Ball screw device

Abstract

To provide a ball screw device capable of avoiding enlargement of a nut in an axial direction.SOLUTION: A ball screw device is equipped with a screw shaft that designates a first direction at one end, designates a second direction at the other end, and a nut penetrated by a screw shaft, a plurality of balls disposed between the screw shaft and the nut, and a plurality of circulating portions that returns the balls moving 1 one lead by one lead. The nut has a nut body provided with an inner peripheral raceway surface on an inner peripheral surface, and a flange projecting outward in a diametrical direction from an end portion in the first direction of the nut body. On end surface in the first direction of the nut body, a storage portion recessed in the second direction and opening to an inner peripheral surface of the nut body is provided. The plurality of circulating portions has an end surface piece that is inserted into the storage portion from the first direction and is provided with an S-shaped groove surface on a side surface turning inward in the diametrical direction, and at least one or more S-shaped groove surfaces that are molded on the inner peripheral surface of the nut body and a part disposed closer to the second direction relative to the flange.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A ball screw device includes a screw shaft, a nut penetrated by the screw shaft, and a plurality of balls disposed between the screw shaft and the nut. An outer peripheral raceway surface is provided on the outer peripheral surface of the screw shaft. An inner peripheral raceway surface facing the outer peripheral raceway surface is provided on the inner peripheral surface of the nut. A spiral raceway is formed between the outer peripheral raceway surface and the inner peripheral raceway surface. A plurality of balls are disposed in this raceway. Further, the ball screw device includes a circulation part for circulating the balls. As an example of the circulation part, an S-shaped groove surface formed on the inner peripheral surface of the nut can be mentioned. According to this S-shaped groove surface, the balls that have moved one lead can be returned by one lead. Also, as a circulation part for returning the balls that have moved one lead by one lead, a separator can be mentioned. The separator is a separate part from the nut and is inserted into a through hole that penetrates the outer peripheral surface of the nut in the radial direction inward. In addition, the nut may have a flange that protrudes outward in the radial direction as shown in the following patent document. Further, the flange of the following patent document has a rolling surface for the balls provided on the outer peripheral surface.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, when forming an S-shaped groove surface on the inner circumference of a nut by forging, if there is a flange on the radially outer side, the nut's material has difficulty escaping radially outward, making it difficult to form the S-shaped groove surface. Also, if there is a rolling surface on the outer circumference of the flange, it is not possible to form a through hole for inserting the bearings. In other words, it is difficult to provide a circulation section (S-shaped groove surface and bearings) on the radially inner side of the flange in nuts with flanges. For these reasons, nuts with flanges do not have an inner circumferential raceway surface formed on the radially inner side of the flange. On the other hand, in such nuts, the inner circumferential raceway surface is positioned axially offset from the flange, and the nut is enlarged in the axial direction.

[0005] This disclosure has been made in view of the above, and aims to provide a ball screw device that can avoid increasing the axial size of the nut. [Means for solving the problem]

[0006] To achieve the above objective, a ball screw device according to one aspect of the present disclosure comprises a screw shaft having one end pointing in a first direction and the other end pointing in a second direction, a nut passing through the screw shaft, a plurality of balls disposed between the screw shaft and the nut, and a plurality of circulation parts that return a ball that has moved one lead by one lead. The nut has a nut body having an inner raceway surface on its inner circumferential surface, and a flange protruding radially outward from the end of the nut body in the first direction. The end face of the nut body in the first direction is provided with a housing portion that is recessed in the second direction and opens to the inner circumferential side of the nut body. The plurality of circulation parts have an end face piece inserted into the housing portion from the first direction and having an S-shaped groove surface on its side facing radially inward, and at least one S-shaped groove surface formed on the inner circumferential surface of the nut body in a portion located further inward than the flange.

[0007] The ball screw device of this disclosure has an end face nut, and an inner circumferential raceway surface is formed on the radially inward side of the flange. Therefore, an increase in the axial size of the nut is avoided.

[0008] A preferred embodiment of the ball screw device described above includes a bolt that passes through the end face block and fastens the end face block to the nut.

[0009] According to the above configuration, it is possible to prevent the end face piece from falling off the nut.

[0010] A preferred embodiment of the ball screw device described above includes a rotation stopper facing the end face of the nut body in the first direction. The rotation stopper is fixed to the screw shaft. The head of the bolt protrudes in the first direction beyond the end face of the nut body in the first direction and contacts the rotation stopper.

