Ball spring device

Abstract

To provide a ball screw device for miniaturizing a radial direction of a top.SOLUTION: A ball screw device according to the present disclosure comprises a screw shaft, a nut penetrating through the screw shaft, plural balls arranged between the screw shaft and the nut, and at least one or more tops for circulating the balls. An inner peripheral face of the nut has a concave face indented to outside in a radial direction from the inner peripheral face and housing the top inside, and a direction in which the concave face is arranged when seen from a center shaft of the nut is a top insertion direction. The top has an inside diameter face directed to an inner peripheral side of the nut, an outside diameter face directed to an outer peripheral side of the nut, an S-shaped groove face indented to outside in the radial direction from the inside diameter face, and a bottom wall part arranged between the S-shaped groove face and the outside diameter face. The S-shaped groove face has an indentation amount in the top insertion direction gradually getting larger as it approaches to a center part in a longitudinal direction of the S-shaped groove face from both ends in the longitudinal direction of the S-shaped groove face. A through hole penetrating in the top insertion direction and notching one part of the bottom wall part is provided at the center part of the S-shaped groove face.SELECTED DRAWING: Figure 9

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 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] However, if the radial thickness of the block is increased, the depth of the concave surface of the nut increases, resulting in a larger nut. For this reason, there is a demand for the development of a block that is smaller in diameter.

[0005] The present disclosure has been made in view of the above, and aims to provide a ball screw device that reduces the radial size 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 disposed between the screw shaft and the nut, and at least one or more bearings for circulating the balls. The inner peripheral surface of the nut has a concave surface recessed radially outward from the inner peripheral surface and accommodating the bearings. The direction in which the concave surface is disposed as viewed from the central axis of the nut is defined as the bearing insertion direction. The bearing has an inner diameter surface facing the inner peripheral side of the nut, an outer diameter surface facing the outer peripheral side of the nut, an S-shaped groove surface recessed radially outward from the inner diameter surface, and a bottom wall portion disposed between the S-shaped groove surface and the outer diameter surface. The S-shaped groove surface is gradually recessed in the bearing insertion direction from both ends of the S-shaped groove surface in the longitudinal direction toward the center of the S-shaped groove surface in the longitudinal direction. A through hole is provided in the center of the S-shaped groove surface, penetrating in the inserting direction of the piece and cutting out a part of the bottom wall.

[0007] In conventional tops, a bottom wall portion is provided along the entire length of the S-shaped groove surface. In contrast, in the top of the present disclosure, a portion of the bottom wall portion is cut out by a through hole. This reduces the radial size of the top. Furthermore, the portion of the bottom wall portion cut out by the through hole is located radially outward relative to the center of the S-shaped groove surface in the length direction. The S-shaped groove surface is positioned radially outward as it approaches the center of the length direction. Therefore, the portion of the bottom wall portion cut out by the through hole has a thin radial thickness. When resin tops are manufactured by injection molding, the thin portion reduces the fluidity of the resin. This can result in the top not being molded to the desired shape or having insufficient strength. In contrast, in the present disclosure, the thin portion that reduces the fluidity of the resin is cut out. This prevents the top from being molded to the desired shape or having insufficient strength, even if the resin top is manufactured by injection molding. Furthermore, the top of the present disclosure does not require a through hole to be formed on the outer peripheral surface of the nut. This allows the nut's outer peripheral surface to slide, allowing the nut itself to function as a piston, or to directly press-fit bearings, motor rotors, reduction gears, belt pulleys, etc., onto the nut's outer peripheral surface. Furthermore, the nut's outer peripheral surface has no through-holes, making it highly dust-proof. Alternatively, the nut of the present disclosure is smaller and lighter than a nut with a through-hole provided on its outer peripheral surface and a component for blocking the through-hole.

[0008] In the above-described ball screw device, the ball may come into contact with the concave surface through the through hole, or may not come into contact with the concave surface through the through hole.

[0009] In a preferred embodiment of the ball screw device, the intersecting direction is a direction intersecting the inserting direction when viewed from an axial direction parallel to the central axis of the nut. 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 from each other in the intersecting direction. The concave surface abuts the outer diameter surface and has a support surface that supports the inserting direction. The support surface is arc-shaped when viewed from the axial direction, with one end in the intersecting direction connected to the first corner and the other end in the intersecting direction connected to the second corner.

[0010] According to the above configuration, the support surface is a single arcuate surface. Therefore, when forming a concave surface on the nut, a rotating cutting tool is placed on the inner periphery of the nut and the arcuate support surface can be formed simply by moving the cutting tool radially outward. In other words, there is no need to move the cutting tool in the cross direction, which improves nut productivity.

[0011] In a preferred embodiment of the ball screw device, the intersecting direction is a direction intersecting the inserting direction when viewed from an axial direction parallel to the central axis of the nut. 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 spaced apart in the intersecting direction. The concave surface has a support surface that abuts the outer diameter surface and supports the inserting direction. The support surfaces have a first arcuate surface and a second arcuate surface that are spaced apart in the intersecting direction and approach each other as the inserting direction moves from the first corner or the second corner, and a flat surface that extends in the intersecting direction and has one end connected to the first arcuate surface and the other end connected to the second arcuate surface. The outer diameter surface of the inserting direction has an opposing flat surface that extends in the intersecting direction and faces the flat surface.

