Nut, manufacturing method thereof, and feed screw device

Abstract

To realize a structure capable of effectively suppressing resistance to relative rotation of a nut and a rod, as well as backlash between the nut and the rod.SOLUTION: A slit 18 is formed to be extended in a direction orthogonal to a direction of a lead angle at a part where the slit 18 crosses, of a screw thread 21 constituting a female screw portion 22. In a case where the slit 18 is inclined in a direction from one side in a width direction toward the other side as it goes from one side in an axial direction to the other side when observed from a radial direction of a cylindrical portion 17, rigidity is gradually increased from one side in the axial direction toward the other side at a circumferential one-side part of circumferential both-side vicinity parts holding the slit 18, of the cylindrical part 17, and rigidity is gradually decreased from one side in the axial direction toward the other side at the circumferential other side part.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a nut having a slit and configured so that its inner diameter can be expanded or contracted, a manufacturing method thereof, and a feed screw device using said nut. [Background technology]

[0002] 11 to 13(b) show an example of a conventional structure of a feed screw device described in International Publication WO 03 / 078234 (Patent Document 1). The feed screw device 100 includes a nut 101, a rod 102, and a bolt 103.

[0003] The nut 101 comprises a tubular portion 105 having a female thread portion 104 on its inner surface, a slit 106 formed in the tubular portion 105 so as to extend in the axial direction, and a pair of fastening holes 107a, 107b formed in portions of the tubular portion 105 that are aligned with each other across the slit 106, in a direction perpendicular to the extension direction (formation direction) of the slit 106.

[0004] The rod 102 has an external thread 108 on its outer circumferential surface that screws into the internal thread 104 .

[0005] The bolt 103 is inserted through one fastening hole 107a of a pair of fastening holes 107a, 107b, and is screwed into the other fastening hole 107b.

[0006] In the feed screw device 100, by adjusting the amount of tightening of the bolt 103 against the other fastening hole 107b, the width of the slit 106 is expanded or contracted, and the inner diameter of the tubular portion 105 is expanded or contracted, thereby suppressing backlash at the threaded portion between the female threaded portion 104 of the nut 101 and the male threaded portion 108 of the rod 102.

[0007] In the structure described in WO 03 / 078234, a slit 106 is formed in a nut 101, extending in an axial direction parallel to the central axis of the nut 101, and a bolt 103 for expanding and contracting the width of the slit 106 is disposed in a direction perpendicular to the extension direction of the slit 106. In contrast, the threads of the female threaded portion 104 and the threads of the male threaded portion 108 have a lead angle and are inclined with respect to the axial direction of the bolt 103 (the up-down direction in FIG. 13(a)), which corresponds to the expanding and contracting direction of the nut 101.

[0008] Therefore, when the inner diameter of the tubular portion 105 is reduced by increasing the tightening amount of the bolt 103, as shown in Figures 13(a) and 13(b), uneven contact occurs between the flank surface of the thread that constitutes the female thread portion 104 and the flank surface of the thread that constitutes the male thread portion 108. When such uneven contact occurs, friction acting between the flank surface of the thread that constitutes the female thread portion 104 and the flank surface of the thread that constitutes the male thread portion 108 increases, and the gap that causes unavoidable backlash increases.

[0009] In contrast, WO 2019 / 142378 (Patent Document 2) describes a feed screw device in which a slit is formed to extend in a direction perpendicular to the direction of the lead angle at the portion of the thread (thread groove) constituting the female thread provided on the inner peripheral surface of the nut that the slit crosses, and a bolt for reducing the inner diameter of the nut is arranged in a direction perpendicular to the extension direction of the slit. The feed screw device described in WO 2019 / 142378 can bring the flank surface of the thread constituting the female thread and the flank surface of the thread constituting the male thread provided on the outer peripheral surface of the rod closer to each other and slidably abut (surface contact) when the tightening amount of the bolt is increased to reduce the inner diameter of the nut. The feed screw device described in WO 2019 / 142378 can bring these surfaces closer to each other and slidably abut (surface contact) while maintaining the thickness of the gap between the flank surface of the thread constituting the female thread and the flank surface of the thread constituting the male thread provided on the outer peripheral surface of the rod. This prevents the friction acting between the female threaded portion of the nut and the male threaded portion of the rod from becoming too large, and also reduces the gap between the flank surface of the thread that constitutes the female threaded portion and the flank surface of the thread that constitutes the male threaded portion, which causes backlash. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 03 / 078234 Brochure [Patent Document 2] International Publication No. 2019 / 142378 Brochure Summary of the Invention [Problem to be solved by the invention]

[0011] The feed screw device described in WO 2019 / 142378 has room for improvement in the following respects. That is, in the structure described in WO 2019 / 142378, a pair of fastening holes are formed in a direction perpendicular to the extension direction of the slit on both sides of the center position in the extension direction of the slit. A bolt for reducing the inner diameter of the cylindrical part of the nut is inserted into one of the fastening holes and screwed into the other fastening hole.

[0012] Therefore, when the amount of tightening of the bolt to the other tightening hole is increased in order to reduce the inner diameter of the cylindrical portion, the cylindrical portion is deformed so that the width of the slit is narrowest in the center of the extension direction and becomes wider toward both sides in the extension direction. That is, the cylindrical portion is deformed so that the inner diameter is smallest in the axial middle portion and becomes larger toward both sides in the axial direction. As a result, in the axial middle portion of the cylindrical portion, friction acting between the flank surface of the thread constituting the female thread portion provided on the inner peripheral surface of the cylindrical portion and the flank surface of the thread constituting the male thread portion provided on the outer peripheral surface of the rod may increase. In addition, there may be a problem that the pitch of the female thread portion is narrowest in the axial middle portion and becomes wider toward both sides in the axial direction. These problems are likely to be prominent in nuts in which the ends of the slit on both sides in the extension direction are not open to the end faces on both axial sides of the cylindrical portion.

[0013] In consideration of the above-mentioned circumstances, the present invention aims to realize a structure that can more effectively suppress resistance to relative rotation between a nut and a rod, and backlash between the nut and the rod. [Means for solving the problem]

[0014] The nut according to one aspect of the present invention is A cylindrical portion having an internal thread formed by forming a screw thread helically on an inner peripheral surface thereof; The cylindrical portion has a slit formed at one location in the circumferential direction thereof and opening to the outer circumferential surface and the inner circumferential surface of the cylindrical portion.

[0015] The slit is formed so as to extend in a direction perpendicular to the direction of the lead angle of the portion of the thread that it traverses.

[0016] In particular, in a nut according to one aspect of the present invention, when the slit is inclined in the direction from one circumferential side to the other as it goes from one axial side to the other when viewed from the radial direction of the tubular portion, in the portions of the tubular portion near both sides in the circumferential direction on either side of the slit, the rigidity (rigidity against deformation in the direction of reducing the diameter) of the portion on one circumferential side increases as it goes from one axial side to the other, and the rigidity of the portion on the other circumferential side decreases as it goes from one axial side to the other, or alternatively, the rigidity of the portion on one circumferential side decreases as it goes from one axial side to the other, and the rigidity of the portion on the other circumferential side increases as it goes from one axial side to the other.

