Ball spring device

Abstract

To provide a ball screw device capable of restraining rotation of a top while simplifying a shape of the top.SOLUTION: A ball screw top device according to the present disclosure comprises a screw shaft, a nut, plural balls, and at least one or more tops. An inner peripheral face of the nut has a concave face indented to an outer side in a radial direction from the inner periphery and housing the top inside. A direction, in which the concave face is arranged when seen from a center axis of the nut is a top insertion direction. A direction crossing with the top insertion direction when seen from an axial direction parallel to the center shaft of the nut is a crossing direction. The concave face has: a first arc face and a second arc face arranged away from each other in the crossing direction and approaching to each other as they move in the top insertion direction; and a plane arranged between the first and second arch faces. An outside diameter face of the top has: a first opposite arc face opposed to the first arch face; a second opposite arc face opposed to the second arc face; and an opposite face opposed to the plane.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a ball screw device. [Background technology]

[0002] The ball screw device includes a nut, a screw shaft passing through the nut, a plurality of balls arranged between the nut and the screw shaft, and a circulating element. The inner peripheral surface of the nut is formed with an inner raceway surface. The outer peripheral surface of the screw shaft is formed with an outer raceway surface facing 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 element 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 element is a ball return mechanism 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 ball is housed inside the concave surface. The ball in the following patent document is provided with a pair of protrusions protruding in the spiral direction. The pair of protrusions are inserted into a thread groove on the inner peripheral surface of the nut to position the ball. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Chinese Utility Model No. 209638346 Summary of the Invention [Problem to be solved by the invention]

[0004] One method for forming a concave surface is to cut the inner peripheral surface of the nut by applying a rotating cutting tool to the inner peripheral surface of the nut. This method results in an arc-shaped surface when viewed from a direction parallel to the rotation center of the cutting tool. Furthermore, the outer diameter surface of the top also has 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, assembling the top in a predetermined orientation is time-consuming. On the other hand, providing a pair of protrusions as in the top described in the above patent document complicates the shape of the top, reducing the productivity of the top. Therefore, it is desirable to be able to suppress top rotation while simplifying the shape of the top.

[0005] The present disclosure has been made in view of the above, and aims to provide a ball screw device that can suppress rotation of the top while simplifying the shape of the 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 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 spaced apart from each other in the intersecting direction and approach each other as the bearings move in the bearing insertion direction, and a flat surface located between the first and second arcuate surfaces. The outer circumferential surface of the bearing has a first opposing arcuate surface that faces the first arcuate surface, a second opposing arcuate surface that faces the second arcuate surface, and a flat opposing flat surface that faces the flat surface.

[0007] According to the present disclosure, a flat surface is formed between the first arcuate surface and the second arcuate surface. In other words, the surface formed by combining the first arcuate surface, the flat surface, and the second arcuate surface is not arc-shaped (arc surface). Therefore, the top is less likely to rotate along the surface formed by combining the first arcuate surface, the flat surface, and the second arcuate surface. As a result, the top can be assembled in a predetermined position, making the top assembly easier. Furthermore, when assembling the top, the opposing flat surface of the top is abutted against the flat surface of the concave surface. This positions the top so that the opposing flat surface is parallel to the intersecting direction. Furthermore, the top does not have any positioning protrusions or the like, resulting in a simple shape. This makes the top easier to manufacture. Furthermore, the top of the present disclosure does not require a through-hole in the outer peripheral surface of the nut. This eliminates the need for a through-hole in the outer peripheral surface of the nut. This allows the nut itself to function as a piston by sliding its outer peripheral surface, or to directly press-fit bearings, motor rotors, reduction gears, belt pulleys, etc., onto the outer peripheral surface of the nut. Furthermore, since there are no through holes on the outer peripheral surface of the nut, the nut has high dust resistance. Alternatively, the nut of the present disclosure is smaller and lighter than a nut having through holes on the outer peripheral surface and further having a component for closing the through holes.

