Ball screw device

Abstract

To provide a ball screw device that is easy to manufacture. [Solution] The circulating component of the ball screw device has a pair of tip portions positioned at both ends in the longitudinal direction of the circulating component, and a main body portion connecting the pair of tip portions. The tip portions have an opening that connects the track and the circulation path, and a tongue that scoops up the balls rolling on the track. The circulating component has a dividing surface that divides a part of the tip portion. The dividing surface has a pair of first dividing surfaces that extend from the edge of the opening toward the main body portion and divide it into a concave first wall portion and a second wall portion, and a second dividing surface that separates the first wall portion from a portion positioned closer to the center in the longitudinal direction relative to the first wall portion. The circulating component is divided by the dividing surface into a first component in which the main body portion and a pair of second wall portions are integrally formed, and a pair of second components that are first wall portions and have a tongue formed on them.

Description

Technical Field

[0005]

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

Background Art

[0002] A ball screw device includes a screw shaft, a nut, a plurality of balls that roll in a track between the screw shaft and the nut, and a circulation component that returns the balls that have rolled from one end of the track to the other end to the one end of the track. As an example of the circulation component, there is a tubular one. This tubular circulation component includes a main body portion that extends along the outer peripheral surface of the nut and a tip portion that penetrates the nut. The tip portion is inserted into a through-hole that penetrates the outer peripheral surface and the inner peripheral surface of the nut. Then, the balls are scooped up from the track at the tip of the leg portion, or the balls are returned to the track from the tip of the tip portion. Further, in the circulation component of the following document, the main body portion and the tip portion are manufactured separately and are separate components. Hereinafter, the direction in which the resin component extends may be referred to as the length direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the separate component (tip portion) of the above Document 1 is cylindrical (annular) and is difficult to manufacture by metal powder injection molding or resin injection molding. If the tip portion is manufactured by metal powder injection molding or resin injection molding, the tip portion needs to be further divided and the divided components need to be assembled. For this reason, the manufacturing man-hours increase and it becomes difficult to manufacture the ball screw device.

[0005] The present disclosure has been made in view of the above, and an object thereof is to provide a ball screw device that is easy to manufacture.

Means for Solving the Problems

[0006] To achieve the above objective, a ball screw device according to one aspect of the present disclosure comprises a screw shaft, a nut inserted into the screw shaft, a plurality of balls arranged in a raceway between the screw shaft and the nut, and a cylindrical circulating component with a circulation path formed inside. The circulating component has a pair of tip portions arranged at both ends in the longitudinal direction of the circulating component, and a main body portion arranged closer to the center in the longitudinal direction of the circulating component than the pair of tip portions, and connecting the pair of tip portions. The nut has a pair of through holes that penetrate the outer and inner surfaces of the nut, into which the pair of tip portions are inserted. The tip portions have an opening that connects the raceway and the circulation path, and a tongue that scoops up the balls rolling in the raceway. The circulating component has a dividing surface that divides a part of the tip portion. The dividing surface includes a pair of first dividing surfaces that extend from the edge of the opening toward the main body and divide the cylindrical wall portion constituting the tip into a concave first wall portion and a second wall portion when viewed from the longitudinal direction, and a second dividing surface that extends in the circumferential direction, connecting the ends of the pair of first dividing surfaces and separating the first wall portion from a portion located closer to the center in the longitudinal direction relative to the first wall portion. The circulating component is divided by the dividing surface into a first component in which the main body portion and the pair of second wall portions are integrally formed, and a pair of second components which are the first wall portions and on which the tongue is formed.

[0007] The second component (first wall) of this disclosure is a concave wall and can be manufactured by metal powder injection molding or resin injection molding. Furthermore, the second wall is integrated with the first component. This eliminates the need for the process of manufacturing the tip by combining the first and second walls. Therefore, an increase in manufacturing man-hours is avoided, and the manufacturing of ball screw devices becomes easier. In addition, the tang of the circulating component requires high strength. According to this disclosure, the strength of the second component (tang) can be increased by simply increasing the thickness of the second component. Furthermore, conventional tip portions are annular. Therefore, when the tip portion and the parts other than the tip portion are combined, the mating surface (dividing surface) extends in the circumferential direction and becomes annular. In other words, the mating surface (dividing surface) forms an annular step, which may hinder the movement of the ball. On the other hand, in this disclosure, a pair of first dividing surfaces extend in the longitudinal direction of the circulating component, and only the second dividing surface extends in the circumferential direction. Therefore, the balls are less likely to get stuck, and their movement is smoother than that of the circulating component in Patent Document 1.