[0017] In a nut according to one embodiment of the present invention, in the circumferential portions of the tubular portion near both sides of the slit, the height of the thread can be made greater in the circumferential portion on one side as it moves from one axial side to the other, and the height of the thread can be made smaller in the circumferential portion on the other side as it moves from one axial side to the other; or, alternatively, the height of the thread can be made smaller in the circumferential portion on one side as it moves from one axial side to the other, and the height of the thread can be made greater in the circumferential portion on the other side as it moves from one axial side to the other.

[0018] In the nut according to one aspect of the present invention, grinding marks can be formed on the flank surface of the thread in the direction in which the thread is formed.

[0019] In the nut according to one aspect of the present invention, the ends of the slit in the extension direction may not be open to the end faces of both axial sides of the cylindrical portion, or the ends of the slit in the extension direction may be open to the end faces of both axial sides of the cylindrical portion.

[0020] In the nut according to one aspect of the present invention, the female thread portion may be configured as a multiple-start thread having a number of threads (number of threads) of 2 or more. Alternatively, the female thread portion may be configured as a single-start thread.

[0021] A nut according to one aspect of the present invention may have a pair of fastening holes formed in both side portions of the tubular portion that are aligned with each other across the slit, in a direction perpendicular to the extension direction of the slit.

[0022] A method for manufacturing a nut according to one aspect of the present invention is as follows: forming a female screw portion by forming a screw thread helically on an inner peripheral surface of the cylindrical portion; forming a slit at one location in the circumferential direction of the cylindrical portion, the slit opening into the outer peripheral surface and the inner peripheral surface of the cylindrical portion, so as to extend in a direction perpendicular to the direction of the lead angle at a portion of the thread that the slit crosses; a step of performing cutting processing with an end mill on portions of the cylindrical portion sandwiching the slit from both sides in the width direction, so that, when viewed from the radial direction of the cylindrical portion, the slit is inclined in a direction from one circumferential side to the other as it goes from one axial side to the other, in the portions of the cylindrical portion near both sides in the circumferential direction sandwiching the slit, decreasing the height of the thread in one circumferential side portion as it goes from one axial side to the other and increasing the height of the thread in the other circumferential side portion as it goes from one axial side to the other, or increasing the height of the thread in one circumferential side portion as it goes from one axial side to the other and decreasing the height of the thread in the other circumferential side portion as it goes from one axial side to the other; Equipped with.

[0023] In one embodiment of the nut manufacturing method of the present invention, the end mill is inserted from one axial end of the tubular portion and displaced along the extension direction of the slit, thereby enabling cutting to be performed on portions of the tubular portion near both circumferential sides of the slit. In this case, the end mill may have an outer diameter that is 50% or more and 90% or less of the inner diameter of the female thread portion.

[0024] A feed screw device according to one aspect of the present invention comprises: A nut according to one aspect of the present invention, comprising: a nut having a pair of fastening holes; A rod having an external thread portion on an outer circumferential surface thereof, the external thread portion being engaged with the internal thread portion; A bolt that is inserted or screwed into the pair of fastening holes and that expands or reduces the distance between the slits; Equipped with. Effect of the Invention

[0025] According to the present invention, it is possible to more effectively suppress resistance to relative rotation between the nut and the rod, and backlash between the nut and the rod. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a side view showing an electric steering wheel position adjustment device according to one embodiment of the present invention, where FIG. 1(a) is a view showing the steering wheel in the uppermost position, FIG. 1(b) is a view showing the steering wheel in the intermediate position, and FIG. 1(c) is a view showing the steering wheel in the lowermost position. [Diagram 2] FIG. 2(a) is a side view of a nut according to one embodiment of the present invention as viewed from the radial outside, and FIG. 2(b) is a side view as viewed from an angle different from that of FIG. 2(a). [Diagram 3] FIG. 3 is a schematic cross-sectional view of a feed screw device according to an embodiment of the present invention. [Figure 4] 4(a) is a cross-sectional view taken along line AA in FIG. 3, showing the nut removed, FIG. 4(b) is a cross-sectional view taken along line BB in FIG. 3, showing the nut removed, and FIG. 4(c) is a cross-sectional view taken along line CC in FIG. 3, showing the nut removed. [Diagram 5] FIG. 5 is a cross-sectional view taken along line DD of FIG. [Figure 6] FIG. 6 is an end view of the cylindrical portion of the nut as viewed from one axial side. [Figure 7] 7(a) to 7(c) are plan views showing the process of cutting a thread with an end mill in sequence. [Figure 8] FIG. 8 is a view taken along the arrow E in FIG. [Figure 9] FIG. 9 is a side view showing how the female thread portion of the nut is finish-ground. [Figure 10] FIG. 10 is a cross-sectional view taken along line FF of FIG. [Figure 11] FIG. 11 is a side view showing an example of a conventional feed screw device. [Figure 12] FIG. 12 is a cross-sectional view taken along line G-G of FIG. [Figure 13] FIG. 13(a) is a schematic cross-sectional view for explaining the problems with a feed screw device of a conventional structure, and FIG. 13(b) is an enlarged view of a portion H in FIG. 13(a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] An embodiment of the present invention will be described with reference to Figures 1 to 10. This embodiment is an example in which a feed screw device of the present invention is applied to an electric position adjuster for a steering wheel, which is provided with a tilt mechanism for adjusting the vertical position of the steering wheel.

[0028] The steering wheel position adjustment device includes a column bracket 1, a steering column 2, a steering shaft 3, and an electric actuator 4.

[0029] The column bracket 1 comprises a mounting part 6 which is supported and fixed to a vehicle body 5, a front support part 7 which is bent downward from a widthwise edge of a front part of the mounting part 6, and a rear support part 8 which is bent downward from a rear end edge of the mounting part 6. A cylindrical sleeve 9 is supported and fixed to a vertically intermediate part of the front side surface of the rear support part 8.

[0030] The steering column 2 is configured to be cylindrical as a whole. The front end of the steering column 2 is supported by a front support portion 7 of a column bracket 1 so as to be capable of swinging displacement about a pivot 10 disposed in the width direction of a vehicle body 5.

[0031] The steering shaft 3 is rotatably supported on the inner diameter side of the steering column 2. A steering wheel (not shown) is supported and fixed to the rear end of the steering shaft 3.

[0032] The electric actuator 4 includes an electric motor 11 and a feed screw device 12. The output shaft of the electric motor 11 is disposed parallel to the axial direction of the steering column 2, and is supported and fixed to the steering column 2. Worm teeth 13 are provided on the outer circumferential surface of the output shaft of the electric motor 11.

[0033] The feed screw device 12 includes a nut 14, a rod 15, and a bolt 16 (only shown in FIG. 3).

[0034] The nut 14 includes a cylindrical portion 17 , a slit 18 , a pair of fastening holes 19 a and 19 b , and an engagement arm portion 20 .

[0035] The cylindrical portion 17 has an internal thread portion 22 formed by forming a screw thread 21 having a triangular cross-sectional shape in a spiral shape on its inner peripheral surface. The screw thread 21 has grinding marks on its flank surface (the surface connecting the crest and the root) along the formation direction (spiral direction) of the screw thread 21. In short, the grinding marks are formed in the sliding direction between the flank surface of the screw thread 21 constituting the internal thread portion 22 of the nut 14 and the flank surface of the screw thread constituting the external thread portion 26 of the rod 15 when the feed screw device 12 is constituted by combining the nut 14 and the rod 15.

