Ball spring device, and ball spring device manufacturing method

Abstract

To facilitate assembly of a top.SOLUTION: A top is housed in a concave face of a nut of a ball screw device according to the present disclosure. A direction in which the concave face is arranged when seen from an axial direction is a top insertion direction, and an opposite direction is a top withdrawal direction. A direction crossing with the top insertion direction when seen from the axial direction is a crossing direction. The concave face has: a first arc face and a second arc face separating from each other in the crossing direction as they move in the top withdrawal direction; and a first extension arc face and a second extension arc face extending in the top withdrawal direction from ends of the first and second arc faces. The top has: a first opposite arc face and a second opposite arc face opposed to the first arc face or the second arch face; and a first extension opposite arc face and a second extension opposite arc face opposed to the first extension arc face or the second extension arc face. The first extension arc face is arranged outside a first virtual circle with the same diameter as the first arc face with a center of the first arc face as a center, and the second extension arc face is arranged outside a second virtual circle with the same diameter as the second arc face with a center of the second arc face as a center.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a ball screw device and a method for manufacturing a ball screw device. [Background technology]

[0002] The ball screw device includes a nut, a screw shaft that passes through the nut, a plurality of balls arranged between the nut and the screw shaft, and a circulating part. An inner peripheral surface of the nut is formed with an inner raceway surface. An outer peripheral surface of the screw shaft is formed with an outer raceway surface that faces the inner raceway surface. A spiral track is formed between the inner raceway surface and the outer raceway surface. A plurality of balls are arranged on the track and move in a spiral direction along the track. The circulating part returns balls that have moved from one end of the track to the other end of the track to the other end of the track. One example of the circulating part is a top that returns balls by one lead. In the ball screw device disclosed in the following patent document, a concave surface with a bottom is formed on the inner peripheral surface of the nut. A top is housed inside the concave surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2019 / 0277380 Summary of the Invention [Problem to be solved by the invention]

[0004] The method for forming the concave surface in the above-mentioned patent document includes a method in which a rotating cutting tool is brought into contact with the inner peripheral surface of the nut to cut the inner peripheral surface of the nut. According to this method, when viewed from a direction parallel to the rotation center of the cutting tool, an arc-shaped surface is formed. In other words, at least a portion of the concave surface includes an arc-shaped surface. Furthermore, the outer diameter surface of the top also includes an arc-shaped surface corresponding to the concave surface. With such a shape, there is a possibility that the top will rotate inside the concave surface when assembled inside the concave surface. Therefore, it is time-consuming to assemble the top in the specified orientation.

[0005] The present disclosure has been made in view of the above, and aims to provide a ball screw device and a method for manufacturing a ball screw device that facilitates the assembly of a top. [Means for solving the problem]

[0006] To achieve the above object, a ball screw device according to one aspect of the present disclosure includes a screw shaft, a nut inserted through the screw shaft, a plurality of balls arranged between the screw shaft and the nut, and at least one or more bearings for circulating the balls. The inner circumferential surface of the nut has a concave surface recessed radially outward from the inner circumferential surface and accommodating the bearings. The direction in which the concave surface is arranged as viewed from the central axis of the nut is defined as a bearing insertion direction. The direction opposite to the bearing insertion direction is defined as a bearing removal direction. The direction intersecting the bearing insertion direction as viewed from an axial direction parallel to the central axis of the nut is defined as an intersecting direction. The concave surface has first and second arcuate surfaces that are arcuate and move apart in the intersecting direction as the bearing moves in the bearing removal direction, and first and second extended arcuate surfaces that are arcuate and move apart in the intersecting direction as the bearing moves in the bearing removal direction from ends of the first or second arcuate surfaces in the bearing removal direction. The outer diameter surface of the top has a first opposing arcuate surface that faces the first arcuate surface, a second opposing arcuate surface that faces the second arcuate surface, a first opposing arcuate surface that faces the first expanded arcuate surface, and a second opposing arcuate surface that faces the second expanded arcuate surface. The first expanded arcuate surface is centered on the center of the first arcuate surface and is located outside a first imaginary circle having the same diameter as the first arcuate surface. The second expanded arcuate surface is centered on the center of the second arcuate surface and is located outside a second imaginary circle having the same diameter as the second arcuate surface.

[0007] According to the present disclosure, when a top is assembled inside a concave surface, even if a load that rotates the top along the first or second arcuate surface of the concave surface acts on the top, the first expanded opposing arcuate surface catches on the first expanded opposing arcuate surface, or the second expanded opposing arcuate surface catches on the second expanded opposing arcuate surface. In other words, rotation of the top is restricted inside the concave surface. This allows the top to be assembled in a predetermined position, making assembly of the top easier. Furthermore, the top disclosed herein does not require a through-hole on the outer peripheral surface of the nut. This allows the nut itself to function as a piston by sliding its outer peripheral surface, or meets the needs for directly press-fitting bearings, motor rotors, reduction gears, belt pulleys, etc., onto the outer peripheral surface of the nut. Furthermore, the absence of a through-hole on the outer peripheral surface of the nut provides high dust resistance. Alternatively, the nut disclosed herein is smaller and lighter than a nut with a through-hole on its outer peripheral surface and a component for blocking the through-hole.

[0008] In a preferred embodiment of the ball screw device, the first arcuate surface, the second arcuate surface, the first extended arcuate surface, and the second extended arcuate surface have the same curvature.

[0009] According to the above configuration, when the inner peripheral surface of the nut is cut with a rotating cutting tool to form the first arcuate surface, the second arcuate surface, the first extended arcuate surface, and the second extended arcuate surface, there is no need to change the cutting tool, which makes it easier to form the concave surface and improves nut productivity.

[0010] In the ball screw device, the curvature of the first arcuate surface and the curvature of the second arcuate surface may be the same, but the curvatures of the first arcuate surface and the second arcuate surface may be different from the curvatures of the first extended arcuate surface and the second extended arcuate surface.

[0011] In a preferred embodiment of the ball screw device, the first arcuate surface and the second arcuate surface are connected to each other and cooperate to form a single arcuate surface.

[0012] According to this configuration, a single arcuate surface is formed simply by moving the rotating cutting tool radially outward from the central axis of the nut. In other words, after forming the first arcuate surface, it is not necessary to move the cutting tool in a cross direction to form the second arcuate surface. This makes it easier to form the concave surface, improving nut productivity.

[0013] In addition, in a preferred embodiment of the ball screw device, the angle formed by an imaginary line drawn from the center of the single arc surface to one end of the single arc surface in the intersecting direction and an imaginary line drawn to the other end of the single arc surface in the intersecting direction is less than 180 degrees.

[0014] According to this configuration, the shank of the cutting tool and the inner peripheral surface of the nut do not come into contact with each other.

[0015] In a preferred embodiment of the ball screw device, the concave surface has a flat surface disposed between the first arcuate surface and the second arcuate surface, and an opposing flat surface facing the flat surface is formed on the outer diameter surface of the top.

[0016] According to the above configuration, the opposing flat surfaces of the top abut against the flat surfaces of the concave surface. Therefore, the top is less likely to rotate than when the outer diameter surface is a single arc surface, making the top assembly easier. Furthermore, when assembling the top, the opposing flat surfaces of the top abut against the flat surfaces of the concave surface. This positions the top so that the opposing flat surfaces are parallel to the cross direction.

[0017] In a preferred embodiment of the ball screw device, an angle formed by an imaginary line drawn from the center of the first arcuate surface to the end of the first arcuate surface in the piece removal direction and an imaginary line drawn to the end of the first arcuate surface in the piece insertion direction is less than 90 degrees.An angle formed by an imaginary line drawn from the center of the second arcuate surface to the end of the second arcuate surface in the piece removal direction and an imaginary line drawn to the end of the second arcuate surface in the piece insertion direction is less than 90 degrees.

[0018] According to this configuration, the shank of the cutting tool and the inner peripheral surface of the nut do not come into contact with each other.

[0019] In the ball screw device, the inner peripheral surface of the nut has a corner where the concave surface and the inner peripheral surface intersect, and has a first corner and a second corner that are spaced apart from each other in an intersecting direction. The first expanding arc surface may extend from the first corner in the block insertion direction, and the second expanding arc surface may extend from the second corner in the block insertion direction.

[0020] In a preferred embodiment of the ball screw device, the inner peripheral surface of the nut is a corner where the concave surface and the inner peripheral surface intersect, and has a first corner and a second corner spaced apart in the intersecting direction. The concave surface has a planar corner-side first flat surface that extends from the first corner in the block insertion direction and connects to the first expanding arc surface, and a planar corner-side second flat surface that extends from the second corner in the block insertion direction and connects to the second expanding arc surface. The outer diameter surface of the block has a planar corner-side first opposing flat surface that faces the corner-side first flat surface, and a planar corner-side second opposing flat surface that faces the corner-side second flat surface.

[0021] According to this configuration, when a load that would cause the top to rotate acts on the top, the first expanded opposing arcuate surface or the second expanded opposing arcuate surface catches on the first expanded opposing arcuate surface or the second expanded opposing arcuate surface, and the corner-side first opposing surface or the corner-side second opposing surface comes into contact with the corner-side first flat surface or the corner-side second flat surface, thereby reliably restricting the top from rotating.

