JP2009204030A - Screw fastening mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw fastening mechanism which includes a simple structure, and easily performs an effective locking when a nut and a bolt are fastened with a predetermined axial force. <P>SOLUTION: When a fastening bolt 81 is fastened to a nut 71, screw threads 713D, 713E and 713F of the nut 71 are elastically deformed because they are strongly pushed to screw threads 812D, 812E and 812F of the fastening bolt 81 respectively, so that a frictional resistance between the nut 71 and the bolt 81 increases. Therefore, when a female thread 712 of the nut 71 is processed with a threading tool, machining excellent in accuracy is possible, and setting a frictional resistance to a predetermined magnitude is easy since a pitch of a part of thread of the female thread 712 of the nut 71 is only machined smaller than the pitches of the other threads. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steering device, and more particularly, to a screw fastening mechanism used for a universal joint that connects a shaft that transmits rotational torque of a steering wheel.

  In such a screw fastening mechanism used for a universal joint of a steering device, it is necessary to prevent the bolts tightened on the nut from being loosened due to vibrations of the vehicle body, and various mechanisms are used as a locking mechanism for that purpose. Has been.

  As a conventional anti-loosening mechanism, there is a mechanism that tightens the end face of the nut or coats the thread to increase the frictional resistance of the threaded surface of the screw thread of the nut and bolt to prevent loosening. . However, with this method, the frictional resistance variation of the threaded surfaces of the nut and bolt threads increases, making it difficult to manage the nut and bolt with a predetermined axial force using the bolt tightening torque. Become.

  In addition, the locking mechanism disclosed in Patent Document 1 increases the frictional resistance of the screwing surface of the screw thread between the nut and the bolt by inserting a tightening ring that can be expanded and contracted between the bolt and the nut. It is one that has been loosened.

  In addition, the locking mechanism disclosed in Patent Document 2 forms a coarse thread and a narrow thread on a single bolt, and is tightened with a double nut of a locking nut and a locking nut so that the tightening nut rotates in the loosening direction. This is to prevent it from loosening. Although the locking mechanism disclosed in Patent Document 1 and Patent Document 2 has high reliability of the locking function, the structure is complicated and the number of parts increases, resulting in an increase in manufacturing cost.

JP-A-9-166121 JP 2003-220438 A

  It is an object of the present invention to provide a screw fastening mechanism that is simple in structure and easy to effectively prevent loosening when a nut and a bolt are fastened with a predetermined axial force.

  The above problem is solved by the following means. That is, the first invention is a screw fastening mechanism configured by screwing together a male screw of a bolt and a female screw of a nut, and the screw fastening mechanism has a shape of a thread of a part of the female screw of the nut. Is a screw fastening mechanism in which the bolt and the nut are prevented from loosening by increasing the frictional resistance of the threaded portion by forming the pin into a shape different from the shape of the other screw threads.

  A second invention is a screw fastening mechanism according to the first invention, wherein the thread pitch of a part of the female screw of the nut is made different from the pitch of the other screw thread. is there.

  The third invention is characterized in that, in the screw fastening mechanism of the first invention, the angle of the thread of a part of the female thread of the nut is formed larger than the angle of the thread of another thread. A screw fastening mechanism.

  A fourth invention is characterized in that, in the screw fastening mechanism of the first invention, the height of a part of the female thread of the nut is formed to be higher than the height of the other thread. This is a screw fastening mechanism.

  A fifth aspect of the invention is a screw fastening mechanism in which the screw fastening mechanism according to any one of the first to fourth aspects of the invention is used for a steering apparatus having a universal joint.

  In the screw fastening mechanism of the present invention, by forming the shape of a part of the thread of the female thread of the nut to be different from the shape of the other thread, the frictional resistance of the threaded portion is increased, and the bolt and the nut are It is locking.

  Therefore, when machining the internal thread of the nut, it is only necessary to process the shape of a part of the thread of the female thread of the nut different from the shape of the other thread. It becomes easy to set the frictional resistance between the bolts to a predetermined size.

  Therefore, when the bolt is tightened to the nut with a predetermined tightening torque, the frictional resistance between the nut and the bolt is set to a predetermined magnitude, and the bolt is reliably prevented from loosening with respect to the nut. Further, since the processing is simple and the number of parts does not increase, the increase in manufacturing cost can be reduced.

