Ball screw device

Abstract

This invention provides a ball screw device that reduces the axial size of the nut. [Solution] The ball screw device comprises a screw shaft, a nut, a plurality of balls, and a rotating part connected to the end of the screw shaft in a second direction. The rotating part has a first projection axially positioned relative to the second end face of the nut. The nut has a cylindrical nut body having an inner circumferential raceway surface and a second end face, a second projection protruding from the second end face in a second direction, and a concave surface recessed from the second end face in a first direction. The second projection enters the trajectory of the first projection, which rotates relative to the second projection, and contacts the first projection. The second projection faces one side in the circumferential direction and has a contact surface that contacts the first projection. The concave surface has a first concave surface positioned adjacent to the second projection on one side in the circumferential direction. The first concave surface extends in a direction perpendicular to the central axis of the screw shaft, and has a first bottom surface at the other end in the circumferential direction that intersects with the contact surface. The corner where the first bottom surface and the contact surface intersect is rounded.

Description

Technical Field

[0001] This disclosure relates to a ball screw device.

Background Art

[0002] A ball screw device is a device that converts rotational motion into linear motion. The ball screw device has a screw shaft, a nut penetrated by the screw shaft, and a plurality of balls disposed between the screw shaft and the nut. In the following patent documents, the ball screw device is used by rotating the screw shaft so that the nut moves in the axial direction.

[0003] In addition, the ball screw device of the following patent document has a rotating part attached to the screw shaft. The rotating part has a first protrusion facing the end face of the nut. A second protrusion protruding toward the rotating part side is formed on the end face of the nut. Then, during the operation of the ball screw device, when the advanced nut retreats and the nut tries to return to a predetermined position (hereinafter referred to as the initial position), the first protrusion and the second protrusion come into contact. Thereby, the rotation of the screw shaft stops, and the nut is surely arranged at the initial position. Hereinafter, the surface of the second protrusion that contacts the first protrusion is referred to as the contact surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in order to avoid stress concentration at the base (root) of the second projection, the corner where the end face of the nut and the contact surface of the second projection intersect often has a rounded (R) cross-sectional shape. On the other hand, the part of the contact surface where the R-shaped section is formed cannot be used as the part that the first projection contacts. For this reason, forming the R-shaped section increases the amount of protrusion of the second projection by the length of the R-shaped section, and the nut becomes larger in the axial direction.

[0006] This disclosure has been made in view of the above, and aims to provide a ball screw device that reduces the axial size of the nut. [Means for solving the problem]

[0007] To achieve the above objective, a ball screw device according to one aspect of the present disclosure comprises: a screw shaft having one end pointing in a first direction and the other end pointing in a second direction, and having an outer peripheral raceway surface formed on its outer peripheral surface; a nut penetrating the screw shaft and having an inner peripheral raceway surface formed on its inner peripheral surface; a plurality of balls arranged in a raceway between the outer peripheral raceway surface and the inner peripheral raceway surface; and a rotating part connected to the end of the screw shaft in the second direction and rotating together with the screw shaft. The direction parallel to the screw shaft is defined as the axial direction. The rotating part has a first projection positioned in the axial direction relative to the second end face of the nut facing the second direction. The nut has a cylindrical nut body having the inner peripheral raceway surface and the second end face, a second projection protruding from the second end face in the second direction, and a concave surface recessed from the second end face in the first direction. The second projection enters the trajectory of the first projection, which rotates relative to the second projection, and contacts the first projection. The second projection faces one direction in the circumferential direction and has a contact surface that contacts the first projection. The concave surface has a first concave surface that is positioned adjacent to the second projection on one side in the circumferential direction. The first concave surface extends in a direction perpendicular to the central axis of the screw shaft and has a first bottom surface at the other end in the circumferential direction that intersects the contact surface, and a first wall surface that connects the first bottom surface and the second end surface. The corner where the first bottom surface and the contact surface intersect is a first radiused portion.

[0008] According to this disclosure, at least a portion of the first R portion is housed in the first concave surface. Therefore, the amount of protrusion of the second projection projecting in the second direction from the second end face is reduced by the depth of the first concave surface. As a result, the nut is made smaller in the axial direction. In addition, stress concentration at the corner on the contact surface side of the first projection can be avoided.

[0009] Furthermore, in the ball screw device described above, the concave surface has a second concave surface that is recessed in the first direction from the second end surface. The second concave surface is positioned adjacent to the second projection on the other side in the circumferential direction. The second projection has a back surface facing the other side in the circumferential direction. The second concave surface has a second bottom surface that extends in a direction perpendicular to the central axis and whose one end in the circumferential direction intersects with the back surface, and a second wall surface that connects the second bottom surface and the second end surface. The corner where the second bottom surface and the back surface intersect is a second radius portion.

[0010] According to the above configuration, it is possible to avoid stress concentration at the corner on the back side of the second projection.