[0022] In a preferred embodiment of the ball screw device, the concave surface has an opening that opens toward the inner periphery of the nut, and the opening is formed in a rectangular shape when viewed from the central axis of the nut.

[0023] If the opening were circular, after inserting the block into the concave surface, it would be necessary to position the block so that the S-shaped groove surface of the block and the inner raceway surface of the nut are contiguous. On the other hand, with the above configuration, the block is positioned. In other words, this eliminates the need to position the block so that the S-shaped groove surface of the block and the inner raceway surface are contiguous. This makes it easier to assemble the block.

[0024] In a preferred embodiment of the ball screw device, the concave surface has an opening that opens toward an inner peripheral side of the nut, and the length of the opening in the transverse direction is greater than the length in the axial direction.

[0025] With this configuration, the length of the top in the circumferential direction is greater than that in the axial direction. In other words, the ratio of the direction in which the S-shaped groove surface of the top extends is increased. This makes the curve of the S-shaped groove surface gentler, allowing the ball to move smoothly within the S-shaped groove surface.

[0026] The concave surface of the ball screw device may have an opening that opens toward an inner peripheral side of the nut, and the opening may be formed in a circular shape when viewed from a central axis of the nut.

[0027] The concave surface of the ball screw device has a third corner and a fourth corner that are corners where the concave surface and the inner circumferential surface intersect, and are spaced apart from each other in the axial direction. The third corner and the fourth corner may extend in the circumferential direction and intersect with the spiral direction.

[0028] The concave surface of the ball screw device has a third corner and a fourth corner that are corners where the concave surface and the inner peripheral surface intersect, and are spaced apart from each other in the axial direction. The third corner and the fourth corner may extend in the helical direction.

[0029] To achieve the above object, a manufacturing method of a ball screw device according to one aspect of the present disclosure includes a nut preparation step of preparing the nut and a link assembly step of assembling the link to the nut. The nut preparation step includes a concave surface forming step of forming the concave surface on the inner peripheral surface of the nut. The concave surface forming step includes a step of placing a cutting tool on the inner peripheral side of the nut, a first cutting step of moving the cutting tool in the link assembly insertion direction to form one of the second expanded arc surfaces of the first expanded arc surface, a second cutting step of moving the cutting tool in the intersecting direction and further in the link assembly insertion direction to form the first arc surface and the second arc surface, and a third cutting step of moving the cutting tool in the link assembly removal direction and further in the intersecting direction to form the other of the second expanded arc surfaces of the first expanded arc surface.

[0030] According to the present disclosure, even if a load that rotates the top along the first or second arcuate surface of the concave surface acts on the top during the top assembly process, the first expanded opposing arcuate surface catches on the first expanded opposing arcuate surface, and the second expanded opposing arcuate surface catches on the second expanded opposing arcuate surface. In other words, rotation of the top is restricted within the concave surface. This allows the top to be assembled in a predetermined position, making top assembly easier. [Effects of the Invention]

[0031] According to the ball screw device and the method for manufacturing the ball screw device of the present disclosure, the assembly of the top becomes easy. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a cross-sectional view of a ball screw device according to a first embodiment taken along the axial direction. [Figure 2] FIG. 2 is a cross-sectional view of the nut of the first embodiment cut in the axial direction. [Figure 3] 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. [Figure 4] FIG. 4 is an enlarged view of the concave surface of the nut of the first embodiment. [Figure 5]5 is a cross-sectional view of the nut of the first embodiment taken along line VV in FIG. 2 and viewed from the direction of the arrow. [Figure 6] FIG. 6 is a rear view of the piece of the first embodiment as seen from the piece insertion direction. [Figure 7] 7 is a cross-sectional view taken along the line VII-VII in FIG. [Figure 8] FIG. 8 is a flowchart showing a method for manufacturing the ball screw device of the first embodiment. [Figure 9] FIG. 9 is an enlarged view showing a part of the inner peripheral surface of the nut after the thread groove forming step of the first embodiment. [Figure 10] FIG. 10 is a flow chart showing the concave surface forming step of the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view of the ball screw device of Modification 1 taken in a direction perpendicular to the axial direction, and more specifically, is a cross-sectional view of the ball screw device of Modification 1 taken in the same manner as in FIG. [Figure 12] FIG. 12 is an enlarged view of the inner peripheral side of the nut of the ball screw device of the second modified example. [Figure 13] FIG. 13 is a cross-sectional view of the ball screw device of Modification 3 taken in a direction perpendicular to the axial direction, and more specifically, a cross-sectional view of the ball screw device of Modification 3 taken in the same manner as in FIG. [Figure 14] FIG. 14 is a cross-sectional view of the nut of the ball screw device of the fourth modification taken along the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0034] (Embodiment 1) Fig. 1 is a cross-sectional view of a ball screw device of embodiment 1 taken in the axial direction. As shown in Fig. 1, the ball screw device 100 of embodiment 1 includes a screw shaft 1, a nut 2, a plurality of balls 3, and three blocks 4 (only two are shown in Fig. 1; the remaining one is shown in Fig. 2). Hereinafter, the direction parallel to the central axis O2 of the nut 2 will be referred to as the axial direction.

[0035] The ball screw device 100 is a device that converts rotational motion into linear motion and linear motion into rotational motion. Such a ball screw device 100 is used in an electric actuator that is mounted on an electric brake, a shift actuator, or the like. Note that the ball screw device 100 of the present disclosure may also be used in devices other than electric actuators, and is not particularly limited thereto.

[0036] 1, the screw shaft 1 of the first embodiment is composed only of a screw shaft body 10. The screw shaft body 10 has a first end face 11 facing one side in the axial direction and a second end face 12 facing the other side in the axial direction.

[0037] Hereinafter, the axial direction in which the first end face 11 faces will be referred to as the first direction X1, and the axial direction in which the second end face 12 faces will be referred to as the second direction X2. Furthermore, the rotation direction will be based on the view from the first direction X1. The left-handed (counterclockwise) direction as viewed from the first direction X1 will be referred to as the first rotation direction L1 (see FIG. 3), and the right-handed (clockwise) direction as viewed from the first direction X1 will be referred to as the second rotation direction L2 (see FIG. 3).

[0038] As shown in FIG. 1, an outer circumferential raceway surface 14 is formed on the outer circumferential surface 13 of the screw shaft body 10. The outer circumferential raceway surface 14 of the present disclosure may have a Gothic arc shape or a circular arc shape, and is not particularly limited. The outer circumferential raceway surface 14 extends in a spiral direction. In this embodiment, the spiral direction is a right-handed thread (when the nut 2 is fixed and the screw shaft 1 is rotated in a second rotation direction L2 (see FIG. 3), the screw shaft 1 moves in a second direction X2).

[0039] Although the screw shaft 1 of the present embodiment is composed only of the screw shaft body 10, the screw shaft of the present disclosure may have, for example, a shaft portion extending in the axial direction from the first end face 11 or the second end face 12 of the screw shaft body 10. Such a shaft portion may be a portion into which a bearing device that rotatably supports the screw shaft 1 is fitted when the screw shaft 1 performs rotational motion, or a portion to which a piston or the like is connected when the screw shaft 1 performs linear motion, and there is no particular limitation on the use.

[0040] Fig. 2 is a cross-sectional view of the nut of the first embodiment taken in the axial direction. Of the three links 4, only the link 4 arranged closest to the first direction X1 is shown in Fig. 2. As shown in Fig. 2, the nut 2 is cylindrical and has an inner circumferential surface 20 and an outer circumferential surface 21. When viewed from the axial direction, the inner circumferential surface 20 and the outer circumferential surface 21 are formed in a circular shape centered on the central axis O2. The inner circumferential surface 20 has three inner circumferential raceway surfaces 22 and three concave surfaces 30 formed thereon.

[0041] The inner circumferential raceway surface 22 extends in the spiral direction. Note that the inner circumferential raceway surface 22 of the present disclosure may have a Gothic arc shape or a circular arc shape, and is not particularly limited. The inner circumferential raceway surface 22 extends approximately one turn (approximately one lead) in the spiral direction. One end 22a and the other end 22b of the inner circumferential raceway surface 22 are connected to the same concave surface 30. Note that the inner circumferential raceway surface 22 is not formed over the entire inner circumferential surface 20 of the nut 2.

[0042] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. In Fig. 3, to make the cross-sectional shape easier to understand, only some of the balls 3 arranged on the raceway 5 and the inner raceway surface 22 are shown. As shown in Fig. 3, the inner raceway surface 22 and the outer raceway surface 14 face each other in the radial direction. A spiral space (raceway 5) is defined between the inner raceway surface 22 and the outer raceway surface 14. A plurality of balls 3 are arranged in this raceway 5.

[0043] The concave surfaces 30 are recessed radially outward from the inner circumferential surface 20. The blocks 4 are housed inside the concave surfaces 30. The three concave surfaces 30 are arranged at 120-degree intervals from one another. In other words, when viewed from the axial direction, the three concave surfaces 30 are arranged at equal intervals in the circumferential direction. Details of the concave surfaces 30 will be described later.

[0044] 2, the piece 4 has an inner diameter surface 40 facing radially inward (toward the inner periphery of the nut 2). When viewed from the axial direction, the inner diameter surface 40 is formed in an arc shape centered on the central axis O2 (see FIG. 3).

