Ball screw device

Abstract

A ball screw device according to the present disclosure comprises a nut, a screw shank, a plurality of balls, and at least one piece. The outer circumferential surface of the screw shank is provided with at least one recess that is recessed radially inward and that accommodates the piece therein. The recess has a first bottom surface that faces radially outward. At least a portion of the first bottom surface is formed to be a flat surface. The piece has: a second bottom surface that abuts the first bottom surface; a circulation groove surface which is recessed radially outward from the second bottom surface and which forms an internal space that constitutes a circulation path; a bottom opening that opens the circulation path radially inward; a pair of piece-side openings that open the circulation path in the circumferential direction and that connect the circulation path and a raceway; and a pair of tongues that guides, radially inward, the balls that have entered the circulation path from the raceway. In the first bottom surface, a portion that closes the bottom opening serves as a rolling surface for the balls that move along the circulation path.

Description

Ball screw device

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

[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 raceway surface is formed on the inner peripheral surface of the nut. An outer peripheral raceway surface that faces the inner peripheral raceway surface is formed on the outer peripheral surface of the screw shaft. A spiral track is formed between the inner peripheral raceway surface and the outer peripheral raceway surface. The 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. One example of the circulating part is a top that returns the balls by one lead.

[0003] In the ball screw device disclosed in the following patent document, a recess recessed radially inward is formed on the outer peripheral surface of the screw shaft. A bearing is inserted into the recess and attached to the screw shaft. The bearing has an outer diameter surface facing radially outward and a circulation groove surface recessed radially inward from the outer diameter surface. The circulation groove surface is S-shaped when viewed from the radial outside. Balls move radially inward within the circulation groove surface of the bearing and ride over the threads of the nut.

[0004] Japanese Patent Application Laid-Open No. 2004-225770

[0005] According to the above-mentioned patent document, when the balls move radially inward, they may become pinched between the circulation groove surface and the inner raceway surface of the nut. This prevents the balls from rolling smoothly. Furthermore, if the balls become pinched, the groove shoulder of the circulation groove surface may be damaged.

[0006] The present disclosure has been made in view of the above, and aims to provide a ball screw device that allows balls to roll smoothly and prevents damage to the bearings.

[0007] To achieve the above object, a ball screw device according to one aspect of the present disclosure includes a nut having an inner circumferential raceway surface on its inner circumferential surface, a screw shaft penetrating the nut and having an outer circumferential raceway surface on its outer circumferential surface, a plurality of balls arranged in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface, and at least one or more rollers for circulating the balls. The outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the rollers. The recess has a first bottom surface facing radially outward. At least a portion of the first bottom surface is flat. The roller has a second bottom surface abutting the first bottom surface, a circulation groove surface recessed radially outward from the second bottom surface and whose internal space forms a circulation path, a bottom opening that opens the circulation path radially inward, a pair of roller-side openings that open the circulation path circumferentially and connect the circulation path to the raceway, and a pair of tangs that guide the balls that enter the circulation path from the raceway radially inward. The portion of the first bottom surface that closes the bottom opening serves as a rolling surface for the balls that move through the circulation path.

[0008] According to the ball screw device of the present disclosure, the balls are guided radially inward by the tang. This prevents the balls from becoming pinched between the circulation groove surface and the inner circumferential raceway surface. This means that the balls roll smoothly, and damage to the groove shoulder of the circulation groove surface is also avoided. Furthermore, the depth of the recess can be measured using the plane of the first bottom surface of the recess as a reference plane, making it easy to manage the dimensions of the recess. Furthermore, the circulation path of the bearing is open radially inward. This means that when manufacturing the bearing using a mold, the mold that forms the circulation path (circulation groove surface) can be moved radially inward (demolded). This makes it easier to manufacture bearings than when the radially inner side of the circulation path is blocked.

[0009] In a preferred embodiment of the ball screw device, the first bottom surface is entirely flat.

[0010] According to the above configuration, the entire first bottom surface is flat, making it easy to form the first bottom surface. Furthermore, when viewed from the axial direction, the circulation path is linear, allowing the balls to roll smoothly. Furthermore, when the balls enter the circulation path from the orbit, they change course radially inward from the extension of the orbit. In other words, the balls' course bends radially inward from the orbit. If the first bottom surface were concave, the bending angle of the balls' course would be large. On the other hand, according to the present disclosure, the first bottom surface is flat, making the bending angle of the balls' course small. Therefore, the balls move (roll) smoothly between the outer circumferential orbit surface and the circulation path.

[0011] In a preferred embodiment of the ball screw device, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft when viewed from the axial direction. A concave surface recessed radially inward is provided at a central portion of the first bottom surface in the intersecting direction. Flat surfaces are provided on both sides of the concave surface in the intersecting direction.

[0012] The end of the first bottom surface in the intersecting direction is flat, and the bending angle of the ball path is small. Therefore, even with this configuration, the balls move (roll) smoothly between the outer circumferential raceway surface and the circulation path. Furthermore, a concave surface is provided in the center of the first bottom surface in the intersecting direction. Therefore, both ends (flat surfaces) of the first bottom surface in the intersecting direction are positioned radially outward compared to when the entire first bottom surface is flat. As a result, the area of ​​the outer circumferential raceway surface cut out by the concave portions is smaller, and the load capacity of the ball screw device is improved.

[0013] In a preferred embodiment of the ball screw device, the tongue is provided with a rib that protrudes radially outward.

[0014] According to the above configuration, the strength of the tongue is improved by the rib.

[0015] In a preferred embodiment of the ball screw device, the recess has an annular inner peripheral surface surrounding the periphery of the top, and the inner peripheral surface has a pair of side surfaces sandwiching the top from both sides in a direction intersecting an imaginary line extending radially outward from the center of the screw shaft.

[0016] According to this configuration, the piece is sandwiched between the pair of side surfaces, which prevents the piece from moving in the intersecting direction and falling out of the recess.

[0017] In addition, as a preferred embodiment of the ball screw device, the distance from the center of the screw shaft to the thread of the nut is R, the diameter of the ball is Dw, the distance between the portion of the outer diameter surface of the top that faces the thread of the nut and the thread of the nut is 0.2 mm or more and 1.5 mm or less, the thickness from the portion of the outer diameter surface of the top that faces the thread of the nut to the circulation groove surface is 0.3 mm or more and 1.0 mm or less, the radial gap of the circulation path is 0.05 × Dw or more and 0.25 × Dw or less, and the distance h between the first bottom surface and the center of the screw shaft satisfies the following formula (1).

[0018]

[0019] According to the above configuration, the first bottom surface is disposed radially outward, which increases the length of the raceway and improves the load resistance of the ball screw device.

[0020] In a preferred embodiment of the ball screw device, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction that intersects with an imaginary line extending radially outward from the center of the screw shaft. The recess has at least one opening that opens in the intersecting direction. The top is movable in the intersecting direction along the first bottom surface. Alternatively, in a preferred embodiment of the ball screw device, the recess has two openings. The two openings are one opening that opens on one side of the intersecting direction and the other opening that opens on the other side of the intersecting direction.

[0021] According to the above configuration, the top can be attached from the direction crossing the recess. Also, the top can be attached from the radially outer side of the recess. This increases the options for the top attachment direction and improves the top attachment efficiency.

[0022] In addition, in a preferred embodiment of the ball screw device, the recess has a pair of opposing surfaces that face each other in the axial direction. The top has a pair of side surfaces that face the axial direction and face the pair of opposing surfaces. At least one of the pair of opposing surfaces has a groove that is recessed in the axial direction and extends in the intersecting direction. At least one of the pair of side surfaces has a protrusion that protrudes in the axial direction and is accommodated in the groove. Alternatively, in a preferred embodiment of the ball screw device, the groove is formed on both of the pair of opposing surfaces. The protrusion is formed on both of the pair of side surfaces.

[0023] According to this configuration, when a load acts on the top in the radially outward direction, the protrusion gets caught in the groove, thereby restricting the top from moving radially outward.

[0024] In a preferred embodiment of the ball screw device, the recess has a pair of opposing surfaces that face each other in the axial direction, and the top has an interference with the pair of opposing surfaces and is sandwiched between the pair of opposing surfaces.

[0025] According to this configuration, the top is less likely to move radially outward and in the transverse direction, thereby preventing the top from falling out of the recess.

[0026] In a preferred embodiment of the ball screw device, a direction perpendicular to both the axial direction and the transverse direction is defined as an orthogonal direction. Among the orthogonal directions, a direction in which the center of the screw shaft is disposed as viewed from the first bottom surface is defined as a first orthogonal direction. At least one of both end portions of the top in the transverse direction is formed with a crimped portion that protrudes beyond the first bottom surface in the first orthogonal direction.

