Ball spring device

Abstract

To provide a ball screw device for improving assemblability of a top.SOLUTION: A nut of a ball screw device according to the present disclosure has: a concave part; a first corner part and a second corner part as corners of the concave face; an inner peripheral raceway surface connected to the first and second corner parts; and a fir screw groove face and a second screw groove face extending on an extension line of the inner peripheral raceway surface. A direction of the concave face when seen from a central axis is a top insertion direction, a direction of the first corner part when seen from the second corner part is a first crossing direction, and a direction of the second corner part when seen from the first corner part is a second crossing direction. The concave face has; a first arc face gradually arranged in the second crossing direction as it moves in the top insertion direction; and a second arc face gradually arranged in the first crossing direction as it moves in the top insertion direction from the second corner part. The top has a first protrusion arranged on the first screw groove face, and a second protrusion arranged on the second screw groove face. A distance between the other end of the first screw groove face and the first protrusion, and a distance between the other end of the second screw groove face and the second protrusion are smaller than a diameter of a ball.SELECTED DRAWING: Figure 2

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

[0005] Furthermore, the nut in the above-mentioned patent document has a continuous screw groove formed on its inner peripheral surface in the helical direction. Here, a part of the screw groove forms an inner peripheral raceway surface, but the rest of the screw groove does not. This is undesirable because there is a possibility that the balls may be erroneously placed in the remaining part of the screw groove when assembling the ball screw device.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a ball screw device that facilitates the assembly of the bearing and further restricts the placement of balls in screw grooves other than the inner circumferential raceway surface. [Means for solving the problem]

[0007] 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 rollers 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 rollers therein, a first corner portion and a second corner portion that are corner portions where the concave surface and the inner circumferential surface intersect and are spaced apart from each other in the circumferential direction, an inner circumferential raceway surface extending in a spiral direction and 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 circumferential 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 one end of the inner circumferential raceway surface across the concave surface and having one end connected to the second corner portion. The direction in which the concave surface is arranged as viewed from the central axis of the nut is the block insertion direction. The direction in which the first corner is arranged as viewed from the second corner is the first intersecting direction. The direction in which the second corner is arranged as viewed from the first corner is the second intersecting direction. The concave surface has a first arc-shaped surface that extends from the first corner in the block insertion direction and gradually becomes arranged in the second intersecting direction as the user moves in the block insertion direction, and a second arc-shaped surface that extends from the second corner in the block insertion direction and gradually becomes arranged in the first intersecting direction as the user moves in the block insertion direction. The outer diameter surface of the block has a first opposing arc-shaped surface that faces the first arc-shaped surface, a second opposing arc-shaped surface that faces the second arc-shaped surface, a first protrusion that protrudes from the first opposing arc-shaped surface and is arranged inside the first thread groove surface, and a second protrusion that protrudes from the second opposing arc-shaped surface and is arranged inside the second thread groove surface. The distance between the other end of the first thread groove surface and the tip of the first protrusion is smaller than the diameter of the ball. The distance between the other end of the second thread groove surface and the tip of the second protrusion is smaller than the diameter of the ball.

[0008] According to the present disclosure, when a top is assembled inside a concave surface, even if a load that would cause the top to rotate along the first arcuate surface or the second arcuate surface of the concave surface acts on the top, the first protrusion will catch on the first thread groove surface, and the second protrusion will catch on the second thread groove surface. Therefore, rotation of the top inside the concave surface is restricted. This allows the top to be assembled in a predetermined position, making assembly of the top easier. Furthermore, because the distance between the other end of the first thread groove surface and the tip of the first protrusion is smaller than the diameter of the ball, a ball cannot be inserted into the first thread groove surface. Similarly, because the distance between the other end of the second thread groove and the tip of the second protrusion is smaller than the diameter of the ball, a ball cannot be inserted into the second thread groove surface. Therefore, placement of a ball on the first thread groove surface and the second thread groove surface is restricted. Furthermore, the first thread groove surface and the second thread groove surface are formed on an extension of the inner peripheral 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 peripheral raceway surface. Therefore, even if the nut has a first thread groove surface and a second thread groove surface, an increase in manufacturing steps is suppressed. Furthermore, according to the top of the present disclosure, there is no need to provide a through hole on the outer peripheral surface of the nut. This allows the nut itself to function as a piston by sliding the outer peripheral surface of the nut, 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, dust resistance is high. Alternatively, the nut of the present disclosure is smaller and lighter than a nut with a through hole on the outer peripheral surface and a component for blocking the through hole.

