Ball screw device

Abstract

To provide a ball screw device that suppresses rotation of a slider while improving the mountability of the slider.SOLUTION: A ball screw device comprises a screw shaft, a nut, a plurality of balls, and one or more sliders. A recessed surface is formed on an inner circumferential surface which is recessed radially outward from the inner circumferential surface and in which the slider is stored. The slider has an inner diameter surface facing radially inward, an outer diameter surface facing radially outward, and an S-shaped groove surface recessed radially outward from the inner diameter surface and extending from one circumferential end of the inner diameter surface to the other end. The recessed surface has a bottom surface that comes into contact with the outer diameter surface. The outer diameter surface and the bottom surface are each formed at least partially in an arc shape when viewed in an axial direction parallel to the screw shaft. A central part in the circumferential direction of the inner diameter surface serves as a support surface that is arcuate or planar when viewed in the axial direction. A pair of contact parts positioned radially inward of the support surface are formed at the circumferential one end and other end of the inner diameter surface.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] A ball screw device is a device that converts rotational motion into linear motion and linear motion into rotational motion. The ball screw device includes a screw shaft, a nut inserted into the screw shaft, a plurality of balls arranged between the screw shaft and the nut, and a circulation unit that circulates the balls. An example of the circulation unit is a ball that returns the balls by approximately one lead. In Patent Document 1 listed below, a concave surface is formed on the inner peripheral surface of the nut, and a ball is housed inside the concave surface. [Prior art documents] [Patent documents]

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

[0004] The top has an outer diameter surface facing radially outward. This outer diameter surface faces the bottom surface of the concave surface. The outer diameter surface and the bottom surface of Patent Document 1 are formed in an arc shape when viewed from the axial direction. Therefore, there is a possibility that the top will rotate inside the concave surface.

[0005] Furthermore, the top is attached to the concave surface by supporting it with fingers against the inner diameter surface of the top and inserting the top into the concave surface. Note that, in addition to fingers, a jig or the like may be placed against the inner diameter surface of the top to support it. Hereinafter, anything that is placed against the inner diameter surface of the top to support it will be collectively referred to as fingers or the like. However, the inner diameter surface of the top in Patent Document 1 has a protrusion that is integrated with the tongue. This makes it difficult to support the top with fingers or the like, impairing the attachability of the top.

[0006] The present disclosure has been made in view of the above, and aims to provide a ball screw device that suppresses rotation of the top and improves the mountability of the top. [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 into the screw shaft, a plurality of balls arranged between the screw shaft and the nut, and at least one bearing for circulating the balls. The inner peripheral surface of the nut is formed with a concave surface recessed radially outward from the inner peripheral surface of the nut, and the bearing is housed therein. The bearing has an inner diameter surface facing radially inward, an outer diameter surface facing radially outward, and an S-shaped groove surface recessed radially outward from the inner diameter surface and extending from one circumferential end of the inner diameter surface to the other. The concave surface has a bottom surface that abuts the outer diameter surface. At least a portion of the outer diameter surface and the bottom surface are formed in an arc shape when viewed from an axial direction parallel to the screw shaft. A circumferential central portion of the inner diameter surface forms a support surface that is arc-shaped or flat when viewed from the axial direction. A pair of contact portions are formed at one end and the other end in the circumferential direction of the inner diameter surface, and are positioned radially inward of the support surface.

[0008] In the top (concave surface) of the present disclosure, at least a portion of the outer diameter surface (bottom surface) is formed in an arc shape. Therefore, the top easily rotates inside the concave surface. If a load that rotates the top is applied, one of the pair of contact portions comes into contact with the screw shaft. Therefore, the rotation of the top is restricted. In addition, the circumferential center portion (support surface) of the inner diameter surface of the top is formed in an arc shape or flat shape and does not have any protrusions. Therefore, it is easy to support the top by placing fingers or the like on the support surface, improving the mountability of the top to the concave surface.

[0009] Furthermore, with regard to the ball screw device described above, the direction in which the concave surface is disposed as viewed from the central axis of the screw shaft is defined as a block insertion direction. As viewed from the axial direction, a virtual circle having its center at a point disposed in the block insertion direction from the central axis of the screw shaft is defined as an eccentric virtual circle. As viewed from the axial direction, the inner diameter surface overlaps with the eccentric virtual circle from one end to the other end in the circumferential direction. The inner diameter surface is positioned radially inward as it approaches one end or the other end from the center in the circumferential direction. The one end and the other end in the circumferential direction of the inner diameter surface may form a pair of the contact portions.

