Ball screw

Abstract

To provide a ball screw provided with a movable element capable of being molded by die molding.SOLUTION: A ball screw is composed of a screw shaft, a nut, balls, and a movable element in which a circulation path is provided. The circulation path includes an introduction section, a discharge section, and an intermediate section. In the introduction section, a first tongue portion 800 is provided to scoop up a ball that has rolled to the end point of the ball rolling path after entering the screw groove of the screw shaft, while in the discharge section, a second tongue portion 801 is provided to guide a ball, which has rolled through the circulation path after entering the screw groove of the screw shaft, toward the starting point of the ball rolling path. The circulation path is structured so that the inner peripheral surface extending from the first tongue portion 800 to the second tongue portion 801 is not open on the radially inner side. The movable element is equipped with a first divided body 511 and a second divided body, which are assembled to form the circulation path. The first divided body 511 and the second divided body are arranged so that the circulation path is split along the trajectory of the center of the balls within the circulation path as seen from the axial direction of the screw shaft.SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] Conventionally, in a ball screw in which a ball return passage that returns the ball rolling groove by one turn is provided in a deflector to form an infinite track for the balls, it has been proposed to form the ball return passage in a tunnel shape to isolate the balls from the outer peripheral surface of the screw shaft, and to form U-shaped ball scooping sections at both ends of the ball return passage (see Patent Document 1).

[0003] The deflector is constructed by combining a pair of deflector halves that are radially divided along the center line of the ball return passage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-165274 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, various shapes of the circulation passage such as the ball return passage described above have been considered so that the balls can roll smoothly. Depending on the shape of this circulation passage, when dividing the circulation passage in the radial direction along the center line of the circulation passage as described above, undercuts may occur, making it difficult to mold the circulation passage using a die.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a ball screw having a bearing member that can be molded by die. [Means for solving the problem]

[0007] One aspect of the present invention comprises a threaded shaft having a screw groove on its outer peripheral surface, a nut fitted onto the threaded shaft and having a screw groove formed on its inner peripheral surface which forms a ball rolling path together with the screw groove, a ball disposed in the ball rolling path, and a top member having a circulation path formed therein for returning the ball from an end point of the ball rolling path to a start point thereof, the circulation path having an introduction portion that guides the ball from the end point of the ball rolling path to the circulation path, an outlet portion that guides the ball from the circulation path to the start point of the ball rolling path, and an intermediate portion between the introduction portion and the outlet portion, and the introduction portion is provided with a ball that has entered the screw groove of the threaded shaft and rolled to the end point of the ball rolling path. the lead-out portion is provided with a first tongue portion that scoops up the ball that has entered the screw groove of the screw shaft and rolled along the circulation path, and the lead-out portion is provided with a second tongue portion that guides the ball that has entered the screw groove of the screw shaft and rolled along the circulation path toward the start of the ball rolling path, the circulation path is configured such that the inner circumferential surface formed from the first tongue portion to the second tongue portion does not open radially inward, the top member includes a first divided body and a second divided body that are combined with each other to form the circulation path, and the first divided body and the second divided body are configured such that the circulation path is divided along the trajectory of the center of the ball in the circulation path when viewed from the axial direction of the screw shaft. Effect of the Invention

[0008] According to the present invention, it is possible to provide a ball screw having a bearing member that can be molded by a die. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing a ball screw according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic diagram of a ball screw with the nut and the bearing member shown in a transparent state. [Diagram 3] FIG. 4A is a schematic diagram showing a top member according to the present embodiment, and FIG. 4B is a schematic diagram showing a nut according to the present embodiment. [Figure 4] Exploded view of the top parts. [Diagram 5] FIG. [Figure 6] FIG. 4 is a schematic diagram showing the movement trajectory of a ball in the circulation path when viewed from the axial direction. [Figure 7] FIG. 13 is a diagram showing the movement trajectory of the balls in the circulation path as viewed from the radial direction. [Figure 8] FIG. 4A is a perspective view of the first divided body, FIG. 4B is a plan view of the first divided body, and FIG. [Figure 9] FIG. 4A is a perspective view of the second divided body, FIG. 4B is a bottom view of the second divided body, and FIG. [Figure 10] 13A and 13B are diagrams showing a top member according to a modified example, in which FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Ball screw schematic configuration> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing a ball screw 1 according to this embodiment, which includes a screw shaft 2, a nut 3, balls 4 (see Fig. 2), and a top member 5. A helical screw groove 21 is formed on the outer circumferential surface of the screw shaft 2 with a predetermined lead angle, and a nut 3 is fitted onto the outside of the screw shaft 2.