[0011] According to the above configuration, the nut or screw shaft that moves in the axial direction can be positioned in the initial position. In addition, a bolt is used as the part that contacts the rotation stopper, which reduces the number of parts.

[0012] In a preferred embodiment of the ball screw device described above, a groove extending in the circumferential direction is provided at the end of the inner circumferential surface of the nut body in the first direction. A retaining ring is provided which is housed in the groove and contacts the end face piece from the first direction.

[0013] According to the above configuration, it is possible to prevent the end face piece from falling off the nut.

[0014] In a preferred embodiment of the ball screw device described above, the end face bolster is press-fitted into the housing portion.

[0015] According to the above configuration, it is possible to prevent the end face piece from falling off the nut. In addition, bolts and retaining rings are not required, which reduces the number of parts.

[0016] In a preferred embodiment of the ball screw device described above, the multiple circulation units are arranged at equal intervals in the circumferential direction.

[0017] The screw shaft is supported by the nut via balls. However, if a load acts on the screw shaft in the direction in which the circulation section is located, viewed from the center line of the screw shaft, the screw shaft will not be supported by the nut via the balls. On the other hand, according to the above configuration, the circulation section is arranged at equal intervals in the circumferential direction and is distributed in the circumferential direction. Therefore, the screw shaft is supported by the nut from all directions in the circumferential direction.

[0018] In a preferred embodiment of the ball screw device described above, the outer circumferential surface of the flange is provided with a guide groove that is recessed radially inward and opens in the first and second directions. A guide parallel to the screw shaft is fitted into the guide groove.

[0019] According to the above configuration, the nut having a flange is prevented from rotating.

[0020] In a preferred embodiment of the ball screw device described above, the flange is positioned radially inward of the outer ring of the bearing device. The outer circumferential surface of the flange is provided with grooves on which the rolling elements of the bearing device can roll.

[0021] According to the above configuration, there is no need to separately prepare an inner ring for the bearing device, thus reducing the number of parts.

[0022] In a preferred embodiment of the ball screw device described above, the nut rotates due to rotational motion transmitted from a planetary gear mechanism. The planetary gear mechanism includes a sun gear, an internal gear which is a ring gear surrounding the outer circumference of the sun gear, a plurality of planetary gears arranged between the sun gear and the ring gear, and a carrier which rotatably supports the plurality of planetary gears. The flange constitutes the carrier.

[0023] According to the above configuration, there is no need to prepare a separate carrier, and the number of parts can be reduced. [Effects of the Invention]

[0024] According to the ball screw device of this disclosure, it is possible to avoid increasing the axial size of the nut.

Brief Description of the Drawings

[0025] [Figure 1] FIG. 1 is a cross-sectional view of the ball screw device of Embodiment 1 cut axially. [Figure 2] FIG. 2 is an exploded perspective view of the nut of Embodiment 1 viewed from the first direction. [Figure 3] FIG. 3 is a cross-sectional view of the nut when cut in a plane including the center line of the screw shaft and the center of the female screw hole. [Figure 4] FIG. 4 is a cross-sectional view of the nut, and more specifically, a cross-sectional view viewed from the direction of arrow IV in FIG. 1. [Figure 5] FIG. 5 is a perspective view of the ball screw device of Modification 1. [Figure 6] FIG. 6 is a cross-sectional view of the nut of the ball screw device of Modification 2. [Figure 7] FIG. 7 is a view of the nut of the ball screw device of Modification 2 viewed from the first direction X1. [Figure 8] FIG. 8 is a cross-sectional view of the ball screw device of Modification 3. [Figure 9] FIG. 9 is a cross-sectional view of the ball screw device of Modification 9.

Embodiments for Carrying Out the Invention

[0026] Embodiments for implementing the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the content described in the following description. Also, the components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the components described below can be combined as appropriate.

[0027] (Embodiment 1) Figure 1 is a cross-sectional view of the ball screw device of Embodiment 1, cut in the axial direction. Figure 2 is an exploded perspective view of the nut of Embodiment 1, viewed from a first direction. Figure 3 is a cross-section of the nut when cut by a plane containing the center line of the screw shaft and the center of the female screw hole. Figure 4 is a cross-sectional view of the nut, more specifically a cross-sectional view taken from the direction of arrow IV in Figure 1.