[0027] According to this configuration, when a load acts on the top in the transverse direction, the protrusion catches on the outer circumferential surface of the screw shaft, thereby restricting movement of the top in the transverse direction.

[0028] In a preferred embodiment of the ball screw device, a direction perpendicular to both the axial direction and the transverse direction is defined as an orthogonal direction. A second orthogonal direction is defined as a direction opposite to a direction in which the center of the screw shaft is disposed as viewed from the first bottom surface. The screw shaft is provided with a crimped portion that is disposed on at least one of both sides of the block in the transverse direction and protrudes beyond the first bottom surface in the second orthogonal direction.

[0029] According to this configuration, when a load acts on the link in the transverse direction, the crimped portion catches on the link in the transverse direction, thereby restricting movement of the link in the transverse direction.

[0030] In a preferred embodiment of the ball screw device, the first bottom surface has one or more holes formed therein, and the second bottom surface has protrusions formed therein that fit into the holes.

[0031] According to this configuration, when a load is applied to the top in the transverse direction, the protrusion is caught in the hole, thereby restricting the top from moving radially outward.

[0032] The ball screw device of the present disclosure ensures smooth rolling of the balls and also prevents damage to the groove shoulder of the circulation groove surface.

[0033] FIG. 1 is a cross-sectional view of a brake caliper according to a first embodiment. FIG. 2 is a perspective view of a bearing and a recess of a ball screw device according to the first embodiment. FIG. 3 is a perspective view of a recess of the first embodiment. FIG. 4 is an enlarged view of the recess and bearing of the first embodiment as viewed from the radial outside. FIG. 5 is a schematic cross-sectional view of the bearing and the screw shaft of the first embodiment taken along the circulation path, specifically a cross-sectional view taken along the arrow V-V in FIG. 4. FIG. 6 is a schematic cross-sectional view of the bearing and the screw shaft of the first embodiment taken along the axial direction, specifically a cross-sectional view taken along the arrow VI-VI in FIG. 4. FIG. 7 is a plan view of the bearing of the first embodiment as viewed from the second bottom surface. FIG. 8 is a schematic cross-sectional view of the ball screw device according to the first embodiment and a comparative example taken along the raceway and the circulation path. FIG. 9 is a plan view of the recess of a ball screw device according to a second embodiment as viewed from the radial direction. FIG. 10 is a cross-sectional view of the ball screw device according to the second embodiment taken along the raceway and the circulation path. FIG. 11 is a cross-sectional view of the top and recess of a ball screw device of embodiment 3, taken in the axial direction and the radial direction. FIG. 12 is a cross-sectional view of the top and recess of a ball screw device of embodiment 4, taken in the axial direction and the radial direction. FIG. 13 is a perspective view of the recess and the top of embodiment 5. FIG. 14 is a perspective view of the recess of the screw shaft of embodiment 5. FIG. 15 is a view of the recess of embodiment 5 viewed from the transverse direction. FIG. 16 is a cross-sectional view taken along the arrow XVI-XVI in FIG. 15. FIG. 17 is a view of the top of embodiment 5 viewed from the second bottom surface. FIG. 18 is a cross-sectional view of the recess and the top of embodiment 5 taken in a direction perpendicular to the axial direction, more specifically, a cross-sectional view of the recess and the top taken along the line XVIII-XVIII in FIG. 15. FIG. 19 is a view of the recess and the top of modification 1 viewed from the transverse direction. FIG. 20 is a perspective view of the recess of the screw shaft of modification 1. FIG. 21 is a view of the recess and the top of modification 2 viewed from the transverse direction. Fig. 22 is a view of the recess and the top of Modified Example 3 as viewed from the intersecting direction. Fig. 23 is a cross-sectional view of the recess and the top of Modified Example 4 taken in a direction perpendicular to the axial direction. Fig. 24 is a view of the top of Modified Example 5 as viewed from the second bottom surface. Fig. 25 is a cross-sectional view of the ball screw device of Modified Example 5 taken in a direction perpendicular to the axial direction. Fig. 26 is a perspective view of the recess of Modified Example 6. Fig. 27 is a view of the top of Modified Example 6 as viewed from the second bottom surface. Fig. 28 is a cross-sectional view taken along line XXVIII-XXVIII in Fig. 26.

[0034] 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.

[0035] (Embodiment 1) Figure 1 is a cross-sectional view of a brake caliper of embodiment 1. As shown in Figure 1, the brake caliper 100 is a device for suppressing the rotational movement of a wheel (not shown) by sandwiching a brake disc 101, which rotates together with the wheel, between two brake pads 102 and 103. The brake caliper 100 includes the brake disc 101, the two brake pads 102 and 103, an electric actuator 104 that actuates the brake pad 102, and a housing 120.

[0036] The electric actuator 104 includes a motor 110 that generates rotational motion and a ball screw device 1 that converts the rotational motion into linear motion. Hereinafter, a direction parallel to the center O1 of the screw shaft 2 of the ball screw device 1 will be referred to as the axial direction. In addition, within the axial direction, the direction in which the brake disc 101 is disposed as viewed from the ball screw device 1 will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2.

[0037] The motor 110 includes a stator 111 fixed to the inner circumferential surface of a housing 120, a rotor 112 arranged on the inner circumferential side of the stator 111, and an output shaft 113 rotatably supported by the housing 120. The stator 111, the rotor 112, and the output shaft 113 are each arranged concentrically around a center O1. The output shaft 113 is fitted to the inner circumferential side of the rotor 112. When power is supplied to the stator 111, a rotating magnetic field is generated, and the rotor 112 and the output shaft 113 rotate around the central axis O. In addition, a recess 114 into which the screw shaft 2 is fitted is formed on the end face of the output shaft 113 in the first direction X1.

[0038] The ball screw device 1 includes a screw shaft 2, a nut 6, balls 4 (not shown in FIG. 1; see FIG. 5), and a plurality of blocks 5.

[0039] The screw shaft 2 includes a connecting portion 10 rotatably supported by a bearing 117, and a screw shaft body 11 disposed in the first direction X1 relative to the connecting portion 10. The end 10a of the connecting portion 10 facing the second direction X2 is fitted into a recess 114. The connecting portion 10 and the output shaft 113 are connected so as not to rotate relative to each other. Therefore, when the output shaft 113 rotates, the screw shaft 2 also rotates. The outer peripheral surface of the screw shaft body 11 is provided with an outer peripheral raceway surface 13 extending in the spiral direction and a plurality of recesses 14 recessed radially inward.

[0040] The nut 6 is formed in a cylindrical shape. The nut 6 is provided with a lid portion 7 that closes an opening of the nut 6 in the first direction X1. The inner peripheral surface of the nut 6 is provided with an inner peripheral raceway surface 6a that faces an outer peripheral raceway surface 13. A spiral raceway 8 is formed between the outer peripheral raceway surface 13 and the inner peripheral raceway surface 6a. A plurality of balls 4 are arranged in this raceway 8.

[0041] The outer peripheral surface of the nut 6 abuts against the support surface 121 of the housing 120. The outer peripheral surface of the nut 6 and the support surface 121 each form a circle centered on the center O1. A small gap is provided between the outer peripheral surface of the nut 6 and the support surface 121. This allows the nut 6 to slide freely in the axial direction relative to the support surface 121. A rotation prevention member (not shown) is provided on the outer peripheral surface of the nut 6. This rotation prevention member prevents the nut 6 from rotating around the center O1.

[0042] The cover portion 7 closes the opening of the nut 6 in the first direction X1. A surface 7a of the cover portion 7 facing the first direction X1 is in contact with the brake pad 102.

[0043] As described above, when the nut 6 moves in the first direction X1 due to rotation of the screw shaft 2, the brake pad 102 moves in the first direction X1. The brake pad 102 presses the brake disc 101 in the first direction X1, and the brake disc 101 comes into contact with the brake pad 103. As a result, the brake disc 101 is sandwiched between the brake pads 102 and 103, and rotation of the wheel (not shown) is restricted.

[0044] The top 5 is a circulation device that returns the balls 4 that have moved one lead along the track 8 by one lead. Furthermore, one top 5 is attached to one recess 14. Note that in the present disclosure, there is no particular restriction on the method of fixing the top 5 to the recess 14. That is, the top 5 may or may not be fixed to the recess 14. Therefore, in the present disclosure, the top 5 may be loosely fitted into the recess 14. Alternatively, the top 5 may be fitted into the recess 14 with an interference. Alternatively, the top 5 may be glued to the recess 14. Alternatively, the top 5 may be fixed to the recess 14 by crimping. In this manner, there is no particular restriction on whether the top 5 is fixed or not.