[0036] The slit 18 is formed at one location in the circumferential direction of the cylindrical portion 17 so as to open on the outer peripheral surface and the inner peripheral surface of the cylindrical portion 17. In particular, in this example, the slit 18 is formed to extend not in an axial direction parallel to the central axis of the nut 14 (cylindrical portion 17) but in a direction perpendicular to the lead angle direction (perpendicular to the tooth trace direction) at the portion of the thread 21 constituting the female thread portion 22 where the slit 18 crosses. For this reason, the radially inner end of the slit 18 opens on the inner peripheral surface of the cylindrical portion 17 so as to cross the tooth trace (peak) of the thread 21 constituting the female thread portion 22 at a right angle. Note that the term "perpendicular" includes not only the case where the angle between the lead angle direction of the thread 21 and the extension direction of the slit 18 (formation direction, central axis direction) is 90°, but also the case where it is close to 90°, specifically, about 85° to 95°. In this embodiment, the opening width of the slit 18 is substantially constant over its entire length, except for unavoidable manufacturing errors.

[0037] In this example, both ends of the slit 18 in the extension direction are not open to the end faces on both sides of the axial direction of the cylindrical portion 17. In other words, the slit 18 is formed of an elongated hole, and both ends in the extension direction are closed. Specifically, as shown in FIG. 2(a), the radially inner parts of both ends of the slit 18 in the extension direction are not open to both axial end faces of the cylindrical portion 17, whereas the cutting marks generated by forming the slit 18 by cutting are open to both axial end faces of the cylindrical portion 17 in the radially outer parts of both ends of the slit 18 in the extension direction. However, it is also possible to prevent the cutting marks from being generated in the radially outer parts of both ends of the slit 18 in the extension direction. Therefore, as described later, even if the inner diameter of the cylindrical portion 17 is reduced, it is possible to make it difficult for the pitch of the female thread portion 22 to deviate from the circumferential direction of the slit 18. The circumferential position of the slit 18 is appropriately determined in consideration of the rigidity of the nut 14 and the rigidity of the steering column 2 on which the nut 14 is supported.

[0038] The pair of fastening holes 19a, 19b are formed coaxially in a direction perpendicular to the extension direction of the slit 18 (a direction parallel to the lead angle direction at the portion of the thread 21 constituting the female thread portion 22 where the slit 18 crosses) in the cylindrical portion 17, on both sides of the slit 18. In this example, one fastening hole 19a of the pair of fastening holes 19a, 19b is a circular hole, and the other fastening hole 19b is a threaded hole. Note that if the overall length of the slit 18 is long, a plurality of pairs of fastening holes 19a, 19b can be provided in both sides of the cylindrical portion 17 that sandwich the slit 18.

[0039] The engaging arm 20 has a spherical portion 23 at its tip, the outer circumferential surface of which is a spherical convex surface, and the spherical portion 23 is engaged with the inner circumferential surface of the sleeve 9 without any radial rattle. This supports the nut 14 on the column bracket 1, which is a portion that does not displace in the vertical direction, which is the adjustment direction of the steering wheel, when adjusting the vertical position of the steering wheel. The engaging arm 20 is provided so as to protrude in the radial direction from the outer circumferential surface of the cylindrical portion 17, which is a portion that is circumferentially deviated from the portion where the slit 18 is formed. In this example, the engaging arm 20 is provided at a position that is shifted in phase by about 120° from the portion where the slit 18 is formed. However, for example, the engaging arm 20 can be provided at a position that is shifted in phase by 90° from the portion where the slit 18 is formed, or at a position that is radially opposite the portion where the slit 18 is formed.

[0040] In this example, the rigidity of the tubular portion 17 is adjusted in the vicinity of both circumferential sides sandwiching the slit 18. Specifically, when the slit 18 is inclined from one circumferential side to the other circumferential side (from the bottom to the top in Figs. 3 and 5) as it goes from one axial side to the other axial side (from the left to the right in Figs. 3 and 5) as viewed from the radial direction of the tubular portion 17, i.e., from the direction perpendicular to the central axis of the tubular portion 17 and the extension direction of the slit 18 (the front-to-back direction in Figs. 3 and 5), the rigidity (rigidity against deformation in the direction of reducing the diameter) of the one circumferential side portion of the tubular portion 17 increases as it goes from one axial side to the other axial side, and the rigidity of the other circumferential side portion decreases as it goes from one axial side to the other axial side.

[0041] More specifically, in the circumferentially adjacent portions of the cylindrical portion 17 on both sides of the slit 18, the height of the thread 21 is increased from one axial side to the other axial side in the circumferentially adjacent portion, and the height of the thread 21 is decreased from one axial side to the other axial side in the circumferentially adjacent portion on the other side of the circumferentially adjacent portion. In other words, in the circumferentially adjacent portions of the cylindrical portion 17 on both sides of the slit 18, the wall thickness (radial thickness) is increased from one axial side to the other axial side in the circumferentially adjacent portion, and the wall thickness is decreased from one axial side to the other axial side in the circumferentially adjacent portion on the other side of the circumferentially adjacent portion. In other words, the inner peripheral surface of the cylindrical portion 17 has a recess 24 extending in the extension direction of the slit 18 and recessed toward the radially outward side in a portion including the portion where the slit 18 is formed. The recess 24 opens to the end faces on both axial sides of the cylindrical portion 17 and has an arc-shaped cross section. Moreover, the depth of the recess 24 becomes shallower from one axial side to the other at one circumferential side of the slit 18, and becomes deeper from one axial side to the other at the other circumferential side. The circumferential width of the portion of the recess 24 on one circumferential side of the slit 18 becomes smaller from one axial side to the other, and the circumferential width of the portion of the recess 24 on the other circumferential side of the slit 18 becomes larger from one axial side to the other.

[0042] With its central axis oriented in the axial direction of the steering column 2 (parallel to the central axis) and in a direction perpendicular to the width direction of the vehicle body 5 (vertical direction in FIG. 1(b)), the rod 15 is supported so as to be rotatable only on the widthwise side surface of the steering column 2, which is the part that displaces together with the steering wheel in the vertical direction, which is the adjustment direction of the steering wheel, when adjusting the vertical position of the steering wheel. The rod 15 has wheel teeth 25 that mesh with the worm teeth 13 on the outer circumferential surface of its lower end, and a male thread portion 26 that screws into the female thread portion 22 on the outer circumferential surface of its upper side. In other words, the rod 15 can be rotated by the electric motor 11.