[0028] As shown in Figure 1, the ball screw device 100 of Embodiment 1 comprises a screw shaft 1, a nut 2, a plurality of balls 3, a plurality of circulation parts 4, and a housing 110. Hereinafter, the direction parallel to the center line O1 of the screw shaft 1 will be referred to as the axial direction.

[0029] The screw shaft 1 comprises a screw shaft body 10 and a connecting portion 11. The screw shaft body 10 has an outer peripheral raceway surface 12 on its outer peripheral surface. The screw shaft body 10 passes through the nut 2. Of the axial directions, the direction in which the connecting portion 11 is located, as viewed from the screw shaft body 10, is referred to as the first direction X1. The direction opposite to the first direction X1 is referred to as the second direction X2.

[0030] The connecting portion 11 is the part to which rotational motion is input from another device. Therefore, in this embodiment, rotational motion is input to the screw shaft 1, causing the nut 2 to move in the axial direction. However, in the ball screw device of this disclosure, rotational motion may be input to the nut 2, causing the screw shaft 1 to move in the axial direction. Also, if the screw shaft 1 moves in the axial direction, the connecting portion 11 becomes unnecessary. In other words, in the screw shaft 1 of this disclosure, the connecting portion 11 is not an essential component.

[0031] The outer circumferential surface of the connecting portion 11 is provided with shaft splines. The connecting portion 11 is spline-fitted to the power transmission portion 120. A tightening allowance is provided in the spline fitting, and the connecting portion 11 is connected to the power transmission portion 120 in a way that prevents axial movement. When the power transmission portion 120 rotates, the screw shaft 1 rotates integrally with the power transmission portion 120.

[0032] The nut 2 comprises a cylindrical nut body 20 and a flange 21 that protrudes radially outward from the nut body 20. The flange 21 is located at the end of the nut body 20 in a first direction X1.

[0033] The inner circumferential surface 20a of the nut body 20 is provided with an inner circumferential raceway surface 22 that faces the outer circumferential raceway surface 12. The space between the inner circumferential raceway surface 22 and the outer circumferential raceway surface 12 forms a raceway 5. Multiple balls 3 are arranged in the raceway 5.

[0034] The area of ​​the inner circumferential surface 20a of the nut body 20 in which the inner circumferential raceway surface 22 is formed extends from near the end in the first direction X1 to near the end in the second direction X2. Therefore, the portion of the inner circumferential raceway surface 22 closer to the end in the first direction X1 is positioned radially inward relative to the flange 21 (see auxiliary line H). Note that auxiliary line H is a virtual line drawn radially inward from the end face 21a of the flange 21 facing the second direction X2.

[0035] Furthermore, the nut body 20 has a first end face 23 facing a first direction X1. The first end face 23 is provided with a housing portion 24 that is recessed in a second direction X2. The housing portion 24 accommodates the end face piece 41 of the circulation section 4.

[0036] As shown in Figure 2, the housing portion 24 opens on the inner circumference side of the nut body 20. The housing portion 24 also has a first housing portion 25 and a second housing portion 26, which have different depths in the second direction X2. The first housing portion 25 extends from the first end face 23 in the second direction X2 and cuts out a portion of the inner circumferential raceway surface 22. The second housing portion 26 extends from the first end face 23 in the second direction X2, but has a depth that does not cut out the inner circumferential raceway surface 22.

[0037] The first housing section 25 has an arc shape when viewed from the axial direction. The first housing section 25 has a pair of opposing walls 25a and 25b that face each other in the circumferential direction, a first outer peripheral wall 25c that surrounds the radially outer side, and a first bottom surface 25d that forms the bottom surface.

[0038] The second housing section 26 is positioned adjacent to the first housing section 25 in the circumferential direction. The second housing section 26 has a second bottom surface 26a that forms the bottom surface and a second outer peripheral wall 26b that surrounds the radially outer side. The second bottom surface 26a is provided with a female screw hole 26c into which a bolt 6 is screwed.

