Ball screw

Abstract

To provide a ball screw that can realize effective utilization of a lubricant by returning the lubricant attached to land parts, to screw grooves.SOLUTION: A ball screw comprises a screw shaft in which an outer peripheral screw groove is formed, a nut in which an inner peripheral screw groove is formed, and a plurality of balls housed in a rolling passage formed by the outer peripheral screw groove and the inner peripheral screw groove opposed to each other. In the screw shaft, an outer peripheral helical groove is formed in an outer peripheral land part between portions of the outer peripheral screw groove, and an outer peripheral spline groove connecting the outer peripheral helical groove and the outer peripheral screw groove is formed along an axis of the screw shaft. In the nut, an inner peripheral helical groove is formed in an inner peripheral land part between portions of the inner peripheral screw groove, and an inner peripheral spline groove connecting the inner peripheral helical groove and the inner peripheral screw groove is formed along an axis of the nut.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A ball screw includes a generally rod-shaped screw shaft having a helical groove on its outer circumferential surface, a generally cylindrical nut having a helical groove on its inner circumferential surface that faces the helical groove of the screw shaft, and a number of balls loaded so as to roll freely in a helical rolling path formed by both the helical grooves. When the nut and the screw shaft, which are screwed together via the balls, are rotated relative to each other, the nut and the screw shaft move relative to each other in the axial direction via the rolling of the balls in the rolling path.

[0003] Such ball screws operate while being lubricated by a lubricant applied directly to the screw shaft, or by grease or oil placed in the rolling path from the nut. However, much of this lubricant adheres to the spiral groove land portion other than the rolling path, and is wasted without being used for lubrication. However, in order to prevent poor lubrication of the rolling groove, it is necessary to supply more lubricant than is necessary for lubrication, even if waste occurs, and therefore effective use of the lubricant is an issue.

[0004] As a measure to solve such problems, Patent Document 1 proposes a technology to easily supply lubricant to the load path where the balls roll by providing a separate part that prevents the lubricant from flowing. However, the technology of Patent Document 1 requires a separate part made of an elastic material to be installed between the screw shaft and the nut to prevent the lubricant from flowing to the land portion, which not only increases costs but also poses new issues such as wear and durability of the elastic material that slides due to the relative movement between the screw shaft and the nut.

[0005] Also, Patent Document 2 proposes a technology in which a spiral groove is formed in the land portion of the screw shaft, a lubricant is held by a holding member attached to the spiral groove, and the rolling surface is lubricated by the lubricant. However, the technology of Patent Document 2 has a problem in that the amount of lubricant remaining on the holding member itself and in the spiral groove increases, making it difficult to effectively use the lubricant adhering to the land portion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5120488 [Patent Document 2] JP 2008-202718 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of such problems, and has an object to provide a ball screw that can achieve effective use of lubricant by returning lubricant adhering to the land portion to the screw groove. [Means for solving the problem]

[0008] The ball screw of the present invention has: A screw shaft having an outer peripheral screw groove formed thereon; A nut having an internal thread groove; a plurality of balls accommodated in a rolling path formed by the opposing outer peripheral screw groove and the inner peripheral screw groove; In the screw shaft, an outer peripheral spiral groove is formed in an outer peripheral land portion between the outer peripheral thread grooves, and an outer peripheral spline groove connecting the outer peripheral spiral groove and the outer peripheral thread groove is formed along the axis of the screw shaft.

