Ball screw device

Abstract

To provide a ball screw device capable of downsizing a return path body in a radial direction and preventing deformation of the return path body.SOLUTION: A ball screw device comprises a cylindrical nut with an inner peripheral surface and an outer peripheral surface, a screw shaft passing through the nut, a plurality of balls disposed between the nut and the screw shaft, and a circulation component inside which a return path is formed. Two leg holes passing through the inner peripheral surface and the outer peripheral surface are formed in the nut. The circulation component has two legs which are inserted into the leg holes, and a return path body disposed on an outer peripheral side of the nut to connect the two legs with each other. The return path has a first return path formed inside the return path body and a second return path formed inside the leg. The return path body has a cylindrical wall part where the first return path is formed. On the wall part, at least any one of a first opening passing through a radially outer portion of the first return path and a second opening passing through a radially inner portion of the first return path, is provided.SELECTED DRAWING: Figure 10

Description

[Technical field]

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

[0002] A ball screw device is a device that converts rotational motion into linear motion and linear motion into rotational motion. The ball screw device includes a screw shaft, a nut that is inserted into the screw shaft, a number of balls, and a circulating part. The balls move along a track between the screw shaft and the nut. The circulating part returns the balls that have moved from one end of the track to the other end of the track.

[0003] As shown in Patent Document 1, a guide cap type circulation part is an example of a circulation part. The guide cap type circulation part includes a return path main body extending along the outer circumferential surface of the nut, and two legs extending radially inward from both ends of the return path main body. Each of the return path main body and the legs is formed in a cylindrical shape, and the inside serves as a return path. In addition, an entrance and exit for the return path is formed at the tip of the leg. The leg is inserted into a leg hole penetrating the outer circumferential surface and the inner circumferential surface of the nut. A ball moving on the track enters the return path from one of the two legs. The ball moving on the return path returns to the track from the other leg.

[0004] Moreover, the guide cap type circulation component of Patent Document 2 has a plate-shaped return path body that faces the outer peripheral surface of the nut. The return path body has an opposing surface that faces the outer peripheral surface of the nut and a groove surface formed in the opposing surface. The balls are sandwiched between the outer peripheral surface of the nut and the groove surface, and the balls are circulated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-046570 A [Patent Document 2] Japanese Patent Application Publication No. 1-261551 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the circulation part described above has a large amount of protrusion from the outer peripheral surface of the nut toward the outside in the radial direction. In other words, the nut is enlarged in the radial direction. For this reason, it is desirable to reduce the size of the return path body of the circulation part in the radial direction. Hereinafter, the surface of the return path body facing toward the outside in the radial direction may be referred to as the top surface. Also, the surface of the return path body facing toward the inside in the radial direction may be referred to as the bottom surface.

[0007] Here, as a method for making the return path body smaller in the radial direction, it is possible to position the top surface of the return path body on the radial inside, or to position the bottom surface of the return path body on the radial outside. However, with this method, the radially outer and inner parts of the return path body relative to the ball become thin. Then, the thinned parts are deformed by contact with the ball. Therefore, there is a possibility that the ball will not move smoothly.

[0008] The present disclosure has been made in consideration of the above, and aims to provide a ball screw device that prevents deformation of the return path main body while reducing the radial size of the return path main body. [Means for solving the problem]

[0009] In order to achieve the above object, a ball screw device according to one aspect of the present disclosure includes a cylindrical nut having an inner peripheral surface and an outer peripheral surface, a screw shaft penetrating the nut, a plurality of balls arranged between the nut and the screw shaft, and a circulation part having a return path formed therein. The nut is formed with two leg holes penetrating the inner peripheral surface and the outer peripheral surface. The circulation part has two legs inserted into the leg holes and a return path main body arranged on the outer peripheral side of the nut and connecting the two legs to each other. The return path main body has a cylindrical wall part in which the first return path is formed. The wall part is provided with at least one of a first opening penetrating a radially outer portion of the wall part of the first return path and a second opening penetrating a radially inner portion of the wall part of the first return path.

[0010] If the top surface of the return path body is positioned radially inward, or the bottom surface is positioned radially outward, a thin portion occurs in the wall portion at the radially outer or inner portion of the first return path. On the other hand, the wall portion of the present disclosure is provided with at least one of the first opening and the second opening. In other words, the thin portion can be removed by the first opening or the second opening. This prevents the wall portion at the radially outer or inner portion of the first return path from being deformed due to contact with the ball. Therefore, it is possible to prevent deformation of the return path body while reducing the radial size of the return path body.

[0011] In a ball screw device according to another aspect of the present disclosure, the wall portion may be provided with both the first opening and the second opening. Alternatively, the wall portion may be provided with only the first opening. Alternatively, the wall portion may be provided with only the second opening.

[0012] In addition, as a desirable aspect of the ball screw device according to the aspect of the present disclosure, a fixing part that covers the return path main body from a radial outside of the return path main body and fixes the circulation part to the nut is provided. The first opening is closed by the fixing part.

[0013] According to the above configuration, the fixed component serves as a radially outer wall of the first return path, so that the return path main body does not need to have a radially outer portion of the first return path, and the return path main body can be further downsized.