[0045] In addition, although not shown, when the multiple blocks 5 (multiple recesses 14) are viewed from the axial direction, the multiple blocks 5 are arranged in different directions from the center O1. This allows the load acting on the screw shaft 2 from the nut 6 via the balls 4 to be evenly distributed in the circumferential direction. It is more preferable that the multiple blocks 5 be arranged at equal intervals in the circumferential direction.

[0046] Fig. 2 is a perspective view of the top and recess of the ball screw device of the first embodiment. As shown in Fig. 2, the top 5 is a component having a circulation path 30 formed therein. Examples of materials for forming the top 5 include metal and resin, but the present disclosure is not particularly limited to these. The top 5 has the circulation path 30, a pair of top-side openings 31 (only one of which is shown in Fig. 2) that connect the circulation path 30 to the raceway 8 (the outer peripheral raceway surface 13), and a pair of tongues 40, 40. The recess 14 and the top 5 will be described in detail below.

[0047] Fig. 3 is a perspective view of the recess of embodiment 1. As shown in Fig. 3, a recess 14 is formed by cutting out a portion of the outer circumferential raceway surface 13 of the screw shaft 2 from the radially outer side. The recess 14 has an inner circumferential surface 15 that surrounds the periphery of the link 5 and a first bottom surface 16 that faces radially outward. In the following description, as shown in Fig. 5, an imaginary line that is perpendicular to the first bottom surface 16 and perpendicular to the center O1 will be referred to as an imaginary line K1.

[0048] Figure 4 is an enlarged view of the recess and the block of the first embodiment as viewed from the radially outer side. The imaginary line Z in Figure 4 is a virtual line passing through the center of the groove width of the outer circumferential raceway surface 13 and extends in a spiral direction. Hereinafter, the direction parallel to the imaginary line Z will be referred to as the spiral direction. The imaginary line W in Figure 4 is a virtual line passing through the center of the groove width of the circulation path 30. Hereinafter, the path along the circulation path 30 may be referred to as the length direction of the circulation path 30.

[0049] As shown in FIG. 4 , the recess 14 has a rectangular (quadrilateral) shape when viewed from the radially outward direction. While the recess 14 of the embodiment has a rectangular (quadrilateral) shape when viewed from the radially outward direction, the present disclosure is not limited to the example shown in the embodiment and may have, for example, an oval shape. The inner circumferential surface 15 of the recess 14 has a pair of first opposing surfaces 17, 17 that face each other in the axial direction and a pair of second opposing surfaces 18, 18 that face each other in the intersecting direction Y. As shown in FIG. 5 , the intersecting direction Y is a direction that intersects (is perpendicular to) a virtual line K1 that extends radially outward from a center O1 (not shown in FIG. 5 ) when viewed from the axial direction.

[0050] The first opposing surface 17 is formed by cutting out a part of the thread 13a of the outer circumferential raceway surface 13. Therefore, a thin portion 19 having a small thickness H1 (thickness in a direction perpendicular to the spiral direction) is provided in a part of the thread 13a.

[0051] The first opposing surface 17 extends along the spiral direction. That is, the thickness H1 of the thin portion 19 is uniform throughout the direction in which the thin portion 19 extends (the spiral direction). Therefore, the thin portion 19 of this embodiment has relatively few weak portions, and deformation of the thread 13 a (thin portion 19) is suppressed. Note that the present disclosure is not limited to the example shown in the embodiment, and the first opposing surface 17 may extend in the transverse direction Y.

[0052] The second opposing surface 18 extends in the axial direction when viewed from the radial outside. As shown in Fig. 3, a portion of the second opposing surface 18 is cut out by the outer circumferential raceway surface 13. In other words, the second opposing surface 18 is provided with a screw shaft-side opening 13b. Therefore, the second opposing surface 18 is composed of an end face 13c of the thread 13a located in the axial center of the second opposing surface 18 and partial end faces 13d of the thread 13a located at both axial ends of the second opposing surface 18.

[0053] The end face 13c of the thread 13a has the same cross-sectional shape as the thread 13a. When viewed from the transverse direction Y, the partial end face 13d of the thread 13a has the same shape as one of the two halves obtained by dividing the end face 13c of the thread 13a in the axial direction. As shown in Figure 4, when viewed from the radially outer side, the partial end face 13d of the thread 13a has an arc shape (R-shape).

[0054] 4, the pair of second opposing surfaces 18 are a pair of side surfaces that sandwich the top 5 from both sides in the transverse direction Y. This restricts movement of the top 5 in the transverse direction Y.

[0055] As shown in FIG. 3 , no concave surface or the like is formed on a portion of the first bottom surface 16. In other words, the entire first bottom surface 16 is flat. According to this embodiment, the depth of the recess 14 can be measured using the flat surface (first bottom surface 16) as a reference surface. If the first bottom surface 16 were concave, the depth of the recess 14 would vary depending on the measurement position on the first bottom surface 16, making it difficult to measure the depth of the recess 14. For these reasons, according to this embodiment, the dimensions of the recess 14 can be easily controlled, and the manufacturing of the recess 14 is simplified.

[0056] Fig. 5 is a diagram schematically showing a cross section of the link and screw shaft of embodiment 1 cut along the circulation path, specifically a cross section as seen from the arrow V-V in Fig. 4. Fig. 6 is a diagram schematically showing a cross section of the link and screw shaft of embodiment 1 cut along the axial direction, specifically a cross section as seen from the arrow VI-VI in Fig. 4.

[0057] As shown in Fig. 5 , when viewed from the axial direction, the first bottom surface 16 extends linearly in the transverse direction. As shown in Fig. 6 , when viewed from the transverse direction, the first bottom surface 16 extends linearly in the axial direction. That is, the first bottom surface 16 is a plane extending in both the transverse direction and the axial direction. As shown in Fig. 6 , the first opposing surface 17 is perpendicular to the first bottom surface 16. As shown in Fig. 5 , the second opposing surface 18 (only the partial end surface 13 d is shown in Fig. 5 ) is perpendicular to the first bottom surface 16.

[0058] As shown in Fig. 5, the central portion 16a of the first bottom surface 16 in the transverse direction is closer to the center O1 (not shown in Fig. 5) than both end portions 16b of the first bottom surface 16 in the transverse direction. The depth H2 of both end portions 16b of the first bottom surface 16 in the transverse direction is the same depth as the central portion of the groove width (groove bottom) of the outer peripheral raceway surface 13. Therefore, as shown in Fig. 3, the first bottom surface 16 is connected to the central portion of the groove width (groove bottom) of the outer peripheral raceway surface 13 without any step.

[0059] As shown in Figure 4, the top 5 is formed symmetrically with respect to the center C (see Figure 4). The top 5 has an outer peripheral surface 24 that is annular with the center C as the center. The outer peripheral surface 24 has a pair of first side surfaces 25, 25 that face the pair of first opposing surfaces 17, 17, and a pair of second side surfaces 26, 26 that face the pair of second opposing surfaces 18, 18.

[0060] The circulation path 30 of the block 5 is formed in an S-shape when viewed from the radially outer side. When the ball 4 moves through this circulation path 30, it returns one lead. Note that although the circulation path 30 in the embodiment is S-shaped when viewed from the radially outer side, in the present disclosure, it may be a straight line connecting the screw shaft side openings 13b, and is not particularly limited thereto. A block side opening 31 is provided on the second side surface 26. As a result, the ball 4 rolling on the outer circumferential raceway surface 13 of the screw shaft 2 enters the circulation path 30 of the block 5 through the block side opening 31.

[0061] As shown in Figure 2, the top 5 has an outer diameter surface 41 facing radially outward. This outer diameter surface 41 has two protrusions 42. The protrusions 42 extend in a spiral direction. The two protrusions 42 are spaced apart from each other in the axial direction. Therefore, a groove surface 43 is provided between the two protrusions 42, recessed radially inward and extending in the spiral direction.

[0062] As shown in Figure 6, the cross section of the protrusion 42 is semicircular. The protrusion 42 is housed inside the inner circumferential raceway surface 6a of the nut 6. The protrusion 42 and the inner circumferential raceway surface 6a are spaced apart. The thread 6b of the nut 6 is housed inside the groove surface 43. The groove surface 43 and the thread 6b are spaced apart. As described above, the nut 6 and the block 5 do not interfere with each other.

[0063] 2, the tongue 40 protrudes in a spiral direction from the protruding portion 42. The width H3 of the tongue 40 (see FIG. 7) gradually decreases toward the tip 40a of the tongue 40, forming a tapered shape.

[0064] As shown in Figure 5, the tongue 40 is housed inside the inner circumferential raceway surface 6a of the nut 6. The tongue 40 is spaced apart from the inner circumferential raceway surface 6a of the nut 6 so as not to come into contact with it. The tip end portion 40a is located radially outward of an imaginary curve M connecting the centers O4 of the balls 4 rolling on the raceway 8. Furthermore, in this embodiment, the step amount H4 between the groove bottom of the inner circumferential raceway surface 6a and the tip end portion 40a is small.