[0011] Furthermore, in the ball screw device described above, the nut body has at least one inner circumferential raceway surface and the same number of circulation paths as the inner circumferential raceway surface, connecting both ends of the inner circumferential raceway surface. The concave surface may be positioned circumferentially offset from the second direction circulation path, which is the second direction circulation path that is positioned furthest in the second direction.

[0012] Furthermore, in the ball screw device described above, a virtual circle is defined as a virtual circle that extends circumferentially along the inner surface of the nut body. This virtual circle is in contact with the portion of the second-direction circulation path that is most closely located in the second direction. The concave surface is recessed in the first direction more than the virtual circle.

[0013] According to the aforementioned ball screw device, the dead space (the area where the inner circumferential raceway surface is not located) positioned in the first direction relative to the virtual circle is used as a concave surface. This allows for miniaturization of the nut in the axial direction.

[0014] Furthermore, in the ball screw device described above, a virtual line extending axially from the point of contact between the virtual circle and the second direction circulation path is defined as the reference line. The relative rotation direction of the screw shaft when the screw shaft rotates relative to the nut, causing the nut to move relative to the screw shaft in the first direction is defined as the first rotation direction. The concave surface is positioned in a range of 5° to 300° from the reference line in the first rotation direction.

[0015] In the range of 5° to 300° from the reference line in the first rotational direction, the axial length of the dead space is relatively large. Therefore, according to the above configuration, there is a large amount of dead space that can be used as a concave surface.

[0016] Furthermore, in the ball screw device described above, the concave surface is positioned in a range of 10° to 240° from the reference line in the first rotational direction.

[0017] In the range of 10° to 240° from the reference line in the first rotational direction, the axial length of the dead space becomes even larger. Therefore, according to the above configuration, the dead space that can be used as a concave surface is further expanded.

[0018] Furthermore, in the ball screw device described above, the axial depth of the first concave surface may be greater than or equal to the axial length of the first R portion.

[0019] Furthermore, in the ball screw device described above, the axial depth of the first concave surface may be less than the axial length of the first R portion.

[0020] Furthermore, in the ball screw device described above, the axial depth of the second concave surface may be greater than or equal to the axial length of the second R portion.

[0021] Furthermore, in the ball screw device described above, the axial depth of the second concave surface may be less than the axial length of the second R portion. [Effects of the Invention]

[0022] According to the ball screw device of the present disclosure, the nut is miniaturized in the axial direction.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a view of the ball screw device of Embodiment 1 as viewed from the outside in the radial direction of the nut. [Figure 2] FIG. 2 is a cross-sectional view of the ball screw device in FIG. 1 with the nut cut axially. [Figure 3] FIG. 3 is a view of the ball screw device of Embodiment 1 as viewed from the second direction. [Figure 4] FIG. 4 is a developed view of the inner peripheral surface of the nut of Embodiment 1 cut axially. [Figure 5] FIG. 5 is a perspective view of the nut of Embodiment 1 as viewed from the second direction. [Figure 6] FIG. 6 is a cross-sectional view taken along the arrow VI-VI in FIG. 3. [Figure 7] FIG. 7 is a schematic view showing a cross-section of the second protrusion of the nut of the comparative example, specifically, a cross-sectional view cut in a direction orthogonal to the contact surface and in the direction in which the second protrusion protrudes. [Figure 8] FIG. 8 is a cross-sectional view of the second protrusion and the concave surface of Modification 1 cut in the circumferential direction. [Figure 9] FIG. 9 is a cross-sectional view of the second protrusion and the concave surface of Modification 2 cut in the circumferential direction. [Figure 10] FIG. 10 is a cross-sectional view of the second protrusion and the concave surface of Modification 3 cut in the circumferential direction. [Figure 11] FIG. 11 is a developed view of the inner peripheral surface of the nut of Modification 4 cut axially.

Modes for Carrying Out the Invention

[0024] The forms for implementing this disclosure will be described in detail with reference to the drawings. This disclosure is not limited by the contents described below. Furthermore, the components described below include those that are readily conceivable to a person skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate.

[0025] (Embodiment 1) Figure 1 is a view of the ball screw device of Embodiment 1 from the radially outer side of the nut. As shown in Figure 1, the ball screw device 100 of Embodiment 1 comprises a screw shaft 1, a nut 2, a plurality of balls (not shown), and a stopper 3 which is a rotating component. The ball screw device 100 is a device that converts rotational motion into linear motion or linear motion into rotational motion.

[0026] In this embodiment, we will use as an example a case in which a ball screw device 100 is used to transmit torque to the screw shaft 1 so that the nut 2 moves in a linear motion. In the following description, the direction parallel to the central axis O of the screw shaft 1 will be referred to as the axial direction, and the direction perpendicular to the central axis O will be referred to as the radial direction.

[0027] Figure 2 is a cross-sectional view of the ball screw device of Figure 1, with the nut cut in the axial direction. As shown in Figure 2, the screw shaft 1 comprises a connecting portion 10, a male spline portion 11, and a screw shaft body 12, which are arranged in order in the axial direction. Hereinafter, the direction in which the screw shaft body 12 is positioned when viewed from the connecting portion 10 in the axial direction will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2.