[0014] In a preferred aspect of the ball screw device according to the aspect of the present disclosure, the outer circumferential surface of the nut closes the second opening.

[0015] According to the above configuration, the nut serves as a radially inner wall of the first return path, so the return path main body does not need to have a radially inner portion of the first return path, and the return path main body can be further reduced in size.

[0016] In a preferred embodiment of the ball screw device according to the present disclosure, the outer peripheral surface of the nut has an arc-shaped surface when viewed from an axial direction parallel to the screw shaft, and a plane perpendicular to a virtual line extending in a radial direction when viewed from the axial direction. The two leg holes are provided on the plane. The return path body is disposed radially outward of the plane.

[0017] According to the above-mentioned configuration, the flat surface of the nut is recessed radially outward from the arc surface, so that even if the return path main body is disposed radially outward from the flat surface, it is possible to prevent the return path main body from protruding from the outer peripheral surface of the nut, thereby preventing the nut from becoming large in the radial direction. Effect of the Invention

[0018] According to the ball screw device of the present disclosure, the return path body can be made smaller in the radial direction. In addition, deformation of the return path body is prevented, and smooth movement of the balls is ensured. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is an exploded perspective view of a part of the ball screw device according to the first embodiment. FIG. [Diagram 2]FIG. 2 is a view of the nut of the first embodiment as viewed from a direction opposite to the flat surface of the nut. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view of the circulation component of the first embodiment as viewed from the radial outside. [Diagram 5] FIG. 5 is a perspective view of the circulation component of the first embodiment as viewed from the radially inner side. [Figure 6] FIG. 6 is a cross-sectional view showing a state in which the circulation component is assembled to the nut in the first embodiment, and more specifically, a cross-sectional view taken along line VII-VII in FIG. [Figure 7] FIG. 7 is a view showing a state in which a circulation component is assembled to a nut in the first embodiment, as viewed from a direction opposite to a flat surface of the nut. [Figure 8] FIG. 8 is a side view of the common parts constituting the circulatory part of the first embodiment, as viewed from the mating surface. [Figure 9] FIG. 9 is a cross-sectional view of the ball screw device of the first embodiment. [Figure 10] FIG. 10 is an enlarged view of the return path main body and its vicinity in FIG. [Figure 11] FIG. 11 is a cross-sectional view of a return path body of a comparative example. [Figure 12] FIG. 12 is a cross-sectional view of the return path main body of the first modification taken in an orthogonal direction. [Figure 13] FIG. 13 is a cross-sectional view of the return path main body of the second modification taken in an orthogonal direction. [Figure 14] FIG. 14 is a cross-sectional view of the return path main body of the third modification taken in an orthogonal direction. [Figure 15] FIG. 15 is a cross-sectional view of the return path main body of the fourth modification taken in an orthogonal direction. [Figure 16] FIG. 16 is a cross-sectional view of the return path body of the fifth modification taken in an orthogonal direction. [Figure 17] FIG. 17 is a cross-sectional view of the return path body of the sixth modification taken in an orthogonal direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The embodiment of the invention will be described in detail with reference to the drawings. The present disclosure is not limited to the contents described in the following description. The components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the components described below can be appropriately combined.

[0021] (Embodiment 1) Fig. 1 is an exploded perspective view of a part of a ball screw device of the first embodiment. As shown in Fig. 1, the ball screw device 100 of the first embodiment includes a screw shaft (not shown) (see center line O1 of the screw shaft), a cylindrical nut 1, a plurality of balls 2 (see Fig. 9, etc.), a guide cap type circulation part 3, and a fixed part 5. The screw shaft is a cylindrical part, and an outer circumferential raceway surface is formed on the outer circumferential surface. Hereinafter, the direction parallel to the center line O1 of the screw shaft is referred to as the axial direction X.

[0022] The nut 1 is formed in a cylindrical shape centered on a center line O1. An inner peripheral surface 10 of the nut 1 is formed with an inner peripheral raceway surface 11 that faces an outer peripheral raceway surface of the screw shaft. A spiral raceway is formed between the outer peripheral raceway surface and the inner peripheral raceway surface 11. A plurality of balls 2 are arranged on this raceway.

[0023] Fig. 2 is a view of the nut of the first embodiment as viewed from a direction opposite to the flat surface of the nut. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. As shown in Figs. 2 and 3, the cross-sectional shape of the outer peripheral surface 13 of the nut 1 is D-shaped. Thus, the outer peripheral surface 13 of the nut 1 has an arcuate surface 14 and a flat surface 15. In addition, a ridge line 16 extending in the axial direction X is formed at the boundary between the arcuate surface 14 and the flat surface 15.

[0024] As shown in Fig. 3, the arc surface 14 is formed in an arc shape centered on the center line O1. The dashed line K14 in Fig. 3 is a virtual line when the arc surface 14 is extended in the circumferential direction. The plane 15 has a virtual line K15 extending radially from the center line O1 as a perpendicular line. In other words, when viewed from the axial direction X, the plane 15 extends linearly in a direction perpendicular to the virtual line K15.

