Ball screw and ball screw manufacturing method

Abstract

To provide a ball screw capable of reducing a nut, and a ball screw manufacturing method.SOLUTION: A ball screw 1 comprises: a screw shaft 2, on the outer periphery 2a of which a screw groove 21 is formed; a nut 3 having a body part 31, on the inner periphery 31b of which a screw groove 33 and a circulation groove 34 are formed; and plural balls 4 arranged on a rolling path 10 formed by the screw groove 21 and the screw groove 33, circulated via the circulation groove 34 and rolling on the rolling path 10. The nut 3 further has a flange part 32 projecting outward from an outer periphery 31a of the body part 31 in a radial direction. The screw groove 33 and the circulation groove 34 are formed on an inner periphery of a flange formation portion 311 overlaid on the flange part 32 in a radial direction of the body part 31.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ball screw and a method for manufacturing a ball screw. [Background technology]

[0002] The nut of a ball screw may be formed with a flange portion for various purposes. For example, in the ball screw described in Patent Document 1, the inner ring raceway surface of the bearing is formed on the outer peripheral surface of the flange portion, and the nut functions as the inner ring of the bearing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] European Patent No. 3208164 Summary of the Invention [Problem to be solved by the invention]

[0004] In a ball screw, balls roll in a rolling path formed between a screw shaft and a nut. A circulation path is provided to circulate the balls in the rolling path. A possible method of providing a circulation path is to attach a circulation part in which a circulation path is formed to the nut, as in the ball screw described in Patent Document 1. Alternatively, a circulation groove constituting the circulation path may be formed on the inner peripheral surface of the nut.

[0005] However, in both methods, it is difficult to form a circulation path in the part of the nut where the flange portion is formed, and the circulation path and screw groove are not formed in that part. This is because in the former method described above, a circulation part cannot be attached to the part where the flange portion is formed. In addition, in the latter method described above, when a circulation groove is formed on the inner peripheral surface of the nut by forging, for example, the part where the flange portion is formed is thick and difficult to deform, so the circulation groove cannot be formed. For the above reasons, in the conventional ball screw, it is not possible to form a circulation path and screw groove in the part of the nut where the flange portion is formed, and the length of the nut in the axial direction becomes long.

[0006] Therefore, an object of the present invention is to provide a ball screw that allows the nut to be shortened, and a method for manufacturing such a ball screw. [Means for solving the problem]

[0007] The ball screw of the present invention is [1] "a ball screw comprising: a threaded shaft having a first thread groove formed on its outer peripheral surface; a nut having a body portion having a second thread groove and a circulation groove formed on its inner peripheral surface; and a plurality of balls arranged in a rolling path formed by the first thread groove and the second thread groove and rolling in the rolling path while being circulated via the circulation groove, wherein the nut further has a flange portion protruding radially outward from the outer peripheral surface of the body portion, and the second thread groove and the circulation groove are formed on the inner peripheral surface of the body portion that radially overlaps with the flange portion."

[0008] In this ball screw, a second thread groove and a circulation groove are formed on the inner surface of the portion of the main body that radially overlaps with the flange portion (hereinafter also referred to as the "flange forming portion"), making it possible to shorten the nut compared to a case in which the second thread groove and rolling path are not formed in the flange forming portion.

[0009] The ball screw of the present invention may be [2] "the ball screw according to [1], in which a recess is formed on the outer peripheral surface of the flange portion so as to overlap with the circulation groove in the radial direction." Such a ball screw may be manufactured, for example, through a process of forming a circulation groove at a position radially overlapping with the recess in a state in which a recess is formed on the outer peripheral surface of the flange portion. In this case, the circulation groove can be formed by partially thinning the thickness of the flange forming portion by the recess, and the circulation groove can be formed on the inner peripheral surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0010] The ball screw of the present invention may be [3] "the ball screw according to [2], in which the recess overlaps the entire circulation groove in the radial direction." In the manufacturing process of such a ball screw, the circulation groove can be well formed on the inner circumferential surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0011] The ball screw of the present invention may be [4] "the ball screw according to [2] or [3], in which the bottom surface of the recess is curved so as to protrude radially outward when viewed from the axial direction." In the manufacturing process of such a ball screw, a circulation groove can be favorably formed on the inner peripheral surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0012] The ball screw of the present invention may be [5] "the ball screw according to any one of [2] to [4], in which the width of the circulation groove is equal to or less than the width of the recess when viewed from the axial direction." In the manufacturing process of such a ball screw, the circulation groove can be well formed on the inner circumferential surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0013] The ball screw of the present invention may be [6] "the ball screw according to any one of [2] to [5], in which the thickness of the nut at the position where the circulation groove and the recess are formed is less than four times the depth of the circulation groove." In the manufacturing process of such a ball screw, the circulation groove can be well formed on the inner circumferential surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0014] The ball screw of the present invention may be [7] "the ball screw according to any one of [2] to [6], in which an adjustment recess is formed on the outer peripheral surface of the flange portion for adjusting the weight balance of the nut in the radial direction in relation to the recess, and the adjustment recess is arranged so as not to overlap with the circulation groove in the radial direction." In this case, even when a recess is formed, the weight balance of the nut in the radial direction can be adjusted.