[0045] As shown in FIG. 2, an S-shaped groove surface 41 is formed on the inner diameter surface 40, recessed radially outward from the inner diameter surface 40. The S-shaped groove surface 41 is formed in an S shape when viewed from the direction of the central axis O2. Hereinafter, the direction in which the S-shaped groove surface 41 extends will be simply referred to as the longitudinal direction. One end 41a of the S-shaped groove surface 41 in the longitudinal direction is connected to one end 22a of the inner circumferential raceway surface 22. The other end 41b of the S-shaped groove surface 41 in the longitudinal direction is connected to the other end 22b of the inner circumferential raceway surface 22. Therefore, the inner circumferential raceway surface 22 and the S-shaped groove surface 41 cooperate with each other to form an annular groove surface.

[0046] As shown in Fig. 3, the S-shaped groove surface 41 is positioned radially outward from one end 41a and the other end 41b toward a central portion 41c in the longitudinal direction. In other words, the recess amount of the S-shaped groove surface 41, based on the inner diameter surface 40, gradually increases from one end 41a and the other end 41b toward the central portion 41c. The recess amount of the central portion 41c of the S-shaped groove surface 41 is set to an extent that a ball 3 (see ball 3A among the multiple balls 3 in Fig. 3) rolling on the central portion 41c can clear the thread 15 of the screw shaft 1.

[0047] As described above, when the ball 3 enters the S-shaped groove surface 41 from one end of the raceway 5 and rolls along the S-shaped groove surface 41, it gradually moves radially outward and passes over the thread 15 of the screw shaft 1. Thereafter, the ball 3 gradually moves radially inward and circulates to the other end of the raceway 5. In addition, in this embodiment, when the ball 3 rolls on one end 41a (or the other end 41b) of the S-shaped groove surface 41, it is sandwiched between the outer circumferential raceway surface 14 and the S-shaped groove surface 41 and pushed outward in the radial direction. For this reason, the block 4 does not have a tang.

[0048] Furthermore, when the ball 3 rolls near the central portion 41c of the S-shaped groove surface 41, it cannot transmit the load from the screw shaft 1 to the nut 2 (see ball 3A in FIG. 3). In other words, even if an external load acts on the screw shaft 1 in the direction in which the top 4 is arranged as viewed from the central axis O2, the nut 2 cannot support the screw shaft 1. The direction in which the top 4 is arranged as viewed from the central axis O2 is the direction in which the top 4 is inserted into the concave surface 30, and will be referred to as the top insertion direction Z1 below. The direction opposite to the top insertion direction Z1 as viewed from the central axis O2 is the direction in which the top 4 is removed from the concave surface 30, and will be referred to as the top removal direction Z2 below.

[0049] On the other hand, in this embodiment, the concave surfaces 30 are arranged at 120-degree intervals, and therefore the three pieces 4 are also arranged at 120-degree intervals. In other words, the three pieces 4 are arranged in different directions when viewed from the central axis O2. Therefore, the nut 2 can support the screw shaft 1 from all directions in the circumferential direction.

[0050] Next, the configuration of the nut 2 near the concave surface 30 and the block 4 will be described in detail.

[0051] Fig. 4 is an enlarged view of the concave surface of the nut of embodiment 1. Fig. 5 is a cross-sectional view of the nut of embodiment 1 taken along line VV in Fig. 2, viewed from the direction of the arrow. As shown in Fig. 4, four corners 50 are provided on the inner peripheral side of the nut 2 where the inner peripheral surface 20 and the concave surface 30 intersect. Note that the corners 50 of the present disclosure may be pointed, tapered, or R-chamfered, and are not particularly limited.

[0052] The four corners 50 are a first corner 51 and a second corner 52 that are spaced apart from each other in the circumferential direction, and a third corner 53 and a fourth corner 54 that are spaced apart from each other in the axial direction. The first corner 51 is arranged in a first rotation direction L1 (see FIG. 3) when viewed from the concave surface 30. The second corner 52 is arranged in a second rotation direction L2 (see FIG. 3) when viewed from the concave surface 30.

[0053] 5, a direction that intersects (is perpendicular to) the piece insertion direction Z1 when viewed from the axial direction is referred to as the intersecting direction. Among the intersecting directions, a direction in which the first corner 51 is disposed when viewed from the second corner 52 is referred to as the first intersecting direction Y1. Among the intersecting directions, a direction in which the second corner 52 is disposed when viewed from the first corner 51 is referred to as the second intersecting direction Y2.

[0054] As shown in Fig. 4, the first corner 51 and the second corner 52 each extend linearly and are parallel to the axial direction. One end 22a of the inner circumferential raceway surface 22 is connected to the first corner 51. Therefore, a portion of the first corner 51 is cut out. Furthermore, the other end 22b of the inner circumferential raceway surface 22 is connected to the second corner 52. Therefore, a portion of the second corner 52 is cut out.

[0055] The third corner portion 53 is disposed in the first direction X1 when viewed from the concave surface 30. The fourth corner portion 54 is disposed in the second direction X2 when viewed from the concave surface 30. The third corner portion 53 and the fourth corner portion 54 are not connected to the inner circumferential raceway surface 22. Therefore, the third corner portion 53 and the fourth corner portion 54 are not cut out. Furthermore, the third corner portion 53 and the fourth corner portion 54 extend in the circumferential direction and intersect with the spiral direction.

[0056] The opening 55 of the concave surface 30, surrounded by the four corners 50, is rectangular (quadrilateral) when viewed from the inner periphery. Therefore, the top 4 also has a rectangular (quadrilateral) shape when viewed from the central axis O2 (see FIG. 2). Furthermore, the distance W1 of the opening 55 in the cross direction is greater than the distance W2 of the opening 55 in the axial direction.

[0057] The concave surface 30 has a first arcuate surface 31, a second arcuate surface 32, a first side surface 33, a second side surface 34, a first extended arcuate surface 131, and a second extended arcuate surface 132. The first side surface 33 is a flat surface that extends from the third corner 53 in the piece insertion direction Z1 and faces the second direction X2. The second side surface 34 is a flat surface that extends from the fourth corner 54 in the piece insertion direction Z1 and faces the first direction X1.

[0058] As shown in FIG. 5 , the first arcuate surface 31 and the second arcuate surface 32 are arcuate surfaces that move away from each other in the intersecting direction as they move in the piece removal direction Z2. Specifically, the first arcuate surface 31 extends in the piece insertion direction Z1 from an end 131a of the first expanding arcuate surface 131 in the piece removal direction Z1. That is, an end 31b of the first arcuate surface 31 in the piece removal direction Z2 is connected to the end 131a of the first expanding arcuate surface 131 in the piece insertion direction Z1. The first arcuate surface 31 is gradually positioned in the second intersecting direction Y2 as it moves in the piece insertion direction Z1. Therefore, the first arcuate surface 31 is formed in an arc shape when viewed from the axial direction. Furthermore, a tangent K1 to the end 31a of the first arcuate surface 31 in the second intersecting direction Y2 is perpendicular to the piece insertion direction Z1.

[0059] The second arcuate surface 32 extends in the piece insertion direction Z1 from an end 132a of the second expanding arcuate surface 132 in the piece insertion direction. That is, an end 32b of the second arcuate surface 32 in the piece removal direction Z2 is connected to an end 132a of the second expanding arcuate surface 132 in the piece insertion direction Z1. The second arcuate surface 32 is gradually positioned in the first intersecting direction Y1 as it moves in the piece insertion direction Z1. Therefore, the second arcuate surface 32 is formed in an arc shape when viewed from the axial direction. The curvature of the second arcuate surface 32 is the same as the curvature of the first arcuate surface 31. Furthermore, a tangent K2 to the end 32a of the second arcuate surface 32 in the first intersecting direction Y1 is perpendicular to the piece insertion direction Z1.

[0060] An end 31a of the first arcuate surface 31 and an end 32a of the second arcuate surface 32 are connected. Furthermore, a tangent K1 to the end 31a and a tangent K2 to the end 32a are a common tangent. Therefore, the surface formed by combining the first arcuate surface 31 and the second arcuate surface 32 is also arc-shaped. In other words, the first arcuate surface 31 and the second arcuate surface 32 cooperate with each other to form a single arcuate surface (hereinafter referred to as a single arcuate surface 35).

[0061] As shown in FIG. 5, the first extended arc surface 131 and the second extended arc surface 132 move away from each other in the intersecting direction as they move in the piece removal direction Z2. Specifically, the first extended arc surface 131 extends from the first corner 51 in the piece insertion direction Z1. The first extended arc surface 131 is gradually positioned in the second intersecting direction Y2 as it moves in the piece insertion direction Z1. The first extended arc surface 131 is formed in an arc shape when viewed from the axial direction. The second extended arc surface 132 extends from the second corner 52 in the piece insertion direction Z1. The second extended arc surface 132 is gradually positioned in the first intersecting direction Y1 as it moves in the piece insertion direction Z1. The second extended arc surface 132 is formed in an arc shape when viewed from the axial direction.

[0062] The curvature of the first extended arc surface 131 is the same as the curvature of the second extended arc surface 132. In addition, the curvatures of the first extended arc surface 131 and the second extended arc surface 132 are the same as the curvatures of the first arc surface 31 and the second arc surface 32. In other words, the first extended arc surface 131 and the second extended arc surface 132 have the same diameter as the single arc surface 35 (the first arc surface 31 and the second arc surface 32).

