Ball screw device

Abstract

This ball screw device comprises: a nut having a female thread and two outer raceways; a screw shaft having a male thread and two inner raceways; a plurality of balls arranged in each of two rolling paths; and two circulating parts provided at one end and the other end of the nut to cause the balls to circulate. The female thread and the male thread sandwich the balls. The nut comprises: a cylindrical section of a cylindrical shape that has a male thread and an outer raceway; and two return passages that penetrate the cylindrical section in an axial direction parallel to the axis of the screw shaft. The circulating parts comprise: a body section fixed to the cylindrical section of the nut; two connecting passages that penetrate the body section and that connect the two rolling paths to the two return passages; a partition wall for the connecting passages that lies between the two connecting passages and that partitions the two connecting passages; and two tangs that protrude from the body section into the rolling paths.

Description

[Technical Field]

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

[0002] The ball screw device of Patent Document 1 has a two-thread rolling path for the balls. Furthermore, in the ball screw device of Patent Document 1, the female threads of the nut and the male threads of the screw shaft are alternately arranged in the two-thread rolling path. Furthermore, the distance between the female thread and the male thread is smaller than the diameter of the ball. As a result, the balls are sandwiched between the female thread and the male thread, and a preload is applied to the balls. Furthermore, the ball screw device of Patent Document 1 is equipped with two tubes as components for circulating the balls. The interior of these tubes serves as a return passage through which the balls pass. Furthermore, the tips of the two tubes are arranged next to each other, and the first-thread balls and second-thread balls scooped up from the rolling path enter these tubes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 56-147954 Summary of the Invention [Problem to be solved by the invention]

[0004] In ball screw devices, there is a demand for reducing the axial size of the nut. One possible way to achieve this size reduction is to reduce the axial width of the female or male thread. Note that reducing the axial width of the female or male thread reduces the center-to-center distance between the first and second rolling paths. This requires reducing the distance between the centers of the ends of the two tubes, i.e., the portion that scoops up the balls. However, if the center-to-center distance between the ends of the two tubes is too small, there is a risk that the annular walls that make up the tubes will come into contact with each other. For this reason, the ball screw device of Patent Document 1 cannot reduce the center-to-center distance between the two tubes. Therefore, the ball screw device of Patent Document 1 cannot reduce the axial size of the nut.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a ball screw device that allows the nut to be made smaller in size in the axial direction. [Means for solving the problem]

[0006] In order to achieve the above object, a ball screw device according to one aspect of the present disclosure includes a nut having a female screw and two outer peripheral raceway surfaces arranged between the female screw, a screw shaft having a male screw and two inner peripheral raceway surfaces arranged between the male screw, a plurality of balls arranged in each of two rolling paths between the two outer peripheral raceway surfaces and the two inner peripheral raceway surfaces, and two circulation parts provided at one end and the other end of the nut to circulate the balls, and the female screw and the male screw are The nut clamps the ball and has a cylindrical shape and includes a cylindrical portion having the male thread and the outer peripheral raceway surface, and two return passages that penetrate the cylindrical portion in an axial direction parallel to the axis of the screw shaft. The circulation part includes a main body portion fixed to the cylindrical portion of the nut, two communicating passages that penetrate the main body portion and connect the two rolling paths with the two return passages, a communicating passage partition wall located between the two communicating passages and separating the two communicating passages, and two tangs that protrude from the main body portion into the rolling paths.

[0007] In the ball screw device of the present disclosure, balls are circulated through two return passages and two communication passages. The distance between the centers of the two communication passages can be reduced by adjusting the thickness of the communication passage partition wall. Therefore, the distance between the centers of the two communication passages can be made the same as the distance between the centers of the first-thread balls and the second-thread balls. As a result, the width of the female or male thread can be reduced, thereby making the nut smaller in axial size.

[0008] In one aspect of the ball screw device, the body of the nut has two accommodating grooves recessed into both end faces in the axial direction to accommodate the circulative component. The circulative component is disposed in the accommodating grooves.