[0028] The connecting portion 10 is the part that connects to other parts. Furthermore, by connecting the connecting portion 10 to other parts, the screw shaft 1 is supported so that it can rotate freely around the central axis O. When the ball screw device 100 is driven, torque is transmitted to the connecting portion 10 from the other parts. This causes the screw shaft 1 to rotate.

[0029] Other components that rotatably support the screw shaft 1 include, for example, planetary gear mechanisms and reduction devices such as pulleys, but the present disclosure may also include devices other than reduction devices. Furthermore, although the connecting portion 10 shown in Figures 1 and 2 is cylindrical, the present disclosure is not limited to this shape. In the present disclosure, the connecting portion may be composed of, for example, a male spline portion, and the shape of the connecting portion is not particularly limited.

[0030] The male spline portion 11 is the part for attaching the stopper 3. The male spline portion 11 is formed to have a smaller diameter than the screw shaft body 12. The male spline portion 11 extends in the second direction X2 from the end face 13 of the screw shaft body 12 in the second direction X2.

[0031] Figure 3 is a view of the ball screw device of Embodiment 1 from a second direction. As shown in Figure 3, a plurality of external teeth 14 extending in the axial direction are formed on the outer circumferential surface of the male spline portion 11.

[0032] As shown in Figure 2, an outer peripheral raceway surface 15 extending in the helical direction is formed on the outer peripheral surface of the screw shaft body 12. The end face 13 of the screw shaft body 12 in the second direction X2 is a plane perpendicular to the central axis O. The end face 13 abuts against the end face of the stopper 3 in the first direction X1. As a result, the stopper 3 is positioned so as not to move in the first direction X1 relative to the screw shaft 1. In addition, although not specifically shown, the stopper 3 is restricted from moving in the second direction X2 relative to the screw shaft 1 by a retaining mechanism. As an example of a retaining mechanism, a groove extending in the circumferential direction is formed in the male spline portion 11, and a retaining ring that fits into that groove is mentioned, but this disclosure is not particularly limited to the type of retaining mechanism.

[0033] As shown in Figure 1, the nut 2 comprises a nut body 20, a second projection 23 protruding in the second direction X2 from a second end face 22 of the nut body 20 in the second direction X2, and a concave surface 40 recessed in the first direction X1 from the second end face 22. The first end face 21 of the nut body 20 in the first direction X1 is formed flat and does not have a projection or concave surface.

[0034] As shown in Figure 3, the nut body 20 is formed in a cylindrical shape around a central axis O. Furthermore, the nut body 20 is supported by components such as a housing so that it cannot rotate but can move in the axial direction. Therefore, even if the screw shaft 1 rotates, the nut 2 does not rotate with the screw shaft 1 but moves in the axial direction.

[0035] Hereinafter, the direction of rotation of the nut 2 when the screw shaft 1 rotates relative to the nut 2, causing the nut 2 to move relative to the screw shaft 1 in a first direction X1, will be referred to as the first rotation direction L1 (see Figure 3). Also, the direction of rotation of the screw shaft 1 when the nut 2 moves in a second direction X2 will be referred to as the second rotation direction L2 (see Figure 3).

[0036] As shown in Figure 2, the inner circumferential surface 24 of the nut body 20 has multiple inner raceway surfaces 25 and multiple circulation sections 26 (not shown in Figure 2; see Figure 4). The inner raceway surfaces 25 face the outer raceway surface 15. The space between the inner raceway surfaces 25 and the outer raceway surface 15 constitutes a raceway. Multiple balls (not shown) are arranged in the raceway.

[0037] Figure 4 is an unfolded view of the inner circumferential surface of the nut of Embodiment 1, cut axially. As shown in Figure 4, the inner circumferential raceway surface 25 extends spirally for approximately one turn (approximately 1 lead). Each inner circumferential raceway surface 25 is formed individually by machining. Therefore, no groove surfaces extending in the spiral direction are formed between the inner circumferential raceway surfaces 25.

[0038] The circulation section 26 circulates the balls that have moved from one end of the track to the other back to the other end of the track. In this embodiment, the circulation section 26 is composed of an S-shaped circulation path 26a formed by forging (cold forging) the inner circumferential surface 24 of the nut 2. However, in this disclosure, the circulation path 26a may be formed by cutting.

[0039] In this embodiment, five inner circumferential raceway surfaces 25 and five circulation paths 26a are formed. The inner circumferential raceway surface 25 located furthest in the second direction X2 is referred to as the second direction side inner circumferential raceway surface 125. The circulation path 26a connecting both ends of the second direction side inner circumferential raceway surface 125 is referred to as the second direction side circulation path 126. Although there are five inner circumferential raceway surfaces 25 and circulation paths 26a (circulation section 26) in this embodiment, this disclosure only requires one or more, and there are no particular limitations. The second projection 23 and the concave surface 40 will be described later.

