Fastening structure

Abstract

To avoid a catching phenomenon in which a small screw is caught on an inclined surface of a washer by screwing and is not smoothly rotated, and to reduce a processing cost.SOLUTION: In a fastening structure, a screw rod 1a of a bolt 1 for mounting a mounting object is passed through a mounting hole of a member 2 to be mounted so as to project a tip portion, and a small screw 5 mounted in the nut 4 through a washer 3 is screwed into the tip portion so as to fix the mounting object to the member 2 to be mounted. In the washer 3, an inclined surface 3b is formed on a first surface 3A facing the nut 4, and a second surface 3B on an opposite side of the first surface 3A is made a flat surface. The inclined surface 3b is formed so that a height is gradually lower toward a fastening direction of the nut 4. The small screw 5 having a spherical shaped tip 5b is screwed into the nut 4 so that a screw axis line is parallel to an axis line of the nut 4 and the small screw 5 has the tip 5b projecting to be brought into contact with the inclined surface 3b. The inclined surface 3b has a frictional coefficient smaller than that of the second surface 3B of the washer 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a fastening structure using nuts and bolts.

Background Art

[0002] Conventionally, regarding anti-loosening, many devices have been devised and put into practical use, such as a method using a spring washer, a method using double nuts, a method of passing a split pin through a nut and a bolt, etc. However, the effects are insufficient and loosening may occur due to vibration or the like, or the mechanism and processing are complicated and costly.

[0003] Therefore, a locking pin mechanism that generates anti-loosening pressure by expanding the inner surface of the nut by inserting a locking pin into a hole provided on the inner surface of the nut, or a locking pin insertion hole that penetrates obliquely at a position slightly separated from the inner surface of the nut, and after inserting a locking pin that is slightly longer than the length of the locking pin insertion hole and has a pointed tip, the nut is manually rotated and fitted onto the male screw portion of the bolt until it reaches the washer, and then firmly tightened using a commercially available tool such as a wrench, so that the object to be fixed sandwiched between the two washers is fixed. Further tightening causes the locking pin to be pushed by the washer and the tip of the locking pin to firmly contact the male screw portion, thereby pushing the male screw portion to produce an anti-loosening effect. When tightened more strongly, the tip of the locking pin bites into the male screw portion like a pile, and a locking pin mechanism with an even greater anti-loosening effect has been proposed (see, for example, Patent Documents 1 and 2).

[0004] The devices described in Patent Documents 1 and 2 fix by expanding the inner surface of the nut or by biting the tip of the locking pin into the screw rod of the bolt, so the screw rod (screw portion) is damaged and cannot be reused even if the nut is loosened for maintenance or the like.

[0005] Therefore, as a fastening structure that does not loosen in the fastened state, can be easily loosened during maintenance, and enables reuse of bolts and nuts, the threaded rod of the bolt for attaching the object to be attached is passed through the attachment hole of the attached member so that the tip portion protrudes, and a small screw attached to the nut via a washer is screwed into the tip portion with an appropriate torque to fix the object to be attached to the attached member. In this fastening structure, the washer has an inclined surface formed on the first surface facing the nut, while the second surface on the side opposite to the first surface is a flat surface. The inclined surface is formed so that the height gradually decreases in the tightening direction of the nut. The small screw is screwed into the nut so that the axis is orthogonal to the inclined surface, and the tip of the small screw protrudes so as to contact the inclined surface. A structure is proposed in which the inclined surface has a smaller coefficient of friction than the second surface of the washer (see, for example, Patent Document 3).

[0006] In this way, since the small screw is screwed into the nut so that the axis is orthogonal to the inclined surface on the first surface of the washer, the threaded rod (threaded portion) of the bolt is not damaged and can be reused. Further, even if the nut tries to rotate due to vibration or the like in the loosening direction, the inclined surface has a smaller coefficient of friction than the second surface, and the small screw tries to move in the direction of climbing the inclined surface, and a force that presses the washer against the attached member acts, so that the nut can be made difficult to loosen.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, with the structure of Patent Document 3 described above, (i) since a large number of inclined surfaces (equal to the number of small screws) overlap on the washer, the cost increases due to these machining processes. (ii) Since the small screws being screwed in are inclined, it is necessary to machine the screw holes for the small screws at an angle with respect to the nut axis, which also results in high costs in this regard. (iii) The tip of the small screw is designed to hit the inclined surface of the washer at a right angle. However, when the small screw is strongly screwed in, it will slightly sink into the inclined surface. When the nut tries to loosen (in the counterclockwise direction) due to vibration, there is a risk that the small screw (with a slightly sunken tip) will get caught on the inclined surface of the washer and not rotate smoothly. That is, there are problems such as a catching phenomenon where the washer is also rotated together with the nut when it gets caught.