[0043] The bolt 16 is inserted through one of the fastening holes 19a, which is a circular hole, and the tip of the bolt 16 is screwed into the other fastening hole 19b, which is a screw hole. Therefore, the bolt 16 is arranged in a direction perpendicular to the extension direction of the slit 18, that is, in the direction of the lead angle of the thread 21 at the portion where the slit 18 crosses. In the feed screw device 12 of this example, the interval of the slit 18 can be expanded or contracted by adjusting the amount of fastening (amount of screwing) of the bolt 16 with respect to the other fastening hole 19b, and the inner diameter of the cylindrical portion 17 can be expanded or contracted. However, it is also possible to configure the pair of fastening holes 19a, 19b as circular holes, and to screw a nut other than the nut 14 onto the tip of the bolt 16 inserted into each of the fastening holes 19a, 19b. In any case, by expanding or contracting the inner diameter of the tubular portion 17, it is possible to suppress backlash between the female threaded portion 22 and the male threaded portion 26 while preventing an excessive increase in resistance to the relative rotation of the male threaded portion 26 with respect to the female threaded portion 22.

[0044] In this example, the bearing surface of the head of the bolt 16 is configured as a flat surface perpendicular to the central axis of the bolt 16. However, the bearing surface of the bolt head can also be configured as a convex curved surface with an arc-shaped cross section. In this case, the portion of the nut that comes into contact with the bearing surface of the bolt can be a flat surface or a concave curved surface with an arc-shaped cross section.

[0045] A method of adjusting the vertical position of the steering wheel in the electric steering wheel position adjustment device of this embodiment will be described. First, when the steering wheel is displaced upward, for example, as shown in FIG. 1(b)→FIG. 1(a), the electric motor 11 is energized to rotate the output shaft of the electric motor 11 in a predetermined direction, and the rod 15 is rotated through the meshing portion between the worm teeth 13 and the wheel teeth 25. The rotation of the rod 15 is converted into an upward displacement of the rod 15 by the screwing of the female thread portion 22 and the male thread portion 26. When the rod 15 is displaced upward, the rear end of the steering column 2 supporting the rod 15 is displaced upward about the pivot 10, and the steering wheel is displaced upward. In addition, with the upward displacement of the steering column 2, the nut 14 swings upward about the spherical engagement portion between the spherical portion 23 and the inner peripheral surface of the sleeve 9. After the steering wheel is adjusted to a desired position, the power supply to the electric motor 11 is stopped, the rotation of the rod 15 is stopped, and the position of the steering wheel is maintained.

[0046] When the steering wheel is displaced downward, for example, as shown in FIG. 1(b)→FIG. 1(c), the output shaft of the electric motor 11 is rotated in the direction opposite to the predetermined direction, and the rod 15 is rotated. The rotation of the rod 15 is converted into a downward displacement of the rod 15 by the engagement of the female threaded portion 22 with the male threaded portion 26. When the rod 15 is displaced downward, the rear end of the steering column 2 is displaced downward about the pivot 10, and the steering wheel is displaced downward. In addition, with the downward displacement of the steering column 2, the nut 14 swings downward about the spherical engagement portion. After the steering wheel is adjusted to a desired position, the power supply to the electric motor 11 is stopped, the rotation of the rod 15 is stopped, and the position of the steering wheel is maintained.

[0047] An example of a method for manufacturing the nut 14 constituting the feed screw device 12 of this embodiment will be described with reference to Figs. 7(a) to 10.

[0048] When making the nut 14, first, a metallic material is subjected to necessary processing such as casting, forging, cutting, and heat treatment to produce a cylindrical member having a cylindrical portion 17 and an engaging arm portion 20 that protrudes radially from the cylindrical portion 17. Next, a cutting process is performed with a milling cutter at one location in the circumferential direction of the cylindrical portion 17 to form a slit 18, and the inner circumferential surface of the cylindrical portion 17 is subjected to cutting or rolling to form a helical thread 21 to form a female thread portion 22.

[0049] 7(a) to 8, the inner circumferential surface of the cylindrical portion 17 is subjected to cutting processing using an end mill 27 to form the recesses 24. That is, the inner circumferential surface of the cylindrical portion 17 is cut by the end mill 27 in the vicinity of both circumferential sides of the slits 18 along the extension direction of the slits 18 to form the recesses 24.

[0050] More specifically, first, as shown in Fig. 7(a) and Fig. 8, the tip of the end mill 27 is inserted from one end of the axial direction of the tubular portion 17 while the central axis of the end mill 27 is inclined by the lead angle of the thread 21 with respect to the central axis of the tubular portion 17. Then, the other circumferential side portion of the portion near both sides of the slit 18 on the inner peripheral surface of the end of the axial direction of the tubular portion 17 (the tip of the thread 21) is cut. Next, as shown in Fig. 7(a) → Fig. 7(b) → Fig. 7(c), the end mill 27 is displaced along the extension direction of the slit 18 to cut the portion near both sides of the slit 18 on the inner peripheral surface of the tubular portion 17 (the tip of the thread 21).

[0051] When the end mill 27 is displaced along the extension direction of the slit 18, as shown in Fig. 7(b), when the tip of the end mill 27 is located at the axial middle part of the cylindrical part 17 (the central position in the extension direction of the slit 18), the parts (tip parts of the thread 21 present in) adjacent to both circumferential sides of the slit 18 are cut on the inner peripheral surface of the axial middle part of the cylindrical part 17. Also, as shown in Fig. 7(c), when the tip of the end mill 27 is located at the end part on the other axial side of the cylindrical part 17, the part (tip part of the thread 21 present in) adjacent to both circumferential sides of the slit 18 is cut on one circumferential side of the inner peripheral surface of the end part on the other axial side of the cylindrical part 17.

[0052] The outer diameter of the end mill 27 is not particularly limited as long as the recess 24 can be formed by moving the end mill 27 once from one axial side to the other inside the cylindrical portion 17, but can be, for example, 50% to 90% of the inner diameter of the female thread portion 22, preferably 71% to 83%. In other words, the radius of curvature of the cross-sectional shape of the recess 24 can be 50% to 90% of the inner diameter of the female thread portion 22, preferably 71% to 83%. In this example, the radius of curvature of the cross-sectional shape of the recess 24 is 50% to 90% of the inner diameter of the female thread portion 22.

[0053] In this manner, recesses 24 are formed on the inner surface of tubular portion 17 in the vicinity of both circumferential sides of slit 18, the recesses 24 becoming shallower from one axial side to the other on one circumferential side of slit 18, and becoming deeper from one axial side to the other on the other circumferential side.

[0054] Next, finish grinding is performed on the female thread portion 22 provided on the inner peripheral surface of the cylindrical portion 17. The finish grinding is performed using a grinding tool 28 as shown in Figures 9 and 10. The grinding tool 28 has a thread portion 30 with a screw thread 29 formed helically on its outer peripheral surface, and groove portions 31 formed at multiple locations on the outer peripheral surface in the circumferential direction so as to extend in the axial direction.

[0055] The threaded portion 30 has a tapered portion 32, a main ground portion 33, and a back taper portion 34.

[0056] The tapered portion 32 is provided at the axial front portion (left side portion in FIG. 9) of the threaded portion 30, and the outer diameter (nominal diameter) of the thread 29 increases toward the axial rear side (right side in FIG. 9).

[0057] With respect to the grinding tool 28, the axial front side refers to the front side in the direction of insertion into the nut 14 when the grinding tool 28 is used to perform finish grinding on the female thread portion 22 of the nut 14, and refers to the left side in Figure 9, and the axial rear side refers to the rear side in the direction of insertion into the nut 14, and refers to the right side in Figure 9.