[0015] The ball screw of the present invention may be [8] "a ball screw according to any one of [2] to [7], in which the circulation groove extends in an S-shape when viewed from the radial direction, and the recess is formed in a shape corresponding to the circulation groove when viewed from the radial direction." In the manufacturing process of such a ball screw, the circulation groove can be well formed on the inner circumferential surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0016] The ball screw of the present invention may be [9] "the ball screw according to any one of [1] to [8], in which an insertion hole extending along the axial direction is formed in an end face of the flange portion in the axial direction." In this case, for example, by inserting a pinion shaft of a planetary gear into the insertion hole, the nut can be used as a carrier of the planetary gear.

[0017] The ball screw of the present invention may be

[10] "the ball screw according to any one of [1] to [9], in which a raceway groove extending along the circumferential direction is formed on the outer peripheral surface of the flange portion." In this case, for example, the nut can be used as the inner ring of the bearing.

[0018] The ball screw of the present invention may be

[11] "the ball screw according to any one of [1] to [9], in which a groove extending along the axial direction is formed on the outer peripheral surface of the flange portion." In this case, for example, by engaging a part of the object to which the nut is attached with the groove in the rotational direction, the nut and the object to which the nut is attached can be prevented from rotating, and the nut can be used as a rotation preventing member.

[0019] The ball screw of the present invention may be

[12] "the ball screw according to any one of [1] to [9], in which a spline is formed on the outer peripheral surface of the flange portion." In this case, the nut can be engaged with an object to be attached by the spline.

[0020] The manufacturing method of the ball screw of the present invention is

[13] "A manufacturing method of a ball screw as described in any one of [1] to

[12] , comprising a step of forming the circulation groove on an inner circumferential surface of the portion of the main body portion that radially overlaps with the flange portion, and in the step of forming the circulation groove, with a recess formed on the outer circumferential surface of the flange portion, the circulation groove is formed at a position that radially overlaps with the recess."

[0021] In this method of manufacturing a ball screw, in the process of forming the circulation groove, a recess is formed on the outer peripheral surface of the flange portion, and the circulation groove is formed at a position overlapping the recess in the radial direction. This makes it possible to form the circulation groove by partially thinning the thickness of the flange forming portion with the recess, and the circulation groove can be formed on the inner peripheral surface of the flange forming portion. As a result, it is possible to shorten the nut.

[0022] The ball screw of the present invention may be the ball screw manufacturing method according to

[14] "wherein, when viewed from the axial direction, at the start of the step of forming the circulation groove, the bottom surface of the recess extends along a tangent to the outer circumferential surface of the portion of the body where the flange portion is not formed, or coincides with the outer circumferential surface." In this case, the depth of the recess can be sufficiently ensured, and the circulation groove can be well formed on the inner circumferential surface of the flange-forming portion. Effect of the Invention