[0009] In a preferred embodiment of the ball screw device, an end of the first arcuate surface in the second intersecting direction and an end of the second arcuate surface in the first intersecting direction are connected to each other, and the first arcuate surface and the second arcuate surface cooperate with each other to form a single arcuate surface.

[0010] According to the above configuration, a single arcuate surface is formed simply by moving the rotating cutting tool radially outward from the central axis of the nut. In other words, there is no need to move the cutting tool in the first intersecting direction or the second intersecting direction. This makes it easier to form the concave surface, improving nut productivity.

[0011] In addition, in a preferred embodiment of the ball screw device, the angle formed by an imaginary line drawn from the center of the single arc surface to the first corner and an imaginary line drawn from the center of the single arc surface to the second corner is less than 180 degrees.

[0012] 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.

[0013] In a preferred embodiment of the ball screw device, the concave surface has a flat surface disposed between the first arcuate surface and the second arcuate surface, and an opposing flat surface facing the flat surface is formed on the outer diameter surface of the top.

[0014] According to the above configuration, the opposing flat surfaces of the top abut against the flat surfaces of the concave surface. Therefore, the top is less likely to rotate than when the outer diameter surface is a single arc surface, making the top assembly easier. Furthermore, when assembling the top, the opposing flat surfaces of the top abut against the flat surfaces of the concave surface. This positions the top so that the opposing flat surfaces are parallel to the cross direction.

[0015] 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.

[0016] 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.

[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 the inner peripheral side of the nut, and third and fourth corners that are corners where the concave surface and the inner peripheral surface intersect and are spaced apart from each other in an axial direction parallel to the central axis of the nut. The distance between the first corner and the second corner of the opening is greater than the distance between the third corner and the fourth corner.

[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 arranged at a corner where the concave surface and the inner circumferential surface intersect, and are spaced apart from each other in an axial direction parallel to the central axis of the nut. 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 an axial direction parallel to the central axis of the nut. The third corner and the fourth corner may extend in the spiral direction. [Effects of the Invention]

[0024] The ball screw device of the present disclosure facilitates the assembly of the top, and restricts the placement of balls on the thread grooves (the first thread groove surface and the second thread groove surface) other than the inner peripheral raceway surface. [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] 7 is a cross-sectional view taken along the line VII-VII in FIG. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. [Figure 9] FIG. 9 is an enlarged view showing a part of the inner peripheral surface of the nut after the thread groove forming step of the first embodiment. [Figure 10] FIG. 10 is a view showing the concave surface forming step of the first embodiment when viewed from the first direction of the nut. [Figure 11] FIG. 11 is a cross section of the ball screw device of Modification 1 taken in a direction perpendicular to the axial direction, and more specifically, a cross section of the ball screw device of Modification 1 taken in the same way as in FIG. [Figure 12] FIG. 12 is an enlarged view of the inner peripheral side of the nut of the ball screw device of the second modified example. 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. 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.

[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. 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 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.

[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 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 cut along line VV in FIG. 2, viewed from the direction of the arrow. As shown in FIG. 4, a first thread groove surface 23 and a second thread groove surface 24 are formed on the inner peripheral surface 20 of the nut 2. 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 shorter lengths in the helical direction than the inner peripheral raceway surface. 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 will be described later.

[0045] 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 K1 of the other end 22b of the inner circumferential raceway surface 22, with the concave surface 30 in between. One end 23a of the first thread groove surface 23 is connected to the concave surface 30. The other end 23b of the first thread groove surface 23 is not connected to the concave surface 30. As shown in FIG. 5, a first wall surface 23c extending in the radial direction is provided at the other end 23b of the first thread groove surface 23.