[0008] Furthermore, in the ball screw device, a recess is formed on the outer circumferential surface of the nut, which is located at the edge of the through hole. The second component has a fitting portion that fits into the recess.

[0009] According to the above configuration, the second component is positioned. Therefore, the tip of the tongue can be positioned in a predetermined location, and the ball can be scooped up smoothly.

[0010] Furthermore, in the ball screw device, the first component is made of a metal material. The thickness of the first component is uniform in the longitudinal direction of the first component and is smaller than the thickness of the second component.

[0011] According to the above configuration, the first component can be manufactured by pressing or bending, making manufacturing easier.

[0012] Furthermore, in the ball screw device, the center line of the circulation path at the tip of the circulation component is tangent to a virtual circle connecting the centers of the multiple balls rolling along the track.

[0013] According to the above configuration, the movement of the ball from the track to the circulation path, or from the circulation path to the track, becomes smooth.

[0014] Furthermore, in the ball screw device, the first component is composed of a pair of third components divided by a pair of third dividing surfaces extending in the longitudinal direction.

[0015] According to the above configuration, since the third component is a concave component, it can be manufactured by metal powder injection molding or resin injection molding. [Effects of the Invention]

[0016] The ball screw device of this disclosure is easy to manufacture. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 is a cross-sectional view of the ball screw device of Embodiment 1, cut in a direction perpendicular to the axial direction. [Figure 2] Figure 2 is a view of the ball screw device of Embodiment 1 from the radially outer side of the circulating component. [Figure 3] Figure 3 shows the nut of Embodiment 1 viewed from the radially outer side. [Figure 4] Figure 4 is a cross-sectional view of the nut of Embodiment 1, cut in a direction perpendicular to the axial direction. [Figure 5] Figure 5 is a side view of the circulating component of Embodiment 1. [Figure 6] Figure 6 is an enlarged view of the circulation component of Embodiment 1, seen from the opening at the tip. [Figure 7] Figure 7 is a view of the main body of Embodiment 1 from a plan view. [Figure 8] Figure 8 is a cross-sectional view of the ball screw device of Modification 1, cut in a direction perpendicular to the axial direction. [Figure 9] Figure 9 is a perspective view of the third part of the modified example 1. [Figure 10]FIG. 10 is a perspective view of the second component of the modified example 2.

Embodiments for Carrying Out the Invention

[0018] The embodiments for carrying out the invention 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 constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be combined as appropriate.

[0019] (Embodiment 1) FIG. 1 is a cross-sectional view of the ball screw device of Embodiment 1 cut in a direction orthogonal to the axial direction. FIG. 2 is a view of the ball screw device of Embodiment 1 viewed from the outside in the radial direction of the circulation component. In order to make the circulation component 4 visible, the illustration of the fixed component 5 is omitted in FIG. 1. As shown in FIGS. 1 and 2, the ball screw device 100 of Embodiment 1 includes a screw shaft 1, a nut 2, a plurality of balls 3, a circulation component 4, and a fixed component 5 (not shown in FIG. 1; refer to FIG. 2). Also, in the ball screw device 100 of the present embodiment, the number of circulation components 4 is one, but in the present disclosure, the number of circulation components 4 may be two or more. Further, when there are two or more circulation components 4, with respect to the position of the circulation component 4 viewed from the central axis O1 of the screw shaft, each of the circulation components 4 may be arranged in different directions or in the same direction. Also, a plurality of circulation components 4 may be arranged at equal intervals in the circumferential direction, such as arranging two circulation components 4 at an interval of 180°. In the present disclosure, there is no particular limitation regarding the position of the circulation component 4.