[0063] The center O131 of the first extended arcuate surface 131 (see FIG. 5) and the center O132 of the second extended arcuate surface 132 (see FIG. 5) do not overlap with the center O35 of the single arcuate surface 35. In other words, the first extended arcuate surface 131, the second extended arcuate surface 132, and the single arcuate surface 35 are not concentric. Therefore, the portion where the end 131a of the first extended arcuate surface 131 and the end 31b of the first arcuate surface 31 connect is a corner (hereinafter referred to as a first corner 133 within the concave surface). Similarly, the portion where the end 132a of the second extended arcuate surface 132 and the end 32b of the second arcuate surface 32 connect is a corner (hereinafter referred to as a second corner 134 within the concave surface). In the present disclosure, the first corner portion 133 within the concave surface and the second corner portion 134 within the concave surface may be sharp, tapered, or rounded, and are not particularly limited.

[0064] 5, the angle θ1 formed by the imaginary line K3 drawn from the center O35 of the single arcuate surface 35 to the first corner 133 within the concave surface and the imaginary line K4 drawn from the center O35 to the second corner 134 within the concave surface is less than 180 degrees.

[0065] The first extended arcuate surface 131 is disposed in a first intersecting direction Y1 with respect to the imaginary circle K35. The second extended arcuate surface 132 is disposed in a second intersecting direction Y2 with respect to the imaginary circle K35. Therefore, the first extended arcuate surface 131 and the second extended arcuate surface 132 are disposed outside the imaginary circle K35. Note that, since the first arcuate surface 31 constitutes a part of the single arcuate surface 35, the imaginary circle K35 corresponds to a first imaginary circle K31 having a center at the center of the first arcuate surface 31 and the same diameter as the first arcuate surface 31. Similarly, since the second arcuate surface 32 constitutes a part of the single arcuate surface 35, the imaginary circle K35 corresponds to a second imaginary circle K32 having a center at the center of the second arcuate surface 32 and the same diameter as the second arcuate surface 32. Therefore, when the first extended arc surface 131 and the second extended arc surface 132 are positioned outside the virtual circle K35, this means the same as when the first extended arc surface 131 is positioned outside the first virtual circle K31 and the second extended arc surface 132 is positioned outside the second virtual circle K32.

[0066] Fig. 6 is a rear view of the block of embodiment 1 as seen from the block insertion direction. Fig. 7 is a cross-sectional view taken along the line VII-VII in Fig. 2. As shown in Fig. 6, the block 4 has opposing surfaces (first opposing surface 42, second opposing surface 43) facing the axial direction and an outer diameter surface 44 facing radially outward (toward the outer periphery of the nut 2).

[0067] As shown in Fig. 6, the first opposing surface 42 faces the first direction X1 and is formed in a flat shape. The second opposing surface 43 faces the second direction X2 and is formed in a flat shape. When the top 4 is assembled inside the recessed surface 30, as shown in Fig. 2, the first opposing surface 42 faces the first side surface 33. The second opposing surface 43 faces the second side surface 34.

[0068] As shown in Figure 7, the outer diameter surface 44 has a first opposing arc surface 45 opposing the first arc surface 31, a second opposing arc surface 46 opposing the second arc surface 32, a first extended opposing arc surface 141 opposing the first extended arc surface 131, and a second extended opposing arc surface 142 opposing the second extended arc surface 132.

[0069] The first opposing arcuate surface 45 is an arcuate surface with the same curvature as the first arcuate surface 31. Therefore, when viewed from the axial direction, the first opposing arcuate surface 45 has the same shape as the first arcuate surface 31. The second opposing arcuate surface 46 is an arcuate surface with the same curvature as the second arcuate surface 32. Therefore, the second opposing arcuate surface 46 has the same shape as the second arcuate surface 32. The first opposing arcuate surface 45 and the second opposing arcuate surface 46 are connected to each other, and the combined surface of the first opposing arcuate surface 45 and the second opposing arcuate surface 46 also has an arc shape. In other words, the first opposing arcuate surface 45 and the second opposing arcuate surface 46 cooperate with each other to form a single arcuate surface (hereinafter referred to as the opposing arcuate surface 47). The opposing arcuate surface 47 has the same curvature as the single arcuate surface 35, and the entire surface of the opposing arcuate surface 47 abuts against the single arcuate surface 35.

[0070] The first extended opposing arcuate surface 141 is an arcuate surface having the same curvature as the first extended arcuate surface 131. Therefore, when viewed from the axial direction, the first extended opposing arcuate surface 141 has the same shape as the first extended arcuate surface 131. Furthermore, the second extended opposing arcuate surface 142 is an arcuate surface having the same curvature as the second extended arcuate surface 132. Therefore, the second extended opposing arcuate surface 142 has the same shape as the second extended arcuate surface 132. Furthermore, since the first extended opposing arcuate surface 131 and the second extended arcuate surface 132 are disposed outside the imaginary circle K35, the first extended opposing arcuate surface 141 and the second extended opposing arcuate surface 142 are also disposed outside the imaginary circle K35.

[0071] 2, the top 4 is formed point-symmetrically about a center O4 located at the center of the top 4 in the axial direction and the center in the transverse direction. Therefore, the top can be assembled even when rotated 180 degrees relative to the concave surface 30. Next, a manufacturing method of the ball screw device 100 of the first embodiment will be described.

[0072] 8 is a flow diagram showing a manufacturing method S100 of the ball screw device of Embodiment 1. The manufacturing method S100 of the ball screw device 100 includes a nut preparation step S1 of preparing the nut 2, a block assembly step S2 of assembling the block 4 to the concave surface 30 of the nut 2, a ball placement step S3 of placing balls 3 in the nut 2, and a screw shaft assembly step S4 of assembling the screw shaft 1 to the nut 2. The nut preparation step S1 will be described later.

[0073] In the piece assembling process S2, the piece 4 is placed on the inner periphery of the nut 2 and inserted into the concave surface 30 of the nut 2. If the piece 4 placed inside the concave surface 30 is not in a predetermined position, the balls 3 will not be transferred smoothly between the inner raceway surface 22 and the S-groove surface 41. Therefore, the piece 4 needs to be assembled so that it is in a predetermined position inside the concave surface 30, in other words, so that the piece 4 does not rotate along the single arc surface 35 (first arc surface 31 and second arc surface 32) of the concave surface 30.

[0074] In the ball placement process S3, first, a cylindrical temporary shaft 200 is inserted into the nut 2. This causes the outer peripheral surface of the temporary shaft 200 to face the inner raceway surface 22 of the nut 2 in the radial direction. The temporary shaft 200 is inserted to such an extent that a portion of the inner raceway surface 22 of the nut 2 is released from the temporary shaft 200 (i.e., is not facing the temporary shaft 200). Then, balls 3 are inserted into the released portion of the inner raceway surface 22. This ball 3 insertion operation is repeated until the inner raceway surface 22 and the S-shaped groove surface 41 are filled with balls 3. Once the inner raceway surface 22 and the S-shaped groove surface 41 are filled with balls 3, the insertion depth of the temporary shaft 200 is increased. This prevents the balls 3 placed on the inner raceway surface 22 and the S-shaped groove surface 41 from falling out radially inward. This operation is repeated until balls 3 are placed on all of the inner raceway surfaces 22 and S-shaped groove surfaces 41, and this process is completed.

[0075] In the screw shaft assembling step S4, first, the end face of the temporary shaft 200 and the second end face 12 of the screw shaft 1 are brought into contact with each other. Next, while the screw shaft 1 is being pushed toward the temporary shaft 200 (see arrow F4 in FIG. 8 ), the screw shaft 1 and the nut 2 are rotated relative to each other. As a result, the temporary shaft 200 moves in the second direction X2, and the screw shaft 1 enters the nut 2. Furthermore, the balls 3 arranged on the inner peripheral raceway surface 22 enter the outer peripheral raceway surface 14 of the screw shaft 1. Then, once the plurality of balls 3 have entered the outer peripheral raceway surface 14 of the screw shaft 1, the action of pushing the screw shaft 1 in the second direction X2 is stopped. Then, only the relative rotation between the screw shaft 1 and the nut 2 is performed, and the screw shaft 1 is moved in the second direction X2. Then, once the balls 3 arranged on the inner peripheral raceway surfaces 22 have entered the outer peripheral raceway surface 14 of the screw shaft 1 and the temporary shaft 200 has fallen off the nut 2, the screw shaft assembling step S4 is completed, and the ball screw device 100 is completed.

[0076] Although the manufacturing method of the ball screw device 100 of the present embodiment has been described as an example of a manufacturing method using the temporary shaft 200, the present disclosure does not necessarily require the use of the temporary shaft 200. Furthermore, the present disclosure may be manufactured by a manufacturing method other than the above-described manufacturing method.

[0077] Next, the nut preparation step S1 will be described. The nut preparation step S1 includes a thread groove forming step S10, a concave surface forming step S11, and a heat treatment step (not shown).