[0008] In a preferred embodiment of the ball screw device, the inner peripheral surface of the nut has a first corner and a second corner that are spaced apart from each other in an intersecting direction, where the concave surface and the inner peripheral surface intersect. The first arcuate surface extends from the first corner in the inserting direction. The second arcuate surface extends from the second corner in the inserting direction.

[0009] If a flat surface were provided between the first corner portion and the first arc surface, the depth of the concave surface would increase. Furthermore, if a predetermined thickness was to be ensured from the concave surface of the nut to its outer peripheral surface, the nut would become larger. On the other hand, with the above configuration, no flat surface is provided between the first corner portion and the first arc surface. Therefore, the depth of the concave surface becomes relatively small, allowing the nut to be made smaller.

[0010] 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 arcuate 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 arcuate surface. The outer diameter surface of the block has a planar corner-side first opposing surface that faces the corner-side first flat surface, and a planar corner-side second opposing surface that faces the corner-side second flat surface.

[0011] According to the above configuration, the corner-side first flat surface of the concave surface abuts against the corner-side first opposing surface of the top. When assembling the top, if a rotational load is applied such that the first opposing arcuate surface of the top moves from the first arcuate surface of the concave surface toward the second arcuate surface of the top, the corner-side first flat surface supports the top so that it does not rotate. Thus, rotation of the top is suppressed. Furthermore, the corner-side second flat surface of the concave surface abuts against the corner-side second opposing surface of the top. When assembling the top, if a rotational load is applied such that the second opposing arcuate surface of the top moves from the second arcuate surface of the concave surface toward the first arcuate surface of the top, the corner-side second flat surface supports the top so that it does not rotate. Thus, rotation of the top is suppressed in this case as well. From the above, rotation of the top can be more reliably prevented.

[0012] In a preferred embodiment of the ball screw device, the angle formed by an imaginary line drawn from the center of the first arcuate surface to the first corner and an imaginary line drawn from the center of the first arcuate surface to a connection portion of the first arcuate surface and the plane is less than 90 degrees. The angle formed by an imaginary line drawn from the center of the second arcuate surface to the second corner and an imaginary line drawn from the center of the second arcuate surface to a connection portion of the second arcuate surface and the plane is less than 90 degrees.

[0013] 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.

[0014] In a preferred embodiment of the ball screw device, the length of the plane in the intersecting direction is equal to or greater than half the length of the first arcuate surface in the intersecting direction.

[0015] According to this configuration, the proportion of flat surfaces in the concave surface is large, making it more difficult for the top to rotate inside the concave surface.

[0016] The nut of the ball screw device has an inner peripheral surface formed with a thread groove extending in a spiral direction. The thread groove surface has an inner peripheral raceway surface connected to the S-shaped groove surface of the top, and and an outer circuit thread groove surface that is not connected to the S-groove surface.

[0017] In a preferred embodiment of the ball screw device, the inner peripheral surface of the nut is formed with a thread groove surface extending in a spiral direction, and the thread groove surface has only an inner peripheral raceway surface connected to the S-shaped groove surface of the top.

[0018] According to the above-described configuration, since the circuit outer screw groove surface is not formed, it is possible to avoid placing balls on the circuit outer screw groove surface when assembling the ball screw device.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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. [Effects of the Invention]

[0026] According to the ball screw device of the present disclosure, the top is less likely to rotate inside the concave surface. In addition, the shape of the top is simplified, which improves the productivity of the top. [Brief explanation of the drawings]

[0027] [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 perspective view of the top of the first embodiment. [Figure 7] 7 is a cross-sectional view taken along the line VII-VII in FIG. [Figure 8] FIG. 8 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 9] FIG. 9 is a view of the nut during the concave surface forming step of the first embodiment, as viewed from a first direction. [Figure 10] FIG. 10 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, a cross-sectional view of the ball screw device of Modification 1 taken in the same manner as in FIG. [Figure 11] FIG. 11 is an enlarged view of the inner peripheral side of the nut of the ball screw device of the second modified example. [Figure 12] FIG. 12 is a cross-sectional view of the nut of the ball screw device of the third modification taken along the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0028] 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.

[0029] (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.