[0040] As shown in Figure 3, the stopper 3 has a main body 30 and a first projection 31. The main body 30 is formed in a disc shape with a central axis O. A female spline hole 32 is formed in the center of the main body 30, penetrating the main body 30 in the axial direction. Multiple internal teeth 33 extending in the axial direction are formed on the inner circumferential surface of the female spline hole 32.

[0041] The male spline portion 11 is inserted into the female spline hole 32 and spline-fitted. Specifically, the external teeth 14 of the male spline portion 11 are inserted between the internal teeth 33 of the female spline hole 32. The external teeth 14 and the internal teeth 33 are in contact with each other in the circumferential direction. This spline fitting connects the stopper 3 and the screw shaft 1 so that they cannot rotate relative to each other. In this embodiment, the screw shaft 1 and the stopper 3 are connected by spline fitting, but other connection methods may also be used in this disclosure.

[0042] The outer diameter R of the main body 30 is smaller than the inner diameter r of the nut body 20. The first projection 31 protrudes radially outward from the outer circumferential surface 34 of the main body 30. Therefore, the first projection 31 and the second end face 22 of the nut 2 face each other in the axial direction.

[0043] When the nut 2 is in its initial position, the first projection 31 is in contact with the second projection 23, as shown in Figures 1 and 3. Although not specifically shown, when a torque in the first rotational direction L1 is transmitted to the screw shaft 1, the nut 2 moves in the first direction X1. As a result, the first projection 31 and the second projection 23 move apart. Also, when a torque in the second rotational direction L2 is transmitted to the screw shaft 1, the nut 2 moves in the second direction X2.

[0044] Here, as the nut 2 moves in the second direction X2 to return to its initial position, the first projection 31 rotates together with the screw shaft 1 (rotating in the second rotational direction L2). Meanwhile, the second projection 23 moves in the second direction X2 together with the nut 2. As the nut 2 approaches its initial position, the second projection 23 enters the trajectory of the rotating first projection 31 and comes into contact with the first projection 31. As a result, the screw shaft 1 stops rotating in the second direction X2. The nut 2 also stops moving in the second direction X2 and is positioned in its initial position.

[0045] Next, we will explain the details of the second projection 23 and the concave surface 40.

[0046] Figure 5 is a perspective view of the nut of Embodiment 1, viewed from a second direction. As shown in Figure 5, the second projection 23 has a contact surface 27 facing the first rotation direction L1 and a back surface 28 facing the second rotation direction L2. The contact surface 27 is the surface that contacts the first projection 31 when the nut 2 is in its initial position.

[0047] The concave surface 40 has a first concave surface 41 and a second concave surface 42. The first concave surface 41 is positioned in a first rotational direction L1 relative to the second projection 23. The second concave surface 42 is positioned in a second rotational direction L2 relative to the second projection 23. The first concave surface 41 and the second concave surface 42 are adjacent to each other in the circumferential direction relative to the second projection 23. In addition, the first concave surface 41 and the second concave surface 42 open radially outward and radially inward, respectively.

[0048] Figure 6 is a cross-sectional view taken along the line VI-VI in Figure 3. As shown in Figure 6, the axial depth (hereinafter referred to as depth) of the concave surface 40 is formed to H1. More specifically, the depth from the second end surface 22 by the first concave surface 41 and the depth from the second end surface 22 by the second concave surface 42 are both formed to the same H1.

[0049] The first concave surface 41 has a first bottom surface 44 and a first wall surface 45 positioned between the second end surface 22 and the first bottom surface 44. The second concave surface 42 has a second bottom surface 46 and a second wall surface 47 positioned between the second end surface 22 and the second bottom surface 46.

[0050] The first bottom surface 44 and the second bottom surface 46 extend radially. The first wall surface 45 and the second wall surface 47 are inclined surfaces located in the second direction X2 as they move away from the second projection 23 in the circumferential direction. The present disclosure is not particularly limited, and the first wall surface 45 and the second wall surface 47 may be perpendicular to the second end surface 22.

[0051] The axial length of the second projection 23 is H2. The axial length H2 of the second projection 23 is greater than the depth H1 of the concave surface 40 (first concave surface 41 and second concave surface 42). Therefore, the second projection 23 protrudes from the second end surface 22 in the second direction X2.

[0052] The end of the first base surface 44 in the second rotational direction L2 intersects with the contact surface 27 of the second projection 23. The corner where the first base surface 44 and the contact surface 27 intersect is an R-shaped section (hereinafter referred to as the first R-shaped section 51). The cross-sectional shape of the first R-shaped section 51, when cut along a virtual plane perpendicular to the contact surface 27 and the first base surface 44, is arc-shaped. This prevents stress concentration on the base side (end side in the first direction X1) of the contact surface 27 of the second projection 23.

[0053] Furthermore, the end of the second base surface 46 in the first rotational direction L1 intersects with the back surface of the second projection 23. The corner where the second base surface 46 and the back surface 28 intersect has a curved cross-sectional shape (hereinafter referred to as the second R-shaped section 52). As a result, stress concentration on the base side (end side in the first direction X1) of the back surface 28 of the second projection 23 is avoided.