[0010] Furthermore, with regard to the ball screw device, when viewed from the axial direction, a virtual circle centered on the central axis of the screw shaft is defined as a coaxial virtual circle. The inner diameter surface overlaps the coaxial virtual circle from one end to the other end in the circumferential direction when viewed from the axial direction. A pair of protrusions protruding radially inward from the inner diameter surface are formed at one end and the other end in the circumferential direction of the inner diameter surface. The pair of protrusions may serve as a pair of the contact portions.

[0011] Furthermore, with regard to the ball screw device described above, the direction in which the concave surface is disposed as viewed from the central axis of the screw shaft is defined as a block insertion direction. As viewed from the axial direction, an imaginary circle having its center at a point disposed in the block insertion direction from the central axis of the screw shaft is defined as an eccentric imaginary circle. As viewed from the axial direction, an imaginary circle having its center at the central axis of the screw shaft is defined as a coaxial imaginary circle. The eccentric imaginary circle and the coaxial imaginary circle have two intersections. As viewed from the axial direction, the support surface extends between the two intersections along the eccentric imaginary circle. One end and the other end in the circumferential direction of the inner diameter surface extend from the intersections along the coaxial imaginary circle as viewed from the axial direction. One end and the other end in the circumferential direction of the inner diameter surface may form a pair of the contact portions.

[0012] Furthermore, in the ball screw device described above, the inner diameter surface is formed with a pair of stepped surfaces extending radially inward from both circumferential ends of the support surface. When viewed from the axial direction, a virtual circle centered on the central axis of the screw shaft is defined as a coaxial virtual circle. When viewed from the axial direction, one end and the other end of the inner diameter surface in the circumferential direction extend along the coaxial virtual circle. The one end and the other end of the inner diameter surface in the circumferential direction may form a pair of the contact portions.

[0013] Furthermore, in the ball screw device, the bottom surface and the outer diameter surface form a single arc surface when viewed from the axial direction.

[0014] According to this configuration, a single arcuate surface (bottom surface) can be 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 a crosswise direction. This makes it easier to form the concave surface, improving nut productivity. [Effects of the Invention]

[0015] According to the ball screw device of the present disclosure, rotation of the top is suppressed and the mountability of the top is improved. [Brief explanation of the drawings]

[0016] [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 a perspective view of the top of the first embodiment. [Figure 5] FIG. 5 is a diagram showing the state in which the top is attached to the nut of FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8]FIG. 8 is a cross-sectional view of the ball screw device of Modification 1 taken in a direction perpendicular to the central axis, and more specifically, a cross-sectional view taken so as to overlap the contact portion (protrusion). [Figure 9] FIG. 9 is a perspective view of a top of the first modified example. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. [Figure 11] FIG. 11 is a cross-sectional view of the ball screw device of the second modification taken along the first opposing surface and viewed from a first direction. [Figure 12] FIG. 12 is a cross-sectional view of the ball screw device of the third modification taken along the first opposing surface and viewed from a first direction. [Figure 13] FIG. 13 is a cross-sectional view of the nut of the fourth modification taken along a radial direction. DETAILED DESCRIPTION OF THE INVENTION

[0017] The ball screw device of 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.

[0018] (Embodiment 1) Fig. 1 is a cross-sectional view of a ball screw device of embodiment 1 taken along 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). Hereinafter, the direction parallel to the central axis O1 of the screw shaft 1 will be referred to as the axial direction.

[0019] 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 may be used in an electric actuator 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.

[0020] As shown in Fig. 1, the outer peripheral surface 10 of the screw shaft 1 has a circular shape centered on the central axis O1 (see Fig. 6). On the outer peripheral surface 10 of the screw shaft 1, an outer peripheral raceway surface 11 extending in the spiral direction is formed.