[0009] The function of this structure is that, under the condition that the nut and the washer do not rotate together, the small screw slides up the inclined surface of the washer, and even if the axial force of the bolt increases and it is subjected to vibration, it does not loosen. However, due to the above-mentioned catching phenomenon, this function is often at risk of being lost.

[0010] An object of the present invention is to provide a fastening structure that can avoid the above-mentioned catching phenomenon and reduce the processing cost.

Means for Solving the Problems

[0011] The present invention is a fastening structure for fixing an object to be attached to a member to be attached by passing a threaded rod of a bolt for attaching the object to be attached through a mounting hole of the member to be attached and protruding a tip portion, and screwing a small screw attached to a nut via a washer to the tip portion. The washer has an inclined surface formed on a first surface facing the nut, while a second surface opposite to the first surface is a flat surface. The inclined surface is formed such that its height gradually decreases in the tightening direction of the nut. A small screw with a curved surface at its tip is screwed into the nut so that the screw axis is parallel to the axis of the nut. The tip of the small screw protrudes from the nut and contacts the inclined surface. The inclined surface is characterized by having a smaller friction coefficient than the second surface of the washer.

[0012] In this way, the screw hole machining for the small screw is simple, the threaded rod (threaded portion) of the bolt is not damaged, and it is reusable. Also, even if the nut or bolt tries to rotate due to vibration or the like in the loosening direction, the friction coefficients of the inclined surface and the second surface of the washer are made different, and the washer is pressed against the member to be attached by the movement of the small screw, so it is difficult to loosen. In addition, when the nut tries to rotate in the loosening side (counterclockwise direction) due to vibration, since the tip of the small screw has a curved surface shape, it is easy to slide without getting caught. Therefore, the phenomenon that the small screw (which is slightly recessed) gets caught on the inclined surface of the washer and does not rotate smoothly (that is, the catching phenomenon where the washer is also rotated together with the nut when caught) is avoided.

[0013] In this case, the curved surface shape of the tip of the small screw can be a spherical shape. And it is desirable that when the spherical shape is pressed against the inclined surface of the washer and tightened, as the shape of the tip gradually changes and becomes flat, at the time when the small screw is tightened with a specified maximum force, it fits exactly to the inclined surface of the washer. In this way, the average surface pressure of the tip end surface of the small screw can be reduced when the small screw is fully tightened.

[0014] Further, it is desirable that the inclined surface is smoother in surface roughness than the second surface, the inclined surface is finish-machined, and the second surface is rough-machined. Also, the inclined surface may be formed singly or plurally in the circumferential direction around the center hole of the washer.

[0015] Furthermore, the present invention can be applied not only to a fastening structure in which an object to be attached is attached using a nut via a washer, but also to a fastening structure in which the object to be attached is fixed to a member to be attached by a bolt with a head. That is, the present invention is a fastening structure in which an object to be attached is fixed to a member to be attached by a bolt with a head, a washer is disposed on the threaded rod of the bolt adjacent to the head of the bolt, the washer has an inclined surface formed on a first surface facing the head of the bolt, while a second surface on the side opposite to the first surface is a flat surface, the inclined surface is formed so as to gradually decrease in height toward the tightening direction of the bolt, a small screw having a curved surface at the tip is screwed into the head of the bolt such that the screw axis is parallel to the axis of the nut, the tip of the small screw protrudes from the nut and contacts the inclined surface, and the inclined surface has a smaller friction coefficient than the second surface of the washer.