[0039] The second outer wall 26b is located radially outward from the first outer wall 25c. Therefore, the second bottom surface 26a extends radially outward from the first bottom surface 25d. This makes it possible to position the female screw hole 26c further radially outward. When the female screw hole 26c is positioned further radially outward, the distance W1 between the female screw hole 26c and the inner circumferential raceway surface 22 increases, as shown in Figure 3. In other words, it is possible to avoid a decrease in the rigidity of the nut body 20 due to the thinning of the portion of the nut body 20 between the female screw hole 26c and the inner circumferential raceway surface 22.

[0040] In this embodiment, an opening 27 is provided at the corner 26d between the second bottom surface 26a and the second outer peripheral wall 26b. Therefore, the second housing section 26 is in communication with the space in the second direction X2 relative to the end face 21a of the flange 21.

[0041] As shown in Figure 2, the outer circumferential surface 21b of the flange 21 is circular in shape with respect to the center line O1. Furthermore, guide grooves 21c are provided on the outer circumferential surface 21b of the flange 21, recessed radially inward. The guide grooves 21c open in a first direction X1 and a second direction X2. Three guide grooves 21c are provided at 120-degree intervals. In other words, multiple guide grooves 21c are provided at equal intervals in the circumferential direction.

[0042] As shown in Figure 1, a guide 111 provided on the housing 110 is positioned on the outer circumference of the flange 21. The guide 111 extends axially and passes through the guide groove 21c in the axial direction. Therefore, the nut 2 is supported by the housing 110 so as not to rotate around the center line O. In addition, the nut 2 is supported by the housing 110 so as to be movable in the axial direction along the guide 111.

[0043] Each of the multiple circulation sections 4 is equipped with three S-shaped groove surfaces 40 (only one is shown in Figure 1; see Figure 4 for the remaining two) and one end face piece 41. The S-shaped groove surfaces 40 are groove surfaces formed on the inner circumferential surface 20a of the nut body 20 by forging. The three S-shaped groove surfaces 40 may be referred to as the first S-shaped groove surface 40a, the second S-shaped groove surface 40b, and the third S-shaped groove surface 40c, in order from the first direction X1.

[0044] As shown in Figure 4, the first S-shaped groove surface 40a is located in the second direction X2 relative to the auxiliary line H. Therefore, the remaining second S-shaped groove surface 40b (see Figure 1) and the third S-shaped groove surface 40c are also located in the second direction X2 relative to the auxiliary line H. In other words, the three S-shaped groove surfaces 40 are offset from the flange 21 in the axial direction of the second direction X2 (axial direction). This makes it possible to form the S-shaped groove surfaces 40 by forging.

[0045] As shown in Figure 1, the end face block 41 is inserted (housed) into the housing portion 24 from the first direction X1 of the first end face 23. A portion of the end face block 41 is positioned radially inward of the flange 21. The manufacturing method of the end face block 41 is not particularly limited. For example, the end face block 41 may be a resin molded product. Alternatively, the end face block 41 may be manufactured by cutting metal. Alternatively, the end face block 41 may be manufactured by metal powder injection molding. As shown in Figure 2, the end face block 41 comprises a block body 42 housed in the first housing portion 25 and a fastened portion 43 housed in the second housing portion 26.

[0046] As shown in Figure 4, the spinning top body 42 is provided with an S-shaped groove surface 44 on the radially inward-facing surface. As a result, the ball 3 rolling on the inner circumferential raceway surface 22 located radially inward of the flange 21 is returned by the groove surface 44 of the spinning top body 42 by one lead. In addition, the spinning top body 42 is in contact with the pair of opposing walls 25a and 25b of the first housing section 25, the first outer circumferential wall 25c, and the first bottom surface 25d. Therefore, the spinning top body 42 is positioned and its posture is stabilized. Furthermore, the transfer of balls between the groove surface 44 and the inner circumferential raceway surface 22 is made smooth. Note that the groove surface 44 in this embodiment does not have a tongue, but it may have a tongue in this disclosure. Also, in this disclosure, the spinning top body 42 does not have to be in contact with all of the pair of opposing walls 25a and 25b of the first housing section 25, the first outer circumferential wall 25c, and the first bottom surface 25d. In other words, the spinning top body 42 may have a small gap due to tolerances between each or any of the faces of the pair of opposing walls 25a, 25b, the first outer peripheral wall 25c, and the first bottom surface 25d. Alternatively, the spinning top body 42 may be press-fitted into the first housing section 25.