[0021] Figure 2 is a cross-sectional view of the nut of embodiment 1 taken in the axial direction. The nut 2 is a cylindrical part. The nut 2 has an annular first end face 5 facing one axial direction and an annular second end face 6 facing the other axial direction. Hereinafter, the axial direction in which the first end face 5 faces will be referred to as the first direction X1, and the axial direction in which the second end face 6 faces will be referred to as the second direction X2.

[0022] The inner peripheral surface 20 and the outer peripheral surface 21 of the nut 2 are formed in a circular shape centered on the central axis O1 (see FIG. 3). The inner peripheral surface 20 is formed with a thread groove surface 22 and three concave surfaces 30.

[0023] The concave surface 30 is recessed radially outward from the inner circumferential surface 20 of the nut 2. The block 4 is housed inside the concave surface 30 (see FIG. 5). In this embodiment, three concave surfaces 30 are formed. Each concave surface 30 has a first opposing surface 31 and a second opposing surface 32 that face each other in the axial direction, and a bottom surface 33 that faces radially inward.

[0024] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. As shown in Fig. 3, the direction in which the concave surface 30 (the piece 4) is arranged as viewed from the central axis O1 is the direction in which the piece 4 is inserted into the concave surface 30, and is hereinafter referred to as the piece insertion direction Z. Furthermore, the direction intersecting (orthogonal to) the piece insertion direction Z as viewed from the axial direction is referred to as the intersecting direction Y.

[0025] The bottom surface 33 is formed in an arc shape when viewed from the axial direction. More specifically, the bottom surface 33 overlaps with an imaginary circle C30 centered at the center O30 when viewed from the axial direction, forming a single arc surface (hereinafter, sometimes referred to as a single arc surface). An imaginary line connecting one end 33a of the bottom surface 33 in the transverse direction to the center O30 is defined as L1. An imaginary line connecting the other end 33b of the bottom surface 33 in the transverse direction to the center O30 is defined as L2. The angle θ1 formed by the imaginary line L1 and the imaginary line L2 is less than 180°. The bottom surface (single arc surface) 33 is formed by moving a rotating cutting tool radially outward from the central axis O1 of the nut 2. In other words, there is no need to move the cutting tool in the transverse direction Y. This facilitates the formation of the concave surface 30, improving the productivity of the nut 2.

[0026] 2, when viewed from the piece insertion direction Z, the first opposing surface 31 and the second opposing surface 32 extend in the intersecting direction Y. The axial width of the concave surface 30 (the distance between the first opposing surface 31 and the second opposing surface 32) is W1.

[0027] The thread groove surface 22 extends in the helical direction and faces the outer peripheral raceway surface 11 (see FIG. 1 ). The thread groove surface 22 is divided into an inner peripheral raceway surface 23 and an outer circuit thread groove surface 24. The inner peripheral raceway surface 23 extends approximately one turn (approximately one lead) in the helical direction. One end 23 a and the other end 23 b of the inner peripheral raceway surface 23 are connected to the same concave surface 30. On the other hand, one end and the other end of the outer circuit thread groove surface 24 are connected to different concave surfaces 30, or one end or the other end opens from the first end face 5 or the second end face 6 of the nut 2.

[0028] As shown in Fig. 1, a raceway is formed between the inner peripheral raceway surface 23 and the outer peripheral raceway surface 11. A plurality of balls 3 are arranged in this raceway. On the other hand, no balls 3 are arranged between the circuit outer thread groove surface 24 and the outer peripheral raceway surface 11. Note that the present disclosure may also be directed to a thread groove surface 22 that is formed only by the inner peripheral raceway surface 23.

[0029] Fig. 4 is a perspective view of the top of the first embodiment. As shown in Fig. 4, the top 4 has a first side surface 41 facing the first direction X1, a second side surface 42 (not shown in Fig. 4; see Fig. 5) facing the second direction X2, an outer diameter surface 43 facing radially outward, and an inner diameter surface 50 facing radially inward (toward the inner periphery of the nut 2). The inner diameter surface 50 has an S-shaped groove surface 51 recessed radially outward from the inner diameter surface 50. Hereinafter, the corner where the inner diameter surface 50 and the S-shaped groove surface 51 intersect will be referred to as a groove shoulder 55.

