Ball screw device

Abstract

The ball screw device of the present disclosure includes a nut, a screw shaft, a plurality of balls, and one or more tops. The outer peripheral surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the tops. The recess has a first bottom surface facing radially outward. At least a portion of the first bottom surface is flat. The top has a second bottom surface that abuts 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 toward the radially inward direction, a pair of top-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 enter the circulation path from the raceway to the radially inward direction. The portion of the first bottom surface that blocks the bottom opening is a rolling surface for the balls that move through the circulation path.

Description

[Technical field]

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

[0002] The ball screw device includes a nut, a screw shaft penetrating 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 facing 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 the balls that have moved from one end of the track to the other end of the track to one 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 of the following patent document, a recess is formed on the outer circumferential surface of the screw shaft, recessed radially inward. A top is inserted into the recess and attached to the screw shaft. The top 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. The balls move radially inward within the circulation groove surface of the top and ride over the threads of the nut. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-225770 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the above-mentioned patent document, when the ball moves radially inward, the ball may be pinched between the circulation groove surface and the inner raceway surface of the nut. Therefore, the smooth rolling of the ball is not ensured. In addition, if the ball is pinched, the groove shoulder of the circulation groove surface may be damaged.

[0006] The present disclosure has been made in consideration of the above, and has an object to provide a ball screw device that enables the balls to roll smoothly and prevents damage to the pieces. [Means for solving the problem]

[0007] In order to achieve the above object, a ball screw device according to one aspect of the present disclosure includes a nut having an inner peripheral raceway surface on its inner peripheral surface, a screw shaft penetrating the nut and having an outer peripheral raceway surface on its outer peripheral surface, a plurality of balls arranged on a raceway between the outer peripheral raceway surface and the inner peripheral raceway surface, and at least one or more tops for circulating the balls. The outer peripheral surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the tops. The recess has a first bottom surface facing radially outward. At least a portion of the first bottom surface is flat. The top has a second bottom surface that abuts 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 toward the radially inward direction, a pair of top-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 enter the circulation path from the raceway to the radially inward direction. 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.

[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 being pinched between the circulation groove surface and the inner circumferential raceway surface. In other words, the balls roll smoothly, and damage to the groove shoulder of the circulation groove surface is also avoided. In addition, the depth of the recess can be measured using the plane of the first bottom surface of the recess as a reference surface, making it easy to manage the dimensions of the recess. In addition, the circulation path of the top opens radially inward. In other words, when manufacturing the top using a mold, the mold that forms the circulation path (circulation groove surface) can be moved radially inward (released from the mold). This makes it easier to manufacture the top than when the radial inside 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. Also, when viewed from the axial direction, the circulation path is linear, making the balls roll smoothly. Also, 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 course of the balls bends radially inward from the orbit. If the first bottom surface is concave, the bending angle of the course of the balls is large. On the other hand, according to the present disclosure, since the first bottom surface is flat, the bending angle of the course of the balls is 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 a virtual 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 center of the first bottom surface in the intersecting direction. Flat surfaces are provided on both sides of the intersecting direction of the concave surface.

[0012] The end of the first bottom surface in the intersecting direction is flat, and the bending angle of the ball's path is small. Therefore, with the above configuration, the balls move (roll) smoothly between the outer circumferential raceway surface and the circulation path. Also, 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 first bottom surface is entirely flat. As a result, the area of ​​the outer circumferential raceway surface that is cut out by the concave portions is reduced, and the load-bearing 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 this 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 the above-mentioned configuration, the top is sandwiched between the pair of side surfaces, which prevents the top 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 facing 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 facing 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]

number

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

[0020] In addition, as a preferred aspect 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 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. The top is movable in the intersecting direction along the first bottom surface. Alternatively, as a preferred aspect of the ball screw device, the recess has two of the openings. The two openings are the opening that opens to one side of the intersecting direction and the opening that opens to the other side of the intersecting direction.

[0021] According to the above-mentioned configuration, the top can be attached from the cross direction of 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, improving the ease of attachment of the top.

[0022] In addition, as a preferred aspect 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 received in the groove. Alternatively, as a preferred aspect 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 the above-mentioned 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 opposed to each other in the axial direction. The top has an interference with the pair of opposing surfaces and is sandwiched between the pair of opposing surfaces.

[0025] According to the above-described configuration, the top is less likely to move radially outward and in the transverse direction, thereby preventing the top from falling off the recess.

[0026] In a preferred embodiment of the ball screw device, a direction perpendicular to both the axial direction and the intersecting direction is defined as an intersecting direction. Among the intersecting 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 intersecting direction. At least one of both ends of the top in the intersecting direction is formed with a crimped portion that protrudes in the first intersecting direction beyond the first bottom surface.

[0027] According to the above-mentioned 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 the 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 intersecting direction is defined as an intersecting direction. A second intersecting 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 crimping 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 intersecting direction.

[0029] According to the above-mentioned configuration, when a load acts on the top in the transverse direction, the crimped portion catches the top from the transverse direction, thereby restricting the movement of the top 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 a protrusion that fits into the hole.

