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 technology]

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

[0003] [Patent Document 1] JP 2001-050366 A [Patent Document 2] JP 2012-037063 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to properly 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, if the size of the through hole is increased in the ball screws described in Patent Documents 1 and 2, the balls may come into contact with the edge of the opening of the through hole, which may cause damage to various parts. 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] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a ball screw that can ensure a through hole of a sufficient size for supplying grease or lubricating oil. [Means for solving the problem]

[0006] The ball screw of the present invention is [1] "a ball screw comprising: a threaded shaft having a first thread groove formed on its outer peripheral surface; a nut having a plurality of second thread grooves and a plurality of circulation grooves formed on its inner peripheral surface; and a plurality of balls arranged in each of a plurality of rolling paths formed by the first thread groove and the plurality of second thread grooves and rolling in each of the plurality of rolling paths via each of the plurality of circulation grooves, wherein the plurality of second thread grooves include a pair of second thread grooves adjacent to each other in the axial direction, and the plurality of circulation grooves include a pair of circulation grooves corresponding to the pair of second thread grooves and arranged at different positions from each other in the circumferential direction, and the nut has a through hole opening into a region of the inner peripheral surface surrounded by the pair of second thread 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 second screw grooves adjacent in the axial direction are arranged at different positions in the circumferential direction, and a through hole formed in the nut opens into a 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 portions of the opening of the through hole from hanging on the pair of second screw grooves and the pair of circulation grooves (i.e., the balls from contacting the edge portions of the opening of the through hole). Therefore, according to the ball screw described in [1] above, a through hole of a size sufficient for supplying grease or lubricating oil can be ensured.

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

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

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

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

[0012] The ball screw of the present invention may be [6] "the ball screw according to the above [5], in which the pin is embedded in the through hole." According to the ball screw according to [6], when a member is disposed on the radial outside of the nut, physical interference between the member and the pin can be prevented.

[0013] The ball screw of the present invention may be [7] "the ball screw described in [5] above, in which the pin protrudes from the outer peripheral surface of the nut." According to the ball screw described in [7], the part of the pin protruding from the outer peripheral surface of the nut can be used as a rotation stopper.

[0014] The ball screw of the present invention may be [8] "the ball screw according to any one of the above [5] to [7], wherein the pin is press-fitted into the through hole." According to the ball screw according to [8], the configurations 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 the above [5] to [7], in which the pin is screwed into the through hole." According to the ball screw according to [9], the pin can be attached to and detached from the through hole, so that grease can be supplied from the through hole as necessary. Effect of the Invention

[0016] According to the present invention, it is possible to provide a ball screw capable of ensuring a through hole of a sufficient size for supplying grease or lubricating oil. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional view of a ball screw according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of the nut shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view of the nut shown in FIG. 2. [Figure 4] 4 is a development view of the inner peripheral surface of the nut shown in FIG. 3. [Diagram 5] FIG. 11 is a cross-sectional view of a modified nut. [Figure 6] 6 is a development view of the inner peripheral surface of the nut shown in FIG. 5. [Figure 7] FIG. 11 is a cross-sectional view of a portion of a modified ball screw. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.

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

[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 at the same pitch as the screw groove 22 of the screw shaft 2. Each screw groove 32 has a length of, for example, one lead. The screw groove 22 of the screw shaft 2 and the plurality of screw grooves 32 of the nut 3 form a plurality of rolling paths 10. In addition, for example, a spline or serration is formed on the outer peripheral surface of one end 23 of the screw shaft 2.

[0021] 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 grooves 32 and circulation grooves 33, the circulation grooves 33 connect one end and the other end of the screw grooves 32. When viewed from the axial direction, the plurality of circulation grooves 33 are arranged at different positions from each other in the circumferential direction (for example, at equal angular intervals).

[0022] As shown in Fig. 1, a plurality of balls 4 are arranged in each rolling path 10. When passing through the circulation groove 33, the plurality of balls 4 pass over the threads (land portion) of the outer peripheral surface 21 of the screw shaft 2, and thereby circulate infinitely in each rolling path 10. In other words, the plurality of balls 4 roll in each rolling path 10 via each circulation groove 33. Note that while only some of the balls 4 are shown in Fig. 1, in reality, the plurality of balls 4 are lined up along the rolling path 10 indicated by the two-dot chain line.