  Embodiments 1 to 3 of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall front view of a steering device including a universal joint having a screw fastening mechanism (screw fastening device) according to an embodiment of the present invention. FIG. 2 is a side view showing a universal joint having a screw fastening mechanism according to the first embodiment of the present invention. 3 is a cross-sectional view taken along the line AA in FIG. 4A is a cross-sectional view taken along the line B-B in FIG. 3, and is a cross-sectional view showing a state where the shaft and the universal joint are positioned and tightened at a normal axial position, and FIG. 4B is a cross-sectional view of FIG. It is CC sectional drawing of). FIG. 5 is an enlarged cross-sectional view showing a threaded portion between a nut and a fastening bolt of the screw fastening mechanism according to the first embodiment of the present invention.

  As shown in FIG. 1, a steering apparatus having a universal joint having a screw fastening mechanism according to an embodiment of the present invention includes a steering shaft 12 on which a steering wheel 11 can be mounted on the rear side of the vehicle body (right side in FIG. 1), A steering column 13 inserted through the steering shaft 12, an assist device (steering assisting portion) 20 for applying auxiliary torque to the steering shaft 12, and a vehicle body front side (left side in FIG. 1) of the steering shaft 12 are illustrated. And a steering gear 30 connected via a rack / pinion mechanism.

  The steering shaft 12 is spline-fitted between a female steering shaft 12A and a male steering shaft 12B so as to be able to transmit rotational torque and to be relatively movable in the axial direction. Therefore, when the female steering shaft 12A and the male steering shaft 12B collide, the spline fitting portion moves relative to each other so that the total length can be shortened.

  Further, the cylindrical steering column 13 inserted through the steering shaft 12 combines the outer column 13A and the inner column 13B so that they can be telescopically moved. It has a so-called collapsible structure in which the entire length is shortened while absorbing water.

  The vehicle body front side end portion of the inner column 13B is press-fitted and fixed to the vehicle body rear side end portion of the gear housing 21. Further, the front end portion of the male steering shaft 12B on the vehicle body is passed through the inside of the gear housing 21 and connected to the rear end portion of the assist device 20 on the rear side of the input shaft (not shown).

  The steering column 13 is supported by a support bracket 14 at a middle portion thereof on a part of the vehicle body 18 such as a lower surface of the dashboard. Further, a locking portion (not shown) is provided between the support bracket 14 and the vehicle body 18, and when an impact in a direction toward the front side of the vehicle body is applied to the support bracket 14, the support bracket 14 is locked to the locking bracket 14. It moves away from the vehicle and moves to the front side of the vehicle.

  The upper end portion of the gear housing 21 is also supported on a part of the vehicle body 18. In the case of this embodiment, by providing a tilt mechanism and a telescopic mechanism, the position of the steering wheel 11 in the longitudinal direction of the vehicle body and the height position can be freely adjusted. Such a tilt mechanism and a telescopic mechanism are well known in the art and are not characteristic features of the present invention, and thus detailed description thereof is omitted.

  The output shaft 23 protruding from the front end face of the gear housing 21 on the vehicle body is connected to the rear end portion of the intermediate shaft 15 via a universal joint (upper universal joint) 4. Further, a pinion shaft (hereinafter referred to as a shaft) 6 of the steering gear 30 is connected to the front end portion of the intermediate shaft 15 via another universal joint (lower universal joint) 5. The intermediate shaft 15 is fitted on the vehicle body front side of the male intermediate shaft (male shaft) 15A on the vehicle body rear side of the female intermediate shaft (female shaft) 15B so as to be able to transmit rotational torque and relatively move in the axial direction. Is fitted.

  A pinion (not shown) is formed at the lower end (front end of the vehicle body) of the shaft 6. A rack (not shown) meshes with the pinion, and rotation of the steering wheel 11 moves the tie rod 31 to steer a wheel (not shown).

  A case 261 of an electric motor 26 is fixed to the gear housing 21 of the assist device 20, and a worm is coupled to a rotating shaft (not shown) of the electric motor 26. A worm wheel (not shown) is attached to the output shaft 23, and the worm of the rotating shaft of the electric motor 26 is engaged with the worm wheel.

  A torque sensor (not shown) is provided around the intermediate portion of the output shaft 23. The direction and magnitude of the torque applied from the steering wheel 11 to the steering shaft 12 is detected by a torque sensor, and the electric motor 26 is driven in accordance with the detected value via a reduction mechanism comprising a worm and a worm wheel. Then, the output shaft 23 is caused to generate auxiliary torque with a predetermined magnitude in a predetermined direction.