[0025] Hereinafter, the direction parallel to the plane 15 when viewed from the axial direction X (the direction perpendicular to the virtual line K15) is referred to as the orthogonal direction Y. The direction perpendicular to the plane 15 (the direction parallel to the virtual line K15) is referred to as the vertical direction. Among the vertical directions, the direction in which the center line O1 is disposed when viewed from the plane 15 is referred to as the first vertical direction Z1, and the opposite direction is referred to as the second vertical direction Z2.

[0026] The plane 15 is recessed radially inward from the arcuate surface 14. Therefore, a space (hereinafter referred to as an accommodation space 20) located radially inward from the arcuate surface 14 is provided in the second perpendicular direction Z2 (radially outward) of the plane 15.

[0027] Further, two leg holes 17 are formed in the nut 1. The two leg holes 17 penetrate the inner circumferential raceway surface 11 (inner circumferential surface 10) and the flat surface 15 (outer circumferential surface 13). The leg holes 17 communicate the internal space of the nut 1 with the accommodation space 20 (space on the outer circumferential side of the nut 1).

[0028] As shown in Fig. 2, the two leg holes 17 are symmetrical with respect to point P on plane 15. Point P on plane 15 refers to the center of plane 15 in the axial direction X and also the center of plane 15 in the perpendicular direction Y. Edges 17a of leg holes 17 are chamfered (see Fig. 3).

[0029] 2 and 3, flanges 18 are provided at both ends in the axial direction X of the outer peripheral surface 13 of the nut 1. The flanges 18 are circular when viewed from the axial direction. The flanges 18 have a larger diameter than the arcuate surface 14. The arcuate surface 14 and the flat surface 15 are disposed between the two flanges 18.

[0030] Fig. 4 is a perspective view of the circulation part of the first embodiment as viewed from the radial outside. Fig. 5 is a perspective view of the circulation part of the first embodiment as viewed from the radial inside. As shown in Figs. 4 and 5, the circulation part 3 has a return path main body 30 formed in a substantially plate shape, and two legs 31 protruding in the same direction from one surface (bottom surface 32) of the return path main body 30. The return path main body 30 has a bottom surface 32 on which the legs 31 are formed, and an upper surface 33 facing in the opposite direction to the bottom surface 32. The bottom surface 32 and the upper surface 33 are each flat.

[0031] Fig. 6 is a cross-sectional view of the state in which the circulation part is assembled to the nut in the first embodiment, and more specifically, a cross-sectional view taken along line VII-VII in Fig. 7. Such a circulation part 3 is assembled to the nut 1 in the following procedure. First, as shown in Fig. 6, the circulation part 3 is placed in the second vertical direction Z2 of the plane 15 (see the imaginary line K3 in Fig. 6). In addition, the bottom surface 32 of the circulation part 3 is made to face the plane 15. Next, as shown by the arrow A in Fig. 6, the circulation part 3 is moved in the first vertical direction Z1.

[0032] During this movement, the legs 31 are inserted into the leg holes 17. The edges 17a of the leg holes 17 are chamfered to facilitate the insertion of the legs 31. Then, as shown in FIG. 6, when the bottom surface 32 comes into contact with the flat surface 15, the movement in the first vertical direction Z1 is stopped and the assembly of the circulation part 3 is completed. As a result, when the circulation part 3 moves in the direction opposite to the arrow A (the second vertical direction Z2), the circulation part 3 falls off the nut 1.

[0033] When the circulation part 3 is assembled to the nut 1, the upper surface 33 of the return path body 30 faces the second vertical direction Z2. Moreover, the return path body 30 is accommodated in the accommodation space 20 of the nut 1. In other words, the upper surface 33 of the return path body 30 does not protrude radially outward beyond the dashed line K14 (arc surface 14).

[0034] The bottom surface 32 faces the first vertical direction Z1, and abuts against the plane 15. Therefore, the circulation part 3 is positioned so as not to move in the first vertical direction Z1. In addition, the legs 31 are inserted into the leg holes 17. Therefore, the circulation part 3 is positioned so as not to move in a direction parallel to the plane 15.

[0035] A second return path 8 extending in the vertical direction is formed inside the leg 31. An opening 34 and a tongue 35 are formed at the end of the leg 31 in the first vertical direction Z1. The opening 34 opens the second return path 8 in the first vertical direction Z1. The tongue 35 scoops up the ball 2 moving on the track and causes the ball 2 to enter the second return path 8 from the opening 34.

[0036] Fig. 7 is a view showing a state in which the circulation component is assembled to the nut in embodiment 1, as viewed from a direction opposite to the flat surface of the nut. Fig. 8 is a side view showing common components constituting the circulation component of embodiment 1, as viewed from a mating surface. The common components will be described later.

[0037] 7, a first return path 7 is formed inside the return path body 30. When viewed from the second vertical direction Z2, the first return path 7 extends linearly so as to connect the two leg holes 17. For this reason, a center line O7 of the first return path 7 is not parallel to the center line O1 of the screw shaft but intersects with it.