[0031] According to the above-mentioned configuration, when a load is applied to the top in the transverse direction, the projection is caught in the hole, thereby restricting the top from moving radially outward. Effect of the Invention

[0032] According to the ball screw device of the present disclosure, smooth rolling of the balls is ensured, and damage to the groove shoulder of the circulation groove surface is also avoided. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a cross-sectional view of a brake caliper according to a first embodiment. [Diagram 2] FIG. 2 is a perspective view of a top and a recess of the ball screw device of the first embodiment. [Diagram 3] FIG. 3 is a perspective view of a recess in the first embodiment. [Figure 4] FIG. 4 is an enlarged view of the recess and the link of the first embodiment as viewed from the radially outer side. [Diagram 5] FIG. 5 is a schematic cross-sectional view of the link and screw shaft of the first embodiment taken along a circulation path, and more specifically, a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a schematic view showing a cross section of the link and the screw shaft of the first embodiment taken along the axial direction, and more specifically, a cross section taken along the line VI-VI of FIG. [Figure 7] FIG. 7 is a plan view of the frame of the first embodiment seen from the second bottom surface side. [Figure 8] FIG. 8 is a schematic diagram showing cross sections of the ball screw device of the first embodiment and the comparative example taken along the raceway and the circulating path. [Figure 9] FIG. 9 is a plan view of the recess of the ball screw device of the second embodiment as viewed from the radial direction. [Figure 10] FIG. 10 is a cross-sectional view of the ball screw device of the second embodiment taken along the raceway and the circulating path. [Figure 11] FIG. 11 is a cross-sectional view of a top and a recess of a ball screw device of the third embodiment taken in an axial direction and a radial direction. [Figure 12] FIG. 12 is a cross-sectional view of a top and a recess of a ball screw device of the fourth embodiment taken in an axial direction and a radial direction. [Figure 13] FIG. 13 is a perspective view of a recess and a piece according to the fifth embodiment. [Figure 14] FIG. 14 is a perspective view of a recess of a screw shaft of the fifth embodiment. [Figure 15] FIG. 15 is a view of the recess of the fifth embodiment as viewed from the intersecting direction. [Figure 16] FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. [Figure 17] FIG. 17 is a view of the frame of the fifth embodiment seen from the second bottom surface side. [Figure 18] FIG. 18 is a cross-sectional view of the recess and the piece of the fifth embodiment taken in a direction perpendicular to the axial direction, and more specifically, a cross-sectional view of the recess and the piece taken along line XVIII-XVIII in FIG. [Figure 19] FIG. 19 is a view of the recess and the piece of the first modification seen from the intersecting direction. [Figure 20] FIG. 20 is a perspective view of a recess of a screw shaft of the first modified example. [Figure 21] FIG. 21 is a view of the recess and the piece of the second modification seen from the intersecting direction. [Figure 22] FIG. 22 is a view of the recess and the piece of the third modification seen from the intersecting direction. [Figure 23] FIG. 23 is a cross-sectional view of the recess and the piece of the fourth modification taken in a direction perpendicular to the axial direction. [Figure 24] FIG. 24 is a view of the frame of the fifth modified example seen from the second bottom surface side. [Diagram 25] FIG. 25 is a cross-sectional view of the ball screw device of the fifth modification taken in a direction perpendicular to the axial direction. [Figure 26] FIG. 26 is a perspective view of a recess in the sixth modified example. [Figure 27] FIG. 27 is a view of the frame of the sixth modified example seen from the second bottom surface side. [Figure 28] FIG. 28 is a cross-sectional view taken along line XXVIII-XXVIII in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, the present disclosure will be described in detail 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 a person skilled in the art can easily imagine, 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 appropriately combined.

[0035] (Embodiment 1) Fig. 1 is a cross-sectional view of a brake caliper of embodiment 1. As shown in Fig. 1, the brake caliper 100 is a device for suppressing the rotational motion 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, 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 a rotational motion, and a ball screw device 1 that converts the rotational motion into a linear motion. Hereinafter, a direction parallel to a center O1 of a screw shaft 2 of the ball screw device 1 will be referred to as an axial direction. In addition, within the axial direction, a direction in which the brake disc 101 is disposed as viewed from the ball screw device 1 will be referred to as a first direction X1, and a direction opposite to the first direction X1 will be referred to as a 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 about 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 an 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 links 5.

[0039] The screw shaft 2 includes a connecting part 10 rotatably supported by a bearing 117, and a screw shaft body 11 arranged in a first direction X1 relative to the connecting part 10. An end 10a of the connecting part 10 in the second direction X2 is fitted into a recess 114. The connecting part 10 and the output shaft 113 are connected to each other so as not to rotate relative to each other. Therefore, when the output shaft 113 rotates, the screw shaft 2 also rotates. The outer circumferential surface of the screw shaft body 11 is provided with an outer circumferential 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 cover portion 7 that closes an opening of the nut 6 in the first direction X1. The nut 6 has an inner peripheral surface that 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 a 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 a 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 about the center O1.