[0011] The nut 3 has a generally cylindrical shape into which the screw shaft 2 is inserted, and has an inner diameter larger than the outer diameter of the screw shaft 2. As shown in Fig. 2, in which the nut 3 and the top member 5 are shown in a transparent state, a helical thread groove 31 is formed on the inner peripheral surface of the nut 3 with the same lead angle as that of the screw shaft 2. This thread groove 31 faces the thread groove 21 of the screw shaft 2 and constitutes the rolling path 6 for the balls 4 together with the thread groove 21.

[0012] The top member 5 is attached to the mounting holes 32 formed in the nut 3, and has a circulation path 7 that returns the balls from the end point of the rolling path 6 to the start point. The nut 3 is formed with a plurality of mounting holes 32 (three in this embodiment) at different positions in the circumferential and axial directions, and the top member 5 is attached to each mounting hole 32. In this embodiment, the nut 3 is provided with a plurality of mounting holes 32 at different phases, but these plurality of mounting holes 32 may be provided such that at least any combination of the mounting holes 32 are aligned at different axial positions in the same circumferential phase (in a horizontal row).

[0013] The circulation path 7 of the top member 5, together with the above-mentioned rolling path 6, forms an infinite circulation path in which the balls 4 circulate infinitely. For this reason, in the ball screw 1, when the screw shaft 2 rotates, the balls 4 in the above-mentioned rolling path 6 and circulation path 7 roll, and the nut 3, which is fixed to a mechanical part or the like so as not to rotate, moves linearly in the axial direction. The nut 3 is provided with an attachment part 33 for attaching the above-mentioned mechanical part or the like, and by rotating the screw shaft 2 relative to the nut 3, the mechanical part attached to the nut 3 can be positioned, etc.

[0014] <Detailed configuration of the top parts> Next, a detailed configuration of the top member 5 will be described. As shown in Fig. 3(a), the top member 5 is configured to include a main body portion 51 and a flange portion 52, and is attached to the attachment hole 32 of the nut 3. As shown in Fig. 3(b), the attachment hole 32 includes a bottom surface 321, a through hole 322 formed in the bottom surface 321, and an inner wall 323 erected from the bottom surface 321. The top member 5 is attached to the attachment hole 32 by inserting the main body portion 51 of the top member 5 into the through hole 322 and seating the flange portion 52 of the top member 5 on the bottom surface 321.

[0015] More specifically, the above-mentioned through hole 322 is an elongated hole that penetrates all the way to the hollow portion of the nut 3, and the main body 51 of the top member 5 also has an elliptical cross section that corresponds to the above-mentioned through hole 322. Therefore, the main body 51 of the top member 5 can be inserted into the above-mentioned through hole 322 with a predetermined tolerance, and the position of the top member 5 in the rotational direction is thereby determined.

[0016] As described above, the flange portion 52 of the top member 5 is configured to seat on the bottom surface 321 of the mounting hole 32, thereby positioning the top member 5 in the radial direction (height direction). As shown in FIG. 2, a stop ring 85 is disposed on the radial outer side of the top member 5 in the large-diameter circular recess 324 formed by the bottom surface 321 and the inner wall 323 to prevent the top member 5 from coming off. The stop ring 85 is a restricting member that restricts only the radial movement of the top member 5 without restricting the movement of the top member 5 in the rotational direction, thereby preventing the top member 5 from coming off the mounting hole 32, and the stop ring 85 prevents the top member 5 from coming off in the radial direction. In other words, the stop ring 85 as a fixing device does not fix the top member 5 in the rotational direction, but fixes it only in the radial direction, so that the top member 5 is in a floating state in the rotational direction.

[0017] Therefore, when the ball 4 is introduced into / exited from the circulation path 7 and a reaction force acts in the rotational direction, the top member 5 moves in the rotational direction within the gap between the main body portion 51 and the through hole 322, so that the circulation path 7 naturally aligns with the inlet / outlet of the rolling path 6.

