Lock nut

Abstract

To reduce a variation in prevailing torque.SOLUTION: A lock nut 1 includes a nut body 2, and a cylindrical protrusion part 3 protruded upward from the upper face of the nut body 2 along the axial direction, wherein a female screw 4 is provided over the nut body 2 and the protrusion part 3 in their inner peripheries. On the inner periphery of the protrusion part 3, the female screw 4 is formed in an elliptical shape with long and short diameters in view from the axial direction. On the inner periphery of the protrusion part 3, the female screw 4 is displaced downward at the short diameter side of the female screw 4 and the female screw is displaced upward at the long diameter side of the female screw 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a locking nut. [Background technology]

[0002] The applicant of the present application has been developing a space lock nut ("Space Lock" is a registered trademark of the applicant of the present application), which is a single-nut type anti-loosening nut that exhibits high anti-loosening performance, and is disclosed, for example, in Patent Document 1 described below. A thin space lock nut specialized for mounting bearings is manufactured and sold under the product name "SLB" (a registered trademark of the applicant of the present application).

[0003] This space lock nut has a nut body that can be engaged with a tool, a cylindrical protrusion that protrudes from the nut body in the axial direction, and a female thread is provided on the inner circumference of the nut body and the cylindrical protrusion. The cylindrical protrusion is pressed and deformed radially inward at multiple locations in the circumferential direction, so that the female thread on the inner circumference is slightly displaced radially inward in the press-deformed portion. In order to efficiently perform such press deformation processing using a press die, the outer circumferential surface of the cylindrical protrusion is formed into a truncated cone shape. Then, as shown in FIG. 3 of Patent Document 1, a press die having a truncated cone-shaped concave portion corresponding to the truncated cone shape of the cylindrical protrusion is moved along the axial direction relative to the cylindrical protrusion, thereby pressing and deforming only the multiple locations in the circumferential direction radially inward.

[0004] When a conventional space lock nut is screwed onto a bolt, the multiple press-deformed points of the cylindrical protrusion come into contact with the bolt relatively strongly, generating a prevailing torque, which prevents the nut from loosening. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-286649 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional space lock nuts can have variations in prevailing torque due to manufacturing tolerances of the outer circumferential surface of the cylindrical protrusion and the female thread on the inner surface.

[0007] An object of the present invention is to reduce the variation in prevailing torque. [Means for solving the problem]

[0008] The locking nut according to the present invention comprises a nut body and a cylindrical protruding portion protruding upward along the axial direction from the top surface of the nut body. A female thread is provided on the inner periphery of the nut body and the cylindrical protruding portion. On the inner periphery of the cylindrical protruding portion, the female thread is formed in an elliptical shape having a major axis and a minor axis when viewed from the axial direction. On the inner periphery of the cylindrical protruding portion, the female thread is displaced downward on the minor axis side of the female thread, and is displaced upward on the major axis side of the female thread.

[0009] The female thread may be a perfect circle having a predetermined effective diameter when viewed from the axial direction on the inner circumference of the nut body. Preferably, the female thread has a minor diameter smaller than the effective diameter and a major diameter larger than the effective diameter on the inner circumference of the cylindrical protrusion. The effective diameter may be the diameter of the female thread before it is deformed on the inner circumference of the cylindrical protrusion as described below.

[0010] Preferably, the downward displacement amount of the female thread on the minor diameter side and the upward displacement amount of the female thread on the major diameter side are both greater than 0.25% of the thread pitch of the female thread. The maximum value of the downward displacement amount of the female thread on the minor diameter side and the maximum value of the upward displacement amount of the female thread on the major diameter side are both greater than 0.5% of the thread pitch of the female thread.

[0011] Preferably, on the inner circumference of the cylindrical protrusion, the axial length of the complete thread portion of the female thread is twice the basic pitch P or more.