[0078] FIG. 9 is an enlarged view showing a portion of the inner peripheral surface of the nut after the thread groove forming step of the first embodiment. As shown in FIG. 9, the thread groove forming step S10 is a step of forming a thread groove 80 on the inner peripheral surface 20 of the nut 2. The thread groove 80 is formed by bringing the teeth of a cutting tool into contact with the inner peripheral surface 20 of the nut 2 and rotating the nut 2 in a spiral direction. This forms a spiral thread groove 80 on the inner peripheral surface 20. The length of the thread groove 80 is approximately one lead. Note that in the thread groove forming step of this embodiment, the cutting tool is fixed and the nut 2 is rotated in a spiral direction. However, it is also possible to move the cutting tool in the axial direction and simply rotate the nut 2 about the central axis O2. The present disclosure does not particularly limit the method of forming the thread groove 80.

[0079] 10 is a flow diagram showing the concave surface forming step of embodiment 1. The concave surface forming step S11 is a step of forming a concave surface 30 on the inner peripheral surface 20 of the nut 2. Specifically, the concave surface forming step S11 includes a step S12 of arranging a cutting tool 90 on the inner peripheral side of the nut 2, a first cutting step S13, a second cutting step S14, and a third cutting step S15.

[0080] The cutting tool 90 used in the concave surface forming step S11 has a plurality of cutting blades arranged in the circumferential direction on its outer peripheral surface. The cutting tool 90 rotates around a shaft portion 91. In step S12 of arranging the cutting tool 90 on the inner peripheral side of the nut 2, the cutting tool 90 is arranged so that the shaft portion 91 is parallel to the central axis O2 of the nut 2, as shown in FIG.

[0081] In the first cutting step S13, first, the cutting tool 90 is rotated. Then, the cutting tool 90 is moved radially outward (in the block insertion direction Z1) (see arrow Z13 in FIG. 10), and the cutting teeth of the cutting tool 90 cut the inner circumferential surface 20. As a result, a first extended arcuate surface 131 is formed.

[0082] The second cutting step S14 is a step of forming the first arcuate surface 31 and the second arcuate surface 32. In this embodiment, the first arcuate surface 31 and the second arcuate surface 32 constitute a single arcuate surface 35. Therefore, in the second cutting step S14 of this embodiment, the single arcuate surface 35 is formed. Specifically, in the second cutting step S14, the cutting tool 90 is moved in the intersecting direction (second intersecting direction Y2) and then further moved radially outward (block insertion direction Z1) (see arrow Z14 in FIG. 10). This forms the single arcuate surface 35 (the first arcuate surface 31 and the second arcuate surface 32).

[0083] In the next third cutting step S15, the cutting tool 90 is moved radially inward (the link removal direction Z2) and then moved in the intersecting direction (second intersecting direction Y2) (see arrow Z15 in FIG. 10). This forms the second extended arc surface 132, and the entire concave surface 30 is formed. Next, the cutting tool 90 is returned to the inner peripheral side of the nut 2 (see arrow Z16 in FIG. 10), and the concave surface forming step S11 is completed.

[0084] According to the concave surface forming step S11, arc surfaces having approximately the same outer diameter (curvature) as the cutting tool 90, i.e., the first extended arc surface 131, the single arc surface 35 (the first arc surface 31 and the second arc surface 32), and the second extended arc surface 132, are formed. Furthermore, according to this step, as shown in Fig. 9, both ends of the thread groove 80 (see the area surrounded by the imaginary line K10 in Fig. 9) are cut. As a result, the inner circumferential raceway surface 22 connected to the concave surface 30 is formed.

[0085] As described above, the movement of the cutting tool 90 in the concave surface forming step S11 is limited to either radial movement or transverse movement (see arrows Z12 to Z14 in FIG. 10). In other words, it does not include movement in a diagonal direction that combines the radial and transverse directions. This simplifies the manufacturing process. In addition, in this embodiment, the first arcuate surface 31 and the second arcuate surface 32 form a single arcuate surface 35. Therefore, in the second cutting step S14, after cutting the first arcuate surface 31, it is not necessary to move the cutting tool 90 in the transverse direction to cut the second arcuate surface 32 (see arrow Z13 in FIG. 10). This further simplifies the manufacturing of the nut 2.

[0086] In addition, the angle θ1 (see FIG. 5) of the single arcuate surface 35 is less than 180 degrees. Therefore, in the second cutting step S14, the shank 91 of the cutting tool 90 does not contact the inner peripheral surface 20 of the nut 2. Furthermore, in the above-described concave surface forming step S11, an example is given in which the nut 2 is fixed and the cutting tool 90 is moved. However, in the present disclosure, the concave surface 30 may be formed by fixing the cutting tool 90 and moving the nut 2. Furthermore, in the present embodiment, the first extended arcuate surface 131 is formed in the first cutting step S13 and the second extended arcuate surface 132 is formed in the third cutting step S15. However, in the present disclosure, the second extended arcuate surface 132 may be formed in the first cutting step S13 and the first extended arcuate surface 131 may be formed in the third cutting step S15.

[0087] The heat treatment process (not shown) is a process of hardening and tempering the inner peripheral surface 20 of the nut 2. In the present disclosure, carburizing may be performed before hardening. The hardening method may be induction hardening. This allows the inner peripheral surface 20 of the nut 2 to obtain the desired hardness and toughness. In the present disclosure, the heat treatment method may be other than the above-mentioned method and is not particularly limited. In addition, the present disclosure may include a polishing process of polishing the inner peripheral raceway surface 22 after the heat treatment process.

[0088] Next, the effects of this embodiment will be described.

[0089] As shown in Fig. 8, the method of assembling the top 4 to the nut 2 is performed by moving the top 4 arranged on the inner peripheral side of the nut 2 in the top insertion direction Z1 and arranging the top 4 inside the concave surface 30. Here, as shown in Fig. 7, the force that moves the top 4 in the top insertion direction Z1 may act not on the center of the inner diameter surface 40 in the intersecting direction but on the end of the inner diameter surface 40 in the first intersecting direction Y1 (see arrow F1 in Fig. 7). This causes the first opposing arcuate surface 45 of the top 4 to be pressed against the first arcuate surface 31.

[0090] If the first extended opposing arcuate surface 141 and the second extended opposing arcuate surface 142 were not provided, the top 4 would be guided by the first arcuate surface 31 and move in the second intersecting direction Y2 (see arrow F2 in FIG. 7 ). As a result, the end of the inner diameter surface 40 in the second intersecting direction Y2 would protrude from the concave surface 30 (see arrow F3 in FIG. 7 ). In other words, as viewed from the first direction X1, the top 4 may rotate clockwise around the center O35 of the imaginary circle K35. On the other hand, according to this embodiment, the first extended opposing arcuate surface 141 is positioned outside the imaginary circle K35 and protrudes radially outward from the imaginary circle K35. Therefore, the first extended opposing arcuate surface 141 is caught by the first extended arcuate surface 131. This restricts the top 4 from rotating clockwise within the concave surface 30.

[0091] Furthermore, if the force during assembly is applied toward the end of the inner diameter surface 40 in the second intersecting direction Y2, the top 4 may be guided by the second arcuate surface 32, causing the top 4 to rotate counterclockwise around the center O35 of the imaginary circle K35 as viewed from the first direction X1. According to this embodiment, the second extended opposing arcuate surface 142 is positioned outside the imaginary circle K35 and protrudes radially outward from the imaginary circle K35. Therefore, the second extended opposing arcuate surface 142 engages with the second extended arcuate surface 132, restricting the top 4 from rotating counterclockwise within the concave surface 30. As a result, the top 4 is assembled in a predetermined orientation without rotating. This eliminates the need to correct the orientation of the top 4, making assembly of the top 4 easier.

[0092] Furthermore, in this embodiment, no thread groove surface is formed over the entire inner peripheral surface 20 of the nut 2. In other words, only the inner peripheral raceway surface 22 is formed, and no circuit outer thread groove surface that is not connected to the S-groove surface 41 is formed. Therefore, there is no risk that the balls 3 will be positioned on a thread groove surface other than the inner peripheral raceway surface 22.

[0093] As shown in FIG. 4, the distance W1 of the opening 55 in the cross direction is greater than the distance W2 of the opening 55 in the axial direction. Therefore, the length of the top 4 in the circumferential direction is greater than the length in the axial direction. This increases the ratio of the direction in which the S-shaped groove surface 41 extends in the top 4, and the curvature of the S-shaped groove surface 41 becomes gentler. In other words, as shown in FIG. 2, the inclination angle θ3 with respect to the spiral direction can be made relatively small. Furthermore, as shown in FIG. 3, the inclination angle θ4 with respect to the circumferential direction can also be made relatively small. Therefore, the ball 3 moves smoothly along the S-shaped groove surface 41.

[0094] Furthermore, in this embodiment, the opening 55 of the concave surface 30 and the link 4 are formed in a rectangular shape when viewed from the central axis O2. If the opening 55 and the link 4 were circular when viewed from the central axis O2, it would be necessary to insert the link 4 into the concave surface 30 and then position the link 4 so that the S-shaped groove surface 41 and the inner circumferential raceway surface 22 are continuous. However, according to this embodiment, the link 4 is positioned so that the S-shaped groove surface 41 and the inner circumferential raceway surface 22 are continuous when it is inserted into the concave surface 30. This eliminates the need to position the link 4 so that the S-shaped groove surface 41 and the inner circumferential raceway surface 22 are continuous.