[0046] As shown in FIG. 4, 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 K2 of one end 22a of the inner circumferential raceway surface 22, sandwiching the concave surface 30. One end 24a of the second thread groove surface 24 is connected to the concave surface 30. The other end 24b of the second thread groove surface 24 is not connected to the concave surface 30. As shown in FIG. 5, 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.

[0047] 4, four corners 50 are provided on the inner periphery of the nut 2 where the inner periphery surface 20 and the concave surface 30 intersect. Note that the corners 50 of the present disclosure may be sharp, tapered, or R-chamfered, and are not particularly limited.

[0048] 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.

[0049] Hereinafter, the direction in which the first corner 51 and the second corner 52 are arranged will be referred to as the intersecting direction. Among the intersecting directions, the direction in which the first corner 51 is arranged as viewed from the second corner 52 will be referred to as the first intersecting direction Y1. Furthermore, among the intersecting directions, the direction in which the second corner 52 is arranged as viewed from the first corner 51 will be referred to as the second intersecting direction Y2.

[0050] The first corner portion 51 and the second corner portion 52 each extend linearly and are parallel to the axial direction. One end 22a of the inner circumferential raceway surface 22 and one end 23a of the first thread groove surface 23 are connected to the first corner portion 51. Therefore, a portion of the first corner portion 51 is cut out. Furthermore, the other end 22b of the inner circumferential raceway surface 22 and one end 24a of the second thread groove surface 24 are connected to the second corner portion 52. Therefore, a portion of the second corner portion 52 is cut out.

[0051] The third corner 53 is disposed in the first direction X1 when viewed from the concave surface 30. The fourth corner 54 is disposed in the second direction X2 when viewed from the concave surface 30. The third corner 53 and the fourth corner 54 are not connected to the inner circumferential raceway surface 22, etc. Therefore, the third corner 53 and the fourth corner 54 are not cut out. Furthermore, the third corner 53 and the fourth corner 54 extend in the circumferential direction and intersect with the spiral direction.

[0052] 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 between the first corner 51 and the second corner 52 is greater than the distance W2 between the third corner 53 and the fourth corner 54.

[0053] The concave surface 30 has a first arcuate surface 31, a second arcuate surface 32, a first side surface 33, and a second side surface 34. The first side surface 33 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 34 is a flat surface that extends from the fourth corner 54 in the piece insertion direction Z and faces the first direction X1.

[0054] 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 K3 to the end 31a of the first arcuate surface 31 in the second intersecting direction Y2 is perpendicular to the piece insertion direction Z.

[0055] 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 K4 to the end 32a of the second arcuate surface 32 in the first intersecting direction Y1 is perpendicular to the piece insertion direction Z.

[0056] An end 31a of the first arcuate surface 31 and an end 32a of the second arcuate surface 32 are connected. Furthermore, a tangent K1 to the end 31a and a tangent K2 to the end 32a are a common tangent. Therefore, the surface formed by combining the first arcuate surface 31 and the second arcuate surface 32 is also arc-shaped. In other words, the first arcuate surface 31 and the second arcuate surface 32 cooperate with each other to form a single arcuate surface (hereinafter referred to as a single arcuate surface 35). Furthermore, an angle θ1 formed by an imaginary line K5 drawn from the center O35 of the single arcuate surface 35 to the first corner 51 and an imaginary line K6 drawn from the center O35 to the second corner 52 is less than 180 degrees.

[0057] 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.

[0058] 2, the first opposing surface 42 faces the first direction X1, is formed in a flat shape, and faces the first side surface 33. The second opposing surface 43 faces the second direction X2, is formed in a flat shape, and faces the second side surface 34. As shown in FIG. 7, the outer diameter surface 44 has a first opposing arcuate surface 45 facing the first arcuate surface 31 and a second opposing arcuate surface 46 facing the second arcuate surface 32.

