JP7597372B2 - Nut, manufacturing method thereof, and feed screw device - Google Patents

Description

The present invention relates to a nut that has a slit and is configured so that its inner diameter can be expanded or contracted, a method for manufacturing the nut, and a feed screw device that uses the nut.

Figures 11 to 13(b) show an example of a conventional structure of a feed screw device described in International Publication No. 03/078234 (Patent Document 1). The feed screw device 100 includes a nut 101, a rod 102, and a bolt 103.

The nut 101 has a cylindrical portion 105 having a female thread portion 104 on its inner peripheral surface, a slit 106 formed in the cylindrical portion 105 so as to extend in the axial direction, and a pair of fastening holes 107a, 107b formed in portions of the cylindrical 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.

The rod 102 has a male threaded portion 108 on its outer circumferential surface that screws into the female threaded portion 104.

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

In the feed screw device 100, the amount of tightening of the bolt 103 against the other tightening hole 107b is adjusted to expand or reduce the width of the slit 106 and the inner diameter of the cylindrical portion 105, thereby reducing backlash in the screwed portion between the female threaded portion 104 of the nut 101 and the male threaded portion 108 of the rod 102.

In the structure described in WO 03/078234, a slit 106 is formed in the 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 arranged 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 vertical direction in FIG. 13(a)), which corresponds to the expansion and contraction direction of the nut 101.

Therefore, when the inner diameter of the tubular portion 105 is reduced by increasing the amount of tightening of the bolt 103, as shown in Figures 13(a) and 13(b), an offset 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 an offset contact occurs, the 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.

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 portion 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, when the amount of tightening of the bolt is increased to reduce the inner diameter of the nut, bring the flank surface of the thread constituting the female thread portion and the flank surface of the thread constituting the male thread portion provided on the outer peripheral surface of the rod closer to each other and slidably abut (surface contact) while maintaining the thickness of the gap between them approximately constant. This makes it possible to prevent the friction acting between the female thread of the nut and the male thread of the rod from increasing, and also to reduce the gap between the flank surface of the thread that constitutes the female thread and the flank surface of the thread that constitutes the male thread, which causes backlash.

International Publication No. WO 03/078234 International Publication No. 2019/142378

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.

Therefore, when the amount of tightening of the bolt against 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. In other words, 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 noticeable in nuts in which the ends of the slit on both sides in the extension direction do not open to the end faces on both axial sides of the cylindrical portion.

In view of the above circumstances, the present invention aims to realize a structure that can more effectively suppress resistance to relative rotation between the nut and the rod, and backlash between the nut and the rod.

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 peripheral surface and the inner peripheral surface of the cylindrical portion.

The slit is formed so that it extends in a direction perpendicular to the lead angle direction at the portion of the thread that the slit crosses.

In particular, in a nut according to one aspect of the present invention, when the slit is inclined from one circumferential side to the other as it moves from one axial side to the other when viewed from the radial direction of the cylindrical portion, in the portions of the cylindrical portion adjacent to both sides in the circumferential direction sandwiching the slit, the rigidity (rigidity against deformation in the direction of reducing the diameter) of the one circumferential side portion increases as it moves from one axial side to the other, and the rigidity of the other circumferential side portion decreases as it moves from one axial side to the other, or the rigidity of the one circumferential side portion decreases as it moves from one axial side to the other, and the rigidity of the other circumferential side portion increases as it moves from one axial side to the other.

In a nut according to one aspect of the present invention, in the circumferential portions of the cylindrical portion near both sides of the slit, the height of the threads can be increased in one circumferential portion from one axial side to the other, and decreased in the other circumferential portion from one axial side to the other, or the height of the threads can be decreased in one circumferential portion from one axial side to the other, and increased in the other circumferential portion from one axial side to the other.

In one aspect of the nut 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.

In a nut according to one aspect of the present invention, the ends on both sides of the slit in the extension direction may not open to the end faces on both axial sides of the cylindrical portion. Alternatively, the ends on both sides of the slit in the extension direction may open to the end faces on both axial sides of the cylindrical portion.