[0054] The axial length of the contact surface 27 is H4. This axial length H4 of the contact surface 27 is long enough to contact the first projection 31 and reliably stop the movement of the second projection 23. The axial length of the first R portion 51 is H3. The axial length H2 of the second projection 23 is the sum of the axial length H4 of the contact surface 27 and the axial length H3 of the first R portion 51. Therefore, the second projection 23 is larger by the axial length H3 than if the first R portion 51 were not formed.

[0055] Furthermore, the axial length of the second R portion 52 is the same as the axial length H3 of the first R portion 51. The axial lengths H3 of the first R portion 51 and the second R portion 52 coincide with the depth H1 of the first concave surface 41. Therefore, the first R portion 51 and the second R portion 52 do not protrude from the second end face 22 in the second direction X2.

[0056] Next, the effects of Embodiment 1 will be explained using a comparative example.

[0057] Figure 7 is a schematic diagram showing a cross-section of the second projection of the nut of the comparative example, and more specifically, it is a cross-sectional view taken in a direction perpendicular to the contact surface and in the direction in which the second projection protrudes. As shown in Figure 7, a second projection 202 is formed on the second end face 201 of the nut 200 of the comparative example. An R-shaped portion 204 is formed at the corner between the contact surface 203 of the second projection 202 and the second end face 201. Therefore, the difference from the embodiment is that the concave surface 40 (first concave surface 41) is not formed in the comparative example.

[0058] The axial length H34 of the contact surface 203 of the comparative example is the same as the axial length H4 of the contact surface 27 of Embodiment 1 (H34 = H4). The axial length H33 of the R portion 204 of the comparative example is the same as the axial length H3 of the first R portion 51 of Embodiment 1 (H33 = H3). Therefore, the axial length H32 of the second protrusion 202 of the comparative example is the same as the axial length H2 of the second protrusion 23 of Embodiment 1 (H32 = H2).

[0059] According to the comparative example, the protrusion amount H35 of the second protrusion 202 protruding from the second end face 201 in the second direction X2 is equal to the axial length H32 of the second protrusion 202 (H35 = H32). On the other hand, in Embodiment 1, the protrusion amount of the second protrusion 23 protruding from the second end face 22 in the second direction X2 is H5 obtained by subtracting the depth amount H1 of the concave surface 40 from the axial length H2 of the second protrusion 23. Therefore, the protrusion amount H5 of the second protrusion 23 of the present embodiment is smaller than the protrusion amount H35 of the second protrusion 202 of the comparative example (H5 < H35). For this reason, the nut 2 of Embodiment 1 is miniaturized in the axial direction.

[0060] Next, the relationship between the nut 2 and the concave surface 40 will be described. As shown in FIG. 4, on the inner peripheral surface 24 of the nut 2, the groove surface most disposed in the second direction X2 is the second-direction side circulation path 126. The virtual circle W in FIG. 4 is drawn in the circumferential direction from the portion of the second-direction side circulation path 126 most disposed in the second direction X2. In the present embodiment, the distance from the second end face 22 to the virtual circle W is H6. And between the virtual circle W and the second-direction side inner peripheral track surface 125, there is a dead space 130 where the inner peripheral track surface 25 and the circulation path 26a are not formed. Therefore, the distance H6 is the distance from the second end face 22 to the dead space 130.

[0061] If the concave surface 40 is disposed in the second direction X2 of the second-direction side circulation path 126, it is necessary to prevent the concave surface 40 from interfering with the second-direction side circulation path 126. That is, it is necessary to dispose the concave surface 40 in the second direction X2 rather than the virtual circle W (see the virtual line P in FIG. 4).

[0062] On the other hand, the concave surfaces 40 (first concave surface 41, second concave surface 42) of this embodiment are positioned offset in the circumferential direction from the second direction circulation path 126. Also, the distance H6 is smaller than the depth H1 of the concave surface 40. In other words, the concave surface 40 is recessed in the first direction X1 beyond the virtual circle W. Therefore, the concave surface 40 of this embodiment utilizes a portion of the dead space 130. For this reason, the nut 2 of Embodiment 1 is smaller in the axial direction than when the concave surface 40 is positioned in the second direction X2 of the second direction circulation path 126 (see the dashed line P in Figure 4).

[0063] Furthermore, the virtual line extending axially from the point of contact between the virtual circle W and the second direction circulation path 126 is defined as the reference line Q. Here, the axial length of the dead space 130 differs depending on the position in the circumferential direction. For example, the axial length of the dead space 130 is relatively large in the range Q1 from 5° to 300° in the first rotation direction L1 from the reference line Q. Also, the range Q2 from 10° to 240° in the first rotation direction L1 from the reference line Q is even larger. Therefore, it is preferable to position the first concave surface 41 and the second concave surface 42, respectively, in a range Q1 from 5° to 300° in the first rotation direction L1 from the reference line Q, in order to expand the range of usable dead space 130. Furthermore, it is even more preferable to position the first concave surface 41 and the second concave surface 42, respectively, in a range Q2 from 10° to 240° in the first rotation direction L1 from the reference line Q, in order to further expand the range of usable dead space 130.

