ball screw

Abstract

The ball screw nut includes a nut body and a bearing (12) attached to the nut body. The bearing (12) is disposed within a receiving hole recessed radially outward from the inner circumferential surface of the nut. The bearing (12) includes a bearing body (30) having a circulation path (33), a protrusion (31), and a recess (32). The protrusion (31) protrudes in a direction intersecting with one side surface (41) of the bearing body (30) and engages with the nut body to prevent the bearing (12) from falling out radially outward from the receiving hole. The recess (32) is located at a position corresponding to a base end (39) of the protrusion (31) and is recessed toward the bearing body (30) relative to the one side surface (41) of the bearing body (30). A chamfer (34) is provided between the base end (39) of the protrusion (31) and the recess (32).

Description

[Technical Field]

[0001] The present invention relates to a ball screw. This application claims priority based on Japanese Patent Application No. 2024-160114, filed September 17, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, in a ball screw having a nut, a screw shaft, and a plurality of balls (rolling elements), one known circuit structure for circulating the plurality of balls is a structure that has a groove for a return path (circulation path) formed on the inner surface of the nut, separate from a groove for a main path (rolling path).

[0003] For example, Patent Document 1 discloses a ball screw including a screw shaft, multiple rolling elements, and a nut with a bearing that forms a circulation path that returns the rolling elements from the end point of the rolling path to the start point. The bearing is inserted from the inner diameter side of the nut into a through hole that penetrates the nut radially. The bearing also has a protrusion that protrudes in the width direction of the circulation path, and this protrusion is disposed in a recess formed on the inner peripheral surface of the nut. Furthermore, an outer fitting member is attached to the outer periphery of the nut so as to cover the through hole, and this outer fitting member and the above-mentioned protrusion prevent the bearing from coming out radially. According to the technology described in Patent Document 1, when the back surface of the top (the part facing outward in the radial direction) is in contact with the outer fitting member, a gap is formed between the protrusion of the top and the recess of the nut, so that the force of the rolling elements in the circulation path pushing up the top is not input to the protrusion of the top. As a result, compared to conventional top-type ball screws, the protrusion that prevents the top from coming off is less likely to be damaged, and the top is less likely to come off the nut. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-137743 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology described in Patent Document 1, because the rolling elements in the circulation path alone cannot withstand the force pushing up the top, an outer fitting member is provided as a backup. Therefore, the installation of the outer fitting member is necessary, which could increase the number of parts. The increased number of parts could increase manufacturing costs. Furthermore, in conventional ball screws with a top that does not have an outer fitting member, the rolling elements pushing up the top can cause interference between the top and the nut body, which can damage the protrusions on the top and cause the top to fall off the nut.

[0006] Therefore, in the prior art described in Patent Document 1 and the like, in a ball screw equipped with a nut having a piece with a circulation path formed therein, there was room for improvement in terms of suppressing an increase in the number of parts and thus suppressing cost increases, as well as suppressing the piece from falling off compared to the prior art.

[0007] Therefore, an object of the present invention is to provide a ball screw that can suppress an increase in the number of parts and therefore costs, and can suppress the falling off of the ball compared to conventional techniques. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention proposes the following means. A ball screw according to a first aspect of the present invention comprises a screw shaft having a spiral outer peripheral rolling groove on its outer peripheral surface, a nut having a spiral inner peripheral rolling groove on its inner peripheral surface, and a plurality of rolling elements arranged in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft, wherein the nut has a nut body and a roller attached to the nut body and forming a circulation path that returns the rolling elements from one end of the rolling path to the other end, the roller is arranged in a receiving hole recessed radially outward from the inner peripheral surface of the nut, and the roller has a roller body having the circulation path, a protrusion that protrudes in a direction intersecting one side surface of the roller body and is engaged with the nut body to prevent the roller from falling out radially outward from the receiving hole, and a recess that is provided at a position corresponding to at least a base end of the protrusion and is recessed toward the roller body more than the one side surface, and a chamfered portion is provided between the base end of the protrusion and the recess. [Effects of the Invention]

[0009] According to the ball screw of the present invention, it is possible to provide a ball screw that can suppress an increase in the number of parts and therefore costs, and that can suppress the falling off of the bearings compared to the prior art. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a ball screw according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional perspective view of the nut according to the first embodiment. [Figure 3] FIG. 2 is a perspective view of a top according to the first embodiment. [Figure 4] FIG. 2 is a front view of the top according to the first embodiment. [Figure 5] A view of the nut with the bearing attached from the radial outside. [Figure 6] Enlarged view of part VI in Figure 2. [Figure 7] FIG. 10 is an enlarged view showing a protrusion of a piece according to a first modified example of the first embodiment. [Figure 8] FIG. 10 is an enlarged view showing a protrusion of a piece according to a second modified example of the first embodiment. [Figure 9] FIG. 10 is a perspective view of a top according to a third modified example of the first embodiment. [Figure 10] FIG. 10 is a perspective view of a top according to a second embodiment. [Figure 11] FIG. 10 is an enlarged view of the protrusion of the link according to the second embodiment, seen from a different angle. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction relative to the center axis C of the ball screw 1, unless otherwise specified.