[0012] According to the above configuration, 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. This makes it difficult for the top to rotate within the concave surface. Furthermore, when the top is assembled, 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.

[0013] In a preferred embodiment of the ball screw device, the intersecting direction is a direction intersecting the inserting direction when viewed from an axial direction parallel to the central axis of the nut. 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 from each other in the intersecting direction. The concave surface has a support surface that abuts the outer diameter surface and supports the inserting direction. The support surface has a planar first plane extending from the first corner in the inserting direction, a planar second plane extending from the second corner in the inserting direction, and a plane extending in the intersecting direction, one end of which connects with the first plane and the other end of which connects with the second plane.

[0014] According to the above configuration, the surfaces supporting the top are the flat surface, the first flat surface, and the second flat surface, and each surface is flat. Therefore, the top does not rotate inside the concave surface, making it extremely easy to assemble the top.

[0015] In a preferred embodiment of the ball screw device, the inner peripheral surface of the nut extends in the spiral direction and has an inner peripheral raceway surface having one end connected to the first corner portion and the other end connected to the second corner portion, a first thread groove surface extending on an extension of the other end of the inner peripheral raceway surface across the concave surface and having one end connected to the first corner portion, and a second thread groove surface extending on an extension of the one end of the inner peripheral raceway surface across the concave surface and having one end connected to the second corner portion. The block has a first protrusion disposed inside the first thread groove surface and a second protrusion disposed inside the second thread groove surface.

[0016] According to the above configuration, when a load that rotates the top acts inside the concave surface, the first protrusion gets caught on the first thread groove surface, or the second protrusion gets caught on the second thread groove surface. Therefore, the rotation of the top is restricted, and the top is assembled in a predetermined position. Furthermore, the first thread groove surface and the second thread groove surface are formed on an extension of the inner circumferential raceway surface. In other words, the first thread groove surface and the second thread groove surface can be formed simultaneously in the process of forming the inner circumferential raceway surface. Therefore, even if the nut has the first thread groove surface and the second thread groove surface, an increase in manufacturing man-hours is suppressed.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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]

[0024] According to the ball screw device of the present disclosure, the top can be made smaller in the radial direction. [Brief explanation of the drawings]

[0025] [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] FIG. 7 is a plan view of the piece of the first embodiment as seen from the piece insertion direction. [Figure 8] FIG. 8 is a rear view of the piece of the first embodiment as seen from the opposite direction to the piece insertion direction. [Figure 9] FIG. 9 is a cross-sectional view taken along the line IX-IX in FIG. [Figure 10] FIG. 10 is a cross-sectional view taken along the line XX in FIG. [Figure 11] FIG. 11 is a cross-sectional view taken along the line XI-XI in FIG. [Figure 12] FIG. 12 is a cross-sectional view taken along the line XII-XII in FIG. [Figure 13] FIG. 13 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 14] FIG. 14 is a view of the nut during the concave surface forming step of the first embodiment, viewed from a first direction. [Figure 15] FIG. 15 is a cross-sectional view of the ball screw device of the first modification taken in a direction perpendicular to the axial direction. [Figure 16] FIG. 16 is a view showing the concave surface forming step of the first modification example when viewed from a first direction of the nut. [Figure 17] FIG. 17 is a view of the top assembled to the nut of the second modification, viewed from the inner peripheral side. [Figure 18] FIG. 18 is an enlarged view of the concave surface of the nut of the second modification, viewed from the inner peripheral side. [Figure 19] FIG. 19 is a perspective view of a top of the second modified example. [Figure 20] FIG. 20 is a cross-sectional view taken along line XX-XX in FIG. [Figure 21] FIG. 21 is an enlarged view showing a part of the inner peripheral surface of the nut after the thread groove forming step of the second modification. [Figure 22] FIG. 22 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, is a cross-sectional view of the ball screw device of Modification 3 taken in the same manner as in FIG. [Figure 23] FIG. 23 is a cross-sectional view of the ball screw device of the fourth modification taken along a direction perpendicular to the longitudinal direction of the S-shaped groove surface at the center thereof. [Figure 24] FIG. 24 is an enlarged view of the inner peripheral side of the nut of the ball screw device of the fifth modified example. [Figure 25] FIG. 25 is a cross-sectional view of the nut of the ball screw device of the sixth modification taken along the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Note that Fig. 3 shows only some of the balls 3 arranged on the raceway 5 and the inner raceway surface 22 to make the cross-sectional shape easier to understand. 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.

[0036] 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.

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Next, the configuration of the nut 2 near the concave surface 30 and the block 4 will be described in detail.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The second arcuate surface 32 extends from the second corner 52 in the piece insertion direction Z. As the second arcuate surface 32 moves in the piece insertion direction Z, it is gradually positioned in the first intersecting direction Y1. 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.

[0053] 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.

[0054] The flat surface 33 extends in the transverse direction and the axial direction. The flat surface 33 is disposed between the first arcuate surface 31 and the second arcuate surface 32. An end 33a of the flat surface 33 in the first transverse direction Y1 is connected to the end 31a of the first arcuate surface 31. An end 33b of the flat surface 33 in the second transverse direction Y2 is connected to the end 32a of the second arcuate surface 32. The first arcuate surface 31, the second arcuate surface 32, and the flat surface 33 support the nut 2 from the radially outer side. Hereinafter, the surface formed by combining the first arcuate surface 31, the second arcuate surface 32, and the flat surface 33 will be referred to as a support surface 36.