[0065] With the tongue 40 described above, the ball 4 entering the circulation path 30 from the top-side opening 31 comes into contact with the tip 40a of the tongue 40. Furthermore, the tip 40a of the tongue 40 comes into contact with a portion of the ball 4 that is radially outward from the center O4 of the ball 4 (see ball 4A among the multiple balls 4 shown in FIG. 5 ). Therefore, a radially inward load acts on the ball 4. As a result, the path of the ball 4 is radially inward from the track 8 (spiral direction), and the ball 4 smoothly enters the circulation path 30. Furthermore, because the step amount H4 of the tip 40a is small, the ball 4 moves smoothly without getting caught when it comes into contact with the tip 40a.

[0066] The top 5 has a second bottom surface 50 facing radially inward. The second bottom surface 50 abuts against the first bottom surface 16 of the recess 14. The second bottom surface 50 extends linearly in the transverse direction Y. As shown in Fig. 6 , the second bottom surface 50 extends linearly in the axial direction when viewed from the transverse direction Y. In other words, the second bottom surface 50 is a plane extending in the transverse direction Y and the axial direction.

[0067] FIG. 7 is a plan view of the top of the embodiment, viewed from the second bottom surface. As shown in FIG. 7 , the second bottom surface 50 has a circulation groove surface 51 recessed radially outward from the second bottom surface 50. The internal space of the circulation groove surface 51 forms the circulation path 30. As shown in FIG. 6 , the cross section of the circulation groove surface 51 cut in the groove width direction has a U-shape. That is, the second bottom surface 50 has a bottom opening 53 that opens the circulation path 30 radially inward. This allows the mold that forms the circulation path 30 (circulation groove surface 51) to be moved radially inward (demolded) when manufacturing the top 5. This makes it easier to manufacture the top 5 than when the radially inner side of the circulation path 30 is blocked.

[0068] 5 and 6, the bottom opening 53 is closed by the first bottom surface 16 of the recess 14. Therefore, as shown in Fig. 3, the portion of the first bottom surface 16 that closes the bottom opening 53 (see the portion between two imaginary lines K54 in Fig. 3) serves as the rolling surface 54 on which the balls 4 moving through the circulation path 30 roll. As described above, the balls 4 moving through the circulation path 30 are surrounded by the circulation groove surface 51 and the rolling surface 54 and do not come into contact with the threads 6b of the nut 6.

[0069] 5, the depth H5 of the circulation groove surface 51 from the second bottom surface 50 (first bottom surface 16) is constant along the length of the circulation path 30. In other words, the groove bottom of the circulation groove surface 51 is parallel to the first bottom surface 16 when viewed from the axial direction. Therefore, when viewed from the axial direction, the circulation path 30 is linear in the transverse direction Y. This allows the balls 4 to move smoothly.

[0070] Next, the effects of the ball screw device 1 of the first embodiment will be described with reference to FIG. 8 . FIG. 8 is a schematic diagram illustrating cross sections of the ball screw device of the first embodiment and a comparative example taken along the raceway and the circulation path. Also, the imaginary line K10 shown in FIG. 8 is a curve connecting the centers of the balls 4 rolling on the raceway 8 (outer circumferential raceway surface 13). The imaginary line K11 shown in FIG. 8 is a line connecting the centers of the balls 4 rolling on the circulation path 30 (first bottom surface 16). Point K12 is the intersection of the imaginary line K10 and the imaginary line K11. The imaginary line K13 is a tangent to the imaginary line K10 that passes through point K12.

[0071] The effects of the first embodiment will be described in comparison with a comparative example. As shown in FIG. 8, the ball screw device of the comparative example differs from the first embodiment in that the bottom surface 1016 is concave when viewed from the axial direction. Also, the imaginary line K1011 shown in FIG. 8 is a line connecting the centers of the balls 4 rolling in the circulation path (bottom surface 1016). Point K1012 is the intersection of the imaginary line K10 and the imaginary line K1011. The imaginary line K1013 is a tangent to the imaginary line K10 that passes through point K1012. The imaginary line K1014 is a tangent to the imaginary line K1011 that passes through point K1012.

[0072] According to the first embodiment, the ball 4 that enters the circulation path 30 from the raceway 8 comes into contact with the tongue 40 (not shown in FIG. 8 ; see FIG. 5 ). As a result, the ball 4 changes course radially inward from the tongue 40 and enters the circulation path 30. Here, when viewed from the axial direction, the trajectory (see imaginary line K10) of the ball 4 moving on the raceway 8 (outer peripheral raceway surface 13) is arc-shaped. When the ball 4 comes into contact with the tongue 40, the course of the ball 4 bends radially inward from the imaginary line K10. The bending angle of this course of the ball 4 is θ11.

[0073] On the other hand, in the comparative example, the bending angle at which the balls 4 enter the circulation path (bottom surface 1016) from the raceway 8 (outer peripheral raceway surface 13) is θ1011. The bending angle θ1011 in the comparative example is larger than the bending angle θ11 in this embodiment. This is because, in the comparative example, both end portions 1016b of the bottom surface 1016 in the intersecting direction are recessed radially inward. From the above, in this embodiment, the bending angle θ11 is small, so that the movement of the balls 4 between the raceway 8 and the circulation path 30 is smooth.

[0074] As described above, the ball screw device 1 of the first embodiment includes the nut 6 having an inner peripheral raceway surface 6a on its inner peripheral surface, the screw shaft 2 that penetrates the nut 6 and has an outer peripheral raceway surface 13 on its outer peripheral surface, a plurality of balls 4 arranged in a raceway 8 between the outer peripheral raceway surface 13 and the inner peripheral raceway surface 6a, and at least one or more rollers 5 that circulate the balls 4. The outer peripheral surface of the screw shaft 2 is provided with at least one recess 14 that is recessed radially inward and that accommodates the rollers 5. The recess 14 has a first bottom surface 16 that faces radially outward. At least a portion of the first bottom surface 16 is flat. The top 5 has a second bottom surface 50 that abuts against the first bottom surface 16, a circulation groove surface 51 that is recessed radially outward from the second bottom surface 50 and whose internal space constitutes the circulation path 30, a bottom opening 53 that opens the circulation path 30 radially inward, a pair of top-side openings 31 that open the circulation path 30 in the circumferential direction and connect the circulation path 30 to the raceway 8, and a pair of tangs 40 that guide the balls 4 that enter the circulation path 30 from the raceway 8 radially inward. The portion of the first bottom surface 16 that closes the bottom opening 53 serves as a rolling surface 54 for the balls 4 that move through the circulation path 30.

[0075] According to the first embodiment, the balls 4 are reliably guided radially inward by the tangs 40. This prevents the balls 4 from being pinched between the circulation groove surface 51 and the inner circumferential raceway surface 6a. This allows the balls 4 to roll smoothly, and prevents damage to the groove shoulder of the circulation groove surface 51. Furthermore, the dimensions can be controlled using the flat first bottom surface 16 as a reference surface, making it easier to manufacture the recesses 14. Furthermore, because the circulation path 30 of the link 5 opens radially inward, the link 5 can be easily manufactured using a mold.

[0076] In the first embodiment, the entire first bottom surface 16 is flat.

[0077] According to the first embodiment, it is easy to form the first bottom surface 16. Furthermore, the bending angle of the path of the ball 4 when it enters the circulation path 30 is small. Therefore, the ball 4 moves smoothly between the track 8 and the circulation path 30.

[0078] In addition, in the ball screw device 1 of Embodiment 1, when viewed from the axial direction, the first bottom surface 16 extends in a transverse direction Y that intersects with an imaginary line K1 that extends radially outward from the center O1 of the screw shaft 2. The recess 14 has an annular inner peripheral surface 15 that surrounds the periphery of the top 5. The inner peripheral surface 15 has a pair of side surfaces (second opposing surfaces 18) that sandwich the top 5 from both sides in the transverse direction Y.

[0079] According to the first embodiment, it is possible to prevent the top 5 from moving in the transverse direction Y and falling off the recess 14 .

[0080] Next, a ball screw device according to another embodiment will be described. Note that the following description will focus on changes from the first embodiment.

[0081] (Embodiment 2) Fig. 9 is a plan view of the recess of a ball screw device of embodiment 2 as viewed from the radial direction. Fig. 10 is a cross-sectional view of the ball screw device of embodiment 2 cut along the raceway and the circulation path. Note that the imaginary line K16 in Fig. 10 is the first bottom surface 16 of embodiment 1. The imaginary line K51 is the circulation groove surface 51 of embodiment 1. Therefore, the area between the imaginary line K16 and the imaginary line K51 is the circulation path 30 of embodiment 1.