[0030] 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.

[0031] As shown in FIG. 1, the screw shaft 1 has a screw shaft body 10, a first cylindrical portion 11 arranged on one side of the screw shaft body 10 in the axial direction, and a second cylindrical portion 12 arranged on the other side of the screw shaft body 10 in the axial direction.

[0032] Hereinafter, within the axial direction, the direction in which the first cylindrical portion 11 is disposed as viewed from the screw shaft body 10 will be referred to as the first direction X1. The direction in which the second cylindrical portion 12 is disposed as viewed from the screw shaft body 10 will be referred to as the second direction X2. Furthermore, the rotational direction will be based on the view from the first direction X1. As viewed from the first direction X1, the left-handed direction (counterclockwise direction) will be referred to as the first rotational direction L1 (see FIG. 3), and the right-handed direction (clockwise direction) will be referred to as the second rotational direction L2 (see FIG. 3).

[0033] 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).

[0034] When the screw shaft 1 performs rotational motion, the first cylindrical portion 11 and the second cylindrical portion 12 are portions into which a bearing device that rotatably supports the screw shaft 1 is fitted. Alternatively, when the screw shaft 1 performs linear motion, the first cylindrical portion 11 and the second cylindrical portion 12 are portions into which a piston or the like is connected. Note that the screw shaft 1 of the present disclosure may be composed only of the screw shaft main body 10 and may not have the first cylindrical portion 11 and the second cylindrical portion 12.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 2, the piece 4 has an inner diameter surface 40 facing radially inward. 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).

[0040] 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.

[0041] As shown in Fig. 3, the S-shaped groove surface 41 is positioned gradually outward in the radial direction from one end 41a and the other end 41b toward the center 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 center 41c. The recess amount of the center 41c of the S-shaped groove surface 41 is such that the ball 3 (see ball 3A among the multiple balls 3 in Fig. 3) rolling on the center 41c can clear the thread 15 of the screw shaft 1.

[0042] 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.

[0043] Furthermore, when the ball 3 rolls near the central portion 41c of the S-shaped groove surface 41, the load from the screw shaft 1 cannot be transmitted 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 Z below.

[0044] 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 from all directions in the circumferential direction.

[0045] Next, the configuration of the nut 2 near the concave surface 30 and the block 4 will be described in detail.

[0046] 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.

[0047] 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.

[0048] 5, a direction that intersects (is perpendicular to) the piece insertion direction Z when viewed from the axial direction is referred to as the intersecting direction. The direction in the intersecting 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. The direction in the intersecting 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The concave surface 30 has a first arcuate surface 31, a second arcuate surface 32, a flat surface 33, a first side surface 34, and a second side surface 35. The first side surface 34 is a flat surface that extends from the third corner 53 in the piece insertion direction Z and faces the second direction X2. The second side surface 35 is a flat surface that extends from the fourth corner 54 in the piece insertion direction Z and faces the first direction X1.

[0053] 5, the first arcuate surface 31 extends from the first corner 51 in the piece insertion direction Z. As the first arcuate surface 31 moves in the piece insertion direction Z, it is gradually positioned in the second intersecting direction Y2. Therefore, the first arcuate surface 31 is formed in an arc shape when viewed from the axial direction. In addition, 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 Z.

[0054] The second arcuate surface 32 is a surface that extends from the second corner 52 in the piece insertion direction Z. The second arcuate surface 32 is gradually positioned in the first intersecting direction Y1 as it moves in the piece insertion direction Z. 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. In addition, 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 Z.

[0055] Additionally, the angle θ1 formed by the imaginary line K3 drawn from the center O31 of the first arcuate surface 31 to the first corner 51 and the imaginary line K4 drawn from the center O31 of the first arcuate surface 31 to the end 31 a of the first arcuate surface 31 is less than 90 degrees. The angle θ2 formed by the imaginary line K5 drawn from the center O32 of the second arcuate surface 32 to the second corner 52 and the imaginary line K6 drawn from the center O32 of the second arcuate surface 32 to the end 32 a of the second arcuate surface 32 is less than 90 degrees.