[0055] Fig. 6 is a perspective view of the block of embodiment 1. Fig. 7 is a plan view of the block of embodiment 1 as viewed from the block insertion direction. Fig. 8 is a rear view of the block of embodiment 1 as viewed from the opposite direction to the block insertion direction. Fig. 9 is a cross-sectional view taken along the line IX-IX in Fig. 2. As shown in Figs. 6 to 8, the block 4 has opposing surfaces (first opposing surface 42, second opposing surface 43) facing in the axial direction and an outer diameter surface 44 facing radially outward (toward the outer periphery of the nut 2).

[0056] 7 and 8, 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, the first opposing surface 42 faces the first side surface 34 as shown in FIG. 2. The second opposing surface 43 faces the second side surface 35.

[0057] 9, the outer diameter surface 44 faces the support surface 36 and abuts against the support 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.

[0058] 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 transverse 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 support surface 36 abuts against the outer diameter surface 44.

[0059] 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.

[0060] FIG. 10 is a cross-sectional view taken along the arrow XX in FIG. 7. FIG. 11 is a cross-sectional view taken along the arrow XI-XI in FIG. 7. FIG. 12 is a cross-sectional view taken along the arrow XII-XII in FIG. 2. As shown in FIG. 10, the groove width E of the S-shaped groove surface 41 gradually decreases as one moves from the inner diameter surface 40 toward the outer diameter surface 44. The groove width E is the length perpendicular to both the radial direction and the length direction of the S-shaped groove surface 41. Therefore, the cross-sectional shape of the S-shaped groove surface 41 is approximately V-shaped. The maximum groove width E1 of the S-shaped groove surface 41 is at the radially outer side. The block 4 has a bottom wall portion 60 disposed between the S-shaped groove surface 41 and the outer diameter surface 44.

[0061] As shown in Fig. 7, a through-hole 61 is formed in the central portion 41c in the longitudinal direction of the S-shaped groove surface 41, penetrating in the block insertion direction Z. The through-hole 61 has a shape that approximates an ellipse that is long in the longitudinal direction of the S-shaped groove surface 41. For this reason, as shown in Fig. 11, a part of the bottom wall portion 60 and a part of the outer diameter surface 44 (opposing flat surface 47) are cut out. As shown in Fig. 12, the width E2 of the through-hole 61 is smaller than the maximum groove width E1 of the S-shaped groove surface 41.

[0062] As shown in FIG. 7 , the through hole 61 has an elliptical shape that is elongated in the longitudinal direction of the S-shaped groove surface 41. Therefore, the through hole 61 extends in the longitudinal direction of the S-shaped groove surface 41. Furthermore, as shown in FIG. 8 , a tip 61a of the through hole 61 in the first intersecting direction Y1 slightly extends beyond the ridge line H1 that marks the boundary between the first opposing arcuate surface 45 and the opposing flat surface 47. A tip 61b of the through hole 62 in the second intersecting direction Y2 slightly extends beyond the ridge line H2 that marks the boundary between the second opposing arcuate surface 46 and the opposing flat surface 47. Therefore, as shown in FIG. 11 , the through hole 61 has a notched bottom wall portion 60 between the S-shaped groove surface 41 and the opposing flat surface 47. Therefore, the bottom wall portion 60 of this embodiment is composed of a first bottom wall portion 63 that is between the S-shaped groove surface 41 and the first opposing arcuate surface 45 and a second bottom wall portion 64 that is between the S-shaped groove surface 41 and the second opposing arcuate surface 46.

[0063] 12, the through hole 61 is closed by the flat surface 33 (support surface 36) of the concave surface 30. In this embodiment, when the ball 3 moves near the central portion 41c of the S-shaped groove surface 41, the ball 3 comes into contact with the flat surface 33 via the through hole 61. In other words, the ball 3 rolls on the flat surface 33, and the flat surface 33 serves as a rolling surface.

[0064] 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.

[0065] FIG. 13 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. 13, 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 method of forming the thread groove 80 involves 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.

[0066] Fig. 14 is a view of the nut during the concave surface forming process of embodiment 1, 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. 14, 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.

[0067] Next, the shaft 91 is rotated to move the cutting tool 90 radially outward (see arrow Z1 in FIG. 14). Then, the cutting teeth of the cutting tool 90 cut the inner circumferential surface 20. Note that imaginary lines Q90 and Q91 in FIG. 14 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.

[0068] Next, the cutting tool 90 is moved in the second intersecting direction Y2 (see arrow Z2 in FIG. 14). Note that imaginary lines R90 and R91 in FIG. 14 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. In addition, 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.

[0069] 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. 14), and this process ends. Furthermore, according to this process, as shown in FIG. 13, both ends of the thread groove 80 (see the area surrounded by the imaginary line K10 in FIG. 14) are cut. As a result, the inner peripheral raceway surface 22 connected to the concave surface 30 is formed.

[0070] 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. 14) or movement in the transverse direction (see arrow Z2 in FIG. 14). In other words, movement in a diagonal direction that combines the radial direction and the transverse direction is not included. 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. 14, 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. 14).