  2 to 5 show the screw fastening mechanism of the first embodiment of the present invention, and show an example applied to the screw fastening mechanism of the universal joint 5 of FIG. The screw fastening mechanism of the present invention may be applied to the screw fastening mechanism of the universal joint 4 of FIG.

  As shown in FIGS. 2 to 5, the universal joint 5 having the screw fastening mechanism according to the first embodiment of the present invention has a pair of yokes 51 and 52 coupled to each other via a cross shaft 53. The four end portions provided on the cross shaft 53 are swingably supported by the tip portions of the yokes 51 and 52 via needle bearings (not shown). Accordingly, the rotational force is transmitted between the yokes 51 and 52 even if the centers of the yokes 51 and 52 are not located on the same straight line.

  When the steering device is assembled using such a universal joint 5, for example, one (right side in FIG. 2) yoke 52 is integrally formed on the vehicle body front end of the female intermediate shaft 15B, and the other (see FIG. 2). 2) The left yoke 51 is coupled to the rear end of the shaft 6 on the vehicle body. In order to perform such assembling work, usually, after attaching the steering device in which the intermediate shaft 15 is connected to the output shaft 23 via the universal joint 4 (upper universal joint) to the vehicle body 18, the universal joint ( The yoke 51 on the left side of the lower universal joint 5 is coupled to the shaft 6.

  The left yoke 51 constituting the universal joint 5 is a so-called horizontal insertion type that can perform a coupling operation without moving the shaft 6 in the axial direction. As shown in FIG. 4A, the yoke 51 has a U-shaped cross-section in a plane orthogonal to the axial direction of the shaft 6, and holding plate portions 54A and 54B constituting U-shaped parallel portions. And a U-shaped recess, and an arcuate connecting portion 55 that connects the lower ends of the holding plate portions 54A and 54B. The holding plate portions 54 </ b> A and 54 </ b> B have an opening 56 on the opposite side of the connecting portion 55 (the upper side in FIG. 4 (1)).

  The holding plate portions 54A and 54B that are spaced apart from each other in parallel form the inner side surfaces as holding surfaces 541A and 541B that are substantially parallel to each other. A small diameter through hole (bolt hole) 57 perpendicular to the axial direction of the shaft 6 is provided in one holding plate portion 54A. Further, a through hole 58 that is concentric with the through hole 57 and larger in diameter than the through hole 57 is formed in the other holding plate portion 54B.

  A nut 71 separate from the restraining plate portion 54B is disposed on the restraining plate portion 54B side at a position concentric with the through hole 58 of the restraining plate portion 54B. In the nut 71, an eccentric cam portion 711 is formed on the outer periphery, and a female screw 712 is formed on the inner periphery. A nut holder 72 is fixed to the outer side surface 542B of the holding plate portion 54B, and a rubber or resin bush 722 is attached to the through hole 721 of the nut holder 72 from below in FIG. The outer periphery of the front end of the bush 722 is fitted into the female screw 712 of the nut 71, and the nut 71 is temporarily held by the nut holder 72.

  On the other hand, the shaft 6 coupled to the tip of the yoke 51 configured as described above has the shape of the tip as shown in FIGS. That is, as shown in FIGS. 2 and 3, the outer peripheral surface of the tip of the cylindrical shaft 6 has a substantially oval shape, and a pair of flat surfaces 61 and 61 parallel to each other are formed.

  When the yoke 51 and the shaft 6 are connected, the flat surfaces 61 and 61 and the holding surfaces 541A and 541B are brought into close contact with each other to prevent rotation of the shaft 6 with respect to the yoke 51. The arcuate upper surface 63 is formed with an upper flat surface 65 that is recessed downward from the arcuate upper surface 63.

  When a fastening bolt (bolt) 81 is inserted from the through hole 57 of the holding plate portion 54A and the male screw 811 formed at the tip of the fastening bolt 81 is screwed into the female screw 712 of the nut 71, the nut 71 moves toward the fastening bolt 81. Be drawn. As a result, the bush 722 is disengaged from the female screw 712 of the nut 71, and the temporary holding of the nut 71 with respect to the nut holder 72 is released. For the material of the tightening bolt 81 and the nut 71, for example, a general material such as carbon steel for machine structure or chrome molybdenum steel can be used.

