Fastening Nut

Abstract

Provided is a nut that extends the fatigue life of a bolt in a bolt-nut fastening and is easy to manufacture. The nut (1) has a nut body (2) having a flange portion (5), and has a shallow recess (7) with a depth of less than 1.5 pitches on the axial side of a bearing surface (5s), which is a flat surface extending perpendicular to the axis on the fastening side of the nut body (2). This nut (1) preferably has an additional rigidity portion (6) on the release side.

Description

[Technical field]

[0001] The present disclosure relates to a nut used in bolt-nut fastening to achieve normal fastening, which reduces the load on the first thread of fastening engagement. [Background technology]

[0002] Bolts and nuts are often used to fasten various structures, and bolts and nuts are commonly used for many things such as aircraft, automobiles, and railroad cars, machine tools, civil engineering machines, agricultural machines, various manufacturing equipment, bridges, and building structures. However, there have been many cases of bolts and nuts breaking at the first engagement point due to fatigue when fastening with bolts and nuts, and it has been pointed out that the cause of this is crack axial breakage at the first engagement point of the bolt while in use, especially near the thread root. When a bolt breaks, the fastener itself is separated, and the magnitude of the impact is also an issue.

[0003] In conventional screw fastenings, repeated external loads during use are applied in addition to the initial fastening load, so the fatigue fracture strength is lowest at the root of the thread at the first thread of engagement of the bolt, where the cross-sectional area is the smallest and the load distribution is the greatest. It is known that many cracks and axial fractures occur at this location.

[0004] Many ideas have been proposed for improving the fatigue fracture life of the nut at the root of the first thread engagement of the bolt, but they are all merely ideas, each with their own advantages and disadvantages, and none have been put to practical use in nuts, which are general-purpose mass-produced parts.

[0005] Typically, there is a proposal to reduce the load on the thread root of the first engagement thread of the bolt by forming a notch (recess) on the seating surface (fastening surface) of the hexagonal nut (for example, Patent Document 1). Patent Document 1 describes that, based on the JIS standard hexagonal nut, the width (diameter) of the notch is about 1.3 times the bolt diameter, and the depth of the notch is about 1.5 to 2 times the thread pitch for fine threads. In addition, Patent Document 2 also discloses, in FIG. 2(a) and other figures, a nut in which a notch is formed on the seating surface of the hexagonal nut on the thread hole side, similar to Patent Document 1.

[0006] However, in the shape of the hexagonal nut as in Patent Documents 1 and 2, the area of ​​the bearing surface is reduced by the amount of the notch formed, so that the narrow bearing surface portion of the nut sinks into the fastened object at a fastening force lower than the fastening force required for fastening, and the nut cannot be tightened any further, making it impossible to obtain the desired fastening force. Alternatively, there is a risk that the notched and narrow bearing surface portion buckles and breaks during or after fastening. Therefore, the hexagonal nut of Patent Document 1 has low practicality and has not actually been put to practical use.

[0007] Also disclosed are nuts in which expanding legs are provided on the seat side of the hexagonal nut and deep cuts or convex spaces are formed on the screw hole side (for example, Patent Documents 3 and 4). Patent Documents 3 and 4 propose that by forming deep cuts or convex spaces, the rigidity of the threaded shank present inside is reduced and flexibility is imparted, thereby reducing the load on the thread root portion near the first engagement thread.

[0008] However, in nuts such as those in Patent Documents 3 and 4, the depth of the cuts and the convex space is made deep, such as 7 or more pitches of the thread pitch, or 4 or more pitches, and when trying to commercially manufacture and process the nuts, because the cuts and the convex space are deep and have complex shapes, and because the nuts are small parts, it is necessary to use small and complex-shaped forging dies or cutting tools, and the life of the forging dies or tools is too short, resulting in significantly poor manufacturability and productivity, and making them unsuitable for commercial production of nuts, which are general-purpose parts. The same manufacturability and processability problems exist with the hexagonal nut in Patent Document 1, because the cuts are deep.

[0009] Patent Document 5 discloses a flange nut having a seating surface that is inclined relative to a direction perpendicular to the axis and an annular groove that is deeper than the seating surface. However, this nut is based on a structure and principle in which, when the nut is fastened, the inclined seating surface of the nut deforms so that the direction is perpendicular to the axis, and as a result, the threads of the nut deform so as to move away from the threads of the bolt, thereby reducing the load on the first thread of the bolt-nut engagement, and is completely different in both the nut structure and the principle of reducing the load on the first thread of the engagement thread from the nut of the present disclosure, which has a seating surface that is a flat surface perpendicular to the axis and a recess.

[0010] Patent Document 6 discloses a suspension nut having a threaded portion and a hollow portion extending from the threaded portion to the free end face, the bore diameter of which is larger than the root diameter of the threaded portion. However, this nut has no notch or recess on the seat surface of the nut, and is not related to reducing the load on the bolt thread root of the first thread of fastening engagement. The use of the nut is also extremely limited due to its structure. Furthermore, the length of the hollow portion from the threaded portion to the free end face is usually set to be more than three times the pitch of the bolt from the nut, so it does not disclose the structure of the open side additional rigidity portion of the nut disclosed herein (less than twice the thread pitch). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Utility Model Registration Application No. 57-142522 (Japanese Utility Model Application Publication No. 1937-45320) [Patent Document 2] Japanese Patent Application Publication No. 57-177922 [Patent Document 3] US Patent Application Publication No. 2016 / 0123161 [Patent Document 4] International Patent Application Publication No. 2019 / 131685 [Patent Document 5] U.S. Patent No. 5,927,921 [Patent Document 6] Japanese Utility Model Application Publication No. 61-37004 Summary of the Invention [Problem to be solved by the invention]

[0012] In view of the above problems, the present disclosure has an object to provide a nut that reduces the load on the bolt thread root of the first tightening meshing peak, and has a simple structure and is easy to manufacture. [Means for solving the problem]

[0013] In order to solve the above problems, the present disclosure provides a nut having the following aspects. (Aspect 1) A nut (1) consisting of a nut body (2) and a screw hole (3), The nut (1) has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) is defined as follows: the axial side in the radial direction (X) is called the "inner side", and the side away from the axis is called the "outer side" or "outer peripheral side". In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension", which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), and a screw pitch P, The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface (4) inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rnо of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange (5) portion has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion (5) has a bearing surface (5s) at the fastening end, the bearing surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, The recess (7) has a maximum depth Dm in the axial direction (Z) from the extension surface (5e) of the seat surface that is less than 1.5 times the thread pitch P (Dm<1.5P), preferably 1.25 times or less (Dm≦1.25P), and more preferably 1.0 times or less (Dm≦1.0P) or less than 1.0 times (Dm<1.0P). A nut (1) characterized by: (Aspect 2) A nut (1) consisting of a nut body (2) and a screw hole (3), The nut (1) has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) is defined as follows: the axial side in the radial direction (X) is called the "inner side", and the side away from the axis is called the "outer side" or "outer peripheral side". In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension", which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), and a screw pitch P, The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rnо of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange portion (5) has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion (5) has a bearing surface (5s) at the fastening end, the bearing surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, The area Sm (=S3-S2) obtained by subtracting the area S2 of the shaft side having the shaft side end (5si) of the bearing surface as its outer edge from the area S3 of the shaft side having the outermost peripheral portion (5оm) of the flange portion (5) as its outer edge when viewed from the axial direction (Z) is 0.55 times or more (S≧0.55Ss) of the area Ss (=Sn-S0) obtained by subtracting the area S0 of the circle having the radius R0 of the thread root radius from the area Sn of the circle having the radius Rn of the outer peripheral inscribed cylinder of the square nut portion (4), The maximum depth Dm of the recess (7) from the extension surface (5e) of the bearing surface in the axial direction (Z) is less than 1.5 times the thread pitch P (Dm<1.5P). A nut (1) characterized by: (Aspect 3) A nut (1) consisting of a nut body (2) and a screw hole (3), The nut (1) has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) is defined as follows: the axial side in the radial direction (X) is called the "inner side", and the side away from the axis is called the "outer side" or "outer peripheral side". In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension", which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), and a screw pitch P, Here, the thread pitch P is a thread pitch based on the JIS standard for threads or the standard of each country or international organization corresponding to the JIS standard (hereinafter, JIS and the like are collectively referred to as "standards"). The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rnо of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange portion (5) has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion has a bearing surface (5s) at the fastening end, the bearing surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, The maximum depth Dm of the recess (7) from the extension surface (5e) of the bearing surface in the axial direction (Z) is less than 1.5 times the thread pitch P (Dm<1.5P). A nut (1) characterized by: (Aspect 4) A nut (1) consisting of a nut body (2) and a screw hole (3), The nut has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) is defined as follows: the axial side in the radial direction (X) is called the "inner side", and the side away from the axis is called the "outer side" or "outer peripheral side". In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension", which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), and a screw pitch P, Here, the thread pitch P is a thread pitch based on the JIS thread standard or the standard of a country or international organization corresponding to the JIS (hereinafter, collectively including the JIS, simply referred to as the "standard"); The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rnо of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange portion (5) has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion (5) has a bearing surface (5s) at the fastening end, the bearing surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, The recess (7) has a maximum depth Dm in the axial direction from the extension surface (5e) of the seat surface less than 1.5 times the thread pitch P (Dm<1.5P) when the thread pitch P of the screw hole (3) is the thread pitch of a fine thread in the standard specification, and has a maximum depth Dm in the axial direction (Z) from the extension surface (5e) of the seat surface less than 1.0 times the thread pitch P (Dm<1.0P) when the thread pitch P of the screw hole is the thread pitch of a coarse thread in the standard specification. A nut (1) characterized by: (Aspect 5) A nut (1) consisting of a nut body (2) and a screw hole (3), The nut has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) is defined as follows: the axial side in the radial direction (X) is called the inner side, and the side away from the axis is called the outer side or outer circumferential side. In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension", which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw thread roots (3b) of the screw hole (3), a female thread root diameter φ, which is the diameter of the screw thread cylindrical surface (3e), and a screw pitch P, Here, the thread pitch is P (unit: mm), the root diameter of the nut's female thread is φ (unit: mm), and the following relationship exists: When 0.5<φ≦1.3, P≦(1 / 20)φ+0.17, When 1.3<φ≦2.3, P≦(0.12 / 0.8)φ+0.07, When 2.3<φ≦6.5, P≦(0.6 / 4)φ+0.02, When 6.5<φ≦12, P≦(0.55 / 4)φ-0.07, When 12<φ≦41, P≦(2.55 / 29)φ+0.48 , When 41<φ≦125, P≦(2 / 85)φ+3.06, When 125<φ≦320, P≦7.80 or The table below: [Table 1] The relationship shown in The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rnо of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange portion (5) has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion (5) has a bearing surface (5s) at the fastening end, the bearing surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, The maximum depth Dm of the recess from the extension surface (5e) of the bearing surface in the axial direction (Z) is less than 1.5 times the thread pitch P (Dm<1.5P). A nut (1) characterized by: (Aspects 2 to 5) Aspects 2 to 5 each have additional features with respect to aspect 1, but aspects 2 to 5 may satisfy one or more of the additional features of aspect 1 and aspects 2 to 5. (Aspect 6) The recess (7) is the nut (1) according to any one of aspects 1 to 5, in which the maximum axial depth Dm from the extension surface (5e) of the seat surface is less than 1.0 times the thread pitch P (Dm < 1.0P). (Aspect 7) In a longitudinal section including the axis of the nut (1) (hereinafter, also simply referred to as "nut longitudinal section"), the nut body (2) has an open-side additional rigidity portion at the open-side end, and the open-side additional rigidity portion is a portion where the radial dimension R1 of its radially inner surface is larger than the thread valley radius dimension R0. The axial dimension Ha of the open-side additional rigidity portion is 0.5 times or more the thread pitch P (Ha ≥ 0.5P), preferably 0.6 times or more (Ha ≥ 0.6P), more preferably 0.7 times or more (Ha ≥ 0.7P), preferably 2 times or less (Ha ≤ 2P), more preferably 1.5 times or less (Ha ≤ 1.5P), and still more preferably 1.0 times or less (Ha ≤ 1.0P). The nut (1) according to any one of aspects 1 to 6. (Aspect 8) The depth Di in the axial direction from the extension surface (5e) of the seat surface at the axial end (7о) of the recess (7) is smaller than the maximum depth Dm of the recess (7) (Di < Dm). Preferably, the difference Dd = (Dm - Di) between the maximum depth Dm of the recess (7) and the depth Di is larger than 0 times the thread pitch P and 1.3 times or less (0 < Dd ≤ 1.3P), more preferably 0.1 times or more and 1.0 times or less or less than 1.0 times (0.1P ≤ Dd ≤ 1.0P or 0.1P ≤ Dd < 1.0P), and still more preferably 0.2 times or more and 0.8 times or less (0.2P ≤ Dd ≤ 0.8P). The nut according to any one of aspects 1 to 7. (Aspect 9) The flange portion (5) has a dimensional difference Lfd = (Rfm - Rn) between the maximum radius dimension Rfm of the flange portion (5) and the outer circumferential inscribed cylindrical radius dimension Rn of the square nut portion (4), which is based on the radial dimension Ln from the thread valley cylindrical surface (3e) of the square nut portion (4) to the outer circumferential inscribed cylindrical surface, and is 0.4 times or more (Lfd ≧ 0.4Ln), preferably 0.45 times or more (Lfd ≧ 0.45Ln), more preferably 0.5 times or more (Lfd ≧ 0.5Ln); or the dimensional difference Lfd is 1.8 times or more (Lfd ≧ 1.8P), preferably 2.0 times or more (Lfd ≧ 2.0P), more preferably 2.1 times or more (Lfd ≧ 2.1P) of the thread pitch P. The nut (1) according to any one of the first to eighth aspects. (Aspect 10) The flange portion (5) has an axial height Hfm from the seat surface (5s) to the boundary (5fm) between the flange portion (5) and the square nut portion (4), which is based on the overall length Hz, which is the axial height of the nut (1), and is 0.2 times or more (0.2Hz≦Hfm), preferably 0.25 times or more and 0.5 times or less (0.25Hz≦Hfm≦0.5Hz), more preferably 0.3 times or more and 0.4 times or less (0.3Hz≦Hfm≦0.4Hz); alternatively, the height Hfm is 1.5 times or more (1.5P≦Hfm), preferably 2 times or more and 6 times or less (2P≦Hfm≦6P), more preferably 2.4 times or more and 4 times or less (2.4P≦Hfm≦4P), and even more preferably 2.6 times or more and 3.5 times or less (2.6P≦Hfm≦3.5P). The nut (1) according to any one of the first to ninth aspects. (Aspect 11) In the longitudinal section of the nut, the flange portion (5) includes a flange outermost portion (5оm) which is a portion of the flange portion (5) having a maximum radius Rfm, an inclined portion (5c) connecting the flange outermost portion (5оm) and the square nut portion (4), and a stress relaxation portion (5r) formed of a stress relaxation curve connecting the flange outermost portion (5оm) and the seat surface (5s), and the flange outermost portion (5оm) may be a straight line or a point extending in the axial direction (Z), The outermost peripheral part of the flange (5оm) has an axial height Hf from the extension plane (5e) of the seating surface at the boundary (5m) between the outermost peripheral part of the flange (5оm) and the inclined part (5c) that is greater than the maximum depth Dm of the recess (7) (Hf > Dm). Preferably, the height Hf is 1.1 times or more (Hf ≥ 1.1Dm), more preferably 1.5 times or more (Hf ≥ 1.5Dm), even more preferably 1.8 times or more (Hf ≥ 1.8Dm) based on the maximum depth Dm of the recess (7). Alternatively, the height Hf is 1.2 times or more (Hf ≥ 1.2P) of the thread pitch P, more preferably 1.4 times or more (Hf ≥ 1.4P), even more preferably 1.6 times or more (Hf ≥ 1.6P). The nut according to any one of Aspects 1 to 10. (Aspect 12)(1) The radial dimension Lm from the thread groove cylindrical surface (3e) to the outer end (7о) of the recess (7) is greater than 1.0 times the thread pitch P (1.0P < Lm), and the radial dimension Lm is smaller than the radial dimension Ln from the thread groove cylindrical surface (3e) of the square nut part (4) to the outer circumferential inscribed cylindrical surface (Lm < Ln). Preferably, the radial dimension Lm is 1.5 times or more (1.5P ≤ Lm) of the thread pitch P, more preferably 2.0 times or more (2.0P ≤ Lm), 2.5 times or more (2.5P ≤ Lm), 2.8 times or more (2.8P ≤ Lm). Alternatively, the radial dimension Lm is 0.5 times or more (Lm ≥ 0.5Ln), 0.7 times or more (Lm ≥ 0.7Ln), 0.8 times or more (Lm ≥ 0.8Ln), 0.9 times or more (Lm ≥ 0.9Ln) of the radial dimension Ln. The nut (1) according to any one of Aspects 1 to 11. (Aspect 13) The recess (7) has a part with the maximum depth Dm, and the part with the maximum depth Dm is at a radial dimension Ldm from the thread groove cylindrical surface (3e). The radial dimension Ldm is greater than two-fifths of the radial dimension Lm from the thread groove cylindrical surface (3e) to the outer end (7о) of the recess (7), preferably greater than one-half, more preferably greater than two-thirds. The nut (1) according to Aspect 12. (Aspect 14) In the longitudinal section of the nut, the recess (7) includes a stress-relieving curve portion, preferably a higher-order curve portion, that extends from the boundary (7о) between the recess (7) and the seating surface (5s) toward the axial-side end (7i) of the recess (7) and includes a portion of the maximum depth Dm, and optionally, a straight-line portion, particularly a straight-line portion (7il) extending in a substantially radial direction (X) and / or a chamfered portion, on the axial side of the stress-relieving curve portion. The nut (1) according to aspect 13. (Aspect 15) In the longitudinal section of the nut, the recess (7) includes a first straight-line portion, preferably a first straight-line portion that extends toward the open side while being inclined at an angle of 45° or less, more preferably 15° or less, with respect to the seating surface (5s) or from perpendicular to the axial side with respect to the seating surface (5s), from the boundary between the recess (7) and the seating surface (5s), and a stress-relieving curve portion, preferably a higher-order curve portion, that extends radially inward from the end of the first straight-line portion and has a portion of the maximum depth Dm, and optionally, a second straight-line portion (7il) that extends substantially radially to the axial-side end (7i) of the recess (7). The nut (1) according to aspect 13. (Aspect 16) In the longitudinal section of the nut, the radius dimension Rr of the boundary (7о) between the recess (7) and the seating surface (5s), that is, the inner-side end (5si) of the seating surface, is smaller than the radius dimension Rn of the inscribed cylinder of the outer circumference of the square nut portion (4) (Rr < Rn). Preferably, the difference Ld = (Rn - Rr) between Rn and Rr is 0.1 times or more (Ld ≧ 0.1Ln) or 0.2 times or more (Ld ≧ 0.2Ln), further 0.1 times or more and 0.5 times or less (0.2Ln ≦ Ld ≦ 0.5Ln), based on the radial dimension Ln from the root cylinder surface (3e) of the thread of the square nut portion (4) to the inscribed cylinder surface of the outer circumference, or alternatively, the difference Ld between Rn and Rr may be 0.05 times or more (Ld ≧ 0.0P), 0.1 times or more (Ld ≧ 0.1P) or 0.2 times or more (Ld ≧ 0.2P), further 0.1 times or more and 1.0 times or less (0.1P ≦ Ld ≦ 1.0P). The nut (1) according to any one of aspects 1 to 15. (Aspect 17) The radial dimension Ls from the inner end (5si) to the outer end (5sо) of the bearing surface (5s) is 0.3 times or more (Ls≧0.3Ln) of the radial dimension Ln based on the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut portion (4) to the outer peripheral inscribed cylindrical surface (Ls≧0.4Ln), preferably 0.4 times or more (Ls≧0.4Ln), and further 0.45 times or more (Ls≧0.45Ln); alternatively, the radial dimension Ls is 1.0 times or more (Ls≧1.0P) of the thread pitch P, preferably 1.5 times or more (Ls≧1.5P), and more preferably 1.7 times or more (Ls≧1.7P). The nut (1) according to any one of the first to sixteenth aspects. (Aspect 18) The area Sm (=S3-S2) obtained by subtracting the area S2 of the circle having the radius of the shaft end (5si) of the bearing surface from the area S3 of the circle having the radius Rfm of the outermost flange portion (5 оm) of the flange portion (5) as viewed from the axial direction (Z) is 0.55 times or more (S≧0.55Ss) of the area Ss, preferably 0.6 times or more and 1.2 times or less (0.6Ss≧S≦1.2Ss), and more preferably 0.7 times or more and 1.1 times or less (0.7Ss≦S≦1.1Ss), based on the area Ss=(Sn-S0) obtained by subtracting the area S0 of the circle having the radius R0 of the thread groove (3b) from the area Sn of the circle having the radius Rn of the outer circumferential inscribed cylinder of the square nut portion (4). A nut (1) according to any one of aspects 1 to 17, in particular claims 1 and 3 to 17. (Aspect 19) The area S of the bearing surface (5s) is 0.55 times or more (S≧0.55Ss) of the area Ss, which is calculated by subtracting the area S0 of a circle having a radius R0 of the thread groove (3b) from the area Sn of a circle having a radius Rn of the outer circumferential inscribed cylinder of the square nut portion (4), (Sn-S0), preferably 0.6 times or more and 1.2 times or less (0.6Ss≦S≦1.2Ss), and more preferably 0.7 times or more and 1.1 times or less (0.7Ss≦S≦1.1Ss). The nut (1) according to any one of the first to eighteenth aspects. (Aspect 20) The radial dimension Lr = (Rfm - Rsm) of the stress relaxation portion (5r) of the flange portion (5) is 0.15 times or more (Lr ≥ 0.15Ln) of the radial dimension Ln from the thread groove cylindrical surface (3e) of the square nut portion (4) to the outer peripheral inscribed cylindrical surface, preferably 0.2 times or more (Lr ≥ 0.2Ln), 0.25 times or more (Lr ≥ 0.25Ln), or alternatively, the radial dimension Lr is 0.7 times or more of the thread pitch P (Lr ≥ 0.7P), preferably 0.8 times or more (Lr ≥ 0.8P), and further preferably 0.9 times or more (Lr ≥ 0.9P). The nut (1) according to any one of Aspects 11 to 19. (Aspect 21) In the longitudinal section of the nut, the inclined portion (5c) of the flange portion (5) has an angle θ within a range of 15° to 60° (15° ≤ θ ≤ 60°) with respect to the radial direction, preferably 15° to 45° (15° ≤ θ ≤ 45°), and more preferably 20° to 40° (20° ≤ θ ≤ 40°). The nut (1) according to any one of Aspects 11 to 20. (Aspect 22) The nut body has a reduced diameter portion at the open side end, where the radial dimension R3 of the radially outer surface is smaller than the outer peripheral inscribed cylindrical radius dimension Rn of the square nut portion (4) (R3 < Rn), and the axial dimension Hc of the reduced diameter portion is larger than the axial dimension Ha of the open side additional rigidity portion. The nut (1) according to any one of Aspects 1 to 21. (Aspect 23) A bolt - nut fastening structure for fixing a fastened object to a base material, characterized by using the nut (1) according to any one of Aspects 1 to 22 and a bolt corresponding to the nut (1). (Aspect 24) The bolt - nut fastening structure according to Aspect 23, wherein the fastening structure is used in an environment including at least one of vibration, temperature change, pressure change, and corrosive environment. (Aspect 25) 25. The bolt and nut fastening structure according to aspect 23 or 24, wherein the fastening structure is used for an application selected from the group consisting of automobiles, aircraft, space equipment, bridges, prime movers (motors, engines), wind power generators, construction machinery, civil engineering machinery, mining machinery, railway vehicles, cranes, ships, power generation equipment, power transmission equipment (steel towers), pipelines (flange connections), elevators (elevators, escalators), vacuum equipment, semiconductor manufacturing equipment, casting and forging / iron-making machinery, machine tools, and steel buildings. Effect of the Invention