[0038] As shown in Fig. 8, both ends of the first return path 7 are connected to the second return path 8. In other words, the first return path 7 connects the two second return paths 8 to each other. According to this circulation device 3, when the ball 2 enters one of the second return paths 8, the ball 2 moves along the second return path 8 in the second vertical direction Z2 (see arrow B1). Also, when the ball 2 moves from the second return path 8 to the first return path 7, the ball 2 moves along the first return path 7 (see arrow B2).

[0039] Subsequently, when the ball 2 moves from the first return path 7 to the other second return path 8, the ball 2 moves along the second return path 8 in the first vertical direction Z1 (see arrow B3). Then, the ball 2 returns to the orbit from the opening 34 of the leg portion 31. Hereinafter, the passage combining the first return path 7 and the two second return paths 8 is referred to as the return path 6.

[0040] Moreover, the shape of the circulable part 3 in this embodiment is point-symmetric with respect to point P on the plane 15. In other words, the circulable part can be assembled even in a state rotated 180°, which can reduce the labor required for assembly.

[0041] 4 and 5, the circulative part 3 is composed of a first part 301 and a second part 302 that are divided into two parts in an orthogonal direction along the center line of the return path 6. The shape of the circulative part 3 is point-symmetric with respect to a point P on the plane 15, and when the first part 301 is rotated 180° with respect to the point P, it becomes the second part 302. In other words, the first part 301 and the second part 302 are simply the common part 300 with the orientation changed. Therefore, according to this embodiment, it is possible to save the effort of manufacturing two parts with different shapes.

[0042] 8, a concave surface 311 is formed on a mating surface 310 of the common part 300. When two common parts 300 (first part 301 and second part 302) are combined, the internal space of this concave surface 311 forms the return path 6. In addition, the mating surface 310 is provided with a protrusion 313 and a recess 314 into which the protrusion 313 fits. Therefore, when the first part 301 and the second part 302 are combined, no misalignment occurs.

[0043] In this embodiment, an example is given in which the circulating part 3 is composed of two parts (first part 301 and second part 302), but the present disclosure is not limited to this, and the circulating part 3 may be composed of three or more parts, or the circulating part 3 may be a single part that cannot be divided.

[0044] Fig. 9 is a cross-sectional view of the ball screw device of embodiment 1. As shown in Fig. 9, the fixed part 5 is a sleeve 50 that fits onto the outer periphery of the nut 1. The sleeve 50 has a cylindrical sleeve body 51 and two protrusions 53 that protrude radially inward from an inner periphery 52 of the sleeve body 51.

[0045] The sleeve body 51 covers the outer circumferential side of the return path body 30 of the circulation part 3. The inner circumferential surface 52 of the sleeve body 51 abuts against the upper surface 33 of the return path body 30. This restricts the circulation part 3 from moving in the second vertical direction Z2, that is, from falling off the nut 1. The sleeve body 51 is C-shaped when viewed from the axial direction. That is, a notch 54 extending in the axial direction is provided between the circumferential ends 51a, 51a of the sleeve body 51. The notch 54 is disposed on the opposite side of the two protrusions 53 across the center line O1.

[0046] Furthermore, an axial end face 51b (see FIG. 1) of the sleeve body 51 abuts against the flange 18 of the nut 1 from the axial direction X. Therefore, even if a load in the axial direction X acts on the sleeve 50, movement of the sleeve 50 in the axial direction X is restricted. In other words, the sleeve 50 is prevented from falling off the nut 1 in the axial direction X.

[0047] The sleeve 50 is attached to the nut 1 in the following manner. First, a force is applied to the circumferential ends 51a, 51a of the sleeve body 51 so that they are separated from each other, and the sleeve body 51 is expanded in diameter. The sleeve body 51 is also deformed so that the size of the notch 54 becomes larger than the outer diameter of the nut 1. Next, the nut 1 is moved so as to pass through the notch 54, and the sleeve 50 is attached from the radial outside of the nut 1. Then, the force applied to the sleeve body 51 is removed, and the sleeve body 51 is reduced in diameter (elastically deformed). As a result, the inner peripheral surface 52 of the sleeve body 51 comes into contact with the arc surface 14 (outer peripheral surface 13) of the nut 1, and the sleeve 50 is fitted to the outer peripheral side of the nut 1. As a result, the sleeve 50 is fixed to the nut 1.

[0048] The method of mounting the sleeve 50 to the nut 1 is not limited to the above-mentioned method. For example, the sleeve body 51 may be deformed so that the sleeve body 51 has a larger diameter than the flange 18 of the nut 1. Then, the nut 1 may be moved in the axial direction to insert the nut 1 into the sleeve body 51.

[0049] In addition, in the present disclosure, when the sleeve 50 is attached to the nut 1, an elastic deformation force that reduces the diameter of the sleeve body 51 may remain. According to this, even if a force that expands the diameter of the sleeve body 51 acts on the sleeve body 51, the sleeve body 51 resists this force. Therefore, the sleeve body 51 is less likely to expand in diameter, and the sleeve 50 is prevented from falling off the nut 1. On the other hand, in the present disclosure, when the sleeve body 51 is attached to the outer circumferential surface 13 of the nut 1, an elastic deformation force that reduces the diameter of the sleeve body 51 may not remain.