[0082] 9, the ball screw device 1A of the second embodiment differs from the ball screw device 1 of the first embodiment in that the recess 14 of the screw shaft 2 is a first bottom surface 16A instead of the first bottom surface 16. The first bottom surface 16A has a concave surface 201 located in a central portion 16a in the transverse direction Y and two flat surfaces 202 located on both sides of the concave surface 201 in the transverse direction Y.

[0083] 10 , the concave surface 201 is formed in an arc shape when viewed from the axial direction, and is recessed radially inward as it approaches the central portion 16 a in the transverse direction. The central portion of the concave surface 201 is in contact with the imaginary line K16. That is, the distance from the center O1 (not shown in FIG. 10 ) of the central portion 16 a of the concave surface 201 in the transverse direction is the same as that of the first bottom surface 16 in the first embodiment.

[0084] The second embodiment of the block 5A also differs from the first embodiment of the block 5 in that a convex portion 251 that protrudes radially outward is provided at the longitudinal center of the circulation groove surface 51A. Therefore, the circulation groove surface 51A has a shape corresponding to the first bottom surface 16A. Furthermore, the flat surface 202 extends in the axial direction and the transverse direction, similar to the first bottom surface 16 of the first embodiment.

[0085] As described above, according to the second embodiment, the circulation path 30A is not linear, but is a path in which the central portion in the longitudinal direction is sunken radially inward. In other words, the plane 202 of the first bottom surface 16A is disposed radially outward from the first bottom surface 16 (see imaginary line K16) of the first embodiment. Therefore, the length of the outer circumferential raceway surface 13 is longer by L (see FIG. 10 ) than in the first embodiment, improving the load-bearing capacity of the ball screw device 1A.

[0086] In addition, flat surfaces 202 are disposed on both ends of the first bottom surface 16A in the intersecting direction. Therefore, the bending angle when the balls 4 enter the circulation path 30A from the track 8 is smaller in the second embodiment than in the case where the entire first bottom surface 16 is concave, as in the first embodiment. Therefore, in the second embodiment as well, the balls 4 move smoothly between the track 8 and the circulation path 30A.

[0087] Although the concave surface 201 in the second embodiment has an arc shape when viewed from the axial direction, the present disclosure may have a triangular shape and is not limited to the example shown in the embodiment.

[0088] (Embodiment 3) Fig. 11 is a cross-sectional view of a top and a recess of a ball screw device of embodiment 3 taken in the axial and radial directions. As shown in Fig. 11, a top 5B of a ball screw device 1B of embodiment 3 differs from embodiment 1 in that a rib 60 is provided on the outer circumferential side of the protrusion 42. This rib 60 extends in the spiral direction and is also provided on the outer circumferential surface of the tongue 40. According to embodiment 3, the strength of the tongue 40 is improved by the rib 60, making the tongue 40 less susceptible to breakage.

[0089] Although the embodiments have been described above, the present disclosure may also be applied to the ball screw device shown below.

[0090] (Embodiment 4) Figure 12 is a cross-sectional view of the top and recess of a ball screw device of embodiment 4, taken in the axial and radial directions. As shown in Figure 12, in a ball screw device 1C of embodiment 4, the distance between the first bottom surface 16C and the center O1 is defined as h. The distance from the center O1 to the thread 6b of the nut 6 is defined as R. The diameter of the ball 4 is defined as Dw. When the distance L1 between the thread 6b and the groove surface 43 (the portion of the outer diameter surface 41 of the top 5C that faces the thread 6b of the nut 6) is 0.2 mm or more and 1.5 mm or less, and the thickness L2 of the top 5C (the thickness from the portion of the outer diameter surface 41 of the top 5C that faces the thread 6b of the nut 6 (groove surface 43) to the circulation groove surface 51) is 0.3 mm or more and 1.0 mm or less, and the radial gap L3 of the circulation path 30 is 0.05 × Dw or more and 0.25 × Dw or less, it is desirable that the distance h satisfy the following formula (2).

[0091]

[0092] If the distance h satisfies the formula (2), the value of the distance h is relatively large. In other words, the first bottom surface 16C is disposed radially outward, and the raceway 8 is lengthened. Therefore, the load capacity of the ball screw device 1C is improved.

[0093] The first to fourth embodiments have been described above. Although the recess 14 in the first to fourth embodiments has a pair of second opposing surfaces 18 (see FIGS. 3 and 4 ) that sandwich the link 5 from both sides in the cross direction Y, the present disclosure is not limited to such recesses. In the following fifth embodiment, a recess that does not have a pair of second opposing surfaces 18 will be described.

[0094] 13 is a perspective view of the recess and the top of the fifth embodiment. The ball screw device 1D of the fifth embodiment differs from the first embodiment in that the top 5D is exposed in the transverse direction Y from the recess 14D of the screw shaft 2. Details will be described below.

[0095] 14 is a perspective view of a recess of a screw shaft of embodiment 5. A recess 14D of a screw shaft 2 of a ball screw device 1D of embodiment 5 differs from the recess 14 of embodiment 1 in that it has a pair of openings 150, 150 that open on both sides in the transverse direction Y. In other words, the recess 14D of embodiment 5 does not have a pair of second opposing surfaces 18 (see FIGS. 3 and 4) that sandwich the top 5D from both sides in the transverse direction Y. Therefore, the top 5D is exposed in the transverse direction Y from the recess 14D. Note that in the present disclosure, the pair of openings 150, 150 may be referred to as two openings.

[0096] Similarly to the first embodiment, the recess 14D of the fifth embodiment has a first bottom surface 16 and a pair of first opposing surfaces 17, 17 that are opposed to each other in the axial direction.

[0097] One of the pair of openings 150, 150 opens in one direction in the transverse direction Y, and the other opens in the other direction in the transverse direction Y. In the fifth embodiment, a pair of openings 150, 150 is formed, and the wall portions constituting the pair of second opposing surfaces 18 are cut out. Therefore, the first bottom surface 16 and the pair of first opposing surfaces 17, 17 are larger in the transverse direction Y than in the first embodiment. In other words, the recess 14D is larger in the transverse direction Y than the recess 14 of the first embodiment. Furthermore, the frame 5D of the fifth embodiment is also larger in the transverse direction Y than the frame 5 of the first embodiment (see FIG. 13 ).

[0098] Fig. 15 is a view of the recess of embodiment 5 as viewed from the transverse direction Y. As shown in Fig. 15, when viewed from the transverse direction Y, the opening 150 has a shape (rectangular) that conforms to the first bottom surface 16 and the pair of first opposing surfaces 17, 17. In other words, no protrusions or the like that protrude into the opening 150 are formed on the first bottom surface 16 or the pair of first opposing surfaces 17, 17. Therefore, the top 5 is movable in the transverse direction Y along the first bottom surface 16 and the pair of first opposing surfaces 17, 17.

[0099] Figure 16 is a cross-sectional view taken along the line XVI-XVI in Figure 15. As shown in Figure 16, according to the fifth embodiment, the top 5D can be attached to the recess 14D by inserting the top 5D from the intersecting direction Y of the recess 14D (see arrow A1 in Figure 16). Furthermore, in the fifth embodiment, similar to the recess 14 of the first embodiment, the top 5D can be attached to the recess 14D by arranging the top 5D radially outward from the recess 14D and moving the top 5D radially inward (see arrow A2 in Figure 16). This increases the options for the direction in which the top 5D can be attached, improving the attachability of the top 5D.

[0100] In the first embodiment, the screw shaft-side opening 13b is formed in the second opposing surface 18 (see FIGS. 3 and 4). On the other hand, as shown in FIG. 14, the screw shaft-side opening 13b in the fifth embodiment is formed in the first bottom surface 16. Therefore, both end portions 16b of the first bottom surface 16 in the transverse direction Y are cut out by the screw shaft-side opening 13b.

[0101] 17 is a view of the top of embodiment 5 as seen from the second bottom surface. Like embodiment 1, top 5D has a second bottom surface 50 that abuts against first bottom surface 16. In addition, a non-contact surface 160 that does not abut against first bottom surface 16 is formed on a portion of second bottom surface 50.

[0102] 18 is a cross-sectional view of the recess and the link of the fifth embodiment taken in a direction perpendicular to the axial direction, specifically, a cross-sectional view of the recess and the link taken along line XVIII-XVIII in FIG. 15. As shown in FIG. 18, the non-contact surface 160 is disposed radially outward of the circuit outer thread groove surface 213 of the screw shaft 2 and is spaced apart from the circuit outer thread groove surface 213. Therefore, in the fifth embodiment, a portion of the link 5D is disposed radially outward of the circuit outer thread groove surface 213, not in the recess 14D. Hereinafter, the portion of the link 5D disposed radially outward of the circuit outer thread groove surface 213 will be referred to as the recess outer wall portion 161. The recess outer wall portion 161 is formed at both ends of the link 5D in the transverse direction Y (see FIG. 17).