[0056] The plane 33 extends in the intersecting direction and the axial direction. The plane 33 is disposed between the first arcuate surface 31 and the second arcuate surface 32. An end 33a of the plane 33 in the first intersecting direction Y1 is connected to an end 31a of the first arcuate surface 31. An end 33b of the plane 33 in the second intersecting direction Y2 is connected to an end 32a of the second arcuate surface 32. The first arcuate surface 31, the plane 33, and the second arcuate surface 32 cooperate with one another to form a substantially C-shaped bottom surface (hereinafter referred to as a C-shaped bottom surface 36) when viewed from the axial direction.

[0057] As shown in Fig. 4, the length of the plane 33 in the intersecting direction is W3. The length of the first arcuate surface 31 in the intersecting direction is W4. The length of the second arcuate surface 32 in the intersecting direction is the same as the length W4 of the first arcuate surface 31 in the intersecting direction. The length W3 of the plane 33 in the intersecting direction is slightly longer than half the length W2 of the first arcuate surface 31 in the intersecting direction (W3 ≥ W4 / 2).

[0058] Fig. 6 is a perspective view of the block of embodiment 1. Fig. 7 is a cross-sectional view taken along the line VII-VII in Fig. 2. The block 4 has opposing surfaces (first opposing surface 42, second opposing surface 43 (see Fig. 2)) facing in the axial direction, and an outer diameter surface 44 facing radially outward.

[0059] 2, the first opposing surface 42 faces the first direction X1, is formed in a planar shape, and faces the first side surface 34. The second opposing surface 43 faces the second direction X2, is formed in a planar shape, and faces the second side surface 35.

[0060] 7, the outer diameter surface 44 faces the C-shaped bottom surface 36 and abuts against the C-shaped bottom surface 36. In detail, the outer diameter surface 44 has a first opposing arcuate surface 45 facing the first arcuate surface 31, a second opposing arcuate surface 46 facing the second arcuate surface 32, and an opposing flat surface 47 facing the flat surface 33.

[0061] 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. Furthermore, 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 opposing flat surface 47 extends in the axial direction and the intersecting direction and is parallel to the flat surface 33. Furthermore, the opposing flat surface 47 has the same size as the flat surface 33. As described above, the entire surface of the C-shaped bottom surface 36 abuts against the outer diameter surface 44.

[0062] 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 of the top 4 in the transverse direction. Therefore, the top can be assembled to the concave surface 30 even when rotated 180 degrees.

[0063] Next, a description will be given of a method for manufacturing the nut 2. The method for manufacturing the nut 2 includes a thread groove forming step, a concave surface forming step, and a heat treatment step.

[0064] FIG. 8 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. 8, the thread groove forming step 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.

[0065] 9 is a view of the nut during the concave surface forming process of the first embodiment, viewed from a first direction. The concave surface forming process is a process of forming a concave surface 30 on the inner peripheral surface 20 of the nut 2. To form the concave surface 30, as shown in FIG. 9, a cutting tool 90 is placed on the inner peripheral side of the nut 2. A plurality of cutting blades are arranged in the circumferential direction on the outer peripheral surface of the cutting tool 90. The cutting tool 90 rotates around a shaft portion 91. The shaft portion 91 of the cutting tool 90 is placed so as to be parallel to the central axis O2 of the nut 2.

[0066] Next, the shaft 91 is rotated to move the cutting tool 90 radially outward (see arrow Z1 in FIG. 9). Then, the cutting teeth of the cutting tool 90 cut the inner circumferential surface 20. Note that imaginary lines Q90 and Q91 in FIG. 9 show the cutting tool 90 and the shaft 91 that have moved radially outward. As a result, an arcuate surface that is approximately the same as the outer diameter of the cutting tool 90, i.e., the first arcuate surface 31, is formed.