[0071] 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.

[0072] 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.

[0073] Next, the effects of this embodiment will be described.

[0074] 9, when the ball 3 passes near the central portion 41c of the S-shaped groove surface 41, the ball 3 comes into contact with the flat surface 33 of the concave surface 30 through the through hole 61. In this manner, the through hole 61 is formed in the top 4, and a portion of the bottom wall portion 60 is cut out.

[0075] 9 is a line showing the position of the opposing plane 47 when it is assumed that the bottom wall portion 60 is provided in the central portion 41c of the S-shaped groove surface 41. Also, the imaginary line K21 in Fig. 9 is a line showing the position of the outer peripheral surface 21 of the nut 2 when it is assumed that the bottom wall portion 60 is provided in the central portion 41c of the S-shaped groove surface 41.

[0076] As shown in FIG. 9, if the bottom wall portion 60 is provided along the entire length of the S-shaped groove surface 41, the opposing flat surface 47 of the link 4 overlaps the imaginary line K47 and is positioned radially outward relative to the opposing flat surface 47 of the first embodiment. This increases the depth of the concave surface 30. Furthermore, to ensure a predetermined thickness of the nut 2, the outer diameter of the nut 2 increases. That is, the outer diameter of the nut 2 overlaps the imaginary line K21, making it larger than the nut 2 of the first embodiment. According to this embodiment, the bottom wall portion 60 is cut out near the center portion 41c of the S-shaped groove surface 41. Therefore, the link 4 is made smaller in the radial direction by the thickness of the bottom wall portion 60, and the nut 2 is also made smaller in the radial direction.

[0077] Furthermore, the portion of the bottom wall 60 cut out by the through hole 61 is the central portion 41c of the S-shaped groove surface 41, which is a thin portion located between the S-shaped groove surface 41 and the opposing flat surface 47. If the through hole 61 were not formed, the thin portion would remain in the top 4. Here, when manufacturing the top 4 made of resin by injection molding, the thin portion can cause a decrease in the fluidity of the resin. Note that a decrease in the fluidity of the resin may result in the top not being molded into the desired shape or insufficient strength. For these reasons, in this embodiment, the thin portion is cut out by the through hole 61. Therefore, even when manufacturing the top 4 made of resin by injection molding, it is possible to avoid not being molded into the desired shape or insufficient strength.

[0078] It should be noted that the link 4 of the present disclosure is not limited to being made of resin. In other words, the link 4 may be made of a material other than resin. Furthermore, even if the link 4 of the present disclosure is made of resin, it may be manufactured by a manufacturing method other than injection molding. This is because, according to the present embodiment, even if the link 4 is made of a material other than resin or manufactured by a manufacturing method other than injection molding, the link 4 can be made smaller in the radial direction.

[0079] 9, the method of assembling the top 4 to the nut 2 is performed by moving the top 4 arranged on the inner periphery of the nut 2 in the top insertion direction Z and arranging 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.

[0080] 9, the force that moves the piece 4 in the inserting direction Z may act on the end of the inner diameter surface 40 in the first intersecting direction Y1 (see arrow F1 in FIG. 9) rather than on the central part 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.

[0081] If the concave surface 30 did not have the flat surface 33 (if it 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. 9). 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. 9). In other words, there is a possibility that the top 4 would rotate clockwise when viewed from the first direction X1.

[0082] On the other hand, the support 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 support surface 36 has a shape that makes it difficult for the top 4 to rotate. For this reason, it is difficult for the top 4 to rotate clockwise along the support surface 36 when viewed from the first direction X1.

[0083] Furthermore, if the force during assembly is directed 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 support surface 36 has a flat surface 33, which is shaped to make it difficult for the top 4 to rotate. Therefore, it is unlikely that the top 4 will rotate counterclockwise along the support surface 36 as viewed from the first direction X1.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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 bearings 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 bearing 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 bearing insertion direction Z. The bearing 4 has an inner diameter surface 40 facing the inner circumferential side of the nut 2, an outer diameter surface 44 facing the outer circumferential side of the nut 2, an S-shaped groove surface 41 recessed radially outward from the inner diameter surface 40, and a bottom wall portion 60 arranged between the S-shaped groove surface 41 and the outer diameter surface 44. The S-shaped groove surface 41 gradually becomes more recessed in the piece insertion direction Z from both ends of the S-shaped groove surface 41 in the length direction toward the center 41c of the S-shaped groove surface 41 in the length direction. A through-hole 61 is provided in the center 41c of the S-shaped groove surface 41, penetrating in the piece insertion direction Z and cutting out a part of the bottom wall portion 60.

[0090] According to the ball screw device 100 of the first embodiment, the radial size of the top 4 can be reduced. Furthermore, 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.

[0091] 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.

[0092] (Variation 1) FIG. 15 is a cross-sectional view of the ball screw device of Modification 1 taken in a direction perpendicular to the axial direction. As shown in FIG. 15, Modification 1 differs from Embodiment 1 in that a support surface 36A of a concave surface 30A of a nut 2A does not have a flat surface 33. That is, the support surface 36A of Modification 1 is composed of a first arcuate surface 31 and a second arcuate surface 32, and an end 31a of the first arcuate surface 31 is connected to an end 32a of the second arcuate surface 32. Therefore, 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 37). An angle θ5 formed by an imaginary line K3 drawn from a center O37 of the single arcuate surface 37 (support surface 36A) to the first corner 51 and an imaginary line K5 drawn from the center O37 to the second corner 52 is less than 180 degrees.

