Ball screw

Abstract

To provide a ball screw which can secure a penetration hole having a size sufficient for supplying grease or lubricant.SOLUTION: A ball screw comprises: a screw shaft with a screw groove formed in an outer peripheral surface; a nut 3 with a plurality of screw grooves 32 and a plurality of circulation grooves 33 formed in an inner peripheral surface 31; and a plurality of balls which are arranged in a plurality of rolling paths constituted of the screw groove of the screw shaft and the plurality of screw grooves 32 of the nut 3, and roll on the plurality of rolling paths via the plurality of circulation grooves 33, respectively. The plurality of screw grooves 32 include a pair of screw grooves 32a which adjoin each other in an axial direction. The plurality of circulation grooves 33 include a pair of circulation grooves 33a which correspond to the pair of screw grooves 32a and are arranged at different positions in a circumferential direction. The nut 3 has a penetration hole 34 which is open in a region 31a of the inner peripheral face 31 that is surrounded by the pair of screw grooves 32a and the pair of circulation grooves 33a.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] For lubrication of a ball screw, grease or lubricating oil is generally used. In the ball screw described in Patent Document 1, a through hole formed in the nut for supplying grease to the rolling path opens at the land portion between the thread grooves. Further, in the ball screw described in Patent Document 2, a through hole formed in the nut for supplying grease to the rolling path opens at the bottom surface of the thread groove.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to appropriately supply grease or lubricating oil to the rolling path, it is necessary to form a through hole of a sufficient size in the nut. However, in the ball screws described in Patent Documents 1 and 2, if the size of the through hole is increased, the ball may contact the edge portion of the opening of the through hole, and damage may occur to each part due to this. Therefore, in the ball screws described in Patent Documents 1 and 2, it is difficult to form a through hole of a sufficient size in the nut for supplying grease or lubricating oil.

[0005] Therefore, an object of the present invention is to provide a ball screw capable of securing a through hole of a sufficient size for supplying grease or lubricating oil.

Means for Solving the Problems

[0006] The ball screw of the present invention is [1] a screw shaft having a first screw groove formed on its outer circumference, a nut having a plurality of second screw grooves and a plurality of circulation grooves formed on its inner circumference, and a plurality of balls arranged in each of the plurality of rolling paths formed by the first screw groove and the plurality of second screw grooves, and rolling in each of the plurality of rolling paths via each of the plurality of circulation grooves, wherein the plurality of second screw grooves include a pair of second screw grooves adjacent in the axial direction, the plurality of circulation grooves include a pair of circulation grooves corresponding to the pair of second screw grooves and arranged at different positions in the circumferential direction, and the nut has a through hole opening in the region of its inner circumference surrounded by the pair of second screw grooves and the pair of circulation grooves.

[0007] In the ball screw described in [1] above, a pair of circulation grooves corresponding to a pair of adjacent second screw grooves in the axial direction are arranged at different positions in the circumferential direction, and the through hole formed in the nut opens in the region of the inner circumferential surface surrounded by the pair of second screw grooves and the pair of circulation grooves. This makes it possible to increase the size of the through hole while preventing the edge portion of the opening of the through hole from overlapping with the pair of second screw grooves and the pair of circulation grooves (i.e., preventing the ball from contacting the edge portion of the opening of the through hole). Therefore, the ball screw described in [1] above makes it possible to secure a through hole of sufficient size for supplying grease or lubricating oil.

[0008] The ball screw of the present invention may also be [2] "the ball screw described in [1] above, wherein the through hole extends in the radial direction." According to the ball screw described in [2], the configuration of the through hole can be simplified.

[0009] The ball screw of the present invention may also be [3] "the ball screw according to [1] or [2] above, wherein the region on the inner circumferential surface of the nut in which the plurality of second screw grooves are formed is defined as the screw groove forming region, and the pair of second screw grooves are the two second screw grooves that are closest to the center position of the screw groove forming region in the axial direction among the plurality of second screw grooves." According to the ball screw according to [3], grease or lubricating oil supplied from the through hole can be efficiently distributed throughout the entire area of ​​the plurality of rolling paths.

[0010] The ball screw of the present invention may also be [4] "a ball screw according to any one of [1] to [3] above, further comprising a reference portion provided on the nut and positioned at a predetermined location relative to the region." According to the ball screw according to [4], when forming a through hole in the nut, the through hole can be reliably opened in the region surrounded by a pair of second screw grooves and a pair of circulation grooves.

[0011] The ball screw of the present invention may also be [5] "a ball screw according to any one of [1] to [4] above, further comprising a pin that seals the through hole." According to the ball screw described in [5], for example, by sealing the through hole with a pin after supplying grease through the through hole, it is possible to prevent grease in the rolling path from leaking out of the through hole to the outside, or external particles from entering the rolling path through the through hole.