[0067] Next, the cutting tool 90 is moved in the second intersecting direction Y2 (see arrow Z2 in FIG. 9). Note that imaginary lines R90 and R91 in FIG. 9 show the cutting tool 90 and the shank 91 moved in the second intersecting direction Y2. As a result, a plane 33 extending in the intersecting direction and the axial direction is formed. Also, a circular arc surface having approximately the same diameter as the outer diameter of the cutting tool 90, i.e., a second circular arc surface 32, is formed.

[0068] As a result, the area indicated by the imaginary line K10 is cut, forming the concave surface 30. Next, the cutting tool 90 is returned to the inner peripheral side of the nut 2 (see arrow Z3 in FIG. 9), and this process ends. Furthermore, according to this process, as shown in FIG. 8, 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 peripheral raceway surface 22 connected to the concave surface 30 is formed.

[0069] As described above, the movement of the cutting tool 90 in the concave surface forming process is limited to either radial movement (see arrows Z1 and Z3 in FIG. 9) or movement in the transverse direction (see arrow Z2 in FIG. 9). In other words, it does not include movement in a diagonal direction that combines the radial direction and the transverse direction. This facilitates the manufacture of the nut 2. Furthermore, the angle θ1 of the first arcuate surface 31 and the angle θ2 of the second arcuate surface 32 are less than 90 degrees (see FIG. 5). Therefore, as shown in FIG. 9, the shank 91 of the cutting tool 90 does not come into contact with the inner peripheral surface 20 of the nut 2 (see imaginary lines Q91 and R91 in FIG. 9).

[0070] In addition, the above-mentioned concave surface forming process has been described as an example in which the nut 2 is fixed and the cutting tool 90 is moved, but in the present disclosure, the concave surface 30 may also be formed by fixing the cutting tool 90 and moving the nut 2.

[0071] The heat treatment process 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.

[0072] Next, the effects of this embodiment will be described.

[0073] The method for assembling the top 4 to the nut is to move the top 4 arranged on the inner periphery of the nut 2 in the top insertion direction Z and arrange the top 4 inside the concave surface 30. Here, the top 4 is arranged so that the opposing flat surface 47 abuts against the flat surface 33 of the concave surface 30. This positions the top 4 so that the opposing flat surface 47 is parallel to the intersecting direction when viewed from the axial direction. In other words, it is possible to prevent the top 4 from being assembled in an inclined (rotated) state.

[0074] 7, the force moving the piece 4 in the inserting direction Z may be applied to the end of the inner diameter surface 40 in the first intersecting direction Y1 (see arrow F1 in FIG. 7) rather than to the center of the inner diameter surface 40 in the intersecting direction. This causes the first opposing arcuate surface 45 of the piece 4 to be pressed against the first arcuate surface 31.

[0075] If the concave surface 30 did not have the flat surface 33 (if the concave surface 30 were composed only of the first arcuate surface 31 and the second arcuate surface 32), 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, there is a possibility that the top 4 would rotate clockwise when viewed from the first direction X1.

[0076] On the other hand, the C-shaped bottom surface 36 of this embodiment has a flat surface 33 disposed between the first arcuate surface 31 and the second arcuate surface 32, and is not a single arcuate surface. In other words, the C-shaped bottom surface 36 has a shape that makes it difficult for the top 4 to rotate. Therefore, when viewed from the first direction X1, it is difficult for the top 4 to rotate clockwise along the C-shaped bottom surface 36.

[0077] 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 and rotate counterclockwise as viewed from the first direction X1. However, according to this embodiment, the C-shaped bottom surface 36 has a flat surface 33, which makes it difficult for the top 4 to rotate. Therefore, it is unlikely that the top 4 will rotate counterclockwise along the C-shaped bottom surface 36 as viewed from the first direction X1.

[0078] As a result, the top 4 is assembled in a predetermined orientation inside the recessed surface 30. This eliminates the need to correct the orientation of the top 4, making assembly of the top 4 easy.

[0079] 4, the length W3 of the flat surface 33 in the intersecting direction is equal to or greater than half the length W2 of the first arcuate surface 31 in the intersecting direction (W3≧W4 / 2). Therefore, the flat surface 33 occupies a large proportion of the C-shaped bottom surface 36. This further reduces the possibility that the top 4 will rotate along the C-shaped bottom surface 36.