[0012] The present invention also provides a method for manufacturing a locking nut comprising a nut body and a cylindrical protruding portion protruding upward from an upper surface of the nut body along an axial direction, A step of forming a circular female thread at a predetermined basic pitch P on the inner circumference of the nut body and the cylindrical protrusion portion when viewed in the axial direction; and a process of deforming the female thread on the inner circumference of the cylindrical protrusion by pressing radially inward at two diametrically opposing locations in a region below the axial midpoint of the cylindrical protrusion, but not applying a radially inward pressing force in a region above the axial midpoint of the cylindrical protrusion, thereby (A) deforming the female thread on the inner circumference of the cylindrical protrusion into an ellipse having a major axis and a minor axis when viewed from the axial direction, and (B) deforming the female thread so that the female thread is displaced downward on the minor axis side of the cylindrical protrusion, and displaced upward on the major axis side of the female thread.

[0013] Preferably, the cylindrical protruding portion is pressed and deformed radially inward so that the female thread is displaced radially inward at two predetermined diametrical locations. Preferably, the thread pitch of the female thread near the inner circumference of the cylindrical protruding portion at the two diametrical locations is smaller than the thread pitch of the female thread at the inner circumference of the nut body, and the thread pitch of the female thread near the inner circumference at a position 90 degrees circumferentially away from the two diametrical locations of the cylindrical protruding portion is larger than the thread pitch of the female thread at the inner circumference of the nut body. Effect of the Invention

[0014] According to the present invention, in an anti-loosening nut which has a cylindrical protrusion protruding upward along the axial direction from the upper surface of the nut body, and in which the cylindrical protrusion is deformed radially inward so as to generate a prevailing torque, it is possible to reduce variation in the prevailing torque. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view of a locking nut and a screw shaft according to an embodiment of the present invention. [Diagram 2] FIG. [Diagram 3] FIG. 4 is a right side view of the locking nut. [Figure 4] FIG. [Diagram 5] FIG. 2 is a vertical cross-sectional view of the locking nut as viewed from the front. [Figure 6] FIG. 2 is a vertical cross-sectional side view of the locking nut. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 1 to 6 show a locking nut 1 according to one embodiment of the present invention. The locking nut 1 comprises a nut body 2 having a tool engagement portion on its outer periphery, and a cylindrical protruding portion 3 protruding upward along the axial direction from the top surface of the nut body 2. In the illustrated example, the nut body 2 is configured in the shape of a hexagonal nut. A female thread 4 is provided on the inner periphery of the nut body 2 and the cylindrical protruding portion 3.

[0017] The nut 1 is screwed onto a screw shaft 10 having a male thread 11 on its outer periphery. A key groove 12 extending along the axial direction and having a predetermined width W is provided in a portion of the circumference of the screw shaft 10. The key groove 12 is used, for example, to non-rotatably engage a bearing washer with the screw shaft 10. The width of the key groove 12 may be, for example, the key groove width of a shaft axis defined in JIS B1554.

[0018] A pair of pressure members 5a, 5b for deforming the cylindrical protrusion 3 by pressing two diametrically inward are provided at diametrically symmetrical positions on the outer periphery of the cylindrical protrusion 3. Each pressure member 5a, 5b is formed of a thick-walled portion that protrudes radially outward compared to other portions of the cylindrical protrusion 3 (hereinafter referred to as "thin-walled portions"). The thin-walled portion of the cylindrical protrusion 3 has a uniform thickness along the circumferential direction. Each pressure member 5a, 5b has a predetermined width a. Preferably, the width a of each pressure member 5a, 5b is 1.8 times or more the width W of the key groove 12.

[0019] On the inner circumference of the cylindrical protruding portion 3, the axial length of the complete thread portion of the female thread 4 is more than twice the thread pitch of the female thread 4. By ensuring a sufficient axial length of the female thread 4 on the inner circumference of the cylindrical protruding portion 3 in this manner, a prevailing torque can be generated stably regardless of the thread phase.