[0012] (First embodiment) FIG. 1 is a cross-sectional view of a ball screw 1 according to the first embodiment. FIG. 2 is a cross-sectional perspective view of a nut 3 according to the first embodiment. In FIG. 1, a portion of the inner circumferential rolling groove 7 formed in the nut 3 is omitted, but in reality, in this embodiment, the inner circumferential rolling groove 7 is formed over the entire axial direction of the nut 3. Note that the inner circumferential rolling groove 7 may be formed over the entire axial direction of the nut 3 as in this embodiment, or may be formed only at predetermined locations as shown in FIG. 1. The ball screw 1 is a device that converts rotational motion into linear motion. As shown in FIG. 1, the ball screw 1 includes a screw shaft 2, a nut 3, and a plurality of rolling elements 4.

[0013] In the ball screw 1 of this embodiment, for example, the nut 3 rotates around the central axis C. The nut 3 is rotatable around the central axis C but does not move in a direction along the central axis C. The screw shaft 2 connected to a driven member (not shown) does not rotate around the central axis C but is movable in a direction along the central axis C. When the nut 3 rotates, the screw shaft 2 moves in a direction along the central axis C. The ball screw 1 is used, for example, as an electric brake device for moving a brake pad (not shown) of a vehicle, which is an example of a driven member.

[0014] The screw shaft 2 is formed in a cylindrical shape centered on a central axis C. The screw shaft 2 is disposed inside a nut 3, which will be described later. A spiral outer circumferential rolling groove 6 is formed on the outer periphery of the screw shaft 2. The cross-sectional shape of the outer circumferential rolling groove 6 is a Gothic arch including two circular arcs.

[0015] The nut 3 is formed in a cylindrical shape centered on a central axis C. The screw shaft 2 is inserted into the nut 3. A spiral inner circumferential rolling groove 7 is formed on the inner circumferential surface of the nut 3. The cross-sectional shape of the inner circumferential rolling groove 7 is a Gothic arch including two circular arcs. The inner circumferential rolling groove 7 is formed over almost the entire nut 3 in the axial direction. The detailed configuration of the nut 3 will be described later.

[0016] A plurality of rolling elements 4 are disposed between the nut 3 and the screw shaft 2. The rolling elements 4 are, for example, balls. When the nut 3 and the screw shaft 2 are assembled together, an inner peripheral rolling groove 7 formed in the nut 3 and an outer peripheral rolling groove 6 formed in the screw shaft 2 form a spiral rolling path 9. The rolling elements 4 move in this spiral rolling path 9. In FIG. 1 , one rolling element 4 is indicated by a two-dot chain line. In reality, the ball screw 1 is equipped with a plurality of rolling elements 4.

[0017] Next, the configuration of the nut 3 will be described. As shown in Figures 1 and 2, the nut 3 has a cylindrical nut body 11 and a plurality of blocks 12 attached to the nut body 11. As described above, the spiral inner circumferential rolling groove 7 is formed on the inner circumferential surface of the nut body 11. Furthermore, the nut body 11 is formed with a plurality of accommodating holes 21 for accommodating the plurality of blocks 12, which will be described in detail later. The accommodating holes 21 are arranged at equal intervals in the axial and circumferential directions. Each of the accommodating holes 21 accommodates a block 12.

[0018] The accommodation hole 21 is formed so as to be recessed radially outward from the inner circumferential surface of the nut body 11. In this embodiment, the accommodation hole 21 penetrates the nut body 11 in the radial direction. The accommodation hole 21 is formed so that its outer shape and size become constant from the inner to the outer radial direction. This makes it easy to form the accommodation hole 21 in the nut body 11. In this embodiment, the accommodation hole 21 is formed in a rectangular shape with sides along the circumferential and axial directions. The outer shape and size of the accommodation hole 21 are approximately equal to the outer shape and size of the block 12 to be accommodated in the accommodation hole 21. In this embodiment, the accommodation hole 21 is formed so as to be the same size as or slightly smaller than the block 12. Therefore, the block 12 is attached to the accommodation hole 21 by light press-fitting. Note that the accommodation hole 21 may be formed smaller than the block 12. In this case, the block 12 may be attached to the accommodation hole 21 by press-fitting. Alternatively, the accommodation hole 21 may be formed larger than the block 12. In this case, the top 12 may be attached to the receiving hole 21 by a clearance fit. Note that, in the case of a clearance fit, the top 12 is able to move radially inward, but the presence of the rolling elements 4 prevents the top 12 from falling off after assembly. In the case of a clearance fit, grease or the like may be applied between the receiving hole 21 and the top 12 during assembly to prevent the top 12 from falling off.

[0019] Fig. 3 is a perspective view of the block 12 according to the first embodiment. Fig. 4 is a front view of the block 12 according to the first embodiment as seen from the radial outside. Fig. 5 is a view of the nut 3 with the block 12 attached as seen from the radial outside. Note that the "axial direction," "radial direction," and "circumferential direction" in the drawings correspond to the axial direction, radial direction, and circumferential direction of the nut 3 when the block 12 is attached to the nut body 11. Since the multiple blocks 12 are each formed to have the same shape, the following description will focus on one block 12. As shown in Figures 2 to 5, the block 12 has a block body 30, a circulation path 33, a relief portion 32, a protrusion 31, and a chamfered portion 34. The block 12 is formed from, for example, synthetic resin.