[0080] Furthermore, the block 4 of this embodiment is not provided with any protrusions that protrude from the outer diameter surface 44, etc. Therefore, the block 4 has a simple shape and is easy to manufacture.

[0081] 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 in a thread groove other than the inner peripheral raceway surface 22.

[0082] 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.

[0083] 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.

[0084] 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 circumferential surface 20 of the nut 2 has a concave surface 30 recessed radially outward from the inner circumferential surface 20 and 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 defined as the block insertion direction Z. The direction intersecting the block insertion direction Z as viewed from an axial direction parallel to the central axis O2 of the nut 2 is defined as the intersecting direction. The concave surface 30 has a first arcuate surface 31 and a second arcuate surface 32 that are spaced apart from each other in the intersecting direction and approach each other as they move in the block insertion direction Z, and a flat surface 33 that is located between the first arcuate surface 31 and the second arcuate surface 32. The outer diameter surface 44 of the top 4 has a first opposing arc surface 45 that is arc-shaped and faces the first arc surface 31, a second opposing arc surface 46 that is arc-shaped and faces the second arc surface 32, and a flat opposing plane 47 that faces the plane 33.

[0085] According to this embodiment, the shape of the top 4 can be simplified while suppressing rotation of the top 4. Furthermore, according to this 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 is provided to block the through hole.

[0086] Next, a description will be given of a modified example of the ball screw device 100 of the first embodiment. The following description will focus on the differences from the first embodiment.

[0087] (Variation 1) 10 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, 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. 10, the concave surface 30A of the nut 2A of Modification 1 differs from that of Embodiment 1 in that it has a corner-side first flat surface 37 and a corner-side second flat surface 38. Furthermore, the outer diameter surface 44 of the link 4A of Modification 1 differs from that of Embodiment 1 in that it has a corner-side first opposing surface 48 and a corner-side second opposing surface 49. The differences will be explained below.

[0088] The corner-side first flat surface 37 extends from the first corner 51 in the frame insertion direction Z. The corner-side second flat surface 38 extends from the second corner 52 in the frame insertion direction Z. The corner-side first flat surface 37 and the corner-side second flat surface 38 are flat surfaces that extend in the axial direction and the frame insertion direction Z, respectively. The corner-side first flat surface 37 and the corner-side second flat surface 38 face each other in the intersecting direction. An end 37a of the corner-side first flat surface 37 in the frame insertion direction Z is connected to an end 31b of the first arcuate surface 31 on the opposite side of the frame insertion direction Z. An end 38a of the corner-side second flat surface 38 in the frame insertion direction Z is connected to an end 32b of the second arcuate surface 32 on the opposite side of the frame insertion direction Z.

[0089] With respect to the block 4A, the first corner-side opposing surface 48 and the second corner-side opposing surface 49 are planes extending in the axial direction and the block insertion direction Z, respectively. The first corner-side opposing surface 48 faces the first corner-side plane 37 and abuts against it. The second corner-side opposing surface 49 faces the second corner-side plane 38 and abuts against it. An end 48a of the first corner-side opposing surface 48 in the block insertion direction Z is connected to an end 45b of the first opposing arcuate surface 45 in the opposite direction to the block insertion direction Z. An end 49a of the second corner-side opposing surface 49 in the block insertion direction Z is connected to an end 46b of the second opposing arcuate surface 46 in the opposite direction to the block insertion direction Z.

[0090] According to Modification 1, similar to Embodiment 1, a flat surface 33 is provided between the first arcuate surface 31 and the second arcuate surface 32, making it difficult for the top 4A to rotate. However, according to the structure of Embodiment 1, if the force applied when assembling the top 4A (see arrow F4 in FIG. 10) is large, the first opposing arcuate surface 45 of the top 4A may move in the second intersecting direction Y2 and ride up onto the flat surface 33 (see arrow F5 in FIG. 10). In other words, there is a possibility that the top 4A may rotate clockwise when viewed from the first direction X1.