[0103] The above-mentioned circuit outer thread groove surface 213 is a thread groove surface formed when the outer peripheral surface of the screw shaft 2 is continuously cut in a spiral direction to form the outer peripheral raceway surface 13. Therefore, the circuit outer thread groove surface 213 extends in the same spiral direction as the outer peripheral raceway surface 13, but is not connected to the circulation path 30 of the block 5D. In other words, no balls 4 are arranged on the circuit outer thread groove surface 213.

[0104] Even in the ball screw device 1D of the above-described fifth embodiment, the balls 4 are reliably guided radially inward by the tangs 40 (see FIGS. 13 and 18 ). Therefore, similar to the first embodiment, the balls 4 are prevented from being pinched between the circulation groove surface 51 and the inner circumferential raceway surface 6 a. Note that, although the first opposing surfaces 17 of the fifth embodiment extend along the spiral direction as described in the first embodiment, the present disclosure does not limit the direction in which the first opposing surfaces 17 extend (the angle with respect to the transverse direction Y).

[0105] Next, a first modification in which a part of the ball screw device 1D of the fifth embodiment is modified will be described.

[0106] (Modification 1) Fig. 19 is a view of the recess and the link of Modification 1 as viewed from the transverse direction. Fig. 20 is a perspective view of the recess of the screw shaft of Modification 1. In a ball screw device 1E of Modification 1, the recess 14D differs from that of Embodiment 5 in that a pair of grooves 220, 220 recessed in the axial direction are formed on a pair of first opposing surfaces 17, 17. Furthermore, a link 5D of Modification 1 differs from that of Embodiment 5 in that a pair of protrusions 230, 230 protruding in the axial direction are formed on a pair of first side surfaces 25, 25. Note that in the present disclosure, the pair of first opposing surfaces 17, 17 may be referred to as a pair of opposing surfaces. Furthermore, the pair of first side surfaces 25, 25 may be referred to as a pair of side surfaces.

[0107] As shown in Fig. 20, the groove 220 extends in the transverse direction Y. The groove 220 also extends to both ends of the first opposing surfaces 17 in the transverse direction Y. Both ends of the groove 220 in the transverse direction Y are open in the transverse direction Y. As shown in Fig. 19, the distance between the pair of first opposing surfaces 17, 17 is W1. The distance W2 between the pair of grooves 220, 220 is greater than W1 (W2 > W1).

[0108] The radial position of the groove 220 (height from the first bottom surface 16) is the radially innermost position of the first opposing surface 17. Therefore, the radially inner end 220 a of the groove 220 is connected to the first bottom surface 16.

[0109] The protrusion 230 is formed to have the same shape as the groove 220 when viewed from the transverse direction Y. Furthermore, although not particularly shown, the protrusion 230 extends in the transverse direction Y along the first side surface 25. As shown in FIG. 19 , the radial position of the protrusion 230 is disposed at the radially innermost position of the first side surface 25. Therefore, the protrusion 230 faces the groove 220 in the axial direction and is recessed into the groove 220. Note that, although the protrusion 230 in the embodiment extends in the transverse direction Y, in the present disclosure, it is not necessary for the protrusion 230 to extend in the transverse direction Y. Furthermore, the protrusion 230 may extend intermittently in the transverse direction Y.

[0110] With regard to the axial thickness of the top 5E, the thickness W3 between the pair of first side surfaces 25, 25 is equal to or less than the dimension W1 between the first opposing surfaces 17, 17 (W1≧W3). Therefore, the pair of first side surfaces 25, 25 of the top 5E are not sandwiched between the first opposing surfaces 17, 17.

[0111] The thickness W4 between the pair of protrusions 230, 230 is smaller than the dimension W2 between the pair of grooves 220, 220 (W2>W4), and therefore the pair of protrusions 230 can be accommodated in the pair of grooves 220, 220. Furthermore, the thickness W4 between the pair of protrusions 230, 230 is larger than the dimension W1 between the pair of first opposing surfaces 17, 17 (W4>W1).

[0112] In the method of attaching the top 5D of the first modification, first, the top 5D is placed in the intersecting direction Y of the recess 14D. Next, the pair of protrusions 230, 230 are inserted into the pair of grooves 220, 220, and the top 5D is pushed into the recess 14D. This attaches the top 5D to the recess 14D.

[0113] According to the first modification, even if a load acts on the top 5D in the radially outward direction, the pair of protrusions 230, 230 are caught in the pair of grooves 220, 220. This restricts the top 5D from moving radially outward. Note that in the first modification, the grooves 220 are formed on each of the pair of first opposing surfaces 17, 17, but in the present disclosure, the grooves 220 may be formed on one of the pair of first opposing surfaces 17, 17. In such a case, the protrusions 230 accommodated in the grooves 220 are formed on one of the pair of first side surfaces 25, 25.

[0114] Next, Modification 2, which is a modification of Modification 1, will be described.

[0115] 21 is a cross-sectional view of the recess and the link of Modification 2. As shown in Fig. 21, the ball screw device 1F of Modification 2 differs from Modification 1 in that the radial positions of the pair of grooves 220F and the pair of protrusions 230F are changed.

[0116] Specifically, the pair of grooves 220F, 220F of the recess 14D are disposed in a radially intermediate portion of the first opposing surface 17. Similarly, the pair of protrusions 230F, 230F are disposed in a radially intermediate portion of the first side surface 25. In this second modification, as in the first modification, the radially outward movement of the top 5D is restricted.

[0117] In the above-mentioned variants 1 and 2, examples have been given in which a pair of grooves 220, 220 and a pair of protrusions 230, 230 are provided to restrict the radially outward movement of the top 5D, but the present disclosure may also be as shown in the following variant 3.

[0118] (Variation 3) FIG. 22 is a view of the recess and the top of Variation 3 as viewed from the transverse direction. The ball screw device 1G of Variation 3 differs from Embodiment 5 in that the top 5D is sandwiched between the pair of first opposing surfaces 17, 17 of the recess 14D. Specifically, the distance between the pair of first opposing surfaces 17, 17 is W5. Meanwhile, the axial thickness W6 of the top 5D (the distance between the pair of first side surfaces 25, 25) is greater than the distance W5 between the pair of first opposing surfaces 17, 17 before attachment to the recess 14D. In other words, the top 5D has an interference with the pair of first opposing surfaces 17, 17 and is attached to the recess 14D by press-fitting. As described above, according to Variation 3, the top 5D is restricted from moving radially outward and in the transverse direction Y.

[0119] Note that the top 5D of the above-described Modifications 1 and 2 may move in the transverse direction Y. To restrict this movement of the top 5D in the transverse direction Y, the content of Modification 3 may be applied. Specifically, the thickness W3 between the pair of first side surfaces 25, 25 may be made larger than the dimension W1 between the first opposing surfaces 17, 17 (see FIG. 19 ). In this case, the top 5D has an axial interference with the recess 14D. As a result, movement of the top 5D in the transverse direction Y is restricted.

[0120] Furthermore, in order to restrict movement of the top 5D of Modification 1 and Modification 2 in the transverse direction Y, the present disclosure may also be modified as follows: Modifications 4 to 6. In the following description, a direction perpendicular to both the axial direction and the transverse direction Y is referred to as an orthogonal direction. Among the orthogonal directions, a direction in which the center O1 of the screw shaft 2 is disposed as viewed from the first bottom surface 16 is referred to as a first orthogonal direction Z1 (see FIG. 23 , etc.). Among the orthogonal directions, a direction opposite to the direction in which the center O1 of the screw shaft 2 is disposed as viewed from the first bottom surface 16 is referred to as a second orthogonal direction Z2 (see FIG. 23 , etc.).

[0121] (Modification 4) Figure 23 is a cross-sectional view of the recess and the top of Modification 4 taken in a direction perpendicular to the axial direction. As shown in Figure 23, a ball screw device 1H of Modification 4 differs from Modification 1 in that the top 5D has a crimped portion 161H. This crimped portion 161H is formed by crimping the recess outer material portion 161 of the top 5D from the radially outer side (see arrow A3 in Figure 23) after the top 5D is attached to the recess 14D.

[0122] In addition, in the fourth modification, a pair of recess outer wall portions 161 (only one recess outer wall portion 161 is shown in FIG. 23; see FIG. 17 ) are each crimped. Thus, a pair of crimped portions 161H (only one crimped portion 161H is shown in FIG. 23 ) are formed on both sides of the link 5D in the transverse direction Y.