[0020] An outer peripheral raceway groove 10 extending in the spiral direction is formed on the outer peripheral surface of the screw shaft 1. Hereinafter, the direction parallel to the central axis O1 of the screw shaft 1 is referred to as the axial direction X. Also, the direction orthogonal to the central axis O1 of the screw shaft is referred to as the radial direction.

[0021] As shown in Figure 1, an inner circumferential groove 20 extending in the helical direction is formed on the inner circumferential surface of the nut 2. The inner circumferential groove 20 is radially opposite to the outer circumferential groove 10. The space between the outer circumferential groove 10 and the inner circumferential groove 20 constitutes a raceway 6. Multiple balls 3 are arranged in this raceway 6. Note that in Figure 1, only some of the multiple balls 3 are shown in order to make the other components easier to see.

[0022] A flat surface 22 is formed on the outer circumferential surface 21 of the nut 2. The flat surface 22 is positioned in the direction in which the circulating component 4 is arranged, when viewed from the central axis O1 of the screw shaft 1. The flat surface 22 serves as a seating surface for the straight portion of the circulating component 4, which will be described later. Hereinafter, a hypothetical line K will be defined as a straight line that extends radially from the central axis O1 and intersects the flat surface 22 perpendicularly.

[0023] The nut 2 has a through hole 23 that penetrates both the inner and outer circumferential surfaces 21 of the nut 2. The through hole 23 extends in a direction parallel to the imaginary line K. The circulating component 4 is attached to the nut 2 by first positioning the circulating component 4 radially outward from the plane 22 of the nut 2. Next, the circulating component 4 is moved in a direction parallel to the imaginary line K, and the tip 31 of the circulating component 4 is inserted into the through hole 23. Hereinafter, the direction parallel to the imaginary line K will be referred to as the attachment direction Y. The direction that intersects both the axial direction X and the attachment direction Y will be referred to as the intersecting direction Z.

[0024] Figure 3 is a view of the nut of Embodiment 1 from the radially outer side. As shown in Figure 3, two through holes 23 are formed for one circulating component 4. Hereinafter, the two through holes 23 may be referred to as a pair of through holes 23. In Embodiment 1, since there is one circulating component 4, one pair of through holes 23 (two in total) is formed.

[0025] Viewed from the mounting direction Y, the through hole 23 is longer in the intersecting direction Z than in the axial direction X, and has an oval shape. The through hole 23 is positioned to cut out the end 22a of the plane 22 in the intersecting direction Z. Also, as shown in Figure 3, a screw hole 24 for fixing the fixing part 5 is formed.

[0026] Figure 4 is a cross-sectional view of the nut of Embodiment 1, cut in a direction perpendicular to the axial direction. As shown in Figure 4, a recess 25 is formed on the outer circumferential surface 21 of the nut 2, recessed radially inward. As shown in Figure 3, two recesses 25 are formed. The recesses 25 are formed in an arc shape when viewed from the mounting direction. The recesses 25 are formed to overlap with the plane 22. The recesses 25 are also formed on the edge of the through hole 23. Therefore, as shown in Figure 4, the recesses 25 cut out a portion of the inner circumferential surface of the through hole 23.

[0027] Figure 5 is a side view of the circulation component of Embodiment 1. The circulation component 4 is formed in a cylindrical shape, and its internal space is a circulation path 30. The center line M in Figure 5 is the center line of the circulation path 30. The circulation component 4 has a pair of tip portions 31 that are inserted into the through hole 23, and a main body portion 32 that connects the pair of tip portions 31.

[0028] The tip portion 31 has an opening 33, a tongue 34, and a fitting portion 35. As shown in Figure 1, the tip portion 31 extends parallel to the mounting direction Y. The opening 33 opens toward the track 6. This connects the track 6 to the circulation path 30.

[0029] When a ball rolling along track 6 comes into contact with the tip of tongue 34, the ball 3 is scooped up radially outward. Thus, the movement from track 6 to circulation path 30 is smooth.