[0042] The cover portion 7 closes an 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] From the above, when the nut 6 moves in the first direction X1 due to the 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 the rotation of the wheel (not shown) is restricted.

[0044] The top 5 is a circulation device that returns the ball 4 that has moved one lead on the track 8 by one lead. Also, one top 5 is attached to one recess 14. In this disclosure, the method of fixing the top 5 to the recess 14 is not particularly important. That is, the top 5 may or may not be fixed to the recess 14. Therefore, in this disclosure, the top 5 may be loosely fitted into the recess 14. Alternatively, the top 5 may be fitted into the recess 14 with a tightening margin. 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 way, there is no particular issue as to whether the top 5 is fixed or not.

[0045] In addition, although not shown, when the multiple pieces 5 (multiple recesses 14) are viewed from the axial direction, the multiple pieces 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 pieces 5 are 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 in which a circulation path 30 is formed. The top 5 can be made of metal, resin, etc., 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 is shown in Fig. 2) that connect the circulation path 30 and the raceway 8 (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 the embodiment 1. As shown in Fig. 3, a recess 14 is formed by cutting out a part of the outer circumferential raceway surface 13 of the screw shaft 2 from the radial outside. The recess 14 has an inner circumferential surface 15 surrounding the periphery of the link 5 and a first bottom surface 16 facing 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 is referred to as an imaginary line K1.

[0048] Fig. 4 is an enlarged view of the recess and the link of the first embodiment as viewed from the radial outside. Note that the imaginary line Z in Fig. 4 is an imaginary 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. Also, the imaginary line W in Fig. 4 is an imaginary 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 shape (quadrangular shape) when viewed from the radial outside. Although the recess 14 of the embodiment has a rectangular shape (quadrangular shape) when viewed from the radial outside, the present disclosure may have an oval shape, for example, and is not limited to the example shown in the embodiment. The inner peripheral surface 15 of the recess 14 has a pair of first opposing surfaces 17, 17 facing each other in the axial direction, and a pair of second opposing surfaces 18, 18 facing each other in the intersecting direction Y. The intersecting direction Y is a direction intersecting (perpendicular to) a virtual line K1 extending from a center O1 (not shown in FIG. 5) to the radial outside when viewed from the axial direction, as shown in FIG. 5.

[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 (thickness in a direction perpendicular to the helical direction) H1 is provided in a part of the thread 13a.

[0051] The first opposing surface 17 extends along the helical direction. In other words, the thickness H1 of the thin portion 19 is uniform throughout the direction in which the thin portion 19 extends (the helical direction). Therefore, the thin portion 19 of this embodiment does not have a relatively weak portion, and deformation of the thread 13a (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 cross 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 part of the second opposing surface 18 is cut out by the outer circumferential raceway surface 13. That is, 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 center of the second opposing surface 18 in the axial direction and partial end faces 13d of the thread 13a located at both ends of the second opposing surface 18 in the axial direction.

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

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

[0055] As shown in FIG. 3, no concave surface 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 schematic cross-sectional view of the link and screw shaft of the first embodiment taken along a circulation path, more specifically, a cross-sectional view taken along the line VV in Fig. 4. Fig. 6 is a schematic cross-sectional view of the link and screw shaft of the first embodiment taken along the axial direction, more specifically, a cross-sectional view taken along the line 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 intersecting direction. As shown in Fig. 6, when viewed from the intersecting direction, the first bottom surface 16 extends linearly in the axial direction. In other words, the first bottom surface 16 is a plane extending in the intersecting 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 13d 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 intersecting 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 intersecting direction. The depth H2 of both end portions 16b of the first bottom surface 16 in the intersecting direction is the same as the central portion (groove bottom) of the groove width of the outer peripheral raceway surface 13. Therefore, as shown in Fig. 3, the first bottom surface 16 is connected to the central portion (groove bottom) of the groove width of the outer peripheral raceway surface 13 without any step.

[0059] As shown in Fig. 4, the top 5 is formed point symmetrically with respect to a center C (see Fig. 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 top 5 is formed in an S-shape when viewed from the radial outside. When the ball 4 moves through this circulation path 30, it returns one lead. Although the circulation path 30 of the embodiment is S-shaped when viewed from the radial outside, the present disclosure may be a straight line connecting the screw shaft side openings 13b, and is not particularly limited. The second side surface 26 is provided with a top side opening 31. 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 top 5 through the top side opening 31.

[0061] As shown in Fig. 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 the spiral direction. The two protrusions 42 are spaced apart from each other in the axial direction. Thus, a groove surface 43 is provided between the two protrusions 42, recessed radially inward and extending in the spiral direction.

[0062] As shown in Fig. 6, the cross-sectional shape of the protrusion 42 is semicircular. The protrusion 42 is accommodated inside the inner raceway surface 6a of the nut 6. The protrusion 42 and the inner raceway surface 6a are spaced apart. Furthermore, the thread 6b of the nut 6 is accommodated inside the groove surface 43. The groove surface 43 and the thread 6b are spaced apart. As a result, 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 size H3 (see FIG. 7) of the tongue 40 in the width direction gradually decreases toward the tip portion 40a of the tongue 40, forming a tapered shape.