[0050] Furthermore, two recesses 56 recessed radially inward are provided on the outer circumferential surface 55 of the sleeve body 51. When a force is applied to expand the diameter of the sleeve body 51, the internal space of the recesses 56 is crushed in the circumferential direction. This makes it easier for the sleeve body 51 to deform, and suppresses plastic deformation of the sleeve 50.

[0051] The two protrusions 53 are disposed circumferentially spaced from each other. The return path body 30 of the circulation part 3 is disposed between the two protrusions 53. Therefore, when a circumferential load acts on the sleeve body 51, one of the two protrusions 53 gets caught on the return path body 30, restricting the rotation of the sleeve 50. This prevents the sleeve 50 from rotating in the circumferential direction and the notches 54 from overlapping with the circulation part 3 in the radial direction, i.e., prevents the circulation part 3 from falling off the notches 54.

[0052] In addition, the two protrusions 53 are disposed in the accommodation space 20 (see Figs. 3 and 6). This prevents the sleeve 50 from expanding radially outward (increasing in size radially outward) due to the protrusions 53. This prevents the nut 1 from coming into contact with other components while the ball screw device 100 is in operation.

[0053] Fig. 10 is an enlarged view of the return path main body and its vicinity in Fig. 9. Next, details of the return path main body 30 will be described. As shown in Fig. 10, the return path main body 30 includes a cylindrical wall portion 40 having the first return path 7 formed therein, a first opening 41, and a second opening 42.

[0054] The size of the first return path 7 of the wall portion 40 is slightly larger than the diameter of the ball 2. Therefore, the ball 2 moves smoothly through the first return path 7. Moreover, the width of the first return path 7 in the orthogonal direction Y is L1.

[0055] The first opening 41 penetrates a portion of the wall portion 40 that is radially outside (in the second vertical direction Z2) of the first return path 7. The first opening 41 also extends along the first return path 7 (see FIG. 4). The first opening 41 is closed by an inner circumferential surface 52 of the sleeve body 51 from the second vertical direction Z2.

[0056] The width L2 of the first opening 41 in the orthogonal direction Y is smaller than the width L1. Therefore, a part of the wall portion 40 remains in the second vertical direction Z2 (radially outward) of the first return path 7. The width L2 of the first opening 41 is set to a size that prevents the ball 2 from jumping out radially outward from the first opening 41. Therefore, the ball 2 does not come into contact with the inner circumferential surface 52 of the sleeve main body 51. In other words, the sleeve 50 of this embodiment does not function as a radially outer wall portion of the first return path 7.

[0057] As a result, the ball 2 moving along the first return path 7 moves along the first return path 7 while contacting a portion of the remaining wall portion 40. Hereinafter, the portion of the wall portion 40 remaining in the second vertical direction Z2 (radially outside) of the first return path 7 will be referred to as an outer wall 43.

[0058] The first opening 41 is provided in the center of the outer wall 43 in the orthogonal direction Y. Therefore, the outer wall 43 is composed of two partial outer walls 44 separated in the orthogonal direction Y. A surface 44a of the partial outer wall 44 in the second vertical direction Z2 constitutes a part of the upper surface 33 of the return path body 30 and is flat. In addition, the surface 44a of the partial outer wall 44 in the second vertical direction Z2 abuts against the sleeve 50.

[0059] The surface 44b of the partial outer wall 44 in the first vertical direction Z1 surrounds the first return path 7 in the second vertical direction Z2 and serves as a contact surface that comes into contact with the ball 2. The surface 44b of the partial outer wall 44 in the first vertical direction Z1 moves away from the upper surface 33 of the return path body 30 as it moves from the center (first opening 41) in the orthogonal direction Y toward the outside in the orthogonal direction Y.

[0060] Each of the two partial outer walls 44 has a smaller thickness in the vertical direction (radial direction) toward the first opening 41. Therefore, the portion of the partial outer wall 44 with the smallest vertical (radial) thickness is the end portion closest to the first opening 41. Furthermore, the thickness H1 of the end portion closest to the first opening 41 of the partial outer wall 44 is a thickness that provides sufficient rigidity to prevent deformation due to contact with the ball 2. In other words, the outer wall 43 (the two partial outer walls 44) does not deform due to contact with the ball 2.

[0061] The second opening 42 penetrates a portion of the wall 40 on the radial inside (first vertical direction Z1) of the first return path 7. The width L3 of the second opening 42 in the orthogonal direction Y is the same as the width L1. Therefore, the portion of the wall 40 in the first vertical direction Z1 of the first return path 7 (hereinafter, may be referred to as the bottom wall) is entirely cut out. In addition, the second opening 42 is blocked from the first vertical direction Z1 by the flat surface 15 (outer peripheral surface 13) of the nut 1. Therefore, the ball 2 moving through the first return path 7 moves through the first return path 7 while contacting the flat surface 15 of the nut 1.

[0062] 8, the first opening 41 is defined by a first notch 341 formed in the mating surface 310 of the common component 300. The second opening 42 is defined by a second notch 342 formed in the mating surface 310 of the common component 300.