[0093] Furthermore, the outer diameter surface 44A of the link 4A of Modification 1 differs from that of Embodiment 1 in that it does not have an opposing flat surface 47. That is, the first opposing arcuate surface 45 and the second opposing arcuate surface 46 are connected to each other. The first opposing arcuate surface 45 and the second opposing arcuate surface 46 cooperate with each other to form a single arcuate surface. That is, the outer diameter surface 44A of Modification 1 is a single arcuate surface. The outer diameter surface 44A has the same curvature as the single arcuate surface 37, and the entire surface of the outer diameter surface 44A abuts against the single arcuate surface 37.

[0094] As described above, in the ball screw device 100A of the first modified example, the through hole 61 is formed in the top 4A, so that the nut 2 can be made smaller in size, as in the first embodiment.

[0095] Fig. 16 is a view showing the concave surface forming step of Modified Example 1 as viewed from a first direction of the nut. In the method of forming the concave surface 30A of Modified Example 1, as shown in Fig. 16, a cutting tool 90 is placed on the inner peripheral side of the nut 2A. The cutting tool 90 is placed so that the shank 91 is parallel to the central axis O2 of the nut 2. The shank 91 is rotated to move the cutting tool 90 radially outward (see arrow Z4 in Fig. 16). Then, the inner peripheral surface 20 is cut with the cutting teeth of the cutting tool 90.

[0096] Note that imaginary lines Q90 and Q91 in FIG. 16 indicate the cutting tool 90 and shank 91 moved radially outward. This forms a circular arc surface, i.e., a concave surface 30A, that is, a surface approximately the same diameter as the outer diameter of the cutting tool 90. Once the concave surface 30A is formed, the cutting tool 90 is returned to the inner periphery of the nut 2A, completing this process. Therefore, according to Modification 1, there is no need to move the cutting tool 90 in the cross direction (see arrow Z2 in FIG. 14), making it easier to manufacture the nut 2A. Additionally, the angle θ5 (see FIG. 15) of the single circular arc surface 37 is less than 180 degrees. Therefore, as shown in FIG. 16, the shank 91 of the cutting tool 90 does not contact the inner periphery 20 of the nut 2A.

[0097] (Variation 2) Fig. 17 is a view of a top assembled to a nut of Modified Example 2, viewed from the inner peripheral side. Fig. 18 is an enlarged view of the concave surface of the nut of Modified Example 2, viewed from the inner peripheral side. Fig. 19 is a perspective view of the top of Modified Example 2. Fig. 20 is a cross-sectional view taken along line XX-XX in Fig. 17. Modified Example 2 is an example in which a portion of Modified Example 1 is modified. As shown in Fig. 17, Modified Example 2 differs from Modified Example 1 in that a first thread groove surface 23 and a second thread groove surface 24 are formed on the inner peripheral surface 20 of a nut 2B of Modified Example 2.

[0098] As shown in Fig. 18, the first thread groove surface 23 and the second thread groove surface 24 each extend in the helical direction. The first thread groove surface 23 and the second thread groove surface 24 have a shorter length in the helical direction than the inner peripheral raceway surface 22. The first thread groove surface 23 and the second thread groove surface 24 are formed in the same process (thread groove forming process) as the inner peripheral raceway surface 22. The first thread groove surface 23 and the second thread groove surface 24 have the same shape (gothic arc shape or circular arc shape) as the inner peripheral raceway surface 22. The thread groove forming process of Modified Example 2 will be described later.

[0099] The first thread groove surface 23 is disposed in the first direction X1 at one end 22a of the inner circumferential raceway surface 22. The first thread groove surface 23 extends on an extension line K7 of the other end 22b of the inner circumferential raceway surface 22, with the concave surface 30A in between. One end 23a of the first thread groove surface 23 is connected to the concave surface 30A. The other end 23b of the first thread groove surface 23 is not connected to the concave surface 30A. As shown in FIG. 20 , a first wall surface 23c extending in the radial direction is provided at the other end 23b of the first thread groove surface 23.

[0100] As shown in FIG. 18 , the second thread groove surface 24 is disposed in the second direction X2 at the other end 22b of the inner circumferential raceway surface 22. The second thread groove surface 24 extends on an extension line K8 of the one end 22a of the inner circumferential raceway surface 22, sandwiching the concave surface 30A. One end 24a of the second thread groove surface 24 is connected to the concave surface 30A. The other end 24b of the second thread groove surface 24 is not connected to the concave surface 30A. As shown in FIG. 20 , a second wall surface 24c extending radially is provided at the other end 24b of the second thread groove surface 24. Note that, although the first wall surface 23c and the second wall surface 24c in the embodiment extend radially, in the present disclosure, they may be gradually raised so as to be positioned radially inward as they move away from the concave surface 30. In other words, the present disclosure does not particularly limit the shapes of the first wall surface 23c and the second wall surface 24c.