[0020] The block body 30 is disposed in the receiving hole 21 of the nut body 11. As shown in particular in Figures 4 and 5, when attached to the nut body 11, the block body 30 is formed into a rectangular shape having a pair of side walls 41, 41 (one aspect of the claims) opposing each other in the circumferential direction and a pair of side walls 42, 42 opposing each other in the axial direction when viewed from the outside in the radial direction. The block body 30 of this embodiment is formed into a rectangular shape in which the distance between the pair of side walls 41, 41 opposing each other in the circumferential direction is greater than the distance between the pair of side walls 42, 42 opposing each other in the axial direction. Note that the shape of the block body 30 is not limited to the shape of the above-described embodiment.

[0021] As shown in FIG. 2, a circulation path 33 is formed on the radially inward surface (inner peripheral surface) of the ball bearing body 30. The circulation path 33 connects one end 17 and the other end 18 of the spiral rolling path 9 formed by the nut body 11 and the screw shaft 2 (see FIG. 1) to form an infinite circulation circuit. A plurality of rolling elements 4 are filled in this infinite circulation circuit, causing the rolling elements 4 to circulate endlessly within the infinite circulation circuit. In other words, the ball screw 1 of this embodiment is a so-called ball bearing type ball screw 1. More specifically, the inner peripheral surface of the ball bearing 12 is curved with a curvature corresponding to the curved surface forming the inner peripheral surface of the nut body 11 and is located at the same height as the threads of the inner peripheral rolling groove 7. The inner peripheral surface of the ball bearing 12 and the threads of the inner peripheral rolling groove 7 may be located at different heights. It is also preferable that the center (central axis C) of the nut 3 and the center of the radius of curvature of the inner peripheral surface of the ball bearing 12 coincide with each other. A groove-like circulation path 33 is formed on the inner peripheral surface of the block 12. The circulation path 33 is formed in a curved shape with a U-shaped cross section corresponding to the spherical surface of the rolling element 4. The circulation path 33 is greatly curved on the inner peripheral surface of the block 12, for example, in an S-shape. An inlet / outlet 33a at one end of the circulation path 33 is connected to one end 17 of the inner peripheral rolling groove 7. An inlet / outlet 33b at the other end of the circulation path 33 is connected to the other end 18 of the inner peripheral rolling groove 7. The inner peripheral rolling groove 7 makes approximately one revolution from one end 17 to the other end 18, along the inner peripheral surface of the nut 3, and one thread of the screw shaft 2 exists between the inlet / outlet 33a and the inlet / outlet 33b. The circulation path 33 is gently curved in the axial and circumferential directions of the nut 3 so as to ride over the thread of the screw shaft 2 between the inlet / outlet 33a and the inlet / outlet 33b. In addition, in order to make it easier for the rolling elements 4 to climb over the threads of the screw shaft 2, the circulation path 33 is formed so that the amount of recession radially outward increases as it approaches the center in the circulation direction of the rolling elements 4.

[0022] As a result, the rolling element 4 moves to one end 17 of the inner circumferential rolling groove 7, then passes through the entrance / exit 33a, changes its direction of travel, and enters the circulation path 33. After entering the circulation path 33, the rolling element 4 moves along the circulation path 33, moves over one thread, changes its direction of travel, and moves through the entrance / exit 33b to the other end 18 of the inner circumferential rolling groove 7. After moving to the other end 18 of the inner circumferential rolling groove 7, the rolling element 4 makes one revolution around the inner surface of the nut body 11 along the inner circumferential rolling groove 7, and then returns to the one end 17 of the inner circumferential rolling groove 7. The ball screw 1 of this embodiment has a plurality of infinite circulation circuits, each consisting of the inner circumferential rolling groove 7 (i.e., the rolling path 9) and the circulation path 33 of the block 12.

[0023] As shown in FIGS. 2 to 4 , the protrusions 31 protrude toward the outside (outside in the circumferential direction) of the block body 30 from a pair of circumferentially opposing side walls (one side surface) 41, 41 of the block body 30. A pair of protrusions 31 is provided for each block 12. Each protrusion 31 is formed toward one end of the side wall 41 when viewed from the outside in the radial direction, i.e., toward the corner between the side wall 42 and the orthogonal side wall 42. The protrusions 31 are formed on the inner circumferential surface (inner in the radial direction) of the block body 30 in the radial direction. As shown in FIG. 2 , when the block 12 is attached to the nut body 11, the protrusions 31 are engaged with the inner circumferential rolling groove 7 of the nut body 11. The protrusions 31 are engaged with the inner circumferential rolling groove 7 adjacent to the inner circumferential rolling groove 7 (one end 17 and the other end 18 of the inner circumferential rolling groove 7) connected to the circulation path 33. By engaging the protrusions 31 with the inner peripheral rolling grooves 7, the protrusions 31 prevent the tops 12 from coming out (falling off) radially outward from the accommodating hole 21 of the nut body 11. Therefore, the ball screw 1 of this embodiment is formed without having a sleeve or the like on the outer periphery of the nut 3 to prevent the tops 12 from falling off radially outward.

