Lock nut

Abstract

To provide a lock nut for generating prevailing torque with no sense of discomfort even when threaded to a screw shaft having a key groove.SOLUTION: A fastening device according to this invention includes a screw shaft 10 provided with a male screw 11 on the outer periphery, and a lock nut 1 threaded to the screw shaft 10, the nut 1 having a cylindrical protrusion part 3 protruded upward from the upper face of a nut body 2 along the axial direction. On the outer periphery of the protrusion part 3, pressure parts 5a, 5b are provided at predetermined positions in the peripheral direction for pressing and deforming the protrusion part 3 radially inward. The breadth a of each of the pressure parts 5a, 5b is 1.8 times a breadth W of a key groove 12 of the screw shaft 10.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] In a locking nut that generates a prevailing torque by plastic deformation, such as a conventional space lock nut, if the screw shaft to be screwed is provided with a keyway for a bearing washer, the prevailing torque may disappear temporarily when the diameter-reduced deformation part that generates the prevailing torque fits into the keyway when the nut is tightened. Also, when the prevailing torque generating part rides up from the keyway, a prevailing torque is generated, so this does not cause a problem in terms of locking performance, but it can lead to an uncomfortable feeling in operation. Also, depending on the material of the nut and screw shaft, the sudden generation of prevailing torque when the prevailing torque generating part rides up from the keyway may cause wear or chipping of the contact parts.

[0007] An object of the present invention is to generate a prevailing torque that does not cause an uncomfortable feeling even when screwing into a screw shaft having a key groove. [Means for solving the problem]

[0008] The fastening device according to the present invention comprises a threaded shaft having a male thread on its outer periphery, and an anti-loosening nut screwed onto the threaded shaft, a key groove extending along the axial direction and having a predetermined width is provided on a portion of the circumference of the threaded shaft, the nut comprises a nut body and a cylindrical protrusion protruding upward along the axial direction from the upper surface of the nut body, and a female thread is provided on the inner circumference of the nut body and the cylindrical protrusion, and a first pressure portion for pressing and deforming the cylindrical protrusion radially inward is provided at one location on the outer periphery of the cylindrical protrusion, the first pressure portion having a predetermined width, and the width of the first pressure portion being 1.8 times or more the width of the key groove.

[0009] Preferably, a second pressure applying portion is provided on the outer periphery of the cylindrical protrusion portion at a position diametrically symmetrical to the first pressure applying portion, the second pressure applying portion having a predetermined horizontal width, and the horizontal width of the second pressure applying portion being 1.8 times or more the horizontal width of the key groove.

[0010] Preferably, the wall thickness of the cylindrical protrusion is greatest at the first pressure portion. Effect of the Invention

[0011] According to the present invention, it is possible to eliminate the fluctuation in prevailing torque when the pressure portion, which is pressed and deformed radially inward, overcomes the key groove. [Brief description of the drawings]

[0012] [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. [Figure 7] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 8] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 9] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 10] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 11] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 12] 4 is a graph showing the results of a fastening characteristic test of the locking nut on a screw shaft with a key groove. [Figure 13] 13 is a graph showing the relationship between the average value of the load torque other than the portion where the load torque is reduced by the key groove and the pressure portion width. [Figure 14] 13 is a graph showing the relationship between the deviation value of the load torque other than the portion where the load torque is reduced by the key groove and the pressure portion width. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] 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.

[0015] A pair of pressure parts 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 part 5a, 5b is formed of a thick-walled part that protrudes radially outward compared to other parts of the cylindrical protrusion 3 (hereinafter referred to as "thin-walled parts"). The thin-walled part of the cylindrical protrusion 3 has a uniform thickness along the circumferential direction. Each pressure part 5a, 5b has a predetermined width a. By setting the width a of each pressure part 5a, 5b to be 1.8 times or more the width W of the key groove 12 as described later, it is possible to prevent fluctuations in the prevailing torque and generate a stable anti-loosening action.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 the above-mentioned minor diameter smaller than the effective diameter and the above-mentioned major diameter larger than the effective diameter.

[0023] 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.