[0059] The first opposing arcuate surface 45 is an arcuate surface with the same curvature as the first arcuate surface 31. Therefore, when viewed from the axial direction, the first opposing arcuate surface 45 has the same shape as the first arcuate surface 31. The second opposing arcuate surface 46 is an arcuate surface with the same curvature as the second arcuate surface 32. Therefore, the second opposing arcuate surface 46 has the same shape as the second arcuate surface 32. The first opposing arcuate surface 45 and the second opposing arcuate surface 46 are connected to each other, and the combined surface of the first opposing arcuate surface 45 and the second opposing arcuate surface 46 also has an arc shape. In other words, the first opposing arcuate surface 45 and the second opposing arcuate surface 46 cooperate with each other to form a single arcuate surface (hereinafter referred to as the opposing arcuate surface 47). The opposing arcuate surface 47 has the same curvature as the single arcuate surface 35, and the entire surface of the opposing arcuate surface 47 abuts against the single arcuate surface 35.

[0060] 6, the top 4 has a first protrusion 61 protruding from the first opposing arcuate surface 45 and a second protrusion 62 protruding from the second opposing arcuate surface 46. The first protrusion 61 and the second protrusion 62 each extend in a spiral direction.

[0061] As shown in FIG. 7 , the first protrusion 61 is disposed inside the first thread groove surface 23. The second protrusion 62 is disposed inside the second thread groove surface 24. A distance W3 between a tip 61 a of the first protrusion 61 and the first wall surface 23 c is smaller than the diameter of the ball 3. Similarly, a distance W4 between a tip 62 a of the second protrusion 62 and the second wall surface 24 c is smaller than the diameter of the ball 3. Therefore, during the assembling operation of the ball 3, the ball 3 cannot be disposed inside the first thread groove surface 23 and the second thread groove surface 24.

[0062] Fig. 8 is a cross-sectional view taken along the line VIII-VIII in Fig. 7. As shown in Fig. 8, a gap S is formed between the first protrusion 61 and the first thread groove surface 23. In addition, although not shown, a gap S is also formed between the second protrusion 62 and the second thread groove surface 24. Therefore, even if the first protrusion 61 and the second protrusion 62 are manufactured with a large thickness in the block insertion direction Z due to a manufacturing error, this is absorbed by the gap S. Therefore, the opposing arcuate surface 47 of the block 4 is reliably abutted against the single arcuate surface 35 of the concave surface 30.

[0063] 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.

[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. 9 is an enlarged view showing a portion of the inner circumferential surface of the nut after the thread groove forming step of the first embodiment. As shown in FIG. 9, the thread groove forming step is a step of forming a thread groove 80 on the inner circumferential surface 20 of the nut 2. The thread groove 80 is formed by contacting the teeth of a cutting tool with the inner circumferential 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 circumferential surface 20. The length of the thread groove 80 is approximately one and a half leads. In other words, the inner circumferential raceway surface 22, the first thread groove surface 23, and the second thread groove surface 24 are all formed continuously. 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. 10 is a view of the concave surface forming step of the first embodiment as viewed from a first direction of the nut. The concave surface forming step is a step 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. 10, 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. Next, the shaft portion 91 is rotated to move the cutting tool 90 radially outward (see arrow Z1 in FIG. 10). Then, the inner peripheral surface 20 is cut with the cutting teeth of the cutting tool 90.

[0067] Note that imaginary lines Q90 and Q91 in FIG. 10 show the cutting tool 90 and shank 91 moved radially outward. This forms a circular arc surface that is approximately the same as the outer diameter of the cutting tool 90, i.e., a concave surface 30 (see imaginary line K10 in FIG. 10). Once the concave surface 30 is formed, the cutting tool 90 is returned to the inner peripheral side of the nut 2, and this process is completed. Furthermore, according to this process, as shown in FIG. 9, a portion of the thread groove 80 (see the area surrounded by imaginary line K10 in FIG. 9) is cut. That is, one thread groove 80 is divided into three parts: one end 81, the other end 82, and an intermediate portion 83. This forms 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).