[0101] 19, the top 4B of Modification 2 differs from Modification 1 in that it includes a first protrusion 161 and a second protrusion 162. The first protrusion 161 protrudes from the first opposing arcuate surface 45 in the first intersecting direction Y1. The second protrusion 162 protrudes from the second opposing arcuate surface 46 in the second intersecting direction. The first protrusion 161 and the second protrusion 162 each extend in a spiral direction.

[0102] 17 and 20, the first protrusion 161 is disposed inside the first thread groove surface 23. The second protrusion 162 is disposed inside the second thread groove surface 24. As shown in FIG. 20, a distance W3 between a tip 161a of the first protrusion 161 and the first wall surface 23c is smaller than the diameter of the ball 3. Similarly, a distance W4 between a tip 162a of the second protrusion 162 and the second wall surface 24c is smaller than the diameter of the ball 3. In other words, the ball 3 cannot be disposed inside the first thread groove surface 23 and the second thread groove surface 24 during the assembling operation of the ball 3.

[0103] According to the second modification, when the top 4B is assembled, if a load (see arrow F5 in FIG. 20) that rotates the top 4B clockwise as viewed from the first direction X1 acts on the top 4B, the first protrusion 161 catches on the first thread groove surface 23. Therefore, the top 4B is prevented from rotating clockwise inside the concave surface 30A. Furthermore, when the top 4B is assembled, if a load (see arrow F6 in FIG. 20) that rotates the top 4B counterclockwise as viewed from the first direction X1 acts on the top 4B, the second protrusion 162 catches on the second thread groove surface 24. Therefore, the top 4B is prevented from rotating counterclockwise inside the concave surface 30A. From the above, the top 4B inserted into the concave surface 30A is assembled to the nut 2B in a predetermined orientation, eliminating the need to correct the orientation of the top 4B.

[0104] Although the first protrusion 161 and the second protrusion 162 in Modification 2 extend in the spiral direction, the present disclosure is not particularly limited to the shapes of the first protrusion 161 and the second protrusion 162 as long as they can be disposed inside the first thread groove surface 23 or the second thread groove surface 24. Therefore, the first protrusion 161 and the second protrusion 162 may extend in the circumferential direction or the intersecting direction instead of the spiral direction.

[0105] Fig. 21 is an enlarged view showing a portion of the inner peripheral surface of the nut after the thread groove forming step of Modification 2. As shown in Fig. 21, the thread groove forming step of Modification 2 differs from Modification 1 in that the length of the thread groove 80B formed on the inner peripheral surface 20 is formed to be approximately one and a half leads. In other words, the inner peripheral raceway surface 22, the first thread groove surface 23, and the second thread groove surface 24 are all formed continuously.

[0106] When the concave surface 30A is formed in the concave surface forming step (see FIG. 16), a portion of the thread groove 80B (see the area surrounded by the imaginary line K30 in FIG. 21) is cut. As a result, one thread groove 80B is divided into three parts: one end portion 81, the other end portion 82, and an intermediate portion 83. In other words, the inner circumferential raceway surface 22 (intermediate portion 83), the first thread groove surface 23 (other end portion 82), and the second thread groove surface 24 (one end portion 81) are formed.

[0107] In addition, in variant example 2, an example was described in which the first screw groove surface 23, the second screw groove surface 24, the first protrusion 161 and the second protrusion 162 were applied to the ball screw device 100A of variant example 1, but they may also be applied to the ball screw device 100 of embodiment 1.

[0108] (Variation 3) 22 is a cross-sectional view of a 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. 9. As shown in FIG. 22, a nut 2C of Modification 3 differs from Embodiment 1 in that a support surface 36C of a concave surface 30C has a first flat surface 31C and a second flat surface 32C instead of the first arcuate surface 31 and the second arcuate surface 32. Furthermore, a link 4C of Modification 3 differs from Embodiment 1 in that an outer diameter surface 44C has a first opposing flat surface 45C and a second opposing flat surface 46C instead of the first opposing arcuate surface 45 and the second opposing arcuate surface 46.

[0109] The first plane 31C and the second plane 32C are planes that extend in the axial direction and the piece insertion direction Z, respectively. The first plane 31C extends in the piece insertion direction Z from the first corner 51. The end of the first plane 31C in the piece insertion direction Z is connected to the end of the plane 33 in the first intersecting direction Y1. Therefore, the portion where the plane 33 and the first plane 31C intersect is the first corner 38.

[0110] The second plane 32C extends in the piece insertion direction Z from the second corner 52. An end of the second plane 32C in the piece insertion direction Z connects to an end of the plane 33 in the second intersecting direction Y2. Therefore, the intersection of the plane 33 and the second plane 32C forms a second corner 39.

[0111] The first opposing flat surface 45C and the second opposing flat surface 46C of the link 4C of Modification 3 are flat surfaces that extend in the axial direction and the link insertion direction Z, respectively. The first opposing flat surface 45C faces the first flat surface 31C and abuts against the first flat surface 31C. The second opposing flat surface 46C faces the second flat surface 32C and abuts against the second flat surface 32C. The intersection of the opposing flat surface 47 and the first opposing flat surface 45C forms a first intersecting direction corner 48 that corresponds to the first corner 38. Furthermore, the intersection of the opposing flat surface 47 and the second opposing flat surface 46C forms a second intersecting direction corner 49 that corresponds to the second corner 39.