[0047] Furthermore, as shown in Figures 1 and 4, the groove surface 44 of the end face block 41, the first S-shaped groove surface 40a, the second S-shaped groove surface 40b, and the third S-shaped groove surface 40c are arranged in that order from the first direction X1. These groove surfaces 44, the first S-shaped groove surface 40a, the second S-shaped groove surface 40b, and the third S-shaped groove surface 40c are arranged at 90-degree intervals. Therefore, the multiple circulation sections 4 are arranged at equal intervals in the circumferential direction.

[0048] Furthermore, with respect to loads acting radially in the direction from the center line O1 to the direction in which the circulation section 4 is positioned, the nut 2 cannot support the screw shaft 1 via the ball 3 in the portion where the circulation section 4 is provided. On the other hand, according to this embodiment, the four circulation sections 4 are arranged at equal intervals in the circumferential direction and are distributed in the circumferential direction. Therefore, the screw shaft 1 is supported by the nut 2 from all directions in the circumferential direction.

[0049] As shown in Figure 3, the fastened portion 43 is positioned to abut against the second bottom surface 26a. The fastened portion 43 is also provided with a hole 43a through which the shaft portion 6a of the bolt 6 passes. The fastened portion 43 is then tightened onto the head 6b of the bolt 6. This prevents the end face piece 41 from detaching from the nut 2.

[0050] The fastened portion 43 has a small axial thickness. Therefore, the head 6b of the bolt 6 is also housed in the second housing portion 26. Thus, the bolt 6 does not protrude beyond the first end face 23 in the first direction X1, which would increase the space occupied by the nut 2.

[0051] As described above, the ball screw device 100 of Embodiment 1 comprises a screw shaft 1 having one end pointing to a first direction X1 and the other end pointing to a second direction X2, a nut 2 passing through the screw shaft 1, a plurality of balls 3 positioned between the screw shaft 1 and the nut 2, and a plurality of circulation parts 4 that return the balls 3 that have moved one lead by one lead. The nut 2 has a nut body 20 with an inner circumferential raceway surface 22 provided on its inner circumferential surface 20a, and a flange 21 that protrudes radially outward from the end of the nut body 20 in the first direction X1. The end face (first end face 23) of the nut body 20 in the first direction X1 is provided with a housing part 24 that is recessed in the second direction X2 and opens to the inner circumferential side of the nut body 20. Each of the multiple circulation sections 4 is inserted into the housing section 24 from a first direction X1 and has an end face section 41 with an S-shaped groove surface 44 on its radially inward-facing side surface, and at least one S-shaped groove surface 40 formed on the inner circumferential surface 20a of the nut body 20, in a portion located in a second direction X2 relative to the flange 21.

[0052] According to Embodiment 1, an inner circumferential raceway surface 22 is formed on the radially inner side of the flange 21, which avoids increasing the axial size of the nut 2.

[0053] Furthermore, the ball screw device 100 of Embodiment 1 is equipped with a bolt 6 that passes through the end face block 41 and fastens the end face block 41 to the nut 2.

[0054] With this bolt 6, the end face piece 41 will not fall off the nut 2.

[0055] Furthermore, in the ball screw device 100 of Embodiment 1, the multiple circulation units 4 are arranged at equal intervals in the circumferential direction.

[0056] In Embodiment 1, the screw shaft 1 is supported by the nut 2 from all directions in the circumferential direction.

[0057] Furthermore, in the ball screw device 100 of Embodiment 1, the outer circumferential surface of the flange 21 is provided with a guide groove 21c that is recessed radially inward and opens in a first direction X1 and a second direction X2. A guide 111 parallel to the screw shaft 1 is fitted into the guide groove 21c.

[0058] According to Embodiment 1, the rotation of the nut 2 is restricted.

[0059] Next, a modified example of the ball screw device 100 of Embodiment 1 will be described. The following description will focus on the differences from Embodiment 1.

[0060] (Variation 1) Figure 5 is a perspective view of the ball screw device of Modification 1. As shown in Figure 5, the ball screw device 100A of Modification 1 differs from the ball screw device 100 of Embodiment 1 in that an end face block 41A is used instead of the end face block 41. The ball screw device 100A of Modification 1 also differs from the ball screw device 100 of Embodiment 1 in that a rotation stopper 130 is attached to the connecting portion 11 of the screw shaft.