[0068] As described above, the movement of the cutting tool 90 in the concave surface forming step is limited to radial movement. Therefore, there is no need to move the cutting tool 90 in a cross direction, simplifying the manufacturing process. In addition, the angle θ1 (see FIG. 5) of the single arc surface 35 is less than 180 degrees. Therefore, as shown in FIG. 10, the shank 91 of the cutting tool 90 does not come into contact with the inner peripheral surface 20 of the nut 2. Note that, although the concave surface forming step described above exemplifies a case in which the nut 2 is fixed and the cutting tool 90 is moved, the present disclosure also allows the concave surface 30 to be formed by fixing the cutting tool 90 and moving the nut 2.

[0069] 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.

[0070] Next, the effects of this embodiment will be described.

[0071] 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 place the top 4 inside the concave surface 30. Here, as shown in FIG. 7, the force that moves the top 4 in the top insertion direction Z may be applied not to the center of the inner diameter surface 40 in the intersecting direction, but toward the end of the inner diameter surface 40 in the first intersecting direction Y1 (see arrow F1 in FIG. 7). This causes the first opposing arcuate surface 45 of the top 4 to be pressed against the first arcuate surface 31.

[0072] If the first protrusion 61 were not present, 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.

[0073] On the other hand, according to this embodiment, when the above-mentioned force acts on the top 4, the first protrusion 61 gets caught on the first thread groove surface 23. Therefore, the top 4 is restricted from rotating in the clockwise direction inside the concave surface 30. On the other hand, 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 when viewed from the first direction X1. However, according to this embodiment, the second protrusion 62 gets caught on the second thread groove surface 24. Therefore, the top 4 is also restricted from rotating counterclockwise inside the concave surface 30. As a result, the top 4 inserted into the concave surface 30 is assembled to the nut 2 in a predetermined orientation. This eliminates the need to correct the orientation of the top 4, making the assembly of the top 4 easier.

[0074] In this embodiment, a first thread groove surface 23 and a second thread groove surface 24 are formed in addition to the inner peripheral raceway surface 22. However, restrictions are placed so that the balls 3 cannot be placed on the first thread groove surface 23 and the second thread groove surface 24. In other words, there is no risk of the balls 3 being placed on any thread groove surface other than the inner peripheral raceway surface 22.

[0075] In this embodiment, the inner peripheral raceway surface 22, the first thread groove surface 23, and the second thread groove surface 24 are simultaneously formed in the thread groove forming step. Therefore, even if the first thread groove surface 23 and the second thread groove surface 24 are formed on the inner peripheral surface 20, the number of manufacturing steps does not increase.

[0076] In this embodiment, as shown in FIG. 4, the distance W1 between the first corner 51 and the second corner 52 is greater than the distance W2 between the third corner 53 and the fourth corner 54. 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. That is, as shown in FIG. 2, the inclination angle θ2 with respect to the spiral direction can be made relatively small. Furthermore, as shown in FIG. 3, the inclination angle θ3 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.

[0077] 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.