[0018] In the above embodiment, the through hole 322 is an elongated hole, but is not limited to this. As long as the fit between the main body 51 and the through hole 322 can regulate the rotational position (rotation range) of the top member 5, the through hole 322 may have any shape, such as an elliptical shape or a rectangular shape.

[0019] 4, the top member 5 is divided into a plurality of divided bodies 511, 512 (two in this embodiment). Of the first and second divided bodies 511, 512, the second divided body 512 is provided with a circular protrusion 53, and a metal shim plate (not shown) is fitted to the circular protrusion 53 in a manner interposed between the retaining ring 85 and the flange portion 52. Similarly, a ring-shaped metal shim plate (not shown) is fitted to the main body portion 51 of the top member 5. The divided bodies 511, 512 are connected in the circumferential direction by the fitting of the first and second divided bodies 511, 512, and are connected in the assembly direction of the second divided body 512 to the first divided body 511 by being held down by the above-mentioned retaining ring 85 so as not to be separated. The divided structure of the top member 5 will be described in detail later.

[0020] Next, the configuration of the circulation path 7 of the top member 5 will be described in detail. As shown in Fig. 5, the circulation path 7 includes an introduction section 71 that introduces the ball 4 from the end point of the rolling path 6 into the circulation path 7, an outlet section 72 that leads the ball 4 from the circulation path 7 to the start point of the rolling path 6, and an intermediate section 73 that is located between the introduction section 71 and the outlet section 72 and moves the ball 4 to the adjacent screw groove 21 (rolling path 6) by climbing over one thread of the screw thread 22 of the screw shaft 2. In addition, the introduction section 71 and the outlet section 72 are provided with tongue sections 800, 801 that enter the screw groove 21 of the screw shaft 2 and guide the ball 4, and the ball 4 is scooped up from the rolling path 6 into the circulation path 7 by the tongue sections 800, 801 and sent out from the circulation path 7 to the rolling path 6.

[0021] As shown in Fig. 6, the circulation path 7 is configured such that a movement locus 74 of the center of the ball 4 in the circulation path 7 is in the shape of a circular arc when viewed from the axial direction of the screw shaft 2. Specifically, the movement locus 74 is configured to include a tangent 76 to the ball center diameter 75 at an intersection T0 between the rake angle α and the ball center diameter 75 of the nut 3 (rolling path 6), a circular arc 77 tangent to the tangent 76, and a tangent 78 described in detail below. At least a part of the tangent portion (first portion) 76 of the movement locus 74 between the point T0 and T1, which is the starting point of the arc 77, is located in the introduction portion 71 and scoops up the ball 41 and removes it from the rolling path 6, so that the ball 41 can be scooped up by the ball center diameter 75 of the nut 3 (rolling path 6) and smoothly removed from the rolling path 6.

[0022] The scooping angle α is the angle between an imaginary line L1 connecting the center C1 (above point T0) of the ball 41 at the starting point where guiding of the ball by the top member 5 begins and the central axis X of the nut 3, and an imaginary line L2 connecting the central axis X of the nut 3 and the center C2 of the ball 42 located at the apex position of the movement trajectory 74 (apex position of the arc 77). The ball center diameter, which can also be called the pitch circle diameter, is the diameter of a cylinder that includes the center of the ball 4 where the screw shaft 2 and the nut 3 are in contact at a theoretical contact point.

[0023] Furthermore, in the movement trajectory 74, at least a part of an arc portion (second portion) 77 between points T1 and T2 is located in the intermediate portion 73, where the ball 42 climbs over the thread 22, and at least the ball 42 at the apex position of the arc portion 77 is located radially outward from the outer diameter (thread 22) of the screw shaft 2. More specifically, in this embodiment, the arc 77 is tangent to the tangent 76 at point T1 of the introduction portion 71 of the circulation path 7 where the tongue portion 800 is provided. Therefore, the ball 41 that has moved in the direction of the tangent 76 can be smoothly placed on the trajectory 77, which is a single arc, and climb over the thread 22.

[0024] Furthermore, by designing the ball 42 to climb over the thread 22 at the apex of the arc 77, it is possible to reduce the thickness of the top member 5 when forming the circulation path 7, and the ball screw 1 has a radially compact configuration.