[0095] As described above, the ball screw device 100 of the first embodiment includes a screw shaft 1, a nut 2 inserted through the screw shaft 1, a plurality of balls 3 arranged between the screw shaft 1 and the nut 2, and at least one or more blocks 4 for circulating the balls 3. The inner peripheral surface 20 of the nut 2 is recessed radially outward from the inner peripheral surface 20 and has a concave surface 30 for accommodating the blocks 4 therein. The direction in which the concave surface 30 is arranged as viewed from the central axis O2 of the nut 2 is the block insertion direction Z1, and the direction opposite to the block insertion direction Z1 is the block removal direction Z2. As viewed from the axial direction parallel to the central axis O2 of the nut 2, the direction intersecting the block insertion direction Z1 is the intersecting direction. The concave surface 30 has a first arcuate surface 31 and a second arcuate surface 32 which are arcuate and move apart in the intersecting direction as they move in the top removal direction Z2, and a first extended arcuate surface 131 and a second extended arcuate surface 132 which extend in the top removal direction Z2 from the end of the first arcuate surface 31 or the second arcuate surface 32 in the top removal direction Z2 and move apart in the intersecting direction as they move in the top removal direction Z2. The outer diameter surface 44 of the top 4 has a first arcuate opposing arcuate surface 45 which faces the first arcuate surface 31, a second arcuate opposing arcuate surface 46 which faces the second arcuate surface 32, a first arcuate opposing arcuate surface 141 which faces the first extended arcuate surface 131, and a second arcuate opposing arcuate surface 142 which faces the second extended arcuate surface 132. The first extended arc surface 131 and the second extended arc surface 132 are centered on the center of the single arc surface 35 (first arc surface 31 and second arc surface 32) and are positioned outside a virtual circle K35 (first virtual line and second virtual line) of the same diameter as the single arc surface 35 (first arc surface 31 and second arc surface 32).

[0096] According to the first embodiment, the ease of assembly of the link 4 can be improved. Also, according to the first embodiment, there is no need to provide a through hole in the outer peripheral surface 21 of the nut 2. This meets the needs of sliding the outer peripheral surface 21 of the nut 2 to make the nut 2 itself function as a piston, or directly press-fitting a bearing, a motor rotor, a reduction gear, a belt pulley, etc. into the outer peripheral surface 21 of the nut 2. Furthermore, since there is no through hole in the outer peripheral surface 21 of the nut 2, dust resistance is high. Alternatively, the nut 2 is smaller and lighter than when a through hole is provided in the outer peripheral surface 21 of the nut 2 and a part that blocks the through hole is provided.

[0097] Next, a description will be given of a modified example of the ball screw device 100 of the embodiment 1. The following description will focus on differences from the example described above.

[0098] (Variation 1) FIG. 11 is a cross-sectional view of the ball screw device of Modification 1 taken in a direction perpendicular to the axial direction. Specifically, it is a cross-sectional view of the ball screw device of Modification 1 taken in the same manner as in FIG. 7. As shown in FIG. 11, the concave surface 30A of the nut 2A of Modification 1 differs from that of Embodiment 1 in that it has a flat surface 36 disposed between the first arcuate surface 31 and the second arcuate surface 32. The outer diameter surface 44A of the top 4A of Modification 1 also differs from that of Embodiment 1 in that it has an opposing flat surface 48 opposed to the flat surface 36. Note that Modification 1 is similar to Embodiment 1 in that the first extended arcuate surface 131 is disposed outside the first virtual circle K31, and the second extended arcuate surface 132 is disposed outside the second virtual circle K32. In other words, Modification 1 also achieves the same effect as Embodiment 1, namely, the rotation of the top 4 is restricted during assembly.

[0099] The plane 36 extends in the intersecting direction and the axial direction. An end 36a of the plane 36 in the first intersecting direction Y1 is connected to an end 31a of the first arcuate surface 31 in the second intersecting direction Y2. An end 36b of the plane 36 in the second intersecting direction Y2 is connected to an end 32a of the second arcuate surface 32 in the first intersecting direction Y1. When the concave surface 30A is formed in the concave surface forming step S11, the cutting tool 90 (see FIG. 10) is moved in the block insertion direction Z1 to form the first arcuate surface 31 in the second cutting step S14, and then the cutting tool 90 is moved in the second intersecting direction Y2 to form the plane 36 and the second arcuate surface 32.

[0100] Furthermore, the angle formed by the imaginary line K11 drawn from the center O31 of the first arcuate surface 31 to the first concave corner portion 133 and the imaginary line K12 drawn from the center O31 of the first arcuate surface 31 to the end portion 31 a of the first arcuate surface 31 is less than 90 degrees. Furthermore, the angle formed by the imaginary line K13 drawn from the center O32 of the second arcuate surface 32 to the second concave corner portion 134 and the imaginary line K14 drawn from the center O32 of the second arcuate surface 32 to the end portion 32 a of the second arcuate surface 32 is less than 90 degrees. As a result, when forming the first arcuate surface 31 and the second arcuate surface 32, the shank 91 (see FIG. 10) of the cutting tool 90 does not come into contact with the inner circumferential surface 20 of the nut 2A.

[0101] According to the above-described first modification, when the top 4A is assembled, the opposing flat surface 48 of the top 4A is positioned so that it abuts against the flat surface 36 of the concave surface 30A. This positions the top 4A so that the opposing flat surface 48 is parallel to the intersecting direction when viewed from the axial direction. This prevents the top 4A from being assembled in a tilted (rotated) state. Furthermore, according to the first modification, the flat surface 36 is provided between the first arcuate surface 31 and the second arcuate surface 32, making it difficult for the top 4A to rotate. Therefore, according to the first modification, the rotation of the top 4A is more reliably restricted than in the first embodiment. The opposing flat surface 48 may be formed to be the same size as the flat surface 36 or slightly smaller than the flat surface 36. In other words, the present disclosure does not particularly care about the sizes of the opposing flat surface 48 and the flat surface 36.

[0102] (Variation 2) FIG. 12 is an enlarged view of the inner peripheral side of the nut of the ball screw device of Modification 2. As shown in FIG. 12, nut 2B of Modification 2 differs from Embodiment 1 in that the orientation of concave surface 30B is changed. A first corner 51B and a second corner 52B of concave surface 30B intersect with the axial direction. A third corner 53B and a fourth corner 54B extend in the spiral direction. Such a concave surface 30B can be formed when the shank 91 of the cutting tool 90 is inclined with respect to the central axis O2 during the concave surface forming process. Even in Modification 2, as in Embodiment 1, assembly of the link 4 is easy.

[0103] (Variation 3) 13 is a cross-sectional view of the ball screw device of Modification 3 taken in a direction perpendicular to the axial direction, and more specifically, a cross-sectional view of the ball screw device of Modification 3 taken in the same manner as in FIG. 7. As shown in FIG. 13, the concave surface 30C of the nut 2C of Modification 3 differs from that of Embodiment 1 in that it has a corner-side first flat surface 137 and a corner-side second flat surface 138. Furthermore, the outer diameter surface 44 of the link 4C of Modification 3 differs from that of Embodiment 1 in that it has a corner-side first opposing surface 148 and a corner-side second opposing surface 149.

[0104] The corner-side first flat surface 137 extends from the first corner 51 in the frame insertion direction Z1. The corner-side second flat surface 138 extends from the second corner 52 in the frame insertion direction Z1. The corner-side first flat surface 137 and the corner-side second flat surface 138 are flat surfaces that extend in the axial direction and the frame insertion direction Z, respectively. An end 137a of the corner-side first flat surface 137 in the frame insertion direction Z1 is connected to an end 131b of the first extended arc surface 131 in the frame removal direction Z2. An end 138b of the corner-side second flat surface 138 in the frame insertion direction Z1 is connected to an end 132b of the second extended arc surface 132 on the opposite side of the frame removal direction Z2.

[0105] With respect to the link 4C, the corner-side first opposing surface 148 and the corner-side second opposing surface 149 are planes extending in the axial direction and the link insertion direction Z, respectively. The corner-side first opposing surface 148 faces the corner-side first flat surface 137. The corner-side second opposing surface 149 faces the corner-side second flat surface 138. Note that in FIG. 13 , a gap is provided between the corner-side first opposing surface 148 and the corner-side first flat surface 137, but in the present disclosure, the corner-side first opposing surface 148 and the corner-side first flat surface 137 may abut against each other. Similarly, a gap is provided between the corner-side second opposing surface 149 and the corner-side second flat surface 138, but in the present disclosure, the corner-side second opposing surface 149 and the corner-side second flat surface 138 may abut against each other.

[0106] According to Modification 3, when a load acts on the top 4C in a clockwise direction as viewed from the first direction X1, the first extended opposing arcuate surface 141 catches on the first extended arcuate surface 131. Furthermore, the corner-side first opposing surface 148 comes into contact with the corner-side first flat surface 137, so rotation of the top 4C is reliably restricted. On the other hand, when a load acts on the top 4C in a counterclockwise direction as viewed from the first direction X1, the second extended opposing arcuate surface 142 catches on the second extended arcuate surface 132. Furthermore, the corner-side second opposing surface 149 comes into contact with the corner-side second flat surface 138, so rotation of the top 4C is reliably restricted. From the above, rotation of the top 4C is reliably restricted.