[0009] With this, the circulating part is accommodated in the accommodation groove, and the nut is made smaller in size in the axial direction. [Effects of the Invention]

[0010] According to the ball screw device of the present disclosure, the nut can be made smaller in size in the axial direction. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a ball screw device according to an embodiment. [Figure 2] FIG. 2 is a view of the nut of the embodiment as viewed from one side in the axial direction. [Figure 3] FIG. 3 is a view of the nut of the embodiment as viewed from the other axial direction. [Figure 4] FIG. 4 is a perspective view of the screw shaft and the circulation device according to the embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a diagram showing the relationship between the screw shaft and the tube in the ball screw of the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0013] Fig. 1 is a schematic diagram of a ball screw device of an embodiment. Fig. 2 is a view of a nut of an embodiment as viewed from one axial direction. Fig. 3 is a view of the nut of an embodiment as viewed from the other axial direction. Fig. 4 is a perspective view of the screw shaft and circulation device of an embodiment. Fig. 5 is a cross-sectional view taken along line VV in Fig. 1. Fig. 6 is a cross-sectional view taken along line VI-VI in Fig. 1. Fig. 7 is a view showing the relationship between the screw shaft and tubes in a ball screw of a comparative example.

[0014] (Embodiment) 1, the ball screw device 1 includes a screw shaft 2, a nut 10, a plurality of balls 3 arranged between the screw shaft 2 and the nut 10, and two circulation components 40, 40. The screw shaft 2 includes a male thread 4 that protrudes radially outward from its outer peripheral surface, and two inner peripheral drive surfaces, a first 5 and a second 6, that are arranged between the male threads 4. Hereinafter, the direction parallel to the axis X of the screw shaft 2 will be referred to as the axial direction.

[0015] The nut 10 includes a cylindrical tube portion 11 that is inserted through the screw shaft 2, two return passages 21, 22 (see FIGS. 2 and 3 for the return passage 22), a return passage partition wall 23, and accommodation grooves 24, 24. The tube portion 11 includes an internal thread 12 that protrudes radially inward from its inner circumferential surface, and two threads of a first outer peripheral drive surface 13 and a second outer peripheral drive surface 14 that are arranged between the internal threads 12.

[0016] The second outer peripheral drive surface 14 faces radially to the first inner peripheral drive surface 5. A first thread rolling path 31 is formed between the first inner peripheral drive surface 5 and the second outer peripheral drive surface 14. The first outer peripheral drive surface 13 faces radially to the second inner peripheral drive surface 6. A second thread rolling path 32 is formed between the second inner peripheral drive surface 6 and the first outer peripheral drive surface 13. The female thread 12 is arranged axially offset from the male thread 4 by half a lead of the male thread 4. In other words, the male threads 4 and the female threads 12 are arranged alternately between the rolling paths 31 and 32.

[0017] A plurality of balls 3 are arranged in each of the first rolling path 31 and the second rolling path 32. The diameter of the balls 3 is slightly larger than the distance between the male thread 4 and the female thread 12. In other words, the balls 3 are sandwiched between the male thread 4 and the female thread 12 and preloaded. As a result, the balls 3 are in two-point contact between the male thread 4 and the female thread 12, and their behavior is stable. In addition, the balls 3 in the first rolling path 31 and the balls 3 in the second rolling path 32 are mated back to back.

[0018] As shown in Figures 2 and 3, the end faces 15, 16 of the tubular portion 11 of the nut 10 have a circular outer shape. The end faces 15, 16 of the main body are provided with a storage groove 24 recessed in the axial direction. The storage groove 24 is a space for storing the circulative component 40. This prevents the circulative component 40 from protruding axially from the end faces 15, 16 of the tubular portion 11, preventing the nut 10 from becoming larger in the axial direction. The shape of the storage groove 24 when viewed axially corresponds to the axial shape of the circulative component 40. The tubular portion 11 also has an inner surface 24a that surrounds the inner periphery of the storage groove 24, a bottom surface 24b of the storage groove 24, and an outer surface 24c that surrounds the outer periphery of the storage groove 24.

[0019] The return passages 21, 22 penetrate the cylindrical portion 11 and extend linearly in the axial direction. The openings of the return passages 21, 22 are provided in the bottom surface 24b. The return passages 21, 22 are separated by a return passage partition wall 23, which is part of the cylindrical portion 11. The diameters of the return passages 21, 22 are slightly larger than the diameter of the ball 3. Therefore, the ball 3 rolls smoothly inside the return passages 21, 22.

[0020] 1, the axial length L1 of the female thread 12 of the nut 10 is shorter than the axial length L2 of the male thread 4 of the screw shaft 2. Therefore, the axial length of the nut 10 is reduced by the amount that the female thread 12 is shortened in the axial direction. This also reduces the distance L3 (see FIGS. 1 and 4) between the centers of the first and second rolling paths 31 and 32, which are arranged on either side of the male thread 4.