In one aspect of the nut of the present invention, the female thread portion can be configured as a multiple-start thread with two or more threads (number of threads). Alternatively, the female thread portion can be configured as a single-start thread.

The nut according to one aspect of the present invention can have a pair of fastening holes formed in both sides of the tubular portion that are aligned with each other across the slit, in a direction perpendicular to the extension direction of the slit.

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.

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.

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.

The present invention can more effectively reduce resistance to relative rotation between the nut and the rod, and backlash between the nut and the rod.

FIG. 1 is a side view showing an electric steering wheel position adjustment device according to one embodiment of the present invention, in which FIG. 1(a) is a view showing the steering wheel in the upper end 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 lower end position. FIG. 2(a) is a side view of a nut according to an 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). FIG. 3 is a schematic cross-sectional view of a feed screw device according to an embodiment of the present invention. 4(a) is a cross-sectional view taken along line A-A in FIG. 3, showing the nut removed, FIG. 4(b) is a cross-sectional view taken along line B-B 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. FIG. 5 is a cross-sectional view taken along line DD of FIG. FIG. 6 is an end view of the cylindrical portion of the nut as viewed from one axial side. 7(a) to 7(c) are plan views showing the process of cutting a screw thread with an end mill in sequence. FIG. 8 is a view seen from the arrow E in FIG. FIG. 9 is a side view showing how the female thread portion of the nut is finish-ground. FIG. 10 is a cross-sectional view taken along the line FF of FIG. FIG. 11 is a side view showing an example of a conventional feed screw device. FIG. 12 is a cross-sectional view taken along line GG of FIG. 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).

One embodiment of the present invention will be described with reference to Figures 1 to 10. In this embodiment, the feed screw device of the present invention is applied to an electric steering wheel position adjustment device equipped with a tilt mechanism for adjusting the vertical position of the steering wheel.

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

The column bracket 1 comprises an attachment portion 6 that is supported and fixed to the vehicle body 5, a front support portion 7 that is bent downward from the widthwise edge of the front portion of the attachment portion 6, and a rear support portion 8 that is bent downward from the rear end edge of the attachment portion 6. A cylindrical sleeve 9 is supported and fixed to the vertical middle portion of the front side surface of the rear support portion 8.

The steering column 2 is configured to be cylindrical as a whole. The front end of the steering column 2 is supported by the front support part 7 of the column bracket 1, allowing for pivotal displacement around a pivot 10 disposed in the width direction of the vehicle body 5.

The steering shaft 3 is supported rotatably 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.

The electric actuator 4 includes an electric motor 11 and a feed screw device 12. The output shaft of the electric motor 11 is arranged parallel to the axial direction of the steering column 2 and is supported and fixed to the steering column 2. The outer peripheral surface of the output shaft of the electric motor 11 is provided with worm teeth 13.

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

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

The cylindrical portion 17 has an internal thread 22 formed by forming a screw thread 21 having a triangular cross-sectional shape in a spiral shape on its inner circumferential 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 formed by combining the nut 14 and the rod 15.

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 "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 example, the opening width of the slit 18 is substantially constant over its entire length, except for unavoidable manufacturing errors.

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 by a long 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 radially outer parts of both ends of the slit 18 in the extension direction have cutting marks formed by cutting the slit 18 open to both axial end faces of the cylindrical portion 17. However, it is also possible to prevent cutting marks from being formed in the radially outer parts of both ends of the slit 18 in the extension direction. For this reason, 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 positioned in consideration of the rigidity of the nut 14 and the rigidity of the steering column 2 on which the nut 14 is supported.

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

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 engages 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 radially from the outer circumferential surface of the cylindrical portion 17, which is a portion that is circumferentially deviated from the portion in which the slit 18 is formed. In this example, the engaging arm 20 is provided at a position that is approximately 120° out of phase with the portion in which the slit 18 is formed. However, for example, the engaging arm 20 can also be provided at a position that is 90° out of phase with the portion in which the slit 18 is formed, or at a position that is radially opposite the portion in which the slit 18 is formed.