[0014] According to the present disclosure, it has surprisingly been discovered that by providing a shallow recess on the inside (axis side) of the fastening side seating surface of a flange nut that is less than 1.5 times the thread pitch, preferably 1.25 times or less, and more preferably 1.0 times or less or less than 1.0 times, the load distribution rate to the first thread of the fastening meshing threads can be significantly reduced, and further the structure of the recess is simple, providing a nut that is suitable for commercial production. [Brief description of the drawings]

[0015] [Figure 1-1] FIG. 1(a) is an end view of one half of an axial line in a longitudinal section of an example of a nut 1 of the present disclosure. [Figure 1-2] 1(b) and (c) are side views of the nut 1 in FIG. 1(a) viewed from two angles. [Figure 1-3] FIG. 1(d) is a plan view of the nut 1 in FIG. 1(a) seen from above, and FIG. 1(e) is a bottom view of the nut in FIG. 1(a) seen from below. [Figure 1-4] 1(f) and (g) are photographs of prototype examples of the nut of the present disclosure. [Figure 2-1] FIG. 2-1 is a vertical sectional end view illustrating a schematic example of a bolt and nut fastening structure according to the present disclosure. [Figure 2-2] FIG. 2-2 is a partially enlarged end view of the flange portion 5 of the nut 1 of FIG. [Figure 2-3] FIG. 2-3 is a partially enlarged end view of the square nut portion 4 of the nut 1 of FIG. [Diagram 3]FIG. 3 is a vertical cross-sectional end view of another example N1 of the nut of the present disclosure. [Figure 4] FIG. 4 is a vertical cross-sectional end view of another example N5 of the nut of the present disclosure. [Diagram 5] FIG. 5 is a vertical cross-sectional end view of the nut D1 of the first reference example. [Figure 6] FIG. 6 is a graph showing a comparison of the load sharing rate for each thread of the nut N2 and the nut D1. [Figure 7] FIG. 7 is a graph showing the relationship between the depth of the recess of nuts D1 and N1 to N6 and the load sharing rate of the first meshing ridge. [Figure 8] FIG. 8 is a vertical cross-sectional view that illustrates a schematic example of a bolt and nut fastening structure according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present disclosure is similar to the prior art in that it proposes a structure that reduces the burden share of the first thread engagement on the fastening side in order to improve the fatigue fracture life of the thread root of the first thread engagement of the bolt. However, in the prior art, generally, all of them were merely ideas (conceived ideas) or proposals based on partial empirical knowledge. Therefore, as described in the Background Art section, those proposals were either not usable in practice, or even if they were usable, they had both advantages and disadvantages in terms of structure, and were not practical for nuts as general-purpose mass-produced parts. In response to this, the present disclosure is exploring a structure that reduces the burden share of the first thread engagement on the fastening side of the nut by utilizing the fact that it is possible to comprehensively know what physical stress is applied to the entire nut and each part by devising the structure and shape of the nut through finite element analysis (FEM analysis) using a supercomputer (Patent Document 4). The present inventor, by carrying out FEM analysis using this supercomputer, has found that, completely unexpected from conventional knowledge, by simply providing a shallow recess on the axial side of the fastening side end face (bearing surface) of a nut having a flange portion, which is less than 1.5 times the thread pitch (even 1.25 times or less, 1.0 times or less, or less than 1.0 times, 0.5 times or less), which was not considered in conventional proposals, the burden share rate of the first thread engagement on the fastening side of the nut can be unexpectedly and significantly reduced, and the degree of reduction is comparable to the best that can be finally achieved with the complex structure of the conventional technology, and because the recess is shallow and simple, the change in other structures of the nut can be kept to a minimum by maintaining rigidity with the flange portion, and, most importantly, the manufacturing and processing of the nut are simple, so that the nut structure can be practically used as a general-purpose mass-produced part in terms of both manufacturing process and manufacturing cost. The structure and effects of the present disclosure were first discovered, confirmed, and proposed by utilizing FEM analysis using a supercomputer.

[0017] In this disclosure, the dimensions of each portion of the nut are described in single or multiple numerical ranges for simplicity, however, the upper and lower limits in each of these numerical ranges are not inseparable, and the upper limit or the lower limit alone is meaningful, and therefore the numerical ranges in this disclosure may be a numerical range composed of any combination of any upper limit and any lower limit in multiple numerical ranges.

[0018] Hereinafter, preferred embodiments of the nut of the present disclosure will be described with reference to the drawings. However, the drawings and reference signs are merely for the convenience of explanation, and the present disclosure is not limited by the descriptions of the drawings and reference signs.

[0019] Figures 1-1, 1-2 and 1-3 (these figures, together with Figure 1-4, are also collectively referred to as Figure 1) show a hexagonal nut (hereinafter simply referred to as a nut) as an example of a preferred embodiment of the present disclosure, specifically, Figure 1(a) is an end view of a vertical section including the axis of the nut (hereinafter simply referred to as a "nut vertical section"), and Figures 1(b) to (e) are two side views, a plan view and a bottom view of the nut. Figures 1(f) and (g) are photographs of a prototype nut based on the present disclosure.

[0020] Fig. 2-1 is an enlarged end view showing half of the nut longitudinal section of the nut in Fig. 1. Fig. 2-2 is an enlarged end view of a part of the flange portion of the nut in Fig. 2-1. Fig. 2-3 is an enlarged end view of a part of the square nut portion of the nut in Fig. 2-1. In Figs. 1-1 to 1-3, 2-1 and 2-2, the axial direction is Z and the radial direction is X.

[0021] In Fig. 1(a)-(e), reference numeral 1 is a nut, 2 is a nut body, 3 is a screw hole, 4 is a square nut part, 5 is a flange part, 6 is an additional rigidity part on the open side (part with hatching and sand), and 7 is a recess. In Fig. 1(d), reference numeral Rn represents the radius of a cylindrical surface (virtual) inscribed on the outer periphery of the square nut part 4, and Rnо represents the radius of a cylindrical surface (virtual) circumscribed on the outer periphery of the square nut part 4. When the nut is viewed from the open side, lines that coincide with the cylindrical surfaces inscribed and circumscribed on the outer periphery of the square nut part 4 may be seen, but the definitions of Rn and Rnо are based on the virtual cylindrical surfaces inscribed and circumscribed on the outer periphery of the square nut part 4. In the longitudinal section of the nut, the outer periphery dimensions differ depending on the position of the outer periphery of the square nut part in the cross section, but the structure is the same. The longitudinal cross-sectional views of the present disclosure are basically longitudinal cross-sectional views in which the outer periphery of the square nut portion is a cylindrical surface inscribed in the outer periphery of the square nut portion, but when describing, for example, a cylindrical surface circumscribing the outer periphery, the longitudinal cross-sectional views of the present disclosure may be considered to be longitudinal cross-sectional views representing a cylindrical surface circumscribing the outer periphery.

[0022] nut The nut 1 of the present disclosure is a flange nut having a nut body 2 and a screw hole 3, and the nut body 2 has a square nut portion 4 and a flange portion 5 along its axis Z. In the nut 1 of the present disclosure, in the direction of the axis Z, the flange portion 5 side is the fastening side where a fastening object that may include a washer or the like is present, and the square nut portion 4 side is the opposite side to the fastening side and is called the open side. Here, in the conventional technology, generally, only the annular portion on the fastening side of the shaft body (nut body) of the square nut, whose radial dimension is larger than that of the shaft body, is often called the flange portion, but in the present disclosure, not only the annular portion whose radial dimension is larger than that of the shaft body (flange portion in the narrow sense) but also the shaft body portion that exists radially inside corresponding to that portion is called the flange portion for convenience (flange portion in the broad sense). Similarly, only the portion of the nut body excluding the flange portion in the broad sense (shaft body portion whose outer diameter dimension is not expanded) is called the square nut portion. In the nut 1 of the present disclosure, in the radial direction X perpendicular to the axis (axial direction) Z, the side closer to the axis Z is also called the inner side (inner surface side), and the side farther from the axis Z is also called the outer side (outer peripheral side).

[0023] The shape, dimensions, strength class, material, etc. of nuts are specified in standard specifications such as ISO and JIS, and in particular the various dimensions are specified for each screw hole diameter (for example, M12 is a nut with a screw hole diameter, which is the diameter of the thread root, of 12 mm), and in the nuts disclosed herein, too, for parts not specifically specified, the standard shape, dimensions, strength class, material, etc. specified in the standard specifications can be used as a base.

[0024] Nut body The nut 1 of the present disclosure has various dimensions in the radial direction X perpendicular to the axis Z. In this disclosure, unless otherwise specified, the term "radial dimension" ("radius") of each portion refers to the dimension (radius) from the axis to a specific portion in the radial direction, with the axis as the starting point, and the term "radial dimension" refers to the dimension between specific portions in the radial direction (particularly other than the axis).

[0025] In the present disclosure, the nut body 2 has a square nut portion 4 and a flange portion 5, and the flange portion 5 is located on the fastening side of the square nut portion 4 and has a radius (for example, Rfm) larger than the maximum radius Rnо of the outer periphery of the square nut portion 4. Here, the square nut portion 4 has an outer periphery inscribed cylindrical radius Rn, which is the radius of the cylindrical surface inscribed in the outer periphery, and an outer periphery circumscribed cylindrical radius (maximum outer periphery radius) Rno, which is the radius of the cylindrical surface circumscribed in the outer periphery (see Figs. 1(b)(c)(d)). Here, the cylindrical surface inscribed or circumscribed in the outer periphery of the square nut portion 4 is a virtual surface. For example, in a hexagonal nut or the like, it is known that in a plan view of the nut seen from the axial direction, the outer periphery dimension (outer diameter) has a diagonal dimension ("diagonal"), which is the distance between two opposing corners passing through the axis, and a "flat diameter" ("two-face width"), which is the distance between two parallel sides. The diagonal dimension is the diameter of the circumscribed cylinder, and the flat diameter (width across two faces) is the diameter of the inscribed cylinder. In this disclosure, since the transmission of fastening force is the subject of the discussion, the radius dimension of the outer periphery of the square nut portion 4 is basically the radius dimension Rn of the inscribed cylinder, and unless otherwise specified, this means the radius dimension Rn of the inscribed cylinder, but in some cases, for example in the definition of the flange portion, the radius dimension Rno of the circumscribed cylinder is also referred to.

[0026] The shape, dimensions, strength class, material, etc. of the nut body 2 are also specified in standard specifications such as JIS, ISO, EN, etc., and in particular the various dimensions are specified for each diameter of the screw hole. In the nut of the present disclosure, the shape, dimensions, strength class, material, etc. of the nut body 2, in particular the square nut portion 4 (for example, the height of the hexagonal nut, the shape, dimensions, strength class, material, etc. of the hexagonal nut portion viewed from the axial direction) can be adopted based on the standard specifications specified in those standard specifications.

[0027] The nut 1 of the present disclosure is characterized by having a recess 7 at the fastening side end of the nut body 2, and in a preferred embodiment has an open-side additional rigidity portion 6, etc. The shape and dimensions, etc. of the nut body 2 of the present disclosure are modified and changed from the standard shape and dimensions, etc., because it has the recess 7 and, optionally, the open-side additional rigidity portion 6, etc. The influence of the recess 7 and the open-side additional rigidity portion 6, etc. on the shape and dimensions, etc. of the nut 1 of the present disclosure will be described later.

[0028] The nut 1 of the present disclosure is also characterized by having a flange portion 5 corresponding to the recess 7. There are standard specifications such as JIS for the shape and dimensions of flange nuts, and the nut 1 of the present disclosure can also adopt these standard specifications as a base. The shape and dimensions of the flange portion 5 may be modified in relation to the recess 7, but the shape and dimensions of the flange portion 5 will be described later.

[0029] The nut 1 of the present disclosure has a height (total length) Hz in the axial direction. The height Hz of the nut 1 is the maximum dimension in the axial direction from the bearing surface 5s or its extension surface (5e; imaginary surface), which is a flat surface extending in the radial direction at the end of the flange portion 5, to the open side end surface 6s of the square nut portion 4. In a preferred embodiment, the nut 1 of the present disclosure includes an open side additional rigidity portion 6 at the open side end of the square nut portion 4, as described later. In this case, the height Hz of the nut 1 is the dimension including the open side additional rigidity portion 6.

[0030] The height Hz of the nut 1 of the present disclosure may be a standard height or a height based on the standard, but may be preferably greater than the standard height or the height based on the standard when the nut has an open-side additional rigidity portion 6. The relationship between the height Hz of the nut 1 of the present disclosure and the standard height or the height based on the standard will be described later in connection with the open-side additional rigidity portion 6.