  When the tightening bolt 81 is further screwed in, the eccentric cam portion 711 of the nut 71 presses the upper flat surface 65 of the shaft 6 downward, and the arc-shaped lower surface 62 of the shaft 6 is connected to the arc-shaped inner surface 551 of the connecting portion 55 of the yoke 51. (See FIG. 4 (1)).

  Therefore, when the shaft 6 is mounted on the yoke 51 at the normal axial position, the eccentric cam portion 711 presses the upper flat surface 65 of the shaft 6 downward, and the arcuate lower surface 62 of the shaft 6 is connected to the connecting portion of the yoke 51. It can be firmly clamped by being brought into close contact with the arcuate inner surface 551 of 55.

  When the end portion of the shaft 6 is connected and fixed to the yoke 51, first, the end portion of the shaft 6 is disposed in the opening 56 (FIG. 4 (1)) of the yoke 51 as shown by a solid line in FIG. Then, from this state, by rotating the yoke 51 around the cross shaft 53, the yoke 51 is swung clockwise in FIG. 2 from the solid line state to the chain line state in FIG. The end portions are inserted into the holding surfaces 541A and 541B of the holding plate portions 54A and 54B of the yoke 52. Before the end portion of the shaft 6 is inserted into the holding surfaces 541A and 541B, the tightening bolt 81 (FIG. 3) is not inserted into the through hole 57.

  As described above, if the end of the shaft 6 is inserted into the holding surfaces 541A and 541B of the yoke 51 and the holding surfaces 541A and 541B are opposed to the flat surfaces 61 and 61 of the shaft 6, the through holes 57, the fastening bolt 81 is inserted, and the male screw 811 formed at the tip of the fastening bolt 81 is screwed into the female screw 712 of the nut 71.

  When the tightening bolt 81 is further screwed into the female screw 712, the nut 71 is pulled into the tightening bolt 81 side. As a result, the bush 722 is disengaged from the female screw 712 of the nut 71, and the temporary holding of the nut 71 with respect to the nut holder 72 is released.

  When the tightening bolt 81 is further screwed in, the nut 71 rotates, the eccentric cam portion 711 of the nut 71 presses the upper flat surface 65 of the shaft 6 downward, and the arc-shaped lower surface 62 of the shaft 6 is connected to the connecting portion of the yoke 51. The arc-shaped inner surface 551 of 55 is brought into close contact with the inner surface. When the pressing force of the eccentric cam portion 711 is increased, a predetermined torque is generated in the tightening bolt 81, so that it can be easily determined that it is assembled at a regular axial position.

  As shown in FIG. 3, stepped portions 611 and 611 are formed on the front end of the vehicle body (the left side in FIG. 3) of the flat surfaces 61 and 61 of the shaft 6. The step portions 611 and 611 are formed wider than the interval between the holding surfaces 541A and 541B of the holding plates 54A and 54B of the yoke 51. Therefore, when the shaft 6 is further inserted into the yoke 51 than the normal axial position, the step portions 611 and 611 of the shaft 6 abut against the front end surface 59 of the vehicle body of the yoke 51, and the shaft 6 is moved to the yoke 51. It is restricted so that it cannot be inserted.

  FIG. 5 is an enlarged cross-sectional view of the screw fastening mechanism including the nut 71 and the fastening bolt 81 of the universal joint 5, showing the screwed portion of the screw fastening mechanism according to the first embodiment of the present invention. As shown in FIG. 5, the tightening bolt 81 has pitches PB1 to PB5 of the threads 812A, 812B, 812C, 812D, 812E, and 812F of the male screw 811 all having the same pitch.

  On the other hand, in the nut 71, pitches PN1 and PN2 between the threads 713A, 713B and 713C of the female screw 712 and pitches PN4 and PN5 between the threads 713D, 713E and 713F are formed at the same pitch. However, only the pitch PN3 between the thread 713C and the thread 713D is formed smaller than the pitch of the other threads.

  Accordingly, when the tightening bolt 81 is tightened to the nut 71, the threads 713D, 713E, and 713F of the nut 71 are strongly pressed against the threads 812D, 812E, and 812F of the tightening bolt 81 and elastically deformed. The frictional resistance between the bolts 81 increases, and the tightening bolt 81 is prevented from loosening with respect to the nut 71.