In this example, 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 from one circumferential side to the other side (from the bottom to the top in FIGS. 3 and 5) as it moves from one axial side to the other side (from the left to the right in FIGS. 3 and 5) as it moves from one axial side to the other side, the rigidity (rigidity against deformation in the direction of diameter reduction) of the tubular portion 17 in the vicinity of both sides in the circumferential direction sandwiching the slit 18 increases as it moves from one axial side to the other side, and the rigidity of the circumferential portion in the other circumferential direction decreases as it moves from one axial side to the other side.

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, including the portion where the slit 18 is formed, has a recess 24 that extends in the extension direction of the slit 18 and is recessed radially outward. The recess 24 opens to the end faces on both axial sides of the cylindrical portion 17 and has an arc-shaped cross-sectional shape. In addition, the depth of the recess 24 becomes shallower in the circumferential portion on one side of the slit 18 as it moves from one axial side to the other, and becomes deeper in the circumferential portion on the other side. The circumferential width of the portion of the recess 24 on one circumferential side of the slit 18 becomes smaller as it moves 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 as it moves from one axial side to the other.

The rod 15 is supported so as to be rotatable only on the widthwise side 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, with its central axis positioned 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 has wheel teeth 25 on the outer circumferential surface of the lower end that mesh with the worm teeth 13, and a male threaded portion 26 on the outer circumferential surface of the upper side that screws into the female threaded portion 22. In other words, the rod 15 can be rotated by the electric motor 11.

The bolt 16 is inserted through one of the tightening holes 19a, which is a circular hole, and the tip is screwed into the other tightening 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 part where the slit 18 crosses. In the feed screw device 12 of this example, the tightening amount (screw amount) of the bolt 16 to the other tightening hole 19b can be adjusted to expand and contract the interval of the slit 18 and expand and contract the inner diameter of the cylindrical part 17. However, it is also possible to configure the pair of tightening 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 tightening holes 19a, 19b. In any case, by expanding or contracting the inner diameter of the cylindrical portion 17, it is possible to suppress backlash between the female thread portion 22 and the male thread portion 26 while preventing an excessive increase in resistance to the relative rotation of the male thread portion 26 with respect to the female thread portion 22.

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 head of the bolt can also be configured as a convex curved surface with an arc-shaped cross section. In this case, the part of the nut that abuts against the bearing surface of the bolt can be a flat surface or a concave curved surface with an arc-shaped cross section.

In the electric steering wheel position adjustment device of this example, a method of adjusting the vertical position of the steering wheel will be described. First, when the steering wheel is displaced upward, for example, as shown in FIG. 1(b) → FIG. 1(a), the output shaft of the electric motor 11 is rotated in a predetermined direction by energizing the electric motor 11, 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 around the pivot 10, and the steering wheel is displaced upward. In addition, as the steering column 2 is displaced upward, the nut 14 swings upward around the spherical engagement portion between the spherical portion 23 and the inner circumferential surface of the sleeve 9. After the steering wheel is adjusted to the 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.

When the steering wheel is to be 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 around the pivot 10, and the steering wheel is displaced downward. In addition, as the steering column 2 is displaced downward, the nut 14 swings downward around the spherical engagement portion. After the steering wheel is adjusted to the 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.

An example of a method for manufacturing the nut 14 that constitutes the feed screw device 12 of this example is described with reference to Figures 7(a) to 10.

When making the nut 14, first, a metal material is subjected to the 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 surface of the cylindrical portion 17 is subjected to cutting or rolling to form a helical thread 21, forming a female thread portion 22.

Next, as shown in Figures 7(a) to 8, the inner circumferential surface of the cylindrical portion 17 is cut using an end mill 27 to form the recess 24. That is, the end mill 27 cuts the inner circumferential surface of the cylindrical portion 17 near both sides of the slit 18 in the circumferential direction along the extension direction of the slit 18 to form the recess 24.