[0009] The ball screw of the present invention has: A screw shaft having an outer peripheral screw groove formed thereon; A nut having an internal thread groove; a plurality of balls accommodated in a rolling path formed by the opposing outer peripheral screw groove and the inner peripheral screw groove; The nut is characterized in that an inner spiral groove is formed on an inner land portion between the inner screw grooves, and an inner spline groove connecting the inner spiral groove and the inner screw groove is formed along the axis of the nut. Effect of the Invention

[0010] According to the present invention, it is possible to provide a ball screw that can realize effective use of the lubricant by returning the lubricant adhering to the land portion to the screw groove. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view of a nut of a ball screw according to a first embodiment. [Diagram 2] FIG. 2 is a view of an end portion of the ball screw of this embodiment as viewed in the direction of arrow II, but balls are not shown. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of the configuration of FIG. 2 taken along line III-III and viewed in the direction of the arrows. [Figure 4] FIG. 4 is an enlarged schematic view showing the vicinity of the thread groove of the screw shaft in FIG. [Diagram 5] FIG. 5 is a schematic diagram of one of the land portions of the screw shaft as viewed from the shaft end side. [Figure 6] FIG. 6 is a schematic diagram showing the movement of the lubricant along the outer circumferential spline groove. [Figure 7] FIG. 7 is a partial view of a screw shaft according to the second embodiment, seen in the axial direction. [Figure 8] FIG. 8 is an axial cross-sectional view of an end portion of a ball screw according to a third embodiment. [Figure 9] FIG. 9 is an enlarged view of portion IX in FIG. [Figure 10] FIG. 10 is a view of the ball screw in FIG. 8 cut along line XX and viewed in the direction of the arrow. [Figure 11]FIG. 11 is a diagram showing a schematic view of the fiber flow in a cross section obtained by cutting the outer circumferential land portion along the axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of a ball screw according to the present invention will be described with reference to the drawings. The ball screw of this embodiment is lubricated with a lubricant such as grease or oil, and is suitable for use in a variety of machines, such as the drive units of electric injection molding machines, drive units of electric press machines, and machine tools.

[0013] (First embodiment) FIG. 1 is a cross-sectional view of a nut of a ball screw according to a first embodiment. FIG. 2 is a view of an end of a ball screw according to this embodiment as viewed in the direction of an arrow II, but balls are not shown. FIG. 3 is a view of the configuration of FIG. 2 cut along line III-III as viewed in the direction of the arrows. FIG. 4 is an enlarged view of the screw shaft of FIG. 3. FIG. 5 is a schematic view of one of the land portions of the screw shaft as viewed from the shaft end side. FIG. 6 is a schematic view showing the movement of a lubricant along an outer circumferential spline groove.

[0014] 1, the ball screw has a screw shaft 10 on which an outer peripheral screw groove 11 is formed, a nut 30 on which an inner peripheral screw groove 31 is formed, and a plurality of balls 20 accommodated in a rolling path formed by the opposing outer peripheral screw groove 11 and inner peripheral screw groove 31. Sealing members (not shown) are provided on both ends of the nut 30. In addition, the nut 30 is provided with a ball circulation member (not shown).

[0015] 1, a tubular nut 30 equipped with a flange 30a has, in addition to an inner circumferential screw groove 31, inner circumferential land portions 32 formed between adjacent inner circumferential screw grooves 31, an inner circumferential spiral groove 33 formed along the center of the inner circumferential land portions 32, and a plurality of (six in this example) inner circumferential spline grooves 34 extending along the axial direction of the nut 30. Furthermore, the nut 30 is formed with an oil supply hole 35 extending from its outer periphery toward the inner circumferential screw groove 31. Lubricant is supplied from the outside through the oil supply hole 35.

[0016] The cross-sectional shape of the inner screw groove 31 is a Gothic arch, and the cross-sectional shapes of the inner spiral groove 33 and the inner spline groove 34 are partially circular.

[0017] The depths of the inner screw groove 31 and the inner spiral groove 33 are constant, but the inner spline groove 34 has a shape in which the depth gradually decreases toward the axial direction. In this case, the depth of the inner spline groove 34 in the inner land portion 32 is shallower than the depth of the inner screw groove 31 and deeper than the depth of the inner spiral groove 33.

[0018] In addition to the outer peripheral thread groove 11, the screw shaft 10 has an outer peripheral land portion 12 formed between adjacent outer peripheral thread grooves 11, an outer peripheral spiral groove 13 formed along the center of the outer peripheral land portion 12, and a plurality of (here, six) outer peripheral spline grooves 14 extending along the axial direction of the screw shaft 10.