Advantages of the Invention

[0016] In the present invention, screw hole machining for the small screw is simple, the threaded rod (threaded portion) of the bolt is not damaged, and it is reusable. Also, even if the nut or bolt tries to rotate due to vibration or the like in the loosening direction, since the friction coefficients of the inclined surface and the second surface of the washer are different, the washer is pressed against the member to be attached by the movement of the small screw, making it difficult to loosen. In addition, when the nut tries to rotate in the loosening side (counterclockwise direction) due to vibration, the small screw can be caught on the inclined surface of the washer to avoid the catching phenomenon of not rotating smoothly.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments according to the present invention will be described.

[0019] FIG. 1 is a cross-sectional view showing the fastening structure according to the present invention, and FIG. 2 is an enlarged view of part A in FIG. 1.

[0020] As shown in FIGS. 1 and 2, the fastening structure according to the present invention penetrates the threaded rod 1a of the bolt 1 for attaching an object to be attached (not shown) to the attached member 2 through the attachment hole of the attached member 2 and projects the tip portion, and applies a nut 4 to the tip portion via a washer 3 to fix the object to be attached to the attached member 2. It is a fastening structure.

[0021] As shown in FIG. 3, the washer 3 has a central hole 3a through which the threaded rod 1a passes. And on the first surface 3A facing the nut 4, an inclined surface 3b is formed along the circumferential direction around the central hole 3a. On the other hand, the second surface 3B is a flat surface. The inclined surface 3b may be singular or plural, and the number of inclined surfaces is irrelevant to the number of small screws 5 described later. FIG. 3 illustrates the case where there are two inclined surfaces 3b.

[0022] The inclined surface 3b is continuous with a wall surface 3c that rises from the end on the tightening direction side of the nut 4. Those surfaces 3b and 3c are orthogonal. The inclined surface 3b is inclined at an angle of at least the lead angle of the screw of the nut (or bolt) with respect to the second surface 3B at θ = about 3 to 20°.

[0023] Further, the first surface 3A (inclined surface 3b) and the second surface 3B of the washer 3 have different surface roughnesses, thereby changing the friction coefficient. The inclined surface 3b is smoother than the second surface 3B, and the friction coefficient is reduced. For example, the inclined surface 3b is finish-machined, and the second surface 3B is rough-machined.

[0024] The nut 4 is formed with a threaded hole 4a around the center hole of the nut 4 corresponding to the inclined surface 3b so that the threaded axis is parallel to the nut axis for screwing in the small screw 5. The small screw 5 is screwed into the threaded hole 4a of the nut 4, and the tip 5b projects from the nut 4 and the tip 5b is in contact with the inclined surface 3b. The tip 5b of the small screw 5 has a curved surface shape (for example, a spherical shape) with the center part being the most protruding and has a rounded shape.

[0025] Here, if the tip of the small screw is flat, the maximum outer diameter portion (= edge) contacts the inclined surface 3b at a substantially right angle, so the edge of the recessed small screw 5 is likely to be caught by the inclined surface 3b. However, if the tip is formed into a curved surface shape and rounded as in the present invention, the tip portion (rounded portion) of the small screw 5 is slightly recessed, and at the same time, a rounded portion on the inclined surface side also slightly sinks into the inclined surface 3b. By adjusting the size of the roundness, while creating a slight recess in the inclined surface 3b, it becomes easy to slide without being caught due to the roundness.

[0026] In this way, if the tip of the small screw 5 is formed into a curved surface shape and rounded, the small screw 5 does not necessarily contact the inclined surface 3b of the washer 3 at a right angle, and the small screw 5 does not need to be tilted with respect to the nut 4. Therefore, the threaded hole 4a into which the small screw 5 is screwed can be provided such that its axis is parallel to the axis of the nut 4. As a result, there is a great merit that the processing cost can be significantly reduced while maintaining the function of making it difficult to loosen.

[0027] That is to say, with such a structure, if the nut 4 tries to rotate due to vibration etc. in the loosening direction (= counterclockwise), the small screw 5 will move in the climbing direction on the inclined surface 3b of the washer 3. As a result, the distance between the upper surface of the nut 4 and the second surface 3B of the washer 3 will tend to increase. At this time, since the friction coefficients of the first and second surfaces 3A, 3B of the washer 3 are different, the sliding between the inclined surface 3b on the washer 3 with a smaller friction coefficient and the tip of the small screw 5 will occur first, that is, it will slide relative to each other before the second surface 3B and the mounted member 2. Once it slides even a little, the distance will expand so as to become longer, and the second surface 3B of the washer 3 will be pressed more strongly against the seating surface (mounted member 2), so it becomes increasingly difficult to slide.