[0024] As shown in FIG. 3, the portion of the protrusion 31 that faces the inner circumferential rolling groove 7 of the nut 3 (the outer surface of the protrusion 31) is at least partially formed in a curved shape that follows the shape of the inner circumferential rolling groove 7. In this embodiment, the outer surface of the protrusion 31 is entirely formed in an arc shape that follows the shape of the inner circumferential rolling groove 7. Also, as shown in FIG. 2, the inner surface of the protrusion 31 is formed in a flat shape that is flush with the inner circumferential surface of the link body 30. Therefore, in this embodiment, the protrusion 31 is formed in a semicircular shape when viewed in a cross section perpendicular to the protruding direction of the protrusion 31.

[0025] FIG. 6 is an enlarged view of portion VI in FIG. 2. As shown in FIGS. 3 to 6, the recess 32 is provided on the side walls 41 of the block body 30 at a position corresponding to at least the base end 39 of the protrusion 31. The recess 32 is formed to be recessed more inwardly of the block body 30 than the side walls 41 of the block body 30. In this embodiment, the recess 32 is provided over the entire block body 30 in the radial direction. "Provided over the entire block body 30 in the radial direction" refers to, for example, the recess 32 (recess) being provided over the entire region above the protrusion 31 (radially outward) in FIG. 3. The recess 32 is provided to have a plane 45 intersecting the protruding direction of the protrusion 31. Furthermore, as shown in detail in FIGS. 4 and 5, in this embodiment, the recess 32 is formed to have an inclined surface that avoids the corner 22 of the receiving hole 21 when viewed from the radial outside. In other words, when the block 12 is attached to the nut body 11, the plane 45 constituting the escape portion 32 is provided at a position corresponding to the corner portion 22 of the accommodating hole 21 of the nut 3, and is inclined relative to each of the side walls 41 and 42 when viewed from the outside in the radial direction.

[0026] 6, by providing the relief portion 32 at a position corresponding to the base end portion 39 of the protrusion 31, interference between the protrusion 31 and the inner peripheral surface of the nut 3 (more specifically, the corner portion 25 located at the boundary between the thread between the inner peripheral rolling grooves 7 and the inner peripheral rolling groove 7) is suppressed at the base end portion 39 of the protrusion 31. In other words, the relief portion 32 suppresses interference between the protrusion 31 of the link 12 and the inner peripheral surface of the nut 3.

[0027] As shown in FIG. 3 , the chamfered portion 34 is provided between the base end 39 of the protrusion 31 and the relief portion 32. In this embodiment, the chamfered portion 34 is a rounded chamfer. The chamfered portion 34 may be formed to have a flat inclined surface. The chamfered portion 34 is formed to have a uniform radius of curvature R over the entire circumference between the base end 39 of the protrusion 31 and the relief portion 32. The chamfered portion 34 may be formed so that the radius of curvature R is largest at a portion of the base end 39 of the protrusion 31 that faces radially outward. In other words, the radius of curvature R of the chamfered portion 34 may vary depending on the position. By providing the recess 32 at the base end 39 of the protrusion 31, it is possible to ensure a larger radius of curvature R of the chamfered portion 34 compared to when the recess 32 is not provided.

[0028] (Action, effect) According to the ball screw 1 of this embodiment, the ball screw 1 includes a nut 3 having a block 12 with a circulation path 33 formed therein, and the block 12 has a protrusion 31. The protrusion 31 is engaged with the nut body 11, preventing the block 12 from falling off from the nut body 11. This prevents the block 12 from falling off without providing a sleeve or the like on the outside of the nut 3, thereby reducing the number of parts compared to conventional techniques that use a sleeve to prevent the block 12 from falling off. The block 12 has a recess 32 that is recessed toward the block body 30 relative to one side surface 41 of the block body 30, and a chamfered portion 34 is provided between the base end 39 of the protrusion 31 and the recess 32. The recess 32, recessed inward relative to the one side surface 41, is provided at a position corresponding to the base end 39 of the protrusion 31, preventing interference between the protrusion 31 and the nut body 11 (more specifically, an edge or corner 25 formed by providing the receiving hole 21 in the nut body 11). This prevents the block 12 from being scraped or damaged due to interference with the nut body 11. Therefore, compared to the conventional technology in which the block 12 is prone to damage due to interference with the nut body 11, the strength required for the protrusion 31 can be ensured for the block 12 alone. As a result, even without a sleeve, the protrusion 31 alone can prevent the block 12 from falling off. Therefore, compared to the conventional technology in which a sleeve is used, the number of parts can be reduced, and manufacturing costs can be reduced. Furthermore, by providing the relief portion 32 so that it is recessed inward from the one side surface 41, the chamfered portion 34 between the base end 39 of the protrusion 31 and the relief portion 32 can be made large. For example, if the chamfered portion 34 is a rounded chamfer, the radius of curvature R of the rounded chamfer can be made large. This reduces the concentration of stress on the base end 39 of the protrusion 31 when the rolling elements 4 push up the top 12 during circulation, allowing the top 12 to withstand the pushing force without providing a sleeve. This therefore extends the life of the top 12, maintains the required strength of the protrusion 31, and further prevents the top 12 from falling off due to breakage or the like. Therefore, it is possible to provide a ball screw 1 that can suppress an increase in the number of parts and hence an increase in costs, and that can suppress the falling off of the top 12 compared to the prior art. Furthermore, compared to the prior art, interference between the block 12 and the nut body 11 can be avoided, which reduces the generation of burrs and cutting chips caused by scraping the block 12. This makes it possible to provide a high-quality ball screw 1 that prevents scraping of the block 12 and the inclusion of impurities.