[0019] The cross-sectional shape of the outer peripheral screw groove 11 is a Gothic arch shape, and the cross-sectional shapes of the outer peripheral spiral groove 13 and the outer peripheral spline groove 14 are partially circular.

[0020] The outer peripheral thread groove 11 and the outer peripheral spiral groove 13 have a constant depth, but the outer peripheral spline groove 14 has a shape in which its depth gradually decreases toward the axial direction. In this case, the depth of the outer peripheral spline groove 14 in the outer peripheral land portion 12 is shallower than the depth of the outer peripheral thread groove 11 and deeper than the depth of the outer peripheral spiral groove 13. Here, the outer peripheral spline groove 14 is formed straight over the entire length of the screw shaft 10, but is interrupted by the deeper outer peripheral thread groove 11. Here, for convenience, the one formed in one outer peripheral land portion 12 may be referred to as the outer peripheral spline groove 14.

[0021] More specifically, the shape of the outer spline groove 14 will be described. In the cross section shown in Fig. 4, the distance between the groove bottom of the outer thread groove 11 and the outer peripheral surface of the outer land portion 12 is W, the distance between the groove bottom of the outer spiral groove 13 and the outer peripheral surface of the outer land portion 12 is H, the length along the radial direction of the chamfered portion 16 connecting the outer peripheral surface of the outer land portion 12 and the outer thread groove 11 is C, the inclination angle of the outer spline groove 14 with respect to the outer peripheral surface of the outer land portion 12 is M (≠ 0), and the distance between the groove bottom of the outer spline groove 14 and the outer peripheral surface of the outer land portion 12 is S. The distance S gradually decreases or increases depending on the axial distance from the reference position and the inclination angle M, but the following formula (1) always holds. 0.25×W ≧ C ≧ S > H (1)

[0022] However, if the screw shaft 10 does not have the chamfered portion 16, the following formula (2) holds. 0.25×W≧S>H (2)

[0023] In the above formula, the distance S between the groove bottom of the outer peripheral spline groove 14 and the outer peripheral surface of the outer peripheral land portion 12 is set to 25% or less of the distance W between the groove bottom of the outer peripheral thread groove 11 and the outer peripheral surface of the outer peripheral land portion 12, in order to prevent flaking of the outer peripheral land portion 12 due to the balls 20 riding over it.

[0024] As shown in Figure 5, when one outer-periphery spline groove 14 is viewed in the axial direction, the outer-periphery spline groove 14 is inclined with respect to the outer peripheral surface of the outer peripheral land portion 12. Therefore, when the outer-periphery spline groove 14 intersects with the chamfered portion 16, the end cross section of the outer-periphery spline groove 14 has a shallow arc C1 on one end side and a deep arc C2 on the other end side, and the inner peripheral surface of the outer-periphery spline groove 14 becomes part of a conical surface.

[0025] The above relationships, including the relationships of formulas (1) and (2), are the same for the internal thread groove 31, the internal land portion 32, the internal spiral groove 33, and the internal spline groove 34. In other words, the distance from the inner circumferential surface of the inner land portion 32 to the groove bottom of the internal spline groove 34 is smaller than the distance from the inner circumferential surface of the inner land portion 32 to the groove bottom of the internal thread groove 31, and is greater than the distance from the inner circumferential surface of the inner land portion 32 to the groove bottom of the internal spiral groove 33. In addition, the groove bottom of the internal spline groove 34 is inclined with respect to the axis of the nut 30.

[0026] (Ball screw operation) When the nut 30 and the screw shaft 10 are rotated relative to each other, the balls 20 roll along the rolling path between the inner peripheral screw groove 31 and the outer peripheral screw groove 11, thereby causing relative movement in the axial direction between the nut 30 and the screw shaft 10. The balls 20 that reach one end of the rolling path are returned to the other end of the rolling path by a circulation part (not shown) and roll within the rolling path again.