[0078] As described above, the ball screw device 100 of embodiment 1 comprises a screw shaft 1, a nut 2 that is inserted into 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 tops 4 that circulate the balls 3. The inner peripheral surface 20 of the nut 2 has a concave surface 30 that is recessed radially outward from the inner peripheral surface 20 and accommodates a block 4 therein; a first corner portion 51 and a second corner portion 52 that are corner portions where the concave surface 30 and the inner peripheral surface 20 intersect and are arranged circumferentially spaced apart from each other; an inner peripheral raceway surface 22 that extends in the spiral direction and has one end 22a connected to the first corner portion 51 and the other end 22b connected to the second corner portion 52; a first thread groove surface 23 that extends on an extension of the other end 22b of the inner peripheral raceway surface 22 across the concave surface 30 and has one end 24a connected to the first corner portion 51; and a second thread groove surface 24 that extends on an extension of the one end 22a of the inner peripheral raceway surface 22 across the concave surface 30 and has one end 24a connected to the second corner portion 52. The direction in which the concave surface 30 is disposed when viewed from the central axis O2 of the nut 2 is the block insertion direction Z. The direction in which the first corner 51 is disposed when viewed from the second corner 52 is the first intersecting direction Y1. The direction in which the second corner 52 is disposed when viewed from the first corner 51 is the second intersecting direction Y2. The concave surface 30 has an arc-shaped first arc surface 31 that extends from the first corner 51 in the block insertion direction Z and gradually becomes more aligned in the second intersecting direction Y2 as it moves in the block insertion direction Z, and a second arc surface 32 that extends from the second corner 52 in the block insertion direction Z and gradually becomes more aligned in the first intersecting direction Y1 as it moves in the block insertion direction Z. The outer diameter surface 44 of the block 4 has a first opposing arcuate surface 45 that is arcuate and faces the first arcuate surface 31, a second opposing arcuate surface 46 that is arcuate and faces the second arcuate surface 32, a first protrusion 61 that protrudes from the first opposing arcuate surface 45 and is disposed inside the first thread groove surface 23, and a second protrusion 62 that protrudes from the second opposing arcuate surface 46 and is disposed inside the second thread groove surface 24. A distance W3 between the other end of the first thread groove surface 23 and a tip 61a of the first protrusion 61 is smaller than the diameter of the ball 3. A distance W4 between the other end of the second thread groove surface 24 and a tip 62a of the second protrusion 62 is smaller than the diameter of the ball 3.

[0079] According to this embodiment 1, the ease of assembly of the link 4 can be improved. Moreover, the balls 3 are not arranged in any thread groove other than the inner circumferential raceway surface 22. Moreover, according to embodiment 1, 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.

[0080] 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.

[0081] (Variation 1) 11 is a cross section of the ball screw device of Modification 1 taken in a direction perpendicular to the axial direction, and more specifically, a cross section of the ball screw device of Modification 1 taken in the same manner as in FIG. 7. As shown in FIG. 11, the concave surface 30A of the nut 2A of Modification 1 differs from that of Embodiment 1 in that it has a flat surface 36 disposed between the first arcuate surface 31 and the second arcuate surface 32. Furthermore, the outer diameter surface 44A of the link 4A of Modification 1 differs from that of Embodiment 1 in that it has an opposing flat surface 48 that faces the flat surface 36.

[0082] The plane 36 extends in the intersecting direction and the axial direction. An end 36a of the plane 36 in the first intersecting direction Y1 is connected to an end 31a of the first arcuate surface 31 in the second intersecting direction Y2. An end 36b of the plane 36 in the second intersecting direction Y2 is connected to an end 32a of the second arcuate surface 32 in the first intersecting direction Y1. With this type of concave surface 30, the plane 36 and the second arcuate surface 32 are formed by moving a cutting tool 90 (see FIG. 10 ) in the block insertion direction Z to form the first arcuate surface 31, and then moving the cutting tool 90 in the second intersecting direction Y2.

[0083] Furthermore, the angle formed by the imaginary line K11 drawn from the center O31 of the first arcuate surface 31 to the first corner 51 and the imaginary line K12 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. Furthermore, the angle formed by the imaginary line K13 drawn from the center O32 of the second arcuate surface 32 to the second corner 52 and the imaginary line K14 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. As a result, when forming the first arcuate surface 31 and the second arcuate surface 32, the shank 91 (see FIG. 10 ) of the cutting tool 90 does not come into contact with the inner circumferential surface 20 of the nut 2.