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

[0065] According to the tongue 40 described above, the ball 4 that enters 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 load acts on the ball 4 in the radially inward direction. As a result, the path of the ball 4 becomes radially inward from the track 8 (spiral direction), and the ball 4 smoothly enters the circulation path 30. Furthermore, since 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 piece 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 seen from the second bottom surface. As shown in FIG. 7, the second bottom surface 50 is provided with a circulation groove surface 51 recessed radially outward from the second bottom surface 50. The internal space of the circulation groove surface 51 constitutes the circulation path 30. As shown in FIG. 6, the cross section of the circulation groove surface 51 cut in the groove width direction is U-shaped. That is, the second bottom surface 50 is provided with a bottom opening 53 that opens the circulation path 30 toward the radially inward direction. According to this, when the top 5 is manufactured, the mold that molds the circulation path 30 (circulation groove surface 51) can be moved radially inward (released). Therefore, the top 5 is easier to manufacture 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. For this reason, as shown in FIG. 3, the portion of the first bottom surface 16 that closes the bottom opening 53 (see between two imaginary lines K54 in FIG. 3) serves as a rolling surface 54 on which the balls 4 moving through the circulation path 30 roll. As a result, 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, a depth H5 of the circulation groove surface 51 from the second bottom surface 50 (first bottom surface 16) is constant in the length direction 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 intersecting direction Y. This allows the balls 4 to move smoothly.

[0070] Next, the effect of the ball screw device 1 of the first embodiment will be described with reference to FIG. 8. FIG. 8 is a schematic diagram of a cross section of the ball screw device of the first embodiment and a comparative example taken along the raceway and the circulation path. Moreover, the imaginary line K10 shown in FIG. 8 is a curved line 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. 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, as shown in Fig. 8. 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). This causes the ball 4 to change course radially inward from the tongue 40 and enter 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 an arc. 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 the course of the ball 4 is θ11.

[0073] On the other hand, in the comparative example, the bending angle at which the ball 4 enters 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 in the intersecting direction of the bottom surface 1016 are recessed radially inward. From the above, in this embodiment, the bending angle θ11 is small, so that the movement of the ball 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 penetrating the nut 6 and having an outer peripheral raceway surface 13 on its outer peripheral surface, a plurality of balls 4 arranged on a raceway 8 between the outer peripheral raceway surface 13 and the inner peripheral raceway surface 6a, and at least one or more tops 5 for circulating 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 accommodates the tops 5. The recess 14 has a first bottom surface 16 facing 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 tongues 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 is 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 tongues 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. In addition, the dimensions can be controlled using the flat first bottom surface 16 as a reference surface, making it easy to manufacture the recesses 14. In addition, since the circulation path 30 of the link 5 opens radially inward, it is easy to manufacture the link 5 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. In addition, the bending angle of the path of the ball 4 when it enters the circulation path 30 is small. Therefore, the ball 4 moves between the track 8 and the circulation path 30 smoothly.

[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 a virtual line K1 that extends radially outward from the center O1 of the screw shaft 2. The recess 14 has an annular inner circumferential surface 15 that surrounds the periphery of the top 5. The inner circumferential 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, the movement of the top 5 in the cross direction Y and the top falling off from the recess 14 are prevented.

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

[0082] 9, the ball screw device 1A of the embodiment 2 differs from the ball screw device 1 of the embodiment 1 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 center 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 16a in the intersecting direction. The central portion of the concave surface 201 is in contact with the imaginary line K16. In other words, the distance from the center O1 (not shown in FIG. 10) of the central portion 16a in the intersecting direction of the concave surface 201 is the same as that of the first bottom surface 16 in the first embodiment.

[0084] The frame 5A of the second embodiment is different from the frame 5 of the first embodiment in that a convex portion 251 that protrudes radially outward is provided at the center of the length of the circulation groove surface 51A. Therefore, the circulation groove surface 51A has a shape corresponding to the first bottom surface 16A. In addition, 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 has a central portion in the longitudinal direction that is sunk 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 than that of the first embodiment by L (see FIG. 10), improving the load resistance of the ball screw device 1A.

[0086] In addition, flat surfaces 202 are arranged on both ends of the first bottom surface 16A in the intersecting direction. Therefore, the bending angle when entering the circulation path 30A from the track 8 is smaller in the second embodiment than when the entire first bottom surface 16 is a concave surface, 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 likely to break.

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

[0090] (Embodiment 4) FIG. 12 is a cross-sectional view of the top and recess of the ball screw device of the fourth embodiment cut in the axial and radial directions. As shown in FIG. 12, in the ball screw device 1C of the fourth embodiment, the distance between the first bottom surface 16C and the center O1 is h. The distance from the center O1 to the thread 6b of the nut 6 is R. The diameter of the ball 4 is 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 facing 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 (groove surface 43) facing the thread 6b of the nut 6 of the outer diameter surface 41 of the top 5C 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 preferable that the distance h satisfies the following formula (2).

[0091]

number

[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 becomes longer. This improves the load resistance of the ball screw device 1C.