  In the first embodiment, when the internal thread 712 of the nut 71 is processed with a thread cutting tool, it is only necessary to process the pitch of some thread threads of the internal thread 712 of the nut 71 smaller than the pitch of other thread threads. Therefore, it is easy to set the frictional resistance between the nut 71 and the tightening bolt 81 to a predetermined size.

  Accordingly, when the tightening bolt 81 is tightened to the nut 71 with a predetermined tightening torque, the frictional resistance between the nut 71 and the tightening bolt 81 is set to a predetermined magnitude, and the tightening bolt 81 is surely loosened with respect to the nut 71. Stopped. Further, since the processing is simple and the number of parts does not increase, the increase in manufacturing cost can be reduced.

  In the first embodiment, the pitch of some thread threads of the female thread 712 of the nut 71 is processed to be smaller than the pitch of other thread threads, but the pitch of some thread threads of the female thread 712 of the nut 71 is changed to other pitches. The pitch of a part of the female thread 712 of the nut 71 may be processed so as to be larger than the pitch of the thread, and the pitch of the other thread may be made different.

  Next, a second embodiment of the present invention will be described. FIG. 6 is an enlarged cross-sectional view of the screw fastening mechanism including the nut 71 and the fastening bolt 81, showing a screwed portion between the nut and the fastening bolt of the screw fastening mechanism according to the second embodiment of the present invention. In the following description, only structural portions and operations different from those of the first embodiment will be described, and overlapping descriptions will be omitted. Further, the same parts will be described with the same numbers.

  As shown in FIG. 6, the tightening bolt 81 is formed such that the mountain angles θB1 to θB6 of the threads 812A, 812B, 812C, 812D, 812E, and 812F of the male screw 811 are all the same angle.

  On the other hand, in the nut 71, the threads 713A, 713B, 713C, and 713F of the female thread 712 are formed at the same angle, but the thread 713D and the thread 713E are formed. Only the crest angles θN4 and θN5 are formed larger than the angles of the other crests.

  Therefore, when the tightening bolt 81 is tightened to the nut 71, the thread 713D of the nut 71 is strongly pressed against the threads 812D and 812E of the tightening bolt 81, and the thread 713E is strongly pressed against the threads 812E and 812F. Due to elastic deformation, the frictional resistance between the nut 71 and the tightening bolt 81 is increased, and the tightening bolt 81 is prevented from loosening with respect to the nut 71.

  In the second embodiment, when the internal thread 712 of the nut 71 is processed with the thread cutting tool, the angle of the thread ridge of a part of the internal thread 712 of the nut 71 is simply processed to be larger than the angle of the other thread ridge. Therefore, processing with high accuracy is possible, and it becomes easy to set the frictional resistance between the nut 71 and the tightening bolt 81 to a predetermined size.

  Accordingly, when the tightening bolt 81 is tightened to the nut 71 with a predetermined tightening torque, the frictional resistance between the nut 71 and the tightening bolt 81 is set to a predetermined magnitude, and the tightening bolt 81 is surely loosened with respect to the nut 71. Stopped. Further, since the processing is simple and the number of parts does not increase, the increase in manufacturing cost can be reduced. In Example 2, the angle of the two thread threads is formed larger than the angle of the other thread threads, but the angle of one or more thread threads is equal to the other thread angles. You may form larger than the angle of the thread ridge.

  Next, a third embodiment of the present invention will be described. FIG. 7 is an enlarged cross-sectional view of the screw fastening mechanism including the nut 71 and the fastening bolt 81, showing a screwed portion between the nut and the fastening bolt of the screw fastening mechanism according to the third embodiment of the present invention. In the following description, only structural portions and operations different from the above embodiment will be described, and redundant description will be omitted. Further, the same parts will be described with the same numbers.

  As shown in FIG. 7, in the tightening bolt 81, the thread heights HB1 to HB6 of the thread threads 812A, 812B, 812C, 812D, 812E, and 812F of the male thread 811 are all formed at the same height.

  On the other hand, in the nut 71, the thread heights HN1, HN2, HN3, HN5, and HN6 of the thread threads 713A, 713B, 713C, 713E, and 713F of the female thread 712 are formed at the same height. Only the peak height HN4 of the peak 713D is formed larger than the heights of the other thread peaks.