[0063] Next, a description will be given of the effect of the return path main body 30 having the first opening 41 and the second opening 42. In addition, in this description, a return path main body (comparative example) not having the first opening 41 and the second opening 42 will be used.

[0064] FIG. 11 is a cross-sectional view of the return path body of the comparative example. The broken line in FIG. 11 is the return path body 30 of the first embodiment. In addition, in FIG. 11, the center line O7 of the first return path 7 of the first embodiment and the center line O207 of the first return path 207 of the comparative example are illustrated so as to overlap. As shown in FIG. 11, the return path body 230 of the comparative example differs from the first embodiment in that it does not have the first opening 41 and the second opening 42. Therefore, the return path body 230 of the comparative example has an outer wall 243 and a bottom wall 245 that are not open.

[0065] The surface 243a of the outer wall 243 in the second vertical direction Z2 is flat, as in the first embodiment, and constitutes a part of the upper surface 233 of the return path main body 230. The surface 243b of the outer wall 243 in the first vertical direction Z1 is an arcuate surface along the ball 202, as in the first embodiment. Therefore, in the comparative example, the central part of the outer wall 243 in the orthogonal direction Y has the smallest thickness in the vertical direction. Also, the thickness H2 of the central part of the outer wall 243 in the orthogonal direction Y is the same as the thickness H1 (see FIG. 10) in order to avoid deformation due to contact with the ball 202.

[0066] The bottom wall 245 is a portion of the wall portion 240 that is disposed radially inward of the first return path 207. The bottom wall 245 has a surface 245a in a first vertical direction Z1 and a surface 245b in a second vertical direction Z2. The surface 245a constitutes a part of the bottom surface 232 of the return path main body 230. The surfaces 245a and 245b are each flat. Thus, the thickness H3 of the bottom wall 245 in the vertical direction is constant. Moreover, the thickness H3 of the bottom wall 245 is the same as the thickness H1 (see FIG. 10) in order to avoid deformation due to contact with the ball 202.

[0067] From the above, the upper surface 233 of the return path body 230 of the comparative example is located in the second vertical direction Z2 by a thickness H4 from the upper surface 33 of the return path body 30 of embodiment 1. Also, the bottom surface 232 of the return path body 230 of the comparative example is located in the first vertical direction Z1 by a thickness H3 from the bottom surface 32 of the return path body 30 of embodiment 1. Therefore, the return path body 30 of embodiment 1 is made smaller in the vertical direction (radial direction) by the sum of the thicknesses H4 and H3.

[0068] In the first embodiment, the portion of the return path body 30 whose thickness is less than H1 due to the radial reduction in size is cut out by the first opening 41 and the second opening 42. This prevents the wall portion 40 from being deformed by contact with the ball 2, preventing the ball 2 from moving smoothly.

[0069] As described above, the ball screw device 100 of the first embodiment includes a cylindrical nut 1 having an inner peripheral surface 10 and an outer peripheral surface 13, a screw shaft penetrating the nut 1, a plurality of balls 2 arranged between the nut 1 and the screw shaft, and a circulation part 3 having a return path 6 formed therein. The nut 1 is formed with two leg holes 17 penetrating the inner peripheral surface 10 and the outer peripheral surface 13. The circulation part 3 has two legs 31 inserted into the leg holes 17 and a return path body 30 arranged on the outer peripheral side of the nut 1 and connecting the two legs 31 to each other. The return path 6 has a first return path 7 formed inside the return path body 30 and a second return path 8 formed inside the leg 31. The return path body 30 has a cylindrical wall portion 40 in which the first return path 7 is formed. The wall portion 40 is provided with at least one of a first opening 41 penetrating a portion of the wall portion 40 on the radial outer side of the first return passage 7 and a second opening 42 penetrating a portion of the wall portion 40 on the radial inner side of the first return passage 7. In the first embodiment, both the first opening 41 and the second opening 42 are provided.

[0070] According to the first embodiment, it is possible to reduce the size of the return path main body 30 in the radial direction, while preventing deformation of the return path main body 30 (wall portion 40).

[0071] Above, the first embodiment has been described. Next, a modified example of a part of the first embodiment will be described. Note that the modified example will be described by focusing on the differences from the first embodiment.

[0072] (Variation 1) Fig. 12 is a cross-sectional view of the return path body of Modification 1 cut in the orthogonal direction. As shown in Fig. 12, the return path body 30A of Modification 1 differs from the first embodiment in that the width L4 of the second opening 42A is smaller than the width L1 of the first return path 7. Therefore, the bottom wall 45A remains on the wall portion 40A. In addition, the bottom wall 45A has two partial bottom walls 46 separated in the orthogonal direction Y.

[0073] On the other hand, the surface 46a of the partial bottom wall 46 in the second vertical direction Z2 is a contact surface surrounding the first return path 7 in the first vertical direction Z1. Moreover, the surface 46a of the partial bottom wall 46 in the second vertical direction Z2 moves away from the bottom surface 32 of the return path main body 30 as it moves from the center (second opening 42A) in the orthogonal direction Y toward the outside in the orthogonal direction Y. Therefore, the two partial bottom walls 46 each have a smaller thickness in the vertical direction (radial direction) as it approaches the second opening 42. Moreover, the thickness H5 of the end of the partial bottom wall 46 near the second opening 42A is the same as the thickness H1 to avoid deformation due to contact with the ball 2.