[0107] The concave surface 30C of Modification 3 has a corner-side first flat surface 137 and a corner-side second flat surface 138. Therefore, the depth of the concave surface 30C in the block insertion direction Z1 is greater than that of the concave surface 30 of Embodiment 1. Regarding the thickness of the nut 2C, if a predetermined thickness is to be secured from the first arcuate surface 31 and the second arcuate surface 32 of the concave surface 30C to the outer peripheral surface 21 of the nut 2C, the outer diameter of the nut 2C is greater than the outer diameter of the nut 2 of Embodiment 1 (see imaginary line K21 in FIG. 13 ). Therefore, Embodiment 1 has the advantage that the nut 2 can be made smaller than Modification 3.

[0108] The above has described Modification 3. Here, Modification 3 has been described by taking as an example an example in which the corner-side first flat surface 137, the corner-side second flat surface 138, the corner-side first opposing surface 148, and the corner-side second opposing surface 149 are added to the ball screw device 100 of Embodiment 1, but the present disclosure may also add them to Modification 1.

[0109] (Variation 4) FIG. 14 is a cross-sectional view of a nut of a ball screw device of Modification 4 taken along the axial direction. As shown in FIG. 14, nut 2D of Modification 4 differs from embodiment 1 in that a thread groove surface 70 is formed on the entire inner peripheral surface 20. That is, the thread groove surface 70 has an inner peripheral raceway surface 22 that connects to the S-shaped groove surface 41 of the link 4, and an outer-circuit thread groove surface 71 that is not connected to the S-shaped groove surface 41. Even with nut 2D of Modification 4, rotation of link 4 can be restricted, as with embodiment 1. Furthermore, in the thread groove forming step S10 (see FIG. 10 ), the thread groove surface (inner peripheral raceway surface) is formed on the inner peripheral surface 20 of nut 2 by cutting, but the nut 2D of Modification 4 is not limited to cutting. That is, the thread groove surface 70 of nut 2D of Modification 4 may be formed by rolling.

[0110] Although the above describes the embodiments and modified examples, the present disclosure is not limited to the above. For example, while the first embodiment has three concave surfaces 30 and three link members 4, the present disclosure requires at least one of each. The first arcuate surface 31 and the second arcuate surface 32 may cooperate to form a single elliptical surface. The opening 55 of the concave surface 30 has a cross-directional distance W1 that is longer than the axial distance W2. However, the distances W1 and W2 may be equal; the present disclosure is not particularly limited. The opening 55 is rectangular, but may be circular or elliptical. Each corner 50 is linear, but may be arcuate. Each corner 50 may be partially linear and partially arcuate; the shape of the corner 50 is not particularly limited in the present disclosure.

[0111] Furthermore, although the first opposing arcuate surface 45 in the first embodiment has the same curvature as the first arcuate surface 31, in the present disclosure, the curvature of the first opposing arcuate surface 45 may be slightly smaller than the curvature of the first arcuate surface 31. In addition, in the present disclosure, the curvature of the second opposing arcuate surface 46 may be slightly smaller than the curvature of the second arcuate surface 32. In other words, the opposing arcuate surfaces of the top 4 (first opposing arcuate surface 45, second opposing arcuate surface 46) do not have to have the same curvature as the arcuate surfaces of the concave surface 30 (first arcuate surface 31, second arcuate surface 32).

[0112] Furthermore, although the first extended opposing arcuate surface 141 in the first embodiment has the same curvature as the first extended arcuate surface 131, in the present disclosure, the first extended opposing arcuate surface 141 may have a curvature slightly smaller than that of the first extended arcuate surface 131. Similarly, in the present disclosure, the curvature of the second extended opposing arcuate surface 142 may have a curvature slightly smaller than that of the second extended arcuate surface 132.

[0113] Furthermore, the curvatures of the first arcuate surface 31 and the second arcuate surface 32 are the same as the curvatures of the first expanded opposing arcuate surface 141 and the second expanded opposing arcuate surface 142, but in the present disclosure, the curvatures may be different. However, if the curvatures of the first arcuate surface 31 and the second arcuate surface 32 are different from the curvatures of the first expanded opposing arcuate surface 141 and the second expanded opposing arcuate surface 142, it is necessary to move the cutting tool 90 in an arc shape in the concave surface forming step S11, which increases the effort required to manufacture the nut 2.

[0114] Furthermore, although the first arcuate surface 31, the second arcuate surface 32, the first extended arcuate surface 131, and the second extended arcuate surface 132 in the embodiments and the like are each arc-shaped, in the present disclosure, the "arc" is not limited to a curved surface with a constant curvature. In other words, the "arc" in the present disclosure may be an arc shaped like a part of a perfect circle, an arc shaped like a part of an ellipse, or an arc whose curvature gradually increases (or decreases) from one end of the curved surface to the other. Similarly, in the present disclosure, the first opposing arcuate surface 45, the second opposing arcuate surface 46, the first extended opposing arcuate surface 141, and the second extended opposing arcuate surface 142 are not limited to arcs with a constant curvature.

[0115] In addition, in the present disclosure, there are no particular limitations on the material or manufacturing method of the top. For example, the top may be manufactured from a resin material by injection molding. Alternatively, the top may be manufactured by metal powder injection molding. Alternatively, the top may be manufactured by cutting a metal material.

[0116] Furthermore, in the present disclosure, there is no particular restriction on the method of fixing the top 4 to the concave surface 30. In other words, the top 4 may or may not be fixed to the concave surface 30. That is, in the present disclosure, the top 4 may be loosely fitted into the concave surface 30. Alternatively, the top 4 may be fitted into the concave surface 30 with an interference. Alternatively, the top 4 may be glued to the concave surface 30. Alternatively, the balls (see balls 3B and 3C among the multiple balls 3 in FIG. 3) rolling on one end 41a and the other end 41b of the S-shaped groove surface may come into contact with the outer circumferential raceway surface 14, thereby restricting the radially inward movement of the top 4. Alternatively, the top 4 may be fixed to the concave surface 30 by crimping. In this manner, there is no particular restriction on whether the top 4 is fixed. Furthermore, in this specification, "same" or "equal" includes not only completely identical things, but also things that are considered to be substantially "same" or "equal" due to tolerances (the range of general manufacturing errors).

[0117] The present disclosure may also be implemented as a combination of the following configurations. (1) A screw shaft, a nut inserted through the screw shaft; a plurality of balls disposed between the screw shaft and the nut; At least one or more pieces for circulating the ball; Equipped with The inner circumferential surface of the nut has a concave surface that is recessed radially outward from the inner circumferential surface and accommodates the piece therein, The direction in which the concave surface is arranged as viewed from the central axis of the nut is defined as a block insertion direction, The direction opposite to the inserting direction is the removing direction, When viewed from an axial direction parallel to the central axis of the nut, a direction intersecting the inserting direction of the link is defined as a transverse direction, The concave surface is a first arc surface and a second arc surface that are arc-shaped and move away from each other in the intersecting direction as the piece moves in the separation direction; a first extended arc surface and a second extended arc surface that extend in the piece removal direction from an end of the first arc surface or the second arc surface in the piece removal direction and move apart from each other in the intersecting direction as they move in the piece removal direction; and The outer diameter surface of the piece is a first opposing arcuate surface that is arcuate and faces the first arcuate surface; a second opposing arcuate surface that is arcuate and faces the second arcuate surface; a first extended opposing arcuate surface that is arcuate and faces the first extended arcuate surface; a second extended opposing arcuate surface having an arc shape opposing the second extended arcuate surface; and a first extended arcuate surface is disposed outside a first imaginary circle having a center on the center of the first arcuate surface and the same diameter as the first arcuate surface; The second extended arcuate surface is centered on the center of the second arcuate surface and is disposed outside a second imaginary circle having the same diameter as the second arcuate surface. Ball screw device. (2) The first arcuate surface, the second arcuate surface, the first extended arcuate surface, and the second extended arcuate surface have the same curvature. The ball screw device according to (1). (3) the curvature of the first arcuate surface and the curvature of the second arcuate surface are the same; The curvatures of the first arcuate surface and the second arcuate surface are different from the curvatures of the first extended arcuate surface and the second extended arcuate surface. The ball screw device according to (1). (4) The first arcuate surface and the second arcuate surface are connected to each other and cooperate to form a single arcuate surface. A ball screw device according to any one of (1) to (3). (5) The angle formed by an imaginary line drawn from the center of the single arcuate surface to one end of the single arcuate surface in the intersecting direction and an imaginary line drawn to the other end of the single arcuate surface in the intersecting direction is less than 180 degrees. (4) The ball screw device according to (4). (6) the concave surface has a plane disposed between the first arcuate surface and the second arcuate surface, An opposing flat surface facing the flat surface is formed on the outer diameter surface of the piece. A ball screw device according to any one of (1) to (3). (7) An angle formed by an imaginary line drawn from the center of the first arcuate surface to an end of the first arcuate surface in the piece removal direction and an imaginary line drawn to an end of the first arcuate surface in the piece insertion direction is less than 90 degrees, An angle formed by an imaginary line drawn from the center of the second arcuate surface to an end of the second arcuate surface in the piece removal direction and an imaginary line drawn to an end of the second arcuate surface in the piece insertion direction is less than 90 degrees. (6) The ball screw device according to (6). (8) The inner circumferential surface of the nut has a corner where the concave surface and the inner circumferential surface intersect, and has a first corner and a second corner arranged apart from each other in an intersecting direction, the first extended arc surface extends from the first corner portion in the piece insertion direction, The second extended arc surface extends from the second corner portion in the inserting direction of the piece. A ball screw device according to any one of (1) to (7). (9) The inner circumferential surface of the nut has a corner where the concave surface and the inner circumferential surface intersect, and has a first corner and a second corner arranged apart from each other in an intersecting direction, The concave surface is a first flat surface on the corner side extending from the first corner in the inserting direction and connecting to the first extended arc surface; a second flat surface on the corner side extending from the second corner in the inserting direction and connected to the second extended arc surface; and The outer diameter surface of the piece is a flat corner-side first opposing surface opposed to the corner-side first flat surface; a flat corner-side second opposing surface opposed to the corner-side second flat surface; have A ball screw device according to any one of (1) to (7). (10) The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening is formed in a rectangular shape when viewed from the central axis of the nut. A ball screw device according to any one of (1) to (9). (11) The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening has a length in the cross direction that is greater than a length in the axial direction. A ball screw device according to any one of (1) to (9). (12) The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening is formed in a circular shape when viewed from the central axis of the nut. A ball screw device according to any one of (1) to (9). (13) The concave surface is a corner portion where the concave surface and the inner circumferential surface intersect, the corner portion having a third corner portion and a fourth corner portion spaced apart from each other in the axial direction; The third corner portion and the fourth corner portion extend in the circumferential direction and intersect with the spiral direction. A ball screw device according to any one of (1) to (9). (14) the concave surface is a corner where the concave surface and the inner circumferential surface intersect, and has a third corner and a fourth corner that are spaced apart from each other in the axial direction, The third corner portion and the fourth corner portion extend in a spiral direction. A ball screw device according to any one of (1) to (13). (15) A method for manufacturing the ball screw device according to claim 1, a nut preparing step of preparing the nut; a link assembling step of assembling the link to the nut; Including, The nut preparation step includes a concave surface forming step of forming the concave surface on the inner circumferential surface of the nut, The concave surface forming step includes: a step of placing a cutting tool on an inner peripheral side of the nut; a first cutting step of moving the cutting tool in the inserting direction to form one of the second extended arc surfaces of the first extended arc surface; a second cutting step of moving the cutting tool in the intersecting direction and further in the block insertion direction to form the first arcuate surface and the second arcuate surface; a third cutting step of moving the cutting tool in the link removal direction and further in the intersecting direction to form the other of the second extended arc surfaces of the first extended arc surface; Contains A method for manufacturing a ball screw device. [Explanation of symbols]