[0012] The ball screw of the present invention may also be [6] "the ball screw described in [5] above, wherein the pin is embedded in the through hole." According to the ball screw described in [6], if any member is placed on the outside of the nut in the radial direction, physical interference between the member and the pin can be prevented.

[0013] The ball screw of the present invention may also be [7] "the ball screw described in [5] above, wherein the pin protrudes from the outer surface of the nut." According to the ball screw described in [7], the portion of the pin that protrudes from the outer surface of the nut can be used as an anti-rotation device.

[0014] The ball screw of the present invention may be "[8] the ball screw according to any one of [5] to [7] above, wherein the pin is press-fitted into the through hole". According to the ball screw described in [8], the structures of the through hole and the pin can be simplified.

[0015] The ball screw of the present invention may be "[9] the ball screw according to any one of [5] to [7] above, wherein the pin is screwed into the through hole". According to the ball screw described in [9], the pin can be attached to and detached from the through hole, so that grease can be supplied from the through hole as needed.

Effects of the Invention

[0016] According to the present invention, it is possible to provide a ball screw that can secure a through hole of a sufficient size for supplying grease or lubricating oil.

Brief Description of the Drawings

[0017] [Figure 1] It is a cross-sectional view of a ball screw according to an embodiment. [Figure 2] It is a perspective view of the nut shown in FIG. 1. [Figure 3] It is a cross-sectional view of the nut shown in FIG. 2. [Figure 4] It is a developed view of the inner peripheral surface of the nut shown in FIG. 3. [Figure 5] It is a cross-sectional view of a nut according to a modification. [Figure 6] It is a developed view of the inner peripheral surface of the nut shown in FIG. 5. [Figure 7] It is a cross-sectional view of a part of a ball screw according to a modification.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0019] As shown in FIG. 1, the ball screw 1 includes a screw shaft 2, a nut 3, and a plurality of balls 4. Hereinafter, the direction parallel to the center line of the screw shaft 2 is referred to as the axial direction, the direction perpendicular to the center line of the screw shaft 2 is referred to as the radial direction, and the direction along the circumference centered on the center line of the screw shaft 2 when viewed from the direction parallel to the center line of the screw shaft 2 is referred to as the circumferential direction.

[0020] A screw groove (first screw groove) 22 is formed on the outer peripheral surface 21 of the screw shaft 2. The screw groove 22 extends in a spiral shape. A plurality of screw grooves (second screw grooves) 32 are formed on the inner peripheral surface 31 of the nut 3. The plurality of screw grooves 32 extend in a spiral shape with the same pitch as the screw groove 22 of the screw shaft 2. Each screw groove 32 has a length corresponding to, for example, one lead. The screw groove 22 of the screw shaft 2 and the plurality of screw grooves 32 of the nut 3 constitute a plurality of rolling paths 10. Note that, for example, splines or serrations are formed on the outer peripheral surface of one end portion 23 of the screw shaft 2.

[0021] As shown in FIGS. 2 and 3, a plurality of circulation grooves 33 are formed on the inner peripheral surface 31 of the nut 3. The plurality of circulation grooves 33 correspond to the plurality of screw grooves 32. In the corresponding screw groove 32 and circulation groove 33, the circulation groove 33 connects one end and the other end of the screw groove 32. The plurality of circulation grooves 33 are arranged at different positions (for example, at equal angular intervals) in the circumferential direction when viewed from the axial direction.

[0022] As shown in FIG. 1, the plurality of balls 4 are arranged in each rolling path 10. The plurality of balls 4 circulate infinitely in each rolling path 10 by passing over the thread crest (land portion) of the outer peripheral surface 21 of the screw shaft 2 when passing through the circulation groove 33. That is, the plurality of balls 4 roll in each rolling path 10 via each circulation groove 33. In FIG. 1, only some of the balls 4 are shown, but actually, a plurality of balls 4 are arranged along the rolling path 10 indicated by the two-dot chain line.

[0023] Figure 4 is an unfolded view of the inner circumferential surface 31 of the nut 3. As shown in Figure 4, the multiple screw grooves 32 include a pair of screw grooves (second screw grooves) 32a that are adjacent in the axial direction. The multiple circulation grooves 33 include a pair of circulation grooves 33a that correspond to a pair of screw grooves 32a and are located at different positions in the circumferential direction. In the corresponding screw grooves 32a and circulation grooves 33a, the circulation grooves 33a connect one end and the other end of the screw grooves 32a. As described above, since the pair of circulation grooves 33a are located at different positions in the circumferential direction, there is a region 31a on the inner circumferential surface 31 that is wider than the width of the threads between the pair of screw grooves 32a. The region 31a is the area of ​​the inner circumferential surface 31 enclosed by the pair of screw grooves 32a and the pair of circulation grooves 33a.