[0093] Above, the first to fourth embodiments have been described. 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 piece 5 from both sides in the cross direction Y, but the present disclosure is not limited to such recesses. In the next 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 embodiment 5. A ball screw device 1D of the embodiment 5 is different from the embodiment 1 in that a top 5D is exposed in the intersecting direction Y from a 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 the fifth embodiment. A recess 14D of a screw shaft 2 of a ball screw device 1D of the fifth embodiment differs from the recess 14 of the first embodiment 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 the fifth embodiment does not have a pair of second opposing surfaces 18 (see FIGS. 3 and 4) that sandwich the top 5 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 opposing each other in the axial direction.

[0097] One of the pair of openings 150, 150 opens in one direction of the cross direction Y, and the other opens in the other direction of the cross 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 enlarged in the cross direction Y compared to the first embodiment. That is, the recess 14D is enlarged in the cross direction Y compared to the recess 14 of the first embodiment. Also, the frame 5D of the fifth embodiment is enlarged in the cross direction Y compared to the frame 5 of the first embodiment (see FIG. 13).

[0098] Fig. 15 is a view of the recess of the fifth embodiment as viewed from the intersecting direction. As shown in Fig. 15, when viewed from the intersecting direction Y, the opening 150 has a shape (rectangular shape) along the first bottom surface 16 and the pair of first opposing surfaces 17, 17. In other words, the first bottom surface 16 or the pair of first opposing surfaces 17, 17 does not have any protrusions or the like that protrude into the opening 150. Therefore, the top 5 is movable in the intersecting direction Y along the first bottom surface 16 and the pair of first opposing surfaces 17, 17.

[0099] Fig. 16 is a cross-sectional view taken along the line XVI-XVI in Fig. 15. As shown in Fig. 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 Fig. 16). Also, in the fifth embodiment, similarly to the recess 14 in the first embodiment, the top 5D can be disposed radially outside the recess 14D and the top 5 can be moved radially inward (see arrow A2 in Fig. 16) to attach the top 5D to the recess 14D. This increases the options for the direction in which the top 5D can be attached, improving the ease of attachment 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 intersecting 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 the first bottom surface 16. In addition, a non-contact surface 160 that does not abut against the first bottom surface 16 is formed on a part of the second bottom surface 50.

[0102] 18 is a cross-sectional view of the recess and the piece of the fifth embodiment cut in a direction perpendicular to the axial direction, and more specifically, a cross-sectional view of the recess and the piece cut along line XVIII-XVIII in FIG. 15. As shown in FIG. 18, the non-contact surface 160 is disposed radially outside the circuit outer thread groove surface 213 of the screw shaft 2 and is separated from the circuit outer thread groove surface 213. Therefore, in the fifth embodiment, a part of the piece 5D is disposed radially outside the circuit outer thread groove surface 213, not the recess 14D. Hereinafter, the part of the piece 5D disposed radially outside the circuit outer thread groove surface 213 is referred to as the recess outer wall portion 161. The recess outer wall portion 161 is formed at both ends of the piece 5D in the cross 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 helical direction to form the outer peripheral raceway surface 13. Therefore, the circuit outer thread groove surface 213 extends in the same helical direction as the outer peripheral raceway surface 13, but is not connected to the circulation path 30 of the piece 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-mentioned embodiment 5, the balls 4 are reliably guided radially inward by the tang 40 (see Figs. 13 and 18). Therefore, similar to embodiment 1, the balls 4 are prevented from being pinched between the circulation groove surface 51 and the inner circumferential raceway surface 6a. Note that, although the first opposing surface 17 of embodiment 5 extends along the spiral direction as described in embodiment 1, in the present disclosure, the first opposing surface 17 may extend in the intersecting direction Y, and there is no particular limitation on the direction in which the first opposing surface 17 extends (the angle with respect to the intersecting 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] (Variation 1) FIG. 19 is a view of the recess and the top of the modified example 1 viewed from the cross direction. FIG. 20 is a perspective view of the recess of the screw shaft of the modified example 1. In the ball screw device 1E of the modified example 1, the recess 14D is different from the embodiment 5 in that a pair of grooves 220, 220 recessed in the axial direction are formed on the pair of first opposing surfaces 17, 17. Also, the top 5D of the modified example 1 is different from the embodiment 5 in that a pair of protrusions 230, 230 protruding in the axial direction are formed on the pair of first side surfaces 25, 25. In this disclosure, the pair of first opposing surfaces 17, 17 may be referred to as a pair of opposing surfaces. Also, 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 intersecting direction Y. The groove 220 also extends to both ends of the first opposing surfaces 17 in the intersecting direction Y. Both ends of the groove 220 in the intersecting direction Y are open in the intersecting direction Y. As shown in Fig. 19, the size between the pair of first opposing surfaces 17, 17 is W1. The size W2 between the pair of grooves 220, 220 is larger than W1 (W2>W1).