[0058] The main grinding portion 33 is provided in the axially intermediate portion of the threaded portion 30, and the outer diameter of the thread 29 does not change along the axial direction.

[0059] The back taper portion 34 is provided in the axially rear portion of the threaded portion 30, and the outer diameter of the thread 29 becomes smaller toward the axially rear side.

[0060] The axial dimensions (lengths) of the tapered portion 32, the main ground portion 33, and the back taper portion 34 are appropriately determined according to the size (axial length, inner diameter) of the nut 14 and the processing device (grinder).

[0061] The grinding tool 28 does not provide a relief angle (second relief) on the flank surface of the thread 29 over the entire axial range of the threaded portion 30, i.e., the relief angle (second relief) is set to 0°. Therefore, as shown in Fig. 10, the crests of the thread 29 in the main grinding portion 33 are located on the same circumference centered on the central axis O in a cross section of the grinding tool 28 perpendicular to the central axis O.

[0062] In addition, abrasive grains are fixed to the entire surface of the threaded portion 30, that is, the flank surface and crest of the thread 29, as well as the entire valley bottom, in the entire axial range from the axial front end to the axial rear end of the threaded portion 30. In other words, the entire axial range of the surface of the threaded portion 30 is used as a grinding surface for grinding the female threaded portion 22 of the nut 14. As the abrasive grains, for example, high-hardness abrasive grains such as diamond, cubic boron nitride (CBN), boron carbide (B4C), silica (SiO2), tungsten carbide (WC), and alumina (Al2O3) can be used. As a method for fixing the abrasive grains to the surface of the threaded portion 30, for example, electroplating, resin, and metal bond in which metal powder and abrasive grains are mixed and sintered can be used. Alternatively, the metal material constituting the threaded portion 30 can be bonded to the abrasive grains by a binder such as vitrified.

[0063] The grooves 31 are formed in a plurality of circumferential positions on the outer peripheral surface of the grinding tool 28 so as to extend in the axial direction. In the illustrated example, the grooves 31 are formed in parallel to the axial direction at four equally spaced circumferential positions in the axial range of the outer peripheral surface of the grinding tool 28 from the axial front end to the axial middle portion of the small diameter cylindrical portion 35 described later. That is, the grooves 31 are formed so as to cross the threaded portion 30 in the axial direction. The grooves 31 can also be formed so as to extend in a direction perpendicular to the lead angle of the portion of the thread 29 that the grooves 31 cross. The number of the grooves 31 can also be three or less, or five or more. Note that the grooves 31 are omitted in FIG. 9.

[0064] The illustrated grinding tool 28 further includes a guide portion 36 , a small diameter cylindrical portion 35 , and a shank portion 37 .

[0065] The guide portion 36 is disposed axially forward of the threaded portion 30 (axially forward of the tapered portion 32), and its outer diameter does not change in the axial direction. That is, the portion of the outer circumferential surface of the guide portion 36 that is circumferentially offset from the groove portion 31 exists on the same cylindrical surface.

[0066] The small diameter cylindrical portion 35 is disposed axially rearward of the back taper portion 34, and its outer diameter does not change in the axial direction. That is, the portion of the outer circumferential surface of the small diameter cylindrical portion 35 that is circumferentially offset from the groove portion 31 exists on the same cylindrical surface.

[0067] The shank portion 37 is provided at the axial rear end of the grinding tool 28 and has a circular cross-sectional shape. The shank portion 37 is a portion for supporting the grinding tool 28 on a grinding machine. That is, the grinding machine supports the grinding tool 28 by gripping the shank portion 37 with a chuck.

[0068] When the above-mentioned grinding tool 28 is used to perform finish grinding on the female thread portion 22 of the nut 14, the nut 14 is first supported (floating supported) by a vice of a grinding machine so as to be capable of axial displacement but not to be rotated. Next, as shown by a solid line in FIG. 9, the guide portion 36 of the grinding tool 28 is inserted into the radial inside of the nut 14. This allows the nut 14 and the grinding tool 28 to be axially aligned. Next, the grinding tool 28 is rotated in a predetermined direction (the direction of the arrow α in FIG. 9 (clockwise)). Then, the grinding tool 28 is slightly displaced axially forward, and the thread portion 30 of the grinding tool 28 and the female thread portion 22 of the nut 14 are slightly screwed together. Then, based on the screwing of the thread portion 30 of the grinding tool 28 and the female thread portion 22 of the nut 14, the nut 14 moves axially backward relative to the thread portion 30, and the surface of the female thread portion 22 is ground by the surface of the thread portion 30. In addition, grinding chips generated by grinding the surface of the female thread portion 22 are discharged to the outside through the groove portion 31. Then, as shown by the two-dot chain line in Fig. 9, the position of the nut 14 with respect to the thread portion 30 is moved toward the rear side in the axial direction until the axial front end (end on one side in the axial direction) of the nut 14 is positioned around the back taper portion 34 of the thread portion 30. When the nut 14 moves to be positioned around the back taper portion 34, a gap is generated between the female thread portion 22 and the thread portion 30, and grinding chips present between the female thread portion 22 and the thread portion 30 are easily discharged.

[0069] Thereafter, the grinding tool 28 is rotated in the direction opposite to the predetermined direction (the direction of the arrow β in FIG. 9 (counterclockwise)). Then, based on the screwing of the screw portion 30 with the female thread portion 22, the nut 14 moves axially forward relative to the screw portion 30, while the surface of the female thread portion 22 is ground by the surface of the screw portion 30. Grinding chips generated by grinding the surface of the female thread portion 22 are discharged to the outside through the groove portion 31. Thereafter, the grinding tool 28 is further rotated in the direction opposite to the predetermined direction, the screwing of the screw portion 30 with the female thread portion 22 is released, and the grinding tool 28 is pulled out from the radially inner side of the nut 14.

[0070] In this manner, the female thread portion 22 of the nut 14 is finish-ground by the grinding tool 28 .

[0071] According to the feed screw device 12 of this example, for reasons similar to those of the feed screw device described in International Publication No. 2019 / 142378, resistance to relative rotation between the nut 14 and the rod 15 and backlash between the female thread portion 22 of the nut 14 and the male thread portion 26 of the rod 15 can be reduced.

[0072] That is, in this example, the slit 18 is formed in the cylindrical portion 17 of the nut 14 so as to extend in a direction perpendicular to the direction of the lead angle of the thread 21 at the portion where the slit 18 crosses, and the bolt 16 is arranged in a direction perpendicular to the extension direction of the slit 18. Therefore, when the amount of fastening of the bolt 16 to the other fastening hole 19b is increased to reduce the inner diameter of the cylindrical portion 17, the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread 21 constituting the male thread portion 26 can be brought close to each other and slidably abutted (surface contact) while keeping the thickness of the gap existing between them almost constant. Therefore, it is possible to prevent the friction acting between the female thread portion 22 and the male thread portion 26 from increasing, while keeping the gap between the female thread portion 22 and the male thread portion 26, which causes backlash, small.

[0073] In addition, the surface pressure at the contact portion between the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread constituting the male thread portion 26 can be made substantially constant and kept low over the length direction (helical direction) of the contact portion. Therefore, the rattle between the female thread portion 22 and the male thread portion 26 that occurs during operation of the feed screw device 12 can be reduced, and the durability of the female thread portion 22 and the male thread portion 26 against rattle can be improved.