[0030] 5 is a diagram showing the state in which the top is attached to the nut of FIG. 2. The first side surface 41 faces the first opposing surface 31. The second side surface 42 faces the second opposing surface 32. The axial size of the top 4 (the distance between the first side surface 41 and the second side surface 42) is W2. The size W2 of this top 4 is slightly smaller than the width W1 of the concave surface 30 (see FIG. 2). Therefore, the top 4 fits loosely inside the concave surface 30 and is not fixed.

[0031] The S-shaped groove surface 51 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 51 extends will be referred to as the longitudinal direction. One longitudinal end 51a of the S-shaped groove surface 51 is connected to one end 23a of the inner circumferential raceway surface 23. The other longitudinal end 51b of the S-shaped groove surface 51 is connected to the other end 23b of the inner circumferential raceway surface 23. Therefore, the inner circumferential raceway surface 23 and the S-shaped groove surface 51 cooperate with each other to form an annular groove surface.

[0032] Fig. 6 is a cross-sectional view taken along the line VI-VI in Fig. 5. As shown in Fig. 6, the S-shaped groove surface 51 is positioned radially outward from the one end 51a and the other end 51b toward the central portion 51c in the longitudinal direction. Therefore, when the ball 3 moves along the central portion 51c of the S-shaped groove surface 51, it is positioned at the outermost radial position.

[0033] Furthermore, the S-shaped groove surface 51 is formed so that when the ball 3 moves in the central portion 51c, the ball 3 is located radially outward of the outer circumferential surface 10 of the screw shaft 1. As described above, the ball 3 that enters the S-shaped groove surface 51 from one end of the raceway moves along the S-shaped groove surface 51, gradually moving radially outward and crossing the threads of the screw shaft 1. Thereafter, the ball 3 gradually moves radially inward and circulates to the other end of the raceway.

[0034] The outer diameter surface 43 of the top 4 abuts against the bottom surface 33. The outer diameter surface 43 and the bottom surface 33 have the same shape when viewed in the axial direction. In other words, the outer diameter surface 43 has an arc shape (a single arc surface) when viewed in the axial direction. Therefore, when the ball screw device 100 is in operation, if a load acts on the top 4 from the ball 3 or vibration is transmitted to the top from the nut 2, causing the top 4 to move along the bottom surface 33 (see arrows A1 and A2 in FIG. 6), there is a possibility that the top 4 will rotate inside the concave surface 30.

[0035] The inner diameter surface 50 is formed in an arc shape when viewed from the axial direction. More specifically, the inner diameter surface 50 overlaps with a first imaginary circle C1 when viewed from the axial direction. This first imaginary circle C1 is an imaginary circle (eccentric imaginary circle) centered at a point O50 that is disposed in the link insertion direction Z relative to the central axis O1 of the screw shaft 1. A diameter r1 of the first imaginary circle C1 is smaller than the inner diameter R1 of the nut 2.

[0036] Therefore, the inner diameter surface 50 of this embodiment is positioned radially inward from the circumferential central portion 50a toward the one end portion 50b and the other end portion 50c. Also, the gap S formed between the outer peripheral surface 10 of the screw shaft 1 and the inner diameter surface 50 becomes smaller from the central portion 50a toward the one end portion 50b and the other end portion 50c. The gap S between the one end portion 50b and the other end portion 50c and the outer peripheral surface 10 of the screw shaft 1 is very small.

[0037] 5, the top 4 is formed point-symmetrically about the center O4 of the top 4. Therefore, the top 4 can be attached even when rotated 180° relative to the concave surface 30.

[0038] Next, the effects of the ball screw device 100 of the first embodiment will be described. As shown in Fig. 6, when attaching the top 4 to the concave surface 30, the top 4 is supported by placing a finger 200 near the center 50a of the inner diameter surface 50. Hereinafter, the center 50a of the inner diameter surface 50 will be referred to as the support surface 52. Note that while the present embodiment provides an example in which the finger 200 is placed against the inner diameter surface 50 of the top 4, the present disclosure also provides for the use of a jig or the like.

[0039] If there were protrusions on the support surface 52, the contact area between the support surface 52 and the fingers 200 would be small, and the top 4 would not be able to be stably supported. On the other hand, the support surface 52 of this embodiment is formed in an arc shape when viewed from the axial direction, and has no protrusions. In other words, the contact area between the support surface 52 and the fingers 200 is large, and the top 4 can be stably supported. This improves the attachability of the top 4.