[0084] According to the above-described first modification, when the top 4A is assembled, the opposing flat surface 48 of the top 4A is positioned so that it abuts against the flat surface 36 of the concave surface 30A. This positions the top 4A so that the opposing flat surface 48 is parallel to the intersecting direction when viewed from the axial direction. This prevents the top 4A from being assembled in a tilted (rotated) state. Furthermore, according to the first modification, the flat surface 36 is provided between the first arcuate surface 31 and the second arcuate surface 32. This means that the bottom surface of the concave surface 30A is not arcuate, making it difficult for the top 4A to rotate. Therefore, according to the first modification, the rotation of the top 4A is more reliably restricted than in the first embodiment. The opposing flat surface 48 may be formed to be the same size as the flat surface 36 or slightly smaller than the flat surface 36. In other words, the present disclosure does not particularly care about the sizes of the opposing flat surface 48 and the flat surface 36.

[0085] (Variation 2) FIG. 12 is an enlarged view of the inner peripheral side of the nut of the ball screw device of Modification 2. As shown in FIG. 12, the nut 2B of Modification 2 differs from Embodiment 1 in that the orientation of the concave surface 30B is changed. The first corner 51B and the second corner 52B of the concave surface 30B intersect with the axial direction. The third corner 53B and the fourth corner 54B extend in the spiral direction. Such a concave surface 30B can be formed when the shank 91 of the cutting tool 90 is inclined with respect to the central axis O2 during the concave surface forming process. Even in Modification 2, as in Embodiment 1, the assembly of the top 4 is easy. Furthermore, the placement of the balls 3 in the thread grooves other than the inner circumferential raceway surface 22 is restricted.

[0086] 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.

[0087] 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. Similarly, 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. Similarly, in the present disclosure, the curvature of the opposing arcuate surface 47 may be slightly smaller than the curvature of the single arcuate surface 35. In other words, the opposing arcuate surfaces of the top 4 (the first opposing arcuate surface 45, the second opposing arcuate surface 46, and the opposing arcuate surface 47) do not have to have the same curvature as the arcuate surfaces of the concave surface 30 (the first arcuate surface 31, the second arcuate surface 32, and the single arcuate surface 35).

[0088] 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.

[0089] Furthermore, although the first protrusion 61 and the second protrusion 62 in the first embodiment extend in the spiral direction, the present disclosure is not particularly limited to the shapes of the first protrusion 61 and the second protrusion 62 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 61 and the second protrusion 62 may extend in the circumferential direction or the transverse direction instead of the spiral direction.

[0090] 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.

[0091] 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).

[0092] 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 peripheral surface of the nut is a concave surface recessed radially outward from the inner circumferential surface and accommodating the piece therein; a first corner portion and a second corner portion that are corner portions where the concave surface and the inner circumferential surface intersect and are spaced apart from each other in the circumferential direction; 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 direction in which the concave surface is arranged as viewed from the central axis of the nut is defined as a block insertion direction, a direction in which the first corner portion is disposed as viewed from the second corner portion is defined as a first intersecting direction; a direction in which the second corner portion is disposed as viewed from the first corner portion is defined as a second intersecting direction; The concave surface is a first arcuate surface extending from the first corner in the piece insertion direction and gradually shifting in the second intersecting direction as the first arcuate surface moves in the piece insertion direction; a second arcuate surface extending from the second corner in the piece insertion direction and gradually shifting in the first intersecting direction as the second arcuate surface moves in the piece insertion direction; and The outer diameter surface of the piece is a first opposing arcuate surface that is arcuate and faces the first arcuate surface; a second opposing arcuate surface that is arcuate and faces the second arcuate surface; a first protrusion protruding from the first opposing arcuate surface and disposed inside the first thread groove surface; A second protrusion protruding from the second opposing arcuate surface and disposed inside the second thread groove surface; and a distance between the other end of the first thread groove surface and the tip of the first protrusion is smaller than a diameter of the ball, The distance between the other end of the second thread groove surface and the tip of the second protrusion is smaller than the diameter of the ball. Ball screw device. (2) an end of the first arcuate surface in the second intersecting direction and an end of the second arcuate surface in the first intersecting direction are connected to each other, The first arcuate surface and the second arcuate surface cooperate with each other to form a single arcuate surface. The ball screw device according to (1). (3) An angle formed by an imaginary line drawn from the center of the single arcuate surface to the first corner and an imaginary line drawn from the center of the single arcuate surface to the second corner is less than 180 degrees. The ball screw device according to (2). (4) the concave surface has a plane disposed between the first arcuate surface and the second arcuate surface, An opposing flat surface facing the flat surface is formed on the outer diameter surface of the piece. The ball screw device according to (1). (5) 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. (4) The ball screw device according to (4). (6) 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 (5). (7) The concave surface is an opening that opens toward the inner peripheral side of the nut; The concave surface is a corner where the concave surface and the inner circumferential surface intersect, and includes 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; and The distance between the first corner and the second corner of the opening is greater than the distance between the third corner and the fourth corner. A ball screw device according to any one of (1) to (6). (8) 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 (5). (9) 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 (8). (10) 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 spiral direction. A ball screw device according to any one of (1) to (8). [Explanation of symbols]