[0091] On the other hand, according to the first modification, when the top 4A tries to rotate clockwise as viewed from the first direction X1, the corner-side first opposing surface 48 presses against the corner-side first flat surface 37 (see arrow F6 in FIG. 10). In other words, the movement (rotation) of the top 4A is restricted by the corner-side first flat surface 37. Therefore, the top 4A is unlikely to rotate clockwise as viewed from the first direction X1.

[0092] On the other hand, when the top 4A tries to rotate counterclockwise as viewed from the first direction X1, the corner-side second opposing surface 49 presses against the corner-side second flat surface 38. In other words, the movement (rotation) of the top 4A is restricted by the corner-side second flat surface 38. Therefore, the top 4A is unlikely to rotate counterclockwise as viewed from the first direction X1.

[0093] As described above, according to Modification 1, the top 4A is less likely to rotate inside the concave surface 30A than in Embodiment 1. Furthermore, even the top 4A of Modification 1 does not have any protrusions that protrude from the outer diameter surface 44, etc. Therefore, the top 4A is easy to manufacture.

[0094] According to the first modification, the concave surface 30A has a first corner-side flat surface 37 and a second corner-side flat surface 38. That is, the depth of the concave surface 30A in the insert direction Z is greater than that of the concave surface 30 of the first embodiment. Furthermore, if a predetermined thickness is to be ensured for the thickness W10 from the flat surface 33 of the concave surface 30A to the outer peripheral surface 21, the outer diameter of the nut 2A will be greater than the outer diameter of the nut 2 of the first embodiment (see the imaginary line K20 in FIG. 10). Therefore, the first embodiment has the advantage that the nut 2 can be made smaller than the first modification.

[0095] (Variation 2) FIG. 11 is an enlarged view of the inner peripheral side of the nut of the ball screw device of Modification 2. As shown in FIG. 11, 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, the shape of top 4 can be simplified while suppressing rotation of top 4.

[0096] (Variation 3) FIG. 12 is a cross-sectional view of a nut of a ball screw device of Modification 3 cut in the axial direction. As shown in the figure, the nut 2C of Modification 3 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 this nut 2C, as with Embodiment 1, the shape of the link 4 can be simplified while suppressing rotation of the link 4. Furthermore, in the thread groove surface forming step (see FIG. 8) of Embodiment 1, the thread groove surface (inner peripheral raceway surface) is formed on the inner peripheral surface 20 of the nut 2 by cutting, but the nut 2C of Modification 3 is not limited to cutting. That is, the thread groove surface 70 of the nut 2C of Modification 3 may be formed by rolling.

[0097] 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. Furthermore, in the first embodiment, the length W3 of the plane 33 in the crossing direction is equal to or greater than half the length W2 of the first arcuate surface 31 in the crossing direction (W3≧W4 / 2), but in the present disclosure, the length W3 of the plane 33 in the crossing direction is less than half the length W2 of the first arcuate surface 31 in the crossing direction (W3 <W4 / 2)であってもよい。

[0098] 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. Furthermore, 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). Furthermore, although the opposing flat surface 47 in the first embodiment has the same size as the flat surface 33, it may be formed slightly smaller. In other words, in the present disclosure, the sizes of the opposing flat surface 47 and the flat surface 33 are not particularly important.

[0099] Furthermore, although the first arcuate surface 31 and the second arcuate surface 32 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 and the second opposing arcuate surface 46 are not limited to arcs with a constant curvature.

[0100] 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.

[0101] 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).