[0074] In addition, the reaction force applied to the bolt 16 can be reduced as the bolt 16 is tightened. From this viewpoint, the surface pressure between the female thread portion 22 and the male thread portion 26 can be kept low, and the tightening torque of the bolt 16 can be reduced. Therefore, by finely adjusting the tightening amount of the bolt 16, the adjustment range of the backlash existing between the female thread portion 22 and the male thread portion 26 can be widened. In other words, it is possible to easily adjust the backlash existing between the female thread portion 22 and the male thread portion 26 and the sliding resistance between the female thread portion 22 and the male thread portion 26 according to the performance required of the feed screw device 12.

[0075] Furthermore, the gap between the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread constituting the male thread portion 26 can be adjusted while absorbing the single pitch error and the cumulative pitch error. Therefore, it is not necessary to excessively increase the machining accuracy of the female thread portion 22 and the male thread portion 26, and the manufacturing cost of the feed screw device 12 can be reduced.

[0076] In addition, according to this embodiment, the tightening torque of the bolt 16 required to reduce the inner diameter of the cylindrical portion 17 can be reduced. When the slit is formed in the axial direction of the nut, in order to properly engage the female thread of the nut with the male thread of the rod, it is necessary to shift the circumferential side portions of the cylindrical portion of the nut that sandwich the slit in opposite directions with respect to the axial direction of the nut. In contrast, in the feed screw device 12 of this embodiment, the slit 18 is formed in the cylindrical portion 17 of the nut 14 so as to extend in a direction perpendicular to the lead angle direction of the thread 21 at the portion where the slit 18 crosses. Therefore, when the tightening amount of the bolt 16 is increased, the amount of axial displacement of the circumferential side portions of the cylindrical portion 17 that sandwich the slit 18 can be reduced compared to a structure in which the slit is formed in the axial direction. Therefore, when the inner diameter of the cylindrical portion 17 is reduced, the thickness of the gap between the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread constituting the male thread portion 26 can be more reliably maintained constant, and these surfaces can be brought closer to each other and slidably abutted (surface contacted). In other words, it is easy to improve the screw engagement state between the female thread portion 22 of the nut 14 and the male thread portion 26 of the rod 15. Therefore, the assembly cost of the feed screw device 12 can be kept low. In addition, the resistance to the relative rotation between the nut 14 and the rod 15 and the backlash between the nut 14 and the rod 15 can be more effectively suppressed. Furthermore, the tightening torque of the bolt 16 can be kept low, which also helps to keep the assembly cost of the feed screw device 12 low.

[0077] Furthermore, in the nut 14 of this embodiment, the rigidity of the tubular portion 17 in the vicinity of both sides in the circumferential direction sandwiching the slit 18 is adjusted. Specifically, when the slit 18 is inclined in the direction from one axial side to the other axial side as viewed from the radial direction of the tubular portion 17, the rigidity of the tubular portion 17 in the vicinity of both sides in the circumferential direction sandwiching the slit 18 increases from one axial side to the other axial side in the circumferential direction one side portion, and the rigidity of the circumferential portion in the circumferential direction other side portion decreases from one axial side to the other axial side. Therefore, when the bolt 16 is fastened to the other fastening hole 19b in order to reduce the inner diameter of the tubular portion 17, elastic deformation starts from the portion with low rigidity first, and as the tightening amount of the bolt 16 increases, the portion with high rigidity elastically deforms. That is, the inner diameter of the tubular portion 17 is reduced while the entire tubular portion 17 is elastically deformed so that the portion with high rigidity is twisted toward the portion with low rigidity. Specifically, one axial side portion of tubular portion 17 elastically deforms in the direction toward the other circumferential side, and the other axial side portion of tubular portion 17 elastically deforms in the direction toward one circumferential side, while the inner diameter of tubular portion 17 decreases.

[0078] For this reason, the width of the slit 18 can be narrowed while being more reliably kept almost constant in the extension direction. In other words, according to the nut 14 of this example, as in the feed screw device described in International Publication No. 2019 / 142378, the cylindrical portion 17 can be prevented from being deformed so that the width of the slit 18 is narrowest at the center in the extension direction and becomes wider toward both sides in the extension direction. From this perspective, when the inner diameter of the cylindrical portion 17 is reduced, the thickness of the gap between the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread constituting the male thread portion 26 can be more reliably kept almost constant while these surfaces are brought closer to each other and slidably abutted against each other. As a result, the assembly cost of the feed screw device 12 can be kept low, and the resistance to the relative rotation of the nut 14 and the rod 15 and the backlash between the nut 14 and the rod 15 can be more effectively suppressed.

[0079] In this example, the recess 24 is formed in the inner peripheral surface of the cylindrical portion 17, including the portion where the slit 18 is formed, to adjust the rigidity of the portions of the cylindrical portion 17 adjacent to both sides of the slit 18 in the circumferential direction. The radius of curvature of the cross-sectional shape of the recess 24 is relatively large, specifically, 50% to 90% of the inner diameter of the female thread portion 22. Therefore, by increasing the amount of fastening of the bolt 16 to the other fastening hole 19b, it is possible to prevent localized elastic deformation of the portions adjacent to both sides of the slit 18 in the circumferential direction when the cylindrical portion 17 is reduced in diameter. From this viewpoint, the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread 26 constituting the male thread portion 26 can be brought close to each other and slidably abutted against each other while maintaining the thickness of the gap existing between these surfaces almost constant.

[0080] In this embodiment, the recess 24 is formed by simply moving the end mill 27 once from one axial side to the other inside the cylindrical portion 17. Specifically, the tip of the end mill 27 is inserted from one axial end of the cylindrical portion 17 while the central axis of the end mill 27 is inclined by the lead angle of the thread 21 relative to the central axis of the cylindrical portion 17. Then, the end mill 27 is displaced along the extension direction of the slit 18 to cut the inner peripheral surface of the cylindrical portion 17 near both sides in the circumferential direction sandwiching the slit 18, thereby forming the recess 24. Therefore, according to the manufacturing method of the nut of this embodiment, as described above, it is possible to relatively easily manufacture the nut 14 that can more effectively suppress the resistance to the relative rotation between the nut 14 and the rod 15 and the backlash between the nut 14 and the rod 15.

[0081] In this example, both ends of the slit 18 in the extension direction are not open to both end faces in the axial direction of the cylindrical portion 17. Therefore, even if the tightening amount of the bolt 16 to the other fastening hole 19b is increased to reduce the inner diameter of the cylindrical portion 17, it is possible to make it difficult for the pitch of the female thread portion 22 to be shifted in the circumferential direction on both sides of the slit 18. That is, in a structure in which both ends of the slit in the extension direction are open to the end faces on both axial directions of the cylindrical portion, if the tightening amount of the bolt is increased to reduce the inner diameter of the cylindrical portion, there is a possibility that inconveniences such as a shift in the pitch will occur because the part of the cylindrical portion on one side of the slit in the circumferential direction and the part on the other side of the circumferential direction will shift in opposite directions in the axial direction. In contrast, in this example, both ends of the slit 18 in the extension direction are not open to the end faces on both axial sides of the tubular portion 17, so that even if the tightening amount of the bolt 16 is increased, the part of the tubular portion 17 on one circumferential side of the slit 18 and the part on the other circumferential side can be prevented from shifting in opposite directions in the axial direction. From this viewpoint, when the inner diameter of the tubular portion 17 is reduced, the flank surface of the thread 21 constituting the female thread portion 22 and the flank surface of the thread 26 constituting the male thread portion 26 can be brought close to each other and brought into slidable contact with each other while maintaining the thickness of the gap between these surfaces approximately constant.