[0061] The end face 46 of the end face insert 41A in the first direction X1 is flush with the first end face 23 of the nut body 20. Therefore, the head 6b of the bolt 6 protrudes in the first direction X1 beyond the first end face 23 of the nut body 20.

[0062] The rotation stopper 130 has an annular portion 131 that spline-fits to the connecting portion 11, and a projection 132 that protrudes radially outward from the annular portion 131. The rotation stopper 130 is prevented from rotating by the connecting portion 11 and rotates integrally with the screw shaft 1. Hereinafter, when viewed from the first direction X1, counterclockwise rotation will be referred to as the first rotation direction L1, and clockwise rotation will be referred to as the second rotation direction L2. The projection 132 faces the first end face 23. The projection 132 has a contact surface 132a facing the second rotation direction L2. The contact surface 132a is in contact with the head 6b of the bolt 6.

[0063] According to the ball screw device 100A of Modified Example 1, when the screw shaft 1 rotates in the first rotational direction L1 from the state shown in Figure 5, the nut 2 moves in the second direction X2. When the screw shaft 1 rotates in the second rotational direction L2, the nut 2 moves in the first direction X1. Furthermore, when the screw shaft 1 rotates in the second rotational direction L2 while the nut 2 has moved in the second direction X2, the head 6b of the bolt 6 enters the trajectory of the projection 132 of the rotation stopper 130, which rotates integrally with the screw shaft 1, and comes into contact with the contact surface 132a of the projection 132. As a result, the rotation of the screw shaft 1 in the second rotational direction L2 is restricted, and the movement of the nut 2 in the first direction X1 is stopped. Therefore, according to Modified Example 1, the nut 2 can be reliably positioned in its initial position (the state in which the contact surface 132a and the bolt 6 are in contact). In addition, according to Modified Example 1, the bolt 6 is used as the part that contacts the rotation stopper 130, thus reducing the number of parts.

[0064] (Modification 2) Figure 6 is a cross-sectional view of the nut of the ball screw device of Modification 2. Figure 7 is a view of the nut of the ball screw device of Modification 2 from the first direction X1. As shown in Figure 6, the nut 2B of the ball screw device 100B of Modification 2 differs from the ball screw device 100 of Embodiment 1 in that it has a retaining ring 6B instead of a bolt 6.

[0065] A cylindrical surface 28 is provided at the end of the inner circumferential surface 20a of the nut 2B in the first direction X1. The cylindrical surface 28 is positioned in the first direction X1 relative to the housing portion 24. The diameter of the cylindrical surface 28 is the same as the diameter of the first outer circumferential wall 25c of the housing portion 24. A groove 28a extending in the circumferential direction is provided on the cylindrical surface 28. The outer circumference of the retaining ring 6B is fitted into the groove 28a. The retaining ring 6B is in contact with the end face block 41B from the first direction X1. As a result, the end face block 41B does not detach from the nut 2B.

[0066] In Embodiment 1, the end face of the end face block 41 was not flat in the first direction X1 (see Figure 2), but in Modification 2, the end face 46 of the end face block 41B in the first direction X1 is flat. The end face 46 abuts against the retaining ring 6B from one end to the other in the circumferential direction. Therefore, in Modification 2, one end or the other end of the end face block 41B in the circumferential direction is supported so as not to wobble in the axial direction.

[0067] Furthermore, in Modification 2, the bolt 6 is not used. Therefore, as shown in Figure 7, the end face block 41B in Modification 2 consists only of the block body 42. In other words, the end face block 41B does not have a fastened portion 43. Also, the housing portion 24 of the nut 2 does not have a second housing portion 26, and only has a first housing portion 25. Therefore, the thinning of the wall portion of the nut body 20 due to the female screw hole 26c is avoided.

[0068] The above describes Modification 2, in which an example was described in which the bolt 6 is replaced with a retaining ring 6B for fixing. However, in this disclosure, the end face piece may be fixed to the nut 2 by press-fitting it into the housing 24. As an example of fixing by press-fitting, the end face piece may be clamped from the circumferential direction against a pair of opposing walls 25a and 25b (see Figure 4) of the first housing 25. Alternatively, the end face piece 41B of Modification 2 may be press-fitted into the housing 24. This would result in the end face piece 41B being fixed more firmly than when it is fixed with only the retaining ring 6B.