[0031] Screw hole The threaded hole 3 is a hole into which the threaded portion of a bolt or male thread is inserted, and is a cylindrical hole having a female thread groove. The female thread is a helical thread groove formed on the inner surface of the nut. Here, the thread groove is composed of a ridge (head), a valley (bottom), and a portion (inclined portion) connecting the ridge and valley. In the nut 1, the thread ridge is on the inside (shaft side) of the nut 1 in the radial direction, and the thread valley is on the outside of the nut 1 in the radial direction. The thread ridge and valley may refer to the high and low parts of the thread groove, but in certain cases they refer to the top and bottom of the thread groove. For example, when referring to the threaded hole diameter (valley diameter of the female thread), it refers to the diameter of the valley bottom of the thread groove.

[0032] The screw hole 3 has a screw hole radius (also referred to as a "screw hole radius dimension") R0, which is half the screw hole diameter (female thread root diameter) φ. In the drawings, only the screw hole radius R0 is shown, and the female thread root diameter φ is not shown, but the female thread root diameter φ is a diameter (φ=2RO) that completely corresponds to the screw hole radius R0. Here, the screw hole diameter refers to the diameter of the screw thread root cylindrical surface 3e formed by connecting the screw thread roots 3b of the screw hole 3, so the screw thread root radius dimension R0 is the radial dimension (radius) from the axis Z to the screw thread root cylindrical surface 3e. In addition, the screw thread root cylindrical surface 3e of the screw hole 3 is a virtual surface, and in the present disclosure, it refers to a cylindrical surface including not only a portion that actually has a screw thread root in the axial direction, but also portions extending on both sides of the axial direction. In addition, the thread groove cylindrical surface 3e of the screw hole 3 becomes a straight line 3e connecting the thread grooves 3b in a longitudinal section including the nut axis Z (hereinafter also referred to simply as the "nut longitudinal section"), but in the present disclosure, both the thread groove cylindrical surface and the straight line are represented by the same reference symbol "3e."

[0033] The diameter of the screw hole of the nut 1, more specifically, the root diameter φ of the female thread, is defined in the standard specifications for screws and nuts, and is a diameter corresponding to the outer diameter of the male thread (called the nominal diameter of the thread). The root diameter φ of the female thread can be determined and measured from the shape and dimensions of the female thread (particularly the inclined surface from the crest to the root of the female thread), but is generally measured using a thread gauge. The screw hole of the female thread may actually have a portion deeper than the root diameter (nominal diameter) of the female thread to smoothly engage with the male thread, but the portion deeper than the root diameter of the female thread is redundant as a female thread and is not included in the root diameter of the female thread. However, if necessary, the root diameter may be the diameter of the bottom of the redundant portion deeper than the root diameter of the female thread defined above.

[0034] Moreover, the screw hole 3 has a screw pitch P. The screw pitch P is the axial distance when the screw groove of the screw hole 3 rotates 360° and moves a specific distance in the axial direction, and can be defined as the axial dimension (distance) from one screw root 3b of the screw hole 3 to the adjacent screw root 3b, or from one crest to the adjacent crest of the screw hole 3.

[0035] The thread pitch P of the screw hole 3 of the nut is specified for each screw hole diameter (root diameter of the female thread) of the nut in standards such as JIS (especially JIS-B0205, JIS-B0206, etc.) and standards of national and international organizations corresponding to JIS, for example, ASTM (American Society for Testing and Materials) in the United States, BS (British Standards) in the United Kingdom, DIN (Deutsche Industrie-Norm) in Germany, GB Standard (Guo jia Biao zhun) in China, CNS Standard (Chinese National Standards) in Taiwan, KS Standard (Korean Standards) in Korea, and ISO as an international standard, and the thread pitch P of the standard can be adopted for the nut 1 of the present disclosure. Since these standards are basically compatible, it is sufficient to refer to JIS or ISO and other standards as necessary.

[0036] There are metric thread standards (e.g., JIS-B0205) and unified thread standards (e.g., JIS-B0206) for thread standards. The metric thread standard specifies the thread pitch relative to the nominal diameter (external diameter of the male thread and the root diameter of the female thread), whereas the unified thread standard specifies the external diameter of the male thread and the root diameter of the female thread relative to the nominal thread (number of threads per inch). The two standards of metric threads and unified threads are not identical, particularly due to the relationship in which the nominal diameter and nominal value are rounded off, but are similar to each other in terms of substantial dimensions. The nut of the present disclosure can be preferably applied to nuts based on both metric threads and unified thread standards, but is particularly preferably applied to nuts based on metric thread standards. The screw hole diameter is called the nominal diameter. For example, M12 is a nut used for a bolt with an external diameter of 12 mm, and the screw hole diameter (root diameter of the female thread) can be considered to be substantially about 12 mm.

[0037] In the above-mentioned standard, there are standards for coarse threads and fine threads with respect to the pitch of the thread, and many standard dimensions specify whether the thread is a coarse thread or a fine thread. However, for example, in "Table 1: Reference Dimensions" of "General Metric Threads - Part 4: Reference Dimensions" of JIS B0205-4 (ISO-724), multiple thread pitches are listed for the same female thread root diameter (nominal diameter) without specifying whether it is a coarse thread or a fine thread. In this case, the largest thread pitch is a coarse thread, and any thread pitch smaller than that is a fine thread. The nut of the present disclosure can be applied to both coarse threads and fine threads, and more specifically, to all threads. One preferred embodiment is a metric fine thread or a unified fine thread, but is particularly suitable for a metric fine thread, which is a commonly adopted standard.

[0038] The nut (1) of the present disclosure is particularly useful for fine threads. In applications requiring durability and long life against harsh environments such as vibration, temperature change, pressure change, and corrosive environment (environment more corrosive than air), such as automobiles, aircraft, space equipment, bridges, prime movers (motors, engines), wind power generators, construction machinery, civil engineering machinery, mining machinery, railroad vehicles, cranes, ships, power generation equipment, power transmission equipment (steel towers), pipelines (flange connections), elevators (elevators, escalators), vacuum equipment, semiconductor manufacturing equipment, casting and forging / iron-making machinery, machine tools, and steel buildings, fine threads are used to achieve strong fastening. In addition, in such harsh environment applications, bolts and nuts are fastened with high fastening force, but because of this, bolts and nuts, especially bolts, are more likely to break in the threaded portion of the first thread of the mating thread, especially in the case of long-term use, making it difficult to have a long life, and the effectiveness of the nut of the present disclosure is remarkable.

[0039] In applications requiring durability against harsh environments and a long life span as described above, screws and nuts with a large thread diameter are preferably used to achieve strong fastening. Although the present disclosure is not limited by the thread diameter, for example, thread diameters of 6 mm or more, 8 mm or more, 10 mm or more are preferably used, and the effects of the present disclosure are more remarkable and more useful in nuts used with screws with such large thread diameters. In addition, although the maximum thread diameter is 310 mm in the above example, nuts with a larger thread diameter are also useful. Nuts that are generally widely used are M6 to M120 (thread diameter 6 to 120 mm), and the nuts of the present disclosure can also be preferably used for nuts of M6 to M120. However, the nuts of the present disclosure are not limited to these.

[0040] One preferred embodiment of the present disclosure can be obtained from a graph showing a metric thread and a unified thread with the thread pitch P on the vertical axis and the thread pitch on the horizontal axis, as a range of thread pitch P smaller than the thread pitch of both the metric thread and the unified thread. If the thread pitch is P (unit: mm) and the root diameter (diameter) of the nut's female thread is φ (unit: mm), the following relationship is satisfied, that is, When 0.5<φ≦1.3, P≦(1 / 20)φ+0.17, When 1.3<φ≦2.3, P≦(0.12 / 0.8)φ+0.07, When 2.3<φ≦6.5, P≦(0.6 / 4)φ+0.02, When 6.5<φ≦12, P≦(0.55 / 4)φ-0.07, When 12<φ≦41, P≦(2.55 / 29)φ+0.48 , When 41<φ≦125, P≦(2 / 85)φ+3.06, When 125<φ≦320, P≦7.80 Within these preferred ranges, the maximum value of P may be reduced by 0.01 mm. For example, when 0.5<φ≦1.2, P≦(1 / 20)φ+0.16, or even P≦(1 / 20)φ+0.15, when 1.2<φ≦2, P≦(0.12 / 0.8)φ+0.06, and more preferably, When 0.5<φ≦1.3, P≦(1 / 15)φ+0.14, When 1.3<φ≦2, P≦(1.3 / 9)φ+0.06, When 2<φ≦6.5, P≦(0.09 / 0.8)φ+0.08, When 6.5<φ≦12, P≦(0.55 / 4)φ-0.19, When 12<φ≦41, P≦(2.55 / 29)φ+0.28, When 41<φ≦125, P≦(1 / 78)φ+3.46, When 125<φ≦320, P≦7.50, P≦7.00, and even P≦6.50 In these preferred and more preferred ranges, the maximum value of P may be made smaller in increments of 0.01 mm, for example, in the preferred range, when 0.5<φ≦1.2, P≦(1 / 20)φ+0.16, or even P≦(1 / 20)φ+0.15, or when 1.2<φ≦2, P≦(0.12 / 0.8)φ+0.06. In addition, although the above preferred and more preferred ranges are each an integral range, the range of the thread pitch P may be changed to the more preferred range only in the range of one or more subdivisions of the female thread root diameter φ of the more preferred range of the thread pitch P.

[0041] Another preferred embodiment of the present disclosure can be obtained as a range of thread pitch P for each range of thread root diameter (diameter) φ of the female thread of the nut in the standard specifications for metric threads and unified threads, which is smaller than the thread pitch of both the coarse threads of the metric threads and unified threads, by using a table showing the thread pitch P and the thread pitch P of the female thread in the standard specifications for metric threads and unified threads. If the thread pitch is P (unit: mm) and the thread root diameter (diameter) of the female thread of the nut is φ (unit: mm), the relationship shown in Table B (Tables B1 to B-4) below may be satisfied. Table B also shows examples of preferred combinations of thread pitch P and thread root diameter φ of the female thread of the nut based on the standard specifications. Note that in Table B, there are some cases where multiple ranges are listed in the column for the range of the same thread pitch P. In some examples of pitch P, there are multiple Ps for the same female thread root diameter. Furthermore, the upper limit value of the thread pitch P range in the preferred range, more preferred range, and even more preferred range of pitch P listed in Table B may be further reduced in 0.01 mm units.

[0042] [Table 2]

[0043] [Table 3]

[0044] [Table 4]

[0045] [Table 5]

[0046] Square nut part The square nut part 4 of the nut body 2 is, when viewed in the axial direction (or in a cross section perpendicular to the axis), a hexagon, as well as various other square shapes such as octagons, pentagons, and squares, preferably even-numbered square shapes, but typically a hexagonal square shape, and unless otherwise specified, the square nut part 4 will be described below based on a hexagonal nut part. However, it is clear that the nut of the present disclosure is not limited to a hexagonal nut. The square nut part 4 has an outer circumferential inscribed cylindrical radius dimension Rn, which is the radius dimension of the cylindrical surface inscribed on the outer circumferential surface, and an outer circumferential circumferential cylindrical radius dimension (maximum outer circumferential radius) Rno, which is the radius dimension of the cylindrical surface circumscribed on the outer circumferential surface. Here, the cylindrical surface inscribed or circumscribed on the outer circumferential surface of the square nut part 4 is a virtual surface. In this disclosure, since the transmission of fastening force is the issue, the radius dimension of the outer periphery of the square nut part 4 is basically the outer periphery inscribed cylindrical radius dimension Rn, and unless otherwise specified, the outer periphery inscribed cylindrical radius dimension Rn is meant, but in some cases, for example, in the definition of the flange part, the outer periphery circumscribed cylindrical radius dimension Rno is also referred to. In the attached drawings, since the structure is the same whether the outer periphery of the square nut part 4 represents an inscribed or circumscribed cylindrical surface, the case where the outer periphery of the square nut part 4 is the outer periphery inscribed cylindrical radius dimension is indicated as Rn, and the case where it is the outer periphery circumscribed cylindrical radius dimension is indicated as Rnо (in parentheses).

[0047] In this disclosure, the square nut portion 4 refers to the portion of the nut body 2 from the open side end of the nut body 2 to the boundary 5fm with the flange portion 5 in the axial direction. In a preferred embodiment, the nut 1 can have an open side additional rigidity portion 6 described below, in which case the square nut portion 4 is defined as including the open side additional rigidity portion 6. Even in a standard flange nut that does not have an open side additional rigidity portion, the square nut portion 4 may have a chamfered open side end of the screw hole 3, and the relationship between the chamfered portion and the open side additional rigidity portion 6 in this case will be described later in connection with the definition of the open side additional rigidity portion 6.

[0048] Flange The flange portion 5 of the nut body 2 is a portion located on the axial fastening side of the square nut portion 4 and has a radius dimension larger than the maximum radius dimension (the radius dimension of the circumscribed cylinder) Rnо of the outer periphery of the square nut portion 4. The flange portion 5 has a seating surface 5s that forms a flat surface in the radial direction (perpendicular to the axis) at the fastening side end, and an outer circumferential surface (5r, 5о, 5c in the figure) that extends from the radial outer end 5sо of the seating surface 5s to the boundary 5fm between the flange portion 5 and the square nut portion 4. In the nut 1 of the present disclosure, the seating surface 5s is located at the fastening side end and is a flat surface (plane) that extends in the radial direction (perpendicular to the axis). The seating surface 5s of the nut 1 is a flat surface that contacts the surface of the object to be fastened (the surface on the fastening side, the nut side) when fastened. As the object to be fastened, a washer may be interposed at the point of contact with the seating surface 5s. The portion that comes into contact with the seat surface 5s of the nut 1 of the object to be fastened is a flat surface that extends in the radial direction (direction perpendicular to the axis) of the nut 1 or bolt.

[0049] Depression The nut 1 of the present disclosure has a recess 7 that is annular when viewed in the axial direction and has a depth on the axially open side based on a plane [seat surface 5s and extended surface 5e of the seat surface] that exists in the radial direction at the fastening side end of the flange portion 5. The recess 7 is located radially inside the seat surface 5s (the side closer to the screw hole), and the seat surface 5s is on the outer periphery side of the recess 7. The recess 7 has a maximum depth Dm (hereinafter sometimes simply referred to as the "depth of the recess") in the axial direction from the extended surface 5e of the seat surface.

[0050] According to the present disclosure, it has been found that when the depth Dm of the recess 7 of the nut 1 is less than 1.5 pitches, particularly 1 pitch or less, the load sharing rate of the first thread is significantly reduced compared to a standard nut without a recess, even though the recess 7 is extremely shallow. Furthermore, it has been found that, up to about 1 pitch, the deeper the depth Dm of the recess 7, the more the load sharing rate of the first thread is reduced, but when the depth Dm of the recess 7 becomes deeper beyond about 1 pitch, the load sharing rate of the first thread increases, but, when the depth Dm of the recess 7 is less than 1.5 pitches, the load sharing rate of the first thread is significantly reduced compared to a standard nut without a recess. In addition, since the depth Dm of the recess 7 of the nut 1 is shallow, the degree to which the rigidity, strength, and durability of the nut 1 is reduced by forming the recess 7 can be minimized, and is smaller than the corresponding reduction in rigidity, etc., in the case of forming a deep notch or recess in the prior art. In the prior art, the technology for reducing the load sharing rate of the first meshing thread by forming a notch (recess) on the screw hole side of the seating surface of the nut was based on the idea that by interposing a notch (recess) between the seating surface and the first meshing thread and making the depth of the notch (recess) as deep as possible beyond one thread, the stress that flows from the seating surface to the first meshing thread can be reduced as much as possible, thereby reducing the stress sharing rate of the first meshing thread. However, according to the FEM analysis by the present inventor, it is not so important that the recess 7 formed on the inside of the seating surface of the nut is deeper than one thread, and it is crucial that the recess 7 is radially away from the thread groove by a predetermined dimension, and when the depth of the recess 7 becomes deeper than one thread, the load sharing rate of the first meshing thread rather increases. Therefore, the present inventor has unexpectedly found that the depth of the recess 7 is not as important as expected, contrary to the knowledge of the prior art, and has completed the present disclosure.

[0051] In a preferred embodiment, the recess 7 extends from the inner end 5si of the seating surface, i.e., the boundary 7о between the recess 7 and the seating surface 5s, to the screw hole 3 on the extension surface 5e of the seating surface, and is preferably annular when viewed in the axial direction. Here, the recess 7 being annular means that it is preferably completely or almost concentric, but it may be a recess that surrounds the screw hole, is inside the seating surface, and is continuous in the circumferential direction. In addition, the recess 7 preferably has a positive depth D (D>0) from the extension surface 5e of the seating surface 5s toward the axial opening side so that the entire surface of the recess 7, i.e., the entire surface from the inner end 5si of the seating surface to the screw hole 3, does not come into contact with the object to be fastened, even when a specified tightening force is applied to the nut 1, when viewed in the axial direction.

[0052] In the recess 7 of a preferred embodiment, the depth D at each portion of the recess 7 is a positive value throughout the entire recess 7, but the depth is zero at the boundary 5si with the bearing surface 5s, and there is always a portion where the depth increases linearly or non-linearly from zero toward the radially inward (axial side) from the boundary 5si, and the depth inside the portion may be any depth. It is preferable that the depth D of the recess 7 is concentrically uniform from the viewpoint of stability and reliability. However, it is not excluded that the depth D of the recess 7 is not concentric but is displaced. The depth D of the recess 7 may be, for example, 0.05 times or more (D≧0.05P), 0.1 times or more (D≧0.1P), 0.2 times or more (D≧0.2P), or even 0.3 times or more (D≧0.3P) of the thread pitch P, except for the portion adjacent to the boundary 5si with the bearing surface. In other words, except for the portion adjacent to the boundary 7o with the seat surface, the minimum depth D of the recess 7 is preferably, for example, 0.05 times or more (D≧0.05P), 0.1 times or more (D≧0.1P), 0.2 times or more (D≧0.2P), or even 0.3 times or more (D≧0.3P) of the thread pitch P.

[0053] In the nut 1 of the present disclosure, from the viewpoint of achieving both the effect of reducing the load sharing rate of the first meshing thread (hereinafter sometimes simply referred to as the first thread) and ease of manufacturing / machining the nut, the maximum depth Dm of the recess 7 from the extension surface 5e of the seat is less than 1.5 times the thread pitch P (Dm<1.5P). It is preferable that the maximum depth Dm of the recess 7 is 1.25 times or less the thread pitch P (Dm≦1.25P), 1.0 times or less the pitch P (Dm≦1.0P), or less than 1.0 times the pitch P (Dm<1.0P). Furthermore, from the viewpoint of further improving the ease of manufacture / machining of the nut without losing the effect of reducing the load sharing rate of the first thread, in one preferred embodiment, the maximum depth Dm of the recess 7 may be 1.0 times or less of the pitch P (Dm≦1.0P) or less than 1.0 times (Dm<1.0P), 0.8 times or less (Dm≦0.8P), 0.6 times or less (Dm≦0.6P), and particularly 0.5 times or less (Dm≦0.5P).