[0023] According to the present invention, it is possible to provide a ball screw that allows the nut to be shortened, and a method for manufacturing such a ball screw. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a cross-sectional view of a ball screw according to an embodiment. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] 5(a) and (b) are diagrams for explaining a manufacturing method of a ball screw, where (a) is a cross-sectional view of a nut and (b) is a front view of the nut. FIG. [Figure 7] 5A, 5B, 5C, and 5D are cross-sectional views illustrating a manufacturing method of a ball screw according to a reference example. [Figure 8] 5A, 5B, and 5C are cross-sectional views for explaining a method for manufacturing a ball screw according to an embodiment. [Figure 9] FIG. 4 is a cross-sectional view of a ball screw according to a first modified example. [Figure 10] FIG. 13 is a perspective view of a nut according to a first modified example. [Figure 11] 6(a) and (b) are diagrams illustrating a manufacturing method of a ball screw according to a first modified example, where (a) is a cross-sectional view of a nut and (b) is a front view of the nut. FIG. [Figure 12] 6(a) and (b) are diagrams illustrating a manufacturing method of a ball screw according to a first modified example, where (a) is a cross-sectional view of a nut and (b) is a front view of the nut. FIG. [Figure 13] FIG. 13 is a perspective view of a nut according to a second modified example. [Figure 14] FIG. 13 is a perspective view of a nut according to a third modified example. [Figure 15] FIG. 13 is a diagram for explaining another modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or corresponding elements are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0026] 1, the ball screw 1 includes a screw shaft 2, a nut 3, and a plurality of balls 4. The ball screw 1 can be used in an electric actuator, for example, an EHB (Electro-Hydraulic Brake). Hereinafter, a direction parallel to the center line of the screw shaft 2 is referred to as an axial direction, a direction perpendicular to the center line of the screw shaft 2 is referred to as a radial direction, and a direction along a circumference centered on the center line of the screw shaft 2 when viewed from a direction parallel to the center line of the screw shaft 2 is referred to as a circumferential direction.

[0027] A screw groove (first screw groove) 21 is formed on the outer peripheral surface 2a of the screw shaft 2. The screw groove 21 extends in a spiral shape. For example, splines or serrations are formed on the outer peripheral surface of one end portion 2b of the screw shaft 2.

[0028] As shown in Figs. 1 to 5, the nut 3 has a cylindrical main body 31 and a flange 32 protruding radially outward from an outer circumferential surface 31a of the main body 31. A plurality of screw grooves (second screw grooves) 33 are formed on an inner circumferential surface 31b of the main body 31. The plurality of screw grooves 33 extend in a spiral shape at the same pitch as the screw groove 21 of the screw shaft 2. Each screw groove 33 has a length of, for example, about one lead. The screw groove 22 of the screw shaft 2 and the plurality of screw grooves 33 of the nut 3 form a plurality of rolling paths 10. Note that Fig. 3 shows the relationship between the recesses 41 to 43 described later and the circulation groove 34 formed in the flange forming portion 311, and the screw groove 33 and the circulation groove 34 formed in the portion 312 other than the flange forming portion 311 are omitted. This also applies to Fig. 12(b) described later.

[0029] In addition to the multiple screw grooves 33, multiple circulation grooves 34 are formed on the inner peripheral surface 31b of the main body 31. The multiple circulation grooves 34 correspond to the multiple screw grooves 33. In the corresponding screw grooves 33 and circulation grooves 34, the circulation grooves 34 connect one end and the other end of the screw grooves 33. The multiple circulation grooves 34 are arranged at equal intervals in the circumferential direction when viewed from the axial direction, for example. Each circulation groove 34 extends in an S-shape (crank shape) when viewed from the radial direction. In this example, the circulation groove 34 has a shape in which a pair of extension parts 34a extending along the extension direction of the screw groove 33 are connected by a curved part 34b (FIGS. 4 and 5). Further details of the nut 3 including the flange part 32 will be described later.

[0030] As shown in Fig. 1, a plurality of balls 4 are arranged in each rolling path 10. When passing through the circulation groove 34, the plurality of balls 4 climb over the threads (land portion) on the outer peripheral surface 2a of the screw shaft 2, and thereby circulate endlessly in each rolling path 10. That is, the plurality of balls 4 roll in each rolling path 10 while being circulated via the circulation groove 34. Note that while only some of the balls 4 are shown in Fig. 1, in reality, a large number of balls 4 are lined up throughout the entire rolling path 10.

[0031] Further details of the nut 3 including the flange portion 32 will be described. As shown in Figs. 1 to 5, the flange portion 32 protrudes radially outward from a flange forming portion 311 of the main body portion 31. The flange forming portion 311 is a portion of the main body portion 31 where the flange portion 32 is formed, and is a portion overlapping with the flange portion 32 in the radial direction. The flange forming portion 311 constitutes one end portion of the main body portion 31 in the axial direction. The flange portion 32 has a cylindrical portion 35 and an annular plate-shaped flange portion 36 protruding radially outward from one end portion of the cylindrical portion 35 in the axial direction.