More specifically, first, as shown in Fig. 7(a) and Fig. 8, 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 cylindrical portion 17, and the tip of the end mill 27 is inserted from one end of the axial side of the cylindrical portion 17. Then, the other circumferential side portion (the tip of the thread 21) of the inner peripheral surface of the end of the cylindrical portion 17 on one axial side 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, and the inner peripheral surface of the cylindrical portion 17 on both circumferential sides (the tip of the thread 21) is cut.

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 tubular part 17 (the center position in the extension direction of the slit 18), the circumferential both sides of the slit 18 are cut on the inner circumferential surface of the axial middle part of the tubular part 17 (the tip of the thread 21). Also, as shown in FIG. 7(c), when the tip of the end mill 27 is located at the other axial end part of the tubular part 17, the circumferential one side part of the circumferential both sides of the slit 18 are cut on the inner circumferential surface of the other axial end part of the tubular part 17 (the tip of the thread 21).

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, and 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, and 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.

In this way, a recess 24 is formed on the inner circumferential surface of the cylindrical portion 17 in the vicinity of both sides of the slit 18 in the circumferential direction, which becomes shallower from one axial side to the other on one side of the slit 18, and becomes deeper from one axial side to the other on the other circumferential side.

Next, the female thread portion 22 on the inner peripheral surface of the cylindrical portion 17 is subjected to finish grinding. 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 on its outer peripheral surface, in which a screw thread 29 is formed in a helical shape, and groove portions 31 formed at multiple points in the circumferential direction of the outer peripheral surface so as to extend in the axial direction.

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

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

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 FIG. 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 FIG. 9.

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

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 rearward portion.

The axial dimensions (lengths) of the taper section 32, main grinding section 33, and back taper section 34 are appropriately determined according to the size (axial length, inner diameter) of the nut 14 and the processing device (grinder).

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 perpendicular to the central axis O of the grinding tool 28.

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 (B ₄ C), silica (SiO ₂ ), tungsten carbide (WC), and alumina (Al ₂ O ₃ ) 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 adopted. Alternatively, the metal material constituting the threaded portion 30 can be bonded to the abrasive grains by a binder such as vitrified.

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 on the outer peripheral surface of the grinding tool 28 in the axial range 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 at the portion of the thread 29 that the grooves 31 cross. The number of grooves 31 can also be three or less, or five or more. Note that the grooves 31 are omitted in FIG. 9.

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

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. In other words, the portion of the outer peripheral surface of the guide portion 36 that is circumferentially removed from the groove portion 31 exists on the same cylindrical surface.

The small diameter cylindrical section 35 is located axially rearward of the back taper section 34, and its outer diameter does not change in the axial direction. In other words, the portion of the outer peripheral surface of the small diameter cylindrical section 35 that is circumferentially removed from the groove section 31 exists on the same cylindrical surface.

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 the grinding machine. In other words, the grinding machine supports the grinding tool 28 by gripping the shank portion 37 with a chuck.

When finish grinding the female thread portion 22 of the nut 14 using the grinding tool 28 as described above, first, the nut 14 is supported (floating support) by the vise of the grinding machine so that it can be displaced in the axial direction but cannot rotate. Next, as shown by the solid line in Figure 9, the guide portion 36 of the grinding tool 28 is inserted into the radial inside of the nut 14. This aligns the nut 14 with the grinding tool 28. Next, the grinding tool 28 is rotated in a predetermined direction (the direction of the arrow α in Figure 9 (clockwise)). Then, the grinding tool 28 is slightly displaced axially forward to slightly screw the thread portion 30 of the grinding tool 28 into the female thread portion 22 of the nut 14. Then, based on the screwing of the threaded portion 30 of the grinding tool 28 and the female threaded portion 22 of the nut 14, the surface of the female threaded portion 22 is ground by the surface of the threaded portion 30 while the nut 14 moves toward the axial rear side relative to the threaded portion 30. Grinding chips generated by grinding the surface of the female threaded 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 relative to the threaded portion 30 is moved toward the axial rear side until the axial front end (end on one side of the axial direction) of the nut 14 is positioned around the back taper portion 34 of the threaded portion 30. When the nut 14 moves to the periphery of the back taper portion 34, a gap is generated between the female threaded portion 22 and the threaded portion 30, and grinding chips present between the female threaded portion 22 and the threaded portion 30 are easily discharged.