[0028] The larger the inclination angle of the inclined surface 3b, the stronger the second surface 3B of the washer 3 is pressed against the seating surface, so the frictional force further increases and it becomes increasingly difficult to rotate. That is to say, this nut 4 is difficult to loosen.

[0029] As an example, when the bolt 1 has a diameter of 36 mm (M36), a length 5 times the diameter (180 mm), and a bolt axial force (= tightening force) of 350 kN, and the inclination depth of the inclined surface 3b of the washer 3 is 0.6 mm, the force (= axial force or rotational torque) required to loosen the nut 4 (by force) is 196% (about twice) when the tightening time is taken as 100.

[0030] When the diameter of the bolt 1 is 64 mm and the axial force is 1150 kN (assuming other conditions are the same), the force required to loosen it is 153% (1.5 times). The force for the previous nut 4 to loosen varies depending on the inclination depth (height of the wall surface 3c) of the inclined surface 3b on the washer 3, and the greater the depth, the greater the force (loosening rotational torque or axial force) required.

[0031] The fact that a force of 153 - 196% is required to loosen it by force is the same as the nut 4 not loosening. Because usually bolts are fastened at 60 - 90% of the yield point, if a loosening torque (or axial force) nearly twice as large is applied, the bolt will break (before loosening).

[0032] However, the nut 4 usually needs to be easily loosened for maintenance or the like. That is, any nut must never be loosened, but opposite performances are required, that is, it is desired to be easily loosened when loosening.

[0033] This fastening structure exactly meets the above requirements. In the relationship between the nut 4 and the washer 3, even if it is subjected to vibration or the like, the nut 4 will never loosen naturally. On the other hand, if you want to loosen the nut 4 for maintenance, for example, it can be easily loosened with a single wrench. That is, by loosening the small screw 5 with a single wrench, even if it is slightly tighter than the initial tightening, the nut 4 can be easily loosened.

[0034] That is, according to this fastening structure, in the relationship between the nut 4 (small screw 5) and the washer 3 (inclined surface 3b), even if it is subjected to vibration or the like, the nut 4 will not loosen naturally. However, if you want to loosen the nut 4 for maintenance, for example, it can be easily loosened with a single wrench.

[0035] By the way, in paragraph 0050 of the above Patent Document 3, as a measure to make the axis of the small screw parallel to the axis of the screw of the nut, the tip of the small screw is made hemispherical, and the inclined surface side of the washer is also made hemispherical so that the tip of the small screw conforms to the hemispherical portion of the small screw. On the other hand, it is disclosed that a concave groove having a semi-circular cross-section along the inclined surface is dug in the inclined surface, and the same effect can be obtained even if the small screw is made vertical without tilting it at an angle. This is because by digging a concave groove having a semi-circular cross-section along the inclined surface in the inclined surface, the contact area between the tip of the small screw and the concave groove of the inclined surface is increased and the contact surface pressure is reduced ( = averaged). Otherwise, if the inclined surface is a flat surface, the surface pressure at the tip of the small screw will rise extremely and it will be crushed.

[0036] However, digging a concave groove with a semi-circular cross-section in the washer in this way is costly. Moreover, there is naturally a gap (play) between the inner diameter of the washer and the diameter of the small screw. Therefore, when installing the small screw, the washer may deviate from the axis of the nut by this amount of play. Due to this deviation, the center of the concave groove on the washer side may always deviate from the center of the small screw. And when it deviates, the hemispherical tip of the small screw may interfere with the side surface of the concave groove, causing malfunction.

[0037] On the other hand, in the present invention, since the inclined surface of the washer is a flat surface, even if the inner diameter of the washer is installed deviating from the central axis of the nut diameter, the tip of the small screw only moves on the flat surface, so there is no interference problem with the concave groove as in the structure of Patent Document 3. More importantly, the roundness of the tip of the small screw is an R shape (= a slight spherical shape) that is so large that it cannot be recognized as hemispherical, and this R dimension is determined by the stress and strain calculated accurately by Hertz's equation in physics. Specifically, when the spherical tip of the small screw is pressed against the washer surface and tightened, (since the small screw is an elastic body) as the shape of the spherical tip changes, it gradually becomes flat, and when the small screw is tightened with the specified maximum force, it is designed to fit exactly on the flat surface of the inclined surface. As a result, the average surface pressure of the end face of the tip of the small screw is reduced ( = averaged) at the time of tightening.