[0064] Although Embodiment 1 has been described above, this disclosure is not limited to the example shown in Embodiment 1. For example, Embodiment 1 described a case where torque is transmitted to the screw shaft 1, but this disclosure may also describe a case where torque is transmitted to the nut 2 and the screw shaft 1 moves in a linear motion. In this case, the first projection 31, which moves in the axial direction, enters the trajectory of the rotating second projection 23 and makes contact with the second projection 23. Even when used in a way that torque is transmitted to the nut 2, the second projection 23 enters the trajectory of the first projection 31, which rotates relative to the second projection 23, and makes contact with the first projection 31, similar to Embodiment 1. In addition, when used to transmit torque to the nut 2, or when used to cause the screw shaft 1 to move in a linear motion, a piston or the like may be connected to the connecting part 10.

[0065] Furthermore, while the depth H1 of the concave surface 40 in Embodiment 1 is greater than the distance H6 to the virtual circle W, in this disclosure it may be less than the distance H6. In other words, in this disclosure the entire concave surface 40 may be positioned in the second direction X2 relative to the virtual circle W. Also, the concave surface 40 may be positioned in the second direction X2 of the second direction side circulation path 126 (see dashed line P in Figure 4).

[0066] Furthermore, while the depth of the first concave surface 41 and the depth of the second concave surface 42 are the same in Embodiment 1, they may be different in this disclosure.

[0067] Next, a modified example of the ball screw device 100 of Embodiment 1 will be described. The following description will focus on the differences from Embodiment 1.

[0068] (Variation 1) Figure 8 is a cross-sectional view of the second projection and concave surface of Modified Example 1, cut in the circumferential direction. As shown in Figure 8, Modified Example 1 differs from Embodiment 1 in that the concave surface 40A of the nut 2A does not have a second concave surface 42. In other words, the concave surface 40A of Modified Example 1 has only a first concave surface 41. According to Modified Example 1, the second R portion 52 is positioned in the second direction X2 relative to the second end face 22. That is, the axial length of the back surface 28 is smaller than that of Embodiment 1. On the other hand, the axial length of the contact surface 27 of Modified Example 1 is the same as that of the contact surface 27 of Embodiment 1. Also, the amount of protrusion of the second projection 23 that protrudes from the second end face 22 in the second direction X2 is the same as that of Embodiment 1. Therefore, in Modified Example 1, as in Embodiment 1, the axial size of the nut 2A can be reduced. Furthermore, in the modified example 1, when the concave surface 40A utilizes a portion of the dead space 130, it is preferable that the first concave surface 41 be positioned in a range Q1 from 5° to 300° in the first rotational direction L1 from the reference line Q. More specifically, it is preferable that the first concave surface 41 be positioned in a range Q2 from 10° to 240° in the first rotational direction L1 from the reference line Q.

[0069] Next, we will describe modified examples 2 and 3, in which the size of the R-shaped parts (first R-shaped part 51, second R-shaped part 52) ​​has been changed. In the following explanation, we will use the first R-shaped part 51 as an example.

[0070] (Variation 2, Variation 3) Figure 9 is a cross-sectional view of the second projection and concave surface of Modified Example 2, cut in the circumferential direction. As shown in Figure 9, Modified Example 2 differs from Embodiment 1 in that the nut 2B of Modified Example 2 has an axial length of the first R portion 51B changed to H13. The length H13 of the first R portion 51B is smaller than the depth H1 of the first concave surface 41 (concave surface 40).

[0071] Figure 10 is a cross-sectional view of the second projection and concave surface of Modified Example 3, cut in the circumferential direction. As shown in Figure 10, Modified Example 3 differs from Embodiment 1 in that the nut 2C of Modified Example 3 has an axial length of the first R portion 51C changed to H23. The length H23 of the first R portion 51C is greater than the depth H1 of the first concave surface 41 (concave surface 40).

[0072] According to the above-described modifications 2 and 3, the amount of protrusion of the second projections 23B and 23C projecting from the second end face 22 in the second direction X2 is reduced by the depth H1 of the first concave surface 41 (concave surface 40). Therefore, similar to embodiment 1, the nuts 2B and 2C are miniaturized in the axial direction.

[0073] Modifications 2 and 3 have been described above. In addition, the circulation section 26 in the embodiment is composed of a circulation path 26a formed on the inner circumferential surface 24 of the nut 2, but in this disclosure, the circulation section 26 may be a spindle, a tube, or the like. Modification 4, in which a spindle is used as the circulation section, will be described below.