[0030] As shown in Figures 1 and 2, the fitting portion 35 is fitted into the recess 25. This positions the tip portion 31 in the mounting direction Y. In other words, the tip portion of the tongue 34 can be accurately positioned at a predetermined location. Therefore, the scooping up of the ball 3 by the tongue 34 becomes smooth.

[0031] As shown in Figure 5, the main body portion 32 is located closer to the center of the circulating component 4 in the longitudinal direction than the pair of tip portions 31. The main body portion 32 has a straight portion 37 that extends linearly along the plane 22 (outer peripheral surface 21) of the nut 2, and a pair of bent portions 38 that bend from both ends of the straight portion 37.

[0032] The straight section 37 is positioned on the plane 22 and extends parallel to the plane 22 (see Figure 1). Also, when viewed from the mounting direction Y, the straight section 37 extends linearly between the pair of through holes 23 (see Figure 2).

[0033] As shown in Figure 5, the bent portion 38 connects the tip portion 31 and the straight portion 37 and is bent at a 90° angle. Therefore, the orientation of the ball 3 moving within the bent portion 38 is changed from the mounting direction Y to a direction parallel to the plane 22.

[0034] As shown in Figure 5, a dividing surface 40 is formed on the circulating component 4. Therefore, a part of the tip portion 31 is divided. More specifically, the dividing surface 40 has a pair of first dividing surfaces 41 that extend in the longitudinal direction of the circulating component 4, and a second dividing surface 42 that extends in the circumferential direction of the circulating component 4. The first dividing surfaces 41 extend from the edge portion 33a of the opening 33 toward the main body portion 32.

[0035] Figure 6 is an enlarged view of the circulation component of Embodiment 1, viewed from the opening at the tip. The cylindrical wall portion constituting the tip portion 31 is divided into a concave first wall portion 44 and a second wall portion 45 when viewed from the longitudinal direction by a pair of first dividing surfaces 41. The tongue 34 and the fitting portion 35 are formed on the first wall portion 44. The angle θ at which the straight line M1 connecting one first dividing surface 41 and the center line M of the circulation path 30 intersects with the straight line M2 connecting the other first dividing surface 41 and the center line M of the circulation path 30 is 180°. Therefore, the proportions occupied by the first wall portion 44 and the second wall portion 45 in the tip portion 31 are equal.

[0036] As shown in Figure 5, the second dividing surface 42 extends in the circumferential direction and connects the ends of the pair of first dividing surfaces 41. As a result, the first wall portion 44 is separated from the portion (bent portion 38) located closer to the center in the longitudinal direction relative to the first wall portion 44.

[0037] As a result of the division surface 40 described above, the circulating component 4 is divided into three parts: a first component 50 and a pair of second components 51 which are the first wall portions 44.

[0038] Figure 7 is a view of the first part of Embodiment 1 from a plan view. As shown in Figure 7, the first part 50 is integrally formed with a main body 32 (straight section 37 and a pair of bent sections 38) and a pair of second wall sections 45. The first part 50 is formed in a cylindrical shape, and the thickness H1 from the inner surface to the outer surface is uniform. Therefore, when the first part 50 is manufactured from a metal material, it can be manufactured by pressing sheet metal or bending pipe material, making manufacturing easier. In addition, both ends of the first part 50 have a first mating surface 52 formed by the first dividing surface 41 and an arc-shaped second mating surface 53 formed by the second dividing surface 42.

[0039] As shown in Figure 6, the second part 51 is the first wall portion 44 and is not formed in an annular shape. Therefore, the second part 51 can be manufactured by metal powder injection molding or resin injection molding. In addition, the thickness H2 of the tongue 34 of the second part 51 is greater than the thickness H1 of the first part 50 (see Figure 7). For this reason, the second part 51 has higher strength than the first part 50. The second part 51 also has a third mating surface 54 formed by the first dividing surface 41 and a fourth mating surface 55 formed by the second dividing surface (see Figure 5).

[0040] As shown in Figure 2, the fixing part 5 is a strip-shaped metal part. Both ends of the fixing part 5 are fixed to the plane 22 by screws 7. The fixing part 5 presses the first part 50 toward the plane 22. As a result, the first part 50 does not separate from the nut 2.