[0118] 1 Screw shaft 2, 2A, 2B, 2C, 2D Nut 3 Ball 4, 4A, 4C frames 14 Outer raceway surface 20 Inner surface 21 Outer surface 22 Inner raceway surface 30, 30A, 30B, 30C concave 31 First circular arc surface 32 Second arc surface 33 First aspect 34 Second aspect 35 Single arc surface 36 plane 40 Inner diameter surface 41 S-shaped groove surface 42 First opposing surface 43 Second opposing surface 44, 44A outer diameter surface 45 First opposing arc surface 46 Second opposing arc surface 47 Opposite arc surfaces 48 Opposite planes 50 Corner 51, 51B 1st corner 52, 52B Second corner 53, 53B 3rd corner 54, 54B 4th corner 55 Opening 90 Cutting tools 91 Shaft 100 Ball screw device 131 First extended arc surface 132 Second extended arc surface 137 Corner side first plane 138 Corner side second plane 141 First extended opposing arc surface 142 Second extended opposing arc surface 148 Corner side first opposing surface 149 Corner side second opposing surface 200 Temporary axis

Claims

1. A screw shaft, a nut inserted through the screw shaft; a plurality of balls disposed between the screw shaft and the nut; At least one or more pieces for circulating the balls; Equipped with The inner circumferential surface of the nut has a concave surface that is recessed radially outward from the inner circumferential surface and accommodates the piece therein, The direction in which the concave surface is arranged as viewed from the central axis of the nut is defined as a block insertion direction, The direction opposite to the inserting direction is the removing direction, When viewed from an axial direction parallel to the central axis of the nut, a direction intersecting the inserting direction of the link is defined as a transverse direction, The concave surface is a first arc surface and a second arc surface that are arc-shaped and move away from each other in the intersecting direction as the piece moves in the separation direction; a first extended arc surface and a second extended arc surface, each of which has an arc shape, extending in the piece removal direction from an end of the first arc surface or the second arc surface in the piece removal direction and moving away from each other in the intersecting direction as the first arc surface or the second arc surface moves in the piece removal direction; and The outer diameter surface of the piece is a first opposing arcuate surface that is arcuate and faces the first arcuate surface; a second opposing arcuate surface that is arcuate and faces the second arcuate surface; a first extended opposing arcuate surface that is arcuate and faces the first extended arcuate surface; a second extended opposing arcuate surface having an arc shape opposing the second extended arcuate surface; and a first extended arcuate surface is disposed outside a first imaginary circle having a center on the center of the first arcuate surface and the same diameter as the first arcuate surface; The second extended arcuate surface is centered on the center of the second arcuate surface and is disposed outside a second imaginary circle having the same diameter as the second arcuate surface. Ball screw device.

2. The first arcuate surface, the second arcuate surface, the first extended arcuate surface, and the second extended arcuate surface have the same curvature. The ball screw device according to claim 1 .

3. the curvature of the first arcuate surface and the curvature of the second arcuate surface are the same; The curvatures of the first and second arcuate surfaces are different from the curvatures of the first and second extended arcuate surfaces. The ball screw device according to claim 1 .

4. The first arcuate surface and the second arcuate surface are connected to each other and cooperate to form a single arcuate surface. The ball screw device according to claim 1 .

5. An angle formed by an imaginary line drawn from the center of the single arcuate surface to one end of the single arcuate surface in the intersecting direction and an imaginary line drawn to the other end of the single arcuate surface in the intersecting direction is less than 180 degrees. The ball screw device according to claim 4.

6. the concave surface has a plane disposed between the first arcuate surface and the second arcuate surface, An opposing flat surface facing the flat surface is formed on the outer diameter surface of the piece. The ball screw device according to claim 1 .

7. an angle formed by a virtual line drawn from the center of the first arcuate surface to an end of the first arcuate surface in the piece removal direction and a virtual line drawn to an end of the first arcuate surface in the piece insertion direction is less than 90 degrees; An angle formed by an imaginary line drawn from the center of the second arcuate surface to an end of the second arcuate surface in the piece removal direction and an imaginary line drawn to an end of the second arcuate surface in the piece insertion direction is less than 90 degrees. The ball screw device according to claim 6.

8. The inner circumferential surface of the nut has a corner where the concave surface and the inner circumferential surface intersect, and has a first corner and a second corner arranged apart from each other in an intersecting direction, the first extended arc surface extends from the first corner portion in the piece insertion direction, The second extended arc surface extends from the second corner portion in the inserting direction. The ball screw device according to claim 1 .

9. The inner circumferential surface of the nut has a corner where the concave surface and the inner circumferential surface intersect, and has a first corner and a second corner arranged apart from each other in an intersecting direction, The concave surface is a first flat surface on the corner side extending from the first corner in the inserting direction and connecting to the first extended arc surface; a second flat surface on the corner portion side extending from the second corner portion in the inserting direction and connecting to the second extended arc surface; and The outer diameter surface of the piece is a flat corner-side first opposing surface opposed to the corner-side first flat surface; a flat corner-side second opposing surface opposed to the corner-side second flat surface; have The ball screw device according to claim 1 .

10. The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening is formed in a rectangular shape when viewed from the central axis of the nut. The ball screw device according to any one of claims 1 to 9.

11. The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening has a length in the cross direction that is greater than a length in the axial direction. The ball screw device according to any one of claims 1 to 9.

12. The concave surface has an opening that opens toward the inner peripheral side of the nut, The opening is formed in a circular shape when viewed from the central axis of the nut. The ball screw device according to any one of claims 1 to 9.

13. The concave surface is a corner portion where the concave surface and the inner circumferential surface intersect, the corner portion having a third corner portion and a fourth corner portion that are spaced apart from each other in the axial direction; The third corner portion and the fourth corner portion extend in the circumferential direction and intersect with the spiral direction. The ball screw device according to any one of claims 1 to 9.

14. the concave surface is a corner where the concave surface and the inner circumferential surface intersect, and has a third corner and a fourth corner that are spaced apart from each other in the axial direction, The third corner portion and the fourth corner portion extend in a spiral direction. The ball screw device according to any one of claims 1 to 9.

15. A method for manufacturing a ball screw device according to claim 1, a nut preparing step of preparing the nut; a link assembling step of assembling the link to the nut; Including, The nut preparation step includes a concave surface forming step of forming the concave surface on the inner circumferential surface of the nut, The concave surface forming step includes: a step of placing a cutting tool on an inner peripheral side of the nut; a first cutting step of moving the cutting tool in the inserting direction to form one of the second extended arc surfaces of the first extended arc surface; a second cutting step of moving the cutting tool in the intersecting direction and further in the block insertion direction to form the first arcuate surface and the second arcuate surface; a third cutting step of moving the cutting tool in the link removal direction and further in the intersecting direction to form the other of the second extended arc surfaces of the first extended arc surface; Contains A method for manufacturing a ball screw device.

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