[0032] An insertion hole 37 extending along the axial direction is formed in an end surface 35a of the cylindrical portion 35 in the axial direction. In this example, three insertion holes 37 are formed, and each insertion hole 37 penetrates the cylindrical portion 35 along the axial direction. For example, a pinion shaft S of a planetary gear constituting a planetary gear mechanism is inserted into each insertion hole 37 (FIG. 1). This allows the nut 3 to be used as a carrier of the planetary gear. Each insertion hole 37 is arranged so as not to overlap with recesses 41 to 43 described later in the radial direction. In other words, the phases of the three insertion holes 37 are shifted from the phases of the recesses 41 to 43.

[0033] In this example, a bearing 7 is attached to the outer circumferential surface 35b of the cylindrical portion 35. The bearing 7 is, for example, a ball bearing, and has an inner ring 71, an outer ring 72, and a plurality of balls 73 arranged between the inner ring 71 and the outer ring 72. The inner ring 71 is fitted with the outer circumferential surface 35b of the cylindrical portion 35 and is in contact with the flange portion 36 in the axial direction, and is rotatable together with the nut 3.

[0034] In the ball screw 1, the thread groove 33 and the circulation groove 34 are formed on the inner circumferential surface 31b of the main body 31 not only in a portion 312 other than the flange forming portion 311 of the main body 31 but also in the flange forming portion 311. That is, the thread groove 33 and the circulation groove 34 are formed in a region spanning the flange forming portion 311 and the portion 312.

[0035] A plurality of (three in this example) recesses 41, 42, 43 are formed in the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32. The recesses 41 to 43 are recesses formed to partially thin the cylindrical portion 35. The recesses 41, 42 are disposed so as to overlap with the circulation groove 34 in the radial direction.

[0036] 5, in this example, the recess 41 is formed in an elliptical shape consisting of a pair of linear portions and a pair of arcuate portions connecting the ends of the linear portions when viewed from the radial direction. The recess 41 overlaps with the entire circulation groove 34 in the radial direction. That is, the entire edge 41a of the recess 41 is located outside the circulation groove 34. The distance between the edge 41a of the recess 41 and the circulation groove 34 is, for example, 3 mm or less over the entire edge 41a.

[0037] 3, the bottom surface 41b of the recess 41 and the bottom surface 42b of the recess 42 are curved so as to protrude radially outward when viewed from the axial direction. The recess 42 overlaps in the radial direction with a circulation groove 34 that is different from the circulation groove 34 with which the recess 41 overlaps in the radial direction. The recess 43 is disposed so as not to overlap with the circulation groove 34 in the radial direction.

[0038] The recess 43 is an adjustment recess for adjusting the weight balance of the nut 3 in the radial direction in relation to the recesses 41, 42. That is, the formation of the recesses 41, 42 may reduce the weight balance of the nut 3 in the circumferential direction, but the formation of the recess 43 can improve the weight balance of the nut 3 in the circumferential direction. The shape of the recess 43 may be any shape, and may be, for example, a simple round hole.

[0039] When viewed from the axial direction, the width W34 of the circulation groove 34 is equal to or smaller than the width W41 of the recess 41 and the width W42 of the recess 42. The widths W34, W41, and W42 are lengths in a direction perpendicular to the axial direction. At the position where the circulation groove 34 and the recess 41 are formed, the thickness T3 of the nut 3 is smaller than four times the depth T34 of the circulation groove 34. At the position where the circulation groove 34 and the recess 42 are formed, the thickness T3 of the nut 3 is smaller than four times the depth T34 of the circulation groove 34. The depths of the recesses 41 and 42 are set deep enough to allow the circulation groove 34 to be formed in a circulation groove forming step described later.

[0040] An example of a manufacturing method of the ball screw 1 (nut 3) will be described with reference to FIG. 6. As shown in FIG. 6, first, a nut 3 having recesses 41 to 43 formed therein is prepared (preparation step). The preparation step includes, for example, a step of forming the recesses 41 to 43 in the nut 3. In the nut 3 prepared in the preparation step, the bottom surface 41b of the recess 41 and the bottom surface 42b of the recess 42 are flat surfaces perpendicular to the radial direction. In the nut 3 prepared in the preparation step, the screw groove 33 and the circulation groove 34 are not formed. Note that, in the nut 3 prepared in the preparation step, the bottom surface 41b of the recess 41 and the bottom surface 42b of the recess 42 may extend in an arc shape along the circumferential direction when viewed from the axial direction.