[0021] The circulation part 40 is a resin part that guides the balls 3 in the rolling paths 31, 32 to the return paths 21, 22 of the nut 10 and circulates the balls 3. The circulation part 40 includes a main body 41 that is fitted into the accommodating groove 24 of the nut 10, two communication paths 42, 43, a communication path partition wall 44, and two tongues 45, 46 (see FIG. 1).

[0022] As shown in Fig. 1, the main body 41 of the circulation part 40 is disposed in the accommodation groove 24 of the nut 10. The main body 41 is sandwiched between the inner surface 24a and the outer surface 24c of the accommodation groove 24 (see Figs. 2 and 3), and is fixed to the nut 10. Furthermore, as shown in Fig. 4, the main body 41 has an outer peripheral surface 41a facing radially outward. This outer peripheral surface 41a faces the outer surface 24c.

[0023] As shown in Fig. 4, the communicating passages 42, 43 are open radially outward. In other words, the communicating passages 42, 43 are cut out of the outer peripheral surface 41a of the main body 41, and the communicating passages 42, 43 are exposed from the outer peripheral surface 41a of the main body 41. The radially outer sides of the communicating passages 42, 43 are closed by the outer surface 24c of the nut. Therefore, the ball 3 rolls along the communicating passages 42, 43. The diameters of the communicating passages 42, 43 are slightly larger than the diameter of the ball 3. Therefore, the ball 3 rolls smoothly inside the communicating passages 42, 43.

[0024] As shown in Figures 5 and 6, the communicating passages 42, 43 include first communicating passages 42a, 43a that extend radially outward from the rolling paths 31, 32 and then extend circumferentially, and second communicating passages 42b, 43b that extend axially from the first communicating passages 42a, 43a.

[0025] 4, the communication passage partition wall 44 is a wall portion that separates the communication passages 42 and 43. The communication passage partition wall 44 also has a first communication passage partition wall 44a interposed between the first communication passages 42a and 43a, and a second communication passage partition wall 44b interposed between the second communication passages 42b and 43b.

[0026] The thickness L10 of the first communication passage partition wall 44a is the same as the axial length L1 of the female thread 12. Therefore, the distance L11 between the centers of the first communication passages 42a, 43a is the same as the distance L3 between the centers of the first rolling path 31 and the second rolling path 32.

[0027] The thickness of the second communication passage partition wall 44b is the same as that of the return passage partition wall 23. In other words, the distance between the centers of the second communication passages 42b, 43b and the distance between the centers of the return passages 21, 22 is the same.

[0028] As shown in FIGS. 5 and 6, the tongues 45 and 46 enter the first rolling path 31 and the second rolling path 32 and scoop up the balls 3 into the communicating paths 42 and 43.

[0029] Next, the effects of the ball screw device 1 of this embodiment will be described. First, a comparative example will be described with reference to Fig. 7. In the comparative example, a ball screw device 101 equipped with two tubes 140, 141 as circulation components will be described. As shown in Fig. 7, the tubes 140, 141 have annular wall portions 140a, 141a, and the insides of the wall portions 140a, 141a form return passages 140b, 141b.

[0030] Tips 140c and 141c of the two tubes 140 and 141 open toward the rolling paths 131 and 132 to scoop up the balls 3 in the rolling paths 131 and 132. Two wall portions 140a and 141a are interposed between the return paths 140b and 141b. Therefore, the distance L20 between the centers of the return paths 140b and 141b is relatively large. As a result, the distance L21 between the centers of the rolling paths 131 and 132, which corresponds to the distance L20, is also large. In other words, when the two tubes 140 and 141 are used as circulation components, it is difficult to reduce the axial size of the female thread of the nut (not shown) sandwiched between the rolling paths 131 and 132.

[0031] 4, in this embodiment, the two first communication passages 42a, 43a are separated by a single first communication passage partition wall 44a, and the distance L11 between the centers of the first communication passages 42a, 43a is short. This makes it possible to reduce the distance L3 between the centers of the first rolling path 31 and the second rolling path 32, in other words, to reduce the axial length of the female thread 12.

