided on the nut body. Preferably, at least a part of the second thread region of the internal thread is provided on the convex portion.

[0037] Preferably, (another) part of the second thread region of the internal thread is provided on the nut body. Preferably, the diameter of a part of the second thread region provided on the convex portion is smaller than the diameter of a part of the second thread region provided on the nut body.

[0038]

Examples

[0039] Hereinafter, preferred embodiments of the thread member and the thread structure according to the present disclosure will be described based on the drawings.

[0040] Thread member.

[0041] Figure 1 An embodiment of a threaded member and a threaded structure according to the present disclosure is shown. The threaded structure includes a bolt 1 as a first threaded member and a locknut 2 as a second threaded member. The bolt 1 has a threaded shaft with an external thread 10 formed on its outer peripheral surface. The nut 2 has a threaded hole with an internal thread 20 formed on its inner peripheral surface that engages with the external thread 10. The bolt 1 can be a commercially available existing bolt.

[0042] Also as Figure 4 shown, the internal thread 20 of the nut 2 has a first thread region 21 disposed on the seat surface (the bottom surface of the nut in the illustrated example) side, and a second thread region 22 disposed axially farther from the seat surface than the first thread region 21.

[0043] In a state where the external thread 10 is engaged with the internal thread 20, in the first thread region 21, the load-bearing side thread surface 21a of the internal thread 20 contacts the load-bearing side thread surface 10a of the external thread 10, but there is a gap between the clearance side thread surface 21b of the internal thread 20 and the clearance side thread surface 10b of the external thread 10. Further, in a state where the external thread 10 is engaged with the internal thread 20, in the second thread region 22, the load-bearing side thread surface 22a and the clearance side thread surface 22b of the internal thread 20 contact the load-bearing side thread surface 10a and the clearance side thread surface 10b of the external thread 10, respectively.

[0044] In the first thread region 21, the load-bearing side thread surface 21a and the clearance side thread surface 21b of the internal thread 20 are flat in a longitudinal section.

[0045] In the second thread region 22, both the load-bearing side thread surface 22a and the clearance side thread surface 22b of the internal thread 20 have a convex arc shape in a longitudinal section. In Figure 4 it, the convex arc-shaped thread surfaces 22a, 22b observed from the inside of the section are indicated by hatching. It should be noted that either the load-bearing side thread surface 22a or the clearance side thread surface 22b can be set to have a convex arc shape in a longitudinal section, while the other is flat in a longitudinal section.

[0046] The nut 2 has a nut body 2A having a seat surface, and a convex portion 2B protruding axially from the top of the nut body 2A and having an outer diameter smaller than that of the nut body 2A. The threaded hole having the internal thread 20 penetrates through the nut body 2A and the convex portion 2B.

[0047] The first thread region 21 of the internal thread 20 is provided at the bottom of the nut body 2A, and the second thread region 22 is provided within the range from the top of the nut body 2A to the convex portion 2B.

[0048] The outer peripheral shapes of the nut body 2A and the convex portion 2B are not particularly limited, but in one embodiment, asFigure 2 As shown, the nut body 2A is configured in the shape of a hexagonal nut, and the convex portion 2B is configured in the shape of a frustum of a cone. The convex portion 2B has the largest outer diameter at its bottom. The nut body 2A has the smallest outer diameter at the left and right central portions of the side surface of the hexagonal nut. The largest outer diameter of the convex portion 2B is smaller than the smallest inner diameter of the nut body 2A. Thus, the convex portion 2B is more likely to deform in the radial direction than the nut body 2A.

[0049] It should be noted that, as Figure 3 shown, the convex portion 2B may include a plurality of blocks arranged neatly in the circumferential direction. Preferably, adjacent blocks are connected and integrated with each other by a connecting portion that is thinner than the radial wall thickness of the block itself. For example, by forming a plurality of longitudinal grooves on the outer periphery of the convex portion 2B, a structure in which a plurality of blocks are connected by a connecting portion can be obtained. It should be noted that when a slit penetrating in the radial direction is provided between adjacent blocks and the plurality of blocks are structurally divided, the radial deformability of each block becomes too large, and the effect brought by the arc-shaped thread surface is limited.

[0050] For the convex portion 2B, it may also be that, as Figure 5 shown, by performing stamping from the radial outside, in a state where the internal thread 20 is not screwed onto the external thread 10, the diameters of a part 22a', 22b' of the second thread region 22 provided on the convex portion 2B are smaller than the diameters of a part 22a, 22b of the second thread region 22 provided on the nut 2A body. There are manufacturing errors in the external threads of commercially available bolts, but by pre-deforming the internal thread provided on the inner periphery of the convex portion 2B to reduce the diameter, it is possible to reliably bring the pressure-bearing side and the clearance-side thread surfaces 22a', 22b' of the second thread region 22 into contact with the pressure-bearing side and the clearance-side thread surfaces of the external thread when the internal thread is screwed onto the external thread. In addition, by adjusting the amount of diameter reduction deformation of the convex portion 2B, the magnitude of the generated leading torque can be adjusted.

[0051] According to the thread structure of this embodiment, it is possible to suppress galling and avoid stress concentration on the first thread tooth of the internal thread 20 of the internal thread nut 2, thereby improving the tolerance to axial force. In addition, even if the seating surface pressure disappears instantaneously in a vibrating environment, since the external thread and the internal thread come into contact on both thread surfaces, it is possible to prevent the axial vibration of the internal thread relative to the external thread, thereby exerting a high anti-loosening effect.

Claims

1. A thread structure, comprising: a first thread member having a thread shaft with an external thread formed on an outer peripheral surface; and a second thread member having a thread hole with an internal thread formed on an inner peripheral surface and screwed with the external thread, wherein, the internal thread has a first thread region and a second thread region, the external thread and the internal thread are configured such that, in a state where the external thread is screwed with the internal thread, in the first thread region, a pressure-side thread surface of the internal thread contacts a pressure-side thread surface of the external thread, but there is a gap between a clearance-side thread surface of the internal thread and a clearance-side thread surface of the external thread, and in the second thread region, the pressure-side thread surface and the clearance-side thread surface of the internal thread contact the pressure-side thread surface and the clearance-side thread surface of the external thread, respectively.

2. The thread structure according to claim 1, wherein, in the first thread region, the pressure-side thread surface and the clearance-side thread surface of the internal thread are flat in a longitudinal section, in the second thread region, at least one of the pressure-side thread surface and the clearance-side thread surface of the internal thread has a convex arc shape in a longitudinal section.

3. The thread structure according to claim 2, wherein, in the second thread region, both the pressure-side thread surface and the clearance-side thread surface of the internal thread have a convex arc shape in a longitudinal section.

4. The thread structure according to claim 1, 2 or 3, wherein, the second thread member has a main body and a convex portion protruding axially from an end surface of the main body and having an outer diameter smaller than that of the main body, and the thread hole extends through the main body and the convex portion, at least a part of the first thread region of the internal thread is provided in the main body, at least a part of the second thread region of the internal thread is provided in the convex portion.

5. The thread structure according to claim 4, wherein, a part of the second thread region of the internal thread is provided in the main body, in a state where the internal thread is not screwed with the external thread, a diameter of a part of the second thread region provided in the convex portion is smaller than a diameter of a part of the second thread region provided in the main body.

6. The thread structure according to claim 1, 2 or 3, wherein, the first thread member is a bolt and the second thread member is a nut.

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