[0027] Here, the lubricant that has entered the rolling paths via the oil supply holes 35 is pushed away by the rolling balls 20 towards the inner circumferential land portion 32 and the outer circumferential land portion 12 .

[0028] Focusing on the screw shaft 10, a portion of the lubricant pushed up onto the outer peripheral surface of the outer peripheral land portion 12 enters the outer peripheral spiral groove 13 or the outer peripheral spline groove 14. The lubricant RB that entered the outer peripheral spiral groove 13 flows toward the deeper outer peripheral spline groove 14 under its own weight, and then moves along the outer peripheral spline groove 14. Since the groove bottom of the outer peripheral spline groove 14 is inclined with respect to the axis of the screw shaft 10, the lubricant that entered the outer peripheral spline groove 14 moves to the deeper groove bottom under its own weight, and is returned to the outer peripheral thread groove 11. The lubricant returned to the outer peripheral thread groove 11 is pushed up again toward the inner peripheral land portion 32 and the outer peripheral land portion 12 by the rolling balls.

[0029] In this way, the lubricant moves in a circulating manner along the outer peripheral thread groove 11, the outer peripheral land portion 12, the outer peripheral spiral groove 13, and the outer peripheral spline groove 14. Therefore, even if the lubricant is pushed away toward the outer peripheral land portion 12 by the rolling balls 20, it does not remain there but is returned to the outer peripheral thread groove 11 and used for lubrication, so that a lubricated state can be maintained for a long period of time with a small amount of lubricant, and the lubricant can be used effectively.

[0030] In addition, in general, a ball screw has a finite length of the screw shaft, so the screw shaft and the nut do not rotate in one direction infinitely. Therefore, when the screw shaft 10 rotates relative to the nut 30, acceleration or deceleration inevitably occurs.

[0031] For example, assuming that the screw shaft 10 rotates and accelerates or decelerates, as shown in Fig. 5, the lubricant in the outer-periphery spline groove 14 is subjected to an inertial force that presses it against the side surface of the outer-periphery spline groove 14. This inertial force depends on the mass of the lubricant and the acceleration or deceleration (differential value of the circumferential speed). Since the outer-periphery spline groove 14 is inclined with respect to the axis, the circumferential speed of the lubricant in the outer-periphery spline groove 14 differs partially depending on the difference in distance from the center O of the screw shaft 10.

[0032] 5, when an inertial force F1 acts on the lubricant at the end of the arc C1 of the outer-periphery spline groove 14 and an inertial force F2 acts on the lubricant at the end of the arc C2, the circumferential speed of the lubricant at the end of the arc C1 away from the center O of the screw shaft 10 is greater than the circumferential speed of the lubricant at the end of the arc C2 close to the center O, and therefore F1>F2 is established. Therefore, different inertial forces are applied to the lubricant in the outer-periphery spline groove 14 at different positions of the outer-periphery spline groove 14, and coupled with the fact that the inner circumference of the outer-periphery spline groove 14 is a conical surface, the movement of the lubricant from the outer-periphery spline groove 14 to the outer-periphery screw groove 11 can be promoted as shown in FIG.

[0033] The above-mentioned lubricant circulation effect is similarly achieved in the inner screw groove 31, the inner land portion 32, the inner spiral groove 33, and the inner spline groove .

[0034] The movement of the lubricant in the outer peripheral spline groove 14 and the inner peripheral spline groove 34 due to its own weight is limited to the case where the outer peripheral spline groove 14 is located above the screw shaft 10 in the direction of gravity, and the inner peripheral spline groove 34 is located below the nut 30 in the direction of gravity. However, if at least one of the outer peripheral spline groove 14 and the inner peripheral spline groove 34 has the effect of returning the lubricant to the outer peripheral thread groove 11 or the inner peripheral thread groove 31, the lubricant can be effectively utilized. Furthermore, if one of the outer peripheral spline groove 14 and the inner peripheral spline groove 34 is provided, the lubricant can be returned to the thread groove.