[0029] The relief portion 32 is provided so as to have a plane 45 that intersects with the protruding direction of the protrusion 31. Forming the relief portion 32 in a flat shape makes it easier to form a larger chamfered portion 34 between the base end 39 of the protrusion 31 and the relief portion 32. This further alleviates stress concentration at the base end 39 of the protrusion 31, and allows the protrusion 31 to maintain the required strength even without providing a sleeve. This further prevents the link 12 from falling off due to breakage or the like of the link 12.

[0030] When the block 12 is attached to the nut body 11, the relief portion 32 is provided across the entire block body 30 in the radial direction. By forming the relief portion 32 in this manner, the relief portion 32 can be easily formed, particularly when the block 12 is formed by resin molding. Therefore, an increase in the cost of manufacturing the block 12 can be suppressed.

[0031] The chamfered portion 34 is a rounded chamfer, and is formed so that the radius of curvature R is greatest at the portion of the base end 39 of the protrusion 31 that faces the insertion direction of the link 12 (radially outward). This allows the chamfer R to be large at the location where stress is most likely to concentrate when the rolling elements 4 push up the link 12. Therefore, compared to when the chamfer R is large around the entire circumference of the base end 39 of the protrusion 31, it is possible to ensure the required strength of the protrusion 31 while preventing the link 12 from becoming larger, and to effectively prevent the link 12 from falling off due to breakage or the like of the link 12.

[0032] When the nut 3 is viewed from the outside in the radial direction, the relief portion 32 is formed to have an inclined surface so as to avoid the corner portion 22 of the accommodation hole 21 of the nut 3. This makes it possible to further suppress interference between the edge of the nut 3 and the block 12 at the corner portion 22 of the accommodation hole 21.

[0033] (First Modification of the First Embodiment) Next, first to third modified examples of the first embodiment will be described. In each description of the first to third modified examples, the same components as those in the first embodiment described above will be assigned the same reference numerals and will not be described as appropriate. Note that the specific configuration is not limited to these embodiments and can be modified as appropriate without departing from the spirit of the present invention. FIG. 7 is an enlarged view showing the protrusion 31 of the block 212 according to the first modified example of the first embodiment. The first modified example of the first embodiment differs from the first embodiment described above in that a chamfered portion 234 is provided so as to extend continuously from the side wall 41 to the protrusion 31.

[0034] In the first modified example, the relief portion 232 is formed to have a flat surface 45 that is inclined relative to each of the side walls 41 and 42 when viewed from the outside in the radial direction, as in the first embodiment described above. In the first modified example, the chamfered portion 234 is formed as a rounded chamfer having a non-uniform radius of curvature at the base end 39 of the protrusion 31. Specifically, in a portion of the base end 39 of the protrusion 31 that is located near the side wall 41 (for example, the portion indicated by arrow A), the chamfered portion 234 is formed on a second surface 245 that is provided to protrude more toward the side wall 41 than the flat surface 45 of the relief portion 232. On the other hand, in a portion of the base end 39 of the protrusion 31 that is located in the center (for example, the portion indicated by arrow B), the chamfered portion 234 is formed between the flat surface 45 of the relief portion 232 and the protrusion 31. As a result, the radius of curvature R3 of the chamfer in the portion indicated by arrow B is greater than the radius of curvature R4 of the chamfer in the portion indicated by arrow A (R3>R4).

[0035] In the ball screw 1 of the first modified example, the radius of curvature R3 of the R-chamfer at the central portion (portion indicated by arrow B) of the base end 39 of the protrusion 31 is larger than the radius of curvature R4 of the R-chamfer at the end portion (portion indicated by arrow A) of the base end 39 of the protrusion 31. Here, when the rolling elements 4 push up the top 212 in the assembled ball screw 1, stress is generated in the base end 39 of the protrusion 31, pushing up the top body 30 mainly radially outward. Therefore, the greatest stress acts on the portion of the base end 39 of the protrusion 31 facing the radially outward (i.e., the central portion of the entire circumference of the base end 39 (portion indicated by arrow B)). In the ball screw 1 of the first modified example, the chamfered portion 234 with a larger radius of curvature can be provided in the portion of the base end 39 of the protrusion 31 where the greatest stress acts, so that the top 212 can withstand the pushing-up force. This extends the life of the link 212, maintains the required strength of the protrusion 31, and further prevents the link 212 from falling off due to breakage or the like. Also, compared to when a chamfered portion 234 with a large radius of curvature is provided around the entire circumference of the base end 39 of the protrusion 31, the area where the chamfered portion 234 and the relief portion 232 are formed can be kept small. This prevents the link 212 from becoming excessively large, and allows the link 212 to be formed with a high degree of freedom in shape.