[0108] Moreover, the radial position of the groove 220 (the height from the first bottom surface 16) is the radially innermost position of the first opposing surface 17. Therefore, the radially inner end 220a 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. 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 inserted into the groove 220. Note that, although the protrusion 230 of the embodiment extends in the transverse direction Y, the protrusion 230 of the present disclosure does not necessarily have to extend in the transverse direction Y. 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 smaller 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] A thickness W4 between the pair of protrusions 230, 230 is smaller than a size W2 between the pair of grooves 220, 220 (W2>W4). Therefore, the pair of protrusions 230 is large enough to be housed in the pair of grooves 220, 220. In addition, a thickness W4 between the pair of protrusions 230, 230 is larger than a size W1 between the pair of first opposing surfaces 17, 17 (W4>W1).

[0112] The method of attaching the top 5D of the first modification is to first place 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 5E is pushed into the recess 14D. This causes the top 5D to be attached 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. In the first modification, the grooves 220 are formed in each of the pair of first opposing surfaces 17, 17, but in the present disclosure, the grooves 220 may be formed in one of the pair of first opposing surfaces 17, 17. In such a case, the protrusion 230 accommodated in the groove 220 is formed in 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] (Variation 2) Fig. 21 is a view of the recess and the piece of the modified example 2 viewed from the intersecting direction. As shown in Fig. 21, the ball screw device 1F of the modified example 2 differs from the modified example 1 in that the radial positions of the pair of grooves 220F, 220F and the pair of protrusions 230F, 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 modification 2 as well, as in modification 1, 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 the modified example 3 viewed from the intersecting direction. In the ball screw device 1G of the modified example 3, the top 5D is different from the embodiment 5 in that it is sandwiched between the pair of first opposing surfaces 17, 17 of the recess 14D. In detail, the space between the pair of first opposing surfaces 17, 17 is a size W5. On the other hand, the axial thickness W6 of the top 5D (the space between the pair of first side surfaces 25, 25) is larger than the space between the pair of first opposing surfaces 17, 17 before attachment to the recess 14D. In other words, the top 5D has a tightening margin with respect to the pair of first opposing surfaces 17, 17, and is attached to the recess 14D by press-fitting. As described above, according to the modified example 3, the movement of the top 5D in the radial outward direction and in the intersecting direction Y is restricted.

[0119] The top 5D of the above-mentioned modified examples 1 and 2 may move in the transverse direction Y. In order to restrict the movement of the top 5D in the transverse direction Y, the contents of modified example 3 may be applied. Specifically, the thickness W3 between the pair of first side surfaces 25, 25 may be made larger than the size W1 between the first opposing surfaces 17, 17 (see FIG. 19). In this way, the top 5D has an axial tightening margin with respect to the recess 14D. As a result, the movement of the top 5D in the transverse direction Y is restricted.

[0120] In addition, the present disclosure may be modified examples 4 to 6 described below in order to restrict the movement of the top 5D of modified example 1 and modified example 2 in the transverse direction Y. In the following description, a direction perpendicular to both the axial direction and the transverse direction Y is defined 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 defined 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 defined as a second orthogonal direction Z2 (see FIG. 23, etc.).

[0121] (Variation 4) Fig. 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 Fig. 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 Fig. 23) after the top 5D is attached to the recess 14D.

[0122] 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 cross direction Y.

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

[0124] In addition, in Modification 4, the recess outer flesh portion 161 is crimped, but in the present disclosure, a portion other than the recess outer flesh portion 161 may be crimped to form the crimped portion 161H. In addition, in Modification 4, the crimped portion 161H is adapted to be hooked onto the circuit outer screw groove surface 213, but in the present disclosure, it may be adapted to be hooked onto the thread 13a (outer peripheral surface) of the screw shaft 2. In addition, in Modification 4, a portion of the piece 5D is crimped and deformed (bent) in the orthogonal direction, but in the present disclosure, a portion of the piece 5D may be deformed in the axial direction to form the crimped portion 161H.

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

[0126] In addition, in Modification 4, a pair of crimped portions 161H is formed at both ends of the top 5D in the transverse direction Y, but in the present disclosure, the crimped portion 161H may be formed at 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 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 at the time of manufacturing the top 5D.

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

[0128] Also, when viewed from the perpendicular direction, 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 piece 5I.

[0129] Also, the fifth modification is different from the first modification 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 particularly shown, the crimped portions 163 are formed on both ends of the first bottom surface 16 in the cross 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 are caught by the cutout surfaces 162. Therefore, the movement of the top 5D in the transverse direction Y is restricted.

[0131] In addition, in the modified example 5, the first bottom surface 16 is crimped, but in the present disclosure, the thread 13a of the screw shaft 2 may be crimped. In addition, when the crimped portion 163 is formed in the thread 13a of the screw shaft 2, the notch surface 162 does not need to be formed in the link 5I. In other words, in the present disclosure, the shape of the link is not particularly important. In addition, in the modified example 5, a part of the screw shaft 2 is crimped and deformed (bent) in the orthogonal direction, but in the present disclosure, a part 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 fastening 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 fastening portions 163 may be formed before the top 5D is attached to the recess 14D.