[0074] (Modification 4) Figure 11 is an unfolded view of the inner circumferential surface of the nut of Modification 4, cut axially. As shown in Figure 11, Modification 4 differs from Embodiment 1 in that a screw groove surface 70 is formed on the entire inner circumferential surface 24 of the nut 2D. A portion of the screw groove surface 70 is an inner raceway surface 25D. In Modification 4, five inner raceway surfaces 25D are formed. The remaining portion of the screw groove surface 70 is a non-rolling surface 71 on which the ball does not roll.

[0075] Furthermore, the nut 2D in Modified Example 4 differs from that in Embodiment 1 in that it has multiple slotted holes 80 that penetrate radially through the nut 2D. A slotted 26D, which is the circulation section 26, is inserted into the slotted holes 80. The slotted 26D has an S-shaped circulation path 26a formed on its radially inner surface. In Modified Example 4, five slotted 26D are provided. Therefore, there are five circulation paths 26a in Modified Example 4, which is the same number as the inner circumferential raceway surface 25D.

[0076] As described above, in the modified example 4, the axial size of the nut 2D can be reduced in the same way as in the embodiment 1.

[0077] Although Embodiment 1 and its various modifications have been described above, Embodiment 1 uses a stopper 3 as an example of a rotating part, but this disclosure is not limited to this. The rotating part may be a carrier, pulley, gear, or sprocket of a planetary gear mechanism. Furthermore, while the manufacturing method of the concave surface 40 of the nut 2 may be forging or cutting, this disclosure is not particularly limited to the manufacturing method of the concave surface 40.

[0078] Furthermore, although the first end face 21 of the nut body 20 is formed flat, the disclosure is not limited thereto. For example, a projection may be provided on the first end face 21 of the nut body 20, and a stopper may be provided at the end of the screw shaft 1 in the first direction X1. Then, when the nut 2 moves a predetermined amount in the first direction X1, the projection on the first end face 21 of the nut 2 may come into contact with the projection of the stopper at the end of the screw shaft 1 in the first direction X1. This makes it possible to limit the distance the nut 2 moves in the first direction X1 from its initial position.

[0079] Furthermore, this disclosure may also be a combination of the following configurations. (1) A screw shaft having one end pointing in a first direction and the other end pointing in a second direction, and having an outer raceway surface formed on its outer surface, A nut that penetrates the aforementioned screw shaft and has an inner raceway surface formed on its inner surface, A plurality of balls arranged in a track between the outer circumferential track surface and the inner circumferential track surface, A rotating part connected to the end of the screw shaft in the second direction and rotating together with the screw shaft, Equipped with, The direction parallel to the screw shaft is defined as the axial direction. The rotating part has a first projection positioned in the axial direction relative to the second end face of the nut facing the second direction, The aforementioned nut is A cylindrical nut body having the inner circumferential raceway surface and the second end surface, A second projection extending from the second end face in the second direction, A concave surface that extends in the first direction from the second end face, It has, The second projection enters the trajectory of the first projection, which rotates relative to the second projection, and comes into contact with the first projection. The second projection faces one direction in the circumferential direction and has a contact surface that contacts the first projection. The concave surface has a first concave surface that is positioned adjacent to the second projection in one circumferential direction, The first concave surface is, A first bottom surface extending in a direction perpendicular to the central axis of the screw shaft, with the other end in the circumferential direction intersecting the contact surface, A first wall surface connecting the first bottom surface and the second end surface, It has, The corner where the first bottom surface and the contact surface intersect is a first radiused section. Ball screw device. (2) The concave surface has a second concave surface that is recessed in the first direction from the second end surface, The second concave surface is positioned adjacent to the second projection in the other direction in the circumferential direction, The second projection has a back surface facing the other direction in the circumferential direction, The second concave surface is A second bottom surface extending in a direction perpendicular to the central axis, with one end in the circumferential direction intersecting the back surface, A second wall surface connecting the second bottom surface and the second end surface, It has, The corner where the second bottom surface and the back surface intersect is a second rounded section. (1) The ball screw device described above. (3) The nut body is, At least one of the inner circumferential raceway surfaces, Connecting both ends of the inner circumferential track surface, and the same number of circulation paths as the inner circumferential track surface, It has, The concave surface is positioned circumferentially offset from the second-direction-side circulation path, which is the second-direction-side circulation path that is positioned furthest in the second direction among the circulation paths. (1) or (2) the ball screw device described above. (4) Let the virtual circle be defined as the virtual circle that extends circumferentially along the inner surface of the nut body. The virtual circle is in contact with the portion of the second direction circulation path that is located most in the second direction, The concave surface is recessed in the first direction compared to the virtual circle. (3) The ball screw device described above. (5) A virtual line extending axially from the point of contact between the virtual circle and the second direction-side circulation path is used as the reference line. The direction of relative rotation of the screw shaft when the screw shaft rotates relative to the nut, causing the nut to move relative to the screw shaft in the first direction, is defined as the first rotation direction. The concave surface is positioned within a range of 5° to 300° from the reference line in the first rotational direction. (4) The ball screw device described above. (6) The concave surface is positioned within a range of 10° to 240° from the reference line in the first rotational direction. (5) The ball screw device described above. (7) The axial depth of the first concave surface is greater than or equal to the axial length of the first R portion. A ball screw device as described in any one of (1) to (6). (8) The axial depth of the first concave surface is less than the axial length of the first R portion. A ball screw device as described in any one of (1) to (6). (9) The axial depth of the second concave surface is greater than or equal to the axial length of the second R portion. (2) The ball screw device described above. (10) The axial depth of the second concave surface is less than the axial length of the second R portion. (2) The ball screw device described above. [Explanation of symbols]