[0041] As shown in Figure 1, the second mating surface 53 of the first part 50 is in contact with the fourth mating surface 55 of the second part 51. Therefore, the second part 51 does not detach radially outward from the through hole 23.

[0042] As shown in Figure 1, the first mating surface 52 of the first part 50 is in contact with the third mating surface 54 of the second part 51. The outer circumferential surfaces of the tip portion 31 (the second wall portion 45 of the first part 50 and the first wall portion 44 of the second part 51) are in contact with the inner circumferential surface of the through hole 23. As a result, the first part 50 and the second part 51 do not move in the axial direction X or the intersecting direction Z.

[0043] As described above, the second part 51 of Embodiment 1 is concave and can therefore be manufactured by metal powder injection molding or resin injection molding. Furthermore, the second wall portion 45 is integrally formed with the first part 50. This eliminates the need for the process of manufacturing the tip portion 31 by combining the first wall portion 44 and the second wall portion 45. In other words, an increase in manufacturing man-hours is avoided, and the manufacturing of the ball screw device 100 becomes easier. In addition, the thickness H2 of the second part 51 is greater than the thickness H1 of the first part 50, resulting in higher strength. Therefore, even if the ball 3 comes into contact with the tongue 34 of the second part 51, it is less likely to be damaged.

[0044] Furthermore, if the second part 51 were formed in a cylindrical (annular) shape, the dividing surface with the first part 50 would extend in the circumferential direction and become annular. In other words, an annular step would be formed between the first part 50 and the second part 51. On the other hand, in this embodiment, a step surface extending in the circumferential direction is formed between the second mating surface 53 and the fourth mating surface 55. In other words, the step surface is a semicircular arc and is shorter than when the second part 51 is cylindrical (annular). For this reason, with the circulating part 4 of this embodiment, the ball 3 is less likely to get caught on the step surface, and the ball 3 moves smoothly within the circulation path 30.

[0045] Furthermore, the fitting portion 35 of the second part 51 is fitted into the recess 25 of the nut 2. As a result, the tongue 34 formed on the second part 51 is positioned in a predetermined location, allowing the ball 3 to be scooped up smoothly.

[0046] Furthermore, the first part 50 is cylindrical and has a small thickness H1. Therefore, the first part 50 can be manufactured by pressing or bending, making its production easy.

[0047] The ball screw device of Embodiment 1 has been described above. Next, a modified example in which a part of the ball screw device 100 of Embodiment 1 is modified will be described. In the following description, we will focus on the differences from Embodiment 1.

[0048] (Variation 1) Figure 8 is a cross-sectional view of the ball screw device of Modification 1, cut in a direction perpendicular to the axial direction. Figure 9 is a perspective view of the third component of Modification 1. As shown in Figure 8, the ball screw device 100A of Modification 1 differs from Embodiment 1 in that the tip portion 31 of the circulating component 4 is inclined with respect to the mounting direction Y. More specifically, the center line M of the circulating path 30 at the tip portion 31 (not shown in Figure 8; see Figure 5, etc.) is tangent to a virtual circle N connecting the centers of the multiple balls 3 rolling on the track 6. As a result, the scooping up of the balls 3 is smoother.

[0049] As shown in Figures 8 and 9, the first part 50 of the circulating part 4 in the modified example 1 has a pair of third dividing surfaces 60 formed thereon. Therefore, the first part 50 differs from the first embodiment in that it is composed of a pair of third parts 61. As shown in Figure 9, the third part 61 has a pair of fifth mating surfaces 62 formed by the pair of third dividing surfaces 60. The pair of fifth mating surfaces 62 extend in the longitudinal direction of the first part 50 and are continuous with the pair of first dividing surfaces 41. In other words, the third part 61 is a concave part. Therefore, the third part 61 has a shape that can be manufactured by metal powder injection molding or resin injection molding.

[0050] (Modification 2) Figure 10 is a perspective view of the second part of Modification 2. As shown in Figure 10, the second part 51 of Modification 2 differs from Modification 1 in that it has a protruding portion 70 that protrudes from the third mating surface 54. The inner surface 71 of the protruding portion 70 abuts against the outside of the second wall portion 45 of the first part 50. Also, the outer surface (opposite the inner surface) of the protruding portion 70 abuts against the inner circumferential surface of the through hole 23. This makes it less likely for a step to occur between the first mating surface 52 and the third mating surface 54.