[0112] As described above, according to Modification 3, each face (first plane 31C, second plane 32C, and plane 33) of the support surface 36C of the concave surface 30C is flat. Furthermore, each face (first opposing plane 45C, second opposing plane 46C, and opposing plane 47) of the outer diameter surface 44C of the block 4C corresponding to the support surface 36C is also flat. Therefore, the block 4C does not rotate inside the concave surface 30C. This allows the block 4C to be assembled in a predetermined position, making assembly extremely easy. Furthermore, in Modification 3, a through hole 61 is formed in the block 40C, which allows for a more compact nut 2C, as in the first embodiment. Note that, in the present disclosure, the plane 33 and the first plane 31C do not necessarily intersect at a right angle. Similarly, the plane 33 and the second plane 32C do not necessarily intersect at a right angle.

[0113] (Variation 4) 23 is a cross-sectional view of a ball screw device of Modification 4, taken along a direction perpendicular to the longitudinal direction of the center of the S-shaped groove surface. As shown in FIG. 23, a top 4D of Modification 4 differs from Embodiment 1 in that the ball 3 moving along the center 41c of the S-shaped groove surface 41 does not come into contact with the support surface 36 (flat surface 33) of the concave surface 30 via the through hole 61. Even in Modification 4, the through hole 61 cuts out a portion of the bottom wall 60, thereby reducing the size of the top 4D in the radial direction. In other words, in the present disclosure, it does not matter whether the ball 3 comes into contact with the concave surface 30.

[0114] (Variation 5) FIG. 24 is an enlarged view of the inner peripheral side of the nut of the ball screw device of Modification 5. As shown in FIG. 24, the nut 2E of Modification 5 differs from Embodiment 1 in that the orientation of the concave surface 30E is changed. The first corner 51E and the second corner 52E of the concave surface 30E intersect with the axial direction. The third corner 53E and the fourth corner 54E extend in the spiral direction. Such a concave surface 30E can be formed by tilting the shank 91 of the cutting tool 90 with respect to the central axis O2 during the concave surface forming process. Because the through hole 61 is formed even in the link 40E of Modification 5, the nut 2E can be made smaller, as in Embodiment 1.

[0115] (Variation 6) FIG. 25 is a cross-sectional view of a nut of a ball screw device of Modification 6 taken along the axial direction. As shown in FIG. 25, the nut 2F of Modification 6 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. The nut 2F of Modification 6 also allows for the miniaturization of the nut 2E, as in Embodiment 1. Furthermore, in the thread groove surface forming step (see FIG. 13 ), 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 2F of Modification 6 is not limited to cutting. That is, the thread groove surface 70 of the nut 2F of Modification 6 may be formed by rolling. In addition, in variant example 2, the first thread groove surface 23 and the second thread groove surface 24 are listed as the thread groove surfaces in which the first protrusion 161 and the second protrusion 162 are accommodated, but the present disclosure may also accommodate the first protrusion 161 and the second protrusion 162 in the circuit outer thread groove surface 71 shown in variant example 6.

[0116] 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.

[0117] Furthermore, the through hole 61 is not limited to the size, length, and shape described in the embodiment. For example, the through hole 61 in the first embodiment has a shape that approximates an ellipse, but may also be rectangular. Furthermore, the ends (tips 61a, 62a) of the through hole 61 in the first embodiment extend beyond the ridge lines H1 and H2 (see FIG. 8), but the ends (tips 61a, 62a) of the through hole in the present disclosure do not have to extend beyond the ridge lines H1 and H2. In other words, the present disclosure may also be a through hole in which only the opposing flat surface 47 is cut out.

[0118] Furthermore, although the first opposing arcuate surface 45 in the first embodiment has the same curvature as the first arcuate surface 31, the present disclosure may also provide a configuration in which the curvature of the first opposing arcuate surface 45 is slightly smaller than that of the first arcuate surface 31. The present disclosure may also provide a configuration in which the curvature of the second opposing arcuate surface 46 is slightly smaller than that of the second arcuate surface 32. In other words, the opposing arcuate surfaces of the top 4 (the first opposing arcuate surface 45 and the second opposing arcuate surface 46) do not have to have the same curvature as the arcuate surfaces of the concave surface 30 (the first arcuate surface 31 and the second arcuate surface 32). The opposing flat surface 47 may be formed to be the same size as the flat surface 33 or slightly smaller than the flat surface 33. In other words, the present disclosure does not particularly care about the sizes of the opposing flat surface 47 and the flat surface 33.

[0119] 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.

[0120] 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.

[0121] 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).