[0082] Furthermore, in a structure in which both ends in the extension direction of the slit are open to the end faces on both axial sides of the cylindrical portion, when the female thread portion is ground with the grinding tool 28, the cylindrical portion is likely to elastically deform in the radial direction (elastically expand in diameter), which may make it difficult to ensure the pressing pressure of the flank surface of the thread 29 constituting the threaded portion 30 of the grinding tool 28 against the flank surface of the thread that constitutes the female thread portion. In this example, since both ends in the extension direction of the slit 18 are not open to the end faces on both axial sides of the cylindrical portion 17, the pressing pressure of the flank surface of the thread 29 against the flank surface of the thread 21 that constitutes the female thread portion 22 can be sufficiently ensured, and it is easy to ensure good properties of the flank surface of the thread 21.

[0083] However, both ends of the slit in the extension direction may be open to both axial end faces of the cylindrical portion. That is, the cylindrical portion may be configured as a partially cut cylinder. Alternatively, only one end of the slit in the extension direction may be open to the axial end face of the cylindrical portion.

[0084] In addition, in this example, when the nut 14 is manufactured, finish grinding, which improves the surface roughness by grinding the surface of the female thread portion 22, is performed in a separate (independent) step from the process of forming the female thread portion 22 by cutting or rolling the inner peripheral surface of the nut 14. This makes it easier to improve the surface roughness of the flank surfaces and crests of the threads 21 that constitute the female thread portion 22, and also makes it easier to ensure good shape precision of the threads 21. The reason for this will be explained below.

[0085] When the female thread portion is formed by cutting, the cutting edge of a cutting tap is used to cut the inner peripheral surface of the nut to form a thread groove, whereas when the female thread portion is formed by rolling, the cutting edge of a rolling tap is used to crush the inner peripheral surface of the nut and raise the adjacent portion to form a thread. Whether the female thread portion is formed by cutting or rolling, the cutting edge may bite into the inner peripheral surface of the nut when the inner peripheral surface of the nut is cut or crushed by the tap. If the cutting edge bites into the inner peripheral surface of the nut excessively, the cutting edge is elastically deformed so that it is pushed back by the reaction. If such elastic deformation occurs repeatedly, the tap vibrates, and the cutting edge bites into and retreats from the flank surface of the female thread portion repeatedly, problems such as billeting (periodic height difference) may occur on the flank surface of the female thread portion, or the accuracy of the female thread portion may not be sufficiently ensured. If such burrs occur, the flow of grease that lubricates the female and male threaded portions may be impeded, or the burrs may come into local contact with the flank surface of the thread that makes up the male threaded portion, which may increase the relative rotational torque between the nut and the rod.

[0086] In the above-mentioned manufacturing method, the finish grinding is performed in a separate process from the process of forming the female thread portion 22 by cutting or rolling the inner peripheral surface of the nut 14, so that there is no problem that the grinding tool 28 vibrates during the finish grinding. Therefore, the flank surface of the thread 29 constituting the thread portion 30 of the grinding tool 28 can be stably brought into contact (sliding contact) with the flank surface of the thread 21 constituting the female thread portion 22 of the nut 14. Furthermore, in the grinding tool 28, abrasive grains are fixed to at least the flank surface and the valley bottom of the surface of the thread portion 30 over the entire axial range from the axial front end to the axial rear end of the thread portion 30. Therefore, during finish grinding with the grinding tool 28, a sufficient amount of contact (sliding length) can be ensured between the portion of the surface of the threaded portion 30 to which the abrasive grains are attached and the surface of the female threaded portion 22 of the nut 14, making it easier to improve the surface roughness of the flank surfaces and crests of the threads 21 that constitute the female threaded portion 22 and to ensure good shape precision of the threads 21.

[0087] In the method using the grinding tool 28, grinding streaks are formed on the flank surface of the thread 21 constituting the female thread portion 22 of the nut 14 after the finish grinding along the formation direction (spiral direction) of the thread 21. In short, the formation direction of the grinding streaks can be the sliding direction between the flank surface of the thread 21 constituting the female thread portion 22 of the nut 14 and the flank surface of the thread constituting the male thread portion 26 of the rod 15 when the feed screw device 12 is constituted by combining the nut 14 with the rod 15. Therefore, the flow of grease lubricating the female thread portion 22 and the male thread portion 26 can be made smooth. From this point of view, the properties of the female thread portion 22 of the nut 14 can be improved.

[0088] In addition, since the finish grinding is performed in a separate process from the process of forming the female thread portion 22 by cutting or rolling the inner peripheral surface of the nut 14, the amount of grinding waste generated by the finish grinding using the grinding tool 28 is not so large. Therefore, the total volume of the grooves 31 can be made smaller than the total volume of the threads 29. In other words, the circumferential width of the land between the grooves 31 adjacent to each other in the circumferential direction can be sufficiently secured. From this point of view, the amount of contact between the surface of the thread portion 30 and the surface of the female thread portion 22 of the nut 14 can be secured, and the surface roughness of the flank surface and the crest of the thread 21 constituting the female thread portion 22 can be easily improved, and the shape precision of the thread 21 can be easily secured.

[0089] Furthermore, the grinding tool 28 does not provide a relief angle (second relief) on the flank surface of the thread 29 that constitutes the thread portion 30. Therefore, when the female thread portion 22 of the nut 14 is finish ground, the entire circumferential range of the surface of the thread 29 can be brought into contact with the surface (flank surface and root) of the female thread portion 22. This allows the grinding performance of the grinding tool 28 to be maintained well for a long period of time, suppressing increases in costs and work time required for maintaining the grinding tool 28, and improving the productivity of the nut 14.

[0090] Furthermore, because the grinding tool 28 does not provide a clearance angle on the flank surface of the thread 29, the cross-sectional shape of the thread 29 is constant in the formation direction (helical direction) of the thread 29 in the main grinding portion 33 of the thread portion 30. Therefore, the way in which the surface of the thread 29 in the main grinding portion 33 contacts the surface of the female thread portion 22 can be made the same regardless of the rotation direction of the grinding tool 28, and deterioration of the properties of the female thread portion 22 can be prevented.

[0091] Furthermore, the grinding tool 28 has a back taper portion 34 at the axial rear portion of the threaded portion 30, where the outer diameter of the thread 29 becomes smaller toward the axial rear. This makes it possible to prevent the torque from becoming unnecessarily large when the grinding tool 28 starts to rotate in the direction opposite to the predetermined direction in order to pull the grinding tool 28 out from the radial inside of the nut 14, and makes it possible to smoothly feed the grinding tool 28. This also makes it possible to improve the properties of the female threaded portion 22.