[0036] (Second Modification of the First Embodiment) Next, a second modified example of the first embodiment will be described. Fig. 8 is an enlarged view showing the protrusion 31 of the block 312 according to the second modified example of the first embodiment. The second modified example of the first embodiment differs from the first embodiment in that the relief portion 332 is formed in a flat shape parallel to the side wall 41, rather than in an inclined surface.

[0037] In the second modified example, the recess 332 is formed so as to be recessed more inward of the top body 30 than the side walls 41, 41 of the top body 30. The recess 332 is provided so as to have a plane 45 that is approximately perpendicular to the protruding direction of the protrusion 31. That is, in the second modified example, the recess 332 is formed so as to have a plane 45 that is parallel to the side wall 41.

[0038] According to the ball screw 1 of the second modified example, it is possible to achieve the same effects as those of the first embodiment described above, even when the relief portion 332 is formed to have the flat surface 45 parallel to the side wall 41. Therefore, it is possible to improve the degree of freedom in the shape of the relief portion 332.

[0039] (Third Modification of the First Embodiment) Next, a third modified example of the first embodiment will be described. Fig. 9 is a perspective view of a top 412 according to the third modified example of the first embodiment. The third modified example of the first embodiment differs from the first embodiment in that a relief portion 432 is provided only in a part of the top body 30 in the radial direction.

[0040] In the third modified example, the relief portion 432 is provided in a position on the side walls 41, 41 of the top body 30 that corresponds to at least the base end 39 of the protrusion 31. The relief portion 432 is formed so as to be recessed more inward of the top body 30 than the side walls 41, 41 of the top body 30. In the third modified example, the relief portion 432 is provided in a part of the inner peripheral surface of the top body 30 in the radial direction. The radially outer part of the side wall 41 of the top body 30 where the relief portion 432 is not formed becomes a roof portion 449 formed by extending the side walls 41 and 42, respectively.

[0041] According to the ball screw 1 of the third modified example, the radially outer end of the recess 432 is covered by the roof portion 449. Therefore, when the block 412 is attached to the nut body 11, the entire receiving hole 21 is covered by the block body 30 (see also FIG. 5 ). This prevents foreign matter generated on the outer periphery of the nut 3 from passing through the receiving hole 21 and entering the rolling path 9. Even with the roof portion 449, the same effects as those of the first embodiment can be achieved. That is, the radius of curvature R of the chamfered portion 34 can be formed larger than in the prior art. This reduces stress concentration when the rolling element 4 pushes up the block 412, allowing the block 412 to withstand the pushing-up force. Furthermore, the provision of the recess 432 prevents interference between the base end 39 of the protrusion 31 and the inner circumferential surface of the nut 3. This maintains the required strength of the protrusion 31 of the block 412 and prevents the block 412 from falling off due to breakage or the like.

[0042] (Second embodiment) Next, a second embodiment of the present invention will be described. In the description of the second embodiment, the same components as those in the first embodiment described above will be denoted by the same reference numerals, and the description thereof will be omitted as appropriate. Note that the specific components are not limited to these embodiments and can be modified as appropriate without departing from the spirit of the present invention. FIG. 10 is a perspective view of a top 512 according to the second embodiment. FIG. 11 is an enlarged view of the protrusion 531 of the top 512 according to the second embodiment, viewed from a different angle. In the second embodiment, the shape of the protrusion 531 of the top 512 differs from that of the first embodiment described above.

[0043] As shown in FIGS. 10 and 11 , the recess 32 of the second embodiment is formed in a flat shape inclined relative to the side walls 41 and 42, similar to the recess 32 of the first embodiment. The protrusion 531 protrudes from the recess 32 in a direction substantially perpendicular to the side wall 41. In the second embodiment, the protrusion 531 is formed in a rectangular shape in a cross section perpendicular to the protrusion direction of the protrusion 531. The protrusion 531 has a top surface 561 facing radially outward when the top 512 is attached to the nut body 11, a bottom surface 563 facing radially inward, and a pair of side surfaces 562, 562 connecting the top surface 561 and the bottom surface 563. The bottom surface 563 is flush with the inner circumferential surface of the top body 30. The pair of side surfaces 562, 562 contact the inner circumferential rolling groove 7 when the top 512 is attached to the nut body 11. The surface of the side surface 562 may be formed in a curved shape that follows the groove shape of the inner circumferential rolling groove 7. A first chamfered portion 565 is formed between the top surface 561 and the relief portion 32. Second chamfered portions 566, 566 (see FIG. 11) are formed between the pair of side surfaces 562, 562 and the relief portion 32, respectively. The radius of curvature R5 of the first chamfered portion 565 is larger than the radius of curvature R6 of the second chamfered portion 566 (R5>R6).