  Accordingly, when the tightening bolt 81 is tightened to the nut 71, the thread 713D of the nut 71 is strongly pressed against the threads 812D and 812E of the tightening bolt 81 and elastically deforms, so that the frictional resistance between the nut 71 and the tightening bolt 81 is increased. The tightening bolt 81 is prevented from loosening with respect to the nut 71.

  In the third embodiment, when the internal thread 712 of the nut 71 is processed with a thread cutting tool, the height of a part of the thread ridge of the internal thread 712 of the nut 71 is only processed to be larger than the height of the other thread ridges. Therefore, processing with high accuracy is possible, and it becomes easy to set the frictional resistance between the nut 71 and the fastening bolt 81 to a predetermined size.

  Accordingly, when the tightening bolt 81 is tightened to the nut 71 with a predetermined tightening torque, the frictional resistance between the nut 71 and the tightening bolt 81 is set to a predetermined magnitude, and the tightening bolt 81 is surely loosened with respect to the nut 71. Stopped. Further, since the processing is simple and the number of parts does not increase, the increase in manufacturing cost can be reduced. In Example 3, the height of one thread is greater than the height of the other thread, but the height of two or more threads is equal to the other thread. You may form larger than the height of the mountain.

  In the above embodiment, the example in which the present invention is applied to the screw fastening mechanism of the universal joint that connects the pinion shaft and the intermediate shaft has been described. However, the present invention can be applied to any screw fastening mechanism constituting the steering device. .

It is the whole steering device provided with the universal joint which has the screw fastening mechanism of the example of the present invention. It is a side view which shows the universal joint which has the screw fastening mechanism of Example 1 of this invention. It is AA sectional drawing of FIG. (1) is a cross-sectional view taken along the line BB in FIG. 3, and is a cross-sectional view showing a state in which the shaft and the universal joint are positioned and tightened at a normal axial position, and (2) is a cross-sectional view taken along the line CC in (1). FIG. It is an expanded sectional view which shows the screwing part of the nut and fastening bolt of the screw fastening mechanism of Example 1 of this invention. It is an expanded sectional view which shows the screwing part of the nut of a screw fastening mechanism of Example 2 of this invention, and a fastening bolt. It is an expanded sectional view which shows the screwing part of the nut and fastening bolt of the screw fastening mechanism of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Steering shaft 12A Female steering shaft 12B Male steering shaft 13 Steering column 13A Outer column 13B Inner column 14 Support bracket 15 Intermediate shaft 15A Male intermediate shaft 15B Female intermediate shaft 18 Car body 20 Assist device 21 Gear housing 23 Output shaft 26 Electric Motor 261 Case 30 Steering gear 31 Tie rod 4 Universal joint (upper universal joint)
5 Universal joint (lower universal joint)
51, 52 Yoke 53 Cross shaft 54A, 54B Holding plate portion 541A, 541B Holding surface 542B Outer side surface 55 Connecting portion 551 Arc-shaped inner surface 56 Opening portion 57, 58 Through hole 59 Car body front side end surface 6 shaft (pinion shaft)
61 Flat surface 611 Stepped portion 62 Arc-shaped lower surface 63 Arc-shaped upper surface 65 Upper flat surface 71 Nut 711 Eccentric cam portion 712 Female thread 713A, 713B, 713C, 713D, 713E, 713F Screw thread 72 Nut holder 721 Through hole 722 Bushing 81 Tightening bolt (bolt)
811 Male thread 812A, 812B, 812C, 812D, 812E, 812F Thread

Claims (5)

A screw fastening mechanism configured by screwing together a male screw of a bolt and a female screw of a nut,
The screw fastening mechanism is
A part of the thread of the female thread of the nut is formed in a shape different from the shape of the other thread, thereby increasing the frictional resistance of the threaded portion and preventing the bolt and nut from loosening. Screw fastening mechanism. The screw fastening mechanism according to claim 1,
A screw fastening mechanism characterized in that a pitch of a part of the female thread of the nut is different from a pitch of another thread. The screw fastening mechanism according to claim 1,
A screw fastening mechanism, wherein an angle of a thread of a part of the female thread of the nut is formed larger than an angle of a thread of another thread. The screw fastening mechanism according to claim 1,
A screw fastening mechanism, wherein the height of a part of the female thread of the nut is greater than the height of the other thread. The screw fastening mechanism according to any one of claims 1 to 4 is used for a steering device having a universal joint.

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