[0025] 6, at least a part of the tangent portion (fifth portion) 78 between points T2 and T3 of the moving path 74 is located in the lead-out portion 72, and is a tangent to the ball center diameter 75 at the intersection (point T3) between the center C3 of the ball at the end point where the ball 4 is guided by the circulation path 7 and the ball center diameter 75 of the nut 3 (rolling path 6), and the arc 77 is tangent to the tangent 78 at point T2. Therefore, the ball 4 that has rolled in the circulation path 7 faces the tangent direction of the ball center diameter 75 of the rolling path 6 at point T3, and the ball 4 can be smoothly sent out from the circulation path 7 to the rolling path 6. In this embodiment, the angle that the virtual line L3 connecting point C3 and the central axis X of the nut 3 makes with the virtual line L2 is the same as the above-mentioned rake angle α.

[0026] 7, when viewed from the inside in the radial direction, the movement trajectory 80 of the center of the ball 4 is an S-shaped curve. Note that although the movement trajectory 80 is the same as the movement trajectory 74 described above, for the sake of convenience, the movement trajectory viewed from the axial direction is indicated by reference numeral 74, and the movement trajectory viewed from the radial direction is indicated by reference numeral 80.

[0027] Specifically, the movement path 80 includes connection parts 81, 82 inclined at the same lead angle as the screw groove 21 of the screw shaft 2 and the screw groove 31 of the nut 3 described above, and an intermediate part 83 connecting these connection parts 81, 82. The connection part (third part) 81 of the movement path 80 corresponds to the tangential part 76 described above, at least a part of which is located in the introduction part 71 and inclined at the same angle as the lead angle of the rolling path 6. The straight part of the connection part 81 inclined at this lead angle has the straight part having a length equal to or greater than the radius of the ball 4, and the circulation path 7 is configured so that the ball 41 rolling from the rolling path 6 smoothly enters the circulation path 7 at the same angle as the rolling path 6. The connection part 81 is connected to an intermediate part (fourth part) 83 described in detail later by a connection arc 811, and the connection arc 811 is a large arc having a radius equal to or greater than the radius of the ball. For this reason, the ball 4 smoothly rolls to the intermediate part 83. In addition, the straight line portion of the connection portion 81 has a length equal to or greater than the radius of the ball 4, and is therefore equal to or greater than the radius of the ball 4, with the connection point between the straight line portion and the connection arc 811 as its center.

[0028] Similarly, the connection portion (fifth portion) 82 of the movement path 80 corresponds to the tangential portion 78, at least a part of which is located in the lead-out portion 72 and is inclined at the same angle as the lead angle of the rolling path 6. The straight portion of the connection portion 82 inclined at this lead angle has a length equal to or greater than the radius of the ball 4, and is configured so that the ball 41 that rolls in the circulation path 7 is smoothly sent to the rolling path 6 at the same angle as the lead angle of the rolling path 6. The connection portion 82 is connected to the intermediate portion 83 by a connecting arc 821, and the connecting arc 821 is a large arc having a radius equal to or greater than the radius of the ball 4. Therefore, the ball 4 smoothly rolls from the intermediate portion 83 to the connection portion 82. The straight portion of the connection portion 82 has a length equal to or greater than the radius of the ball 4, and is therefore a straight portion having a radius equal to or greater than the radius of the ball 4, with the connecting point of the straight portion and the connecting arc 821 as the center.

[0029] Furthermore, the intermediate portion (fourth portion) 83 of the movement locus 80 corresponds to the above-mentioned arc portion 77, and at least a part of it is located in the intermediate section 73, and is connected to the connection portion 81 at one end side (upstream side in the rolling direction of the ball 4) and is connected to the connection portion 82 at the other end side (downstream side in the rolling direction of the ball 4). The intermediate portion 83 is inclined at a predetermined S-shaped angle β so that a part of it overlaps with the tongue portions 800, 801 when viewed from the radial direction. The S-shaped angle β is the angle formed by the plane P perpendicular to the central axis X of the nut 3 and the intermediate portion 83 of the movement locus 80, and is 45° in this embodiment.