[0024] If the region on the inner circumferential surface 31 of the nut 3 in which multiple screw grooves 32 are formed is defined as the screw groove forming region 310, then a pair of screw grooves 32a are the two screw grooves 32 that are closest to the center position of the screw groove forming region 310 in the axial direction. If two screw grooves 32 are formed on the inner circumferential surface 31 of the nut 3, then these two screw grooves 32 constitute a pair of screw grooves 32a. If three screw grooves 32 are formed on the inner circumferential surface 31 of the nut 3, then the two screw grooves 32 excluding the screw groove 32 at one end constitute a pair of screw grooves 32a. If 2n (where n is an integer greater than or equal to 2) or more screw grooves 32 are formed on the inner circumferential surface 31 of the nut 3, and if 2n+1 or more screw grooves 32 are formed on the inner circumferential surface 31 of the nut 3, then the nth and (n+1)th screw grooves 32a from either end constitute a pair of screw grooves 32a. The thread groove forming region 310 is a cylindrical region on the inner circumferential surface 31 of the nut 3 that includes all the thread grooves 32. The center position of the thread groove forming region 310 in the axial direction may coincide with the center position of the nut 3 in the axial direction, or it may not coincide with the center position of the nut 3 in the axial direction.

[0025] The nut 3 has a through hole 34 that opens into region 31a. As shown in Figure 1, the nut 3 extends radially from region 31a and opens into the outer circumferential surface 35 of the nut 3. In this embodiment, the through hole 34 is a straight hole with a constant inner diameter. The through hole 34 is blocked by a pin 5. The pin 5 is press-fitted into the through hole 34. The pin 5 is embedded in the through hole 34. That is, the pin 5 does not protrude radially inward from the inner circumferential surface 31 of the nut 3, nor does it protrude radially outward from the outer circumferential surface 35 of the nut 3. In this embodiment, the pin 5 is a straight pin with a constant outer diameter. In the ball screw 1, for example, after grease is supplied from the through hole 34, the through hole 34 is blocked by the pin 5.

[0026] As shown in Figures 2 and 3, the nut 3 is provided with a reference portion 6 positioned at a predetermined location relative to the region 31a. In this embodiment, the reference portion 6 is a stopper provided on the end face of the nut 3 in the axial direction (the end face of the nut 3 opposite to the end portion 23 shown in Figure 1). The stopper engages with a member provided on the end of the screw shaft 2 opposite to the end portion 23, thereby stopping the movement of the nut 3 in the axial direction away from the end portion 23.

[0027] As described above, in the ball screw 1, a pair of circulation grooves 33a corresponding to a pair of adjacent screw grooves 32a in the axial direction are arranged at different positions in the circumferential direction, and the through hole 34 formed in the nut 3 opens into a region 31a of the inner circumferential surface 31 surrounded by the pair of screw grooves 32a and the pair of circulation grooves 33a. This makes it possible to increase the size of the through hole 34 while preventing the edge portion of the opening of the through hole 34 from overlapping with the pair of screw grooves 32a and the pair of circulation grooves 33a (i.e., preventing the ball 4 from contacting the edge portion of the opening of the through hole 34). Therefore, with the ball screw 1, it is possible to secure a through hole 34 of a sufficient size for supplying grease or lubricating oil.

[0028] In the ball screw 1, the through hole 34 extends radially. This simplifies the structure of the through hole 34.

[0029] In the ball screw 1, the pair of screw grooves 32a are the two screw grooves 32 that are closest to the center of the screw groove forming region 310 in the axial direction among the multiple screw grooves 32. This allows the grease or lubricating oil supplied from the through hole 34 to be efficiently distributed throughout the entire area of ​​the multiple rolling paths 10.

[0030] In the ball screw 1, a reference portion 6 is provided on the nut 3, positioned at a predetermined location relative to region 31a. This ensures that when forming a through hole 34 in the nut 3, the through hole 34 is reliably opened in region 31a surrounded by a pair of screw grooves 32a and a pair of circulation grooves 33a.

[0031] In the ball screw 1, the through hole 34 is blocked by a pin 5. This prevents grease from leaking out of the through hole 34 or foreign matter from entering the rolling path 10 through the through hole 34 by blocking the through hole 34 with the pin 5 after supplying grease from the through hole 34.

[0032] In the ball screw 1, the pin 5 is embedded in the through hole 34. This prevents physical interference between the pin 5 and any component that is placed outside the nut 3 in the radial direction.

[0033] In the ball screw 1, the pin 5 is press-fitted into the through hole 34. This simplifies the configuration of the through hole 34 and the pin 5.

[0034] The present invention is not limited to the embodiments described above. For example, in the nut 3, as shown in Figures 5 and 6, a plurality of parts 37, each having a circulation groove 33, may be provided separately as components in the main body 36, which has a plurality of screw grooves 32.