[0054] In the nut 1 of the present disclosure, the maximum depth Dm of the recess 7 may be less than 1.5 times the thread pitch P (Dm<1.5P). Patent document 1 discloses providing a recess with a depth of 1 pitch or more on the seat side of a hexagonal nut with a coarse thread, but since the hexagonal nut of Patent document 1 is not a flange nut, providing a recess reduces the strength and durability of the nut, and therefore the fatigue life extension effect like that of the nut of the present disclosure cannot be obtained. On the other hand, the recess in the hexagonal nut with a fine thread of Patent document 1 has a depth of 1.5 pitches or more, which is different from the depth of the recess in the nut of the present disclosure. However, even in the nut of the present disclosure, it is preferable that the maximum depth Dm of the recess 7 is less than 1.0 times the thread pitch P (Dm<1.0P), not only for fine threads but especially for coarse threads.

[0055] In a preferred embodiment of the nut 1 of the present disclosure, the thread pitch P, which defines the depth of the recess 7, may be the thread pitch already mentioned in the description of the threaded hole.

[0056] Therefore, it should be understood that the mechanism by which the recess 7 in the nut 1 of the present disclosure reduces the load sharing rate of the first meshing thread thread is essentially different from the mechanism by which the recess 7 in the nut 1 of the present disclosure reduces the load sharing rate of the first meshing thread thread thread in the prior art. The recess 7 in the nut 1 of the present disclosure is conceptually (essentially) completely different from the deep cuts and convex spaces of the prior art.

[0057] Furthermore, what is important is that the nut 1 of the present disclosure has a shallow recess 7 and a simple shape, so that the nut can be easily manufactured and processed without compromising the lifespan of the manufacturing equipment and processing tools. Unlike nuts proposed conventionally, the nut 1 has the characteristics of being suitable for commercial manufacture of nuts, being possible and easy to manufacture commercially, and is therefore a disclosure that is essentially different from the prior art.

[0058] (Size of the dent) The recess 7 preferably extends in the radial direction from the boundary 5si with the seat surface to the screw hole 3 and is annular when viewed from the fastening side of the nut. The recess 7 is such that the radial dimension Lm from the screw hole 3, more specifically from the screw groove cylindrical surface 3e, to the outer end 7o of the recess 7, i.e., the boundary 5si with the seat surface, is preferably smaller than the radial dimension Ln from the screw groove cylindrical surface 3e of the square nut portion 4 to the outer periphery (inscribed cylindrical surface) (Lm < Ln). It is preferable that the position of the outer end 7o of the recess, i.e., the boundary 5si with the seat surface, is radially inward of the position of the outer periphery (inscribed cylindrical surface) of the square nut portion 4, because the square nut portion 4 can receive a greater force directed toward the release side from the seat surface 5s during fastening. The radial dimension Lm from the screw groove cylindrical surface 3e to the outer end 7o of the recess 7 may be 0.2 times or more (Ld ≧ 0.2Ln), 0.3 times or more (Ld ≧ 0.3Ln), further 0.5 times or more (Ld ≧ 0.5Ln), 0.7 times or more (Ld ≧ 0.7Ln), 0.8 times or more (Ld ≧ 0.8Ln), 0.9 times or more (Ld ≧ 0.9Ln), further 0.95 times or more (Ld ≧ 0.95Ln) based on the radial dimension Ln from the screw groove cylindrical surface 3e of the square nut portion 4 to the outer periphery inscribed cylindrical surface. Alternatively, the radial dimension Lm of the recess 7 is preferably greater than 1.0 times the screw pitch P (1.0P < Lm), more preferably 1.5 times or more (1.5P ≦ Lm), 2.0 times or more (2.0P ≦ Lm), further 2.5 times or more (2.5P ≦ Lm), 2.7 times or more (2.7P ≦ Lm), 2.8 times or more (2.8P ≦ Lm), 2.9 times or more (2.9P ≦ Lm), 3.0 times or more (3.0P ≦ Lm), 3.1 times or more (3.1P ≦ Lm). When the radial dimension Lm of the recess 7 is greater than a predetermined dimension, the fastening force entering the nut body 2 from the seat surface 5s enters from a position far from the screw hole 3 in the radial direction and then moves toward the release side, so that the load sharing ratio for the first thread engagement can be reduced.According to the present disclosure, even if the size of the recess 7 (radial dimension Lm or radius dimension Rr) is large, the nut 1 can ensure the rigidity, strength, and durability of the fastening side of the nut 1 by having the flange portion 5. Furthermore, the maximum depth Dm of the recess 7 is shallow, such as less than 1.5 pitches, or even less than 1.0 pitch, minimizing the decrease in rigidity, etc., of the fastening side portion of the nut 1 despite the presence of a recess. As a result, the size of the recess 7, i.e., the radius dimension Rr of the outer end 7o of the recess 7, can be made larger than in the case of a deeper recess (recess), and it is thought that there is also a synergistic effect in that the burden on the threaded portion near the first thread of engagement can be reduced by the amount that the radius dimension Rr of the outer end 7o of the recess 7 can be made larger, even if the depth of the recess 7 is shallow.

[0059] Preferably, in the longitudinal section of the nut, the radius dimension Rr of the inner end 5si of the seating surface is smaller than the radius dimension Rn of the inscribed cylinder of the outer periphery of the square nut portion 4 (Rr < Rn). For example, the dimensional difference Lm between the radial dimension Lm from the root cylinder surface 3e of the thread to the outer end 7o of the recess 7 and the radial dimension Ln to the outer periphery (inscribed cylinder surface) of the square nut portion 4 (the dimensional difference between the radius dimension Rr of the outer end 7o of the recess 7 and the radius dimension Rn of the outer periphery (inscribed cylinder surface) of the square nut portion 4) Ld = (Ln - Lm = Rn - Rr) is 0.1 times or more (Ld ≥ 0.1Ln), 0.2 times or more (Ld ≥ 0.2Ln), 0.4 times or more (Ld ≥ 0.4Ln), and further 0.1 times or more and 0.5 times or less (0.2Ln ≤ Ld ≤ 0.5Ln) based on the radial dimension Ln from the root cylinder surface 3e of the thread of the square nut portion 4 to the inscribed cylinder surface of the outer periphery. Alternatively, the dimensional difference Ld is preferably 0.05 times or more (Ld ≥ 0.05P) of the thread pitch P, more preferably 0.1 times or more (Ld ≥ 0.1P), 0.15 times or more (Ld ≥ 0.15P), 0.2 times or more (Ld ≥ 0.2P) of the thread pitch P. Also, it may be 0.3 times or more (Ld ≥ 0.3P), 0.4 times or more (Ld ≥ 0.4P), 0.5 times or more (Ld ≥ 0.5P), 0.8 times or more (Ld ≥ 0.8P), 1.0 times or more (Ld ≥ 1.0P), etc. In one preferred embodiment, Ld is 0.1 times or more and 1.0 times or less (0.2P ≤ Ld ≤ 1.0P) of the thread pitch P. The fastening force received by the seating surface 5s moves axially outward from the side of the threaded hole 3 due to the presence of the recess 7. However, if there is a portion where the square nut portion 4 and the seating surface 5s overlap in the radial position, the square nut portion 4 can also receive the fastening force flowing axially outward from the seating surface 5s. Since the axial dimension and strength of the square nut portion 4 are larger than those of the flange portion 5, it is preferable from the viewpoint of suppressing the strength reduction of the nut 1 due to the recess 7 and preventing brittle fracture of the nut 1. The upper limit of the dimension Ld is related to both the radius dimension of the square nut portion 4 and the outer diameter dimension of the flange portion 5. For example, it may be 1.5 times or less (Ld ≤ 1.5P), 1.0 times or less (Ld ≤ 1.0P), 0.5 times or less (Ld ≤ 0.5P), 0.3 times or less (Ld ≤ 0.3), 0.2 times or less and more than 0.1 times (Ld ≥ 0.1P) of the thread pitch P.

[0060] (Shape of the recess) In the longitudinal section of the nut, the shape of the recess 7 may be, for example, a shape in which the axial depth (hereinafter simply referred to as "depth") increases from the boundary 7o, 5si between the recess 7 and the seating surface toward the screw hole 3 side, reaching a maximum depth Dm at the end on the screw hole 3 side, or a shape in which the maximum depth Dm is reached halfway from the boundary 7o between the recess 7 and the seating surface toward the screw hole 3 side and then the maximum depth Dm is maintained up to the screw hole 3 (a radial straight line in the longitudinal section), or a shape in which the depth D reaches the maximum depth Dm halfway from the boundary 7o between the recess 7 and the seating surface toward the screw hole 3 side and then decreases, or a shape in which there are two or more maximum depths halfway from the boundary 7o between the recess 7 and the seating surface toward the screw hole 3 side.

[0061] In the above shape, the shape of the boundary 7o side of the recess with the seating surface may be a shape that rises vertically from the seating surface 5 at the boundary 7o between the recess and the seating surface, or a shape that rises in a straight line extending to the open side at the boundary 7o between the recess and the seating surface at an angle other than a right angle to the seating surface, preferably an angle of 45° or less with respect to the axial direction, more preferably an angle of 15° or less. In one preferred embodiment, the shape may be such that the boundary 7o between the recess and the seating surface rises vertically from the seating surface 5 in the axial direction and then connects to a curve (particularly a stress relaxation curve) to further increase in depth.

[0062] The shape of the recess 7, in which the depth D decreases from the location of the maximum depth Dm of the recess 7 toward the axial end 7i, may be formed of any of a straight line, a curve (particularly a stress relaxation curve), or a combination of a curve (particularly a stress relaxation curve) and a straight line in the longitudinal section of the nut. The nut of the present disclosure may have a shape in which the depth of the recess 7 has one or more other maximum depths in addition to the maximum depth Dm.

[0063] The axial end 7i of the recess 7 has a positive depth D from the extension surface of the seating surface 5 to the open side. In one preferred embodiment, at least the radially closest portion of the axial end 7i of the recess 7 may be shaped to form a straight line (radial straight line) having the same depth in the nut vertical section. This is particularly preferred when the recess 7 has a shape in which the depth D decreases toward the screw hole 3 near the axial end 7i of the screw hole 3. Here, the same depth may be approximately the same. The radial dimension of the portion of the same depth immediately adjacent to the axial end 7i of the recess 7 is preferably 0.1 times or more, more preferably 0.15 times or more, 0.17 times or more, or 0.19 times or more of the thread pitch P, and may extend to the boundary 7o between the recess 7 and the seating surface with no particular upper limit, but may be 0.4 times or less, 0.3 times or less, or 0.25 times or less of the thread pitch P. In the longitudinal section of the nut, the depth may increase in a straight or curved manner from the boundary 7o between the recess 7 and the seat surface, and may have a portion of the same depth immediately adjacent to the axial end 7i of the recess 7. However, the depth of the portion in the radial direction immediately adjacent to the axial end 7i of the recess 7 may vary to an extent that it cannot be said to be uniform, and may be a straight line inclined relative to the radial direction.

[0064] A thread portion exists on the inside of the axial end 7i of the recess 7. In Figs. 2-1 and 2-2, the thread portion is cut in the axial direction deeper than the depth Di of the axial end 7i of the recess 7, but it does not have to be cut in the axial direction deeper than the depth Di, and in many cases, there is an incomplete thread portion from the axial end 7i to the complete thread portion (the depth of the beginning of the complete thread portion varies depending on the circumferential position of the screw hole 3). In general, as described below, the thread portion or the portion including the thread portion is chamfered, so that the incomplete thread portion or the portion including the incomplete thread portion is cut deeper than the depth Di at the chamfer angle passing through the radial straight line 7il or the axial end 7i of the recess 7. It may be chamfered toward the axial center through the curved end 7ci of the recess 7 in Fig. 4, and the portions 7il and 7i inside the curved end 7ci may be part of the chamfered portion, and there may be an incomplete thread portion of the thread further inside. In addition, the thread portion may have a radially extending straight line shape in the longitudinal section of the nut. When the thread portion has a radially straight line shape, the above-mentioned radially extending straight line portion immediately outside the axial end 7i of the recess 7 may or may not be present.

[0065] The shape of the recess 7 may be composed of only straight lines, only curves (particularly stress relaxation curves), or a combination of straight lines and curves in the nut longitudinal section, but either only curves or a combination of straight lines and curves is preferable. Even when the shape is basically composed of only straight lines, it is generally preferable that the recess 7 is composed of a stress relaxation curve, since the intersections between the straight lines may be small.

[0066] Optionally, a portion near the axial end 7i of the recess 7, a portion on the radially inner side of the recess, and a portion forming a spiral groove of the female thread may be chamfered (chamfer not shown). The shape of the chamfer may generally be the same as the chamfer (virtual chamfer) in a nut without a recess when the recess 7 is ignored. Referring to FIG. 5, the virtual chamfer is a straight line having an angle γ with respect to the axial direction, and the radial dimension from the cylindrical surface connecting the thread valleys in the extension surface of the seat surface is less than 0.5 times, particularly 0.4 times or less, or 0.3 times or less of the thread pitch P, and the angle γ is within the range of 30 to 60°, particularly about 45°, about 60°. The chamfer may be curved rather than linear in the nut longitudinal section. However, in the nut of the present disclosure, unlike the virtual chamfer shape shown in FIG. 5, since the recess 7 is present, the portion where the virtual chamfer and the recess 7 overlap is not chamfered, and only the remaining portion (if any) excluding the portion where the virtual chamfer and the recess 7 overlap from the shape of the virtual chamfer is chamfered. In addition, in the nut of the present disclosure, since the recess 7 is present near the screw hole 3, chamfering may be omitted. When the recess 7 is chamfered near the axial end 7i, the strength may be ensured by having a portion of the same depth as described above on the outer circumferential side of the chamfered portion, depending on the shape of the recess. When chamfered, the depth from the extension surface 5e of the seat surface of the portion forming the helical groove of the chamfered female thread is deeper than the depth Di of the recess 7 before chamfering at the portion 7i where the recess 7 before chamfering intersects with the thread root cylindrical surface 3e. Also, the chamfered portion of the axial end of the recess 7 is deeper than the depth Di of the recess at the portion 7i where the recess 7 before chamfering intersects with the thread root cylindrical surface 3e.

[0067] In a preferred embodiment, the depression 7 may have a depth Di (Di < Dm) at the axial end 7i of the depression, where the depth D gradually increases from the boundaries 7o, 5si with the seating surface towards the screw hole 3, reaches a maximum depth Dm, and then gradually decreases from the maximum depth Dm. At this time, in the nut longitudinal section, the shape of the depression 7 is preferably composed of a curve (particularly a stress relaxation curve) or a combination of a curve (particularly a stress relaxation curve) and a straight line. Optionally, the depth D may first increase linearly perpendicular to the seating surface or inclined with respect to the axial direction, and then gradually increase by a curve or a straight line to reach the maximum depth Dm. At this time, the depth D is preferably inclined, for example, vertically or at an angle of 45° or less, more preferably 15° or less, from the vertical towards the axial side. Also, in the vicinity of the axial end 7i of the depression, it is preferable from the viewpoint of the strength in the vicinity of the axial end 7i of the depression that a flat surface 7il having a constant depth Di and extending in the radial direction has a predetermined width Li (for example, about 0.2 pitch) in the radial direction. When the depression 7 has a depth Di smaller than the maximum depth Dm at the axial end 7i and the maximum depth Dm is at a position 7dm closer to the seating surface 5s than to the screw hole, it becomes more difficult for the flow of the fastening force from the seating surface 5s towards the open side of the flange portion 5 during fastening to enter the first engaged thread 3a from the portion 7dm having the maximum depth Dm, or the force transmission path from the boundaries 7o, 5si with the seating surface to the first engaged thread of the nut / bolt is lengthened, so that the load sharing ratio of the first engaged thread 3a can be further decreased.

[0068] The difference (Dm−Di)=Dd between the maximum depth Dm of the recess 7 and the depth Di at the axial end 7i is greater than 0 times and less than 1.5 times the thread pitch P (0 < Dd < 1.5P), preferably, it is 1.4 times or less (0 < Dd ≤ 1.4P), more preferably 0.1 times or more and 1.2 times or less, 1.0 times or less, or less than 1.0 times the thread pitch P (0.1 ≤ Dd ≤ 1.2P or 0.1 ≤ Dd ≤ 1.0P or 0.1 ≤ Dd < 1.0P), and further preferably 0.2 times or more and 0.8 times or less the thread pitch P (0.2P ≤ Dd ≤ 0.8P). Here, the depth Di at the axial end 7i of the recess 7 is the depth of the part (the part where the chamfered recess before chamfering intersects with the chamfer) defined above when the axial end 7i of the recess 7 is chamfered. Also, from the viewpoint of the manufacturability and workability of the recess 7, in a preferred embodiment, the dimension Dd=(Dm−Di) may be 0.2 times or more and 0.7 times or less (0.2 ≤ Dd ≤ 0.7P), and further preferably 0.4 times or more and 0.6 times or less (0.2 ≤ Dd ≤ 0.6P) the thread pitch P.

[0069] In a preferred embodiment, for the recess 7, when the part 7dm having the maximum depth Dm [when the part having the maximum depth Dm extends in the radial direction, it is the outer end in the radial direction of the part having the maximum depth Dm], the radial dimension Ldm from the thread groove cylindrical surface 3e of the bolt is greater than two-fifths of the radial dimension Lm from the axial end 7i of the recess to the boundary 5si with the seating surface, preferably greater than half, more preferably three-fifths, and further preferably greater than two-thirds of the radial dimension Lm. The reason is that even when having the same maximum depth Dm, it can make the flow of the force from the seating surface 5s towards the inside of the flange part 5 towards the open side during fastening, direct it towards the thread crest on the open side, and thus has the effect of further reducing the load sharing ratio on the first engaged thread.