[0044] According to the ball screw 1 of the second embodiment, the protrusion 531 is formed in a rectangular shape in a cross section perpendicular to the protruding direction of the protrusion 531. By forming the portion of the protrusion 531 facing radially outward (for example, the top surface 561 in this embodiment) in a flat shape, it is possible to form a larger chamfered portion (first chamfered portion 565) in the stress concentration portion of the top 512 when the rolling element 4 pushes up the top 512. This further alleviates the stress concentration at the base end 39 of the protrusion 531, and further prevents the top 512 from falling off due to breakage or the like of the top 512. In addition, the degree of freedom in the shape of the protrusion 531 can be improved.

[0045] The protrusion 531 has a top surface 561 facing radially outward and a pair of side surfaces 562, 562 provided at both ends of the top surface 561. A first chamfered portion 565 provided between the top surface 561 and the relief portion 32 has a larger radius of curvature R5 than a second chamfered portion 566 provided between the side surface 562 and the relief portion 32. As described above, the flat top surface 561 formed on the protrusion 531 can increase the radius of curvature of the first chamfered portion 565 at the stress concentration portion of the top 512 when the rolling element 4 pushes up the top 512. This reduces stress concentration at the base end 39 of the protrusion 531 and prevents the top 512 from falling off due to breakage or the like of the top 512. On the other hand, since the rolling elements 4 hardly exert an upward force on the portions of the protrusion 531 other than the portion facing radially outward (i.e., the base ends of the pair of side surfaces 562, 562 of the protrusion 531), the radius of curvature R6 of the corresponding second chamfered portion 566 can be made relatively small. Therefore, the required strength of the protrusion 531 can be ensured while preventing the top 512 from becoming excessively large, and the detachment of the top 512 due to breakage or the like of the top 512 can be effectively prevented.

[0046] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiments, the protrusions 31, 531 of the blocks 12, 212, 312, 412, 512 protrude along the circumferential direction of the nut 3 when the blocks 12, 212, 312, 412, 512 are attached to the nut body 11. However, this is not limiting. When the blocks 12, 212, 312, 412, 512 are attached to the nut body 11, the protrusions 31, 531 may protrude toward the axial direction of the nut 3. In this case, recesses or holes for engaging the protrusions 31, 531 may be separately formed on the inner circumferential surface of the nut body 11. However, the configuration of this embodiment in which the protrusions 31, 531 protrude along the circumferential direction is advantageous in that the protrusions 31, 531 can be engaged with the already-formed inner circumferential rolling grooves 7, thereby reducing the amount of work required for machining.

[0047] The tops 12, 212, 312, 412, and 512 may be made of metal. However, according to the configuration of this embodiment, even if the tops 12, 212, 312, 412, and 512 made of synthetic resin are used, damage to the protrusions 31 and 531 is unlikely to occur. Therefore, the configuration of this embodiment using the tops 12, 212, 312, 412, and 512 made of synthetic resin is advantageous in that it allows for cost reduction and weight reduction. In the first embodiment, the first and third modifications of the first embodiment, and the second embodiment, the inclination angle of the relief portions 32, 232, 432 as viewed from the outside in the radial direction is not limited to the above-mentioned angles or the angles shown in the drawings. The shape of the relief portions 32, 232, 432 as viewed from the outside in the radial direction is not limited to the above-mentioned shapes as long as they do not interfere with the circulation path 33. In each of the above-described embodiments and modified examples, the protrusion 31 may protrude from any position of the recesses 32, 232, 332, 432 formed in the block body 30. For example, taking the protrusion 31 located at the lower right of Fig. 4 as an example, it is sufficient that the protrusion 31 is formed so that the chamfered portion 34 fits inside the area AR surrounded by the imaginary line L1 extending the side wall 41 to the right, the imaginary line L2 extending the side wall 42 downward, and the plane 45 forming the recess 32. The protruding position of the protrusion 31 relative to the recess 32 and the shape of the chamfered portion 34 are not limited to the configurations of the above-described embodiments.

[0048] The accommodation hole 21 does not have to penetrate the nut body 11. For example, the accommodation hole 21 may be a hole (recess) recessed from the inner circumferential surface of the nut body 11 radially outward. In each of the above-described embodiments, the ball screw 1 in which the nut 3 rotates and the screw shaft 2 moves in a direction along the central axis C has been described, but this is not limited to this. The configurations of the above-described embodiments may be applied to a ball screw 1 in which the screw shaft 2 rotates and the nut 3 moves in a direction along the central axis C.