[0032] As described above, the ball screw device 1 of the embodiment includes a screw shaft 2, a nut 10, balls 3, and two circulating members 40. The screw shaft 2 has a male thread 4 and two inner peripheral raceway surfaces (first inner peripheral drive surface 5, second inner peripheral drive surface 6) arranged between the male threads 4. The nut 10 has a female thread 12 and two outer peripheral raceway surfaces (first outer peripheral drive surface 13, second outer peripheral drive surface 14) arranged between the female threads 12. A plurality of balls 3 are arranged in each of the two rolling paths 31, 32 between the two outer peripheral raceway surfaces and the two inner peripheral raceway surfaces. The circulating members 40 are provided at one end and the other end of the nut 10 and circulate the balls 3. The female thread 12 and the male thread 4 hold the balls 3 between them. The nut 10 is cylindrical and includes a cylindrical portion 11 having an external thread 4 and an outer peripheral raceway surface (a first outer peripheral drive surface 13, a second outer peripheral drive surface 14), and two return passages 21, 22 that axially penetrate the cylindrical portion 11. The circulation component 40 includes a main body 41 fixed to the cylindrical portion 11 of the nut 10, two communicating passages 42, 43 that penetrate the main body 41 and connect the two rolling paths 31, 32 to the two return passages 21, 22, a communicating passage partition wall 44 located between the two communicating passages 42, 43 and separating the two communicating passages 42, 43, and two tangs 45, 46 that protrude from the main body 41 into the rolling paths 31, 32.

[0033] According to the embodiment, the axial length of the female thread 12 is reduced, so that the nut 10 can be made smaller in size in the axial direction.

[0034] Moreover, the cylindrical portion 11 of the nut 10 of the embodiment has two accommodating grooves 24, 24 recessed at both axial end faces for accommodating the circulative part 40. The circulative part 40 is disposed in the accommodating groove 24.

[0035] According to this, the circulation part 40 does not protrude from the end faces 15, 16 of the nut 10. Therefore, it is possible to prevent the nut 10 from becoming large in size in the axial direction.

[0036] Although the embodiments have been described above, the ball screw device of the present disclosure is not limited to the above examples. For example, in the embodiment, the thread between the first rolling path 31 and the second rolling path 32 was the female thread 12, but the ball screw device of the present disclosure may be the male thread 4. This reduces the axial length of the male thread 4, and as a result, the lead distance of the male thread 4 is shortened. This reduces the axial size of the nut 10. Furthermore, in the embodiment, the balls 3 arranged in the first rolling path 31 and the second rolling path 32 are arranged back-to-back, but they may also be arranged face-to-face. Furthermore, the thickness L10 of the first communication passage partition wall 44a and the thickness of the second communication passage partition wall 44b may be the same. [Explanation of symbols]

[0037] 1. Ball screw device 2 screw shaft 3 Ball 4 male threads 5 First inner driving surface 6 Second inner driving surface 10 nuts 11 Cylinder part 12 Female thread 13 First peripheral driving surface 14 Second peripheral driving surface 21, 22 Return passage 23 Return passage partition wall 24 Storage groove 31, 32 Rolling path 40 Rotable Parts 41 Main body 42, 43 communication passage 44 Connecting passage partition wall 44a Partition wall for first connecting passage 44b Partition wall for second connecting passage 45, 46 Tongue

Claims

1. a nut having an internal thread and two outer peripheral raceways disposed between the internal threads; a screw shaft having a male thread and two inner peripheral raceway surfaces arranged between the male threads; a plurality of balls disposed in two rolling paths between the two outer circumferential raceway surfaces and the two inner circumferential raceway surfaces; two circulation parts provided at one end and the other end of the nut to circulate the balls; Equipped with the female screw and the male screw sandwich the ball, The nut is a cylindrical portion having the male thread and the outer peripheral raceway surface; two return passages passing through the cylindrical portion in an axial direction parallel to the axis of the screw shaft; Equipped with The circulating part is a main body portion fixed to the cylindrical portion of the nut; two communication passages that penetrate the main body and communicate the two rolling paths with the two return passages; a single communication passage partition wall disposed between the two communication passages and separating the two communication passages; two tongues protruding from the main body portion into the rolling path; Equipped with Ball screw device.

2. the cylindrical portion of the nut has two accommodation grooves recessed at both end surfaces in the axial direction to accommodate the circulating component; The circulable part is disposed in the accommodation groove. The ball screw device according to claim 1 .

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