Then, 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 and the female screw portion 22, the nut 14 moves axially forward relative to the screw portion 30, while the surface of the female screw portion 22 is ground by the surface of the screw portion 30. Grinding debris generated by grinding the surface of the female screw portion 22 is discharged to the outside through the groove portion 31. Then, the grinding tool 28 is further rotated in the direction opposite to the predetermined direction to disengage the screwing of the screw portion 30 and the female screw portion 22, and the grinding tool 28 is pulled out from the radial inside of the nut 14.

In this manner, the grinding tool 28 is used to perform finish grinding on the female thread portion 22 of the nut 14.

The feed screw device 12 of this example can reduce resistance to relative rotation between the nut 14 and the rod 15, and reduce backlash between the female thread portion 22 of the nut 14 and the male thread portion 26 of the rod 15, for the same reasons as the feed screw device described in WO 2019/142378.

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 tightening of the bolt 16 to the other fastening hole 19b is increased to reduce the inner diameter of the cylindrical portion 17, 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 kept substantially constant, and these surfaces can be brought close to each other and slidably abutted (surface contact). Therefore, the gap between the female thread portion 22 and the male thread portion 26, which causes backlash, can be kept small while preventing the friction acting between the female thread portion 22 and the male thread portion 26 from increasing.

In addition, the surface pressure at the contact area 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 kept substantially constant and low throughout the length (helical direction) of the contact area. This makes it possible to reduce the rattle between the female thread portion 22 and the male thread portion 26 that occurs during operation of the feed screw device 12, and improve the durability of the female thread portion 22 and the male thread portion 26 against rattle.

In addition, the reaction force applied to the bolt 16 can be reduced by tightening the bolt 16. From this perspective, the surface pressure between the female threaded portion 22 and the male threaded 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 play existing between the female threaded portion 22 and the male threaded portion 26 can be widened. In other words, it is possible to easily adjust the play existing between the female threaded portion 22 and the male threaded portion 26 and the sliding resistance between the female threaded portion 22 and the male threaded portion 26 according to the performance required of the feed screw device 12.

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, there is no need to increase the machining accuracy of the female thread portion 22 and the male thread portion 26 excessively, and the manufacturing cost of the feed screw device 12 can be reduced.

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 kept small. When the slit is formed in the axial direction of the nut, in order to properly engage the female thread of the nut and 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 kept small 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, while these surfaces can be brought closer to each other and slidably abutted (surface contact). 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. This makes it possible to reduce the assembly cost of the feed screw device 12. In addition, 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 reduced. Furthermore, the tightening torque of the bolt 16 can be reduced, which also makes it possible to reduce the assembly cost of the feed screw device 12.

Furthermore, in the nut 14 of this example, the rigidity of the circumferentially adjacent portions of the tubular portion 17 sandwiching the slit 18 is adjusted. Specifically, when the slit 18 is inclined in the direction from one circumferential side to the other circumferential side as it moves from one axial side to the other axial side as viewed from the radial direction of the tubular portion 17, the rigidity of the circumferentially adjacent portions of the tubular portion 17 sandwiching the slit 18 increases as it moves from one axial side to the other axial side, and the rigidity of the circumferentially adjacent portions of the tubular portion 17 decreases as it moves from one axial side to the other axial side. Therefore, when the bolt 16 is tightened against the other tightening hole 19b to reduce the inner diameter of the tubular portion 17, elastic deformation begins first from the portion with low rigidity, 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 of the cylindrical portion 17 elastically deforms in a direction toward the other circumferential side, and the other axial side of the cylindrical portion 17 elastically deforms in a direction toward the one circumferential side, while the inner diameter of the cylindrical portion 17 decreases.