[0049] The present disclosure may also be implemented as a combination of the following configurations. (1) a screw shaft having a spiral outer peripheral rolling groove on its outer peripheral surface; a nut having a spiral inner peripheral rolling groove on its inner peripheral surface; a plurality of rolling elements disposed in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft; Equipped with The nut is The nut body and a roller attached to the nut body and forming a circulation path for returning the rolling element from one end to the other end of the rolling path; The block is disposed in an accommodating hole recessed radially outward from the inner circumferential surface of the nut, The frame is a top body having the circulation path; a protrusion that protrudes in a direction intersecting with one side surface of the block body and is engaged with the nut body to prevent the block from falling out of the receiving hole to the outside in the radial direction; a recess provided at a position corresponding to at least the base end of the protrusion and recessed toward the top body side relative to the one side surface, a chamfered portion is provided between the base end of the protrusion and the recess; Ball screw. (2) The recessed portion is provided so as to have a plane intersecting with a protruding direction of the protruding portion. (1) The ball screw described in (1). (3) When the top is attached to the nut body, the relief portion is provided over the entire top body in the radial direction. The ball screw according to (1) or (2). (4) The chamfered portion is an R chamfer, The chamfered portion is formed so that the radius of curvature of the portion of the base end of the protrusion facing the insertion direction of the block into the nut body is the largest. A ball screw according to any one of (1) to (3). (5) The relief portion has a surface that is inclined so as to avoid corners of the accommodation hole when viewed from the radial direction. A ball screw according to any one of (1) to (4). (6) The protrusion is formed in a rectangular shape in a cross section perpendicular to a protruding direction of the protrusion. A ball screw according to any one of (1) to (5). (7) The protrusion has a top surface facing outward in the radial direction and a pair of side surfaces connected to the top surface and facing at least one of the axial direction and the circumferential direction of the nut, a radius of curvature of the chamfered portion provided between the top surface and the recessed portion is larger than a radius of curvature of the chamfered portion provided between the side surface and the recessed portion; (6) The ball screw according to (6). [Explanation of symbols]

[0050] 1 ball screw 2 screw shaft 3 nuts 4 rolling elements 6 Outer periphery rolling groove 7 Inner rolling groove 9 Rolling Path 11 Nut body 12,212,312,412,512 pieces 17 (One end of the rolling path) 18 (the other end of the rolling path) 21 Storage Cave 22 Corner 30 Frame body 31,531 Protrusion 33 Circulation path 32,232,332,432 Relief 34,234,334 Chamfered part 39 (protrusion) base end 41 Side wall (one side) 45 plane 561 Top 562 Pair of Sides 565 First chamfered part (chamfered part) 566 Second chamfer (chamfer) R,R3,R4,R5,R6 Radius of curvature

Claims

1. a screw shaft having a spiral outer peripheral rolling groove on its outer peripheral surface; a nut having a spiral inner peripheral rolling groove on its inner peripheral surface; a plurality of rolling elements disposed in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft; Equipped with The nut is The nut body and a roller attached to the nut body and forming a circulation path for returning the rolling element from one end to the other end of the rolling path; The block is disposed in an accommodating hole recessed radially outward from the inner circumferential surface of the nut, The frame is a top body having the circulation path; a protrusion that protrudes in a direction intersecting with one side surface of the block body and is engaged with the nut body to prevent the block from falling out of the receiving hole to the outside in the radial direction; a recess provided at a position corresponding to at least the base end of the protrusion and recessed toward the top body side relative to the one side surface, a chamfered portion is provided between the base end of the protrusion and the recess, The relief portion has a surface that is inclined so as to avoid corners of the accommodation hole when viewed from the radial direction. Ball screw.

2. A screw shaft having a spiral outer peripheral rolling groove on its outer peripheral surface; a nut having a spiral inner peripheral rolling groove on its inner peripheral surface; a plurality of rolling elements disposed in a rolling path formed by the inner peripheral rolling groove of the nut and the outer peripheral rolling groove of the screw shaft; Equipped with The nut is The nut body and a roller attached to the nut body and forming a circulation path for returning the rolling element from one end to the other end of the rolling path; The block is disposed in an accommodating hole recessed radially outward from the inner circumferential surface of the nut, The frame is a top body having the circulation path; a protrusion that protrudes in a direction intersecting with one side surface of the block body and is engaged with the nut body to prevent the block from falling out of the receiving hole to the outside in the radial direction; a recess provided at a position corresponding to at least the base end of the protrusion and recessed toward the top body side relative to the one side surface, a chamfered portion is provided between the base end of the protrusion and the recess, The protrusion is formed in a rectangular shape in a cross section perpendicular to a protruding direction of the protrusion, The protrusion has a top surface facing outward in the radial direction and a pair of side surfaces connected to the top surface and facing at least one of the axial direction and the circumferential direction of the nut, a radius of curvature of the chamfered portion provided between the top surface and the recessed portion is larger than a radius of curvature of the chamfered portion provided between the side surface and the recessed portion; Ball screw.

3. The recessed portion is provided so as to have a plane intersecting with a protruding direction of the protruding portion. The ball screw according to claim 1 or 2.

4. When the top is attached to the nut body, the relief portion is provided over the entire top body in the radial direction. The ball screw according to claim 1 or 2.

5. the chamfered portion is an R-chamfer, The chamfered portion is formed so that the radius of curvature of the portion of the base end of the protrusion facing the insertion direction of the block into the nut body is the largest. The ball screw according to claim 1 or 2.

6. The protrusion is formed in a rectangular shape in a cross section perpendicular to a protruding direction of the protrusion.

2. The ball screw according to claim 1.

7. The protrusion has a top surface facing outward in the radial direction and a pair of side surfaces connected to the top surface and facing at least one of the axial direction and the circumferential direction of the nut, a radius of curvature of the chamfered portion provided between the top surface and the recessed portion is larger than a radius of curvature of the chamfered portion provided between the side surface and the recessed portion; 7. The ball screw according to claim 6.

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