[0020] As shown in FIG. 1, the cylindrical protrusion 3 is deformed by pressing the outer circumferential surfaces of the pressurizing parts 5a and 5b from both diametrical sides in the radially inward direction by a pressing member 20 such as a press mold. Here, the pressing member 20 is configured to apply a pressing force in the radially inward direction only to the vicinity of the base end (i.e., the lower end) of the cylindrical protrusion 3, rather than to apply a pressing force to the entire outer circumferential surfaces of the pressurizing parts 5a and 5b. In the illustrated example, the outer circumferential surfaces of the pressurizing parts 5a and 5b are vertical surfaces, and the pressing surface of the pressing member 20 (the surface facing and contacting the outer circumferential surfaces of the pressurizing parts 5a and 5b) is also configured as a vertical surface. When the pressurizing parts 5a and 5b are pressed in the radially inward direction by such a pressing member 20, the entire outer circumferential surfaces of the pressurizing parts 5a and 5b come into contact with the pressing surface of the pressing member 20 and are pressed in the radially inward direction at the beginning of pressing. However, as the deformation of the cylindrical protrusion 3 progresses, the pressure applying portions 5a, 5b are deformed so that the upper sides of the pressure applying portions 5a, 5b fall radially inward as shown in Fig. 5, and as a result, a gap is generated between the upper parts of the pressure applying portions 5a, 5b and the pressure applying member 20, resulting in a non-contact state, and the pressure applying portions 5a, 5b are strongly pressed radially inward only near the base end of the cylindrical protrusion 3. The pressure applying member 20 may also be configured to abut against the pressure applying portions 5a, 5b only near the base end of the cylindrical protrusion 3 from the initial stage of pressing.

[0021] Since the vicinity of the base end of the cylindrical protrusion 3 is close to the nut body 2, which has high rigidity, when the pressure member 20 presses only the lower sides of the pressure portions 5a, 5b radially inward, the entire cylindrical protrusion 3 is deformed into an elliptical cylinder shape.

[0022] In the case of the pressing method disclosed in the above-mentioned Patent Document 1, only the circumferential portion in contact with the tapered inner peripheral surface of the press die is pressed and deformed radially inward, and other portions are hardly deformed. As a result, the female thread on the inner circumference of the protruding portion is slightly deformed radially inward only in the pressed and deformed portion, and as a whole, it is deformed into an irregular shape rather than an elliptical shape.

[0023] On the other hand, according to the deformation method of this embodiment, the female thread 4 is formed in an ellipse having a major axis and a minor axis when viewed from the axial direction on the inner circumference of the cylindrical protrusion 3. That is, the inner circumference of the pressurizing parts 5a, 5b is the minor axis, and the inner circumference at a position 90 degrees circumferentially relative to the pressurizing parts 5a, 5b is the major axis. Furthermore, in the minor axis portion, the upper part of the cylindrical protrusion 3 is deformed so as to be inclined radially inward, so that the female thread 4 in that portion is slightly displaced downward compared to the standard thread shape. On the other hand, in the major axis portion, the upper part of the cylindrical protrusion 3 is deformed so as to be inclined radially outward, so that the female thread 4 in that portion is slightly displaced upward compared to the standard thread shape. Due to such deformation of the female thread 4, on the inner circumference of the protrusion 3, the female thread 4 is displaced downward on the minor axis side of the female thread 4, and the female thread is displaced upward on the major axis side of the female thread 4. Furthermore, due to this displacement, on the inner circumference of the cylindrical protrusion 3, the thread pitch on the minor diameter side of the female thread 4 becomes slightly smaller than the thread pitch P (basic pitch) before deformation, and the thread pitch on the major diameter side of the female thread 4 becomes slightly larger than the thread pitch P before deformation. In this way, by mixing negative pitch errors and positive pitch errors, a prevailing torque can be generated stably.

[0024] In the vicinity of the bearing surface of the nut body 2, the influence of deformation of the cylindrical protrusion 3 is almost zero, and the shape conforming to the standard crest shape is maintained.

[0025] Furthermore, since the nut body 2 is not affected by the deformation of the cylindrical protrusion 3, or even if the nut body 2 is deformed, the amount of deformation is small compared to that of the cylindrical protrusion 3, on the inner circumference of the nut body 2, the female thread 4 is a perfect circle having a predetermined effective diameter when viewed from the axial direction, and on the inner circumference of the cylindrical protrusion 3, the female thread 4 has a minor diameter smaller than the effective diameter and a major diameter larger than the effective diameter. EXAMPLES

[0026] An M20 nut (thread pitch 1.0 mm) having the structure shown in Figures 1 to 5 was manufactured, and the amount of deformation of the cylindrical protrusion 3 was measured. The results are shown in Figures 5 and 6.

