Ball screw

Abstract

Provided is a ball screw comprising a circulation member 5 that is mounted in a fitting hole 6 disposed in a nut 3, and that causes a rolling ball to circulate. The circulation member 5 includes engagement parts 12 which, in a state where the circulation member is mounted in the fitting hole 6, engage with the fitting hole 6 by being bent. When viewed from the radially outer side of the nut 3, the engagement parts 12 engage with the fitting hole 6 in a state of being bent in an arc shape around the center P of the fitting hole 6.

Description

ball screw

[0001] The present invention relates to a ball screw having a circulating member for circulating balls.

[0002] A known ball screw used in general industrial machine tools or automotive actuators includes a nut having a helical thread groove on its inner peripheral surface, a screw shaft having a helical thread groove on its outer peripheral surface, a plurality of balls rollably housed between the thread grooves of the nut and the screw shaft inserted into the nut, and a circulation member for circulating the balls.

[0003] For example, Patent Document 1 (Patent Publication No. 4756645) discloses a method of fixing a circulation member within a fitting hole provided in a nut, in which, as shown in Figure 13, a circulation member 500 is inserted into a fitting hole 600 of a nut 300, and a convex engaging portion (guide wall) 120 provided on the circulation member 500 is tightened outward (see the dotted line portion in Figure 13), and the engaging portion 120 engages with the edge of the fitting hole 600.

[0004] Furthermore, in Patent Document 1, in order to reduce the amount of springback of the engaging portion after plastic deformation, a method is proposed in which, when crimping the engaging portion, a crimping jig is brought into point contact with both end portions 120a of the inner surface of the engaging portion 120 shown in Figure 13, thereby pressing the engaging portion 120.

[0005] Patent No. 4756645

[0006] While the above-described point-contact crimping method can reduce the amount of springback after plastic deformation, excessive stress acts on the pressing portion of the crimping jig when pressing the engagement portion. This can easily accelerate deterioration of the crimping jig. Furthermore, when crimping by point contact, the position of the circulation member relative to the crimping jig is difficult to stabilize, making it difficult to perform accurate crimping. Specifically, in the ball screw described in Patent Document 1, the arm portion provided on the circulation member is fitted into the thread groove of the nut, thereby roughly positioning the circulation member in the axial direction of the screw shaft and the rotational direction within the fitting hole, but is not positioned perpendicular to the axial direction of the screw shaft. Therefore, when attempting to fix the circulation member using the method described in Patent Document 1, there is a risk of significant misalignment of the circulation member in the direction perpendicular to the axial direction of the screw shaft.

[0007] Therefore, an object of the present invention is to suppress deterioration of the crimping jig and to stabilize the position of the circulating member relative to the crimping jig.

[0008] In order to solve the above problems, the present invention provides a ball screw comprising a nut having a spiral thread groove on its inner peripheral surface, a screw shaft having a spiral thread groove on its outer peripheral surface, a plurality of balls that are rollably accommodated between the opposing thread grooves of the nut and the screw shaft, and a circulation member that is mounted in a mating hole provided in the nut and circulates the rolling balls, wherein the circulation member has an engaging portion that is crimped and engages with the mating hole when mounted in the mating hole, and the engaging portion engages with the mating hole in a state where it is crimped in an arc shape centered on the center of the mating hole when viewed from the outer diameter side of the nut.

[0009] As described above, in the ball screw according to the present invention, the engaging portion of the circulation member engages with the fitting hole in a state in which the engaging portion is crimped in an arc shape centered on the center of the fitting hole when viewed from the outer diameter side of the nut. This arc-shaped engaging structure is obtained by bringing the crimping jig into line contact with the engaging portion. That is, by bringing the crimping jig into line contact with the engaging portion in an arc shape centered on the center of the fitting hole, the engaging portion is crimped in an arc shape.

[0010] As described above, in the present invention, by bringing the crimping jig into line contact with the engaging portion, the contact area of ​​the crimping jig with the engaging portion is larger than in conventional crimping methods using point contact, and the stress acting on the crimping jig can be reduced. This makes it possible to prevent deterioration of the crimping jig due to excessive stress acting on the crimping jig. Furthermore, by bringing the crimping jig into line contact with the engaging portion, the position of the circulating member relative to the crimping jig is more likely to be stabilized, thereby preventing misalignment of the circulating member and enabling crimping to be performed with high precision.