[0070] The shape of the recess 7 may be composed of only straight lines in the nut longitudinal section, but is preferably composed of a stress relaxation curve or a combination of straight lines and stress relaxation curves. Referring to FIG. 4 as an example, the shape of the recess 7 preferably includes a first straight line portion 7l extending from the outer end 7o of the recess 7 toward the inner end 7i, preferably a first straight line portion 7l extending perpendicularly to the seating surface 5s or inclined at an angle of 45° or less, more preferably 15° or less, toward the axial side from the perpendicular to the seating surface 5s and toward the open side, a stress relaxation curve portion 7c extending beyond the portion 7dm of the maximum depth Dm from the end of the first straight line portion 7l, preferably a high-order curve portion, and a second straight line portion 7il extending in a substantially radial direction. In the nut longitudinal section, it is preferable to have the first straight line portion 7l rising in the axial direction or in a direction close to the axial direction from the position of the boundary 5si with the seating surface, since the effect of directing the force during fastening toward the open side can be increased. The stress relaxation curve portion 7c is preferably a high-order curve (part thereof) such as a circular arc, an elliptical arc, etc. As the stress relaxation curve portion 7c, an elliptical arc is particularly preferable because it can be a stress relaxation curve having a portion with a maximum depth Dm at a position closer to the inner end 5si of the seating surface, and is easy to manufacture / process.

[0071] Flange (continued) (Flange shape) The flange portion 5 is located on the fastening side of the square nut portion 4 of the nut body 2, and is a portion whose outer periphery radius (particularly Rfm) is larger than the circumscribed cylindrical surface radius Rno of the outer periphery of the square nut portion 4. Generally, a flange portion is referred to as a flange portion if it has a radius larger than the radius Rn of the flat portion (inscribed cylinder) in the axial extension of the flat portion of the square nut portion. In the present disclosure, the flange portion has a radius larger than the radius Rno of the maximum outer periphery (circumscribed cylinder) of the square nut portion.

[0072] The flange portion 5 has a seat 5s which is a flat surface extending radially at the fastening side end of the flange portion 5, a recess 7 which extends from the inner end 5si of the seat to the screw hole 3 and has a depth on the axially open side, and a flange outer periphery 5о which extends from the outer end 5so of the seat 5s to the boundary 5fm between the flange portion 5 and the square nut portion 4.

[0073] (Outer periphery of flange) By having the flange portion 5, the flange outer periphery 5о has an outer radius dimension (particularly the outermost radius Rfm) larger than the outer circumscribing cylindrical radius dimension Rnо of the square nut portion 4, and the outer end 5so of the bearing surface of the nut 1 can have an outer radius dimension Rr larger than the outer circumscribing cylindrical radius dimension Rnо of the square nut portion 4. By making the radial dimension (particularly Rfm) of the flange outer periphery 5о and the radius dimension Rsm of the outer end 5so of the bearing surface larger than the outer circumscribing cylindrical radius dimension Rnо of the square nut portion 4, it is possible to complement the strength of the nut fastening side portion and the area of ​​the bearing surface 5s that are reduced due to the recess 7, and it is possible to avoid excessive concentration of force applied to the bearing surface 5s during fastening, prevent damage to the nut, and enable the nut 1 to fully receive the required fastening force.

[0074] In a preferred embodiment, in the longitudinal section of the nut, the outer peripheral portion 5о of the flange portion 5 is composed of: an outermost flange portion 5om including the portion of the flange portion 5 whose radial dimension is the maximum diameter Rfm; a stress relaxation portion 5r composed of a stress relaxation curve connecting the outermost flange portion 5om and the seating surface 5s; and an inclined portion 5c connecting the outermost flange portion 5om and the square nut portion 4.

[0075] (Flange height) In a longitudinal section passing through the axis of the square nut portion 4 and the outer circumferential corner portion (herein also referred to as the "nut corner portion longitudinal section"), the flange portion 5 has a height (maximum height) Hfm in the axial direction from the extension surface 5e of the bearing surface at the boundary 5fm between the flange portion 5, particularly the inclined portion 5c, and the outer circumscribed cylindrical portion (portion of radial dimension Rnо) of the square nut portion 4. Here, in the nut corner portion longitudinal section, when the vicinity of the boundary is configured with a curve, the above-mentioned boundary 5fm may be considered as the intersection 5fm of the straight line of the flange portion 5, particularly the straight line of the inclined portion 5c, and the outer circumscribed cylindrical surface of the outer periphery of the square nut portion 4 in the nut longitudinal section. In the flat portion, not the corner portion, of the outer periphery of the square nut portion 4, the radius dimension is smaller than the radius dimension Rnо of the circumscribed cylinder of the outer periphery of the square nut portion 4, so the inclined portion 5c of the flange portion 5 can extend further toward the axially open side than the boundary 5fm with the outer periphery of the circumscribed cylinder of the square nut portion 4 (Fig. 1(b)(c)). However, the inclined portion may be removed in the portion on the axially open side of the boundary 5fm with the outer periphery of the square nut portion 4, and the height Hfm of the flange portion 5 is the axial dimension from the extension surface 5e of the seat surface to the intersection 5fm of the straight line of the inclined portion 5c of the flange portion 5 and the circumscribed cylinder surface of the outer periphery of the square nut portion 4. The height Hfm of the flange portion 5 may be more than half the height Hz of the nut 1, as long as the nut 1 can be tightened and loosened by using a tool such as a spanner on the square nut portion 4 on the open side of the flange portion 5. However, since the height Hfm of the flange portion 5 only needs to be able to deliver the stress received by the seat surface 5s of the flange portion 5 to the thread at the release end, it is preferable that the height Hfm is 0.2 times or more (0.2Hz≦Hfm) based on the total length Hz, which is the axial height of the nut 1, more preferably 0.25 times or more (0.25Hz≦Hfm), and even more preferably 0.3 times or more (0.3Hz≦Hfm). For example, the height Hfm may be 2 times or more (2P≦Hfm) of the thread pitch P, preferably 2.2 times or more (2.2P≦Hfm), more preferably 2.4 times or more (2.4P≦Hfm), and even more preferably 2.6 times or more (2.6≦Hfm) or 2.7 times or more (2.7≦Hfm).The height Hfm of the flange portion 5 is preferably 0.6 times or less (Hfm≦0.6Hz) based on the total length Hz of the nut 1, and may further be 0.5 times or less (Hfm≦0.5Hz), 0.45 times or less (Hfm≦0.45Hz), or 0.4 times or less (Hfm≦0.4Hz). For example, it may be 6 times or less (Hfm≦6P) of the thread pitch P, and more preferably 4 times or less (Hfm≦4P), 3.5 times or less (Hfm≦3.5P), or further 3.2 times or less (Hfm≦3.2P), or 3.0 times or less (Hfm≦3.0P). Since the height Hfm of the flange portion 5 has a predetermined size, the upward fastening force received by the seat surface 5s can be guided in a direction closer to the axial direction (vertical), i.e., farther toward the open side (toward the open side thread of the square nut portion), thereby making it possible to reduce the load sharing rate on the first thread of the interlocking thread.

[0076] (Outermost flange part) The outermost flange portion 5om is a portion having the maximum radial dimension Rfm in the nut body 2 and the flange portion 5, and is preferably configured as a straight line extending in the axial Z direction in the nut longitudinal section. However, in the nut longitudinal section, the outermost flange portion 5om may be a curved line convex toward the outer periphery, and in this case, the portion having the maximum radial dimension Rfm may be a point. In the nut longitudinal section, when the outermost flange portion 5om is connected to the inclined portion 5c by a curve, the intersection 5m between the axial straight line representing the maximum radial dimension Rfm of the outermost flange portion 5om and the extension line of the straight line of the inclined portion 5c may be considered as the boundary between the outermost flange portion 5om and the inclined portion 5c. The height Hf of the outermost flange portion 5om is the height of this boundary.

[0077] The radial dimension Rfm of the outermost flange portion 5om is larger than the circumscribed cylindrical radius dimension Rnо of the outer periphery of the square nut portion 4, and preferably the difference (Rfm-Rn) = Lfd between the dimension Rfm and the circumscribed cylindrical radius dimension Rn of the outer periphery of the square nut portion 4 is 0.4 times or more (Lfd≧0.4Ln), preferably 0.45 times or more (Lfd≧0.45Ln), and more preferably 0.5 times or more (Lfd≧0.5Ln) based on the radial dimension Ln from the thread root cylindrical surface 3e of the square nut portion 4 to the outer periphery inscribed cylindrical surface. Alternatively, the dimensional difference Lfd is 1.8 times or more (Lfd≧1.8P) of the thread pitch P, more preferably 2.0 times or more (Lfd≧2.0P), 2.1 times or more (Lfd≧2.1P), or 2.3 times or more [Lfd)≧2.3P], and may be 2.5 times or more [Lfd=(Rfm-Rn)≧2.5P]. If the radial dimension Rfm of the outermost flange portion (5om) is large, even if the nut 1 has a recess 7, the bearing surface (5s) Since the force received by the nut 1 can be received by the portion equivalent to the outermost periphery (5om) of the flange, which has a large cross-sectional area, the strength, durability, and life of the nut 1 that are reduced due to the recess 7 can be improved, and the nut can be prevented from being destroyed and its life can be extended. The upper limit of the dimension Lfd is not limited, but may be, for example, 3.5 times or less (Lfd≦3.5P), 3.0 times or less (Lfd≦3.0P), or 2.5 times or less (Lfd≦2.5P) of the thread pitch P.

[0078] When the nut 1 has a recess 7 at the fastening end, the portion of the nut 1 that can receive the fastening force at the fastening end is reduced due to the recess 7, but since the nut 1 has a flange portion, the rigidity, strength, and durability of the portion that receives the fastening force at the fastening end of the nut 1 can be ensured, and the nut 1 can maintain its rigidity, strength, and durability even with the recess 7. As an index representing the rigidity, strength, and durability of the fastening side (flange portion 5) of the nut 1 having the recess 7, the area Sm (=S3-S2) obtained by subtracting the axial side area S2 having the axial side end 5si of the bearing surface as an outer edge from the axial side area S3 having the flange outermost peripheral portion 5оm of the flange portion 5 of the nut 1 as an outer edge when viewing the nut from the axial direction Z can be considered. Referring to FIG. 2-1, in a typical example in which the outermost flange portion 5оm and the outer peripheral end 7о of the recess are both circular, the area S3 is the area of ​​a circle with the outermost flange portion 5оm as its periphery, i.e., the area of ​​a circle with a radius dimension Rfm, and S2 is the area of ​​a circle with the outer peripheral end 7о of the recess (the boundary between the recess and the seating surface) as its periphery, i.e., the area of ​​a circle with a radius dimension Rr. The area Sm is the area of ​​the annular portion (the portion with the radial dimension Ls+Lr) with the shaft side end 5si of the seating surface as its inner edge and the outermost flange portion 5оm as its outer edge. On the other hand, the area that serves as a comparison standard corresponding to the area Sm in a conventional square nut that does not have a flange portion or a recess is the area Ss=(Sn-S0) obtained by subtracting the area S0 of a circle with a radius dimension R0 of the thread groove 3b from the area Sn of a circle with a radius Rn of the outer peripheral inscribed cylinder of the square nut portion 4. In the nut 1 of the present disclosure, the area Sm is preferably 0.55 times or more (Sm≧0.55Ss) of the area Ss based on the area Ss, and may further be 0.6 times or more (Sm≧0.6Ss), 0.65 times or more (Sm≧0.65Ss), 0.7 times or more (Sm≧0.7Ss), 0.75 times or more (Sm≧0.75Ss), 0.8 times or more (Sm≧0.8Ss), 0.9 times or more (Sm≧0.9Ss), or 1.0 times or more (Sm≧1.0Ss).The upper limit of the area Sm is not particularly limited, but may be 1.5 times or less (Sm≦1.5Ss), 1.3 times or less (Sm≦1.3Ss), 1.2 times or less (Sm≦1.2Ss), 1.1 times or less (Sm≦1.1Ss), 1.0 times or less (Sm≦1.0Ss), 0.9 times or less (Sm≦0.9Ss), or 0.8 times or less (S≦0.8Ss). In a square nut that does not have a flange portion, if a notch (recess) is provided on the bearing surface to reduce the stress applied to the first thread of the thread engagement, in order to make the effect of the recess effective, it is desirable to make the outer end of the notch (recess) as far away as possible in the radial direction from the thread groove, but if this is done, the rigidity of the fastening side of the nut will correspondingly decrease, making it unable to withstand the necessary fastening force and making the nut prone to buckling. In contrast, the nut 1 of the present disclosure has a flange portion 5, which allows the radial dimension Lm of the recess 7 to be the size necessary to sufficiently reduce the stress on the first thread engagement, while still allowing the nut 1 to have a sufficient area Sm of the flange portion and also the area S of the seating surface 5s, thereby ensuring the rigidity and durability of the nut 1.

[0079] When the flange portion 5 has a stress relief portion 5r at the fastening end, the area S of the seating surface is reduced by the amount corresponding to the stress relief portion 5r, but the fastening stress received by the seating surface 5s is transferred to the flange outermost periphery 5оm or the stress relief portion 5r, which is located on the outer periphery side of the seating surface 5s, so even when the stress relief portion 5r is present, the dimensions of the flange outermost periphery 5оm are still important for the rigidity of the flange portion. Furthermore, even in the conventional square nut, which is the comparison standard, a stress relief portion is usually provided on the outer periphery side of the nut seating surface, so the area Ss is appropriate as the comparison standard when considering the area Sm, regardless of whether the nut has a stress relief portion or not. The area S of the seating surface 5s assuming that the flange portion 5 has the stress relief portion 5r will be described later.

[0080] In the nut 1 of the present disclosure, the depth Dm of the recess 7 is shallow, so that the reduction in the rigidity, strength, and durability of the nut body 2, particularly the fastening side portion, due to the formation of the recess 7 can be minimized, and as a result, the size of the flange portion 5, particularly the size of the outermost flange portion 5om, which is added to compensate for the reduction in the rigidity of the nut body 2, can also be minimized. In the nut having deep notches or recesses of the prior art, in order to compensate for the large reduction in the rigidity of the nut body due to the formation of deep notches or recesses, the rigidity of the structure of the legs and the like provided on the outer periphery of the deep recesses or recesses must also be large, and the shape of the structure of the deep notches or recesses and the legs and the like on the outer periphery must be large and complicated, which leads to problems such as difficulty in processing, increased manufacturing costs, and reduced practicality. The flange portion 5 of the nut 1 of the present disclosure can be a simple flange portion, and does not need to have a structure like the large and complicated legs in the prior art.

[0081] (Shoulder height of flange) The flange outermost portion 5om has a height Hf, which is an axial dimension from the extension surface 5e of the seating surface at the boundary 5m between the flange outermost portion 5om and the inclined portion 5c in the nut longitudinal section. In the following disclosure, unless otherwise specified, "height" refers to the axial dimension from the seating surface 5s or the extension surface 5e of the seating surface. Here, since the boundary 5m between the flange outermost portion 5om and the inclined portion 5c is generally curved, it may be considered to be the intersection of an axial straight line having the maximum diameter Rfm of the flange outermost portion 5om and an extension line of the straight line of the inclined portion 5c. There is no reason not to include a straight line portion in the inclined portion 5c, but if it is a curve such as an S-shape, a straight line (the most approximate straight line) representing the inclination of the entire curve may be calculated, and the straight line may be used as the inclination of the inclined portion 5c. In a preferred embodiment, the height Hf of the outermost flange portion 5om (flange shoulder height) is greater than the maximum depth Dm of the recess 7 (Hf>Dm), and the shoulder height Hf of the flange portion is preferably 1.1 times or more (Hf≧1.1Dm), more preferably 1.5 times or more (Hf≧1.5Dm), or even 1.8 times or more (Hf≧1.8Dm) based on the maximum depth Dm of the recess (7), or may be 1.2 times or more (Hf≧1.2P), more preferably 1.3 times or more (Hf≧1.3P), 1.4 times or more (Hf≧1.4P), or even 1.44 times or more (Hf≧1.44P), 1.5 times or more (Hf≧1.5P), or 1.6 times or more (Hf≧1.6P). By having the height Hf of the flange outermost periphery (5om) have a predetermined size, it becomes possible for the flange portion 5 to receive the fastening force at the time of fastening higher outside the recess 7. The upper limit of the height (flange shoulder height) Hf of the flange outermost periphery 5om is not limited, but may be, for example, 3.0 times or less (Lfd≦3.0P), 2.5 times or less (Lfd≦2.5P), or 2.0 times or less (Lfd≦2.0P) of the thread pitch P.

[0082] In the nut 1 of the present disclosure, since the depth Dm of the recess 7 is shallow, the reduction in the rigidity, strength, and durability of the nut body 2 due to the formation of the recess 7 can be minimized, and furthermore, since the depth Dm of the recess 7 is shallow, it is clear that the shoulder height Hf of the flange portion 5 added to compensate for the reduction in the rigidity, etc. of the nut body 2 can also be correspondingly minimized. Furthermore, since the depth Dm of the recess 7 is extremely shallow in the nut 1 of the present disclosure, the nut body 2 having the recess 7 has a shape and structure that is almost the same as when the recess 7 is not present, and the stress propagating from the seat surface 5s having the flange portion 5 to the shaft side and the thread groove side also reaches the robust shaft portion of the nut body on the release side of the shallow recess 7 at the closest distance, so that the structure of the portion on the outer periphery side of the recess 7 of the flange portion 5 does not need to be a large and complex rigid structure like the leg portion disclosed in the prior art, and in this sense, the structure of the flange portion 5 can be simple and the shoulder height Hf can also be minimized.