[0038] That is, the structure described in paragraph 0050 of Patent Document 3 is a method of reducing the surface pressure by increasing the contact area of the tip of the small screw from the beginning. In the present invention, the tip of the small screw is in "point contact" with the washer surface at the initial time (when contacting) when the tightening load is small (see Fig. 4(a)), but at the time of tightening (when fastening), the tip becomes close to a flat surface and the surface pressure on the washer decreases (see Fig. 4(b)). Such a physical difference between the two is significant. In this case, the flat surface side of the washer will also be slightly concave, but this amount of concavity is also calculated by Hertz's equation, and through repeated actual experiments, finally the curvature R dimension of the tip of the small screw is determined so that the small screw can slide up smoothly on the inclined surface of the washer without hindrance when the nut loosens or moves.

[0039] As described above, the embodiments of the present invention have been described with reference to the drawings. However, various additions or changes are possible without departing from the spirit of the present invention. For example, in the above embodiment, a fastening structure using the relationship between a nut and a washer is employed. However, for example, a fastening structure using the relationship between the head 1b of the headed bolt 1 and the washer 3 as shown in FIG. 5 can be similarly applied. In this case, a small screw 5 having a spherical tip 5b is screwed into a screw hole 1c in the head 1b of the bolt 1 such that the screw axis is parallel to the axis of the bolt 1, and the tip 5b of the small screw 5 is in contact with the inclined surface 3b. In this case, the head 1b of the headed bolt 1 is not limited to a hexagonal cross-section and may have a circular cross-section.

Explanation of Reference Numerals

[0040] 1 Bolt 1a Threaded rod 1b Head 1c Screw hole 2 Mounting member 3 Washer 3A First surface 3a Central hole 3B Second surface 3b Inclined surface 3c Wall surface 4 Nut 4a Screw hole 5 Small screw 5a Threaded portion 5b Tip

Claims

1. A fastening structure for fixing an object to be attached to a member to be attached, comprising passing a threaded rod of a bolt for attaching the object to be attached through a mounting hole of the member to be attached and protruding a tip portion, and screwing a small screw attached to a nut via a washer into the tip portion, wherein the washer has an inclined surface formed on a first surface facing the nut, while a second surface opposite to the first surface is a flat surface, the inclined surface is formed such that the height gradually decreases in the tightening direction of the nut, a small screw having a curved surface at its tip is screwed into the nut so that the screw axis is parallel to the axis of the nut, and the tip of the small screw protrudes from the nut and contacts the inclined surface, the inclined surface has a smaller coefficient of friction than the second surface of the washer, characterized in that the fastening structure.

2. The fastening structure according to claim 1, wherein the curved surface shape of the tip of the small screw is a spherical shape.

3. The spherical shape is such that when the tip is pressed against the inclined surface of the washer and tightened, the shape of the tip gradually becomes flat as it changes, and at the time when the small screw is tightened with a specified maximum force, it fits exactly against the inclined surface of the washer, according to the fastening structure of claim 2.

4. The inclined surface is smoother in surface roughness than the second surface, the inclined surface is finish-machined, and the second surface is rough-machined, according to the fastening structure of claim 1.

5. The inclined surface is formed singly or plurally in the circumferential direction around the center hole of the washer, according to the fastening structure of claim 1.

6. A fastening structure for fixing an object to be attached to a member to be attached by a bolt with a head, a washer is disposed on the threaded rod of the bolt adjacent to the head of the bolt, the washer has an inclined surface formed on a first surface facing the head of the bolt, while a second surface opposite to the first surface is a flat surface, the inclined surface is formed such that the height gradually decreases in the tightening direction of the bolt, a small screw having a curved surface at its tip is screwed into the head of the bolt so that the screw axis is parallel to the axis of the nut, and the tip of the small screw protrudes from the nut and contacts the inclined surface, the inclined surface has a smaller coefficient of friction than the second surface of the washer, characterized in that the fastening structure.

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