Therefore, 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, it is possible to prevent the cylindrical portion 17 from being deformed so that the width of the slit 18 is narrowest in the center of the extension direction and becomes wider toward both sides of the extension direction, as in the feed screw device described in WO 2019/142378. 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 26 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.

In this example, the rigidity of the circumferential both sides of the slit 18 in the tubular portion 17 is adjusted by forming a recess 24 in the part of the inner circumferential surface of the tubular portion 17 including the part where the slit 18 is formed. 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 tightening of the bolt 16 to the other fastening hole 19b, it is possible to prevent local elastic deformation of the circumferential both sides of the slit 18 when the tubular portion 17 is reduced in diameter. From this perspective, 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 kept almost constant while these surfaces are brought close to each other and slidably abutted against each other.

In this example, 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 with the central axis of the end mill 27 tilted 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 of the slit 18 in the circumferential direction, thereby forming the recess 24. Therefore, according to the nut manufacturing method of this example, as described above, it is relatively easy to manufacture a 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.

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. Therefore, even if the amount of tightening of the bolt 16 to the other tightening hole 19b is increased to reduce the inner diameter of the tubular portion 17, it is possible to prevent the pitch of the female thread portion 22 from shifting in the circumferential direction on both sides of the slit 18. In other words, in a structure in which both ends of the slit in the extension direction are open to the end faces on both axial sides of the tubular portion, if the amount of tightening of the bolt is increased to reduce the inner diameter of the tubular portion, the part of the tubular portion on one circumferential side of the slit and the part on the other circumferential side of the slit may shift in opposite directions in the axial direction, causing inconvenience such as a shift in the pitch. In contrast, in this example, both ends of the slit 18 in the extension direction do not open to the end faces on both axial sides of the tubular portion 17, so 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. This also means that when the inner diameter of the tubular portion 17 is reduced, the thickness of the gap between the flank surface of the thread 21 that constitutes the female thread portion 22 and the flank surface of the thread that constitutes the male thread portion 26 can be kept almost constant, and these surfaces can be brought close to each other and slidably abutted against each other.

In addition, in a structure in which both ends of the slit in the extension direction 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 of the slit 18 in the extension direction 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.

However, both ends of the slit in the extension direction can be open to both axial end faces of the cylindrical part. In other words, the cylindrical part can be configured as a partially cut cylinder. Alternatively, only one end of the slit in the extension direction can be open to the axial end face of the cylindrical part.

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) process 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 surface and crest of the thread 21 that constitutes the female thread portion 22, and also makes it easier to ensure good shape precision of the thread 21. The reasons for this are explained below.

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

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 there is no problem of the grinding tool 28 vibrating when performing the finish grinding. Therefore, the flank surface of the thread 29 constituting the thread portion 30 of the grinding tool 28 can be stably contacted (sliding) 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 make up the female threaded portion 22, and also making it easier to ensure good shape precision of the threads 21.

In the method using the grinding tool 28, grinding streaks are formed on the flank surface of the thread 21 that constitutes the female thread portion 22 of the nut 14 after finish grinding along the formation direction (helical 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 that constitutes the female thread portion 22 of the nut 14 and the flank surface of the thread that constitutes the male thread portion 26 of the rod 15 when the feed screw device 12 is formed by combining the nut 14 with the rod 15. This makes it possible to smooth the flow of grease that lubricates the female thread portion 22 and the male thread portion 26. This also improves the properties of the female thread portion 22 of the nut 14.

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 groove portion 31 can be made smaller than the total volume of the thread 29. In other words, the circumferential width of the land existing between the groove portions 31 adjacent in the circumferential direction can be sufficiently secured. From this aspect, 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.

The grinding tool 28 does not have a relief angle (second relief) on the flank surface of the thread 29 that constitutes the threaded portion 30. Therefore, when the female threaded portion 22 of the nut 14 is subjected to finish grinding, the entire circumferential range of the surface of the thread 29 can be brought into contact with the surface (flank surface and valley bottom) of the female threaded 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 maintenance of the grinding tool 28 and improving the productivity of the nut 14.