[0083] (Stress relief part of flange) The part connecting the seating surface 5s of the flange portion 5 and the outermost flange portion 5om may be a straight line extending in the axial direction in the nut longitudinal section, but is preferably a stress relaxation part 5r constituted by a part of a stress relaxation curve, typically a circular arc, an ellipse, or a high-order curve. The boundary of the stress relaxation part 5r on the seating surface 5s side is a part that contacts the seating surface 5s, but the boundary on the outermost flange portion 5om side may be a part where the radial dimension of the stress relaxation part 5r reaches the maximum radial dimension Rfm. If the stress relaxation part 5r of the flange portion 5, i.e., the part where the outer periphery of the flange portion 5 contacts the seating surface 5s, is constituted by a stress relaxation curved surface, it is possible to prevent the flange portion 5 from sinking into the fastened object during fastening, resulting in insufficient fastening force, if the outermost periphery of the seating surface 5s of the flange portion 5 is not a stress relaxation curved surface. In addition, the presence of this stress relaxation curved surface prevents the fastened member from being scratched even when the fastened member vibrates up and down (in the axial direction), and reduces the aggressiveness to the fastened member. The radial dimension (Rfm-Rsm)=Lr of the stress relaxation curve from the outer end 5so of the bearing surface to the outermost peripheral portion 5om of the flange is preferably 0.15 times or more (Lr≧0.15Ln), more preferably 0.2 times or more (Lr≧0.2Ln), or 0.25 times or more (Lr≧0.25Ln) based on the radial dimension Ln from the thread valley cylindrical surface 3e of the square nut part 4 to the outer peripheral inscribed cylindrical surface. Alternatively, the radial dimension Lr may be 0.5 times or more (Lr≧0.5P) of the pitch P, but is preferably 0.7 times or more (Lr≧0.7P), 0.8 times or more (Lr≧0.8P), 0.9 times or more, 0.95 times or more (Lr≧0.95P), or 1.0 times or more (Lr≧1.0P) of the pitch P. The dimension Lr is, for example, preferably 1.1 times or less the thread pitch P (Lr≦1.1P), and may be 1.0 times or less (Lr≦1.0P), 0.95 times or less (Lr≦0.95P), or 0.9 times or less (Lr≦0.9P).

[0084] (slanted part) In a preferred embodiment, the flange portion 5 has an inclined portion 5c connecting the flange outermost periphery portion 5om and the square nut portion 4. The inclined portion 5c of the flange portion 5 has an angle θ with respect to the radial direction in the nut longitudinal section. The angle θ is not particularly limited, but may be, for example, 10° to 60° (10°≦θ≦60°), preferably 15° to 45° (15°≦θ≦45°), more preferably 20° to 40° (20°≦θ≦40°), further 25° to 35° (25°≦θ≦35°), and particularly more than 25° to 35° (25°<θ≦35°). In the nut longitudinal section, the angle θ of the inclined portion 5c of the flange portion 5 is the angle that the straight line of the inclined portion 5c forms with respect to the radial direction, starting from the intersection 5m of the straight line of the inclined portion 5c and the axial straight line 5mo representing the maximum radial dimension Rfm of the flange outermost periphery portion 5om described later. It is preferable for reducing the load sharing rate of the first meshing peak when the inclined portion 5c of the flange portion 5 has such an angle θ. When the inclined portion 5c of the flange portion 5 has such an angle θ, particularly when the angle θ is large, the flow of fastening force flowing from the seat surface 5s to the opening side can be sent farther to the opening side, which is thought to be the direction that can further reduce the load sharing rate of the first meshing peak.

[0085] (Seat) The seating surface 5s is a flat surface (plane) extending in the radial direction at the fastening side end of the nut body 2 and the flange portion 5. In the nut 1 of the present disclosure, the outer end 5so of the seating surface 5s is the boundary between the seating surface 5s and the flange outer periphery 5о, and the inner end 5si of the seating surface 5s is the boundary between the seating surface 5s and the recess 7. In a preferred embodiment, the flange outer periphery 5о has a stress relief portion 5r in the boundary region with the seating surface 5s, so that the outer end 5so of the seating surface 5s is the boundary 5so between the seating surface 5s and the stress relief portion 5r.

[0086] In a preferred embodiment, the seat surface 5s may be an annular flat surface having the boundary 5si with the annular depression 7 as the inner circumference and the radially outer end 5so of the seat surface 5s as the outer circumference. The inner radius dimension Rr of the seat surface 5s is the radius dimension of the inner end 5si of the seat surface 5s, that is, the boundary between the seat surface 5s and the depression 7, and is also the radius dimension of the outer end 7o of the depression 7. The inner radius dimension Rr of the depression 7 is defined as R0, which is the thread root radius that is the radius dimension of the thread root cylindrical surface 3e, and Lm is the radial dimension from the thread root cylindrical surface 3e to the outer end 7o of the depression 7. Then, they are in the relationship of Rr = (R0 + Lm). The outer radial dimension Lm of the depression 7 is, as described above, preferably greater than 1.0 times the thread pitch P (1.0P < Lm), and the radial dimension Lm is smaller than the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut portion (4) to the outer circumferential inscribed cylindrical surface (Lm < Ln). More preferably, the radial dimension Lm is 1.5 times or more the thread pitch P (1.5P ≦ Lm), more preferably 2.0 times or more (2.0P ≦ Lm), 2.5 times or more (2.5P ≦ Lm), 2.8 times or more (2.8P ≦ Lm), or alternatively, the radial dimension Lm is 0.5 times or more (Lm ≧ 0.5Ln), 0.7 times or more (Lm ≧ 0.7Ln), 0.8 times or more (Lm ≧ 0.8Ln), 0.9 times or more (Lm ≧ 0.9Ln) based on the radial dimension Ln.

[0087] When there is no stress relief portion 5r or the stress relief portion 5r is small, the outer radial dimension of the bearing surface (5s) may be considered to be equal to the outer radial dimension (particularly Rfm) of the flange outer peripheral portion 5o. However, in a preferred embodiment, the outer radial dimension of the bearing surface 5s is the radial dimension Rsm of the boundary 5so between the bearing surface 5s and the stress relief portion 5r, that is, the dimension Rsm obtained by subtracting the radial dimension Lr of the stress relief portion 5r from the radial dimension Rfm of the outermost peripheral portion of the flange portion 5. In this case, it is preferable that the outer radial dimension Rsm of the bearing surface 5s is larger than the radial dimension Rn of the square nut portion 4. More preferably, the dimensional difference Lsd between the outer radial dimension Rsm of the bearing surface 5s and the radial dimension Rn of the square nut portion 4 is 0.5 times or more (Lsd≧0.5P), 0.7 times or more (Lsd≧0.7P), or even 0.8 times or more (Lsd≧0.8P) of the thread pitch P. This is because the flow of the fastening force received by the seating surface 5s and directed toward the open side is firmly received by the flange portion 5 located on the axially open side of the seating surface 5s.

[0088] The radial dimension Ls of the bearing surface 5s from the outer end 5so to the inner end 5si in the radial direction of the bearing surface 5s is 0.3 times or more (Ls≧0.3Ln) based on the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut part (4) to the outer peripheral inscribed cylindrical surface, and may be preferably 0.4 times or more (Ls≧0.4Ln), and further 0.45 times or more (Ls≧0.45Ln). Alternatively, the radial dimension Ls of the bearing surface 5s is preferably 1.0 times or more (Ls≧1.0P) of the thread pitch P, and may be 1.2 times or more (Ls≧1.2P), further 1.5 times or more (Ls≧1.5P), 1.7 times or more (Ls≧1.7P), or 1.8 times or more (Ls≧1.8P). Although the seat surface 5s on which the nut 1 should receive the fastening force at the fastening side end is reduced due to the recess 7, it is preferable that the nut 1 has a flange portion and the radial dimension Ls of the seat surface 5s is within the above range, since the strength of the seat surface 5s portion receiving the fastening force can be maintained. The radial dimension Ls of the seat surface 5s is preferably 4.0 times or less (Ls≦4.0P) of the thread pitch P, and may be 3.0 times or less (Ls≦3.0P), 2.5 times or less (Ls≦2.5P), or even 2.0 times or less (Ls≦2.0P). Since the nut 1 of the present disclosure has a flange portion 5, the size and area of ​​the seat surface (5s) can be set to the required size and area.

[0089] For the same reason, as already mentioned, it is preferable that the area Sm (=S3-S2) obtained by subtracting the axial side area S2 having the axial side end 5si of the bearing surface as an outer edge from the axial side area S3 having the outer edge of the flange outermost peripheral portion 5оm of the flange portion 5 of the nut 1 when viewing the nut in the axial direction Z is a predetermined size based on the area Ss corresponding to the above area Sm of a conventional nut that does not have a flange portion, that is, the area Ss=(Sn-S0) obtained by subtracting the area S0 of a circle having a radius R0 of the thread groove 3b from the area Sn of the circle having a radius Rn of the outer periphery of the inscribed cylinder of the square nut portion 4.

[0090] For the same reason, the area S of the seat 5s of the nut 1 of the present disclosure is preferably 0.55 times or more (S≧0.55Ss), 0.6 times or more (S≧0.6Ss), and further 0.65 times or more (S≧0.65Ss), 0.7 times or more (S≧0.7Ss), 0.75 times or more (S≧0.75Ss), 0.8 times or more (S≧0.8Ss), 0.9 times or more (S≧0.9Ss), 1.0 times or more (S≧1.0Ss), based on the area Ss of the seat 5s of a square nut that does not have a flange portion, that is, the area Ss=(Sn-S0) obtained by subtracting the area S0 of a circle whose radius is the radius dimension R0 of the thread groove (3b) from the area Sn of a circle whose radius is the inscribed cylinder radius dimension Rn of the outer periphery of the square nut portion 4. The area S of the bearing surface (5s) may be 1.5 times or less (S≦1.5Ss), 1.3 times or less (S≦1.3Ss), 1.2 times or less (S≦1.2Ss), 1.1 times or less (S≦1.1Ss), 1.0 times or less (S≦1.0Ss), 0.9 times or less (S≦0.9Ss), or 0.8 times or less (S≦0.8Ss). Here, the area S of the bearing surface 5s of the nut 1 may be measured by actually measuring the area of ​​the bearing surface 5s, but in the case of a typical annular bearing surface, it is the area of ​​the annular part obtained by subtracting the area S2 of the circle having a radius of the dimension Rr from the axis to the shaft side end 5si of the bearing surface 5s, from the area S1 of the circle having a radius of the dimension Rsm from the axis to the outer peripheral end 5sо of the bearing surface 5s. When the flange portion 5 has a stress relief portion 5r, the area S of the seat surface 5s excludes the cross-sectional area of ​​the stress relief portion 5r, but even conventional nuts that do not have a flange portion usually have a stress relief portion, and the area of ​​the seat surface of the conventional nut is smaller than the reference area Ss. However, since the dimensions of the stress relief portion of the conventional nut are not uniform, the above area Ss is used as the comparison standard for the area S of the seat surface instead of the area of ​​the seat surface of the conventional nut. Note that the fastening stress received by the seat surface 5s also flows around the stress relief portion 5r on the outside of the seat surface 5s, so the presence of the stress relief portion 5r contributes to improving the rigidity, strength, and durability of the flange portion 5. For these reasons, it should be noted that in a normal nut 1 in which the flange portion 5 has a stress relief portion 5r, the flange portion 5 contributes substantially to ensuring the rigidity, strength, and durability of the nut 1 more than the numerical value of the area S of the seat surface 5s.In a square nut without a flange portion, if a recess is provided on the seating surface to reduce the stress applied to the first thread of the thread engagement, the outer end of the recess must be as far away from the thread as possible to make the effect of the recess effective, but then the area of ​​the seating surface of the nut is rapidly reduced, and the nut cannot receive the necessary fastening force and is prone to buckling. In contrast, the nut 1 of the present disclosure has a flange portion 5, so that the radial dimension Lm of the recess 7 is set to a size necessary to sufficiently reduce the stress applied to the first thread engagement, while the nut 1 can have a sufficient seating surface area S, and the rigidity and durability of the nut 1 can be ensured. Furthermore, since the depth Dm of the recess 7 of the nut 1 of the present disclosure is shallow, the reduction in the rigidity of the nut body 2 is minimal, and the fastening stress is immediately propagated from the seating surface 5s to the robust shaft side on the open side of the shallow recess 7 of the nut body 2, the size of the flange portion 5 and the area S of the seating surface 5s can be smaller than expected.

[0091] Additional rigidity on the open side In a preferred embodiment, the nut 1 of the present disclosure has an open-side additional rigidity portion 6 at the open-side end of the nut body 2, and the radially inner surface (axial side surface; 6is) of the open-side additional rigidity portion 6 has a radial dimension R1 larger than the radial dimension R0 of the thread groove cylindrical surface 3e, and the axial dimension Ha of the open-side additional rigidity portion 6 is 0.5 times or more the thread pitch P (Ha≧0.5P). The open-side additional rigidity portion 6 is the portion shown by hatching and sand in Figures 2 and 2-3.

[0092] The present inventors have discovered that when the nut 1 has an open-side additional rigidity portion 6, the load sharing rate of the first meshing thread can be reduced more than when the nut does not have the open-side additional rigidity portion 6. When the open-side additional rigidity portion 6 is provided, the threads on the open-side end side can more firmly withstand the fastening force from the seat surface (5s) compared to when the nut does not have the open-side additional rigidity portion 6. This increases the load sharing rate of the open-side thread and reduces the load sharing rate of the first meshing thread.

[0093] An example of the nut 1 of the present disclosure having an open-side additional rigidity portion 6 will be described with reference to FIG. 2-3. FIG. 2-3 is a partially enlarged longitudinal sectional view of the axial open side and radial axial side of the nut body 2 or the square nut portion 4. In FIG. 2-3, the square nut portion 4 has an open-side end surface 6s extending radially at the open-side end, and a radially inner surface 6is located radially inside and facing the screw hole 3. The inner surface 6is of the square nut portion 4 may be composed of, in the nut longitudinal section, an inclined straight line portion A1 which is a straight line inclined with respect to the axial direction, a first curved line portion A2 which is a convex curve on the upper left side (the nut body side) of FIG. 2-3, a horizontal straight line portion A3 which is a straight line extending in the axial direction, and a second straight line or curved line portion A4 whose radial dimension expands toward the open side of the open-side end of the horizontal straight line portion A3, in that order. In this way, in the nut longitudinal section, the inner surface 6is of the part on the axial open side and the radial axial side of the square nut part 4 is preferably configured as a stress relief line consisting of straight lines and curved lines. Figures 2-3 do not limit the present disclosure, and for example, the inclined straight line part A1, the horizontal straight line part A3, and the second straight line or curved line part A4 may be omitted. The shape of the first curved line part A2 is arbitrary. The second straight line or curved line part A4 may be a straight line or a curved line, or may be a combination of a curved line and an inclined straight line.

[0094] The example in Figure 2-3 is merely one example and is not limiting, but the fastening side end 6ii of the portion where the radius dimension R1 is larger than the thread root radius dimension R0 is located near the boundary between the inclined straight portion A1 and the first curved portion A2, so that the portion where the radius dimension R1 is smaller than the thread root radius dimension R0 is the inclined straight portion A1, and the portion where the radius dimension R1 is larger than the thread root radius dimension R0 is the first curved portion A2, the horizontal straight portion A3, and the second straight or curved portion A4.

[0095] However, the fastening side end 6ii of the open-side additional rigidity portion 6, where the radius R1 is greater than the thread root radius R0, may be in the inclined straight line portion A1 or the first curved line portion A2. It may also be in the second straight line or curved line portion A4. Of the portion where the radius R1 is greater than the thread root half radius R0, the position where the axial dimension from the fastening side is 0.5 times the thread pitch P is preferably in the first curved line portion A2 or the horizontal straight line portion A3, but may be in the inclined straight line portion A1 or the second straight line or curved line portion A4.

[0096] The axial dimension Ha of the opening side additional rigidity portion 6 may be 0.5 times or more (Ha≧0.5P) of the thread pitch P, more preferably more than 0.5 times (Ha>0.5P), 0.6 times or more (Ha≧0.6P), 0.7 times or more (Ha≧0.7P), and even more preferably 0.8 times or more (Ha≧0.8P), or 0.9 times or more (Ha≧0.9P). When the axial dimension Ha of the opening side additional rigidity portion 6 is larger than a predetermined dimension, it has the effect of further reducing the load sharing rate of the first meshing thread.

[0097] The axial dimension Ha of the opening-side additional rigidity portion 6 may be 2.0 times or less (Ha≦2.0P), 1.5 times or less (Ha≦1.5P), or even 1.0 times or less (Ha≦1.0P) the thread pitch P. The above-mentioned effect of the opening-side additional rigidity portion 6 is greater as the axial dimension Ha is larger, so there is no theoretical upper limit, but the above-mentioned effect gradually saturates, so the upper limit may be determined in relation to the practical dimension of the nut (nut height).

[0098] In the nut longitudinal section, the radius R2 of the horizontal straight portion A3 of the opening side additional rigidity portion 6 may be larger than the thread root radius R0 to avoid contact with the bolt, but preferably the dimensional difference Lad=(R2-R0) from the thread root radius R0 is 0.1 times the thread pitch P or more (Lad≧0.1P), more preferably 0.2 times the thread pitch P or more (Lad≧0.1P). The dimensional difference Lad is preferably 0.3 times the thread pitch P or less (Lad≦0.3P), more preferably 0.2 times the thread pitch P or less (Lad≦0.1P). If the radius of the inner surface of the opening side additional rigidity portion 6 is in such a range, it is preferable for the effect of the opening side additional rigidity portion 6 (reduction of the load sharing rate of the first meshing thread).

[0099] The inclination angle β of the inclined straight portion A1 may be about 40° to 70°, about 45° to 60°, and particularly about 45°, based on the axis in the nut longitudinal section. The inclined straight portion A1 may be only a portion where the radial dimension R1 is smaller than the thread root radius R0, as shown in FIG. 2-3, but may also include a portion where the radial dimension R1 is larger than the thread root radius R0. The portion of the inclined straight portion A1 where the radial dimension R1 is smaller than the thread root radius R0 generally extends from the radial dimension of the thread root to the radial dimension of the thread depending on the position on the circumference. The axial dimension B of the portion of the inclined straight portion A1 where the radial dimension R1 is smaller than the thread root radius R0 is arbitrary, but is usually about 0.5 times the thread pitch P.

[0100] The first curved portion A2 may be a stress relaxation curve connecting the inclined straight portion A1 and the horizontal straight portion A3, for example, a circular arc or an elliptical arc, and its axial dimension Hai may be a dimension depending on the curve when connecting the specific inclined straight portion A1 and the horizontal straight portion A3 with a natural stress relaxation curve. If the curvature of the first curved portion A2 is too large (the radius of curvature is too small), the radius dimension R2 of the horizontal straight portion A3 cannot be large, but if the curvature is too small, the radius dimension R2 of the horizontal straight portion A3 becomes larger than necessary, so it is only necessary to take these factors into consideration when determining the dimension. The inclined straight portion A1 generally rises at a large angle of about 45° to 60° with respect to the axial direction, so even if the curvature is relatively small, it can be connected to the horizontal straight portion A3 as a stress relaxation curve.

[0101] The second straight line or curved portion A4 need only make the intersection between the inner surface 6is of the open-side additional rigidity portion 6 and the open-side end surface 6s curved rather than being a corner or acute angle, and does not need to have a small curvature (large radius of curvature).