[0041] Next, the circulation groove 34 is formed on the inner circumferential surface 31b of the main body 31 of the nut 3 (circulation groove forming process) (FIG. 4). In the circulation groove forming process, the circulation groove 34 is formed on both the flange forming portion 311 of the main body 31 of the nut 3 and the portion 312 other than the flange forming portion 311. The circulation groove 34 is formed, for example, by forging. In the circulation groove forming process, the circulation groove 34 is formed at a position overlapping the recesses 41, 42 in the radial direction in a state in which the recesses 41, 42 are formed on the outer circumferential surface 35b of the cylindrical portion 35 of the flange portion 32. As a result, the thickness of the flange forming portion 311 is partially thinned by the recesses 41, 42, making it possible to form the circulation groove 34, and the circulation groove 34 can be formed on the inner circumferential surface of the flange forming portion 311. After the circulation groove forming process is completed, the bottom surfaces 41b, 42b of the recesses 41, 42 are curved surfaces that are curved so as to protrude radially outward when viewed from the axial direction.

[0042] Next, a screw groove 33 is formed on the inner peripheral surface 31b of the body portion 31 of the nut 3 (screw groove forming step) (FIG. 4). In the screw groove forming step, the screw groove 33 is formed on both the flange forming portion 311 of the body portion 31 of the nut 3 and a portion 312 other than the flange forming portion 311. The screw groove 33 is formed by, for example, cutting. The nut 3 is obtained by the above steps. The ball screw 1 is obtained by combining the nut 3 with the screw shaft 2 and balls 4. [Action and Effects]

[0043] In the ball screw 1, the thread groove 33 (second thread groove) and the circulation groove 34 are formed on the inner peripheral surface of the portion (flange forming portion 311) of the main body portion 31 that overlaps with the flange portion 32 in the radial direction, so that it is possible to shorten the nut 3 compared to a case where the thread groove 33 and the rolling path 10 are not formed in the flange forming portion 311. In addition, the number of parts does not increase compared to the conventional case.

[0044] The recesses 41, 42 are formed on the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32 so as to overlap with the circulation groove 34 in the radial direction. Such a ball screw 1 can be manufactured, for example, through a process of forming the circulation groove 34 at a position overlapping with the recesses 41, 42 in the radial direction in a state in which the recesses 41, 42 are formed on the outer peripheral surface 35b of the cylindrical portion 35. In this case, the recesses 41, 42 partially reduce the thickness of the flange forming portion 311, thereby making it possible to form the circulation groove 34, and the circulation groove 34 can be formed on the inner peripheral surface of the flange forming portion 311. As a result, the nut 3 can be shortened.

[0045] This point will be described with reference to Figures 7 and 8. As shown in Figures 7(a) and 7(b), in the portion of the body 31 of the nut 3 where the flange 32 is not formed (portion 312 other than the flange forming portion 311), a circulation groove 34 can be formed using a forging die A. This is because, as shown in Figure 7(b), when the circulation groove 34 is formed on the inner peripheral surface 31b of the body 31 in the portion 312, excess metal B can be formed so as to bulge toward the outer peripheral surface 31a of the body 31. This excess metal B is removed in a later process.

[0046] On the other hand, as shown in Figures 7(c) and 7(d), it has been difficult to form the circulation groove 34 by forging in the portion (flange forming portion 311) where the flange portion 32 is formed in the body portion 31 of the nut 3. This is because, as shown in Figure 7(d), the flange forming portion 311 is thick due to the formation of the flange portion 32, and it has been difficult to deform the flange forming portion 311 by the die A.

[0047] 8(a) and 8(b), in the manufacturing method of the ball screw 1 described above, in a state where the recesses 41, 42 are formed on the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32, the circulation groove 34 is formed at a position overlapping with the recesses 41, 42 in the radial direction (circulation groove forming step). As a result, the thickness of the flange forming portion 311 is partially thinned by the recesses 41, 42, so it is possible to form the circulation groove 34 by deforming the flange forming portion 311.

[0048] As shown in Fig. 8(a) and Fig. 8(b), the recesses 41, 42 become shallower after the circulation groove 34 is formed compared to before the circulation groove 34 is formed. Also, as shown in Fig. 8(a), the bottom surfaces 41b, 42b of the recesses 41, 42 may extend along a tangent to the portion 312 of the main body 31 other than the flange forming portion 311 when viewed from the axial direction at the start of the circulation groove forming process. Alternatively, as described above, when the bottom surface 41b of the recess 41 and the bottom surface 42b of the recess 42 extend in an arc shape along the circumferential direction when viewed from the axial direction at the start of the circulation groove forming process, the bottom surfaces 41b, 42b of the recesses 41, 42 may coincide with the outer peripheral surface of the main body 31 other than the flange forming portion 311 when viewed from the axial direction at the start of the circulation groove forming process. In these cases, the depth of the recesses 41, 42 can be sufficiently ensured, and the circulation groove 34 can be well formed on the inner peripheral surface of the flange forming portion 311. In this specification, the term "match" does not only mean a perfect match, but also includes a case where there is a deviation within the range of manufacturing error or the like.