[0133] In addition, in the fifth modification, 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 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) Fig. 26 is a perspective view of the recess of the modified example 6. Fig. 27 is a view of the top of the modified example 6 viewed from the second bottom surface. Fig. 28 is a cross-sectional view taken along the line XXVIII-XXVIII in Fig. 26. As shown in Fig. 26, the ball screw device 1J of the modified example 6 is different from the modified example 1 in that two holes 240 are formed in the first bottom surface 16 of the recess 14D of the screw shaft 2. Also, as shown in Fig. 27, the top 5D of the modified example 6 is different from the modified example 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 is applied to 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 of attaching the top 5D is to place 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 toward 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 with the hole 240 in the perpendicular direction, the protrusion 241 returns to its original shape and enters the hole 240. This allows the top 5D to be attached 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 that is easily elastically deformed is preferable.

[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 provides excellent attachment of the top 5D.

[0138] In addition, while the number of holes 240 and protrusions 241 is two in Modification 6, the present disclosure is not limited to the number shown in the modification as long as the number of holes 240 and protrusions 241 is one or more. In addition, the present disclosure is not particularly limited with respect to the shape of hole 240, and may be, for example, a hemisphere, a truncated cone, a truncated pyramid, a cone, or a pyramid.

[0139] Although the fourth to sixth modifications have been described above, the present disclosure may apply the contents of the fourth to sixth modifications to the third modification. This makes it possible to more reliably restrict the movement of the top in the intersecting direction Y.

[0140] Although each embodiment and each modified example have been described above, the circulation groove surface 51 of the present disclosure may be a square groove having a cross-sectional shape of a square. Or, 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. In addition, in the ball screws of the first to fourth embodiments, the top may have a tightening margin in the recess, and the top may be attached to the recess by press-fitting. In addition, the recess 14B of the fifth embodiment and each modified example has two openings 150, 150, but the present disclosure may have one opening 150. In other words, the recess may be open only in one of the cross directions Y.

[0141] The present disclosure may also be implemented in the following combinations: (1) A nut having an inner raceway on its inner circumferential surface; A screw shaft that passes through the nut and has an outer circumferential raceway on its outer circumferential surface; a plurality of balls disposed in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; At least one piece for circulating the ball; Equipped with The outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the piece, The recess has a first bottom surface facing radially outward, At least a portion of the first bottom surface is a flat surface, The frame is: a second bottom surface in contact with the first bottom surface; A circulation groove surface that is recessed radially outward from the second bottom surface and has an internal space that forms a circulation path; A bottom opening that opens the circulation path toward the inside in the radial direction; A pair of frame-side openings that open the circulation path in a circumferential direction and connect the circulation path and the track; a pair of tangs for guiding the ball that has entered the circulation path from the raceway radially inward; having 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 entire first bottom surface is flat. A ball screw device as described in (1). (3) When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual line extending radially outward from the center of the screw shaft, A concave surface recessed radially inward is provided at a central portion of the first bottom surface in the intersecting direction, A flat surface is provided on both sides of the concave surface in the intersecting direction. A ball screw device as described in (1). (4) The tongue is provided with a rib that protrudes radially outward. A ball screw device according to any one of (1) to (3). (5) When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual line extending radially outward from the center of the screw shaft, The recess has an annular inner circumferential surface surrounding the periphery of the piece, The inner circumferential surface has a pair of side surfaces sandwiching the piece from both sides in the intersecting direction. A ball screw device according to any one of (1) to (4). (6) 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 piece 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 of the outer diameter surface of the piece from the portion 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×Dw or more and 0.25×Dw or less, A distance h between the first bottom surface and the center of the screw shaft satisfies the following formula (3): A ball screw device according to any one of (1) to (5).

[0142]

number

[0143] (7) When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual 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. A ball screw device according to any one of (1) to (4). (8) The recess has two of the openings, The two openings are The opening portion opens in one of the intersecting directions; The opening portion is open to the other side of the intersecting direction. A ball screw device as described in (7). (9) The recess has a pair of opposing surfaces opposed to each other in the axial direction, The top has a pair of side surfaces facing the axial direction and opposed to the pair of opposed surfaces, At least one of the pair of opposing surfaces is formed with a groove recessed in the axial direction and extending in the intersecting direction, 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. A ball screw device as described in (7) or (8). (10) The groove is formed in both of the pair of opposing surfaces, The protrusions are formed on both of the pair of side surfaces. A ball screw device as described in (9). (11) The recess has a pair of opposing surfaces opposed to each other in the axial direction, The block has a clamping margin with respect to the pair of opposed surfaces and is sandwiched between the pair of opposed surfaces. A ball screw device according to any one of (7) to (10). (12) A direction perpendicular to both the axial direction and the intersecting 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 ends of the piece in the cross direction is formed with a crimped portion that protrudes in the first orthogonal direction beyond the first bottom surface. A ball screw device according to any one of (7) to (11). (13) A direction perpendicular to both the axial direction and the intersecting direction is defined as an orthogonal direction, Among the orthogonal directions, the direction opposite to the direction in which the center of the screw shaft is disposed as viewed from the first bottom surface is defined as a second orthogonal direction, The screw shaft is provided with a crimping portion that is disposed on at least one of both sides of the piece in the intersecting direction and that protrudes in the second orthogonal direction beyond the first bottom surface. A ball screw device according to any one of (7) to (11). (14) The first bottom surface has one or more holes formed therein; The second bottom surface is formed with a protrusion that fits into the hole. A ball screw device according to any one of (7) to (11). [Explanation of symbols]