[0035] Furthermore, as shown in Figure 7(a), the through hole 34 may be a counterbore hole that is enlarged on the radially outer side. In this example, the pin 5 is press-fitted into the radially outer counterbore portion of the through hole 34 and is embedded in the counterbore portion.

[0036] Furthermore, as shown in Figure 7(b), the pin 5 may protrude radially outward from the outer circumferential surface 35 of the nut 3. In this case, the portion of the pin 5 that protrudes from the outer circumferential surface 35 of the nut 3 can be used as an anti-rotation device (i.e., an anti-rotation device to prevent the nut 3 from rotating together when the screw shaft 2 rotates and the nut 3 moves). Note that in the example shown in Figure 7(a), the pin 5 may also protrude radially outward from the outer circumferential surface 35 of the nut 3.

[0037] Furthermore, as shown in Figure 7(c), the pin 5 may be screwed into the through hole 34. This allows the pin 5 to be attached to and detached from the through hole 34, and grease can be supplied from the through hole 34 as needed. When a bolt with a head is used as the pin 5, it is preferable to flatten the area of ​​the outer circumferential surface 35 of the nut 3 that the seating surface of the head contacts. When the portion of the pin 5 that protrudes from the outer circumferential surface 35 of the nut 3 is used as an anti-rotation device, it is preferable to use a hex socket head bolt as the pin 5 and to make the surface of the portion of the pin 5 that protrudes from the outer circumferential surface 35 of the nut 3 a smooth surface.

[0038] Furthermore, the reference portion 6 may be a keyway, notch, mark, etc., formed on the outer circumferential surface 35 of the nut 3. The mark may include a code indicating production history management information.

[0039] Furthermore, the through-hole 34 does not need to extend radially, as long as it opens into at least region 31a. Also, the pair of screw grooves 32a does not need to be the two screw grooves 32 closest to the center of the screw groove forming region 310 in the axial direction, as long as they are a pair of adjacent screw grooves 32 in the axial direction. Also, a single nut 3 may have multiple through-holes 34. Also, the cross-sectional shape of the through-hole 34 may be a shape other than circular. Also, the through-hole 34 does not need to be blocked by the pin 5. Also, the nut 3 does not need to be provided with a reference portion 6. [Explanation of Symbols]

[0040] 1...Ball screw, 2...Screw shaft, 3...Nut, 4...Ball, 5...Pin, 6...Reference part, 10...Rolling path, 21...Outer surface, 22...Screw groove (first screw groove), 31...Inner surface, 31a...Region, 32,32a...Screw groove (second screw groove), 33,33a...Circulation groove, 34...Through hole, 35...Outer surface, 310...Screw groove forming region.

Claims

1. A screw shaft having a first screw groove formed on its outer surface, A nut having multiple second screw grooves and multiple circulation grooves formed on its inner surface, A plurality of balls are arranged in each of the plurality of rolling paths formed by the first screw groove and the plurality of second screw grooves, and roll in each of the plurality of rolling paths via each of the plurality of circulation grooves, Equipped with a pin, The plurality of second screw grooves include a pair of second screw grooves adjacent to each other in the axial direction. The plurality of circulation grooves include a pair of circulation grooves that correspond to the pair of second screw grooves and are arranged at different positions in the circumferential direction. The nut has a through hole that opens in the region of its inner circumferential surface surrounded by the pair of second screw grooves and the pair of circulation grooves, The pin blocks the through hole and protrudes from the outer surface of the nut. The portion of the pin that protrudes from the outer surface of the nut is used as a ball screw to prevent the nut from rotating.

2. The ball screw according to claim 1, wherein the through hole extends in the radial direction.

3. The ball screw according to claim 1 or 2, wherein the region on the inner circumferential surface of the nut in which the plurality of second screw grooves are formed is defined as the screw groove forming region, and the pair of second screw grooves are the two second screw grooves that are closest to the center position of the screw groove forming region in the axial direction among the plurality of second screw grooves.

4. The ball screw according to claim 1, wherein the pin is press-fitted into the through hole.

5. The ball screw according to claim 1, wherein the pin is screwed into the through hole.

6. The ball screw according to claim 1, wherein the nut has a main body portion in which the plurality of second screw grooves and the plurality of circulation grooves are formed.

7. The aforementioned nut is The main body portion having the plurality of second screw grooves formed therein, Each of the plurality of circulation grooves is formed in a plurality of parts, The ball screw according to claim 1, wherein the plurality of parts are provided separately from the main body.

8. The nut is provided with a reference portion that is positioned at a predetermined location relative to the region, The ball screw according to claim 1, wherein the reference portion is at least one of a stopper, a keyway, a notch, and a mark.

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