[0030] <Division of the top parts> Next, the division configuration of the top member 5 will be described. In the case of the top member 5 having the tongue portions 800, 801 as in this embodiment, when attempting to divide the top member 5 in the radial direction along the S-shaped movement trajectory 80 as viewed from the radial direction, the shape of the ball groove of the circulation path 7 in the divided body may cause the tongue to be chipped in a plane (cross section) perpendicular to the circulation path 7, or when a division contrivance (embodiment) is made that does not cause the tongue to be chipped, the part corresponding to the tongue may become an arc larger than a semicircle. If the arc of the ball groove becomes larger than a semicircle, that part will become an undercut, making it difficult to mold the part in a die.

[0031] For this reason, in this embodiment, the top member 5 is divided so that the circulation path 7 is divided not by the movement locus 80 when viewed from the radial direction, but by the movement locus 74 when viewed from the axial direction. Specifically, as shown in FIG. 4, the top member 5 is divided into a first divided body 511 and a second divided body 512. As shown in FIGS. 8(a) to 8(c), the first divided body 511 is configured to include a first flange portion 5111, a second flange portion 5112, and a first main body portion 5113, and a mounting recess 5114 for the second divided body 512 is formed by recessing between the first flange portion 5111 and the second flange portion 5112.

[0032] That is, the recess 5114 is formed surrounded by a radial outer side surface 5119 of the first main body portion 5113 and wall surfaces 5111a, 5112a extending radially of the first and second flange portions 5111, 5112. The first flange portion 5111 and the second flange portion 5112 constitute both ends of the flange portion 52 that do not overlap the main body portion 51 in the radial direction, and are integrally connected to the first main body portion 5113 via a pair of engagement projections 5115, 5116 provided on the radial outer side surface 5119. The first main body portion 5113 constitutes a radial inner portion of the main body portion 51 of the top member 5, and as shown in FIG. 8(b), the radial outer side surface 5119 has a dividing surface 5117 of the circulation path 7 and a radial inner side surface 5118 of the circulation path 7.

[0033] The dividing surface 5117 is divided into left and right parts with a radially inner surface (hereinafter also referred to as a ball groove) 5118 in between, and the left and right dividing surfaces 5117 are provided with engagement protrusions 5115, 5116, respectively. As described above, the dividing surface 5117 is configured to divide the circulation path 7 by the movement locus 74, and when viewed from the axial direction, the surface shape is an arc the same as the movement locus 74 (see FIG. 8(c)). In addition, the inner surface 5118 of the circulation path 7 is formed from the first tongue portion 800 to the second tongue portion 801 without opening toward the radially inner side, so that the circulation path 7 does not open toward the radially inner side.

[0034] 9(a) to 9(c), the second divided body 512 is configured to include a third flange portion 5121 and a second main body portion 5122, and is fitted into the mounting recess 5114 of the first divided body 511 described above to configure the top member 5 together with the first divided body 511. The third flange portion 5121 configures the center portion of the flange portion 52 between the first flange portion 5111 and the second flange portion 5112, and this third flange portion 5121 is provided with a circular protrusion 53.

[0035] The second main body 5122 constitutes the radially outer portion of the main body 51 of the top member 5, and as shown in FIG. 9(b), its radially inner surface 5123 has a dividing surface 5124 of the circulation path 7 and a radially outer surface 5125 of the circulation path 7. The dividing surface 5124 is divided into left and right sides with the radially outer surface (hereinafter also referred to as a ball groove) 5125 in between, and this dividing surface 5124 is a mating surface with the dividing surface 5117 of the first divided body 511 described above. For this reason, as shown in FIG. 9(c), when viewed from the axial direction, the dividing surface 5124 of the second divided body 512 also has a surface shape that is the same arc as the movement locus 74.

[0036] Furthermore, the dividing surface 5124 is provided with engagement recesses 5126, 5127 which engage with the engagement protrusions 5115, 5116 of the first divided body 511. When the second divided body 512 is fitted into the mounting recess 5114 of the first divided body 511, the engagement recesses 5126, 5127 engage with the engagement protrusions 5115, 5116 of the first divided body 511, thereby positioning the second divided body 512. When the engagement recesses 5126, 5127 and the engagement protrusions 5115, 5116 are engaged with each other, the dividing surfaces 5117, 5124 described above are brought together, and the circulation path 7 is formed by the ball groove 5118 of the first divided body 511 and the ball groove 5125 of the second divided body 512. At this time, the second partition 512 is restricted in its forward / rearward movement by the engagement between the arc-shaped partition surfaces 5117, 5124 and between the engagement protrusions 5115, 5116 and the engagement recesses 5126, 5127, and its rotational movement is restricted by its side surfaces 5121a, 5121b abutting against the wall surfaces 5111a, 5112a of the first partition 511.