[0102] 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, 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 spaced apart from each other in the crossing direction and approach each other as the frame moves in the frame insertion direction; a plane disposed between the first arcuate surface and the second arcuate surface; 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 faces the second arcuate surface; a flat opposing plane facing the plane; have Ball screw device. (2) 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 arcuate surface extends from the first corner portion in the piece insertion direction, The second arcuate surface extends from the second corner portion in the inserting direction. The ball screw device according to (1). (3) 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 arcuate surface; a corner-side second flat surface extending from the second corner in the inserting direction and connecting to the second arcuate 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 (1). (4) an angle formed by an imaginary line drawn from the center of the first arcuate surface to the first corner portion and an imaginary line drawn from the center of the first arcuate surface to a connection portion of the first arcuate surface and the plane is less than 90 degrees; The angle formed by an imaginary line drawn from the center of the second arcuate surface to the second corner and an imaginary line drawn from the center of the second arcuate surface to the connecting portion of the second arcuate surface and the flat surface is less than 90 degrees. The ball screw device according to (2). (5) The length of the plane in the intersecting direction is equal to or greater than half the length of the first arcuate surface in the intersecting direction. A ball screw device according to any one of (1) to (4). (6) The nut has an inner peripheral surface formed with a thread groove surface extending in a spiral direction, The thread groove surface is an inner raceway surface connected to the S-shaped groove surface of the top; A circuit outer thread groove surface that is not connected to the S-shaped groove surface; have A ball screw device according to any one of (1) to (4). (7) The nut has an inner peripheral surface formed with a thread groove surface extending in a spiral direction, The thread groove surface has only an inner raceway surface that connects to the S-shaped groove surface of the block. A ball screw device according to any one of (1) to (4). (8) 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 (7). (9) 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 (7). (10) 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 (7). (11) 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 arranged 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 (10). (12) 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 (10). [Explanation of symbols]

[0103] 1 Screw shaft 2, 2B, 2C nuts 3 Ball 4, 4A top 5 orbit 14 Outer raceway surface 20 Inner surface 21 Outer surface 22 Inner raceway surface 30, 30A, 30B concave 31 First circular arc surface 32 Second circular arc surface 33 plane 34 First aspect 35 Second aspect 36 C-shaped bottom 37 Corner side first plane 38 Corner side second plane 40 Inner diameter surface 41 S-shaped groove surface 42 First opposing surface 43 Second opposing surface 44 Outer diameter surface 45 First opposing arc surface 46 Second opposing arc surface 47 Opposite planes 48 Corner side first opposing surface 49 Corner side second opposing surface 50 Corner 51 1st corner 52 Second corner 53 Third corner 54 4th corner 70 Thread groove surface 90 Cutting tools 91 Shaft 100 Ball screw device

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, 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 spaced apart from each other in the crossing direction and approach each other as the frame moves in the frame insertion direction; a plane disposed between the first arcuate surface and the second arcuate surface; 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 flat opposing plane facing the plane; have Ball screw device.

2. 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 arcuate surface extends from the first corner portion in the piece insertion direction, The second arcuate surface extends from the second corner in the inserting direction. The ball screw device according to claim 1 .

3. 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 corner-side first flat surface extending from the first corner in the inserting direction and connecting to the first arcuate surface; a corner-side second flat surface extending from the second corner in the inserting direction and connecting to the second arcuate 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 .

4. an angle formed by an imaginary line drawn from the center of the first arcuate surface to the first corner portion and an imaginary line drawn from the center of the first arcuate surface to a connection portion of the first arcuate surface and the plane is less than 90 degrees; An angle formed by an imaginary line drawn from the center of the second arcuate surface to the second corner and an imaginary line drawn from the center of the second arcuate surface to a connecting portion of the second arcuate surface and the flat surface is less than 90 degrees. The ball screw device according to claim 2 .

5. The length of the plane in the intersecting direction is equal to or greater than half the length of the first arcuate surface in the intersecting direction. The ball screw device according to any one of claims 1 to 4.

6. The nut has an inner peripheral surface formed with a thread groove surface extending in a spiral direction, The thread groove surface is an inner raceway surface connected to the S-shaped groove surface of the top; A circuit outer thread groove surface that is not connected to the S-shaped groove surface; have The ball screw device according to any one of claims 1 to 4.

7. The nut has an inner peripheral surface formed with a thread groove surface extending in a spiral direction, The thread groove surface has only an inner raceway surface that connects to the S-shaped groove surface of the block. The ball screw device according to any one of claims 1 to 4.

8. 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 4.

9. 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 4.

10. 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 4.

11. 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 4.

12. 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 4.

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