[0122] 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 frame is an inner diameter surface facing the inner periphery of the nut; An outer diameter surface facing the outer periphery of the nut; an S-shaped groove surface recessed radially outward from the inner diameter surface; a bottom wall portion disposed between the S-shaped groove surface and the outer diameter surface; and the S-shaped groove surface has a gradually increasing recess amount in the inserting direction of the piece as it approaches the center of the S-shaped groove surface from both ends in the length direction of the S-shaped groove surface, A through hole is provided in the center of the S-shaped groove surface, penetrating in the inserting direction of the piece and cutting out a part of the bottom wall. Ball screw device. (2) The ball contacts the concave surface through the through hole. The ball screw device according to (1). (3) The ball does not come into contact with the concave surface through the through hole. The ball screw device according to (1). (4) 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support surface has an arc shape when viewed from the axial direction, and one end in the intersecting direction is connected to the first corner portion, and the other end in the intersecting direction is connected to the second corner portion. A ball screw device according to any one of (1) to (3). (5) 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support 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 from the first corner or the second corner in the frame insertion direction; a plane extending in the intersecting direction, one end of which is connected to the first arcuate surface and the other end of which is connected to the second arcuate surface; and The outer diameter surface of the piece extends in the intersecting direction and has a flat opposing surface facing the flat surface. A ball screw device according to any one of (1) to (3). (6) 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support surface is a first plane extending from the first corner in the inserting direction; a second flat surface extending from the second corner in the inserting direction; a plane extending in the intersecting direction, one end of which is connected to the first plane and the other end of which is connected to the second plane; have A ball screw device according to any one of (1) to (3). (7) The inner peripheral surface of the nut is an inner circumferential raceway surface that extends in a spiral direction, one end of which is connected to the first corner portion and the other end of which is connected to the second corner portion; a first thread groove surface that extends on an extension line of the other end of the inner circumferential raceway surface across the concave surface and has one end connected to the first corner portion; a second thread groove surface that extends on an extension line of one end of the inner peripheral raceway surface across the concave surface and has one end connected to the second corner portion; and The frame is a first protrusion disposed inside the first thread groove surface; a second protrusion disposed inside the second thread groove surface; have A ball screw device according to (4) or (5). (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) 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 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 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 an axial direction parallel to the central axis of the nut, 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 an axial direction parallel to the central axis of the nut, 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]

[0123] 1 Screw shaft 2, 2A, 2B, 2C, 2E, 2F Nut 3 Ball 4, 4B, 4C, 4D pieces 10 Screw shaft body 14 Outer raceway surface 20 Inner surface 22 Inner raceway surface 23 First thread groove surface 24 Second thread groove surface 30, 30A, 30C, 30E concave 31 First circular arc surface 31C 1st plane 32 Second circular arc surface 32C 2nd plane 33 plane 34 First aspect 35 Second aspect 36, 36A, 36C support surface 37 Single arc surface 38 First corner 39 Second corner 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 45C First opposing plane 46 Second opposing arc surface 46C Second opposing plane 47 Opposite planes 48 First crossing direction side corner 49 Second crossing direction side corner 50 Corner 51, 51E 1st corner 52, 52E 2nd corner 53, 53E Third corner 54, 54E Fourth corner 55 Opening 60 Bottom wall 61 Through hole 63 First bottom wall 64 Second bottom wall 100, 100A ball screw device 161 1st protrusion 162 2nd protrusion

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 frame is an inner diameter surface facing the inner periphery of the nut; An outer diameter surface facing the outer periphery of the nut; an S-shaped groove surface recessed radially outward from the inner diameter surface; a bottom wall portion disposed between the S-shaped groove surface and the outer diameter surface; and the S-shaped groove surface has a gradually increasing recess amount in the inserting direction of the piece as it approaches the center of the S-shaped groove surface from both ends in the length direction of the S-shaped groove surface, A through hole is provided in the center of the S-shaped groove surface, penetrating in the inserting direction of the piece and cutting out a part of the bottom wall. Ball screw device.

2. The ball contacts the concave surface through the through hole. The ball screw device according to claim 1 .

3. The ball does not come into contact with the concave surface through the through hole. The ball screw device according to claim 1 .

4. 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support surface has an arc shape when viewed from the axial direction, and one end in the intersecting direction is connected to the first corner portion, and the other end in the intersecting direction is connected to the second corner portion. The ball screw device according to claim 1 .

5. 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support 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 from the first corner or the second corner in the frame insertion direction; a plane extending in the intersecting direction, one end of which is connected to the first arcuate surface and the other end of which is connected to the second arcuate surface; and The outer diameter surface of the piece extends in the intersecting direction and has a flat opposing surface facing the flat surface. The ball screw device according to claim 1 .

6. 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 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 has a support surface that abuts against the outer diameter surface and supports the piece, The support surface is a first plane extending from the first corner in the inserting direction; a second flat surface extending from the second corner in the inserting direction; a plane extending in the intersecting direction, one end of which is connected to the first plane and the other end of which is connected to the second plane; have The ball screw device according to claim 1 .

7. The inner peripheral surface of the nut is an inner circumferential raceway surface that extends in a spiral direction, one end of which is connected to the first corner portion and the other end of which is connected to the second corner portion; a first thread groove surface that extends on an extension line of the other end of the inner circumferential raceway surface across the concave surface and has one end connected to the first corner portion; a second thread groove surface that extends on an extension line of one end of the inner peripheral raceway surface across the concave surface and has one end connected to the second corner portion; and The frame is a first protrusion disposed inside the first thread groove surface; a second protrusion disposed inside the second thread groove surface; have The ball screw device according to claim 4 or 5.

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 6.

9. 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 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 6.

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 6.

11. 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 arranged apart from each other in an axial direction parallel to the central axis of the nut, 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 6.

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 arranged apart from each other in an axial direction parallel to the central axis of the nut, 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 6.

Images