[0024] 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. EXAMPLES

[0025] In order to find the optimal structure for the keyway, the inventors of the present application conducted a test of the fastening characteristics of a locking nut 1 of M25 size and 1.5 mm thread pitch on a screw shaft 10 with a keyway. The width W of the keyway 12 of the screw shaft 10 is a size that allows the key portion determined by the f1 dimension of the straight tongue washer described in JIS B1554 to be inserted. The f1 of a straight tongue washer with an inner diameter of 25 mm, which corresponds to M25, is a maximum of 5 mm, and a keyway with a width of 5 mm was formed on a bolt of M25 size and 1.5 mm thread pitch to evaluate the fastening characteristics of the locking nut 1. Figures 7 to 12 show the values ​​of the load torque versus the rotation angle when the width of the pressure parts 5a and 5b, which are the parts that are partially plastically deformed, is changed from 5.5 mm to 10 mm.

[0026] When the width of the pressure applying portions 5a and 5b is 5.5 mm, it can be seen that the load torque drops significantly for every 180° rotation. This is because the inner peripheral portions of the pressure applying portions 5a and 5b enter the key grooves 12.

[0027] The pressure applying portions 5a and 5b bulge slightly inward and are pressed against the screw shaft 10, increasing the frictional resistance and generating a load torque.

[0028] When the locking nut 1 is tightened, the pressure members 5a and 5b start to engage with the keyway 12. When the keyway 12 and the area of ​​the pressure members 5a and 5b match, friction on one side disappears and the load torque decreases. When the locking nut 1 is tightened further, the area of ​​the pressure members 5a and 5b starts to ride up onto the keyway 12, and the load torque returns to normal.

[0029] It was found that increasing the width of the pressure application portions 5a, 5b reduces the drop in the load torque, and at 10 mm, which is twice the groove width, the drop in the load torque every 180° is improved to the point where it is almost unnoticeable.

[0030] On the other hand, when the width of the pressure applying parts 5a and 5b is 8 mm, the load torque decreases in a repeated pattern of large and small decreases every 180°. This is thought to be a phenomenon that occurs because the pressure applying parts 5a and 5b are not completely symmetrical due to the helical structure of the screw.

[0031] When the average and variance of the load torque are obtained for the portion other than the portion where the load torque is reduced by the key groove 12, the trends shown in Figures 13 and 14 appear. From this trend, it can be seen that the average and the deviation are smallest when the width of the pressure portions 5a, 5b is 9 mm for the 5 mm key groove 12.

[0032] From the above results, it was found that in an anti-loosening nut 1 that has two pressure portions 5a, 5b positioned in the diametrical direction and generates a prevailing torque by crimping the pressure portions 5a, 5b radially inward, in order to eliminate fluctuations in rotational load torque when the area of ​​the pressure portions 5a, 5b is located in the key groove 12 provided in the screw shaft 10, the width a of the pressure portions 5a, 5b should be 1.8 times or more the width W of the key groove 12. [Explanation of symbols]

[0033] 1 Locking nut 2 Nut body 3 Cylindrical protrusion 4 Female thread 5a, 5b Pressurizing section 10 Screw shaft 11 Male thread 12 Keyway

Claims

1. a fastening device comprising: a threaded shaft having a male thread on its outer circumference; and an anti-loosening nut screwed onto the threaded shaft, a key groove extending along the axial direction and having a predetermined width is provided on a circumferential portion of the threaded shaft, the nut comprises a nut body and a cylindrical protrusion protruding upward along the axial direction from an upper surface of the nut body, the nut body and the cylindrical protrusion having an internal thread provided on their inner circumferences, and a first pressure portion for pressing the cylindrical protrusion radially inward and deforming it is provided at one location in the circumferential direction on the outer periphery of the cylindrical protrusion, the first pressure portion having a predetermined width, the width of the first pressure portion being 1.8 times or more the width of the key groove.

2. 2. The fastening device according to claim 1, a second pressure applying portion is provided on an outer periphery of the cylindrical protrusion portion at a position diametrically symmetrical to the first pressure applying portion, the second pressure applying portion having a predetermined width, and the width of the second pressure applying portion is 1.8 times or more the width of the key groove.

3. 2. The fastening device according to claim 1, A fastening device, wherein the wall thickness of the cylindrical protrusion is greatest at the first pressure portion.

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