[0049] Also, as shown in FIG. 8(c), after forming the circulation groove 34, the recesses 41, 42 may be machined to form another structure. For example, as shown in FIG. 8(c), the recesses 41, 42 may be machined to form a raceway groove C in which the rolling elements (e.g., balls) of the bearing roll on the outer circumferential surface 35b of the cylindrical portion 35. Such a removal process of the recesses 41, 42 can be performed well because the fiber flow at the formation portion of the recesses 41, 42 is not cut. The fiber flow is a flow of a fibrous metal structure that occurs after the forging process. If the raceway groove is processed in a state where the metal fibers are cut, there is a possibility that a defect such as peeling will occur starting from the cut surface during use. On the other hand, if the fiber flow is processed in a state where it is not cut, the occurrence of such a defect can be suppressed. The nut 3 formed by such a process will be described later with reference to FIG. 9 to FIG. 12.

[0050] The following further describes the function and effect of the ball screw 1. The recesses 41, 42 overlap the entire circulation groove 34 in the radial direction. In the manufacturing process of such a ball screw 1, the circulation groove 34 can be well formed on the inner circumferential surface of the flange forming portion 311. As a result, the nut 3 can be shortened.

[0051] The bottom surfaces 41b, 42b of the recesses 41, 42 are curved so as to protrude radially outward when viewed from the axial direction. In the manufacturing process of the ball screw 1, the circulation groove 34 can be well formed on the inner circumferential surface of the flange forming portion 311. As a result, the nut 3 can be shortened.

[0052] When viewed from the axial direction, the width W34 of the circulation groove 34 is equal to or smaller than the widths W41, W42 of the recesses 41, 42. In such a manufacturing process for the ball screw 1, the circulation groove 34 can be well formed on the inner circumferential surface of the flange forming portion 311. As a result, the nut 3 can be shortened.

[0053] At the position where the circulation groove 34 and the recesses 41, 42 are formed, the thickness T3 of the nut 3 is smaller than four times the depth T34 of the circulation groove 34. In such a manufacturing process for the ball screw 1, the circulation groove 34 can be well formed on the inner circumferential surface of the flange forming portion 311. As a result, the nut 3 can be shortened.

[0054] A recess 43 (adjustment recess) for adjusting the weight balance of the nut 3 in the circumferential direction in relation to the recesses 41, 42 is formed on the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32, and the recess 43 is arranged so as not to overlap with the circulation groove 34 in the radial direction. This makes it possible to adjust the weight balance of the nut 3 in the circumferential direction even when the recesses 41, 42 are formed.

[0055] An insertion hole 37 extending along the axial direction is formed in an end surface 35a of the cylindrical portion 35 of the flange portion 32 in the axial direction. As a result, for example, by inserting a pinion shaft S of a planetary gear into the insertion hole 37, the nut 3 can be used as a carrier for the planetary gear. [Variations]

[0056] 9 and 10, no flange portion 36 is formed on the flange portion 32, and the flange portion 32 has only a cylindrical portion 35. No insertion hole 37 is formed in an end face 35a of the cylindrical portion 35. No recesses 41-43 are formed on an outer circumferential surface 35b of the cylindrical portion 35, and instead a raceway groove 45 is formed.

[0057] In the first modified example, the cylindrical portion 35 is used as an inner ring of the bearing 7. That is, the raceway groove 45 formed on the outer peripheral surface 35b of the cylindrical portion 35 functions as a raceway groove in which a plurality of balls 73 roll, and the nut 3 is a nut integrated with the inner ring of the bearing 7. The raceway groove 45 extends along the circumferential direction, and has an inner surface curved into a shape corresponding to the balls 73 (rolling elements) in a cross section perpendicular to the circumferential direction, for example.