[0023] FIG. 4 is a development view of the inner peripheral surface 31 of the nut 3. As shown in FIG. 4, the multiple screw grooves 32 include a pair of screw grooves (second screw grooves) 32a adjacent to each other in the axial direction. The multiple circulation grooves 33 include a pair of circulation grooves 33a corresponding to the pair of screw grooves 32a and arranged at different positions in the circumferential direction. In the corresponding screw grooves 32a and circulation grooves 33a, the circulation groove 33a connects one end and the other end of the screw groove 32a. As described above, since the pair of circulation grooves 33a are arranged at different positions in the circumferential direction, the inner peripheral surface 31 has a region 31a having a width wider than the width of the thread between the pair of screw grooves 32a. The region 31a is a region of the inner peripheral surface 31 surrounded by the pair of screw grooves 32a and the pair of circulation grooves 33a.

[0024] If a region of the inner circumferential surface 31 of the nut 3 where a plurality of thread grooves 32 are formed is defined as a thread groove forming region 310, the pair of thread grooves 32a is two of the plurality of thread grooves 32 that are closest to the center position of the thread groove forming region 310 in the axial direction. When two thread grooves 32 are formed on the inner circumferential surface 31 of the nut 3, the two thread grooves 32 are a pair of thread grooves 32a. When three thread grooves 32 are formed on the inner circumferential surface 31 of the nut 3, two thread grooves 32 excluding the thread groove 32 at one end are a pair of thread grooves 32a. When 2n (n is an integer of 2 or more) or more thread grooves 32 are formed on the inner circumferential surface 31 of the nut 3, and when 2n+1 or more thread grooves 32 are formed on the inner circumferential surface 31 of the nut 3, the n-th and n+1-th thread grooves 32a from one end are a pair of thread grooves 32a. The thread groove forming region 310 is a cylindrical region including all the thread grooves 32 on the inner peripheral surface 31 of the nut 3. The center position of the thread groove forming region 310 in the axial direction may or 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 in the region 31a. As shown in FIG. 1, the nut 3 extends radially from the region 31a and opens to an outer circumferential surface 35 of the nut 3. In this embodiment, the through hole 34 is a straight hole having 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, and does not protrude radially outward from the outer circumferential surface 35 of the nut 3. In this embodiment, the pin 5 is a straight pin having 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] 2 and 3, the nut 3 is provided with a reference portion 6 arranged at a predetermined position with respect to the region 31a. In this embodiment, the reference portion 6 is a stopper provided on an end face of the nut 3 in the axial direction (the end face of the nut 3 opposite to the one end 23 shown in FIG. 1). The stopper engages with a member provided on the end of the screw shaft 2 opposite to the one end 23, thereby stopping the movement of the nut 3 in the axial direction opposite to the one end 23.

[0027] As described above, in the ball screw 1, a pair of circulation grooves 33a corresponding to a pair of thread grooves 32a adjacent to each other in the axial direction are disposed at different positions in the circumferential direction, and the through hole 34 formed in the nut 3 opens in a region 31a of the inner circumferential surface 31 surrounded by the pair of thread 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 portions of the opening of the through hole 34 from hanging on the pair of thread grooves 32a and the pair of circulation grooves 33a (i.e., preventing the balls 4 from contacting the edge portions of the opening of the through hole 34). Thus, the ball screw 1 makes it possible to ensure a through hole 34 of a size sufficient for supplying grease or lubricating oil.

[0028] In the ball screw 1, the through hole 34 extends in the radial direction. This allows the configuration of the through hole 34 to be simplified.

[0029] In the ball screw 1, the 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 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 multiple rolling paths 10.

[0030] In the ball screw 1, the reference portion 6 is disposed at a predetermined position with respect to the region 31a and is provided on the nut 3. This allows the through hole 34 to be reliably opened in the region 31a surrounded by the pair of screw grooves 32a and the pair of circulation grooves 33a when the through hole 34 is formed in the nut 3.

[0031] In the ball screw 1, the through hole 34 is blocked by the pin 5. As a result, for example, by supplying grease through the through hole 34 and then blocking the through hole 34 with the pin 5, it is possible to prevent the grease in the rolling path 10 from leaking out through the through hole 34 and to prevent external foreign matter from entering the rolling path 10 through the through hole 34.

[0032] In the ball screw 1, the pin 5 is embedded in the through hole 34. This makes it possible to prevent physical interference between any member disposed radially outside the nut 3 and the pin 5.

[0033] In the ball screw 1, the pin 5 is press-fitted into the through hole 34. This allows the configurations of the through hole 34 and the pin 5 to be simplified.