[0102] When the nut 1 of the present disclosure has the opening-side additional rigidity portion 6, the height (total height) Hz of the nut 1, i.e., the dimension in the axial direction of the nut 1 (the dimension from the fastening-side end face to the opening-side end face) may be the height of the nut specified in the standard. Here, the standard may be a standard such as JIS, ISO, or EN, particularly a JIS standard. The standard specifies the relationship between the screw hole diameter of the nut and the nut height, so that the height of the nut is determined when the screw hole diameter of the nut is determined.

[0103] In a preferred embodiment, the height (overall height) Hz of the nut 1 of the present disclosure is greater than the height of the nut defined in the standard specification. It is preferable that the nut 1 has a nut height greater than the height of the nut defined in the standard specification and has the open-side additional rigidity portion 6 defined above. When the nut 1 has a nut height greater than the standard and has the open-side additional rigidity portion 6, the above-described effect of the open-side additional rigidity portion 6, that is, it acts to flow the fastening force flow to the open side without a thread groove near the open-side end, contributes to reducing the burden fraction rate of the first engagement, and also contributes to reducing the burden fraction rate of the first engagement by increasing the number of threads of the nut. The difference Hd = (Hz - Hzs) between the height Hz of the nut 1 and the height Hzs of the nut defined in the standard specification is a positive value (Hd > 0), or may be 0.1 times or more (Hd ≥ 0.1P), 0.3 times or more (Hd ≥ 0.3P) of the thread pitch P, preferably 0.5 times or more (Hd ≥ 0.5P), 0.6 times or more (Hd ≥ 0.6P), 0.7 times or more (Hd ≥ 0.7P), further 0.8 times or more (Hd ≥ 0.8P), 0.9 times or more (Hd ≥ 0.9P) of the thread pitch P.

[0104] (Diameter-reducing portion) Further, the present inventor has found that in one preferred embodiment, the nut body 2 can have a diameter-reducing portion 8 at the open-side end, regardless of whether it has the open-side additional rigidity portion 6, and particularly when it has the open-side additional rigidity portion 6, the radial outer dimension R3 (outer peripheral surface) at the open-side end is smaller than the radius dimension Rn of the inscribed cylinder of the outer periphery of the square nut portion 4 (R3 < Rn). In other words, the shape of the radial outer surface (outer peripheral surface) of the square nut portion 4 corresponding to the open-side additional rigidity portion 6 can be made smaller than the radius dimension Rn of the inscribed cylinder of the outer periphery of the square nut portion 4 in the nut longitudinal section, and particularly can be composed of a stress relaxation curve in the nut longitudinal section. Thereby, there is an effect that problems such as safety when the open-side outer peripheral portion of the nut is an acute angle or the like can be solved.

[0105] The shape of the outer circumferential side of the reduced diameter portion 8 at the open end of the square nut portion 4 may be any stress relief shape represented by a stress relief curve or a combination of a stress relief curve and a straight line in a cross-sectional view of the nut, but may simply be an arc shape.

[0106] The axial dimension Hc of the reduced diameter portion 8 may be, for example, 2.5 pitches or less, 2.0 pitches or less, or 1.0 pitches or less of the square nut portion 4, or 0.5 pitches or more, 1.0 pitches or more, 1.2 pitches or more, or 1.5 pitches or more. The reduced diameter portion 8 reduces the axial dimension of the flat portion of the outer periphery of the hexagonal nut portion 4, thereby reducing the area of ​​the engagement portion when the nut is tightened with a wrench or the like. Therefore, even if the reduced diameter portion 8 is provided, it is sufficient to solve problems such as safety when the open side outer periphery of the nut has an acute angle. Since the open side end is often chamfered even in conventional nuts, the reduced diameter portion 8 does not need to be chamfered or more.

[0107] Combination of Structures Regarding the nut 1 of the present disclosure, although the combinations of the structures (shapes, dimensions, etc.) in the various embodiments described above are not specifically described, it is clear that they can be adopted in any combination. For example, the shape and dimensions of the recess 7 of the nut 1, the shape and dimensions of the flange portion 5, and the shape and dimensions of the open-side additional rigidity portion 6 are described as structures, and the requirements described as structures of particularly preferred embodiments, can be combined in any combination to realize the characteristics and effects of each embodiment in an additive or composite manner.

[0108] Nut material and strength The material and strength of the nut are not particularly limited, but are specified in standards such as JIS, and the material and strength of the nut of the standard can be adopted in the nut 1 of the present disclosure. In particular, as nuts used in severe environments in which the nuts of the present disclosure are preferably used, the JIS (as of 2022) has six nut strength classes, 5, 6, 8, 9, 10, and 12, but the nuts of the present disclosure are particularly useful in nuts with four strength classes, 8, 9, 10, and 12, three classes, 9, 10, and 12, two classes, 10 and 12, and one class, 12.

[0109] The specific material is not particularly limited as long as it satisfies the above strength classification in a preferred embodiment, but examples thereof include ordinary steel, quenched and tempered carbon steel (SCM435-H, SCM420-H, S45C-H, etc.), stainless steel and other alloy steels, high-strength stainless steel (SUS630 (Fe-17Cr-4Ni-4Cu-0.2Nb)), etc. For example, titanium alloys (Ti-6Al-4V, Ti-15Al-3Cr-3Sn, Ti3(Nb,Ta,V)+(Zr,Hf)+O; superelastic low Young's modulus titanium alloys) are preferred materials.

[0110] Nut manufacturing The nut 1 of the present disclosure can basically be the same as conventionally known nuts except for the recess 7, and therefore can be manufactured by a method in which the outer shape of the nut (a nut having no hole, threads, or recess) is manufactured in a similar manner to conventionally known nuts, and then the recess 7 is formed in the hole and the flange side end face by cutting, and then the threads are created; or by a method in which a nut forging die for creating the recess is used when manufacturing a nut using a forging die in a similar manner to conventionally known nuts.

[0111] Forming the recess 7 on the flange side end face of the nut by cutting can be easily performed using, for example, a lathe. In particular, in the nut 1 of the present disclosure, the recess 7 is shallow and has a simple shape, so the cutting process is also easy and damage to the cutting tool is the same as when there is no recess.

[0112] Manufacturing a forging die for a nut having the recess of the nut 1 of the present disclosure can be easily carried out by a conventional hot forging die manufacturing method or cold forging die manufacturing method, since the recess 7 is shallow and has a simple shape, and since the recess 7 is shallow and has a simple shape, manufacturing the forging die is also easy.

[0113] Also, when manufacturing a nut of a preferred embodiment of the nut 1 of the present disclosure, for example, the shape of the open-side additional rigidity portion 6 is simply an extension of the open-side end portion of the nut body 2, and the shape and dimensions of the flange portion 5 can be changed simply and only slightly, so that they can be made without substantial influence on the conventional manufacturing method. Also, with regard to machine tools such as lathes and tools such as forging dies for manufacturing the nuts of the preferred embodiment, the changes in shape and dimensions are simple and slight, so there is no risk of the tool life being shortened, and the manufacturing of the nut itself is easy.

[0114] The nut 1 of the present disclosure can be manufactured without making major changes to the manufacturing method of conventional nuts, with only minor changes in its shape and dimensions, and its shape being simple rather than complex, so there is no need to worry about damage to tools during the processing process or damage to forging dies, etc., and it is possible to achieve productivity and tool life equivalent to that of conventional nuts.

[0115] Furthermore, although the nut 1 of the present disclosure can achieve productivity and tool life equivalent to those of conventional nuts, it can significantly reduce the load share of the first meshing thread thread (by approximately 20 to 26%) compared to nuts that have been commercially manufactured and used in the past, thereby significantly extending the fatigue life of bolt and nut fasteners in environments with large load fluctuations. The relationship between fatigue failure life (number of cycles Nf) and external load (stress amplitude σr) can generally be expressed by the following empirical formula. Nf (σr) b =C (In the formula, Nf: Number of repeated loads until fatigue failure σr: stress amplitude of the load b: Stress index (generally 3 to 5) C: material constant) Therefore, Nf can be increased by the third to fifth powers of σr. For example, when σr decreases by 20%, it becomes 0.8×0.8×0.8×0.8=0.4096 (4th power of 0.8), and C is the same, so the formula becomes Nf=C / (σr). b When this is transformed, Nf is expected to be the reciprocal of 0.4096 (2.4414), or about 2.4 times. In the above formula, when b = 3, it becomes 1.953 times, and when σr decreases by 10% × b = 3, it becomes 0.9 3 =0.729, and the reciprocal is 1.3717, so the expected life Hf is 1.37 times longer.

[0116] Bolt and nut fastening structure According to the present disclosure, there is also provided a bolt and nut fastening structure 10, which is characterized in that it is a fastening structure for fixing a fastened object 12 to a base material 13 using the above-mentioned nut 1 and a bolt 11 corresponding to the nut 1. Fig. 8 shows a vertical cross-sectional view that shows a schematic view of this bolt and nut fastening structure 10. In Fig. 8, the nut 1 shows a preferred embodiment having an open-side additional rigidity portion 6 together with a recess 7, but the open-side additional rigidity portion 6 is not essential in the present disclosure.

[0117] According to this fastening structure 10, even when the nut 1 is inexpensive and used in harsh environments including at least one of vibration, temperature change, corrosive environments, etc., or for applications selected from the group consisting of automobiles, aircraft, space equipment, bridges, prime movers (motors, engines), wind power generators, construction machinery, civil engineering machinery, railway vehicles, cranes, ships, power generation equipment, power transmission equipment (steel towers), pipelines (flange connections), elevators (elevators, escalators), vacuum equipment, semiconductor manufacturing equipment, etc., the load sharing rate of the first engaging thread of the bolt-nut connection can be significantly reduced and the long-term life of the bolt-nut fastening structure can be significantly increased. EXAMPLES

[0118] Preferred embodiments of the present disclosure will be described below with reference to examples. It should be noted that the present disclosure is not limited to these examples.

[0119] (About FEM analysis) Since it is generally not possible to directly observe the force transmitted through a material, finite element analysis is useful as a method for predicting the state and flow of force within a material. In order to analyze the load sharing rate of each thread in conventional bolt and nut fastening, a simulation analysis of the fastening part was carried out using a CAE (Computer Added Engineering) method that utilizes the finite element method (FEM) to obtain the von Mises equivalent stress distribution of various nuts. The method of obtaining the von Mises equivalent stress distribution itself is known.

[0120] The FEM analysis was carried out using a computer and analytical software (e.g., CAD software for drawing, and a high-performance computer equipped with software capable of analysis using the von Mises equivalent stress for analysis). The tightening force, nut strength, Young's modulus, etc. used during tightening are the same as those of conventional products. The attached longitudinal cross-sectional view of the nut shows only a specific longitudinal cross-section, but the FEM analysis takes into account the fact that the nut has a three-dimensional shape, and for example, the shape (cross-sectional shape) of the nut body, particularly the square nut portion, when viewed from the axial direction is not circular but includes a square portion, and since the screw hole rotates in a spiral manner, the shape and position of the thread valley in the longitudinal cross-section differ depending on the direction in which the longitudinal cross-section including the axis is cut.

[0121] Comparative Example 1 For comparison with the following examples, the manufacture of a hexagonal nut of M12 (thread pitch 1.25 mm) was studied with reference to the description in Patent Document 1 (Japanese Utility Model Application Publication No. 59-45320). Patent Document 1 describes that the width of the notch is 1.3 times the diameter of the bolt, and the depth of the notch is 1.5 to 3 times the thread pitch in the case of fine threads.

[0122] Specifically, assuming a hexagonal nut conforming to the JIS standard (M12 nut without a flange, thread pitch 1.25mm, diagonal dimension 19.6mm, two-face width 16.97mm, material S45C-QT), we considered forming an annular notch on the fastening side seating surface of the hexagonal nut by cutting using a lathe. Hexagonal nut A did not have a stress relief portion (chamfer) on the outer peripheral end of the seating surface of the hexagonal nut, and hexagonal nut B did have a stress relief portion (chamfer radius 0.2mm on the longitudinal section).

[0123] According to the FEM analysis, in the case of Model A, which does not have a stress relief portion (chamfer) on the seating surface, if the hardness of the fastened object is soft, the fastened object will begin to sink into the fastened object during fastening, and Nut A will no longer be able to rotate and cannot be used as a nut.

[0124] In model B, the nut bearing surface thickness is only about 0.5 mm, but because the bearing surface is ring-shaped it is possible for it to rotate, so the bolt and nut were tightened by rotating the bolt side. However, in model B, which has a small bearing surface area, the internal stress distribution analysis showed that the maximum stress concentration was between the outermost contact diameter of the bearing surface and the outermost circumference of the nut notch (rectangular space), and a black area with a diagonal width (high stress area) appeared. It is known that when there is a black area with this diagonal width in the stress distribution, buckling will occur along that diagonal line.

[0125] Based on these results, it is determined that neither Nut A nor Nut B can be expected to provide the reliable fastening capacity required for M12 fine threads. It is clear that the reason the required fastening capacity cannot be expected is because the area of ​​the bearing surface is reduced due to the notch that creates the internal rectangular space in the hexagonal nut, and the rigidity of the fastening side with the notch is greatly reduced. In addition to the problem of the reduced bearing surface area, the provision of space on the bearing surface side of a normal hexagonal nut reduces the number of threads, reducing the normal 7 threads to 5 to 6 threads, and it is clear that in this state the load sharing rate of the first engagement thread is higher than that of the 7 threads.

[0126] Comparative Example 2 The manufacturability of the M12 hex nut (nut C) described in the example (Figure 1-1 of the same document) of Patent Document 4 (WO2019 / 131685) was examined on the premise of the current (prior art) manufacturing process and manufacturing method.

[0127] First, the hot forging method was examined. A mold was devised for forming a convex space in the longitudinal section without increasing the man-hours. In this mold, although it is a convex space in the longitudinal sectional view, actually the convex part is annular. In terms of the width a and the depth b of the mold that reaches the innermost part of the convex space, b is larger than a (a < b). Moreover, with respect to the movement of the hot forging mold (in this case, the vertical movement in the axial direction), the direction of moving the material metal by forging is not uniform left and right, and it is necessary to greatly expand the material on the outer peripheral side. Since the convex part of the mold (the part that creates the convex space) receives a radial reaction force, it was found that uneven wear occurs in the left and right directions. Also, because the convex space is narrow, heat accumulates in the mold of that part and cooling does not occur, resulting in a decrease in hardness and a significant reduction in the durability of the mold, and abnormal wear was also observed in the direction of decreasing the depth of the convex space. Therefore, the convex space forming part of this mold wears out earlier than other parts, resulting in a decrease in the depth of the convex space of the nut to be formed, which leads to a decrease in the ability to reduce the load sharing ratio of the first tooth of meshing and a deterioration in quality (defective products).

[0128] Therefore, forming only the legs of the expanded nut of the hex nut C by hot forging is not only difficult, but even if it is not purely technically impossible, there are problems such as a decrease in product quality as described above, severe wear of the hot forging mold, and the need for an additional inspection process. In particular, the time required for hot forging cannot be suppressed to about several seconds in the flow of heated material input ~ forging ~ removal, and it is concluded that it is not suitable for the commercial production of small mass-produced parts such as nuts.

[0129] Next, we considered forming the convex space by cutting in a post-forging and heat treatment process. The manufacturing method for nut C, which mainly involves cutting, also showed that the convex space is narrow and deep, so the cutting tool wears out quickly, in-process inspection of the product becomes cumbersome, automation is difficult, and the labor required for replacing the tool increases, resulting in a significant increase in manufacturing costs, making the shape of nut C unsuitable for commercial mass production.

[0130] Nut C corresponds to the nut in Patent Document 4, but the nut in Patent Document 3 has an even deeper convex space than that in Patent Document 4, and so it is clear that the problems discussed for Nut C are even more serious and that it is difficult to manufacture, or even if it is manufactured, it is unsuitable for commercial mass production. Also, it is clear that the nut in Figure 2(a) of Patent Document 3 has problems similar to those of Nuts A and B and common to Nut C, based on its shape.

[0131] (Example 1 and Reference Example 1) FEM analysis was performed on six types of nuts N1 to N6 in which the shape and depth of the recess were changed based on the shape shown in the vertical cross-sectional views of Figs. 2-1 to 2-3, and on the original nut D1.

[0132] Figures 2-1 to 2-3 show the nut N2, Figures 3 and 4 show the shapes of nuts N1 and N5, and Figure 5 shows the shape of nut D1. Nut D1 is a nut with a flange portion similar to that of nut N2, but differs from nut N2 in that it does not have a recess and an open-side additional rigidity portion. In Figure 5, M1 and M2 represent the radial dimension of the chamfer, Ha and Em represent the axial dimension of the chamfer, and angles α and δ represent the chamfer angle. The axial dimension Ha of the chamfer of nut D1 is about 0.2 times (0.2P) the thread pitch. Figures 1(f) and (g) show photographs of a prototype of nut N5 seen from the flange portion side, and show a flat circular bearing surface, a shallow circular recess on the inside of the bearing surface, and a bolt hole with an inner thread groove further inside the recess.

[0133] Nut D1 is a reference nut designed to be a suitable standard for evaluating the effectiveness of nuts N1 to N6 under strict conditions. Nut D1 is not necessarily a nut known in the prior art, but it was used as a control example (standard) for evaluating the nuts of the examples of the present disclosure.

[0134] Nuts N1 to N6 are examples, and differ only in the shape and depth of the recesses. The depths (maximum value) of the recesses of N1 to N6 are approximately 0.4 pitch (N1), approximately 0.5 pitch (N2), approximately 0.6 pitch, approximately 0.7 pitch (N4), approximately 0.9 pitch (N5), and approximately 1.1 pitch (N6), respectively.

[0135] The recesses of the nuts N1 to N6 each have a radial dimension Lm (radial dimension from the thread groove cylindrical surface to the boundary between the recess and the seating surface) of about 2.4 pitches on the screw hole side of the seating surface at the fastening end of the flange portion, and a flat portion extending radially at the inner end of the recess. The inner end flat surface of this recess has a depth Di from the seating surface of about 0.3 pitches and a radial dimension from the thread groove cylindrical surface of 0.19 pitches. The position of the deepest part D of the recesses of the nuts N1 to N6 is located at a position where the radial dimension Ldm from the thread groove cylindrical surface increases in order from about 1 pitch (N1) to about 2 pitches (N6).