[0080] 1 Screw shaft 2, 2A, 2B, 2C, 2D nuts 3 Stopper 10 Connection part 11 Male spline section 12 Screw shaft body 15 Outer raceway surface 20 Nut body 21 First end surface 22 Second end face 23, 23B, 23C 2nd protrusion 24 Inner peripheral surface 25, 25D Inner raceway surface 26 Circulation section 26a Circulation route 26D Frame 27 Contact surface 28 Back 30 Main body 31 1st protrusion 32 Female spline holes 33 Inner teeth 34 Outer surface 40, 40A concave 41 1st concave surface 42 Second concave surface 44 1st bottom 45. First Wall 46 Second bottom surface 47. Second Wall 51, 51B, 51C Part 1R 52 Part 2R 70 Screw groove surface 71 Non-rolling surface 80 holes 100 Ball screw device 125 2nd direction inner raceway surface 126 Second direction side circulation path

Claims

1. A screw shaft having one end pointing in a first direction and the other end pointing in a second direction, and having an outer raceway surface formed on its outer surface, A nut that penetrates the aforementioned screw shaft and has an inner raceway surface formed on its inner surface, A plurality of balls arranged in a track between the outer circumferential track surface and the inner circumferential track surface, A rotating part connected to the end of the screw shaft in the second direction and rotating together with the screw shaft, Equipped with, The direction parallel to the screw shaft is defined as the axial direction. The rotating part has a first projection that is positioned in the axial direction relative to the second end face of the nut facing the second direction, The aforementioned nut is A cylindrical nut body having the inner circumferential raceway surface and the second end surface, A second projection extending from the second end face in the second direction, A concave surface that extends in the first direction from the second end face, It has, The second projection enters the trajectory of the first projection, which rotates relative to the second projection, and makes contact with the first projection. The second projection faces one direction in the circumferential direction and has a contact surface that contacts the first projection. The concave surface has a first concave surface that is positioned adjacent to the second projection in one circumferential direction, The first concave surface is, A first bottom surface extending in a direction perpendicular to the central axis of the screw shaft, with the other end in the circumferential direction intersecting the contact surface, A first wall surface connecting the first bottom surface and the second end surface, It has, The corner where the first bottom surface and the contact surface intersect is a first radiused portion. Ball screw device.

2. The concave surface has a second concave surface that is recessed in the first direction from the second end surface, The second concave surface is positioned adjacent to the second projection in the other direction in the circumferential direction, The second projection has a back surface facing the other direction in the circumferential direction, The second concave surface is A second bottom surface extending in a direction perpendicular to the central axis, with one end in the circumferential direction intersecting the back surface, A second wall surface connecting the second bottom surface and the second end surface, It has, The corner where the second bottom surface and the back surface intersect is a second rounded section. The ball screw device according to claim 1.

3. The nut body is, At least one of the inner circumferential raceway surfaces, Connecting both ends of the inner circumferential track surface, and the same number of circulation paths as the inner circumferential track surface, It has, The concave surface is positioned circumferentially offset from the second-direction-side circulation path, which is the second-direction-side circulation path that is positioned most closely in the second direction among the circulation paths. The ball screw device according to claim 1 or claim 2.

4. Let the virtual circle be defined as the virtual circle that extends circumferentially along the inner surface of the nut body. The virtual circle is in contact with the portion of the second direction circulation path that is located most in the second direction, The concave surface is recessed in the first direction compared to the virtual circle. The ball screw device according to claim 3.

5. A virtual line extending axially from the point of contact between the virtual circle and the second direction-side circulation path is used as the reference line. The direction of relative rotation of the screw shaft when the screw shaft rotates relative to the nut, causing the nut to move relative to the screw shaft in the first direction, is defined as the first rotation direction. The concave surface is positioned within a range of 5° to 300° from the reference line in the first rotational direction. The ball screw device according to claim 4.

6. The concave surface is positioned within a range of 10° to 240° from the reference line in the first rotational direction. The ball screw device according to claim 4.

7. The axial depth of the first concave surface is greater than or equal to the axial length of the first R portion. The ball screw device according to claim 1.

8. The axial depth of the first concave surface is less than the axial length of the first R portion. The ball screw device according to claim 1.

9. The axial depth of the second concave surface is greater than or equal to the axial length of the second R portion. The ball screw device according to claim 2.

10. The axial depth of the second concave surface is less than the axial length of the second R portion. The ball screw device according to claim 2.

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