[0035] According to this embodiment, compared to conventional ball screws, the lubricant in the land portion can be effectively guided to the screw groove, thereby reducing the amount of lubricant required for the ball screw, while preventing poor lubrication of the ball screw and extending its life. The ball screw of this embodiment can be easily machined using existing machining equipment and does not require any additional parts, so it is highly productive and low cost.

[0036] Second Embodiment 7 is a partial view of the screw shaft according to the second embodiment as viewed in the axial direction. The nut and balls in this embodiment are the same as those in the first embodiment, so a duplicated description will be omitted. In addition, the screw shaft 10A of this embodiment differs from the first embodiment only in the shape of the outer circumferential spline groove 14A, so a duplicated description will be omitted.

[0037] 7, the screw shaft 10A has an outer peripheral spline groove 14A that has a dovetail shape when viewed in the axial direction. Specifically, the outer peripheral spline groove 14A has a planar bottom surface 14Aa and a pair of planar side surfaces 14Ab, with the bottom surface 14Aa inclined with respect to the axis of the screw shaft 10A and the distance between the side surfaces 14Ab increasing toward the center O of the screw shaft 10A.

[0038] As described with reference to Fig. 5, when the nut and the screw shaft 10A are accelerated or decelerated relative to each other, an inertial force acts on the lubricant in the outer peripheral spline groove 14A toward the side surface 14Ab. According to this embodiment, since the distance between the side surfaces 14Ab increases toward the center O of the screw shaft 10A, even if the lubricant in the outer peripheral spline groove 14A is urged toward the side surface 14Ab by the inertial force, the lubricant is prevented from spilling out onto the outer peripheral surface side of the outer peripheral land portion 12, and the movement from the outer peripheral spline groove 14A to the outer peripheral screw groove 11 (see Fig. 4) can be promoted.

[0039] The inner spline groove of the nut may also be of a dovetail shape, that is, the inner spline groove may have a bottom surface and a pair of side surfaces, the bottom surface may be inclined with respect to the axis of the nut, and the distance between the opposing side surfaces may increase toward the center of the nut.

[0040] (Third embodiment) Fig. 8 is a cross-sectional view of an end portion of a ball screw according to a third embodiment. Fig. 9 is an enlarged view of part IX in Fig. 8. Fig. 10 is a view of the ball screw in Fig. 8 cut along line XX and viewed in the direction of the arrow.

[0041] In this embodiment, a seal member 40 is attached to the end of the nut 30. The rest of the configuration is the same as in the above-described embodiment, so a duplicated description will be omitted.

[0042] The seal member 40 has an annular main body 41 and a single protrusion 42 protruding from the inner circumference of the main body 41. The protrusion 42 has, for example, a partially spherical tip, and is constantly fitted into the outer peripheral spiral groove 13 and can be fitted into the outer peripheral spline groove 14 depending on the relative rotation angle between the nut 30 and the screw shaft 10. The inner peripheral surface of the main body 41 other than the protrusion 42 is separated from the outer peripheral land portion 12. The seal member 40 can be fixed to the nut 30 by using a bolt BT inserted into a mounting hole 36 formed in the nut 30.

[0043] When the screw shaft 10 and the nut 30 rotate relative to each other and move relative to each other in the axial direction, the protrusion 42 fits into the outer peripheral spline groove 14 as shown in Figure 9. This allows the lubricant in the outer peripheral spline groove 14 to be pushed out toward the outer peripheral screw groove 11.

[0044] When the outer peripheral screw groove of the screw shaft of a ball screw is formed by rolling, the material may flow when the outer peripheral surface of the screw shaft is pressed with a die, causing a dent like a wrinkle (also called a seam) along the spiral direction on the outer peripheral land. This wrinkle can be used as the outer peripheral spiral groove 13.

[0045] That is, by forming the outer peripheral screw groove 11 on the screw shaft 10 by rolling, the outer peripheral land portion 12 and the outer peripheral spiral groove 13 can be formed simultaneously, which saves the labor of cutting and reduces the cost of the ball screw. The outer peripheral land portion 12 may be cut after rolling, and the outer peripheral spline groove 14 is formed by cutting.