[0136] Nuts N1 to N6 have an additional rigidity portion (axial dimension 0.8 pitch) on the open side, and a reduced diameter portion with a reduced radial dimension on the outer periphery of the open side end has an arc-shaped longitudinal section, an axial dimension B of approximately 1.2 pitch, and a radial dimension Lr of the stress relief portion of the flange portion is approximately 1.0 pitch.

[0137] Nut D1 differs from nut N1 to N6 in that it has no recess, does not have an open-side additional rigidity portion, and has a vertical cross-sectional radius of curvature of a tapered portion at the open-side end of 0.48 pitches.

[0138] When FEM analysis is performed on the thus designed nuts N1 to N6 and nut D1 using the method described above, for example, for nuts N2 and D1, the load sharing rate for each thread can be obtained as shown in Fig. 6. In Fig. 6, the horizontal axis represents the thread number (1st to 8th threads) from the fastening side, and the vertical axis represents the load sharing rate of the fastening force for each thread.

[0139] According to FIG. 6, in the nut N2, the load sharing rate of the first meshing ridge is the largest, and therefore, it is clear that the damage of the bolt-nut connection mainly occurs at the first meshing ridge, which is consistent with the knowledge of the prior art. Comparing the nut D1 of the reference example with the nut N2 of the embodiment, the load sharing rate of the first meshing ridge is 34.3% in D1, but decreases to 26.6% in N2, a difference of 7.7 points, and the improvement rate (improvement rate) is 22.4%. This improvement rate is extremely remarkable, and is an astonishing value considering that the depth of the recess is only slightly less than 0.5 pitch. It is clear that the fatigue life of the bolt-nut connection structure is greatly improved from this remarkable reduction in the load sharing rate of the first meshing ridge. The improvement in the fatigue life of the bolt-nut connection structure is approximated by the following empirical formula from the reduction in the load sharing rate of the first meshing ridge and the improvement in the reduction rate. Empirical formula for fatigue life: Nf (σr to the power of b) = C (In the formula, Nf is the number of repeated loads until fatigue failure occurs, σr is the stress amplitude of the load, b is the stress exponent (generally 3 to 5), and C is a material constant.) Since the load distribution of the first peak is repeated as the "load stress amplitude", a smaller stress amplitude leads to an increase in Nf. For example, even in applications where the fatigue life in harsh environments has traditionally been measured in decades, it is said that the life can be doubled if the load distribution rate on the threads is reduced by 10%. Although it depends on the type of environment, there is a high possibility that the fatigue life can be improved by more than double if the number of repeated load inputs is increased.

[0140] Similar to the load sharing rate for each thread of nuts N2 and D1 shown in Fig. 6, the reduction rate (improvement rate) of the load sharing rate of the first meshing thread of nuts N1, N3 to N6 compared to nut D1 was calculated and the results are shown in the graph of Fig. 7. In Fig. 7, the horizontal axis represents the depth of the recess / thread pitch, and the vertical axis represents the load sharing rate of the first meshing thread.

[0141] 7, in the case of the nut structure of the present disclosure, compared with nut D1, which is a control example, in nuts N1 to N6 of the examples, the improvement rate is 21.1% for nut N1, and in all of nuts N2 to N6, the improvement rate (22.4 to 25.9%) is higher than the improvement rate of nut N1. Also, the depth of the recess increases from nut N1 to nut N6, but the improvement rate increases from nut N1 to nut N5, but the improvement rate is reversed for nut N6.

[0142] According to conventional knowledge, it was thought that the effect of reducing the load sharing rate of the first meshing peak by forming a notch or a convex space on the seat side of the nut could be increased as the depth of the notch convex space was deeper (although there is an upper limit to the depth based on the dimensions and strength of the nut). However, in the nut of the present disclosure, even if the depth of the recess is extremely shallow, such as less than 1.5 pitches or 1.25 pitches or less, a surprisingly high reduction effect can be obtained, and moreover, in the structure of the nut of the present disclosure, it was found that the reduction effect based on the depth of the recess gradually decreases as the depth increases at approximately 1.0 pitch or more, which was a fact that was not expected at all in the past. In addition, in the present disclosure, even if the depth of the recess is 1.0 pitch or more and less than 1.5 pitches, the effect of reducing the load sharing rate of the first meshing peak can be sufficiently obtained, so the depth range of the recess in the nut of the present disclosure is set to less than 1.5 pitches.

[0143] A process for manufacturing the nut N2 having the shape shown in Figures 2-1 to 2-3 was assumed. First, a nut prototype having the outer diameter shown in Figures 2-1 to 2-3 was produced, and then a CNC lathe program was created for the process of cutting a recess from the flange side seat surface of the nut prototype using a lathe, and the conditions of the cutting tool to be used were input and a simulation was performed. After this, it is easy to drill a screw hole in the center and create a screw. This lathe work can be performed simply by using an end mill or drill with a cutting tip of a simple shape, and can be produced without difficulty. In addition, even if the number of nuts produced is increased, the damage to the cutting tool, end mill, and drill is the same as when the nut prototype is produced by lathe processing, and the wear is only minor and commercially acceptable.

[0144] In addition, a forging die (die) for forging the outer shape of the nut shown in Figures 2-1 to 2-3 was examined using CAD. This forging die (die) has more movement of metal material compared to a die for manufacturing nuts without a recess, but it was confirmed that there is no problem with durability if the die thickness is increased to increase the space somewhat and the cooling performance is improved. It was also confirmed that the damage to the forging die (die) was similar to that of the die for manufacturing nuts without a recess.

[0145] Example 2 Nut N5-1 was designed and analyzed using FEM. Nut N5-1 is similar to nut N5, but differs from nut N5 in that it does not have an additional rigidity portion on the open side (the height of the nut is 0.8 pitches smaller) and the cross-sectional radius of curvature of the arc of the reduced diameter portion on the open side is 0.48 pitches.

[0146] The obtained load sharing rate of the first meshing tooth was 26.3%, which is significantly smaller than that of nut D1, but the load sharing rate of the first meshing tooth increased by 0.7 points compared to nut N5.

[0147] It has been shown that the additional rigidity on the open side affects the load sharing rate of the first tooth of engagement. Example 3 Nut N5-2 was designed and analyzed using FEM. Nut N5-2 is similar to nut N5, but differs from nut N5 in that the radial dimension Lr of the stress relief part of the flange is 0.16 pitches larger than that of nut N5 (the radial dimension Rr of the seat surface is 0.16 pitches smaller than that of nut N5).

[0148] The obtained load sharing rate of the first meshing tooth was 26.2%, which is significantly smaller than that of nut D1, but the load sharing rate of the first meshing tooth increased by 0.8 points compared to nut N5.

[0149] It has been shown that the radial dimension Lr of the stress relief portion of the flange or the size of the seating surface affects the load sharing rate of the first meshing tooth. [Explanation of symbols]

[0150] 1 Nut 2 Nut body 3 Screw holes 4 Square nut part 5 Flange 6 Additional rigidity on the open side 7. Depression 8 Reduced diameter section 10 Bolt and nut fastening structure 11 Volts 12 Object to be fastened 13 Fastening material Rn Radius dimension of the imaginary inscribed cylindrical surface of the outer periphery of the square nut part Rnо Radius dimension of the imaginary circumscribed cylindrical surface of the square nut part Dm Maximum depth of the depression Lm Radial dimension of the recess Ls Radial dimension of bearing surface Lr Radial dimension of the stress relief part of the flange Rfm flange outermost radius dimension Hf Flange shoulder height Hfm Maximum flange height Ha: Axial direction of the additional rigidity part on the open side (part having a hole radius larger than the thread root radius) size Hc Axial dimension of reduced diameter part

Claims

1. A nut (1) consisting of a nut body (2) and a screw hole (3), The nut (1) has an axis, an axial direction (Z) and a radial direction (X) perpendicular to the axis, The nut body (2) has an axial side in the radial direction (X) referred to as the “inner side”, and a side away from the axis referred to as the “outer side” or “outer peripheral side”. In the following, the dimension from the axis of the nut body (2) to a specific position in the radial direction (X) is defined as the "radial dimension", which is distinguished from the "radial dimension" which is the dimension between two specific points in the radial direction (X). The screw hole (3) has a screw thread radius dimension R0, which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), and a screw pitch P, The nut body (2) has a square nut portion (4) and a flange portion (5) in the axial direction (Z). The flange portion (5) side of the nut (1) is the “fastening side” and the square nut portion (4) side is the “open side”. The square nut portion (4) has an outer circumscribing cylindrical radius dimension Rn of the square nut portion (4), which is the radius dimension of a cylindrical surface inscribed in the outer circumscribing surface of the square nut portion (4), and an outer circumscribing cylindrical radius dimension Rno of the square nut portion (4), which is the radius dimension of a cylindrical surface circumscribing the outer circumscribing surface of the square nut portion (4), The flange portion (5) has an outer periphery radius dimension larger than the outer periphery circumscribing cylinder radius dimension Rno, The flange portion (5) has a seat surface (5s) at the fastening end, the seat surface (5s) being a flat surface extending in a direction (X) perpendicular to the axis, The flange portion (5) has a recess (7) on the axial side of the seat surface (5s), the recess (7) being annular as viewed in the axial direction (Z) and having a depth on the open side of the extension surface (5e) of the seat surface, When viewed from the axial direction (Z), the area Sm (=S3-S2) obtained by subtracting the area S2 on the shaft side having the shaft side end (5si) of the bearing surface as the outer edge from the area S3 on the shaft side having the outermost peripheral portion (5om) of the flange portion (5) as the outer edge is 0.55 times or more (S≧0.55Ss) based on the area Ss=(Sn-S0) obtained by subtracting the area S0 of a circle having the radius R0 of the thread root radius from the area Sn of a circle having the radius Rn of the outer circumferential inscribed cylinder of the square nut portion (4), The recess (7) has a maximum depth Dm in the axial direction (Z) from the extension surface (5e) of the bearing surface that is less than 1.5 times the thread pitch P (Dm<1.5P). A nut (1) characterized in that

2. The thread pitch P is a thread pitch based on the JIS thread standard or the standard of each country or international organization corresponding to the JIS standard (hereinafter, JIS and the like are collectively referred to as "standards"). A nut (1) according to claim 1.

3. The thread pitch P is a thread pitch based on the JIS thread standard or the standard of a country or international organization corresponding to the JIS (hereinafter, collectively including the JIS, simply referred to as the "standard"). When the thread pitch P of the screw hole (3) is a thread pitch of a fine thread in a standard specification, the maximum depth Dm of the recess (7) in the axial direction (Z) from the extension surface (5e) of the seat surface is less than 1.5 times the thread pitch P (Dm<1.5P), and when the thread pitch P of the screw hole (3) is a thread pitch of a coarse thread in a standard specification, the maximum depth Dm of the recess (7) in the axial direction (Z) from the extension surface of the seat surface is less than 1.0 times the thread pitch P (Dm<1.0P). A nut (1) according to claim 1.

4. The screw hole (3) has a screw thread radius dimension R0 which is the radius dimension of a screw thread cylindrical surface (3e) formed by connecting the screw threads (3b) of the screw hole (3), a female thread root diameter φ which is the diameter of the screw thread cylindrical surface (3e), and a screw pitch P, The thread pitch is P (unit: mm) and the root diameter of the nut's female thread is φ (unit: mm), and the following relationship is satisfied: When 0.5<φ≦1.3, P≦(1 / 20)φ+0.17, When 1.3<φ≦2.3, P≦(0.12 / 0.8)φ+0.07, When 2.3<φ≦6.5, P≦(0.6 / 4)φ+0.02, When 6.5<φ≦12, P≦(0.55 / 4)φ−0.07, When 12<φ≦41, P≦(2.55 / 29)φ+0.48, When 41<φ≦125, P≦(2 / 85)φ+3.06, When 125<φ≦320, P≦7.80 or The table below: 【Table 1】 The relationship shown in A nut (1) according to claim 1.

5. The recess (7) has a maximum depth Dm in the axial direction (Z) from the extension surface (5e) of the seat surface that is less than 1.0 times the thread pitch P (Dm<1.0P). The nut according to claim 1.

6. In a longitudinal section including the axis of the nut (1) (hereinafter also referred to simply as the "nut longitudinal section"), the nut body (2) has an open-side additional rigidity portion (6) at an open-side end, the open-side additional rigidity portion (6) is a portion whose radial inner surface has a radius dimension R1 larger than a thread root radius dimension R0, and the axial dimension Ha of the open-side additional rigidity portion (6) is 0.5 to 2 times the thread pitch P (0.5P≦Ha≦2P). A nut (1) according to any one of the preceding claims.

7. The recess (7) has a depth Di in the axial direction (Z) from the extension surface (5e) of the seat surface at the axial end (7o) of the recess (7) that is smaller than the maximum depth Dm of the recess (7) (Di<Dm). A nut (1) according to any one of the preceding claims.

8. The flange portion (5) has a dimensional difference Lfd = (Rfm - Rn) between the maximum radius dimension Rfm of the flange portion (5) and the outer circumferential inscribed cylindrical radius dimension Rn of the square nut portion (4), which is 0.4 times or more (Lfd ≧ 0.4Ln) of the radial dimension Ln based on the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut portion (4) to the outer circumferential inscribed cylindrical surface. A nut (1) according to any one of the preceding claims.

9. The flange portion (5) has an axial height (Z) Hfm from the seat surface (5s) to the boundary (5fm) between the flange portion (5) and the square nut portion (4), and the axial height (Z) Hfm is 0.2 times or more (0.2Hz≦Hfm) of the overall length Hz, which is the axial height of the nut (1). A nut (1) according to any one of the preceding claims.

10. In the longitudinal section of the nut, the flange portion (5) includes a flange outermost periphery (5om) which is a portion of the flange portion (5) having a maximum radial dimension Rfm, and an inclined portion (5c) which connects the flange outermost periphery (5om) and the square nut portion (4), The height Hf of the outermost flange portion (5om) in the axial direction (Z) from the extension surface (5e) of the seat surface at the boundary (5m) between the outermost flange portion (5om) and the inclined portion (5c) is greater than the maximum depth Dm of the recess (7) (Hf>Dm); A nut (1) according to any one of the preceding claims.

11. The radial dimension Lm from the thread root cylindrical surface (3e) to the outer end (7o) of the recess (7) is greater than 1.0 times the thread pitch P (1.0P<Lm), and the radial dimension Lm is smaller than the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut portion (4) to the outer peripheral inscribed cylindrical surface (Lm<Ln); A nut (1) according to any one of the preceding claims.

12. The recess (7) has a portion having a maximum depth Dm, and the portion having the maximum depth Dm is located at a position of a radial dimension Ldm from the thread root cylindrical surface (3e), and the radial dimension Ldm is greater than two-fifths of the radial dimension Lm based on the radial dimension Lm from the thread root cylindrical surface (3e) to the outer end (7o) of the recess (7). A nut (1) according to claim 11.

13. In the longitudinal section of the nut, the recess (7) includes a stress relief curve portion extending from the boundary (7o) between the recess (7) and the seat surface (5s) toward the axial end (7i) of the recess (7) and including a portion of maximum depth Dm, and optionally a straight line portion, particularly a straight line portion (7il) extending substantially in the radial direction (X) and / or a chamfered portion on the axial side of the stress relief curve portion. A nut (1) according to claim 12.

14. In the longitudinal section of the nut, the recess (7) includes a first straight line portion from a boundary (7o) between the recess (7) and the seat surface (5s), a stress relaxation curve portion extending radially inward from an end of the first straight line portion and having a portion of a maximum depth Dm, and optionally a second straight line portion (7il) extending in a substantially radial direction (X) to an axial end (7i) of the recess (7). A nut (1) according to claim 12.

15. In the nut longitudinal section, the radius Rr of the inner end (5so) of the bearing surface (5s) is smaller than the radius Rn of the outer circumferential inscribed cylinder of the square nut portion (4) (Rr<Rn). A nut (1) according to any one of the preceding claims.

16. The radial dimension Ls from the inner end (5si) to the outer end (5so) of the bearing surface (5s) is 0.4 times or more (Ls≧0.4Ln) of the radial dimension Ln from the thread groove cylindrical surface (3e) to the outer peripheral inscribed cylindrical surface of the square nut portion (4). A nut (1) according to any one of the preceding claims.

17. The area S of the bearing surface (5s) is 0.55 times or more (S≧0.55Ss) of the area Ss = (Sn-S0) obtained by subtracting the area S0 of a circle having a radius R0 of the thread groove from the area Sn of a circle having a radius Rn of the outer circumferential inscribed cylinder of the square nut portion (4). A nut (1) according to any one of the preceding claims.

18. The radial dimension Lr = (Rfm - Rsm) of the stress relaxation portion (5r) of the flange portion (5) is 0.2 times or more (Lr ≧ 0.2Ln) of the radial dimension Ln from the thread root cylindrical surface (3e) of the square nut portion (4) to the outer circumferential inscribed cylindrical surface. A nut (1) according to claim 10.

19. In the nut longitudinal section, the inclined portion of the flange portion (5) has an angle θ in the range of 15° to 60° (15°≦θ≦60°) with respect to the radial direction (X). A nut (1) according to claim 10.

20. The nut body (2) has a reduced diameter portion (8) at the open side end, the radial dimension R3 of the radially outer surface of which is smaller than the radial dimension Rn of the outer circumferential inscribed cylinder of the square nut portion (4) (R3<Rn), and the axial dimension Hc of the reduced diameter portion (8) is larger than the axial dimension Ha of the open side additional rigidity portion (6). A nut (1) according to any one of the preceding claims.

21. A bolt and nut fastening structure (10) for fixing a fastened object (12) to a base material (13) using a nut (1) according to any one of claims 1 to 20 and a bolt (11) corresponding to the nut (1).

22. 22. The bolt and nut fastening structure (10) according to claim 21, wherein the fastening structure (10) is used in an environment including at least one of vibration, temperature changes, pressure changes, and a corrosive environment.

23. The bolt and nut fastening structure (10) according to claim 21 or 22, wherein the fastening structure (10) is used for an application selected from the group consisting of automobiles, aircraft, space equipment, bridges, prime movers (motors, engines), wind power generators, construction machinery, civil engineering machinery, mining machinery, railway vehicles, cranes, ships, power generation equipment, power transmission equipment (steel towers), pipelines (flange connections), elevators (elevators, escalators), vacuum equipment, semiconductor manufacturing equipment, casting and forging / steel-making machinery, machine tools, and steel buildings.

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