[0037] In this manner, in this embodiment, the piece member 5 is divided so as to be divided along the movement trajectory 74 when the circulation path 7 is viewed from the axial direction. As a result, even in the case of a piece member 5 having tongue portions 800, 801, for example, the cross-sectional shape of the ball grooves 5118, 5125 of the circulation path 7 can be an arc of less than a semicircle, and the piece member 5 can be divided in a shape that does not produce an undercut. At this time, the direction in which the divided bodies 511, 512 are removed from the mold is the radial direction (the direction in which the second divided body is attached and detached).

[0038] Furthermore, when the top member 5 is divided as in this embodiment, the thickness of the tip portions 51131, 51132 of the first divided body 511 in the rolling direction of the balls 4 (extension direction of the circulation path 7) becomes thin as shown in FIG. 8(c). Here, if the size of the top member 5 is small, it is considered that the thickness of the tip portions 51131, 51132 becomes too thin. Therefore, as shown in FIGS. 10(a) and 10(b), the tip portions 51131A, 51132A of the first divided body 511A may be formed shorter than the tip portions 5121, 5122 of the second divided body 512, so that the thickness of the tip portions 51131A, 51132A of the first divided body 511A can be secured.

[0039] Furthermore, in the above-described embodiment, the circulation path 7 is configured so that the movement trajectory 74 has tangents 76, 78 and an arc 77, and the movement trajectory 80 has connection portions 81, 82 and an intermediate portion 83, but this is not limited thereto, and for example, at the connection portion of the movement trajectories 74, 80, there may be a portion intervening that results in a trajectory with a different curvature or inclination than the above-described portions.

[0040] Moreover, the tangents 76, 78 do not necessarily have to be tangents to the ball center diameter at the starting point where the circulation path 7 starts guiding the ball 4 or at the release point where the ball 4 is sent out, but may be tangents to the ball center diameter at other points within the introduction part 71 or the outlet part 72. For example, the tangent at the introduction part 71 may be a tangent to the ball center diameter at the point where the tongue part 800 starts scooping up the ball 4.

[0041] Furthermore, in the above-mentioned embodiment, the restricting member is constituted by the snap ring 85, but the restricting member may be constituted by any material as long as it is possible to restrict the rotational position of the top member 5 in a floating state. Also, the inventions described in the above-mentioned embodiment may be combined in any manner. [Explanation of symbols]

[0042] 1: ball screw / 2: screw shaft / 3: nut / 4: ball / 5: ball bearing member / 6: ball rolling path / 7: circulation path / 21: screw groove / 71: introduction section / 72: outlet section / 73: middle section / 74: trajectory / 511: first division / 512: second division / 800: first tongue section / 801: second tongue section

Claims

[Claim 1] A screw shaft having a screw groove on its outer circumferential surface; A nut is fitted onto the screw shaft and has a screw groove formed on an inner peripheral surface thereof, which forms a ball rolling path together with the screw groove; A ball disposed in the ball rolling path; a ball member having a circulation path formed therein for returning the ball from the end point of the ball rolling path to the start point thereof; the circulation path has an introduction portion that guides the ball from an end point of the ball rolling path to the circulation path, an introduction portion that guides the ball from the circulation path to a start point of the ball rolling path, and an intermediate portion between the introduction portion and the introduction portion, The introduction portion is provided with a first tongue portion that enters the screw groove of the screw shaft and scoops up the ball that has rolled to the end point of the ball rolling path, The lead-out portion is provided with a second tongue portion that guides the ball that has entered the screw groove of the screw shaft and rolled along the circulation path toward the start point of the ball rolling path, The circulation path is configured such that an inner circumferential surface formed from the first tongue portion to the second tongue portion does not open radially inward, The top member includes a first divided body and a second divided body which are combined with each other to form the circulation path, and the first divided body and the second divided body are configured so that the circulation path is divided along a trajectory of the center of the ball in the circulation path when viewed from the axial direction of the screw shaft. A ball screw characterized by:

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