[0093] 1 Screw shaft 2, 2A, 2B nuts 3 Ball 4 frames 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, 30B concave 31 First circular arc surface 32 Second circular arc surface 33 First aspect 34 Second aspect 35 Single arc surface 36 plane 41 S-shaped groove surface 42 First opposing surface 43 Second opposing surface 44, 44A outer diameter surface 45 First opposing arc surface 46 Second opposing arc surface 47 Opposite arc surfaces 48 Opposite planes 50 Corner 51, 51B 1st corner 52, 52B Second corner 53, 53B 3rd corner 54, 54B 4th corner 55 Opening 61 1st protrusion 62 2nd protrusion 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 peripheral surface of the nut is a concave surface recessed radially outward from the inner circumferential surface and accommodating the piece therein; a first corner portion and a second corner portion that are corner portions where the concave surface and the inner circumferential surface intersect and are spaced apart from each other in the circumferential direction; 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 direction in which the concave surface is arranged as viewed from the central axis of the nut is defined as a block insertion direction, a direction in which the first corner portion is disposed as viewed from the second corner portion is defined as a first intersecting direction; a direction in which the second corner portion is disposed as viewed from the first corner portion is defined as a second intersecting direction; The concave surface is a first arcuate surface extending from the first corner in the piece insertion direction and gradually shifting in the second intersecting direction as the first arcuate surface moves in the piece insertion direction; a second arcuate surface extending from the second corner in the piece insertion direction and gradually shifting in the first intersecting direction as the second corner moves in the piece insertion direction; and The outer diameter surface of the piece is a first opposing arcuate surface that is arcuate and faces the first arcuate surface; a second opposing arcuate surface that is arcuate and faces the second arcuate surface; a first protrusion protruding from the first opposing arcuate surface and disposed inside the first thread groove surface; a second protrusion protruding from the second opposing arcuate surface and disposed inside the second thread groove surface; and a distance between the other end of the first thread groove surface and the tip of the first protrusion is smaller than a diameter of the ball, The distance between the other end of the second thread groove surface and the tip of the second protrusion is smaller than the diameter of the ball. Ball screw device.

2. an end of the first arcuate surface in the second intersecting direction and an end of the second arcuate surface in the first intersecting direction are connected to each other, The first arcuate surface and the second arcuate surface cooperate with each other to form a single arcuate surface. The ball screw device according to claim 1 .

3. An angle formed by an imaginary line drawn from the center of the single arcuate surface to the first corner and an imaginary line drawn from the center of the single arcuate surface to the second corner is less than 180 degrees. The ball screw device according to claim 2 .

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

5. 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 4.

6. 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 claim 1 .

7. The concave surface is an opening that opens toward the inner peripheral side of the nut; a third corner portion and a fourth corner portion which are corner portions where the concave surface and the inner circumferential surface intersect and are spaced apart from each other in an axial direction parallel to the central axis of the nut; and The distance between the first corner and the second corner of the opening is greater than the distance between the third corner and the fourth corner. The ball screw device according to claim 1 .

8. 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 claim 1 .

9. 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 8.

10. 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 spiral direction. The ball screw device according to any one of claims 1 to 8.

Images