[0040] Furthermore, when a load acts on the top 4 and the top 4 attempts to move in the direction of arrow A1, one end 50b of the inner diameter surface 50 moves radially inward (see arrow B1). Then, the one end 50b of the inner diameter surface 50 comes into contact with the outer peripheral surface 10 of the screw shaft 1. Therefore, the top 4 is restricted from rotating in the counterclockwise direction when viewed from the first direction X1.

[0041] When a load acts on the top 4 and the top 4 attempts to move in the direction of arrow A2, the other end 50c of the inner diameter surface 50 moves radially inward (see arrow B2). Then, the other end 50c of the inner diameter surface 50 comes into contact with the outer peripheral surface 10 of the screw shaft 1. Therefore, the top 4 is restricted from rotating in the clockwise direction when viewed from the first direction X1.

[0042] As described above, in this embodiment, the one end 50b and the other end 50c of the inner diameter surface 50 form a pair of contact portions that restrict the rotation of the top 4.

[0043] Fig. 7 is a cross-sectional view taken along line VII-VII in Fig. 5. The block 4 of this embodiment does not have a tang that scoops up the ball 3 radially outward. Instead, as shown in Fig. 7, the ball 3 is sandwiched between the groove shoulder 55 of the block 4 and the groove shoulder 12 of the screw shaft 1, thereby scooping up the ball 3.

[0044] More specifically, a load F1 acts on the ball 3 from the groove shoulder 55 of the block 4 toward the center O3 of the ball 3, and a load F2 acts on the ball 3 from the groove shoulder 12 of the screw shaft 1 toward the center O3 of the ball 3. The combined load F3, which is the combination of the loads F1 and F2, includes a radially outward load. As a result, the ball 3 moves radially outward.

[0045] The imaginary line shown in Fig. 7 indicates the comparative example of the top 300. When viewed from the axial direction, the inner diameter surface 350 of the comparative example of the top 300 extends along the imaginary circle C300 shown in Fig. 6 and is formed in an arc shape. The imaginary circle C300 is an imaginary circle whose center is the central axis O1 of the screw shaft 1 and is tangent to the circumferential central portion 50a of the inner diameter surface 50 of this embodiment.

[0046] From the above, the distance from the central axis O1 to the circumferential center and both end portions is equal in the inner diameter surface 350 of the comparative example block 300. Therefore, according to the block 4 of this embodiment, one end portion 50b and the other end portion 50c of the inner diameter surface 50 are located radially inward relative to both end portions of the inner diameter surface 350 of the comparative example.

[0047] For this reason, as shown in Figure 7, the groove shoulder 55 of the block 4 of this embodiment is positioned radially inward relative to the groove shoulder 355 of the block 300 of the comparative example. Therefore, the contact angle θ2 between the groove shoulder 55 of the block 4 and the ball 3 is larger than the contact angle θ3 between the groove shoulder 355 of the comparative example and the ball 3. Therefore, the radially outward load component included in the combined load F3 is larger in this embodiment than in the comparative example, and the ball 3 is reliably scooped up.

[0048] As described above, the ball screw device 100 of the first embodiment includes a screw shaft 1, a nut 2 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 rollers 4 for circulating the balls 3. The inner circumferential surface 20 of the nut 2 is formed with a concave surface 30 that is recessed radially outward from the inner circumferential surface 20 of the nut 2 and accommodates the roller 4 therein. The roller 4 has an inner diameter surface 50 facing radially inward, an outer diameter surface 43 facing radially outward, and an S-shaped groove surface 51 that is recessed radially outward from the inner diameter surface 50 and extends from one end 50b to the other end 50c in the circumferential direction of the inner diameter surface 50. The concave surface 30 has a bottom surface 33 that abuts the outer diameter surface 43. The outer diameter surface 43 and the bottom surface 44 are each at least partially arc-shaped when viewed from an axial direction parallel to the screw shaft 1. A central portion 50a in the circumferential direction of the inner diameter surface 50 forms an arc-shaped or flat support surface 52 when viewed from the axial direction. A pair of contact portions located radially inward of the support surface 52 are formed at one end portion 50b and the other end portion 50c in the circumferential direction of the inner diameter surface 50.