[0011] Furthermore, it is preferable that the contact area of ​​the crimping jig with the engaging portion is the entire circumferential direction of the engaging portion. In this case, contact marks caused by contact with the crimping jig are formed over the entire circumferential direction of the engaging portion. By bringing the crimping jig into contact with the engaging portion over the entire circumferential direction of the engaging portion in this way, the crimping process can be performed evenly, and the stress acting on the crimping jig is also made uniform. In other words, it is possible to avoid localized increases in the stress acting on the crimping jig, thereby more effectively suppressing deterioration of the crimping jig.

[0012] According to the present invention, it is possible to suppress deterioration of the crimping jig and stabilize the position of the circulating member relative to the crimping jig.

[0013] FIG. 1 is a plan view of a ball screw according to one embodiment of the present invention. FIG. 2 is a longitudinal sectional view of the ball screw according to the present embodiment. FIG. 3 is a longitudinal sectional view of the nut according to the present embodiment. FIG. 4 is a sectional perspective view showing a state before a circulation member is attached to the nut according to the present embodiment. FIG. 5 is a perspective view of a crimping jig according to the present embodiment. FIG. 6 is a longitudinal sectional view of the crimping jig according to the present embodiment. FIG. 7 is a front view of the crimping jig according to the present embodiment, viewed from the tip side. FIG. 8 is a view for explaining a method for fixing a circulation member. FIG. 9 is a view for explaining a method for fixing a circulation member. FIG. 10 is a view showing a state before an engaging portion is crimped. FIG. 11 is a view showing a state where the inner surface of the engaging portion and the tapered surface of the crimping portion are in line contact. FIG. 12 is a view showing a state where the engaging portion has been crimped. FIG. 13 is a view showing a conventional crimping method using point contact.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members or components having the same function or shape are designated by the same reference numerals as far as they can be distinguished. Therefore, a description of a component that has already been described will be omitted.

[0015] The overall configuration of a ball screw according to one embodiment of the present invention will be described with reference to Figures 1 to 4. Figure 1 is a plan view of the ball screw according to this embodiment, and Figure 2 is a longitudinal cross-sectional view of the ball screw. Figure 3 is a longitudinal cross-sectional view of a nut provided in the ball screw, and Figure 4 is a cross-sectional perspective view showing the nut in a state before a circulation member is attached thereto.

[0016] As shown in FIGS. 1 and 2 , a ball screw 1 according to this embodiment includes a screw shaft 2 , a nut 3 , a plurality of balls 4 , and a circulation member 5 .

[0017] The screw shaft 2 has a helical thread groove 2a on its outer circumferential surface and is inserted into a cylindrical nut 3. On the other hand, the nut 3 has a helical thread groove 3a on its inner circumferential surface that faces the thread groove 2a of the screw shaft 2. A plurality of balls 4 are housed between these thread grooves 2a, 3a in a rollable manner.

[0018] The cross-sectional shape of each of the thread grooves 2a, 3a may be a circular arc shape or a gothic arc shape. In this embodiment, each of the thread grooves 2a, 3a is formed in a gothic arc shape, which allows a large contact angle with the ball 4 and a small axial clearance. This increases the rigidity of each of the thread grooves 2a, 3a against axial loads and suppresses the occurrence of vibration.

[0019] The nut 3 is provided with a circular fitting hole 6 that penetrates from its inner peripheral surface to its outer peripheral surface and cuts out a part of the thread groove 3a. A circulation member 5 having a substantially circular cross section is inserted into this fitting hole 6.

[0020] The circulation member 5 has a connecting groove 5a that connects adjacent thread grooves 3a of the nut 3 for one revolution. Therefore, as shown in FIG. 3 , when the circulation member 5 is inserted into the fitting hole 6, the S-shaped connecting grooves 5a connect adjacent thread grooves 3a of the nut 3, and the connecting grooves 5a and approximately one revolution of the thread grooves 3a form a rolling path for the balls 4. As a result, the multiple balls 4 are guided by the connecting grooves 5a of the circulation member 5, ride over the threads of the screw shaft 2, and return to the adjacent thread grooves 3a. The multiple balls 4 then circulate by rolling again along the thread grooves 2a, 3a. The depth of the connecting grooves 5a is set to a depth that allows the balls 4 to ride over the threads of the screw shaft 2 within the connecting grooves 5a.