[0144] 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1J Ball screw device 2 Screw shaft 4. Ball 5, 5A, 5B, 5D pieces 6 Nuts 6a Inner raceway surface 8 orbits 13 Outer raceway surface 14, 14D recess 15 Inner surface 16, 16A 1st bottom 17 First opposing surface 18 Second opposing surface 13a thread 13b Screw shaft side opening 13c End face 13d partial end face 25 First aspect 26 Second aspect 30, 30A circulation path 31 Frame side opening 40 Tongue 41 Outer diameter surface 42 Protrusion 43 Groove surface 50 2nd bottom surface 51 Circulation groove surface 53 Bottom opening 54 Rolling surface 60 Ribs 100 Brake Caliper 104 Electric Actuator 120 Housing 150 Opening 160 Uncontacted Surface 161 Concave outer wall 161H, 163 Crimping part 162 Cutout surface 201 Concave 202 plane 213 Circuit outer screw groove surface 220, 220F groove 230, 230F protrusion 240 holes 241 Protrusion 251 Convex

Claims

1. A nut having an inner raceway on its inner circumferential surface; A screw shaft that passes through the nut and has an outer circumferential raceway on its outer circumferential surface; a plurality of balls disposed in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; At least one or more pieces for circulating the ball; Equipped with The outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the piece, The recess has a first bottom surface facing radially outward, At least a portion of the first bottom surface is a flat surface, The frame is: a second bottom surface in contact with the first bottom surface; a circulation groove surface that is recessed radially outward from the second bottom surface and has an internal space that constitutes a circulation path; A bottom opening that opens the circulation path toward the inside in the radial direction; A pair of frame-side openings that open the circulation path in a circumferential direction and connect the circulation path and the track; a pair of tangs for guiding the ball that has entered the circulation path from the raceway radially inward; having 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 entire first bottom surface is a flat surface. The ball screw device according to claim 1 .

3. When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual line extending radially outward from the center of the screw shaft, A concave surface recessed radially inward is provided at a central portion of the first bottom surface in the intersecting direction, A flat surface is provided on both sides of the concave surface in the intersecting direction. The ball screw device according to claim 1 .

4. The tongue is provided with a rib that protrudes radially outward. The ball screw device according to claim 1 .

5. When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual line extending radially outward from the center of the screw shaft, The recess has an annular inner circumferential surface surrounding the periphery of the piece, The inner circumferential surface has a pair of side surfaces sandwiching the piece from both sides in the intersecting direction. The ball screw device according to claim 1 .

6. 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 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 of the outer diameter surface of the piece from a portion 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×Dw or more and 0.25×Dw or less, A distance h between the first bottom surface and the center of the screw shaft satisfies the following formula (1): The ball screw device according to any one of claims 1 to 5. [0010]

7. When viewed from an axial direction parallel to the screw shaft, the first bottom surface extends in an intersecting direction intersecting a virtual 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. The ball screw device according to claim 1 .

8. The recess has two of the openings, The two openings are The opening portion opens in one of the intersecting directions; The opening portion is open to the other side of the intersecting direction. The ball screw device according to claim 7.

9. The recess has a pair of opposing surfaces opposed to each other in the axial direction, The top has a pair of side surfaces facing the axial direction and opposed to the pair of opposed surfaces, At least one of the pair of opposing surfaces is formed with a groove recessed in the axial direction and extending in the intersecting direction, 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. The ball screw device according to claim 7.

10. The groove is formed in both of the pair of opposing surfaces, The protrusions are formed on both of the pair of side surfaces. The ball screw device according to claim 9.

11. The recess has a pair of opposing surfaces opposed to each other in the axial direction, The block has a clamping margin with respect to the pair of opposed surfaces and is sandwiched between the pair of opposed surfaces. The ball screw device according to any one of claims 7 to 10.

12. A direction perpendicular to both the axial direction and the intersecting 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 ends of the piece in the cross direction is formed with a crimping portion that protrudes in the first orthogonal direction beyond the first bottom surface. The ball screw device according to any one of claims 7 to 10.

13. A direction perpendicular to both the axial direction and the intersecting direction is defined as an orthogonal direction, Among the orthogonal directions, a direction opposite to a direction in which the center of the screw shaft is disposed as viewed from the first bottom surface is defined as a second orthogonal direction, The screw shaft is provided with a crimping portion that is disposed on at least one of both sides of the piece in the intersecting direction and protrudes in the second orthogonal direction beyond the first bottom surface. The ball screw device according to any one of claims 7 to 10.

14. The first bottom surface has one or more holes formed therein; The second bottom surface is formed with a protrusion that fits into the hole. The ball screw device according to any one of claims 7 to 10.

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