[0049] According to the first embodiment, when a load that rotates the top 4 acts on it, one of the pair of contact portions (one end 50b and the other end 50c) comes into contact with the screw shaft 1. This restricts the rotation of the top 4. Furthermore, since no protrusions are formed on the support surface 52, it is easy to support the top 4 by placing a finger or the like on the support surface 52. This improves the ease of attachment of the top 4 to the concave surface 30.

[0050] The above has described embodiment 1. Next, some modifications of embodiment 1 will be described.

[0051] (Variation 1) Fig. 8 is a cross-sectional view of the ball screw device of Modification 1 taken in a direction perpendicular to the central axis, more specifically, a cross-sectional view taken so as to overlap the contact portion (protrusion). Fig. 9 is a perspective view of a top of Modification 1. Fig. 10 is a cross-sectional view taken along line XX in Fig. 8.

[0052] The inner diameter surface 50A of the link 4A of Modification 1 differs from that of Embodiment 1 in that it is formed along a second imaginary circle C2 when viewed in the axial direction. This second imaginary circle C2 is an imaginary circle (a coaxial imaginary circle) centered on the central axis O1 of the screw shaft 1. Therefore, on the inner diameter surface 50A, the circumferential central portion 50a and the circumferential one end portion 50b and the other end portion 50c are equidistant from the central axis O1. In other words, in Modification 1, the one end portion 50b and the other end portion 50c are not disposed radially inward of the central portion 50a (support surface 52).

[0053] 9, a pair of protrusions 60 are formed on the inner diameter surface 50A, protruding radially inward from the inner diameter surface 50A. The protrusions 60 are arranged on one end 50b and the other end 50c of the inner diameter surface 50.

[0054] 10 , the protrusion 60 is disposed radially outward of the outer circumferential raceway surface 11 of the screw shaft 1. The protrusion 60 has a first side surface 61 facing the first direction X1, a second side surface 62 facing the second direction X2, a tip end surface 63 facing radially inward, a first corner portion 64, and a second corner portion 65.

[0055] The first corner 64 is formed at the intersection of the first side surface 61 and the tip surface 63. The second corner 65 is formed at the intersection of the second side surface 62 and the tip surface 63. The axial width W3 of the protrusion 60 (the distance between the first side surface 61 and the second side surface 62) becomes smaller as it approaches the radially inner side.

[0056] Furthermore, the tip end of the protrusion 60 is recessed into the outer circumferential raceway surface 11. That is, the tip end face 63, the first corner 64, and the second corner 65 are recessed into the outer circumferential raceway surface 11. Furthermore, a minute gap (not shown) is formed between the first side surface 61 and the groove shoulder 12. Similarly, a minute gap (not shown) is formed between the second side surface 62 and the groove shoulder 12.

[0057] As described above, according to the top 4A of Modification 1, when a load that rotates the top 4A inside the concave surface 30 acts, the protrusion 60 moves radially inward. Then, the first side surface 61 and the second side surface 62 of the protrusion 60 contact the groove shoulder 12 of the screw shaft 1, restricting the rotation of the top 4A. At this time, the first corner portion 64 and the second corner portion 65 do not contact the outer peripheral raceway surface 11. As described above, in Modification 1, the pair of protrusions 60 constitute a pair of contact portions. Furthermore, according to Modification 1, the protrusion 60 is not disposed at the center portion 50a (support surface 52) of the inner diameter surface 50A. Therefore, as in the first embodiment, it is easy to support the top 4 by placing fingers or the like on the support surface 52, improving the mountability of the top 4 to the concave surface 30.

[0058] (Variation 2) 11 is a view of a ball screw device of Modification 2 cut along the first opposing surface and viewed from a first direction. The inner diameter surface 50B of a link 4B of Modification 2 is the same as that of Embodiment 1 in that a circumferential center portion 50a is formed along a first imaginary circle C1 (eccentric imaginary circle). On the other hand, one end portion 50b and the other end portion 50c of the inner diameter surface 50 are different from those of Embodiment 1 in that they are formed along a third imaginary circle C3.