[0034] The present invention is not limited to the above-described embodiment. For example, in the nut 3, as shown in Fig. 5 and Fig. 6, a main body 36 having a plurality of thread grooves 32 formed therein may have a plurality of portions 37 each having a circulation groove 33 formed therein, which are provided separately as pieces.

[0035] 7(a), the through hole 34 may be a countersunk hole whose diameter is enlarged on the radially outer side. In this example, the pin 5 is press-fitted into the countersunk portion on the radially outer side of the through hole 34 and embedded in the countersunk portion.

[0036] 7(b), the pin 5 may protrude radially outward from the outer circumferential surface 35 of the nut 3. In this way, the portion of the pin 5 protruding from the outer circumferential surface 35 of the nut 3 can be used as a rotation stopper (i.e., a rotation stopper for preventing the nut 3 from rotating when the screw shaft 2 rotates and the nut 3 moves). Note that, even in the example shown in FIG. 7(a), the pin 5 may protrude radially outward from the outer circumferential surface 35 of the nut 3.

[0037] 7(c), the pin 5 may be screwed into the through hole 34. This allows the pin 5 to be attached and detached to the through hole 34, so that grease can be supplied from the through hole 34 as necessary. When a bolt having a head is used as the pin 5, it is preferable to flatten the area of ​​the outer peripheral surface 35 of the nut 3 with which the seating surface of the head comes into contact. When the part of the pin 5 protruding from the outer peripheral surface 35 of the nut 3 is used as a rotation stopper, it is preferable to use a hexagonal socket bolt as the pin 5 and to smooth the surface of the part of the pin 5 protruding from the outer peripheral surface 35 of the nut 3.

[0038] Moreover, the reference portion 6 may be a key groove, a notch, a mark, or the like formed on the outer circumferential surface 35 of the nut 3. The mark includes a code or the like indicating production history management information.

[0039] In addition, the through hole 34 does not have to extend in the radial direction as long as it is open at least in the region 31a. In addition, the pair of thread grooves 32a does not have to be the two thread grooves 32 that are closest to the center position of the thread groove forming region 310 in the axial direction among the multiple thread grooves 32, as long as they are a pair of thread grooves 32 adjacent to each other in the axial direction. In addition, one nut 3 may have multiple through holes 34. In addition, the cross-sectional shape of the through hole 34 may be a shape other than a circle. In addition, the through hole 34 does not have to be blocked by the pin 5. In addition, the nut 3 does not have to be provided with the reference portion 6. [Explanation of symbols]

[0040] 1...ball screw, 2...screw shaft, 3...nut, 4...ball, 5...pin, 6...reference portion, 10...rolling path, 21...outer surface, 22...screw groove (first screw groove), 31...inner surface, 31a...area, 32, 32a...screw groove (second screw groove), 33, 33a...circulation groove, 34...through hole, 35...outer surface, 310...screw groove forming area.

Claims

1. A screw shaft having a first screw groove formed on an outer peripheral surface, A nut having a plurality of second screw grooves and a plurality of circulation grooves formed on an inner peripheral surface, A plurality of balls are disposed in each of a plurality of rolling paths constituted by the first screw groove and the plurality of second screw grooves, and roll in each of the plurality of rolling paths through each of the plurality of circulation grooves, and The plurality of second screw grooves include a pair of adjacent second screw grooves in an axial direction, The plurality of circulation grooves include a pair of circulation grooves corresponding to the pair of second screw grooves and disposed at different positions in a circumferential direction, The nut has a through hole that opens in a region surrounded by the pair of second screw grooves and the pair of circulation grooves on the inner peripheral surface, a ball screw.

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

3. When a region on the inner peripheral surface of the nut where the plurality of second screw grooves are formed is defined as a screw groove formation region, the pair of second screw grooves are the two second screw grooves closest to a center position of the screw groove formation region in the axial direction among the plurality of second screw grooves, the ball screw according to claim 1 or 2.

4. The nut further includes a reference portion provided at a predetermined position with respect to the region, the ball screw according to claim 1.

5. The ball screw according to claim 1 further includes a pin that closes the through hole.

6. The pin is embedded in the through hole, the ball screw according to claim 5.

7. The pin protrudes from an outer peripheral surface of the nut, the ball screw according to claim 5.

8. The pin is press-fitted into the through hole, the ball screw according to claim 5. Claim 9 The ball screw according to claim 5, wherein the pin is screwed into the through hole. Claim 10: 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. Claim 11: The nut has a main body portion in which the plurality of second screw grooves are formed, and a plurality of portions each having one of the plurality of circulation grooves formed therein, and the plurality of portions are provided separately from the main body portion. The ball screw according to claim 1.

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