[0058] As shown in FIG. 11, when manufacturing the ball screw 1 of the first modified example, first, a nut 3 having recesses 41, 42 formed therein is prepared (preparation step). Then, as shown in FIG. 12, a circulation groove 34 is formed on the inner peripheral surface 31b of the main body portion 31 of the nut 3 (circulation groove forming step). In the circulation groove forming step, in a state in which the recesses 41, 42 are formed on the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32, the circulation groove 34 is formed at a position overlapping the recesses 41, 42 in the radial direction. Then, a screw groove 33 is formed on the inner peripheral surface 31b of the main body portion 31 (screw groove forming step). Then, a raceway groove 45 is formed on the outer peripheral surface 35b of the cylindrical portion 35. During this processing, the recesses 41, 42 are removed. The nut 3 is obtained by the above steps.

[0059] As in the above embodiment, the ball screw 1 of the first modified example also makes it possible to shorten the nut 3. In addition, since the raceway groove 45 extending in the circumferential direction is formed on the outer circumferential surface 35b of the cylindrical portion 35 of the flange portion 32, the nut 3 can be used as an inner ring of the bearing 7, for example.

[0060] In the second modified example shown in FIG. 13, the flange portion 32 does not have a flange portion 36, and the flange portion 32 has only a cylindrical portion 35. The end face 35a of the cylindrical portion 35 does not have an insertion hole 37. In addition to the recesses 41 to 43, a plurality of (four in this example) groove portions 46 are formed on the outer peripheral surface 35b of the cylindrical portion 35 of the flange portion 32. The end face 35a of the cylindrical portion 35 does not have an insertion hole 37. In this example, each groove portion 46 extends straight along the axial direction, and the four groove portions 46 are arranged at equal intervals in the circumferential direction. For example, a part (engagement portion) of the attachment target of the nut 3 is arranged in the groove portion 46, whereby the nut 3 and the attachment target are engaged in the rotational direction to prevent rotation. In this way, the nut 3 of the second modified example can be used as a rotation-stopping member.

[0061] Similarly to the above embodiment, the ball screw 1 of the second modified example also makes it possible to shorten the nut 3. In addition, for example, by engaging a part of an object to which the nut 3 is attached with the groove portion 46 in the rotational direction, it is possible to prevent the nut 3 from rotating against the object to which the nut 3 is attached, and the nut 3 can be used as a rotation-preventing member.

[0062] In a third modified example shown in Fig. 14, no collar portion 36 is formed on the flange portion 32, and the flange portion 32 has only a cylindrical portion 35. No insertion hole 37 is formed in an end face 35a of the cylindrical portion 35. No recesses 41-43 are formed on the outer circumferential surface 35b of the cylindrical portion 35, and instead a spline 47 is formed. In this example, the spline 47 is configured by forming a plurality of grooves that extend straight along the axial direction and are aligned in the circumferential direction.

[0063] Similarly to the above embodiment, the ball screw 1 of the third modified example also makes it possible to shorten the nut 3. Also, the nut 3 can be engaged with the attachment object by the spline 47. Note that serrations or gears may be formed instead of the spline 47.

[0064] 15, the recess 41 may be formed in a shape corresponding to the circulation groove 34 (a shape similar to the circulation groove 34) when viewed in the radial direction. In this example, the recess 41 extends in an S-shape (crank shape) when viewed in the radial direction. In this example, the recess 41 also overlaps with the entire circulation groove 34 in the radial direction. That is, the entire edge 41a of the recess 41 is located outside the circulation groove 34. The distance between the edge 41a of the recess 41 and the circulation groove 34 is, for example, 3 mm or less over the entire edge 41a.

[0065] The present invention is not limited to the above-described embodiment and modified examples. For example, the materials and shapes of the components are not limited to those described above, and various materials and shapes can be adopted.

[0066] In the above embodiment, two recesses (recesses 41, 42) overlapping with circulation groove 34 in the radial direction are provided, but only one recess or three or more recesses overlapping with circulation groove 34 in the radial direction may be provided. Recess 41 does not necessarily have to overlap with the entire circulation groove 34 in the radial direction; for example, only a portion of recess 41 may overlap with circulation groove 34.

[0067] After the circulation groove forming step is completed, the bottom surfaces 41b, 42b of the recesses 41, 42 may extend in an arc shape along the circumferential direction when viewed from the axial direction. Alternatively, after the circulation groove forming step is completed, the bottom surfaces 41b, 42b of the recesses 41, 42 may be flat surfaces perpendicular to the radial direction. The width W34 of the circulation groove 34 may be larger than the widths W41, W42 of the recesses 41, 42. The thickness T3 of the nut 3 may be four times or more the depth T34 of the circulation groove 34. The recesses 43 for adjusting the weight balance may be omitted. The recesses 41 to 43 may be arranged at equal intervals in the circumferential direction when viewed from the axial direction.