[0059] The third imaginary circle C3 is a imaginary circle (coaxial imaginary circle) centered on the central axis O1 of the screw shaft. The third imaginary circle C3 intersects with the first imaginary circle C1, and two intersection points P1 and P2 are present. Therefore, the inner diameter surface 50B of the top 4B between the two intersection points P1 and P2 forms the support surface 52. Therefore, in the second modification, the top 4 can be stably supported.

[0060] Furthermore, when a load is applied that rotates the top 4B inside the concave surface 30, one end 50b or the other end 50c of the inner diameter surface 50B moves radially inward. Then, the one end 50b or the other end 50c comes into contact with the outer peripheral surface 10 of the screw shaft 1, restricting the rotation of the top 4B. Therefore, in Modification 2, the one end 50b and the other end 50c form a pair of contact portions.

[0061] The block 4B also differs from the first embodiment in that it has a third side surface 56 and a fourth side surface 57 facing the intersecting direction Y. The third side surface 56 and the fourth side surface 57 are formed in a portion of the block 4B that is located radially inward of the concave surface 30. In other words, the third side surface 56 and the fourth side surface 57 are not contained within the concave surface 30. The third side surface 56 and the fourth side surface 57 are also parallel to the block insertion direction Z and the axial direction. Thus, the present disclosure does not particularly care about the shape of the side surfaces that are not contained within the concave surface 30.

[0062] (Variation 3) 12 is a cross-sectional view of a ball screw device of Modification 3 taken along the first opposing surface, viewed from a first direction. As shown in FIG. 12, a top 4C of Modification 3 differs from Embodiment 1 in that, when viewed from the axial direction, a circumferential center portion 50a (support surface 52) of an inner diameter surface 50C is a flat surface parallel to the transverse direction Y. Even in this top 4C, no protrusions are formed on the support surface 52. This makes it easy to support the top 4 by placing fingers or the like on the support surface 52, improving the ease of attachment of the top 4 to the recessed surface 30.

[0063] Furthermore, the inner diameter surface 50C of Modification 3 is formed with a first step surface 58 and a second step surface 59 extending radially inward from both ends of the support surface 52 in the circumferential direction (transverse direction Y). Therefore, one end 50b and the other end 50c of the inner diameter surface 50C are positioned radially inward of the support surface 52 and form a pair of contact portions. Furthermore, the one end 50b and the other end 50c of the inner diameter surface 50C overlap with the third imaginary circle C3 described in Modification 2. Therefore, in Modification 3, when a load is applied that rotates the top 4C inside the concave surface 30, the one end 50b or the other end 50c moves radially inward. Then, the one end 50b or the other end 50c comes into contact with the outer circumferential surface 10 of the screw shaft 1, restricting the rotation of the top 4C.

[0064] Although the first embodiment and the various modifications have been described above, the present disclosure is not limited to the above examples. For example, in the third modification, the support surface 52 of the frame 4C is parallel to the transverse direction Y, but in the present disclosure, the support surface 52 may be formed in an arc shape.

[0065] Furthermore, in the embodiments and the like, the bottom surface 33 and the outer diameter surface 43 are formed in an arc shape, but the present disclosure is not limited thereto. FIG. 13 is a schematic diagram of a nut of Modification Example 4 cut in the radial direction. As shown in FIG. 13, a flat surface 37 parallel to the intersecting direction Y may be formed in the circumferential center of the bottom surface 33D of the concave surface 30D. Furthermore, an opposing surface 47 opposing the flat surface 37 may also be formed on the opposing outer diameter surface 43. Even with such a shape, there is a possibility that the top 4D may rotate inside the concave surface 30. Therefore, it is necessary to apply the present disclosure and restrict the rotation of the top 4D.

[0066] Furthermore, although the first opposing surface 31 and the second opposing surface 32 in the embodiments and the like extend in the cross direction Y, in the present disclosure they may extend in the spiral direction and are not particularly limited. Furthermore, in the present disclosure, there are no particular limitations on the shapes of the link 4 and the concave surface 30 as viewed from the link insertion direction Z.

[0067] Furthermore, the present disclosure does not place any particular limitations on the material of the link 4. Therefore, the present disclosure may be a link 4 made of resin formed by, for example, injection molding. Alternatively, it may be a metallic link 4 formed by machining such as cutting. Alternatively, it may be a link 4 formed by MIM (Metal Injection Molding). Furthermore, it may be a link 4 manufactured by press working or plastic working, and the link 4 of the present disclosure is not limited in terms of the manufacturing method.