[0069] (Variation 3) Figure 8 is a cross-sectional view of the ball screw device of Modification 3. As shown in Figure 8, the ball screw device 100C of Modification 3 differs from the ball screw device 100 of Embodiment 1 in that it is equipped with a bearing device 140. Furthermore, the ball screw device 100C of Modification 3 differs from the ball screw device 100 of Embodiment 1 in that a groove surface 21d is provided on the outer circumferential surface 21b of the flange 21.

[0070] The outer ring 141 of the bearing device 140 is fitted into the housing 110. A flange 21 is positioned radially inward of the outer ring 141. The groove surface 141a of the outer ring 141 and the groove surface 21d of the flange 21 face each other. In addition, multiple rolling elements 142 are positioned between the groove surface 141a and the groove surface 21d. In other words, the nut 2C is rotatably fixed to the housing 110 by the bearing device 140.

[0071] Therefore, in modified example 3, rotational motion is input to the nut 2, causing the screw shaft 1C to move in the axial direction.

[0072] (Modification 4) Figure 9 is a cross-sectional view of the ball screw device of Modification 9. As shown in Figure 9, the ball screw device 100D of Modification 4 differs from the ball screw device 100C of Modification 3 in that it has a planetary gear mechanism 150. The planetary gear mechanism 150 includes an input shaft 151, a sun gear 152, a ring gear 153, a plurality of planetary gears 154, a plurality of transmission shafts 155, and a carrier 156.

[0073] Rotational motion is input to the input shaft 151 from another device. The input shaft 151 is located coaxially with the center line O1. The sun gear 152 passes through the input shaft 151 and rotates integrally with the input shaft 151. The ring gear 153 is an internal gear centered on the input shaft 151. The outer circumferential surface of the ring gear 153 is fitted into the housing 110.

[0074] The planetary gear 154 is positioned between the sun gear 152 and the ring gear 153. The planetary gear 154 also meshes with the sun gear 152 and the ring gear 153. The planetary gear 154 passes through the transmission shaft 155. The planetary gear 154 is rotatably supported around the transmission shaft 155.

[0075] The carrier 156 is an annular component centered on the center line O. In modified example 4, the flange 21 of the nut 2D forms the carrier 156. The flange 21 is provided with a through hole 21e that penetrates axially. The transmission shaft 155 is inserted into the through hole 21e of the flange 21 and supported by the flange 21. As described above, according to modified example 4, there is no need to prepare a separate carrier 156, and the number of parts can be reduced.

[0076] Although Embodiment 1 and its various modifications have been described above, this disclosure is not limited to those described above. For example, Embodiment 1 has three S-shaped groove surfaces 40, but in this disclosure, it is sufficient to have at least one S-shaped groove surface.

[0077] Furthermore, this disclosure may also be a combination of the following configurations. (1) A ball screw device comprising: a screw shaft having one end pointing in a first direction and the other end pointing in a second direction; a nut passing through the screw shaft; a plurality of balls positioned between the screw shaft and the nut; and a plurality of circulation parts that return a ball that has moved one lead by one lead, wherein the nut has a nut body with an inner raceway surface on its inner circumferential surface and a flange protruding radially outward from the end of the nut body in the first direction, the end face of the nut body in the first direction is provided with a housing portion that is recessed in the second direction and opens to the inner circumferential side of the nut body, and the plurality of circulation parts are end face pieces inserted into the housing portion from the first direction and having an S-shaped groove surface on the side facing radially inward, and at least one S-shaped groove surface formed on the inner circumferential surface of the nut body in a portion positioned in the second direction from the flange. (2) The ball screw device according to (1), further comprising a bolt that passes through the end face piece and fastens the end face piece to the nut. (3) The ball screw device according to (2), further comprising a rotation stopper facing the end face of the nut body in the first direction, wherein the rotation stopper is fixed to the screw shaft, and the head of the bolt protrudes in the first direction beyond the end face of the nut body in the first direction and contacts the rotation stopper. (4) The ball screw device according to (1), wherein the end of the inner circumferential surface of the nut body in the first direction is provided with a groove extending in the circumferential direction, and a retaining ring is housed in the groove and contacts the end face piece from the first direction. (5) The end face piece is press-fitted into the housing portion. A ball screw device according to any one of (1) to (4). (6) A ball screw device according to any one of (1) to (5), wherein the plurality of circulation units are arranged at equal intervals in the circumferential direction. (7) The ball screw device according to any one of (1) to (6), wherein the outer circumferential surface of the flange is provided with a guide groove that is recessed radially inward and opens in the first and second directions, and a guide parallel to the screw shaft is fitted into the guide groove. (8) The ball screw device according to any one of (1) to (6), wherein the flange is positioned radially inward of the outer ring of the bearing device, and the outer circumferential surface of the flange is provided with a grooved surface on which the rolling elements of the bearing device can roll. (9) The ball screw device according to any one of (1) to (6), wherein the nut rotates when rotational motion is transmitted from the planetary gear mechanism, the planetary gear mechanism comprises a sun gear, an internal gear which is a ring gear surrounding the outer circumference of the sun gear, a plurality of planetary gears arranged between the sun gear and the ring gear, and a carrier which rotatably supports the plurality of planetary gears, and the flange constitutes the carrier. [Explanation of symbols]