[0046] When the outer peripheral spiral groove 13 is formed using wrinkles generated during rolling, as shown in the cross section of Fig. 11, the fiber flow (metal structure) FF in the material of the screw shaft 10 continues uninterrupted in the outer peripheral spiral groove 13. On the other hand, when the outer peripheral spiral groove 13 is formed by cutting, the fiber flow is interrupted, which can be distinguished from the case of rolling.

[0047] The present invention is not limited to the above-described embodiment. Any of the components of the above-described embodiment may be modified within the scope of the present invention. In addition, any of the components of the above-described embodiment may be added or omitted. [Explanation of symbols]

[0048] 10,10A screw shaft 11 Outer Circumferential Thread Groove 12 Outer periphery land 13 Outer circumferential spiral groove 14,14A Outer periphery spline groove 20 Ball 30 Nut 31 Internal thread groove 32 Inner land 33 Inner spiral groove 40 Sealing material

Claims

1. A screw shaft having an outer peripheral screw groove formed thereon; A nut having an internal thread groove; a plurality of balls accommodated in a rolling path formed by the opposing outer peripheral screw groove and the inner peripheral screw groove; In the screw shaft, an outer peripheral spiral groove is formed on an outer peripheral land portion between the outer peripheral screw grooves, and an outer peripheral spline groove connecting the outer peripheral spiral groove and the outer peripheral screw groove is formed along the axis of the screw shaft. A ball screw characterized by:

2. a distance from an outer peripheral surface of the outer peripheral land portion to a groove bottom of the outer peripheral spline groove is smaller than a distance from an outer peripheral surface of the outer peripheral land portion to a groove bottom of the outer peripheral thread groove and is larger than a distance from an outer peripheral surface of the outer peripheral land portion to a groove bottom of the outer peripheral spiral groove, 2. The ball screw according to claim 1 .

3. The groove bottom of the outer circumferential spline groove is inclined with respect to the axis of the screw shaft so that the distance from the axis to the groove bottom gradually decreases or increases.

2. The ball screw according to claim 1 .

4. The outer circumferential spline groove has a bottom surface and a pair of side surfaces, the distance between the side surfaces increasing toward the center of the screw shaft.

4. The ball screw according to claim 3.

5. A seal member having a protrusion that can be fitted into the outer peripheral spiral groove is disposed on the nut.

2. The ball screw according to claim 1 .

6. The screw groove of the screw shaft is formed by rolling, and when the screw shaft is cut in a cross section including the axis line, the fiber flow on the cut surface of the outer peripheral land portion is not interrupted by the outer peripheral spiral groove.

2. The ball screw according to claim 1 .

7. A screw shaft having an outer peripheral screw groove formed thereon; A nut having an internal thread groove; a plurality of balls accommodated in a rolling path formed by the opposing outer peripheral screw groove and the inner peripheral screw groove; In the nut, an inner spiral groove is formed on an inner land portion between the inner screw grooves, and an inner spline groove connecting the inner spiral groove and the inner screw groove is formed along the axis of the nut. A ball screw characterized by:

8. a distance from an inner peripheral surface of the inner peripheral land portion to a groove bottom of the inner peripheral spline groove is smaller than a distance from an inner peripheral surface of the inner peripheral land portion to a groove bottom of the inner peripheral thread groove and is larger than a distance from the inner peripheral surface of the inner peripheral land portion to a groove bottom of the inner peripheral spiral groove, 8. The ball screw according to claim 7.

9. The groove bottom of the inner peripheral spline groove is inclined with respect to the axis of the nut so that the distance from the axis to the groove bottom gradually decreases or increases.

8. The ball screw according to claim 7.

10. The inner spline groove has a bottom surface and a pair of side surfaces, the distance between the side surfaces increasing toward the center of the screw shaft.

10. The ball screw according to claim 9.

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