[0021] 3, the circulation member 5 is provided with a pair of arms 9 that protrude in opposite directions. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, each arm 9 of the circulation member 5 fits into the thread groove 3a of the nut 3, thereby positioning the circulation member 5 in the axial direction with respect to the nut 3 and preventing the circulation member 5 from falling off in the radial direction of the nut. Note that each arm 9 engages with the thread groove 3a where the balls 4 do not roll so as not to interfere with the rolling of the balls 4.

[0022] 1 , a pair of engagement portions 12 are provided on the outer diameter side of the nut of the circulation member 5 so as to protrude in the outer diameter direction. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, the engagement portions 12 are pressed outward (away from each other) and tightened, whereby the engagement portions 12 engage with the edges of the fitting hole 6. This fixes the circulation member 5 to the nut 3.

[0023] Next, a crimping jig for crimping and fixing the circulation member 5 to the nut 3 according to this embodiment will be described.

[0024] FIG. 5 is a perspective view of the crimping jig according to this embodiment, FIG. 6 is a vertical cross-sectional view of the crimping jig, and FIG. 7 is a front view of the crimping jig as viewed from the tip end side.

[0025] As shown in FIGS. 5 to 7, the jig 20 has a cylindrical main body 21 and a pair of crimping portions 23 protruding from the main body 21.

[0026] The pair of crimping portions 23 have tapered surfaces 23a that are inclined (reduced in diameter) toward the tip so as to approach the center line L (see FIG. 6) of the main body portion 21. These tapered surfaces 23a function as pressing portions that press the engaging portions 12 when the engaging portions 12 of the circulation member 5 are crimped.

[0027] Next, a method for fixing the circulation member 5 using the crimping jig 20 according to this embodiment (a method for manufacturing a ball screw) will be described.

[0028] 8, the circulation member 5 is inserted into the fitting hole 6 from the inner diameter side of the nut 3, and the arm portion 9 of the circulation member 5 is fitted into the thread groove 3a. This positions the circulation member 5 relative to the nut 3.

[0029] 9 , the crimping jig 20 is pressed against the positioned circulation member 5 from the outer diameter side of the nut 3. At this time, the tapered surfaces 23a of the pair of crimping portions 23 are pressed against the inner surfaces 12a of the engagement portions 12 of the circulation member 5, causing each engagement portion 12 to plastically deform so as to tilt outward. As a result, each engagement portion 12 engages with the edge of the fitting hole 6, and the circulation member 5 is fixed within the fitting hole 6 of the nut 3.

[0030] 10 , when the circulation member 5 is inserted into the fitting hole 6 (before the engaging portions 12 are crimped), each engaging portion 12 is formed in an arc shape centered at the center of the fitting hole 6. In this embodiment, a pair of crimping portions 23 having the same arc-shaped tapered surfaces 23 a as the engaging portions 12 are pressed against each engaging portion 12 formed in such an arc shape.

[0031] 11, the tapered surface 23a of each crimping portion 23 is in line contact with the inner surface 12a of each engaging portion 12. That is, since the inner surface 12a of the engaging portion 12 and the tapered surface 23a of the crimping portion 23 are formed in arc-shaped cross sections of the same radius R centered at the center P of the fitting hole 6, these surfaces 12a, 23a are in line contact with each other.

[0032] In this embodiment, since the tapered surface 23a of the crimping portion 23 and the inner surface 12a of the engaging portion 12 are in line contact, when the crimping jig 20 is pushed in, as shown in Figure 12, each engaging portion 12 is plastically deformed so as to spread radially from the center P of the fitting hole 6 when viewed from the outer diameter side of the nut 3, and is crimped in an arc shape centered on the center P of the fitting hole 6.

[0033] In contrast, in the conventional case shown in Figure 13, the crimping jig is brought into point contact with both end portions 120a of the engaging portion 120, so as shown by the dotted lines in the figure, both end portions 120a of the engaging portion 120 and the surrounding areas are locally plastically deformed to a large extent, and the shape after crimping is not arc-shaped.