[0074] As described above, according to the first modification, as in the first embodiment, the radial thickness of the return path body 30A is smaller than that in the case where the first opening 41 and the second opening 42A are not provided. Moreover, the outer wall 43 and the bottom wall 45A are not deformed even when they come into contact with the ball 2. According to the first modification, since the bottom wall 45A is provided, the radial thickness is larger than that of the first embodiment by the thickness H5 of the bottom wall 45A.

[0075] (Variation 2) FIG. 13 is a cross-sectional view of the return path body of the second modification cut in an orthogonal direction. As shown in FIG. 13, the return path body 30B of the second modification differs from the first embodiment in that the width L5 of the first opening 41B is the same as the width L1 of the first return path 7. Therefore, the wall portion 40B does not have the outer wall 43 (partial outer wall 44). According to the second modification, the radial thickness is smaller than that of the first embodiment by the thickness H1. In addition, since there is no outer wall 43 (see FIG. 10) or bottom wall 45A (see FIG. 12), the wall portion does not deform due to contact with the ball 2. Furthermore, in the second modification, the ball 2 moves through the first return path 7 while contacting the inner circumferential surface 52 of the sleeve 50. Therefore, the sleeve 50 (fixed part) of the second modification plays the role of the radially outer wall portion of the first return path 7.

[0076] Modifications 1 and 2 have been described above. In the first embodiment, both the first opening 41 and the second opening 42 are provided in the wall portion 40, but in the present disclosure, it is sufficient that at least one of the first opening 41 and the second opening 42 is provided in the wall portion 40. Below, examples in which only the first opening 41 is provided will be described in Modifications 3 and 4. Also, examples in which only the second opening 42 is provided will be described in Modifications 5 and 6.

[0077] (Variation 3) FIG. 14 is a cross-sectional view of the return path body of the third modification taken in an orthogonal direction. As shown in FIG. 14, the return path body 30C of the third modification differs from the first embodiment in that only the first opening 41 is provided in the wall portion 40C. That is, in the third modification, the second opening 42 is not provided in the return path body 30C. Even in the third modification, the radial thickness can be reduced by the thickness H4 (see FIG. 11) compared to the comparative example. In addition, in the bottom wall 45C of the present disclosure, when the second opening 42 is not provided, the surface 46a in the second vertical direction Z2 may be an arc surface along the ball 7.

[0078] (Variation 4) FIG. 15 is a cross-sectional view of the return path body of the fourth modification cut in an orthogonal direction. As shown in FIG. 14, the return path body 30D of the fourth modification differs from the third modification in that the width L6 of the first opening 41D is the same as the width L1 of the first return path 7. Therefore, the wall portion 40D does not have an outer wall 43 (partial outer wall 44). Therefore, the fourth modification can have a smaller radial thickness than the third modification. Also, in the fourth modification, the ball 2 contacts the inner circumferential surface 52 of the sleeve 50. Therefore, the sleeve 50 (fixed part) plays the role of a wall portion on the radial outside of the first return path 7.

[0079] (Variation 5) Fig. 16 is a cross-sectional view of the return path body of Modification 5 cut in an orthogonal direction. As shown in Fig. 16, the return path body 30E of Modification 5 differs from Modification 2 in that only the second opening 42A is provided in the wall portion 40E. That is, in Modification 5, the return path body 30E does not have the first opening 41. Even in such Modification 5, it is possible to reduce the radial thickness compared to the comparative example.

[0080] (Variation 6) FIG. 17 is a cross-sectional view of the return path body of the sixth modification cut in an orthogonal direction. As shown in FIG. 17, the return path body 30F of the sixth modification differs from the fifth modification in that the width L7 of the second opening 42F is the same as the width L1 of the first return path 7. That is, the wall portion 40F does not have a bottom wall 45A (partial bottom wall 46). According to the sixth modification, the radial thickness can be made smaller than that of the fifth modification. Also, in the sixth modification, the ball 2 contacts the flat surface 15 of the nut 1. Thus, the nut 1 serves as a wall portion on the radial inner side of the first return path 7.

[0081] Although the embodiment and the modified examples have been described above, the present disclosure is not limited to those exemplified in the embodiment and the modified examples. For example, in the embodiment, a sleeve is used as a part for fixing the circulation part, but in the present disclosure, the return path body may be fixed by a screw fastened to the nut. Alternatively, the movement of the return path body in the second vertical direction may be restricted by an annular fixing ring fitted to the nut. Alternatively, the circulation part may be fixed to the nut by tightening a part of the circulation part, and the method of fixing the circulation part in the present disclosure is not limited to the above-mentioned one.

[0082] In addition, in Modification 2, the sleeve 50 that fits onto the nut 1 is used as a part that contacts the ball 2 while closing the first opening 41B, but the present disclosure may use a cover that does not fit onto the nut 1. In other words, the cover may be fixed to the nut with a screw or the like, and the cover may cover the outer circumferential side of the return path main body 30.