[0092] The grinding tool 28 has a guide portion 36 at the end portion on the axial front side. Therefore, by inserting the guide portion 36 into the radial inside of the nut 14, it is possible to roughly align the axial direction of the nut 14 with the grinding tool 28 without screwing the female thread portion 22 of the nut 14 with the thread portion 30 of the grinding tool 28. In short, it is possible to facilitate the rough axial alignment work between the nut 14 and the grinding tool 28, and to improve the efficiency of the work. Such an effect can be obtained remarkably when the grinding process of the nut 14 by the grinding tool 28 is automated.

[0093] In the feed screw device 12 of this example, the rod 15 is configured to be rotatably driven by the electric motor 11, but the nut 14 can also be configured to be rotatably driven by the electric motor 11. Also, in this example, the nut 14 is supported via the column bracket 1 to the vehicle body 5, which is a part that does not move in the vertical direction when adjusting the vertical position of the steering wheel, and the rod 15 is supported by the steering column 2, which moves in the vertical direction together with the steering wheel. However, the nut 14 can also be supported by a part that moves in the vertical direction together with the steering wheel when adjusting the vertical position of the steering wheel, specifically, for example, the steering column 2 or the steering shaft 3, and the rod 15 can also be supported by a part that does not move in the vertical direction, specifically, for example, the column bracket 1.

[0094] In this example, the female thread portion 22 and the male thread portion 26 are configured with a single thread, but they may be configured with a multiple thread such as a double thread. In this case, it is preferable to find the average value of the lead angles of the multiple thread grooves that configure the female thread portion 22, and to form the slit 18 in a direction shifted by about 90° (about 85° to 95°) from the magnitude of this average value.

[0095] In this example, when the slit 18 is inclined from one circumferential side to the other as it goes from one axial side to the other as viewed from the radial direction of the cylindrical portion 17, the rigidity of the cylindrical portion 17 in the vicinity of both circumferential sides sandwiching the slit 18 is increased in one circumferential side as it goes from one axial side to the other, and the rigidity of the cylindrical portion in the vicinity of both circumferential sides sandwiching the slit is decreased in one circumferential side as it goes from one axial side to the other, and the rigidity of the cylindrical portion in the vicinity of both circumferential sides sandwiching the slit can also be decreased in one circumferential side as it goes from one axial side to the other, and increased in the other circumferential side as it goes from one axial side to the other. In this case, specifically, for example, in the circumferential portions of the tubular portion near both sides of the slit, the height of the threads constituting the female thread portion formed on the inner surface of the tubular portion can be made lower in one circumferential side portion as one moves from one axial side to the other, and the height of the threads can be made higher in the other circumferential side portion as one moves from one axial side to the other. [Explanation of symbols]

[0096] 1 Column bracket 2 Steering column 3 Steering shaft 4 Electric Actuators 5. Body 6 Mounting part 7 Front support part 8 Rear support part 9 Sleeve 10. Axis 11 Electric motor 12 Lead screw device 13 worm teeth 14 Nut 15 Rod 16 Volts 17 Cylindrical section 18 Slit 19a, 19b Fastening holes 20 Engagement arm 21 Threads 22 Female thread 23 Spherical part 24 Recess 25 Wheel Teeth 26 Male thread 27 End Mill 28 Grinding Tools 29 Threads 30 Threaded section 31 Groove 32 Tapered section 33 Main grinding section 34 Back taper section 35 Small diameter cylindrical section 36 Guide part 37 Shank 100 Lead screw device 101 Nut 102 Rod 103 Volts 104 Female thread 105 Cylindrical part 106 Slit 107a, 107b Fastening holes 108 Male thread

Claims

1. A cylindrical portion having an internal thread formed by forming a screw thread helically on an inner peripheral surface thereof; a slit formed at one location in the circumferential direction of the cylindrical portion and opening to an outer peripheral surface and an inner peripheral surface of the cylindrical portion; the slit is formed to extend in a direction perpendicular to a lead angle direction at a portion of the thread that is traversed by the slit, When viewed from the radial direction of the cylindrical portion, if the slit is inclined in a direction from one circumferential side to the other as it goes from one axial side to the other, among the portions of the cylindrical portion near both sides in the circumferential direction sandwiching the slit, in the portion on one circumferential side, the rigidity becomes greater as it goes from one axial side to the other, and in the portion on the other circumferential side, the rigidity becomes smaller as it goes from one axial side to the other, or in the portion on one circumferential side, the rigidity becomes smaller as it goes from one axial side to the other, and in the portion on the other circumferential side, the rigidity becomes greater as it goes from one axial side to the other. nut.

2. In the tubular portion, in the portions near both sides in the circumferential direction sandwiching the slit, in one circumferential side portion, the height of the thread increases from one axial side to the other axial side, and in the other circumferential side portion, the height of the thread decreases from one axial side to the other axial side, or in the one circumferential side portion, the height of the thread decreases from one axial side to the other axial side, and in the other circumferential side portion, the height of the thread increases from one axial side to the other axial side. The nut according to claim 1.

3. A grinding streak is formed on the flank surface of the thread along the direction in which the thread is formed. The nut according to claim 1 or 2.

4. The ends of the slit on both sides in the extending direction are not open to the end faces on both sides in the axial direction of the cylindrical portion. The nut according to any one of claims 1 to 3.

5. The female thread portion is configured by a multiple thread. The nut according to any one of claims 1 to 4.

6. The cylindrical portion has a pair of fastening holes formed in both side portions of the cylindrical portion that are aligned with each other across the slit, the fastening holes being formed in a direction perpendicular to the extension direction of the slit. The nut according to any one of claims 1 to 5.

7. forming a female screw portion by forming a screw thread helically on an inner peripheral surface of the cylindrical portion; forming a slit at one location in the circumferential direction of the cylindrical portion, the slit opening into the outer peripheral surface and the inner peripheral surface of the cylindrical portion, so as to extend in a direction perpendicular to the direction of the lead angle at a portion of the thread that the slit crosses; and performing a cutting process with an end mill on adjacent portions of the cylindrical portion on both sides in the circumferential direction sandwiching the slit, so that, when viewed from the radial direction of the cylindrical portion, the slit is inclined in a direction from one axial side to the other, the height of the thread is reduced in the one axial side of the adjacent portions of the cylindrical portion on one side in the circumferential direction and the height of the thread is increased in the other axial side of the adjacent portions on the other side in the circumferential direction, or the height of the thread is increased in the one axial side of the adjacent portions on one side in the circumferential direction and the height of the thread is reduced in the other axial side of the adjacent portions on the other side in the circumferential direction. How nuts are manufactured.

8. The end mill is inserted from one end of the axial direction of the cylindrical portion and displaced along the extension direction of the slit, thereby performing cutting processing on both circumferentially adjacent portions of the cylindrical portion that sandwich the slit. A method for manufacturing the nut according to claim 7.

9. The end mill has an outer diameter that is 50% or more and 90% or less of the inner diameter of the female thread portion. A method for manufacturing the nut according to claim 8.

10. A nut according to claim 6; A rod having an external thread portion on an outer circumferential surface thereof, the external thread portion being engaged with the internal thread portion; A bolt that is inserted or screwed into the pair of fastening holes and that expands or reduces the distance between the slits; A feed screw device comprising:

Images