[0068] The shape of the recess 41 when viewed from the radial direction is not limited and may be, for example, a circular or elliptical shape. Two or more recesses may be formed for one circulation groove 34. For example, two recesses may be arranged so as to overlap with the circulation groove 34 in the radial direction. As a mode of use of the ball screw 1, the nut 3 may rotate and the screw shaft 2 may move linearly, or the screw shaft 2 may rotate and the nut 3 may move linearly. [Explanation of symbols]

[0069] 1...ball screw, 2...screw shaft, 2a...outer peripheral surface, 21...screw groove (first screw groove), 3...nut, 31...main body, 31a...outer peripheral surface, 31b...inner peripheral surface, 311...flange forming portion, 312...portion where flange portion is not formed, 32...flange portion, 33...screw groove (second screw groove), 34...circulation groove, 35...cylindrical portion, 35a...end face, 35b...outer peripheral surface, 37...insertion hole, 41, 42...recess, 41b, 42b...bottom surface, 43...recess (adjustment recess), 45...raceway groove, 46...groove portion, 47...spline, 4...ball, 10...rolling path, W34, W41, W42...width.

Claims

1. A screw shaft having a first screw groove formed on an outer peripheral surface thereof; A nut having a main body portion on an inner circumferential surface of which a second screw groove and a circulation groove are formed; A plurality of balls are disposed in a rolling path formed by the first screw groove and the second screw groove, and roll in the rolling path while being circulated via the circulation groove, The nut further has a flange portion protruding radially outward from an outer circumferential surface of the main body, A ball screw, wherein the second screw groove and the circulation groove are formed on an inner circumferential surface of a portion of the main body that overlaps with the flange portion in the radial direction.

2. 2. The ball screw according to claim 1, wherein a recess is formed on an outer circumferential surface of the flange portion so as to overlap with the circulation groove in the radial direction.

3. The ball screw according to claim 2 , wherein the recess overlaps with the entire circulation groove in the radial direction.

4. 4. The ball screw according to claim 2, wherein a bottom surface of the recess is curved so as to protrude radially outward when viewed from the axial direction.

5. 4. The ball screw according to claim 2, wherein a width of the circulating groove is equal to or smaller than a width of the recess when viewed in the axial direction.

6. 4. The ball screw according to claim 2, wherein the thickness of the nut at a position where the circulation groove and the recess are formed is smaller than four times the depth of the circulation groove.

7. 4. The ball screw according to claim 2 or 3, wherein an adjustment recess is formed on an outer peripheral surface of the flange portion for adjusting a weight balance of the nut in a circumferential direction in relation to the recess, and the adjustment recess is positioned so as not to overlap with the circulation groove in a radial direction.

8. The circulation groove extends in an S-shape when viewed in a radial direction, 4. The ball screw according to claim 2, wherein the recess is formed into a shape corresponding to the circulation groove when viewed in a radial direction.

9. The ball screw according to any one of claims 1 to 3, wherein an insertion hole extending along the axial direction is formed in an end face of the flange portion in the axial direction.

10. 4. The ball screw according to claim 1, wherein a raceway groove is formed on an outer circumferential surface of the flange portion and extends in a circumferential direction.

11. The ball screw according to any one of claims 1 to 3, wherein a groove portion extending along the axial direction is formed on an outer circumferential surface of the flange portion.

12. The ball screw according to any one of claims 1 to 3, wherein a spline is formed on an outer circumferential surface of the flange portion.

13. A method for manufacturing a ball screw according to any one of claims 1 to 3, forming the circulation groove on an inner circumferential surface of the portion of the main body that overlaps with the flange portion in the radial direction, A method for manufacturing a ball screw, in which, in the process of forming the circulation groove, a recess is formed on the outer peripheral surface of the flange portion, and the circulation groove is formed at a position that overlaps with the recess in the radial direction.

14. 14. The method for manufacturing a ball screw according to claim 13, wherein, at the start of the process of forming the circulation groove, when viewed from the axial direction, the bottom surface of the recess extends along a tangent to an outer peripheral surface of a portion of the main body where the flange portion is not formed, or is coincident with the outer peripheral surface.

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