[0123] The crimping portions 161H protrude in the first orthogonal direction Z1 beyond the first bottom surface 16. Therefore, when a load is applied to the top 5D in the transverse direction Y, the pair of crimping portions 161H catch on the circuit outer thread groove surfaces 213. Therefore, movement of the top 5H in the transverse direction Y is restricted.

[0124] In Modification 4, recess outer wall portion 161 is crimped, but in the present disclosure, crimped portion 161H may be formed by crimping a portion other than recess outer wall portion 161. Furthermore, crimped portion 161H in Modification 4 is configured to hook onto circuit outer thread groove surface 213, but in the present disclosure, it may be configured to hook onto thread 13a (outer peripheral surface) of screw shaft 2. Furthermore, in Modification 4, a portion of link 5D is crimped and deformed (bent) in the orthogonal direction, but in the present disclosure, a portion of link 5D may be deformed in the axial direction to form crimped portion 161H.

[0125] In addition, in variant example 4, after the top 5D is attached to the recess 14D, both ends of the top 5D in the cross direction Y are crimped, but in the present disclosure, one end of the top 5D in the cross direction Y may also be crimped before the top 5D is attached to the recess 14D.

[0126] Furthermore, in Modification 4, a pair of crimped portions 161H are formed on both ends of the top 5D in the transverse direction Y, but in the present disclosure, the crimped portion 161H may be formed on only one of the ends of the top 5D in the transverse direction Y. In such a top 5D, it is necessary to form in advance, at the time of manufacturing the top 5D, a protrusion (not shown) that protrudes in the first orthogonal direction Z1 beyond the first bottom surface 16 on one side of the top 5D in the transverse direction Y.

[0127] (Modification 5) Fig. 24 is a view of a top of Modification 5 as viewed from the second bottom surface. Fig. 25 is a cross-sectional view of the ball screw device of Modification 5 cut in a direction perpendicular to the axial direction. As shown in Fig. 24, top 5D of Modification 4 differs from Modification 1 in that cutout surfaces 162 are formed by cutting out arc-shaped portions of both ends of top 5D in the transverse direction Y. The cutout surfaces 162 are formed by cutting out a pair of recess outer solid portions 161.

[0128] 25, the cutout surface 162 is larger than the screw shaft-side opening 13b. Therefore, as shown in FIG. 25, a part of the first bottom surface 16 (the edge of the screw shaft-side opening 13b) is not covered by the second bottom surface 50 of the link 5I.

[0129] Modification 5 also differs from Modification 1 in that a crimped portion 163 is formed on the first bottom surface 16 of the recess 14D. After the top 5D is attached to the recess 14D, the crimped portion 163 is formed by crimping the edge of the screw shaft side opening 13b of the first bottom surface 16. Although not specifically shown, the crimped portions 163 are formed on both ends of the first bottom surface 16 in the transverse direction Y.

[0130] The crimping portions 163 protrude in the second orthogonal direction Z2 beyond the first bottom surface 16. Therefore, when a load is applied to the top 5D in the transverse direction Y, the pair of crimping portions 163 catch on the cutout surfaces 162. Therefore, movement of the top 5D in the transverse direction Y is restricted.

[0131] In Modification 5, the first bottom surface 16 is crimped, but in the present disclosure, the thread 13a of the screw shaft 2 may be crimped. Furthermore, when the crimped portion 163 is formed on the thread 13a of the screw shaft 2, the notched surface 162 does not need to be formed on the link 5I. In other words, in the present disclosure, the shape of the link is not particularly important. Furthermore, in Modification 5, a portion of the screw shaft 2 is crimped and deformed (bent) in the orthogonal direction, but in the present disclosure, a portion of the screw shaft 2 may be deformed in the axial direction to form the crimped portion 163.

[0132] In addition, in variant example 5, after the top 5D is attached to the recess 14D, a pair of crimping portions 163 are formed on both sides of the top 5D in the cross direction Y, but in the present disclosure, one of the pair of crimping portions 163 may be formed before the top 5D is attached to the recess 14D.

[0133] Furthermore, in Modification 5, a pair of crimped portions 163 are formed on both sides of the top 5D in the transverse direction Y, but in the present disclosure, the crimped portion 163 may be formed on only one of the both sides of the top 5D in the transverse direction Y. In such a recess 14D, at the time of manufacturing the screw shaft 2, it is necessary to form in advance a protrusion (not shown) that protrudes in the second orthogonal direction Z2 beyond the first bottom surface 16 on one side of the top 5D in the transverse direction Y.

[0134] (Variation 6) Figure 26 is a perspective view of a recess of Variation 6. Figure 27 is a view of the top of Variation 6 as viewed from the second bottom surface. Figure 28 is a cross-sectional view taken along line XXVIII-XXVIII in Figure 26. As shown in Figure 26, a ball screw device 1J of Variation 6 differs from Variation 1 in that two holes 240 are formed in the first bottom surface 16 of the recess 14D of the screw shaft 2. Furthermore, as shown in Figure 27, a top 5D of Variation 6 differs from Variation 1 in that two protrusions 241 are formed in the second bottom surface 50.

[0135] 28 , the protrusion 241 fits into the hole 240. Therefore, when a load acts on the top 5D in the transverse direction Y, the protrusion 241 gets caught in the hole 240. Therefore, the movement of the top 5D in the transverse direction Y is restricted.

[0136] The method for attaching the top 5D involves placing the top 5D in the intersecting direction Y of the recess 14D. Next, the pair of protrusions 230, 230 are inserted into the pair of grooves 220, 220, and the top 5D is pushed into the recess 14D. At this time, the protrusion 241 is pressed against the first bottom surface 16 and deformed. Then, when the protrusion 241 overlaps the hole 240 in the perpendicular direction, the protrusion 241 returns to its original shape and enters the hole 240. This attaches the top 5D to the recess 14D. Note that the top of the present disclosure may be made of either metal or resin, as described above, but in this modified example, a resin top is preferable because it is easily elastically deformed.

[0137] Furthermore, the two holes 240 and the two protrusions 241 are arranged symmetrically with respect to the center C (see FIG. 4) of the top 5D. Therefore, even if the top 5D is attached in a state rotated 180 degrees relative to the recess 14D, the protrusions 241 fit into the holes 240. This allows for easy attachment of the top 5D.

[0138] Although the sixth modification has two holes 240 and two protrusions 241, the present disclosure is not limited to the number shown in the sixth modification, and the number of holes 240 and protrusions 241 may be one or more. The present disclosure is not particularly limited to the shape of the holes 240, and may be, for example, a hemisphere, a truncated cone, a truncated pyramid, a cone, or a pyramid.

[0139] Modifications 4 to 6 have been described above, but the present disclosure may also apply the contents of Modifications 4 to 6 to Modification 3. This will more reliably restrict movement of the top in the transverse direction Y.

[0140] While the above describes each embodiment and each modified example, the circulation groove surface 51 of the present disclosure may be a square groove having a cross-sectional shape. Alternatively, the cross-sectional shape of the circulation groove surface 51 may be a Gothic arc shape, and is not limited to the examples shown in the embodiments. Furthermore, in the ball screws of embodiments 1 to 4, the top may have an interference in the recess, and the top may be attached to the recess by press-fitting. Furthermore, while the recess 14B of embodiment 5 and each modified example has two openings 150, 150, the present disclosure may have only one opening 150. In other words, the recess may be open only in one direction in the transverse direction Y.

[0141] The present disclosure may also be implemented as a combination of the following configurations. (1) A nut having an inner circumferential raceway surface on its inner circumferential surface; a screw shaft penetrating the nut and having an outer circumferential raceway surface on its outer circumferential surface; a plurality of balls arranged in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; and at least one or more rollers for circulating the balls, wherein the outer circumferential surface of the screw shaft is provided with at least one or more recesses that are recessed radially inward and accommodate the rollers, the recesses having a first bottom surface facing radially outward, and at least a portion of the first bottom surface being flat, the rollers having: a second bottom surface abutting against the first bottom surface; a circulation groove surface that is recessed radially outward from the second bottom surface and whose internal space constitutes a circulation path; a bottom opening that opens the circulation path radially inward; a pair of roller-side openings that open the circulation path in the circumferential direction and connect the circulation path to the raceway; and a pair of tangs that guide the balls that have entered the circulation path from the raceway to the radially inward. (2) A ball screw device according to (1), in which a portion of the first bottom surface that closes the bottom opening serves as a rolling surface for the balls that move through the circulation path. (3) The ball screw device according to (1), in which, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction that intersects with an imaginary line that extends radially outward from the center of the screw shaft, and a concave surface recessed radially inward is provided in a central portion of the first bottom surface in the intersecting direction, and flat surfaces are provided on both sides of the concave surface in the intersecting direction. (4) The ball screw device according to any one of (1) to (3), in which the tongue is provided with a rib that protrudes radially outward. (5) A ball screw device according to any one of (1) to (4), wherein, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft, the recess has an annular inner peripheral surface surrounding the periphery of the top, and the inner peripheral surface has a pair of side surfaces sandwiching the top from both sides in the intersecting direction.(6) A ball screw device according to any one of (1) to (5), wherein R is the distance from the center of the screw shaft to the thread of the nut, Dw is the diameter of the ball, the distance between a portion of the outer diameter surface of the top that faces the thread of the nut and the thread of the nut is 0.2 mm or more and 1.5 mm or less, and the thickness from the portion of the outer diameter surface of the top that faces the thread of the nut to the circulation groove surface is 0.3 mm or more and 1.0 mm or less, and the radial gap of the circulation path is 0.05 × Dw or more and 0.25 × Dw or less, and the distance h between the first bottom surface and the center of the screw shaft satisfies the following formula (3).