[0034] As described above, in the embodiment of the present invention, the crimping jig 20 is brought into line contact with the engaging portion 12 of the circulation member 5, so compared to the conventional method in which the crimping jig is brought into point contact, the contact area of ​​the crimping jig 20 with the engaging portion 12 is larger, and it is possible to reduce the stress acting on the crimping jig 20. This makes it possible to avoid applying excessive stress to the crimping jig 20, and therefore to suppress deterioration of the crimping jig 20.

[0035] Furthermore, by bringing the crimping jig 20 into line contact with the engaging portion 12, the position of the circulation member 5 relative to the crimping jig 20 is more likely to be stabilized. This suppresses misalignment of the circulation member 5, enabling accurate crimping. In this embodiment, as shown in FIG. 5 , the pair of crimping portions 23 have tapered surfaces 23 a. When the tapered surfaces 23 a are pressed against the inner surfaces 12 a of the engaging portions 12, the engaging portions 12 are guided by the tapered surfaces 23 a, and the circulation member 5 moves to follow the center line of the crimping jig 20, thereby correcting the misalignment of the circulation member 5. In particular, in this embodiment, correction of misalignment of the circulation member 5 in a direction perpendicular to the axial direction of the screw shaft 2 can be expected. That is, in this embodiment, the arm portions 9 of the circulation member 5 are fitted into the thread grooves 3 a of the nut 3, thereby positioning the circulation member 5 in the axial direction of the screw shaft 2 and in the rotational direction within the fitting hole 6. Therefore, correction of misalignment of the circulation member 5 is mainly performed in a direction perpendicular to the axial direction of the screw shaft 2. Furthermore, according to the present invention, correction of positional misalignment of the circulation member 5 is possible not only in the direction perpendicular to the axial direction of the screw shaft 2, but also in the direction of slight misalignment in the axial direction of the screw shaft 2 and in the rotational direction within the fitting hole 6.

[0036] 1, the circulation member 5 according to this embodiment has a pair of flat surfaces 5b facing in opposite directions, and therefore, when the circulation member 5 is inserted into the fitting hole 6, a gap 15 with a D-shaped cross section is formed between these flat surfaces 5b and the inner peripheral surface of the fitting hole 6. Furthermore, since each flat surface 5b is formed in a direction substantially perpendicular to the axial direction of the screw shaft 2, it is possible to easily check the presence or absence and degree of misalignment of the circulation member 5 by looking at it.

[0037] Furthermore, it is preferable that the contact area of ​​the crimping jig 20 with the engaging portion 12 be the entire circumferential direction of the engaging portion 12. Here, the "circumferential direction" of the engaging portion 12 refers to the circumferential direction of a circle arranged along the arc-shaped engaging portion 12. In this case, a contact mark caused by contact with the crimping jig 20 is formed on the inner surface 12a of the arc-shaped crimped engaging portion 12 along the entire circumferential direction. By contacting the crimping jig 20 along the entire circumferential direction of the engaging portion 12 in this manner, crimping can be performed evenly along the entire circumferential direction of the engaging portion 12, and stress acting on the crimping jig 20 can also be made uniform. In conventional crimping by point contact, contact marks are formed only at the crimped position of the engaging portion 12, resulting in stress concentration. In contrast, when the contact area is the entire circumferential direction of the engaging portion 12, as in the embodiment of the present invention, it is possible to avoid localized increases in stress acting on the crimping jig 20, thereby more effectively suppressing deterioration of the crimping jig 20.

[0038] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified as appropriate within the scope of the gist of the invention.

[0039] REFERENCE SIGNS LIST 1 ball screw 2 screw shaft 2a screw groove 3 nut 3a screw groove 4 ball 5 circulation member 6 fitting hole 12 engagement portion 20 caulking jig P center of fitting hole

Claims

1. A ball screw comprising: a nut having a helical thread groove on its inner surface; a screw shaft having a helical thread groove on its outer surface; a plurality of balls rollably accommodated between the opposing thread grooves of the nut and the screw shaft; and a circulation member that is mounted in a fitting hole provided in the nut and circulates the rolling balls, wherein the circulation member has an engagement portion that is crimped and engages with the fitting hole when mounted in the fitting hole, and the engagement portion engages with the fitting hole in a state where it is crimped in an arc shape centered on the center of the fitting hole when viewed from the outer diameter side of the nut.

2. A ball screw as set forth in claim 1, wherein said engaging portion that is crimped in an arc shape has a contact mark caused by contact with a crimping jig over its entire circumferential direction.

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