[0078] 100, 100A, 100B, 100C, 100D Ball Screw Device 1 Screw shaft 2, 2B nut 3 balls 4 Circulation section 6 volts 6B Retaining ring 110 Housing 10 Screw shaft body 12 Outer raceway surface 20 Nut body 21 Flange 21b Outer surface 21c guide groove 22 Inner raceway surface 23 1st end face (end face) 24 Storage Unit 25. First Detention Unit 26. Second Detention Unit 26c Female threaded hole 40 S-shaped groove surface 40a 1st S-shaped groove surface 40b 2nd S-shaped groove surface 40c 3rd S-shaped groove surface 41, 41A End face insert 42 Frame Body 43 Part to be fastened 44 Groove surface 130 Rotation Stopper 132 Protrusion 132a Contact surface 140 Bearing device 141 Outer ring 142 Rolling element 150 Planetary gear mechanism 156 Careers

Claims

1. A screw shaft with one end pointing in a first direction and the other end pointing in a second direction, A nut that passes through the aforementioned screw shaft, A plurality of balls are arranged between the screw shaft and the nut, Multiple circulation units that move the ball one lead and then return it one lead, Equipped with, The aforementioned nut is A nut body having an inner raceway surface on its inner surface, A flange protruding radially outward from the end of the nut body in the first direction, It has, The end face of the nut body in the first direction is provided with a housing portion that is recessed in the second direction and opens to the inner circumference side of the nut body. The multiple circulation units are, An end face piece is inserted into the housing from the first direction and has an S-shaped groove surface on its radially inward-facing side, At least one S-shaped groove surface formed on the inner circumferential surface of the nut body, in a portion that is positioned in the second direction relative to the flange, A ball screw device having a ball screw mechanism.

2. The bolt penetrates the end face piece and fastens the end face piece to the nut. The ball screw device according to claim 1.

3. The nut body is provided with a rotation stopper facing the end face in the first direction, The rotation stopper is fixed to the screw shaft, The head of the bolt protrudes in the first direction beyond the end face of the nut body in the first direction and contacts the rotation stopper. The ball screw device according to claim 2.

4. A groove extending in the circumferential direction is provided at the end of the inner circumferential surface of the nut body in the first direction. It has a retaining ring housed in the groove and in contact with the end face piece from the first direction. The ball screw device according to claim 1.

5. The end face piece is press-fitted into the housing portion. The ball screw device according to claim 1.

6. The multiple circulation units are arranged at equal intervals in the circumferential direction. A ball screw device according to any one of claims 1 to 5.

7. The outer circumferential surface of the flange is provided with guide grooves that are recessed radially inward and open in the first and second directions. A guide parallel to the screw shaft is fitted into the guide groove. A ball screw device according to any one of claims 1 to 5.

8. The flange is positioned radially inward of the outer ring of the bearing device. The outer circumferential surface of the flange is provided with grooves on which the rolling elements of the bearing device can roll. A ball screw device according to any one of claims 1 to 5.

9. The aforementioned nut rotates as rotational motion is transmitted from the planetary gear mechanism. The aforementioned planetary gear mechanism is Sangia and, It is an internal gear, and a ring gear surrounds the outer circumference of the sun gear, A plurality of planetary gears are arranged between the sun gear and the ring gear, A carrier that rotatably supports the aforementioned multiple planetary gears, It has, The flange constitutes the carrier. A ball screw device according to any one of claims 1 to 5.

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