[0068] The present disclosure has been described above, and in this specification, "identical" or "equal" includes not only things that are completely identical, but also things that are considered to be substantially "identical" or "equal" due to tolerances (the range of general manufacturing errors). [Explanation of symbols]

[0069] 1 Screw shaft 2 nuts 3 Ball 4, 4A, 4B, 4C, 4D pieces 11 Outer raceway surface 12 Groove shoulder 20 Inner surface 22 Thread groove surface 33 bottom 23 Inner raceway surface 30, 30D concave 43 Outer diameter surface 50, 50A, 50B, 50C inner surface 51 S-shaped groove surface 55 Groove Shoulder 50a central section 50b One end 50c Other end 52 Support surface 56 Third aspect 57 Fourth aspect 58 1st step surface 59 2nd step surface 60 Protrusion 100 Ball screw device

Claims

1. A screw shaft, a nut inserted onto 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 formed with a concave surface that is recessed radially outward from the inner peripheral surface of the nut and accommodates the piece therein, The frame is an inner diameter surface facing radially inward; an outer diameter surface facing radially outward; an S-shaped groove surface recessed radially outward from the inner diameter surface and extending from one end to the other end in the circumferential direction of the inner diameter surface; and the concave surface has a bottom surface that abuts against the outer diameter surface, The outer diameter surface and the bottom surface are each formed with at least a portion having an arc shape when viewed from an axial direction parallel to the screw shaft, a circumferential center portion of the inner diameter surface forms an arc-shaped or planar support surface when viewed from the axial direction, A pair of contact portions are formed at one end and the other end in the circumferential direction of the inner diameter surface, and are positioned radially inward of the support surface. Ball screw device.

2. The direction in which the concave surface is arranged as viewed from the center axis of the screw shaft is defined as a block insertion direction, When viewed from the axial direction, a virtual circle having a center at a point disposed in the inserting direction from the central axis of the screw shaft is defined as an eccentric virtual circle, the inner diameter surface overlaps with the eccentric virtual circle from one end to the other end in the circumferential direction when viewed from the axial direction, the inner diameter surface is positioned radially inward from the central portion in the circumferential direction toward one end or the other end, One end and the other end in the circumferential direction of the inner diameter surface form a pair of the contact portions. The ball screw device according to claim 1 .

3. When viewed from the axial direction, a virtual circle centered on the central axis of the screw shaft is defined as a coaxial virtual circle, the inner diameter surface overlaps with the coaxial virtual circle from one end to the other end in the circumferential direction when viewed from the axial direction, a pair of protrusions protruding radially inward from the inner diameter surface are formed at one end and the other end in the circumferential direction of the inner diameter surface, The pair of protrusions constitutes the pair of contact portions. The ball screw device according to claim 1 .

4. The direction in which the concave surface is arranged as viewed from the center axis of the screw shaft is defined as a block insertion direction, When viewed from the axial direction, a virtual circle having a center at a point disposed in the inserting direction from the central axis of the screw shaft is defined as an eccentric virtual circle, When viewed from the axial direction, a virtual circle centered on the central axis of the screw shaft is defined as a coaxial virtual circle, the eccentric virtual circle and the coaxial virtual circle have two intersection points, the support surface extends between the two intersection points along the eccentric virtual circle when viewed from the axial direction, one end and the other end in the circumferential direction of the inner diameter surface extend from the intersection point along the coaxial virtual circle when viewed in the axial direction, One end and the other end in the circumferential direction of the inner diameter surface form a pair of the contact portions. The ball screw device according to claim 1 .

5. A pair of stepped surfaces extending radially inward from both circumferential ends of the support surface are formed on the inner diameter surface, When viewed from the axial direction, a virtual circle centered on the central axis of the screw shaft is defined as a coaxial virtual circle, one end and the other end in the circumferential direction of the inner diameter surface extend along the coaxial virtual circle when viewed in the axial direction, One end and the other end in the circumferential direction of the inner diameter surface form a pair of the contact portions. The ball screw device according to claim 1 .

6. When viewed from the axial direction, the bottom surface and the outer diameter surface form a single arc surface. The ball screw device according to any one of claims 1 to 5.

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