[0083] In addition, in the present disclosure, a separate part may be provided on the outer periphery of the sleeve, and this separate part may prevent the sleeve from falling off the nut. In addition, the material of the circulating part of the present disclosure may include metal, resin, etc., but the present disclosure is not limited thereto. Furthermore, when the circulating part is manufactured from metal, an example of a manufacturing method may include MIM (Metal Injection Molding), but the present disclosure may be manufactured using other manufacturing methods. In addition, the material of the sleeve may include resin, metal, etc., as with the resin part, but the present disclosure is not limited thereto. When the sleeve is manufactured from metal, iron-based or stainless steel-based materials may be used, but the present disclosure may be manufactured using other metals.

[0084] The present disclosure may also be implemented in the following combinations: (1) A cylindrical nut having an inner circumferential surface and an outer circumferential surface; A screw shaft passing through the nut; A plurality of balls disposed between the nut and the screw shaft; A circulation part having a return path formed therein; Equipped with The nut is formed with two leg holes penetrating the inner circumferential surface and the outer circumferential surface, The circulating part is Two legs inserted into the leg holes; A return path body that is disposed on an outer peripheral side of the nut and connects the two leg portions to each other; having The return path is A first return passage formed inside the return passage body; A second return passage formed inside the leg portion; having The return path body has a cylindrical wall portion in which the first return path is formed, The wall portion is provided with at least one of a first opening penetrating a portion of the wall portion on the radial outer side of the first return passage and a second opening penetrating a portion of the wall portion on the radial inner side of the first return passage. Ball screw device. (2) The wall portion is provided with both the first opening and the second opening. A ball screw device as described in (1). (3) The wall portion is provided with only the first opening. A ball screw device as described in (1). (4) The wall portion is provided with only the second opening. A ball screw device as described in (1). (5) a fixing component that covers the return path body from a radially outer side of the return path body and fixes the circulation component to the nut; The first opening is closed by the fixing component. A ball screw device as described in (2) or (3). (6) The outer peripheral surface of the nut closes the second opening. A ball screw device as described in (2) or (4). (7) The outer peripheral surface of the nut is When viewed from an axial direction parallel to the screw shaft, an arcuate surface having an arc shape; A plane perpendicular to a virtual line extending in a radial direction when viewed from the axial direction; having The plane is provided with the two leg holes, The return path body is disposed radially outward of the plane. A ball screw device according to any one of (1) to (6). [Explanation of symbols]

[0085] 100 Ball screw device 1 Nut 2. Ball 3 Rotable parts 5 Fixing parts 6 Return Route 7, 207 1st Return Road 8 Second Return Path 13 Outer surface 14 Circular Surface 15 plane 17 Leg hole 18 Flange 30, 30A, 30B, 30C, 30D, 30E, 30F, 230 Return path body 31 Legs 32, 232 Bottom 33, 233 top surface 34 Aperture 40, 40A, 40B, 40C, 40D, 40E, 40F Wall section 41, 41B, 41D 1st opening 42, 42A, 42F 2nd opening 43, 243 Exterior wall 44 Partial exterior wall 45A, 245 bottom wall 46 Partial bottom wall 50 Sleeve 51 Sleeve body 53 Protrusion 54 Cut 56 Recess 300 Common Parts 301 1st part 302 2nd Part 310 Mating surface 311 Concave

Claims

1. A cylindrical nut having an inner circumferential surface and an outer circumferential surface; A screw shaft passing through the nut; A plurality of balls disposed between the nut and the screw shaft; A circulation part having a return path formed therein; Equipped with The nut is formed with two leg holes penetrating the inner circumferential surface and the outer circumferential surface, The circulating part is Two legs inserted into the leg holes; A return path body that is disposed on an outer circumferential side of the nut and connects the two legs to each other; having The return path is A first return passage formed inside the return passage body; A second return passage formed inside the leg portion; having The return path body has a cylindrical wall portion in which the first return path is formed, The wall portion is provided with at least one of a first opening penetrating a portion of the wall portion on the radial outer side of the first return passage and a second opening penetrating a portion of the wall portion on the radial inner side of the first return passage. Ball screw device.

2. The wall portion is provided with both the first opening and the second opening. The ball screw device according to claim 1 .

3. The wall portion is provided with only the first opening. The ball screw device according to claim 1 .

4. The wall portion is provided with only the second opening. The ball screw device according to claim 1 .

5. a fixing component that covers the return path body from a radially outer side of the return path body and fixes the circulation component to the nut; The first opening is closed by the fixing component. The ball screw device according to claim 2 or 3.

6. The outer peripheral surface of the nut closes the second opening. The ball screw device according to claim 2 or 4.

7. The outer peripheral surface of the nut is When viewed from an axial direction parallel to the screw shaft, an arcuate surface having an arc shape; A plane perpendicular to a virtual line extending in a radial direction when viewed from the axial direction; having The plane is provided with the two leg holes, The return path body is disposed radially outward of the plane. The ball screw device according to any one of claims 1 to 4.

Images