[0142]

[0143] (7) The ball screw device according to any one of (1) to (4), wherein, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft, the recess has at least one opening that opens in the intersecting direction, and the top is movable in the intersecting direction along the first bottom surface. (8) The ball screw device according to (7), wherein the recess has two openings, and the two openings are the opening that opens to one side in the intersecting direction and the opening that opens to the other side in the intersecting direction. (9) The ball screw device according to (7) or (8), wherein the recess has a pair of opposing surfaces opposing in the axial direction, the top has a pair of side surfaces facing the axial direction and opposing the pair of opposing surfaces, at least one of the pair of opposing surfaces has a groove formed therein that is recessed in the axial direction and extends in the intersecting direction, and at least one of the pair of side surfaces has a protrusion formed thereon that protrudes in the axial direction and is received in the groove. (10) The ball screw device according to (9), wherein the groove is formed on both of the pair of opposing surfaces, and the protrusion is formed on both of the pair of side surfaces. (11) The ball screw device according to any one of (7) to (10), wherein the recess has a pair of opposing surfaces opposing in the axial direction, and the top has an interference with the pair of opposing surfaces and is sandwiched between the pair of opposing surfaces. (12) A ball screw device according to any one of (7) to (11), wherein a direction perpendicular to both the axial direction and the intersecting direction is defined as an intersecting direction, a direction in which the center of the screw shaft is located as viewed from the first bottom surface is defined as a first intersecting direction, and a crimped portion that protrudes in the first intersecting direction beyond the first bottom surface is formed on at least one of both end portions of the top in the intersecting direction.(13) The ball screw device according to any one of (7) to (11), wherein a direction orthogonal to both the axial direction and the intersecting direction is defined as an orthogonal direction, a direction opposite to a direction in which a center of the screw shaft is disposed as viewed from the first bottom surface is defined as a second orthogonal direction among the orthogonal directions, and the screw shaft is formed with a crimped portion that is disposed on at least one of both sides of the top in the intersecting direction and protrudes beyond the first bottom surface in the second orthogonal direction. (14) The ball screw device according to any one of (7) to (11), wherein one or more holes are formed in the first bottom surface, and a protrusion that fits into the hole is formed in the second bottom surface.

[0144] REFERENCE SIGNS LIST 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J Ball screw device 2 Screw shaft 4 Ball 5, 5A, 5B, 5D Top 6 Nut 6a Inner peripheral raceway surface 8 Raceway 13 Outer peripheral raceway surface 14, 14D Recessed portion 15 Inner peripheral surface 16, 16A First bottom surface 17 First opposing surface 18 Second opposing surface 13a Thread 13b Screw shaft side opening 13c End surface 13d Partial end surface 25 First side surface 26 Second side surface 30, 30A Circulation path 31 Top side opening 40 Tongue 41 Outer diameter surface 42 Protrusion 43 Groove surface 50 Second bottom surface 51 Circulation groove surface 53 Bottom opening 54 Rolling surface 60 Rib 100 Brake caliper 104 Electric actuator 120 Housing 150 Opening 160 Non-contact surface 161 Outer wall portion of recess 161H, 163 Crimped portion 162 Notched surface 201 Concave surface 202 Flat surface 213 Outer thread groove surface of circuit 220, 220F Groove 230, 230F Protrusion 240 Hole 241 Protrusion 251 Convex portion

Claims

a nut having an inner circumferential raceway surface on its inner circumferential surface; a screw shaft penetrating the nut and having an outer circumferential raceway surface on its outer circumferential surface; a plurality of balls arranged in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; and at least one or more blocks for circulating the balls, wherein the outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the blocks, the recess having a first bottom surface facing radially outward, and at least a portion of the first bottom surface is flat, the blocks having: a second bottom surface abutting the first bottom surface; a circulation groove surface that is recessed radially outward from the second bottom surface and whose internal space constitutes a circulation path; a bottom opening that opens the circulation path radially inward; a pair of block side openings that open the circulation path in the circumferential direction and connect the circulation path to the raceway; and a pair of tangs that guide the balls that have entered the circulation path from the raceway radially inward, A ball screw device in which a portion of the first bottom surface that closes the bottom opening serves as a rolling surface for the balls that move through the circulation path.

2. The ball screw device according to claim 1, wherein the first bottom surface is entirely flat.

3. A ball screw device as described in claim 1, wherein, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft, a concave surface recessed radially inward is provided at the center of the first bottom surface in the intersecting direction, and flat surfaces are provided on both sides of the intersecting direction of the concave surface.

4. A ball screw device according to any one of claims 1 to 3, wherein the tang is provided with a rib protruding radially outward.

5. A ball screw device as described in any one of claims 1 to 4, wherein, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft, the recess has an annular inner circumferential surface surrounding the top, and the inner circumferential surface has a pair of side surfaces sandwiching the top from both sides in the intersecting direction.

6. A ball screw device as claimed in any one of claims 1 to 5, wherein R is the distance from the center of the screw shaft to the thread of the nut, Dw is the diameter of the ball, the distance between a portion of the outer diameter surface of the top facing the thread of the nut and the thread of the nut is 0.2 mm or more and 1.5 mm or less, and the thickness from the portion of the outer diameter surface of the top facing the thread of the nut to the circulation groove surface is 0.3 mm or more and 1.0 mm or less, and the radial gap of the circulation path is 0.05 x Dw or more and 0.25 x Dw or less, and the distance h between the first bottom surface and the center of the screw shaft satisfies the following formula (1):

7. A ball screw device as described in any one of claims 1 to 4, wherein, when viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting an imaginary line extending radially outward from the center of the screw shaft, the recess has at least one opening that opens in the intersecting direction, and the top is movable in the intersecting direction along the first bottom surface.

8. A ball screw device as described in claim 7, wherein the recess has two openings, and the two openings are an opening that opens to one side of the intersecting direction and an opening that opens to the other side of the intersecting direction.

9. A ball screw device as described in claim 7 or claim 8, wherein the recess has a pair of opposing surfaces facing each other in the axial direction, the top has a pair of side surfaces facing the axial direction and facing the pair of opposing surfaces, at least one of the pair of opposing surfaces is formed with a groove that is recessed in the axial direction and extends in the intersecting direction, and at least one of the pair of side surfaces is formed with a protrusion that protrudes in the axial direction and is received in the groove.

10. The ball screw device according to claim 9, wherein the groove is formed on both of the pair of opposing surfaces, and the protrusion is formed on both of the pair of side surfaces.

11. A ball screw device as claimed in any one of claims 7 to 10, wherein the recess has a pair of opposing surfaces opposed to each other in the axial direction, and the top has a clamping margin with respect to the pair of opposing surfaces and is clamped between the pair of opposing surfaces.

12. A ball screw device as described in any one of claims 7 to 11, wherein a direction perpendicular to both the axial direction and the intersecting direction is defined as an orthogonal direction, a direction in which the center of the screw shaft is located when viewed from the first bottom surface is defined as a first orthogonal direction, and at least one of both end portions of the top in the intersecting direction is formed with a crimped portion that protrudes in the first orthogonal direction beyond the first bottom surface.

13. A ball screw device as described in any one of claims 7 to 11, wherein a direction perpendicular to both the axial direction and the intersecting direction is defined as an orthogonal direction, a direction opposite to the direction in which the center of the screw shaft is located when viewed from the first bottom surface is defined as a second orthogonal direction, and the screw shaft is formed with a tightening portion that is located on at least one of both sides of the top in the intersecting direction and protrudes in the second orthogonal direction beyond the first bottom surface.

14. A ball screw device as described in any one of claims 7 to 11, wherein one or more holes are formed in the first bottom surface, and a protrusion that fits into the hole is formed on the second bottom surface.

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