[0051] Although Embodiment 1 and its various modifications have been described above, this disclosure is not limited to the examples described above. For example, in order to prevent a step from occurring on the fifth mating surface 62 of the pair of third parts 61, fitting portions that fit together may be formed on the third parts 61.

[0052] Furthermore, although the fixing part 5 in Embodiment 1 is configured to fix the first part 50 (main body 32), the present disclosure may also provide a fixing part 5 that covers the entire circulating part 4. In addition, the fixing part 5 may be configured to abut against the fitting portion of the second part from the radially outer side. This prevents the second part from falling out radially outward from the through hole.

[0053] Furthermore, although the proportions occupied by the first wall portion 44 and the second wall portion 45 are equal in the tip portion 31, the disclosure is not limited thereto. For example, the angle θ (see Figure 6) at which the straight line M1 connecting one first dividing surface 41 and the center line M of the circulation path 30 intersects with the straight line M2 connecting the other first dividing surface 41 and the center line M of the circulation path 30 may be 120° or the like. [Explanation of symbols]

[0054] 1 Screw shaft 2 nuts 3 balls 4 Circulation parts 5 Fixing parts 23 Through hole 25 recesses 30 Circulation path 31 Tip 32 Main body 33 Opening 34 Tang 35 Fitting part 37 Straight section 38. Bending section 40 split plane 41 1st dividing plane 42 Second dividing plane 44 1st wall section 45 Second wall section 50 Part 1 51 Part 2 52 First mating surface 53 Second mating surface 54 Third mating surface 55 Fourth mating surface 60 Third dividing plane 61 Part 3 62 Fifth mating surface 70 Protrusion 100 Ball screw device

Claims

1. Screw shaft and The nut inserted into the screw shaft, Multiple balls arranged in the track between the screw shaft and the nut, A cylindrical circulating component with a circulation path formed inside, Equipped with, The aforementioned circulating component is, A pair of tip portions are arranged at both ends in the longitudinal direction of the aforementioned circulating component, A main body portion is positioned closer to the center of the circulating component in the longitudinal direction than the pair of aforementioned tip portions, and connects the pair of aforementioned tip portions together. It has, The nut has a pair of through holes that penetrate the outer and inner surfaces of the nut, into which the pair of tip portions are inserted. The aforementioned tip portion has, The opening connecting the aforementioned track and the aforementioned circulation path, A tongue that scoops up the ball rolling along the aforementioned trajectory, Formed, The aforementioned circulating component has a dividing surface formed to divide a part of the tip portion, The aforementioned dividing surface is A pair of first dividing surfaces extend from the edge of the opening toward the main body and divide the cylindrical wall portion constituting the tip into a concave first wall portion and a concave second wall portion when viewed from the longitudinal direction, A second dividing surface extends in the circumferential direction, connecting the ends of the pair of first dividing surfaces, and separating the first wall from the portion located closer to the center in the longitudinal direction relative to the first wall; It has, The aforementioned circulating component is, by the dividing surface, A first component in which the main body and a pair of the second wall portions are integrally formed, The first wall portion and the pair of second parts on which the tongue is formed, It is divided into Ball screw device.

2. A recess is formed on the outer surface of the nut, which is located at the edge of the through hole. The second component has a fitting portion that fits into the recess. The ball screw device according to claim 1.

3. The first component is made of a metal material, The thickness of the first component is uniformly formed in the longitudinal direction of the first component and is smaller than the thickness of the second component. The ball screw device according to claim 1 or claim 2.

4. The center line of the circulation path at the tip of the circulation component is tangent to a virtual circle connecting the centers of the multiple balls rolling along the track. The ball screw device according to claim 1 or claim 2.

5. The first component is composed of a pair of third components divided by a pair of third dividing surfaces extending in the longitudinal direction. The ball screw device according to claim 1 or claim 2.

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