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 main grinding portion 33 of the threaded portion 30 along the direction in which the thread 29 is formed (the helical direction). This allows the surface of the thread 29 in the main grinding portion 33 to contact the surface of the female threaded portion 22 in the same way regardless of the rotation direction of the grinding tool 28, preventing deterioration of the properties of the female threaded portion 22.

The grinding tool 28 also has a back taper section 34 at the axial rear portion of the threaded portion 30, where the outer diameter of the thread 29 decreases toward the axial rear. This prevents 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 allows the grinding tool 28 to be fed smoothly. This also improves the properties of the female threaded portion 22.

The grinding tool 28 has a guide portion 36 at the axially forward end. Therefore, by inserting the guide portion 36 radially inward of the nut 14, it is possible to roughly align the nut 14 and the grinding tool 28 without screwing the female thread portion 22 of the nut 14 and the thread portion 30 of the grinding tool 28 together. In short, it is possible to facilitate the rough alignment of the nut 14 and the grinding tool 28, and to make the work more efficient. This effect can be obtained significantly when automating the grinding process of the nut 14 using the grinding tool 28.

In this example, the feed screw device 12 is configured so that the rod 15 can be rotated by the electric motor 11, but the nut 14 can also be configured so that it can be rotated 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 displace in the vertical direction when adjusting the vertical position of the steering wheel, and the rod 15 is supported on the steering column 2, which displaces in the vertical direction together with the steering wheel. However, the nut 14 can also be supported on a part that displaces 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 be supported on a part that does not displace in the vertical direction, specifically, for example, the column bracket 1.

In this example, the female thread portion 22 and the male thread portion 26 are configured with a single thread, but they can also be configured with multiple threads such as a double thread. In this case, it is preferable to determine the average value of the lead angle of the multiple thread grooves that make up the female thread portion 22, and form the slit 18 in a direction shifted by about 90° (85° to 95°) from the magnitude of this average value.

In this example, when viewed from the radial direction of the cylindrical portion 17, if the slit 18 is inclined in the direction from one axial side to the other axial side, the rigidity of the cylindrical portion 17 in the vicinity of both sides of the circumferential direction sandwiching the slit 18 is increased in the circumferential direction one side portion toward the other axial side, and the rigidity of the cylindrical portion in the vicinity of both sides of the circumferential direction sandwiching the slit is decreased in the circumferential direction one side portion toward the other axial side, and the rigidity of the cylindrical portion in the vicinity of both sides of the circumferential direction sandwiching the slit can be decreased in the circumferential direction one side portion toward the other axial side, and the rigidity of the cylindrical portion in the vicinity of both sides of the circumferential direction sandwiching the slit can be increased in the circumferential direction one side portion toward the other axial side. In this case, specifically, for example, in the circumferential portions of the cylindrical portion near both sides of the slit, the height of the threads constituting the female thread portion formed on the inner peripheral surface of the cylindrical portion is lower in one circumferential portion from one axial side to the other, and the height of the threads can be increased in the other circumferential portion from one axial side to the other.

REFERENCE SIGNS LIST 1 Column bracket 2 Steering column 3 Steering shaft 4 Electric actuator 5 Vehicle body 6 Mounting portion 7 Front support portion 8 Rear support portion 9 Sleeve 10 Pivot 11 Electric motor 12 Lead screw device 13 Worm teeth 14 Nut 15 Rod 16 Bolt 17 Cylindrical portion 18 Slits 19a, 19b Fastening holes 20 Engagement arm portion 21 Thread 22 Female thread portion 23 Spherical portion 24 Recess 25 Wheel teeth 26 Male thread portion 27 End mill 28 Grinding tool 29 Thread 30 Thread portion 31 Groove portion 32 Tapered portion 33 Main grinding portion 34 Back taper portion 35 Small diameter cylindrical portion 36 Guide portion 37 Shank portion 100 Lead screw device 101 Nut 102 Rod 103 Bolt 104 Female thread portion 105 Cylindrical portion 106 Slits 107a, 107b Fastening hole 108 Male thread portion

Claims (10)

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

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