[0027] Inside the pressurized portions 5a and 5b, which are the short diameter portions, the female thread 4 is displaced downward by 25 μm or more overall, and at the portion with the largest displacement, it is displaced by 50 μm or more. On the other hand, inside the long diameter portion, the female thread 4 is displaced upward by 25 μm or more overall, and at the portion with the largest displacement, it is displaced by 50 μm or more. The M20 nut with a thread pitch of 1.0 mm has a gap of about 50 μm in the vertical direction between the thread of the male thread and the thread of the female thread due to the fit with the screw shaft. In the locking nut of this embodiment, the cylindrical protruding portion 3 is deformed into an ellipse, and the female thread is deformed so as to wave up and down along the helical direction, thereby generating a stable frictional force against the screw shaft and generating a stable prevailing torque. [Explanation of symbols]

[0028] 1 Locking nut 2 Nut body 3 Cylindrical protrusion 4 Female thread

Claims

1. A locking nut comprising a nut body and a cylindrical protruding portion protruding upward from an upper surface of the nut body along an axial direction, the nut body and the cylindrical protruding portion having an internal thread on their inner peripheries, The female thread is formed in an elliptical shape having a major axis and a minor axis when viewed from the axial direction on the inner circumference of the cylindrical protrusion, An anti-loosening nut, characterized in that, on the inner circumference of the cylindrical protrusion portion, the female thread is displaced downward on the short diameter side of the female thread, and the female thread is displaced upward on the long diameter side of the female thread.

2. The locking nut according to claim 1, On the inner circumference of the nut body, the female thread is a perfect circle having a predetermined effective diameter when viewed in the axial direction, A locking nut, wherein the female thread has an inner periphery of the cylindrical protrusion, the minor diameter of the female thread being smaller than the effective diameter and the major diameter of the female thread being larger than the effective diameter.

3. The locking nut according to claim 1, An anti-loosening nut, wherein the downward displacement amount of the female thread on the minor diameter side and the upward displacement amount of the female thread on the major diameter side are both greater than 0.25% of the thread pitch of the female thread.

4. The locking nut according to claim 3, A locking nut, wherein the maximum value of the downward displacement of the female thread on the short diameter side and the maximum value of the upward displacement of the female thread on the long diameter side are both greater than 0.5% of the thread pitch of the female thread.

5. The locking nut according to claim 1, A locking nut, wherein the axial length of the complete thread portion of the female thread on the inner circumference of the cylindrical protrusion is at least twice the thread pitch of the female thread.

6. A method for manufacturing a locking nut comprising a nut body and a cylindrical protruding portion protruding upward from an upper surface of the nut body along an axial direction, forming a circular female thread at a predetermined basic pitch P on the inner periphery of the nut body and the cylindrical protruding portion when viewed in the axial direction; and a step of deforming the female thread on the inner circumference of the cylindrical protrusion portion by pressing radially inward at two diametrically opposed locations in a region below the axial midpoint of the cylindrical protrusion portion, but not applying a radially inward pressing force in a region above the axial midpoint of the cylindrical protrusion portion, thereby (A) deforming the female thread on the inner circumference of the cylindrical protrusion portion into an elliptical shape having a major axis and a minor axis as viewed from the axial direction, and (B) deforming the female thread so that the female thread is displaced downward on the minor axis side of the cylindrical protrusion portion and displaced upward on the major axis side of the female thread. A method for manufacturing anti-loosening nuts.

7. The method for manufacturing a locking nut according to claim 6, a downward displacement amount of the female thread on the minor diameter side and an upward displacement amount of the female thread on the major diameter side are both greater than 0.25% of the thread pitch of the female thread.

8. The method for manufacturing a locking nut according to claim 7, a maximum value of a downward displacement amount of the female thread on the short diameter side and a maximum value of an upward displacement amount of the female thread on the long diameter side are both greater than 0.5% of the thread pitch of the female thread.

9. The method for manufacturing a locking nut according to claim 6, A method for manufacturing an anti-loosening nut, wherein, on the inner circumference of the cylindrical protrusion, the axial length of the completely threaded portion of the female thread is at least twice the thread pitch of the female thread.

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